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Advanced applications of numerical modelling techniques for clay extruder design.
KANDASAMY, Saravanakumar.
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KANDASAMY, Saravanakumar. (2013). Advanced applications of numerical modelling techniques for clay extruder design. Doctoral, Sheffield Hallam University (United Kingdom)..
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Advanced Applications of Numerical Modelling Techniques for Clay Extruder Design
Saravanakumar Kandasamy
A thesis submitted in partial fulfilment of the requirements of Sheffield Hallam University for the degree of Master of Philosophy
April-2013
AcknowledgementI would like to offer my sincere thanks to Sheffield Hallam University-United
Kingdom, for offering me the opportunity to pursue this research work and
providing me with adequate resources required to complete this research
work. I would like to thank Dr. Abhishek Asthana, Dr. Andrew Young,
Dr. Francis Clegg and Prof. Graham Cockerham for their enduring support
and guidance in completing this research work. I also thank the CAD
technicians Mr. John Stanley and Mr. Steve Brandon, for their support.
I also would like to offer my gratitude to Prof. Alan Smith, Prof. Doug
Cleaver and all the other non-teaching staff members at Materials and
Engineering Science Research Institute (MERI), for their timely support and
guidance.
I am grateful to the board of directors at Group Rhodes Limited-United
Kingdom, for offering me this wonderful opportunity of undertaking a
research work at their esteemed workplace. I would like to thank Mr. Mark
Ridgway-OBE, whose vision for developing technically superior products and
interests in research and development helped in establishing a strong
platform for undertaking this research work. I would like to thank Mr. Barry
Richardson, whose ideas and zest for knowledge created this research
requirement and also helped in building strong and focused objectives for
this research work. I also would like to thank Mr. Ian Ridgway and Mr. Peter
Anderton, for their support in providing adequate resource for completing this
project work.
I would like thank the design, sales and manufacturing team at Group
Rhodes Limited and a special thanks to Mr. Dave Pearson, Mr. Kevin Hall,
Mr. Glynn Dixon, Mr. Mick Tinker and Mr. Edwin, for sharing their knowledge
and experience in the field of clay extrusion and supporting with required
scientific data required to complete this research work.
I also would like to thank the engineering and production team at
M/s Hepworth Wavin Limited- United Kingdom, M/s Dreadnought Tiles-
United Kingdom, M/s Ibstock Bricks Limited- United Kingdom, M/s HansonI
Brick Limited-United Kingdom and M/s Blockley's Limited-United Kingdom,
for their interest and technical contributions made to this research work.
Last but not the least; I would like to thank my parents and all my friends for
their support offered during this research work.
PrefaceA major portion of the research work discussed in this report was completed
through Knowledge Transfer Partnership (KTP) programme
(Ref.No:KTP007670), between Sheffield Hallam University (SHU), United
Kingdom (U.K) and Craven Fawcett Limited (C.F Ltd) - a part of Group
Rhodes Limited, U.K.
KTP is a U.K government initiated programme intended to support mainly the
small and medium scale business sectors in the U.K. It focuses on improving
their business prospects, either by solving any technological or management
issues existing in their business structure or to improve their product quality
and introduce new products. The main aim is to increase the
competitiveness and create healthy business prospects within the economy.
The required objectives of a KTP programme will be achieved by
establishing a short term partnership between a Higher Educational
Institution and a company registered in the U.K. The aim and objectives of
the project will be defined clearly by the members of participating
organisation and will be achieved through a working member, called an
Associate.
Established in the year 1836, Sheffield Hallam University is one among the
top 50 higher education institutions in the U.K, to undertake research works
in the subject of engineering. It has dedicated research institutions and lab
facilities for carrying out world class research works under the supervision of
academic experts from various areas of mechanical and materials
engineering. It also possesses a dedicated team of academics and experts
to support industrial partnership based projects and research works in the
field of engineering.
Craven Fawcett Limited, established in the year 1843, is a subsidiary
company of Group Rhodes Limited. It specialises in design and
manufacturing of clay working machines, which has its application mainly in
heavy clay structural ceramics industry. The range of products offered by
them includes box feeders, grinding mills, mixers, conveyors and extruders.
Being an ISO 9001 certified organisation and a well reputed company in U.K
and worldwide, it places a greater emphasis on design, and material
selection for the components of their products, optimising the production
process and time and improving the quality and efficiency of their products.
Combined de-airing type (Vacuum type) extruder is a specialised product of
C.F Ltd. and being a market leader in this segment, the management has a
keen interest in introducing and using advanced computer aided techniques
such as Computational Fluid Dynamics and Finite Element Analysis to
improve their current designs and to fast track the development of new
extruders and its components. Through this they are intended to achieve a
better and energy efficient extruders, for the use of ceramic industries. Since
the company did not have any experience and expertise available in-house
to accomplish this, a KTP programme was established and the research
work was undertaken to meet the required objectives. This report
summarises the research work undertaken and accomplishments towards
the company's intended requirement.
IV
AbstractCeramic materials play a vital role in our day to day life. Recent advances in
research, manufacture and processing techniques and production
methodologies have broadened the scope of ceramic products such as
bricks, pipes and tiles, especially in the construction industry. These are
mainly manufactured using an extrusion process in auger extruders. During
their long history of application in the ceramic industry, most of the design
developments of extruder systems have resulted from expensive laboratory-
based experimental work and field-based trial and error runs. In spite of
these design developments, the auger extruders continue to be energy
intensive devices with high operating costs. Limited understanding of the
physical process involved in the process and the cost and time requirements
of lab-based experiments were found to be the major obstacles in the further
development of auger extruders.
An attempt has been made herein to use Computational Fluid Dynamics
(CFD) and Finite Element Analysis (FEA) based numerical modelling
techniques to reduce the costs and time associated with research into design
improvement by experimental trials. These two techniques, although used
widely in other engineering applications, have rarely been applied for auger
extruder development. This had been due to a number of reasons including
technical limitations of CFD tools previously available. Modern CFD and FEA
software packages have much enhanced capabilities and allow the modelling
of the flow of complex fluids such as clay.
This research work presents a methodology in using Herschel-Bulkley's fluid
flow based CFD model to simulate and assess the flow of clay-water mixture
through the extruder and the die of a vacuum de-airing type clay extrusion
unit used in ceramic extrusion. The extruder design and the operating
parameters were varied to study their influence on the power consumption
and the extrusion pressure. The model results were then validated using
results from experimental trials on a scaled extruder which seemed to be in
reasonable agreement with the former. The modelling methodology was then
extended to full-scale industrial extruders. The technical and commercial
V
suitability of using light weight materials to manufacture extruder components
was also investigated. The stress and deformation induced on the
components, due to extrusion pressure, was analysed using FEA and
suitable alternative materials were identified. A cost comparison was then
made for different extruder materials. The results show potential of significant
technical and commercial benefits to the ceramic industry.
VI
Contents
Acknowledgement.................................................................................................... I
Preface................................................................................................................... Ill
Abstract....................................................................................................................V
List of figures........................................................................................................... X
List of tables..........................................................................................................XX
Chapter-1 Introduction........................................................................................ 1
1.1 Bricks........................................................................................................ 2
1.2 ............... 2
1.3 Objectives................................................................................. ............... 2
1.4 Research methodology........................................................... ............... 3
1.5 Previous works........................................................................ ............... 3
1.6 Thesis outline........................................................................... ................4
Chapter-2 Review of existing work for ceramic extrusion............. ................5
2.1 Introduction.............................................................................. ................6
2.2 Modelling and simulation of extruder system...................... ................6
2.3 Design and performance evaluation of extruders.............. ............. 13
2.4 Clay-Water rheology............................................................... ............. 24
2.5 Conclusion............................................................................... ............. 28
Chapter-3 CFD modelling of clay extruder...................................... ............. 29
3.1 Introduction.............................................................................. ............. 30
3.2 Fundamental classification of fluids...................................... ............. 30
3.3 Process of CFD modelling..................................................... ............. 36
3.4 CFD modelling of extruder..................................................... ............. 40
3.4.1 Geometry creation............................................................................ 40
3.4.2 Geometry discretisation....................................................................41
3.4.3 Boundary conditions......................................................................... 45
VII
3.4.4 Solver settings.................................................................................. 47
3.5 Experimental validation of CFD modelling...........................................51
3.6 CFD modelling of a scaled extruder......................................................56
3.7 Experimental study of clay rheology.....................................................59
3.8 Performance assessment of extruders with different diam eters 61
3.9 Performance assessment of a 500 mm extruder................................. 71
3.9.1 Effect of varying feed rate on performance of extruder.................71
3.9.2 Effect of varying auger speed on performance of extruder...... 75
3.9.3 Effect of varying pitch distance on performance of extruder.... 79
3.9.4 Effect of varying die shapes on performance of extruder.........83
3.9.5 Effect of varying number of split worms on performance of
extruder..........................................................................................................88
3.10 Performance assessment of a 600 mm extruder............................. 93
3.10.1 Effect of varying feed rate on performance of extruder.......... 93
3.10.2 Effect of varying auger speed on performance of extruder... 97
3.11 Conclusion..........................................................................................101
Chapter-4 Finite Element Analysis of clay extruder.....................................102
4.1 Introduction:............................................................................................103
4.2 FEA of clay extruder components........................................................103
4.2.1 Barrel.................................................................................................103
4.2.2 Distance piece................................................................................107
4.2.3 L iner..................................................................................................111
4.2.4 Auger.................................................................................................114
4.3 Conclusion..............................................................................................118
Chapter-5 Conclusion and future directions................................................. 119
5.1 Conclusion..............................................................................................120
5.2 Future directions.................................................................................... 121
VIII
References.......................................................................................................... 123
Appendix-A......................................................................................................... 129
Appendix-B..........................................................................................................175
Appendix-C..........................................................................................................182
Appendix-D......................................................................................................... 204
IX
List of figuresFigure 2-1 Extrusion pressure at various length of extruder.............................8
Figure 2-2 Dynamic pressure at various length of extruder..............................9
Figure 2-3 Dynamic pressure variation with respect to auger speed .............. 9
Figure 2-4 Clay velocity at various lengths of extruder....................................10
Figure 2-5 Viscosity profile for Bingham and Casson model flu ids ................11
Figure 2-6 Stress induced on die mandrel during wet clay extrusion............ 12
Figure 2-7 Effect of auger pitch variation on extruder performance...............15
Figure 2-8 Performance characteristics profile for a typical auger.................15
Figure 2-9 Pressure waves experienced in auger with half flights .................17
Figure 2-10 Typical pressure distribution in an extruder..................................18
Figure 2-11 Effect of extrusion rate on die pressure ........................................ 18
Figure 2-12 Forming pressure profile under normal condition ........................19
Figure 2-13 Effect of increasing clay stiffness on extrusion pressure ........... 20
Figure 2-14 Effect of decreasing clay stiffness on extrusion pressure 20
Figure 2-15 Effect of changing die geometry on extrusion pressure............. 21
Figure 2-16 Effect of changing feed rate on extrusion pressure .................... 21
Figure 2-17 Effect of die shape on extrusion pressure and power.................22
Figure 2-18 Effect of die shape on quality of extruded product...................... 23
Figure 2-19 Viscosity of pure clay sewer paste .................................................24
Figure 2-20 Viscosity profile of a typical shear thinning fluid...........................26
Figure 3-1 Newtonian flu ids.................................................................................30
Figure 3-2 Pseudoplastic fluids........................................................................... 32
Figure 3-3 Visco plastic flu ids ............................................................................. 33
Figure 3-4 Dilatant fluids...................................................................................... 34
Figure 3-5 Thixotropic fluids.................................................................................34
Figure 3-6 Rheopectic flu ids ................................................................................35
Figure 3-7 Visco-elastic fluids............................................................................. 35
Figure 3-8 Flow physics features in CFD ...........................................................37
Figure 3-9 CFD modelling process flow diagram ..............................................39
Figure 3-10 430 mm extruder- Auger volume-1................................................42
Figure 3-11 430 mm extruder- Auger volume-2................................................42
Figure 3-12 430 mm extruder - Clearance volume........................................... 43
X
Figure 3-13 430 mm extruder - Die/ extruder mouth volume........................ 43
Figure 3-14 430 mm extruder- Liner volume....................................................44
Figure 3-15 430 mm extruder components and die assembled view...........44
Figure 3-16 Moving volumes..............................................................................47
Figure 3-17 Stationary volumes........................................................................ 47
Figure 3-18 Scaled extruder...............................................................................52
Figure 3-19 Experimental set up layout...........................................................52
Figure 3-20 Scaled extruder-auger shaft.........................................................56
Figure 3-21 clearance.........................................................................................56
Figure 3-22 Scaled extruder-transition piece.................................................. 56
Figure 3-23 Scaled extruder-auger shaft meshed.......................................... 57
Figure 3-24 Scaled extruder-clearance meshed.......................... .................. 57
Figure 3-25 Scaled extruder- transition piece meshed...................................58
Figure 3-26 Parallel plate viscometer-Anton Parr (MCR301)........................59
Figure 3-27 Apparent viscosity vs. Strain rate of clay- measured
experimentally........................................................................................................60
Figure 3-28 Static pressure contour (full view)-430 mm Case 1...................62
Figure 3-29 Static pressure contour (sectional view) - 430 mm Case 1.......63
Figure 3-30 Static pressure profile-430 mm Case 1........................................63
Figure 3-31 Flow velocity during extrusion (sectional view)- 430 mm Case I
.................................................................................................................................64
Figure 3-32 Molecular viscosity vs. Strain rate- 430 mm Case 1..................65
Figure 3-33 Residual convergence-430 mm Case 1.......................................66
Figure 3-34 Mass flow rate convergence- 430 mm Case 1............................66
Figure 3-35 Extrusion pressure and Energy consumption vs. Diameter
(Case-1)...................................................................................................................67
Figure 3-36 Static pressure contour (full view)-430 mm Case I I ..................68
Figure 3-37 Static pressure contour (sectional view)- 430 mm Case II.......68
Figure 3-38 Static pressure profile-430 mm Case II.......................................69
Figure 3-39 Flow velocity during extrusion (sectional view)- 430 mm Case II
.................................................................................................................................69
Figure 3-40 Molecular viscosity vs. Strain rate-430 mm Case I I .................... 70
Figure 3-41 Extrusion pressure, Energy consumption vs. Diameter (Case-11)
.................................................................................................................................70XI
Figure 3-42 Static pressure contour (full view) - feed rate 10 kgs'1.............. 72
Figure 3-43 Static pressure contour (sectional view) - feed rate 10 kgs'1.... 72
Figure 3-44 Static pressure profile- feed rate 10 kgs'1................................... 73
Figure 3-45 Flow velocity during extrusion (sectional view)- feed rate 10 kgs'1
................................................................................................................................ 73
Figure 3-46 Molecular viscosity vs. Strain rate- feed rate 10 kgs'1................ 74
Figure 3-47 Extrusion pressure, Energy consumption vs. Feed rate ............ 74
Figure 3-48 Static pressure contour (full view) - auger speed 10 rpm 76
Figure 3-49 Static pressure contour (sectional view) - auger speed 10 rpm76
Figure 3-50 Static pressure profile-auger speed 10 rpm................................. 77
Figure 3-51 Flow velocity during extrusion (sectional view) - auger speed 10
rpm.......................................................................................................................... 77
Figure 3-52 Molecular viscosity vs. Strain rate - auger speed 10 rpm ..........78
Figure 3-53 Extrusion pressure, Energy consumption vs. Auger speed .......79
Figure 3-54 Static pressure contour (full view)-pitch dist. 246.13 mm........... 80
Figure 3-55 Static pressure contour (sectional view)-pitch dist. 246.13 mm 80
Figure 3-56 Static pressure profile-pitch dist. 246.13 mm............................... 81
Figure 3-57 Flow velocity during extrusion (sectional view)-pitch dist. 246.13
mm.......................................................................................................................... 81
Figure 3-58 Molecular viscosity vs. Strain rate-pitch dist. 246.13 m m .......... 82
Figure 3-59 Extrusion pressure, Energy consumption vs. Auger pitch
distance..................................................................................................................83
Figure 3-60 Types of die design investigated...................................................84
Figure 3-61 Static pressure contour (full view)-die type-11............................... 85
Figure 3-62 Static pressure contour (sectional view)-die type-11.................... 85
Figure 3-63 Static pressure profile-die type-11...................................................86
Figure 3-64 Flow velocity during extrusion (sectional view)-die type-ll.........86
Figure 3-65 Molecular viscosity vs. Strain rate- die type-ll........................... 87
Figure 3-66 Extrusion pressure, Energy consumption vs. Die design........... 87
Figure 3-67 Types of split worm design investigated.......................................89
Figure 3-68 Static pressure contour (full view)-two split worms..................... 89
Figure 3-69 Static pressure contour (sectional view)-two split worms........... 90
Figure 3-70 Static pressure profile-two split worms......................................... 90
Figure 3-71 Flow velocity during extrusion (sectional view)-two split worms 91XII
Figure 3-72 Flow pattern with no split worm .....................................................91
Figure 3-73 Flow pattern with one split w orm ................................................. 91
Figure 3-74 Flow pattern with two split worms................................................ 92
Figure 3-75 Molecular viscosity vs. Strain rate-two half flights....................... 92
Figure 3-76 Extrusion pressure, Energy consumption vs. Split worm s.........93
Figure 3-77 Static pressure contour (full view) - feed rate 8.1 k g s 1.............. 94
Figure 3-78 Static pressure contour (sectional view) - feed rate 8.1 k g s 1... 95
Figure 3-79 Static pressure profile- feed rate 8.1 kg s1................................... 95
Figure 3-80 Flow velocity during extrusion (sectional view)-feed rate 8.1 kgs'1
................................................................................................................................ 96
Figure 3-81 Molecular viscosity vs. Strain rate- feed rate 8.1 k g s 1............... 96
Figure 3-82 Extrusion pressure, Energy consumption vs. feed rate.............. 97
Figure 3-83 Static pressure contour (full view) - auger speed 15 rpm ...........98
Figure 3-84 Static pressure contour (full view) - auger speed 15 rpm ...........98
Figure 3-85 Static pressure profile- auger speed 15 rpm ................................ 99
Figure 3-86 Flow velocity during extrusion (sectional view) - auger speed 15
rpm .......................................................................................................................... 99
Figure 3-87 Molecular viscosity vs. Strain rate- auger speed 15 rpm 100
Figure 3-88 Extrusion pressure, Energy consumption vs. auger speed 101
Figure 4-1 430 mm extruder barrel geom etry............................................... 104
Figure 4-2 430 mm extruder barrel- load applied..........................................104
Figure 4-3 Stress induced in barrel @ 2.6 MPa load .....................................105
Figure 4-4 Deformation in barrel @2.6 MPa loa d ......................................... 106
Figure 4-5 430 mm extruder distance piece geometry...................................107
Figure 4-6 430 mm extruder distance piece- load applied ............................ 108
Figure 4-7 Stress induced in distance piece @ 2.6 MPa load...................... 109
Figure 4-8 Deformation in distance piece @2.6 MPa load...........................110
Figure 4-9 430 mm extruder liner geometry.................................................... 111
Figure 4-10 430 mm extruder liner - load applied .......................................... 111
Figure 4-11 Stress induced in liner @ 2.6 MPa load......................................112
Figure 4-12 Deformation in liner @ 2.6 MPa load .......................................... 113
Figure 4-13 430 mm extruder auger shaft geometry......................................114
Figure 4-14 430 mm extruder auger shaft - load applied.............................. 114
Figure 4-15 Stress induced in auger shaft @ 2.6 MPa load..........................115XIII
Figure 4-16 Deformation in auger shaft @ 2.6 MPa load............................ 116
Figure A-A- 1 500 mm extruder volumes and mesh generated ..................130
Figure A-A-2 600 mm extruder volumes and mesh generated ...................130
Figure A-A-3 Static pressure contour (full view)-500 mm Case 1............... 131
Figure A-A-4 Static pressure contour (sectional view)-500 mm Case 1...131
Figure A-A-5 Static pressure profile -500 mm Case 1....................................131
Figure A-A-6 Flow velocity during extrusion (sectional view)-500 mm Case I
............................................................................................................................. 132
Figure A-A-7 Molecular viscosity vs. Strain rate-500 mm Case 1.................132
Figure A-A-8 Static pressure contour (full view)-600 mm Case 1.................133
Figure A-A-9 Static pressure contour (sectional view)-600 mm Case 1.....133
Figure A-A-10 Static pressure profile -600 mm Case 1.................................. 134
Figure A-A-11 Flow velocity during extrusion (sectional view)-600 mm Case I
............................................................................................................................. 134
Figure A-A-12 Molecular viscosity vs. Strain rate-600 mm Case..1..............135
Figure A-A-13 Static pressure contour (full view)-500 mm Case I I 135
Figure A-A-14 Static pressure contour (sectional view)-500 mm Case II... 136
Figure A-A-15 Static pressure profile -500 mm Case II..................................136
Figure A-A-16 Flow velocity during extrusion (sectional view)-500 mm Case
II........................................................................................................................... 136
Figure A-A-17 Molecular viscosity vs. Strain rate-500 mm Case I I 137
Figure A-A-18 Static pressure contour (full view)-600 mm Case I I 137
Figure A-A-19 Static pressure contour (sectional view)-600 mm Case II... 138
Figure A-A-20 Static pressure profile -600 mm Case II..................................138
Figure A-A-21 Flow velocity during extrusion (sectional view)-600 mm Case
II........................................................................................................................... 138
Figure A-A-22 Molecular viscosity vs. Strain rate-600 mm Case I I 139
Figure A-A-23 Static pressure contour (full view) - feed rate 15 k g s 1 139
Figure A-A-24 Static pressure contour (sectional view) - feed rate 15 k g s 1
..............................................................................................................................140
Figure A-A-25 Static pressure profile- feed rate 15 k g s 1.............................140
XIV
Figure A-A-26 Flow velocity during extrusion (sectional view)-feed rate 15
kg s1..................................................................................................................... 140
Figure A-A-27 Molecular viscosity vs. Strain rate- feed rate15 k g s 1 141
Figure A-A-28 Static pressure contour (full view) - feed rate 25 kgs'1 141
Figure A-A-29 Static pressure contour (sectional view) - feed rate 25 kgs'1
.............................................................................................................................. 142
Figure A-A-30 Static pressure profile- feed rate 25 kgs'1........................... 142
Figure A-A-31 Flow velocity during extrusionfsectional view)-feed rate 25
kg s1......................................................................................................................142
Figure A-A-32 Molecular viscosity us. Strain rate- feed rate 25 kgs'1.......... 143
Figure A-A-33 Static pressure contour (full view) - feed rate 30 kgs'1......... 143
Figure A-A-34 Static pressure contour (sectional view) - feed rate 30 kgs'1
............................................................................................................................. 144
Figure A-A-35 Static pressure profile- feed rate 30 kgs'1.............................144
Figure A-A-36 Flow velocity during extrusionfsectional view)-feed rate 30
k g s 1..................................................................................................................... 144
Figure A-A-37 Molecular viscosity vs. Strain rate- feed rate 30 kgs'1 145
Figure A-A-38 Static pressure contour (full view) - feed rate 40 kgs'1 145
Figure A-A-39 Static pressure contour (sectional view) - feed rate 40 kgs'1
............................................................................................................................. 146
Figure A-A-40 Static pressure profile- feed rate 40 kgs'1.............................146
Figure A-A-41 Flow velocity during extrusion (sectional view)-feed rate 40
kgs'1..................................................................................................................... 146
Figure A-A-42 Molecular viscosity vs. Strain rate- feed rate 40 kgs'1 147
Figure A-A-43 Static pressure contour (full view) - feed rate 50 kgs'1 147
Figure A-A-44 Static pressure contour (sectional view) - feed rate 50 kgs'1
..............................................................................................................................148
Figure A-A-45 Static pressure profile- feed rate 50 kgs'1.............................148
Figure A-A-46 Flow velocity during extrusion (sectional view)-feed rate 50
kgs'1..................................................................................................................... 148
Figure A-A-47 Molecular viscosity vs. Strain rate- feed rate 50 kgs'1 149
Figure A-A-48 Static pressure contour (full view) - auger speed 15 rpm.... 149
Figure A-A-49 Static pressure contour (sectional view) - auger speed 15 rpm
..............................................................................................................................150XV
Figure A-A-50 Static pressure profile- auger speed 15 rpm..........................150
Figure A-A-51 Flow velocity during extrusion(sectional view)-auger speed 15
rpm........................................................................................................................150
Figure A-A-52 Molecular viscosity vs. Strain rate - auger speed 15 rpm ... 151
Figure A-A-53 Static pressure contour (full view) - auger speed 20 rpm.... 151
Figure A-A-54 Static pressure contour (sectional view) - auger speed 20 rpm
.............................................................................................................................. 152
Figure A-A-55 Static pressure profile- auger speed 20 rpm..........................152
Figure A-A-56 Flow velocity during extrusion (sectional view)-auger speed 20
rpm........................................................................................................................152
Figure A-A-57 Molecular viscosity vs. Strain rate - auger speed 20 rpm ... 153
Figure A-A-58 Static pressure contour (full view) - auger speed 25 rpm.... 153
Figure A-A-59 Static pressure contour (sectional view) - auger speed 25 rpm
............................................................................................................................. 154
Figure A-A-60 Static pressure profile- auger speed 25 rpm.......................154
Figure A-A-61 Flow velocity during extrusion (sectional view)-auger speed 25
rpm....................................................................................................................... 154
Figure A-A-62 Molecular viscosity vs. Strain rate - auger speed 25 rpm ... 155
Figure A-A-63 Static pressure contour (full view) - auger speed 40 rpm.... 155
Figure A-A-64 Static pressure contour (sectional view) - auger speed 40 rpm
..............................................................................................................................156
Figure A-A-65 Static pressure profile- auger speed 40 rpm........................ 156
Figure A-A-66 Flow velocity during extrusion(sectional view)-auger speed 40
rpm....................................................................................................................... 156
Figure A-A-67 Molecular viscosity vs. Strain rate - auger speed 40 rpm ... 157
Figure A-A-68 Static pressure contour (full view) - auger speed 50 rpm.... 157
Figure A-A-69 Static pressure contour (sectional view) - auger speed 50 rpm
...............................................................................................................................158
Figure A-A-70 Static pressure profile- auger speed 50 rpm..........................158
Figure A-A-71 Flow velocity during extrusion(sectional view)-auger speed 50
rpm........................................................................................................................ 158
Figure A-A-72 Molecular viscosity vs. Strain rate - auger speed 50 rpm ... 159
Figure A-A-73 Static pressure contour (full view)-pitch 338.012 mm 159
Figure A-A-74 Static pressure contour (sectional view)-pitch 338.012 mm 160XVI
Figure A-A-75 Static pressure profile-pitch 338.012 m m ............................ 160
Figure A-A-76 Flow velocity during extrusion(sectional view)-pitch 338.012
mm........................................................................................................................160
Figure A-A-77 Molecular viscosity vs. Strain rate-pitch 338.012 mm .......... 161
Figure A-A-78 Static pressure contour (full view)-die type-l..........................161
Figure A-A-79 Static pressure contour (sectional view)-die type-1.............. 162
Figure A-A-80 Static pressure profile-die type-1............................................. 162
Figure A-A-81 Flow velocity during extrusion (sectional view)-die type-1... 162
Figure A-A-82 Molecular viscosity vs. Strain rate- die type-1........................ 163
Figure A-A-83 Static pressure contour (full view)-die type-ill....................... 163
Figure A-A-84 Static pressure contour (sectional view)-die type-lll............ 164
Figure A-A-85 Static pressure profile-die type-ill........................................... 164
Figure A-A-86 Flow velocity during extrusion (sectional view)-die type-lll. 164
Figure A-A-87 Molecular viscosity vs. Strain rate- die type-lll.....................165
Figure A-A-88 Static pressure contour (full view) - feed rate 11.8 kgs'1 165
Figure A-A-89 Static pressure contour (sectional view) - feed rate 11.8 kgs'1
166
Figure A-A-90 Static pressure profile- feed rate 11.8 kgs'1...........................166
Figure A-A-91 Flow velocity during extrusionfsectional view)-feed rate 11.8
kgs'1...................................................................................................................... 166
Figure A-A-92 Molecular viscosity vs. Strain rate- feed rate 11.8 kgs'1.......167
Figure A-A-93 Static pressure contour (full view) - feed rate 19 kgs'1......... 167
Figure A-A-94 Static pressure contour (sectional view) - feed rate 19 kgs'1
168
Figure A-A-95 Static pressure profile- feed rate 19 kgs'1.............................. 168
Figure A-A-96 Flow velocity during extrusion (sectional view)-feed rate 19
kgs'1...................................................................................................................... 168
Figure A-A-97 Molecular viscosity vs. Strain rate- feed rate 19 kgs'1.......... 169
Figure A-A-98 Static pressure contour (full view) - auger speed 30 rpm.... 169
Figure A-A-99 Static pressure contour (sectional view) - auger speed 30 rpm
............................................................................................................................... 170
Figure A-A-100 Static pressure profile- auger speed 30 rpm........................170
Figure A-A-101 Flow velocity during extrusionfsectional view)-auger speed
30 rpm................................................................................................................... 170XVII
Figure A-A-102 Molecular viscosity vs. Strain rate- auger speed 30 rpm ..171
Figure A-A-103 Static pressure contour (full view)-scaled extruder-T1.......171
Figure A-A-104 Static pressure contour (sectional view)-scaled extruder-T1
.............................................................................................................................. 172
Figure A-A-105 Flow velocity during extrusion (sectional view)-scaled
ext rude r-T1 ..........................................................................................................172
Figure A-A-106 Molecular viscosity vs. Strain rate-scaled extruder-T1.......172
Figure A-A-107 Static pressure contour (full view)-scaled extruder-T2.......173
Figure A-A-108 Static pressure contour (sectional view)-scaled extruder-T2
............................................................................................................................. 173
Figure A-A-109 Flow velocity during extrusion (sectional view)-scaled
extruder-T2..........................................................................................................174
Figure A-A-110 Molecular viscosity vs. Strain rat e-scaled extruder-T2 174
Figure A-B- 1 Stress induced in barrel @1.8 MPa load ...............................176
Figure A-B- 2 Deformation in barrel @1.8 MPa load.................................... 177
Figure A-B- 3 Stress induced in distance piece @1.8 MPa load..................178
Figure A-B- 4 Deformation in distance piece @1.8 MPa load ...................... 178
Figure A-B- 5 Stress induced in liner @1.8 MPa load....................................179
Figure A-B- 6 Deformation in liner @1.8 MPa load ........................................ 180
Figure A-B- 7Stress induced in auger shaft @1.8 MPa load.......................... 180
Figure A-B- 8 Deformation in auger shaft @1.8 MPa load............................ 181
Figure A-C- 1 Energy consumption pattern of U.K brick industries..............184
Figure A-C- 2 Typical brick making process flow diagram ............................ 186
Figure A-C- 3 Classification of clay mineral groups ....................................... 187
Figure A-C- 4 Quarries for brick clay in U.K .................................................... 188
Figure A-C- 5 Quarry operated with mechanical extraction process............189
Figure A-C- 6 Hand moulding process............................................................. 191
Figure A-C- 7 Mechanized soft moulding machine ........................................ 192
Figure A-C- 8 Typical De-Boer soft mud moulding machine.........................192
Figure A-C- 9 Soft moulding machine-Aberson type...................................... 193
Figure A-C- 10 Vacuum extruder.....................................................................194
XVIII
Figure A -C -11 Hydraulic press type tile making machine............................195
Figure A-C- 12 Typical cutting system used in a brick production line 199
Figure A-C- 13 Tunnel dryer............................................................................201
Figure A-C- 14 Tunnel kiln-Type 1....................................................................202
Figure A-C- 15 Tunnel kiln-Type 2 ...................................................................202
Figure A-D- 1 Piston extruder...........................................................................206
Figure A-D- 2 Europresse extruder..................................................................207
Figure A-D- 3 Electrophoretic extruder........................................................... 208
Figure A-D- 4 Vacuum extruder-Centex model.............................................. 212
Figure A-D- 5 Mixing chamber.........................................................................213
Figure A-D- 6 Components of an extruder system.........................................214
Figure A-D- 7 Auger geometrical parameters................................................ 217
Figure A-D- 8 Vacuum extruder pressure profile............................................ 219
XIX
List of tablesTable 3-1 Craven Fawcett extruders for brick making..................................... 40
Table 3-2 Extruder mesh details........................................................................ 45
Table 3-3 Variables for Herschel- Bulkley's model..........................................49
Table 3-4 Experimental analysis results-trial 1 ................................................ 54
Table 3-5 Experimental analysis results-trial 2 ................................................ 55
Table 3-6 Herschel- Bulkley's model values for scaled extruder CFD analysis
................................................................................................................................ 58
Table 3-7 Result comparison for scaled extruder............................................. 59
Table 3-8 Data set for varying extruder diameter and moisture content
analysis.................................................................................................................. 61
Table 3-9 Data set for varying feed rate analysis............................................. 71
Table 3-10 Data set for varying auger speed analysis.................................... 75
Table 3-11 Data set for varying pitch distance analysis.................................. 79
Table 3-12 Data set for varying die design analysis.........................................83
Table 3-13 Data set for varying split worm analysis.........................................88
Table 3-14 Data set for varying feed rate analysis........................................... 94
Table 3-15 Data set for varying auger speed analysis.................................... 97
Table 4-1 Stress results-barrel.......................................................................... 105
Table 4-2 Deformation results- barre l.............................................................106
Table 4-3 Manufacturing cost comparison for extruder barrel.....................107
Table 4-4 Stress results-distance p iece ...........................................................108
Table 4-5 Deformation results- distance piece.............................................. 109
Table 4-6 Manufacturing cost comparison for distance p iece .......................110
Table 4-7 Stress results-liner........................................................................... 112
Table 4-8 Deformation results-liner...................................................................113
Table 4-9 Stress results-auger shaft...............................................................115
Table 4-10 Deformation results-auger shaft.................................................... 116
Table 4-11 Manufacturing cost comparison for auger.................................. 117
Table A-C- 1 Various shaping techniques and their applicability............... 198
Table A-D- 1 Extruder classification based on process parameters 210X X
1.1 BricksCeramic products like bricks, pipes and tiles have been used extensively in
the construction industry for many years. The demand for ceramic products
especially bricks have rapidly increased over the past few decades due to
the excessive growth in population. This burgeoning demand has opened up
a huge market potential for ceramic industries to thrive upon. In order to
utilise the market potential to its full capacity, the brick industry needs to
overcome some key challenges like better and efficient production methods,
reduction of energy usage during manufacturing and reduced impact on
environment through sustainable operation. The ceramic industry, compared
to its predecessors has made significant and laudable changes in terms of
production techniques and machines used. The modern industry is
incorporated with completely automated production process and looks
entirely different from how it was in the olden days. Energy efficiency in its
operation is still an arduous task that needs to be accomplished. It requires
an integrated effort from all the entities embedded in its entire supply chain,
which includes raw material suppliers, other major systems and equipment
providers. Brick industry, being energy intensive, faces an increasing
pressure from the government and environmental organisations for reducing
its environmental impact, by cutting down its energy consumption and
emissions. This in turn has increased the scope for further research works in
this field and a definite need to identify key areas in the brick manufacturing
process and improve their performance.
