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Guru

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Induction heating of 316 SS rod loss of coupling m

08/29/2009 8:29 AM

We are using a 25KW Miller Induction machine to heat the treaded ends of 316 SS to 1900-2100-degrees F.. If we heat the bar twice we are unable to couple and the machine drops out.

We are heating in an argon environment. We have been heating the ends to 600 in air to get the correct coil setting/spacing. We then try to heat the rod in argon but are unable to couple with the rod.

If we heat the rod the first time we can heat to 2000-degrees with no problem but still unable to heat the second time.

We need to get the correct coil spacing to achieve the correct temperature profile.

This a proof of principle be for going in to production and we have spent too much time and money, but must continue or loose our shirts (we already lost our shoes and socks)!

Thanks

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Guru
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#1

Re: Induction heating of 316 SS rod loss of coupling m

08/29/2009 8:47 AM

Good one!

BTW, what's the purpose of heating the threaded end of the shaft? Some sort of plating/covering/...?

300 series is austenitic. Austenite is not magnectic, another complication in relation to induction stuff...

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Guru

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#4
In reply to #1

Re: Induction heating of 316 SS rod loss of coupling m

08/30/2009 11:16 AM

When cutting threads in 316 SS it becomes work hardened and it is necessary to heat them to 1900-2100-degrees F. to normalize the material.

It was necessary to heat the material (test pieces) to prove the process and in order to get the best temperature profile across the machined surfaces the coils had to be readjusted while heating.

We heated some pieces to 2000-degrees to prove that we could eliminate oxidation. We found that we did not have a good temperature control across the heated area.

We could not reheat the bars as we could not remain coupled with the induction machine and the machine kicked out. The induction machine is a self adjusting machine in that it senses the best frequency to obtain best coupling and heating.

We are shipping another machine that is manually controlled to site and will try and see if it will accomplish the needed heating.

The client does not want to go into production heat treating until we resolve the problem.

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#5
In reply to #4

Re: Induction heating of 316 SS rod loss of coupling m

08/30/2009 8:17 PM

The coil design is not correct and the automatic machine cannot compensate ?

Manual operation should give you a better shot at the problem, there are company's who will design the coil to your requirements have you checked this out?

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Guru

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#2

Re: Induction heating of 316 SS rod loss of coupling m

08/29/2009 9:23 AM

Sorry but your question is not very clear.

You are heating a bar of SS316 by induction heating to 21000F ie about 1150 0C ?

Why? isn't that too much of a temperature? you are crossing the critical temperature and then when you cool i don't know the method you are likely to disturb the whole microstructure and land up in dimensional changes- Austenite decomposition.

And then you are doing it twice ?

Earlier practice was to heat it to 6000F ie about 3150C. This looks to be a good value. Why did yo go to this high temperature ?

Are you trying to Induction harden?

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Guru
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#3
In reply to #2

Re: Induction heating of 316 SS rod loss of coupling m

08/30/2009 8:24 AM

You cannot harden 316 SS by heat treatment.

Raising the temperature to 1150 °C will anneal th SS and restore its initial properties when cooled in water from this temperature, presumably some normalising is required after the ends have been machined or whatever process has been applied to them.

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