Magnets and temperature

[evolDiesel]

Explain this (please!)

We are taking magnets running tests:

N42 Rare Earth Magnet
140 degrees F down to -10 degrees F
9 hour cycles
8 repetitions.

When we do this, the magnets loose their magnetic force.

Any cycle going in either direction from ambient to "cold", we are OK.

But anything to "hot", we loose magnetic force.

Vendor specs state magnet stable to 176 degree F.

Do you guys have any ideas on this?

 

[sreid]

Is there any other magnetic field that is trying to demagnetize the permenant magnet?

 

[MagMike]

How much magnetism do they lose?

What is the shape of the magnet? They might be be operating close to the knee of the BH curve.

The reversible temperature coefficient of NdFeB is 0.1% per degree centigrade. This is true for any formulation of NdFeB, even the "stable ones"

 

[MJR2]

This is a common problem with vendors of neo. They give you something which does not work in a circuit. For me, almost never is the 'rating' of the material good enough.

First ask them for a set of BH curves at different tempratures. The reason is that neo will permanently demagnetize at elevated temperatures. You will use these curves to help you decide that.

If they cannot provide the data they don't know what they are selling.

Then determine the permeance of your magnets in the magnetic circuit they are in. Draw that line otherwise known as a load line on the family of curves. You will see the temperature at which you have fallen over the 'knee' of the curve and demagnetized.

Often material like N42 is not adequate for above 60C. I have attemped to put it in circuits at which 45C would have demaged it.

Mike