The difference between sliding bearings and rolling bearings
As an essential and important part of mechanical products, bearings play an important role in supporting the rotating shaft. According to the different friction properties in bearings, bearings are divided into rolling friction bearings (referred to as rolling bearings) and sliding friction bearings (referred to as sliding bearings).
 
1. Comparison of structure and movement mode
     The most obvious difference between rolling bearings and sliding bearings is whether there are rolling elements.
(1) Rolling bearings have rolling bodies (balls, cylindrical rollers, tapered rollers, needle rollers), which support the rotating shaft by their rotation, so the contact part is a point. The more rolling bodies, the more contact points.
(2) The sliding bearing has no rolling body, and the rotating shaft is supported by a smooth surface, so the contact part is a surface. The difference in the structure of the two determines that the motion mode of the rolling bearing is rolling, and the motion mode of the sliding bearing is sliding, so the friction situation is completely different.
 
2. Comparison of carrying capacity
     Generally speaking, due to the large pressure bearing area of sliding bearings, their load-bearing capacity is generally higher than that of rolling bearings, and the ability of rolling bearings to withstand impact loads is not high. large shock loads. When the rotational speed is high, the centrifugal force of the rolling elements in the rolling bearing increases, and its carrying capacity should be reduced (noise is prone to occur at high speeds). For dynamic pressure sliding bearings, their load carrying capacity increases with the increase of rotational speed.
 
3. Comparison of friction coefficient and starting friction resistance
     Under normal working conditions, the friction coefficient of rolling bearings is lower than that of sliding bearings, and the value is relatively stable. The lubrication of sliding bearings is easily affected by external factors such as speed and vibration, and the friction coefficient varies in a large range.
     When starting, since the sliding bearing has not yet formed a stable oil film, the resistance is greater 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
     Rolling bearings are limited by the centrifugal force of the rolling elements and the temperature rise of the bearings, so the speed cannot be too high, and it is generally suitable for medium and low speed working conditions. Due to the heat and wear of the bearing, the working speed of the incomplete liquid lubricated bearing should not be too high. The high-speed performance of completely liquid-lubricated bearings is very good, especially when the hydrostatic sliding bearing uses air as lubricant, its speed can reach 100,000r/min.
 
5. Power loss comparison
     Due to the small friction coefficient of rolling bearings, its power loss is generally not large, which is smaller than that of incomplete liquid lubricated bearings, but it will increase sharply when lubricated and installed improperly. The frictional power loss of fully liquid lubricated bearings is lower, but for hydrostatic sliding bearings, the total power loss may be higher than that of hydrodynamic sliding bearings due to the power loss of the oil pump.
 
6. Comparison of service life
     Due to the impact of material pitting and fatigue, rolling bearings are generally designed for 5 to 10 years, or replaced during overhaul. The bearing pads of incompletely liquid lubricated bearings are severely worn and need to be replaced periodically. The life of fully liquid lubricated bearings is theoretically infinite, but in practice due to stress cycles, especially in hydrodynamic sliding bearings, fatigue failure of the bearing pad material may occur.
 
7. Comparison of rotation accuracy
     Due to the small radial clearance of rolling bearings, the rotation accuracy is generally high. The incomplete liquid lubricated bearing is in the boundary lubrication or mixed lubrication state, the operation is unstable, the wear is serious, and the precision is low. Due to the existence of oil film, the fully liquid lubricated bearing can cushion and absorb vibration and have high precision. Hydrostatic sliding bearings have higher rotational accuracy.
 
8. Comparison with other aspects
     Rolling bearings use oil, grease or solid lubricants, the amount is small, and the amount is large at high speeds. The cleanliness of the oil is required to be high, so sealing is required, but the bearings are easy to replace and generally do not need to repair the journal.
     For sliding bearings, except for incomplete liquid lubricated bearings, the lubricant is generally liquid or gas, and the amount used is large, and the oil cleanliness is also very high. The bearing bush needs to be replaced frequently, and sometimes the journal is repaired.