The friction of Rolling bearing mainly comes from the following three major aspects: pure sliding friction between rolling elements and raceways, sliding contact parts, and viscous friction of lubricants.
These three categories can be subdivided into the following 10 categories:
1. Rolling friction caused by elastic hysteresis (compared with other frictions, the friction and energy loss caused by it is small)
2. Friction caused by differential sliding
Differential sliding refers to the bearing that is in contact with the curved bus bar. Except for the two points where the relative rotation axis of the two objects intersects the contact surface, the linear velocity of the two objects on the contact surface is not the same. Microscopic sliding is called differential sliding. The differential sliding is closely related to the tightness between the rolling elements and the raceway. The greater the tightness, the greater the differential interaction.
3. Friction caused by spin slip
Spin sliding: In ball and roller bearings with a contact angle greater than zero (except for tapered roller bearings), the sliding caused by the rotation of the rolling elements around the normal line of the contact surface of the raceway is called spin sliding.
For low- and medium-speed thrust cylindrical roller bearings, spin sliding is very serious because the contact angle is 90°. Using several short rollers instead of one long roller in each pocket can reduce spin sliding
4. Friction caused by rolling element slippage
In high-speed and light-loaded bearings: due to centrifugal force → rolling element presses outward raceway → insufficient frictional drag force of inner raceway to rolling element → inner ring slips relative to the rolling element. Slippage is severe sliding friction.
5. Friction caused by the spinning of the steel ball top
In high-speed light-load angular contact ball bearings, the spinning of the steel ball is also a serious sliding friction.
Preventive measures: add axial preload, increase friction coefficient, reduce friction angle
6. Friction caused by roller skew
Roller skew: Refers to the reason for the skew of the roller around the Z axis: conical or cylindrical roller bearings subjected to axial load and roller bearings with inclined inner and outer ring axes will cause friction to be distributed along the full length of the roller Uneven, resulting in a moment that causes the roller to skew.
7. Sliding friction between the end face of the roller and the flange of the ring
Measures to reduce the sliding lubrication:
(1) Improve the design of roller end surface and guide surface to achieve point contact, making it easy to form a dynamic pressure lubricant film
(2) Adopt under-ring lubrication, ferrule with oil hole
8. Cage and rolling element
⑴ The lubrication friction between the rolling elements and the pockets of the cage. The size of the friction depends on the nature of the lubricant between the rolling elements and the pockets, the speed of the rolling elements and the geometry of the pockets. The pocket geometry is the most important. (Example: The solid cage is changed to a straight hole)
⑵ The sliding friction between the cage and the inner or outer guide ribs. The magnitude of friction depends on the friction coefficient of the two contact surfaces. The roughness of the two processed surfaces should be small.
9. Viscous friction of lubricant
The rolling elements rotate in the bearing filled with oil and gas mixture:
When it revolves, it receives the flow resistance of the fluid, and when it rotates, it receives the friction torque of the fluid.
The friction of the grease is the main component of the friction torque of the bearing, and the amount of grease is small, and the friction is small;
10. Friction of the sealing ring
The sliding friction force between the contact surface of the sealing ring and the flange of the ferrule is large, the gap is large, and the friction is small. But the oil leaks; the clearance is small and the friction is large. The clearance should be appropriate to form an oil film. It can be used to improve the processing accuracy of the contact surface and reduce the roughness, lengthen the length of the gap between the contact surfaces, with low friction and no oil leakage.
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