Induction heating...

Discussion in 'General Electronics Chat' started by PackratKing, Sep 28, 2015.

  1. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
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    I've been reading hither & yon about industrial uses for induction heating, as applied to welding -
    silver-brazing a piece of Carbide tooling to a lesser steel substrate... Since I absolutely suck at torch-brazing...

    Most articles recommend a higher frequency... I have the parts, etc, to do a bare-bones hookup through a transformer, directly to the working coil... which will presumably hopefully, do the deed at 60 Hz.

    I understand from reading, the higher frequency, will heat the surface to a depth of say... 1/8 inch of a given workpiece... a 1" dia. length of Hot-drawn steel, for the purpose of case-hardening, conversely, straight-up 60 Hz would heat it clear to the core, which is what I need for bending large [ 1" steel ] stock...

    Any ideas... I am wanting to proceed with cautious experimentation, as I have some nondescript junky transformers, and other parts that I don't care if I burn them up just for oservation sake...
     
  2. Dodgydave

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    Jun 22, 2012
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  3. PackratKing

    Thread Starter Well-Known Member

    Jul 13, 2008
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    Nope... 60 Hz... I could take the time to build a circuit to boost frequency, but my needed uses are so limited, it won't be cost-efficient in time... OTOH... with better equipment, comes more potential use...

    I will look into 400 Hz, as that sounds achievable for a packrat, and true, 400Hz will shake up the molecular heating process better than 60...
    Thank you for the link... I hadn't found that particular source of info yet...
     
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I've been looking into a similar project for a while now, too... but Dodgydave is right, that sort of circuit requires around 200 KILO Hertz... that's 200,000 Hz
    I very much doubt you can reach a practical temperature at a lower frequency, since what you want is for the electric field to resonate in the material... just like a microwave oven works.
     
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  5. Kermit2

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    Feb 5, 2010
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    Consider that transformers operate at 60Hz and the slow change of polarity, while causing heat build up, will not come anywhere close to generating the red hot heating levels needed for brazing.

    Either huge expenditure of energies is required (not a good financial choice) or a much higher operating frequency should be used.

    100 kilohertz is a good choice that can be easily reached.
     
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  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have worked on industrial HF units from 60hz-360hz for heating large (150Lb) iron ingots for forging after heating to silver soldering of the gas filler pipe in a auto gas tank, these ran at 455Khz.
    The silver soldering was done with a single coil in the tank pipe, with the S.S. ring on the outside, the heating of the pipe melted and drew the S.S. into the join by capillary action.
    This is a nice home built one. http://kaizerpowerelectronics.dk/general-electronics/royer-induction-heater/
    Max.
     
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  7. Kermit2

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  8. cmartinez

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    That's a beautiful, simple coil driving circuit... though I'm having a little difficulty in understanding why and how it oscillates. I'm going to try to sim it in LTspice, if I can.

    This is what (I think) I understand, so far:
    • D1 and D2 are there to protect the mosfet's gates from overvoltage
    • R1 and R3, and R2 and R4 are connected as voltage dividers that also limit current to the mosfet's gates
    • I am NOT SURE what D3 and D4 are doing

    How are L1 and L2, and the bank of capacitors related? are they an LC circuit intended to oscillate?
     
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  9. MaxHeadRoom

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    Jul 18, 2013
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  10. Dodgydave

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    Last edited: Sep 28, 2015
  11. MaxHeadRoom

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    Jul 18, 2013
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    The one draw back is that the resonant tank freq must be known in order to switch the bridge at the correct freq, rather than the self oscillating Royer.
    Max.
     
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