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Molten salt paint and coating removal

M

Madis Reivik

Hot Rolled
Joined
Jan 23, 2011
Location
Estonia
Hello !

I'm looking a method to remove thick epoxy coating from small parts. Sandblasting is doable but very hard.
I read about molten salt baths but have no experience and found no composition recipes from internet.

Anyone have experience or recommendations ? I want to make only small scale experiment and I hope I can get salts from local chemical supplier (nitrate, NaOH, whatever)
 
there are chemical paint strippers that will remove epoxies very easily, not regular paint strippers available in hardware stores though, auto body paint shops might have them, can also ask in powder coating shops

I've used chloroform also when couldn't find appropriate paint stripper, it softens up epoxy to a point where a brass brush will remove it, but it dries very fast so you have to repeatedly soak the part, and do this in a well ventilated area obviously
 
Boil it off in antifreeze? Worth a try. A friend cleaned his old spray gun that way. All paint gone and one part was assembled with epoxy. Was is the key word. Corrosion protection from the antifreeze too.
 
If you're planning a shop experiment with molten salt baths, another possible technique is fluidized combustion beds. Briefly, fuel gas is piped into the bottom of a container of sand or other high-temp resistant particles (like porcelean beads). The gas lifts (fluidizes) the sand and combustion takes place inside the volume of the sand. Items to be cleaned are lowered into the combustion bed, where a combination of heat, chemical action from combustion radicals, and mechanical scrubbing from turbulent sand cleans off the item surfaces.
 
sfriedberg said:
If you're planning a shop experiment with molten salt baths, another possible technique is fluidized combustion beds. Briefly, fuel gas is piped into the bottom of a container of sand or other high-temp resistant particles (like porcelean beads). The gas lifts (fluidizes) the sand and combustion takes place inside the volume of the sand. Items to be cleaned are lowered into the combustion bed, where a combination of heat, chemical action from combustion radicals, and mechanical scrubbing from turbulent sand cleans off the item surfaces.
Click to expand...
That sounds like the cleanest anything could possibly be.

Sent from my SM-G930R4 using Tapatalk
 
molten salt baths are very nasty. most likely they will destroy the parts. I know, a friend of mine who uses molten salt in his work has to make new titanium tongs every couple of years because the salt destroys them. When water, say, sweat dripping off your nose, lands in molten salt, you get a little explosion of 900 degree salt. If it lands on your skin, you burn. My friend has a variety of interesting scars as a result of this. I do not recommend it.

Bigger commerical powdercoaters use burnout ovens to burn off powder and epoxy coatings before sandblasting.
A shop I used to do a lot of business with in Southern California had about a 6' cube oven fired by natural gas that got up well over 1000 degrees, and they had a little railroad track and a very stout steel dolly they would roll the parts in on.

Most commercial sandblasters just refuse to sandblast powdercoating, because customers never want to pay for the time it takes to do it.

If you have the outdoor space and lack of regulation, use a big rosebud on a propane or acetylene torch, and toast it, then sandblast.
 
Ries said:
molten salt baths are very nasty. most likely they will destroy the parts. I know, a friend of mine who uses molten salt in his work has to make new titanium tongs every couple of years because the salt destroys them. When water, say, sweat dripping off your nose, lands in molten salt, you get a little explosion of 900 degree salt. If it lands on your skin, you burn. My friend has a variety of interesting scars as a result of this. I do not recommend it.

Bigger commerical powdercoaters use burnout ovens to burn off powder and epoxy coatings before sandblasting.
A shop I used to do a lot of business with in Southern California had about a 6' cube oven fired by natural gas that got up well over 1000 degrees, and they had a little railroad track and a very stout steel dolly they would roll the parts in on.

Most commercial sandblasters just refuse to sandblast powdercoating, because customers never want to pay for the time it takes to do it.

If you have the outdoor space and lack of regulation, use a big rosebud on a propane or acetylene torch, and toast it, then sandblast.
Click to expand...

Yup, Yup, and YES!

To add...Motor rewind shops have the same type ovens (with the rails & car) for "burn out" in which they burn out/off all the varnish (it's epoxy these days) to make coil removal easier/possible.
Followed by glass bead or now plastic blasting to clean up.

FWIW in Pennsylvania, the burn out ovens have a secondary "burner" to incinerate emissions up the stack. I would think Kalifornia has just outlawed the ovens completely ?
 
digger doug said:
Yup, Yup, and YES!

To add...Motor rewind shops have the same type ovens (with the rails & car) for "burn out" in which they burn out/off all the varnish (it's epoxy these days) to make coil removal easier/possible.
Followed by glass bead or now plastic blasting to clean up.

FWIW in Pennsylvania, the burn out ovens have a secondary "burner" to incinerate emissions up the stack. I would think Kalifornia has just outlawed the ovens completely ?
Click to expand...

Local powder coater has one.
 
Usually in California you need a permit for an oven that does 1 million BTU per hour or more- depends on local pollution regs. I would imagine permits would describe how it must be built and what you are allowed to put in it. But they are legal, with permits, in most of california. Sample regs are like this- Stationary Sources


Burnout Ovens

its been a while since I had my shop in California, but when I was there, it was possible to have a burnout oven, you just had to follow the rules. I am pretty sure that is still true in most places.
 
