Air and moisture trapped in cast aluminum, sand castings, hot-dip galvanizing, welds and some extrusions expand as the part heats and push up through the melting powder. If the film gels first the gas leaves pinholes, bubbles or volcano craters. Remedies are pre-baking, coating parts warm, using degassing-additive powders, slowing the ramp and keeping film build down.
Every casting is pinholed, that's outgassing, they need a pre-bake before the booth.
Thicker film rarely buries outgassing pinholes; it usually makes them bigger.
Also heard as
- gassing
- out-gassing
Related terms
Pre-bake
Heating a casting or galvanized part before coating to drive out trapped gas that would blow holes in the film.
Gassy
Describing a casting, galvanized part or batch of metal known to outgas and ruin the finish.
Pinhole
A tiny hole running through the cured film, often down to bare metal.
Hot flocking
Spraying powder onto a part that is already hot, so the powder melts on contact and builds a thick film.