Induction welding plans

Discussion in 'General Electronics Chat' started by sputnikprecision, Sep 13, 2011.

  1. sputnikprecision

    Thread Starter New Member

    Sep 13, 2011
    I have a job which usually employs welding with oxyacetylene. The result is a bit untidy and I was researching the possibility of using Induction welding.
    The items I need to weld to a 1/2 (12.7mm) inch copper tube with a 1mm thickness by 150mm long.
    On one side, I wish to weld a solid brass, 1/2" gas thread nut and on the other is a brass plug for sealing the pipe.
    I have been told that welding copper and brass are an uphill struggle as the copper is a highly conductive metal and needs high power to make red hot.
    would anybody with experience tell how much power I would need to heat and braze/silver solder/ copper filler weld these three parts?
    I think I would have two heating coils to siut each end as each end would need different power.
    Would any body suggest what KW power I would need for each application,
    and possibly availability of any circuit. I have seen an induction heating project employing a Variac and a power meter which would allow the user to peak the power and adjust it to obtain obtimum settings. something like that would be fantastic. Any idea or link is appreciated.
    As the username inplies, I am in precision engineering stuff and I have access to machinery which will help me build my own. I have done advanced level physics and maths and have put my hand in electronics on many occasions... any help would be welcome.
    Thanks in advance!
  2. someonesdad

    Senior Member

    Jul 7, 2009
    I can concur about welding brass -- I've done it with an acetylene torch and it's hard if you're not used to it because it conducts the heat away quickly and reaches liquidus pretty suddenly and, because of the thermal conduction, not infrequently through the whole chunk of metal (and I was only welding 1/8 inch sheet).

    In asking for the induction power needed, that's a tough question. Unless someone with actual experience speaks up, that's something that would have to be estimated with the principles of heat transfer. And that would likely mean solving the heat equation and dealing with conduction, radiation, and convection -- all three heat loss mechanisms are going to be important.

    If I had to attack the problem, I'd get out my old heat transfer text by Holman and see if I could sit down and make some useful approximations.
  3. shortbus

    AAC Fanatic!

    Sep 30, 2009
    That sounds more like a job for 'furnace brazing'. You would put the brazing compound on the parts and join them together, then put many of the parts at a time in the furnace and heat them to the temperature required. Parts are usually held in a fixture while doing this type brazing.
  4. sputnikprecision

    Thread Starter New Member

    Sep 13, 2011
    I have spoken with a guy who has a blog on the subject and has numerous projects for one to copy and produce.
    He said that he has tested a prototype on brass and copper pipe but it was 3/8" and his usnit delivered 20Kw and was on the verge of bursting with the power which was absorbed.
    I suspect that at 30Kw I would be ok for a 1/2" pipe but I never said it not to influence. Also I have read that in case of aluninium and very conductive materials (copper as well) the frequency has to be very low.
    Welding them with conventonal heat is something I wish to avoid. I usually do about 500 at a time but takes days and the welding is not uniform to the eye and the flux makes a mess. The part has to be mounted in a unit by the customer, used for a hygenic process and it would need to be cleaned thoroughly. Induction heating is very clean and uniform.