How do ball bearings work?
Ball bearings are among the most commonly use bearings in applications involving rotary motion. They consist of a row or rows of balls between inner and outer raceways. This design takes advantage of the concept that rolling elements create less friction than sliding elements. One ring is usually attach to the rotating assembly or shaft, and as it rotates, the balls roll on the inner raceway while the other ring remains stationary. This allows rotational motion with an extremely low coefficient of friction, making it ideal for applications with high speeds and low friction requirements.
The concept behind a bearing is very simple: things roll better than they slide. Bearings reduce friction by providing smooth metal balls or rollers and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers “carry” the load, allowing the device to rotate smoothly.
Bearings typically have to support two types of loads: Axial loads and radial loads. Axial loads, also known as thrust loads, are forces acting parallel to the bearing axis, while radial loads act perpendicular to the bearing axis. Ball bearings can support both axial and radial loads.
However, they have a relatively low load carrying capacity, so they are typically use in applications with lower load requirements. The spherical roller shape results in very small contact points between the balls and the raceways. This allows for the smooth motion but lowers load carrying capabilities. However, ball bearings can accommodate some misalignment of the inner and outer raceways.
Types of ball bearings
There are several designs of these bearings, specializing in different applications:
– Angular contact ball bearings: these bearings have axially asymmetrical raceways. This redistributes the radial loads through the bearing, making them ideal for supporting combined loads or loads in both axial and radial directions. Larger contact angles generally support higher axial loads and lower radial loads, while the reverse is true for smaller contact angles.
– Axial/thrust: Axial bearings use multiple raceways side by side. As the name implies, they specialize in axial loads; radial loads can damage the bearing by forcing the raceways apart.
– Deep groove ball bearings: a unique raceway design allows these bearings to support higher loads than other ball bearings. However, they cannot accommodate as much misalignment as normal ball bearings.
Features of ball bearings
As with most bearings, ball bearings have a number of features that help the bearing perform in different ways.
– Rows: Most bearings are install in pairs to distribute loads more evenly. Double-row bearings have two rows of balls instead of just one, eliminating the need to install multiple bearings. While this is a cost- and space-saving substitute for a pair of single-row bearings, it usually requires better alignment.
– Flange: This is a type of bearing housing that can be install to secure the bearing to the mounting surface. This simplifies mounting and axial location.
– Cage: Cages secure the balls in the bearing to hold them in place and reduce friction. They are usually made of steel or polyamide plastic, depending on the application. They are cheaper to manufacture, but plastic cages may not be suitable for high temperatures or strenuous environments.
– Material: Ball bearings are usually made of stainless steel, chrome steel, or ceramic. Ceramic bearings are typically use in applications with strenuous or difficult conditions, such as underwater or in a vacuum. Ceramic has a 40% lower density than steel; these bearings are corrosion resistant and do not require the lubrication, but are more brittle and susceptible to cracking than steel. Hybrid bearings with steel raceways and ceramic balls are often use to reduce the friction. Lighter balls allow faster rotation and lower energy consumption for the rotational motion.
– Self-aligning: Self-aligning ball bearings have an outer ring with a spherical raceway. This allows the bearing to tolerate angular errors that can result from housing or shaft deflections or improper mounting. These bearings typically have a lower load carrying capacity than other ball bearings and are commonly use in applications with a long shaft, such as gearboxes or textile mills.
Mounting Types
Ball bearings can be mounted in a variety of different ways, which affects the bearing’s load capacity and performance.
– Conrad: In this method, named for its inventor Robert Conrad, the inner ring is placed eccentrically in the outer ring, with a single point of contact. The balls are then insert opposite the contact point and evenly spaced, forcing the rings into the correct position. Typically, a cage is also install to ensure the even distribution of the balls. With this mounting method, only a limited number of balls can be use, which limits the load carrying capacity of the bearing.
– Slot fill: In this mounting method, both raceways are notch so that the balls can be insert. This allows any number of balls to be use, resulting in a higher radial load carrying capacity. However, these bearings have a lower axial load carrying capacity because the notches in the raceways cause discontinuity in the rings, which can affect bearing strength.
– Relieved race: in this design, either the outer diameter of the inner ring or the inner diameter of the outer ring is change to create a larger space for inserting the balls. Again, any number of balls can be use, but bearings with this design can only support axial loads in the direction away from the unloaded race.
– Broken race: one of the rings is cut completely through to allow insertion of the balls, and then reassembled. A pair of steel bands are used to support the broken sections during bearing alignment. This method also allows for any number of balls and can support axial loads in both directions.
With such a wide variety of ball bearing types, it can be difficult to determine which bearing type is most effective for your application. The experts at Abdul Traders are always available to answer questions and help you determine which bearing you need. If you feel any difficulty, then please don’t hesitate to contact us.
