High temperature resistance of zinc plating

A. You will get some accelerated oxidation which will dull the appearance of the finish, but I doubt if you will have a serious affect on galvanizing. On electroplate, it could be a significant factor if it was thin. Yes, you can thermal spray zinc. It is not a cheap initial setup and tends to be as rough as some galvanizing. It also will require breathing protection for the operator and a very good exhaust system to protect other people in your plant. Vaporized zinc causes a significant heavy metal poisoning.

A. Mr Vansidhar,

If the parts are not exposed to flame the zinc plate may stay unaffected. An oven at 220 °C for 20 plus hours is what we know Zinc survives. That is indirect heat.

240 °C needs to be tried on plated zinc to see if the kind of plating and the co-deposits can actually tolerate this treatment, as co-deposits of PLATING BATH impurities can cause all sorts of side effects under high temp conditions. Alkaline Cyanide-Free zinc over steel has withstood 20 Hrs AT 220 °C. No harm in trying out one trial lot for actuals.

A. About your concern on the protection afforded by sprayed zinc, its porous nature will not be a significant factor because zinc protects steel anodically, not by isolation from environment.

A. Hi Lindsey. Asif talked about 220 and 240 °C. So let's write that as 428 and 464 °F so we're on the same frequency, and you can see that your temperatures are very high.

Further, the zinc itself is not black of course; the black color comes from the chromate conversion coating, which is more sensitive to temperature, and may be either a silver-based or non-silver process. I guess I'd say that this is just not the high temperature coating that you require. Perhaps a high temperature black paint would be a better choice, or maybe black nickel plating or black chromium plating? Or do the plating, then the baking, then the chromate. Good luck.

Regards,

A. Hi Mike. I don't think that the application method for the zinc plating is the critical issue, but rather the temperature resistance of the chromate conversion coatings. Chromate conversion coatings are hydrated gels, so they are not particularly compatible with high temperatures. I believe that the guidelines are not to exceed 140 °F for the first 24 hours. After that they should be able to withstand powder coating curing temperature and time. But this talk of 450 - 500 °F applications strikes me as probably the wrong coating for the job.

But contact Plating Systems and Technologies [a finishing.com supporting advertiser] who are the accepted experts in mechanical plating.

Regards,

A. Hi Christine. We appended your inquiry to a thread which may help answer it for you. Between it and letter 2034 on the same subject, you should have some very good conjectures. Good luck.

Regards,

A. Hi Tiffany. I don't think you're on quite the right track. Baking parts with 8 microns of plating at approximately 400 °F is routine and should not cause "issues" -- but you haven't told us yet what the issues are :-)

I would suspect an excess of brighteners, etc., to be a likely cause of issues. Tell us more please.

Regards,