If we break down the rotating mechanical equipment, systems, or mechanisms, different motions of their components are crucial for their functions. For instance, the blades rotate around the hub of a wind turbine to produce electricity. Do you know which device or parts control and dictate required motion within a mechanical system or machinery? The answer is a mechanical bearing. So, various types of bearings with different shapes, sizes, or designs achieve this by allowing motion in only one fixed direction.
Mechanical bearings also reduce the friction between moving parts. However, using the right bearing according to the requirement can only result in smooth and precise motions. Furthermore, we will discuss bearing uses and types, materials, and considerations for choosing the right bearing for your needs.
Why Is Mechanical Bearing Important?
Contact of rotating metal to metal parts causes rapid wear in the contact surface. It lowers the lifetime of machinery and poses a risk to operational safety. So, the mechanical bearing on such joints or connections avoids contact and facilitates smooth motion. The reason behind this is the structure of the rolling element inside the bearing.
Typically, these rolling elements of ball or cylinder shape. They move in a rolling motion, and we know that rolling is a low-friction process than sliding.
- Avoid or reduce the contact surface
- Uniform load distribution
- Reduced friction & lubrication
- Operational efficiency
- Handling of heavy loads
Type 1: Ball Bearings
In the ball bearing, rolling elements are the spherical balls. These balls between two bearing races can support both radial and axial loads. Meanwhile, a component called retainer separates the balls and holds them with uniform spacing. These are typically made with roller-bearing steel or stainless 4401 and 14401, which carry and pass the loads into the inner ring of the bearing.
Next, you can find different ball bearing types based on load direction, raceway design, specific function, and size that can fulfill diverse application requirements.
Deep-Groove Ball Bearings
Like its name, deep-groove ball bearings contain deep grooves in inner and outer raceways to hold the balls. This simple design makes it versatile and applicable in various applications, from electric motors to gearboxes and water pumps.
Consequently, deep groove bearings can handle heavier loads and are suitable for high-speed rotations. The compact structure also facilitates the efficient use of space within the machinery or systems. However, they are sensitive in case of misalignment possibility.
When to Use: High-speed machinery like turbines or motors & limited space applications.
Self-Aligning Ball Bearings
This type of ball bearing contains a cage structure with two rows of balls at a uniform distance between the outer and the inner race. In case of any static or dynamic misalignment, the outer race allows to adjust the bearing position accordingly to correct it.
The prime advantage of self-aligning ball bearings is that they can self-correct the angular misalignment for seamless operation. They are also good at shock and vibration absorption. On the other hand, the complexity increases the bearing cost, and they have limited load capability.
When to Use: If the machinery or systems have misalignment possibilities and for moderate speeds and loads.
Angular-Contact Ball Bearings
In the angular contact ball bearing, balls transfer the forces from the outer to the inner ring at a specific angle (the contact angle). It is possible with a displacement of races to each other. That’s why, angular types of bearings are also known as angled bearings. Moreover, they can handle higher loads and are compatible with high-speed operations.
Although single-row, double-row, and sealed options make angular contact bearing versatile, it can possess higher friction at higher contact angles.
When to Use: If the forces are combined (axial and radial) and heavy.
Thrust Ball Bearings
Thrust ball bearings are simple and low-cost bearings for axial loads. Their structure involves balls in a cage surrounded by two rings, the inner race typically connects the rotating shaft. Consequently, they come in two variations: Single direction and double ball bearing thrust bearings. In double-direction configurations, the balls remain in an alternating pattern or position between the rings.
These thrust bearings can accommodate high-speed axial loads. They are also simple to install and cost less than the other bearings.
Disadvantages: Limited to axial load directions and prone to misalignment & ball skidding.
When to Use: Thrust-bearing applications with dominant axial loads like machine tool spindles and crane hooks.
Miniature Bearings
Miniature type refers to the small-sized micro ball bearings. They are for small spaces and precision load handling. You can imagine how small they can be from the fact that the overall diameter can only be less than 20 mm (according to EU standards).
