Contaminants such as silicone, oil from compressed air, lubricant overspray, hand cream or an incompatible powder speck stop the melt from wetting that spot, so the film pulls back into a bowl with a raised rim, sometimes with a dot in the center. Craters usually appear across many parts at once and point to a contamination source in the plant or the air supply.
Craters on every part since Tuesday, somebody's using a silicone spray near the booth.
Silicone sprays, some mold releases and certain hand creams are banned in many finishing departments because one drop can crater a whole shift.
Also heard as
- fisheye
- cratering
Related terms
Cross-contamination
Specks of a different color or chemistry carried into a powder run from equipment, air or reclaim.
Blow-off
Blasts of compressed air used to clear water from pockets or dust from parts before they are coated.
Water-break test
Quick cleanliness check: a clean surface holds an unbroken sheet of water, an oily one makes it bead and split.
Pinhole
A tiny hole running through the cured film, often down to bare metal.