Compuplast International Inc.

© Compuplast International Inc. 2010All Rights ReservedANALYSIS OF EXTRUSIONPROBLEMS WITHFLOW SIMULATIONVijay KudchadkarCompuplast International Inc.© Compuplast International Inc. 2011All Rights Reserved

Objectives• Demonstrate the application ofCAE/CFD/Simulation towards extrusion• Show how simulation can be used totroubleshoot an extrusion process• Explain certain observations or phenomena withthe aid of simulation.• All simulations performed using theCompuplast® Virtual Extrusion Laboratory(VEL) Suite of CAE Tools for Extrusion© Compuplast International Inc. 2011All Rights Reserved

Problem: Particles in Film Sample• In this system, periodic “showers” of particleswere observed in the film sample.© Compuplast International Inc. 2011All Rights Reserved

Photo of Extruder Screw• The screw used to produce the filmhad a noticeable discoloration in thefeed and compression region.© Compuplast International Inc. 2011All Rights Reserved

Comprehensive Tests with the Macro GlassWindow ExtruderSong, Perdikoulias and Planeta, ANTEC 2000© Compuplast International Inc. 2011All Rights Reserved

Comprehensive Tests with theGlass Window ExtruderLDPE 50 RPM @ W2 & W3, melt @ ~ 17D© Compuplast International Inc. 2011All Rights Reserved

Solid Bed Break-Up• Improper screw design results in solid bedbreak-up and there is no mixer to compensate© Compuplast International Inc. 2011All Rights Reserved

Inhomogeneous MeltFlow Direction• Gray areas represent material that has not been properlymixed or homogenized.© Compuplast International Inc. 2011All Rights Reserved

Define: Solid Bed RatioSolid BedMelt PoolFlowDirectionChannel Width• Ratio of Solid bed width toChannel Width• Indication of meltingcapability of the screw© Compuplast International Inc. 2011All Rights ReservedSolid BedRatio =SB WidthChannel Width

Analysis of Solid Bed RatioSimulation indicates that the Solid bed ratio does not reducegradually as preferred but actually increases near center of screw.© Compuplast International Inc. 2011All Rights Reserved

Solution: Modify Process Conditions,Change Material or Screw Design toachieve better melting performanceGood melting© Compuplast International Inc. 2011All Rights Reserved

Problem: Polymer Degradation• Screen Changer• Flat Die Manifold© Compuplast International Inc. 2011All Rights Reserved

Degradation onSCREW / BARREL / SCREENCHANGER90 mm Diameter250 kg/hr LDPE @ 190 CShear Rate = 1.3/sShear Stress = 5 kPa© Compuplast International Inc. 2011All Rights Reserved

The role of wall shear stress=Velocity= 0 = maxShear StressHigh enough shear stresscleans the wall by scrubbingWhat is high enough?LDPEPVC© Compuplast International Inc. 2011All Rights Reserved30 kPa35 kPaHDPELLDPE30 kPa30 kPa

DegradationSCREW / BARREL / SCREENCHANGER© Compuplast International Inc. 2011All Rights Reserved

Original ShapeShear stresses inside the flow domain© Compuplast International Inc. 2011All Rights Reserved

New ShapeShear stresses inside the flow domain© Compuplast International Inc. 2011All Rights Reserved

Degradation onSCREW / BARREL / SCREENCHANGER(Improved design)© Compuplast International Inc. 2011All Rights Reserved

Problem: Degradation andDamage in Flat Die Manifold• The outer edges of the manifold exhibitdegradation and even corrosion damage.© Compuplast International Inc. 2011All Rights Reserved

Simulation Results: Shear Stress• Low shear stress at outer edge of manifold results ininsufficient purge characteristics.• Polymer exhibits long residence time and ultimatelydegrades.• Some polymer degradation results in corrosivebyproducts.© Compuplast International Inc. 2011All Rights Reserved

Polymer Degradation Solution• Ensure adequate shear stressin all flow channels.– Proper Channel Design– Proper Operation Conditions© Compuplast International Inc. 2011All Rights Reserved

