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Rust powder formation in powder coated panels

Hello all,

We are facing a typical problem of rust dust (powder form) formation in some of our components that we export. We are located in southern part of India, 30 km distance from Sea port. We make our components basically steel panels from CRCA sheets. After several stages of punching, bending and spot welding, the panels are alkaline degreased and Hot Iron phosphating done by spray treatment on conveyor.
Then the panels are dried in dry off oven by hot air circulation before getting powder coated and cured.
The panels are packed using corrugated cartons with Non-virgin kraft paper as interleaving between panels.

But our customer says that he is getting lot of rust powder falling from enclosed parts where only spray had gone in but not the powder.

Please help me sort this out.

Kadhiravan K
Employee - Chennai, India
2007

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Hello, Kadhiravan. You have described the situation in sufficient detail that I think you know what the problem is :-)

If areas of the part do not have powder coverage, but only iron phosphate, they are going to rust. If the powder coating can be improved so that everything is covered, the problem is probably solved. If the geometry of the part is complex, with spot weld seams or crimp lines, or hollow tube areas, such that you will never get full coverage -- then you probably need to electrocoat prime the parts before powder coating. Maybe other readers have ideas for you.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

We are facing problem of rust inside the tubes & piped when powder coated finally used to make Lamps. Appreciate your suggestions to overcome this problem. Thanks.

Harish Jakhar
Buyer - India
May 20, 2009

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May 20, 2009

Hi, Harish. People are probably willing to help you. But there is no way to summarize the subjects of pretreatment and powder coating short of book length, so until you tell us of your procedures, all we can do is recommend Werner Rausch's "Phosphating of Metals" ⇦[this on Amazon or AbeBooks affil links]and Bob Utech's Guide to High Performance Powder Coating [on Amazon affil links].

If you can tell us the diameter of the tubes, whether they go through an immersion or spray phosphate process, whether it's iron phosphate or zinc phosphate, and so on, people may be able to start offering some hints to deal with the rusting issue. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey