Bearing (mechanical)

The bearing is referred to in the machinery and equipment manufacturing an element ( machine element ) for guiding each other of moving parts.

• 3.1 plain bearings
• 3.2 Rolling

Basic distinction of bearings

Bearings allow movements in desired degrees of freedom and prevent unwanted movements in the degrees of freedom. The most common bearings are simple pivot bearing ( radial bearings ) and linear bearings. The desired degree of freedom in both cases f = 1 When radial bearing is only one rotation, the linear bearing only a translation wanted (Free). Some radial bearing can, in addition to the translation in the direction of the axis of rotation, thus have F = 2 (for example, radial bearing). Radial bearings that do not allow this translation, the more familiar term radial -axial bearing ( Radiaxlager ) have. A common pivot bearing, which allows three rotations, the so-called ball joint with f = 3 ( two of the three rotations are in practice but not " rotate " you rotary angle is <360 °).

Depending on the applied operating principle distinction is made in plain and rolling bearings. When plain bearings are touching each other or moving parts are more or less by a lubricating film (liquid, rare gas) separately. When bearings are rolling elements ( balls or rollers ), which perform a rolling motion between the parts.

Distinction according to degree of freedom

The most common bearing names do not indicate the existing freedoms, but refers to the ligated freedoms in the relative motion between the two bearing parts.

Radial bearings

A radial bearing is a rotary bearing, wherein the rotating member is generally an axially extended shaft. It eliminates two degrees of freedom in the radial direction of their circular cross section or transverse to the shaft axis and is therefore also called cross- bearing. The desired degree of freedom is f = 1, three other freedoms are to be prevented. In general, the wave can be denied only the other two rotations, in which the bearing is clearly designed axially extended. The corresponding tilting stress is avoided but, when the shaft is equipped at both ends with a respective bearing. The third translation in the direction of the axis of rotation is usually inhibited significantly loaded only when deep groove ball bearings. A rotary - sliding bearing has the degree of freedom f = 2, when it is not formed as Radiaxlager.

Another common name is journal bearing. This will be discussed that operating forces generally act only radially through the bearing to the machine frame, ie are ablate. Even the weight of the shaft acts in the radial bearing only if it is arranged horizontally.

Thrust bearing

Even if no axial forces are present, the shaft needs to be prevented from being able to perform axial movements. This freedom is to deny her. If significant axial forces from operating or weight are present, a special thrust bearing is required, which is designed for these forces.

Other common terms are thrust bearings, thrust bearing and thrust bearing. It is said thrust bearing, because between the two paired sliding bearing parts only pressure forces can be transmitted ( in the rolling bearing is the type of pairing the same, only the number of pairs is greater than one as a result of this coming rolling elements. Upon axial bearing so that it is pointed out that two axial pairings / bearings are needed.

Radiaxlager

A Radiaxlager a wave in itself has only a required degree of freedom ( f = 1). It is, for example, as a sliding bearing a single-acting radial bearing which is supplemented with two axially acting bearing pairings.

Two needle bearing (including grains stock ) at the ends of a shaft together form a Radiaxlager f = 1 to the tips of both the radial and the axial acting form element are included. Two top bearings are necessary because a single peak receives no force in the opposite direction.

Linear Bearings

A linear bearing is used to perform a linear movement between two bodies. The degree of freedom is f = 1 It is the only camp of its name is recognizable, allowing ( not what it prevented).

Lineargleit and linear ball bearings are guided on rods bushings with f = 2, so two of them are applied in parallel mounted to suppress the freedom of rotation.

Distinction according to mode of action

Plain bearings

In plain bearing, the two mutually 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 lubricant film separating 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. As a separating film is adjacent to liquids (usually oil, less commonly, water) and air ( air bearing ) before. The production of a film with so-called hydrodynamic lubrication requires an additional effort and special operating conditions.

Rolling

When Rolling the relatively moving parts support each other through the rolling elements. The raceways and the rolling elements elastically deform the traveling contact points, leading to a rolling resistance as a result of internal friction. In most camps, the balls are kept at uniform distance from each other with the help of a cage, against the rub. In sum, bearings still have a much smaller resistance to movement than plain bearings.

The relative speed of the rolling element ( the center of gravity and the cage) is against the two parts on which they roll, each half of those relative speed: you and the cage be taken at half speed.

Supporting a shaft

A shaft is usually positioned horizontally and thereby provided because of their length with two radial bearings. Axial forces are often small, at a minimum, the shaft is mounted axially to obstruct random shifts.

Of the two radial bearings than one bearing may be designed as an axial bearing, in addition, in order not to obstruct longitudinal thermal expansion of the shaft.

The standard roller bearing is the deep groove ball bearing, which is not only primarily radial but also axial loads significantly. Both rings of the two bearings in the frame, or on the shaft axially fixed ( " bearing "). From the other camp is one of the two rings mounted axially displaceable ( " floating bearing "). The floating bearing also in axially movable bearing can be installed.

The two parts of the radial bearings are without any special effort on principle against each other axially displaceable. Here, the shaft must be thickened for axial run on both sides of one of two camps. In clearer Axial load a special thrust bearing is provided.

For vertical shafts with predominantly weight load ( turntable motor or plates, the head drum in video recorders, flywheel to capstan shafts ) one often uses two axially movable ball bearing ( " floating bearing " ) and an additional thrust bearing (eg, a ball at the bottom end of the shaft ).

Other types of bearings

• The transfer of force between the two to each other moving parts can also be magnetic: magnetic bearing
• For back and herdrehende movements over a small arc, the two parts can be joined together with an elastic third part ( spring ): spring hinge for watches pendulum, torsion pendulum in the Drehpendeluhr, strap in moving coil instruments, and more. In these examples, the elastic resistance is part of the function. But he will occasionally accepted in favor of the basic freedom of play, which is achievable with a spring joint.
• Structural bearings are no guide elements in the rule. They carry loads from, " store " components to another, for example bridges on foundations. Only for the compensation of expansion corresponding small movable bearings are used, such as bridge bearings, usually with only a role as a sliding bearing or one of the two mutually movable parts of PTFE.