Plain bearings are relatively simple and a inexpensive bearing typically made of two parts. There are a lot more types of bearings, but the plain bearing is the simplest. It can be just a shaft running through a hole and this interface is the bearing. However, more normally the bearing would be made of a material such as phosphor bronze and have a method of lubrication.
Critical aspects of design:
- radial load
- radial accuracy
- specification of the diametrical clearance between the journal and the bearing
- lubrication
- temperature range of operation
- required lifetime of bearing
- cooling requirements
The pV value (pressure (p) multiplied by the speed of operation (V)) is a measure of the ability of the bearing material to accommodate the temperature limit generated by the frictional energy during operation.
Applications
Connecting Rod Bearing – The bearing located in the large end of the connecting rod by which it is attached to the crankshaft.
For most IC engines the bearing at the small and big end of the conrod will be a plain phosphor bronze bearing. In the small end it would be reamed/machined to size and solid as the gudgeon pin slides through the piston and conrod. For the big end the bearing will be split for muli-cylinder engines.
In the case of single cylinder model engines the conrod is aluminium and a solid phosphor bronze bearing is used for both bearings. There is no need to split the big bearing as the conrod fits onto a single pin crank.
Attitude Angle
The angle between the steady state preload through the bearing centreline, and a line drawn between the bearing centre and the shaft centreline.
Babbitt
A soft antifriction metal used to line bearings. Made of tin, antimony, lead, and copper.
Clearance
A rule of thumb is that clearance can be 0.001 to 0.002 times the bearing’s diameter.
A 0.001″ clearance for a 1/2″ shaft and a Phosphor Bronze bearing works really well.
Friction Torque
Torque (TF) caused by the frictional force that occurs when two objects in contact move.
TF = 0.5 µ P d
where: TF = Friction torque [Nm], P = dynamic load [N], µ = coefficient of friction, d = shaft diameter [m]
For a steel shaft and a bronze bearing, µ = 0.1 to 0.25
Hydrodynamic Bearing
A bearing which supports the shaft on a thin film of oil, the fluid-film layer is generated by journal rotation. Often referred to as stable lubrication due to the fact that as the lubrication temperature increases, the viscosity drops. This results in a lower coefficient of friction, that causes the lubrication temperature to drop.
Hydrostatic Bearing
A bearing which supports the shaft on a thin film of oil, the fluid-film layer is generated by externally applied pressure.
Sleeve Bearing
A journal bearing, usually a full journal bearing.
This type of bearing has no rolling elements and the shaft rides on a film of oil.
Spalling
A flaking of the surface of a bearing.