A bearing allows positioning, the transmission of the efforts and the Rotation between two parts by the replacement of the slip by the bearing. This component Mécanique optimizes the Frottement and the precision of the connection.

Roll of the dice

Presentation

A roll of the dice is component a Mécanique ensuring guidance in rotation of a tree in a Palier, by reducing frictions, by bearing of interposed elements. The Celts knew already a kind of roller bearing with cylinders out of wooden. Then Léonard de Vinci imagined and drew ball bearings. The true inventor of the rolls of the dice is English Phillip Vaughan, in 1794. But the rise of the rolls of the dice started only with the German Friedrich Fischer. Thanks to its machine has to rectify balls, invented in 1883, it was from now on possible to industrialize the production of the bearings.

A roll of the dice is appeared as two coaxial rings between which balls are placed, slightly lubricated, and maintained spaced by a cage.

The materials employed depend on the application for which the bearing is designed, but it must be generally very resistant to compression. This is why one often chooses the Acier or the Céramique.

Contrary to an generally accepted idea, the purpose of lubrication is not principal to reduce frictions between the balls and the rings; the lubricant is useful here, above all, to avoid the seizing of the various elements. Moreover, a lubricant excess makes the movement more difficult and causes a heating very prejudicial at the lifespan of the component. These questions are treated in detail in Wikilivre devoted to the tribology.

The bearing is not by tight principle not , it is necessary to take care to protect it from dust and other foreign bodies which could there be placed, accelerating its wear and decreasing its output. The bearings nevertheless are often equipped with Flasques making it possible to avoid having to carry out the sealing. For bearing of a traditional type, the sealing is carried out by joined S to lips.

There exists a standard popular ABEC to measure the quality of the bearings, it is gradually replaced by a standard ISO.

The mechanical Liaison equivalent between the two rings of a bearing depends on the type of elements rolling and the provision of the contacts of these elements with the rings. The local connection obtained between the tree and its housing is of more dependant on the way in which the bearing is fixed at the tree and with the Alésage. It is often necessary, to carry out a connection pivot to use two bearings, one of the isostatic solutions being the association of a connection kneecap and an annular linear .

Travelling elements

By abuse language one uses same designation, roll of the dice to name any kind of bearings. One must however distinguish them by the form from the travelling elements:

• the ball is the most known case, but the cylindrical or conical rollers also are very employed in the assemblies requiring a greater rigidity.
• Certains bearings with kneecap is provided with rollers in the shape of barrel.
• Enfin when they are cylindrical rollers very long in front of their diameter one speaks about needles .

Assembly of a roll of the dice

The assembly of the elements of a roll of the dice does not seem obvious with the sight of the object. It is a delicate operation (should not be damaged the parts) but hardly difficult. Moreover a bearing is component on which one cannot carry out maintenance. The elements are appairés (selected to be assembled as well as possible). The table below thus described the operation of assembly in manufacture of this component, which does not correspond to in no case with a help with the implementation of this component.

For the bearings with oblique contacts and the thrusts, it is possible to separate the rings and the cage. So this problem of assembly does not arise.

Families of bearings

The bearings are characterized by the form and the provision of the travelling elements. With each model correpsond of the particular performances thus a specific use.

For example, the roller bearings support higher loads compared to the rolls of the dice (of equivalent size), because the contact of the travelling elements with the rings is linear. However, it accept less low rotational frequencies. The needle cages are less cumbersome but require a preparation of the ranges (hardening).

Roll of the dice with right contacts

Very economic, they is used in small and average dimensions. They support all the types of loads (moderate with averages): axial, radial and combined. Under load, they behave as a bearing with contact obliques whose angle of inclination would be variable. Alternatives: versions with groove and segment of stop, tight versions on two sides (sealing by sheet flasks or joints elastomers). The tight versions on the 2 sides are lubricated with life.

Roll of the dice with oblique contacts

They support all the types of axial loadings in only one direction. The rings are not separable. The angles of 15°, 25° and 40° are most current. They must be gone up at least per pair and in opposition: they make it possible to regulate the internal play of the connection by preload of the assembly. The version with two lines can be used only (case short tree).

Bearing with double line of balls

Conical roller bearing

They support axial loads and radial great. Because of provision of the contacts of bearing, the rings can be disunited by axial translation. It thus do not pose the same problems of assembly as the rolls of the dice.

They constitute a connection equivalent kneecap (unilateral) between the rings. Of a great rigidity, this type of component is ideal for guidance of high degree of accuracy having to undergo large efforts (pivot of wheel of vehicles, pins of machines).

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