As an essential part of mechanical products, bearing plays an important role in supporting the rotating shaft. According to the different friction properties of bearings, the bearings are divided into rolling friction bearing (rolling bearing) and sliding friction bearing (sliding bearing for short). The two kinds of bearings have their own characteristics in structure and advantages and disadvantages in performance. When selecting bearings, we should consider them comprehensively.
The following is a detailed introduction of the main differences between rolling bearing and sliding bearing
1. Comparison of structure and movement mode
The most obvious difference between rolling bearing and sliding bearing is whether there is rolling element.
Rolling bearing: there are rolling elements (ball, cylindrical roller, tapered roller, needle roller) which support the rotating shaft by its rotation, so the contact part is a point, and the more rolling elements, the more contact points.
Sliding bearing: there is no rolling element and the rotating shaft is supported by a smooth surface, so the contact part is a surface.
The difference of their structures determines that the motion mode of rolling bearing is rolling, and that of sliding bearing is sliding, so the friction situation is completely different.
2. Comparison of bearing capacity
Generally speaking, due to the large bearing area of sliding bearing, its bearing capacity is generally higher than that of rolling bearing, and the bearing capacity of bearing impact load is not high, but the fully liquid lubricated bearing can bear larger impact load because the lubricating oil film plays the role of buffer and vibration absorption. When the speed is high, the centrifugal force of the rolling element in the rolling bearing increases, so the bearing capacity should be reduced (noise is easy to appear at high speed). For the hydrodynamic sliding bearing, the bearing capacity increases with the increase of rotating speed.
3. Comparison of friction coefficient and starting friction resistance
Generally, the friction coefficient of rolling bearing is lower than that of sliding bearing, and the value is stable. However, the lubrication of sliding bearing is easy to be affected by external factors such as speed and vibration, and the friction coefficient has a wide range of variation.
During the start-up, the resistance of the sliding bearing is larger than that of the rolling bearing, but the starting friction resistance and working friction coefficient of the hydrostatic sliding bearing are very small.
4. Applicable working speed comparison
Due to the limitation of centrifugal force and temperature rise of rolling element, the speed of rolling bearing should not be too high, and it is generally suitable for medium and low speed operation. Due to the heating and wear of the bearing, the working speed of the incomplete liquid lubricated bearing should not be too high. The high-speed performance of the fully liquid lubricated bearing is very good, especially when the hydrostatic bearing uses air as lubricant, its speed can reach 100 000 R / min.
5. Power loss comparison
Due to the small friction coefficient of rolling bearing, its power loss is generally small, which is less than that of incomplete liquid lubrication bearing, but it will increase sharply when the lubrication and installation are not proper. The friction power loss of fully liquid lubricated bearing is low, but for hydrostatic bearing, the total power loss may be higher than that of hydrodynamic sliding bearing due to the power loss of oil pump.
6. Service life comparison
Due to the influence of material pitting and fatigue, rolling bearings are generally designed for 5 ~ 10 years, or replaced during overhaul. The bearing bush is not completely lubricated and needs to be replaced regularly. In theory, the life of fully liquid lubricated bearings is infinite. In fact, due to the stress cycle, especially the hydrodynamic sliding bearings, the bearing bush material may appear fatigue failure.
7. Comparison of rotation accuracy
Due to the small radial clearance of rolling bearings, the rotation accuracy is generally high. The incomplete liquid lubrication bearing is in boundary lubrication or mixed lubrication state, and its operation is unstable, and the wear is serious, and the accuracy is low. Due to the existence of oil film, the fully liquid lubricated bearing has high accuracy. Hydrostatic sliding bearing has higher rotation accuracy.
8. Comparison in other aspects
Rolling bearings use oil, grease or solid lubricant, the amount is very small, high speed when the amount is large, oil cleanliness requirements are high, so it requires sealing, but bearing replacement is convenient, generally do not need to repair journal. For sliding bearings, except for the bearings with incomplete liquid lubrication, the lubricant is usually liquid or gas, and the amount of lubricant is very large, and the requirement of oil cleanliness is also very high. The bearing bush needs to be replaced frequently, and sometimes the journal is repaired.
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