Metal finishing Q&As since 1989

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Contaminated Aluminum Powder Coated Parts

2003

We are Nitrogen Laser cutting large panels (2' sq. up to 4' sq) from .080 #5052-H32 aluminum. We then da sand the dross off, form them, or whatever else is needed to complete the part and then powder coat with a high (90+) gloss white TGIC powder.

We are running them through a five stage washer; alkaline wash, rinse, iron phosphate, rinse, seal.
We are having a problem with small specs in the finish.
When looking at these under a magnifying glass in some cases they look like small fibers, and other specs appear to be metal slivers or metal specs of some sort.
We also produce many of the same parts from mild steel and coat with the same powder where the problem is much less to almost non existent.
Is there something with aluminum that because the conductivity is different than steel we could be creating some type of static charge that is attracting dirt?
Does anyone else have a similar problem or suggestions?

William Hentz
- Oshkosh, Wisconsin, USA

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Is your iron phosphate bath compatible with aluminum?
Hydrogen Fluoride additives are usually required for a line processing both aluminum and mild steel. You may want to check with your chemical supplier. The "fibers" on your finish may be some sort of phosphate crystal deposited on the aluminum, but this is about where my experience runs dry.

James Hanley
- Redmond, WA USA
2003