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Fixing auto sheet metal damaged in brush fire ?

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  • Fixing auto sheet metal damaged in brush fire ?

    I know you guys had a lot of brush fires a few months ago and we are having them now ,

    what happens to automotive sheet metal when it gets heated in a fire ?

    How strong is the metal in the chassis., does it loses it temper ?

    does the outer sheet metal lose its temper / strength if the heat is high enough to burn off the paint but the car did not catch on fire inside ?

    at the Malibu fire a few very rare cares were burned to the ground and even melted the the alloy brake drums , while other cars just had the paint scorched and windows cracked ,

    Thanks for your ideas

  • #2
    i know it becomes toxic, we were warned of burnt out cars years ago, i lived in a bad area lol. i'm pretty sure something happens to the steel too as i had a go at repairing a roof skin a few year before coming to OZ and it was like filing hardened steel, the file just skidded across the surface. not sure what steel it was before the fire but still. i have done some repairs on modern cars in the last 10 years while working in melbourne where someone had torch shrunk the panel before and that was the same.

    i'm no metallurgist though lol
    thanks neil


    • #3
      For a time in my career I rebuilt Insurance Salvage vehicles. I have done several fire vehicles where maybe a front end is burned or section of the car. Did a lot of front ends on high dollar cars like that. We could never reuse any sheetmetal that got hot. Inner structures would be ok after media blasting them, then epoxy, but sheet metal was always trash. What happens to the steel is fairly simple, at least this is my suspicion. Fire is burning, metal is hot, Fire department comes and puts the fire out. Cool/cold water on hot steel. Instantly hardens it and definitely makes it brittle. If something gets scorched and then can cool naturally it's ok, but when water is used is when the metal gets hard and brittle. Once I had to re-use a Jaguar front end that got burnt cause there was nothing available used. Told the guy I did it for never again. Trying to work it was a nightmare, especially the hood. Basically any sheetmetal that gets hot and then quenched by a fire hose is scrap.

      And with cars in the last 10 years or so using HSLA steel in body panels as well as structural members, forget it. Junk. Try straightening HSLA unibody rails on something after a collision much less a fire. All they do is tear. Alum Ford F150's here in the US get junked at an incredibly high rate, because the cost to repair them is so high and very few have the equipment or training to do so.
      Last edited by Chris_Hamilton; 14-09-20, 01:30 PM.


      • #4
        Hi , thanks and keep those ideas coming .....

        these would be old cars not HSLA steel but its good to know anyway,

        There are also a lot of old cars that have engine fires , but the rest of the car is OK ,

        Anyway i would love to hear more of what you have fixed or could not fix .


        • #5
          Most of what I was referring to was about conventional steel. Just went off on a tangent in the last paragraph. Conventional cold rolled will respond the same way, it will harden and get brittle when quenched while hot. Because of that it shrinks which in turn cause the sheet metal to warp. I did a lot of engine fire cars and the ones that didn't get doused by the fire department and cooled on their own were OK to work. I had one guy that bought a lot of classics that had fires, 68-69 Camaros, 65-70 Mustangs, Tri-Fives, other muscle cars, most of the time we would replace the sheetmetal and media blast the front inner structure (after pulling everything) epoxy (DP40 back in the day), SPI epoxy now and then reassemble and paint. Trying to work the burned fenders and hoods that got doused (hoods, forget about it) was a challenge. It was always much easier to replace with used or reproduction sheet metal. The guy that was bringing them to me made very good money on those cars. Relatively simple and not a massive amount of parts to replace. Nowadays a different story. I got pretty good at making wire harnesses for GM's and Fords of that era.


          • #6
            just a thought! if you had an induction heater maybe you could re-heat panels you can't obtain, then let them cool naturally.

            anyone have thoughts on that or would the temper not return to normal?
            thanks neil


            • #7
              I would be interested in what the induction heaters can do for dents etc , I am not sure you could get one large enough to do a panel ,

              they "fix" hail dents with the smaller induction heaters or at least "Sell" them for hail dents , I never used one

              but it could also be just more VooDoo to separate you and your money


              • #8
                i have used them to remove plastic boot floors from modern cars, the do get the metal warm, it might be worth a go, as for hail dents nah still use dent rods lol
                thanks neil


                • #9
                  I once read a post on a Land Rover forum where a badly burnt chassis, axles Had been reused. Unfortunately for the poster most of the steel components cracked in use.

                  His advice was to walk away from a burnt car.


                  • #10
                    Orange/ yellow colour of Fire 🔥 is around 1100 degrees C.
                    Last edited by Moving molecules .; 23-09-20, 02:11 PM.