The small designs of bearings in this form open the use of ball bearings in precise applications like electronics and medical equipment. Also, miniature bearings produce minimal noises during operation.
Disadvantages: Low load capacity and vulnerable to contamination.
When to Use: For small machinery & precision applications.
Thin Section Bearings
This type of bearing contains a thin layer of inner and outer race so they can fit in minimal space. The rolling element could be a ball or cylindrical bars. Although the weight is less in thin-section bearings, they do not compromise with the accuracy and friction-reducing capability. Additionally, various configurations, including open, shielded, and sealed section bearings are available in the market for different applications.
Disadvantages: Lower load capability and misalignment sensitivity.
When to Use: High-performance applications like defense, aerospace, and electronics.
Flanged Bearings
A flanged bearing contains an extended flange on the outer race of the bearing radially outward. The flange is for a strong attachment of bearing on the frame or machine wall. For that, the flange also includes a mounting arrangement in it like a bolt or screw. Predominantly, flanged bearings are for radial loads, but they can also handle low levels of axial stress.
Disadvantages: Limited load capability and the flange can interfere with the other components, especially in small-size machinery.
When to Use: For high speeds with low loads and excessive vibration scenarios.
Brief Comparison: Thrust Bearing vs. Ball Bearing
Thrust bearings are mainly for high axial loads, whereas ball bearings are mainly for radial loads. The structure of the ball or other rolling element arrangement includes an alternative positioning between two rings. It increases the exposure surface area to the stress, which improves the axial load-bearing capacity.
There is also a similarity between the thrust bearing vs. ball bearing. A thrust bearing can have a ball as the rolling element. However, this is not always the case. It can also have a roller or other rolling element.
Let’s see the differences in these two bearing types through a comparison table;
| Criteria | Ball Bearings | Thrust Bearings |
| Rolling Element | Balls | Balls or rollers |
| Load Orientation | Radial | Axial |
| Load Capability | High radial Load capacity, high speed | High axial load capacity, high speed |
| Friction | Generally low friction | Low to moderate friction depending on the design |
| Application examples | Electric motors, conveyors, automotive wheels, machine tools, etc. | Thrust reversers in aircraft engines, ball screws, crane hooks, etc. |
| Cost | Highly Cost-effective | Relatively higher cost |
| Complexity | Simple design with fewer components | More complex than standard ball bearings. |
| Maintenance | Low maintenance requirement with periodic lubrication | It Requires alignment verification & lubrication frequently |
Type 2: Roller Bearings
As the name indicates, roller bearings contain rollers of different shapes to transmit stress. The shape can be cylindrical, spherical, conical, or even a needle. The main reason for using rollers, instead of balls is to increase the exposed surface area for higher loads. The rolling motion of rollers carries the rotating load of the shaft.
Moreover, the variations of roller bearings support the radial, axial, or combined loads. Similar to ball bearings, this bearing kind minimizes friction and optimizes the performance of moving parts.
Here are the common variations of roller bearings.
Tapered Roller Bearings
This kind of roller bearing involves both a tapered inner race (called a cone) and an outer race (called a cup) with tapered rollers arranged in a cage between them. The contact angle (tapered angle) of the outer ring typically ranges from 10° and 30°.
Here, the tapered shape can uniformly distribute the heavy axial load of the shaft, and it can also accommodate the radial loads along with it. The compact design makes them consolidated bearings and saves space. Moreover, tapered roller beading provides greater stability and can adjust a certain level of misalignment itself.
Disadvantages: Complexity, relatively higher prices, and limited load capability in some designs.
When to Use: Heavy equipment with high axial & radial loads, such as railway systems and mining tools.
Spherical Roller Bearings
The structure of roller bearings consists of spherical rollers of two rows in a cage divided by a separator. The rolling of these elements reduces the friction and supports large loads from the shaft. Additionally, spherical roller bearings have the capability of self-adjusting the angular misalignment of the shaft concerning the outer ring.
