What are the differences between sliding bearings and rolling bearings
As an indispensable important component in mechanical products, bearings play an important role in supporting the rotating shaft. According to the different friction properties in bearings, the bearings are divided into rolling bearings and sliding friction bearings.
The two types of bearings have their own characteristics in structure and their advantages and disadvantages in performance. When selecting, they must be considered in combination with the actual situation.
Next, let's briefly introduce the difference between sliding bearings and rolling bearings:
1. Structure and movement comparison
The most obvious difference between rolling bearings and sliding bearings is whether there are rolling elements.
Rolling bearings have rolling elements (balls, cylindrical rollers, tapered rollers, needle rollers), which rely on their rotation to support the rotating shaft, so the contact point is a point. The more rolling elements, the more contact points. Sliding bearings have no rolling elements, and rely on a smooth surface to support the rotating shaft, so the contact part is a surface.
The difference in structure between the two determines that the rolling bearing movement is rolling, and the sliding bearing movement is sliding, so the friction situation is completely different.
2. Comparison of carrying capacity
In general, due to the large bearing area of the sliding bearing, its bearing capacity is generally higher than that of the rolling bearing, and the ability of the rolling bearing to withstand the impact load is not high, but the completely liquid lubricated bearing can withstand more Large impact load. When the rotational speed is higher, the centrifugal force of the rolling element in the rolling bearing increases, and its load-bearing capacity must be reduced (noise is likely to occur at high speed). For dynamic pressure sliding bearings, the load-bearing capacity increases as the speed increases.
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 widely.
When starting, since the sliding bearing has not 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 static pressure 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, and the rotation speed cannot be too high. It is generally suitable for medium and low speed working conditions. Due to the heat and wear of the bearing, the working speed cannot be too high for incomplete liquid lubricated bearings. The high-speed performance of the completely liquid lubricated bearing is very good, especially when the static pressure sliding bearing uses air as a lubricant, its speed can reach 100000r / min.
5. Power loss comparison
Due to the low friction coefficient of rolling bearings, the power loss is generally not large, which is less than that of incomplete liquid lubricated bearings, but when the lubrication and installation are not correct, they will increase dramatically. The frictional power loss of fully liquid lubricated bearings is low, but for static pressure sliding bearings, due to the power loss of the oil pump, the total power loss may be higher than that of dynamic pressure sliding bearings.
6. Service life comparison
Due to the influence of material pitting corrosion and fatigue, the rolling bearing is generally designed for 5 to 10 years, or replaced during overhaul. Bearing bushes with incomplete liquid lubricated bearings are badly worn and need to be replaced regularly. The life of fully liquid lubricated bearings is theoretically infinite. In fact, due to stress cycles, especially dynamic pressure sliding bearings, the bearing materials may suffer fatigue damage.
7. Comparison of rotation accuracy
Due to the small radial clearance of rolling bearings, the rotation accuracy is generally higher. Incomplete liquid lubricated bearings are in the state of boundary lubrication or mixed lubrication, the operation is unstable, and the wear is serious, and the accuracy is low. The completely liquid lubricated bearings have high accuracy due to the presence of oil film, which absorbs vibration and absorbs vibration. The rotating precision of hydrostatic sliding bearing is higher.
8. Other comparisons
Rolling bearings use oil, grease or solid lubricants, the amount is very small, the amount is large at high speed, and the cleanliness of the oil is required to be high, so the seal is required, but the bearing is easy to replace, and generally does not need to repair the journal. For sliding bearings, in addition to incomplete liquid lubricated bearings, the lubricant is generally liquid or gas, the amount is large, the cleanliness of the oil is also very high, the bearing bush needs to be replaced frequently, and sometimes the journal is repaired.