How Do Screws Affect Motor Lamination Integrity?

[Jdo300]

Hello All,

I am currently working on a project where a special out-runner switched-reluctance type motor is being designed. The rotor for the motor (see attached PDF) has holes drilled through the laminations to secure the stack (which is 1" thick in this case) to the back side of the housing, which is designed to fit in a wheel hub configuration.

I am wondering if when putting screws/shoulder bolts through the laminations, if there will be any significant issues if the screws (which would be metal) make electrical contact with and short the laminations where the holes are? The holes do somewhat interfere with the flux path of the magnetic fields, but I am not sure how concerned I should be about this. What is the standard practice when dealing with a situation where screws or bolts are needed to fasten the motor laminations together? I believe I have seen similar situations with transformers that used bolts or something to hold the corners together but how does it work in this case?

As for the laminations themselves, they are coated with a layer of insulating material (whatever the standard is for M-19 silicon steel is), and will be laser cut to make the shape shown in the attached file. Any comments or suggestions appreciated as I am wondering if this would be a potential problem or an insignificant detail to be concerned with.

Thank you,
Jason O

 

[Tom.G]

...if there will be any significant issues if the screws (which would be metal) make electrical contact with and short the laminations where the holes are?

Yup, sure will. If the bolts make electrical contact they will act as a shorted turn on the rotor. Much current, much heat, little torque.