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Thread: Can Thermite do this weld?

  1. #1
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    Default Can Thermite do this weld?

    Over on the IForgeIron blacksmiths' board, someone asked if Thermite could be used to reweld on a broken anvil horn, or other similar uses.

    That got me wondering if Thermite could be used to weld on a new faceplate to an anvil.

    Many older anvils have had a great deal of use, and cracked, chipped or swaybacked faces, and many cheap import anvils are naught but cast iron, too soft and pretty much worthless as a usable anvil.

    A faceplate is easy to fabricate (say, a plate of S7, milled in the annealed state) but very difficult to properly attach to the anvil body. The old way- turn of the century- was to forge weld them all together, but this takes a great deal of heat, time and skill.

    Modern electrical welding is ill suited for a 2" or 3" deep weld, and is used mainly just for repair or refacing using hardfacing electrodes. Brazing has been suggested as possible- requiring less heat than forge welding- but likely to produce occlusions, and an overall-lower-quality join than a true weld.

    But what about thermite? From what little I know about it- largely from YouTube videos - it seems it might be as simple as, say, making a fireclay/firebrick "dam" around the face of the anvil body, pouring on perhaps a quarter-inch of thermite, laying the milled tool steel faceplate on top, and lighting 'er off.

    Depending on how it works and the materials involved, one might or might not quench (to get the faceplate hardened) but it seems to me the two parts would be pretty thoroughly welded.

    I suppose it's something that would simply need some experimenting to see how it'd work, but I wonder if there'd be a risk of occlusions or voids... maybe lay the anvil on the side, let the weld burn vertically?

    I may be interested in trying it- I have a century-old anvil I've been slowly repairing with hardfacing rods and other techniques (both MIG and TIG) but it's looking like the faceplate already had a great many small cracks before I ever started welding on it.

    As bad as it is- and the labor it's taking to repair it with electrical welding- I'd love to be able to mill off some or all of the original face, and somehow apply a shiny new, flat and straight face, if it were, that is, as easy as a little fireclay, maybe some sand, and a few ounces of Thermite. (Where would one even buy it? I assume it'd be a closely-controlled substance...)

    Any opinions or experiences? I know it's used to weld train tracks, and it's been used to weld large copper conductors, and the weld would be basically pure iron- though that's not a problem, my anvil body is pure wrought iron as it is. I don't see why it wouldn't work, but I can hardly afford to buy a bunch of plate tool steel, thermite, and chunks of heavy steel to practice welding together.

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

  2. #2
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    Doc, I'm not familiar with thermite but I can tell that in my industry, we do some massive buildups using weld. I've goughed out cracks in big coal mining equipment that where up to three feet long, six inches wide and almost a foot deep. Obviously the cracks themselves where not six inches wide but you have to make them this wide to get the gougher in there. These cracks are then filled with sometimes hundreds of passes of weld. Depending on the metal we work on we use either LA T-91 1/16" flux core or SS wire.
    If we had to do a job like yours we'd bevel the top plate right up to within 1/4" from the top and in as far as a pipeliner nozzle would reach. Pre heat the anvil to 250F and maintain the heat with a propane torch throughout the welding. On something like this I'd use temp sticks to maintain an interpass temperature of 350F maximum. We generally stop welding a couple hours before shift ends and keep the heat on then wrap the thing in insulation (we had ceramic wool blankets). Some things are very critical and the welding never stops. Two shifts at 12 hours each keeps going til it's done.
    Sounds like your Thermite idea would be quicker than that.
    Russ
    I have tools I don't even know I own...

  3. #3
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    I too wonder whether it's still possible to buy thermite. Probably not.

    I remember seeing it used to weld streetcar tracks, when I was a kid. Same deal, they'd build up a fireclay dam around the joint, then the thermite went into something that looked like a flowerpot, stood on top of the dam. There was some kind of priming powder, which in turn was lighted by either a magnesium ribbon or an oxyacet torch, that got the thermite going.

    I also remember my high-school chemistry teacher demonstrating the reaction. She put about a tablespoonful into a paper cone that was suspended over a porcelain tray full of sand. When it went off, it burned the paper instantly, the thermite fell into the sand, and burned its way through the sand, through the tray, and through the tabletop. I suspect that was the last time she ever tried that!! The wonders of chemistry...

    Pete in NJ

  4. #4
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    How about explosive welding?Seems would be ideal since you want to join two large flat surfaces together.

  5. #5
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    Maybe implosive welding rather than explosive welding. The explosive welding would blow the parts apart. However, if you use implosive welding the parts would be sucked together.

    It's been a while since I read about thermite welding but it seems it was the heat from the thermite mix that heated the parts and melted the metal mixed with the thermite and when the thermite was burned off what was left was the joined parts with the added metal. I would assume the mass of the two welded parts would have to be equal or nearly so or one of them would be consumed in the heat process. Which would mean the top plate would get hotter than the anvil.

    I suppose you could dam the whole top plate and melt it into the anvil to form a top that would be for all practicle purposes be one with the anvil. It may work, because the thermite between the anvil and top would melt both surfaces and maybe the whole top plate.

    The idea of thermite welding was similar to localized recasting the part not as much as to welding the parts together. It is basically a melting furnace type of welding.
    Last edited by Carld; 11-25-2007 at 10:57 AM.
    It's only ink and paper

  6. #6
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  7. #7
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    WOW, the posibilities of thermite.
    It's only ink and paper

  8. #8
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    Thermite joining is used in the electric field to join wire connections, I believe it was Ideal came out with a new line of equipment and procedures in the last couple of years. And it is still popular for heavy welding fast on certain things. On another metal arts board the consensus is that for most application on anvils the easiest, fastest way is to silver solder the pieces together.
    Glen
    Been there, probably broke it, doing that!
    I am not a lawyer, and never played one on TV!
    All the usual and standard disclaimers apply. Do not try this at home, use only as directed, No warranties express or implied, for the intended use or the suggested uses, Wear safety glasses, closed course, professionals only

  9. #9
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    I don't think that you could use thermite to weld a hard plate to a soft base, the thermite part of the joint would simply be too big by the time you had enough mass for the weld. It'd sure be fun trying.

    In the "fun to try" department the explosive bonding would have a chance to work. Folks do that south of here out near Socorro in the "Energetics Materials Research and Testing" lab. They do a lot of explosive bonding, using explosives detonated in a wave to provide welding pressures to bond materials not usually bonded. If you had the materials this would be the least expensive. From what I've seen it has a lot of waste around the edges and might not be suitable for welding plate to an anvil.

    The brazing methods might work best but will approach the annealing temperatures of most anything you're likely to use as a hard plate. It might be a good way to do it in the end - pin the plate on using pins of the same material as the plate and lay it on a good bed of braze. Heat to the melting point of the braze then quench outside with a firehose after being sure that you have bonding all the way around.

    The surest way is still the "build up with soft rod, cover with a couple of layers of hardface" method. 7014 to interface with the anvil and the hardface, then hardface for hammering. Seems to last a good while but it's sure a PITA to put down (but not as hard to use as little pieces of roller bearing material).

  10. #10
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    do it the old fashioned way- get everything to welding heat and beat it all back together-

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