Craters in the Paint

Q. We have started having problems with craters in the paint film on the motorcycle parts we manufacture. This problem is very peculiar because it seems to come and go. For example, when we start up the line at 8 a.m. the paint film is OK, but by 9 a.m. the crater problem suddenly begins occurring. We often have the problem until 5 p.m., when the paint film becomes OK again. The next day the problem might start and end at different times, and its duration also changes from day to day. I can’t find a core reason for the crater problem. Do you have any suggestions? F.H.

A. The problem you describe generally is caused by contaminants falling on the surface of the parts to be painted. These contaminants are often present in shop air and drawn into a paint spray booth along with make-up air. To solve this problem, you must isolate the contamination source or the painting operation.

A typical contaminant is silicone, both liquid and solid, which could be coming from an operation elsewhere in your shop. From what you described, perhaps you are having the problem shortly after an unknown contaminating operation starts and the problem goes away after that contaminating operation stops. Furthermore, this problem started recently, perhaps after the addition of a new operation or use of a new material in your factory? These contaminants have been known to travel hundreds of feet in shop air from one area to another.

Your part surfaces also could be getting contaminated by passing near a contaminant-producing operation while being transported from another area in your factory to the painting area.

Try the following steps:

1) Identify the contaminant by a chemical analysis. It is usually present in the center of the crater.

2) Find the contamination source.

3) Isolate the contaminant or isolate the paint spray booth.