Demagnetizing Coil

[bhrollin]

I am a machinist and know next to nothing about electricity
and nothing about magnetism. I have a very valuable surface
grinder chuck, a 6x4x20 inch piece of laminated steel and
brass which has become magnetized. I would like to demagnetize it by passing it through a 10-12 inch diameter alternating current (120 volt) coil wrapped around a piece of steel or plastic (which would be better?) pipe. From reading some web sites on demagnetization I think this will work. I can buy insulated solid copper wire at Home Depo. My question is: what size wire and how many turns should I use?

Any information would be a great help as I know nothing about what I am doing.

 

[230842]

Demagnetization procedure needs alternate current but the current must decrease to zero from a value high enough. So, you need one demagnetization coil, a power alternating source and an intermediate element allowing current variation. This latter can be (preferably) a variable autotransformer (VARIAC).
According to your data, pipe for coil must be plastic. Winding lengh: 20 inch; copper wire diameter:.2 to .3 inch ; number of turns: 60 to 100 ; voltage: from 240 V to zero; current values are not easy to calculate, but my best estimate is from 20 A to zero. VARIAC must allow 240 V and 20 A.
Process can be very brief: power connection, voltage reduction to zero, end: 2 or 3 seconds. Grinder chuck and coil should be both firmly hold due to high electrodynamic forces.
Demagnetization is not guaranteed since it highly depends on grinder chuck size and shape.
Good luck. Julian

 

[buypogi]

Can you send the topics about the definition of demagnetizing and cross-magnetizing in armature reaction in DC motors. thank you very much

 

[nbucska]

You don't have to vary the current: you just insert the object , turn on the current and remove the object before
turning off the current.

As the distance in increasing (during removal) the object
is repeatedly magnetized in alternating direction with
decreasing field.

<nbucska@pcperipherals.com>

 

[peebee]

Why not buy a demagnetizer? Do a Google search on &quot;demagnetizer&quot; and you'll find a bunch. Go to Grainger.com and search on &quot;demagnetizer&quot; and four pop up, including this one: &quot;Manual Demagnetizer, For Use on the 6 x 18 Inches Surface Grinder $118.40&quot; and a couple others for $3.

 

[StanStep3]

would simply heating it be an option? Use a torch or boil it in water.

best of luck,

Stan

 

[nbucska]

Yes StanS, you can heat it up to red hot. Boiling in water
is not enough to completly destroy it, even if it gets
rusty, it may still remain usable.

You may try some acid...

<nbucska@pcperipherals.com>

 

[Chuckles159]

Call a TV repair shop and see if you can borrow their degaussing coil. Every person who does component level repair on CRT based video equipment owns one.
Alternately go to any place that sells parts to TV service technicians and buy a degaussing coil. It should be less than $40.00.

 

[eztech]

Inside some computer monitors have degauss button one possibiliity for finding a junk degausser. Or make one:

http://www.antennex.com/hws/ws0300/magdemag.htm

 

[Chuckles159]

Unfortunately the degaussing coil inside a monitor is very weak. It is meant to only compensate for the effect of magnetic buildup of the earth's rotation. Also, these are designed to work with a posistor on the main board of monitor. Plugging in a coil salvaged from a monitor without this posistor in series is going to result in a very hot coil in a very short time. However, if you do use the posistor, the amount of demagnetizing will likely be too weak or too short to do the job well.
Get hold of a proper technician's TV degaussing coil.