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Q&As since 1989


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Prepping alum for powder coating

We have changed over to powder coating but have a hard time keeping the powder sticking if we do not clean with Laqor thinner. We are pushing to get the thinnner out of the plant. 99% of what we coat is alum. either bent, machined, or cast. is there a fast cheap solution. Or something that can be added to make our transition easier?
thanks,

Martin Baker
PROCESS ENGINEER - Sweetwater, Texas
2007

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The good news is that solvent cleaning was never the right approach in the first place, so you shouldn't miss it, Martin :-)

Solvent cleaning removes grease and some soils but it does not pretreat aluminum, as should be done. The aluminum should ideally be chromate conversion coated. This process is more easily applied to a large quantity of small parts than a small quantity of large parts, but can be done either way. These days there are hex-chrome free and totally chrome free conversion coating processes.

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

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Martin, you don't give much information to go on. I assume you are not using anything more than lacquer thinner [on eBay or Amazon] to clean your substrate (aluminum). This is fine if you're using an oil based liquid topcoat (I.E. Xylene [on eBay or Amazon], toluene, mineral spirits [on eBay or Amazon] , etc.), because the oil based topcoat will adhere to the same base as is a lacquer thinner . Thus, one of the problems is that lacquer thinner is that it is oil based and can leave residuals on your substrate. You would be better off using isopropyl alcohol [on eBay or Amazon] which is oil free. I think really you should use the proper method which would be using either acids or mild alkaline cleaners and a good rinse. Both will give your substrate an acceptable surface profile in which the powder can stick to. Generally speaking, aluminum will not accept a phosphate coating, but usually there is some transfer of the coating and some chemical companies now offer products that will make their product coat onto aluminum.

Bob Utech
Benson, Minnesota
2007