1.2 AimThe main aim of this research work is to assess and improve the design of
auger extruders used in clay extrusion process using computational fluid
dynamics (CFD) and Finite Element Analysis (FEA).
1.3 ObjectivesThe main objectives of this research work includes,
• Conduct a thorough literature search on previously completed
research works in the clay extrusion process.
2
• Investigate suitable CFD techniques to model the clay extrusion
process.
• Analyse the flow parameters like pressure and velocity for various
designs and operating conditions.
• Assess the performance of the clay extruder with changes in design.
• Investigate alternate designs and materials to improve the
performance of the extruders and reduce their capital costs.
• Experimentally validate the results obtained from the applied CFD
modelling technique.
1.4 Research methodologyThe objectives of this research work were achieved in three stages:
1. The first stage was dedicated to the use of computational methods for
determining the extrusion pressure and the power requirement of
extruders for various design and operational parameters.
2. The focus in the second stage was on experimental tests to assess
the performance of a miniature scaled extruder. The results obtained
from the experiments were used to validate the computational
methodology used in first stage.
3. The third stage of this research focused on using FEA to predict the
stresses induced on extruder components during the process of
extrusion, for various materials. It also looked at the costs and
technical benefits that could be achieved by using alternate materials.
1.5 Previous worksA similar effort was made by Jonathan Headley in 2009 and Alex Poyser in
2011, MSc. students at Sheffield Hallam University. In their work, both of
them have used CFD techniques to study the flow characters of the clay and
water system during the process of extrusion and assessed the performance
of extruders. A detailed review of their works and the results obtained are
discussed in Chapter-2.
3
1.6 Thesis outlineThis report is divided into five chapters suitably to give the reader a clear
picture about the need for design improvements of extruders used in brick
industries and the use of CFD, FEA based numerical modelling technique to
accomplish that.
A brief introduction is presented in Chapter 1, detailed review of existing
research in the modelling of extruders, experimental studies and clay
rheology is presented in Chapter-2. Experimental validation of the numerical
modelling approach and assessing the performance and flow parameters of
extruders and clay extrusion process using the CFD technique is presented
in Chapter 3. Assessing mechanically induced stresses using FEA
technique, potential alternative cost effective and light weight materials for
improving the efficiency of extruders is presented in Chapter 4. Conclusions
and suggestions for the future research work in this area are presented in
Chapter 5.
A brief review on the prospect of brick industries and brick manufacturing
process is presented in Appendix C.
Design, functional and process requirements of vacuum type de-airing
extruder and the association of flow parameters to the performance of the
system is reviewed in Appendix D.
4
Chapter-2 Review of existing work forceramic extrusion
2.1 IntroductionThe aim of this chapter is to provide a comprehensive review of scientific
works undertaken by academic researchers and industrial professionals,
focused on studying the flow parameters of clay and assess the performance
of extruders using numerical and empirical methods. The results obtained
and conclusions drawn from their studies are presented and discussed. The
review is based on three key areas that are necessary to build and simulate
a CFD model successfully; that includes numerical modelling methods for
simulating clay extrusion or a ceramic shaping process, experimental studies
conducted to assess key performance variables (like extrusion pressure)
involved in ceramic shaping process and works related to rheological
characters of clay-water system.
Even though there are different types of mechanical systems, which are
termed as extruders, were used in the process of shaping, discussed briefly
in Appendix- D, henceforth in this report the term extruders commonly refer
to auger extruders, unless and until specified. The extruder system
considered for this research work is vacuum type de-airing extruder, falls
under the category of stiff extruders used in the heavy clay structural ceramic
industries.
Due to the limitation in the availability of published works, that specifically
discuss the simulation of the extrusion process and design assessment of
extruders using CFD based numerical modelling technique, most of the work
discussed here do not have direct relation to this research work. However it
presents the reader with various scientific approaches and methods that
were used and how significant those works were to the methodology used
and results obtained from the numerical modelling approach undertaken
through this research work.
2.2 Modelling and simulation of extruder systemZhang et al. (2011) have investigated the process of clay extrusion in a de
airing type extruder, using CFD technique. In their research work they
investigated the velocity of the clay material, during the process of extrusion,
along the entire length of the auger and have assessed the variation of clay
velocity along the radial and longitudinal direction within the extruder
chamber. They have also studied the effect of varying moisture contents and
the auger speed on the velocity of the clay within the extruder chamber. In
their work they have used a Bingham Fluid model to represent the flow
physics of clay and water mixture and have assumed the flow process to be
isothermal and laminar. The effect of gravity and inertial force were not
accounted for in their model. Using a 3-D model with an unstructured T-grid
mesh, they have solved their model in FLUENT-CFD solver and have
presented their results.
It is understood from their work that the velocity of clay particles varies both
along the longitudinal and radial directions of an extruder chamber, during
the process of extrusion and also depends upon the moisture condition of the
clay.
They have also predicted from their model that the velocity of clay near the
wall zones (both at the hub's outer edge and barrel's inner edge) is almost
zero and the maximum value is observed in the middle (area between hub
and the barrel); which is demonstrated by the formation of an oval shaped
pattern for the velocity of clay at different sections of the auger.
The formation of the secondary flow zone (a circular flow pattern), as
discussed by them- demonstrates the plastic and elastic properties
possessed by the clay during extrusion. The change from elastic zone to
plastic zone is subjected to shear force experienced from the extruder
components.
They have concluded from their study that the radial velocity is an important
component for the mixing and plasticity of the material and the axial velocity
is important for discharge rate. They have also mentioned that both these
velocity components are influenced by the moisture content in the clay
material used.
Hedley (2009) attempted to study the flow of clay through full scale de-airing
type vacuum extruders using CFD technique. In his work he has used a 3-D,
multiphase laminar flow approach and Herschel-Bulkley's fluid model to
define the flow physics of the clay. He has assessed the dynamic pressure7
developed during extrusion and velocity of clay in the direction of extrusion;
with respect to various pitch length and speed of auger. He has used
unstructured T-grid mesh elements to mesh the components of extruder and
solved the model using FLUENT solver. In order to achieve a good quality
mesh and avoid complexity while meshing the geometry, he has used a
simplified geometry (uniform rectangular cross section) for the auger and
neglected the effects of barrel and liner geometry. Using a constant density
value for the clay material, the model has been solved with the effect of
gravity. From his work it is understood that the pressure during extrusion
rises gradually from the inlet of the auger and reaches a maximum value at a
certain length of the auger and further down along the length of the auger the
pressure reduces as the material approaches the exit area, as shown in
Figure 2-1.
Pressure gradient along the length of screw 1 and 2
300
250
£ 200 «^ 150 wV)2 100 Q.
50
0
.
- * - ..—t ‘ ' Vly.J
r . p ' . *'V ,-jr *' ; . -•*/» I**J
t-'
—- • ~ : ■- ;
♦ Screw 1• Screw 2
200 400 600 800 1000 1200 1400 *600
Screw length (mm)
Figure 2-1 Extrusion pressure at various length o f extruder
[Source: Hedley, 2009]
Also the dynamic pressure varies at different sections of auger with respect
to the change in pitch length and speed of auger, as shown in Figure 2-2 and
2-3.
8
Dyn
amic
p
ress
ure
(P
a)
Effect of pitch length on pressure gradient along the screw
« Sere* 3
■ Screw 4
Screw 5
Screw 6
0 200 400 600 800 1000 1200 1400 1600
Distance along the sscrcw
Figure 2-2 Dynamic pressure at various length of extruder
[Source: Hedley, 2009]
Affect on the magnitude of dynamic pressure acting on the screw hub and spiral as RPM increases
250
re"t 200a>UI 150
S' 100EreI 50 O
0
Figure 2-3 Dynamic pressure variation with respect to auger speed
[Source: Hedley, 2009]
The same trend was observed in the velocity as well, shown in Figure 2-4.
5 RPM = 15 screw hub ■ RPM = 22.5 screw hub□ RPM = 15 spiral front face□ RPM = 22.5 spiral front face
Screw component at specified RPM
9
Effect of velocity magnitude of the clay over the length of the screw
♦ Screw 1 ■ Screw 2
Screw 3
Screw 4
* Screw 5
• Screw 6
+ Screw 7
- Screw 8- Screw 9
Screw 10— Poty. (Screw 7)
0 200 400 600 800 100C 1200 1400 1600
Screw length (mm)
Figure 2-4 Clay velocity at various lengths of extruder
[Source: Hedley, 2009]
The results and discussions presented in his work, clearly indicates that the
dynamic pressure and the velocity of clay observed during extrusion is
influenced by the pitch length and speed of the auger.
Poyser (2011) attempted to use CFD technique to assess the performance
of lab-scale model of an extruder system. Using a 3-D steady state, single
phase laminar flow model approach with Herschel-Bulkley's fluid model for
clay, he has assessed the performance of the scaled extruder. In his model,
he has used unstructured T-grid mesh to discretize the geometry and Fluent-
CFD solver to solve the model. From the results obtained through his work,
he has suggested that the use of unsteady state method in CFD modelling
could help to gain a better understanding of the flow process within an
extruder system.
Handle (2007) has discussed about the application of simulation in ceramics.
He has reviewed about numerical simulation of ceramic extrusion using CFD
technique, and has presented various governing equations that typically
represent the flow physics of ceramic materials. The author proposes that
the ceramic material exhibits visco-plastic behaviour and is expected to take
0 7
I & ■o3
0 6
0 5
0 3
0.2
0 1
0
10
the form of either a Bingham or Casson model. Figure 2-5 shows typical
viscosity profiles of materials that follow the above mentioned fluid models.
,x1oP
(0 ‘ CL 'P->%*</> O .8 1*>i—(C<1)x:<o L
Bingham
«BCasson
0 2 4 I5 3 1shear rater [s’ ]
Figure 2-5 Viscosity profile for Bingham and Casson model fluids
[Source: Handle, 2007]
[Note: Unit for Shear viscosity is Pa.s, it is misprinted as Pa in the above picture]
Continuity equations for mass, momentum and energy, proposed by the
authors are based on incompressible, Bingham fluid model. The reason for
including the energy equation in the numerical model is because the
viscosity of ceramic material is temperature dependent. He recommends that
the accurate definition of ceramic material properties like density, viscosity
and specific heat capacity at constant volume and specific heat conductivity
is a vital part in ceramic extrusion process simulation.
Bouzakis et al. (2008) have investigated the stress distribution on the
surface of a die mandrel, during the process of extrusion, using experimental
and numerical modelling techniques. Using Finite Element Method (FEM)
based numerical simulation (DEFORM); they have assessed the clay sliding
velocity; various stress elements and its distribution on the surface of the
mandrel. They have also compared the results obtained with the
experimental results. Figure 2-6 shows the investigated model and results
obtained.
11
Supporting pdMandrel
Die with mandrel used for the study
Figure 2-6 Stress induced on die mandrel during wet clay extrusion
[Source: Bouzakis et al. (2008)]
Through the experimental and numerical model results, they have derived a
characteristic equation that represents the rigid- viscoplastic behaviour of wet
clay, observed during extrusion. Based on the assumptions they made to
include the frictional factor during extrusion, they suggests that the flow
pattern of the rigid viscoplastic material like clay, is not effected by the friction
on the wall surfaces and the stress induced on the die wall depends on the
speed of extrusion .
Doltsinis and Schimmler (1998), using FEM, have investigated the process
of ram extrusion used in making ceramic tubular components. In their work,
considering the ceramic paste to be a viscous compressible fluid, they have
developed a suitable numerical model to represent the flow features of the
material. Using an analytical approach to determine material parameters
12
Sliding Velocity of elay-dbtribution pattern on mandrelFlow stress (Mpa]
1 0 30 0 40 0 5 0 0 6 0
Flow stress observed in clay column
[rrm/scc A = 180 00r s ?io noC - 74(1 UO U = ii/U U J E = 3COOO F = 33000 G =200 00
required for the numerical model they have predicted the flow velocity of the
material within the barrel, die and the tool. By applying the developed FE
model to an actual industrial scale system and through the results obtained,
they have concluded that the FEA is adequate enough to represent the flow
of such viscous materials and such computational methods can be used for
modelling ceramic extrusion process to a higher degree of appropriateness.
Discussion:-
The efforts undertaken by professionals in various scientific communities, to
apply numerical modelling and simulation as a tool to model the clay
extrusion process, clearly indicates that there is an indisputable need for
such tools in the ceramic industries. With the availability of wide range of
fluid flow models and modelling techniques that are suitable, as illustrated
above, there is inadequate evidence on the applicability of a particular
numerical modelling technique and methodology suitable for auger extrusion
process. Though Zhang et al. (2011), Hedley (2009), Poyser (2011), have
attempted to use CFD to model the auger extrusion process and assess the
performance of an extruder, their methodology does not really account for all
the major features of an auger extrusion process. For instance, in all their
work, the material density is considered to be a constant, which is not true in
a real scenario. Also they have not given much importance to the clearance
volume between the auger and the barrel in their model, which is considered
to have a major influence on the extrusion pressure and the material flow.
The modelling technique and methodology used in this research work has
taken into consideration of additional factors like change in density,
temperature and temperature dependant properties that influences the
process of extrusion and performance of an extruder. A detailed description
about the CFD modelling approach undertaken in this research is presented
in Chapter 3.
2.3 Design and performance evaluation of extrudersJohnson (1962) studied the design parameters of variable pitch or variable
volume augers that influence the performance of an extruder system used in
sewer pipe production using experimental methods. Combining both
13
geometrical and experimental methods, he has analysed the influence of
auger diameter, pitch and conditions of raw material on the extruder
performance. He has proposed that the determination of Displacement
Volume Ratio (DVR) (function of pitch of the auger) of augers using
mathematical methods is a significant approach in studying and comparing
their performance.
The result obtained through his work indicates that the volumetric efficiency
of a variable extruder increases when the size of the extrudate increases,
even if the type of clay remains the same. He suggests that the efficiency of
an extruder system depends on extrusion pressure, clay particle size and
design modifications to the pitch and diameter of an auger. Suitable
considerations to these parameters at the design stage could result in a
more efficient system.
Lund et al. (1962) have studied the operating characteristics of augers used
in pipe clay extrusion, with respect to various design parameters at specific
moisture content of clay. In their work they have assessed the performance
of constant and variable pitch augers. They have also determined the validity
of scaled extruder results when extrapolating it to a full scale system. Based
on the design data available for the augers used in production and using an
empirical approach, they have designed experimental augers and assessed
their performance. Using the approach of calculating DVR value to compare
the performance of auger system, as discussed by Johnson (1962) and by
employing a special device to maintain the consistency of the clay, they have
assessed the extrusion rate, power consumption; die pressure and internal
radial barrel pressure for constant and variable pitch auger systems. Figure
2-7 shows the effect of varying the displacement volume on the performance
characters of augers for a constant pitch auger and Figure 2-8 shows the
characteristic curves of the various experimental augers used in their study.
14
l / l 6 " BA R R LL G L E A i^A g.C E ,- S O F T - AG ED - D E A IR E D
4 0
0.6
3 5>4
12 -
02 0POWER __CONSUMPTION 16 RP*M
2 510-
2 0BARREL S T R E S S -16 RPpm
0 5EXT. R ATE - 2 6 RPUA
DISPLACEMENT VOLUME,
Figure 2-7 Effect of auger pitch variation on extruder performance
[Source: Lund et al. (1962)]
AUGER NUM BER PO W ER - 4 2 RPM
POWER - 2 6 i RPM
POWER - 16 IR P M
2 IB 'l
Si2 Oo
EXT. RATE 4 2 RPM
EXT R ATE — 2 6 RPMzo10o£EI-
EXT. RATE — 16 RPMTHRUST-26 RPW* OR STIFF CLAY THRUST-16RPNM OR SOFTCLAY
aUJ*Oa.
(£UJ
XUJ
BARREL STR-ESS - 2 6 RPM BARREL S T R ttS S — 16 RPM
D ISPLACEM ENT VOLUM E /R E V . (DVR.
Figure 2-8 Performance characteristics profile for a typical auger
[Source: Lund et al. (1962)]
From the results obtained through their work on constant pitch auger, it is
understood that the increase in auger speed and decrease in DVR (pitch)
increases the extrusion rate. Also that power consumption is a function of
15
auger speed and clay consistency. Barrel stress increases with increase in
auger speed, clay stiffness and clay particle size.
The results obtained through their work on variable pitch auger indicate that
the extrusion rate for a variable volume or variable pitch auger is higher than
that of a constant pitch auger. Also the compression ratio (ratio of change in
volume between successive auger flights) of variable pitch auger influences
the extrusion rate. They have also noted that changes in the tip volume of an
auger also influence the extrusion rate.
In both the cases, they have noted that extruding clay with smaller particle
size resulted in an increased extrusion rate and better flow character,
compared to extruding clay with large particle size. This also confirms to the
suggestion by Norton (1954).
Seanor and Schweizer (1962) have investigated about mechanical and
physical factors that affect auger design and its performance. They have
suggested that the co-efficient of friction is an important factor that has
significant effect on auger's performance. Also in order to have a better flow,
the clay contacting surface in an auger should be sufficiently sloped to
achieve better sliding for the clay, which enhances its flow. Hence they
believed that reducing the pitch of auger will reduce the co-efficient of friction
and will lessen the augers performance. This contradicts the above
discussed results, presented by Lund, et al. (1962). They had also
postulated suitable design modifications for the leading face of an auger
(working face of an auger which is subjected to stress and wear is called the
leading face of an auger), to enhance the performance of a new auger and
increase its life, right from installation. Since they did not validate their
suggestions with any experimental results and also the co-efficient of friction
varies with respect to clay stiffness, clay material and auger material, it is
hard to include it at the earlier stages when designing an auger.
They have also studied the effect of adding half pitch augers or wings or half
flights, to the tip of main auger system. Through investigating the
performance of the extruder system by having single, double and triple wings
at the end of the main auger, they have suggested that having wings in the
16
tip ensures smooth and uniform feeding of clay to the die section from
extruder and ensures uniform pressure distribution over the entire area of
die, as shown in Figure 2-9. Also an auger with three wings performs more
efficiently than augers with single and double wings, when it is ensured that
the die is mounted properly.
4 SECONIDuration 3\ litensity \ 180°
Seci
SINGLE WING
90°± SecsIntensity
Duration IDOUBLE WING
Ir tensity 60° Durption l|Sec.
120° 240° ____DEGREES OF ROTATION
360'TRIPLE WING
Figure 2-9 Pressure waves experienced in auger with half flights
[Source: Seanor and Schweizer, 1962]
Parks and Hill (1959) have developed mathematical equations for the
purpose of designing augers and die for extrusion application. Through
performing experiments in clay like plastic material with specific moisture
content, they have developed a mathematical representation for calculating
extrusion rate for auger and die section. They have also mentioned that the
extruder system comprising the barrel, auger and die, is divided into different
zones based on the functions they perform at different stages of extrusion
process and the pressure during extrusion varies across each of these
zones, as shown in Figure 2-10.
17
Toed
D t l14 ] l-J—( b )
{ D ieC on vey ing ( | )
M e t e r in g
Atm os - pheric
Figure 2-10 Typical pressure distribution in an extruder
[Source: Parks and Hill, 1959]
It is understood from their mathematical model that the extrusion rate at
auger section is a function of outside diameter of auger, depth of auger
channel, helix angle, clay material and speed of auger. Whereas the
extrusion rate at die section is a function of pressure and it has linear relation
as shown in Figure 2-11.
Die Hole Die Thic
D iam . - O :kn ess - I "
25“ y
\\
\
0 2 4 6P ressu re ( Ib ./s q . in .) x IO - 2
Figure 2-11 Effect of extrusion rate on die pressure
[Source: Parks and Hill, 1959]
It is clearly understood from their results that the pressure increases as the
extrusion rate increases in the die section. They suggests that, though this
linear relationship curve was not obtained for an actual clay material, but still
it holds a good representation of what happens in clay extruding augers.
Handle (2007) suggests that the pressure developed within the extruder and
die has greater influence on the quality of extruded product and performance
18
of extruder. He has discussed the effects of changing geometric, process
and operating parameters on the extrusion or pressure developed during an
extrusion process. The results presented by him show, under normal
circumstances the pressure profile for an extruder system will be like as
shown in Figure 2-12.
length of nozzle length of cylinder
o oSSP'
pressure generatorpressure consumer
RSP1
length of backlog
Figure 2-12 Forming pressure profile under normal condition
[Source: Handle, 2007]
As mentioned earlier it is clear that the pressure within the extruder unit rises
gradually from a lower value to a peak value at a certain length of auger and
then it gradually decreases within die section to attain ambient conditions.
The author describes these functions as pressure generator and pressure
consumer. It is also understood from the above figure that the maximum
extrusion pressure is experienced at the tip of the extruder. This pressure
profile is similar to the other theories about extrusion pressure proposed by
other authors, whose works were discussed earlier in this chapter.
According to him, modification to clay moisture content, die (nozzle)
geometry and feed rate has a significant effect in the extrusion pressure
formation and distribution within the extruder and die system. The various
pressure profile observed for such changes, suggested by him is shown from
Figure 2-13 to 2-16.
19
length of nozzle length of cylinder
o o•RSPl!
pressure generatorpressure consumer
P3
A A1length of backlog
Figure 2-13 Effect of increasing clay stiffness on extrusion pressure
[Source: Handle, 2007]
length of norzle length of cylinder
o o;r s p RSP2i RSP3
V
pressure generatori
!
I
I
RSP1 RSP3
length of backlogi
Figure 2-14 Effect of decreasing clay stiffness on extrusion pressure
[Source: Handle, 2007]
20
length of nozzle length of cylinder
o& x > o
0 /v\ RSP2 / \r s p i ;V Y-v S
pressure generatorp re ss u re
I/A1 RSP2IRSP1
length of backlog
Figure 2-15 Effect of changing die geometry on extrusion pressure
[Source: Handle, 2007]
length of nozzle length of cylinder
& % f fO OA
\ R S P 2 / \r s p i ;
pressure generatorpressure consumer
R 5P 2IRSP1
tenglh of backlog
Figure 2-16 Effect of changing feed rate on extrusion pressure
[Source: Handle, 2007]
21
The effects of changing process, operating and design parameters on the
extrusion pressure, as discussed by Handle (2007), clearly indicates that the
performance of an extruder system depends on one or more independent
variables. It is also evident that the process of experimental analysis, to
study the effect of each such change consumes time and resource.
Kocserha and Kristaly (2010) have theoretically and experimentally
investigated the effect of die shape on the performance of an extruder
system and on the quality of extrudate. They have used a Bingham fluid
model for representing the flow parameters of clay in their theoretical
evaluation. They suggest that the optimization of extruder component
geometries or rotation speed of the auger have beneficial effects on
extrudate quality and power consumption. They also suggest that the
extrusion pressure depends on rheology of the clay. The plastic flow
character of clay throughout the entire cross section of the die is considered
as an important factor to avoid crack formation that occurs during lateral
processing of the extrudate. The results obtained from their work for a
specific clay water mixture proportion demonstrates, a) the effect of die
shape on extrusion pressure and power consumption at different auger
speeds, shown in Figure 2-17, b) the effect of die shape on the physical
properties of extrudate, shown in Figure 2-18.
w 2.5 -
0.5-
Rotation, 1/min
Extrusion pressure Vs Auger speed for various die shapes
Power consumption Vs Auger speed for various die shapes
■ Spherical R25
■Cone
850-
i 800 ■
I 750-
I 700-
| 650 - | 600-
| 550-
| 500-
§ 450 - | 400-
o 350 -
300 -35
Rotation, 1/min
Figure 2-17 Effect of die shape on extrusion pressure and power
[Source: Kocserha and Kristaly , 2010]
22
40.00
35.00
“ 30.00 .c£ 25.00 £" 20.00
15.00—it—Spherical R25
^H-Cone - O - Torus R25
10.00
5.00
0.0015 35 55
Rotation, 1/min
13
12.5
12
2 11.5
Spherical R25
- ♦ -C o n e
-O —Torus R2510.5
105515 35
Rotation. 1/min
Strength of extrudate Vs Auger speed for various die shapes
Density of final product Vs Auger speed for various
die shapes
1.84
■S 1.82 -
| 1.76
0 1.74 - -♦ -S p h e rica l R25
-♦ -C o n e
-O -T o ru s R25c 1.72 -
Rotation. 1/mln
Water absorption rate of extrudate Vs
Auger speed for various die shapes
Figure 2-18 Effect of die shape on quality of extruded product
[Source: Kocserha and Kristaly, 2010]
It is understood form their work that any change made to the geometrical
parameters of the extruder components not only affects the performance of
the extruder, but also the physical characters of the product.
Discussion:-
The work undertaken and the results obtained by various authors, as
presented above, clearly illustrates that an optimised design of extruder
components, die and material properties of clay plays a vital role in
determining the performance of an extruder system. Most of their works
focused to determine the optimised design requirement has resulted from
time and cost consuming experimental works and none of them considered
using computer based modelling techniques to reduce cost and time.
However the valuable results and suggestions for various design changes,
acquired from their work, were used to justify the results obtained from the
computer based modelling work presented in this report.
23
2.4 Clay-Water rheologyThe rheological properties of clay-water system, has been a subject of
interest in different fields of engineering for many years, that includes for
example soil, civil engineering, and ceramics etc. A number of research
works have been undertaken to develop mathematical models to predict and
understand the flow physics of clay-water system. Some of those key works
and significant findings were useful in choosing a suitable flow model used in
the CFD modelling work undertaken through this research work and are
discussed here.
Amin et al. (2009) have discussed their experimental work on optimizing the
mixing variables that influences the rheology of clay sewer pipe paste
(Aswan clay-found in Upper Egypt). In their work they have clearly illustrated
the effect of water content in a clay water system on the viscosity, as a
function of shear rate, shown in Figure 2-19.
500
2500
£ 2000
-fc'mI> 1500
S
% water = 25 j
Vo water - 27
% water — 30
% w a te r — 32
°/n w a ter — 35
% water = 37
Vo water = 40
250 300
Shear rate ( s' 1 )
Figure 2-19 Viscosity of pure clay sewer paste
[Source: Amin et al, 2009)]
The result obtained by them is for a pure clay water mixture, with the particle
size of 0.2 mm. They suggest that additives like grog or any adhesive to the
pure form of clay will alter the above shown results. Also the mathematical
model that fits well to predict the above shown results, as suggested by them
is the Bingham model (Equation 2.1).
t = k.y + t 0 2 .1
24
Where, r= shear stress (Pascal), y = strain rate (s'1), k= consistency index
(Pa.sn), x 0= yield stress (Pascal). (When x > t 0 flow & x < t 0 solid)
The values of the constants k and x0 are said to vary with respect to water
content. The results obtained from their work indicates that when the clay is
soft (more water content), it tends to yield quicker and the viscosity attains a
lower value in less time, compared to stiffer clays. Also the value of k and x0
dictates the initial viscosity values and the flow curves of a fluid based on
Bingham model.
Ormsby and Marcus (1963) have discussed the variation of clay viscosity
with respect to the size of clay particle. Through their work they have noticed
that the flow curve for various types of clays varies with respect to particle
size, even when the amount of moisture is maintained to the same level.
They suggest that when clay added with 50% of water to the weight, 1)
behaves like a Newtonian fluid for particle size with 44-10, 10-5, 5-2 micron
fractions, 2) behaves like a pseudoplastic fluid for 1-0.5 and 0.5-0.25 micron
fractions and 3) like a dilatant fluid for 2-1 micron fractions. They have also
observed dilatant behaviour for clay water mixture, even at lower percentage
of water content. It is clear from their work that one should account for the
particle size of clays as well, while determining or choosing a value for the
variables associated with the rheology of clay.
Al-Zahrani (1997) has developed a generalised mathematical model to
predict the viscosity as a function of shear rate for non-Newtonian fluids. He
claims that the model is suitable to predict the behaviour of shear thinning
fluids like clay water, polymer melts, paints and paper pulps etc. and is better
than the traditionally used Power law and Herschel-Bulkley's model. The
mathematical models proposed by him are shown in Equation 2.2 and 2.3.
25
Where, t= shear stress (Pa), A, B= Constants, n=model index and y= shear rate (s'1)
The results obtained by using his model to predict the viscosity of a gelex
polymer fluid is shown in Figure 2-20.
6
5
4
3
2
1
O
100 200O 300 400 500 700600
Figure 2-20 Viscosity profile of a typical shear thinning fluid
[Source: Zahrani, 1997]
He claims that the predicted result using his model is accurate when
compared to the experimental results and suggests it to be an alternate and
improved approach to Herschel-Bulkley's model. The key things to be noted
from his work includes, the viscosity profile of a shear thinning fluid as a
function of shear rate and suggestion about the suitability of Herschel-
Bulkley's model in predicting the shear thinning fluid rheology.
Maciel et al. (2009) have studied the physical and rheological properties of
Kaolinite clay and water mixture using Herschel-Bulkley's model. They
suggest that material, like clay-water mixtures, could be well represented by
Herschel-Bulkley's viscoplastic non-linear rheological model. Their study was
focused to develop behaviour laws for predicting the flow behaviour of mud
found in torrential lavas. Based on the experimental and mathematical model
results obtained from their work, they suggest that the flow characters of
Kaolinite clay and water systems predicted using Herschel- Bulkley's model
was in good agreement with the measured values. They also suggest that
Herschel-Bulkley's model is better for predicting the yield stress (deformation
of the fluids) experienced at lower shear rates than the Bingham model,
which is good for fluids yield at high shear rate.
26
Nelson and Andrews (1959) have experimentally investigated the forces
required to shear plastic clay (Florida Kaolin), both within its own structure
and at clay-metal surface interface. They suggest that, in addition to the
basic factors like type of clay material and water content, the shearing of
plastic clay is also influenced by pressure distributed within the clay and
speed of rotation of metal surface that comes in contact with the clay.
Results obtained through their investigation indicate that the pressure
distribution in a clay water system is a function of yield value and the force
required to shear plastic clay increases with increase in pressure to a certain
extent and remains constant. It also increases with the speed of the metal
surface with which the clay encounters.
Mahajan and Budhu (2008) have proposed an analytical model to
determine shear viscosity of clay-water system (Kaolin clay), using Casson's
Model. They suggest that it is applicable for mixtures with very low water
content. The results obtained through their work indicate that the shear
viscosity reduces with increase in percentage of water content. They also
suggest that the accurate prediction of viscosity of clay water system using
numerical model depends on the rheological model used.
Andrade et al. (2010) have developed a mathematical model for evaluating
the clay plasticity. Comparing their model with experimental results, they had
confirmed that their model gives a more accurate approach in obtaining the
plasticity for wide range of ceramic materials, with different mineral and
moisture content. From the results obtained through their work, it is
understood that the plasticity value of clay varies with respect to its mineral
contents, even if the moisture content remains the same.
Discussion
It is evident from the above information that the flow physics of clay-water
system have been studied for many years. The research activities
undertaken and results obtained clearly indicate that the flow characteristic of
clay-water system varies with respect to the type of clay, additives, particle
size and moisture content. It also influences the performance of the machine
that it encounters. From various mathematical models used to represent
27
highly viscous materials like clay water mixture, the choice of an appropriate
numerical model, that suits the problem of investigation, depends upon
experimental and availability of other resources.
2.5 ConclusionThus a review of previously completed works relevant to the subject of
interest in this research was presented in this chapter. The various
methodologies used, results obtained, their advantages and disadvantages
were briefed clearly for further understanding and also to acquire substantial
validation to the methodology and modelling technique used in this research
work.
28
Chapter-3 CFD modelling of clay extruder
29
3.1 IntroductionThis chapter presents a brief review about the basic classification of fluids
and available numerical models for modelling the viscosity of non-Newtonian
fluids (exhibited by the clay-water mixture). It also reviews the basics about
CFD modelling technique. The CFD modelling approach used in this
research work is discussed, explaining the background concepts involved in
modelling various physical processes involved in the clay extrusion.
Experimental validation of the modelling approach, results obtained from
various CFD simulations along with the evaluation of performance characters
for various design and operating conditions of the extruder are presented
and discussed.
3.2 Fundamental classification of fluidsFundamental classification of fluids includes Gases- substances that deform
under shear stress and Liquids- substances that continuously deform under
shear stresses. The dependency of continuous deformation of liquids
subjected to shear stress is an inherent property of the substance and this
has led to further classification of fluids,
1. Newtonian fluids: The fluids that have a constant viscosity or deform
linearly to the applied shear stress, as shown in Figure 3-1, are called
Newtonian fluids.
Y
Shear stress vs. Strain rate Viscosity vs. Strain rate
Figure 3-1 Newtonian fluids
[Source: Brookfield Engineering, 2010]30
Newtonian fluids are commonly agreed to obey the Navier-Stokes
equation and the best curve fit mathematical model, accepted and used
widely to describe the flow of such substances is shown in
Equation 3-1.
duT = #t— = / t * y - - 3 . i
du . 1Where p= Shear viscosity (Pa.s), — or y = Rate of shear (s )uy
2. Non-Newtonian fluids: Fluids that do not obey the basic
principles of Newtonian fluids are commonly described as non-
Newtonian fluids. The flow of such liquids is subjected to shear
stress and is influenced by more than one factor under certain
circumstances. There are various types of such fluids that exist in
nature. The three basic categories under which these types of
fluids are grouped include a) time independent non-Newtonian
fluids, b) Time dependant non-Newtonian fluids, and c) Visco
elastic fluids.
a. Time-Independent non-Newtonian fluids: The rate of shear for such
type non-Newtonian fluids depends only on the instantaneous value of
the shear stress and is independent of time. It is also referred as non-
Newtonian viscous fluids [Wilkinson,1960].Depending on the function
of rate of shear to the applied shear stress, the different types of fluids
grouped under this category includes I) Pseudoplastic fluids or Shear-
thinning fluids II) Visco-Plastic fluids or Bingham plastics III) Dilatant
fluids or Shear thickening fluids.
