Download - ME3180 Lubrication 112114
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November 21, 2014
ME 3180
Lubrication
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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
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Either oil or grease may be used, with each having
advantages in certain situations.
Bearing Lubrication
Shigleys Mechanical
Engineering Design
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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
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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
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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
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Linear Sliding Wear Shigleys Mechanical
Engineering
Design
Fig. 1238