Disadvantages: Not suitable for high-speed applications.
When to Use: Misalignment-prone applications with heavy loads and moderate to high speeds like off-road cars & marine propulsion.
Spherical Roller Thrust Bearings
The thrust roller or spherical roller thrust bearings include a similar structure to the thrust ball bearing, except for lengthy spherical rollers instead of balls. These are for the unidirectional heavy axial loads and a considerable amount of radial loads.
These roller bearings also permit misalignment and are flexible with the operating speeds, so are popular in industrial setups.
Disadvantages: Only flexible with heavy loads in the axial direction. Next, the misalignment increases the friction.
When to Use: As the industrial bearing, in high-duty applications. For instance, turbines and compressors.
Cylindrical Roller Bearings
The cylindrical rollers can carry higher radial loads because of linear contact between rollers and rings. However, they also support a moderate level of axial forces. Meanwhile, the cylinder roller configuration can have one or multiple rows. The large surface contact of the cylindrical roller with the outer race uppers the load-bearing limit. But, at the same time, it increases the friction.
Disadvantages: Only focuses on the radial load and sometimes the stress can be concentrated on the edges of rollers.
When to Use: In high radial load conditions, like tool spindle and drilling rigs. Thor half-shape variation is also popular as a saddle bearing in hydraulic pumps.
Needle Roller Bearings
The structure and working of needle roller bearings are similar to the cylindrical roller bearings. The only difference is the size of the cylindrical rollers inside the bearing needle bearings are tiny roller bearings. Cylinders are very thin with small diameters as compared to the length. Here, the diameter is ≦6 mm is only considered as the needle. The lower-weight roller also allows high speed. So, these types of bearings provide higher radial-load support in a compact space.
Disadvantages: Edge loading & relatively higher friction.
When to Use: Application with variable loads and jerk. For instance, piston pin bearing.
Cross Roller Bearings
The cross roller bearing consists of cylindrical-shaped rollers in a cross pattern. It means the alternative rollers intersect each other at 90°. This arrangement of rollers promotes rigidity and precision in handling axial and radial stresses. Consequently, cross-rollers are ideal for rotational motion control.
Disadvantages: Complex installation and risk of misalignment.
When to Use: For heavy radial loads and accurate motion control.
Type 3: Plain Bearings
Plain bearings are the simplest form of bearing with no rolling elements, just a cylindrical bore to hold the shaft or similar components. They are also known as the sleeves or bushes. The plain surface of the plain bearing stabilizes the heavy radial & axial load and also lowers the friction. So, the use of low-friction material is critical to making plain types of bearings like brass or hard polymer. Additionally, they can be both lubricated and dry types.
Furthermore, the plain bearings come in various configurations like cylindrical, thrust washer, flanged, and sliding plates. Moreover, the bearings can also include features like grooves, holes, notches, or tabs in the contact surface to reduce friction and support the application requirement.
Advantages of Plain Bearings
- Simple design and easy installation.
- The plain bearings are applicable for rotating, sliding, oscillating, and reciprocating motions.
- They support heavy radial loads and moderate axial loads, suitable for applications with high load requirements.
- Lightweight, low-cost, less noise, and durable.
- Suitable for both static and dynamic loads.
Disadvantages of Plain Bearings
- Only fits for low to moderate-speed applications because of high friction than ball or roller bearings.
- Plain bearings require more frequent maintenance and lubrication.
- They have low vibration & shock-absorption capabilities.
When to Use Plain Bearings?
The pain bearings are best for low-speed & heavy-load mechanical operations where the risk of misalignment and oscillation is a critical issue like industrial cranes or agricultural machinery. Also, these are excellent choices for bespoke bearings, where cost is a big concern.
