Spot Welding Electrodes

  1. amron Member

    Messages:
    126
    Hi
    does anybody knows what kind of kind of material (I know it"s some sort of copper ) the electrodes of a spot welding machine are made of? I would like to know the material"s no. as per some standard.
    Thanks
    Amron
     
  2. Robotstar5

    Robotstar5 Casanunda Staff Member

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    15,778
    Location:
    Birmingham
  3. supinder Member

    Messages:
    3
    INDIA
    Normally 99.9% copper is used for spot welding, but for large scale production chromium zirconium copper is used ( Cu-Cr-Zr). It has more hardness (83B rockwell) and much higher annealing temperature around 500 degree centigrade as compared to pure cooper which is 200 degree centigrade. For current detail of different capacity spot welders follow: http://www.sohalwelding.com/06-welding-machines-spot-welders.html
     
  4. GeorgeB pre-moderated

    Messages:
    879
    London, UK
    Does anyone know why shielding gas nor any kind of flux is required for spot welding?
     
  5. English Steve

    English Steve Senior Bumpkin

    Spot welding is 'resistance welding'. The two pieces of metal are clamped together between the electrodes, and a current is passed through them. The resistance caused at the join causes the metal to heat up to a welding temperature and the clamping pressure of the electrodes helps the metal to fuse locally. The outer surfaces of the metal remain relatively cool due to the heat dissipation into the electrodes (which on industrial units are usually water cooled), usually reaching a 'plastic' condition resulting in slight indentations on the surface caused by the clamping pressure of the electrodes.
    There is no arc or flame present and as such you are not actually burning anything, therefore no oxidation and no need for flux or shielding gas. The metal needs to be very clean to give a good contact and good results.

    I am sure someone will be able to give a more in-depth explanation.

    Regards

    Steve
     
    Last edited: Apr 1, 2008
  6. GeorgeB pre-moderated

    Messages:
    879
    London, UK
    I'm not sure they need to, thanks, because your explanation strikes me as excellent. My understanding is still partial however as to when exactly shielding gas or flux is needed and when it may not be required for welding type work. I mean shielding gas isn't used in steel or aluminium works, for example, when molten metal is being poured from a furnace into moulds. I would have expected the metal to get oxidised and spoiled whilst being poured. Is it just the presence of an arc which lead to oxidation? And if there's no arc, there's no oxidation?
     
  7. English Steve

    English Steve Senior Bumpkin

    Hi George.
    This is stretching my knowledge a bit, but here goes...

    When melting iron in a cupola for casting etc, flux is added in the form of limestone to remove non-metallic impurities. These impurities then float to the top of the molten iron and form a slag cap which effectively prevents air coming into contact with the iron. Periodically the slag is tapped off. The molten iron is always removed from the bottom of the cupola as this is where the 'cleanest' material lies.
    The molten iron is then often treated by adjusting the temperature and adding calcium carbide or similar desulphurising agent. Magnesium treatment is also carried out if SG iron is required. Finally, the iron is innoculated by adding a mixture based on ferro silicon immediately before the pour.
    With molten steel, basic slags are used to control the levels of phosphorous and sulphur, and the steel is 'boiled' by injecting oxigen into the molten bath which removes unwanted disolved gasses. In some steelworks Argon Oxigen Decarburisation (AOD) is practiced in treating stainless and low alloy steels.
    By the above methods, most unwanted impurities are removed before the pour, and the pour itself (if done properly ie smoothly) will not pick up any further impurities from the surrounding atmosphere.
    When electric welding, the transfer of metal from electrode to workpiece is quite violent and results in the entrapment of impurities from the surrounding atmosphere and the workpiece. Thus either a shielding gas is required to keep the atmosphere inert, or a flux is used to form a slag to remove the impurities from the weld pool. Oxy Acetylene welding is less violent so you can generally get away with not using a flux or shielding gas.
    Re-reading the welding bit above it doesn't sound quite right, but you get the general idea. Again, someone on here will be able to give a better explanation of the welding requirements for shielding gas and flux.

    Steve
     
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