Cast-steel welding
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  1. #1

    Cast-steel welding

    I'm looking for some advice on how to repair the cast base of a large motor. We have pretty good mig welding ability in house and can also stick weld although we don't do that very much. Any insights and suggestions on the best way to do this repair is appreciated.
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  2. #2
    Join Date
    Jun 2008
    Near Ottawa Ont

    Re: Cast-steel welding

    Big problem there I think is that it must have broke for a reason and it would be hard to make a weld repair to be as strong as the original. So what ever weld repair was done would be likely to fail again.

    Cast rod (nickel) with good pre heating, short welds and beat them with a hammer then slowed cooling would likely be the best repair. Weld in same direction and stagger the ends of the short overlapping passes to minnimize concentraiting internal stresses.

    Not right, but MIG has surprised me in the past in being able to hold cast back together, Notched out well, preheated then the crack filled up slowly with low heat and smallest stainless wire.

    What are the options to repair it then bolt plates in front and/or behind the break area to strengthen it?
    Last edited by Timberwolf; 07-07-2009 at 07:55 AM.
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  3. #3
    Join Date
    Oct 2007
    Vandalia, Ohio near Dayton

    Re: Cast-steel welding

    Is the base really cast steel? It's tough to be certain, the but the surface of the crack looks typical of grey cast iron.

    Your pictures show a clean fracture surface everywhere, except for the bottom of that internal reinforcing rib. The bottom of the rib looks dirty. This suggests to me that a crack started there, where that rib would be under maximum tension from the applied load of the motor. That small crack grew over time, which would explain the dirty/rusted fracture surface. Then the whole base plate failed catastrophicly; leaving a clean fracture surface.

    I agree with Timberwolf that you have to fix the root cause of the break, in addition to repairing the motor base. Otherwise it'll just crack again.

    Was the bolt at the top of the crack overtightened? Maybe this motor was moved and reinstalled right before the failure?

    Or were the base plate bolts not torqued down enough, allowing the motor to move and fatigue crack the base plate with vibration?

    I also think Timberwolf has the right welding procedure; if the base is cast iron. If it really is cast steel, then you can weld it with 7018 rods or ER70S-6 wire.

    I'm not sure I agree with drilling and bolting a plate over teh repair though. Unless it's done exactly right, drilling more holes in the base plate just creates future places for cracks to start from. I couldn't even begin to suggest the best procedure for this kind of repair. Better to weld and also figure out why it cracked in the first place.

    Timberwolf, the nickel rod and stainless MIG wire both form an austenitic weld deposit. Keeping the steel microstructure as austenite reduces some of the shrinkage stresses that normally occur in iron alloys as they cool. This, combined with a thorough preheat to ~400°F and slow cooling, keep the thermal stresses to the part as small as possible.
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  4. #4
    Join Date
    Nov 2006

    Re: Cast-steel welding

    The base is cast iron... and an excellent candidate for a braze repair.

    Vee and braze is how I'd repair it.

    Good Luck

  5. #5
    Join Date
    Jun 2009
    Springfield, IL.

    Re: Cast-steel welding

    Quote Originally Posted by A_DAB_will_do View Post
    Is the base really cast steel? It's tough to be certain, the but the surface of the crack looks typical of grey cast iron...
    I agree on that crystalline look
    Try shaving a sliver off an edge with a utility knife or sharp chisel. If you can get an actual sliver to form it’s probably some alloy of cast steel. If all you get is short broken chips it’s most likely cast iron.

    Also, this works, I have done it myself-
    Last edited by milwiron; 07-07-2009 at 11:34 AM.

  6. #6

    Re: Cast-steel welding

    Just wanted to follow up on the repair...thanks for the advice. I talked to the rep at our local welding shop and he told me the piece was actually cast iron. He recommended as you did to stick weld with nickel rod. I used Eni-CI electrodes and preheated the material. I also welded in small bits at a time. Lastly, I attached a mild steel plate to the side using the same rod. We think the casting broke because a bolt that held it to the base frame had come loose which resulted in the frame (to which the motor was attached) cracking and we have addressed that problem. So if it breaks again it won't be for lack of good advise rather it'll be due to lack of operational skill. But you can't get better if you don't practice right? Thanks again.
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