Spoke to a paintless dent guy this past week. We were BS'ing about this business and it's history and he brought up the dry ice thing. I asked him if it ever worked. He said "no".
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July 3, 2011 8:11 a.m. ddavidv SuperDork
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July 3, 2011 12:59 p.m. Tom Suddard SonDork
I tried it a few years ago, it was absolutely hopeless. No results whatsoever for me.
At the body shop we don't even mess around with that kind of thing. Watch out for paintless dent guys, too. A lot of them will drill holes all over the place in order to gain access to the backside of a panel, even if the offending brace/bracket/etc. can simply be unbolted.
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July 3, 2011 4:27 p.m. ransom HalfDork
Is the hope that it would work in the same manner as heating up the metal and then hitting it with a wet rag?
The big difference there seems to me that with the torch you're getting the metal hot enough to be malleable, and have some hope of actually getting it to change thickness and take a set when it's cool.
Dry ice seems like just a relatively strong version of normal heating/cooling expansion/contraction, though localized. The metal isn't going to be malleable, and it seems like if it did work it would only be on things that could just be bumped from behind to restore their shape... You're not going to either stretch or shrink the metal with this approach.
As I understand it, those are the only things you can do with sheetmetal: cut, bend, stretch (that is, elongate and thin), or shrink (gather up and thicken).
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July 3, 2011 5:04 p.m. Rad_Capz Reader
I have experienced disasterous results (ya, really bad)from heating and then rapidly cooling painted metal surfaces on vehicles. The rapid cooling of the paint compared to the metal (mass holds the heat better) can cause the mechanical bond of the paint to the metal to be compromised. Then over time as the heating/cooling cycles continue as they normally would the paint literally starts to peel off the metal. It might be days, weeks, or months before the problem is noticable.
The same effect can occur more slowly and is sometimes noticed as "ghosting". It can happen when body patch panels are welded into areas of cars exposed to direct sunlight if they've been installed with a metal overlap or thick weld. Welding byproducts and other possibilities are often blamed but the difference in expansion rates causes it frequently.
You may have seen this effect on vehicles that had the door handles removed and the openings smoothed? A year or two later you can see where the patch panels had been welded in on a lot of them.
It takes longer for the thicker weld area to cool and heat up because of the difference in mass so just moving the car from shade to sun stresses the mechanical paint bond where the thicker area meets with the original sheetmetal. The area of greater mass shrinks and expands at a slower rate than the surrounding metal. So over time a sort of "fault line" appears where the quicker and slower reacting masses meet because the paint is not elastic enough to compensate for the different rates of change.
I've had very good luck with the paintless dent guys. As mentioned, be there and offer to remove panels if necessary so they don't make additional holes (which they plug) if you care about them in door jambs etc.
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July 4, 2011 2:45 p.m. grafmiata Dork
Can you get to the dent from the back-side of it? If so, and there's a little bit of space between the dent and a solid part of the tub, or a brace or something, try stuffing some sort of deflated ball in there. Heat the paint a bit, and SLOWLY inflete the ball. Should pop out ok. A football worked well for me.
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July 5, 2011 9:21 a.m. ww SuperDork
Wow! This thread was dragged out of the graveyard from 2008! ;)
Anyway, if you do a search on Google for "dent repair compressed air" you'll get a mixed bag.
I agree with grafmiata that most of these can be dealt with by getting access to the panel from behind and gently pushing it out.
Regardless of how well it works initially, you're likely to loose all the paint in the "affected" area at some point down the road for all the reasons mentioned by Rad_Capz above.
Here's one that's pretty illustrative of a "success": http://www.youtube.com/watch?v=ILVWPzO_swY
In about 6 to 8 months that patch of paint will likely be falling off the side of the car.
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July 5, 2011 9:37 a.m. N Sperlo HalfDork
RichardM wrote:
The theory is that if you get the metal very warm say by leaving it out in the Texas sun in August, then rapidly cool it by the application of dry ice, the metal will contract in the area being cooled and the dent will pop out. Try it and let us know if it works.
Sounds like this week would be perfect. My focus had a ding dead center if the door. Live to hear results.
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July 6, 2011 2:59 p.m. kangoo New Reader
kangoo wrote:
I have tried dry ice it today on the hood of my Ford Escape 2005, my car has hail damage. Today's temperature is 89F and I used the dry ice after driving the car so the hood was pretty hot and DOESN'T WORK
