Topic: Zinc gasing thru powder coating.

We have zinc plated parts then sent to powder coat, the powder coaters keep saying that the zinc is gassing causing eyes in powder. We have used three different coaters but problem seems to be different with each. We have ran sample pieces no problem, one problem none of the coaters have ran the parts the same thru their processes. One even says if they are plated no need to clean parts, told them they are wrong. We use alkaline zinc, with yellow chromate, never have had a problem before with powder. We have let the parts cure over three days and even heated some of the parts to help if they are gassing. Any suggestions that might help on my end to eliminate problem from plating end. The samples we have ran has been done with hex-yellow, hex-black, and tri-clear, they all passed which makes me believe the coaters are doing something wrong, but Im not an expert in powder.


Re: Zinc gasing thru powder coating.

Have you tried parts without the conversion coating? The chromate conversion coatings are gelatinous and contain small amounts of water, which could be evaporating while curing in the oven. You might also try sending some parts through the curing oven without any powder as a way to de-gas the parts. Have you tried running any non-plated parts? Or tried using a phosphate coating instead?

-Dustin Gebhardt, CEF

Advanced Manufacturing/Finishing Engineer


Sanford, NC


Re: Zinc gasing thru powder coating.

yes we have sent some with no chromate on them waiting for results. The non plated parts we fine. But what we cant get past is all the samples we have ran pass. I didnt mention these parts have been stripped at least 3 times with blasting media. The first reject was because of masked area masking was removed. My guess is all the blasting is having sum effect on the final appearance. Also the coaters all prep the parts different. Another issue is there is 4 parts to this cabinet, only to smaller parts are having the issue 2 biggier parts look good.


Re: Zinc gasing thru powder coating.

"We have zinc plated parts then sent to powder coat." De-gas first, then plate, then p-coat.

Out gas of zinc parts when P-Coating is not that unusual me thinks. Let me say this a couple of ways. I'm thinking Ertl Toy

After wash, either dry at a temperature about 100 deg F higher then the cure oven temperature used for the powder coat cure when a batch oven set-up is used.

One batch oven. Two batch's. Two temperatures.

Substrate must be raised to a hotter temp clean through. Then coated and cured at a lower temp. Might include a function of time. Don't p-coat hot unless your looking for mil build.

If a conveyorized combination oven is used. I don't like to do that because of the moisture in the Dry-Off Oven if exhaust to atmosphere is minimized, may be high and effect the p-coat. The zinc needs to see the heat twice. First cycle high, second cycle lower temperature.

Once hot but un coated to drive the trapped gas out. Cool.

Then p-coat and run a second time for cure at a cooler temperature so any gas still within the zinc work remains at a low pressure at a lower temperature and stays trapped in the metal.

Not popping through the castings and destroying the finish.

That's the simple answer.

Blasting has nothing to do with gassing. Stripping has nothing to do with gassing, but will effect adhesion. But that is another discipline requiring a test. Scratch-pull. Salt spray or ???


Last edited by skip (02/01/2010 - 02:56 PM)

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