Heat treatment machine using resistance heating

[Viktor]

I am offered to buy a heat treatment (stress relive, quenching and tempering) machine which utilized resistance heating for a long tubes of non-regular cross-section. (4130). I have no experience in such a process and have a number of reasonable doubts about this process. Can anybody share with me his/her experience in using this process?

Thank you.
Viktor

http://viktorastakhov.tripod.com

 

The process you are refering to is known as 'induction hardening' and is quite effective in heat treating materials (4130, 4340, etc). The problem is that most of the machines currently on the market put a case on the outside of bars. If you are looking to heat treat the ID of tube, you may have problems with distortion.

 

[Viktor]

I am talking not about induction heating – it is rather direct the so-called resistance heating. Two water-cooled cables are connected to the both ends of the workpiece so that electrical current is passed through the workpiece heating it. Then, the workpiece (in the considered case is a tube of irregular shape) is dipped into a quenching bath and then a cycle repeats for tempering. During this process, the tube is stretched by applying an axial force to keep it straight (allegedly). An infrared thermo sensor is to control the temperature and thus time of heating in both cases. As advertised, stress relief, quenching and tempering +loading-unloading take 120s so there is no need for expensive vacuum furnace. An inert gas is used to protect the tube from oxidation. Looks suspiciously simple and fast.

My concerns are: how uniform is heating; how to grip a tube of non-regular cross section; when would happen when the tube is realized – I mean, if the residual stresses will distort the tube; how accurate the thermo sensor should be placed to control temperature for tubes of different diameters and lengths, etc.
Viktor

http://viktorastakhov.tripod.com