De-magnetiser

Does anybody know the effectiveness of de-magnetisers such as this one?
http://www.ebay.co.uk/itm/Silverline-Magnetiser-Demagnetiser-50-x-55-x-30mm-/400217714598?pt=UK_Hand_Tools_Equipment&hash=item5d2ed5afa6
I was under the impression one needed a rapidly reversing magnetic field of decreasing strength to remove magnetism from a tool, whereas this tool appears to be nothing than a permanent magnet.
Cliff Coggin.
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You can demagnetise by applying a sufficiently strong magnetising field aligned in the opposite direction to the field of your magnetized object, although if you overdo it you will magnetise in the opposite direction.
Personally I prefer the AC coil !
Alan
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Alan Bain wrote:

WIHA (a company with a good reputation) make a "static" one;
http://www.wihatools.com/400seri/40010ser.htm
Video!

http://www.youtube.com/watch?v=vl0QXxkZPhU

BugBear
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wrote:

That video pointedly did not show de-magnetising which is what I am interested in, though other examples on You tube seem to do so, and yet I am not convinced that drawing a tool across a permanent magnet will de-magnetise enough for my purposes, which is the handling of tiny watch and clock parts. A scientific explanation might persuade me otherwise.
Cliff.
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On Wed, 07 Sep 2011 10:50:50 +0100, Cliff Coggin wrote:

A way to demagnetise with a permanent magnet, is to rotate it rapidly (e.g. with a drill) with the poles facing in appropriate directions, bring the component up to it, and withdraw it slowly to some great distance before switching the drill off.
This is of course just another way of generating an alternating (well, rotating) magnetic field.
- Brian
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On 07/09/2011 12:10, Brian Drummond wrote:

A tape head demagnetiser (Ebay ?) should be more than adequate for small tools, such as tweezers, jewellers screwdrivers etc.
For an even cheaper solution. look in junk box and strip out the coil and armature from an ac contactor or octal based mains relay. Should be more than enough to get the job done...
Regards,
Chris
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That's what I did an dit works fine as you suggest. I have no idea about the reactance and whether the lack of a core might eventually cause overheating, but it's only on for 20 secs at a time at most so I have had no problems. An old transformer will work fine too if you can get the core out, some (much) older ones are more amenable, but careful use of a hacksaw is also sometimes possible.
Richard
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I have some 110v tools and I have a little 500W 240/110V transformer in my workshop. When I want to de-magnetize something I just hold it close to the lid of the transformer and draw it slowly away. It isn't very efficient, and ususally serves to only reduce the magnetism quite a lot but not remove it completely.
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