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Steel tubes bending

  1. Jan 17, 2008 #1
    My name is Gai Abraham, an automotive engineer trying to build a little LEV (low emission vehicle)

    I have contacted you previously and I wish to ask further help on the bending of steel tubes.

    Namely I have designed a chassis from bent steel tube, the technical sheet on S.S. astm 301 allows, depending on the hardness of the tube, to have elongations ranging from 40% (for annealed) up to 9% (for full hard) from original length.

    The issue I am trying to solve is whether the original length is the midline of the tube, giving during bending, compression on the inlay and tension on the outlay for final plastic bending

    or the original length is the inside radius of the curved tube and gradually all the tube stands deformation up to a maximum value on the outer side?

    I think that if the tube is held in position and supported on the inside while curving it, the original length is the inside radius since it was not able to compress.

    thank you
  2. jcsd
  3. Jan 18, 2008 #2
    I gotta ask: How would you support the inside of the tube? If you could do that, you are correct in saying the inner radius would be the length. But, I've never seen anything even close to that.
  4. Jan 20, 2008 #3
    that's the real question, I don't really know how the bending machine works, I guess that there is a concave roller on either side of the tube and the roller turns on a radious predefined supporting the inner tube while the outer roller goes on bending it on the outside.

    what's your e-mail add?

  5. Jan 20, 2008 #4


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    An old trick to consider, is to fill the tube with sand, pack it as tight as possible, plug both ends,( you might need to have a pair of plugs machined, kind of like thermos bottle stoppers) this will make the tube almost as solid as a rod. After bending the end plugs are removed and the sand will pour out.
  6. Jan 20, 2008 #5
    Probably for your application, I'd suggest you go to the Pirate4X4 website and find tubing fabrication hints.
  7. Jan 21, 2008 #6
    thank you all
    as I will try to take this Lev to production I am hoping to use the Stainless steel ASTM 301 in its 1/2 or 3/4 hard modes.

    the limit of bending of these two is bound by the percentage of longation so if I use a too small a radius I might crack it.

    on the autocad program I have modelled the bending radius of 90 deg. and I have found that if I take the values of the inner radius and th outermost radius of the bent I am out of the elongation percentage stated but if I use the midline, then I pretty close.

    as such I was wondering if the tube is being supported from the inside, then the midline stretches and the outer line stretches even more, on the other hand I might just as well take the midline as being stable i.e. original lebngth, and on either side I have got a compression and an extension.
    but as I don't want to buy a stock load of steell tubes of one grade to then find out it doesn't cope with bending I thought to hear some views about it.

    BTW I like it the PIRATE 4X4 stuff, Thanks TVP45
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