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"No-PreHeat" Cast Iron Repair Technique

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  • "No-PreHeat" Cast Iron Repair Technique

    Goodafternoon, everyone!!


    So, this is the latest of my Cast Iron welding videos... I repaired a "crack" in a transmission housing without any kind of a preheat, or a post-heat:





    Basically, Cast Iron cracks when it's heated and/or cooled rapidly, hence the reason why its usually pre-heated and allowed to cool slowly, but theres a chance that you can get around this by just not getting it very hot...


    I used a Nickel-99 electrode to make welds under 1" in length, which I then peened and allowed to cool completely, so that I could run my fingers directly over the weld, at which point I ran another short weld using the "back-stepping" technique, and repeated...


    This is a technique that can be used with any of the main electric arc welding processes... I've seen it done with TIG using stainless filler, and I've heard of people having success with it running MIG , again with stainless filler...


    Its just a little technique that I heard of, and had to try, I made a video about it and just thought i'd share... Doesnt seem like a bad way to weld a cracked engine block or something along those lines...


    Well, hope you guys like the video... Have a great week, everyone!!

  • #2
    Originally posted by ChuckE2009 View Post
    Basically, Cast Iron cracks when it's heated and/or cooled rapidly, hence the reason why its usually pre-heated and allowed to cool slowly, but theres a chance that you can get around this by just not getting it very hot...
    Someone correct me if I'm wrong, but my understanding is that one of the reasons cast iron cracks after welding it with normal steel electrodes is because some of the carbon in the cast iron (which has more carbon than even high-carbon steel) dissolves into the weld deposit, in effect creating a "high-carbon steel" weld deposit.

    If the surrounding cast iron isn't pre-heated and post-heated, this "high carbon steel" weld deposit is effectively "quenched" by the surrounding cast iron, which quickly draws the heat out of the weld deposit.

    This "quenching" causes the weld deposit to get much harder and less ductile than normal mild steel, and when everything shrinks after the welding is done, the lack of ductility in the weld deposit causes cracks.

    This is one of the reasons nickel electrodes are used ... because nickel is far more ductile than cast iron or even mild steel, and because adding carbon from the cast iron into the (mostly nickel) weld deposit doesn't have the same hardening effect as with a normal steel electrode.

    Anyway, long story short, pre-heat and post-heat is probably always going to be the better bet...IMHO.

    Again, I'm far from an expert, so if this isn't accurate, someone please correct/clarify. And thanks for posting up ChuckE2009, your videos are great...

    Comment


    • #3
      Yes, I don't doubt that mild steel electrodes are far from an ideal way to weld cast iron (even tho I've welded it with 7018 before), but these are expensive nickel electrodes, Ni-99s to be exact, which helps with it.

      Im sure cracking is caused in part by what you describe, but its also largly because cast iron doesnt bend... It can't "distort" from heat input like mild steel can, thus then you weld it and dont manage the heat input, it "pulls" the weld apart just from stress.

      Comment


      • #4
        I think the point of the video wasn't how to do it the 'best' way when one had all the right equipment, etc. but how one could perform this task in less than ideal conditions when the immediate need was present.

        Keep 'em coming Lance! Once more the only thing I find wrong with your videos is there aren't enough of them. :-) I don't know what I'd do without you and Jody at weldingtipsandtricks.

        Comment


        • #5
          I do it 2-3 times a week. The rod specs set whether it needs preheat or not. I don't just use any old flea market rod or old rods from an old shop i get quality rods and most of them don't require preheat but i do cool it as slow as i can with insulation. I have had an ad on CL for months and get all kinds of different parts to fix....Bob

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          • #6
            Always has been to two schools of thought concerning welding cast, hot & fast or slow & cool, nothing new here.

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            • #7
              Cast iron cracks, especially on something like a cast iron engine block because the material around the weld is constrained. When the weld is made the material is superheated and expands (you can't weld it cold, your arc is around 2500 degrees) this expanding material has no where to grow so instead the material thickens, as it cools back down the thickened material tries to go back its original shape and pulls the surrounding material causing a crack.

              Comment


              • #8
                There was a fantastic video on YouTube on the topic that demonstrated the problem with trying to weld a constrained cast iron crack. The proper way to fix one is to dril tap and pin the crack with overlapped threaded "pins"

                Comment


                • #9
                  Prob 90% of my cast repair now is with a mig and Crown Alloys 44-30 cast iron mig wire. I can do repairs that a few years ago i just dreamed about. Here is a tractor manifold i fixed for my neighbor. Yes i know a new one is only 39 bucks but i wanted to try out the wire. I welded it cold with the mig building up the bad area and he filed it to suit. He said the tractor has never been so quiet. I welded a BB Chevy for a guy 2 states away and he drove the block to me to fix. The repair took 15 minutes and he drove 11 hours to get it to me...Bob
                  Attached Files

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                  • #10
                    the most important thing this gentleman mentioned is the back stepping technique, one should always weld in the direction of weld that is cooling, not the opposite, a weld that is building heat, this technique works great on long butt welds

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                    • #11
                      I have tried the utp 55, and 99. And lots of other techniques. The very best I have found that I always use is tig weld silicon bronze. Its a bit too hard to drill but if your just repairing cracks...try it. I guarantee you'll never use anything else

                      Comment


                      • #12
                        Originally posted by aametalmaster View Post
                        Prob 90% of my cast repair now is with a mig and Crown Alloys 44-30 cast iron mig wire. I can do repairs that a few years ago i just dreamed about. Here is a tractor manifold i fixed for my neighbor. Yes i know a new one is only 39 bucks but i wanted to try out the wire. I welded it cold with the mig building up the bad area and he filed it to suit. He said the tractor has never been so quiet. I welded a BB Chevy for a guy 2 states away and he drove the block to me to fix. The repair took 15 minutes and he drove 11 hours to get it to me...Bob
                        I see that Crown Alloys 44-30 specs out some pretty high voltage. Have you found that to be a problem at all?

                        Comment


                        • #13
                          Cast iron welding

                          I'm sure there are many good ways to weld cast iron; last fall when I need to repair a set of old cast iron stove legs I asked for some suggestions. Recieved a lot of informative suggestions. Bob (aametalmaster) suggested crown alloy 44-30 and mig. Had a problem locating the wire in a small size spool but ultimately found it; all I can say is wow what a surprise. welded the crack, welded in the broken piece and cut up an old frying pan to make a missing piece. Really looked like new. Much belated but many thanks Bob great suggestion and wonderful advice. The peaple who's camp it went to in the Adirondacks were extremly pleased also.

                          Harold

                          Comment


                          • #14
                            Lanse, another good video. It's expecially nice to see one WITHOUT all the commercial interruptions! Thanks...

                            Comment


                            • #15
                              Originally posted by Sandy View Post
                              I see that Crown Alloys 44-30 specs out some pretty high voltage. Have you found that to be a problem at all?
                              Nope no problem. I really don't have a meter just taps so i just play it by the job...Bob

                              Comment

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