Summary for chromate based paints Discussion
Chromate based paints versus surface treatments is clarified by the responders as a distinction between different coating technologies, not interchangeable terms. Michael Grant asked whether industry standards define a treatment versus a paint, and whether chromate-based treatments and chromate-based paints could be considered the same, including primers. Brian Terry said chromate conversion processes and paint primers should not be treated as the same or equivalent, noting that conversion coatings are often used as a key for paint and that a chromated primer is typically the next layer in aerospace and defense work. Daniel Montañés added that chromate post-treatments are conversion coatings over metals such as zinc, zinc-nickel, zinc-iron, or tin, while chromate-based primers are paints: the first coating layer that provides corrosion resistance before topcoats are applied. The thread points readers to finishing handbooks for further reference.
Q. Are there industry standard definitions that specifically define what is a treatment compared to what is a paint. Is there a distinct difference in the definition between chromate based treatments versus chromate based paints. Could it be argued that they are one in the same.
Are Primers considered paints or treatment?
Michael Grant
– Australia, Eden NSW
August 14, 2012
A. Hi Michael,
I don’t think that you ever consider chromate conversion processes and paint primers as the same, interchangeable or even equivalent. These coatings are different on so many levels.
Often you will find conversion coatings called up as a key for paint. The typical next coating would be a chromated primer (for Defence and Aerospace anyway).
I don’t think you will find specific texts that will tell you that the two processes are not equivalent, probably because the technologies are so very different.
If you want a few references then look in the books section on this site, but maybe as a start you can look at the Metal Finishing Guidebook, The Organic Finishing Guidebook, Electroplater’s Engineering Handbook, Canning Handbook just to mention a few to get you going.
Brian Terry
Aerospace – Yeovil, Somerset, UK
First of two simultaneous responses — August 16, 2012
A. Dear Michael,
There are chromate post treatments (as chromate conversion coatings over zinc, zinc-nickel, zinc-iron, tin or other metals that can be passivated) that are complementary to electrolytic (or, in some cases, hot dip) surface treatments.
And, there are chromate based paints. Chromate based primers are paints, it is the first layer of coating you must apply, and it is the layer that gives corrosion resistance. Over the primer you apply one or more layers of different paints or topcoats.
Hope this distinction can reply your inquiry! Regards,
Daniel Montañés
Self-Drilling Fasteners Manufacturer – Cañuelas, Buenos Aires, Argentina
Second of two simultaneous responses — August 16, 2012