November 21, 2014

ME 3180

Lubrication

Bearing Lubrication

The purposes of bearing lubrication

To provide a film of lubricant between the sliding and

rolling surfaces

To help distribute and dissipate heat

To prevent corrosion of the bearing surfaces

To protect the parts from the entrance of foreign

matter

Shigleys Mechanical

Engineering Design

Either oil or grease may be used, with each having

advantages in certain situations.

Bearing Lubrication

Shigleys Mechanical

Engineering Design

Types of Lubrication Hydrostatic lubricant constantly supplied to

interface at elevated hydrostatic pressure

Elastohydrodynamic nonconforming

contact surfaces (e.g., gear teeth)

Hydrodynamic relative motion of surfaces

Shaft

is stationary

Sleeve

Bearing

Shaft

starts to rotate

Shaft

rotating

rapidly

Metal-to-metal

contact

Boundary lubrication,

oil pulled into interface

No direct contact

Between shaft and sleeve

Figure 12-15 in

Shigleys 9th edition

(from Raimondi and

Boyd)

Shaft center moves to

the left of the sleeve

center

Offset e is the

eccentricity

Eccentricity ratio

e = e / c

c = radial clearance

Boundary-Lubricated Bearings

Relative motion between two surfaces with only a

partial lubricant film (not hydrodynamic) is called

boundary lubrication or thin-film lubrication.

Even hydrodynamic lubrication will have times

when it is in thin-film mode, such as at startup.

Some bearings are boundary lubricated (or dry) at

all times.

Such bearings are much more limited by load,

temperature, and speed.

Shigleys

Mechanical

Engineering

Design

Linear Sliding Wear Shigleys Mechanical

Engineering

Design

Fig. 1238