CA glue and magnetism

[Bill PhinnParticipant @billphinn90025]

I’ve encountered a problem that is new to me.

I’ve just replaced the fibre linings on my bench vice’s six inch detachable soft jaws because they were worn out. I used nitrile rubber instead of fibre. Each soft vice jaw has four neodymium magnets set into the back, two of these being original and two being ones I added for extra holding power. Their hold on the cast iron vice jaws has always been excellent.

…Until now. After using CA glue to stick the nitrile linings to the jaws I find that there is virtually no magnetism in any of the eight magnets – so little that even an M8 BZP hex nut stuck directly to one of the magnets will slide off under gravity.

Can anyone explain this and suggest whether the magnetism of the magnets will return?

[Clive FosterParticipant @clivefoster55965]

Most odd.

I’ve used CA glue to stick neodymium magnets to various things, including alloy jaws, with no apparent effect on the magnetic strength.

Clive

[DiogenesParticipant @diogenes]

I’d guess that way you have arranged them is causing them to cancel out each others fields?

Maybe you need to re-align your poles..?

[Robert Atkinson 2Participant @robertatkinson2]

+1 for poorly arranged poles. CA adhesives are excellent for gluing magnets due to their thin glue lines.

Robert.

[SillyOldDufferModerator @sillyoldduffer]

Very strange, no way should glue mess up a magnet.  If the magnetism has gone, won’t come back on it’s own.  Replace the magnets.

Maybe something happened to them whilst the fibre was being replaced.  Dropped, or got hot somehow?   Heat and mechanical shock are both very bad for magnets.  Neodymium magnets being made of sintered powder are mechanically weak – are they in good physical condition?

Eclipse used to warn against disassembling their older chucks.  The problem was due to Alinco, then best magnetic alloy, except the flux needed to be managed. Not likely to be Bill’s problem – Neodymium should be fine.

I blame Gremlins!

Dave

[Mark RandParticipant @markrand96270]

You didn’t heat the jaws up to release the original faced did you? NiB magnets, depending on formulation, can be demagnetised as low as 80°C

[John HaineParticipant @johnhaine32865]

They also really don’t like having their plating damaged!  Once exposed to air the material can degrade.

[Michael GilliganParticipant @michaelgilligan61133]

Is it plausible that we are looking at the wrong suspect?

Nitrile Rubber is available in ‘Loaded’ versions, for screening, etc.

MichaelG.

[Bill PhinnParticipant @billphinn90025]

Many thanks to everyone for the replies.

Having done a bit of rooting, I see that, as Mark points out, heating can cause loss of magnetism.

This is where things get confusing because, although I certainly did heat one of the soft jaws (before deciding to replace the fibre face) in order to repair it using Alusol after some heavy duty work had damaged the aluminium in places, I believe I didn’t even touch the other jaw with heat during the process. And yet the magnets in both jaws show an equal and almost total loss of magnetism. If the other jaw did get any heat, it cannot have been more than a few stray wafts of the propane torch. If these were enough to raise things to a critical magnetism-destroying temperature I’m astonished at neodymium magnets’ susceptibility to heat.

Although heat seems like the most plausible explanation for the demagnetisation here, I could swear the loss of magnetism followed straight after the CA gluing of the nitrile strips on to the aluminium jaws and not before. The heating took place a week previously.

One thing I do know is that if you try to grind away a neodymium magnet in order to remove it from a recess, beware of sparks! The grinding produces these in abundance. Presumably neodymium magnets are banned in the petrol-chemical industry.

 

[Bill Phinn]

On Bill Phinn Said:

… If these were enough to raise things to a critical magnetism-destroying temperature I’m astonished at neodymium magnets’ susceptibility to heat.

One source says 80°C, so a hot cup of tea would do it!

Although heat seems like the most plausible explanation for the demagnetisation here, I could swear the loss of magnetism followed straight after the CA gluing of the nitrile strips on to the aluminium jaws and not before. The heating took place a week previously.

Weird innit!  Maybe you just didn’t notice.

One thing I do know is that if you try to grind away a neodymium magnet in order to remove it from a recess, beware of sparks! The grinding produces these in abundance….

 

Grinding them best avoided, and if necessary outside wearing a mask:

In terms of risk though, there’s a big difference between a Model Engineer grinding a few small magnets out once every 50 years and an industrial worker who does it day after day after day.

I think heat is the most likely cause, but odd that not all the magnets were warmed up.  What fun!

Dave

 

[Michael GilliganParticipant @michaelgilligan61133]

Perhaps worth noting:

https://appliedmagnets.com/blog/can-neodymium-magnet-be-magnetized-again-after-overheating-and-lost-magnetism/#:~:text=While%20overheating%20can%20cause%20neodymium,degree%20of%20recovery%20may%20vary.

MichaelG.

[John HaineParticipant @johnhaine32865]

Just to reiterate my point about the plating.  I have had the same experience when trying to use superglue to fix a small magnet to a pulley.  Though it stuck initially it later came off and I found that some plating had been removed and the magnet no longer worked.  Neo magnets are cheap enough (try First4Magnets), use epoxy to fix next time.

[bernard towersParticipant @bernardtowers37738]

I have found in the past that glue is useless for magnets so when I use them I design so the magnet can be sunk into the job (good fit) then 3 small dot ounces on the edge of the mount and its fixed.

[Pete RimmerParticipant @peterimmer30576]

I was gluing neodinium mangets onto prototype brushless DC motor rotors way back in 1989, which were then ground on a lathe with a toolpost grinder. So gluing and losing the plating CAN be perfectly fine. If you lose the plating use another coating to keep the air off the magnet. The grinding was done with a LOT of coolant and small depth of cut.

[HacksawParticipant @hacksaw]

You haven’t stuck the keepers to the nitrile by mistake ? And there’ s  8 magnets  sitting on the bench , with you thinking they’re the keepers ..

Have you tried  sticking them to the vice ? I mean , the ‘  BZP nut ‘  isn’t actually Stainless steel, is it ?

[Bill PhinnParticipant @billphinn90025]

Dave, I wasn’t aware of the dangers from the dust. Thanks for the warning. Hopefully no worse than the dust from carbon fibre, which was flying everywhere today while I sawed out a carbon fibre seatpost that was stuck in a bicycle frame. Strange unpleasant smell to it as well.

Michael, it’s good to know these magnets are remagnetisable in the right circumstances, though a bit late for the present batch as they went in the bin.

John, I’ve noticed plating coming off neodymium magnets in the past, though I don’t remember there being any loss of magnetism. I see Pete suggests there isn’t necessarily in all cases. I’ll certainly have a look at the supplier you mention.

Bernard, sorry but I’m not sure what you mean by dot ounces. Punch marks, perhaps.

Hacksaw, no definitely the magnets, not the keepers, which I don’t have many of and they look very different. I’ve tried sticking all sorts of iron and steel objects to them, as well as the BZP nut; the magnetism is well and truly gone.

Anyway, new magnets are now installed, and the job is good again. Lesson learned.

[MacolmParticipant @macolm]

The thing about (serviceable) magnets is that the domains, or whatever internal structure, must be correctly and rigidly fixed in space. A jar of diametrically magnetised spheres will not result in a useful magnet, since the poles will arrange themselves for minimum external flux. Magnetic powder would be similarly useless.

Rare earth magnets are known to be fragile, so it seems likely just enough internal damage happened for domains to realign, which clearly will be so as to minimise the external field.

[bernard towersParticipant @bernardtowers37738]

sorry Phil yes dot punches a bit of a typo!

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