Constitutive Characterization of Extruded Rubber …...Constitutive Characterization of Extruded...
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Constitutive Characterization of Extruded Rubber Blends by means of an Extrusion Rheometer Herbert W. MÜLLNER*, André WIECZOREK**, Sabine SEILER**, Josef EBERHARDSTEINER* ** Semperit Technische Produkte Ges.m.b.H., Wimpassing im Schwarzatale, Austria * Institute for Mechanics of Materials and Structures, Vienna University of Technology, Austria Literature: [1] S. Arrhenius: Über die Dissociationswärme und den Einfluss der Temperatur auf den Dissociationsgrad der Elektrolyte. Zeitschrift für physikalische Chemie, 4 (1889): 96-116. [2] M. Klüppel, R. Badura, R.H. Schuster: Thermodynamik und Rheologie weichgemachter Nitrilkautschuke – Kapillarrheologische Korrekturen. Kautschuk Gummi Kunststoffe 45 (1992): 614-619. [3] A. Limper, D. Schramm, M. Glabisch: Praktische Erprobung eines Extrusionsrheometers zur schnellen Beurteilung von Verarbeitungseigenschaften. Kautschuk Gummi Kunststoffe 52 (1999): 644-651. [4] H.W. Müllner, J. Eberhardsteiner, P. Mackenzie- Helnwein: Constitutive Characterization of Rubber Blends by Means of Capillary-Viscometry, Journal of Non- Newtonian Fluid Mechanics, 141 (2007): submitted. The influence of an extrusion process on the viscosity function of rubber blends is identified. This knowledge is required for performance of realistic numerical simulations of injection heads and extrusion tools for rubber profile production. The experimental basis of this investigation are tests with both, capillary and extrusion rheometer. The latter is a combination of an industrial extruder and a circular cross-sectional extrusion tool, allowing the application of material characterization methods used for capillary experiments. Thus, determination of the viscosity function of extruded rubber blends is possible. Additional capillary experiments allow an identification of the influence of extrusion on the viscosity of rubber blends. For the material characterization a nonlinear iteration scheme is used, which is proven to be applicable for rubber compounds and rubber blends. Successful verification of extrusion rheometer tests are performed with numerical back- calculation of the corresponding pressure measurements. In order to identify the influence of an extrusion process on the viscosity more precisely, an extrusion rheometer is used [3]. It consists of a vertical extruder and a specified extrusion tool. In order to avoid the disadvantages of capillary viscometry, an extrusion tool with a circular cross-section has been built. Thus, determination of the viscosity is possible under usage of character- ization methods, which are standardly applicable for capillary experiments with rubber blends. The influence of salt bath vulcanization on the profile shape is not relevant, there- fore is it not investigated. The diameter of the cylinder is 14˚mm, therefore pos- itioning of pressure trans- ducers within the cylinder is possible. The length of the cylinder is 133˚mm. This length allows arrangement of three pressure trans- ducers and two temperature sensors. The distances of the pressure transducers avoid significant flow inter- action. top left: extrusion tool top right: dimensions of tool middle left: vertical extruder middle right: supply of raw material bottom left: melt pressure bottom right: melt temperature The determination of viscoelastic properties of rubber blends by capillary viscometry is characterized by different viscosity functions due to different geometries of capillary dies. According to Klüppel et al. [2] the occurrence of wall slippage is one possibility for this phenomenon. Due to different diameters of capillary dies (D = 0.5, 1.0, 2.0˚mm) and extrusion tool (D = 14˚mm) the viscosity functions cannot be compared. The investigation of extruded materials under usage of capillary viscometry allows verification of interaction between extrusion process and viscosity as well as geometry dependence of viscosity functions. Because of usage of circular geometries for both experiments, capillary and extrusion rheometer tests, the consistency factors of different experiments can be compared. For raw and extruded rubber blends a clear relation between viscosity and geometry of the extrusion tool is identified. 