Grease for Mounted Unit Bearings

NTN insert bearings are sealed and factory pre-lubricated for the life of the bearing. Generally, the bearing will not need regreasing, 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 relubrication of the unit.

The standard grease chosen by NTN 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 NTN inserts. This fill will accommodate most applications. However, the JL, RL, UR and AR 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 NTN customers may specify different greases and/or grease fills.

Maintenance-free Units

These units make no provision for relubrication or regreasing 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 relubrication process, the maintenance-free units also prevent premature bearing failure due to over-lubrication, or the mixing of incompatible greases, contaminants introduced during relubrication, or blown seals.

Maintenance free units may be used under normal operating conditions and in temperatures up to 212°F (100°C).

Relubrication Type Units

Relubrication Type Unit with Grease Fitting

Some medium- to heavy-duty applications require the insert bearing to be relubricated at regular intervals. The relubrication 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.