What is Bearing?
Bearings are machine elements that allow components to move with respect to each other. There are two types of bearings: contact and non-contact. Contact-type bearings have mechanical contact with equipment, which includes sliding, rolling, or flexural bearings.
Non-contact bearings include liquid, air, mixed-phase, and magnetic bearings. The lack of mechanical contact eliminates static friction.
A bearing is a machine element that constrains relative motion to only the desired motion and reduces friction between moving parts.
The design of the bearing may, for example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may prevent a motion by controlling the vectors of normal forces that bear on the moving parts.
Most bearings facilitate the desired motion by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or the directions of the loads (forces) applied to the parts.
How Does a bearing work?
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 “bear” the load, allowing the device to spin smoothly.
The bearing makes many of the machines we use every day possible. Without bearings, we would constantly be replacing parts that wear out from friction. Objects roll more easily than they slide. The wheels on your car are like big bearings. If you had something like skis instead of wheels, your car would be much more difficult to push down the road.
Bearing loads
Bearings typically experience two kinds of loading radial and thrust. Depending on where the bearing is used, it may see radial loading, thrust loading, or a combination of both.
The bearings in an electric motor and pulley combination face only a radial load. Most of the load comes from the tension in the belt connecting the pulleys.
The bearings in barstools and lazy Susan’s are totally thrust loaded. The entire load comes from the weight of the objects.
The bearing in the hub of your car wheel must support both radial and thrust loads. The radial load comes from the weight of the car; the thrust load comes from the cornering forces when you go around a turn.
Parts of a Standard Bearing
The standard essential components of a bearing are as follows:
1. Inner Ring
The Inner Ring is the smaller of the two bearing rings. It has a groove on its outer diameter to form a raceway for the balls. The surface of the outside diameter path is finished to extremely tight tolerances and is honed to be a very smooth surface. The inner ring is mounted on the shaft and it is the rotating element.
2. Outer Ring
The Outer Ring is the larger of the two bearing rings. On the outer ring, there is a groove on its inside diameter to form a pathway for the balls. It also has the same high-precision finish as the inner ring. The outer ring is usually held stationary.
3. Rolling Element (Balls, Cylindrical Rollers, Spherical Rollers, Tapered Rollers, Needle Rollers)
The rolling elements separate the inner ring and outer ring and permit the bearing to rotate with minimal friction. The dimension of the rolling elements is made slightly smaller than the track on the inner and outer rings.
Rolling element dimensions are controlled to very high accuracy. Surface finish and size variations are important attributes. These attributes are controlled to a micro inch level.
4. Cage (Retainer)
The purpose of the cage in bearings is to separate the rolling elements, maintain a constant spacing between the inner and outer rings, accurately guide the rolling elements in the path during rotation, and to prevent the rolling elements from falling out.
5. Lubrication
The lubricant is an integral part of a bearing’s standard components. Lubrication is added to reduce friction losses in bearing between inner and outer rings.
6. Other Optional Bearing components
The other additional components shields and seals enhance the performance and life of the ball bearing. These optional components are added to the bearing as per the customer’s requirement to increase the performance of the bearing.
7. Shields
The shield is a stamped, profiled sheet metal disc. The shield is pressed into a very small groove on the inside edge diameter of the outer ring. A small space or gap remains open between the outside diameter of the inner ring and shield.
Because the shield does not contact the inner ring of the bearing, there is no added friction between the shield and bearing. This results in a bearing that has very low torque. The purpose of shields is to keep larger particles of contamination from entering the bearing.
8. Seals
The seal is also inserted into the very small groove on the inside, edge diameter of the outer ring. The inner edge of the seal is molded into a specifically designed lip configuration.
Types of Bearings
- Rolling Element Bearings
- Ball Bearings
- Deep Groove Ball Bearings
- Angular Contact Ball Bearings
- Self-Aligning Ball Bearings
- Thrust Ball Bearings
- Roller Bearings
- Cylindrical Roller Bearings
1. 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.
2. 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.
3. Deep Groove Ball Bearings
This is 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.
4. Angular Contact Ball Bearings
In this ball bearing type, the inner and outer races are displaced with respect to each other along the bearing axis. This type is designed to handle greater amounts of axial loads in both directions in addition to radial loads.
Due to the shift in the inner and outer races, the axial load can be transferred through the bearing to the housing. This bearing is suitable for applications where rigid axial guidance is required.
