Lesson 1: What is a bearing?
Basic knowledge that must be understood and the function of bearings.
Do you know what type of mechanical component a bearing is? Bearings, known as “the foundation of the machinery industry”, are important components widely used in various machines. In Bearing Column Lesson 1, we will explain the basic knowledge and function of bearings.
1. What is a bearing?
A bearing is a component that helps objects rotate. As the name suggests, a bearing is a component that supports the “shaft” that rotates inside a machine.
Machines that use bearings include cars, planes, generators and more. Bearings are also used in household appliances such as refrigerators, vacuum cleaners and air conditioners. In these machines, the bearings are responsible for supporting the “shaft” which has various components, such as wheels, gears, turbines, rotors, etc., installed on it, helping the shaft to rotate smoothly.
As a large number of rotating “shafts” are used in various types of machines, bearings have become an indispensable component known as “the basic element of the machinery industry”. Although bearings may seem inconspicuous, they are actually essential. Without them, we would not be able to lead a normal life.
2. Why are bearings important? What is the function of bearings?
To run machines smoothly, what exactly is the role of bearings?
There are two main functions of bearings:
Friction occurs between the rotating “shaft” and its support, but the bearing is installed between them to reduce friction, making rotation smoother and reducing energy consumption. This is the function of the bearings.
The rotating “axis” and its supporting structure withstand a significant amount of force. The bearings prevent damage to the rotating support due to this force and help keep the rotating “axis” in the correct position. It is because of these functions of bearings that we can use machines repeatedly for a long time.
3. How many bearings are used? What if the bearings were not used?
It is unimaginable how many bearings support our daily lives, as bearings cannot be seen directly with our eyes. Let's take a common car as an example. Have you ever played with a battery-powered racing toy when you were young? Many people may remember that a bearing was installed in the support structure of the car's wheels. So how many bearings does a car really need?
①Powertrain system (components)
Examples: AC generator, turbocharger, etc.
②Steering system (components)
Examples: steering box, pump, etc.
③Power transfer system (components)
Examples: Transmission, differential gears, etc.
④Suspension system (components)
Examples: Wheels, suspension, etc.
State-of-the-art automobiles can use up to 150 bearings and they all play an essential role. If there were no bearings in automobiles, the components would not rotate smoothly, they would consume more energy and the parts that support the rotation would soon be damaged, which would mean that the vehicle could not operate safely and comfortably. Therefore, countless bearings run silently behind our wonderful lives.
Conclusion
Bearing components are operating for our lives. Because bearings are essential components that support our lives, high durability and precision have been demanded of them throughout history. Furthermore, with the continuous development of mechanical technology, new and increasingly specialized bearings will be developed and applied to adapt to harsh environments.
In the future, bearings will continue to improve and develop to keep our lives running.
Lesson 2: Leonardo da Vinci, the “Father of Bearings” – The unexpected story of bearings.
As we already discussed in Lesson 1, bearings are tools that reduce friction and help objects move smoothly. But when and how were they invented and how did they evolve and spread? This lesson will introduce you to the unexpected history of bearings.
1. Did bearings originate before AD?
In ancient times, humans created many ways to reduce friction, and we can see an example from the construction of the Egyptian pyramids.
The huge pyramids, which were built by accumulating huge “heavy blocks of stone”, still inspire awe in countless people around the world today. So how did people in ancient times move these “heavy blocks of stone”? The answer has been roughly inferred from numerous wall paintings found in ancient Egypt.
Several wall paintings in ancient Egypt depict the construction of the pyramids, some showing scenes of people placing circular wooden objects under the “heavy blocks of stone” and rolling them. It can be inferred that the ancient Egyptians reduced friction and moved the “heavy blocks of stone” with less force by using wooden rolling objects.
This transportation method resembles the use of rolling elements (rollers) in bearings.
Records of human attempts to reduce friction can be found around the world, although they vary in terms of time period and methods employed. This demonstrates the significant value placed on smooth transportation of goods through reducing friction throughout human history.
