HYDRODYNAMIC BEARINGS

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

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

Working of Hydrodynamic Bearings

Lubricants for Journal Bearing Applications

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)

Substitute all the above parameters in the basic Reynolds equation

For infinitely long journal bearing

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

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

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,

Selection of Journal Bearings