Pseudoplastic fluids: In such fluids, the rate of shear is not linear to
the applied shear stress, the viscosity decreases with increase in shear
rate and it becomes linear only at a very high shear rate, as shown in
Figure 3-2.
31
T *1i \
A B
Shear stress vs. Strain rate Viscosity vs. Strain rate
Figure 3-2 Pseudoplastic fluids
[Source: Brookfield Engineering, 2010]
The viscosity values are termed as Zero shear viscosity and infinite
shear viscosity. The mathematical models that best describes the
behaviour of such fluids include,
Power law model= t = kyn 3.2
Where k = Flow consistency index (Pa.sn), n=power law index (<1 for shear thinning fluids)
Where p 0lPoo= Zero and infinite shear viscosity (Pa.s), X = time
constant, n=flow index.
The other, not widely used models include the Prandtl, Eyring, Powell-
Eyring and Williamson.
Viscoplastic fluids: These type of fluids when subjected to shear
stress will start to flow only after a certain value of stress is reached.
This value is commonly described as yield stress and beyond this value
the flow could be linear or non-linear as shown in Figure 3-3.
Carreau Model= ~ —~Ho-Hoo
Cross model= °°H-Hoo _ iHo —Hoo l + ( * Y x y )
32
A BStrain rate vs. Shear stress Viscosity vs. Strain rate
Figure 3-3 Visco plastic fluids
[Source: Brookfield Engineering, 2010]
Viscoplastic fluids that have a linear profile after the minimum yield
stress are called as Bingham plastic fluids. Mathematical models
commonly used to describe the behaviour of such fluids include,
Bingham plastic model=x - t0 = K y 3.5
Herschel-Bulkley's model= t = t0 + kyn — 3.6
Where r 0=minimum yield stress threshold (Pa),
And, Cross model-another type of recommended mathematical model,
for studying the behaviour of such fluids.
Dilatant fluids: It is similar to Pseudoplastic fluids [Wilkinson 1960]. In
this type of fluids, the fluid viscosity increases with rate of shear, as
shown in Figure 3-4. Clay slurries, candy compounds and sand-water
mix are few examples.
Shear stress vs. Strain rate Viscosity vs. Strain rate
Figure 3-4 Dilatant fluids
[Source: Brookfield Engineering, 2010]
It is suggested that even power law model could be used to model such
fluids, with flow index value greater than unity [Wilkinson 1960].
b. Time-dependent non-Newtonian fluids: The rate of shear and shear
stress, for such type of non-Newtonian fluids, are functions of time.
Such type of complex fluids is further divided into a) Thixotropic fluids-
characterised by decreasing apparent viscosity or shear stress with
respect to time, when subjected to constant rate of shear. As shown in
Figure 3-5. b) Rheopectic fluids - characterised by increasing apparent
viscosity or shear stress with time, when subjected to constant rate of
shear. As shown in Figure 3-6.
--------------------------> t
Figure 3-5 Thixotropic fluids
[Source: Brookfield Engineering, 2010]
34
1]A
------------------------------ > t
Figure 3-6 Rheopectic fluids
[Source: Brookfield Engineering, 2010]
c. Visco-elastic fluids: This type of fluids exhibits both elastic characters
like solids and viscous character like fluids, as shown in Figure 3-7.
The suggested mathematical model that represents the behaviour of
such fluids is Maxwell's model, shown in Equation 3.7.
Where, G = rigidity modulus (Pa), t= Rate of shear stress (Pa).
Through the knowledge gained from the classification of fluids, basic working
principle of extruders and various scientific works completed previously, it is
sensible to consider the clay-water system as a non-Newtonian fluid and
exhibits a Visco-plastic fluid or shear thinning fluid character. Its behaviour
could be summarised as, the mixture when subjected to a shear force does
not deforms readily until it reaches as particular value and this value is
tFigure 3-7 Visco-elastic fluids
[Source: Brookfield Engineering, 2010]
35
termed as the minimum yield stress threshold. Once this value is attained, it
continuously deforms under the action of shear stress to the extent where
the viscosity reduces to a very low value and remains constant (at this point
the fluid is set to have reached the Newtonian fluid flow regime). Herschel-
Bulkley's model, discussed above along with other available mathematical
models for non-Newtonian fluids, which includes the functions representing
both yield stress region and constant viscosity region, proves to be the best
suitable model for clay like materials. Due to its extensive use in various
fields for studying clay-water rheology and recommended for CFD modelling
of clay like materials [Ansys-Fluent 12.0 user's guide 2010], in this
research work it was decided to use Herschel-Bulkley’s fluid model to
simulate the process of clay extrusion and assess the performance of
extruder using CFD.
3.3 Process of CFD modellingThere are three different types of numerical modelling techniques commonly
used in engineering applications: a) Finite Difference Methods (FDM) b)
Finite Element Method (FEM) and c) Finite Volume Method (FVM). The
fundamental difference between all these techniques is based on the way a
functional variable is represented and with the process of discretisation
[Versteeg and Malalasekera 1995]. CFD is one of the computational
techniques used for solving internal and external fluid flow problems and
associated heat transfer phenomenon. The three common equations
involved in any CFD model are equations for conservation of mass,
momentum and energy. Irrelevant to the nature of problem, these equations
will always be included in the model; additional equations in the model will
depend upon the nature of the problem investigated. The various types of
flow physics that can be modelled and investigated using CFD is shown in
Figure 3-8.
36
| Viscous Fluid
Convection
Fluid
TurbulentLaminar Radiation
Steady
Conduction
Heat TransferInviscid Fluid
T ransient/Unsteady
Compressible (Panel Method)
External (Airfoil, Ship)
Internal (Pipe, Channel)
Compressible (Air, Acoustic)
Incompressible (Water, Low speed air)
Computational Fluid Dynamics & Heat Transfer
Figure 3-8 Flow physics features in CFD
[Source: Jiyuan Tu et al, 2013]
Major steps involved in any CFD modelling process includes,
1) Pre-processing: Generating suitable CAD geometry to represent the
domain or domains of interest and meshing. Meshing is defined as
discretizing the domain or the CAD geometry into suitable finite number of
volumes using any standard mesh generating software. GAMBIT and ICEM-
CFD are some of commonly used meshing software. In this stage, the
physical and chemical phenomenon to be modelled and boundary conditions
will be defined. The boundary conditions can be even defined or altered in
the next step of the modelling process. Gambit was used for meshing the
extruder geometries investigated in this research.
2) Solver setting: A suitably meshed geometry will then be imported to a
solver, where appropriate numerical techniques, flow equations and
variables for solving the problem will be defined. This is required for solving
the physical or chemical phenomenon of a flow process defined earlier.
Examples of commercially available solvers for the application of CFD
problems includes FLUENT, STAR-CD, CFX, FLOW 3D, PHOENICS and
37
FEMLAB and all these solvers are based on FVM technique. In this research
work the extruder model was solved using Ansys- FLUENT 12.0.
3) Post-processing: The primary function in a post processing stage is
reviewing the results obtained from the solver. For example pressure,
velocity and temperature distribution in a flow regime. Recent advancements
in the capability of computer graphics, has enhanced this process and
proves to be more useful tool in communicating the results of a solved flow
problem to end users.
A flow diagram that briefs the various stages involved in a complete CFD
analysis is shown in Figure 3-9.
38
Geometry creation
(2-D or 3-D CAD model of the flo w domain)
Meshing
(Di scretisi ng the domai n usi ng 2-D or 3-D
structured or unstructured grids or mesh and
define boundary conditions)
Quality of mesh
Check the quality
and quantity of the
mesh, w .r .t. solution
and computational
Solver
(I m port the m eshed ge om etry i nto th e solver
and define the required flo w equation, type of
analysis and set the vari abl es accordi ng to the
convergence requirem ent)
Convergence and residual monitoring Solution
dependency on
the mesh
refinem ent
required to be
evaluated
Solution
converged(Is there a significant
convergence noted in
residuals fo r certain
iterations or time steps)
Result evaluation
(Pictorial or graphical representation of the
results fo r fu rther study)
Figure 3-9 CFD modelling process flow diagram
39
3.4 CFD modelling of extruderThe methodology used to set up the flow problem of clay extrusion and
assess the performance of an extruder in the CFD solver is described below
in this section. The process of set up remains the same for all the CFD
analysis discussed in this report.
3.4.1 Geometry creationThe various standard sizes of extruders designed and manufactured by C.F
limited, for the process of ceramic extrusion (mainly bricks) is provided in
Table 3-1.
Machine Size (Extruder diameter)
CENTRIM 406.40 mm (-1 6 inch)
CENTEX430 mm (-1 6 inch) ,
500 mm (-19.68 inch)
60F 422.27 mm (-16.625 inch)
90BD 488.95 mm (-19.25 inch)
Table 3-1 Craven Fawcett extruders for brick making
The Centex series of extruders are the most widely used extruder system by
many of C.F customers. Considering the feasibility in obtaining any valuable
field based data to validate the numerical model investigated in this research,
it was considered to be sensible approach to model and assess the
performance of CENTEX type machines. Flence the various sizes of full
scale extruders from CENTEX series, considered for the investigation
includes 430 mm, 500 mm and 600 mm. The 600 mm extruder is an
extended version of the 500 mm extruder, targeted for higher productivity
rate. Proposed for a specific requirement, it was the first of its kind that the
company were intending to manufacture and the design engineers were very
keen to obtain performance comparison data with respect to its
predecessors. So the 600 mm extruder was also included in this numerical
modelling work and its performance was assessed and compared.
40
The domains of interest include barrel liner, auger with shaft (collectively
called as extruder) and die. The required 3-D geometry of the components
was created using Autodesk-lnventor and Pro-Engineer Wildfire.
3.4.2 Geometry discretisationThe 3-D CAD model of the extruder geometries created in the above step
were discretised using Gambit. The different types of surface mesh elements
available in Gambit are Quad-generates only quadrilateral elements; Tri-
generates only triangular elements, Quad-Tri-generates quadrilateral and
triangular elements at the required areas. The different types of surface
mesh schemes available in Gambit are Map- generates structured grid of
mesh elements, Sub-map- generates a structured grid of mesh elements in a
suitably converted unmappable face, Pave-generates structured or
unstructured mesh elements, Tri-Primitive-generates mapped quadrilateral
elements and Wedge primitive- generates a triangular mesh element for
wedge shaped elements. The different types of volume mesh elements
available in Gambit include Hex, Hex/Wedge, Tet/Hybrid and types of
volume mesh schemes include Map. Sub-map, Tet-Primitive, Cooper,
Stairstep, T-grid and Hexa core [Gambit-2, 2001].
The option of treating the entire geometry as a single volume and generating
a uniformly distributed mesh with suitable size was considered to be a
complex process, due to the nature of the shape of various components.
Hence the system was sub divided into different zones namely, 1) Auger
volume-l, 2) Auger volume-ll, 3) Clearance volume, 4) Die /Mouth piece, 5)
Liner volume. As discussed earlier, based on the available computing power
and solution requirement, unstructured volume mesh with 4-node tetra
hedral mesh elements and t-grid hybrid meshing scheme was used for
meshing the auger, die and liner geometry, and a structured hex mesh for
the clearance volume. The various fluid volumes along with the mesh
generated for a 430 mm extruder, used for the investigation, are shown
below.
41
1) Auger volume-1: Fluid volume around the auger shaft, shown in Figure 3-
10 .
Figure 3-10 430 mm extruder- Auger volume-1
2) Auger volume-2: Solid volume around the auger shaft, shown in Figure 3-
1 1 .
Figure 3-11 430 mm extruder- Auger volume-2
3) Clearance volume: Small gap between the auger shaft and the liners,
shown in Figure 3-12. A structured hexahedral mesh was generated for this
volume.
42
Figure 3-12 430 mm extruder - Clearance volume
4) Die or mouth piece: A round shaped die design was used during the initial
investigation and is shown in Figure 3-13. The geometric details of the other
die shapes used in this research work are available in section 3.9.4.
Figure 3-13 430 mm extruder - D ie/ extruder mouth volume
5) Liner volume: The design and choice of material for liner depends on the
requirement and type of clay extruded. It varies with respect to size of
extruders and sometimes varies even for the same size. The factors that
influence the design include the clay material, production rate and
manufacturing feasibilities. The extruders modelled and investigated in this
research work have different liner designs. Suitable mesh size, meshing
element and meshing scheme was chosen with respect to the design.
Meshed liner geometry of a 430 mm extruder used in the investigation is
shown in Figure 3-14.
43
Figure 3-14 430 mm extruder- Liner volume
The final geometry of a 430 mm extruder, with assembled fluid volumes is
shown Figure 3-15.
Figure 3-15 430 mm extruder components and die assembled view
The meshed geometries of 500 mm and 600 mm extruder are available in
Appendix A - section I. Table 3-2 summarises the details of mesh generated
for various extruders investigated in this research.
44
Extruder sizeAuger and Liner volume
mesh elements
No. of cell
elements
430 mm Tetra hedral,Tgrid-Hybrid 956,143
500 mm Tetra hedral,Tgrid-Hybrid 1,312,961
600 mm Tetra hedral,Tgrid-Hybrid 1,545,053
Table 3-2 Extruder mesh details
3.4.3 Boundary conditionsThe choice of boundary condition for various elements of the geometry
depends on the flow problem being studied and there are 22 different types
of boundary conditions available in GAMBIT, suitable for various flow
problems. It is recommended to choose an appropriate boundary condition
such that it gives an accurate or a fair representation of the real condition.
Due to the lack of availability in previous experimental data and knowledge of
flow physics that occurs in an extruder, it was tedious to choose a precise
boundary condition. However from the various scientific works discussed in
Chapter 2, it was considered pressure inlet or velocity inlet or mass flow rate
for the inlet of an extruder system and for the outlet of die either pressure
outlet or outflow as an appropriate choice of boundary conditions. During the
initial stage of the research, 1) pressure inlet, pressure outlet and 2) velocity
inlet-pressure outlet boundary conditions were used to run the simulation.
Since satisfactory results were not obtained when compared with actual
scenarios, a different approach was undertaken.
It was decided to use mass flow rate for the inlet section of the extruder and
outflow boundary condition for the outlet section of the die. The two main
reasons behind this are,
1) The size of an extruder system is always determined by the number
of bricks to be extruded per hour and the shape of the outlet section of
die is based on the shape and size of the brick. Other components like
liners and barrel chamber are scaled suitably to meet the extrusion
rate requirement.
2) A significant amount of real time data was available for variables
like extrusion rate, compacted and un-compacted clay density, for
45
various size of extruders investigate in this research work. These
facilitated in using sensible values for the boundary condition and
compare the results obtained from the CFD analysis with real time
data.
Wall boundary condition was used for all the other geometrical features,
where fluid volume interacts with solid volumes. Interface boundary condition
was used for connecting surfaces between two fluid zones or components of
extruder, through which transfer of fluid from one to other occurs.
Simulations completed during the initial stage of investigation, using these
boundary conditions, yielded results that were in good agreement to actual
scenarios. Furthermore the solver was stable and a better convergence of
residual was noted for a significant number of iterations, compared to the
other boundary conditions mentioned earlier.
The extruder system is sub-dived into moving and stationary
zones/components. In order to understand the actual flow process and
assess the performance of the system, it was considered that representing
these features in the numerical model is an essential requirement. FLUENT
has different types of in-built modelling features that help to model and
simulate such kind of systems. Dynamic mesh modelling is one such feature
that allows users to specify moving and deforming fluid zones or stationary
fluid zones that exist within a single flow domain (refer to section 3.4.4.2 for
further details). In order to be able to use this feature at the solver stage, it is
necessary to discretise the domain suitably and specify the features of
various zones clearly at this stage of the process. In this research work, the
solid volume of the auger and the fluid volume around the auger were
defined as moving zones and the remaining components were defined as
stationary zones, shown in Figure 3-16 and Figure 3-17.
46
Auger fluid volume
Auger solid volume
Figure 3-16 Moving volumes
Figure 3-17 Stationary volumes
3.4.4 Solver settings
3.4.4.1Flow modelling
Solver settings generally depend upon the flow physics that is being
investigated. So it is necessary to have some preliminary understanding
about the type of flow occurring in the domain of investigation, before setting
up the problem in the solver.
In comparison to Newtonian fluids, there is lack of a standard method or
procedure for determining the Reynolds number of non-Newtonian fluid
flows. Wilkinson (1960) has discussed about the formula used for
calculating the Reynolds number for the flow of time-dependent non-
Newtonian fluids through a pipe channel, both in a laminar and turbulent flow
regime. However considering the highly viscous nature of the material and
speed of the auger, it was clearly understood that the material exhibits
laminar flow throughout the entire length of the extruder and die sections. So
an unsteady state, single phase, laminar flow model with pressure based47
solver and coupled algorithm for pressure-velocity coupling was assigned to
the model. Though the pressure based solver is predominantly used to solve
incompressible flow problems, it is also recommended for solving mildly
compressible flow [Ansys 12.0-User's guide, 2009], as occurs in the case
of clay extrusion.
The generalised form of conservation equations for mass and momentum
solved by FLUENT, for both compressible and incompressible laminar flow
problems are shown in Equations 3.8 and 3.9.
^ + V . ( p v ) = S m 3 . 8
Where, Sm= mass added to the continuous phase, p= density, v=velocity
vector.
— ( p v ) + V . ( p v ! v ) = - V p + V . (T) + p g + F 3 . 9d t '
Where, p=static pressure, f=stress tensor, pg=gravitational force and
F=external body force.
3.4.4.2 Dynamic mesh modellingIt was mentioned earlier that the extruder system comprises of both
stationary and moving zones and the geometry was discretised suitably to
reflect these properties. Using the moving and deforming mesh modelling
feature available in FLUENT, the moving and stationery zones of an extruder
system were defined in the solver.
Dynamic meshes are used in problems where boundaries move rigidly with
respect to one another, may exhibit linear or rotary motion. It can also be
used for deflecting and deforming boundaries (example: balloon, artificial
wall) [Fluent -6.3 user guide]. The mesh generation will be based on the
moving boundary conditions. This feature is used to model flows that involve
change in domain shape with respect to time, due to moving boundaries. The
mesh updates every time step based on new positions of the moving
48
boundary. The different methods by which the solver updates the mesh of
moving boundaries at each time step includes,
• Smoothing method-spring based method, Laplacian method and
boundary layer method.
• Dynamic layering method.
• Local remeshing.
The choice of the mesh updating method depends upon the type of problem,
computation and solution requirements.
3.4.4.3 Material definition and Viscosity modellingAssigning material properties to the discretised fluid and solid volume is the
next and important step in the process of solver settings. As mentioned
earlier, it was decided to use Herschel-Bulkley's model with shear rate
dependent feature to model the viscosity of wet clay used in the extrusion
process. Since clay is not a standard type of fluid that is commonly
encountered in many flow scenarios occurring in the field of engineering, its
properties are not readily available in FLUENT solver. Thus the required
variables of Herschel-Bulkley’s model, relevant for wet clay were added to
the existing material database. Table 3-3 shows the different variable inputs
required for a typical Herschel-Bulkley’s model.
Variables
Consistency Index (k) (Pa.sn)_____Power law index (n)
Yield stress threshold^,) (Pa)
Critical shear rate(C.S.R) (yr) ( (s'1)Table 3-3 Variables for Herschel- Bulkley's model
The above mentioned variables vary with respect to the particle size,
moisture and raw material content of clay. These variables can be related to
each other as shown in Equation 3.10.
= kycn 3.10
The major mineral content found in clays used for making bricks in U.K. is
Kaolinite and widely used size of the clay particle is <2 mm. The uniqueness49
in the mineral content and size of clay particles and the available
mathematical model facilitated in choosing a few sets of values for Herschel-
Bulkley’s model variables, for representing the (kaolinite) clay with different
moisture content. The values of r 0, k, y c and n used in this research work, for
representing clays with moisture content ranging from 7-14% on wet basis
(typical range for clay used in stiff extrusion process), is presented later in
this chapter along with the results of various CFD simulations.
Herschel-Bulkley’s model combines the effect of both Power law fluids and
the Bingham plastic fluids. The viscosity at each time step during an
unsteady state process is determined using the Equations 3.11 or 3.12,
depending upon the y value. [Ansys-Fluent 12.0 user's guide 2010].
For y>yc
For y<Yc,
( 2 “ % c )
T) — t 0 : 1- k [ ( 2 — n ) + ( n - 1 ) t - 3 . 1 2Yc Yc
Where, y = D : D - - 5 . 1 3
Where, D=rate of deformation tensor, rj= viscosity.
3.4.4.4 Temperature dependent properties modellingExtrusion in actual scenario is a non-lsothermal process. The heat generated
during the flow of wet clay through the auger, barrel enclosure and die,
because of frictional forces, is understood to attain a significant value during
stiff extrusion process and also influences the quality of extruded material
and the flow process. The energy equation along with viscous heat
dissipation feature available in the FLUENT was used to model this
phenomenon. The properties of the extruded clay column that are subjected
50
to variation with respect to change in temperature include compacted
density, thermal conductivity and specific heat capacity.
The density (bulk density) of the wet clay that enters the extruder system
varies significantly with respect to the clay column that leaves the extruder
system. In a stiff extrusion process, the density of compacted and un
compacted wet clay typically falls in the range of 1602 kgrrf3 to 1742 kgm'3
[Walker,2012] and the rise in temperature falls in the range of 50°C to 60°C.
These values could be even higher if dies with a single or multiple core is
used. Since such die designs were not considered in this research work, it is
not discussed any further. This change in density along with thermal
conductivity and specific heat capacity of the wet clay was expressed as a
linear function with respect to the temperature rise, experienced during the
extrusion process. Due to the lack of availability of proper material data and
experimental works on the thermal conductivity and specific heat capacity of
wet clay, suitable values were obtained from the work completed by Robie
and Hemingway (1991) and Michot et al. (2008).Though the values
discussed by these authors do not specify the moisture content of the clay,
suggested values were used as a guidance to calculate the values required
for the CFD modelling work undertaken in this research.
3.5 Experimental validation of CFD modellingThe CFD modelling technique for assessing the performance of an extruder
system, discussed above was validated by modelling and comparing the
numerical results with experimental results of a lab scale extruder.
The experimental investigation of performance characters of a lab scale
extruder are discussed in this part. A lab scale extrusion unit with an extruder
of diameter 75 mm was used for the investigation and is shown in Figure 3-
18.
51
Figure 3-18 Scaled extruder
Experimental set up
The extrusion pressure was measured using a special type of pressure
sensor, power consumption using an ammeter and vacuum pressure using a
vacuum gauge. A schematic representation of the experimental set up used
for the investigation is shown in Figure 3-19.
Ammeter
Pug mill
Extruder DiePower Drive unit
Vacuum gauge
Pressuresensor
Transitionpiece
Figure 3-19 Experimental set up layout
52
Extrusion pressure and power consumed by the lab scale extruder was
measured for two different extrusion scenarios (two different clays with
different moisture content). The operating parameters used and results
obtained from the experimental investigation are summarised below.
Trial: 1
In this case, clay from M/s Hanson Brick Limited, Desford, U.K. was used for
the investigation. The actual moisture content of the clay obtained from the
source was assessed based on dry and wet method, and then suitable
amount of water was added per unit mass of clay sample to achieve a
moisture content of 12-13% on dry basis (recommended moisture content
level for stiff extrusion process). Suitable care was taken to prevent
significant loss of moisture content during the experiment. The extrusion
pressure and current consumption was recorded at a point when the
extruded mass of clay reached the right amount of stiffness (2.6 in the
Penetrometer scale). The power consumed was calculated using the current
reading obtained during extrusion and applying the standard formula. Table
3-4 summarises the measured values.
Die used for Trail: 1
Parameters Measured value
Moisture content of the clay Wet basis-11-12%, Dry basis 12-13%
Auger speed 19 rpm
Vacuum pressure -20 mm mercury. (-2666.6 Pa)
Penetrometer scale reading 2.6
Current readingsBefore feeding clay - 2.5-2.6 Amps,
During feeding and when clay reached a certain level in vacuum chamber- 3.1
53
Amps to 3.5 Amps,During continuous extrusion, with right
stiffness- 3.9 Amps.Current consumption by extruder
alone, during extrusion.0.3 to 0.4 Amps
Voltage 415 Volts.
Power consumed by extruder
unit alone, during extrusion.124.5 Watts
Extrusion rate 0.013 to 0.015 kgs'1
Extrusion pressure 13-14 bar
Temperature change in the clay
Initial temperature 296 K and final
temperature of extruded clay 301K (five
degree rise)
Uncompacted density of clay 1298 kgm'3
Compacted density of clay 2270 kgm'3
Table 3-4 Experimental analysis results-trial 1
Trial: 2
In this case, clay from river Humber U.K. was used for the investigation.
Since the clay obtained from the source contained more amount of moisture
content of approximately about 25-30% on wet basis, the sample was
directly used for the experimental investigation, without further addition of
water. The required parameters were then measured and calculated using
the same procedure, as discussed above in Trial: 1. Table 3-5 summarises
the measured values.
54
Die used in Trial:2
Parameters Measured value
Moisture content of the clay Wet basis 25-30%
Auger speed 19 rpm
Vacuum pressure -13 mm mercury. (-1733.19 Pa)
Penetrometer scale reading 2.3
Current readings
Before feeding clay - 2.8 Amps,
During feeding and when clay reached a
certain level in vacuum chamber-
3.2 Amps to 3.3 Amps,
During continuous extrusion, with right
stiffness- 3.4 Amps to 3.5 Amps.
Current consumption by extruder
alone, during extrusion.0.1 Amps
Voltage 415 Volts.
Power consumed by extruder
unit alone, during extrusion.57.5 Watts
Extrusion rate * 0.01014 kgs'1
Extrusion pressure 5.8 bar to 6.0 bar
Temperature change in the clay
Initial temperature 293 K and final
temperature of extruded clay 297 K (four
degree rise)
Uncompacted density of clay 1200 kgm'3
Compacted density of clay 2150 kgm'3
Table 3-5 Experimental analysis results-trial 2
55
3.6 CFD modelling of a scaled extruderThe Performance assessment of the scaled extruder using CFD modelling
technique is discussed in this part of the report.
CAD modelling and discretisation of scaled extruder
3-D CAD model of the scaled extruder components used for the investigation
is shown from Figure 3-20 to 3-22.
Figure 3-20 Scaled extruder-auger shaft
Figure 3-21 clearance
Figure 3-22 Scaled extruder-transition piece
56
The generated CAD model was meshed in Gambit using suitable meshing
schemes for individual components. Tetrahedral / hybrid mesh elements and
T-grid meshing scheme was used to mesh the fluid volume around the auger
shaft and the total number of cell elements obtained was 310,552. The
meshed geometry is shown in Figure 3-23.
Figure 3-23 Scaled extruder-auger shaft meshed
Uniform hexagonal mesh elements with cooper scheme were used to mesh
the clearance volume. The total number of cell elements obtained was
11,778 and the meshed geometry is shown in Figure 3-24.
Figure 3-24 Scaled extruder-clearance meshed
Hex/wedge shaped mesh elements with cooper scheme were used to mesh
the transition piece. The total number of cell elements obtained was 502,199
and the meshed geometry is shown in Figure 3-25.
57
Figure 3-25 Scaled extruder- transition piece meshed
A similar boundary condition and modelling approach, used to model the full
scale extruder, was used to complete the pre and post processor solver
settings of scaled extruder modelling. In the earlier part of this chapter, it was
discussed that the moisture content of clay determines the variable values in
a Herschel-Bulkley’s model and also the performance of an extruder system.
Since in Trial: 1 and Trial: 2 two different clays with different moisture content
was used, the values for Herschel-Bulkley’s model were chosen
appropriately. Table 3-6 summarises the values used for the variables of
Herschel-Bulkley’s model in CFD analysis.
Herschel-
Bulkley's model
variable
Trialil values Trial:2 values
k (Pa.sn) 5206.95 3200
n 0.32 0.2
To (Pa) 6500 3516
C.S.R (s'1) 2.1 1.6
Table 3-6 Herschel- Bulkley's model values for scaled extruder CFD analysis
The values for clay used in Trail: 2 were set to a lower value due to the soft
nature of clay, and such soft clay materials are normally used in soft
extrusion process. Since extruders manufactured by C.F Ltd, for the purpose
of stiff extrusion are sometimes used for soft extrusion process as well, it
was considered to be a useful investigation with the identified CFD
methodology and compare the numerical model results with experimental
results.
The results of CFD analysis for extrusion scenarios Trial: 1 and Trial: 2 are
available in Appendix A- section XII & XIII. Table 3-7 shows results of the
extrusion pressure and power consumption by the scaled extruder under the
two extrusion scenarios, determined experimentally and using CFD analysis.
Process parameters Experimental results CFD results
Trial-I
Extrusion pressure 13-14 bar 13.4 bar
Power consumption 124.5 Watts 114.06 Watts
Trial-ll
Extrusion pressure 5.8-6.0 bar 5.84 bar
Power consumption 57.5 Watts 47 watts
Table 3-7 Result comparison for scaled extruder
3.7 Experimental study of clay rheologyThe most important determinant factor in selection and use of an appropriate
flow model to simulate the process of clay extrusion and assess the
performance of extruders numerically is the shear thinning behaviour of the
clay-water system. In order to demonstrate the shear thinning behaviour of
the clay and to further support the choice of flow model used in this research
work, an attempt was made to study the rheological characters of wet clay by
measuring the viscosity, using oscillatory test in a parallel plate viscometer
(Make: Anton Parr, Model no: MCR301), shown in Figure 3.26.
Figure 3-26 Parallel plate viscometer-Anton Parr (MCR301)59
The viscosity of clay sample used in Trial: 2 experimental work was
measured. The accuracy of the measured results when using a parallel plate
viscometer depends upon the contact established between the sample
surface and measuring plate surface of the instrument (It consists of a
stationary and a moving plate). A gap of 2 mm is recommended to be an
optimised gap between the plates, to get sensible results [Mezger, 2006]. In
order to satisfy this criterion, clay samples with a diameter of 50 mm,
thickness between 2-3 mm and surface free from disparities was prepared.
Values for G' (G-prime) and G " (G-double prime) were measured to identify
suitable frequency value for oscillatory test and then by varying the plate gap
from 2 mm to 2.19 mm, values for the complex modulus, storage modulus,
loss modulus and damping factor were measured and a graphical plot for
Apparent viscosity vs. Strain rate was obtained for the clay sample and is
shown in Figure 3-27.
Clay with 25%-30% water
- KKFS- gap 2.
- KKFS- gap 2.
KKFS- gap 2.
KKFS- gap 2.
- KKFS- gap 2.
02-Plate 17 mm
03-Plate17mm
■04-Plate186mm
■05-Plate17mm
-06-Plate 0 mm
19800 19200 18600 18000 17400 16800 16200 15600 15000 14400 13800 13200 12600
•5T 12000 1140010800
= . 10200 £? 9600 g 9000 <j> 8400> 7800£ 7200£ 6600 2. 6000 3 - 5400
4800 4200 3600 3000 2400 1800 1200
600 0
A p p aren t V isco s ity Vs S train R ate (1/s)
Strain Rate (1/s)
Figure 3-27 Apparent viscosity vs. Strain rate of clay- measured
experimentally
60
The viscosity profile obtained through the viscometer experiment clearly
indicates the shear thinning nature exhibited by wet clay and also
demonstrates the change observed in viscosity value when it is subjected to
a uniform shear. This viscosity profile determined experimentally, when
compared with the CFD analysis results proves the point that, the clay exhibit
shear thinning behaviour during extrusion and is well represented by the flow
model and its variables used in the CFD model.
The use of the CFD modelling technique, discussed above, to assess the
performance characters of full scale extruders is presented further in this
chapter.
3.8 Performance assessment of extruders with
different diametersThe performance of an extruder system varies significantly with respect to
particle size and moisture content of clay. Extruder’s diameter varies with
respect to extrusion rate or number of bricks to be produced per hour and
moisture content varies with respect to strength requirements and extruding
ability of clay. In this part of the research work, the effect of varying the
diameter of an extruder and clay moisture content on the performance
parameters like extrusion pressure (static pressure) and power consumption
during the process of extrusion were investigated using CFD. The variation
of performance parameters was assessed for extruders of size 430 mm, 500
mm and 600 mm, using two sets of Herschel-Bulkley's model values.
Operating parameters used in the CFD model are shown in Table 3-8.
Extruder
Size
Feed
rate
(kgs1)
Auger
speed
(rpm)
Herschel-Bulkley's model value
Case-I Case-ll
430 mm 15 30 k=4908 Pa.sn
n=0.5
t 0=8500 Pa
C.S.R=3 s'1
k=5206.95 Pa.sn
n=0.32
t 0=6500 Pa
C.S.R=2.1 s 1
500 mm 19 30
600 mm 11.8 22.5
Table 3-8 iData set for varying ex truder diameter and moisture content
analysis61
The two data sets used for the variables in the Herschel-Bulkley’s model
represent uncompacted clay with different moisture content. (Value I
represents harder clay and value II for softer clay). Results obtained from the
CFD analysis of 430 mm extruder are summarised below, the results of 500
mm and 600 mm extruders are available in Appendix A from section II to V.
CFD Simulation results of 430 mm extruder with Herschel-Bulkley's
model value-1
Extrusion pressure:
Pressure developed during the extrusion process, along the entire length of
the extruder and die section, obtained from the CFD analysis is shown in
Figure 3-28 and 3-29. The value varied from -605 kPa at the inlet section to a
maximum of 3.4 MPa. (34 bar), observed at the tip of the auger shaft and
further downstream the pressure reduced to an average value of 2.57 MPa.
