A bearing is a mechanical component that supports and guides a rotating or moving part, such as a shaft. It reduces friction and allows for smoother rotation, which in turn lowers energy consumption. Bearings also transmit the load from the rotating element to the housing or frame, and this load can be radial, axial, or a combination of both. Additionally, bearings restrict the movement of parts to predefined directions, ensuring stability and precision.
From the spinning of bicycle pedals to the operation of car engines, the simple action of opening your refrigerator door to the smooth operation of an electric fan motor, all of these rely on bearings for efficiency. Bearings can be called the "joints" of machinery.
In this article, we will take you to observe the structure of bearings and explore their different types available. Through this guide, we believe you will be more confident in choosing the suitable bearings for your specific application.
Basics about Bearings
For our journey into the world of bearings, we first need to familiarize ourselves with their basic definitions, key terminology and classifications. Let's begin by exploring the key elements that compose a bearing.
The Structure of Bearings
1. Bearing Rings /Races
1) For radial bearings, the bearing consists of inner and outer rings that house the rolling elements. These rings provide structure and a guide for the rolling elements to move.
The inner ring is the part that fits onto the rotating shaft and rotates along with it.
The outer ring is inserted into the housing and typically remains fixed, without rotating.
2) For thrust bearings, the term races is used.
The shaft race is the one into which the shaft is inserted.
The housing race is the one that fits into the housing.
2. Rolling Elements
The rolling elements are the parts that move between the rings (or races) to reduce friction. They carry the load and transfer it with minimal resistance. Different types of rolling elements, such as balls or rollers, are used depending on the specific conditions of the bearings ,such as the strength of the supporting force or the speed of the rotation.
Ball
Ball bearing
Cylindrical roller
Roller bearing
Needle roller
Tapered roller (tapered trapezoid)
Convex roller (barrel-shaped)
The different shapes of rolling elements
3. Cage
The cage keeps the rolling elements evenly spaced, preventing contact between them and ensuring smooth rotation. Below shows the two most common types of cage.
Besides these main components, to ensure stable and smooth rotation, a lubricant is essential. Proper lubrication extends bearing life and improves efficiency. Depending on the operating conditions, lubricants can be oil-based or grease-based. Additionally, many bearings are equipped with seals or shields to protect internal components from contamination by dust, debris, or moisture, while also helping to retain the lubricant within the bearing for optimal performance.
Classification of Bearings
Bearings can be classified based on several criteria. Here are two common classifications.
1. According to type of motion, bearings can be divided into rolling bearings and plain bearings. Rolling bearings use rolling elements like to reduce friction. In contrast, plain bearings do not have rolling elements and rely on sliding motion between surfaces.
They can be further divided into two major types: ball bearings and roller bearings, depending on the shape of the rolling element. The table below briefly introduces the main characteristics of both.
Feature
Ball Bearings
Roller Bearings
Contact Type
Point contact
Line contact
Load Capacity
Lower load capacity
Higher load capacity
Friction
Provide low friction,thus little energy loss
Higher friction than ball bearings but still low overall friction
Stability
Less stability under heavy loads
Enhanced stability with lower vibrations
Cost
Generally more affordable
Typically more expensive
Applications
Suitable for high-speed applications (e.g., electric motors, fans)
Ideal for heavy machinery and automotive components (e.g., transmissions, axles)
Difference between ball bearings and roller bearings
2. Based on load direction, bearings can be divided into radial bearings and thrust bearings. Radial bearings are designed to support radial loads, which are perpendicular to the axis of rotation. Thrust bearings, on the other hand, are made to handle axial loads that run parallel to the axis of rotation.
Contact Angle for Bearings
The contact angle in bearings is the angle formed between the line connecting the points of contact between the rolling elements (balls or rollers) and the raceways (the inner and outer rings), and a plane perpendicular to the bearing axis. This angle is pivotal in determining the load-carrying capacity of the bearing, specifically in relation to radial and axial loads.
Bearings with a larger contact angle are better suited for handling axial loads (loads parallel to the bearing axis) . On the other hand, bearings with smaller contact angles are more effective for primarily radial load applications.