Problem: Periodic Lines inTubular Film Bubble• Lines appear as a visual defect in filmproduced on a spiral mandrel type die.© Compuplast International Inc. 2011All Rights Reserved

Potential Problem• With some Spiral Mandrel type dies, aflow defect is sometimes observed thatappears like a weld line in the product.• It may also be observed in the product asa very localized thin section that repeatsaround the circumference of the die asmany times as there are spirals.© Compuplast International Inc. 2011All Rights Reserved

The Spiral Mandrel Flow Field© Compuplast International Inc. 2011All Rights Reserved

Spiral Mandrel Flow Video© Compuplast International Inc. 2011All Rights Reserved

3D FEM - Pressure Drop© Compuplast International Inc. 2011All Rights Reserved

© Compuplast International Inc. 2011All Rights Reserved3D FEM Velocity

3D FEM Velocity (2 of 3 sections)© Compuplast International Inc. 2011All Rights Reserved

3D FEM - Shear StressLow Shear Stress© Compuplast International Inc. 2011All Rights Reserved

3D Flow AnalysisParticle Path Line Seeds• Velocity contours for 2/3 of the die and path line seedlocations© Compuplast International Inc. 2011All Rights Reserved

© Compuplast International Inc. 2011All Rights Reserved3D FEM - Particle Path

3D FEM - Particle PathsParticle PathFrom All Rights Next Reserved Spiral© Compuplast International Inc. 2011

Particle Path Lines• Particle path lines showing "back flow"© Compuplast International Inc. 2011All Rights Reserved

Particle Paths Avoid Low Shear Stress© Compuplast International Inc. 2011All Rights Reserved

The Back-Flow Essentially Forms Weld Line© Compuplast International Inc. 2011All Rights Reserved

Problem: Lines in Flat Film© Compuplast International Inc. 2011All Rights Reserved

Poorly designed flat spiral distributor© Compuplast International Inc. 2011All Rights Reserved

Poorly designed flat spiral distributor© Compuplast International Inc. 2011All Rights Reserved

Spiral Back-Flow Solution• Design spiral distribution systemto control the leakage flow fromthe spirals and ensure adequatevelocity (and shear stress) alongthe entire channel.© Compuplast International Inc. 2011All Rights Reserved

Problem Definition• In a 3 layer coextrusion, the thincenter layer exhibits an interfacialinstability that is observed on theextruded film.• Why?• How can it be removed?© Compuplast International Inc. 2011All Rights Reserved

© Compuplast International Inc. 2011All Rights ReservedFeed-block system

Velocity profile on the original feedblockV max = 113 mm/sV max = 14.6 mm/sV max = 64.6 mm/sCentral layer acceleration 64.6/14.6 = 4.4© Compuplast International Inc. 2011All Rights Reserved

Second material flow passage original designArea of highacceleration© Compuplast International Inc. 2011All Rights Reserved

Deformation rate of the central layer4.5 1/s2.97 1/s© Compuplast International Inc. 2011All Rights Reserved

Velocity profile on modified feedblockV max = 82 mm/sBetterbalancedvelocitiesV max = 26 mm/sV max = 64.6 mm/sCentral layer acceleration 64.6/26 = 2.5© Compuplast International Inc. 2011All Rights Reserved

Second material flow passage modified designLoweracceleration© Compuplast International Inc. 2011All Rights Reserved

Deformation rate of the central layer2.5 1/s1.95 1/s© Compuplast International Inc. 2011All Rights Reserved

Explanation and Solution• It was observed that the flow balancingin the lamella region helped to improvedthe production stability (interfacialinstability disappeared)• The flow balancing reduced theelongational rate of the center layer andthe interface distortion was minimized.© Compuplast International Inc. 2011All Rights Reserved

Concluding Remarks• Process simulation provides moreinformation for correlation betweenprocess conditions and productionproblems.• Simulation gives new insight intoproblems, which can lead to fasterand more precise solutions.© Compuplast International Inc. 2011All Rights Reserved

THANK YOU!!!Questions?Vijay Kudchadkarwww.COMPUPLAST.comvk@compuplast.com© Compuplast International Inc. 2011All Rights Reserved