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Welding cast iron

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  • Welding cast iron

    A friend just bought an ornate cast iron stand. It's not tall enough for the intended application, so a friend of hers is going to cut and piece together the two sides to make one of the correct height. Only one support is needed for the application. Is welding the right way to do this, or maybe brazing? It will be repainted afterwards. Is he going to be able to do a decent job of it?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    most conventional arc welding filler metals intended for steel are no good on cast iron and will crack when they cool.

    Silicon bronze TIG could work. You can get some similar kind of rod for use with an OA rig. Do they have a specific process in mind?

    I once was welding in my garage and some random neighbor walked by. He told me he was a railcar fabricator up in Canada long ago and he loved welding and stood around for a while and watched me TIG. He then disappeared and came back a few minutes later with an old piece of **** shovel with sentimental value, which had a stress crack right in the middle of the blade. I told him I couldn't weld it with the 70S6 rod I had on hand, and was pretty adamant that it would turn out bad, but he wouldn't give up and kept saying "I used to weld iron all the time in Canada, blahblahblah"

    Well, they were arc welding and the yard supplied them with nickel rod or something of that sort. Certainly not 70S6. He insisted it'd work, despite me telling him it'd crack. I drilled the corners of the crack to prevent it from propagating, wire wheeled the crack until it was shiny, then laid down a bead. It was a good looking weld, but obviously it was no good. He came back a day or two later, walking by and told me it cracked, and was kind of upset. I told him it was going to crack with 70S6.

    TLDR; yes it is possible. Have someone who knows what they're doing weld it. Don't get the railcar fabricator guy from Canada unless he borrowed some of the proper rod from the yard before he fled the country.


    • #3
      Don't weld it. Braze it. Doesn't sound like it needs any more than that, and there is a lot less danger of cracking that way. Welding cast iron properly is a lot of work; much easier to braze when you can.


      • #4
        Oh brother, this again.
        Welding iron is not so much about the filler material.
        It is about the pre-heat and post-cool.
        Both need to be slow, especially the post-cool.
        One reason (not the only reason) that brazing works so well,
        is that if you want to pre-heat for welding, you are dragging
        out the torch anyways, so you might as well keep using the
        torch and braze it or even torch weld it. This is not vodoo.
        It is established physics. It is all about the critical-cooling-curve
        of the material being welded, whether it will get too hard and crack.
        If you don't pre-heat and slow-cool when welding cast iron,
        it is not going to work. People are so lazy and try to short cut
        everything. Then they wonder why shlt don't work. They have
        too large of an ego to possibly think THEY could be the problem.
        And life goes on, and history repeats it self.

        Last edited by Doozer; 02-12-2021, 08:59 AM.


        • #5
          Originally posted by eKretz View Post
          ..... Welding cast iron properly is a lot of work; much easier to braze when you can.
          No more work than brazing it .



          • #6
            Originally posted by Doozer View Post

            No more work than brazing it .

            Bull. Brazing does not require near the preheat that proper welding does, nor a slow post-cool if the workpiece is not irregularly shaped or of very thick section. I've done both brazing and welding of iron countless times. And if the object needs to be machined post-welding it can be a crap-shoot whether it will be hard as glass in places even with the correct heat and cooling cycle.

            And although that is a contributing factor, it is NOT only about the critical cooling curve when welding iron. Though that absolutely does affect the hardness of the material. Welding steel or pretty much any other commonly welded metals besides iron, there is a lot more ductility in the material. The lack of ductility is the major cause of the cracking, not hardening alone. Iron is not very ductile even when it is soft, unlike most other commonly welded metals. That is another factor in why it needs to be slowly cooled, to allow the material to evenly cool across its cross section. If it cools too quickly in one area vs. another, the pull of contraction via cooling can very easily cause cracking, even if it's not in a hardened state.


            • #7
              I don't get that "Brazing does not require near the preheat that proper welding does..".
              I mean, you have to heat the metal red to get the braze (bronze) to stick,
              so not sure what you mean about less heat.



              • #8
                I have an older 8" Stanley bench grinder with bolted-on cast iron wheel guards. The grinder stand got tipped over and one of the wheel guards was broken in half.

                A friend suggested MIG welding it using the same wire I use on steel. Sounded totally stupid, but I tried anyway. I welded both sides along the crack line. Then as I was getting ready to bolt it back on I accidently dropped it on the concrete floor from the height of my welding table. It didn't break. Bolted it on and it's been that way for 20 years. Granted, this is not a high stress structural part.

                I'm not suggesting this is a valid process or recommending it, only reporting my experience.


                • #9
                  Originally posted by psomero View Post
                  Silicon bronze TIG could work. You can get some similar kind of rod for use with an OA rig..

                  This is what I have done. Both in TIG and OA. Best method I know of unless you want to do a full on heat treating process. JR


                  • #10
                    I started a post sometime withing the past year asking about silicon bronze mig welding cast iron. Lots of interesting info in there from people who actually know how to weld, if you can find that post. I did finally get a roll and successfully welded a cast iron tool rest for a wood lathe with it. I have a much heavier piece of cast I have not yet tackled.
                    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979


                    • #11
                      I've done ornamental cast iron- of all things, heating radiators.

                      It IS quicker to weld than to braze- preheat to maybe 600f,
                      nickel rod in a STICK welder, work around so it all stays warm.
                      If you're not sure, get it warmer.
                      Not waterproof, but strong enough to not break when dropped off
                      a loading dock. At least, not at the welds.
                      Also, exhaust manifolds. Works there, too.

                      Smaller stuff I braze, bigger stuff, stick weld.

                      it works.

                      MIG did not- I got the project after 'the welder'
                      tried that 4 different ways. Including with some preheat.

                      farmer it up, move it on.
                      rusting in Seattle


                      • #12
                        Oy. Like Doozer said, "this again?"

                        I've asked any number of times about welding cast, and it always devolves into an argument like this.

                        My answer? Muggy Rod. You use it in a stick welder, and it's about as complicated to use as 6011 on mild.

                        The irreplaceable collet closer casting on my '39 turret lathe:

                        Veed out, and welded with zero pre-heat, zero post-heat, no fluxes or fireproof blankets.

                        Ground smooth:

                        I also did the inside:

                        And the opposite side:

                        I've also used it to repair the cracked base of my big Springfield lathe as well as five of the control levers, to repair a drill press that had fallen over and been cracked, damage to the casting of an old "camelback" drill, the table legs and one support arm of a horizontal bandsaw, and a handful of others over the years.

                        No pre-heat, no post-heat, no insulating blankets, no fluxes, no nothing. The only 'trick' is to make short welds, and let them cool before continuing. Depending on the quality of the casting, you'll occasionally get porosity- grind it out and weld again.

                        These days I keep a couple pounds on hand for either day-to-day repairs or upcoming projects. Worth every penny.

                        Doc's Machine. (Probably not what you expect.)


                        • #13
                          Ok, short easy question...
                          I have used 99% nickel rod and 55% nickel rod.
                          I think they run better on AC, but maybe I am doing it wrong,
                          but anyhow, how does this MuggyWeld compare to Nickel rod ?
                          I have never tried it.


                          • #14
                            Only used nickel rod once, on an exhaust manifold, and that was 25 years ago. Can't really say.

                            All I can say is that using Muggy on clean cast iron is very nearly as easy as using 6011 on mild steel.

                            Doc's Machine. (Probably not what you expect.)


                            • #15
                              Doc, are those parts subject to any significant stress, or more just cosmetic-ish?
                              "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979