Sink Mark

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
Sink Mark in Plastic Industry

Injection Molding Error (Image 1): The wing on this piece shows a sink mark.
Injection Molding Error (Image 2): Sink marks due to low packing pressure.

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