The main problems relating to lubrication are failing to achieve a sensible lubrication practise.  Two much grease can be applied, the wrong type of ball bearing lubrication can be used or it is applied too late to have enough impact.  In itself lubrication has many advantages reducing friction, protecting surfaces from rust during idle periods, transferring heat and protecting the bearing from dirt.  This is why, when you get a system in place which works, lubrication will prolong the life of your "electric motor bearings" .  

The purpose of a bearing in an electric motor is to support and locate the rotor, to keep the air gap small and consistent and transfer the loads from the shaft to the motor. The bearings should be able to operate at low and high speeds whilst minimizing frictional loses. At the same time the bearing must be economic and require absolutely minimal maintenance (if any). 

Heavy loads are usually left to roller bearings and lighter loads are carried by ball bearings. Drive forces are only taken into consideration when belts or gears are used. When belts or gears are used then radial and axial forces can develop. Evaluating the magnitudes and directions of all these loads will have direct relevance on your choice of bearing. For example, cylindrical rollers can carry high radial loads but virtually no axial loads. Other bearings such as angular contact ball bearings can carry radial and axial loads. 

The prescribed shaft speed will have a direct effect on the choice of lubricant, bearing size, cage design, internal clearance and shield/seal types. Induction motors and pulse modulation motors can produce electrical pitting or ribbing on bearing raceways, hence insulated nsk bearing options may want to be considered. 

The type of motor connection will produce load on the motors bearings. A coupling drive can produce forces in various directions; hence alignment is of key importance here. In many cases a roller bearing with a degree of shaft float is used at the drive end and at the other a ball bearing, hence fixing the float direction and magnitude. A belt or gear take off can place higher loads than a coupling; hence this should be looked at carefully. 

Motors, which are to be operated vertically, should have special consideration. Timken Bearing arrangement is vital in vertical mounting, as are lubricant requirements. 

BEARING RMS.16

BEARING 3XLJ-21/2

BEARING 51106