Different Types of Bearings
Based on the bearing classifications discussed in the previous section, we will use the diagram above as our main framework to systematically examine the primary types of common bearings.
1. Radial Ball Bearings
Radial ball bearings, as the name suggests, are ball bearings that are primarily designed to handle radial loads (force that is applied perpendicularly to the shaft) efficiently. Typically, they have a contact angle of less than 15°. Radial ball bearings have many subtypes. Here, we focus on three common ones.
Deep Groove Ball Bearings
The most commonly used type of bearings, typically installed as a single unit, making them relatively easy to install and requiring minimal maintenance.
The inner and outer rings have deep, raceway-shaped grooves that allow the bearing to support both radial loads and a limited amount of axial load from both directions simultaneously.
Applications: Well-suited for applications with primarily radial loads and moderate axial support, offering high speed and versatility. They are commonly used in electric motors, fans, blowers, power tools, and household appliances.
Angular Contact Ball Bearings
The inner and outer ring raceways are inclined relative to the bearing axis, creating a contact angle typically between 15° and 45°. Nevertheless, in many engineering and industrial applications, angular contact ball bearings are classified as a subset of radial ball bearings. This configuration allows them to handle greater axial loads in one direction in addition to radial loads.
They can be arranged in pairs (back-to-back, face-to-face, or tandem) to support axial loads from both directions and enhance rigidity.
Applications: Used in situations where combined radial and axial loads occur, particularly when higher axial load capacity and precision are required. They are commonly found in pumps, compressors, automotive components, CNC machining tool spindles, industrial robots, and precision machinery.
Self-Aligning Ball Bearings
Self-aligning ball bearings have two rows of balls, which provide better stability and a higher load-carrying capacity compared to single-row bearings.
The outer ring is spherical, allowing the inner ring, cage, and balls to tilt freely inside the bearing. This feature lets the bearing automatically adjust to compensate for misalignment caused by mounting errors or shaft bending, improving efficiency, reducing wear, and extending the bearing's lifespan.
These bearings are primarily designed to handle radial loads but can also support light axial loads.
Applications: Valued in situations where shaft deflection or alignment issues are common, such as in conveyor systems, steel rolling mills, and agricultural machinery.
2. 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 four major bearing types that are made to suit the type of roller.
Cylindrical Roller Bearings
Use cylindrical rollers as their rolling elements, with the rollers making linear contact with the raceways.This design allows them to carry much heavier radial loads compared to ball bearings.
They have a low friction coefficient and are suitable for very high-speed applications. Their maximum operating speed is second only to that of deep groove ball bearings.
They are available in single-row, double-row, and full-complement types, and also come in split variants to make installation and disassembly easier.
Applications: Commonly used in high-speed, heavy radial load environments like drive shafts, rolling mills, and mining equipment.
Needle Roller Bearings
As the name suggests, needle roller bearings have long, thin rollers resembling needles. This design allows them to support high radial loads while remaining compact and lightweight.
In many applications, needle roller bearings are used without an inner or outer ring, especially when space is limited, and weight reduction is important. In such cases, the shaft and housing act as the raceways. These surfaces must be machined with high precision and have a hardness level similar to that of a standard bearing raceway to ensure proper performance.
Applications: Commonly found in areas with limited radial space, such as internal combustion engines, motorcycles, aerospace components, and robotics.
Tapered Roller Bearings
These bearings feature conical rollers that fit between races shaped like sections of a hollow cone. If extended, the rollers' axes and races would meet at a common point.
Their tapered design enables them to handle higher axial loads besides radial loads. The amount of axial load they can support depends on the contact angle; a larger angle increases the axial load capacity.
They can be categorized into single row, double row, and four-row, and other different types according to the number of rollers installed.
Applications: Suitable for automotive wheel hubs, gearboxes, construction equipment, and precision machinery where rigidity and stability are critical.
Spherical Roller Bearings
Feature barrel-shaped rollers that fit a spherical outer raceway, providing a larger contact area to support heavy radial loads.
The spherical design of the outer raceway enables the bearing to self-align, automatically correcting any misalignment between the shaft and housing.
They can handle heavy radial loads and moderate axial loads in both directions.
