17867 hydrodynamic bearings
DESCRIPTION
hydrodynamic bearingsTRANSCRIPT
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HYDRODYNAMIC BEARINGS
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Bearings
Contact Bearings
Ball BearingsRoller
Bearings
Sliding Bearings
Hydrodynamic Bearings
Thrust Bearings
Journal Bearings
Squeeze film Bearings
Hydrostatic Bearings
Circular step Thrust
Bearings
Annular Step Thrust
Bearings
Rectangular Thrust
Bearings
Journal Bearings
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Advantages and Disadvantages of Sliding Contact Bearings
Advantages
The design of Bearing and the housing
is simple
They occupy less radial space
The design of shaft is simple
They operate silently
They have good shock load capacity
They are ideally suited for medium and
high speed applications
Disadvantages
The frictional power loss is more
They require good attention to lubrication
They are normally designed for radial or axial
loads
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Working of Hydrodynamic Bearings
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Lubricants for Journal Bearing Applications
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Reynolds Equation for Journal Bearings
For most journal bearings, only the journal is rotating and the sleeve is stationary,
U1=0 and V1 =0
The second uid lm boundary is at the journal surface that has a velocity U = R. However, the velocity is not parallel to the x direction (the x direction is along the bearing surface)
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Substitute all the above parameters in the basic Reynolds equation
For infinitely long journal bearing
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Load capacity of a Journal Bearing
Coefficient of friction in Journal Bearing is given by
Power loss in Journal Bearing
W- Load Capacity
- Dynamic viscosity
C ClearanceR Radius of SleeveL Length Of the Bearing Eccentricity ratioU - Velocity
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Bearing Materials
Properties of good Bearing material
Conformability (Low elastic Modulus) and Deformability (Plastic flow)
--- to relieve local pressures caused by misalignment and deflection of shaft
Embeddability or indentation softness
--- to permit small foreign particles to become safely embedded in the material thus protecting the Journal against wear
Low shear strength for easy smoothing of surface asperities
Adequate compressive strength and fatigue strength for supporting for supporting loads and cyclic loads
Should have good thermal conductivity to dissipate the frictional heat and coefficient of thermal expansion
It should be resistant to scoring, welding and seizing
It should have good corrosion resistance against lubricants
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Composition of Bearing materials
Babbits are the most commonly used bearing material
They have excellent embeddability and conformability, but they have low compressive and
fatigue strength
Other materials are,
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Selection of Journal Bearings