Comments by "SeanBZA" (@SeanBZA) on "WeberAuto"
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Grey coating is an insulator, to prevent circulating currents through the bearings from any slight imbalance in magnetic field in the motor. there is a single bearing that is grounded ( the shiny one) to prevent charge build up on the rotor and a flash over to the frame, but the rest have to be insulated so they do not have a shorted turn through the frame that can cause a high circulating current through the bearings that rapidly erodes them through arcing. There are current paths for this current via things like the output shafts and the selector forks, but they probably assumed that, being long thin wall section steel assemblies, this long path would both keep the current low enough not to cause any major extra wear, and also the long output shaft would be mostly self cancelling field wise as well.
A lot of larger electric motors handle this with one end having coated bearings, or they make them with ceramic bearing balls inside, or just make both sides with insulated bearing mounting frames, and provide a grounding carbon brush assembly to handle shaft grounding. Drawback of the coated bearing is that you have to ensure that there is absolutely no damage to the coating on the outside and the side facing the frame, so that there is no metal to metal path. However, depending on the exact coating applied, this coat can be both insulating and tougher than the steel of the bearing itself. grey would point to a spray on ceramic coating, probably vacuum deposited before final bearing assembly or applied as a plasma coating.
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