These three categories can be further 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 are very small)
2. Friction caused by differential sliding
Differential sliding refers to the bearing in curved bus contact. In addition to the two points where the relative rotation axis of the two objects intersects the contact surface under load, the linear velocity of the two objects at other points on the contact surface is not the same. The microscopic sliding caused by this is called differential sliding. Differential slip is closely related to the closeness between the roller and the raceway, and the greater the closeness, the greater the differential interaction.
Spin
sliding: in ball and roller bearings with contact Angle greater than
zero (except tapered roller bearings), the sliding caused by the
rotating motion of the rolling body around the normal of the raceway
contact surface is called spin sliding
Spin sliding is an important factor of friction in high speed angular contact ball bearings
Solutions :(1) Reduce the spin - roll ratio to reduce the spin slip;
(2) The slip-roll ratio decreases, and the spin slip decreases;
(3) The contact Angle decreases and the sliding roll ratio decreases
In
low and medium speed thrust cylindrical roller bearings, the spin slip
is very serious due to the contact Angle of 90°, and the spin slip can
be reduced by replacing one long roller with several short rollers in
each pocket hole.
In
the bearing with high speed and light load: due to the action of
centrifugal force, the rolling body presses to the outer raceway, the
friction drag power of the inner raceway on the rolling body is
insufficient, and the inner ring skids relative to the rolling body.
Slip is severe sliding friction.
5. Friction caused by ball gyro rotation
The gyroscopic rotation of steel ball is also a serious sliding friction in high speed light load angular contact ball bearings.
Preventive measures: add axial preload, increase friction coefficient, reduce friction Angle
6. Friction caused by roller skew
Roller skew: refers to the cause of
the rotation skew of the roller around the Z axis: the tapered or
cylindrical roller bearings under axial load and the roller bearings
with the inclined axis of the inner and outer rings will lead to the uneven distribution of friction along the full length of the roller, thus generating a torque to cause the roller to skew.
The
harm of roller skew: after the roller skew, the roller can not maintain
normal rolling movement in the raceway, which will produce great
sliding friction, especially the friction and wear between the two ends
of the roller and the outer raceway is more serious. At the same time,
the friction between the roller and the cage and between the roller and
the guide flange is intensified.
After the roller is askew, the acting force of the cage on the roller is
to resist the askew, and the acting force of the guard edge on the end
face of the roller also produces a anti-askew moment, so that the roller
is in a stable state with a askew Angle, which is an abnormal stable
state, and the bearing is easy to break.
(1) Formulate the correct roller bearing installation process and testing method;
The
correct use of roller bearings, with the shaft, bearing seat hole
processing accuracy is high, the axis is parallel; Cylindrical rollers
are not subjected to axial force and can be supported by additional
bearings and measures.
(3) Improve the cage and guard to guide the roller.
7. Sliding friction between the roller end face and the ring rim
Measures to reduce the sliding lubrication:
(1)
Improve the design of roller end face and guide surface to realize
point contact, so that it is easy to form dynamic pressure lubricating
oil film
(2) the use of ring lubrication, with oil hole ring
8. Cage and roller
(1)
Lubrication friction between the rolling body and the cage pocket. The
magnitude of the friction depends on the nature of the lubricant between
the rolling body and the pocket, the speed of the rolling body and the
geometry of the pocket. The pocket geometry is the most important.
(example: solid cage changed to straight hole)
(2)
Sliding friction between the cage and the inner or outer guide guards.
The magnitude of the friction depends on the friction coefficient
between the two contact surfaces. Two machining surface roughness to
small, good lubrication
Cage guiding mode:
9. Viscous friction of lubricant
Lubrication:
When
it is rotating, it is subjected to the resistance of fluid, and when it
is rotating, it is subjected to the friction stir torque of fluid.
Grease bearing:
The
friction of grease is the main component of the friction torque of the
bearing, and the amount of grease is small and the friction is small.
The
sliding friction between the contact surface of the sealing ring and
the ring flange is large, the clearance is large and the friction is
small. But the oil; The clearance is small and the friction is large.
The clearance should be suitable to form an oil film. 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 surface,
small friction, and not easy to leak oil.
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