The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Clear Iriditing "burn off"

2005

Hi. I am an OEM that receives my powder-coated aluminum chassis from metal fabricators. In my research into complying with RoHS and the elimination of hexavalent chromium, I have one supplier that told me something I would like to qualify. My belief was that the purpose of the clear Iriditing was not only to prepare the surface to be powder-coated but to also protect the areas not to be powder coated against corrosion (masked off areas).

My supplier tells me that the protective coating from hexavalent chromium "burns-off" at 140 degrees F. Since the powder coating process is 300 F, the protective coating is essentially burned-off in the process. Can someone qualify or contradict this statement.

This supplier is using "Picklex® [affil links]" as the alternative prep.

Thanks,

Mike Demos
- South Carolina

---

2005

Chemical Conversion Coatings will loose a huge percentage of their corrosion protection abilities if heated to over 140 degrees F, but it has always been my understanding that this was due to dehydration of the chromate film rather than any significant chemical change in the coating.

I'm not a chemist, but I'd be very surprised to find out that hex-chrome can be burnt off at temperatures as low as 300 F, and if I were you I certainly wouldn't certify it as being hex-free without a lot more information and/or independent testing.

Jim Gorsich
Compton, California, USA