2. Did Leonardo da Vinci invent the retaining cage bearing?
Leonardo da Vinci was a genius artist from Italy during the Renaissance period. He had a deep connection with bearings and was rightly called the “Father of modern bearings”.
Da Vinci was deeply curious about everything and made significant contributions to mechanical design. His manuscript contained sketches of indispensable bearings for mechanical devices.
With unparalleled creativity, he created a support structure that significantly reduced friction. The frame is a device that sandwiches a rolling ball (rolling element) between two circular plates (track rings). Surprisingly, the bearing design sketch also included a “retaining cage” that prevents the rolling balls from coming into contact with each other.
This structure is almost identical to that used in modern bearings.
Therefore, the “basic bearing structure” consisting of race rings, rolling elements (such as “balls” or “rollers”) and a retaining cage was invented approximately 500 years ago. The brilliant Leonardo da Vinci revolutionized the course with his creativity.
However, even after the invention of the basic structure of bearings, actual manufacturing and mass production were not easy. It was only with the Industrial Revolution that bearings were widely used in machines.
3. The popularity of bearings began with the Industrial Revolution
During the Industrial Revolution, from the mid-18th century to the 19th century, steel began to be produced on a large scale. Therefore, high-strength steel bearings could be mass-produced and widely used in various fields.
One of the great inventions that emerged during the Industrial Revolution was the “vehicle axle that uses bearings”. The first widely used bearings were multipurpose ball bearings used in bicycle axles. Later, roller bearings for car axles using rollers as rolling elements were also invented.
The emergence of the “vehicle axle using bearings” has greatly improved mobility and transportation efficiency. As a result, many industrial machines at that time also actively introduced bearings and made great contributions to industrial development.
During the Industrial Revolution, bearings became an important component supporting behind-the-scenes industrial development and an indispensable tool in people's lives.
Conclusion
The history of the development of bearings is the history of the progress of human civilization. Without the invention of bearings, humans would still have difficulty moving heavy objects, and our lives would not have so many machines to provide us with convenient and comfortable services.
The birth and progress of bearings had a tremendous impact on the development of civilization. It can be said that bearings are the crystallization of the wisdom and technology of our predecessors and the unsung heroes behind the “story of industrial development”.
Class 3: Bearing Structure – Structure to Reduce Friction and Function of Each Part.
In Class 3 we will present the bearing structure and the function of each component.
1. Principle of Bearings
Bearings reduce friction by using rolling motion. As shown in Figure 1, when the “shaft” begins to rotate, several “rolling elements” (such as “balls” or “rollers”) in the bearing will begin to roll. Bearings reduce friction when using this rolling motion.
Compared to “sliding motion” plain bearings, bearings using “rolling motion” are better at reducing friction and minimizing rotational energy consumption. So what is the structure of bearings? Below we will provide a detailed introduction.
2. Bearing structure
Although there are many types of modern bearings, their basic structure is similar to the bearing structure designed by Leonardo da Vinci about 500 years ago.
The components of a bearing include:
- Racing rings… ring-shaped components
- Rolling elements…components that roll between running rings (rolling elements include “balls” and “rollers”)
- Cage… component that prevents rolling elements from contacting each other and keeps them at a certain distance from each other
Racing Rings
Race rings support the force acting perpendicular to the shaft in the case of “radial bearings” shown in Figure 2. In ball bearings, the rolling elements are balls, while in roller bearings, the rolling elements are rollers.
The raceway ring is used for this type of radial bearing.
The race ring mounted on the inner side of the shaft is called the inner ring.
The race ring on the outer side is called the outer ring, which is mounted on the casing (※1: see Figure 3).
Housing
The housing refers to the part that comes into contact with the bearing outer ring when the bearing is mounted.
track ring
The bearing shown in Figure 4 is called a “thrust bearing,” which supports force in the same direction as the shaft.
The raceway ring is used for this type of thrust bearing.
The raceway ring mounted on the shaft side is called the shaft ring.
The race ring mounted on the casing side is called the seat ring.
To achieve smooth rotation, the surface on which the rolling elements of the bearing race ring roll is meticulously smoothed.
rolling element
As shown in Table 1, rolling elements include “balls” and “rollers”.
