Permeability change with Temperature

[MAC3382]

Hello, All:

As always, thank you for your help!

I have a new application where we will be operating a magnet assembly in the 450C temperature range. The magnet assembly will be comprised of permanent magnets and some high permeability metal, yet TBD. At lower temperatures we would typically use some commonly available mild steel because of the good value of u and Bsat. However, your resposnes may drive me to an alternate option.

I can esitimate the effective BHmax of the magnet alloy at temperture and we have selected an alloy which is still "straitline" at 450C. I believe that I should also consider the permeability change in the metal poles, but I am having trouble finding documentation of u vs temp. Should I be worried about 1018's permeability changing much at 450C? I suspect so.

Can anyone shed some light onto this or refer me to a source?

I appreciate your help,

Mac

 

[dgallup]

The critical temperature when the steel becomes non-magnetic will vary greatly with composition but i think in general your temperature is low enough you don't need to worry about it. There is some good info here:

http://books.google.com/books?id=A1...eel non-magnetic critical temperature&f=false

 

[MAC3382]

Thank you dgallup, the link was most helpful,

mac

 

[EdStainless]

Alnico 8 is your magnet?

As far as the soft materials I wouldn't worry.
I am not in my office so I can't look in Bozorth for the curves but at 450C I wouldn't 'expect a low carbon steel to change greatly.

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Plymouth Tube

 

[MagMike]

Ed's mention of Bozorth reminded me that I answered a similar question a few years ago:
thread340-200199

I am in my office and I do have my copy here. The chart for permeability vs. temperature shows maximum permeability rises to about 7000 at 450°C. It is about 2500 at room temperature.

Hope this helps,
Mike

 

[EdStainless]

If this a perm magnet circuit then what really matters is saturation vs temp.
I know that that chart is in there also.

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Plymouth Tube

 

[MagMike]

Excellent point Ed! The chart of saturation vs temp is right above the chart showing permeability.

The saturation remains relatively stable all the way up to 600°C.