Ball bearings can be broadly classified into the following:
Deep-groove ball bearings
The widely used ball bearing to support radial load is ‘Deep-Groove ball bearing’ or ‘Conrad-bearing’ as shown in Fig.11.9.1(a). They are primarily designed to support high radial load and moderate thrust load. They have deep raceways that are continuous (i.e. there are no openings or recesses) over all of the ring circumferences. This type of construction permits the bearings to support relatively high thrust load in either direction. In fact the thrust load capacity is about 70% of the radial load capacity. A ball bearing primarily designed to support radial load can also support high thrust load; because only few balls carry the radial load, whereas all the balls can withstand the thrust load.
The double-row deep-groove ball bearings have two rows of balls rolling in two pairs of races. They have more radial load capacity than that of single row bearings. In other words they are smaller in diameter compared to single row ball bearings for comparable radial load capacity. However, the proper load sharing between the balls mainly depends on the accuracy of manufacturing.
Angular contact bearings
The angular contact bearings (Fig.11.9.1b) are designed such that the centerline of contact between balls and raceways is at an angle to a plane perpendicular to the axis of rotation. This angle is called “contact angle”. The angular contact ball bearing may be of single or two rows of balls. They are meant to carry radial and axial load together or only axial load depending on the magnitude of the angle of contact. The bearings having large contact angle support heavy thrust. The groove curvature radii are generally 52 to 53% of ball diameter. Angular contact single row ball bearings have high radial load and high unidirectional thrust load capacity than the deep groove ball bearings.
The contact angle is usually less than 40°.In the case of angular contact ball bearings, one side of the outer race is cut to insert balls. This permits the bearing to take the thrust load in only one direction. Therefore, single row angular contact ball bearings are generally used in pairs. In the case of double row angular contact ball bearings (duplex), the balls can be arranged ‘back to back’ and face to face’ or ‘tandem’ configurations (Fig.11.9.2). The back to back and face to face duplex bearings can accommodate radial load and axial loads in both directions. The tandem bearings can accommodate radial load and heavy axial load in only one direction.
Fig.11.9.2 Duplex angular contact ball bearings
Self aligning ball bearings
For assembly of shaft and housing which cannot be made perfectly coaxial, the self- aligning ball bearings are best used. They consist of two rows of balls on a common spherical outer race (Fig. 11.9.1c). In such bearings the assembly of inner ring and balls can tilt in the outer ring. The loss of load-carrying capacity is inherent in this construction, due to non-conformity of outer raceway with the balls. This is compensated by having large number of balls in the bearings. Self-aligning ball bearings are used in top drafting rollers and main shaft of ring spinning machine.
Thrust ball bearings
If the contact angle of angular contact bearings exceeds 45°, it is classified as ‘thrust bearing’. The maximum value this angle can assume is 90° . In such case, races are on the sideways as shown in Fig.11.9.1(d). Such a bearing cannot take any radial load, and is used only for thrust loads. The shafts carrying bevel or worm or helical gears should be mounted with thrust bearings, except the shafts carrying honeycomb (Herringbone) gears or crossed helical gears of left- and right hands placed alternatively along the shafts.
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