Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2004

Out Gassing on Cast Iron

Q. I work for a cast iron table leg manufaturer that has just started to drycoat there own part. We use a automated booth with oven, chemclean etc. Most of our parts are running good accept our round castings. After they have been through the cure stage we have noticed bubbling and pin holes in our finish. We think it maybe outgassing but not for sure. Can you give me any suggestions to fix this problem? We are using a black wrinkle dry coat paint. My cure time is around 30 to 45 min. I have tried to adjust amount of paint and the line speed (which changes my cure time more or less). Please email me also so I will not miss your advise. Thank you for your time.

A. Metal and alloy castings are prone to out gassing due mostly to the porosity of the casting which entraps residue from cleaning solutions and air. Usually the quick fix is to preheat the casting which drives out the air and cleaning residue.

If you can prebake the casting for 15 to 20 minutes, then apply the coating. This should correct the problem. Another fix for out gassing is to contact your dry coat or powder coat vendor, they have improved some coating technologies that eliminate the bubble caused by out gassing on cast metal.

Best regards,

Tom Burke