Characteristics and applications of various sliding bearings
1. Fluid lubrication: The two surfaces of the sliding pair are separated by a thick continuous fluid film. The surface peaks are not in direct contact. The friction only occurs inside the fluid, which is called fluid friction. The lubrication state at this time is called It is fluid lubrication, also called complete lubrication.
2. No lubrication: There is no lubricant or protective film between the two surfaces of the sliding pair. The friction state at this time is called dry friction. There is no real dry friction in engineering practice. Generally, it is called dry friction bearing. Refers to bearings that have no lubricant intervention but may have a naturally contaminated film.
3. Boundary lubrication: There is a very thin boundary film between the two surfaces of the sliding pair (the adsorption film and the chemical reaction film are collectively referred to as the boundary film), the strength is low, and the direct contact between the two surface peaks cannot be avoided, but friction and wear conditions It is much better than dry friction, called boundary film), the strength is low, and direct contact between the two surface peaks cannot be avoided, but the friction and wear are much better than dry friction, called boundary friction, and the state of lubrication at this time is called Boundary lubrication.
4. Mixed lubrication: When the two surfaces of the lubrication pair are in a mixed state of boundary friction and fluid friction, it is called mixed friction, and the lubrication state at this time is called mixed lubrication.
5. Incomplete fluid lubrication: boundary lubrication or mixed lubrication is collectively referred to as incomplete fluid lubrication, or incomplete fluid friction.
Characteristics and applications of various sliding bearings
|Incompletely fluid lubricated bearings||Radial sliding bearing||Integral||Generally, grease, oil rope and dripping are used for lubrication. The journal and bearing surface cannot get enough lubricant, and the liquid oil film is discontinuous. Simple structure, large friction factor and large wear||The gap between the shaft and the bearing shell cannot be adjusted, the structure is simple, and the journal can only be assembled and disassembled from the shaft end||Generally used on machines with low speed, light load and allowable assembly and disassembly|
|Split||The gap between the shaft and the bearing shell can be adjusted and the installation is simple||This method is often used when the machine is difficult to assemble and disassemble|
|Self-contained||The bearing shell can swing properly in the bearing seat to adapt to the deflection caused by the bending of the shaft||It is used in the situation where the transmission shaft is skewed, and the joint bearing is used to bear the radial load at the hinged joint of the rods that swing to each other|
|Thrust sliding bearing||Commonly used flat thrust sliding bearings, due to liquid friction conditions, are in an incomplete liquid lubrication state, and need to be used together with radial bearings.||Used to bear axial force|
|Powder metallurgy bearings (oil bearing)||Porous, the oil is stored in the pores, and it can be automatically lubricated without adding lubricating oil for a long time to ensure normal operation. However, due to its relatively soft material, the bearing capacity is low||Used for light load, low speed and difficult to refuel|
|Plastic Bearing||Compared with metal bearings, plastic bearings are lighter and easier to maintain. It has good dumping stability, high wear resistance and fatigue resistance, and has vibration damping, sound absorption, self-lubricating, insulating and self-extinguishing properties. But the coefficient of thermal expansion is large, the coefficient of thermal conductivity is low, the moisture absorption is large, the strength and dimensional stability are not as good as metal||Used in places where the speed is not high or the heat dissipation is good, the working temperature should not exceed 65℃, and the instantaneous working temperature should not exceed 80℃|
|Rubber bearing||It can absorb vibration and impact, and has good wear resistance and corrosion resistance in an environment with impurities, but its unit strength is lower than that of metal, and its heat resistance is poor. It is not suitable for use in high temperature and in contact with oil or organic solvents.||Used for bearing vibration damping in ship shaft tube and working in corrosive environment|
|Wood bearing||Wood bearings are light and cheap, can absorb impact, have little sensitivity to shaft deflection, but have low strength, poor thermal conductivity, moisture resistance, and wear resistance||Used for light-load vibration reduction conditions, such as agricultural machinery disc harrow bearings, large ore transfer pump bearings, etc|
|Fluid-lubricated bearings||Hydrodynamic bearing||The journal and the working surface of the bearing are completely separated by an oil film. The dynamic pressure bearing must have: ①The bearing has enough speed; ②There is enough oil supply, and the lubricating oil has a certain viscosity; ③There is a proper gap between the journal and the bearing working surface. The multi-oil wedge hydrodynamic bearing can meet the high-precision rotation requirements of the shaft and has a long life||Used for high-speed and high-precision machinery, such as bearings of centrifugal compressors, etc.|
|Hydrostatic bearing||The journal and the bearing are completely separated by a load-bearing oil film with a certain pressure supplied from the outside. The formation of the oil film is not limited by the relative sliding speed, and has a large load-bearing capacity at various speeds (including zero speed). The shaft has good stability and can meet the high-precision rotation requirements of the shaft. The friction factor is small, the mechanical efficiency is high, and the service life is long.||Mainly used for: ① places where it is difficult to form a heavy oil film at low speeds, such as vertical lathes, gantry horizontal milling, heavy motors, etc.; ② high rotation accuracy is required|
|Gas dynamic pressure, static pressure bearing||Gas dynamic pressure and static pressure bearings, air or other gases are used as lubricants, with small friction factor and high mechanical efficiency, which can meet the requirements of high-speed operation||Gas bearings are used as bearings for gyro rotors and TV recorders|
|Non-lubricated bearing||Plastic, carbon graphite bearings||Operate without lubricating oil or grease||Less applications|
|otherSolid lubrication bearing||Lubricate with graphite, molybdenum disulfide, phthalocyanine dye, polytetrafluoroethylene and other solid lubricants||Used in special working conditions such as extremely low temperature, high temperature, high pressure, strong radiation, space, vacuum, etc.|
|Magnetic Current Bearing Electrostatic Bearing Magnetic Bearing||Use magnetic fluid as lubricant Use electric field to levitate shaft Use magnetic field to levitate shaft||Mostly used in high-speed machinery and instruments|
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