Induction heating/furnace

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John Hasler
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Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: Induction heating/furnace

Post by John Hasler » Wed Aug 29, 2018 5:16 pm

In copper the skin depth is about 1/3 inch at 60 Hz. In iron its about .009". It decreases with increasing frequency. Thus only the skin gets heated anyway unless your crucible is tiny or you are operating at an impractically low frequency . But then, only the surface gets heated directly in any furnace. Heat gets to the interior by conduction. The difference is that in the induction furnace the heat is generated in the skin. With other methods it must be generated elsewhere and transferred to the metal to be melted by conduction or radiation, requiring that the source be hotter than the target temperature.

The bigger the crucible the bigger the coil. The bigger the coil the larger the inductance. The larger the inductance the lower the maximum frequency at which it can be made to resonate efficiently.

rrnut-2
Posts: 438
Joined: Mon Jul 18, 2011 7:40 pm
Location: New Hampshire

Re: Induction heating/furnace

Post by rrnut-2 » Thu Aug 30, 2018 10:20 am

"Is a protective layer of sand, or other insulating media, used on the floor, Jim, or do they simply work directly on the concrete?"

They simply work on the concrete, no sand involved. What we did do, was to install a 24"x24"x4" fire brick right under the pour spout of the furnace.
This way any "oops" with pouring into a ladle, the steel would land on the firebrick. When the brick wore out, it was easy to replace.

Induction Furnaces: Think of them this way. They are a transformer with a shorted secondary.

Also: Heating done by the skin effect, is done to the metal in the furnace, not by the furnace copper coil. Heat produce in the copper coil is not wanted and removed by the cooling water. This heat is produced through the resistance/inductance of the coil,

The magnetic field produced by the furnace surrounds the furnace (if it is a box furnace) and can transfer to other objects; ie wedding rings and so on.
Steel shell furnaces are less prone to this due to the shielding and shunting of the coil.

Harold; The furnaces that you have are considered box furnaces.

Jim B

John Hasler
Posts: 996
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: Induction heating/furnace

Post by John Hasler » Thu Aug 30, 2018 10:40 am

rrnut2 writes:
This heat is produced through the resistance/inductance of the coil,

Inductance cannot produce heat.

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