Troubleshooting Guide PS Injection moulding Splay marks Trapped air that contains moisture Raise nozzle and front zone temperature. Cool feed zone. Wet feed Dry material, check source of moisture. Irregular or high injection speed Reduce injection pressure. Inadequate venting of mold Increase injection time. Required shot too large for machine Increase barrel temperature. Mold too cold Raise mold temperature. Burning (Black streaks) Trapped air Increase stock temperature. High injection speed Decrease injection pressure. Excessive heat Check and calibrate heaters.
Contamination from other polymers Check source of contamination. High level or wrong type of mold release agent Use small amount or change type. Sink marks Thick section, e.g., ribs and bosses Increase injection pressure, plunger forward time and shot weight. Unbalanced flow pattern Increase gating, increase shot weight, heat nozzle. High mold temperature Reduce mold temperature. Increase cooling capacity of mold. Material too hot or too cold Adjust cylinder temperature. Insufficient dwell time. Increase dwell time. Moisture content of material too high Check moisture level. Pre-dry material. Brittle weld line Inadequate heat Increase cylinder and mold temperature. Increase injection pressure.
Trapped air Increase venting, reduce injection pressure. High level or wrong type of mold release agent Use smaller amount or change type. Inadequate flow Increase cylinder temperature. Poor surface finish Polymer too cold Increase cylinder and mold temperature. Increase cushion. High injection speed Decrease injection rate. Inadequate flow Increase cylinder and mold temperature. Contaminated feed Check feed for foreign material. Pigment agglomerates Increase screw back pressure. Oil or grease on knockout pins Wipe mold surface. Warping
Article removed from mold before adequately cooled Increase mold closed time or increase cooling to the mold. Unbalanced gates on multiple-gated part Increase cylinder temperature. Too many stresses on the article Increase cylinder heat and decrease injection pressure. Non-uniform wall thickness Check mold alignment and redesign components to gently blend any changes in section. Part sticking in mold Packing mold Reduce speed, injection pressure, cylinder temperature or plunger forward time. Undercuts in mold Reduce mold temperature. Polish out undercuts in cavity. Vacuum under large surface area part Increase vent or add air ejection on punch. Interrupting of cycle Reduce injection pressure, take air shot. Poor mold finish Correct knockout design. Use mold-release agent. Repair any damaged surface. Cycle time too short Increase cycle time.
Flash Excessive pressure Reduce injection pressure. Maintain operator rhythm. Excessive temperature Calibrate heaters, reduce temp., maintain operator rhythm. Inadequate clamp Increase clamp pressure, lower cylinder temperature. Part surface area too large for machine Move mold to large capacity press, lower cylinder temperature. Mold misalignment Realign mold or repair mating surface. Injection speed too fast Reduce injection speed. Brittleness Packing the mold Reduce feed and injection pressure. Increase mold close time. Lamination in part Increase mold temperature, reduce mold release, check material. Contamination feed Check feed supply.
Polymer temperature too cold Increase cylinder and/or mold temperature. Mold too hot/cold Adjust mold temperature. Excessive use of regrind Reduce percentage of regrind. Short shots Insufficient pressure Increase polymer and/or mold temperature and/or injection pressure. Inadequate feed Adjust shot weight. Bridging of feed on screw Reduce rear zone temperature. Increase forward zone temperature. Injection speed too low Increase injection speed slightly. Injection time too short Increase injection time.