What Are the Differences Between Bearings? The various types and special features of bearings
There are various types of bearings, and we must select the type of bearing most suited to a particular machine's structure and use.
In this part, we will divide the types of bearings into broad categories, and then explain the main features of bearings.
1. The categorization of bearings
Bearings support forces applied from various directions, and so they can be categorized based on the "direction of the force".
Firstly, we will explain about the forces applied to bearings.
Figure 1 shows the forces applied to the bearing used in a car's wheel with a tire on it.
The force generated by the weight of the vehicle (the blue arrow in Figure 1) is applied perpendicular to the axle.
Conversely, the centrifugal force generated when the car turns(the red arrow in Figure 1) is applied in the same direction as the axle.
Fig. 1: The forces applied to the bearing used in a car's wheel with a tire on it
In this way, bearings at all times have forces applied from various directions.
The bearings are categorized based on which direction the force is coming from and how much force can be applied.
The radial and axial loads applied to a bearing
The force applied to a bearing is called the "load".
The force applied perpendicularly to the shaft is called the "radial load",
and that applied in the same direction as the shaft is called the "axial load".
Fig. 2: The radial and axial loads
The categorization of bearing types
As can be seen in Table 1, bearings can be categorized into four groups based on the direction of the force supported and the shape of the rolling elements.
For more details, please take a look back at Part 3!
Part 3: "What's the Structure of the Bearing? The role of the structure and parts in reducing friction"
Table 1: The categorization of bearing types
Rolling element Ball Roller Direction in which force is mostly applied Perpendicular to the shaft
(radial load) Radial ball bearing Radial roller bearing The same direction as the shaft(axial load) Thrust ball bearing Thrust roller bearing
Of the four types of bearings listed in Table 1, radial ball bearings and radial roller bearings are used most often. We will explain a bit about those two types of bearings.
2. Radial ball bearings
"Radial ball bearings" are ball bearings that can support a force that is applied perpendicularly to the shaft.
Deep groove ball bearings
Deep groove ball bearings are the most widely used among all bearings.
They can support both a radial load and a certain amount of axial load coming from both directions at the same time.
If a bearing to support a very large axial load is needed, the "angular contact ball bearings" explained below are used.
Product information: Deep Groove Ball Bearing
Angular contact ball bearings
Angular contact ball bearings can support a radial load and a one-directional axial load at the same time.
When axial loads coming from both directions are to be supported, two or more angular contact ball bearings are combined together.
Fig. 3: A combination of angular contact ball bearings to support axial loads coming from both directions
Here is a further explanation of the contact angle of the angular contact ball bearings.
The contact angle of the radial and axial loads
Fig. 4: The structure of an angular contact ball bearing supporting radial and axial loads
The contact angle is the angle formed by the direction of the load applied to the bearing rings (races) and rolling elements, and a plain perpendicular to the shaft, when a "radial load" and "axial load" are both applied to a bearing.
Product information: Angular Contact Ball Bearing
3. Radial roller bearings
Radial roller bearings are roller bearings that can support a force perpendicular to the shaft. They can support an even greater load than radial ball bearings, and there are bearing types that are made to suit the type of roller.
Cylindrical roller bearings
These use cylindrical rollers as their rolling elements. Cylindrical roller bearings can support an even greater radial load than deep groove ball bearings, and are used in machinery where they will experience strong impacts.
Product information: Cylindrical Roller Bearing
Needle roller bearings
These use needle rollers as their rolling elements. Needle rollers have a smaller diameter than cylindrical rollers, and so (as can be seen in Figure 5) the bearings have a smaller cross-sectional height and contributed to the down-sizing of machinery.
Fig. 5: The difference in cross-sectional height between a cylindrical roller bearing and a needle roller bearing
Product information: Needle Roller Bearing
Tapered roller bearings
These use tapered rollers in the shape of tapered trapezoids as their rolling elements.
Tapered roller bearings are the most widely used among all roller bearings, and can support a radial load and a one-directional axial load at the same time.
When axial loads coming from both directions are to be supported, two or more tapered roller bearings are combined together.
Fig. 6: A combination of tapered roller bearings to support axial loads coming from both directions
Product information: Tapered Roller Bearing
Spherical roller bearings
These use barrel-shaped convex rollers as their rolling elements. As shown in Figure 7, they are inserted between a spherical outer ring raceway surface and an inner ring raceway surface. This is why the inner ring, rolling elements and cage in a spherical roller bearing are able to rotate while inclined toward the outer ring.
Fig. 7: The structure of a spherical roller bearing
As shown in Figure 8, spherical roller bearings can support a large load, and are used in machines where the shaft is easily bent.
Fig. 8: The bending of a shaft
Product information: Spherical Roller Bearing
Conclusion
There are various types of bearings categorized by the direction and magnitude of the force they can support, and the optimal bearing type is selected, taking the machine's structure into consideration.
There are many other types of bearings we didn't introduce in this article. Difference between Ball Bearing and Roller Bearing
Most of the machines have different components and utilize a variety of bearings which enable their smooth, hassle-free working. Although there are many varieties of bearings, the most used ones are ball bearings and roller bearings. Both types of bearings are meant to provide exemplary and effective operations. There are a few differences between these two types regarding designs or usage. So let us look at a few of them.