Brief Comparison: Plain Bearing vs Ball Bearing
First, the rolling elements’ presence is the structural difference in plain bearing vs ball bearing comparison. Another point is that ball bearings can be applied in more areas due to diverse configurations. For more specific differences, let’s look at the comparison table below;
| Criteria | Plain Bearings | Ball Bearings |
| Design | Cylindrical metal sleeve and shaft | Inner and outer rings with steel balls |
| Friction | Relies on lubrication to reduce friction | Lower friction due to rolling elements (balls) reduces friction |
| Load Capacity | Heavy loads and low-speed operation | Low to moderate weight & high-speed operation |
| Misalignment | They can fix the misalignment and oscillation | Less flexible with misalignment |
| Cost | Highly cost-effective | Costlier and price increases with complexity |
| Applications | Hydraulic cylinders, automotive suspension systems, conveyors, etc. | precision machinery, electric motors, turbines, etc. |
Type 4: Fluid Bearings
The fluid bearings replace the metallic bearings with a thin layer of fluid, air, gas, or lubricant between the housing and rotatory surface. While applying fluid bearings, moving parts don’t contact each other. Instead, the fluid properties hold the load and provide smooth motions to the components. The fluid film is injected into the joint with dedicated holes or channels.
Furthermore, hydrostatic and hydrodynamic are two bearing kinds of this category, which are widely used in precise & high-speed machines to reduce friction and handle heavier loads.
Hydrostatic Bearings
Hydrostatic types of bearing work on the principle of pressurized fluid. It says that if fluid is injected under high pressure between moving parts, it reduces the friction and maintains the relative motion. Here, external pressure is essential for maintaining the operation. Meanwhile, the precision depends on the gap control.
Advantages of Hydrostatic Bearings
- First, hydrostatic bearings can handle way larger loads than ball bearings.
- Although the initial cost is expensive, the long life justifies the price.
- Excellent damping properties & low wear.
- They can precisely control the positioning and motion.
- The performance does not rely on fluid film thickness like in hydrodynamic bearing.
Disadvantages of Hydrostatic Bearings
- Complex setup and installation due to the requirement of external pressure arrangements.
- Any leakage from the bearing can lead to contamination in the mechanical system & environmental effects.
- Energy-intensive mechanical bearing technique.
When to Use?
Hydrostatic bearings are excellent choices for both rotary and liner motions. They can control the motions in precision applications like machining spindles and gas turbines. Additionally, sensitive applications like aircraft control systems also use these types of fluid bearings.
Hydrodynamic Bearings
First, let’s define a term related to bearing part called “journal”. It refers to the portion of the shaft that remains inside the housing. Hydrodynamic bearings provide load support and low friction with the use of this journal. The fluid makes the bearing film using the relative motion of the journal with the contact surface. The performance of this hydrodynamic bearing type relies on the rotation speed, fluid viscosity, and proper alignment.
Advantages of Hydrodynamic Bearings
- They do not require external systems to develop the lubricating film.
- Hydrodynamic bearing has a simpler design than hydrostatic bearing.
- They absorb high-damping energy and reduce vibration in rotating components.
Disadvantages of Hydrodynamic Bearings
- At low speeds, the fluid film of lubrication is challenging to achieve. So, it also causes wear at the start.
- Any surface imperfection of the shaft or housing can lead the misalignment.
- Risk of film delamination due to heat generation.
When to Use?
Hydrodynamic bearings are best for moderate to high-speed applications like pumps or turbines. They are also preferred for marine systems and industrial equipment.
Type 5: Magnetic Bearings
The magnetic bearings use electromagnetic force to rotate or suspend a rotor in a fixed position. The general stricture of a magnetic bearing includes an electromagnetic field inside the bearing, typically wounded wires on ferrous material. Once the magnetic field is activated, the force itself levitates the rotor component and is fixed for optimal rotor dynamics. So, the moving rotor makes no contact with the surface. This makes magnetic bearings capable of operating at extremely high speeds and loads
Furthermore, there are two types of magnetic bearings;
Active Magnetic Bearings
The active magnetic bearings use active control mechanisms to stabilize and control the position of a rotating shaft. The integrated sensors and feedback control mechanism monitor and process the real-time data, and the control unit adjusts the positioning accordingly.
