What is the difference between rolling bearings and plain bearings?

- Oct 08, 2018-

1. Comparison of structure and movement mode The most obvious difference between a rolling bearing and a plain bearing is the presence of a rolling element. Rolling bearings have rolling element (ball, cylindrical roller, tapered roller, needle roller), by its rotation to support the rotation axis, so the contact site is a point, the more rolling body, the more contact Points. The sliding bearing has no rolling body and is supported by a smooth surface to support the rotating shaft, so the contact area is a face. The difference between the two structures determines that the rolling bearing movement is rolling, the sliding bearing movement is the slide, so the friction situation is completely different.

2. Comparison of carrying capacity overall, because the bearing area of the sliding bearings is large, the bearing capacity is generally higher than the rolling bearings, and the bearing capacity of the impact load is not high, but the complete liquid lubrication bearings because of the lubricant film buffer, vibration absorption role, can withstand a large impact load. When the rotational speed is high, the centrifugal force of the rolling bearing increases and the load-carrying capacity of the rolling bearings is reduced (noise is easy at high speed). The bearing capacity of dynamic pressure sliding bearing 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 bearing is lower than that of plain bearing, and the numerical value is more stable. While the lubrication of sliding bearing is susceptible to the influence of external factors such as speed and vibration, the variation range of friction coefficient is large. starting, because the sliding bearing has not yet formed a stable oil film, the resistance is greater than the rolling bearing, but the static pressure sliding bearing starting friction and working friction coefficient are very small.

4, the applicable work speed comparison Rolling bearing due to the centrifugal force and the bearing temperature rise limit, the rotational speed can not be too high, generally suitable for medium and low-speed working conditions. Incomplete liquid lubricated bearings cannot operate at too high a speed due to the heat and wear of the Bearing. The high-speed performance of fully liquid lubricated bearings is very good, especially when hydrostatic plain bearings use air as lubricant, and their rotational speeds can reach 100000r/min.

5. Power Loss Comparison Due to the small friction coefficient of rolling bearings, the power loss is generally small, less than the incomplete liquid lubrication bearings, But when the lubrication and installation will increase dramatically. The frictional power loss of completely liquid lubricated bearings is lower, but for hydrostatic plain bearings, the total power loss may be higher than that of the dynamic pressure bearing because of the loss of oil pump power.

6. Comparison of service life Because of the influence of the material pitting and fatigue, the rolling bearings are generally designed for a period of 5-10 years or replaced during Overhaul. Bearings with incomplete liquid lubrication have serious wear and need to be replaced regularly. The life of a fully liquid lubricated bearing is theoretically infinite, in fact due to the stress cycle, especially the dynamic pressure sliding bearing, The bearing material may appear fatigue damage.

7. Comparison of rotational accuracy Rolling bearings due to the small radial clearance, the rotation accuracy is generally high. Incomplete liquid lubricated bearings are at the boundary lubrication or mixed lubrication state, running unstable, and wear more serious, low Precision. The fully liquid lubricated bearing has a high precision due to the existence of oil film, cushioning and vibration Absorption. Hydrostatic plain bearings have a higher rotational accuracy. 

8, rolling bearings using oil, grease or solid lubricant, the dosage is very small, high-speed use of large, high quality of cleanliness requirements, it is required to seal, but the bearing replacement is convenient, generally do not need to repair the shaft NECK. For plain bearings, In addition to the incomplete liquid lubricated bearings, lubricants are generally liquid or gas, the amount of large, high quality of cleanliness requirements, bearing bearings need to be frequently replaced, and sometimes repair the shaft neck.