Re: A little experiment on demagnetization

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude
<davemucha@j...>" <davemucha@j...> wrote:

> Is magnetism lost over time on a
> shelf ? or in use ? by higher voltage/power ? and disassembly?

More than likely the magnetism is lost over time while
being used. Magnets DO NOT like heat or vibration.
Step motors do a lot of vibrating and heating.
I'm not convinced that slow careful disassembly is
all that destructive. (some loss not much)
I'm stating this from a gut feeling fueled with about 10 years
experience in the magnetic industry, back in the 70's.

The newer fancy magnetic materials are less
susceptible to heat and vibration.

>"are there any shops/people that re-magnetize?"

Should Be.
I just took apart a step motor to look at the magnetic circuit.

On the rotor shaft...
there is a stack of steel laminations,
then a magnet about 1/8" thick (washer shape),
another stack of laminations,
a non magnetic spacer,
stack of laminations,
another magnet,
and a --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude
<davemucha@j...>" <davemucha@j...> wrote:

> Is magnetism lost over time on a
> shelf ? or in use ? by higher voltage/power ? and disassembly?

More than likely the magnetism is lost over time while being
used. Magnets DO NOT like heat or vibration.
Step motors do a lot of vibrating and heating.
I'm not convinced that slow carfull disassembly is
all that destructive.
I'm stating this from a gut feeling fueled with about 10 years
experience in the magnetic industry, back in the 70's.
The newer fancy magnetic materials are less susceptible th this.

>"are there any shops/people that re-magnetize?"

Should Be.
I just took apart a step motor to look at the magnetic circuit.

On the rotor shaft...
there is a stack of steel laminations,
then a magnet about 1/8" thick (washer shape),
another stack of laminations,
a non magnetic spacer,
stack of laminations,
another magnet,
and a finale stack of laminations,

So... when the rotor is removed...
it acts like a bar magnet with the North Pole on the
shaft end and the South Pole on the Bearing end.

This leads me to believe that the motors can be magnetized
fully assembled.

Place the motor in the Magnetizer with the shaft against
the South Pole of the Magnetizer and the bearing end of
the motor against the North Pole of the Magnetizer.
Even Better... To get that North Pole even closer to the
rotor, insert the shaft into the hole of a donut shaped
pole piece.
Size of which would be...
OD ~= OD of Stator
ID = a little larger than shaft size.
Thickness > Shaft length.

(in truth, North/South orientation is probably
of little concern)

Look around for shops that make custom magnetic devices.
Most any city will have one.
Take a copy of this e-mail and a box of donuts with you.
I wouldn't think it would cost much if anything.

If the motors are magnetized using the "Discharge" Type
Magnetizer. I can visualize a heavy coil that the motor
can fit into about 1.5 to twice as long as the rotor.

Tom M.