In order to avoid seizure in hydrodynamic bearings, the operating value of the bearing characteristic number should be at least ____ times the bearing modulus.

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HPCL Engineer Mechanical 04 Nov 2022 Official Paper (Shift 2)

Answer 1

Explanation:

The Mcckees's investigation gives the relation between bearing characteristic (BCN) and bearing modulus (\(\alpha\)).

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Bearing characteristic number (BCN) = \(\frac{\mu{n}}{p}\)

where, \(\mu\) = absolute viscosity (Pas), n = speed (rps), p = bearing pressure (Pa).

Bearing modulus (\(\alpha\)) - The value of the bearing characteristic number at the minimum coefficient of friction.

For stability, the bearing modulus should be equal to a minimum value of the bearing characteristic number.
The bearing characteristic number is always greater than the bearing modulus for hydrodynamic conditions.
To avoid seizing, the value of the bearing characteristic number should be 5 to 6 times the bearing modulus.
For static loading,

\(3\alpha\leq(\frac{\mu{n}}{p})\leq5\alpha\)

\(13\alpha\leq(\frac{\mu{n}}{p})\leq15\alpha\)

Thus, option (2) is the correct answer.