Types of Bearings

Broad classification of bearings can be done according to the principle of operation and the motions they allow. Different types of bearings are used for different purposes. Some common type of bearings are ball bearings, roller bearings, ball thrust bearings, roller thrust bearings and tapered roller thrust bearings.

Ball Bearings
Ball bearings are the most common and most used type of bearing found in a number of objects. Also known as anti-friction bearings, ball bearings are small metallic or ceramic spheres used to reduce friction between axles and shafts in numerous applications. These bearings are able to handle both thrust and radial loads, and are used for applications where the load is relatively small. Load in a ball bearing is transmitted from the outer surface to the ball, and from the ball to the inner surface. Since the ball is spherical in shape, it contacts the inner and outer race at a very small point, which helps it spin evenly and smoothly. But the contact area holding that load is very small, so if the bearing is overloaded then the balls can deform, ruining the bearing. Ball bearings are often used in individual cages to reduce friction in axle assemblies or in a series to absorb the weight placed on a moving part.

Roller Bearings
Roller bearings use cylinders instead of spheres that means the contact between the inner and outer race is a line not a point. Thus the load is spread over a larger area enabling the bearing to handle greater loads than ball bearings. Roller bearings are used in conveyer belt rollers where they hold heavy radial loads, however these bearings are not designed to handle much thrust loading.

Roller bearings are found in different varieties, such as spherical roller bearings, needle roller bearings, cylindrical roller bearing, thrust roller bearing, tapered roller bearing, etc.


Needle Roller Bearing
Needle roller bearings are special roller bearings having slender cylindrical rollers that enable them to bear highest load capacity for a given radial space of all rolling-element bearings. Needle roller bearings are ideal for applications where high radial load carrying capacity is required but radial space is limited. Such bearings also suit applications where high rotational speed is involved but cannot accommodate axial loads.

Compared to the ball bearings, needle bearing have a large surface area that is in contact with the bearing outer surfaces. Additionally they are more compact because there is less difference between the diameter of the shaft and the diameter of the bearing. Thrust needle bearings are flat and use a radial pattern of needles while radial needle bearings are cylindrical and use rollers parallel to the axis of the shaft.

Needle bearings are primarily used in engine components like pumps, compressors, rocker arm pivots, and transmissions.

Tapered Roller Bearing
Tapered roller bearings use conical rollers that run on conical races. Both the inner and outer raceways are segments of cones and the rollers are also made with a taper. Unlike other roller bearings, they support both radial and axial loads, and are able to carry higher loads. The conical geometry of tapered roller bearings provide a larger contact patch, which allows greater loads to be carried as compared to spherical (ball) bearings. The geometry ensures that the tangential speeds of the surfaces of each of the rollers are same as their raceways along the whole length of the contact patch and no differential scrubbing occurs. This greatly reduces rolling friction and avoids rapid wear. Taper roller bearings are used in the wheel bearings of most trucks, buses, cars, and so on. Due to manufacturing complexities, tapered roller bearings are generally more expensive than ball bearings.

Spherical Roller Bearings
Rollers used in spherical roller bearings are thicker in the middle and narrow at the ends, and its race is shaped to match. They can adjust to support misaligned loads.

The construction of spherical rollers are complex and difficult to produce so they are expensive. Apart from that these bearings have higher friction compared to ball bearing because different parts of the spherical rollers run at different speeds on the rounded race. Thus there are opposing forces along the bearing/race contact increasing the friction.

Spherical bearings are used in numerous applications where rotational motion changes the alignment of its axis of rotation. One of its important example is a tie rod on a vehicle suspension. Other important uses of spherical bearings have been in car suspensions, trackballs, computer mouse, heavy machinery, sewing machines, drive shafts, etc.

Thrust Bearings
Thrust bearings are a particular type of rotary bearing that allow rotation between parts used but they are designed to support axial loads like vertical shafts for which spherical, conical or cylindrical rollers are used. They are used in gearsets like in car transmissions between gears and between the housing and the rotating shafts.

Thrust bearings are of different varieties. Ball thrust bearings are composed of ball bearings supported in a ring. They are used in low thrust applications where the radial load is very small. Thurst roller bearings are made of small tapered rollers arranged so that their axes converge at a point on the axis of the bearing.