How i can remove the ferrite ring from the shaft

[eMoto18]

Hello guys,

I need your help.
I want to rebuild a mid drive motor with new bearings. My problem is, I can’t get out the bearing without removing the ferrite ring for the hallsensor. I think the ring is glued and I won’t damage it.
What’s the best way for removing it?
Thanks a lot.

 

[whatever]

r u sure u want to change bearings? looks like a big job, complete teardown, 2:50 mark in this video
gives how to take out axle ( tongshen mid drive)
https://www.youtube.com/watch?v=TZoiQlfIFlg

 

[fechter]

I think you'd want to use a puller to pull the bearing off the shaft and that will push the magnet off.

 

[eMoto18]

The ferrite ring is glued, I think it will break, if I use a puller.

 

[eMoto18]

r u sure u want to change bearings? looks like a big job, complete teardown, 2:50 mark in this video
gives how to take out axle ( tongshen mid drive)
https://www.youtube.com/watch?v=TZoiQlfIFlg

It not a difficult job, the rotor can stay at his place. The bearings are in the lids, only the ferrite is the problem.

 

[amberwolf]

I want to rebuild a mid drive motor with new bearings. My problem is, I can’t get out the bearing without removing the ferrite ring for the hallsensor. I think the ring is glued and I won’t damage it.
What’s the best way for removing it?

Depends on the specific glue. Many glues get softer when heated, but if you heat a magnet too much it will demagnetize, so you'd probably need to be moderate in the heat applied to the shaft (don't apply it to the magnet; it won't conduct the heat to the glue as well as the shaft will).

So you would heat the shaft, then use the puller to gently pull against the cover and bearing, and if the ring does not begin to move then you may need more heat.

It's possible that the heat required to soften the glue enough would be higher than what the magnet can take (especially if it is a plastic ring with magnetic material embedded in it).

It's possible that heat will not soften the glue at all, and that it requires a solvent instead. Or that cooling of the shaft (to cause it to shrink faster than the glue and ring) would work instead.

 

[boudin]

Depends on the specific glue. Many glues get softer when heated, but if you heat a magnet too much it will demagnetize, so you'd probably need to be moderate in the heat applied to the shaft (don't apply it to the magnet; it won't conduct the heat to the glue as well as the shaft will).

While I agree with not heating the magnet directly, do be aware that heating the shaft will cause it to expand and increase its friction interface with the magnet. Your best bet is to do this to break down the glue, then cool the shaft rapidly (ice cubes) so it will shrink before the magnet does. Try removing the magnet while it's still significantly warmer than the shaft.

For breakdown specifics, see your specific material's Curie temperature. Of course, you likely don't have the precise composition of your ferrite bead offhand, so that's difficult to tell. For most non-exotic magnets WITH THE EXCEPTION OF NEODYMIUM, 300C/550F is probably safe, and should exceed most glues' breakdown temperature.

For neodymium, 300C is awfully close to its Curie point of 310, and since you'd probably not be heating in a controlled kiln, probably easy to overshoot with a torch.

 

[fechter]

I'd be really careful with heat but most magnets will be fine with 100C. You could use boiled water to heat the magnet prior to attempting to remove it. If the glue is epoxy, it will soften to a rubbery state and come off fairly easy. If they used Loctite, you want to soak it with acetone for a while. Heat also helps with Loctite.

I don't see any other way other than pulling on the bearing. You don't want to grab the magnet itself as I'm sure it's very easy to break. The idea is to pull on it as evenly as possible.

Can you tell if the magnet is the "rubbery" kind or hard ceramic? Poke it with the edge of a screwdriver.

 

[eMoto18]

Hot water is a good idea. This ferrite ring is like ceramics unfortunatly.
I think first i try Aceton, if it don't works, than hot water.
I've now managed to remove the Rotor, so it is much easier to work on the ferrite.
I will report how it works.

 

[eMoto18]

I did it !
It works with a puller, rust remover and a little bit heat from a heat gun.
Thanks a lot for your advices.

 

[fechter]

Nice.

Keep track of which side of the magnet was facing out. You don't want to flip it over when you put it back.

 

[eMoto18]

I know, thanks.
That's why i took the pic. :wink: