One of the most widely used bearings of all time, ball bearings are used in a plethora of applications because their simple design makes them very versatile. They are often used as wheel bearings and can be found in cars, bicycles, skateboards, and various types of machinery in almost every industry.
Ball bearings are used to reduce rotational friction between two objects. They consist of one or more rows of balls between an inner and outer raceway and take advantage of the concept that rolling elements create less friction than sliding elements. By using balls that roll around the bearing instead of two surfaces sliding against each other, they can provide high speeds with extremely low friction. The invention of the ball bearing led to many similar bearing designs, such as roller bearings, which feature other types of rolling elements instead of balls.
In general, bearings must support axial and radial loads. Axial or thrust loads are forces acting parallel to the bearing axis, while radial loads act perpendicular to the bearing axis. Ball bearings can support both types of loads, which gives them great versatility. However, the spherical nature of balls creates extremely small metal-to-metal contact points within the bearing, which allows for smooth motion but limits the bearing’s load-carrying capacity. Ball bearings are typically used in applications with relatively low load requirements.
Features and components of ball bearings
As mentioned earlier, ball bearings consist of a few different parts: the inner and outer rings, the cage that holds the balls in place, and the balls themselves. These components are typically made of stainless steel, chrome steel, or ceramic. Cages can also be made of polyamide plastic to reduce production costs, but this can affect the bearing’s performance or its capabilities at high temperatures. Steel is the most common material for bearing construction; ceramic is used for applications with demanding or unusual conditions because it resists corrosion and does not require lubrication. Hybrid bearings consist of steel rings and cages and ceramic balls, which reduces friction and the weight of the bearing.
Ball bearings can contain one or more rows of balls, depending on the requirements of the bearing. Single-row bearings offer greater precision and accuracy, but generally must be installed in pairs to distribute loads evenly. Double-row bearings save space by eliminating the need for a second bearing, and they offer higher load capacity but require better alignment. Multi-row bearings are sometimes used for applications with extremely high load requirements.
Bearings can also be supplied with a flange or housing, which is a unit that secures the bearing to the mounting surface. This simplifies mounting and axial location and can provide increased security for the bearing. Depending on the bearing location and the size of the mounting surface, there are several types of housings.
Types of ball bearings
As with any bearing, there are a variety of ball bearing types used for different applications:
– Thrust ball bearings: these feature disc-shaped rings and can only support axial loads, which limits their usefulness. However, they can be designed to support axial loads in both directions and compensate for misalignment using alignment discs or spherical alignment seats.
– Angular contact ball bearings: These bearings have raceways that are displaced parallel to the bearing axis so that they can support a combination of axial and radial loads. Larger contact angles have higher axial load capacity, while smaller contact angles offer improved speed capability. Angular contact ball bearings are available as single or double row bearings. Single-row bearings minimize wobble and friction problems, while double-row bearings avoid diameter matching and runout problems.
– Four-point contact ball bearings: the inner ring of these bearings is split into two parts, giving the balls four points of contact with the raceways. This unique design allows these bearings to support axial loads in both directions as well as radial and axial loads simultaneously. They are designed for tougher conditions and can handle high load ratings compared to angular contact ball bearings. They also eliminate the need for multiple bearings and are more space-efficient than double row bearings. These bearings are best suited for low to medium-speed applications with high oscillating motion.
– Deep groove ball bearings: deep groove ball bearings, as the name implies, have deep running grooves; the inner and outer rings have arcs that are slightly larger than the diameter of the balls. This design is excellent for high-speed applications and can support high radial loads and axial loads in both directions. It produces low friction, temperature, and noise during operation, making it very versatile for a variety of industries.
– Self-aligning ball bearings: These bearings consist of two rows of balls, an inner ring with two deep raceways, and an outer ring with a spherical raceway. While they have a limited load-carrying capacity, they are capable of correcting misalignments that occur during operation. This makes them very suitable for applications with long shafts, such as in gearboxes or textile machines. Due to their low coefficients of friction, low maintenance requirements, and high speed, they are also used in a wide range of other applications.
– Precision ball bearings: These are ball bearings designed to offer significantly improved performance for a very demanding application. Optimal materials and designs provide increased performance at high speeds and under severe conditions. They are typically used when high precision, rigidity, noise reduction, service life, or friction reduction are required, such as in the aerospace, robotics, or medical industries.