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Thread: Thermite Welding

  1. #11
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    Quote Originally Posted by bborr01 View Post
    We were coming through New Mexico a couple of years ago and saw a train hauling an odd bunch of cars. Turned out that it was railroad rails. They looked to be at least a quarter mile long but probably much longer. They were on several cars but in continuous rails. Interesting. I wonder what the process is for making such long steel.

    Brian
    Probably similar process like they do when they make your gutters. When I had our house painted a couple years ago, I also wanted some new long gutters replaced. When the gutter guy first pulled into our driveway, I figured he forgot to bring the damn gutters. Then I watched several guys slowly pull out a 30-35' section of gutter out of the back of the truck. The truck was only ~15' long though
    Work hard play hard

  2. #12
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    Coil stock, roll formed. Any length you want, seamless.

    They don;t do that for copper though
    1601

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    Hashim Khan

  3. #13
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    Quote Originally Posted by J Tiers View Post
    Joints in the rail rarely, yes. Also, with many curves in the track, some of the expansion can be taken up by shifting. Long straight runs would need expansion provisions.

    With 1000m of track, and 6 millionths per unit expansion per deg C, every degree is then 6000 um, and 80C change is then almost half a metre.

    Old time track was in 10m or so sections, IIRC, so then there would be about 100 joints per 1000m, and each joint would have to take up 5mm or so. Perfectly possible. Of course, the force needed th shift the joint would need to be less than the force needed to shift the track position, and those rail joints were normally made up tight.
    My understanding is that the rail ties and bed are nowadays so heavy that they stretch the rail as needed. Rails are usually under tension except on really hot days as its easier to confine their movement in tension vs compression and buckling. AFAIK the neutral design temperature in here is +20cel so there is quite a bit tension and stretch in the tracks at -30cel winter days.
    So expansion is handled by tensioning/stretching the rail, not by curves or expansion joints.
    Again AFAIK, Curves are more tricky as tension tends to cause also sideways shifts in rails.

  4. #14
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    Wiki spoils the fun again. It's normal tracks that are resistance welded together to form 1440 long pieces that are then brought on site. It seems that thermite is mainly used for repairs.

    from https://en.wikipedia.org/wiki/Track_...us_welded_rail
    The preferred process of flash butt welding involves an automated track-laying machine running a strong electric current through the touching ends of two unjoined rails. The ends become white hot due to electrical resistance and are then pressed together forming a strong weld. Thermite welding is used to repair or splice together existing CWR segments. This is a manual process requiring a reaction crucible and form to contain the molten iron. Thermite-bonded joints are seen as less reliable and more prone to fracture or break.[citation needed]

    North American practice is to weld 1⁄4 mile (400 m) long segments of rail at a rail facility and load it on a special train to carry it to the job site. This train is designed to carry many segments of rail which are placed so they can slide off their racks to the rear of the train and be attached to the ties (sleepers) in a continuous operation.
    There is a profound difference between spare parts and extra parts.

  5. #15
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    In Finnish but you can probably follow the math on some pages:
    https://www.theseus.fi/bitstream/han...pdf?sequence=1

    Table 2.4 shows highest compression and tension forces under temperature variations. Largest here used continuous rail profile JK 60 E1 is under 2077kN tension in winter temps. (46 0000 lbs tension in Freedom Units)
    Or 114MPa tensile stress, about 10-15% of the tensile strength of the rail steel.

  6. #16
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    I do not believe you can put rail under tension when laying it. Ties in US are wood, not many concrete ties, which are far more energy intensive to make. The new light rail uses concrete, but so far all railroad usage I have seen is wood.

    The ballast is heavier than the ties... and there is a lot of it.

    Now, if you lay track at 50F, there will be tension when it is -40F/C, of course. But I do not see that there is any deliberate tension used when laying track in the US. They set it, align it, spike it, and move on. The tension, if any, is related to the minimum temp, vs the temp when the track was laid.

    temperature changes have a way of shifting anything that is in their way..... it is a very powerful force. A long thin thing like rails will shift sideways (reference euler formula) under compression.
    Last edited by J Tiers; 01-12-2019 at 06:39 PM.
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  7. #17
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    What they do is heat the rail to about 400F, weld up the joint and let it cool. Guys were telling me there can be 40 to 60 tons of tension on the rails. Last month I was working on a steel gang up in Northern BC, so got to see this up close.
    Flash butt welds are the preferred method as there is too many rail breaks with thermite when the temperature drops down to -20 or lower.

  8. #18
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    Quote Originally Posted by J Tiers View Post
    I do not believe you can put rail under tension when laying it. Ties in US are wood, not many concrete ties, which are far more energy intensive to make. The new light rail uses concrete, but so far all railroad usage I have seen is wood.

    The ballast is heavier than the ties... and there is a lot of it.

    Now, if you lay track at 50F, there will be tension when it is -40F/C, of course. But I do not see that there is any deliberate tension used when laying track in the US. They set it, align it, spike it, and move on. The tension, if any, is related to the minimum temp, vs the temp when the track was laid.

    temperature changes have a way of shifting anything that is in their way..... it is a very powerful force. A long thin thing like rails will shift sideways (reference euler formula) under compression.
    AFAIK They use hydraulic tensioning if they have to weld the tracks in winter. Most of the track repairs at least in here are done during summer months so that takes care of the problem.
    Neutral stress design temperature around here is +17 to +20c. Tension is easier to handle(no buckling) so they bias the expected maximum forces a bit to tension side.

    While 200 tons of tension in the railroad track sounds like huge amount there is also gazillion of ties that share the load.

  9. #19
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    Thanks for posting that video! I have been aware of the Thermit process since my teen years, but the video is the first time I've ever seen it done.

    I have here a copy of "Welding Practice" published by the Railway Training Institute, in 1926. The last four chapters cover Thermit welding as it applies to repairing steam locomotive frames and parts. In this instance, it's much like investment casting. After the frame is prepared by opening up the fracture to about 2 inches or so, cleaning the area to be welded, and stretching or spreading the frame to allow for contraction after the weld cools, a wax patterned is formed around the weld area. Then a mold box is put in place and filled with a refractory molding material which is rammed much like any other foundry mold would be. The necessary vents, preheat gate and pouring gate are incorporated into the mold. Preheating melts out the wax and leaves a cavity for the Thermit to fill. The remainder of the job is very much as shown in the video.

    The temperature of the steel pouring out of the Thermit crucible is much higher than the melting point of steel, so it partially melts the surrounding steel and makes a very homogenous joint.

  10. #20
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    If there are any serious about the assembling of those long sections and building a new siding with switches etc , I have a large file of pictures of the construction of the siding for the "Rail Runner" at Isletta Pueblo (just south of Albuquerque) . I'll be happy to share with anyone who is. e-mail me or PM if so.
    ...lew...

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