10 1 10 2 0 20 40 60 80 100 120 top middle bottom 10 1 10 2 0 20 40 60 80 100 120 top mean bottom melt pressure p [bar] melt temperature T [°C] melt velocity v [mm/s] melt velocity v [mm/s] A numerical simulation of an extrusion rheometer test is performed using the computational fluid dynamics software POLYFLOW Version 3.92 (by Fluent Inc., Belgium). A working point at a tool temperature of 70˚°C and a screw speed of 20˚rpm is considered. Therefore, a comparison between experiment and simulation allows a validation of the present material characterization according to Müllner et al. [4]. For the simulation wall adhesion is considered. The consideration of wall slippage in the framework of numerical simulations is still in progress. Due to symmetry reasons a quarter of the extrusion rheometer is considered. As material description the power law with parameters according to the measurements of the extrusion rheometer is used (values of middle pressure transducer). The distri- butions of various state variables are shown. In addition, the positions of the pressure transducers are indi- cated. A verification of pressure measurements is possible, which is collected in the table situated under this text. The obtained numerical results show a good agreement with experimental data under consideration of energy dissipation according to Arrhenius [1]. Therefore, a satisfactory validation for the material characterization method according to Müllner et al. [4] has been achieved. However, the influence of an extrusion process on the viscosity function has not been identified. For this task, additional capillary experiments with raw and extruded material are required. 10 1 10 2 0 20 40 60 80 100 120 melt velocity v [mm/s] melt pressure p [bar] with correction without correction top bottom middle 10 0 10 1 10 2 10 3 10 4 10 5 shear strain rate ˙ γ [s 1 ] viscosity η [Pas] k = 179640 Pas 0. 145 n = 0.145 k = 186900 Pas 0. 132 n = 0.132 k = 173296 Pas 0. 160 n = 0.160 top bottom middle D = 14.0 mm extruded material EPDM rubber blends capillary viscometer D = 0.5/1.0/2.0 mm capillary viscometer D = 0.5/1.0/2.0 mm geometry dependence influence of extrusion EPDM rubber blends raw material extrusion rheometer 10 0 10 1 10 2 10 3 10 4 10 1 10 2 10 3 10 4 10 5 40/2 20/2 10/2 40/1 20/1 10/1 5/1 10/0.5 5/0.5 2.5/0.5 shear strain rate ˙ γ [s 1 ] viscosity η [Pas] ¯ n = 0.270 ¯ k = 85107 Pas 0. 270 10 0 10 1 10 2 10 3 10 4 10 1 10 2 10 3 10 4 10 5 40/2 20/1 10/1 5/1 2.5/0.5 shear strain rate ˙ γ [s 1 ] viscosity η [Pas] ¯ n = 0.273 ¯ k = 73739 Pas 0. 273 10 10 0 10 1 10 2 10 4 10 5 10 6 vor Extrusion consisteny factor k [Pas n ] diameter of capillary and extrusion tool D [mm] before extrusion after extrusion Top left: consideration of energy dissipation Top right: viscosity of raw rubber blend Bottom left: viscosity with extrusion rheometer Bottum right: viscosity of extruded rubber blend Numerical Validation Experimental Investigations Material Characterization of Extruded Rubber Blends Overview
Transcript of Constitutive Characterization of Extruded Rubber …...Constitutive Characterization of Extruded...
Constitutive Characterization of ExtrudedRubber Blends by means of an Extrusion Rheometer
Herbert W. MÜLLNER*, André WIECZOREK**, Sabine SEILER**, Josef EBERHARDSTEINER*
** Semperit Technische Produkte Ges.m.b.H., Wimpassing im Schwarzatale, Austria
* Institute for Mechanics of Materials and Structures, Vienna University of Technology, Austria
Literature:
[1] S. Arrhenius: Über die Dissociationswärme und denEinfluss der Temperatur auf den Dissociationsgrad derElektrolyte. Zeitschrift für physikalische Chemie, 4 (1889):96-116.[2] M. Klüppel, R. Badura, R.H. Schuster: Thermodynamikund Rheologie weichgemachter Nitrilkautschuke –Kapillarrheologische Korrekturen. Kautschuk GummiKunststoffe 45 (1992): 614-619.[3] A. Limper, D. Schramm, M. Glabisch: PraktischeErprobung eines Extrusionsrheometers zur schnellenBeurteilung von Verarbeitungseigenschaften. KautschukGummi Kunststoffe 52 (1999): 644-651.[4] H.W. Müllner, J. Eberhardsteiner, P. Mackenzie-Helnwein: Constitutive Characterization of Rubber Blendsby Means of Capillary-Viscometry, Journal of Non-Newtonian Fluid Mechanics, 141 (2007): submitted.
The influence of an extrusion process on the viscosityfunction of rubber blends is identified. This knowledgeis required for performance of realistic numericalsimulations of injection heads and extrusion tools forrubber profile production. The experimental basis of thisinvestigation are tests with both, capillary and extrusionrheometer. The latter is a combination of an industrialextruder and a circular cross-sectional extrusion tool,allowing the application of material characterizationmethods used for capillary experiments. Thus,determination of the viscosity function of extruded rubberblends is possible. Additional capillary experiments allowan identification of the influence of extrusion on theviscosity of rubber blends. For the materialcharacterization a nonlinear iteration scheme is used,which is proven to be applicable for rubber compoundsand rubber blends. Successful verification of extrusionrheometer tests are performed with numerical back-calculation of the corresponding pressure measurements.
