Reasons for sink marks:
1. Shrinkage:
Sink marks usually appear in places on the part where various wall thicknesses are placed. For example ribs or other reinforcing geometries may then cause this defect. Likewise on very high wall thicknesses such a phenomenon occurs as well. The reason for this is the shrinkage behavior of the plastic.
To counteract this so-called “feeders” should be used which top up material into the mold. In addition this creates a slight casting pressure which counteracts the shrinkage. The feeders should have approximately the same diameter as the wall thickness of the component at this point.
2. Release agent:
Release agents can also cause sink marks. In the case of a release agent with a very good release effect it may happen that the component is already detached from the mold wall during curing in some places. At these spots the material can then freely disappear which leads to sink marks. We are happy to advise you on a suitable release Agent.