Heating Steel

I tried this once.

See #1.

Only once? I would have persevered.

I pride myself on rarely making the same mistake more than 17 times.

There are electric pipe-thawing heaters, and some arc welders can be set up to do the same thing.

I agree that OP will have to start here and then he will get to answer 6.

That rod will act like a short circuit and the threshold between melting the material and getting it to a controlled heat will need effective control on the low current side witch will be close to 10 Amp considering losses at 220V and even that will demand 2200W controls.

A major problem with steel rod of that size is also thermal run away, as the material heat up the resistance drop and current increase so suddenly that control become impossible.

What will this be used for is another question as contact with other material will alter the response of he rod.

1. Does 20 mm mean "20mm diameter"? "Really round"? It would be easier if it were 1 x 20 mm oblong x 300 mm long.
2. What kind of steel? Some stainless is many times resistivity of mild steel and is non-magnetic.
3. What is your definition of red/orange in degrees Celsius?
4. What is resistance/temperature relation for sample?
5. A welding set, voltmeter, ammeter and a wire sample of your steel might be a good starting point. As might an old laminated car windscreen between you and the bar. Power needed proportional to surface area as a first guess for scale-up, resistance proportional to cross-section area (maybe). Can use your own red/orange then.
   

Related to your number 2, very important. Where induction is via a varying magnetic field, a less-conducting steel might be better suited to Dielectric, which still uses electricity - but at substantially higher frequencies.

Like as mentioned previously, not really a device one should attempt to build from scratch especially if soak time is a consideration or a tight temp range must be hit, because then you're talking pyrometers tied to process control, probably a chart recorder for QA/QC, ad naseum.

Best to seek out a company whose business is making these types of units, there are plenty of them out there.

6. Define "quickly".

http://inductoheat.com/

I agree with tcmtech. It is difficult to build such a transformer which primary will be-let's say 230 V- and secondary 0.35 V for 1.55 kW [4560 A secondary and 6.5 primary current-approx.]. You'll need 676 turns on primary of 3-4 sqr.mm copper and a single bar of 55 mm diameter copper on secondary side.

One inductor going cheap, recently decommissioned

The transformer may be a problem

Thank you to all who have given me some very useful information, I appreciate your input.

Ray

Hello Ray,

A lot depends on how fast you need to heat it. One unusual way might be to try induction heating. In this method you don't need to make electrical contact with the steel. A coil is loaded with high frequency AC, maybe 100kHz or higher. When the steel rod is inserted into the center of the coil eddy currents in the rod will cause it to get very hot, very quickly. How hot and how fast depends on the amount of power sent into the coil and how much is absorbed by the eddy currents. This method was used to heat and purify silicon for use in semiconductors.

Dave

I agree with Dave .If you'll keep 4560 A constant will take more than one minute to reach 800 oC. If you need it in 5 seconds you'll need 14,000 A.

In the case of induction heating-I am not sure-a 4kHz supply converter and a 4kHz transformer it will required. See also[for instance]:

https://www.youtube.com/watch?v=9dK7D8sKeCI

I agree with previous answers about an electrical induction solution, but you need to be a litle more accurate about the temperature set, "red-orange" is a bit higher than 800ºC, I would say around 900ºC.

You can find tipical examples like yours in the automotive industry, but usually going a Little higher in temperature than you, could you provide some more information about material, temperature, heating needed speed, and available power?

Build an inductive heater.

50Khz,300amps,120 volts on the output coil ought to do it.

This will require some rather large SCR's mounted on a water cooled heat sink,and the appropriate high frequency switching control circuit.

Use 1/4 inch tubing for a single turn secondary around the object of interest.

Circulate water through the coil to prevent overheating of the tubing.

Diameter of coil to be as close as possible to clearance around the object.

This will require approximately 50Kw of input power,depending on efficiency of the circuitry.

Do you want one built?

If you have the money $$$$$,I have the time.

Unless the OP comes back and adds some more context to the question I'm at a loss for suggestions.

I have been asked to find a way of heating a 20mm x 300mm steel rod to red/orange hot quickly using electricity. Sounds like a college question to which some good answers have been given. HF and high current induction methods aren't practical for the class room.

If it is for a production environment then as usual cost constraints come in to play.

You can use High Current Rectifier. For example 5 V/1000 A: http://www.volteq.com/volteq-power-supply-hy051000ex-5v-1000a-over-voltage-over-current-protection-220v-input.html

If 2000 $ is too much, you can to looking for cheaper one.