Ceramic Processing 2
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620211 Introduction to Ceramic Engineering
Nutthita Chuankrerkkul
21 January 2011
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CeramicsMetals
Polymers
SiO2
MgO, CaO Al2O3, Fe2O3
CeramicsGlasses
Hydraulicceramics
Advanced oxide ceramics
Advanced non-oxide ceramics
Classic silicateceramics
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• Properties:--Tmelt for glass is moderate, but large for other ceramics.
--Small toughness, ductility; large moduli & creep resist.
• Applications:--High T, wear resistant, novel uses from charge neutrality.
• Fabrication--some glasses can be easily formed
--other ceramics can not be formed or cast.
Glasses Clay
products
Refractories Abrasives Cements Advanced
ceramics
-optical -composite
reinforce -containers/
-household
-whiteware -bricks
-bricks for
high T (furnaces)
-sandpaper -cutting
-polishing
-composites -structural
engine -rotors
-valves -bearings
-sensorsAdapted from Fig. 13.1 and discussion
in Section 13.2-6, Callister 6e.
TAXONOMY OF CERAMICS
www.uwstout.edu/faculty/schultzf/chem-341/docs/Chapter_13.ppt
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Topics
Processing & Machinery: comminution, mixing
Rheology: binder, viscosity
Forming techniques: hand throwing, uniaxial die pressing, isostatic pressing (CIP, HIP), injection moulding, extrusion, slip casting, tape casting, gel casting
Porous ceramics, Ceramic matrix composites (CMC)
Literature review on research & development in ceramics
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กระบวนการผลิตเซรามิก
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Plastic forming
Powder injection moulding
- Ceramic injection moulding (CIM)
- Metal injection moulding (MIM)
Extrusion
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Powder Injection Moulding
เหมาะส าหรับการผลิต
- ชิ้นส่วนขนาดเล็กที่มีรูปร่างซับซ้อน
- วัสดุท่ีมีจุดหลอมเหลวสูง ได้แก่ เซรามิก หรือโลหะบางชนิด
- ชิ้นงานมีรูปร่างใกล้เคียงรูปร่างสุดท้าย (near net shape)
มีข้อดีคือ
- ประหยัด และลดการสูญเสียวัตถุดิบ
- ลดขั้นตอน และลดค่าใช้จ่ายในการตัดแต่งชิ้นงาน
กระบวนการฉีดขึ้นรูปวัสดุผง
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VDO
Powder injection moulding
http://www.youtube.com/watch?v=zCfUd7ZEOjg
http://www.youtube.com/watch?v=Ecn3Gl3AaZ8
MIM
MIM & CIM
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Mixing/Milling
Clay + water
Ceramic powder + binder
Powder A + Powder B
Powder + binder + additives
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Particle size distribution of WC powders, planetary milled
for various times
0
20
40
60
80
100
0.1 1 10 100 1000
Particle Diameter (mm)
Vo
lum
e (
%)
15 min
30 min
45 min
60 min
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Powder Morphology
30 mm
30 mm
WC Powder A (as-received)
WC Powder B (after milling) http://www.purdue.edu/REM/rs/sem.htm
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Density of the mixture
Powder density = 3.9 g/cm3
Binder density = 1.1 g/cm3
Powder 95 wt% + Binder 5 wt%
Density of the mixture =?
3.76 g/cm3 3.46 g/cm3
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The prediction of theoretical density for a mixture of two powders or a powder and a
binder is a common problem that is often solved wrongly.
BAT WWW AWMass of powder A
BWMass of binder B
A
AA
WV
B
BB
WV
VVolume
B
B
A
A
BA
T
TT WW
WW
V
W
Density
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Density of the mixture
Density Powder A = 15.6 g/cm3
Density Powder B = 8.9 g/cm3
Density of the mixture =?
