Operating speed influences operating temperature


Flexible couplings help accommodate misalignment, but only to a point. For best alignment — regardless of coupler type — first secure the driven equipment, then install the coupling. Only after the coupling is attached to the equipment should the motor be aligned and secured.
Of course, loads affect bearing life. The general ABMA and ISO formulas for ball and roller bearings respectively are:

where C = dynamic radial capacity (lb). These life equations can be further tailored for specific reliability targets and environmental conditions.

Operating speed influences operating temperature and, in turn, bearing and lubricant life. High-speed applications tend to favor ball bearings over roller bearings, while extremely high-speed operations may call for precision or hybrid bearings with ceramic rolling elements.

In any case, bearing operating-temperature limits cap motor speed. The highest speeds are possible with hybrid deep-groove ball bearings (pure radial loads) and with angular-contact ball bearings (combined loads).
Bearings in electric motors run at more modest speeds and temperatures generally are lubricated with grease. Grease simplifies housing and sealing designs, better adheres to critical surfaces, and protects against contaminants. How long that grease lasts depends on several factors, including grease type, bearing design, motor speed and orientation, and operating temperature. Small ball bearings in standard-duty electric motors are typically fitted with seals or shields and lubricated for life. Bearings are replaced at normal intervals. Severe-duty motors, regardless of size, often come with open bearings and provisions for regreasing.