How much pre-heat ?

  1. RTFM

    RTFM New Member

    Messages:
    20
    Location:
    UK, Shrewsbury
    Helloooo,

    I’m finally getting back to my bench project - however - having read a few threads on welding benches I’ve changed my plan slightly.
    I’m now going to make the top half slatted (already done) and half solid, b.u.t. to do this I’ll need to join several 150 x 5 plates and 600 long together. There’s an intermediate support at 300.

    I’m thinking to minimise any warpage I should pre-heat. But how much? Warm, radiator hot, 100+ degrees ?

    I will be spot welding every hundred mill around first - also any tips for order of welds?
    I was thinking doing the short ends first then starting from the middle on the long sides and running out?
     
  2. Paul.

    Paul. Moderator Staff Member

    Messages:
    6,155
    Location:
    Northampton. UK
    To reduce distortion you need to keep it cool, preheating wont help at all, its only a bench not a road bridge, so just use enough weld to hold it together and no more, its quite surprising what a few well placed tacks will hold, especially if your design puts the joints in compression when loaded
     
  3. RTFM

    RTFM New Member

    Messages:
    20
    Location:
    UK, Shrewsbury
    Copy that, I’m such a noob lol
     
  4. Richard.

    Richard. Member

    Messages:
    18,197
    Location:
    Cambridgeshire
    Pre heating steel is applied to certain jobs to reduce hydrogen cracking primarily.
    It *is* possible that a throughly evenly warmed through item can help with distortion if cool down time is done very slowly to reduce localised fast contraction.
    It’s not going to work on a bench. It’s not even remotely necessary on a bench.
    Clamps, design and welding sequence as Paul said are the easiest way to control any unwanted warping in a structure. You’d also be surprised at just how easily stuff pulls back when you do get distortion with basic tooling, the odd cleverly placed weld, even a smidge of heat.
     
    stuvy and RTFM like this.
  5. TechnicAl

    TechnicAl Member

    Messages:
    7,044
    Location:
    Rotherham
    I agree with Paul and Richard....its the temp differential that causes distortion but as far as Im aware its not really reduced by preheating. Normalised steel tends to distort less than the as rolled product. The trick is to repeat whatever you do on the other side. Stagger welds rather than one long continuous weld. Its not really an exact science so holding it down also works well...
     
    stuvy and RTFM like this.
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