Cleaning by Heating

This is my first post, so bare with me. [So where is the spell check? LOL]

I have to be flip here.

'Cleaning by heat.' Being an old Blu~Surf guy, I have questions.
You stated; "We have a heat treat furnace (electric), and need to strip old powder coating off of some steel decorative park benches, my question is: what temp and time would be a starting point to strip this finish?"

Sounds simple at first. Maybe even a good idea. But wait one second.

~An 'electric heat treat funace' is not a gas fired 'paint bake-off oven' designed with all the safety's and VOC destruct capabilities.

~And 'some' is how many benches? It is nice to guess at how many pounds of cured powder coat one is dealing with. It's a time-temperature deal.

~Is this a one time deal? If so drag them out back at dusk and light them off in a pan of diesel fuel.

~Ooops, just being silly. This is how we cleaned our powder paint hooks of cured over spray powder coatings for years at Junction Mfg. in Junction, Michigan.

~The word furnace implies an operating temperature greater then 750 deg F. Ovens are 750 deg F or below.

~Are "steel decorative park benches" a weldment, a casting? Poured mold? Forging, What is the substrate other than steel? Will these warp, crack, 'wiggle' around in heat?

~The powder may be a black polyester UV blend, no matter. A lighter color ought to have a lot of titanium dioxide. Once the binders are baked out of the coating, this TD just becomes an ash in the bottom of the oven and does not destruct. But I digress.

To answer the question, ramp up the F. temperature over several hours to 550-650 deg F with the hope of not going to 750 deg F. Figure on holding at 550 deg F. for about 90 minutes, and ramp back down. Figure a goodly part of a day. Keep in mind the coating can burst into flame and if the heat treat furnace exhaust and or spill hood exhaust is not up to the job, then maybe you'll smoke out all the shop rats.

Additionally oxygen is not limited in heat treat furnaces as it is in paint bake-off ovens nor are HTF's equipped with cooling water spray triggered by a high temperature and this may allow a run-a-way fire in the oven. I doubt it. But could happen?

When the park benches cool they will need a spray wash and all the metal pre-treatment required to re-powder coat.

My guess is that you want to toss about 10 to 15 park benches into the HTF and light it off, get them red hot and pull them out for cooling. Which will be fine if the substrate doesn't care.

skip

Last edited by skip (12/14/2009 - 09:04 PM)

Dustin nice to read a reply. Prime answer is 'How to burn off [Bake-off] a cured powder coating. Ramp up to 750 deg F. hold. Ramp back down. Everything else is ancillary.

When I talked about heat treat finances I'm thinking an in line drag conveyor type with work openings at each end. Like at Brillion Foundry in Wisconsin. And I was always thinking gas fired just above stokiemetric having just enough oxygen to support combustion and not the usual 20% excess oxygen for a clean burn.

Electrics are different. fill it shut the door turn it on.

"I don't want to thread-jack this topic, but I did want to point out some other thoughts I had.? Again, thanks for the detailed info. :-)"

I'm not exactly sure what 'thread jack this topic' means.

skip.

Roger that. Thank you.

I have no problem following the thread where ever it goes. But that's just me.

We could start out talking about powder and end up with e-coat. Fine with me.

skip.