The real-time monitoring and self-positioning advantage of active magnetic types of bearings facilitates high precision in motion control and system stability. Next, the contact-less moving produces minimal friction and keeps the system efficient and durable.
On the other hand, active kinds of bearings have a few drawbacks, such as setup complexity, high energy consumption, and thermal sensitivity.
When to Use?
- Heavy industrial applications like turbochargers and machine tools.
- Low-temperature operations.
- Energy storage applications, such as flywheel.
Passive Magnetic Bearings
In passive magnetic bearing, there is no active system or feedback mechanism to adjust the motion. Instead, the permanent magnets inside the bearing are arranged in a way that their repulsive and attractive forces levitate and control the position & rotation.
These magnetic bearing requires less maintenance and are cheaper than the active ones. They are simple in design and operate silently, whereas the use of permanent magnets makes them more reliable. If we talk about their disadvantages, passive magnetic bearings have lower load capacity, and the absence of real-time feedback gives less control over the operation.
When to Use?
- High-speed rotating conditions with moderate load.
- Noise-sensitive environments.
- Compact devices like miniature motors and actuators.
Uses of Bearings
Bearings are necessary for any machines, mechanical systems, and tools with a rotating motion to support the operating load and reduce friction, vibration, and noise. Thus, they can be found in numerous applications, including automotive, aerospace, industrial machinery, and consumer items.
Automotive
The automotive vehicle contains several bearing types in different sections and components. The automotive bearings are responsible for supporting the load and facilitating the motions in different parts.
Examples;
- Tapered roller in the vehicle steering system
- Tapered and needle roller bearings in gearboxes
- Single or double row ball bearing in wheel hub
- Spherical roller bearing in suspension system
Aerospace and Aviation
The bearings are essential in the safety, flight control, performance, and reliability of aerospace applications. You can find bearings in aircraft, missiles, rockets, and other related equipment. Here are the uses of some aviation bearings;
- Airframe bearings and self-lubricating bearings in landing gear.
- Needle and tapered roller bearings for the fuel pump.
- Spherical plain and angular contact bearings in propeller shafts.
Industrial Machinery and Equipment
The rotational motions are the key to the functionality of industrial machinery and equipment. They utilize different types of bearings for the smooth movement of rotating components.
- Cylindrical roller bearings support conveyor belts to pass the materials.
- Milling, drilling, and turning all machines contain angular contact ball bearings.
- Thrust bearings in compressors to withstand axial loads of impellers or rotors.
- Mining, packaging, and other related tools.
Consumer Products
We can also see the different shapes & sizes of bearings in consumer products, from washing machines & refrigerators to furniture items.
- Ball bearings in bicycle hubs
- Sleeve bearings in the cooling fan
- Roller bearings in treadmills
- Hand power tools, drills, grinders, etc.
Considerations When Choosing Metal Bearing
1. Load Capacity
First, you need to consider the load-handling capacity of the bearing. It often consists of axial, radial, or combined loads (moment) rating to gauge the load capacity. Here, the capacity should match the requirements of the application. For example, heavy-duty appliances like washing machines or power tools require bearings with high load capacities.
2. Speed Requirement
All the bearings do not support the high-speed shaft or rotor. Types of bearing like thin-section bearing support very low speeds, whereas roller & deep-groove metal bearings can operate at high rotational speeds. Furthermore, you can reference the ISO 15312 standard for “bearing speed guidelines” to check which bearing can match the intended speed.
3. Rotational Accuracy
It defines the capability of the bearing to maintain a steady position and speed for the shaft or any other rotor. So, identify allowable radial and axial oscillations in your application and look for the bearing with sufficient rotational accuracy. Some applications like aircraft control or electronics might need a high level of accuracy, but other areas like furniture might not need the same accuracy.
4. Operating Environment
The condition of the operating environment like moisture, dust, chemical exposure, temperature, and stress, also affects the selection of bearing. For example, marine applications might require high bearings with highly corrosion-resistant materials. So, list all the operating scenarios and look for the bearing that can operate in that condition without compromising the efficiency.