Table 1 Types of rolling elements
|
Ball | Ball bearings |
|
Cylindrical roller | Cylindrical roller bearings |
|
needle roller | |
|
Conical (conical) roller | |
|
Spherical (barrel-shaped) roller |
Depending on the usage conditions such as load capacity and rotational speed, various types of rolling elements are available for selection. We will discuss the types of bearings in the bearings section of Class 4, and interested students can refer to the next page.
Support
As shown in Figure 5, when the bearing inner ring rotates, the rolling elements also begin to roll. If there is no seal in the bearing, adjacent rolling elements will come into contact with each other.
When the rolling direction of two rolling elements on a contact surface is opposite, it makes the rolling movement of the rolling elements difficult.
To prevent this from happening, a retainer is used to keep adjacent rolling elements apart so they can roll smoothly. Various types of seals are available for selection depending on usage conditions such as load capacity and bearing rotational speed. Figure 6 shows a representative type of containment.
It is clear that the race ring, rolling elements and seal respectively play different roles. These functions complement each other so that the bearing rotates smoothly.
However, with just these constituent parts, the bearing still cannot rotate continuously and smoothly with stability. Next, we will introduce another important component of bearings.
3. Lubricants required for stable rotation
To ensure stable and smooth rotation of the bearings, the friction of the rolling movement must be reduced and wear of the parts must be avoided. That's where lubricants come in.
The lubricants used in bearings are mainly semi-solid (paste-like) “grease” and liquid “oil”.
Furthermore, lubricants also reduce the internal heat inside the rotating bearing and extend the life of the bearing. Therefore, lubricants are also an “important component” to ensure stable and smooth rotation of bearings.
Conclusion
Components and lubricant are necessary to ensure stable and smooth rotation of the bearings.
Bearing components include the race ring, rolling elements, and seal, each performing a different function. These functions complement each other to allow the bearing to rotate smoothly.
Furthermore, “lubricants” help reduce friction in the rolling movement and prevent wear on parts. Each component plays its critical role in allowing the bearing to rotate continuously and smoothly with stability.
Class 4: Differences between Various Types of Bearings – Types and Characteristics of Bearings.
1. Classification of Bearings
Bearings will receive forces from different directions, so they can be classified according to the “direction of force”.
First, let's introduce the bearing force.
Figure 1 shows the force on the bearing used on the wheel of the car with a tire installed. One is the force supporting the weight of the car (shown by the blue arrow in Figure 1), and the bearing must support the force perpendicular to the axis of the car wheel.
Furthermore, centrifugal force occurs when the car rotates (shown by the red arrow in Figure 1), and the bearing will bear the force in the same direction as the car's axis.
As shown above, bearings generally support forces from different directions. Therefore, bearings can be classified according to the direction of force and load capacity. Bearings support radial and axial loads; the force that the bearings support is called “load”; the force perpendicular to the axis is called “radial load”; the force in the same direction as the axis is called “axial load”.
Bearing Classification
According to the direction of force that the bearing can withstand and the shape of the rolling element, bearings can be divided into the four types shown in Table 1.
Table 1: Bearing Classification
| Rolling Element | |||
| Ball | Roll | ||
| Main Force Directorate | Perpendicular to the axis (radial load) | Radial ball bearings | Radial ball bearings |
| Same axis direction (axial load) | Thrust ball bearings | Thrust ball bearings | |
2. Radial ball bearings
Radial ball bearings
Radial ball bearings are “ball” bearings that support force “perpendicular to the direction of the shaft”. Deep groove ball bearings (ball bearings) are a type of radial ball bearing.
Deep groove ball bearings are commonly used types of bearings.
Deep groove ball bearings can not only withstand radial loads, but also withstand a certain degree of bidirectional axial loads. When supporting a larger axial load, angular contact ball bearings must be used, which will be introduced later.
Angular Contact Ball Bearings
Angular contact ball bearings can simultaneously support radial loads and unidirectional axial loads. When supporting bidirectional axial loads, two or more angular contact ball bearings must be used in combination.