Difference between Ball Bearing and Roller Bearing
The main difference between ball bearing and roller bearing is, that the Ball bearings are composed of small spheres, resulting in a small point of contact with the load. Where else the cylindrical-shaped Roller bearings’ area of contact with a load is in a line, supporting the load more effectively and spreading along with it.
Application: Ball bearings are practical when one requires loading small products. As we increase the loads, these bearings tend to break or lose their defined shape. Roller bearings are applicable in conditions where one requires handling large loads. Though, one must not forget that needle bearings, which are a variation of roller options, are essential in case of constraint space.
Maintenance Cost: Roller bearing requires good maintenance to ensure the proper functioning of different industrial machines or applications.
Advantages & Disadvantages of Ball bearing & Roller bearing
Advantages of Ball Bearings
Possess a good wear resistance
Requires less lubrication
Capable of handling thrust loads
Can be replaced easily
Can offer long service
Limitations of Ball Bearings
It can get loud at times
Not competent in handling large weights
Can get damaged due to shocks
Advantages of Roller Bearings
Tapered roller bearings are competent in handling high axial loads
Capable of taking high radial loads
Generates very less friction
Produce fewer vibrations
Limitations of Roller Bearings
Very expensive
It can be very noisy
Types of ball bearings available in the market
Angular Contact Ball Bearings: When it comes to bearings, angular contact balls have a unique contact angle that sets them apart from other varieties. Thus, forces are transferred from one raceway to the next at an angle concerning the first. It is also possible to move loads in which large axial forces have to be conveyed and those transmitted by the ball bearings’ radial motion.
Self-Aligning Ball Bearings: The inner ring and the ball complement may revolve inside the outer ring. Thanks to an outer ring racetrack that runs continuously around the outer ring. In terms of both size and design, the options for Self-Aligning Ball Bearings are almost limitless. Thus it enables the application to self-align to some extent.
Thrust Ball Bearings: As a rule of thumb, thrust ball comprises two bearing discs, each having a raceway for the balls in between. It can absorb axial stresses in one direction and can also be used to position the shaft in one direction.
Deep Groove Ball Bearings: A ring of balls is trapped between the two races that allow rotational motion in this type of bearings. Placed by a retainer, these balls possess very low friction. This type of bearing is optimized with low vibration & noise, which makes it ideal for high-speed applications.
How do ball bearings work?
Ball bearings are among the most widely utilized types of bearings in rotary movement applications, accounting for over half of all such uses. They are made up of a row or many rows of balls sandwiched between the inner and outer raceways.
One ring is generally linked to the rotating assembly or shaft, and when the assembly turns, the balls roll around the inner raceway. In contrast, the other ring stays stationary, as seen in the illustration. This enables the rotational movement with an exceptionally low friction coefficient, making it ideal for applications requiring high speeds while still requiring low friction characteristics.
Types of roller bearings available in the market
Spherical Roller Bearings: The Spherical Roller Bearings function on the same principle as Self-aligning bearings but use spherical rollers rather than ball rollers, which helps them handle heavier loads than ball rollers successfully. Bearings with spherical rollers can sustain high radial loads and low axial forces.
Cylindrical Roller Bearings: These bearings provide the best possible distribution of stress elements at the moment of impact; rolling components and raceways should act into a line. Cylindrical roller bearings can handle huge radial loads. Depending on the design, they may be able to transfer a minor amount of axial stresses.
Tapered Roller Bearings: The term “tapered roller bearings” refers to bearings with tapered raceways in the inner and outer rings and conical rollers located between the two. Tapered roller bearings may absorb large radial and axial forces because of the contact angle.
Needle Roller Bearings: Cylindrical needle roller bearings are made of nylon and have long, thin rolling components known as needle rollers. The ratio of diameter to length is 3:1 to 1:10.
All types of bearings come with some numbering with which one can easily identify the type and other information.
Read more about How to Identify Bearings by Number in this blog post.
Suggested Read: Top 9 Bearing Suppliers in Kolkata That You Can Trust
How do roller bearings work?
Roller bearings are primarily used in conveyer belt rollers, and it is expected to be strong enough to support heavy radial loads. In these bearings, the roller is generally a cylinder, and therefore the area of contact between the outer and inner race is a line, not a point. Thus it easily spreads the load to a larger area and thus allows the bearing to easily hold enough loads than a ball bearing. Single-row or multiple-row bearings are available, and the addition of additional rows may significantly enhance their radial load capability.
When to choose which one?
As a rule of thumb, ball bearings are more often employed in high-speed applications and are less in weight than roller bearings. When exposed to shock and impact load, roller bearings outperform ball bearings.
Unlike multi-row ball bearings, cylindrical roller bearings are standard and may be used interchangeably by different manufacturers. Nevertheless, when choosing a bearing, all you have to do is consider the following factors: the lubricant, grade, any shielding/sealing, and the essential load requirement.
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