write the situations in science diary where rolling friction can reduce friction.
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Answers
Explanation:
Friction in conventional bearings
Friction within a bearing is made up of the rolling and sliding friction in the rolling contacts, in the contact areas between rolling elements and cage, as well as in the guiding surfaces for the rolling elements or the cage, the properties of the lubricant and the sliding friction of contact seals when applicable.
The friction in these bearing is either caused by the metal-to-metal contact of the balls or rollers on the bearing cage, or by the presence of lubrication within the bearing. The manufacturer will be able to supply complete data, but, as an indication, the friction torque, for a roller bearing can be determined using the following generally accepted relationship,
(3.30)
where is the shaft diameter and is the bearing load computed from the radial load, and the axial load, in the bearings, given by,
(3.31)
The value of the coefficient of friction for the bearing, , will be supplied by the manufacturer; typical values are given in Table 3.3.
Table 3.3. Typical coefficients of friction for roller bearings.
Bearing types Coefficient of friction,
Deep grove 0.0015–0.003
Self-aligning 0.001–0.003
Needle 0.002
Cylindrical, thrust 0.004
The friction due to the lubrication depends on the amount of the lubricant, its viscosity, and on the speed of the shaft. At low speeds the friction is small, but it increases as the speed increases. If a high-viscosity grease is used rather than an oil, the lubrication friction will be higher and this can, in extreme cases, give rise to overheating problems. The contribution of the lubricant to the total bearing friction can be computed using standard equations.
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