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Why do modern mining machinery mostly use rolling bearings instead of sliding bearings?

wallpapers Tech 2020-05-29
As an indispensable important component in mechanical products, bearings play an important role in supporting the rotating shaft. According to the different frictional properties of bearings, bearings are divided into rolling friction bearings (referred to as rolling bearings) and sliding friction bearings (referred to as sliding bearings). The two types of bearings have their own characteristics in structure and their advantages and disadvantages in performance. When selecting, they should be considered in combination with the actual situation.
 
Comparison of rolling bearings and sliding bearings
 
1. Comparison of structure and movement
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.
Why do modern mining machinery mostly use rolling bearings instead of sliding bearings?
 
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. 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 should 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. Comparison of applicable working speed
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. Incomplete liquid lubricated bearings due to heat and wear of the bearings, the working speed should not be too high. The high-speed performance of the completely liquid lubricated bearing is very good, especially when the static pressure sliding bearing uses air as the lubricant, its speed can reach 100000r / min.
Why do modern mining machinery mostly use rolling bearings instead of sliding bearings?
 
5. Comparison of power loss
Due to the small friction coefficient of rolling bearings, the power loss is generally not large, which is less than that of incomplete liquid lubricated bearings, but it will increase sharply when lubrication and installation are improper. 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. Comparison of service life
Due to the influence of material pitting corrosion and fatigue, rolling bearings are 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 cycling, 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. Due to the presence of oil film, the fully liquid lubricated bearing has a high vibration damping and high accuracy. The rotating precision of hydrostatic sliding bearing is higher.
Why do modern mining machinery mostly use rolling bearings instead of sliding bearings?
 
8. Comparison in other aspects
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.

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Tag: sliding bearings