Choosing a rolling bearing grease

Marcos Thadeu Lobo

Mechanical Engineer Graduated from the State University of Campinas (Unicamp). He currently works as an Associate Consultant at the company QU4TTUOR CONSULTORIA.

Rolling bearing grease

Grease lubrication in rolling bearings of electric motors and electric power generators has some advantages such as:

Figures 1/2 – Lubrication of open rolling bearings

1. Less tendency to leaks. Grease minimizes contamination of windings, commutators, slip rings, brushes and the outside of the electric motor and electric power generator.
2. The grease effectively seals off solid particulate matter and moisture when proper, well-maintained seals are used.
3. Much less attention to lubrication is normally required during the operation of grease-lubricated rolling bearings.
4. Greater freedom in choosing the mounting position of the equipment.

Figures 3/4 – Open roller bearings in electric motor and electric power generator

Greases for use in open roller bearings in electric motors and electric power generators must meet certain requirements:

1. Consistency: NLGI 2 or NLGI 3 (churning reduction).
2. High stability to thermo-oxidation.
3. Low volatility of base oil.
4. Dn factor suitable for high speeds of electric motors

	Dn – Speed rate or rotation
	n    – Rotation( rpm )
	di   – Bearing bore diameter (mm)
	de  – External bearing diameter ( mm )

5. Kinematic Viscosity of the base oil: ~ 110 cSt at 40ºC.
6. Polyurea-based thickener.

Figures 5/6 – Beware of excess grease in the bearing housings

The proper selection and application of lubricating greases will substantially increase the availability and reliability of rolling bearings, electric motors and electric power generators, avoiding costly and unscheduled downtime.