Induction heating/melting...

[Externet]

Is there a 'resonant/optimal' frequency to be selected for heating a particular metal/alloy, or the dimensions of the part to be worked on has a factor on selecting the frequency ?

[swansont]

Is there a 'resonant/optimal' frequency to be selected for heating a particular metal/alloy, or the dimensions of the part to be worked on has a factor on selecting the frequency ?

 

I would expect so. As you suspect, it should depend on the material and the geometry; since you will have basically an RL circuit, there is a frequency at which you will couple most efficiently.

[JohnB]

I don't know that it makes that much difference, although I would expect some variation in efficiency.

 

I've used the same induction furnace to smelt aluminium, bronze and various grades of iron and steel. They're power sucking brutes and a few percentage points either way in efficiency doesn't seem to bother them.

[CaptainPanic]

I don't understand the question. Are you asking whether the resistance and induction in a material are a function of the frequency?

 

I don't see what could possibly go wrong? Where does the energy go if you have a lower efficiency? Heat! Which is what you want.

Your only efficiency loss could be that you heat the circuits themselves. And if you lose more than a few percent into those circuits, you will have a huge problem (they'll be toast).

 

Please note that I am a chemical engineer, with little expertise in electrical engineering.

[swansont]

I don't understand the question. Are you asking whether the resistance and induction in a material are a function of the frequency?

 

I don't see what could possibly go wrong? Where does the energy go if you have a lower efficiency? Heat! Which is what you want.

Your only efficiency loss could be that you heat the circuits themselves. And if you lose more than a few percent into those circuits, you will have a huge problem (they'll be toast).

 

Please note that I am a chemical engineer, with little expertise in electrical engineering.

 

The heat is in the device generating the field, not the target. But JohnB's point is well-taken — the resonance is broad, which means the efficiency is only going to vary a little bit. If the resonance were sharp, it wouldn't be as useful a tool (unless it were tunable).

[Externet]

I don't understand the question. Are you asking whether the resistance and induction in a material are a function of the frequency?

 

Sorry for my poor expression; some induction heating/melting machines are frequency tuneable, and are adjusted depending the metal/alloy. What I do not know is if the amount of metal (dimensions) deserve also tweaking of the frequency applied.

 

And the frequency set on the induction machine, related to the metal, has any relation/ratio with the nuclear magnetic resonance (NMR) of the particular metal ?, as in

gold 1.729mhz

silver 4.047mhz

copper 26.528mhz

 

A picture of a sample tuneable induction machine

----> http://i00.i.aliimg.com/photo/v0/284854188/Induction_Melting_Furnace.jpg

[louis wu]

Induction heating units are in theory tuned to match the application desired. When a unit is ordered the coils are claimed to have been designed to match the material to be heated (both its composition and size / shape). The power supply and water chiller will be standard off the shelf units, of capacity to match the intended application. In practice any conductive material will be heated by the equipment; some materials will heat better than others. Austenitic stainless steels and nickel alloys are relatively poor at heating whilst ferromagnetic steels are easily heated. Some power supplies are frequency tun-able and some are not.

 

NMR states do not affect the process as far as I know: Rather it is the resistivity and magnetic properties of the material.

[Enthalpy]

I confirm no relation with NMR. But ferromagnetism - hence at moderate temperature! - does have an influence as it concentrates the induced current at the part's surface, depositing heat there, and increasing the part's electrical resistance, which means more heat at the part and less at the inducing coil.

 

Apart from reactance versus resistance, frequency has a serious effect through the Kelvin effect, that is current flowing only in the part's skin, which helps heating the part more than the inducing coil, but doesn't heat in depth. This IS used for surface treatment of steel parts, where the deep material is and stays tempered by the surface is quenched hence hardened following induction heating.