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Backing for welding

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  • Backing for welding

    Hi all,

    A simple question. In a couple of weeks I will start building a new stainless steel exhaust for my motorcycle. Last year I build the exhaust as shown partially in the photo. It was a long time since I Tig welded. Thin sheet also, 1 mm. It's still in one piece, but I need more ground clearance.

    It looked like I need special reading glasses for welding, because it looks like welding is nearer than reading. The geometric drawing of it was fun. But I digress.

    I need backing for the welds. The longitudal welds I backed up by welding on a rod. The round welds burn on the inside. Backing with argon is a bit out of the question.

    Once upon a time I worked at a factory, we used backing tape there, I was'nt that enthousiastic about it and we also used backing sand. The sand worked reasonable.

    I can't find a supplier for it on the net, only that it consists of crushed quartz and resin. Anybody ever used only crushed quartz only or should I go for the real stuff, or is there something hidden in the kitchen?

  • #2
    Why will you not flood it with argon?


    • #3
      I have not tried this but use his aluminum flux.-- c749909615df8d0e7ad293 -------RG


      • #4
        There is a material called "solar flux" that is available at welding supply dealers that is mixed up and painted on the inside of the joint. It vaporises as you weld and turns into a backup agent. Can't tell you if it works very good or not. Another choice is to make backup rings out of the same material and put them behind the weld they fuse into the weld as you go.
        The shortest distance between two points is a circle of infinite diameter.

        Bluewater Model Engineering Society at


        • #5
          I've often used copper plate (flattened copper tubing) for a backer when I weld. I know it will work for flat section, but not sure if it will work for your application. I have never tried it when welding tubing.

          Hope this helps,


          • #6
            If you don't have a spare flow meter it's pretty tough to back purge. Enter (as was mentioned) Solarflux. It is indeed mixed as a paste and spead on the inside.
            Two can only be welded over once. You can't go back over it for a second pass or for touchups without spreading more.
            You have to be pretty religous about getting the flux off the metal. Wire brushing then neutralize with clean water. The flux can eat the joint.
            Backer bands that fuse into the weld...prolly not a good idea for a free flowing exhaust but it'd work. The only problem is you'd still have cooked carbides sticking out the back of those welds. They can crystalize and cause cracking down the road.
            I have tools I don't even know I own...


            • #7
              Originally posted by torker
              They can crystalize and cause cracking down the road.
              Was that pun intended ?


              • #8
                Originally posted by slim_jim
                Was that pun intended ?
                LOL! You caught that huh? I noticed it after I wrote it...
                Also...the correct term for cooking the carbides out is "precipitation of carbides"
                Last edited by torker; 12-04-2007, 01:46 AM.
                I have tools I don't even know I own...


                • #9
                  Thanks for the input, gentlemen, the solar flux seems something to stay away from.
                  Welds out of carbide, stainless and carbon is a no-no. It will indeed cause cracking down the road.

                  The sand was nice, it behaved like the coating of an welding electrode.
                  I will ask at a shop here, otherwise it's backing up with argon.


                  • #10
                    Why didn't I think of that, K.I.S.S.


                    • #11
                      Argon "backing"

                      Argon IS the only way to go here for the type of result you are looking for. You do not have to have an other flow meter as you could purchase a wye fitting (cheaper ) than flowmeter and purge the joints that way ,when you get all the o2 out you will get great roots on those joints.