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...
Identifying and Correcting Problems in Blown Film
Coextrusion to Reduce Scrap and DowntimeAuthored by:
Dr. Karen XiaoExtrusion Development MgrBrampton Engineering
Common issuesCommon issues
Haze linesMelt stabilityGelsInterfacial instabilityPoor gauge
Contributing Factors Contributing Factors ---- Haze LinesHaze Lines
Processing temperaturesTemperature gradientScrew and barrel conditionsDie design
Considerations: Melt stabilityConsiderations: Melt stability
Resin selectionsExtruder sizingScrew design – Good melt temperature controlProduct layflat and blowup ratios
GelsGels
Identify type of gels (degraded or unmelts)Which layer(s) exhibit gels?Resin contaminationScrew and die design
Gels Gels -- UnmeltsUnmelts
Resin sourcesProcessing temperaturesResin blend compatibilityScrew design
Gels Gels -- Degraded GelsDegraded Gels
Resin contaminationProcessing temperaturesScrew and barrel conditions
Interfacial instabilityInterfacial instability
Zig-zag – viscosity mismatch
Interfacial instabilityInterfacial instability
Wave type – elongational viscosity differences between layers
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
Poor GaugePoor Gauge
Temperatures and outputsScrew and barrel conditionsDie designIBC and air ring design and conditionsLocal ambient temperatureHardware failure (Heater bands, T/C’s)
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
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
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
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
Action:ResultsAction:Results
Increase output of specific layer
Better gauge uniformityFaster changeover timesReduced downtime – less cleaning time
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
Information RequiredInformation Required
Resin informationProcess conditions: output and temperaturesMelt temperature measurements
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
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
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
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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Thank you
PRESENTED BY
Jim StobieVP - SalesBrampton [email protected]