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Bowing of thin aluminum roll formed parts during the e-coat process before the ovens

I have just started working for a company in their quality department. I have been around powder coating before but not e-coat. The company has started having a quality problem with a thin roll formed part that is bowing after the e-coat dip process (before the ovens). The part is aluminum and about an inch in with. It's about 16" to 18" long. There is a steel wire of less than an 1/16th of an inch inserted on one side during the roll forming.

I'm seeing some bowing from the roll forming, however, we have sent very straight parts through and they come out bowed across the length of the part. We thought that the heat in the ovens may have caused the problem, but we hung parts right before the ovens and they came out straight. We sent the same parts through and found them to be bowed before the ovens.

Please help with any suggestions.

Martin Wright
quality employee with a comphe uses e-coat - Greenville, North Carolina, USA
April 2, 2008

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April 20, 2008

This is a wild guess on my part, but is it possible that the current from the e-coat process is preferentially moving through one metal, causing it to heat up more than the other, and resulting in a different thermal expansion? My first guess would be differences in thermal expansion coefficients, but your oven test points to something else.

Have you measured the paint thickness on the parts to see if you're getting even coating? E-coat is supposed to be one of those self-limiting processes, but if you're getting a lot more paint in one area than another, that may point to some current issues (which may lead to the phenomena I described above).

Using two dissimilar metals is generally a bad, bad idea anytime corrosion protection is involved....but I realize that there are trade-offs that must be made sometimes.....

Christian Restifo
- Pittsburgh, Pennsylvania