Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 33

Thread: Can Thermite do this weld?

  1. #21
    Join Date
    Aug 2006
    Location
    Taylorsville Ky
    Posts
    5,882

    Default

    I think someone who uses thermite would have a good idea of how much to use to weld bond the plate to the anvil. You need enough to melt the anvil top and the bottom of the plate but not the whole plate and that would be the tricky part. You would have to preheat the anvil and dam the sides if the anvil is standing up.
    It's only ink and paper

  2. #22
    Join Date
    Jun 2006
    Location
    Austin, Texas
    Posts
    15,651

    Default

    Quote Originally Posted by Doc Nickel
    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.
    Doc,

    I'm not familiar with the blacksmithing terminology, but it sounds like you're trying to build-up a 2 - 3" layer of tool steel on the top face of the anvil?
    If that's the case, wouldn't MIG hardfacing wire work? It comes in H13, S7, etc, builds up a Rockwell 45 - 55 hardfacing layer, and can be layered on in regular overlapping patterns.

    Hardfacing wire isn't cheap, and it needs around 175 amps for .045 wire, which is at the limits of the 220V Lincoln/Miller 175 Plus class machines...
    I've seen hardfacing wire go on Ebay for a lot less than the LWS...

    Here's an article on Metalweb News describing the construction of an anvil from plate stock, and he using MIG hardfacing to build-up all the working surfaces:
    http://www.metalwebnews.com/howto/anvil1/anvil2.html



    I'm sure you can mix your own thermite with iron oxide and aluminum powder, but once the burn starts, you can't stop it, so the trick would be knowing how much thermite to use without melting your anvil into a pile of slag...

    Good luck,

    Robert
    Last edited by lazlo; 11-25-2007 at 07:47 PM.

  3. #23
    Join Date
    Mar 2003
    Posts
    3,044

    Default

    Quote Originally Posted by BigBoy1
    About 3 years ago I ordered a 55 gal. drum of thermite for my job and it was shipped as non-HAZMAT and I was really surprised at that.
    -The info over at United Nuclear suggests it's pretty hard to get lit; sometimes even a blowtorch won't do it. They sell a "thermite igniting compound" that I think is mainly magnesium flash-powder type stuff.

    So the shippers probably consider it pretty stable, and probably assume that, by the time the stuff ignites, the truck/plane/cargo container would already be pretty well involved.

    For your welding, I would think a very large quanity of thermite would be needed to provide heat for the parts to be welded. They would have to be heated to melting temperature and then to provide the bond for the parts.
    -That's probably something that'll have to be worked out by experimenting (since I don't have enough math background or knowledge of the stuff to calculate it beforehand.)

    The rail-welding stuff (including the PDF linked earlier) shows a considerable volume of thermite for what appears to be a relatively small weld seam. A lot appears to wind up in the various mold gates and presumably slag traps (doesn't the aluminum bubble up as slag?) plus of course a bunch of volume simply burns away.

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

  4. #24
    Join Date
    Jan 2004
    Location
    Independent principality of Sinquefieldia (formerly Missouri)
    Posts
    16,982

    Default

    Carl is correct.

    Typically, both parts are heated before the weld, the thermite is lit off, and the plug pulled when it's hot to run the stuff in. I've seen it done, but not recently.

    You probably would heat the anvil, but NOT the plate, which would surely be heated sufficiently by the iron. That's assuming it is relatively thin.

    The weight of thermite would be that equivalent in resulting iron content to the thickness of join you want, plus enough extra so that you would not have a shortfall. The thermite makers will know exactly what resulting iron a given weight of material will produce.

    If you had a "chill" for the plate, it might harden it enough. I'd think you would not want it really hard, because it would chip and crack.

    I suspect the difference in mass between the two pieces would make most hardening moot, unless you could keep the plate cool while all that hot anvil iron was cooling.

