ROLLER BEARINGS & BALL BEARINGS - Part 1

Ball Bearings cont.

Ball Bearings - Tolerance - Ball bearing manufacturers offer a guide for maximum safe operating speeds. The speed value (DN) for inner ring rotation, is the product of the ball bearing's bore in millimeters and shaft speed in rpm. Compare DN values with the manufacturer's recommended value to determine type of lubrication and tolerance grade. Table 1 gives safe DN values for standard ball bearings.

Ball Bearings - Required life: How long must the ball bearing operate? Although it is impossible to predict the fatigue life of an individual ball bearing, lives of identical ball bearings from a representative lot tested at common conditions form a definite statistical distribution. Because of variations in individual ball bearing lives, fatigue life of a group of ball bearings is defined as the number of hours of operation at a given speed that 90% of the ball bearings in a lot can achieve before the onset of fatigue failure. This is called the L_l0 life.

Ball Bearings - Environment: Environment takes into account ambient and operating temperatures, and degree and type of contamination. Speed, load, and external heat affect operating temperature. Contaminants, such as dirt, water, or corrosive chemicals, are present in most applications to some degree, and must be excluded from the ball bearing. The greater the potential of contaminants entering the ball bearing, the greater the sealing requirement to exclude contaminants and retain lubricant in the bearing. In cases of extreme infiltration of contaminants, a constant supply of pressurized lubricant can be introduced to the ball bearing to purge contaminants.

Common ball bearings are constructed of SAE 52100 chromium-alloy, high-carbon ball bearing steel, which is suitable for most applications. It offers satisfactory operation at temperatures approaching 250@deg;F with no adverse effect on load capacity. Heat stabilized SAE 52100 steel operates in the 350@deg;F range. Contamination causes more ball bearing failures than fatigue. Specific seals protect against specific types of contamination. Select a seal that provides protection and lubricant retention for your specific application.

Roller Bearings & Ball Bearings

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