Demagnitizer not working

RJT · Mar 7, 2019

Is there any fix to these? Seems like it is working (buzzes and resists the part being dragged across it) but the parts are still very magnetic. It used to do a great job, but now not so much. Before I open it up, is it worthwhile to try to fix / recharge ?

Dumpster_diving · Mar 8, 2019

It's as simple as a coil on the inside. So not much to go wrong.

Are you sure you're using it correctly. I believe the proper procedure is to turn it on, then drag the part across the plate and off to the side and out of the still active magnetic field.

RJT · Mar 8, 2019

Yes, good advice, but we go all the way across, still doesn't demagnetize well.

Gordon Heaton · Mar 8, 2019

RJT said:
Is there any fix to these? . . .

I don't know, but I'll give you fifty bucks for that one that you can put toward its replacement!

DDoug · Mar 8, 2019

Seeing how they vibrate, and the top in non-magnetic.

Could be the wingdings & core have loosened up and fallen away
("down") away from the top surface.

Dumpster_diving · Mar 8, 2019

Time to pull the cover and take a look inside. If the switch and coil are wired-up correctly, really the only thing I think could go wrong would be digger doug's suggestion about the coil being out of place or perhaps a short to ground.

They're really not complicated inside.

Bill D · Mar 8, 2019

How far away do you take the part before power off? Feet or inches? Arms length is a convenient measure.
Bill

Ron Hofer · Mar 9, 2019

Bill D said:
How far away do you take the part before power off? Feet or inches? Arms length is a convenient measure.
Bill

I generally take mine out for dinner and a movie.

jim rozen · Mar 9, 2019

1) place part on demagnetizer.
2) turn demangetizer on.
3) turn demagnetizer off.
4) remove part from demagnetizer.
5) wonder why the thing is so magnetic after it's been on a demagnetizer.

Bonus points if you can make the part stick to a steel wall.

9100 · Mar 9, 2019

jim rozen said:
1) /
5) wonder why the thing is so magnetic after it's been on a demagnetizer.

Because you cut the current on a peak, dummy.

Bill

jim rozen · Mar 10, 2019

I was waiting for the OP to say 'oh that's how I was doing it.'
Because that's just about the only way a degausser doesn't work.

JST · Mar 10, 2019

The OP says it used to do a great job, so presumably he knows how to use it.

My suggestion is that it may have developed a shorted turn, which could drastically change the magnetic field. Those demaggers tend to pull some serious current, and if used a lot they get hot. Most that I have dealt with have some sort of "duty cycle limit" as to how long they can be on without a cool-down time. They did way back when I was associated with a radio station, we had them for erasing tapes.

jim rozen · Mar 10, 2019

Heh.

The bulk tape eraser we use at work for deaguassing items has that feature. If it gets too hot a thermal
switch opens. If this happens while you are degaussing items in a mu metal sheild (gets the remanent field
much lower) it will not only perm up the part, but it will perm up the sheild. This requires a more complicated
degaussing sequence to fix!

andrewmawson · Mar 10, 2019

Mine (an Eclipse) visibly has two poles with a gap between them. No doubt it would not work if the gap was full of iron filings. If yours has a gap under the insulation then presumably you don't know if the gap is holding swarf ?

Gordon Heaton · Mar 10, 2019

JST said:
. . .Most that I have dealt with have some sort of "duty cycle limit". . .

That's what sets IMI apart. Theirs are built for continuous duty.

DDoug · Mar 10, 2019

Has the OP taken the ^%$#@! cover off yet ?..... :skep:

JST · Mar 10, 2019

Gordon Heaton said:
That's what sets IMI apart. Theirs are built for continuous duty.

Interesting, I wonder if they are doing something special with an electronic control. I thought about how that might work as I was reading this and thinking of reasons for the problem. It wold be possible to trigger the thing to full power on a timed cycle when an item is sensed in the demag field. You could actually do a "canned cycle" for reducing the strength of the field as well, dropping off to near zero and having the user remove the part then,.

9100 · Mar 11, 2019

jim rozen said:
Heh.

The bulk tape eraser we use at work for deaguassing items has that feature. If it gets too hot a thermal
switch opens. If this happens while you are degaussing items in a mu metal sheild (gets the remanent field
much lower) it will not only perm up the part, but it will perm up the sheild. This requires a more complicated
degaussing sequence to fix!

Why would that make a difference? As long as you start the new sequence at a higher level than the last cycle, it should wipe out the history, especially with something like mu metal that is formulated for minimum coercive force and remanence. I could see it if the degausser stuck on a high point for a long period there might be a little residual magnetism that is hard to wipe out but presumably in this case the on time for that peak would be shorter.

Bill

jim rozen · Mar 11, 2019

The shields are easy to perm up but to get them degaussed so they can give their best performance the drill is more complicated.

Ideally a cylindrical shield gives between a factor of 100 and a factor of 1000 attenuation depending on how well it is set up and
how badly it's been banged around. The best way to degauss these is to wrap them with many turns of wire, and to put around
1000 amp-turns through the wire, at a low frequency (around 1 Hz or so) that is gradually reduced in amplitude.

We used a Kepco biploar op amp power supply driven by a good low frequency oscillator (minimal distortion) with the two connected
by a log taper ten turn pot. The pot was driven by a gear motor so it ran though its range over a course of about ten minutes.

With around 100 turns of wire you would get the 1000 or so amp turns within the Kepco supplies +/- 10 amp range.

Just dumping the demagnetizer into the shield would help but wasn't enough to do the real job.

The mu-metal needs to be annealled near its melting point (typically in a hydrogen furnace) to get full permeability back
after welding (these are typically sheet, rolled, with an end cap welded on) and whenever they get banged around they
suffer a bit. So I tend to gripe when smaller ones get used as pencil cans, etc....

9100 · Mar 11, 2019

jim rozen said:
The mu-metal needs to be annealled near its melting point (typically in a hydrogen furnace) to get full permeability back
after welding (these are typically sheet, rolled, with an end cap welded on) and whenever they get banged around they
suffer a bit. So I tend to gripe when smaller ones get used as pencil cans, etc....

One time I made a device to measure the quality of anneal of reed switch reeds. It used a reed switch coil in a simple oscillator. A reed inserted in the coil would change the frequency according to its magnetic qualities. Everyone had good results except the plant manager who was only somewhat technically gifted. His readings were always poor. Finally someone noticed that because there were reeds all over, he would bend it first to be sure it had been annealed.

At Lumen Electronics making toroid coils, standing orders were if you dropped a core, it went in the scrap bin.

Bill

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