Diminishing Flux ??

[Randy Gross]

I read a couple of postings wherein reference was made to magnets
demagnetizing though the type of magnet was not revealed.

What circumstance(s) is(are) involved?



Is this a failing common to an alloy or manufacturing process?



What consideration can I implement in projects that require them, good
magnets don't come cheap?



rg

 

[Jasen Betts]

In article <xn0e6kmo9cb3mg000@news.east.earthlink.net>, Randy Gross wrote:

I read a couple of postings wherein reference was made to magnets
demagnetizing though the type of magnet was not revealed.

What circumstance(s) is(are) involved?

extreme heat a the big killer, prolonged harsh vibration is another.

Is this a failing common to an alloy or manufacturing process?

I think mostly to the old steel magnets of 20+ years ago,

What consideration can I implement in projects that require them, good
magnets don't come cheap?

if you use new magnets you should be fine unless you're targeting an
unusually harsh environment...

Bye.
Jasen

 

[ncstateboy81]

All magnets can be demagnetized, but some are much less sensitive than
others. There are demagnetization curves for them. The following
website shows a couple:
http://www.dextermag.com/ViewDocument.aspx?DocumentID=123
Pay more attention to the curve with the knee in it. One axis has the
flux density (B) and the other axis is the applied magnetic field (H).
When designing magnetic systems it is important to stay in the linear
region. When the applied magnetic field goes into the knee of the
curve, and the field is removed, instead of following the original
curve, the new magnetization (the flux density) can be found by tracing
a line parallel to the original linear line from the point in the knee.


As Betts pointed out heat has a huge affect. In the demagnetization
curves there are lines for different temperatures. As the temperature
increases the linear portion drops off at smaller applied fields.