Multiflex Thermoplastic Elastomers Trouble Shooting Guide Injection molding Extrusion Overmolding M a t e r i a l s t o w i n
TROUBLE-SHOOTING GUIDE - INJECTION MOULDING Incomplete fill Air entrapment Check for obstruction of vents Check vent locations Enlarge vents Change filling behaviour by adjusting injection rate and/or pressure Runner system Melt and/or mould too cold Shot weight Enlarge gate Enlarge runners Check for obstruction of gate Increase barrel and nozzle temperature Increase mould temperature Increase injection rate Increase screw speed Increase shot weight Increase melt cushion
TROUBLE-SHOOTING GUIDE - INJECTION MOULDING Sink marks Hold pressure too low Increase hold pressure Melt and mould too hot Reduce barrel and nozzle temperatures Reduce screw speed Burning Melt and mould too hot Reduce barrel and nozzle temperatures Reduce screw speed Mould design Enlarge vents Check for obstruction of vents Check vent locations Odour or yellowing Melt and mould too hot Reduce barrel and nozzle temperatures Reduce screw speed and injection rate
TROUBLE-SHOOTING GUIDE - INJECTION MOULDING Flashing Injection pressure/rate high Reduce injection pressure and rate Increase mould clamp pressure Melt and mould too hot Reduce barrel and nozzle temperatures Reduce screw speed Part distortion Too much orientation Increase melt and mould temperature Reduce injection rate Part is over-packed Uneven mould fill Reduce back pressure Change gate location Ensure uniform mould temperature Black specks Contamination Purge with PP Ensure colour MB is not based on PVC
TROUBLE-SHOOTING GUIDE - INJECTION MOULDING Sticking in mould Part is too hot Reduce barrel and nozzle temperature Increase cooling time Part is over-packed Mould design Reduce shot wt & find correct fill point Increase draft angles Clump formation at gate Moisture Dry pellets Flow lines Melt and/or mould too cold Increase barrel and nozzle temperature Increase mould temperature Increase injection rate Increase screw speed & back pressure Mould design Enlarge gates & runners Change gate location
TROUBLE-SHOOTING GUIDE - OVERMOULDING Poor or no adhesion Processing temperatures low Increase processing temperatures Mould temperatures low Hold pressure too high Injection rate too low Use of lubricants TRANSFER PROCESS Semi-finished part is not free of grease and dust Increase mould temperatures Reduce hold pressure Increase injection rate Do not use lubricants Clean semi finished part Semi-finished part is too cold Pre-heat part. Heat surface to only 80-100C. The preheating process should last a very short while; very important if the substrate material is semi-crystalline
TROUBLE-SHOOTING GUIDE - EXTRUSION Rough extrudate Melt too cold Increase extruder temperature Increase die temperature Inhomogeneous melt / undispersed particles Poor die design Use screw with higher compression ratio or with mixing zone Reduce land length Uneven cross section Surging Reduce throughput Use screw with longer metering section Black specks Contamination Purge with PP Increase back pressure by using a more restrictive screen pack Reduce die temperature Ensure colour MB is not based on PVC
Use screw with lower compression ratio TROUBLE-SHOOTING GUIDE - EXTRUSION Odour or yellowing Melt too hot Reduce barrel temperature Reduce die temperature Reduce screw speed Reduce back pressure Voids / porosity Moisture Dry pellets High pressure & low Melt too cold Increase extruder temperature output Increase die temperature Obstructed screens Clean or replace screens