(25.7 bar) at the outlet.
[Note: The negative value of extrusion pressure observed at the inlet
section of the extruder as discussed above and in other CFD results
discussed further in this chapter is a result of the numerical evaluation
on the vacuum pressure value i.e. set as the inlet boundary condition.
The physical meaning of the negative pressure value is a vacuum
condition exists at the inlet section.]
3.40e+0B 3.21 e+OB 3 07e+062.938+062 78e+062 64e+06 2.50e+06 2.36e+06 2.22e+06 2.08e+06 1.94e+06 1,80e+06 1 65e+06 1.51e+06 1 37e+06 1 23e+06
I 1 09e+06 9 48e+05 8 078+05 6 66e+05 5 25e+053 83e+Q5
.■ 2 42e+05
' -6 05e+05
Contours of Static Pressure (pascal) (T im e=2.0240e+00)
Figure 3-28 Static pressure contour (full view)-430 mm Case I
62
2.78e+0B2B4e*062.50e+062 38e+0B2 22e+082 09e»06I 84e+06t BOe+OB1 65e+081 51e+081.37e+081 23e+061 D9e+069.48e+05B 07e+056.68e+055 25e+053 83e+05242e+D51 Ule+05•4 03e+04-1 82e+05-3 23e<-05■A B4e+05■6 05e+Q5
Contours of Static Pressure (pascal) (Time=2.0240e+00) Oct 2 7 .2 01 '
Figure 3-29 Static pressure contour (sectional view) - 430 mm Case I
Extrusion pressure values discussed above and the profile shown in
Figure 3-30, clearly indicates the trend of pressure developed inside the
extruder and die section during the extrusion process This data obtained
through the numerical simulation confirms the results discussed by [Bender
and Handle,1982] and [Handle,2007].
(Note: The results of trend in pressure development during the process
of extrusion, discussed in this report refer to the pressure development
trend observed in the direction of extrusion.)
3.50e-*06
3 00e+06
2 50e-*06
2 CD e+06
1 50e+06
1 00e+06
5 00e+05
0.00e+00
-5.00e+O5-0.6 -0 5 -0 4
Position (m)
StaticPressure
(pascal)
Static Pressure (Time=2 5050e+00)
Figure 3-30 Static pressure profile-430 mm Case I
63
Material Flow pattern:
857e-01 8 17e-01 7 .70e-O1 7.36O-01 0.94e-O1 0 530-01 6 12©-01 5720-01 5310-01 4 900-01 4 49e-01 4.08e-01 3.67O-01 3 27e-01 2 86e-01 2 45e-01 2.04e-01 1.63e-01
The flow pattern and velocity of clay during extrusion, at various sections of
extruder and die, obtained from the CFD analysis is shown in Figure 3-31. In
the direction of extrusion the average value observed for velocity at outlet
section of die was 0.47 ms'1. It is understood from the results that the
material tends to deform continuously under the action of shear as it
proceeds down from the inlet. It is also clear from the results that, when
moving along the radial direction the material near the hub and middle of the
auger gap tends to flow faster than the material near the liners. This confirms
that the liners are restricting the clay from rotating along with the shaft and
also it facilitates it to move in the direction of extrusion. This data obtained
through numerical simulation confirms with results discussed by Zhang et
al., 2011.
C ontours o f V e loc ity M agn itude (m /s) (T lm e= 2 .0240e+00 )
Figure 3-31 Flow velocity during extrusion (sectional view)- 430 mm Case I
Viscosity profile:
Shear thinning behaviour of clay during the process of extrusion was verified
by plotting a graph with molecular viscosity against strain rate (shear rate) at
different sections of extruder and die. The profile for molecular viscosity vs.
strain rate at the outlet, obtained from the CFD analysis is shown in Figure 3-
32.
64
MolecularViscosity(kg/m-s)
1.00e+04
8.00e+03
6 00e+03
4 00e+03
2 00e+03
0 00e+0020 30 40
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=2,0240e+00) t
Figure 3-32 Molecular viscosity vs. Strain rate- 430 mm Case I
Convergence monitoring:
The accuracy and validity of the solution in any CFD analysis is ensured by
monitoring the convergence of residuals and other problem relevant process
parameters like mass flow rate, velocity components, co-efficient of drag and
pressure components. In this research work it was accomplished through
monitoring the convergence of residuals and mass flow rate at the outlet. It
was very hard to acquire a complete converged solution and hence the
iteration was stopped when the monitored residuals convergence stayed
constant for a certain number of iterations and results were obtained. Figure
3-33 and 3-34 shows the results obtained in this case for convergence
monitoring.
65
1e-02
1e-03
1e-04
1e-06
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
Iterations
Scaled Residuals (Time=2.0240e+00)
Figure 3-33 Residual convergence-430 mm Case I
Mass -13 0000FlowRate
(kg/s) -14.0000
-150000
-1600000 0000 0 2500 0 5000 0 7500 1 0000 1 2500 1 5000 1 7500 2 0000 2 2500
Flow Time
Convergence history of Mass Flow Rate on outlet (Time=2.0240e+00) Oc
Figure 3-34 Mass flow rate convergence- 430 mm Case I
The results of convergence monitoring obtained from other CFD analysis are
similar to the case presented above and hence these results were not
discussed for other cases of CFD analysis presented later in this chapter.
The energy required to extrude per unit mass of clay was calculated for each
case using the torque value at the auger section, obtained from the CFD
analysis. A graph was plotted to analyse the trend of variation in maximum
pressure and energy required during the extrusion process, with respect to
change in diameter of extruder, shown in Figure 3-35.
66
Pressure and Energy consumption @ respective design condition vs Diameter of a u g e r, for Clay Type-1
430 500 600
10
12
- 6
-- 4
- - 2
■o
S *Q -> O*
§1 C **“o 9 o w
2 *UJ
Diam eter of auger (in m m)
■Pressure Vs Diameter of auger
-Energy consumed to extruder per Kg. of clay Vs Diameter of auger
Figure 3-35 Extrusion pressure and Energy consumption vs. Diameter
(Case-1)
The general trend clearly indicates that the pressure and energy
consumption during extrusion varies significantly with respect to design (size)
and operating parameters (speed and feed rate) of an extruder, even if the
type and moisture content of clay material remains the same.
CFD Simulation results of 430 mm extruder with Herschel-Bulkley's
model value-ll
Extrusion pressure:
Pressure developed during extrusion in a 430 mm extruder, with respect to
change in clay moisture content is shown in Figure 3-36 and 3-37.The
pressure varied from a minimum value of -334 kPa at the inlet section to a
maximum of 1.98 MPa (rounded off to 20 bar), observed at the tip of the
auger shaft and further downstream the pressure reduced to an average
value of 1.47 MPa (14.7 bar) at the outlet. In comparison to the case
discussed earlier, the pressure developed during the extrusion of softer clay
is lower than the pressure developed for the harder clay.
67
I
1 98e+0B 1 67e+06 1 78e+0B1 70e+B61 62e+B6I 53e+06 1 45e»0B 1 37e+86 t 28e+08 1 2fle+86 1 12e+061 03e+86 9.51e+05 8 68e+05 7.84e+05 7 01e+05 6 18e+05 5 34e+B5 4.51e+85 3 68e+052 84e+052 01e+85 1 18e+B53 45e+04 -4 88e+B4 -1 32e+B5 -2 15e+05 -2 99e+05 -3.82e+05
Contours of Static Pressure (pascal) (Time=2.0250e+00) Or
Figure 3-36 Static pressure contour (full view)-430 mm Case II
t 98e+B6 1 B7e+08 1 78e*08 1 7Be»061 B2t+06 t 53e+861 45e+061.37e+B6 1 28e+08 I 20e+06 1 12e+0B1 03e+08 9 5!e+05 8 68e+B5 7 84e+B5 7 flle+85 6 18e+B5 5 34e+05 4 51e+B5 3 68e*B52 84e-*05 2 0le+05 1 18e+B5 345e*B4 -4 88e*04 -1 32e+05 -2 15e*05 -2 99e*05 •3 82e*05
Contours of Static Pressure (pascal) (Time=2.0250e+00) Oct 26. 2(
Figure 3-37 Static pressure contour (sectional view)- 430 mm Case II
The trend observed in extrusion pressure, developed during extrusion is
shown in Figure 3-38. No significant variation was noted when compared
with the earlier case.
68
Position (m )
Static Pressure (Time=2.0250e+00) <
Figure 3-38 Static pressure profile-430 mm Case II
Material Flow pattern:
The flow pattern and velocity of clay observed during extrusion is shown in
Figure 3-39. In the direction of extrusion the average value observed for
velocity at outlet section of die was 0.47 ms'1. A significant difference in
material deformation pattern and in velocity was noted within the auger and
barrel section, for softer clay when compared with harder clay. It indicates
that the softer clay deforms more uniformly, observed along the radial
direction, compared to the harder clay, when subjected to equal shear force.
1 IBe+00 1 10e+00 1 06e+001 02e+00982e-019.41e-01 9 0Qe-01 8.59e-01 8.19e-0l 7 78e-017 37e-018 966-01 6 55e-01 6 14e-01 5 73e-D1 5 32e-01 4 91e-0l 4 50e-01 4 09e-013 68e-013 27e-012 86e-01
2 46e-012 05e-01 1 B4e-01 1 23e-018 19e-024 09e-02 0 00e*00
Contours of Velocity Magnitude (m/s) (Time=2.0250e+00) Oct 2 6 ,2C
Figure 3-39 Flow velocity during extrusion (sectional view)- 430 mm Case II
Viscosity profile:
The profile of shear thinning behaviour of clay at the outlet section of die is
shown Figure 3-40. It also indicates that the softer clay deforms more easily
than the harder clay when subjected to shear.
1 OOe+04
8 00e+03
MolecularViscosity(kg/m-s)
6 0 0 e *0 3
4 00e+03
2 00e*03
30 40
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (T im «=2.0250e+00)
Figure 3-40 Molecular viscosity vs. Strain rate-430 mm Case II
The graph shown in Figure 3-41 indicates the trend of variation in energy
required to extrude per unit mass of clay and maximum pressure developed
during extrusion with respect to size of extruder, for softer clay.
Pressure and Energy consumption @ respective design condition vs Diameter of auger, fo r Clay Type-ll
6.005.35
4.29 t S 3.43 o *
+* c^ c n i 'O O
24.3
1.71 3 “-ri
0.00c430 500 600
Diam eter of auger (in m m)
-Pressure Vs Diameter of auger
-Energy consumed to extrude per Kg. of clay Vs Diameter of auger
Figure 3-41 Extrusion pressure, Energy consumption vs. Diameter (Case-11)
The general trend in energy requirement and maximum pressure developed
during extrusion remained the same for both hard and soft clay extrusion. It
70
is clearly understood from the graphs, that irrespective of the extruder size,
the extrusion pressure and power required for extruding clays with high
moisture content will be low compared with extruding harder clay. The
extrusion pressure increases with respect to increase in the size of extruder
even for the clay with same moisture content, but not necessarily the power
required in all cases. It also clearly demonstrates the effect of changing
moisture content of clay on the performance of extruder.
3.9 Performance assessment of a 500 mm extruderThe effect of varying design and operating parameters on the performance of
a 500 mm extruder system was investigated in this part of the research,
using CFD. The results obtained from the CFD analysis are summarised
below.
3.9.1 Effect of varying feed rate on performance of extruderThe effect of changing the feed rate of uncompacted clay, on the
performance of a 500 mm extruder was investigated in this part. The other
parameters like the die design, extruder design, clay material, size, clay
moisture content and auger speed were kept constant. Table 3-9
summarises the operational parameters and material properties used in the
CFD analysis.
Extruder Size
Feed
rate
(kgs1)
Auger
speed
(rpm)
Herschel-Bulkley's
model value
500 mm Varying 30
k=5206.95 Pa.sn
n=0.32
r o=6500 Pa
C.S.R=2.1 s'1Table 3-9 Data set for varying feed rate analysis
The performance characters were assessed for the following feed rates 10
kgs'1, 15 kgs'1, 19 kgs'1, 25 kgs'1, 30 kgs'1, 40 kgs'1 and 50 kgs'1. The results
obtained from the CFD analysis are summarised below.
71
Extrusion Pressure:
Pressure developed during extrusion in a 500 mm extruder with 10 Kgs'1 of
feed rate is shown in Figure 3-42 and 3-43. The pressure varied from a
minimum value of -150 kPa at the inlet section to a maximum of 2.68-2.78
MPa (rounded off to 28 bar) observed at the end of auger shaft and reduced
to an average value of 2.13 MPa (21.3 bar) at the outlet.
Contours of Static Pressure (pascal) (Tlme=4.4200e-01) Oi
Figure 3-42 Static pressure contour (full view) - feed rate 10 kgs'1
2.04e+06 194e+06 1.848+06 1 74e+06 1 65e+06 1 55e+08 1 45e+06 1.35e+06 125e+06 1.15e+08 1 05e+06 9.47e+05 8.47e+05 747e+05 6.4Be+05 5.48e+05 4 48e+05 3.48e+05 249e+05 t.49e+05 4 93e+04 -5 05e+04 -1 50e+05
2448+06
2 248+062 14++062.048+06194e+061 B4e+061 74e+061B5e+061 55e+061.45e+061.358+061.25e+061 15e+061.058+069.47e+05B47e+05747e+05B.46e+055 48e+054 488+05348e+052 498+05149e+054 93e+CM-5 05e+04-1 50e+05
Contours of Static Pressure (pascal) (Time=4.4200e-01) Oct 10.2011
Figure 3-43 Static pressure contour (sectional view) - feed rate 10 k g s 1
The trend of pressure development within the extruder section, observed
during extrusion is shown in Figure 3-44.
72
StaticPressure
(pascal)
1.50e+06
1.00e+06
5.00e+05
0.00e+00
-5 00e-H35-1 -0.9 -0 8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0
Position (m)
Static Pressure (Time=4,4200e-01) I
Figure 3-44 Static pressure profile- feed rate 10 k g s 1
Material Flow pattern:
The flow pattern and velocity of clay observed during extrusion at various
sections of extruder and die, in a 500 mm extruder with 10 kgs'1 feed rate is
shown in Figure 3-45. In the direction of extrusion the average value
observed for velocity at outlet section of die was 0.32 ms'1.
118e-*»1 14fr*O0 1.09e+001.D5e+009 98e-01 9.51e-01 9 03e-01 9 56e-0f8 08e-01 7 Ble-01 7.13e-01 6 .66e-01 6.18e-01 5.71e-01 5 23e-01 4 75e-01 4.28e-013 BOe-01 3.33e-012 85e-01 2 38e-01 1 9D6-01 143e-019 51e-024 75e-02 0 00e+00
Contours of Velocity Magnitude (m/s) (Time=4.4200e-01) Oct 10.201
Figure 3-45 Flow velocity during extrusion (sectional view)- feed rate 10 k g s 1
Viscosity Profile:
The profile of shear thinning behaviour of clay observed at the outlet section
of die in a 500 mm extruder with 10 kgs'1 feed rate is shown in Figure 3-46.
73
The viscosity value was observed to be higher at lower mass flow rate when
compared with higher mass flow rate.
7 00e+03
MolecularViscosity(kg/m-s)
4 00e«-03
2 00e+03
1 00e+030 5 10 15 20 25 30
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (T im e=4.4200e-01) C
Figure 3-46 Molecular viscosity vs. Strain rate- feed rate 10 k g s 1
The results of CFD analysis, for feed rates 15 kgs'1, 19 kgs'1, 25 kgs'1,
30 kgs'1, 40 kgs'1 and 50 kgs'1 is available in Appendix A-section VI.
The trend of variation in maximum extrusion pressure and energy required in
extruding per unit mass of clay, with respect to change in feed rate of clay for
a 500 mm extruder is shown in Figure 3-47.
500mm extruder Pressure and Energy consumption Vs Mass flow rate/Feed rate @ constant speed of 30 rpm, for Clay type-ll
3.20
2.84 at
2.49 | f
2.13 * 2
1.78 | o
o o- 0.71 *2|-60.36 • |
iu1 0.00
Mass flow rate/ Feed rate (in Kg/sec)
500mm extruder Pressure Vs Mass flow rate/Feed rate @ constant speed of 30 rpm
500mm extruder- Energy consumed to extruder per Kg. of clay vs Mass flow rate/Feed rate @ constant speed of 30
_ rom_____________
30
25
202 ^153 fJ 10 U> S I
IS do>- o
5cm3 a | 2 0 .E m2 > cn m-5 2 73
-10-15
Figure 3-47 Extrusion pressure, Energy consumption vs. Feed rate
74
3.9.2 Effect of varying auger speed on performance of
extruderThe effect of varying auger speed on the performance characters of a 500
mm extruder was investigated in this part. The other parameters like the die
design, extruder design, clay material, size, clay moisture content and feed
rate were kept constant. Table 3-10 summarises the operational parameters
and material properties used in the CFD analysis.
Extruder Size
Feed
rate
(kgs1)
Auger
speed
(rpm)
Herschel-Bulkley's
model value
500 mm 19 varying
k=5206.95 Pa.sn
n=0.32
t0=6500 Pa
C.S.R=2.1 s"1
Table 3-10 Data set for varying auger speed analysis
The performance characters were assessed for the following auger speeds-
10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, 40 rpm and 50 rpm. The results
obtained from the CFD analysis are summarised below.
Extrusion Pressure:
Pressure developed during extrusion in a 500 mm extruder with auger speed
of 10 rpm is shown in Figure 3-48 and 3-49. Negative pressure was
observed at the outlet and at the tip auger section of the extruder. The
maximum pressure observed was 192 kPa (1.92 bar) at the inlet section,
which indicates that the speed of the auger is not sufficient enough to induce
the required shear force for the clay to deform and resulting in clay being
stopped at the inlet section.
75
152e+05
l.24e+055.68e+Q4-1.1le+04-7.88e+04-147e+05-2.14e+05-2.82e+05
-3.50e+05
-4.18e+05
-4.85e+05
-5.53e+05
-6.21e+05
-6.89e+05
-7.56e+05 -8.24e+D5
-8.92e+D5
-9.60e+05
-1.03e+06
-1.10e+06
-1 16e+06
Contours of Static Pressure (pascal) (Ttme=2.6040e+00)
Figure 3-48 Static pressure contour (full view) - auger speed 10 rpm
3.71e*M -1-Sle+W -8 29e+04 -111e+05-1.59e+05-2.086+05-2.54e+05 -3 02e+05 -3.5Oe+05 -388e+05 -4.48e+05 -4 93e+05 -541e+05 -589e+05 -6.37e+05 -B85e+05 -7 33e+05 -780e+05 -8 28e+05 -8 76e+05 -9 24e+05 -9 72e+05 -1 02e+08 -1.07e+06 -1 12e+06 -1 t6e+06
Contours of Static Pressure (pascal) (Time=2.6040e+00) Sep 28,:
Figure 3-49 Static pressure contour (sectional view) - auger speed 10 rpm
The trend of pressure development observed within the extruder section,
during extrusion is shown in Figure 3-50.
76
StaticPressure
(pascal)
-4
-6 00e+05
-8.008+05
-1 00e+06
-1 20e+06-1 -0 9 -0.8 -0.7 -0.6 -0.5 -0 4 -0.3 -0 2 -0 1 0
Position (m)
Static Pressure (Time=2.6040e+00)
Figure 3-50 Static pressure profile-auger speed 10 rpm
Material Flow pattern:
The flow pattern and velocity of clay observed during extrusion, at various
sections of extruder and die, in a 500 mm extruder with auger speed of 10
rpm is shown in Figure 3-51.
Jpffi r jg *:9 29e-018 93e-u 18 57e-010 226-017 88e-017 50e-0l7.14e-016.79e-01643e-016 07e-0l5.72e-015 38e-015 00e-014 64e-014.29e-013 93e-0t3.57e-0l3.21e-012 86e-u12 50e-012 14e-0l1 79e-011 43e-011 07e-0i7 14e-023 57e-020 00e+00
Contours of Velocity Magnitude (m /s) (Tim e=2.6040e+00) Sep 28.
Figure 3-51 Flow velocity during extrusion (sectional view) - auger speed 10
rpm
77
Viscosity profile:
The profile of shear thinning behaviour of clay observed at the outlet section
of die in a 500 mm extruder with auger speed of 10 rpm is shown in Figure 3-
52.
6 00e+03
5.0ue+03
4.00e+03MolecularViscosity(kg/m-s) 3 00e+03
2 00e+03
1 OOe+03
0 00e+0020 25 30 35
Strain Rate (1/s)
Molecular Viscosity vs Strain Rate (Time=2 6040e+00)
Figure 3-52 Molecular viscosity vs. Strain rate - auger speed 10 rpm
The results of CFD analysis, for auger speed of 15 rpm, 20 rpm, 25 rpm,
30 rpm, 40 rpm and 50 rpm are available in Appendix A-section VII.
The trend of variation in maximum extrusion pressure and energy required in
extruding per unit mass of clay, with respect to change in auger speed for a
500 mm extruder is shown in Figure 3-53.
78
500 mm extruder pressure VS RPM @ constant extrusion rate
- * -5 0 0 mm extruder- Energy consumed to extruder per kg. of clay Vs RPM @ constant extrusion rate
Figure 3-53 Extrusion pressure, Energy consumption vs. Auger speed
The trend clearly indicates the effect of varying auger speed on the
performance of an extruder. It is also understood that, depending upon the
moisture content of the clay, an optimum auger speed is necessary to induce
the required amount of shear in the clay for generating sufficient extrusion
pressure at specified extrusion rates.
3.9.3 Effect of varying pitch distance on performance of
extruderThe effect of increasing and decreasing the pitch distance of the auger on
the performance characters of a 500 mm extruder was investigated in this
part. The other parameters like the die design, barrel design, auger speed,
clay material, size, clay moisture content and feed rate were kept constant.
Table 3-11 summarises the operational parameters and material properties
used in the CFD analysis.
Extruder Size
Feed
rate
(kgs'1)
Auger
speed
(rpm)
Herschel-Bulkley's
model value
500 mm 19 30
k=4908 Pa.sn n=0.5
t 0=8500 Pa C.S.R=3 s'1
500 mm Extruder Pressure and Energy consumption vs RPM(@ constant extrusion rate, for Clay type-ll
2.97
2.64.2!
22.31*= i5 515W _Q
■65S&
0.99 >>rs a*
0.66 2 c l
Auger RPM
Table 3-11 Data set for varying pitch distance analysis
79
The performance characters were assessed for augers with following pitch
distances 246.13 mm, 292 mm and 338.012 mm. The results obtained from
the CFD analysis are summarised below.
Extrusion Pressure:
Pressure developed during extrusion in a 500 mm extruder with 246.13 mm
auger pitch distance is shown in Figure 3-54 and 3-55. The pressure varied
from a minimum value of -5.2 kPa at the inlet section to a maximum of 4.02
MPa (40.2 bar) observed at the end of auger shaft and reduced to an
average value of 2.92 MPa (29.2 bar) at the outlet.
3 iee+oe3,QQe+06 2 84e+062.68e+062 52e+062.36e+06 2.20e*06 2.048+06 1 88e+06 1 72O+06 1.560+06 1 40©+06 1 24©+061 08e+06 9 220+05 7.620+05 6 020+05 4 410+052 810+05 1 21©+05 -3 91e+04 -1 99©+05 -3 60e+05 -5 20©+05
Contours o f Static Pressure (pascal) (T im e =2 .5 3 50 e +0 0 )
Figure 3-54 Static pressure contour (full view)-pitch dist. 246.13 mm
3490+06ML.1t* Q.
3.160+063 000+06
2 20e+062.048+061 8 8 0+O61.720+061.560+061400+061 248+061 O80+O69 22e+057 62e+056 02e+054 41©+052 810+051 21©+05-3 918+041 990+05
-3 60e+05-5200+05
Contours of Static Pressure (pascal) (Time=2.5350e+-00) Nov 03, 201
Figure 3-55 Static pressure contour (sectional view)-pitch dist. 246.13 mm
80
The trend of pressure development observed within the extruder section,
during extrusion is shown in Figure 3-56.
StaticPressure(pascal)
4 008+06
3 50e+G6
3 0 0 e+06
2 50e+06
2.00e+06
1.50e+06
1 00e+06
5.00e+05
000e+00 -5 00e+05
-0 9 -0 8 -0.7 -0 6 -0,5 -0.4 -0.3 -0 2 -0 1 0
Position (m)
Static Pressure (Time=2.5350e+00) I
Figure 3-56 Static pressure profiIe-pitch dist. 246.13 mm
Material flow pattern:
The flow pattern and velocity of clay observed during extrusion at various
sections of extruder and die, in a 500 mm extruder with 246.13 mm auger
pitch distance is shown in Figure 3-57. In the direction of extrusion the
average value observed for velocity at outlet section of die was 0.59 ms'1.
iContours of Velocity Magnitude (nVs) (Time=2.5350e+00) Nov 03, 201
Figure 3-57 Flow velocity during extrusion (sectional view)-pitch dist. 246.13
mm
81
9.94e-01
9.18©-018.80*4)18.41*4)18 03e-017.656-017.270-016 .886-016.508-016 .126.015.74e-015 .350-014 .970-014 .590-014.21e-013 826-013 448-013 06e-012 .680-012 290-011 916-011 536-011 150-017 65e-02382e-020 000+00
Viscosity profile:
The profile of shear thinning behaviour of clay observed at the outlet section
of die in a 500 mm extruder with 246.13 mm auger pitch distance is shown in
Figure 3-58.
MolecularViscosity(kg/m-s)
5.00O+03
4 .0 0 e + O 3
3.00e+03
2.006+03
1.008+030 5 10 15 20 25 30 35 4 0 45
S tra in R a te (1 /s )
Molecular Viscosity vs. Strain Rate (T im e=2.5350e+00)
Figure 3-58 Molecular viscosity vs. Strain rate-pitch dist. 246.13 mm
The results of CFD analysis for augers with pitch distance of 292 mm are
available in Appendix A- section II and for 338.012 mm distance in Appendix
A- section VIII.
The trend of variation in maximum extrusion pressure and energy required in
extruding per unit mass of clay, with respect to change in auger pitch
distance for a 500 mm extruder is shown in Figure 3-59.
82
500 mm extruder Pressure and Energy consumption vs Auger pitch distance @ constant extrusion rate and RPM, for Clay type I
3 2w -a w c at £
t \3 S'E —■- at2 > n a)
41
40
39
2.5940.22.58
38 2.54
2.52
2.50
2.48
2.46
2.44
2.42
2.40
37
36
35
34
33
32
31
2A1
246.136 292 338.012
4)U _ 3 O) *: *$ ^o* * cTJ O% > £ n3 oJ2 t-i °O o? >-
CUJ
Auger pitch distance (in mm)
-500 mm extruder Pressure vs Auger pitch d istance@ constant extrusion rate and RPM
-500 mm extruder- Energy consumed to extrude per Kg. of clay vs Auger pitch d is ta nce© constant extrusion rate and RPM
Figure 3-59 Extrusion pressure, Energy consumption vs. Auger pitch
distance
The observed trend in the change of performance characters clearly
indicates that reducing pitch distance does not influence the performance
characters of an extruder significantly compared to increasing pitch distance.
3.9.4 Effect of varying die shapes on performance of extruderThe effect of varying the design of die outlet on the performance characters
of a 500 mm extruder was investigated in this part. The other parameters like
the auger design, barrel design, auger speed, clay material, size, clay
moisture content and feed rate were kept constant. Table 3-12 summarises
the operational parameters and material properties used in the CFD analysis.
Extruder Size
Feed
rate
(kgs'1)
Auger
speed
(rpm)
Herschel-Bulkley's
model value
500 mm 19 30
k=4908 Pa.sn
n=0.5
t0=8500 Pa
C.S.R=3 s’1
Table 3-12 Data set for varying die design analysis
83
The performance characters of the extruder were assessed with respect to
three different types of die design, shown in Figure 3-60.
Die Type- Die Type-ll
Die Type-!
Figure 3-60 Types of die design investigated
The above shown die designs are intended to produce clay columns with
different cross sections used by C.F Ltd, in different applications. The results
obtained from the CFD analysis are summarised below.
Extrusion pressure:
Pressure developed during extrusion in a 500 mm extruder with die type-ll is
shown in Figure 3-61 and 3-62. The pressure varied from a minimum value
of -616 kPa at the inlet section to a maximum of 3.54 MPa (35.4 bar) and
reduced to an average value of 2.79 MPa (27.9 bar) at the outlet. The
maximum extrusion pressure developed during extrusion remained constant
even within the die section until the outlet, where the actual reduction
occurred. In the other die designs a gradual decrease in extrusion pressure
was observed along the entire length of the die section.
84
3 54e-*06 3.33e+06 3 12e-»06
■Contours of Static Pressure (pascal) (Time=2.4750e-HII0)
Figure 3-61 Static pressure contour (full view)-die type-ll
Mmys_ ;w r #V'
Contours of Static Pressure (pascal) (Tim e=2.0000e+00)
Figure 3-62 Static pressure contour (sectional view)-die type-ll
The trend of pressure development observed within the extruder section,
during extrusion is shown in Figure 3-63.
85
5 00e-KJ5
-5.00e+05-1 -0.9 -08 -07 -0.6 -0.5 -0 4 -0.3 -0.2 -0.1 0
Position (m)
J 00e+065 0 g hj6
2.00e+06
1 50e+06
1.00e+06
StaticPressure
(pascal)
0 00e+00
Static Pressure (Time=2 OOOOe-KXI)
Figure 3-63 Static pressure profile-die type-ll
Material flow pattern:
A significant change was observed in the flow pattern and the exit velocity
values with respect to the die shape and die outlet flow area. The flow
pattern and velocity of clay observed during extrusion, at various sections of
extruder and die, in a 500 mm extruder with die type-ll is shown in Figure 3-
64. In the direction of extrusion the average value observed for velocity at
outlet section of die was 0.74 ms'1.
l .2 0 e -0 0
1 I3 e *0 01 06e+009 86e-019.15e-01
8.45e-017 .74e-01 f-
7 .04e-01 I
6 .34e-01 *-
5 .63e-01
4 93e-01
4 22e-01
3.52e-012 82e-01
I 1 41e-017.04e-020 00e+00 #
Contours of Velocity Magnitude (m/s) (Time=2 OOOOe-tOO)
Figure 3-64 Flow velocity during extrusion (sectional view)-die type-ll
86
Viscosity profile:
The profile of shear thinning behaviour of clay observed at the outlet section
of die in a 500 mm extruder with die type-ll is shown in Figure 3-65.
M o le c u la rV is c o s ity(k g /m - s )
2 00®+03
1 ,00®+03
O .O O e + O O
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time-2.0000e-*-00) Ju
Figure 3-65 Molecular viscosity vs. Strain rate- die type-ll
The results of CFD analysis, for the other types of die design are available in
Appendix A - section IX.
The trend of variation in average pressure observed at the outlet section of
the die and energy required in extruding per unit mass of clay, with respect to
change in die design for a 500 mm extruder is shown in Figure 3-66. It is
understood from the results that the cross sectional area at the outlet and the
profile of a die has significant effect on the performance characters of an
extruder.
500mm Extruder-Pressure and Energy consumption Vs Die type, with costant extrusion rate and RPM, for Clay type-l
27 97
2.622 *
Type 1 Type 2 Type 3 Die-type
2.70
2.68
2.65
2.63
4>TJ _
E 05
o * ** c •o * >. E n 3 o *2 « -
§ ° O CDp »_ a! * c °- LU
2.60
-500mm Extruder Pressure Vs Die type with costant extrusion rate and RPM
-500mm Extruder- Energy consumed to extrude per Kg. of clay vs Die type with constant extrusion rate and RPM
Figure 3-66 Extrusion pressure, Energy consumption vs. Die design
87
3.9.5 Effect of varying number of split worms on performance
of extruderThe effect of adding split worms or half flight at downstream side of an auger
shaft is understood to have significant effect on the material flow, extrusion
pressure and power consumption in an extruder system [Seanor and
Schweizer, 1962]. The effect of varying the number of split worms on the
performance characters of a 500 mm extruder was investigated in this part
using CFD analysis. The other parameters like the die design, auger pitch,
barrel design, auger speed, clay material, size, clay moisture content and
feed rate were kept constant. Table 3-13 summarises the operational
parameters and material properties used in the CFD analysis.
Extruder Size
Feed
rate
(kgs1)
Auger
speed
(rpm)
Herschel-Bulkley's
model value
500 mm 19 30
k=4908 Pa.sn
n=0.5
t 0=8500 Pa
C.S.R=3 s'1
Table 3-13 Data set for varying split worm analysis
The performance characters of the extruder were assessed for three different
cases, which includes 1) auger shaft with no split worm, 2) auger shaft with
one split worm and 3) auger shaft with two split worms. The position and
orientation of the worms on the auger shaft were as shown in Figure 3-67.
88
One split w ormMo split worm
Two split worms
Figure 3-67 Types of split worm design investigated
The results obtained from the CFD analysis for auger shaft with two split
worms are summarised below.
Extrusion pressure:
Pressure developed during extrusion in a 500 mm extruder with two split
worms at the end of auger shaft is shown in Figure 3-68 and 3-69. The
pressure varied from a minimum value of -237 kPa at the inlet section to a
maximum of 3.79 MPa (rounded off to 38 bar) observed at the end of auger
and reduced to an average value of 2.72 MPa (27.2 bar) at the outlet.
3.79*406 3.59*406 3.39*406 3.19*406 2.98*4062 79*4 -0 6 ^2 5 8 * 4 0 6 2 .3 8 *4 -0 6 2 .1 8**-0 6 1 .9 8 *4-0 6 1 .7 8 *4-0 6 1 .5 7 *4-0 61 .3 7 *4 -0 6 , . 11 1 7 *4 -0 69 .7 1 *4 -0 5
5 .6 8 *4 -0 5 -3 .6 7 *4 -0 5
1 1.65*4-05
I -3.61*404
* -2.37*405
Con to u rs o f S ta tic P res su re (p a s c a l) (T im e = 2 .5 0 0 0 e 4-0 0 )
Figure 3-68 Static pressure contour (full view)-two split worms
89
3.79e+06
3.59e+063.39e*063.19e*D6
2.98e+062 78e+062.58e+06
2 38e*06
2.18e+06
1.98e+06
1.78e+06
1.57e+06
1.37e+06
1.17e+06
9.71 e+05
7.69e+05
5.68e+05
3.67e+05
1.658+05
-3.61 e+04
-2.37e+05
Contours of Static Pressure (pascal) (Time=2.5000e+00)
Figure 3-69 Static pressure contour (sectional view)-two split worms
The trend in the pressure developed during extrusion was linear and similar
to the other cases, as shown in Figure 3-70. The pressure distribution at the
exit of extruder or at the inlet section of the die was observed to be more
uniform, when compared with other cases.
