The main function of motor bearings is to reduce friction and wear on rotating and stationary parts of the motor. Besides, motor bearings provide a relatively rigid support for the output shaft.
Different types of bearings exist: Roller bearings, ball bearings, sleeve bearings and needle bearings.
Sleeve and needle bearings
Sleeve and needle bearings are used in home electrical appliance motors. Normally, this kind of bearings is used in blower applications e.g. in a hairdryer, where a low noise level is important.
Ball bearings are used in virtually all types and sizes of electric motors for industrial or agricultural applications including pump motors. Roller bearings are sometimes used in connection with large power output motors where maximum shaft load capacity is required. The most important features of ball bearings are:
• They are compatible with a wide range of temperatures
• They are suited for high-speed operation
• They provide low friction loss
Different types of ball bearings and roller bearings exist: Open ball bearings, single shielded ball bearings and sealed ball bearings.
Most rolling bearings consist of the same three main components: Rings with raceways (an inner ring and an outer ring), rolling elements (either balls or rollers) and a retainer for the rolling element.The retainer has several functions, e.g. separates the rolling elements, holds them in place between the inner and outer rings and thus prevents them from falling out, and allows them to rotate freely. We distinguish between two types of rolling elements:Balls and rollers. Balls contact the raceways of the inner and outer rings at certain “points” while the contact of rollers is a line contact. Rollers come in four basic styles: Needle, tapered, cylindrical and spherical. The construction of rolling bearings makes the rolling elements rotate and at the same time they rotate around their own axes. The rolling elements and the bearing rings are exposed to the entire load that is applied to the bearings between the rolling elements and raceway surfaces.
The bearings have a combination of numerical code that defines a series of factors in terms of their dimensions, design, internal construction, precision, sealing, etc. The number is derived from several letters and codes of figures, and consists of three main groups of codes: A basic number code and two supplementary codes. The order and definition of these codes are shown in the table on the next page. The basic numerical code contains general information about the bearing design, the dimensions of the limit, etc. and contains information about the contact angle code, the hole diameter number and the bearing series code. The two supplementary codes are derived from a series of prefix code and a series of suffix code. These two codes provide information on internal clearance, bearing accuracy and a variety of other factors related to internal construction and bearing specifications.
Difference between the Rotor and the Stator