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.
What's the Difference Between Bearings?
Bearings are used to help reduce friction. Metal-upon-metal contact produces large amounts of friction. The friction adds to wear and tear of the metal, producing grinding that slowly degrades the metal. Bearings reduce friction by having the two surfaces roll over each other, reducing the amount of friction produced. They consist of a smooth metal ball or roller that rolls against a smooth inner and outer metal surface. The rollers or balls take the load, allowing the device to spin.
The load acted upon a bearing is either a radial or thrust load. Depending on the location of the bearing in the mechanism, it can see all of a radial or thrust load or a combination of both. For example, the bearing in the wheel of your car supports a radial and a thrust load. The weight of the car on the bearing produces a radial load while the thrust load is produced as the car turns a corner. Here we will examine some types of common bearings.
Ball bearings are most common type of bearing and can handle both radial and thrust loads. Ball bearings are also known as deep-groove single-row or Conrad bearings. The inner ring is typically fastened to the rotating shaft and the groove on the outer diameter provides a circular ball raceway. The outer ring is mounted onto the bearing housing. The ball bearings are housed in a race and when the load is applied, it is transmitted from the outer race to the ball and from the ball to the inner race. The raceway grooves have typical curvature radii of 51.5% to 53% of the ball diameter. Smaller curvature raceways can cause high rolling friction due to the tight conformity of the balls and raceways. Higher curvature raceways can shorten fatigue life from increased stress in the smaller ball-race contract area.
Ball bearings, also known as Conrad bearings, are typically used in small load applications.
The contact points between the ball and the outer race is very small due to the spherical shape of the bearing. This also helps the ball spin very smoothly. Since the contact point is so small, the bearing can become overloaded at a specific point causing the ball bearing to become deformed. This will ruin the bearing. Ball bearings are typically used in applications where the load is relatively small.
The table above lists some general types of ball bearings and their typical load capabilities.