3.00e+06
2.50e+06
StaticPressure(pascal)
2.00e+06
i.°0e+06
5.00e+05
0 .0 0 e+ 0 0
-5.008+05-1 -0 9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0
Position (m)
Static Pressure (Time=2.5000e+00)
Figure 3-70 Static pressure profile-two split worms
Material flow pattern:
The flow pattern and velocity of clay observed during extrusion at various
sections of extruder and die, in a 500 mm extruder with two split worms at
the end of the auger shaft is shown in Figure 3-71. In the direction of
90
extrusion the average value observed for velocity at outlet section of die was
0.6 ms'1.
1 236*00 1 16e*001 09e*<30 1 02e*00 9 53e-01 8 85e-01
Contours ofVelocity Magnitude (m/s) (Time=2.5000e+00)
Figure 3-71 Flow velocity during extrusion (sectional view)-two split worms
The effect of split worms on the flow pattern at the exit section of extruder
was also analysed and a significant change was observed. The flow pattern
observed at the exit section of extruder with respect to number of split worms
in the auger shaft is shown from Figure 3-72 to 3-74.
106^00101e*00963e-019.12e-©1 8.61*01 811*01 7 60*01 709*01 659*01 6 08*01 557*01 507*01 4 56*01 4 05*01 3 55*01 3 04*01 2 53*01 203*01 152*01 101*01 507*02 C00**90
1 35e+QO 1 30e+0Q I 25e+QQ 1 20e+Q0 1 156+00 1 10e+0G 1,06e+001 01e+00 9.61 e-01 9 I3e-01 8 65*018 17e-01 7.69e-01 7.21*01 6 72*01 6 24*01 5 76e-01 5.28*01 4.80*01 4 32*01 3.84*013 36*012 88*01 2 40*01 1 92*01 1 44*019 61*024 80e-02 0 00e+00
Contours o f Velocity Magnitude (rrVs) (Time=2 5000e+00)
Figure 3-72 Flow pattern with no
split worm
Contours of Velocity Magnitude (m/s) (Time=2 5050e+00)
Figure 3-73 Flow pattern with one
split worm
91
114e*0C I09e»00 1 05e*0C1 OOe*OC9 576-01 9116-018 656-01 8206-01 7.746-01 7 296-01 6 836-01 6.386-01 5 926-01 5476-01 5016-01 4 55e-0l
106-C'3 646-01 3 196-012 736-01 2 28e-01 1.826-01 137e-019 116-02 4556-02 000e-00
Contours of Velocity Magnitude (m/s) (Time=2.5000e+00)
Figure 3-74 Flow pattern with two split worms
Viscosity prof He:
The profile of shear thinning behaviour of clay observed at the outlet section
of die in a 500 mm extruder with two split worms is shown in Figure 3-75.
6 0 0 *4 0 3
MolecularViscosity(kg/m-s)
5 00*4-03
4 00*+03
3 .0 0 *+ 0 3
2 0 0 *+ 0 3
1 0 0 *4 0 315 20 2 5 30
Strain Rate (1/s)
M o le cu la r V isco s ity vs . S tra in R a te (T im e * 2 5 0 0 0 *4 0 0 )
Figure 3-75 Molecular viscosity vs. Strain rate-two half flights
The results of CFD analysis for auger with no split worms are presented in
Appendix A - section IX (b) and for auger with one split worm are presented
in Appendix A - section II.
The trend of variation in maximum pressure developed during extrusion and
energy required in extruding per unit mass of clay with respect to number of
split worms in an auger shaft, for a 500 mm extruder is shown in Figure 3-76.
92
500 mm extruder-Pressure and Energy consumption Vs No.of Split womrs @ constant extrusion rate and RPM, for Clay type-1
2.72
2.68 * _
2.65 £ f
2.61
2.58 i f ;
2.54.54
o O)2.47 > ;*
2.44 £ o.1U
2.400 2
No.of split worm at the auger
■500 mm extruder Pressure developed and powerconsumption VS No.of splitworms
-500 mm extruder- Energy consumed to extruder per Kg. of clay Vs No.of splitworms
Figure 3-76 Extrusion pressure, Energy consumption vs. Split worms
It clearly indicates that the addition of split worm at the end of auger shaft
influences the extrusion pressure but not the power consumption, confirms
with the recommendations of Seanor and Schweizer (1962) from the ir work.
3.10 Performance assessment of a 600 mm extruderThe effect of varying the design and operating parameters on performance
characters of a 600 mm extruder system, without varying the type of clay
was investigated in this part of the research, using the CFD modelling.
3.10.1 Effect of varying feed rate on performance of
extruder
The effect of increasing the feed rate of uncompacted clay, in a 600 mm
extruder was investigated in this part. The other parameters like the die
design, extruder design, clay material, size, clay moisture content and auger
speed were kept constant. Table 3-14 summarises the operational
parameters and material properties used in the CFD analysis.
93
Extruder Size
Feed
rate
(kgs’1)
Auger
speed
(rpm)
Herschel-Bulkley's
model value
600 mm Varying 22.5
k=5206.95 Pa.sn
n=0.32
t0=6500 Pa
C.S.R=2.1 s'1
Table 3-14 Data set for varying feed rate analysis
The performance characters were assessed for the following feed rates 8.1
kgs'1, 11.8 kgs'1 and 19 kgs'1. The results obtained from the CFD analysis
are summarised below.
Extrusion pressure:
Pressure developed during extrusion in a 600 mm extruder with a feed rate
of 8.1 kgs'1 is shown in Figure 3-77 and 3-78. The pressure varied from a
minimum value of -228 kPa at the inlet section to a maximum of 3.15 MPa
(31.5 bar) observed at the end of the auger shaft and reduced to an average
value of 2.7 MPa (27 bar) at the outlet.
—-ij 3.15e+06
(| 2 98e+G6| 2.81 e+G6
2.64e+06 2 47e+062.31 e+06 2.14e+06
1 97e+06 1 80e+06
1 63e+06
1 46e+06 1 29e+06
1 12e+06 9 54e+05
7.85e+05
k* * 1 6.17e+05
4 48e+05 2.79e+05
1 10e+O5
-5 89e+04 -2.28e+05
Contours of Static Pressure (pascal) (Time=2 6750e+00)
Figure 3-77 Static pressure contour (full view) - feed rate 8.1 k g s 1
94
3.15e+Q62.98e+Q62.81 e+06
2 6 4 e+06 2 47e+062.31 e+06 2 14e+06
1 97e+06 1 80e+06
1 63e+06
1 46e+06 1 29e+061 12e+06 9 54 e+05
7 8 5 e+05 6.17e+05
4 48e+052 79e+05
1 10e+05
-5 8 9 e+04 -2.28e+05
1 ITT
I__I
rContours of Static Pressure (pascal) (Time=2 6750e+00)
Figure 3-78 Static pressure contour (sectional view) - feed rate 8.1 kgs-1
The trend of pressure development observed within the extruder section,
during extrusion is shown in Figure 3-79.
-1 -0.8 -0.6 -0 4
Position (m)
StaticPressure(pascal)
3 00e+06
2 50e+06
2 00e+06
1 50e+06
1 0 0 e+06
5 00e+05
0 00e+00
-5.00e+05
Static Pressure (Time=2.6750e+00) I
Figure 3-79 Static pressure profile- feed rate 8.1 kgs'1
Material flow pattern:
The flow pattern and velocity of clay observed during extrusion at various
sections of extruder and die, in a 600 mm extruder with 8.1 kgs'1 feed rate is
shown in Figure 3-80. In the direction of extrusion the average value
observed for velocity at outlet section of die was 0.07 ms'1.
95
9 916-01
9 42e-018 92e-01
8.43e-01
7.93 e-01
7 43e-01
6 9 4 e-01
6 44 e-01
5.95e-01
5.45e-01
4 96e-01
4 4 6 e-01
3 9 6 e-013 47 e-01
2.97 e-01
2.48e-01
1 98 e-01
1 49 e-01
9.91 e-02
4 96e-02
0 00e+00
r n : . 1 1
I I 1 T J
rContours of Velocity Magnitude (m/s) (Time=2 6750e+00)
Figure 3-80 Flow velocity during extrusion (sectional view)-feed rate 8.1 kgs-1
Viscosity profile:
The profile of shear thinning behaviour of clay observed at the outlet section
of die in a 600 mm extruder with 8.1 kgs'1 feed rate is shown in Figure 3-81.
120e-*-O4
1.10e+04
Molecular iooe+o4 Viscosity (kg/m-s) 9 00e+03
8.00e+Q3
7CX)e+03
6.00e+03
5 00e+030.5 1 1.5 2 2.5 3 3.5 4
Strain Rate (1/s)
Figure 3-81 Molecular viscosity vs. Strain rate- feed rate 8.1 kgs'1
The results of CFD analysis, for feed rates 11.8 kgs'1 and 19 kgs'1 are
available in Appendix A- section X.
The trend of variation in maximum extrusion pressure and energy required in
extruding per unit mass of clay, with respect to change in feed rate of clay for
a 600 mm extruder is shown in Figure 3-82.
96
Sheffie ld Hallam U n iversity
A .iB .o r,
T itle /T hesis 2 ^ 0 f i ^ ^
Degree Py\ D f i j-( I L o S o QC- fvl U M £ iS ( c.C i-^Y ear: *—
2 - ^ 13
C opyr ight Declaration
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Date | Name and Institution /Organisation (in block letters)
Signature
600 mm extruder Pressure and Energy consumption Vs Mass flow rate/Feed rate @ constant speed of 22.5 rpm, for Clay Type-ll
3.14
8.1 11.8 19
7.034)TS _P »
5.86 S *<Kn *
4.69 ~ c-U 13,l i3.52
2.34 | 5o 9O U)1.1/ U) i_0.00
LUMass Flow rate/Feed rate (in Kg/sec)
-600 mm extruder Pressure Vs Mass flow rate/Feed rate ©constant speed of 22.5 rpm
-600 mm extruder- Energy consumed to extrude per Kg. of clay Vs Mass flow rate/Feed rate @ constant speed of 30 rpm
Figure 3-82 Extrusion pressure, Energy consumption vs. feed rate
3.10.2 Effect of varying auger speed on performance of
extruderThe effect of varying auger speed on the performance characters of a 600
mm extruder was investigated in this part. The other parameters like the die
design, extruder design, clay material, size, clay moisture content and feed
rate were kept constant. Table 3-15 summarises the operational parameters
and material properties used in the CFD analysis.
Extruder Size
Feed
rate
(kgs1)
Auger
speed
(rpm)
Herschel-Bulkley's
model value
600 mm 11.8 varying
k=5206.95 Pa.sn
n=0.32
t 0=6500 Pa
C.S.R=2.1 s '1
Table 3-15 Data set for varying auger speed analysis
The performance characters of the extruder were assessed for the following
auger speeds- 15 rpm, 22.5 rpm and 30 rpm. The results obtained from the
CFD analysis are summarised below.
97
Extrusion pressure:
Pressure developed during extrusion in a 600 mm extruder with an auger
speed of 15 rpm is shown in Figure 3-83 and 3-84. The pressure varied from
a minimum value of -181 kPa at the inlet section to a maximum of 1.97 MPa
(19.7 bar) observed at the end of the auger shaft and reduced to an average
value of 1.54 MPa (15.4 bar) at the outlet.
1 9 7 e -0 6 1.86e+06
1 758+061 65e+06
1 5 4 e -0 6 1 43e+06 1 32e+06 1 22e+06 1.11 e+06
1 00e-»06 8 94e+05
7.87e+05 6 .79e+05
5.71 e+05
4 6 4 e *0 5 3 5 6 e -0 5
2 49e+05 1.41 e *0 5 3 .38 e+04
-7 38 e *0 4
-1.81 e+05
Contours of S tatic Pressure (pascal) (T ime=2 6800e+00)
Figure 3-83 Static pressure contour (full view) - auger speed 15 rpm
1 7584061 65e-*06 I 54e-*061 43e406 1.32e406 1 22e406 1.11e406 1.00e406 8.94e405 7.87e405 6.79e405 5.71e4054.64e-*053.5694052.498405 1 41e405 3 38e404 -7 ^ e 4 0 4 -1 81e405
Contours of Static Pressure (pascal) (Time=2 6800e400)
Figure 3-84 Static pressure contour (full view) - auger speed 15 rpm
The trend of pressure development observed within the extruder section,
during extrusion is shown in Figure 3-85.
98
3 00e+06
2 50e+06
2.00e+06
1 50e+06
1 00e+06
5.00e+05
0 00e+00
-0.8 -0 6
Position (m)
Static Pressure (Time=2.6800e+00)
Figure 3-85 Static pressure profile- auger speed 15 rpm
Material flow pattern:
The flow pattern and velocity of clay observed during extrusion at various
sections of extruder and die, in a 600 mm extruder with auger speed of
15 rpm is shown in Figure 3-86. In the direction of extrusion the average
value observed for velocity at outlet section of die was 0.13 ms'1.
6 6 2 e-01
6.29e-01
5.96e-01
5 6 3 e-01
5 3 0 e-01
4 97e-01
4 6 4 e-01
4 30e-013 .97 e-01
3 64 e-01
3.31 e-012 .98 e-01
2 .65 e-012 .32 e-01
1 99 e-01
1 66e-01
1.32 e-01
9.93e-02
6.62e-02
3.31 e-02
0 00e+00
I 1 1 1
l i r
Contours of Velocity Magnitude (m/s) (Time=2 6800e+00)
Figure 3-86 Flow velocity during extrusion (sectional view) - auger speed 15
rpm
99
Viscosity profile:
The profile of shear thinning behaviour of clay observed at the outlet section
of die in a 600 mm extruder with an auger speed of 15 rpm is shown in
Figure 3-87.
t 5" ‘V i ‘■•r;• Sr •'■34. 1
1.00e+04
Molecular ViSCOSity 8.00e+03 (k g /m -s )
6.00e+03
4.00e+03
Z00e+030 1 2 3 4 5 6 7 8
Strain Rate (1 /s )
Figure 3-87 Molecular viscosity vs. Strain rate- auger speed 15 rpm
The results of CFD analysis, for auger speed of 22.5 rpm are available in
Appendix A- section X (a) and 30 rpm are available in Appendix A -section
XI.
The trend of variation in maximum extrusion pressure and energy required in
extruding per unit mass of clay, with respect to change in auger speed for a
600 mm extruder is shown in Figure 3-88.
100
600 mm Extruder Pressure and Energy consumption vs rpm @ constant extrusion rate, for Clay type-ll
■o w * >. E J2
015 22.5
Auger-rpm30
-600mm extruder pressure vs RPM ©constant extrusionrate
-600mm extruder- Energy consumed to extrude per Kg. of clay Vs RPM @ constant extrusion rate____________
Figure 3-88 Extrusion pressure, Energy consumption vs. auger speed
Similar to the 500 mm extruder, the trend observed for variation in
performance characters of a 600 mm extruder with respect to change in
auger speed indicates that the increase in speed will increase the pressure
and energy requirement of an extruder system to a certain extent.
3.11 ConclusionPerformance assessment of extruders using CFD technique along with
experimental validation of the methodology and fluid model used was
presented in this chapter. The ability to use CFD technique to design a clay
extruder system and the advantages that could be gained within the heavy
ceramics industries has clearly been demonstrated through the results
obtained.
101
Chapter-4 Finite Element Analysis of clayextruder
102
4.1 Introduction:In this part of the research work, mechanically induced stress and strain on
the components of a 430 mm extruder were assessed using FEA technique.
Components investigated include barrel, liner, distance piece and auger.
Based upon the maximum extrusion pressure expected under actual working
conditions, the component were assessed for two different load conditions
1) 1.8 MPa and 2) 2.6 MPa.
Stress and deformation induced with respect to applied load were
investigated for three different materials, which include A) Structural steel
(Grade BS EN 10025 Fe 430A), B) Grey Cast Iron (GCI) (Grade: EN-GJL-
250) and C) Austempered Ductile Iron (ADI) (Grade GJS-1400-1). Structural
steel is the most commonly used material by C.F Ltd to manufacture the
majority of extruder components. GCI and ADI are alternate material chosen
to be investigated through this research work, to identify their technical and
commercial suitability for manufacturing extruder components. In recent
years ADI has been proven to be a highly useful material for heavy clay
industrial applications [Da and Jincheng, 2000], [Chowdhury et al., 2010]
[Ductile Iron Society, 2012], due to its excellent wear resistant properties
and light weight. The technical suitability of these alternate materials was
analysed using FEA results for stress and deformation induced due to
extrusion pressure and the commercial feasibility was analysed by
comparing the cost to manufacture with existing and alternate materials. The
finding are summarised below.
4.2 FEA of clay extruder components
4.2.1 BarrelThe stress and deformation induced by the pressure developed during
extrusion, on the barrel was assessed in this part.
Geometry:
The Barrel geometry used for investigation is shown in Figure 4-1.
103
Figure 4-1 430 mm extruder barrel geometry
Load and boundary condition:
The geometry was suitably meshed using tetrahedral mesh and investigated
for two different load conditions, 1) 2.6 MPa and 2) 1.8 MPa. Pressure load
was applied on all the inner surfaces of the barrel and fixed support condition
on the appropriate surfaces, as highlighted in the Figure 4-2.
ise.co «« oi
Figure 4-2 430 mm extruder barrel- load applied
Stress and deformation results:
Values of equivalent stress, obtained for different materials from the analysis,
with respect to applied load conditions are summarised in Table 4-1.
104
Material
Max. Von-Misses
stress value, load-
2.6 MPa
Max. Von-Misses
stress value, load-
1.8 MPa
Structural steel 59.03 MPa 40.87 MPa
GCI 59.938 MPa 41.496 MPa
ADI 60.164 MPa 41.652 MPa
Table 4-1 Stress results-barrel
There was no significant change observed in stress distribution pattern
across the component with respect to applied load conditions. The results of
FEA for applied load of 2.6 MPa is shown in Figure 4-3. The results of FEA
for the applied load of 1.8 MPa is available in Appendix B- section I.
H
a) Structural steel b) GCI
c) ADI
Figure 4-3 Stress induced in barrel @ 2.6 MPa load
105
The strain induced in the barrel was investigated by analysing the
deformation pattern in the direction of extrusion. The results obtained are
summarised in Table 4-2.
MaterialMax. deformation,
load-2.6 MPa
Max. deformation,
load-1.8 MPa
Structural steel 0.071 mm 0.049 mm
GCI 0.129 mm 0.089 mm
ADI 0.088 mm 0.061 mm
Table 4-2 Deformation results- barrel
There was no significant difference noted in the deformation pattern, for both
the load conditions. The deformation pattern observed in barrel for applied
load of 2.6 MPa is shown in Figure 4-4 and the results for applied load of 1.8
MPa is available in Appendix B- section II.
?vit/)ttt im
a) Structural steel b) GCI
Figure 4-4 Deformation in barrel @ 2.6 MPa load
106
The stress and deformation results obtained from the FEA clearly indicates
that, barrel made up of any of the following materials Structural Steel, GCI or
ADI, will be able to withstand the stress induced during extrusion, without
breaking during operation. The material currently used by C.F Ltd is
Structural Steel and its cost of manufacturing was compared with the cost of
alternate materials used in FEA and is summarised in Table 4-3.
Material Cost per piece (in £'s)
Structural steel 6475.00
GCI 3886.00
ADI (cost with pattern) 6680.00
ADI (cost without pattern) 4380.00
'able 4-3 Manufacturing cost comparison for extruder barrel
It is understood from the preliminary investigations that ADI could be used
as an alternate material of construction for extruder barrels. GCI is not
recommended, even though it is cheaper than the other materials, due to its
limitations in manufacturing certain geometrical features.
4.2.2 Distance pieceDistance piece is an intermediate component used to connect the extruder
with the die. The stress and deformation induced by the pressure developed
during extrusion, on distance piece was assessed in this part.
Geometry:
Distance piece geometry used for the investigation is shown in Figure 4-5.
Figure 4-5 430 mm extruder distance piece geometry107
Load and boundary condition:
The geometry was suitably meshed using tetrahedral mesh and investigated
for two different load conditions, applied to the inner surfaces. Pressure load
was applied to appropriate inner surfaces and fixed constraints on the
required external surfaces as shown in Figure 4-6.
Or tfe«4-24Mp*4<»d2 :Ftrtd Support T wm I «2V01/20U 13.J4
9 Pressure: 2.6 MPj
Figure 4-6 430 mm extruder distance piece- load applied
Stress results:
Values of equivalent stress, obtained for different materials from the analysis,
with respect to applied load conditions are summarised in Table 4-4.
Material
Max. Von-Misses
stress value, load-
2.6 MPa
Max. Von-Misses
stress value, load-
1.8 MPa
Structural steel 52.749 MPa 36.519 MPa
GCI 52.403 MPa 36.279 MPa
ADI 52.314 MPa 36.217 MPa
Table 4-4 Stress results-distance piece
There was no significant change observed in the stress distribution pattern
across the component with respect to applied load conditions. The stress
distribution pattern on the distance piece, for applied load of 2.6 MPa is
shown in Figure 4-7 and the results for the applied load of 1.8 MPa is
available in Appendix B- section III
1 0 8
I.QO (mm)
a) Structural steel b) GCI
c) ADI
Figure 4-7 Stress induced in distance piece @2.6 MPa load
The strain induced in the distance piece was investigated by analysing the
deformation pattern in the direction of extrusion. The results obtained are
summarised in Table 4-5.
MaterialMax. deformation,
load-2.6 MPa
Max. deformation,
load-1.8 MPa
Structural steel 0.0317 mm 0.0219 mm
GCI 0.0579 mm 0.0401 mm
ADI 0.0394 mm 0.0273 mm
Table 4-5 Deformation results- distance piece
There was no significant difference noted in the deformation pattern, for both
the load conditions. The deformation pattern observed in liner for applied
load of 2.6 MPa is shown in Figure 4-8 and the results for applied load of 1.8
MPa is available in Appendix B- section IV.
a) Structural steel b) Grey cast iron
c) ADI
Figure 4-8 Deformation in distance piece @ 2.6 MPa load
The material currently used by C.F Ltd is Structural Steel and its cost of
manufacturing was compared with the cost of alternate materials used in
FEA and is summarised in Table 4-6.
Material Cost per piece (in £'s)
Structural steel 2445.00
GCI 1680.00
ADI 2170.00
Table 4-6 Manufacturing cost comparison for distance piece
110
It is clearly understood form the preliminary investigation that both ADI and
GCI have design and cost benefits and can be used as an alternate material
for manufacturing extruder distance piece.
4.2.3 LinerThe stress and deformation induced by the pressure developed during
extrusion, on liners was assessed in this part.
Geometry:
Liner geometry used for the investigation is shown in Figure 4-9.
Figure 4-9 430 mm extruder liner geometry
Load and boundary condition:
The geometry was suitably meshed using tetrahedral mesh and investigated
for two different load conditions, applied to the inner surfaces. Pressure load
was applied to appropriate inner surfaces and fixed constraints on external
surfaces as shown in Figure 4-10.
F«t«i Support
2V9U2QU U: 15
■ PrUMrtt 7* MPl n f Support
Figure 4-10 430 mm extruder liner - load applied
111
Stress results:
Values of equivalent stress, obtained for different materials from the analysis,
with respect to applied load conditions are summarised in Table 4-7.
Material
Max. Von-Misses
stress value, load-
2.6 MPa
Max. Von-Misses
stress value, load-
1.8 MPa
Structural steel 3.363 MPa 2.328 MPa
GCI 3.431 MPa 2.375 MPa
ADI 3.441 MPa 2.387 MPa
Table 4-7 Stress results-liner
The stress distribution pattern on the liner, for the applied load of
2.6 MPa is shown in Figure 4-11 and the results for the applied load of 1.8
MPa is available in Appendix B- section V
JWt/SfUM.H
a) Structural steel b) GCI
c) ADI
Figure 4-11 Stress induced in liner @ 2.6 MPa load
112
The strain induced in the liner was investigated by analysing the deformation
pattern in the direction of extrusion. The results obtained are summarised in
Table 4-8.
MaterialMax. deformation,
load-2.6 MPa
Max. deformation,
load-1.8 MPa
Structural steel 0.0002 mm 0.0001 mm
GCI 0.0004 mm 0.0003 mm
ADI 0.0002 mm 0.0002 mm
Table 4-8 Deformation results-liner
The deformation pattern observed in liner for applied load of 2.6 MPa is
shown in Figure 4-12 and the results for applied load of 1.8 MPa is available
in Appendix B- section VI.
a) Structural steel b) GCI
c) ADI
Figure 4-12 Deformation in liner @ 2.6 MPa load
113
4.2.4 Auger
The stress and deformation induced by the pressure developed during
extrusion, on the auger shaft was assessed in this part.
Geometry:
Auger geometry used for the investigation is shown in Figure 4-13.
Figure 4-13 430 mm extruder auger shaft geometry
Load and boundary condition:
The geometry was suitably meshed using tetrahedral mesh and investigated
for two different load conditions. Pressure load was applied on the all the
faces of worm and auger shaft and fixed constraint at one end of the shaft as
shown in Figure 4-14.
m * m >•
Figure 4-14 430 mm extruder auger shaft - load applied
114
Stress results:
Values of equivalent stress, obtained for different materials from the analysis,
with respect to applied load conditions are summarised in Table 4-9.
Material
Max. Von-Misses
stress value, load-
2.6 MPa
Max. Von-Misses
stress value, load-
1.8 MPa
Structural steel 3.835 MPa 2.655 MPa
GCI 4.131 MPa 2.860 MPa
ADI 13.345 MPa 9.238 MPa
Table 4-9 Stress results-auger shaft
The stress distribution pattern on auger shaft, for applied load of 2.6 MPa is
shown in Figure 4-15 and the results for applied load of 1.8 MPa is available
in Appendix B- section VII'
U!« US.M
a) Structural steel b) GCI
Figure 4-15 Stress induced in auger shaft @ 2.6 MPa load115
The strain induced in the auger shaft was investigated by analysing the
deformation pattern in the direction of extrusion. The results obtained are
summarised in Table 4-10.
MaterialMax. deformation,
load-2.6 MPa
Max. deformation,
load-1.8 MPa
Structural steel 0.004 mm 0.003 mm
GCI 0.009 mm 0.006 mm
ADI 0.198 mm 0.137 mm
Table 4-10 Deformation results-auger shaft
The deformation pattern observed in auger shaft for applied load of 2.6 MPa
is shown in Figure 4-16 and the results for applied load of 1.8MPa are
available in Appendix B- section VIII.
a) Structural steel b) GCI
c) ADI
Figure 4-16 Deformation in auger shaft @ 2.6 MPa load
116
nnxm \i i
The material currently used by C.F Ltd for manufacturing auger is a special
type of alloy material developed in house, designated as CF-28. Material with
equivalent mechanical property was used in FEA. In actual scenario, during
the process of manufacturing, the casted auger has to be heat treated in
order to attain the recommended hardness value of =60 HRC. Hence in
order to have a fair comparison of manufacturing cost, the heat treatment
cost for alternate materials was required. Due to amount of time and cost
involved in obtaining this cost, it was decided to make a comparison without
heat treatment cost and it is summarised in Table 4-11.
Material Cost per piece (in £'s)
Chrome steel 311.00
GCI 200.00-223.00
ADI 227.00-266.00
Table 4-11 Manufacturing cost comparison for auger
It is evident from the above discussion that the alternate materials
considered for manufacturing of augers, possess both design and
commercial advantages.
Clay being a very abrasive substance, the hardness value of the auger is
considered to be very critical to withstand the wear caused by the clay and
also increase the life of auger, in order to make the system to be cost
effective.GCI is not recommended by the users and design engineers, due to
its brittle nature at the early stages of installation. ADI alloy is lighter and
cheaper than the steel alloy which is currently used and also proven to be
useful in such applications. ADI, though, has better mechanical
characteristics and costs less than the existing material, the only limitation is
the maximum hardness value that could be achieved through heat treatment
process. As mentioned earlier it is recommended that certain areas of the
auger should have a hardness value of =60 HRC. The maximum attainable
hardness value in an ADI alloy, with the available methods of heat treatment
is 55 HRC, and this increase in hardness is achievable only to a certain
micron depth. However all the augers that are mounted on the shaft are not
subjected to equal pressure and wear. The field data obtained on the wear
117
life of augers indicates that the auger located at the far end of the extruder or
in other words the augers at the end of the barrel chamber is subjected to
excessive wear. Whereas the augers inside the vacuum chamber are
subjected to less wear. This difference in the pattern of wear characters of
auger provides an opportunity for the use of alternate materials for making
augers which are subjected to less pressure and wear. It is evident from the
above discussion that using ADI as an alternate material for making augers
is not only a cost effective option but also could yield other benefits like less
power consumption at the extruder unit and increases the life of augers.
4.3 ConclusionThus the technical and commercial advantage of using alternate light
materials was presented in this chapter. This clearly demonstrates the ability
and advantages of using FEA techniques to improve the design of clay
extruders within heavy ceramic industries.
118
Chapter-5 Conclusion and future directions
119
5.1 ConclusionThe main aim of this research work was to use CFD and FEA techniques to
assess and improve the design of extruders. The key objectives include
identifying suitable CFD methodology to simulate the clay extrusion process,
assessing the performance character of extruders with respect to various
design and operating parameters and investigate alternate materials for
extruder components that could make the extruder more efficient and cost
effective.
The first part of this research work was dedicated to identifying a suitable
flow model and CFD modelling technique, for assessing the performance
characters of a vacuum type de-airing extruder. The extrusion pressure
developed and power consumed by full scale extruders during the extrusion
was predicted using Herschel-Bulkley's fluid flow based 3-D CFD model. The
extrusion pressure, power consumption and the pressure development trend
were then predicted for different designs of extruder under different operating
conditions, using the 3-D CFD model. The results obtained for extrusion
pressure, flow pattern and velocity of clay during extrusion were in good
agreement with the values suggested in the literature and occurring in actual
scenarios. The results obtained from the model for properties like
temperature and density variation were not very satisfactory and need further
investigation.
The results for shear thinning behaviour exhibited by clay during extrusion
was predicted from the CFD model and compared with the experimental
results obtained from various scientific works. The similarity in the viscosity
profile obtained from the model and the literature indicates that Flerschel-
Bulkley’s flow model used in the CFD analysis is well representing the shear
thinning behaviour of clay exhibited during the process of stiff extrusion.
The second part of this research work was focused in validating the CFD
methodology used in the first stage. The extrusion pressure and power
consumed by the lab-scale extruder was measured experimentally and
compared with the results obtained from CFD analysis. The closeness in the
measured values for extrusion pressure and power consumption clearly
120
demonstrates the suitability of using the identified CFD methodology to
model and assess the performance of full-scale extruders.
The third stage of this research work was dedicated to using the FEA
technique to investigate the technical suitability of alternate light weight
materials and the compare the costs of extruders. The FEA results and the
cost of alternate light weight materials indicate that the use of Austempered
Ductile Iron to manufacture extruder components could result in both
technical and commercial benefits. A careful consideration is required at the
design stage in order to identify a proper area for use of this material.
The results obtained from this research work clearly demonstrate that using
CFD and FEA techniques within the process of clay extruder design could be
cost effective and time saving. It helps in reducing the resource and time
required for developing new extruder components, compared with lab-based
development processes.
5.2 Future directions• Performing more trials in the scaled extruder with an improved
experimental set up could help in obtaining further validation of the
CFD methodology used.
• A further investigation in improving the quality of mesh and further
mesh refinement could be beneficial in obtaining a converged solution
and might improve the results in critical areas of extruder sections.
• Experimental works in a controlled environment that focus in
determining the variables used for Flerschel-Bulkley’s model, for clays
with different moisture content could be undertaken. This will enhance
the accuracy of flow parameters predicted by the current CFD
methodology and also reduce time and computing cost.
• A further investigation of suitable CFD based modelling methods that
can predict temperature dependant properties of clay during extrusion
could be helpful in predicting additional flow parameters, involved
during extrusion. It might also open up new areas for investigation.
• Measuring the viscosity of clay with advanced instruments like Ball
measuring system and Building Material cell, could help in obtaining
121
better results and further understanding in the flow characters of clay
when subjected to shear. This could help in making a fair comparison
with the results predicted from the CFD model and make suitable
design changes to enhance the flow of clay in extruders during
extrusion.
122
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128
I. Extruder geom etry
a. 500 mm extruder
%£gEsS&s&.
