Demagnetize a metal with a dc welder?

[AndVal]

Hello all.

I have a small 45cm x 75cm x 4mm metal that is magnetized and creates some arc blow.
I have a DC stick welder.
I've googled about it and I would like to demagnetize it using the welder.

About creating the reverse magnetic field to naturalize the one in the metal:
How can I know the correct way to wrap the welding cable around the metal clockwise or counter-clockwise?
Or could I wrap the cable either way and then connect the cables to the welder in the appropriate polarity?

Thanks.

 

[voipio]

Demagnetising is best done using a slowly decaying AC magnetic field. The magnetic field causing the arc blow issues might be caused by pockets of magnetism in the metal - is it steel, by the way - and these might be difficult to demagnetise satisfactorily? Welding with DC could remagnetise the metal, in any case.

 

[eLuSiVeMiTe]

One of these came up for sale on fb today.
Can sort a contact number if it's of interest.

 

[Bladevane]

We used to have a dickens of a problem welding steam lines that ran N-S. The welders used to wrap the cable round the pipe in the opposite way of the naturally occurring polarity to neutralise the magnetic field. Otherwise the arc would wander all over the shop.

 

[AndVal]

Thanks for the answers.

Demagnetising is best done using a slowly decaying AC magnetic field. The magnetic field causing the arc blow issues might be caused by pockets of magnetism in the metal - is it steel, by the way - and these might be difficult to demagnetise satisfactorily? Welding with DC could remagnetise the metal, in any case.

Yes, I've read about AC but I don't have one. It is low carbon steel.

One of these came up for sale on fb today.
Can sort a contact number if it's of interest.

Even if the price was good the shipping costs would be huge since I don't live in the UK.

We used to have a dickens of a problem welding steam lines that ran N-S. The welders used to wrap the cable round the pipe in the opposite way of the naturally occurring polarity to neutralise the magnetic field. Otherwise the arc would wander all over the shop.

That's what I would like to know. How to find the direction of magnetic flux lines in the metal?

 

[Bladevane]

Hold a magnetic compass near the job. This will show you where magnetic north is. I seem to remember that the current flow in a wrapped cable has to follow the ends of the N and S. Difficult to describe but draw an N which, if you put arrows on the ends, would give an anti-clockwise direction. Conversely S gives you clockwise. The wrapping must be contra to your magnetism in the workpiece. Wrap it, slowly increase your current until the magnet tells you the magnetism has been neutralised and you should be good to go.

 

[Barking Mat]

@Bladevane , that's interesting...

Never thought of that...

 

[Bladevane]

I can't claim any credit for the idea. When faced with a large butt weld which was so magnetic it was impossible to weld our welders did this until they had the root completed at which point there was no problem.

 

[TechnicAl]

google De Gaussing

 

[Seadog]

google De Gaussing

I can't find that app.

 

[Bladevane]

Wasn’t he a French president some time ago?

 

[Hopefuldave]

If you can spin the piece to be demagged, set the welder lead up with a few turns in a coil, run "a few" amps through it and spin the piece while slowly moving away from the coil, it's pretty much the same as a proper degausser, you'll be putting in a slowly-decreasing alternating field...
I've also seen a lash-up with a strong magnet held in a drill chuck, spin it close to the work and slowly move away.

I got donated an old mag tape degausser ex computer room, it's a bit bulky but really works (take your watch off first or watch the minute hand whizz round).

Dave H. (the other one)

 

[Pigeon_Droppings2]

Isn't there a rule of thumb to work out which way to wrap the cable.

Sadly I can't remember if it's the left or right hand rule anymore

 

[Hopefuldave]

I don't think it'll matter if you're spinning the work, the important bit is that the field changes direction and gets weaker as you move it away

Dave H. (the other one)

 

[rtcosic]

Fleming's Left Hand Rule for motors and Right Rule for generators.

So I'm of no more help!

 

[the snooper]

Just find the biggest transformer you can, plug it in and run it over the steel a few times, used to demag TV screens with a soldering gun

 

[Pigeon_Droppings2]

I would have thought any ac carrying cable would work...ie power extension cable with a load connected...wrapped around the object?

Then slowly remove the object...should produce a diminishing oscillating magnetic field.

 

[daleyd]

RN Ships have massive coils in their hull for degaussing, to reduce their magnetic signature. It only ever got switched on once in a blue moon as it played havoc with all the TV's on board, someone would have to come round with their degaussing wand afterwards, waving them over the TV to remove the wonky colours

 

[Maker]

Fleming's Left Hand Rule for motors and Right Rule for generators.

So I'm of no more help!

I was gonna say that, but I couldn't remember if it was left or right, or what each finger represents, so I just left it.

 

[Pigeon_Droppings2]

I was gonna say that, but I couldn't remember if it was left or right, or what each finger represents, so I just left it.

I couldn't remember the left/right either ....the fingers I do remember

First finger = Field direction
seCond finger = Current
thuMb=Motion