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BEARINGS

 

A bearing is a machine part which supports shafts and spindles. We know bearings to be classified as plain bearings and antifriction bearings.

In plain bearings one friction surface slides upon another. Plain bearings may be of two classes: bearings with a continuous rotary motion and those with an intermittent motion. The first class of plain bearings is represented by journal bearings and thrust bearings. Journal bearings are bearings: carrying a load which acts at right angles to the shaft axis. Thrust bearings take a load acting in the direction of the shaft axis. The second class of plain bearings embraces bearings of parts having a rocking motion, or a linear reciprocating motion.

Antifriction bearings are also subdivided in two main classes depending upon the type of rolling elements: ball bearings and roller bearings. In rotating machines, noise and vibration are indications of faulty operation of ball bearings or roller bearings. A ball bearing consists of two rings: an inner ring and an outer ring between which there are hardened steel balls spaced in a ball retainer or cage. If the inner ring had been lifted to a tilt position, the balls would have been forced to climb one side of the raceway during a part of revolution, with resulting drag on the bearing retainer, then, the balls would have accelerated down the raceway to climb the opposite side in the other part of the revolution, reversing the strains on the bearing retainer. In this instance, the balls, instead of rotating about a true horizontal axis, rush to turn from contact with the sides of the raceway and to reverse their direction of turn during the second half of the revolution. In rotating machines, the balls are spaced so that they do not touch each other, thus reducing wear and noise. They require an absolutely parallel raceway to roll upon, entirely free from eccentricity, wobble or other variations.

 

 

Fig. 44. Single-Row Ball Bearing:

1 - inner ring or inner race; 2 - outer ring or outer race;

3 - ball retainer or cage; 4 – ball

 

Ball bearings may be of the following types: radial bearings, thrust bearings, and radial-thrust bearings. In their turn radial ball bearings which serve to take loads acting at right angles to the shaft axis, may be of two types: single-row (Fig. 44)

and double-row radial bearings. All the radial bearings are used when high speeds are required. The precision-made radial bearings give the finest service together with a long bearing life. Thrust ball bearings are bearings taking axial loads and giving maximum efficiency with combined journal and thrust loads. They are also recommended for thrust duty1 at high speeds. Radial ball bearings can take both radial and axial loads.

In roller bearings hardened steel rollers are used between the rings instead of balls. Roller bearings permit a larger load and have a longer bearing life in comparison with ball bearings. The rollers used in roller bearings may be of different shape: cylindrical, conical, spherical, and concave. Roller bearings, in turn, may be subdivided into single-row and double-row bearings. Bearings with cylindrical rollers are intended to take radial loads, while those with conical rollers may take both radial and axial loads.

1. thrust duty - работа при осевых нагрузках

 


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