As an indispensable part of mechanical products, bearings play an important role in supporting the rotating shaft. According to the different friction properties in the bearing, the bearing is divided into rolling friction bearing (referred to as rolling bearing) and sliding friction bearing (referred to as sliding bearing). Both types of bearings have their own characteristics in structure, and each has its own advantages and disadvantages. When selecting, it must be combined with actual considerations.
Comparison of rolling bearings and plain bearings
1. Comparison of structure and movement mode
The most obvious difference between a rolling bearing and a plain bearing is whether there is a rolling element.
Rolling bearings have rolling elements (balls, cylindrical rollers, tapered rollers, needle rollers) that rotate to support the rotating shaft, so the contact area is a point, and the more rolling elements, the more contact points.
The sliding bearing has no rolling elements and supports the rotating shaft by a smooth surface, so that the contact portion is a face.
The difference in structure between the two determines that the rolling bearing moves in a rolling manner, and the sliding bearing moves in a sliding manner, so the frictional situation is completely different.
2. Comparison of carrying capacity
Generally speaking, due to the large bearing area of the sliding bearing, its bearing capacity is generally higher than that of the rolling bearing, and the rolling bearing is not capable of withstanding the impact load, but the fully lubricated bearing can withstand the effect of damping and vibration absorption by the lubricating oil membrane. Large impact load. When the rotational speed is high, the centrifugal force of the rolling elements in the rolling bearing increases, and the load carrying capacity is lowered (noise is likely to occur at high speed). For dynamic pressure sliding bearings, the load carrying capacity increases as the rotational speed increases.
3. Comparison of friction coefficient and starting friction resistance
Under normal working conditions, the friction coefficient of the rolling bearing is lower than that of the sliding bearing, and the value is relatively stable. The lubrication of the sliding bearing is susceptible to external factors such as rotation speed and vibration, and the friction coefficient varies widely.
At the time of starting, since the sliding bearing has not formed a stable oil film, the resistance is greater than that of the rolling bearing, but the static sliding bearing has a small starting frictional resistance and a working friction coefficient.
4, applicable working speed comparison
Rolling bearings are limited by the centrifugal force of the rolling elements and the temperature rise of the bearings. The speed cannot be too high, and it is generally suitable for medium and low speed working conditions. Incompletely liquid-lubricated bearings cannot be operated at too high a speed due to the heat and wear of the bearings. The high-speed performance of fully liquid-lubricated bearings is very good, especially when the hydrostatic plain bearings use air as a lubricant, the speed can reach 100000r/min.
5, power loss comparison
Due to the small friction coefficient of the rolling bearing, its power loss is generally not large, and it is smaller than the incompletely liquid-lubricated bearing, but it will increase sharply when the lubrication and installation are not proper. Fully fluid-lubricated bearings have lower frictional power losses, but for hydrostatic plain bearings, the total power loss may be higher than dynamic-pressure sliding bearings due to oil pump power loss. 6, life comparison
Rolling bearings are generally affected by pitting and fatigue of materials for a period of 5 to 10 years, or replacement during overhaul. Bearing bushings for incompletely fluid-lubricated bearings are severely worn and require periodic replacement. The life of a fully liquid-lubricated bearing is theoretically infinite. In fact, due to stress cycling, especially dynamic-pressure sliding bearings, the bearing material may experience fatigue damage. 7, comparison of rotation accuracy
Rolling bearings are generally high in rotation accuracy due to the small radial clearance. Incompletely lubricated bearings are in boundary lubrication or mixed lubrication, unstable operation, and are subject to severe wear and low precision. Fully liquid-lubricated bearings have high precision due to the presence of oil film and buffer absorption. Static pressure sliding bearings have higher rotation accuracy.
8, other aspects of comparison
Rolling bearings use oil, grease or solid lubricants, the amount is small, the amount is high at high speed, the oil quality is required to be clean, so sealing is required, but the bearing replacement is convenient, generally no need to repair the journal. For sliding bearings, in addition to incompletely liquid-lubricated bearings, the lubricant is generally liquid or gas, the amount is large, the oil quality is also very clean, the bearing bush needs to be replaced frequently, and sometimes the journal is repaired.
Selection of rolling bearings and plain bearings
Due to the complexity and variety of actual working conditions, there is no uniform standard for the selection of rolling bearings and plain bearings. Rolling bearings have small friction coefficient, small starting resistance, high sensitivity, high efficiency, and have been standardized. They have excellent interchangeability and versatility. They are easy to use, lubricate and maintain. They are generally preferred when selecting, so they are generally used in general machines. widely used. Sliding bearings have their own unique advantages and are generally used in applications where it is not possible, inconvenient, or has no advantage in using rolling bearings.