When bearings support “radial load” and “axial load”, the angle between the direction of the load supported by the raceway ring and rolling element and the direction perpendicular to the shaft is called the contact angle.
The contact angle is generally divided into 15°, 30° and 40°, which are represented by the letters C, A and B, respectively.
3. Radial roller bearings
Radial roller bearings are “roller” bearings that support force “perpendicular to the direction of the shaft”. Radial roller bearings bear greater loads than radial ball bearings and have different types based on the type of roller, such as cylindrical roller bearings, needle roller bearings, tapered roller bearings and spherical roller bearings.
Cylindrical roller bearings
Roller bearings use “cylindrical rollers”. Cylindrical roller bearings support greater radial loads than deep groove ball bearings and can be used in machines that generate impact force.
Needle bearings
Roller bearings use “needle-shaped rollers”. Needle bearings use needle-shaped rollers with a smaller diameter than cylindrical rollers, as shown in Figure 5. The low cross-sectional height of this type of bearing helps achieve machine miniaturization and illumination.
Tapered roller bearings
Tapered roller bearings use “tapered rollers”.
Tapered roller bearings are widely used in radial roller bearings and can simultaneously support radial loads and unidirectional axial loads. When supporting bidirectional axial loads, two or more tapered roller bearings must be combined.
Spherical roller bearings
Spherical roller bearings utilize barrel-shaped “spherical rollers,” as shown in Figure 7, mounted between the “spherical outer ring raceway surface” and the “inner ring raceway surface.” Therefore, the inner ring, rolling element and cage of the spherical roller bearing can rotate while inclined with respect to the outer ring.
As shown in Figure 8, spherical roller bearings are used in machines that support large loads and have shafts prone to bending. Figure 8: Application of spherical roller bearings.
Summary
There are several types of “bearings” available depending on the direction and magnitude of the applied load. The appropriate “bearing” type should be chosen based on the structure or use of the machine. In addition to the types presented here, there are many other types of “bearings”.
Class 5: Uses of Bearings (Part 1)
The automotive application areas for bearings.
1. How are bearings used in automobiles?
In this column we will explain how bearings are used with the example of transmission and differential gears that transmit engine power to the vehicle's axles in automobiles.
2. Bearings used in transmissions
The motive force required for automobiles depends on the driving conditions such as high-speed driving or need for greater motive force on slopes, etc. Transmission is a device that converts engine power into motive force suitable for driving and transmits it to the axle. Within the transmission, different types of bearings are used to perform their respective functions, and many bearings are also used in automobile parts.
Transmission can be divided into two types: manual and automatic. In cars that use a manual transmission, the gear lever is located on the driver's side.
The operator manually operates the gear lever to convert engine power into motive force suitable for driving conditions. The manual transmission is made up of shafts and gears. Below we present the bearings that support these components.
Bearings that support the shafts
The appropriate types of bearings are chosen based on the power of the motor to support the shaft rotation and the force generated by the gears.
Table 1. Bearings that support the shafts.
| Radial load | Axial load | Types of bearings |
| Small | Small | Deep groove ball bearing (ball bearing) |
| Big | Small | Cylindrical roller bearing |
| Big | Big | Tapered roller bearing |
Bearings to support gears
In a manual transmission, the gears are always meshing and rotating.
To transmit the appropriate driving force for driving, select the appropriate gear (A) by operating the lever. The selected gear (A) is then connected to the shaft and rotates at the same speed as the shaft.
When the driving condition changes and a different driving force needs to be transmitted to the wheels, the gear (A) connected to the axle is removed from the axle by operating the lever and the gear (B) suitable for the different driving force is selected. The selected gear (B) is then connected to the shaft and rotates at the same speed as the shaft.
At this moment, the gear (A) that is removed from the shaft rotates at a speed different from that of the shaft. To allow the gear and shaft to rotate at different speeds, needle roller bearings (components with needle rollers and cages) are installed between the inner surface of the gear (inner side) and the outer surface of the shaft (outer side) to scroll between them.
