Open (without seals) backing bearings in cluster mills are lubricated by the rolling oil or water-in-oil emulsion used in the rolling process to remove the bearing frictional heat and the heat produced by the reduction of the material thickness.
The viscosity of the emulsion used for bearing lubrication should be at least 8 to 12 mm2/s at 40 °C (105 °F). This low viscosity is normally insufficient for bearing lubrication and, therefore, the flow rate per backing bearing must be considerably higher than with oil lubrication. Recommended flow rates are listed in table 1.
For oil lubricated backing bearings, the use of a mineral oil with EP additives and a viscosity of 100 to 150 mm2/s at 40 °C (105 °F) is recommended. Recommended oil quantities for the individual lubrication methods are listed in table 2. Higher quantities are required under heavy loads and/or high roll speeds.
Where tapered roller backing bearings are used, it is important to ensure there is sufficient lubrication of the roller end / flange contact area. An oil containing EP additives and having a viscosity of at least 400 mm2/s at 40 °C (105 °F) should be used.