 Induction heater tank
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IamSmooth
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Wed Nov 11 2009, 02:06PM
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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
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Is there any significant difference with effect and performance by chosing capacitor values for a different resonant frequency? Will I see better performance at 100kHz than 200kHz? Or, is the skin effect at higher frequencies more of a factor and a higher Fres is desirable?
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GeordieBoy
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Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
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Higher frequencies decrease the skin depth in the workpiece so are generally used to achieve one of three things:
1. A shallow depth of heat penetration for surface hardening procedures. You heat only the surface to the required temperature, and do it quickly before the heat has chance to conduct deeper into the material.
2. Increase the AC resistivity of highly conductive or non-magnetic materials (such as Al) to make them more efficient to heat by eddy current loss alone.
3. For heating physically small workpieces where skin depth must be very low and the work-coil will naturally also be small to maintain decent coupling.
Note that increasing operating frequency also increases losses in the work-coil and tank capacitor due to skin effect, and losses in the tank capacitor due to dielectric heating.
The choice of operating frequency also tends to be lower where more power is required for practical reasons. It's easy to generate 20 watts at 27Mhz to fire a getter or solder some wires, but harder to generate 500kW at this frequency to melt a vat of steel! A more realistic frequency might be nearer to 20kHz at this power level.
-Richie,
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