Identifying and Correcting Problems in Blown Film ... · Die Design Screw Design Air Ring & IBC...
Transcript of Identifying and Correcting Problems in Blown Film ... · Die Design Screw Design Air Ring & IBC...
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Identifying and Correcting Problems in Blown Film
Coextrusion to Reduce Scrap and DowntimeAuthored by:
Dr. Karen XiaoExtrusion Development MgrBrampton Engineering
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Common issuesCommon issues
Haze linesMelt stabilityGelsInterfacial instabilityPoor gauge
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Contributing Factors Contributing Factors ---- Haze LinesHaze Lines
Processing temperaturesTemperature gradientScrew and barrel conditionsDie design
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Considerations: Melt stabilityConsiderations: Melt stability
Resin selectionsExtruder sizingScrew design – Good melt temperature controlProduct layflat and blowup ratios
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GelsGels
Identify type of gels (degraded or unmelts)Which layer(s) exhibit gels?Resin contaminationScrew and die design
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Gels Gels -- UnmeltsUnmelts
Resin sourcesProcessing temperaturesResin blend compatibilityScrew design
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Gels Gels -- Degraded GelsDegraded Gels
Resin contaminationProcessing temperaturesScrew and barrel conditions
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Interfacial instabilityInterfacial instability
Zig-zag – viscosity mismatch
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Interfacial instabilityInterfacial instability
Wave type – elongational viscosity differences between layers
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Interface instabilityInterface instability
Identify the interface problem –possibly more than one locationChange only one parameter in one layer at a timeLook for layer percentage change and a temperature changeCan be minimized with proper resin selections and die design
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Poor GaugePoor Gauge
Temperatures and outputsScrew and barrel conditionsDie designIBC and air ring design and conditionsLocal ambient temperatureHardware failure (Heater bands, T/C’s)
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Case Study: 7 layer blown film lineCase Study: 7 layer blown film line
Stacked pancake die – inner layer at bottom of stack, outer layer at top of stackTrouble free operation for a few yearsRoutine die cleaningSudden appearance of carbon buildup on die, poor gauge – all after die cleaning
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Information RequiredInformation Required
Recipe change? New structures?What materials in each layer?Layer percentage, outputProcessing temperatures of each layer
- setpoints and actuals if availableScrew RPM of each layerSignificant events –e.g. power outage, extruder failure
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Assessment/EvaluationAssessment/Evaluation
Calculate shear rates and shear stresses- material flow, potential degradation location- premature hardware failure, e.g. screw and barrel wear or heater band failure
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Problem identifiedProblem identified
New recipeOutput rate calculations
Output in one layer too lowShear rates 4-6sec –1
Residence time for that layer too longCarbon build up Change in flow behaviour
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Action:ResultsAction:Results
Increase output of specific layer
Better gauge uniformityFaster changeover timesReduced downtime – less cleaning time
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Case Study: 3Case Study: 3--layer Blown Film Linelayer Blown Film Line
Spiral mandrel die – 3-layerStarting gauge was too high at 12%, 2-sigmaGauge profile shows porting effect
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Information RequiredInformation Required
Resin informationProcess conditions: output and temperaturesMelt temperature measurements
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Assessment/EvaluationAssessment/Evaluation
To make sure that the die is operating under optimal conditions: check output rates and melt temperaturesMake sure that the temperatures are set up properly from the extruders to the die
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Problem identifiedProblem identified
The die temperature setting was too low Caused a differential temperature difference in the melt stream in the diePorting effect was caused which adversely affected gauge
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Action:ResultsAction:Results
Match the die temperature setpoint to melt temperatures coming off the extruders
Improved gauge uniformity from 12% to 7%, 2-sigmaMinimized porting effect
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Common issues in coextrusionCommon issues in coextrusion
Processing Temperatures
Screw and Barrel
ConditionsResin
Selection Die
DesignScrew Design
Air Ring & IBC
ConditionsGels X X X X X Unmelts X X X Gauge X X X X Interfacial Instability X X X
Haze Lines X X X X X
Melt Stability X X X X
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Please remember to turn in your evaluation sheet...
Thank you
PRESENTED BY
Jim StobieVP - SalesBrampton [email protected]