Angular contact bearings are widely used in agricultural equipment, automobiles, gearboxes, pumps, and other high-speed applications.
5. Self-Aligning Ball Bearings
This type of ball bearing is immune to misalignment between the shaft and the housing which may happen due to shaft deflection or mounting errors.
The inner ring has deep grooves similar to deep groove ball bearings followed by two rows of balls and the outer ring. The outer ring has a concave shape and this grants the inner ring some freedom to rearrange itself depending on the misalignment.
6. Thrust Ball Bearings
Thrust ball bearings are a special type of ball bearings designed specifically for axial loads. They cannot sustain radial loads at all.
Thrust ball bearings exhibit low noise, and smooth operation and are capable of high-speed applications.
They are available as single-direction or double-direction bearings and the selection relies on whether the load is unidirectional or bidirectional.
7. Roller Bearings
Roller bearings contain cylindrical rolling elements instead of balls as load-carrying elements between the races. An element is considered a roller if its length is longer than its diameter (even if only slightly). Since they are in line contact with the inner and outer races (instead of point contact as in the case of ball bearings), they can support greater loading.
Roller bearings are also available in various types. The appropriate type may be selected after considering the type and magnitude of loading, service conditions, and the possibility of misalignment among other factors.
8. Cylindrical Roller Bearings
These are the simplest of the roller bearings family. These bearings can face the challenges of heavy radial loading and high speed. They also offer excellent stiffness, axial load transmission, low friction, and long service duration.
The load capacity can be increased further by obviating the use of cages or retainers that are usually in place to hold the cylindrical rollers. This permits the fitting of more rollers to carry the load.
They are available as single-row, double-row, and four-row types. They also come in split and sealed variants.
Split variants are used for areas that are difficult to access such as engine crankshafts. In sealed variants, the bearing contamination is prevented and the lubricant is retained making it a maintenance-free option.
When to Use Ball Bearings?
So, let’s outline some of the working conditions that may require a ball bearing.
- Thrust loads are present. Ball bearings’ design makes them capable of withstanding axial loads.
- No heavy loads. Due to having ball-shaped rolling elements, the bearings concentrate all the force onto a few points of contact. This can result in early failure with high loads.
- High speeds. The ball bearing’s small point of contact also means less friction. So there is less resistance to overcome and thus it is easier to achieve high speeds with these types of bearings.
Selection of bearing type
Selecting a proper bearing for our application is a very important thing. Here is a quick guide for selecting the right bearing.
- For low and medium loads select ball bearings, and for heavy loads select roller bearings
- In case of misalignment between shafts self-aligning ball bearings or roller bearings are used
- For medium thrust loads, radial thrust bearings are selected and for heavy thrust loads cylindrical thrust bearings are used
- For situations where we have both axial and radial components of load, we use deep groove ball bearings, angular contact bearings, and spherical roller bearing
- For high-speed applications deep groove ball bearings, angular contact bearings and cylindrical roller bearings are recommended
- When the rigidity of the system is our main requirement like in machine tools, we use double-row cylindrical roller bearing or taper roller bearing
- When noise reduction is our main criteria, we use a deep groove ball bearing
Applications of Bearing
- Aviation Cargo Systems.
- Aerospace Wing Actuators.
- Anemometer.
- ATMs & Card Readers.
- Bicycles.
- Commercial Blenders.
- Dental Hand Tools.
- Electrical Motors.
Advantages of bearings
- The friction resistance and the power consumption are small, the mechanical efficiency is high, and is easy to start.
- Size standardization, interchangeability, easy to install and disassemble, easy to repair.
- The structure is compact, the weight is light, and the axial size is narrower.
- High precision, large load, and long service life.
- Some bearings have the performance of automatic heart adjustment.
- It is suitable for mass production, the quality is stable and reliable, and the production efficiency is high.
- The friction torque of the transmission is much lower than that of the fluid dynamic pressure bearing, so the friction temperature rise, and the power consumption are low.
- The axial size is less than the traditional fluid dynamic bearing.
- The combined load of radial and thrust can be borne simultaneously.
- Within a large load-velocity range, the unique bearing design can achieve excellent performance.
Disadvantages of rolling bearings
- The noise is great.
- The structure of the bearing seat is complex.
- The cost is high.
- Even if the bearings are lubricated well, installed correctly, and well-sealed, and the operation is normal, they will eventually fail because of the fatigue of the rolling contact surface. If you want to learn more about bearings, please don’t hesitate to contact us.
