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Dimensional Variations

Dimensional Variations
Possible Cause Suggested Remedy
Non-uniform feeding of material a. Adjust temperature profile for optimum feeding
b. Increase shot size to maintain uniform cushion
c. Replace check valve if cushion cannot be held
Large variation in cylinder temperature due to inadequate or defective controllers Replace or calibrate controllers
Unbalanced runner system, resulting in non-uniform cavity pressure a. Increase holding pressure to maximum
b. Increase injection rate
c. Balance/increase runner and gate sizes to provide uniform filling
Insufficient packing of part Increase injection forward time and/or pressure to ensure gate “freeze off”
Regrind not uniformly mixed with virgin a. Review regrind blending procedure
b. Decrease percentage of regrind
Moulding conditions varied from previous run Check moulding records to ensure duplication of process conditions
Part distortion upon ejection See Part Sticking in Mould