Rolling Bearing And Sliding Bearing

Last article, we introduced the bearing steel. As everyone knows, a bearing is a component that supports a mechanical rotating shaft, reducing its friction coefficient and ensuring its accuracy. According to the bearing structure and motion, it can be divided into rolling friction bearing (referred to as rolling bearing) and sliding friction bearing (referred to as sliding bearing). The bearing should be chosen comprehensively because they have different characteristics in terms of structure and performance.


Rolling part is the most obvious difference between rolling bearing and sliding bearing. The rolling bearing rotates the shaft on the rotating support of the rolling body (ball, cylindrical roll, tapered roll). The more rolling body, the more contact points. Plain bearings have no rolling body and rely on a smooth contact surface to support the rotating shaft. This determines the bearing's different motion mode and friction coefficient.


The sliding bearing has a large bearing area and its bearing capacity of impact load is higher than that of rolling bearing. However, the bearing with lubricating oil film can withstand a large impact load. When the rotating speed is high, the increased centrifugal force of the rolling body in the rolling bearing can reduce its bearing capacity (the high speed is prone to noise). The bearing capacity of dynamic pressure sliding bearing increases with the increase of rotating speed.


The friction coefficient of rolling bearing is lower than that of sliding bearing and is stable. The friction coefficient of sliding bearing is unstable because the lubrication is affected by rotation speed and vibration. Since the stable oil film has not been formed, the resistance of the sliding bearing is greater than that of the rolling bearing when starting, but the static pressure sliding bearing is an exception.


Due to the limitation of centrifugal force and bearing temperature rise of the rolling body, the rotating speed of the rolling bearing should not be too high. Bearing with incomplete liquid lubrication due to heat and wear, the working speed should not be too high. Hydrostatic plain bearings with complete liquid lubrication or air lubricants can rotate up to 100000r/min.


The friction coefficient and power loss of rolling bearings are small, but can be greatly increased when lubricated and installed improperly. The friction power loss of fully liquid lubricated bearings is low, but the total power loss of hydrostatic sliding bearings may be higher than that of dynamic sliding bearings due to oil pump power loss.


Influenced by pitting and fatigue, the design life of rolling bearing is 5-10 years. In theory, the service life of the bearing with incomplete liquid lubrication is infinite, especially the bearing material of hydrodynamic sliding bearing may appear fatigue failure due to stress cycle.


The rotation accuracy of rolling bearings is generally higher due to small radial clearance. The incomplete liquid lubricated bearing is in boundary lubrication or mixed lubrication state, the operation is unstable, and the wear is serious, the accuracy is low. Fully liquid lubricated bearings have higher precision due to oil film as well as the hydrostatic sliding bearing has higher rotation accuracy.


Rolling bearings use oil, grease or solid lubricants, small dosage, high speed when the dosage is large, high requirements for oil cleanliness, need to seal, but easy to replace the bearings, generally do not need to repair the journal. In addition to the incomplete liquid lubrication bearings, the lubricant is generally liquid or gas, a large amount of oil cleanliness requirements are needed, bearing bush and journal often need to be replaced or repaired.

The steels used for rolling bearing are high carbon and low chromium bearing steels with  0.95% ~ 1.10% carbon and 0.40% ~ 1.60% chromium, such as AISI 52100, 51100, 50100, etc. Any needs, contact us now!