Plain bearing

The bearing is next to the roller bearing, the most commonly used in machinery and equipment bearing designs.

In plain bearing, the two relatively moving parts have direct contact. They slide on each other against the damage caused by sliding friction resistance. This can be kept low by choosing a low-friction material pairing, by lubrication or by forming a lubricating film (solid lubrication), which separates the two contact surfaces from one another.

Contact between the two parts, as is the case with most used sliding bearings, is formed in the contact surfaces of wear that limits the life span. The generation of the separating lubricant film at full lubrication requires an additional effort, which comes only for large bearings in large machines in question.

The sliding resistance caused conversion of part of the kinetic energy into thermal energy which flows into the support members and is optionally derived.

• 2.1 graphite bearing ( solid)
• 2.2 ceramic bearings
• 2.3 plastic plain bearings
• 2.4 sintered bearings
• 2.5 Steinlager
• 2.6 Notes and references

Distinction on the type of sliding resistance

A distinction ( unlubricated or lubricated with grease ), hydrodynamic bearings and hydrostatic bearings between sleeve bearings. The sliding resistance is solid friction, mixed friction or fluid friction.

Bearings with solid friction

In bearings with solid friction (also dry friction ) are used friction material pairs. Sometimes one of the partners has a so-called " self- lubricating property" (for example, an alloy containing lead or tin material, a plastic such as PTFE or technical ceramics ). The second partner (with radial bearings usually the shaft ) is made ​​of steel.

Bearings with fluid friction

In plain bearings, which are ( for example, in energy conversion in turbines and generators) arrives on longevity and low power loss, full lubrication is applied, in which fluid friction occurs. The lubricant film has to be put under pressure so that it can separate the contact surfaces against the bearing force. With hydrostatic slide bearings, an oil pump is used (for example in internal combustion engines ), in hydrodynamic bearings, the oil pressure generated by the two mutually moving the contact surfaces even in the lubricant film, but this means that during the starting and stopping of the movement no pressure is present and mixed friction is.

Bearing with mixed lubrication

In lubricated bearings occurs with increasing load and decreasing speed mixed friction. In the Stribeck curve is the area left of the minimum, the right of the minimum of the range of wear-free hydrodynamic sliding bearing begins. In the mixed friction range, the lubricant is (solid, greasy or oily) in the micro-roughness ( dimples) of the contact surfaces, while only touching the tips of the asperities, which reduces the sliding resistance compared to non-lubricated bearings.

Bearing materials

The typical slide bearing is a radial bearing for the radial mounting of a shaft, the bearing surfaces are hardened.

The shaft is enclosed by the bushing, the material of which may be quite different, for example:

• Bronze (copper -tin alloy )
• White metal ( lead-tin alloy)
• Alloyed with lead bearing metal
• Aluminum alloys
• Plastics (eg PTFE)
• Ceramics (to a lesser extent, also fiber- reinforced)
• Brass alloys

The material of the bushing is " softer" than that of the shaft chosen so that any wear occurs first there. Their replacement is easier and cheaper than that of the shaft. It is made two - split (two bearings ), can thus be removed radially from the shaft.

Graphite bearing ( solid)

Graphite (carbon) is suitable as a bearing material because its abrasion is self -lubricating. The carbon graphite modification has crystal planes that can easily slide over one another. Graphite bearings are also advantageous when electric currents must be transferred over bearing points, which in other camps - should be avoided as bringing currents through contact points of different metal alloys of material with it - both bearings and ball bearings in particular.

Note that in these bearings increases considerably at a higher load and thus the temperature rises, the friction coefficient. Nevertheless, they are suitable for higher temperatures at which lubricated bearings tend to fail. An example of a graphite bearing is the thrust bearing for operating the clutch of the car Trabant.

See also sliding contact.

Ceramic bearings

As the ceramic material, for example silicon carbide used in pumps, in large pumps also fiber-reinforced. The slide bearings are located in the pump housing and lubricated with the pumped liquid. The corrosion resistance and hardness caused by the extremely low wear are the major advantages of these bearings. Problems arise, however, when dry running of the pump.

Plastic plain bearings

Already in 1869 called Daniel Spill, a partner of Alexander Parkes, the plastic Xylonite as suited to it, " Gears and Friction Wheels" ( gears and friction wheels ) and " Bearings for Machinery ", ie plain bearings manufacture.

Modern plastic plain bearings made ​​of special self-lubricating plastics. They are suitable for low to medium bearing forces. Unlike other materials, the danger of " seizure " is extremely small with them. Plastic plain bearings thus among the most important representatives in the lubrication or maintenance-free bearings.

These are so-called compounds, consisting of base polymer, reinforcing materials (for example, fibers and fillers ) and can consist of embedded solid lubricants or oils. During operation, these lubricants are admitted continuously by micro wear on the surface and thus reduce friction and wear on the bearings. The plastic used is usually PTFE ( polytetrafluoroethylene) for its particularly low coefficient of friction against other substances ( including against steel).

Generally, there are plastic plain bearings in many different versions, depending on the desired property. In general, they are lubrication-free, corrosion-resistant, lightweight and impervious to dirt. For special applications, a variety of special materials manufacturers have on offer, such as electrically - conductive or food grade (FDA compliant ) storage.

In lower quality bearings in which both partners are composed of thermoplastic, PTFE is included in the lubricants required for this.

Sintered bearings

Sintered bronze or iron bushings are less dense than solid. In their pores to retain the lubricant ( mixed friction ). Resinified lubricant can be removed by heating from the pores. Then the liners are newly soaked with oil.

Sintered bearings are located in many small electric motors ( for example, in PC fans) and serve as a guide bushes in linear bearings.

Steinlager

Bearing from largely single-crystal ruby are used particularly in small mechanical watches, instruments and scales. They work against steel and are lubricated at watches, for scales not. Stones are used for higher value watches in greater numbers, at least for the balance storage.