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Fire as paint remover?

Old 01-09-21, 06:53 PM
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Jicafold
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Fire as paint remover?

So I had this frame that someone had repainted. Poorly. I started to strip it with paint stripper. I used both Kwik-Strip in the blue can and Jasco in the red can with so-so results. It was taking forever and using a lot of product. So I said "Screw this" and made a fire in the fire pit and threw it in. I then went section by section and the paint came off like butter with steel wool. I was done in an hour. So...my question is...why don't I strip every frame like this? It was so easy and essentially free. See before and after photos. First photo is with paint stripper frustration. Second photo is after melting the paint off in the fire.



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Old 01-09-21, 07:00 PM
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krakhaus
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Works great on carbon fiber bikes.
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Old 01-09-21, 07:04 PM
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Some metals change hardness through heat treating If you can remember the sticker or know the alloy you can look it up.
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Old 01-09-21, 07:12 PM
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This was a Bertoni frame made with Columbus SL. That being said, the heat from a camp fire would certainly be less that the heat needed for brazing this frame together. So I doubt it would affect the strength of the steel.

Additionally, and as another comment., I can't bring myself to repaint this "electic rose" or "violet mist".


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Old 01-09-21, 07:56 PM
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Beavis approved!
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Old 01-09-21, 08:03 PM
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Originally Posted by krakhaus View Post
Works great on carbon fiber bikes.
hahahahaha! nice!
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Old 01-09-21, 08:17 PM
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Originally Posted by Jicafold View Post
This was a Bertoni frame made with Columbus SL. That being said, the heat from a camp fire would certainly be less that the heat needed for brazing this frame together. So I doubt it would affect the strength of the steel.
The heat from a campfire is definitely enough to reduce the strength of a frame. Also consider that there is a significant loss of strength in the brazing process (look at the Trek brochures from the 80s where they have a chart with strength before brazing and strength after brazing).

The frames are double butted so the material is thicker where the braze occurs. Heating the center section of the tubing would be a bad idea.

For a data point from another field, the US department of transportation requires any steel gas cylinder to be removed from service and condemned if the cylinder is heated to a temperature above 650F, which is much less than a frame brazing temperatures. The temperature limit for aluminum cylinders is lower (350F).
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Old 01-09-21, 08:28 PM
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The heat of even a camp fire could change the crystalline structure and bonds of the metals, maybe not drastically, but it has been altered and its strength is compromised to a degree. As a site engineer, for a GC, on DOD buildings, and structures' projects (now retired,) I had to observe and document the entire process if a structural steel pieced had to be field modified, very strict guidelines were laid out, and had to be approved by a structural engineer before proceeding (if you were even allowed to approach the NAVFAC or USACE officers about it.) Mainly it will depend on the particular alloy of the tubes, luge (if applicable,) and brazing materials.

I was teamed with a Supt, that was a metallurgist, in the nuclear power industry, he could really explain this better than I could, and I had to be certified for metals inspections and failure analysis, for my approval as QCPM before each project began, if structural steel and connections were involved. the Supt had been NRC approved for over 20 years, before coming to work for us. Heat treating and failure analysis were kind of his field of expertise and big thing.

There are some very experienced metallurgist and engineers here, maybe one will give their thoughts. Hope that the build turns out well, and that everything is copacetic.

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Old 01-09-21, 08:38 PM
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Originally Posted by wesley77803 View Post
The heat from a campfire is definitely enough to reduce the strength of a frame. .
that would really depend on the intensity of the fire and the frame's proximity to the hottest sections of the fire. if i can cook on a campfire without burning the food, it's safe to assume that fire couldn't be more than 400 degrees. and, 400 degrees is really a hot fire to be cooking on, in any case. would sub 400 really be hot enough to alter the metal? hasn't affected any of my cookware in any notable way
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Old 01-09-21, 08:49 PM
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Originally Posted by thook View Post
that would really depend on the intensity of the fire and the frame's proximity to the hottest sections of the fire. if i can cook on a campfire without burning the food, it's safe to assume that fire couldn't be more than 400 degrees. and, 400 degrees is really a hot fire to be cooking on, in any case. would sub 400 really be hot enough to alter the metal? hasn't affected any of my cookware in any notable way
Measured camp cooking fires and charcoal grilles with pyro-thermostats, at +500* F. One hour is a pretty good length of time, also.

