Gas lubrication bearing, bearing of knowledge

A, types and characteristics of gas lubricated bearing gas lubricated bearing sliding bearing is used gas as a lubricant. It USES gas transmission ( Diffusivity, viscosity and thermal conductivity) , adsorption and condensability, between the friction pair in the fluid dynamic pressure effect, under the action of static pressure effect and squeezing effect, forming a layer of full film, has the function of bearing load, reducing friction. Gas lubrication bearings generally divided into gas dynamic pressure bearing, aerostatic bearing and three types of gas extrusion bearing. The actual bearing lubrication state often to dynamic and static pressure, dynamic, extrusion, static, and dynamic, static, extruding mixed lubrication status form. The advantages of gas lubrication ( 1) High speed small helium turbine expander speed 650000 r/min, the linear velocity of 238 m/s, calculated according to the dn value has reached 455 x106mm r/min. ( 2) High precision error smoothing effects of gas film, its precision is higher than rolling bearing two orders of magnitude, and little vibration, low noise. ( 3) Small gas viscosity friction loss is only one over one thousand of the lubricating oil viscosity, so the gas film internal friction caused by the friction torque is lower than that of the oil film three orders of magnitude. ( 4) Wide range of applicable temperature and atomic radiation can resistance to high temperature can reach 300 - 500 ℃, the temperature as low as 10 k gas bearing can still work. ( 5) Pollution-free lubricating gas for air or inert gas, commonly released into the atmosphere does not produce pollution. Bearing little vibration, low noise, also does not constitute a pollution to the environment. ( 6) No direct contact with the metal, long life aerostatic bearing theory for infinite life. Consider other conditions, should be in commonly 104 h above. Dynamic pressure gas bearing start-stop moment there is friction between the metal, affected by a certain life, but also in the more than 3000 h. Gas lubricated bearing faults ( 1) Carrying capacity of low gas lubrication bearing with the same kind of oil lubrication bearing ratio, low carrying capacity of about 1 ~ 2 orders of magnitude. According to the bearing capacity per unit area, oil lubrication bearing is commonly ( 5 ~ 2) MPa, while gas lubricated bearing only ( 04) MPa。 ( 2) Poor reliability on the one hand, gas lubricated bearing is easy to instability, a common hammer vibration and vortex instability phenomenon. On the other hand is gas lubricated bearing binding, holding shaft or killed phenomenon also happen from time to tome. ( 3) Need to manufacture high precision, high cost because of the gas film is thin, generally within a few microns to a few microns, and so on parts manufacturing precision demand is higher, increase the cost. In addition, there are small holes and spiral groove, throttling porous materials and other special technical requirements, increase the manufacturing difficulty and cost. ( 4) Working conditions demanding gas lubricated bearing need high cleanliness of the work environment and strictly abide by the operation procedures, to ensure the normal work of the bearing, not an accident. To this end, to a certain extent to limit its wide application and commercialization. Second, gas lubricated bearing application examples in the field of machine tool lubrication bearing gas lubricated bearing in the machine tool is mainly used for the main shaft bearing, including the workpiece axis, cutter shaft, spindle, etc. Machine tool spindle bearings generally USES air static pressure bearing and static pressure bearing two kinds. Small high-speed spindle wave foil bearing may be adopted. Aerostatic bearings used in machine tools, most of which holes throttling and torus throttle bearing is most common. Porous aerostatic bearings are used in recent years, more and more active static mixed lubrication bearing. Floating ring of dynamic and static pressure gas bearing is in recent years, the new development of the gas lubrication bearings, used in high speed spindle bearing is very promising. Ultra-high speed grinding head air bearing inner circle the grinding speed can reach and tiny hole precision grinding. Using air bearing to improve the machining accuracy of machine tools by the 2 - 3 orders of magnitude, and can realize precision mirror surface treatment.