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Thread: Can Cast Iron be Welded

  1. #1
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    Default Can Cast Iron be Welded

    I'm confused. I have heard from several people that cast iron cannot be welded...and I have read that it can be welded.
    If it cannot be welded, can somebody please explain why so that I may better understand. If it is in fact weldable, could you please explain the process since apparently it must be difficult to do. I am not a weldor (obviously), but I can usually get two pieces of metal to stick together, but I haven't tried to weld cast iron. Can it be "welded" to anything other than another piece of cast iron? Can it be stick welded, and if so what would be the recommended rod? Lots of questions. Thanks.
    There is no shortage of experts, the trick is knowing which one to listen to!

  2. #2
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    Cast iron can be welded. Some varieties are not too difficult to weld, but it takes alot of preperation and care to do it right. You can make "bubble gum" repairs using a nickel rod in a stick welder. I've used this to repair non-critical castings. To properly weld cast iron takes more skill and knowledge than I have. I usually resort to brazing and mechanical repairs - i.e. bolts etc.

    The big issue with CI is the tendency to crack as it cools and the porosity of the metal which can absorb surprising quantities of oil or etc.

    Torker will, I am sure, pop in and set us straight on the details.

  3. #3
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    If it has a crack in it drill a hole alittle past the end prior to welding. V it out. preheat and let it cool really slowly. A method to do this is to bury it in ashes while it cools. Use rods for CI, they feel differant while welding. The best I could describe is that they feel like your welding with clay. the shape of the item will determine the difficulty. You want to prevent leaving stresses in it when it cools. Oh yea, Stick welding is what I'm describing.

  4. #4
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    Thanks for the quick responses.
    Fasttrack...Is there a specific number of nickel rod? Is it readily available?
    ahidley...I don't ever recall seeing CI rods. Are they readily available or must they be purchased at a welding specialty.
    As for heat retention, I am short on ashes, but I do have some fine grade of sand that I could preheat and then put the sand and casting inside an insulated vessel. I would think that should reduce the loss of heat for several hours or perhaps a full day. Would that be adequate?
    Nice tip on drilling the hole at the end of the crack. I have used that technique before on a broken crock, and it kept it from spreading further.
    There is no shortage of experts, the trick is knowing which one to listen to!

  5. #5
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    First there is no "one size fits all" when it comes to welding cast iron and some castings are not weldable even if they appear to be welding OK, while most types of castings will weld OK some types simply can not be satisfactorily welded at all. It depends a great deal on WHAT you are welding since high strength Malleable castings should not be welded because just the heat from the welding will destroy the strength even if the weld appears all right. If this is to be a quality repair it is a must to properly identify just what kind of iron you are dealing with and determine what method is best used. If you decide to arc weld this casting use a Nickel rod for cast iron such as the Ni55 or if machining is going to be required then you must use a machinable grade high Nickle content rod such as Ni99. Again if this is Malleable iron and will be used in a critical or high strength situation then it would be best to just replace the part because Malleable iron will be very difficult to even approach the original strength regardless of which filler metal is used. This is due to the fact that once heated to temperatures required for welding the Malleable iron grain structure will be drastically changed and the casting will become a much weaker and brittle form of Grey iron in the heat affected areas. Whatever you decide DO NOT weld it with a steel filler such as E7018, 7014, 6012 or any other steel rod including the stainless rods such as 308, 309, etc.
    Last edited by radkins; 12-03-2008 at 04:17 PM.

