Disintegrating squirrel cages ?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "R.E.Burnett by way of Terry Fritz <twftesla-at-uswest-dot-net>" <R.E.Burnett-at-newcastle.ac.uk>


Hi Guys,

Given that the procedure of modifying induction motors by grinding
flats seems quite common on this list,   I wondered if anyone has
experienced problems with the squirrel cage rotor breaking-up
at speed ?

I have modified a number of small induction motors for synchronous
operation in the past,  and the depth of the flats has always meant
that some of the aluminum shorting-bars of the rotor became exposed.

I had not given much thought to this until it was brought to my
attention today by a man who is milling flats on a 1.5 HP 3000RPM
motor for me.  He was concerned that aluminum which is no longer
covered by the iron laminations could foul the stator due to
"centrifugal force" when the motor is run at speed ?

This is a hazard that I had not thought about,  but will stop worrying
if nobody has experienced any problems.  I guess the rotor is quite
small,  and 3000RPM isn't really that fast,  but I would be interested
to hear other peoples thoughts / experiences about this.

							Cheers,

							-Richie,