In order to identify theinfluence of an extrusionprocess on the viscositymore precisely, an extrusionrheometer is used [3]. Itconsists of a verticalextruder and a specifiedextrusion tool. In order toavoid the disadvantages ofcapillary viscometry, anextrusion tool with a circularcross-section has beenbuilt. Thus, determinationof the viscosity is possibleunder usage of character-ization methods, which arestandardly applicable forcapillary experiments withrubber blends.The influence of salt bathvulcanization on the profileshape is not relevant, there-fore is it not investigated.The diameter of the cylinderis 14 mm, therefore pos-itioning of pressure trans-ducers within the cylinder ispossible. The length of thecylinder is 133 mm. Thislength allows arrangementof three pressure trans-ducers and two temperaturesensors. The distances ofthe pressure transducersavoid significant flow inter-action.
top left: extrusion tool top right: dimensions of toolmiddle left: vertical extruder middle right: supply of raw materialbottom left: melt pressure bottom right: melt temperature
The determination of viscoelastic properties of rubber blends by capillary viscometry is characterized by different viscosity functionsdue to different geometries of capillary dies. According to Klüppel et al. [2] the occurrence of wall slippage is one possibility for thisphenomenon. Due to different diameters of capillary dies (D = 0.5, 1.0, 2.0 mm) and extrusion tool (D = 14 mm) the viscosity functionscannot be compared. The investigation of extruded materials under usage of capillary viscometry allows verification of interactionbetween extrusion process and viscosity as well as geometry dependence of viscosity functions. Because of usage of circulargeometries for both experiments, capillary and extrusion rheometer tests, the consistency factors of different experiments can becompared. For raw and extruded rubber blends a clear relation between viscosity and geometry of the extrusion tool is identified.
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topmiddlebottom
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mel
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melt velocity v [mm/s]melt velocity v [mm/s]
A numerical simulation of an extrusionrheometer test is performed using thecomputational fluid dynamics softwarePOLYFLOW Version 3.92 (by FluentInc., Belgium). A working point at atool temperature of 70 °C and a screwspeed of 20 rpm is considered.Therefore, a comparison betweenexperiment and simulation allows avalidation of the present materialcharacterization according to Müllneret al. [4].For the simulation wall adhesion isconsidered. The consideration of wallslippage in the framework of numericalsimulations is still in progress. Due tosymmetry reasons a quarter of theextrusion rheometer is considered.As material description the power lawwith parameters according to themeasurements of the extrusionrheometer is used (values of middlepressure transducer). The distri-butions of various state variables areshown. In addition, the positions ofthe pressure transducers are indi-cated. A verification of pressuremeasurements is possible, which iscollected in the table situated underthis text.The obtained numerical results showa good agreement with experimentaldata under consideration of energydissipation according to Arrhenius [1].Therefore, a satisfactory validation forthe material characterization methodaccording to Müllner et al. [4] has beenachieved.However, the influence of an extrusionprocess on the viscosity function hasnot been identified. For this task,additional capillary experiments withraw and extruded material arerequired.
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melt velocity v [mm/s]
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tpre
ssur
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[bar
]with correction
without correction
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bottommiddle
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Druck obenDruck mitteDruck unten
shear strain rate γ̇ [s 1]
visc
osity
η[P
as]
k = 179640 Pas0.145 n = 0.145
k = 186900 Pas0.132 n = 0.132
k = 173296 Pas0.160 n = 0.160
top
bottommiddle
D = 14.0 mm
extruded materialEPDM rubber blends
capillary viscometerD = 0.5/1.0/2.0 mm
capillary viscometerD = 0.5/1.0/2.0 mm
geometry dependenceinfluence of extrusion
EPDM rubber blendsraw material
extrusion rheometer
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40/220/210/240/120/110/15/110/0.55/0.52.5/0.5
shear strain rate γ̇ [s 1]
visc
osity
η[P
as]
n̄ = 0.270
k̄ = 85107 Pas0.270
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osity
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k̄ = 73739 Pas0.273
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diameter of capillary and extrusion tool D [mm]
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Top left: consideration of energy dissipationTop right: viscosity of raw rubber blendBottom left: viscosity with extrusion rheometerBottum right: viscosity of extruded rubber blend
Numerical ValidationExperimental Investigations
Material Characterization of Extruded Rubber BlendsOverview