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  7. #7
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    OOPS!! When I made my original reply I unintentionally left out part of what I intended to say and made it look as if I was saying most cast iron is not weldable which of course is not true! I have made corrections to that post. Most iron castings can be welded and my point to the original poster is that some can and some can not which leads to the confusion with why some people say yes and others no. This is why it is usually important to get an idea of what kind of casting someone is working with so a determination can be made as to the process that will be necessary and the procedure that should be used. A case in point about a weld that should NOT be attempted is an after-market front hub spindle on a Nissan truck I saw recently where a guy heated the tie rod socket on this spindle to get the old tie rod to release, not a problem with the factory steel part but another story entirely with the after-market malleable cast iron spindle! When they tapped the tie rod after heating the spindle it cracked through the tapered hole where the tie rod fits so the mechanic removed it and sent it to a weld shop for repair. The part was then preheated, welded with Nickle rod (Ni55) and cooled slowly overnight in a welding rod oven, however 3 days after it was reinstalled the spindle broke about 1/2" from the weld joint, this part should never have been welded. This is a classic case of what happens to this type of iron casting when it is welded, it appears just fine but the transition area between the weld and parent metal has been changed by the welding heat from a malleable iron casting into a much weaker Grey iron. My whole point is that welding cast iron can be done most of the time but there is no "blanket" procedure that applies to all iron castings and the type, size and application all need to be considered when deciding what process to use.

  8. #8
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    I've heard experience trade welders prefer specific brands of Nirod over others but can't recall them now, I don't know if that would have any effect over the type of rod as long as it's all quality stuff but working with CI is temperamental so perhaps theres something to it.

    My buddys Dad in the 40's snapped a little International T20 crawler in half through the bellhousing skidding logs in New Zealand, amazingly he wasn't killed, however having little money back then they either brazed or welded it back together and it's still going today, not used as vigorously now but it was put right back to work after the repair.

    Another buddy had an AC HD14 crawler, fairly large machine for it's day and cracked the rear main chassis and it spread on the cut, everyone who looked at that machine said it was scrap, my buddy being just in high school and ignorant to the experts opinion and large on gumption gutted the back, came up with a crazy clamping setup of I beam, rams, etc and welded inside that housing for 24 hrs straight, once he was done he filled it with floordry or kitty litter and went to bed, 5 days later it was still warm to the touch, that machine worked for years and now sits at a museum without failure.

  9. #9
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    I can relate to the equipment repair because I did something similar a few years ago. A Caterpillar 988 front end loader with a cracked transmission housing, the guy who owned it was already nearly bankrupt on this particular job and as he put it "had nothing to lose" so he asked me to just do the best I could with it and he asked for no guarantees. We just flushed the oil out of the case, beveled the broken area with a grinder, hammered the distorted part back in place, preheated with a torch (rose bud) and welded it with Ni55 filler-I don't however recall the brand. This crack (fracture is a better description) was about 3 1/2 ft long starting on one side and running all the way across the bottom. After grinding all the way through I drilled a hole on each end of the crack and starting from the ends and working toward the center I skip welded the thing with stitch welds about 1 1/2" to 2" long with heavy peening of each bead as it cooled. The process took most of two days after the actual welding started and then a large electric space heater was placed under it and gradually moved back allowing the cooling to take place over a little more than 24 hrs. I would not have given a cent for that thing's chances of success but it did indeed hold up just fine for at least two years after and probably longer but I have no idea what happened after that. So yes cast iron can be welded and sometimes it will work when by all indications it should not but the point I have been trying to make is not all cast iron is the same. When someone says "Cast Iron" they are talking about a whole class of metals with widely varying characteristics that may require a unique approach from one type to another, that is why I said there is no blanket method of repairing cast iron that is to be used with all types, what works well for one type may not work at all for another so identifying what kind of cast iron is being repaired is important.

  10. #10
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    Thanks again to all who responded. I suspected that this might be a can of worms, but I didn't know how big the can was going to be. At least, i now have an idea why I've been confused since it seems that in general there is no straight answer. I think I'll just leave the welding of cast iron to the "experts". I have a broken casting on an olde Monarch lathe that is in need of repair. It's nothing serious or dangerous, but just something that I'd like fixed. If I ever have occasion to remove it, I'll see about getting it repaired, but until then, it will just have to wait.
    There is no shortage of experts, the trick is knowing which one to listen to!

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