G. PULLAIAH COLLEGE OF ENGINEERING
& TECHNOLOGY, KURNOOL
A.SRINIVAS
Asst. Professor
Department of Mechanical Engineering
A bearing is a machine element which support another moving
machine element (known as journal)
There are two types of loads which a bearings can withstands i.e Radial load
(around bearing’s axis of rotation) and Axial load ( acts parallel to the axis of
rotation,thrust).
Sliding Contact Bearing
•Plain bearing is a simple cylinder made to fit around the journal of a shaft.
Lubricant film separates the bearing surface from the journal.
•Plain bearings are usually made of relatively soft material and therefore it
does not scratch the shaft.
•Plain bearings are used mainly to support low speed shafts carrying heavy
loads.
Rolling contact Bearings
Anti-friction bearings provide rolling contact rather then sliding contact therefore the
total effective contact area is much less in anti-friction bearings as compared to plain
bearings (sliding contact bearing). Starting friction of anti-friction bearings is therefore
considerably less than in plain or sleeve bearings
Design Procedure for Journal Bearing
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Determine the bearing length by choosing a ratio of l / d from Table 26.3.
Check the bearing pressure, p = W / l.d from Table 26.3 for probable
satisfactory value.
Assume a lubricant from Table 26.2 and its operating temperature (t0). This
temperature should be between 26.5°C and 60°C with 82°C as a maximum for
high temperature installations such as steam turbines.
Determine the operating value of ZN / p for the assumed bearing temperature
and check this value with corresponding values in Table 26.3, to determine
the possibility of maintaining fluid film operation.
Assume a clearance ratio c / d from Table 26.3.
etermine the coefficient of friction (μ) by using the relation as discussed in
Art. 26.15.
Determine the heat generated by using the relation as discussed in Art. 26.18.
Determine the heat dissipated by using the relation as discussed in Art. 26.18.
Determine the thermal equilibrium to see that the heat dissipated becomes
atleast equal to the heat generated. In case the heat generated is more than
the heat dissipated then either the bearing is redesigned or it is artificially
cooled by water
Dynamic Equivalent Load for Rolling Contact Bearings