Ries said:
Usually in California you need a permit for an oven that does 1 million BTU per hour or more- depends on local pollution regs. I would imagine permits would describe how it must be built and what you are allowed to put in it. But they are legal, with permits, in most of california. Sample regs are like this- Stationary Sources


Burnout Ovens

its been a while since I had my shop in California, but when I was there, it was possible to have a burnout oven, you just had to follow the rules. I am pretty sure that is still true in most places.
Click to expand...

Thank you for the link, however it seems to be approved on a one at a time basis, the document
doesn't seem to indicate exactly what is needed for compliance.
 
If you are trying to convince me that California is run by Marxists and Stalin's grand kids, because the document doesnt tell you everything, I am gonna have to be just a bit dubious. The fact is, if you actually need to have an oven that burns 1 million BTU per hour, you are gonna have to talk to em. Thats hardly Cambodia under Pol Pot.

As mentioned above, there are still powdercoaters, foundries, platers, anodizers, and steel mills in LA county and thruout California.

to the OP- Skip the Salt Bath. Its too dangerous.
Start with brake fluid, work up to a torch if needed.
 
Ries said:
If you are trying to convince me that California is run by Marxists and Stalin's grand kids, because the document doesnt tell you everything, I am gonna have to be just a bit dubious. The fact is, if you actually need to have an oven that burns 1 million BTU per hour, you are gonna have to talk to em. Thats hardly Cambodia under Pol Pot.

As mentioned above, there are still powdercoaters, foundries, platers, anodizers, and steel mills in LA county and thruout California.

to the OP- Skip the Salt Bath. Its too dangerous.
Start with brake fluid, work up to a torch if needed.
Click to expand...

Not at all Ries.
However we have all read articles of industry moving from Kalifornia because of the various laws.
For example (that I stated above) Pennsylvania has similar wording for the permit. What they don't tell you is that the oven needs a complete other powered
system on the roof to add fuel gas, burners & blowers & fans etc.
This only comes out after paying a licensed P.E thousands of dollars.

Ohio ? not so much restrictions.
Nearby West Vir

West Virginia ? Only needs what the original manuf put on it. (very liberal)

What I wanted to know from you is actual example (like from a friends shop) what
all they have to use/run.
 
digger doug said:
Not at all Ries.
However we have all read articles of industry moving from Kalifornia because of the various laws.
For example (that I stated above) Pennsylvania has similar wording for the permit. What they don't tell you is that the oven needs a complete other powered
system on the roof to add fuel gas, burners & blowers & fans etc.
This only comes out after paying a licensed P.E thousands of dollars.

Ohio ? not so much restrictions.
Nearby West Vir

West Virginia ? Only needs what the original manuf put on it. (very liberal)

What I wanted to know from you is actual example (like from a friends shop) what
all they have to use/run.
Click to expand...

there is no doubt that some people have moved out of california.
and others continue to move in.

And the AQMD (air quality management district) in the LA area is particularly strict.
But that doesnt mean there are not still all kinds of suppliers and subs there.

The reason being- its a HUGE manufacturing state, and the LA area, in particular, is full of manufacturing.
There is money to be made there, and, as a result, industry finds ways to make it work.

I had a casting I was having made at a gray iron foundry right in the south suburbs of LA, and they are still there. Most likely they have more pollution control equipment than the foundries in West Virginia. But they make more per piece, too.

It all balances out.
 
Ries said:
Usually in California you need a permit for an oven that does 1 million BTU per hour or more- depends on local pollution regs. I would imagine permits would describe how it must be built and what you are allowed to put in it. But they are legal, with permits, in most of california. Sample regs are like this- Stationary Sources


Burnout Ovens

its been a while since I had my shop in California, but when I was there, it was possible to have a burnout oven, you just had to follow the rules. I am pretty sure that is still true in most places.
Click to expand...

In my very limited experience, at least a fair portion of the "California issues" are due to the national companies not paying attention to the rules. I ordered some one-part polysiloxane paint from Sherwin-Williams. It was going to be picked up by my customer at their local store (in Ventura County). I placed the order and it never arrived. It turns out that Sherwin-Williams thought it wasn't CA-legal, so this just didn't ship it and didn't tell anyone until I bugged the store into calling corporate. The paint is CA-legal, as anyone could easily tell by reading the data sheet. They wouldn't do that, however. I had to call the local CARB office and get an e-mail saying that Sherwin didn't know what they were talking about before they'd ship the paint
 
The problem with burnout ovens is....they get hot.

I guess a lot of stuff doesn't care if it gets hot, but I gotta think a lot of stuff does. A typical motor winding burnout is 750 degrees F. If a shop is doing it right, they will carefully increase the temp at a controlled rate, let it soak, then decrease it at a controlled rate. As we all know, it's an area ripe for cutting corners.

If I had something that was machined to tight tolerances or otherwise susceptible to the effects of heat, I'd do some investigating first.
 
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