Ball bearings are small and hard steel balls placed between moving parts of a machine so that the parts can move smoothly. They reduce rotational friction and supports axial and radial loads. There is minimal contact of the balls with the inner and outer races because of their spherical shape, which is why they can spin smoothly.

They have a simple design, are extremely durable, and can be maintained easily. The bearings can be of many sizes. Some of them are smaller than a grain of rice that can be fitted inside a wristwatch, and there are ball bearings that have a diameter of one meter for power plant and factory applications. There are single and double row ball bearing designs, and sealed and open variants.

Construction

The construction is simple. There are four main parts –

1. Outer ring
2. Inner ring
3. Ball Separator (Retainer)
4. Rolling Bodies (The Balls)

Outer ring	Inner ring	Ball Separator	Rolling Bodies

The Outer Ring

This is the larger of the two rings. In the inside diameter here, there is a groove that forms a pathway for the balls. It is shaped in such a way that the balls can stay a bit loose in the groove. The balls have just a single point contact on each race because of this loose fit. This reduces friction. The outer ring stays stationery.

The Inner Ring

This is the smaller ring, mounted on the shaft. The groove is on the outer diameter here, whereas in the outer and larger ring, it is on the inner diameter. The groove forms a path for the balls. Surface of the outside diameter is extremely smooth and has high tolerance. It has the same high precision finish like the surface of the outer ring. The inner ring is essentially the bearing’s inner circle structure where the balls spin or rotate. Inner races are typically made of ceramic or steel in most spinner bearings.

Retainer

Also called the ball separator or the cage, its purpose is to keep the balls within the two outer and inner rings separated, maintain a constant space between the two rings, guide the balls accurately in the correct path during rotation, and to prevent the balls from falling off. Cages also lubricate the bearing through a coating on the edge. Ball separators are selected based on the size of the bearing, and the performance required.

Balls

These are the rolling bodies located between the two rings, held by the cage or the retainer. The balls are what make the bearing rotate with very little friction. But it is important to remember that there may not be any cages as well. For instance, a model may not have a ball separator if there are enough balls that fill more than half the circumference of the bearing, which makes them stay in place. The ball’s radius is slightly smaller than the outer and inner ring ball tracks. This is what makes the balls have contact with the rings at a single point. The surface finish, size, and ball roundness are all very important. The balls are made of different ceramics and metals, but the most common in chrome steel.

20*47*14mm 6204-2RS C3 Deep Groove Ball Bearing

Lubrication

This is also an important component of the bearing. Lubrication is applied so that the friction loss between the outer and inner rings can be reduced.

Optional Components of the Bearing

There are some other components like seals and shields that improve the life and performance of ball bearings. These are optional components, added to the bearing depending on the requirement of the customer.

Shields – This is a profiled and stamped sheet metal disc that prevents large particles from entering the bearing. The shield is pressed on the outer rings inside diameter. There will be a small gap between the shield and the inner rings diameter. There is no friction between the bearing and the shield as it doesn’t touch the inner ring, and as a result the bearing has a very low torque.

Seals – This is also inserted within the outer rings inside edge diameter. The seal’s inner edge is molded into a lip configuration, which is specifically designed. They snap-fit easily into the ring.

Types of Ball Bearings

There are three main types of bearings. They are –

1. Radial Bearings
2. Angular Contact Bearings
3. Thrust Bearings

Radial Ball Bearings

They are designed so that they can carry both axial and radial loads. Thrust bearings on the other hand are designed just for thrust loads. Also called deep groove bearings, they can take both the loads to varying degrees, but are primarily used when the main load is in radial. These bearings are extremely popular.

Deep Groove Ball Bearings

Deep groove radial ball bearings are some of the most common ones. They are used for transmitting loads from rotating parts to housings with very little friction loss. This is obtained by making sure that there is very little deformation in the bearing elements. Design measures like precision, materials, and radial clearance ensures that the rolling action is undisturbed. Both the outer and inner rings have flat surfaces, so there is a larger contact. This allows high radial load capacity and works well for high speeds. There is low torque capacity at startup and running speeds. They emit low noise, and need little maintenance. The axial load capacity is in both directions.

These bearings are used in many industries including high precision apparatus and heavy machinery.

• Deep groove ball bearings are popular with electric motor manufacturers and motor refurbishments. But it is important to select the right bearing as there are different types of motors.
• In general machinery, these bearings are found in gearboxes, pumps, and compressors. Demands on the bearings vary, depending on the machinery.
• These are also important components in electrical goods too like washing machines and photocopiers. The specification is critical.

There are four main types of deep groove radial ball bearings. They are Single Row Bearings, Extra Small and Miniature Ball Bearings, Maximum Type Bearings, and Magneto Ball Bearings.

Angular Contact Ball Bearings

They are designed in a way to reach high speeds and withstand radial-axial loads. But they can withstand only unidirectional axial loads. They are good for moderate radial loads and heavy thrust loads. When used, these bearings form a contact angle between the balls and the races when used. A major characteristic of the design is that, one shoulder of one or both of the ring races are always higher. For proper functioning, they have to be assembled with a thrust load, which creates a contact angle between the outer and inner races, and the ball. The contact angle can vary between 15° and 40°. The races and balls are typically made of chrome steel. However, sometimes ceramic balls are also used, especially when the operating conditions are severe.

Single Vs. Double Row Angular Bearings – Angular contact bearings are mounted usually in groups of two or more. This is done by matching several single row bearings or by using double row bearings, which is often preferred for economic reasons. But the performance and design flexibility in many cases is better with single row mounts.

Thrust Ball Bearings

Like other ball bearings, they allow rotation between the parts, but they are best used for pure thrust loads. They are unable to handle radial loads. Roller, needle, or a ball can be the rolling element. These bearings are mounted directly on the seating surface and not the shaft or the housing. There are mounting holes on the outer and inner rings, and there can also be integral gears on both the rings, or in any of them. Oil lubrication is necessary for higher speed applications. Typically, these bearings work at lower loads and higher speeds.