Grease life for the relubrication-free variant

The grease used in relubrication-free bearing units can adequately lubricate the bearing throughout its service life provided the bearing unit is suitable for the operating conditions. The relationship between operating conditions and grease service life is shown in diagram 1 and is a function of:
  • the operating temperature [°C]
  • the speed factor A = n dm

    A = speed factor [mm/min]
    n = rotational speed [r/min]
    dm = bearing mean diameter [mm] (table 1)
Provided the operating range of the bearing unit falls within the shaded area of diagram 1, the bearing unit can attain a grease life of L50h = 100 000 hours or more. L50h is the time period at the end of which 50% of the units are still reliably lubricated.
Calculation example

An SKF ConCentra roller bearing unit with a plummer block housing is required for an industrial air handling unit. The following application information is known:

  • required grease life L50h = 100 000 hours
  • equivalent dynamic bearing load P = 7 kN
  • rotational speed n = 1 800 r/min
  • shaft diameter da = 60 mm
  • environmental conditions: relatively clean
  • expected operating temperature: 55 °C

Based on the shaft diameter provided and the plummer block housing requirement, the SYNT 60 bearing unit is selected. As the application is an industrial air handling unit in a relatively clean environment, the relubrication-free variant would be a suitable choice.

From the product table, the basic dynamic load rating C = 156 kN and

when C/P = 156/7 = 22,3

then P = 0,045 C

Therefore, the bearing unit meets the conditions of use for relubrication-free variants, where P ≤ 0,05 C.

For dm = 85 mm (table 1)
A = n dm = 1 800 x 85 = 153 000 mm/min

Using diagram 1, the intersection point of the calculated speed factor and expected operating temperature of 55 °C is located in the shaded area.

The SYNT 60 FW (or SYNT 60 LW) bearing unit meets the grease life requirement and is therefore suitable for the application.

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