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ddavidv
ddavidv SuperDork
7/3/11 8:11 a.m.

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".

Tom Suddard
Tom Suddard GRM+ Memberand SonDork
7/3/11 12:59 p.m.

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.

ransom
ransom GRM+ Memberand HalfDork
7/3/11 4:27 p.m.

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).

Rad_Capz
Rad_Capz Reader
7/3/11 5:04 p.m.

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.

grafmiata
grafmiata Dork
7/4/11 2:45 p.m.

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.

ww
ww SuperDork
7/5/11 9:21 a.m.

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.

N Sperlo
N Sperlo HalfDork
7/5/11 9:37 a.m.
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.

kangoo
kangoo New Reader
7/6/11 2:59 p.m.
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
captdownshift (Forum Supporter)
captdownshift (Forum Supporter) GRM+ Memberand UltimaDork
3/23/21 4:20 p.m.

There was a significant dent on the left quarter of the escort when I got it, a heat gun and dry ice definitely pulled it out about 95% of the way. It's not perfect and there's definitely still some waviness in the panel, but you can't see it from 20ft away anymore. 

NOHOME
NOHOME MegaDork
3/23/21 5:21 p.m.
ACarlson said:

I think my dent fits all the criteria of a case where it's likely to work: shallow, broad, smooth, no body lines, no broken paint.

I'm going to try the ice first, and if that doesn't work, I've seen a method involving a hair drier and the super-cold liquid propellant from the kind of compressed air can they sell to spray off a keyboard. Either way, I'll try to heat the area in the sun and maybe hit it with a heat gun on low, too.

Makes a measure of sense, and both methods can't cost more than $20. What the hell?

I'll report back, probably Sunday or Monday.

It should work for all the reasons that a shrinking disc works. You certainly want to heat the spot up with a heat gun as much as you dare.

 

captdownshift (Forum Supporter)
captdownshift (Forum Supporter) GRM+ Memberand UltimaDork
3/23/21 6:14 p.m.

In reply to NOHOME :

I used welding gloves heated up the quarter panel for about 20 minutes, then took dry ice to it, once the panel was cold, back in the cooler it went and the panel was heated back up for a second round. I ended up doing 4-6 rounds as I recall working to get the deflection points around the perimeter as close to right as possible.

11GTCS
11GTCS HalfDork
3/23/21 7:44 p.m.
NOHOME said:
ACarlson said:

I think my dent fits all the criteria of a case where it's likely to work: shallow, broad, smooth, no body lines, no broken paint.

I'm going to try the ice first, and if that doesn't work, I've seen a method involving a hair drier and the super-cold liquid propellant from the kind of compressed air can they sell to spray off a keyboard. Either way, I'll try to heat the area in the sun and maybe hit it with a heat gun on low, too.

Makes a measure of sense, and both methods can't cost more than $20. What the hell?

I'll report back, probably Sunday or Monday.

It should work for all the reasons that a shrinking disc works. You certainly want to heat the spot up with a heat gun as much as you dare.

 

Holy necrothread Batman...that “update on Sunday or Monday” would have been in 2008!

ClemSparks
ClemSparks UltimaDork
3/24/21 8:21 p.m.

Why would someone NOT bring up an old thread with relevant input?  I really don't understand the "Start a new thread.  This perfectly relevant place to discuss this topic happened before last week!" crowd.

M2Pilot
M2Pilot Dork
3/24/21 9:42 p.m.

In reply to ClemSparks :

Agree

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