5. Precision and Noise Requirements
Precision metallic bearings are essential in applications like electronic devices or audio equipment for high performance and minimal vibration. So, consider the noise level of the bearings and check whether that suits the installation scenarios or not. For instance, deep-groove bearings produce very low noise.
6. Radial Space
It refers to the available space within the machine or design to accommodate itself. Even a slight constraint of space for bearing affects the overall performance and safety. So, choose bearings that not only fit but do not interfere with the operation of other companies. For instance, miniature & needle forms of bearings are flexible with the space, but many are not.
7. Bearing Rigidity
Rigidity means stiffness of the bearing structure and its ability to maintain stable and precise operation under load. The rigidity of the bearing also affects the uniformity of load distribution. Therefore, consider the potential load during operation and rigidity to maintain the stability under that load. Also, some specific bearings offer a high level of rigidity due to their structure, such as tapered bearings & angular-contact bearings. Meanwhile, the bearing material properties also influence the overall rigidity of the bearings.
8. Bearing Vibration
The vibration of the bearing while working affects both performance and user experience. Some products like consumer items need bearings with minimal vibration for smooth operations. So, choose the bearings with vibration within the allowable range according to the requirement.
Materials Used in Bearings
Although metal and alloys are popular as bearing materials, they also can be made with composite, rubber, and plastics. The bearing material is a critical aspect of the performance and durability of bearings. The material properties like hardness, friction-coefficient, and strength directly impact the bearing or machine’s performance.
Metallic Materials
| Material | Properties | Application Example |
| Chrome Steel SAE 52100 | Excellent strength and hardness, wear & corrosion resistance, fatigue resistance, etc. | Ball bearings in automotive applications. |
| Stainless Steel AISI 440C | Excellent corrosion resistance, high hardness & wear resistance, and good thermal & chemical stability. | Food processing equipment bearings. |
| Babbitt Metal | The composition is 93 %tin, 5 % antimony, and 2 % copper. It has good self-lubricating properties. | Plain bearings in machinery. |
| Bronze | Good corrosion resistance, high thermal conductivity, and low friction. | Bushings for marine applications. |
| Copper-Lead Alloys | Good wear resistance and load-carrying capacity, low friction, and vibration-damping properties. | Thrust washers for automotive transmission systems. |
| Cast Iron | High compressive strength and load capacity, and good damping properties. | Heavy-duty bearings. |
| Aluminum Alloys | High strength-to-weight ratio, good corrosion resistance, and thermal conductivity. | Aerospace bearings. |
| Silver | Excellent thermal and electrical conductivity, high corrosion resistance, and relatively malleable. | High-precision electrical bearings. |
Non-Metallic Materials
The non-metallic bearing materials are mainly used in specific scenarios like applications requiring chemical inertness, electrical insulation, and low weights. Here are the kinds of common non-metallic materials and their properties.
| Material | Properties | Applications |
| Nylon | Good wear resistance, lightweight, self-lubricating, and low friction coefficient. | Conveyor rollers, textile machinery, etc. |
| Phenolic Materials | High compressive strength & electrical insulation, lower thermal expansion, etc. | Switchgear assemblies and electric motors. |
| Nitrile Rubber | Excellent resilience, abrasion resistance, oil and grease resistance, etc. | Seals and bearings in automotive applications. |
| Teflon | High chemical and temperature resistance, low friction coefficient, non-sticky, etc. | Bearings for chemical pumps and medical devices. |
Conclusion
The mechanical bearings are essential components of rotatory hardware, machines, and setups. The main purpose of installing bearings is to lower the friction and support the operational forces, whether they are plain, ball, roller, fluid, or magnetic bearings.
However, only the right type of bearing according to requirements can achieve the intended results. Therefore, considering factors like load capacity, vibration, noise, size, and other aspects while choosing the types of bearings can optimize the performance during the operation.
If you are still confused about bearings and which one to choose, consult with our engineers now!