  5. #25
    Join Date
    Jan 2004
    Posts
    782

    Default

    I had a chance to use thermite once in the Navy. It was a slab maybe 14" square by an inch thick. You would put it on top of a rack of equipment and it would melt down to the bottom. I wouldn't try to weld with it.

    I have also used Cad Weld to attach ground wires to radio towers. You had to have a mold to match the type of connection you were doing.

  6. #26
    Join Date
    Jun 2003
    Location
    Cairns, Australia
    Posts
    307

    Default

    Doc,

    Some time ago I was involved with quite a lot of thermit welding of railway rails, and still have the book on the process which I got at the thermit welding school.

    Before welding a rail joint a dam is created for the weld metal using pre-manufactured sand molds contoured to fit each rail type. Good preparation of the rail ends to be welded is very important – the faces must be cut square and parallel, and free of rust. Any fish plate bolt holes in the weld area need to be filled with a fitted steel plug before welding. The gap between the rails needs to be adjusted. To give an idea of the gap needed, for 94 lb/yard rail a 16 mm gap was used.

    The rail ends are pre-heated to at least 950 degreesC, (light red to yellow in color) and both rail ends heated evenly. It is also important to pre-heat the sand moulds.

    When welding rails the Thermit reaction takes place in a separate crucible, which is then tapped to feed the molten metal into the dam around the joint. The pre-packed individual welding portions are fairly bulky and heavy; a pack of 5 portions for five rail welds for 107 lb. rail weighs 39 Kg, which would indicate that a lot of thermit mixture would be needed for an anvil face.

    A fair bit of excess metal needs to be cut off with a hot sett and the weld area around the rail head ground to correct profile before the track can be returned to use. A competent two man gang will average about 8 welds a day.

    Note all the above applies to thermit welding of railway rails – I've never had anything to do with general thermit welding, which I imagine would require a fair bit of experience and skill, since each weld in a general engineering situation can't be “reduced to numbered steps” as is the case with rail work.

    Regards,

    franco

    Added: A lot of people can obviously type quicker than I can!
    Last edited by franco; 11-25-2007 at 08:40 PM.

  7. #27
    Join Date
    Mar 2005
    Location
    Albuquerque, New Mexico USA
    Posts
    745

    Default

    Quote Originally Posted by Doc Nickel
    -The info over at United Nuclear suggests it's pretty hard to get lit; sometimes even a blowtorch won't do it. They sell a "thermite igniting compound" that I think is mainly magnesium flash-powder type stuff.
    We used to light the stuff with potassium permagnate and glycerin or with magnesium ribbon. With the permagnate just make a pile of it, make a dimple in the top and put in about 20% of the volume (check this, I'm going on memory) of glycerine and step back. It might take some time to start but it'll definitely get going.

    The rail-welding stuff (including the PDF linked earlier) shows a considerable volume of thermite for what appears to be a relatively small weld seam. A lot appears to wind up in the various mold gates and presumably slag traps (doesn't the aluminum bubble up as slag?) plus of course a bunch of volume simply burns away.
    The aluminum goes up as Al2O3 (think tons of white smoke), leaving a slag and some relatively pure iron at the bottom of the crucible. The iron makes up a little more than 50% of the mass of the thermite (assuming Fe2O3) and so can't be more than that in the remaining mass. You'll have to have enough mass to retain enough heat to cause fusion with the base and the top plate and not to cool even partially as it passes through the plate (assuming that you're allowing the molten iron to come in from the side of the plate) so figure on preheating the anvil base and top plate to at least a high black heat. Figuring 1/2 gap on a plate 6 x 18 that's 15 pounds of molten iron coming down in one slug from 30+ pounds of thermite (I'd go heavy on the +, say something like 40 pounds unless there's some limestone or other slag forming compound in the thermite where you'll want more).

    Most important: pictures. We want movies of the process if you're crazy enough to do it. Me? I hardfaced a swaybacked anvil many years ago and promptly blew my right elbow apart. I can't hammer 5 minutes without calling for morphine.

