Influence of load and oil viscosity on reference speed/permissible speed

When load and viscosity values higher than the reference values are applied, the frictional resistance will increase so that a bearing cannot operate at the suggested reference speed, unless higher temperatures can be permitted.
The influence of load and kinematic viscosity on the reference speed can be obtained from the diagrams:

Oil lubrication

Values of the adjustment factors for oil lubrication
  • fP : for the influence of the equivalent dynamic bearing load P and
  • fv : for the influence of viscosity
can be obtained from diagrams 1 to 4 as a function of P/C0 and the bearing mean diameter dm

where

P=equivalent dynamic bearing load [kN]
C0=basic static load rating [kN]
dm=bearing mean diameter
= 0,5(d + D) [mm]
The viscosity values in the diagrams are expressed with ISO designations, for example, ISO VG 32, where 32 is the oil viscosity at 40 °C.
If the reference temperature of 70 °C is to remain unchanged, the permissible speed is obtained from


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where

nperm=permissible bearing speed [r/min]
nr=reference speed [r/min]
fP=adjustment factor for bearing load P
fν=adjustment factor for oil viscosity

Grease lubrication

The diagrams are also valid for grease lubrication. However, the reference speed for grease lubrication is based on a base oil viscosity VG 150. The value of fν needs to be calculated as fν for the base oil viscosity at 40 °C of the selected grease, divided by fν for an ISO VG 150 oil, i.e.


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Example 1

An SKF Explorer 6210 deep groove ball bearing is subjected to a load P = 0,24 C0 and has an oil bath lubrication with oil viscosity 68 mm2/s at 40 °C. Which permissible speed can be expected?
For bearing 6210: dm = 0,5(50 + 90) = 70 mm. From diagram 5, with dm = 70 mm and P/C0 = 0,24, fP1 = 0,63 and with P/C0 = 0,24 and ISO VG 68, fv = 0,85.
The permissible bearing speed for which an operating temperature of 70 °C can be expected, nperm, will then be

nperm = 15 000 × 0,63 × 0,85 = 8 030 r/min

Example 2

An SKF Explorer 22222 E spherical roller bearing is subjected to a load P = 0,15 C0 and is grease lubricated having a base oil viscosity 220 mm2/s at 40 °C. Which permissible speed can be expected?
For bearing 22222 E: dm = 0,5(110 + 200) = 155 mm. From diagram 6 with dm = 155 mm and P/C0 = 0,15, fP = 0,53 and with P/C0 = 0,15 and ISO VG 220, fνactual = 0,83; with P/C0 = 0,15 and ISO VG 150, fνISO VG 150 = 0,87.
The permissible bearing speed for which an operating temperature of 70 °C can be expected, nperm, will then be

nperm = 3 000 × 0,53 × 0,83/0,87 = 1 520 r/min
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