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Homework Help: Welding Coursework Problem

  1. Mar 5, 2007 #1
    1. The problem statement, all variables and given/known data
    Given, the density, specific heat per unit volume, latent heat of fusion, melting point and thermal conductivity - calculate the energy needed to melt a cubic mm of carbon steel, starting at 20 celcius.

    Hence find the minimum power needed to generate a bead on a plate weld of 15 mm square cross sectional area at a welding speed of 4mm/s.

    2. Relevant equations
    density ro = 7900 kg/m^3
    specific heat per unit mass Cm = 0.45kJ/Kg/K
    Melting Temperature of Carbon steel Tm= 1535 deg C
    Latent heat of melting deltaHf = 270 kJ/Kg
    deltaT = Tm-starting temp
    3. The attempt at a solution

    Am I right in saying that there are two energies, one to heat the metal up and another energy to overcome the latent heat of fusion?

    If so, I used Q = (mXCmxdeltaT) + (mxdeltaHf).

    When substituting the numbers I got out 7.5 J, which seems a little low.
    As for the second part, I'm not sure how to go about it.
    If anyone is any the wiser please let me know where I have gone wrong?!

    Many thanks, Gavin.
  2. jcsd
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