94 wt% Powder A + 6 wt% Powder B
15.20 g/cm3 14.93 g/cm3
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Source: http://www.azom.com
Source: http://www.designinsite.dk/
Powder Injection Moulding
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กระบวนการฉีดขึ้นรูปวัสดุผง
ตัวประสานส าหรับกระบวนการฉีดขึ้นรูปวัสดุผง เป็นองค์ประกอบที่มีความส าคัญ
- ท าหน้าที่น าพาผงวัสดุเข้าไปในแม่พิมพ์
- ยึดจับอนุภาคท าให้ชิ้นงานคงรูปอยู่ได้ ก่อนที่จะท าการเผาซินเทอร์
- มีบทบาทส าคัญต่อกระบวนการผลิต
- ส่วนใหญ่ใชต้ัวประสานที่เป็นพอลิเมอร์
อย่างไรก็ตามไม่มีตัวประสานชนิดใดที่ดีที่สุด จึงมีการพัฒนาตัวประสานผสม (multi-component binder) เพื่อให้เหมาะกับการผลิตแต่ละประเภท
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กระบวนการฉีดขึ้นรูปวัสดุผง
Feedstock คือ ส่วนผสมส าหรับการฉีดขึ้นรูป ประกอบด้วยผงวัสดุ ตัวประสาน รวมทั้งตัวเติมชนิดต่างๆ
Example of powder-binder mixtures for PIM
powder binder
wt %
solids loading, vol %
density, g/cm3
moulding temp.
ºC
green strength,
MPa
0.4 µm
Al2O3
92 polyethylene
8 paraffin wax 60 2.74 110 5
0.5 µm
Si3N4
65 polyethylene glycol
8 paraffin wax 58 2.28 155 12
10 µm
steel
55 paraffin wax
45 polypropylene
5 stearic acid67 5.60 130 15
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กระบวนการฉีดขึ้นรูปวัสดุผง
นิยมรายงานส่วนผสมเป็นร้อยละโดยปริมาตร (volume%)
ปริมาณตวัประสานอยู่ในช่วง 40-50 vol%
Low density (Al2O3 3.9)
High density (WC-Co 14.93)
Binder (1.1 g/cm3)
60 vol% solids loading => What is the weight % ?
84.2 wt%
95.3 wt%
Feedstock
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กระบวนการฉีดขึ้นรูปวัสดุผง
เพิ่มอุณหภูมิให้กับ feedstock (อุณหภูมิที่ตวัประสานกลายเป็นของเหลว) เพื่อให้ feedstock ถูกฉีดเข้าไปในแม่พมิพ์ได้
http://www.technologystudent.com/equip1/inject1.htm
Injection mouldingFeedstock
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Moulded System
The delivery system provides passage for feedstock from the machine nozzle to the part cavity, generally includes:
a sprue
cold slug wells
a main runner
branch runners
gates
The moulded system includes a delivery system
and moulded parts.
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Injection moulding
: Lab-scale injection
moulding machine
: Industrial-scale injection
moulding machine
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Injection moulding
After moulding, the delivery system is trimmed off and recycled. Therefore, the delivery system is normally designed to consume minimum material, while maintaining the function of delivering feedstock to the cavity in a desirable shape.
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Factors that influence injection pressure requirements
Higher injection
pressure required
http://www.scudc.scu.edu/cmdoc/dg_doc/develop/process/physics/b3200009.htm
Lower injection
pressure required
Part thinkness
Part surface area
Gate size
Flow length
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Factors that influence injection pressure requirements
Higher injection
pressure required
http://www.scudc.scu.edu/cmdoc/dg_doc/develop/process/physics/b3200009.htm
Lower injection
pressure required
Melt temperature
Mould-wall (coolant)
temperature
Ram speed
Melt flow index
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กระบวนการฉีดขึ้นรูปวัสดุผง
Debinding การก าจัดตัวประสาน
1. Thermal debinding สะดวก แต่ นาน
2. Wicking debinding เร็วกว่า แต่ ท าต่อเนื่องไม่ได้
3. Solvent debinding เร็ว แต่ มีข้อจ ากัดกับผงบางชนิด
ตัวท าละลายบางชนิดเป็นพิษ ติดไฟ
4. Catalytic debinding เร็ว แต่ ต้องซื้อ Feedstock ส าเร็จรูป
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กระบวนการฉีดขึ้นรูปวัสดุผง
The binder is degraded to form volatile products.
It diffused through the mouldings to their surfaces.
The formation of gases must be sufficiently slow to prevent bubbles developing and pressure build-up.
This can take up to several days to complete, depending on the thickness of the components.
