Hi Guys,

Just became a new member. I am a graduate student working on a project that requires me to heat up a copper tube to pretty high temperatures (close to melting point). I could switch out the material to something more ferromagnetic but wanted to start out with copper first. We are looking into using inductive heating to achieve this and I have been reading up on how this can be done.

One aspect that I can't fully wrap my head around is resonant frequency. I understand that we can use a resonant tank circuit to our advantage (inductor coil and capacitors) to help determine and run the power supply at the right frequency. But wouldn't the resonant frequency change dependent on the work piece that I am trying to heat? I am having trouble on how we would calculate that.

In order to get a feel for inductive heating, I bought a cheap "Yosoo 100W ZVS Low Voltage Induction board" circuit and have been testing it out. One of the comments said that it automatically adjusts the frequency of the circuit to the resonant frequency? (I measured the frequency around the inductor coil using a regowski coil and it varied from 90 kHz to 92 kHz which no work piece and with a copper tube). It takes a DC input but I'm not getting that good of heating in my work piece so I am trying to profile how much of my input power is going to losses and if I am operating at some resonance frequency or not.

My questions are then:
1. Is the primary reason for using a LC circuit for resonance?
2. How does one calculate the resonance frequency with a work piece in it? Does it even matter or is it mostly dependent on the circuit components, etc.
3. Is skin depth the main characteristic I should base the physical properties of the work coil? (other than material, etc).

Any other suggestions/comments to help me get a better understanding of inductive heating would also be helpful.

Thank you

 

This is an old thread which deals with the subject.
I haven't a clue where this is going but if I wanted to heat a copper tube or 316 stainless tube I would simply pass an electric current through it. I used stainless steel 316 once to super heat steam from a steam generator. Used a few 1,000 Amp DC welding machines as the current source. So while I do not know the goal of heating your copper tubing passing a current through it makes for a simple way of going about it.

Ron

 

Here is a popular circuit using a Royer Osc.
http://kaizerpowerelectronics.dk/general-electronics/royer-induction-heater/
If only skin effect heating is required it requires a higher frequency than through-heating, also depends on the material mass.
Max.