Sliding Bearing | Federal-Mogul Deva - maintenance free and self-lubricating bearings

Glossary

A system is referred to as a sliding bearing in which the relative movement between the shaft and the bearing or an intermediate medium is a sliding movement. Depending on the perspective, plain bearings can be classified differently. Three most common groups are briefly presented below:

Classification according to the lubricant

Non-lubricated bearings
solid lubricated bearings
grease-lubricated bearings
oil-lubricated bearings
water-lubricated bearings
gas lubricated bearings

Classification according to the functional principle

Solid friction bearings – no lubrication, solid friction
Mixed friction plain bearings – lack of lubrication, mixed friction
Hydrodynamic bearings - work by generating dynamic pressure in which a supporting lubricating film is built up solely through the relative movement between the bearing and the mating material
Hydrostatic bearings – work on the principle of external pressure generation, i.e. the necessary lubricant pressure is generated outside the bearing by a pump Aerodynamic bearings – also make use of dynamic pressure generation through the formation of a gaseous lubricating film as a result of fluid dynamic effects
Areostatic bearings – bearing shell and shaft are separated from external pressurization by a gaseous lubricating film
Electromagnetic bearings – an intelligent control makes it possible to keep the rotor (shaft) in suspension using actuating magnets

Classification according to the direction of force

Radial bearing, Cross bearing (support bearing): for radial forces
Axial bearings, longitudinal bearings (track bearings): for axial forces

Depending on the medium and parameters, different friction states occur in plain bearings, such as radial plain bearings:

Solid friction: Friction when two bodies come into direct contact
Boundary friction: Solid friction in which the surfaces of the friction partners are covered with a molecular boundary layer film
Mixed friction: Friction when solid friction and liquid friction coexist
Liquid friction: Friction in a liquid film that completely separates the friction partners and can be generated hydrostatically or hydrodynamically
Gas friction: Friction in a gaseous film that completely separates the friction partners and can be generated aerostatically or aerodynamically

These friction conditions can be defined using the Stribeck curve. They also serve to classify wear and lubrication. The Stribeck diagram shows the coefficient of friction versus the lubrication gap height. In an oil-lubricated system, a radial plain bearing passes through the main friction states of boundary friction, mixed friction and fluid friction, depending on the sliding speed and load. Solid friction does not occur in oil-lubricated systems, since in this case of tribocontact at least 1-molecular layers always occur. In addition to the Stribeck curve, the upper part of the figure also shows the dependence of wear on the friction conditions.

Federal-Mogul Deva GmbH exclusively produces self-lubricating bearings with solid lubricant depots. These are mainly used for dry running, although grease, water or oil-lubricated systems can also be considered, taking certain criteria into account. As a rule, the speeds are low and the loads are so high that hydrodynamics do not take place. The friction conditions to be expected are solid friction, boundary friction and mixed friction, since a boundary lubricating film forms as a result of the solid lubricant.

The calculation bases and use of the Stribeck curve, as is the case for typically hydrodynamically running plain bearings, are therefore not applicable or expedient for self-lubricating plain bearings in practice.