Figure A-A- 1 500 mm extruder volumes and mesh generated
b. 600 mm extruder
f f i w
M :■ f; M™ ! IIP
: %S&0 S0j! t im ?
m s m
Figure A-A-2 600 mm extruder volumes and mesh generated
130
II. CFD Sim ulation results of 500 mm extruder with Herschel-
Bulkley's model value-1
Extrusion pressure:
4 020+06
3 810+06
3.59©-+06
3.38e+06 3.160+06
2.95©-+06
2.7 3 ©+-06
2.52 ©+-06
2.30©+-06
2.09©+-06
1 .87 ©+-06
1.66©+-06
1 .440+06
1.23e+06
1.01 ©+-06
8 .00e+-05
5.85©+-05
3.70©+-05
1.55©+05
-6 .00e+04
-2.75©+05
1
Contours of Static Pressure (pascal) (T im e=2 .5050e+00)
Figure A-A-3 Static pressure contour (full view)-500 mm Case I
C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 5050e+ -00)
Figure A-A-4 Static pressure contour (sectional view)-500 mm Case I
StaticP ressu re
(p ascal)
4.00e+06
3 50e+O 6
3 00e+O 6
2.50e+06
2 00e+06
1 500+06
1 00e+O6
5 00e+05
0 00e+00
-5 000+0543.9 43 8 43.7 43 6 43.5 43 4 43 3 43 2 43.1 O
Position (m )
S ta t ic P re s s u re (T im e = 2 5 0 5 0 e + 0 0 )
Figure A-A-5 Static pressure profile -500 mm Case I
131
Material flow pattern:
i 1 3e»00 1 07e-oo1 ooe+oo9 33e-018.66e-018 00e-01 _ _7.33e-01
6.66e-01
6.00e-015 33e-01
4.66e-01
4 00e-01
3.33e-01
2.67e-01
2.00e-01
1.33e-01
6.66e-02 O.OOe+OO
Contours of Velocity Magnitude (m/s) (Tim e=2.5050e+00)
Figure A-A-6 Flow velocity during extrusion (sectional view)-500 mm Case I
Viscosity profile:
7 0 0 e + 0 3
6 .0 0 e + 0 3
Molecular 5.ooe+o3 Viscosity (kg/m-s) 4.ooe+o3
3.00e+ 03
2 .00e+03
1.00e+030 5 10 15 20 25 30 35 4 0 45
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (T im e=2.5050e+00) Ap
Figure A-A-7 Molecular viscosity vs. Strain rate-500 mm Case I
132
III. CFD Sim ulation results of 600 mm extruder with Herschel-
Bulklev's model value-1
Extrusion pressure:
4.71 e+064 .46e+064 21 e+063 9 6 e+063 71e+063 45e+063.20e+062.95e+062.70e+062 45e+062 19e+061 94e+061 6 9 e+061 44e+061 19e+069 34e+056 8 2 e +054 3 0 e +051 78e+05-7 36e+04-3 26e+05
Contours of Static Pressure (pascal) (T im e=2.6700e+00)
Figure A-A-8 Static pressure contour (full view)-600 mm Case I
4 71e+06
4 4 6 e+064.21 e+06
3 9 6 e+06
3 7 1 e+06
3.45e+063 2 0 e+06
2 9 5 e+06
2 70e+06
2 45e+06
2 19e+06
1 94e+06
1 69e+06
1 44e+06
1 19e+06
9.34e+05
6 8 2 e+054 3 0 e+05
1 78e+05
-7 3 6 e+04
-3.26e+05
s i i i r o n i
■ r r w m
Contours of Static Pressure (pascal) (Time=2 6700e+00)
Figure A-A-9 Static pressure contour (sectional view)-600 mm Case I
133
Position (m )
e+06
4 00e+06
3.00e+06
Static P ressu re 2 00e+06
(pascal)1.00e+O6
Static Pressure (Time=2.6700e+00)
Figure A-A-10 Static pressure profile -600 mm Case I
Material flow pattern:
8 95e-08 46s-017.96 e-01 7 46e-01 6.96e-01
6.47e-01
5.97e-01
5.47e-01
4.97e-01
4 48e-01
3 98e-01
I 3 48e-01
I 2 98e-01
I 2 49e-01
| 1.99 e-01
1 49e-01
9.95e-02
4.97e-02
0 00e+00
B E T Till1“ [ T T
____ I f LJr 2
Contours of Velocity Magnitude (m/s) (Time=2.6700e+00)
Figure A-A-11 Flow velocity during extrusion (sectional view)-600 mm Case I
134
Viscosity profile:
1.10e+04
1 00e+04
Molecular 9.ooe+o3 Viscosity (kg/m-Sj 8 00e+03
7.00e+03
6.00e+03
5.00e+030 1 2 3 4 5 6
Strain Rate (1/s)
Figure A-A-12 Molecular viscosity vs. Strain rate-600 mm Case I
IV. CFD Simulation results of 500 mm extruder with Herschel-
Bulklev's model value-ll
Extrusion pressure:
Contours of S ta tic P ressu re (pascal) (T im e = 2 .5 0 0 0 e + 0 0 )
2 4 3 e + 0 62 3 0 e+0 62 .1 7 e + 0 62 0 4 e + 0 61.91 e+Q61 7 8 e + 0 61 6 5 e+0 61 5 2 e + 0 61 3 8 e + 0 61 2 5 e +061 1 2e +0 69.91 e +058 .60e+ O 57 2 9 e +055 9 8 e+0 54 .6 7 e + 0 53 3 6 e+0 52 0 5 e+0 57 3 5 e +04-5 7 6e + 0 41 8 9 e + 0 5
Figure A-A-13 Static pressure contour (full view)-500 mm Case II
135
2 4 3 e + 0 62 3 0 e + 0 62 1 7 e + 0 6
2 .0 4 e + 0 61 .9 1 e + 0 6
1 7 8 e + 0 66 5 e + 0 6
1 5 2 e + 0 61 3 8 e + 0 6
1 25 e + D 61 1 2 e + 0 69.91 e + 0 58 6 0 e + 0 57 .2 9 e + 0 55 9 8 e + 0 54 6 7 e + 0 53 .3 6 e + 0 52 0 5 e + 0 57 3 5 e + 04-5 7 6 e +041 8 9 e + 0 5
C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .5 0 0 0 e + 0 0 )
Figure A-A-14 Static pressure contour (sectional view)-500 mm Case II
StaticP ressu re
(p ascal)
-1 -0 9 -0 8 -0 .7 -0 6 -0 .5 -0 4 -0 3 -0 .2 -0 1 0
Position (m )
S ta t ic P re s s u re (T im e = 2 5 0 0 0 e + 0 0 ) I
Figure A-A-15 Static pressure profile -500 mm Case II
Material flow pattern:
1 3 5 e-01 6 .7 7 e -02 0 OOe-rOO
: ii '11 CBe-KM
1 01 e + 0 09 47e-01
8 .8 0 e-01 8 12e-01
7 .4 4 e-01 6 7 7 e-01 6 0 9 e-01
5 41 e-014 74e -01
4 06e-013 38e-01
2 71 e-01
C o n to u rs o f V e lo c i ty M a g n itu d e (m /s ) (T im e = 2 5 0 0 0 e + 0 0 )
Figure A-A-16 Flow velocity during extrusion (sectional view)-500 mm Case
II136
Viscosity profile:
7.00e+03
6.00e+03
5.00e+03
Molecular 4.ooe+o3 Viscosity (kg/m-s) 3.ooe+o3
2 .0 0 e + 0 3
1 .0 0 e + 0 3
0 .0 0 e + 0 01 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0 5 5
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=2 5000e+00) Apr
Figure A-A-17 Molecular viscosity vs. Strain rate-500 mm Case II
V. CFD Simulation results of 600 mm extruder with Herschel-
Bulklev's model value-ll:
Extrusion pressure:
Contours of Static Pressure (pascal) (Time=2.6900e+00)
2 9 7 e -0 6
2 8 1 e *06
2.65e+06
2 49e+06
2.33e+06
2 1 7e+06
2 01 e+06
1 86e+06
1,70e+06
1.54e+06
1 06e+06
9.00e+057 41 e+05
5 82e + 05
4.23e+05
2 63e + 05
1 04e+055.51 e+04
2.1 4e + 05
Figure A-A-18 Static pressure contour (full view)-600 mm Case II
137
2 97e+OS2.81 e + 0 6 2 6 5 e 4 0 6 2 .4 9 e + 0 6 2 .3 3 e -K )62.170-MD6 2 .0 1 0 4 0 6 1 86e-H36 1 .7 0 0 4 0 6 1 54e406 1 3 8 e 4 0 6 1 2 2 e 4 0 6 1 0 6 e 4 06 9 .0 0 e 4 0 5 7 41 e 4 0 5 5 .8 2 e 4 0 5 4 2 3 e 4 0 5 2 .6 3 e 4 0 5 1 0 4 e 40 5 -5 .51 e 4 0 4 -2 1 4 e 4 0 5
C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .6 9 0 0 e 40 0 )
Figure A-A-19 Static pressure contour (sectional view)-600 mm Case II
-5 00e+O 5-1 4 -1 2 -1 -0 .0 -0 6 -0 4 -0 .2 O
Position (m )
2 00e+O 6
StaticP ressu re
(pascal)
S ta t ic P re s s u re (T im e = 2 6 9 0 0 6 4 0 0 )
Figure A-A-20 Static pressure profile -600 mm Case II
Material flow pattern:
■
9 9 4 e-01 9 44e-018 9 5 e-018 .4 5 e 0 17 9 5 e-017 46e -01
6 9 6 e-01
6 .4 6 e -0 1
5 9 7 e-01
5 .4 7 e-01
4 9 7 e-01
4 4 7 e-01
3 9 8 e-01
3 4 8 e-01
2 9 8 e-01
2 .4 9 e -0 1
1 9 9 e-01
1 49e -01
9 9 4 e -0 2
4 9 7 e -0 2
0 0 0 e + 0 0
C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 .6 9 0 0 e 4 0 0 )
Figure A-A-21 Flow velocity during extrusion (sectional view)-600 mm Case
II
138
Viscosity profile:
MolecularViscosity(kg/m-s)
4.00(H-03
2.00e+030 1 2 3 4 5 6
Strain Rate (1/s)
Figure A-A-22 Molecular viscosity vs. Strain rate-600 mm Case II
VI. CFD Simulation results of 500 mm extruder with varying feed
rate:-
a. Feed rate:-15 kgs'1
Extrusion pressure:
2.68a+88 2.54e+08 2.44e+06 2348*06 2 24e+06 2.148+06 2.04e+08 1.838+06 1 83e+08 1.73e+06 1.63e+06 1.53e+0B 1 43e+06 1.33e+08 1.23e+08 1.12e+081 02e+08 8.22e+05 8.20e+05 7 18e+05 6.18e+05 5.17e+05 4.15e+05 3.14e+05 2.13e+05 1.11 e+05 1 01e+04 -9 11e+04 -1 92e+05
Contours of Static Pressure (pascal) (T lm e=5.0400e-01)
Figure A-A-23 Static pressure contour (full view) - feed rate 15 kgs-1
139
2 68e+08 2 54e+0B 2-44e+08 2 34e+082 24e*0B 2 14e+0B 2 04e+081 B3e+081 83e+081 73e+0B 1 83e+0B 1.53C+0B 1 43e+0B 1.33C+06 1.23e+0B 1 12e+06 1 02e+0B 9.22e+05 8 20e+05 7 19e+05 6 18e+05 5 17e+05 4 15e+05 3.14e+05 2 13e+05 1 11e+05 1 01e+04 -9 11e+041 -1 92e+05
m h
Contours of Static Pressure (pascal) (Time=5.0400e-01)
Figure A-A-24 Static pressure contour (sectional view) - feed rate 15 k g s 1
.00e+06
S ta t icP re s s u re
(p a s c a l)
-1 -0 9 -0 8 -0 .7 -0 6 -0 .5 -0 4 -0 .3 -0 .2 -0.1 0
Position (m)
S tatic P re s s u re (T lm e= 5 .0400e-01 )
Figure A-A-25 Static pressure profile- feed rate 15 k g s 1
Material flow pattern:
1 35e*00 1.29e*G0 1.24e«-00 1 19e+001 14e+001 10e+001 05e+001 00e*00 953e-01 9 05e-01 8 58e-018 10e-01 7 62e-01 7 15e-01 6.67e-01 6 19e-01 5 72e-01 5 24e-01 4 76e-01 4 29e-013 81e-Ot3 34e-012 86e-012 38e-011 91e-011 43e-019 53e-024 76e-02 0 00e*00
Contours of Velocity Magnitude (m/s) (Time=5 .0400e-01)
Figure A-A-26 Flow velocity during extrusion (sectional view)-feed rate 15
k g s 1140
Viscosity profile:
7 009+03' !' e9T6:006+03
5 00e+03Molecular Viscosi (kg/m
4 000+03
300©+03
2.008+03
1 00e+03
0 00e»0u15 20 25 30
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=5.0400e-01)
Figure A-A-27 Molecular viscosity vs. Strain rate- feed rate15 kgs-1
Results of CFD analysis for feed rate of 19 kgs' 1 are available in Appendix A under Section IV.
a. Feed rate:-25 kgs-1
Extrusion pressure:
2 39e+0B2 27e+062 17e+062 08e+061 98e+061 89e+061 79e+061 70e+0B1.61e+061 61e+06142e+061 32e+061 23e+0B1.14e+061 04e+06947e+058 53e+057 59e+G56 65e+055 7 1 e+054 77e+053 83e+052 89e+051 94e+051 00e+056 25e+03-8 79e+041 82e+052 76e+05
L
Contours of Static Pressure (pascal) (Time=4.2400e-01)
Figure A-A-28 Static pressure contour (full view) - feed rate 25 kgs'1
141
CfflfflEHSSE!239e+08 2.27e*0B 2.17e+O0 2.08e+06 1 98e+08 1.89e+08 1 790+08 1 70e+Q8 1.61e+06 1 51e+0B 1 42e+06 1.32e+08 1.23e+06 1.14e+08 1.04e+06 9.47e+05 8.53e+05 7 59e+05 B.65e+05 5.71e+05 4 77e+05 3.83e+05 2.89e+05 1 94e+05 1 00e+05 6 25e+03 -8 79e+04 -1 82e+05 -2 76e+05
Contours of Static Pressure (pascal) (Time=4.2400e-01) Oct 11. 20
Figure A-A-29 Static pressure contour (sectional view) - feed rate 25 k g s 1
Static 1 2 5 e + 0 6P ressu re
(pascal)
-0 6 -0 .5 -0 .4
Position (m)
S ta t ic P re s s u re (T im e = 4 2 4 0 0 e-01)
Figure A-A-30 Static pressure profile- feed rate 25 kgs'1
Material flow pattern:
Contours of Velocity Magnitude (m/s) (Tim e=4.2400e-01)
Figure A-A-31 Flow velocity during extrusion (sectional view)-feed rate 25
k g s 1
142
Viscosity profile:
4.50e+03
4 00e+03
3.50e+03
MolecularViscosity(kg/m-s)
3.006+03
2.506+03
2.006+03
1 00e+03
5 006+020 10 20 30 40 50 60 70 80
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=4.2400e-01) C
Figure A-A-32 Molecular viscosity vs. Strain rate- feed rate 25 kgs'1
b. Feed rate:-30 Kgs'1
Extrusion pressure:
1,52e+06 1.44e+081 38e+08 t 32e+061 26e+081 20e+06 1 14e+06 1 08e+061 02e+08 959e+05 8 98e+05 8 38e+05 7.78e+05 7 17e+05 657e+05 5 96e+05 5.36e+05 4.76e+05 4 15e+05 3 55e+052 95e+052 34e+05
1 74e+05
1.14e+055 32e+04
-7 14e+03
-6 75e+04
-1 28e+05
-1 88e+05
Contours of Static Pressure (pascal) (Time=5.0400e-01) Oct 17,
Figure A-A-33 Static pressure contour (full view) - feed rate 30 kgs'1
143
11 52e+Q8 1 44e*06 1 38e+061 32e*061 26e+08 1 20e*0B 1 14e-*06 1 08e-*-081 02e+06 9 59e+05 8 98e+05 8 38e+05 7 78e+057 17e+05 ; 6 57e+05 \ 5 96e+05 j 5 36e*05 | 4 76e+05 14 15e+05 3 55e+052 95e+05 2 34e*05 1 74e+05 1 14e+055 32e+04 -7 14e+03 -6 75e-*-04 -1 28e+05
Contours of Static Pressure (pascal) (Time=5.0400e-01) Oct 17. 20
Figure A-A-34 Static pressure contour (sectional view) - feed rate 30 k g s 1
1 00e+O6
-1 -0 .9 -0 .8 0 . 7 - 0 6 - 0 5 -0 .4 -0 .3 -0 .2 -0 1 0
Position (m )
S ta t ic P re s s u re (T im e = 5 0 4 0 0 e -0 1 )
Figure A-A-35 Static pressure profile-
Material flow pattern:
feed rate 30 k g s 1
t 52e+Q01 46e+00 141e+001.35e+001.30e+0D124e+001 18e+00 U3e+00 1 07e+00 1.01e+00 9.58e-01 9 01e-01 8.45e-01 7 89e-01 7 32e-01 6 76e-01 6 20e-01 5 B3e-01 5 07e-014 51e-01 3 94e-01 3 38e-012 82e-012 25e-01 1 69e-011 I3e-015 63e-02 0 00e+00
Contours of Velocity Magnitude (m/s) (Time=5.0400e-01) Oct 17. 201
Figure A-A-36 Flow velocity during extrusionfsectional view)-feed rate 30
k g s 1144
Viscosity profile:
4.50e+03
4 00e+03
3.50e+03
Molecular 3.ooe+o3Viscosity( k n /m - c l 2.50e+03
1 00e+03
5 00e+020 10 20 30 40 50 60 70 80 90
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=5.0400e-01)
Figure A-A-37 Molecular viscosity vs. Strain rate- feed rate 30 k g s 1
c. Feed rate:-40 Kgs'1
Extrusion pressure:
6.88e+056 47e+056 IBe+055 84e+055 53e+055 22e+054.90e+054 59e+054 28e+053.97e+053 65e+053.34e+053 03e+052 71e+052.40e+052.09e+051.77e+051 46e+051 15e+05B.33e+045.20e+042 07e+04-1 07e+04-4 20e+047.33e+04
-1.05e+05-1 36e+05-1 67e+05-1 99e+05
Contours of Static Pressure (pascal) (Tim e=5.0400e-01)
Figure A-A-38 Static pressure contour (full view) - feed rate 40 kgs'1
145
■ n ^ o iB 89e+u56 47e+u5BIBe+055 84e+055 53e+055.22e+054 90e+054 59e+u54 28e+053.97e+053 65e+053 34e+G53 03e+052.71e+052 40e+052 09e+051 77e+051 46e+051 15e+058 33e+045 20e+042 07e+04-1 07e+04-4 20e+04-7 33e+04-1 05e+05
1 36e+u5-1 67e+05
Contours of Static Pressure (pascal) (Time=5.0400e-01) Oct 17. 2011
Figure A-A-39 Static pressure contour (sectional view) - feed rate 40 kgs-1
StaticP ressu re
(p ascal)
S.00e+O5
4 .0 0 e + 0 5
3 .0 0 6 + 0 5
2 .0 0 e + 0 5
1 00e+O 5
0 OOfi +00
-1 0 0 6 + 0 5-1 -0 9 -0 8 -0 .7 -0 6 -0 .5 -0 .4 -0 .3 -0 .2 -0 .1 0
Position (m )
S ta t ic P re s s u re (T im e = 5 .0 4 0 0 e -0 1 ) T
Figure A-A-40 Static pressure profile- feed rate 40 kgs'1
Material flow pattern:
Contours of Velocity Magnitude (m/s) (Time=5.0400e-01) 0 0 17.2011
Figure A-A-41 Flow velocity during extrusion (sectional view)-feed rate 40
k g s 1 146
Viscosity profile:
3.506+03
3.006+03
MolecularViscosity(kg/m-s)
1 0 0 e +03
5 00e+02
0 00e+000 20 40 60 80 100 120
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=5.0400e-01)
Figure A-A-42 Molecular viscosity vs. Strain rate- feed rate 40 kgs-1
d. Feed rate:-50 Kps'1
Extrusion pressure:
MB
I
3 27e+05 2 31e+05 1 60e+05 8 856+041 706+04-5 446+04 -1 26e+05 -1.976+05 -2 69e+05 -3 40e+05 -4 12e+05 -4 83e+05 -5.556+05 -6 26e+05 -6 97e+05 -7 69e+05 -8 40e+05 -9 12e+05 -9 83e+05 -1 05e+06 -1 13e+06 -1 20e+06 -1.27e+06 -1 34 e+06 -1 41e+06 -1 48e+06 -1 55e+06 -1 63e+06 -1 70e+06
t-5?
Contours of Static Pressure (pascal) (Time=4.8400e-01) Oct
Figure A-A-43 Static pressure contour (full view) - feed rate 50 k g s 1
147
3 27e+05
1 60e+05 8 85e+041 70e+04 -5 44e+04 -1 26e+05 -1 97e+05 -2 69©+05 -3 40©+05 -4 126+05 -4 83e+05 -5 55©+05 -6 260+05 -6 970+05 -7 690+05 -8 40e+05 -9 120+05 -9 83e+05 -1 05©+06 -1 130+06 -1 200+06 -1 27©+06 -1 340+06 -1 410+06 -1 48e+06 -1 55e+06 -1 630+06 -1 70©+06
Contours of Static Pressure (pascal) (Tim e=4 8400e- 01) Oct 18, 2011
Figure A-A-44 Static pressure contour (sectional view) - feed rate 50 k g s 1
-2 00e+05
-4 0 0 e +05
-6 .00e+O 5
-8 0 0 e+ 05
-1 0 0 e+ 06
-1 20e+C 6
•1 40 e+06
-1 60e+O 6
StaticP ressure
(pascal)
- 0 6 - 0 5 -0 .4
Position (m )
S ta t ic P re s s u re (T im e = 4 .8 4 0 0 e -0 1 )
Figure A-A-45 Static pressure profile- feed rate 50 k g s 1
Material flow pattern:
2.15e+00 2.069+00 1 96e+00 1.870+00 1.780+00 1 .680+00 1.590+00 1.500+00 1.400+00 1.310+00 1 .2 2 0 + 0 0 1 . 12 0+ 0 0 1.030+00 9 350-01 8 41 e-01 7 480-01 6 54e-01
K 5 61e-01
" 000e+00
Contours of Velocity Magnitude (nVs) (Tim e=4.8400e-01) Oct 18, 201 ’
Figure A-A-46 Flow velocity during extrusion (sectional view)-feed rate 50
kg s 1
148
Viscosity profile:
r
3.00e403
2,50»403
2.006403
M olecularViscosity(kg /m -s)
1.506403
1.006403
5.00e402
0.00640040 60 80 100
Strain R ate (1 /s )
140
Molecular Viscosity vs. Strain Rate (Time=4.8400e-01)
Figure A-A-47 Molecular viscosity vs. Strain rate- feed rate 50 kgs-1
VII. CFD Simulation results of 500 mm extruder with varying auger
speed:-
a. Auger speed:-15 rpm
Extrusion pressure:
-1 27e+04
-6 05e+04
-1 08e+05
-1 56e+05
6 OSe+055.61e+05 5 13e+D5 4 65e+05 4.18e+05 3.70e+05 3.22e+05
2 74e+05
2 26e+05
1.79e+05
1.31e+05
8 29e+04
3.51e+04
iS"
a i#!i p
Contours of Static Pressure (pascal) (Time=3.2460e400) Sep 2S
Figure A-A-48 Static pressure contour (full view) - auger speed 15 rpm
149
Contours of Static Pressure (pascal) (Time=3.2460e+00) Sep 29. 2011
Figure A-A-49 Static pressure contour (sectional view) - auger speed 15 rpm
: 98 .0 0 e + O 5
7 0Ge+O6
6 O ue+ 05
5 0 0 e+05
StaticP ressure
(pascal) 3 0 0 e+ 05
1 00e+O 5
-1 -0 9 -0 8 -0 7 -0 6 -0 .5 -0 .4 -0 .3 -0 .2 -0 1 0
Position (m)
S ta t ic P re s s u re (T im e = 3 2 4 6 0 e + 0 0 )
Figure A-A-50 Static pressure profile- auger speed 15 rpm
Material flow pattern:
750e-017.16e-01079e-O1043e-O10 07e-01 5.72e-01 5.30e-O1 5 00e-01 4 84e-01 4 29e-01 3 93e-01 3 57C-01 3 22e-01 2 86e-01 2 50e-01 2 14e-011 79e-01 1 43e-01
Contours of Velocity Magnitude (m/s) (Time=3.2460e+00) Sep 29. 2011
Figure A-A-51 Flow velocity during extrusion(sectional view)-auger speed 15
rpm
150
Viscosity profile:
7 008+03
6 008+03
5.008+03
MolecularViscosity(kg/m-s)
4.00e+03
3.008+03
2.008+03
1 00e+03
0 00e+0020 25 30 35
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=3.2460e+00)
Figure A-A-52 Molecular viscosity vs. Strain rate - auger speed 15 rpm
b. Auger speed:-20 rpm
Extrusion pressure:
147e+06 1 398+06 1 33e+0B 1 28e+061 22e+081 1Be+06 1 10e+06 1 05e+0B 9 89e+05 932e+05 8 75e+05 8 18e+05 7.60e+05 7 03e+05 646e+05 5 89e+05 5 32e+05 4 75e+05 4 17e+05 3 60e+05 3 03e+05 246e+05 1 89e+05 1 32e+05 7 43e+04 1 72e+04 -4 00e+04 •9 728+04 -1 54e+05
Contours of Static Pressure (pascal) (Time=3.0600e+00) Sep 27
Figure A-A-53 Static pressure contour (full view) - auger speed 20 rpm
151
I 47e+0BI 39e+u81 33e+061 28e+0BJ 22e+0B1 1Be+061 lOe+OB1 05e+0B
9.32e+058 75e+05B.18e+057 60e+057 03e+05
5 89e+055.326+054 75e+054 17e+053 60e+053 03e+052 46e+05I 89e+051 32e+057 43e+04
L1.72e+04-4 00e+049 72e+04
-1.54e+05
Contours of Static Pressure (pascal) (Tim e=3.0600e+00) Sep 27.
Figure A-A-54 Static pressure contour (sectional view) - auger speed 20 rpm
6 OOe+05
0 OOe+OO
1.00e+08
-2 .0 0 8 + 0 5-1 -0 .9 -0 .8 -0 7 -0 .6 -0 5 -0 4 -0 .3 -0 .2 -0 1 0
Position (m)
StaticP ressu re
(p ascal)
S ta t ic P re s s u re (T im e = 3 0 6 0 0 e + 0 0 )
Figure A-A-55 Static pressure profile- auger speed 20 rpm
Material flow pattern:
Contours of Velocity Magnitude (m/s) (Tlm e=3.0600e+00) Sep 27.
Figure A-A-56 Flow velocity during extrusion (sectional view)-auger speed 20
rpm152
Viscosity profile:
6 006+03
5.00e+03
Molecular 4.ooe+03Viscosity(kg/m-s) 3006+03
2 00e+03
1 00e+03
0 5 10 15 20 25 30 35 40 45 50 55
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=3.0600e+00) S
Figure A-A-57 Molecular viscosity vs. Strain rate - auger speed 20 rpm
c. Auger speed:-25 rpm
Extrusion pressure:
Contours
202e+06 1 92e+06 1 84e+06 1 76e+06 1 68e+06 1 61e+06 1 53e+06 145e+06 1 37e+06 1 30e+06 1 22e+06 1.146+06 1 06e+06 9 86e+05 909e+05 831e+05 7.54e+05 6 76e+05 5.99e+05 521e+05 4.436+05 366e+05 288e+05 2.11e+05 1 33e+05 555e+04 -2 216+04 -9 96e+04 -1 77e+05
of Static Pressure (pascal)
Yu
(Time=9.6799e-01) Oct 07,2
Figure A-A-58 Static pressure contour (full view) - auger speed 25 rpm
153
■SUDl&I2 02e*06 1 928+06 1 84e+06 1 76e+06 1 686*-06 1 61e+06 1 53e+06 1 45e+06 1 37e+06 1.308+06 1 22e+061 14e+06„ 1 068+06 986e+05 9 09e+05 8 31e+05 7 54e+05 6 76e+05 . 5 99e+05 5.21e+054 43e+053 66e+052 88e+05 2 11e+05 1 33e+055 55e+04 -2218+04 -9 96e+04 -1 77e+05
Contours of Static Pressure (pascal) (Time=9.6799e-01) Oct 07. 20'
Figure A-A-59 Static pressure contour (sectional view) - auger speed 25 rpm
StaticP ressu re
(pascal)
2 00e+06
1 75e+06
1.50e+O6
1 25e+C6
1 00e+O6
7 50e+05
5 0 0 e + 0 5
2 5 0 e +05
0 OOe+OO- 0 6 -0 .5 - 0 4
Position (m )
S ta t ic P re s s u re (T im e = 9 .6 7 9 9 e -0 1 )
Figure A-A-60 Static pressure profile- auger speed 25 rpm
Material flow pattern:
1 11O+00 1.060+001 02e+00 980e-019410-01902e-01 8 63©-01 8230-01 7 840-01 7.450-01 7.060-016 67©-01 627©-01 5 880-01 549©-01 5 10©-01 4 71©-01 4 31e-01 3 92©-01 3 53©-01 3 14©-012 74e-012 35e-01 1 96e-01 1 570-01 1 18e-017 84©-023 92©-02 0 00e+00
Contours of Velocity Magnitude (m/s) (Time=9.6799e-01)
Figure A-A-61 Flow velocity during extrusion (sectional view)-auger speed 25
rpm
154
Viscosity profile:
7.00e+03
6.00G+03
500e+03
M olecular 4 .000+03 Viscosity(kg /m -s) 3.006+03
2.006+03
1.00e+03
0.00e+0010 15 20 25 30 35
Strain R ate (1/s)
50
Molecular Viscosity vs. Strain Rate (Time=9.S799e-01)
Figure A-A-62 Molecular viscosity vs. Strain rate - auger speed 25 rpm
• Results of CFD analysis for auger speed of 30 rpm auger are
available in Appendix A under Section IV.
d. Auger speed:-40 rpm
Extrusion pressure:
2 79e+08
2 64e+06
2 49e+06
2 34e+06
2 I8e+06
2.03e+0B
1 88e+06
1.73e+06
1 58e+06
1 43e+06
1 28e+06
1.13e+0B
9.79e+05
8.29e+05
6 78e+05
5 27e+05
3.77e+05
2 26e+05
7 52e+04
-7 55e+CM
-2 26e+05u
Contours of Static Pressure (pascal) (Time=1,5020e+00)
Figure A-A-63 Static pressure contour (full view) - auger speed 40 rpm
155
2.79e+0B 2 65e+0B2 54e+0B2 43e+06 2 33e»0B2 22e+0B 2.11e+O0 2.01e+0B 1 .BOe+OB 1 79e*06 1.69e+06 1 58e+06 1 4Be+06 1 37e+06 1 26e+06
I 1 16e»06 1 05e+06 9 44e+058 37e+05
; 7 31e+05 I 6 25e+05
5 18e+05 4 12e+053 06e+05 1.99e*059 29e+04 -1 35e-04 -1 20e*05 -2 26e+D5
Contours of Static Pressure (pascal) (Time=1.5020e+00)
Figure A-A-64 Static pressure contour (sectional view) - auger speed 40 rpm
-0 .6 - 0 5 - 0 4
Position (m )
S ta t ic P re s s u re (Tirr»e=1 5 0 2 0 e + 0 0 )
Figure A-A-65 Static pressure profile- auger speed 40 rpm
Material flow pattern:
t 76e+G0 1 69e+0Q
Contours of Velocity Magnitude (m/s) (Time=1.5020e+00) Oct 03. 20
Figure A-A-66 Flow velocity during extrusionfsectional view)-auger speed 40
rpm156
Viscosity profile:
7 006+03BE
6 00e+03
5 00e+03
MolecularViscosity(kg/m-s)
4.00e+03
3.006+03
2.006+03
1 006+03
0 006+0015 20 25 30 35
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=1,5020e+00)
Figure A-A-67 Molecular viscosity vs. Strain rate - auger speed 40 rpm
e. Auger speed:-50 rpm
Extrusion pressure:
2 12e+06 2.00e+06 1 92e+06 1 84e+061 76e+061 67e+061 59e+0B 1.51e+06 1 42e+06 1 34e+06 1 26e+06 1.18e+06 1 09e+06 1 01e+06 9 27e+058 45e+05 7 62e+05 6 79e+05 5.96e+05 5 13e+05 4.30e+05 347e+05 264e+05 1 82e+059 86e+04 1 58e+04 -6 71e+04 -1 50e+05 -2 33e+05
Contours of S tatic Pressure (pascal) (T im e -2 6790e-01)
Figure A-A-68 Static pressure contour (full view) - auger speed 50 rpm
157
m2 12e+06 2 00e+08 I 92e*06 I 94e+0B 1 7Be+06 1 67e+06 1 58e+0B 1 51e+06 1 42e+06 1 34e+06 1 28e+06 1 IBe+OB , 1 09e+0B ;1 Ole+06 9 27e+05 845e+05 7 62e+05 6 79e+05 5 9Be+05 5 13e+05 4 3De+05 347e+052 64e+05 1 82e+05 9 86e+04 I 5Be+04 -6 71e+04 -1 50e+05 -2 33e+05
Contours of Static Pressure (pascal) (Time=26790e-01) Oct 05.201
Figure A-A-69 Static pressure contour (sectional view) - auger speed 50 rpm
-1 -0 9 -0 8 -0 7 -0 6 -0 5 -0 4 -0 3 -0 .2 -0.1 0
Position (m )
S ta t ic P re s s u re (T im e = 2 6 7 9 0 e -0 1 )
Figure A-A-70 Static pressure profile- auger speed 50 rpm
Material flow pattern:3.85e+003.67e+003.54e+003.40e+003.26e+003.13e+00 2.99e+00 2.86e+00 2.72e+00 2.58e+00 2.45e+00 2.31e+00 2.18e+00 2.04e+00 1 90e+00 1.77e+00 1 63e+00 1 50e+00 1 36e+00 1 22e+001 09e+00 9 52e-01 8 16e-01 6 80e-01 5 44e-01 4 08e-012 72e-01 1 36e-01 0 00e*00
Contours of Velocity Magnitude (m/s) (T ime=2 6790e-01)
Figure A-A-71 Flow velocity during extrusion(sectional view)-auger speed 50
rpm158
Viscosity profile:
4 50e+03
4.00e+G3
3.50e+03
Molecular 3.00e+03
Viscosity(kg/m-s) 2.50e+03
2 00e+03
1 50e+03
1 00e+03
5 00e+0220 30 40 50
Strain Rate (1/s)
Molecular Viscosity vs Strain Rate (Time=2 6790e-01)
Figure A-A-72 Molecular viscosity vs. Strain rate - auger speed 50 rpm
VIII. CFD Simulation results of 500 mm extruder with varying auger
pitch distance:-
a. Pitch distance 338.012 mm
Extrusion pressure:
3 .4 2 e + 0 6
3 .2 3 e + 0 6
3 .0 4 e + 0 6
2 .8 5 e + 0 6
2 .6 6 e + 0 6
2 .4 7 e + 0 6
2 .2 9 e + 0 6
2 .1 0 e + 0 6
1 .9 1 e + 0 6
1 .7 2 e + 0 6
1 .5 3 e + 0 6
1 ,3 4 e + 0 6
1 .1 5 e + 0 6
9 .6 5 e + 0 5
7 .7 7 e + 0 5
5 .8 8 e + 0 5
4 .0 0 e + 0 5
2 .1 1 e + 0 5
2 .2 4 e + 0 4
- 1 .6 6 e + 0 5
- 3 .5 5 e + 0 5Z— 1— x
Y
Contours o f Static Pressure (pascal) (T im e = 2 .5 0 5 0 e + 0 0 )
Figure A-A-73 Static pressure contour (full view)-pitch 338.012 mm
159
3 4 2 e - 0 G
3 .2 3 e + 0 6
■
■ 2.11 e+ 05
2 .2 4 e -0 4
-1 66e-*-05 -3 55 e + 0 5
C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .5 0 5 0 e + 0 0 )
Figure A-A-74 Static pressure contour (sectional view)-pitch 338.012 mm
0 OOe+OO
-1 -0 9 -0 .8 -0 .7 -0 .6 - 0 5 -0 .4 -0 .3 -0 .2 -0 .1 0
P o s itio n (m )
S ta t ic P re s s u re (T im e=2.5050e-H D 0)
Figure A-A-75 Static pressure profile-pitch 338.012 mm
Material flow pattern:
1 3 6 e -0 0
1 2 9 e + u 0
C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 .5 0 5 0 e + 0 0 )
Figure A-A-76 Flow velocity during extrusionfsectional view)-pitch 338.012mm160
Viscosity profile:
9.00e+03
8.00e+03
7.00e+03
6.00e+03
M olecu lar 5.ooe+o3 Viscosity
4.00e+03
3.00e+03
2.00e+03
1.00e+0315 20 25 30
S tra in R a te (1 /s )
Molecular Viscosity vs. Strain Rate (Time=2.5050e+00)
Figure A-A-77 Molecular viscosity vs. Strain rate-pitch 338.012 mm
• The results of CFD analysis with auger pitch distance 292 mm are
presented in Appendix A- section II.
