As an essential part of mechanical products, bearing plays an important role in supporting the rotating shaft. According to the different friction properties of the bearing, the bearing is divided into rolling friction bearing (rolling bearing) and sliding friction bearing (sliding bearing). The two types of bearings have their own characteristics in structure and advantages and disadvantages in performance. When selecting them, they should be considered in combination with the actual situation. The following is a comparative analysis of the specific performance of rolling bearing and sliding bearing.
Next, let's introduce the rolling bearing and sliding bearing, how to choose?
1. Comparison of structure and movement mode
The most obvious difference between rolling bearing and sliding bearing is whether there is a rolling element.
Rolling bearing: there are rolling elements (ball, cylindrical roller, tapered roller, needle), which support the rotating shaft by its rotation, so the contact part is a point. 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 between the two structures determines that the motion mode of rolling bearing is rolling, and the motion mode 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 rolling bearing to bear impact load is not high, but fully liquid lubricated bearing can bear large impact load because of the buffer and vibration absorption function of lubricating oil film. When the rotation speed is high, the centrifugal force of the rolling element in the rolling bearing increases, so the bearing capacity of the rolling element 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
Under general working conditions, the friction coefficient of rolling bearing is lower than that of sliding bearing, and the value is more stable. The lubrication of sliding bearing is easily affected by external factors such as speed and vibration, and the variation range of friction coefficient is large.
When starting, because the sliding bearing has not yet formed a stable oil film, the resistance is greater than that of rolling bearing, but the starting friction resistance and working friction coefficient of 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 rotating speed of rolling bearing should not be too high, which is generally suitable for medium and low speed. Because of the heat and wear of incomplete liquid lubricated bearings, the working speed should not be too high. The high speed performance of fully liquid lubricated bearing is very good, especially when the hydrostatic sliding bearing uses air as lubricant, its speed can reach 1000000r / min.
5. Power loss comparison
Due to the small friction coefficient of rolling bearing, its power loss is generally small, which is smaller than that of incomplete liquid lubricated 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 sliding 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 of incomplete liquid lubricated bearing is worn seriously 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. Incompletely liquid lubricated bearings are in boundary lubrication or mixed lubrication state, with unstable operation, serious wear and low precision. Due to the existence of oil film, the fully liquid lubricated bearing can absorb vibration and has high precision. 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, in addition to the incomplete liquid lubrication bearings, the lubricant is generally liquid or gas, the amount is very large, the oil cleanliness requirements are also very high, the bearing bush needs to be replaced frequently, and sometimes the journal needs to be repaired.
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