Rolling-element bearings are used to ensure smooth, efficient operation in many machines with rotary motion—from car wheels, engines and turbines to medical equipment. A ball bearing is a type of rolling-element bearing that serves three main functions while it facilitates motion: it carries loads, reduces friction and positions moving machine parts.
Ball bearings use balls to separate two “races,” or bearing rings, to reduce surface contact and friction across moving planes. The rotation of the balls causes a reduced coefficient of friction when compared with flat surfaces rubbing against each other. Because there is little surface contact between the balls and races, ball bearings typically have a lower load capacity for their size than other rolling-element bearings.
There are a variety of different designs and applications for ball bearings, and their design is specific to their industrial application and load type. Some common designs of ball bearings include:
Angular Contact Bearings: designed to work under combined radial and axial loads.
Axial Bearings: also called thrust ball bearings, these are designed to work under force applied parallel to the bearing’s axis, or thrust loads.
Deep-Groove Bearings: designed to carry both radial and light axial loads.
Linear Bearings: designed to allow movement in one direction along a linear axis.
Self-aligning Ball Bearings: bearings with two sets of balls that are self-aligning and to carry both radial and light axial loads.
High-Speed Angular Contact Bearings: another type of precision ball bearing is a high-speed angular contact bearing. As the name implies, high-speed bearings are designed to handle high RPMs with precision and accuracy.
Ball bearing sizes vary according to their use. The width of the bearing also depends on the application. For example, thin section bearings are used in situations where space is at a premium. The difference between the diameter of the outside and inside races and width is minimized, allowing for compact designs.
The materials used in ball bearings depend on their application. The vast majority of ball bearings are made from steel. Other material types include stainless steel bearings for improved corrosion resistance and hybrid ball bearings for which ceramic balls are the moving parts of the bearing between the inner and outer races to reach high rotational speeds.
Roller Bearings Information
Roller bearings are used to replace sliding movement with low friction, rolling motion in rotary applications. The principal types of roller bearings are cylindrical, spherical, and tapered. In general, roller bearings offer higher load capacities than ball bearings of the same size.
There are five main types of roller bearings:
Cylindrical Roller Bearings have high radial-load capacity and moderate thrust loads. They contain rollers which are cylindrically-shaped, but crowned or end-relieved to reduce stress concentrations. Cylindrical roller bearings are similar in design to needle roller bearings but the dimensions of diameter and roller length are closer in magnitude.
Spherical Roller Bearings are self-aligning, double row, combination radial and thrust bearings. They use a spherical or crowned roller as the rolling element.
how to select roller bearingsTapered Roller Bearings consist of an inner ring (cone), an outer ring (cup), a cage and rollers, which are profiled to distribute the load evenly across the roller. During operation, tapered roller bearings create a line contact between the raceway and rolling element, distributing loads across a larger area.
Needle Roller Bearings are a type of cylindrical roller bearing where the length of the roller is much larger than then the diameter. Needle roller bearings are designed for radial load applications where a low profile is desired.
Thrust Bearings are designed for pure thrust loads, and can handle little or no radial load. Roller thrust bearings use rollers similar to other types of roller bearings
Radial type roller bearings (cylindrical, tapered, spherical, and needle) consist of four basic components, an inner ring, an outer ring, rollers, and a cage (roller retainer). Under normal operating conditions, bearing rings and rollers carry the load while the cage spaces and retains the rollers on the cone.
how to select roller bearings
Comparison of Cylindrical Roller Bearing and Ball Bearing Components
Image Credit: bridgat
Roller thrust bearings are designed to carry pure thrust loads. Like radial roller bearings, roller thrust bearings also consist of two rings, rollers, and a cage (roller retainer). However, instead of an inner and outer ring concentric to the axis of rotation, they have two rings or thrust washers on either side of the roller.