How to "De-Magnetise tools

[h=3]Degaussing[edit][/h]If the shadow mask becomes magnetized, its magnetic field deflects the electron beams passing through it, causing color purity distortion as the beams bend through the mask holes and hit some phosphors of a color other than that which they are intended to strike; e.g. some electrons from the red beam may hit blue phosphors, giving pure red parts of the image a magenta tint. (Magenta is the additive combination of red and blue.) This effect is localized to a specific area of the screen if the magnetization of the shadow mask is localized. Therefore, it is important that the shadow mask is unmagnetized. (A magnetized aperture grille has a similar effect, and everything stated in this subsection about shadow masks applies as well to aperture grilles.)
Most color CRT displays, i.e. television sets and computer monitors, each have a built-in degaussing (demagnetizing) circuit, the primary component of which is a degaussing coil which is mounted around the perimeter of the CRT face inside the bezel. Upon power-up of the CRT display, the degaussing circuit produces a brief, alternating current through the degaussing coil which smoothly decays in strength (fades out) to zero over a period of a few seconds, producing a decaying alternating magnetic field from the coil. This degaussing field is strong enough to remove shadow mask magnetization in most cases.[SUP][21][/SUP] In unusual cases of strong magnetization where the internal degaussing field is not sufficient, the shadow mask may be degaussed externally with a stronger portable degausser or demagnetizer. However, an excessively strong magnetic field, whether alternating or constant, may mechanically deform (bend) the shadow mask, causing a permanent color distortion on the display which looks very similar to a magnetization effect.
The degaussing circuit is often built of a thermo-electric (not electronic) device containing a small ceramic heating element and a positive thermal coefficient (PTC)resistor, connected directly to the switched AC power line with the resistor in series with the degaussing coil. When the power is switched on, the heating element heats the PTC resistor, increasing its resistance to a point where degaussing current is minimal, but not actually zero. In older CRT displays, this low-level current (which produces no significant degaussing field) is sustained along with the action of the heating element as long as the display remains switched on. To repeat a degaussing cycle, the CRT display must be switched off and left off for at least several seconds to reset the degaussing circuit by allowing the PTC resistor to cool to the ambient temperature; switching the display off and immediately back on will result in a weak degaussing cycle or effectively no degaussing cycle.
This simple design is effective and cheap to build, but it wastes some power continuously. Later models, especially Energy Star rated ones, use a relay to switch the entire degaussing circuit on and off, so that the degaussing circuit uses energy only when it is functionally active and needed. The relay design also enables degaussing on user demand through the unit's front panel controls, without switching the unit off and on again. This relay can often be heard clicking off at the end of the degaussing cycle a few seconds after the monitor is turned on, and on and off during a manually initiated degaussing cycle.
 
For most of the small stuff, i.e. screwdrivers, bits, tweezers, etc., my old Weller soldering gun always works great for demagnetizing. Just pass the object thru the soldering loop and you are ready to go. This actually does a better job than my old tape head demagnetizer for my reel to reel recorder. good luck!
 
Swarfmaster said:
For most of the small stuff, i.e. screwdrivers, bits, tweezers, etc., my old Weller soldering gun always works great for demagnetizing. Just pass the object thru the soldering loop and you are ready to go. This actually does a better job than my old tape head demagnetizer for my reel to reel recorder. good luck!
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For a little larger parts you can replace the tip with a loop of bare copper wire. I use 12 gage. You can also use that 12gag wire to solder with in a pinch
 
I used to service lots of Electron Microscopes and Nuclear Magnetic Resonance Spectrometers in another life. All my tools had to be meticulously demagnetized (degaussed) or the results were disastrous and costly. I still can't abide having stuff cling to my tools. All the commercial degaussers I found were too costly, too small or had terrible duty cycles.

The best degausser I've found for shop use is an old fractional horsepower induction motor stator. Remove the armature (obviously) and remove or open up the end bells to access the open stator ID. Slip a piece of PVC pipe, or other non-metallic/conductive (not just non-magnetic) material to line the stator ID. This protects the windings from your tools and you from the windings.

The current needs to be limited to about the normal operating load of the original motor. A big light bulb wired in series with the motor windings works well for this. 300~500 watt work lamps usually work quite well.

Pass the tool to be degaussed SLOWLY through the motor frame (hold on tight) and continue to SLOWLY draw the tool away in a straight line until your about 2 -5 feet away before you turn off the power.

Here's some background on the process. Magnetization of any (ostensibly Ferrous) material is a realignment of the magnetic poles within it's structure. The mechanical analogy is very much like bending a piece of ductile metal. You can bend any metal so far and it will return to zero. Exceed that degree of bend and it will take a set and remain bent, but not as far as you bent it. To remove the bend it must also be bent BEYOND the point where it is simply straight, so when it relaxes it is straight. In magnetic parlance we call this hysteresis.

If you've ever straightened a rod in the lathe by "leaning on it" with the tools post you know how it can be nicely centered when bending it over 360 degrees while turning and backing off while still turning. The same principle is applied here by using AC current. Only AC fields can effectively demagnetize. The alternating field is "bending" or flipping the magnetic poles back and forth through 360 degrees repeatedly. As the material is withdrawn from the field the peak to peak intensity reduces but zero is still zero. As the rotating field is reduced different poles are left in different states, or positions, as it were. Hopefully, their positions will be evenly shuffled such that their sum magnetic field is zero. Once you're far enough away from the field you should be left with just that, zero net magnetic polarization.

Since induction motors have many poles, using an induction motor stator has the additional advantage of producing multiple loops of magnetic lines within it's core. This helps in getting all the parts more evenly demagnetized, especially good for odd shapes.

Oh! And don't forget to leave your rings and watches, etcetera, somewhere else while playing with AC magnetic fields. :) If your calipers have an electronic LCD readout I would remove it before degaussing.

Hope this is helpful.

Mark S.
 
Hi,
All of your replies have been very useful in helping me understand and solve my magnetic problem.
I've learned alot thank you.
Here is an interesting video, and you'll never guess where I found it ??? Right here in the video's section !
(Video showing what "MWS" was talking about in a simple form, "how to make your own demagnetiser")
Cheers dd :thumbzup:
[video]http://www.hobby-machinist.com/vbtube_show.php?tubeid=438&sti=Homemade-Tool-Demagnetizer[/video]
 
Nicely done video. I use much bigger motor frames 1/2HP, 1/3HP, but the idea is the same.

Solenoids without a core will definitely burn up in no time.

Mark
 
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