TAILIEUCHUNG - Engineering Tribology Episode 2 Part 3

Tham khảo tài liệu 'engineering tribology episode 2 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Hydrostatic Lubrication 275 Gas supply from pUmp id spring Flexible diaphragm Gas flow L to bearing Figure Diaphragm pressure sensor valve developed by Mohsin 5 . There are two basic limitations to diaphragm bearings it is necessary to adjust the spring force on the diaphragm to match the bearing stiffness and high stiffness is only maintained up to a certain load where bearing deflection rises sharply with any further increase in load. More detailed information about pressure sensing valves can be found in 2 . AEROSTATIC BEARINGS in some applications a gas is used to lubricate the bearings and these are known as aerostatic bearings. The mechanism of film generation is the same as in liquid bearings. Gas lubricated bearings offer some advantages such as gas viscosity increases with temperature thus reducing heating effects during overload or abnormal operating conditions some gases are chemically stable over a wider temperature range than hydrocarbon lubricants a non-combustible gas eliminates the fire hazard associated with hydrocarbons if air is selected as the hydrostatic lubricant then it is not necessary to purchase or recycle the lubricant gases can offer greater cleanliness and non-toxicity than fluid lubricants. The viscosities of some gases used in aerostatic bearings are shown in Table . table Viscosities of various gases at 20 C and MPa pressure. Gas Viscosity Pas Hydrogen X 10-6 Helium X 10-5 Nitrogen X 10-5 Oxygen X 10-5 Carbon Dioxide X 10-5 Air X 10-5 TEAM LRN 276 Engineering Tribology Aerostatic bearings are used in the precision machine tool industry metrology computer peripheral devices and in dental drills where the air used in the bearing also drives the drill. They are particularly useful for high speed applications and where precision is required since very thin film thicknesses are possible. The main disadvantage however is that the load capacity of gas lubricated bearings or aerostatic .

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