This program selects a suitable lubrication liquid from the list, according to specified bearing dimensions and loading. The calculation procedure is like the complete bearing checking calculation. The result is, not only a lubricant recommendation, but also the calculation of lubricant temperature at the bearing outlet.
During the selection process for a lubricant, the calculation is based on the minimum oil layer that is necessary for complete separation of bearing sliding faces and for ensuring hydrodynamic lubrication. The minimum thickness of the bearing oil layer, while considering running-in, surface texture of sliding faces and size of hard particles in the lubrication liquid are determined by the oil filter permeability and is determined according to the following equation:
h min - 3.4 (R aH + R aL ) + o [μm]
for the bearing without running-in, the equation is:
h min - 4.5 (R aH + R aL ) + o [μm]
The program calculates the necessary relative journal eccentricity from the minimum oil layer thickness value:
The recommended value of relative journal eccentricity range is from 0.7 to 0.96.
The Sommerfeld number, which describes bearing capacity, is determined from a diagram in relation to the relative journal eccentricity and relative bearing width.
The recommended value of the Sommerfeld number ranges from 1 to 15. The needed lubricant viscosity for the expected mean lubricant temperature at the bearing outlet is easily calculated for the Sommerfeld number, determined in this way.
The program selects a corresponding oil from the list, according to the expected lubricant temperature at the exit and calculated dynamic viscosity. Then the bearing thermal balance is made for this oil. The result of the calculated balance is the mean lubricant temperature at the bearing exit.
If the expected temperature does not correspond to the calculated temperature (2°C is considered to be acceptable), the bearing does not suit the specified lubricant. The whole calculation is again repeated for a new temperature value determined by linear interpolation of expected and calculated temperature. An iteration process of the calculation then continues until the execution of the specified demand.
Meaning of used variables:
|
Δd |
diametral clearance [mm]. |
|
h min |
minimum thickness of lubrication layer, which ensures the total separation of bearing sliding faces [μm]. |
|
o |
size of the smallest hard particles in oil determined by the permeability of oil filter [μm]. |
|
p m |
bearing pressure [MPa]. |
|
R ah |
journal surface texture [μm]. |
|
R aL |
bearing surface texture [μm]. |
|
S o |
Sommerfeld number [-]. |
| ε |
relative journal eccentricity [-]. |
| η |
lubricant dynamic viscosity at its mean temperature at the bearing outlet [Pa s]. |
| φ |
relative diametral clearance [mm]. |
| ω |
hydrodynamically effective angular speed of bearing journal [s -1 ]. |