How do I stress relieve nichrome V wire? 2

[jimav]

I have an application where we are using a nichrome v wire to move a contact. We have a mechanical adjustment to allow calibration of the contact. The calibration however when set during the day, and then verified the next day changes. We bake the unit containing the nichrome wire at 220 deg F for 12 hours. I think this is an attempt to stress relieve or stablize the nichrome wire. Does anyone know what temp would stress relieve the nichrome v wire?

James J Avalle
Jim Avalle Machine & Engineering Service
J.A.M.E.S.

 

[NickE]

The temperature you are using is much to low to really stress relieve much in the type of wire you are using. NiChrome wire has a very high yield point at high temperatures and thermal stress relife (i cant spell occasionaly) is simply using temperature to reduce the yield point below the residual stresses in the material so that the stresses relax.

I'm not sure what NiChrome alloy you are using but my Kanthal Percison book gives operating temps upwards of 2000*F for these alloys. I would try at least 1000*F and see. You can continually increse the temp until you get enough stress reliefe for your application.

Looking further into my guide gives the creep strength (1%elongation 1000 hrs) at 1470*F as 2160psi to 2900psi. Thsi rapidly drops off to <600psi as the temp goes to 1830*F. I'm gonna guess that you may get what you need at ~1800*F.

HTH
nick

 

[arunmrao]

Nichrome wires are used for applications in high temperature regions of 900-1000 Celsius. Thus as NickE has pointed out that your baking temperatures of 200F is insufficient. If you need dimension stability with respect to variation in temperature you can use invar wires. These are very stable as they have nearly zero coefficient of thermal expansion or contraction. Hope this helps.