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Hi Dave,
Thank you very much for your reply. Your experience
give me confidence in experimenting the design.
C F Cheuk
----- Original Message -----
Sent: Wednesday, August 29, 2001 5:49
AM
Subject: Re: [femm] Material for pole
pieces of Magnet
In a message dated
8/27/01 2:06:39 PM Eastern Daylight Time,
c_f_cheuk@xxxxxxxxx writes:
Hi All,
I am in the process of designing a voice coil
actuator (re-inventing
the wheel really). I have always been advised to
use advanced
magnetic material such as Vacoflux 50 for the outer pole
piece . The
magnet I am using is a NdFeB with Hc of 1000000 A/m. The
load line is
above the knee to avoid temperature de-mag effect. Theair
gap need
to be of the order of 3 to 4mm to accommodate the coil. [...]
I think I should make a polepiece out of mild steel and test out the
hypothesis.
Can anyone please enlighten me. What should I watch
out for if I
change the expensive stuff to mild steel. Temperature
effect?
demagnetisation? Can't sleep at night? Am I barking up the wrong
or
the right tree?
I've designed and built this sort
of actuator before for motion control
applications. For the reasons
that you outlined above (i.e. core is
basically carrying DC flux and
there's a big, honking air gap that masks the
core's properties), I have
used low carbon steel before (for example 1018).
It's cheap, and the
actuators worked just like the were predicted to.
Although
materials like Vacoflux-50 (which is a Cobalt Iron--the "50" stands
for
50% cobalt) have a high Curie temperature relative to other types of core
iron, it's hard to imagine that this could be a factor here--the NdFeB
magnet
would be the limiting factor as far as the operating temperature of
your
machine pretty much regardless of the iron that you pick. In
general, it's
best to avoid Vacoflux or Hiperco if you can because ofits
very high cost
and poor mechanical properties.
Dave.
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