The purpose of lubricating the bearing is to cover the rolling contact surfaces and sliding contact surfaces with a thin oil film to avoid direct metal-to-metal contact. Effective lubrication of the rolling-element bearing has the following effects.

1. Reduces friction and abrasion
2. Transports heat generated by friction
3. Prolongation of service life
4. Prevents rust (corrosion)
5. Keeps foreign objects (or contamination) away from rolling elements and raceways

Grease lubrication

Grease is generally used for lubricating rolling-element bearings because it is easy to handle and simplifies the sealing system.

Carefully examine the type and properties of the base oil, thickener and additives of the grease, and select a grease appropriate for the operating condition of the bearing. The general relation between consistency of grease and the application of the bearing is given in Table 1. The types and properties of greases are given in the bearing section of the NTN general catalog.

Oil lubrication

Oil lubrication is generally suitable for high speed or high temperature operations. It is also suitable for carrying heat away from the bearing.

Oil viscosities required for the operating temperatures of bearings are given in Table 2.

Carefully study the viscosity, viscosity index, oxidation resistance, corrosion resistance, foaming resistance, etc. to select an oil. Table 3.5 gives a guide for selecting viscosity.

Fig. 1 shows the variation of viscosity with temperature for several lubricating oils. Use Table 3 to select an oil with an adequate viscosity for the operating temperature of the bearing.

Table 2 : Viscosities Require for Operating Temperatures of Bearings

Bearing Type Kinematic viscosity mm2/s Ball, cylindrical roller and needle roller bearings 13 Self-aligning roller bearings, tapered roller bearings and thrust needle roller bearings 20 Self-aligning thrust roller bearings 30

Table 3 : Selection Guide For Lubrication Oil Viscosity

Bearing operating temperature °C dn value x 104 ISO viscosity grade of oil (VG) Applicated bearing types Normal load Heavy or impact load -30 - 0 Up to allowable speed 22   32 46 All types 0 - 60 - 1.5 46   68 100 All types 1.5 - 8 32   46 68 All types 8 - 15 22   32 32 Except for thrust ball bearings 15 - 50 10 22   32 Single row radial ball bearings Cylindrical roller bearings 60 - 100 - 1.5 150 220 All types 1.5 - 8 100 150 All types 8-15 68 100   150 Except for thrust ball bearings 15 - 50 32 68 Single row radial ball bearings Cylindrical roller bearings 100 - 150 Up to allowable speed 320 All types 0 - 60 Up to allowable speed 46      68 Self-aligning roller bearings 60 - 100 Up to allowable speed 150

Remarks 1. The table above is applicable to oil bath lubrication and recirculation lubrication. 2. Consult NTN if your operating condition is not shown in the table.

Fig. 1: Lubrication oil viscosity-temperature line diagram