IX. CFD Simulation results of 500 mm extruder with varying die
desiqn:-
a. Die type-l
Extrusion pressure:
3 .5 5 e + 0 6
3 .3 5 e + 0 6
3 .1 4 e + 0 6
2 .9 3 e + 0 6
2 .7 2 e + 0 6
2 .5 1 e + 0 6
2 .3 0 e + 0 6
2 .0 9 e + 0 6
1 .8 9 e + 0 6
1 6 8 e + 0 6
1 .4 7 e + 0 6
1 .2 6 e + 0 6
1 .0 5 e + 0 6
8 .4 5 e + 0 5
6 .3 6 e + 0 5
4 .2 8 e + 0 5
2 .1 9 e + 0 5
1 .1 1 6 + 0 4
-1 .9 7 e + 0 5
4 .0 6 e + 0 5
6 .1 4 e + 0 5
Contours o f S tatic Pressure (pascal) (T im e = 2 .5 0 0 0 e + 0 0 )
Figure A-A-78 Static pressure contour (full view)-die type-1
161
3.55e+063 35e+06 3 14e+06 2 9 3 e +06 2.72e+06 2 5 1 e+06 2 3 0 e + 06
2 0 9 e + 0 6
1 8 9 e + 0 6
1 6 8 e + 0 6
1 47 e + 0 6
1 2 6 e + 0 6
1 05e+O 6
8 4 5 e + 0 5
6 3 6 e + 0 5
4 2 8 e + 0 5
2 1 9 e + 0 5
1.11 e + 0 4
-1 9 7 e + 0 5
-4 .0 6 e + 0 5
- 6 .1 4 e + 0 5
C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .5 0 0 0 e + 0 0 )
Figure A-A-79 Static pressure contour (sectional view)-die type-1
S ta ticP re s s u re
(p a s c a l)
TffieOEf2.50e+O6
2.00e+06
1 50e+O6
1 00e+06
5 0 0 e + 0 5
-5 0 0 e + 0 5
-1 -0 9 -0 .8 -0 .7 -0 .6 -0 .5 -0 4 -0 3 -0 .2 -0.1 0
P o s itio n (m )
0 00e+O 0
S ta t ic P re s s u re (T im e = 2 5 0 0 0 e + 0 0 )
Figure A-A-80 Static pressure profile-die type-1
Material flow pattern:
1 35e+O01 28 e-tOO1 2 2 e+ Q 01 1 5 e + 0 01 0 8 e + 0 0
1.01 e+OO9 .4 6 e -0 1
8 .7 8 e -0 18.11 e -017 .43e -01b.7be-U 1B O8e-O1
5 4 0 e -0 14 .7 3e -01
4 0 5 e -0 13 3 8 e -0 1
2 70e-012 O Je-O I
1 3 5 e -0 16 7 6 e -0 2□ OOe-HJO
C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 5 0 0 0 e + 0 0 )
Figure A-A-81 Flow velocity during extrusion (sectional view)-die type-1
Viscosity /profile:
8 00e+03
7.00e+03
6 .00e+03
5 .00e+03Molecular Viscosity 4.ooe+o3 (kg/m-s)
3 .00e+03
2 .00e+03
1 00e+03
0 .0 0 e + 0 020 40 60 80 100
Strain Rate (1/s)120 140
Molecular Viscosity vs. Strain Rate (T im e=2.5000e+00) Jul
Figure A-A-82 Molecular viscosity vs. Strain rate- die type-1
b. Die type-lll
Extrusion pressure:
3.50e+06
3.29e+06
3.09e+06
2.88e+06
2.68e+06
2.47e+06
2.27e+06
2 06e+06
1.85e+06
1.65e+06
1,44e+06
1,24e+06
1 03e+06
8.26e+05
6.20e+05
4.14e+05
2.09e+05
3.05e+03
-2.03e+05
-4.08e+05
-6.14e+05
Contours of Static Pressure (pascal) (Tim e=2.5000e+00)
Figure A-A-83 Static pressure contour (full view)-die type-ill
163
C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 5 0 0 0 e + 0 0 )
3 50e+063 2 9 e-HJB
3 .0 9 e + 0 6
2 .8 8 e + 0 6
2 68e+Q 6
2 4 7 e + 0 62 .2 7 e + 0 6
2 0 6 e + 0 6
1 8 5 e + 0 6
1 .6 5 e + 0 6
1 ,2 4 e + 0 6
1 0 3 e + 0 6
8 .2 6 e + 0 5
6 2 0 e + 0 5
3 .0 5 e + 0 3
4 0 8 e + 0 5
Figure A-A-84 Static pressure contour (sectional view)-die type-ill
3 .5 0 e + 0 6
3 0 0 e + 0 6
2 5 0 e+06
2 .0 0 e + 0 6
S ta tic P re s s u re 1 50e+o6
(p a s c a l)1 0 0 e + 0 6
5 00e+O 5
0 0 0 e + 0 0
-5 .0 0 e + 0 5-0 .9 - 0 8 -0 .7 - 0 6 -0 .5 -0 .4 -0 .3 -0 .2 -0.1
P o s itio n (m )
S ta t ic P re s s u re (T im e = 2 5000e-+C0)
Figure A-A-85 Static pressure profile-die type-ill
Material flow pattern:
1 0 8 e+ O 0
1 0 1 e+OO 9 46e -01
8 78e-01 8 .1 1 e-01
7 43e-01
6 7 6 e-01 S 08e -01
5 40e-01 4 .7 3 e-01
4 0 5 e-01 3 3 8 e-01
2 70e-01 2 0 3 e-01
1 35e-01
B .7 6 e -0 2 0 OOe+OO
1 .3 5e+ O 0
1 28e+ O 0 1 22e+ O 0
1 15e+O 0
C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 .5 0 0 0 e + 0 0 )
Figure A-A-86 Flow velocity during extrusion (sectional view)-die type-lll164
Viscosity profile:
0 o u tle t
9 .00e+03
8.00e+03
7.00e+03
6.00e+03
Molecular 5.ooe+o3 Viscosity (kg/m-s) 4.ooe+o3
3 .0 0 e + 0 3
2 .0 0 e + 0 3
1 0 0 e + 0 30 5 10 15 2 0 2 5 3 0 3 5 4 0 4 5
Strain Rate (1/s)
M olecular Viscosity vs. Strain R ate (T im e = 2 .5 0 0 0 e + 0 0 ) Jul
Figure A-A-87 Molecular viscosity vs. Strain rate- die type-lll
X. CFD Simulation results of 600 mm extruder with varying feed
rate:-
a. Feed rate:-11.8 kgs'1
Extrusion pressure:
2 9 7 e * 0 6
2 8 1 e -0 6
2 65e<-06
2 4 9 e + 0 6
2.33e+06
2 17 e+06
2 01 e+06
1 8 6 e -0 6
1 70e+06
1 S4e+06
1
1
1 06e*06
9.00e+057.41 e+05
5.82e+05
4.23e+05
2.63e+05
1 04e -0 5
-5.51 e+04
-2.1 4e+05
Contours of Static Pressure (pascal) (T im e=2.6900e+00)
Figure A-A-88 Static pressure contour (full view) - feed rate 11.8 k g s 1
165
2 9 7 e + 0 6
2.81 e + 0 6
2 6 5 e + 0 6
2 .4 9 e + 0 6
2 3 3 e + 0 6
2 1 7 e + 0 6
2 01 e + 0 6
1 8 6 e + 0 6
1 70e+ O 6
1 5 4 e + 0 6
1 .3 8 e + 0 6
1 22e+ Q 6
1 06e+ O 6
9 0 0 e + 05
7.41 e+OS
5 8 2 e + 0 5
4 .2 3 e + 0 5
2 6 3 e + 0 5
1 04e+ O 5
-5 .51 e + 0 4
-2 1 4 e + 0 5
C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .6 9 0 0 e + 0 0 )
Figure A-A-89 Static pressure contour (sectional view) - feed rate 11.8 kgs-1
• 1 4 -1 .2 •0 .8 - 0 6
P o s itio n (m )
S ta t ic P re s s u re (T im e=2.6900e-+O 0)
Figure A-A-90 Static pressure profile- feed rate 11.8 k g s 1
Material flow pattern:
9 .9 4 e-01
9 .4 4 e -0 1 8 9 5 e-01
8 45e -017 .9 5 e-01
7 .4 6 e-01 6 9 6 e-01
6 46e -01 5 9 7 e-01
5 4 7 e-01
4 9 7 e-01
4 4 7 e-01
3 9 8 e-01
3 .4 8 e-01
2 98e-01
2 49e-01
1 99e -01
1 4 9 e-01
9 9 4 e -0 2
4 9 7 e -02
0 0 0 e + 0 0
L I 1 11r r t i
C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 .6 9 0 0 e + 0 0 )
Figure A-A-91 Flow velocity during extrusion (sectional view)-feed rate 11.8
k g s 1166
Viscosity profile:
1.60e+04
1.40e+04
1.20&+-04
1.00e+04Molecular Viscosity 8 ooe+03 (kg/m-s)
6.00e+03
4 00e+03
2.00e+030 1 2 3 4 5 6 7
Strain Rate (1/s)
Figure A-A-92 Molecular viscosity vs. Strain rate- feed rate 11.8 k g s 1
b. Feed rate:-19 kgs'1
Extrusion pressure:
■ 2 04e+06
1,93e+06
1.81 e+06
1,70e+06
1 59 e+06
1 48e+06
1 37e+06
1 26e+06
1 14e+06
1 03e+06
9 20e+05
8 08e+05
6.97 e+05
5 85e+05
4.73e+05
, 3 62e+05
| 2 50e+05
H1.38e+05
2 67e+04
-8 50e+04
I -1 97e+05
Contours of Static Pressure (pascal) (Time=2.6750e+00)
Figure A-A-93 Static pressure contour (full view) - feed rate 19 k g s 1
y< &
167
2 U 4 e + 0 6
1 9 3 e + 0 6
1 -81 e + 0 6
1 70e+ O 6
1 5 9 e + 0 6
1 4 8 e + 0 6
1 37 e + 0 6
I 2 6 e + 0 6
1 .1 4 e + 0 6
1 0 3 e + 0 6
9 2 0 e + 0 5
8 .0 8 e + O 5
6 9 7 e + 0 5
5 .8 5 e + 0 5
4 7 3 e + 05
3.62e-H J5
2 .5 0 e + O 5
1 3 8 e + 0 5
2 .6 7 e + 0 4
-8 5 0 e+ O 4
-1 .9 7 e + 0 5
r j
C o n to u rs o f S ta t ic P re s s u re (p a s c a l) (T im e = 2 .6 7 5 0 e + O 0 )
Figure A-A-94 Static pressure contour (sectional view) - feed rate 19 kgs-1
-5 0 0 e + 0 5- 1 4 -1 .2 -1 -0 8 -0 6 -0 4 -0 2 O
P o s itio n (m )
StaticPressure
(pascal)
S ta t ic P re s s u re (T im e = 2 6750e-H30)
Figure A-A-95 Static pressure profile- feed rate 19 k g s 1
Material flow pattern:
9 91 e-01
9 42e -01 8 .9 2 e-01
8 43e -01 7 .9 3 e -0 1
7 .4 4 e-01 6 94e -01
6 44e-01 5 .9 5 e-01 5 45e -01
4 9 6 e-01 4 4 6 e-01
3 9 7 e-01 3 .4 7 e -0 1
2 9 7 e-01 2 48e-01
1 9 8 e-01 1 49e-01
9 91 e -02
4 9 6 e-02 0 OOe+OO
1 1 1 ]
C o n to u rs o f V e lo c i ty M a g n i tu d e (m /s ) (T im e = 2 .6 7 5 0 e + 0 Q )
Figure A-A-96 Flow velocity during extrusion (sectional view)-feed rate 19
k g s 1
168
Viscosity profile:
1.60e+04
1.40e+04
1 20e+04
1 00e+04
US t - t : .
Molecular Viscosity s ooe+03 (kg/m-s)
6 00e+03
4 .00e+03
2 00e+034 6 8 10
Strain Rate (1/s)12 14
Molecular Viscosity vs. Strain Rate (Tim e=2.6750e+00) Feb 23. 2011ANSYS FLUENT 12.1 (3d. pbns. dynamesh. lam. transient)
-1Figure A-A-97 Molecular viscosity vs. Strain rate- feed rate 19 kgs
XI. CFD Simulation results of 600 mm extruder with varying Auger
speed:-
a. Auger speed:-30 rpm
Extrusion pressure:
444e+06 3 24e+06 2 35e+06 t 45e+065 55e+05-3 41e+05 -1 24e+0B -2 13e+06 -3 O3e+OB -3.92e+06 -4 82e+06 -5 71e+06 -6.61 e+06 -7 50e+06 -8 40e+06 -9.30e+O6 -1 02e+07 -1.11 e+07 -1 20e+07 -1 29e+07 -1 38e+07 -1 47e+07 -1 56e+07 -1 65e+07 -1 74e+07 -1 83e+07 -1 91e+07 -7 00e+07 -2 09e+07
IContours of Static Pressure (pascal) (Time=1.5100e+00)
Figure A-A-98 Static pressure contour (full view) - auger speed 30 rpm
169
4 44e*06 3 240*06 2 35©*06 1 45e*065 55©*05 -3 410 *0 5-1 240*06-2 130*06 -3 030*06 -3 92e*06 -4 82e*06 -5 71e*06 -6 61e*06 -7 50e+06 -8 40e *0 6 -9 30©*06 -1 02©*07 -1 110*07 -1 20©*07 -1 29©*07 -1 380*07 -1 47e *0 7 -1 560*07 -1 650*07 -1 74©*07 -1 83e*07 -1 910*07 -2 00©*07 -2 090*07
wr
ST"
M B J/KM1 1
S /
■ . H i
TX— z
Contours of Static Pressure (pascal) (Tim e=1.5100e+00) Oct 31, 2011
Figure A-A-99 Static pressure contour (sectional view) - auger speed 30 rpm
■ ' :s d re \*M n f2 - i
StaticP ressure
(pascal)
6 0 0 e +06
5 .0 0 e + 0 6
4 00e+O 6
3 0 0 e + 0 6
2 0 0 e + 0 6
1 0 0 e + 0 6
0 OOe+OO
-1 OO e + 0 6
i
- 0 8 - 0 6
Position (m )
S t a t ic P r e s s u r e (T im e = 1 5 1 0 0 e + 0 0 )
Figure A -A-100 Static pressure profile- auger speed 30 rpm
Material flow pattern:
1.72e+00 1 64e+00 1 58e+00 1 52e+0Q 1 46e+00 1 40e+Q0 1 33e+00 1 27e+00 1 21e+00 1 15e+00 1 09e+001 0 3 e*00 9 71e-01 9 10e-01 8 49e-01 7 89e-01 7 28e-01 6 67e-01 6 07e-015 46e-01 4 85e-01 4 25e-01 3 64 e-01 3 03e-012 43e-01 1 82e-01 1 21e-016 07 e -0 2 0 00e+00
1 1 1 n
l i r tu
Contours of Velocity Magnitude (rrVs) (Tim e=1.5100e+00) Oct 31, 2011
Figure A-A-101 Flow velocity during extrusionfsectional view)-auger speed
30 rpm
170
Viscosity profile:
1.60e+04
1.40e+04
1.20e+04
1.00e+04
M olecular Viscosity 8 ooe+03 (kg /m -s )
6.00e+03
4.00e+03
2.00e+034 5 6 7 8 9 10
S tra in R a te (1 /s )
Molecular Viscosity vs. Strain Rate (Time=1.5100e+00) O
Figure A-A-102 Molecular viscosity vs. Strain rate- auger speed 30 rpm
XII. CFD Simulation results of Trial:1 experimental set up:-
Extrusion Pressure:
i.2s«+06 . . 1.16«+06
1.07*+06 9.80*405
8.89*405 7.98*405
7.07e+O5
6.16*405 5.25*405
4.34*405 |3.43*405 I 2.52e+051.61*405 ^7.03e+04 -2.06e+O4
-1.12e+05
-2 .03*405 -2.93e+05
-3.84e+05
-4.75e+05
*
L ,
Contours of Static Pressure (pascal) (Time=2.4840e+00) Jan 16. 2012
Figure A-A-103 Static pressure contour (full view)-scaled extruder-T 1
171
■ 1.34e+06 1.256+06 1.16e+06 1.07e+06 9 80e+05 8.89e+05
7.98e+05 7.07e+05 6.16e+05 5.25e+05 4 34e+05 3.43e+05 2.52e+05 1.61 e+05 7.03e+04 -2.06e+04 -1.12e+05 -2.03e+05 -2.93e+05 -3.84e+05 -4.75e+05
IM riY F IT
LContours of Static Pressure (pascal) (Time=2.4840e+00) Jan 16. 2012
Figure A-A-104 Static pressure contour (sectional view)-scaled
extruder-T1
Material flow pattern:1.81 e-01 1 72e-01 1 63e-01 1 54e-01 1 45e-01 1.360-01 1.270-01 1 18e-011 09e-01 9 980-02 9.07e-02 8.17O-02 7 260-02 6 350-02 5 440-02 4.54 e-02 3 63e-022 7 2 0 -02
1 81 0 -0 2 9 .0 7 e -0 3 0.00e+00
C o n to u rs o f V e lo c ity M a g n itu d e (m /s) (T im e = 2 .4 8 4 0 e + 0 0 ) Ja n 1 6 .2 0 1 2
Figure A-A-105 Flow velocity during extrusion (sectional view)-scaled
extrude r-T1
Viscosity profile:
\M olecu larV iscosity(kg /m -s )
8.00e+03
6.006+03
4 .00e+03
2.00e+03
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Tlm e=2.4840e+O 0)
Figure A-A-106 Molecular viscosity vs. Strain rate-scaled extruder-T1172
XIII. CFD Sim ulation results of Trial:2 experimental set up
Extrusion Pressure:
5 84e+05
l 545e+055 05e+05
6Be+054 26e+053-86e+053 47e+05
3 07e+052 68e+05
2 28e+05
t 89e+05
1 49e+05
t 10e+05
7 01e+04
3 06e+04-8 97e+034 35e-U4
-8 81e+04
-1 28e+05
- I 67e+ 05
2 07e+05
Y
Contours of Static Pressure (pascal) (T im e=2.4000e+00)
Figure A-A-107 Static pressure contour (full view)-scaled extruder-T25 84e-05
5450-055 05e+054 669-05
4 26e-05
3860+05
3470-05
3 0 7 e -0 5
2 680-05
2 280+05
1 890-05
1 490-05
1 10e+05 7 01e-043 06e-04
-8 970-03
-4 85e-04
-8 81e-04
-1 280-05
-1 67e-05
-2 07e-05
Contours of Static Pressure (pascal) (Time=2.4000e+00) Mar 02. 201
Figure A-A-108 Static pressure contour (sectional view)-scaled
extrude r-T2
173
Material flow pattern:
v 209e-011980-011880-011.780-01
1670-01
1.570-01
1460-01
1 360-01
1250-01
1 150-01
1 040-01
940O-02
8 360-02 7 31 e-02
6 270-02
5 220-02 4 18e-02
3 13e-022 09e-02
1 04e-02 OOOe-OO
2 X
Contours of Velocity Magnitude im/si (Time=2.4000e+00) Mar 02. 201
Figure A-A-109 Flow velocity during extrusion (sectional view)-scaledextruder-T2
Viscosity profile:
9.50*403
9.00*403
8.50*403
8.00*403
7.50*403
7.00*403
6.50*403
6.00*403
5.50*403
5.00*403
4.50e-K)3
MolecularViscosity(kg/m-s)
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Strain Rate (1/s)
Molecular Viscosity vs. Strain Rate (Time=2.4000e+00) It
Figure A-A-110 Molecular viscosity vs. Strain rate-scaled extruder-T2
174
I. Stress distribution pattern in 430 mm extruder barrel-for applied
load of 1.8 MPa
a) Structural steel b) GCI
I- tfefid banii 140l-Ut%*W3
i w»l) am
c) ADI
Figure A-B- 1 Stress induced in barrel @1.8 MPa load
176
II. Deformation pattern in 430 mm extruder barrel-for applied load of
1.8 MPa:-
a) Structural steel b) GCI
ADI
Figure A-B- 2 Deformation in barrel @1.8 MPa load
III. Stress distribution pattern in 430 mm extruder distance piece- for
applied load of 1.8 MPa:-
23/11/2112 I
a) Structural steel
177
b) GCI
ey&Wiaa
(
Figure A-B- 3 Stress induced in distance piece @1.8 MPa load
IV. Deformation pattern in 430 mm extruder distance piece -for
applied load 1.8 MPa
a) Structural steel b) GCI
A
c) ADI
Figure A-B- 4 Deformation in distance piece @1.8 MPa load
178
V. Stress distribution pattern in 430 mm extruder liner- for applied
load of 1.8 MPa:-
a) Structural steel b) GCI
Figure A-B- 5 Stress induced in liner @1.8 MPa load
VI. Deformation pattern in 430 mm extruder liner -for applied load of
1.8 MPa:-
a) Structural steel b) GCI
179
c) ADI
Figure A-B- 6 Deformation in liner @1.8 MPa load
VII. Stress distribution pattern in 430 mm extruder auger shaft- for
applied load of 1.8 MPa:-
a) Structural steel b) GCI
c) ADI
Figure A-B- 7Stress induced in auger shaft @1.8 MPa load
180
VIII. Deform ation pattern in 430 mm extruder auger shaft -for applied
load of 1.8 MPa:-
c) ADI
Figure A-B- 8 Deformation in auger shaft @1.8 MPa load
a) Structural steel
181
Appendix-C
Brick industry and the brick-makingprocess
182
Prospects for global brick industryGlobally the ceramic industry is considered to be among the other major
revenue yielding industrial sectors, which offers significant contribution to the
economy by creating jobs and income. Brick being the favourable
construction material, brick industry shares the major percentage of output
produced within this sector. The global brick production has increased rapidly
over the past few decades, due to increase in demand in the housing market
from both developed and developing countries. Of the various countries that
produce bricks, China remains the largest producer of bricks with an
estimated production of more the 700 billion bricks in 2000 and showing an
increasing trend for the future [CESST, 2000]. India remains in the second
place with more than 140 billion bricks being produced per year [Asian
Institute of Technology, 2003]. The other major producers include USA,
which produced around seven to nine billion bricks during the year 2010
[Madehow, 2012]. Ceramic industries in European Union (EU) do play a
significant role in the global market for producing quality ceram ic products. It
accounts for 25% of the total global production [European ceramic Industry
Association, 2012]. The major producers in EU include U.K, Spain,
Germany, France, Italy, Czech Republic, Poland and Hungary.
Given the scale of production capacities of brick industries globally, it is
clearly understandable that the amount of energy consumed by brick
industries is high. It is also considered to be one among the other major
energy intensive industries that uses fossil fuels, coal and gas for its various
operations.
U.K. Brick industry- future prospect and challengesIn 2010 the U.K brick industry was valued to be £395 million annually, and it
was predicted to rise on an average of 4% over the next five years and is
expected to reach £471 million by 2015 and is expected to grow further in the
future [AMA research limited 2011]. Gas and coal are the major sources of
fuel used in UK brick industries [Department of Technology and Industry-
2006], and the energy consumed by the industry accounts for 1.5% of the
total energy consumed by all manufacturing industries and it is estimated to
183
be approximately 5.4TWh [Brick Development Association, 2011]. It
accounts for more than 30% of the total cost incurred by the industry
[European Ceramic Industry Association, 2012].Though it appears to be
less in value, considering the current global situation on the availability of fuel
sources and the predicted future demand for bricks, it is a very significant
amount.
The other major challenges faced by the brick industries globally and in the
U.K include reduction in the level of energy consumption and pollutants
(mainly C 02, Hydrogen fluorides and particulates) released from its various
processes. Through the use of advanced technologies, improved machines,
operating procedures and energy regulation policies, the modern brick
industries are considered to be more energy efficient compared to what was
available in the early 1970's. A typical energy consumption pattern of UK
brick industries from 1970-2010 is presented in Figure A -C -1.
1 00 ,000 -r
— Total industrial energy in primary energy equivalents
90,000 Total industrial energy consumption
80,000
| 70,000<o>3ST 60,000O0 tf>01 50,000cco§ 40,000<0 «0 3
£ 30,000r -
20,000
10,000
20101970 1975 1985 1990 1995 2000 20051980
Figure A-C- 1 Energy consumption pattern of U.K brick industries
[Source: DECC, U.K 2011]
Though the energy trends indicate that there is a significant reduction in the
energy consumed, the growing concerns about the climate change and
implementation of new environmental legislations has left the UK brick
industries to face a tougher challenge in-terms of reducing the energy usage
184
and its impact on environment. Hence it is worth looking at what makes this
industry energy intensive, which will be dealt with, further in this chapter.
Brick manufacturingThe process of brick manufacturing is a very complex process. It involves the
use of heavy and rugged high performance power consuming machines and
tools, right from obtaining raw materials to the finished product. A simple
overview of the various process involved in the brick manufacturing is
discussed below.
Manufacturing of bricks briefly involves the following key processes:
• Mining raw materials
• Storage of raw materials
• Preparation of raw materials
• Shaping
• Surface treatment
• Cutting
• Drying
• Firing
• Packing and despatch.
Figure A-C- 2 shows a simple schematic representation of various steps
involved in a typical brick manufacturing process.
185
The Process of Brickmaking (extrusion)
botching & mixing d cow «no*j*ial* (lo c ru ae bricfc body mix)
hotdng <oo«nturmetdryw
lunneIM n
Figure A-C- 2 Typical brick making process flow diagram
[Source: Boral Limited 2002]
Mining raw materials
Clay and loam have been used for making bricks and other ceramic products
for over one thousand years. It is formed by erosion and weathering of rocks,
and gets deposited in different places due to the action of water and wind.
Hence the major mineral constituents of clay are rock minerals [Bender and
Handle, 1982]. Depending upon the geographical location and age of
deposit, the mineral and chemical composition of clay varies significantly and
has a major influence on its flow characters during shaping and drying and in
the aesthetics (like appearance and colour) of the final finished products.
Depending upon the raw material used and applications, bricks are broadly
classified into three different types [Petavratzi and Barton, 2007], namely:
• Clay bricks (Burned bricks):- This includes common building brick,
facing brick, glazing brick, fire brick, flooring brick and Hollow brick etc.
• Cementitious bricks: - This includes bricks that are made up of
cementitious material, which gets its hardness by chemical reaction-
Example: - sand lime brick and sewer brick.
186
• Adobe bricks: - These types of bricks are sun dried bricks, unlike burned
bricks which are dried in special chambers called Kilns (will be reviewed later
in this chapter). The major constituent includes calcareous sandy clay or any
alluvial desert clay with good plastic properties.
The chemical composition of typical pure clay will contain the following
substances in respective proportions as indicated [Petavratzi and Barton,
2007].
• Silica (50-60%)
• Alum ina (20-30%)
• Lime (2- to 5%)
• Oxide of iron (5- 6%, but not greater than 7%)
• Magnesia (<1%)
It is clearly evident from the chemical composition that the major constituent
of clay is silicates. Based on the mineralogical composition and presence of
other chemical substances, clay minerals are classified into various groups
as shown in Figure A-C- 3,
SILICATES
Tectosilicates (Framework silicates)* Zeolites* Quartz* Feldspars
Phyllosilicates (Sheet silicates)
Other silicates
1:1 Phyllosilicates Kaolinite-serpentine
2:1 Phyllosilicates
Kaolinite subgroup* Kaolinite* Halloysite* Dickite* Nacrite
2:1 Inverted ribbons♦ Sepiolite• Palygorskite (attapulgite)
Talc- Pyro p hyl I ite Smectitesl I l
Vermiculites Chlorites Micas
Serpentine subgroup♦ Chysotile♦ Antigorite♦ Lizardite♦ etc.
D ioctahedral smectites• M ontm orillonite• BeidelHte• Nontronite
Dioctahedral m icas• Muscovite* ante♦ Phengite» etc.
Trioctahedral smectites Trioctahedral m icas• Saponite • Biotit e• Hectorlte * etc.• Sauconite
Figure A-C- 3 Classification of clay mineral groups
[Source: Punmia and Jain, 2005]
187
The major constituents of pure clay minerals are Kaolin and Shale and small
amount of additives like manganese, barium. Other additives are blended
with clay to produce different colours [Punmia and Jain,2005].
The major mineral constituent of the clay used in making bricks, in the United
Kingdom, includes,
• Kaolinite.
• lllit.
• lllite.
The clay used in brick manufacturing is extracted from "Quarries". Quarry is
a place where natural deposits of clay and mineral occur in significant
proportion, considered to other geographical locations. It is essential to
obtain approval from the government, local authorities and concerned
environmental organisations before setting up a quarry. This is to ensure that
quarrying operation is not affecting the surrounding localities, natural
vegetation and do not possess any risk to humans or animals living in the
nearby areas. Figure A-C- 4 shows the geographical location of various
quarries, currently under operation in the U.K.
Brick clay resources
& \fm- m
Figure A-C- 4 Quarries for brick clay in U.K
[DEFRA, 2007]
188
There are different ways of extracting clay from quarries. Depending upon
the requirement and factors like economic and efficient operation of a quarry,
there are two commonly used methods, namely a) Opencast mining b)
Underground mining. Since open cast mining is accepted to be more
economical compared to the other technique, it is widely used all over the
world to extract clay used in brick making process. A few of the open cast
methods includes Manual Digging, Mechanical extraction, Blasting, Hydraulic
mining [Bender and Handle, 1982].
Mechanical extraction is the most widely used method; a typical mechanical
extraction using an excavator is shown in Figure A-C- 5.
4*l
Figure A-C- 5 Quarry operated with mechanical extraction process
[Source: Iqsgroup]
Storage of raw materials
Clay extracted from quarries will be transported to the brick manufacturing
facilities through suitable modes. Factories operating on a continuous and
mass production process basis should be supplied with ample amount of raw
materials, to meet their demands. Hence most of the brick manufacturing
industries across the world store the ir raw materials within the factory or
nearby area, enabling them for an easy and quick access during production.
This is considered to be another main reason for such industries to be
located near the quarries. There are different ways to store the raw material
and the most widely used includes open-air storage, storage sheds, large
volume feeders and silos.189
Preparation of raw materials
The stored raw material is pre-processed before being used to make bricks.
The pre-processing of brick clays mainly involves reduction of clay particle
size to the required standards, blending of any additives as required for the
products and process and adding or removing moisture to meet the required
standard. The required size for clay particles is achieved by using bespoke
mechanical equipment called pan mill. Size of clay particles and moisture
content are two other important parameters that have influence on the flow
characters of clay water mixture and hence in-order to have a smooth
shaping process and better product, it is important to implement a controlled
strategy at this stage of the production process. Recommended raw material
size is 2-4 pm, before being mixed with water.
The flow character of clay and water mixture, used in brick making process
and in other applications is defined by two variables namely Plasticity Index
and Liquidity Index. The amount of water content determines the plasticity of
clay during shaping process. Depending upon the type of shaping process
the amount of water content varies. A typical stiff extrusion process has 7-
14% of moisture content depending upon the clay type and extruding
technique.
Shaping
Shaping is the next step involved in the brick making process. The required
shape of a ceramic product, like brick, can be obtained through many
techniques using manually operated and completely automated complex
machines, commonly found in modern brick industries. It is a very important
process which determ ines the shape of the ceramic body and also impacts
the further processes involved, before the product is put into its final use.
Based on the raw material conditions and product requirements, the most
widely used and accepted shaping techniques are divided into four types,
namely, Soft mud moulding, Extrusion, Pressing and Casting.
Soft mud moulding
It is one of the oldest and traditional methods of brick making. In simple
terms it could be defined as filling up of lose clay with high plasticity, either
190
mechanically or manually, into a mould made up of wood or metal. Moulds
made of up of wood were widely used. The clay-water mixture used in this
technique is highly plastic, with water content approximately equal to 30% or
even more sometimes, which gives the ability to have a dry shrinkage value
between 6% - 8% [Bender and Handle, 1982], and also required to avoid
insufficient strength of the product. The preferred or recommended plasticity
value of clay water mixture used in this process is 4 mm - 6 mm residual
height in the Pfefferkorn test. (Pefefferkorn test is one among the other
standard testing methods that are widely used and commonly accepted
testing method in ceramic industries to measure the plasticity value of wet
clay) [Wilkinson, 1960].
