In areas with thick walls and across from ribs, a hollow at the surface might appear.
Sometimes a difference in the gloss to the surrounding surface might be noticed only.
Mass accumulation leads to a higher volumetric shrinkage, which is insufficiently reached by packing pressure.
The surface is pulled to the inside during cooling and a sink mark appears.
Small wall thickness and higher packing pressure in the critical area reduce the risk of sink marks.

Sink Mark in Plastic Industry

Injection Molding Error: The wing on this piece shows a sink mark.

Sink Mark in Plastic Industry

Injection Molding Error: Sink marks due to low packing pressure.

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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
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