A model pore geometry during
thermal debinding
(German and Bose 1997)
Thermal debinding
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กระบวนการฉีดขึ้นรูปวัสดุผง
The components are embedded in a wicking material, such as powders of alumina, silica, clay, graphite or zirconia.
This powder bed helps prevent distortion and provides more uniform heating.
The porous wicking powder allows the liquid binder to be drawn out of the component by capillary action.
Wicking debinding
Wicking debinding with an embedded
part in a low density powder with a
small pore size
(German and Bose 1997)
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กระบวนการฉีดขึ้นรูปวัสดุผง
The binder is depolymerised into its monomer using gaseous nitric acid or oxalic acid as a catalyst.
Gaseous formaldehyde is formed and subsequently burnt out. Loading of the debinding
chamber using oxalic acid
solution
(Ebenhoch and Hesse 1994)
Catalytic debinding
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กระบวนการฉีดขึ้นรูปวัสดุผงSolvent debinding
(a) as-moulded state (b) initial state
(c) intermediate state (d) final state
Diagrams of binder distributions (Yang et al. 2003)
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SEM micrograph shows fracture surface of as-moulded specimen (green sample)
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SEM micrograph of a 316L stainless steel specimen
after water leaching for 120 minutes (Anwar et al. 1995)
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กระบวนการฉีดขึ้นรูปวัสดุผง
Water leaching
*B8 is composed of 60vol% powder loading and 85-15 binder composition
- Various times and temperatures
Leaching test on B8 specimens
0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7
Time (hr)
% P
EG
rem
oved
40 °C
60 °C
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Debinding
Thermal debinding
Advantages
- The application of the process is easy as onefurnace can be used for both debinding andsintering.
- The process is safe.
Disadvantages
- The debinding time is long and depends on thethickness of the mouldings.
- Volatile products, generating from the process,result in defects.
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Debinding
Wicking
Advantages
- Debinding time is short compared to thermaldebinding.
- Shape stability is good.
- The process is simple.
Disadvantages
- It is difficult for fine powders, i.e. ceramiccomponents.
- It is not suitable for continuous processing.
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Debinding
Solvent debinding
Advantages
- Debinding time is comparatively short.
- Control of distortion is better, compared tothermal debinding as the process starts from thesurface and gradually continues into the bulk.
Disadvantages
- Powder corrosion is possible.
- Swelling tendency and cracks can be caused bysolvent attack.
- Toxicity and flammability, when organicsolvents are used.
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Debinding
Catalytic debinding
Advantages
- Debinding time is short.
- Highly accurate temperature control is notmandatory.
- Green strength is good.
Disadvantages
- The process is corrosive to some metal powders.
- Toxic gases are created.
- Hydrogen reduction is occasionally required.
- Only premixed feedstocks are available.
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Powder
Injection moulding
Debinding
Sintering
Feedstock
Binder
Powder injection moulding
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Sintering
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Sintering processing effects, adapted from German (1996)
Changes to aid sintering Effects Advantage Drawback
Decrease in particle size Faster sintering
Greater expense
Higher impurity level
Increased hazards
Increase in time Greater expense
Grain growth and
coarsening
Increase in temperature Greater shrinkage
Grain growth
Greater expense
Less precision
Higher properties
Furnace limitations
Pore coarsening
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Increase in green
density
Less shrinkage
Smaller pores
Higher final density
Uniform dimensions
Density gradients
reduced
Increase in alloying/
additives
Higher strength
Homogeneity problems
Higher sintering
temperatures
Use of sintering aids Faster sintering
Lower sintering
temperature
Embrittlement
Distortion
Grain growth control
Changes to aid sintering Effects Advantage Drawback
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Rheology
Greek: rheos = stream current
Rheology is the science of flow and deformation
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www.vscht.cz/sil/sil_cz/seminar/2003/13_Sarraf_Hamid.ppt
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Newtonian Pseudoplastic Dilatant
(shear thinning) (shear thickening)
Sh
ear
stre
ss
Sh
ear
stre
ss
Shear rate Shear rate Shear rate
Vis
cosi
ty
Vis
cosi
ty
Vis
cosi
tyShear rate Shear rate Shear rate
Common flow behaviours