  8. #28
    Join Date
    Mar 2003
    Posts
    3,044

    Default

    Quote Originally Posted by lazlo
    I'm not familiar with the blacksmithing terminology, but it sounds like you're trying to build-up a 2 - 3" layer of tool steel on the top face of the anvil?
    -Sort of.

    Using my anvil as an example, the main body- the bulk of the weight- is wrought iron. (Anvil was made sometime prior to 1910.) There's a roughly 3/8" thick "tool steel" plate as the working surface.

    The anvil- this one anyway, other makers did other methods- was made in three pieces; the "foot", the body (including the step and horn) and the faceplate, all three of which were forge-welded together all at once. Once welded, the entire anvil was quenched in a huge vat of water, which hardly affected the wrought body, but hardened the face to somewhere north of R60C.

    My example has had a great deal of use, and the faceplate is now swaybacked (there's a "dip" in the center of the working area) chipped (all the edges are heavily rounded off from wear and chipping) and cracked. I've been slowly building up corners, filling in spalls, and patching what cracks I can, but it's slow, expensive, and I'm no longer sure I can repair more than the most superficial cracks.

    Best of all worlds, I'd love to be able to mill off (probably after annealing) most or all of the existing faceplate, and replace it with a newly-machined face of something like S7, around 1/2" to 3/4" thick. Properly welded (I've considered even brazing) and heat-treated to somewhere around 55-58 C.

    If that's the case, wouldn't MIG hardfacing wire work? It comes in H13, S7, etc, builds up a Rockwell 45 - 55 hardfacing layer, and can be layered on in regular overlapping patterns.
    -Yes, it can work, but there's several issues. One, it's expensive. As above, I've seen wire range from $4 to $9 a pound. Two, most wires and quite a few stick hardface rods crack- they're designed to to "self stress relieve". No big deal on an excavator blade, but not what I want for an anvil. And three, R55C is about the lowest I'd like to see for a face- it's purely preference here, but no matter what, you wind up with variable hardness over the face, as a fresh pass tends to slightly anneal a prior pass.

    Here's an article on Metalweb News describing the construction of an anvil from plate stock[...]
    -Yep, I'd already seen that before I even got this anvil, and I referred back to it a couple of times back when I was planning on stick-weld-repairing it, after finding out how bad it was.

    I'm so far unimpressed- but learning- with hardfacing rods. I'd much rather see a uniform, known-alloy plate applied, but the welding will be a trick.

    I'm sure you can mix your own thermite with iron oxide and aluminum powder[...]
    -Yeah, if I only needed a few ounces. Going by the rail-weld information, it's looking like I'd need maybe ten or fifteen pounds of the stuff, not counting however much I'd need for practice shots. That's a lotta grinding and filing.

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

  9. #29
    Join Date
    Aug 2002
    Location
    Albuquerque
    Posts
    2,158

    Default

    Here is one of about 300 shots I took during the RailRunner track
    and switch up grade just south of Albuquerque last fall. If anyone
    is intrested in the whole process, cutting the rails, installing the
    "pot", the results, and then grinding the weld, etc I'll be happy to
    send you as many as youd like. :-) Also moving a pre-fabd switch
    into alignment with the main line etc.
    ...lew...

  10. #30
    Join Date
    Jun 2006
    Location
    Austin, Texas
    Posts
    15,651

    Default

    Quote Originally Posted by Doc Nickel
    Quote Originally Posted by Lazlo
    I'm sure you can mix your own thermite with iron oxide and aluminum powder[...]
    -Yeah, if I only needed a few ounces. Going by the rail-weld information, it's looking like I'd need maybe ten or fifteen pounds of the stuff, not counting however much I'd need for practice shots.
    You can buy iron oxide and aluminum powder at any chemical supply house. Iron Oxide sells on Ebay for $1.60 a pound:

    IRON OXIDE RED 10 Pounds Lab Ceramic Chemical Fe2O3

    Last edited by lazlo; 11-25-2007 at 10:53 PM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •