← Defect Guide
Sink Mark
Concave depressions on the surface of thick sections, caused by internal shrinkage during cooling.
◆ Common Causes
- •Insufficient hold pressure
- •Insufficient hold time
- •Insufficient cooling time
- •Small gate size (premature gate freeze)
- •Uneven wall thickness
◆ Solutions
- ✓Increase hold pressure
- ✓Increase hold time
- ✓Increase cooling time
- ✓Enlarge gate size
- ✓Design change (uniform wall thickness)
◆ Resin-Specific Notes
PA
High shrinkage rate. Sufficient hold pressure required.
POM
Very high shrinkage (2–3%). Critical hold pressure management.
PP
High shrinkage (1.5–2%). Allow sufficient cooling.
PC
Low shrinkage. Sink marks relatively rare.
PBT
Shrinkage reduced with GF reinforcement.
◆ Resins Prone to This Defect
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This content is a field-reference summary. Final judgment requires on-site engineer verification.