Bubbles/fisheyes in Powdercoating?

A. Hi,

This "out gassing" occurs on aluminum castings - to overcome this ask your coater to pre-heat a few samples of your item and whilst still warm apply the powder. Check this against normal production.

-- OR --

The simple answer is to use an anti-gassing powder. This is a standard powder plus an additive to the powder by the mfgr. or the powder applicator -- this slows down the cure of the powder thus allowing the gases to escape before final cure.

A. Mike,

The "bubbles" could be out gassing and the "fish eyes" could be contamination. (It's hard to say without seeing the defects). Either way it is not a viable excuse from the sprayer. There are ways of over coming these defects which are quite basic in the powder coating industry. If you paid for a good finish you should get one and if your workpeice has defects the sprayer should recoat it. Again take no excuse, suggest that he pre-heats the part to overcome the out-gassing and suggest that he cleans the part correctly before coating.

Hope this Helps

A. Fisheyes are usually airborne or air supply contaminates, they are the coaters problem. Parts with fisheyes are usually reworked before the customer is called to pick up the parts to save face(reputation). If "the shop" didn't tell you about, or attempt to fix, the fisheye or outgassing problems before you got there, find another reputable coater and try again. This time, tell them that you want a blemish free finish. Take a tour and look at some of the products that they are currently working on, and expect the same quality. Also expect to pay extra if the parts have to be outgassed prior to the painting. They will basically have to run them through two cure cycles (the first one at a higher temp and longer oven time than the second).

Good Luck.

A. These fisheyes can come from the release agents sometimes used in the foundry. Try each of these suggestions with one piece first. If your product is heavy or larger, perhaps your product needs to be put through a slower pace in the wash system so that the temperature of the wash can assist in cleaning the product properly. Changing to a good alkaline cleaner will help you. Try increasing your concentration of the cleaner/s as well. Then I would preheat the product to off-gas any remaining areas. Lastly, if you need, apply the topcoat over a heated product. Applying the powder over a heated product should only be used if necessary, because the surface will be non uniform in coverage and you will use more powder than is typically necessary.

Bob Utech Benson, Minnesota

Ed. note: Bob is the author of: "High Performance powder Coating" on eBay or AbeBooks or Amazon [affil links]

A. Hi. Since the parts are old and you never suffer this sort of problem despite your similar experiences, I guess I'd tend to doubt "outgassing", although you could try preheating the parts before powder coating. I fear that the customer decided to try a silicone product on them at some point -- silicone causes horrible fisheyes and is virtually impossible to remove. I'd probably try an epoxy undercoat before a final liquid paint.

Regards,

A photo would be very helpful in identifying the fault.
Regards,
Bill

Thanks very much for your responses.

In this case we resolved the issue: keen to get the job done we threw a Hail Mary pass and put the offending parts in the methylene chloride overnight, on the basis that this acts as a degreaser as well as a paint stripper. We gave it a good wash, another light blast and put it in the oven to outgas any residue. Note that after blasting we checked again and the metal was *very* porous.

We pre-heated the part, and this time the etching and coating went on just lovely and stayed that way. Old corroded items are unlikely to have a perfect finish, for our customer we know the result is what they are after. All is well.

Thanks again!

A. Your process is totally out of control.
You need to get an experienced professional in asap.
Hope this helps.
Regards,
Bill