The bearing characteristic number depends on

Concept:

Several dimensionless numbers are used to understand the performance of bearing. Some of them are –

• Bearing Characteristic Number = \( \frac{{Z{N_s}}}{P}\)
• Bearing Modulus: The value of Bearing characteristic number when the co-efficient of friction is minimum.
• Sommerfield number: It is used to co-relate the working condition of a different machine which are operating under the same bearing. It is given by

 \( {\rm{S}} = \left( {\frac{{{\rm{Z}}{{\rm{N}}_{\rm{s}}}}}{{\rm{P}}}} \right){\left( {\frac{{\rm{r}}}{{\rm{C}}}} \right)^2}\)

where Z = Absolute viscosity of the lubricant, Ns = Revolution per sec, P = Bearing pressure, r = Radius of the shaft, c = Radial clearance of bearing and shaft, and ho = film thickness.

• Eccentricity ratio/Attitude: It is the ratio of eccentricity to radial clearance.

\({\rm{e}} = \frac{{{\rm{eccentricity}}}}{{{\rm{radial\;clearance}}}} = \frac{{\left( {R - r} \right) - {h_o}}}{{\left( {R - r} \right)}} = 1 - \frac{{{h_o}}}{c}\)

Explanation:

From the above formula, it is evident that

Bearing characteristic number depends on 

• Z (Viscosity)
• N (Speed of rotation)
• P (Bearing pressure)

Bearing Pressure is dependent on Bearing load and Bearing effective area (length and diameter of the bearing)