Preheating With An Arc Welder

Discussion in 'Shop Talk' started by Ken Scharabok, Aug 21, 2004.

  1. Ken Scharabok

    Ken Scharabok In Remembrance

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    Welding cast iron requires preheating. If you stick a rod to it and let it sit, it will heat up the metal. Does this damage the arc welder?

    Ken Scharabok
     
  2. agmantoo

    agmantoo agmantoo Supporter

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    Ken, I seldom weld cast iron but I have seen a shop that repairs heads for diesel engines and they heat their cast iron with a forge to where the cast is red then they weld.
     

  3. moopups

    moopups In Remembrance

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    Arc welding cast iron can be accomplished without preheating if you weld just a very small length over a longtime, 1 inch or so per application - then let it cool to the touch before returning to weld.
     
  4. Ross

    Ross Moderator Staff Member Supporter

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    I use oxy-propane to preheat and post heat. Not sure if it will damage the welder or not but no doubt you have to mind the duty cycle and stay within its limits.
     
  5. jacki c

    jacki c Guest

    I am a welder by trade. You need to preheat cast iron to prvent cracking. You weld a little, then pean, then preheat again and weld some more then pean again. This will releive stresses and prevent cracking.
     
  6. HermitJohn

    HermitJohn Well-Known Member

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    There are different ways to go about this. When it gets down to the nitty gritty, if you are welding on a good grade of cast iron, you can get by having everything ground clean and go very slowly which in effect does do some preheating. For instance I have repaired and modified intake manifolds with no preheat and never had a single problem with cracking and never had a weld fail.

    Cheap grades cast iron have to be preheated, especially thin castings. Trying to weld an old stove or cookware for instance can be a nightmare, spider cracks galore without preheating, but then brazing is usually lot more economical and effective for them anyway.

    Might mention there is the 99% nickel rod and there is the "cast" rod. The nickel is pricey, but you'll never regret buying it when you actually go to weld. Its got to be the easiest stuff to stick weld with that I have ever seen. On some things its just plain cheaper to buy a replacement than to try and weld it with nickel.

    One make do tip. If you want to preheat with arc welder dont dead stick it, that is hard on welder. Especially cheaper buzzbox welders. Some large engine driven welders people do this to thaw pipes. Or at least used to when steel pipe was more used. A big heavy duty engine welder can handle some abuse like this.

    One way you might try is to set your welder to AC and get some 6010 rod. Its meant for welding with DC. 6010 wont weld on AC but can be used to cut, rather cleanly actually. Keep a wide arc and move around to avoid it cutting. Should warm things up quickly without splatter. Practice on scrap before doing this on real item. It does really dig in if you arent careful.
     
  7. Ken Scharabok

    Ken Scharabok In Remembrance

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    Thank you. What I need to weld is a piece of 1/2" x 3" x 3" quenched mild steel plate to a 3 LB China-import sledge hammer. I don't know what steel the head is, but doubt it is much more than a low-grade of cast steel or even cast iron. I sold one and the guy e-mailed me he had to weld it back on. Said it looked like a 'cold' weld, if I remember correctly, where the head wasn't properly heated. Unless I used a torch, I would not be able to preheat the head since the handle is still in it. I don't want to heat the plate again to possibly lose the hardening of the quench. Will do as advised and weld slow on the first pass around.

    Ken Scharabok
     
  8. HermitJohn

    HermitJohn Well-Known Member

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    Bevel and weld slowly and do as Jacki C suggested and "peen" the weld. It does relieve stress and you get less porous weld although that isnt big problem with nickel rod. Even regular welds can improve whacking at them while they are still hot enough to leave an impression with hammer. I tend to use pointy end of welders hammer.

    Hmm, thinking about it, unless its just absolutely the cheapest of the cheap quality, I would bet sledge is cast steel which would mean you could use say 6011 and you can run a thick electrode (5/32 should do it with high current. (I'd at least try and see if I could weld with 6011 before using nickel) It will really bite in as that is relatively soft steel. Kinda like welding a chunk of butter, if you could weld butter. Lean heavy into the sledge head letting it take the brunt of the weld. You'll get a strong weld. If any help I have welded custom cutting edges made from spring steel to worn out mattocks and picks. They are soft cast steel and dont need nickel. 6011 works fine. No problem with welds whatsoever.
     
  9. Ken Scharabok

    Ken Scharabok In Remembrance

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    The weld is in in a corner so I can only get at it with a chipping hammer. I have been doing the first pass with stainless, then the second and sometimes third with 7018. I have sold over a dozen of these sledge/flatter combinations and the one was the only reported problem.

    Reason I don't take out the handle is they are a very dry and cheap-type wood. When I have put them in with a wedge, they split under the head. Now I just leave them in to start with.

    If you guys are bored sometime, go to www.ebay.com and do a seller search on scharabo. Ask for 200 listings to the page. Take a look at my items and see if you might have a suggest or two on adding something to my line. My store name is Poor Boy Blacksmith Tools as I target the occasional user who doesn't need high qualify stuff.

    Ken Scharabok
     
  10. i can't imagine any hammer head being cast iron it is not suited to beating with it must be cast steel if it is iron pitch it and get a steel head. You should need no preheating to weld cast steel but as heavy as it is i would run hot as possible without blowing out the plate. and try to favor the head getting some melt into it.