Shaft Bearings

The intermediate shafting if supported in plain or tilting pad bearings, has an after most bearing which is lined top and bottom. Roller bearings are installed in many vessels.

Plain and tilting pad bearings

The shaft supported in a plain journal bearing, will as it rotates, carry oil to its underside and develop a film of pressure. The pressure build up is related to speed of rotation. Thus oil delivered as the shaft turns at normal speed, will separate shaft and bearing, so preventing metal to metal contact. Pressure generated in the oil film, is effective over about one third of the bearing area because of oil loss at the bearing ends and peripherally. Load is supported and transmitted to the journal, by the area where the film is generated. The remaining two thirds area does not carry load

Replacement of the ineffective side portions of the journal by pads capable of carrying load will considerably increase its capacity. Tilting pads based on those developed by Mitchell for thrust blocks are used for the purpose. Each pad tilts as oil is delivered to it so that a wedge or oil is formed. The three pressure wedges give a larger total support area than that obtained with a plain bearing. The tilt of the pads automatically adjusts to suit load, speed and oil viscosity. The wedge of oil gives a greater separation between shaft and bearing than does the oil film in a plain journal. The enhanced load capacity of a tilting pad design permits the use of shorter length or less bearings.

Any bearing instability, regardless of its nature is called 'oil whip'.

Bearing instability falls into two types

1. 1. Half frequency whirl
   2. Resonant whip

The most effective bearing to prevent oil whip and dampen shaft vibration is the tilting and multiple shoe bearing.

Oil film operates at a lower temperature than a comparable full sleeved bearing.

Tilting pad bearings are in common use on steam turbines, high speed reduction gears, centrifugal compressors and line shafting.

Split Shaft bearings

Clearance exists between the inner ring and thesplit cartridge. This allows movement of the shaft between thrust pads during ahead and astern movements. This also allows for thermal expansion of the shaft.

Plane white metal bearings offer a relatively high frictional resistance to rolling but are cheap and not subject to brinelling or corrosion.
Roller bearings are expensive but offer little resistance to rolling. However, they are susceptible to brinelling when stationary.
The above design removes the major disadvantage of assembling the bearing onto the shaft which would normally require shaft removal.