From a small supermarket trolley to huge power plants, a great number of light-duty, as well as industrial equipment, could not function without the use of bearings in some form.

Bearings are a crucial tribological component of many types of machinery and exist in a variety of forms and shapes. They can be defined as a machine element that supports/permits only a specific type of motion (restriction of degrees of freedom) in a system that may be under static or dynamic loading.

An example is a sliding door. The door cannot be lifted or removed from its place. It only permits sliding to open it. The possible movement is restricted to sliding motion by bearings.

What Is the Purpose of Bearings?

The main purpose of bearings is to prevent direct metal-to-metal contact between two elements that are in relative motion. This prevents friction, heat generation and ultimately, the wear and tear of parts. It also reduces energy consumption as sliding motion is replaced with low-friction rolling.

They also transmit the load of the rotating element to the housing. This load may be radial, axial, or a combination of both. A bearing also restricts the freedom of movement of moving parts to predefined directions as discussed above.

Rolling Element Bearings

Rolling element bearings contain rolling elements in the shape of balls or cylinders. We know that it is easier to roll a wheel than slide it on the ground as the magnitude of rolling friction is lower than sliding friction. The same principle is in work here. Rolling element bearings are used to facilitate the free movement of parts in rotational motion.

Even when we need linear motion in applications, it is easy to convert rotational motion to sliding motion. Consider an escalator or a conveyor. Even though the motion is linear, it is powered by rollers that are driven by motors.

Another example is a reciprocating pump that can convert rotational energy from a motor into translational motion with the help of linkages. In each of these applications, ball bearings are used to support motor shafts as well as shafts of other rollers in the assembly.

Rolling elements carry the load without much friction as the sliding friction is replaced with rolling friction. Rolling element bearings can be subdivided into two major types: ball bearings and roller bearings.

Ball Bearings

Ball bearings are one of the most common types of bearing classes used. It consists of a row of balls as rolling elements. They are trapped between two annulus-shaped metal pieces. These metal pieces are known as races. The inner race is free to rotate while the outer race is stationary.

Ball bearings provide very low friction during rolling but have limited load-carrying capacity. This is because of the small area of contact between the balls and the races. They can support axial loads in two directions besides radial loads.

Ball bearings are used for controlling oscillatory and rotational motion. For example, in electrical motors where the shaft is free to rotate but the motor housing is not, ball bearings are used to connect the shaft to the motor housing.

Depending on the application, different types of ball bearings are available to choose from.

Advantages of ball bearings:

• Good wear resistance
• Do not need much lubrication
• Provide low friction, thus little energy loss
• Long service life
• Easy to replace
• Small general dimensions
• Comparatively cheap
• Can handle thrust loads

Disadvantages of ball bearings:

• May break due to shocks
• Can be quite loud
• Cannot handle large weights

Deep Groove Ball Bearings

Deep groove ball bearings are the most widely used ball bearing type. Trapped between the two races is a ring of balls that transmit the load and allows rotational motion between the two races. The balls are held in place by a retainer.

They have very low rolling friction and are optimized for low noise and low vibration. This makes them ideal for high-speed applications.

They are comparatively easy to install and require minimal maintenance. Care must be taken during installation to prevent denting of the races as they have to be push fit onto shafts.