Stripping plastisol from plating racks

"Controlled Pyrolysis"
Burn-off Ovens

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A. Hi Katie.

I think these folks are talking about burning it in an enclosed oven with an exhaust stack such that people in the factory are not exposed to the fumes. I worked for a plating equipment manufacturer in the 1970's who did plastisol coating and then used this process to remove it when the time came. However, times change ...

I'd be pretty confident that the air quality regulators will not accept this today without "controlled pyrolysis" burn-off ovens which use afterburners to destroy the volatile organics. I don't know if PVC products are okay in such ovens or not.

I think the best way to remove plastisol these days is probably by immersion in liquid nitrogen. Such freezers are widely used in the food industry but I haven't personally seen the equipment and don't know what mods, if any, are needed to employ them as plastisol stripping machines; but there are a number of European manufacturers who employ the approach to strip plastisol. Google "remove plastisol with liquid nitrogen" for a quick review, then if your studies reveal any details, please come back and fill us in.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi, Francisco. Please tell us what you presently do and any issues you have with that method? We find that when posters present their situation and findings they usually get a good response -- probably because readers can learn something from it; whereas when abstract questions are posed, few readers are interested enough to try to help. Thanks!

A. Nothing you have said so far would give your customers a cause for concern, unless it is their racks.
Copper is the opposite of steel for annealing or hardening. If you take copper to a high enough temp and cool it very fast, it will go dead soft. If you bring down the temp moderately slowly, copper will harden. So, if you do your burn off in the afternoon, you can turn off the heat and let the furnace coast down and, depending on the temperature reached, it will actually harden.

! Jim:

I'm not so sure about your explanation of copper annealing.

I have annealed lots of copper by heating to moderate temperatures, say 450 °F, followed by slow cooling.

Jeffrey Holmes, CEF
Spartanburg, South Carolina

A. I do not have heat treat books anymore, so do not know the temperatures involved. I was referring to taking it to dead soft, which took quite a bit higher temperature. How much hardness change did you get with a 450 °F anneal cycle?
I thought that most burn off ovens went to above 600 °F, but have zero direct knowledge.

James Watts
- Navarre, Florida

A. While there will be some change in the electrical properties of copper after heat exposure, it will be so small for your application as to be irrelevant. Most plating racks are designed to carry more current than they will be used for to prevent any unnecessary temperature rise and thus increasing resistance.
Think about it -- The bulk of the rack is in the process tank, so it cannot rise in temperature but slightly above the tank temp (vs. current carrying capacity in air). Exception is the hook and a small part of the vertical spline(s). A very minor increase in the size of that part of the fixture will more than compensate for any change in the copper.
The customer has far more to worry about the cleanliness of the buss bar and the rack contact points than they would ever find in soft vs. hard copper.
If the plated part meets spec, what is their problem?

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A. Hi Roger. I haven't heard of using liquid nitrogen personally but it sounds feasible. Have you tried any approaches yourself?

Regards,