In most cluster mills the backing bearings are lubricated by the oil or water/oil emulsion used in the rolling process to remove the frictional heat as well as the heat produced by the reduction of the material thickness. This has the advantage that the rolled material is not contaminated by the bearing lubricant.
The viscosity of the emulsion to be used for bearing lubrication should be at least 8 to 12 mm2/s at 40 °C (105 °F). This low viscosity is normally not sufficient to provide adequate bearing lubrication, so that the flow per backing bearing must be much higher than would be needed for conventional oil lubrication. The cleanliness of the rolling oil also has a decisive influence on the bearing service life. Recommended flow rates are listed in table 1.
Where tapered roller backing bearings are used, it's important to ensure a sufficient lubrication of the roller end / flange contacts. An oil containing EP additives and having a viscosity of at least 400 mm2/s at 40 °C (105 °F) should be used.