Insert bearings are sealed and factory pre-lubricated for the life of the bearing. Generally, the bearing will not need re-greasing, however, when subjected to severe operating conditions, insert bearings may require the occasional replenishment of grease, necessitating the addition of a grease fitting in the housing which allows the re-lubrication of the unit.
The standard grease chosen for ball bearing mounted units is Shell Alvania® #3. This is a lithium-based product that maintains proper lubrication over a wide range of operating temperatures -4°F to 275°F (-20°C to 135°C).
The standard factory grease fill is 35% for most inserts. This fill will accommodate most applications. However, some series of inserts have a standard grease fill range of 60–70%. For bearings known to rotate at high speeds, the grease fill should be reduced to prevent excessive heat generation.
A word of caution: some customers may specify different greases and/or grease fills.
These units make no provision for re-lubrication or re-greasing the insert bearing. They contain sufficient grease to last the bearing’s lifetime when used in general applications. The unit’s seal is also of a high quality and has been chosen to prevent any leakage of grease.
In addition to the labor saved by eliminating the re-lubrication process, the maintenance-free units also prevent premature bearing failure due to over-lubrication, or the mixing of incompatible greases, contaminants introduced during re-lubrication, or blown seals.
Maintenance free units may be used under normal operating conditions and in temperatures up to 212°F (100°C).
Re-lubrication Type Units
Some medium- to heavy-duty applications require the insert bearing to be re-lubricated at regular intervals. The re-lubrication type unit has a grease hole in the bearing’s outer ring, a circumferential groove in the bore of the housing and a grease fitting at the housing outside diameter to allow for regreasing. The following conditions are those that typically warrant the use of a relubrication type unit:
- The bearing operates in temperatures in excess of 212°F (100°C)
- In operating conditions with excessive dust, high humidity
- When the bearing may be splashed with water or other liquid
- Under heavy load
- Applications having very small oscillatory motion
- Higher speed applications where noise has to be minimized.