Introduction

Bearings are very important parts of rotating machinery. They are installed around the shaft of the rotating element and serve a number of purposes :

1. In conjunction with oil, bearings help to minimise friction.
2. They support the weight of the rotor.
3. Bearings minimise and control shaft movement which takes place in all directions as follows:
   1. RADIAL MOVEMENT This is movement of the shaft in all vertical, horizontal and other directions ACROSS the cross-section of the shaft.
   2. AXIAL MOVEMENT In all rotating machinery, there is a tendency for a shaft and rotor to move horizontally -ALONG THE LENGTH of the shaft. This is due to a force called ' THRUST ' and is caused by pressure difference across the rotor of the driver -( Turbine ..etc ) or the machine being driven - ( Pump, Compressor ..etc.).

( See Figure : 6 )

SHAFT MOVEMENT

Figure : 6

In modern industry, large powerful, high speed machines normally have some method of monitoring shaft movement and vibration.

Sophisticated electronic equipment is used which constantly measure these movements and, a detection probe, at a pre-set vibration level, will initiate a high vibration alarm.

At some slightly higher setting, a trip device will operate to shut-down the machine automatically and safely.

Highly expensive machine damage and losses of production can be averted by this early warning of impending bearing or rotor problems.