Service Life of Spherical Plain Bearings


In our previous blog entry, we examined static and dynamic load ratings for spherical plain bearings. This week, we continue our look into this bearing segment with some further information on the operating life of spherical plain bearings, and factors which can shorten or extend their use.

The service life of a spherical plain bearing operated under mixed or dry friction conditions is determined by the increase in bearing clearance or bearing friction caused by progressive wear of the sliding surfaces, plastic deformation of the sliding material, or fatigue of the sliding surface. Depending on the application, the permissible wear or permissible increase in friction will be different. This means that under the same operating conditions the service life which can be obtained in practice will be different.

The service life of a spherical plain bearing is the number of oscillating movements, or the number of operating hours, which the bearing will service before a defined increase in bearing clearance or a defined increase in friction is reached.

The effective service life is that life which will be attained by a given spherical plain bearing under actual operating conditions. It is determined by the magnitude and type of load, but also by several other factors, such as contamination, corrosion, high-frequency load and movement cycles, shock etc. Some of these factors are impossible to determine or can only be determined with difficulty.

Spherical Plain Bearing Contact Pressure

If an adequate operating life is to be achieved, a basic requirement is that the bearing contact pressure is compatible with the operating conditions. The bearing contact pressure identifies the surface pressure occurring in the bearing and is a decisive criterion for the assessment of a spherical plain bearing in each individual application. The maximum allowable static contact pressure is 50,000 psi (345 MPa) and the maximum allowable dynamic contact pressure is 12,500 psi (86 MPa). Below is a formula for determining contact pressure in a given application.

p = contact pressure    (N/mm2)
k = contact pressure parameter    (N/mm2)
Cd = Dynamic load rating    (kN)
P = Equivalent dynamic bearing load    (kN)

Contact SurfaceCombinationValue of load
ratio Cd/P
Load factor k
Steel/PTFE Fabric1.75150
Steel/PTFE Composite Material2.00100
Steel/Copper Alloy2.00100

AST Bearings

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