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Oil or Grease? Which Lubricant is Right for Your Application?

Applying a lubricant between the rolling and sliding parts of a bearing will help to improve speed and reduce service life.

Other benefits of lubrication include:

  • Reduction of noise and vibration
  • Heat dissipation
  • Sealant
  • Corrosion protection
  • Maintenance-free operation over a long period of time

But which type of lubricant should you choose? Oil or Grease? See the tables below to find the best lubricant for your application.

Choose The Best Lubricant for Your Application

Lubricant Grease Oil
Use When: a) Max speed of the bearing is less than
the speed factor of the grease (n *dm).
b) The environment almost uniformly dissipates the heat generated by the application.
c) Maintenance-free operation over a long period of time is desired.
a) High operational speeds won’t support the use of grease.
b) The lubricant is required to simultaneously cool the bearing(s).

Bearing Lubrication Selection Chart

Quick comparison of the performance of grease vs oil lubrication.

Lubricant Grease Oil
General Speed suitability in n * dm +++
approx. 2 MM
approx. 3 to 4 MM
Service life +++ +++++
Design / system costs +++++ (low) + (higher)
Operating costs +++++ (low) + (higher)
Heat dissipation ++ ++++
Running in procedure ++ +++
Pollution +++++ (low) + (higher)

+++++: very good
+: poor

Reference Speed Factor: Grease Lubrication

Selecting a suitable grease for high precision bearings is based on the max operating speed and temperature.

The reference speed factor n * dm calculates the operating rotational speed from the center line of the bearing ball diameter and indicates the max speed capacity of the lubricant being specified.

Below is a standard Reference Speed Factor Industry Guide. This Reference Speed Factor Guide helps compare the entire application for grease versus a general shaft or housing RPM.

Reference Speed Factor Guide: n * dm
a) n * dm bearing = n * [(D+d) / 2]
b) n = bearing operating speed [1/min]
c) d = bearing bore diameter [mm]
d) D = bearing outer diameter [mm]
Please note: Many bearing companies provide an exact dm in the catalog

Using this reference speed factor will help you select a lubricant that will not prematurely degrade the bearings performance.

Oil Lubrication

In comparison to grease-lubricated bearings, oil lubrication enables long-term reliable operation at maximum speeds.

There are three main oil lubrication methods:

  • Oil-Mist lubrication
  • Oil-Air / Air-Oil lubrication (minimized lubrication consumption)
  • Oil-Jet injection lubrication (greater cooling effects)
Oil-Mist Oil-Air Oil-Jet
a) Oil-mist is produced in an atomizer & conveyed to the bearing(s) by an air current
b) Air currents also cool the bearings
c) Slightly higher pressure prevents contamination from penetrating the surface of the bearing.
a) Oil is conveyed to the bearing(s) in droplets by compressed air
b) Droplet size & intervals between droplets are controlled
a) Considerable amounts of oil are carried through the bearing by injection
b) Frictional heat generated in the bearing(s) disappears
c) The cooling of the oil is achieved with an oil-to-air heat exchange or other methods
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