The asset is a vertically-mounted, belt driven grinding mill, as shown in Figure 1. The drive spindle has three (3) bearings: two (2) cylindrical roller bearings and one (1) ball bearing. The mill is being belt driven by a 100 hp, two-pole motor. The mill normally operates at 3,150 rpm.
The mill rotor bearings, which are mounted in the steel housing, are two (2) cylindrical roller bearings, NU 316 ECM/C3, and one (1) grooved ball bearing, SKF 6316 C3. The bearings have failed several times over a period of two (2) years. Before this time, the mill had no recorded bearing failures (as confirmed by the CMMS).
In 2007, the vibration spectra began displaying excessive looseness. A work order was submitted by the vibration analyst, and the bearing assembly was rebuilt and reinstalled by on-site mechanics. (See Figure 2.)