Ceramic bodies like bricks, made out of soft-mud moulding are amorphous
and solid in nature and offer a good protection during severe cold weather
conditions. The different methods of soft-mud moulding techniques that were
used are as follows,
1. Hand moulding
A typical hand moulding process is shown in Figure A-C- 6.
mrurn
Figure A-C- 6 Hand moulding process
[Source: Bender and Handle, 1982]
2. Mechanized moulding
a. Soft-mud brick moulding machines with loose moulds
191
A typical brick production line with loose moulds setup is
shown in Figure A-C- 7.
Figure A-C- 7 Mechanized soft moulding machine
[Source: Bender and Handle, 1982]
b. Mould-chain type soft-mud brick moulding
c. Mechanical soft-mud moulding
d. De-Boer soft-mud moulding:-
A typical De-Boer machine is shown in Figure A-C- 8
Mould Washing
Soft Mud Brick Moulding Machine
Figure A-C- 8 Typical De-Boer soft mud moulding machine
[Source: resourceefficientbricks, 2011]
e. The Aberson soft-mud moulding: A typical Aberson soft
moulding machine is shown in Figure A-C- 9.
192
Figure A-C- 9 Soft moulding machine-Aberson type
[Source: Bender and Handle, 1982]
f. The Hubert soft-mud moulding.
A few among the main advantages of soft mud moulding includes lower
power consumption compared to extrusion process, can be used for both
small scale and large scale production and has a lower maintenance and
operational cost.
Extrusion
Invented by Schlickeysen, more than 150 years ago [Bender and Handle,
1982], extrusion is the most commonly used shaping techniques in large
scale ceram ic industries for manufacturing bricks, tiles and pipes etc.
Vacuum extruder is one of the recent advancement from its predecessor, de
airing auger and it is an integrated unit that combines more than one
operation involved in the ceramic product manufacturing, like mixing clay
with water to prepare the Mslip"(Plasticised clay), compress the slip to density
the mass and remove any trapped air with the application of vacuum, density
the slip further by forcing it through a chamber with auger shaft and then
produce the required shape of the clay body by forcing it further through the
die or mouth. The die or the extruder mouth resembles the required cross
sectional shape of the final finished product. A typical vacuum type extruder,
used in heavy clay industries, designed and manufactured by Craven
Fawcett Ltd, U.K is shown in Figure A-C- 10.
193
Figure A-C- 10 Vacuum extruder
[Source:-Craven Fawcett Limited, U.K]
The main aim of this research is to study in detail the flow process of wet
clay within the extruder and assess its performance with respect to various
design conditions. Hence a detailed review about the extruders, its
performance characters and the process of extrusion is presented in
Appendix- D.
Pressing
It is another type of ceramic product shaping technique, mainly used to
manufacture tiles and bricks. In simple terms, the final shape of the ceram ic
body is achieved by applying mechanical compaction force to the raw
material placed in an enclosed chamber called a die. A typical hydraulic
pressing machine used for making tiles is shown in Figure A-C- 11.
194
Figure A-C- 11 Hydraulic press type tile making machine
[Source:-American Ceramic Society]
Based on the pressing technique and raw material condition, the pressing
process is classified into the following types,
1. Dry pressing
2. Isostatic Pressing
3. Sem i-dry brick pressing
4. Tile pressing.
The shape and quality of the final product depends upon the pressure
applied to compact the loose mass of clay and it varies with respect to the
techniques used. Irrespective of the technique used, it is required to take a
proper care regarding the pressure applied and die design, to have a better
product. Most of the pressing techniques mentioned above involves three
main steps - 1) filling the loose clay and water mixture (if required) into the
bottom die cavity, usually attached to the bottom of the press, 2) applying
pressure through the top die attached to a ram and 3) removing the formed
product from the bottom die. The removal of final product from the bottom of
die is an important step in pressing, as it often decides the final quality of the
195
product. If care is not taken at the design stage, it could result in major
problems like cracking and irregular shape of final product. The achievable
technical characteristics of the product, speed, simplicity and
inexpensiveness of the overall production cycle has seen pressing technique
to be used widely and extensively in ceramic industries.
Casting
It is similar to the casting technique applied in the manufacturing of metal
components. Ceramic casting is another type of shaping technique, used
mainly for making ceramic components like tableware, sanitary ware and
advanced ceramics. There are different types of casting techniques used in
the ceramic industries [Handle, 2007], namely
1. Slip casting
2. Pressure slip casting
3. Capillary casting in plaster moulds
4. Pressure casting in polymer moulds.
The raw material condition and final product requirements determine the
appropriate type of technique to be used. However the basic principle of
manufacturing is same for all the above mentioned techniques. A suitable
design of mould resembling the shape of the ceramic product will be made
using Plastercine or Polymers or Acrylic or Plaster of Paris or clay and then
the slip will be introduced into the mould. Slip in this case will be more like a
thick liquid. This liquid mass will then be allowed to dry for a sufficient period,
before it is removed. Depending upon the size and thickness of the product,
the drying time varies from hours to days. The main advantages include the
re-usability of the moulds, geometrical accuracy of components produced
and adaptability to large scale production.
Electrophoretic shaping
Invented in the year 1809 [Bender and Handle, 1982], it is a type of
ceramics shaping technique, developed to a commercial scale for special
requirements. This technique involves the use of electric field, applied to the
raw materials, to achieve a preferred orientation of the clay particles in the
196
finished product. Since it is of not much relevance to this research work, it
has not been discussed in this work. However if the reader is interested in
exploring further about this technique, it is recommended to refer the above
stated reference.
Summary of Shaping methods and its applications:
The shaping process in ceramic manufacturing varies widely with respect to
type of raw material, size of the industry and quantity to be manufactured. It
is an energy intense process, which requires a special attention to improve
the overall efficiency of the whole production cycle. Hence engineers and
industrial experts in this sector take an extra care while choosing the
appropriate techniques to meet their requirement. Table A-C- 1 provides the
details of various shaping techniques and their applicability for producing
ceramic components based on the raw material condition and shapes
[Bender and Handle, 1982].
Raw material
condition,
Requirements,
Shapes.
Hand
m
ould
ing
Extr
usio
n
Ram
Pres
sing
Rol
ling,
Mill
ing
Ram
min
g
Dry
pres
sing
Isos
tatic
pres
sing
Elec
trop
hore
si
Cas
ting
Vibr
atio
n
Cohesive
material + + + + + X X + +
processing
Materials with
Low plasticX X - X X ++ + X X X
Material with high
water content+ + - - 0 0 0 + + X
Material with low
water content- + X X + ++ + 0 0 X
Material with high
compact stability- X X X + ++ + - -
Deaerated
materialX ++ + + X + + X
197
Uniform
compaction+ + + X X ++ X -
High throughput + ++ - - -
Non standards
material, in low
numbers
+
+X + + ++ X +
Products with
certain
texturation
+ + + + X X +
Product without
texturation- X + ++
Dimensionally
stable products- X ++ +
Smooth surfaces - + + + + + X + + +
Rough surfaces + X X X X X + X
Massive blocks + ++ + + + - X
Tiles + + + + ++ + + X X
Extruded
products- ++ 0 0 0 X 0
Compacts for
presses & rollers++ X X
Roofing tiles X ++
Holloware - X X X X ++
Tableware + ++ X +
+= Applicable; - = Inapplicable; x=Applicable with certain conditions
Table A-C- 1 Various shaping techniques and their applicability
[Source: Bender and Handle, 1982]
Surface treatment
It is the process of introducing texturing, glazing, colour and coating to a
ceramic product, to enhance the appearance of the product and make it
appealing. Surface treatment is done mainly to give a specific profile or a
colour to the ceramic products, especially bricks. Coloured bricks, textured
bricks and profiled bricks are a few examples. There are many types of198
surface treatment techniques been developed and used, such as Sanding,
Profiling, Peeling, Colouring, Glazing, Coating, Brushing and Addition of
Combustible materials.
During earlier days, ceramic products with different colours and shapes were
of great appeal to the consumers. This led to the development and
introduction of new techniques in surface treatment, by both small scale and
large scale industries, to capitalise on the demand. But the increase in raw
material cost has led small scale industries to concentrate less on this
process and this factor helped the large scale industries to increase their
market share.
Cutting
With the invention and advent of the extrusion technique in ceram ic-brick
manufacturing, which produces continuous mass of compacted green clay or
wet clay, it was required to introduce a cutting system into the production
process, especially in brick manufacturing, to produce bricks with certain
length and width. The main function of the cutting system is to continuously
cut the compacted mass that comes out of the extruder mouth to the
required size. During the earlier days, it was done manually which is now
replaced by far advanced, efficient and automatic mechanical cutters. A
typical cutter system installed in a brick production line is shown in
Figure A -C -12.
Figure A-C- 12 Typical cutting system used in a brick production line
[Source: Bender and Handle, 1982]
199
The cutting systems currently used in the ceramic industries are classified
into two main groups -
1. Depending upon the cutting direction- Vertical cutters,
horizontal cutters and segmental cutters.
2. Depending upon the type of cutter and application- column
controlled cutters and fixed cycle cutters.
The most commonly used cutting tool is a thin metal wire of gauge size
varying from 0.5 mm to 1.6 mm, depending upon the thickness of the
compacted clay [Madehow, 2012]. In some special cases knives are used
as a cutting tool. The appropriate cutting system and cutting tool depends
upon the ceramic material processed, speed and economy of the overall
production cycle.
Drying
Drying is defined as the process of removing water or moisture content from
the compacted or shaped ceramic product. Drying is completed before the
ceram ic product is fired to achieve the final colour and strength. Drying also
prevents the development of crack in the product during firing. The process
of drying can be achieved either by applying mechanical forces or using
thermal energy. The most common in practice is drying by using thermal
energy, where a hot medium like gas or air (mostly air) is used to heat the
wet ceramic product under a controlled atmosphere and remove the water in
the form of vapour. It is to be noted that after drying, the ceram ic product still
retains some moisture in it and it is soluble in water. The two common types
of drying system used in the ceram ic industries are Tunnel dryers and
Automatic Chamber dryers. The tunnel drying system is a single stage
process, whereas the automatic chamber drying system involves more than
one stage. Automatic transfer cars are used to transfer the ceram ic product
through the various stages of drying process. A typical tunnel drier is shown
in Figure A -C -13.
200
Figure A-C- 13 Tunnel dryer
[Source: Cereamtechno, 2013]
Firing
Firing is the final process involved in the manufacturing of ceram ic products
used in structural applications. It helps the ceramic product to achieve
required compressive strength, build strong cohesion between the particles
and introduces colouring. Since it is the final process, any additives that are
required to produce a ceramic product with certain features must be added
before the firing stage, mostly at the raw material preparation stage.
The firing of green bricks (wet bricks) vaporises the water content left after
the process of drying and induces chemical reaction that involves production
of gases. Most of the gaseous products are hazardous in nature for both the
environment and to the humans (C02 and Hydrogen Fluoride). Flu gas
treatment is another important area involved in the design of efficient, cost
effective and environmental friendly ceramic industries. Since it is of not
much interest pertaining to this research work, it is not reviewed in detail.
The process of firing takes place in a closed and controlled chamber called a
"Kiln". Since the invention of kilns for firing process there have been many
developments to increase the efficiency and safety of this process. Though
there are different types of kilns, which are operational in ceram ic industries
201
worldwide, one type of kiln which is very common and used in brick
manufacturing is "Tunnel Kilns". Tunnel Kilns are further sub divided into
different types based on the firing arrangement. The features like economical
operation, faster heating time, increased capacity and safe design has
offered the advantage for tunnel kilns to be preferred over the other types.
Typical types of tunnel kilns are shown in Figure A -C -14 and A -C -15.
Figure A-C- 14 Tunnel kiln-Type I
[Source: Shinagawa Refactories, 2013]
Figure A-C- 15 Tunnel kiln-Type 2
[Source: West Lothian Archaeology Group, 2013]
Packing and Dispatch
The final stage involved in ceramic (brick) manufacturing process is storing
the product that comes out of the kiln in an appropriate place and keeping it
202
ready for final inspection and dispatch. Considering the number of products
that are produced, it is physically impossible to check the products
individually for the required quality and hence random visual inspection
techniques are used at every stage during the production process, to make
sure the product meets the required standard. The products that pass the
quality check will then be stored appropriately before being packed and
transported to the end users. The products that fail the quality check are
either re-used along with virgin raw materials for making new products or as
aggregates. So in simple terms, there is no waste of product, but the energy
consumed is still lost and hence products with defects are not preferred by
the industries. Packing involves the use of wooden pallets or boards made
up of plastic, onto which the bricks are arranged in a specific pattern to
ensure that the load is evenly distributed and suitable provisions will be
provided to withstand the weather conditions and avoid damage during
transportation. Mechanical or automatic wrapping machines are w idely used
in packing applications.
ConclusionIt is clearly understood from the above discussion that the ceramic industry,
especially brick manufacturing, involves the use of both heavy and light duty
mechanical and electrical systems to achieve the required objectives.
Considering the demand for bricks and the volume of production, it is
impossible to replace it with a human workforce and also it is not good
practice, hence the use of power consuming machines is inevitable. So for
the longer sustainability of the brick industries in terms of its power
consumption and environmental impact, it is necessary to identify and
undertake suitable developmental work in all possible areas of the
manufacturing cycle on a regular basis. With the availability of advanced
computing methodologies and simulation based techniques, improvement in
certain processes and in design of machines used in brick manufacturing can
be accelerated. This research work is one such effort to demonstrate the
application of CFD and FEA techniques towards improving the process of
brick making in heavy clay industries.
203
Appendix-D
Extruder and the process of extrusion
204
IntroductionShaping is an important function in the process of brick making or in any
ceramic product manufacturing. It is also a major power consuming
processes. Most of the brick industries in the U.K and worldwide uses
combined de-airing type extruder to perform this function. As discussed in
previous chapter, due to certain inherent functional aspects, these types of
extruders are used widely. The aim of this chapter is to review the history of
machines used in extrusion process, general design principles applicable in
the design of combined de-airing auger extruders and the flow parameters
that govern the design and power consumption of extruders together with the
process of shaping.
Developments in extruderA wide variety of mechanical systems have been developed and used for the
purpose of shaping ceramic products since the earlier days. However only a
few of them were very successful in achieving the intended functional
requirements and used widely. This includes the following,
• Piston extruder
• Expression rolls
• Electrophoretic extruders
• Auger extruders
Piston extruders
The use of piston extruders began in the year 1807, with the invention of a
hand operated piston extruder used in making drainage pipes [Handle,
2007]. As the name suggests, the working mechanism of this machine is
mainly based on a piston moving inside a closed chamber that pushes the
clay material through the die or mouth, predominantly in a vertical direction.
The main problems faced with this type of machine includes filling up of raw
material after every cycle of operation and removal of air entrapped in the
raw material. Even though design changes were made to overcome these
problems, to gain acceptance in the ceramic industries for manufacturing
205
structural ceramic products, the piston extruders played a less significant
part in ceramic industries. A simple vertical piston extruder developed and
used in the year 1880 is shown in Figure A -D -1.
Figure A-D- 1 Piston extruder
[Source: Handle, 2007]
Expression rolls
The process of extruding a continuous column of clay by pushing it through a
die through a connecting element called a pressure head was born with the
introduction of Expression Rolls in 1830 [Handle, 2007].The first machine
designed by the Englishmen Ainslie [Handle, 2007], served as a blue print
for future machines built using the same principle. Expression rolls capable
of extruding both in vertical and horizontal direction were built and used in
ceram ic industries, especially for making thin tiles. “Europresse” is one of the
most notable developments from the earlier designs of expression rolls. It is
also called as augerless extruder or rotor type extrusion machine. This type
of machine was used for extruding ceram ic product with more than one layer
(multilayer) and each layer will be made up of different or same raw material.
Due its technical advantage and less defect in the extruded product it gained
206
its popularity in fine and advanced ceramic industries. A typical Europresse
type Expression Roll machine is shown in Figure A-D- 2.
m&Ljs
Figure A-D- 2 Europresse extruder
[Source: Bender and Handle, 1982]
Electrophoretic extrusion
Electrophoretic extruder is similar to Expression Roll machine; it was
introduced and used in ceramic industries by 1977. The machines were built
based on the principle of "Electrophoresis" and is used for special
applications in ceramic industry. Due to the complexity involved in the design
and operation of these machines it was seldom used in the structural
ceramic industries. A typical electrophoretic extruding system is shown in
Figure A-D- 3.
207
Figure A-D- 3 Electrophoretic extruder
[Source: Bender and Handle, 1982]
Auger extruders
The use of auger extruders in the process of shaping structural ceramic
products began in the year 1855, with the introduction of Carl Schlickeysen's
"Patent Brick Making Machine"- an upright machine for extruding clay
columns [Handle, 2007]. Thereafter, driven by market requirements and
demands, the auger extruders underwent a series of rapid development
processes in various aspects to make it a more operator friendly system and
meet the mass production requirement. Auger extruders capable of extruding
both in vertical and horizontal direction were developed and used for specific
purposes. Even though there were different types of auger extruders
developed and they all can be grouped into the following three categories,
• Auger extruder without de-airing
• Auger extruder with vacuum device installed in extrusion barrel
• Combined de-airing extrusion units consisting of auger extruder,
vacuum chamber and mixer.
Auger extruders can also be classified into different types based on the
process and design features. The various types that fall under such
classification includes,
2 0 8
• Range of application.
• Product to be extruded - bricks, tiles and pipes etc.
• Auger shaft arrangement and direction of column exit- upright
extruder, horizontal extruder, vertical extruder, hinged type extruder.
• Extruder barrel diameter.
• Number of auger shafts- single auger shaft extruder, combined single
auger de-airing extruder, twin shaft extruder, multiple shaft extruder.
• Consistency of the body to be processed.
• Extruder barrel design- cylindrical, conical, combined
(cylindrical/conical), enlarged barrel, expanded barrel, stepped barrel,
noodle barrel.
• Design and mounting of augers-progressive pitch, acute or decreasing
pitch, linear pitch, combined pitch.
• Special extrusion methods-twin layer extrusion, multiple column
extrusion, hot extrusion and vacuum extrusion.
• De-airing device used.
• Design of the extruder elements- auger, housing, infeed device and
barrel liners etc.
• Design of the de-airing mixer.
• Design of combined de-airing extrusion unit- configuration of mixer
and auger shafts, method of connection between the extruder and
mixer and the construction of de-airing mixer.
The most important types in the above said classifications are based on
application and consistency of the body to be processed, which is elaborated
below.
Extruder classification based on application
Based on the shaping effects, body composition, degree of fineness of the
raw material, throughput and extrusion pressure the extruders are classified
into three categories namely, extruders used in heavy clay industries, fine
ceramic industries and advanced ceramic industries. Auger extruder in heavy
clay industries is used for direct shaping process to achieve the final shape
of the product, example brick and pipe. Whereas in fields like advanced
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ceramics and fine ceramics, it is used for homogenising, de-airing and
improving the plasticity and density of the clay material before the final shape
of product is acquired through other means.
Extruder classification based on body to be processed
The raw material to be extruded varies hugely with respect to products or
even for the same product it might vary in mineral composition and moisture
content. This influences the extrudability of the material and also the function
of the extruder to a greater extent. Based on the moisture content and
pressure developed during extrusion the extruders can be classified into
three categories namely low, medium and high pressure extruders. Table A-
D- 1 provides a rough guide on the classification of extruders based on
process.
Type of extruderLow
pressure
Medium
pressureHigh pressure
Description of extruder Soft Semi-stiff Stiff
Parameter Dimension 1 2 3 4
Moisture
content
%
(dry basis)10-27 15-22 12-18 10-15
Extrusion
pressureBar 4-12 15-22 25-45
up to
300
Penetrometer Nmm"2 <0.20 0.20-0.300.25-
0.450.30
Table A-D- 1 Extruder classification based on process parameters
[Source: Handle, 2007].
It is recommended to refer "Extrusion in Ceramics", mentioned in the
reference section of this report, for more details on the classification of auger
extruders.
De-airing extruderOf the various development works that were undertaken with respect to the
design of an extruder system, the most notable and successful work includes
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the development of de-airing extruders. De-airing is the process of removing
air particles trapped in the clay-water mixture, before being extruded into
continuous column. This helps to increase the plasticity of the mixture and
extrude a dense mass. Failure to do so will cause problems like lamination,
void formation and blistering. The earlier designs of extrusion system had the
de-airing units located separately from the extruder. This type of design
offered certain process advantages like multiple de-airing and less
sophistication in design. The main disadvantages were blockage, back
pressure and uneven de-airing. This led to the development of combined de
airing extruders or vacuum extruders around 1935 [Handle, 2007]. In simple
terms a vacuum extruder incorporates the mixing, de-airing and extruding
unit in a single system, arranged sequentially. Compare with other earlier
designs of extruders, vacuum extruders possessed a numerous advantages.
Like better efficiency, adoptability for mass production requirement (modern
vacuum extruders are capable of extruding 15000-20000 bricks per hour),
manoeuvrability and quality of extrudate. These factors favoured it to gain its
popularity in structural ceramic industries in a very short time. Based on the
design, arrangement of pug mill, extruder and extruding direction, the
vacuum extruders can be classified into different types. The basic building
blocks of any vacuum extruder include pug mill or the mixing chamber,
primary compression zone, vacuum chamber, extruder, die and drive
system. An overview of each component is presented below. A typical
vacuum extruder designed and built by Craven Fawcett Limited, U.K is
shown in Figure A-D- 4 for the purpose of understanding.
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De-airing(Vacuum)chamber
Extruder(auger/barrel
Pug mill Primary compression
Figure A-D- 4 Vacuum extruder-Centex model
[Source:-Craven Fawcett Limited, U.K]
Pug mill
Pug mills or the mixing chamber is a semi enclosed metal chamber, mostly
u-shaped, placed before the vacuum chamber. It will be either in line with the
extruder or placed above the extruder (most of the extruders designed and
manufactured by C.F Ltd, have the pug mill aligned parallel to the extruder's
axis of rotation). It is where the right sized clay particles (usually >2 pm and
<4 pm) that comes out of a rotary silos is mixed with water, supplied through
controlled pipe lines. A rotary silo is a rotating drum made up of wire meshes
of different size, used to filter the over sized clay particle. A fairly
homogenised mixture of clay and water is acquired through the rotating shaft
equipped with paddle or knife like structures placed in this chamber. Most of
the machines used in Europe consist of a twin mixing shaft arrangement in
this chamber. Though a 100% homogenised mixture cannot be achieved
through this type of arrangement, it is accepted in the industries as a better
and more efficient system compared to the earlier systems. This type of212
design offers a great flexibility in controlling the moisture content either
automatically or mechanically, with respect to the quality and stiffness of the
extrudate. A typical pug mill with a twin shaft mixer arrangement is shown in
Figure A-D- 5.
Figure A-D- 5 Mixing chamber
[Source: Bender and Handle, 1982]
Primary compression zone
The connecting element between the vacuum chamber and the mixing unit is
called the primary compression zone, and it is shown in Figure A-D- 4. In
industries this unit is designed with various shapes and accessories attached
to it, depending upon the requirement. In most of the design there will be a
twin conical chamber fitted with small augers in each chamber. The main
function of this unit is to compress the loose wet clay transported from the
pug mill into a mass of substance with medium density called "slip" (as
mentioned in Appendix- C). This helps in creating a bond between the loose
clay and water and removes the trapped air content to a certain extent. The
compressed mass is then cut into suitable lengths using a cutter
arrangement placed at the downstream side of the chamber, in order to
maximise the efficiency of the de-airing process that follows.
De-airing (or) vacuum chamber
The concept of de-airing and the need for it was been discussed earlier in
this chapter. The process of de-airing is achieved by many ways; however in
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modern combined de-airing and vacuum extruders, this is achieved by using
a vacuum pump mounted on top of an enclosed chamber; typical
arrangement of a vacuum chamber is shown in Figure A-D- 4. The slip, after
being sliced to the required length from the preliminary compression zone is
made to fall into the vacuum chamber by the action of gravitational force; the
vacuum created in this chamber facilitates the air, from the slip, to escape in
the direction of suction. The de-aeration depends on few factors like the
vacuum created, specific surface area of slip and on the duration of the
vacuum [Bender and Handle, 1982]. The de-aired mass of clay will then
enter the charging zone or the extruder section.
Extruder
The extruder used in modern machines is a simplified version of earlier
designs and resulted from the process of continuous development. The
extruder section is sub-divided into two main zones namely a charging and
compression zone. The main elements that contribute to these zones include
auger shaft, barrel, and barrel liners. Figure A-D- 6 shows a typical barrel
and an auger shaft used in one of C.F Ltd's vacuum type de-airing extruder
system.
Barrel Auger and shaft assembly
Figure A-D- 6 Components of an extruder system
Charging zone is where the severed slip from the mixing chamber gets
accumulated before it enters into the compression zone. To ensure a uniform
feed of clay during the process of continuous extrusion, maintaining a certain
level of clay in this zone is important. This is achieved by using sensors and
other suitable means of measuring. An excess accumulation of clay in this
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zone could cause deaeration problems and cause severe damage to the
machine by means of overloading.
The auger is an integral element between the charging and compression
zones. The slip from the charging zone is carried forward by these augers
and in order to accommodate the uncompacted nature of the clay and
achieve reliable throughput, the diameter of auger in the charging zone will
be slightly larger than the diameter of auger in compression zone. Suitable
design provisions are available in modern extruders, to prevent the clay from
sticking and rotating along with auger (paddle shaft is one such example).
The extended auger shaft from the charging zone is enclosed within a
cylindrical barrel along with liners, which constitutes the compression zone.
The uncompacted mass of clay that enters the compression zone is mixed
well to achieve a good homogenised mixture of clay and water and then will
be pressed together to form a compacted mass. Any air entrapped further
will be removed because of this pressing action and suction pressure created
by the vacuum pump in the charging zone.
Die
The die or mouth is the final element in an extruder system. A continuous
mass of clay is produced because of the rotation of the auger shaft within
extruder section will force the compacted clay to pass through the openings
in the die section. The opening at the downstream side usually resembles
the required cross sectional shape of the extruded product. The earlier
designs of extruder, used in commercial scale include a pressure head,
connecting element that links the extruder with the die (similar to those used
in expression rolls, discussed earlier). The compacted clay will be pushed
into the die or mouth through the pressure head to acquire the intended final
shape of the extruded product. A careful consideration to the flow conditions
and extensive field knowledge has led the design engineers to integrate the
pressure head and die into a single unit. A further brief review about the flow
process and related flow parameters for the die section of an extruder is
presented later in this chapter. Other significant design advancements in the
die design includes dies with core used for manufacturing perforated bricks
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and hollow blocks etc, and dies with external lubrication arrangement, used
for extruding slip with very less moisture content.
Drive system
The power required to rotate the auger and shafts in the mixing chamber is
obtained through the drive system. The drive system has undergone a series
of many notable developments that includes the use of steam power,
electrical motors and the most recent advancement is the use of planetary
gear boxes. As discussed earlier, the drive system design is another
category for classifying extruders. Most of the modern combined de-airing
type extruder drive system comprises an electric motor combined with a gear
box. The electrical motor (mostly squirrel cage motor, due to the flexibility of
speed control) acts as the primary power source which drives a gear unit,
designed suitably to achieve the required speed with respect to the extrusion
rate required. The electric motor will be coupled to the gear box either
directly or through stepped pulley and belt drive arrangement or through a
clutch system. The gear box will be directly coupled to the shafts in the
extruder and mixing chamber.
Usually a common drive system exists for both the shaft, but there are
extruders with separate drive units for auger and mixing chamber. The
advantage in the latter case is it offers better control of the extrusion process
and reduces complexity in design requirements; the main disadvantage
includes the capital and running cost incurred.
Process of stiff extrusionThe technical aspects of a stiff extrusion process are very sophisticated and
during years of its extensive use in industries, only a very little understanding
has been developed by experts to make any conclusive remarks about the
flow process that occurs inside the auger/barrel and die sections. Smooth
extrusion depends on many factors like the clay particle size, moisture
contents, efficiency of the de-airing system, drive elements and its control
systems, extrusion pressure, die design, pitch and profile of the auger,
clearance between auger tip and the barrel and most importantly the
plasticity of the slip (clay-water mixture).The main performance parameters216
of a de-airing type vacuum extruder includes extrusion rate, extrusion
pressure, material flow velocity at the die section and power consumption.
The geometric and operating parameters that have direct influence on the
performance includes auger speed, auger diameter, uncompacted density of
clay, material of construction of augers and moisture content of the clay. A
brief overview about extruder’s performance characters is presented further
in this chapter.
Extrusion rate
It is quantified by the amount of bricks produced per unit of time (usually rate
per hour). As mentioned earlier in this chapter, modern vacuum extruders
are designed to produce more than 12,000 bricks per hour and this depends
upon two main factors- the auger pitch and plasticity of the clay. Since the
moisture content is controlled by product requirement and other factors, it is
relevant in this context to just to talk about the dependency of extrusion rate
on auger pitch. Figure A-D- 7 shows the various auger geometrical variables
necessary for determining the extrusion rate.
►direction o f extrusion
Figure A-D- 7 Auger geometrical parameters
[Source: Handle, 2007]217
Where,
Ds =Diameter of the auger
f =Flight thickness or auger blade thickness
a =Clearance between the auger and barrel
d =Hub diameter
D =Barrel diameter
h =area of effective gap between hub and barrel
P =helix angle or angle of inclination
S =Pitch distance or effective distance which can be determined
using Equation A.D.1
S = n * D * tan p a — A . D . l
Where, D- diameter of the barrel, pa- Helix angle measured at the tip of the
auger.
Using the above formula, once the auger pitch has been determined, the
swept volume of the auger or the volume of the material discharged per
revolution of the auger shall be determined by Equation A.D.2.
Where, Vs = Swept volume (m3).
The final, volumetric extrusion rate of an auger shall be determ ined using
Equation A.D.3.
Where, Qv= Volumetric discharge rate, n = auger speed in rpm.
It is a common practice in the industries, to express the discharge rate in
terms of mass of clay extruded per unit time. This shall be obtained by
including the density of the final clay column in the above equation as shown
in Equation A.D.4.
Vs = S * h — A.D.2
Where, Qm= discharge rate, p=density of extrudate218
It is clearly evident from the above presented equations that the discharge
rate of an extruder depends on the geometrical and operational parameters
of auger. Hence in actual scenarios the required discharge rate is obtained
by making necessary adjustments to one of the above referred parameters
on a trial and error basis.
Extrusion pressure
Extrusion pressure is another important flow parameter that has a more
significant role in determining the shape, stiffness and quality of the
extrudate (extruded product). The clay material from the charging zone will
flow through the auger convolutions and will fill the extruder and barrel
chamber slowly. The decrease in flow area between the die and auger-barrel
chamber facilitates the material to build up in this zone and imparl pressure
on the extruder and die sections gradually. The extrusion pressure
developed during extrusion depends mostly on the clay moisture content,
extrusion speed, yield point of the material and throughput. The pressure
raises from a negative value (at the entrance of the extruder- charging zone)
to a maximum value at the tip of the auger and then gradually decreases to
reach atmospheric pressure or value equal to the condition at the
downstream side of the die [Bender and Handle, 1982].Figure A-D- 8
shows the pressure profile observed in a typical vacuum type de-airing
extruder.
Figure A-D- 8 Vacuum extruder pressure profile
[Source: Bender and Handle, 1982]
219
It is clearly understood form the graph that the front side of an auger will
always be subjected to high pressure and in turn a high wear rate occurs.
Hence a greater care is required in designing the auger profile and selecting
suitable material of construction. Even though the pressure is dropping in the
die section, the design should be able to accommodate the stress and heat
induced, due to the loss in pressure. While using dies with core in stiff
extrusion process, the dies are designed with sufficient strength and flexibility
to accommodate any stress and forces induced due to the extrusion process.
Significant scientific works dealing with the flow of clay and assessing the
performance characters of an extruder system is reviewed in Chapter 2.
Power
Stiff extrusion is a high pressure extrusion process; extruders used in this
process are always robustly built to withstand this pressure, stress and wear
induced. This makes them to be a significant power consum ing device used
in brick making process. The power consumption depends upon both
operational and performance characters discussed above. Within the
industries, through repeated lab based experimental works and data
obtained from field, guidelines on power consumption pattern are prepared
for the use of design engineers and it varies with respect to machines and
manufacturers. Due to the complexities involved in the process of extrusion
and extruder design, there is a lack of specific data or an empirical method
that provides an overall picture about the power consumption pattern of any
extruder system.
Quality of extrudate
The quality and nature of the extruded product determ ines the clay
preparation, extrusion technique and equipments required. Stiff extrusion is
renowned for producing complex shapes with sharp edges and smooth
surfaces. The quality of a stiff extruded clay column depends upon one or
many of the process and operational parameters discussed above. A Clay
column with right stiffness and free of defects is what required at the end of
process. The stiffness of the material is determined by the extrusion pressure
and by achieving a suitable extrusion pressure for a given raw material
220
condition, column with unique density and mechanical properties can be
produced through stiff extrusion process (density of the loose clay at the
charging zone will be typically around 1600 kgm'3 and the density of
extruded column varies between 2100 kgm'3 to 2800 kgm'3 [Handle, 2007]).
Predominant problems that occur in the extruded products include texturation
(alignment of clay particles- important for uniform mechanical properties in all
direction), void formation (inclusion of air bubbles, which in turn induces
crack during firing process) and lamination.
ConclusionThe use of extruders and the evolution of vacuum extruders in the brick
industry were reviewed in this chapter. The process and operational
parameters that are necessary to assess the performance of an extruder
system was also reviewed. Through the various facts presented above, it is
evident that the development processes that were undertaken to enhance
the design of the extruder system were through empirical methods or
repeated field trials and there is a lack in application of advanced computing
tools towards the design and development of extruders used in the stiff
extrusion process. Through the introduction of such tools towards the design
and development of extruders will not solve the entire problem and the
challenges faced by the brick industry, it will help to speed up the process in
certain areas that will help in the efficient and sustainable operation.
221