Applications: Heavy-duty applications where there are both radial and axial loads, as well as potential shaft misalignment. Common uses include construction equipment, mining machinery, large industrial gearboxes, pulp and paper mills, and wind turbines.
3. Thrust Ball Bearings
In contrast to radial ball bearings, thrust ball bearings are a special type of ball bearing with a 90 ° contact angle, designed to withstand only axial loads.
They come in single-direction or double-direction configurations, depending on whether the load is unidirectional or bidirectional.
Applications: Ideal for applications where axial loads are applied along the shaft at moderate rotational speeds, such as in automotive clutches, gearboxes, rotary tables, and steering systems.
4. Thrust Roller Bearings
Thrust roller bearings are designed to handle high axial loads and come in three types of rollers: cylindrical, tapered and spherical.
Cylindrical thrust roller bearings offer good axial load capacity with minimal radial support and are relatively cheap.
Tapered thrust roller bearings can accommodate slight misalignment during operation and support varying axial and radial loads depending on the cone angle. They carry greater thrust loads than thrust ball bearings but are more expensive to produce.
Spherical thrust roller bearings are designed to take heavy axial loads in one direction and accommodate some radial loads as well. They are self-aligning and are thus unaffected by mounting errors and shaft deflection.
Applications: These bearings are used in high-load environments like gearboxes, heavy machinery, and marine propulsion systems, where both axial and radial loads may be present.
5. Plain Bearings
Plain bearings are the simplest type of bearing, operating through direct contact between the bearing surface (also known as a bushing or sleeve) and the shaft, without any rolling elements.
They rely on lubrication to reduce friction and wear between the surfaces. To ensure smooth movement, materials with low friction coefficients, like various copper alloys, are commonly used.
Plain bearings are suitable for rotating, sliding, oscillating, and reciprocating motions. They are lightweight, cost-effective, and quiet in operation.
Applications: Ideal for low-speed, heavy-load applications with potential misalignment or oscillation, such as industrial cranes and agricultural machinery.
6. Fluid Bearings
Fluid bearings function by creating a thin film of fluid between the housing and the rotating surface. This film separates the moving parts, preventing direct metal-to-metal contact, which reduces wear and extends the bearing's lifespan. hydrostatic and hydrodynamic are two bearing kinds of this category.
In hydrostatic bearings, the fluid film is maintained by an external pump that supplies pressurized fluid (usually oil or air) into the bearing, ensuring a continuous film, even at low or zero speeds.. This allows hydrostatic bearings to support heavy loads and maintain low friction under various operating conditions.they also offer precise control, making them an excellent choice for machining spindles, gas turbines, and aircraft control systems, where stability and precision are crucial.
Hydrodynamic bearings rely on the shaft’s motion to create the fluid film. As the shaft rotates, it pulls the fluid into the gap between the surfaces, generating pressure and forming the lubricating film that supports the load. Hydrodynamic bearings are suited for moderate to high-speed applications, such as pumps, turbines, marine systems, and industrial equipment.
7. Magnetic Bearings
These bearings utilize electromagnetic fields to levitate and stabilize the rotating shaft, allowing it to operate without physical contact.This eliminates friction and wear, allowing for virtually maintenance-free operation.They are broadly classified into two types: active and passive magnetic bearings.
Active magnetic bearings (AMB) use electromagnets and sensors to continuously monitor and adjust the shaft's position in real-time. A control system processes sensor data and adjusts magnetic forces to maintain stability. AMBs are highly precise and can support very high speeds, making them suitable for advanced industrial applications.
Passive magnetic bearings rely on permanent magnets to support the load. They are simpler and do not require a control system or external power source but offer less control and flexibility compared to AMBs. Passive magnetic bearings are often used in applications where simplicity and reliability are more important than precision.
Applications: Magnetic bearings are ideal for applications requiring high speeds, precision, and minimal maintenance, such as turbomachinery, energy systems, and medical equipment.
Considerations When Choosing Metal Bearing
1. Load
1) If the load is mostly radial (perpendicular to the shaft), use a radial bearing; if the load is mostly axial (in the same direction as the shaft), use a thrust bearing. Axial load is also referred to as thrust load.
2) If the bearing load is light, use a ball bearing; if the load is heavy, use a roller bearing.