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Old 01-09-21, 09:16 PM
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Originally Posted by qcpmsame View Post
Measured camp cooking fires and charcoal grilles with pyro-thermostats, at +500* F.

Bill
fair enough. it's like i said, though, it really depends on the intensity of and proximity to. maybe good fortune is the OP's side
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Old 01-09-21, 11:12 PM
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Originally Posted by Jicafold View Post
So I had this frame that someone had repainted. Poorly. I started to strip it with paint stripper. I used both Kwik-Strip in the blue can and Jasco in the red can with so-so results.
I've gone to auto parts stores and had them hot tank steel frames to strip the paint. This is caustic soda in hot water- probably not as hot as your camp fire. It gets the vast majority of paint off the frame, only leaving detail work in the corners of lugs and such. It beats messing around with paint stripper goop.
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Old 01-09-21, 11:39 PM
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Anyone who has thrown a tin can into a campfire knows that a wood fire can get hot enough to seriously deform thin steel. I remember from my wood stove days that wood starts to combusts at about 500f and that the target for a clean fire without visible smoke is around 1,100f. Some air control was generally needed to reach that temperature so I doubt that an open wood fire would get quite that hot very easily.

Brent

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Old 01-09-21, 11:46 PM
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Brings back memories of working in a heat treating facility in my youth. My part of the shop ran carb pots, and everything was 1500 to 1950 degrees F. One day as i walked through another part of the shop, a guy asked me to help him pick up a heavy shaft he had been straightening. I saw it was not glowing red or white, which to my world meant it was cool. So without thinking I picked it up bare handed. It was 500 F. That was the worse burn I ever suffered.

A roundabout way of saying, 500F is used to soften steel.
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Old 01-10-21, 04:43 AM
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I would not use heat on a frame. It depends on the frame. In some cases it may significantly weaken it.
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Old 01-10-21, 06:03 AM
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This is silly.
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Old 01-10-21, 06:46 AM
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Originally Posted by Jeff Wills View Post
I've gone to auto parts stores and had them hot tank steel frames to strip the paint. This is caustic soda in hot water- probably not as hot as your camp fire. It gets the vast majority of paint off the frame, only leaving detail work in the corners of lugs and such. It beats messing around with paint stripper goop.
Um, hot water is, by definition (at normal pressure) less than 100 degrees. Wood fires are 600 degrees and up.

Yes it's cooler (but a wood fire is not six times hotter - do I need to say that?).

And annealing temperatures for steel are from about 300 up, so no, fire is not a Good Thing for bike frames.

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Old 01-10-21, 07:16 AM
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dude....sounds like your frame is... toast...hahaha

but, frankly.....i think your frame just needs s'more paint.....hohohoho

it'll be one smokin' build....<<<buh doomp....pshhh>>>

yes, well done

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Old 01-10-21, 07:23 AM
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I would not even use a torch to burn paint off!

I think your frame is roasted or a t least toast!
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Old 01-10-21, 07:25 AM
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Old 01-10-21, 07:39 AM
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Old 01-10-21, 07:42 AM
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Originally Posted by Jicafold View Post
...I can't bring myself to repaint this "electic rose" or "violet mist".
Why not? It's a great color.
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Old 01-10-21, 08:31 AM
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Originally Posted by qcpmsame View Post
Measured camp cooking fires and charcoal grilles with pyro-thermostats, at +500* F. One hour is a pretty good length of time, also.

Bill
Let me clarify. The frame was above the fire, not in the coals. I heated one section at a time for about 1 minute, then removed it to scrape the paint in that section. Each section worked was roughly 6 inches long. The total process, section by section, took about an hour.
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Old 01-10-21, 09:31 AM
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See, all of this tripping out about weakening the frame after leaving it in a fire for an hour could have been avoided if you just explained the process earlier. ;P
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Old 01-10-21, 09:50 AM
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Originally Posted by Kilroy1988 View Post
See, all of this tripping out about weakening the frame after leaving it in a fire for an hour could have been avoided if you just explained the process earlier. ;P
True. My apologies. I understand about heat and weakening metal...however, I wouldn't think that it should affect the frame to any dangerous level. I'm not sure if I would do it again or not. It's just that this particular frame had multiple layers of paint and it was taking forever with paint stripper.

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