Quick magnets question

[David]

In the new caravan there is a sliding curtain which is supposed to attach to a wall using pairs of magnets, one sewn into the curtain and the other sunk into a vertical wood strip. This is a room divider so the magnets should hold it open (effectively door shut). At least 3 pairs (top, middle, bottom).

I've checked with a steel knife blade and both magnets in the pair are magnetic however there is very little "grab".

I can get one of the magnets to stick if I take all the load off the curtain (that is, from the return spring trying to pull it back into the hollow wall where it normally lives) but it only just sticks and is certainly not strong enough to hold the curtain closed.

I am assuming that the magnets have weakened in some way (although by design they should surely last for decades with only occasional use) so it looks as though this is a fault the dealer should remedy.

Just wondering if there is any simple way that you can boost the magnets.

I remember that the old horseshoe magnets were supposed to have a piece of iron joining the two poles when not in use to keep them strong but this is yeah these many decades ago.

Cheers

Dave R

[The Natural Philosopher]

you can put a solenoid round them and connect that to a car battery or the mains via a fuse that is designed to blow after a few cycles of current or a shirt current in the case of the DC version

[Graham.]

Magnets weaken by vibration. Also if the magnetic circuit is not closed it not being in contact with its mate.

[Graham.]

Not very practical, and the AC version would need the fuse to blow at the peak of a the half- cycle corresponding to the required polarity.

[Brian Reay]

I have a gizmo from Lidl (but I'm sure you can find the on Ebay etc) which is for magnetising screwdrivers.

You stick the blade in one hole, move it around, pull it out.

Another hole demagnetises it.

Under a fiver in my case.

[Harry Bloomfield]

David presented the following explanation :

If both wall and curtain have magnets, they will only properly stick together if they present the correct faces.

You can use a coil of wire to magnetise, demagnetise. To magnetise you pass a DC current through it, then gradually move it away. To demagnetise you pass an AC current through the coil then gradually move it away.

[Chris Hogg]

Two suggestions: either get hold of a defunct hard drive and dismantle it to extract the pair of magnets (they're very powerful), or buy some neodymium magnets, also very powerful, from someone like this

. Then simply glue the magnets over the existing ones in the wooden strip. It will help if you get the polarity the right way round so they grab the magnets in the curtain, but they're so powerful it probably won't make much difference if you don't.

[Brian Gaff]

No there is no way to boost magnets. You will just need bigger magnets or a completely different securing system altogether. I've never found magnetic catches terribly reliable myself, as the critical issue is the distance between the magnetic poles and the metal. If material is bunched up or thicker then the force vanishes. In a caravan the vibration alone might cause this to occur. Brian

[Brian Gaff]

Sorry does not work. You really need a heck of a lot of current to even make this work a little and also if you really want to do it then heat is part of the equation. You have to alien the magnetic poles of the molicules in the material you are magnatising Any material that is easy to magnetise also looses it easily as well. Brian

[Huge]

[31 lines snipped]

IME, eventually they all become magnetised.

[Harry Bloomfield]

It happens that Huge formulated :

Just simply striking a metal rod a few times, can magnetise it.

[David]

The first page of Google hits all seem to be the same advice.

Stroke the weak magnet with the strong magnet to revive it.

Of course, they don't say how to find out which pole is which.

I do have some strong magnets, but I thought I would check with the team before doing anything rash.

Since one magnet is set into the wood (almost flush) and the other is sewn into the end of the curtain changing them is likely to be messy; getting them out may be non-trivial.

Instead of replacing them I would be tempted to use Velcro; stick one side to the wood and stick/sew the other to the curtain.

I think someone has been a little too clever with the fixings.

Cheers

Dave R

[Chris Hogg]

You'll only need to change one lot. It could be that those set in the wood are the magnets, those in the curtain are the keepers, i.e. not magnetic at all. Or vice-versa. They don't both have to be magnets. Nor do they have to be horseshoe magnets, i.e. with two poles facing the same direction. They could be button magnets, with a N-pole on one face and a S-pole on the other.

If you have some strong magnets, and assuming they're button types (which they may not be, of course), put one onto one of magnets in the wood. You'll find that one way round it sticks much more strongly that the other, i.e. when you've got opposite poles in contact they'll stick strongly. Then offer up the curtain and see if it holds strongly enough to the other side of that new magnet.

[Dave W]

Are you saying there's a layer of curtain material between the magnets? If so, maybe the material is new and fluffy, and could be ironed flatter to reduce the gap? Alternatively you could cut away the material from the faces of the magnets so there's no gap between them.

I'm very surprised if both bits are magnetised. I have a plastic concertina door to my bathroom and it's fixed by one magnet in the frame attracting a bit of iron in the door and mating with no air-gap. The magnet has N and S poles both facing the iron.

I suggest you offer up a decent slab of iron to each of your alleged magnets to see if one is particularly weak and might just be iron.

[newshound]

My suggestion too. Old fashioned "iron" magnets do lose their magic over time. Lots of different geometries of rare earth AKA neodymium magnets on eBay. One useful type is like a washer with a countersunk hole, so that it can readily be screwed securely to most surfaces. You probably only need magnets one side, with steel the other.

[David]

Update:

My assumptions were over engineered.

The metal in the blind is magnetic.

The round things on the partition (which I thought were sunk in) are just stick on magnetic stuff.

Two problems:

(1) There are 6 magnets in the curtain and only 3 stuck to the wall.

(2) The 3 on the wall are slightly high so don't quite match the magnets in the curtain.

Solution:

Ship a new pack of 6 stick on magnets and fit them to match the magnets. Recommended fitting method is to attach the magnetic side to the metal tag in the curtain, peel off the paper from the sticky side, then offer the curtain up to the wooden bit and (hey) press(to).

Dealer is being very helpful, which is good.

Cheers

Dave R