ROLLER BEARINGS & BALL BEARINGS - Part 1
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| Figure 5 - Flat-race, flat-seat thrust ball bearing, A, and grooved-race, flat-seat thrust ball bearing, B. |
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Ball Bearings cont.
Ball Bearings - Lubrication: Ball bearings may be lubricated with either oil or grease. Although oil is preferred, grease is often used for convenience. Lubrication minimizes ball bearing rolling resistance due to deformation of the balls and raceways, and reduces sliding friction between the balls, raceways, and retainer. Ball bearing lubricants carry heat away from the contact zone, prevent corrosion, and help exclude contaminants.
Grease quantity and characteristics must satisfy operating conditions. Too much or too viscous a lubricant generates heat due to friction within the lubricant itself or between lubricant and ball bearing. Too little or too light a lubricant provides insufficient film protection.
Many ball bearings are supplied factory-lubricated, also known as lubricated-for-life bearings. These bearings have seals and an initial supply of grease for inaccessible locations or where relubrication is impractical.
Another important characteristic of ball bearings is internal clearance. Radial ball bearings have internal clearances between rings and balls to absorb the effects of press fitting. They compensate for thermal expansion of ball bearing, shaft, and housing, and provide a contact angle in ball bearings after mounting. Before mounting any ball bearings, check the manufacturer's specifications for required shaft and housing tolerances.
Thrust ball bearings - A thrust ball bearing provides axial shaft location and supports axial (thrust) load. Angular-contact ball bearings support radial as well as thrust loads. The ratio of radial to thrust loading depends on the angle of contact between the races and the ball bearing axis.
Flat race, flat seat ball bearings, Figure 5A, consist of two flat washers and a ball retainer assembly. Thrust ball bearings are used where the ball retainer assembly must carry thrust loads without restraining shaft oscillation or flexures. They serve best with light loads and are economical. This ball bearing's load capacity is approximately 28% that of comparable grooved-race ball bearings.
Roller Bearings & Ball Bearings
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