Alvie Rahman ec195bbe66

2023-03-14 10:26:16 +00:00

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Types of Bearings

Plain Journal Bearings

used to support rotating shafts loaded in radial directions
consists of an insert fitted between the shaft and support
the insert may be an aluminium alloy, copper alloy, or other material
the insert provides lower friction and less wear than if just rotating in the support
the bearing may be dry rubbing or lubricated

hydrodynamic---a shaft continuously in oil. the load is carried by pressure generated in the oil as a result of the rotation
hydrostatic---avoids excessive wear at start up by pumping oil into the load bearing area at a pressure that lifts the shaft
solid-firm---a coating of a solid material like graphite or molybdenum disulphide
boundary layer---a thin layer of lubricant which adheres to the surface of the bearing

main load is transferred from rotating shaft to its support by rolling contact from balls
a rolling element bearing consists of an inner race, outer race, rolling elements and a cage

manufactured from sintered metal powders
porous and oil impregnated
more porous is weaker but allows for high speeds
lubricant needs to replenished at regular intervals --- usually every 1000 hours of use

a measure of the bearing's ability to cope with frictional heat generation
rapid wear occurs at pV_\text{max}
if the value is exceeded then overheating, melting, and excessive wear or seizure may follow
general operational range should be around 0.5pV_\text{max}

p = \frac{F_\text{radial}}{bD}

V = \omega\frac D2

p = \frac{4F_\text{axial}}{\pi(D^2-d^2)}

V = \omega\frac{D+d}{4}

K = \frac{W}{FVt}

where K is wear factor (provided by manufacturer), W is wear volume, F is sliding velocity, F is bearing load, and t is elapsed time.