Part 4 of our 9-part series on bearing lubricating procedures gives a 6- step run-in procedure to use after greasing bearings to ensure even grease distribution. The proper run-in process forms a grease collar that releases the ideal amount of base oil to lubricate friction surfaces. Otherwise, excessive operating temperatures and other problems can occur. Next time we’ll look at proper grease gun calibration and operation.
A proper run-in procedure is vital to the performance of the bearing and lubricant in applications where high speeds, fill quantities and certain pre-loads are critical. That’s because during the run-in process, the initial grease fill is evenly distributed around the bearing elements. A grease collar is formed to optimize the release of the base oil in a way that the friction surfaces are wetted with just the right oil quantity. As a result, the rolling elements and the cage don’t entrain the entire lubricating grease, but just the required amount of oil.
If the necessary run-in is omitted, excessive operating temperatures and/or an over-lubrication condition will result. It is best to consult with the lubricant manufacturer if you have any questions in this area, or if your specific application does not reach a stable equilibrium operating temperature after it has been run-in.
A proper run-in procedure:
- Expels the excess grease found in the system
- Orients the lubricating film on each contact surface
- Creates a grease collar to deliver oil to the contact zone
- Establishes a low equilibrium operating temperature
- Achieves a sealed-for-life lubrication condition
Considerations for Run-in Procedures
Most lubricating greases can benefit from the displacement of excess grease, but not all lubricating greases will orient themselves on the bearing surface. There are several factors to consider:
- Certain soap based greases are fibrous in texture and will set up an oriented matrix on the surface of the bearing raceway.
- A benefit to using a polyurea thickened grease is that it does not have this fibrous texture and the run-in procedure can either be reduced or eliminated.
- Follow recommended run-in procedures. Although there are alternatives for applications where speed or temperature cannot be varied or monitored, it is ideal to have some control of these parameters. Each bearing manufacturer has a specific run-in procedure that may differ from the examples below. Always check with your specific equipment/bearing OEM prior to performing a run-in.
To achieve the full benefits from these procedures, bearings should be run-in the same direction in which they will operate. It is also advisable to perform the run-in at the actual application site, because the motion associated with shipping/handling and assembly of the bearings may affect the results of the controlled run-in.
6 Run-in Procedure Steps
- Start at a reasonable low speed, typically 20% of the maximum operating speed. Closely monitor the temperature of the bearings.
- Increase speed incrementally when a stable temperature is reached.
- Continue the incremental increases in speed as described. If a rapid temperature increase occurs, stop the run-in process. This temperature spike indicates a preload due to thermal expansion. Maximum bearing temperatures should not exceed 70°C (158°F). Temperatures in excess of 70°C will cause excessive bearing pre-loads and possible permanent grease or bearing damage.
- Allow the system to cool to room temperature.
- Restart the procedure at the last speed prior to the temperature spike.
- Continue reading the above cycle until an equilibrium temperature is reached at the maximum operating speed of the application. The ideal equilibrium operating temperature is approximately 35°C to 40°C (95°F to 105°F).
Variable-speed run-in procedure: Increase speed incrementally when a stable temperature is reached.
Alternative Run-in Procedure
When speed cannot be varied, run-in at constant speed is still possible. In this operation, the bearing should run at full speed for about 30 seconds. After stopping, the heat in the bearing dissipates. In this way, a dangerous temperature rise is prevented. The non-running time depends on the various design factors, but it should be at least five times greater than the running time. This interval should be repeated until the bearing temperature becomes constant.
What bearing lubrication challenges do you face? Let us know in the comments below.