3) If both radial and axial loads are applied simultaneously (combined load), a light combined load calls for a deep groove ball bearing or an angular contact ball bearing, while a heavy combined load requires a tapered roller bearing.
4) If there is a heavy axial load being applied from both directions, you can combine two or more bearings, or use a double-row bearing.
2. Rotating Speed
1) Generally speaking, for high-speed applications, deep groove ball bearings, angular contact bearings, and cylindrical roller bearings are suitable choices. For lower-speed conditions, tapered roller bearings and thrust ball bearings are appropriate.
2) For the same type of bearings, the smaller the size, the higher the allowable speed. When selecting a bearing, ensure that the operating speed is within the bearing's limit speed to avoid damage.
3) Note that a limiting speed of the bearing is affected not only by the type and size of the bearing but is also greatly affected by such factors as its tolerance, cage type and material, type and amount of lubricant, lubrication method, and so on. For this reason, if you intend to use a bearing at a high rotational speed, please consult with Chiggo before making your decision.
3. Accuracy
1) ISO standards and others define specific tolerances for both boundary dimension accuracy (which relates to the fit and installation of the bearing) and running accuracy (which refers to the precision of the bearing's rotational movement) within each accuracy class.
2) For most general applications, Class 0 bearings is enough to provide adequate performance.
3) For applications requiring high accuracy in rotational runout, precision bearings of Class 5, 4, or 2 should be used.
4. Rigidity
1) Rigidity of a bearing refers to its ability to resist deformation under load. It is directly influenced by the contact area and the internal clearance within the bearing. The larger contact area (line contact) in roller bearings distributes the load over a wider surface, thus, they provide greater rigidity compared to ball bearings with point contact.
2) Bearings like angular contact ball bearings and tapered roller bearings can adjust their contact angles or be arranged in configurations like back-to-back (DB) or face-to-face (DF) to increase rigidity. It is important to note that the DB configuration generally offers higher rigidity than the DF configuration.
3) The internal clearance (the space between the rolling elements and the raceways) also affects rigidity. Smaller clearance allows more rolling elements to contact the raceway, increasing the contact area and thus the bearing's stiffness.
4) Applying preload to reduce the internal clearance to a slightly negative value ensures that all rolling elements are in uniform contact with the raceways. This uniform contact minimizes variations in the elastic deformation of each rolling element, leading to a more even load distribution and enhanced rigidity. However, the amount of preload must be carefully set to avoid negative effects such as reduced service life, temperature increases, or potential bearing failure (seizure).
5. Others
1) Radial Space Constraints: If the available radial space is limited, select bearings that are designed for compact environments, such as needle roller bearings or needle roller and cage assemblies.
2) Vibration and Noise Levels: For applications with strict vibration and noise requirements, such as consumer electronics or audio equipment, deep groove ball bearings are a good choice.
3) Environmental Conditions: For harsh environments (e.g., dusty, corrosive, or wet conditions), use bearings that are sealed, shielded, or made from corrosion-resistant materials (such as stainless steel or coated bearings) to protect against contaminants and ensure durability.
4) Lubrication and Maintenance: In applications where maintenance access is challenging, choose sealed or self-lubricating bearings that retain lubrication for extended periods, reducing the need for frequent servicing and minimizing downtime.
5) Installation and Alignment: Allowable misalignment is vital when selecting bearings. Self-aligning ball bearings are designed with a spherical outer ring raceway, allowing them to accommodate minor angular misalignments (1-2 degrees), making them suitable for applications with potential shaft deflection or misalignment.
On the other hand, spherical roller bearings, with cylindrical or spherical rollers, can handle larger misalignments (2-3 degrees or more). This capability is particularly beneficial in applications subjected to significant shaft deflection, thermal expansion, or dynamic operating conditions.
Conclusion
Mechanical bearings are crucial components in rotating equipment and mechanical assemblies.They help support operational forces, reduce friction, and ensure smooth, efficient operation.
When selecting the right type of bearing, you need to consider factors like load capacity, vibration, noise, size, among others. There are also many other details that can influence your decision. If you're still uncertain about which bearing best fits your needs, feel free to consult our engineers for expert advice.
