Scratched IPM motor laminations

S

sysrq

1 kW
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Does delamination resulting in 0.2-0.3mm gap and some superficial scratches justify replacement of IPM rotor? Google AI says possible shorts caused by scratches will increase eddy currents despite the fact that all of the laminations are shorted together by magnets and axle according to measurements
The caliper kept sticking to the magnets during bearing gap measurements.
Haven't seen anyone wrapping the rotor with protective cover during repairs.
 

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Got a spare rotor and stator to practice pressing on new bearing in order to prepare for unexpected issues with arbor press and compare the symetry of windings with inductance meter and four wire miliohm meter.

Turns out new rotor has even worse delamination despite fallowing the most popular manual rotor removal procedure.

The suseptability of delamination in flat type IPM rotor topology might be another underreported issue for BBSHD motors.

Trying to insert some thin sheets of plastic in the air gap before extraction might be one of the solutions to reduce probability of delamination while keeping the rotor more square.
 

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I don't think it will matter much on the rotor. The flux doesn't change that much. You could put some epoxy into the crack and clamp it until cured. Shorts in the stator laminations would be more of an issue.
 
fechter said:
I don't think it will matter much on the rotor. The flux doesn't change that much. You could put some epoxy into the crack and clamp it until cured. Shorts in the stator laminations would be more of an issue.
Click to expand...
Turns out in some of the BBSHD IPM rotors laminations have uneven radial size on one side resulting in chance of delamination due to removal or insertion and possible imbalance which might increase vibration. Third example has multiple protruding laminations on one side.


Looks like this one has cling film stuck between laminations.
 

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fechter said:
I don't think it will matter much on the rotor. The flux doesn't change that much. You could put some epoxy into the crack and clamp it until cured. Shorts in the stator laminations would be more of an issue.
Click to expand...
If segmentation of magnets is used in other rotors then shorted rotor laminations can increase eddy currents in general. According to some of the posts on endless-sphere sphere and according to Google AI and ChatGPT shorted rotor laminations can cause localized heating.
 
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fechter said:
I don't think it will matter much on the rotor. The flux doesn't change that much. You could put some epoxy into the crack and clamp it until cured. Shorts in the stator laminations would be more of an issue.
Click to expand...
I could use loctite 638 which is rated at 180°C.
Seems like the pressure required to hold this this delamination together is higher than for other rotors.
 
That sounds like good stuff. As long as it’s runny enough to get into the cracks and you clamp it, it should be good. You can heat it a little to make it runnier.
 
fechter said:
That sounds like good stuff. As long as it’s runny enough to get into the cracks and you clamp it, it should be good. You can heat it a little to make it runnier.
Click to expand...
It might cause rotor imbalance depending on thickness required.
Will it adhere to insulated coatings of laminations?
 
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Flat type IPM rotor topology has the worst robustness and easiest manufacturing speed suitable for high profits according to this paper.
www.mdpi.com

Design and Optimization of an Asymmetric Rotor IPM Motor with High Demagnetization Prevention Capability and Robust Torque Performance

In this paper, an asymmetric rotor interior permanent magnet (ARIPM) motor with high demagnetization prevention capability and robust torque performance is proposed. The key contribution of this paper lies in two aspects. On the one hand, a novel asymmetric rotor with a shifted magnet axis is...
www.mdpi.com www.mdpi.com
Adopting V type topology would require different stator configuration.
 
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fechter said:
That sounds like good stuff. As long as it’s runny enough to get into the cracks and you clamp it, it should be good. You can heat it a little to make it runnier.
Click to expand...
Turns out loctite 638 isn't adhering to laminations after 18 hours in bench vice.
 
Bummer. It could be oily or could be some kind of insulation layer it doesn't like. If they used teflon, nothing would stick.
But the deformation is so small I can't imagine it would make a measurable difference in efficiency. If it's rubbing against something, that would be another story and need to be fixed. Even relatively large shorts between laminations don't seem to be too bad as the steel is a pretty poor conductor.
 
fechter said:
Bummer. It could be oily or could be some kind of insulation layer it doesn't like. If they used teflon, nothing would stick.
But the deformation is so small I can't imagine it would make a measurable difference in efficiency. If it's rubbing against something, that would be another story and need to be fixed. Even relatively large shorts between laminations don't seem to be too bad as the steel is a pretty poor conductor.
Click to expand...
Some people were recommending using Loctite 638 for magnet retention on Surron motors but apparently it's intended for cylindrical press fit applications only.

Also tried unopened JB Weld Plastic Bonder but it's not hardening anymore due to short shelf life.
Industrial grade UV cure structural adhesive intended for magnets or laminations such as Loctite AA 3510 might be necessary.


Probably removing whole delaminated section and then gluing it back together might be the most optimal way to avoid dissimilar tension (curently delaminated part requires a lot of pressure to keep it closed probably due to some deformation of metal).

lammotor.com

Motor Bonding Lamination Stacks in China | Lammotor

We glue bonding lamination stacks for the stator & rotor. Elevate motor efficiency & durability with our precision bonding. Contact us.
lammotor.com lammotor.com

Seems weird that nobody else has had recurring issues with bad quality of laminations in bafang rotors since I have ordered two and each one of them has problems (delamination and non-uniform stacking of laminations resulting in uneven air gap between stator and rotor which can cause non-uniform flux density).

Even small deformations can cause harmonic distortions.


Any deviation from design such as short circuits between laminations can cause unpredictable behaviour of eddy currents even if steel is poor conductor.
 
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fechter said:
I don't think it will matter much on the rotor. The flux doesn't change that much. You could put some epoxy into the crack and clamp it until cured. Shorts in the stator laminations would be more of an issue.
Click to expand...
Someone on high voltage discord also reported the same issue and it resulted in excessive vibrations at high speed, excessive heat and metal shavings in stator. At night speeds rotor gets pulled apart and gaps between laminations make in worse due to distortions in harmonic flux density.
So it would also require strong glue to widthstand centrifugal forces.
It has been said that delamination can cause harmonic flux distortions resulting in vibration according to Google AI and ChatGPT so not sure if gaps like these are normal.
 

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If there are metal shavings, it would indicate something is rubbing, which is bad. Out of balance is also bad, but this can be checked with a balancing rig. Since there are multiple laminations that are bent, it might take more force to hold them together than the tensile strength of the glue. Bending them back looks pretty difficult.
But I'm not convinced that amount of gap is going to make a significant difference in efficiency.
 
marty said:
Stop worrying. Stop looking at the internet. Put motor back together. -OR- Buy a new motor and don't take it apart.
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Without taking it apart it's impossible to find bits of metal and cling film under the bearings left behind by the factory.
 
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