Shrinkage

The reduction in the dimensions of a plastic part compared with the mold dimensions.

Shrinkage occurs as the polymer cools and can vary in different directions.

Crystalline and semi-crystalline materials are particularly prone to thermal shrinkage; amorphous materials tend to shrink less. Excessive shrinkage can be caused by:

• Low injection pressure
• Short pack-hold time or cooling time
• High melt temperature
• High mold temperature
• Low holding pressure