3. Bearings used in differential gears
When a car turns left or right, the inner wheel's axle speed is reduced, while the outer wheel's axle speed increases. Differential gear is a device that converts the driving force of the transmission into a larger driving force and transmits it to the left and right wheel axles to achieve different speeds.
The differential gear is installed with the small gear shaft (the transmission side shaft) and the shaft side gear that engages vertically. Bearings support the rotation of the shaft and the force generated by the gears.
Tapered roller bearings for support shaft
The tapered roller bearing combination supports radial and bidirectional axial loads, ensuring proper gear engagement and transmitting large driving forces to the left and right wheel axles.
Summary
This article has introduced the bearings used in devices that transmit power from the engine to the wheel axles, but in automobiles many other parts also use a large number of bearings.
Each bearing plays its own role and improves the driving performance and safety of the vehicle. In order to further improve the safety and comfort of automobiles, the performance and reliability requirements of bearings will continue to increase in the future.
Class 6: The Uses of Bearings (Part 2) – Bearings Used in the Manufacturing of Products
We will introduce the bearings used in machines in the three areas of “energy manufacturing”, “raw material manufacturing” and “product processing”.
1. Bearings Used in Energy Manufacturing – Wind Turbines
Generators are crucial machines for producing energy to power our daily lives. Wind turbines have gained immense popularity across the world.
However, due to the high location of wind turbines, they present significant maintenance challenges. Therefore, bearings used in wind turbines must have high reliability, with minimum failure rates and long service life.
There are many bearings used in wind turbines, and here we will discuss the main spindle bearings responsible for accepting the rotational force of the wind and transmitting it to the generator.
Main shaft bearings
Wind turbines use wind energy to rotate their main spindle and transmit rotational energy to the generator for power generation.
The main spindle bearing is responsible for supporting the weight of the blades and rotating components, while also withstanding uneven wind forces that vary in size and direction. Due to these severe functional requirements, spherical roller bearings are the main choice for main shaft bearings, known for their ability to withstand large forces and excellent self-aligning characteristics.
■ What is the self-alignment property?
Self-aligning refers to the quality of the inner ring, rolling elements and cage to rotate smoothly even when the outer ring is tilted.
To support the significant load, main spindle bearings typically employ large spherical roller bearings, generally larger than 1 meter in size.
2. Bearings Used in the Manufacturing of Raw Materials – Steel Rolling
Steel rolling mills are machines that form the backbone of raw material manufacturing, producing steel materials of various shapes for different uses. Let's introduce this equipment.
Bearings used in manufacturing raw materials – Steel Rolling In a rolling mill, steel materials are pressed and rolled between two counter-rotating rollers.
Furthermore, as the saying goes, “strike while the iron is hot”, steel materials are often rolled at high temperatures. Therefore, the bearings used in this situation must withstand high temperatures and forces to allow the rollers to rotate.
Work Roller Bearings
The work rolls in steel rolling mills are supported by four-row tapered roller bearings to withstand the extremely high radial loads and bidirectional axial loads generated during the rolling process.
Backup Bearings
Despite the tendency of work rolls to deform under the significant loads generated during rolling, support rolls effectively suppress this phenomenon. Support rollers use four-row cylindrical roller bearings that support large radial loads and multi-row tapered roller bearings that support axial loads.
3. Bearings Used in Product Processing – Machining Centers (Machine Tools)
Finally, we will present the equipment commonly used in product processing.
The equipment used to process various products and parts according to their specific use are known as “machine tools”. In recent years, machining centers that perform computer-controlled processing have become increasingly popular.
Machining centers can achieve precision and fine processing that are difficult to achieve manually, while also significantly reducing processing time.
To avoid changes in part dimensions and reduced processing accuracy due to heat generated during machining, the main spindles (where the tool is installed) in machining centers require bearings with low thermal expansion properties.
Main shaft bearings
The main spindle of a machining center uses angular contact ball bearings to support radial and axial loads during processing.
This type of bearing uses ceramic as the bearing material. These ceramic bearings can suppress changes in part sizes while exhibiting low thermal expansion during high-speed rotation.
Additionally, these bearings can deliver the necessary lubricant only to the appropriate locations where heat occurs and discharge it quickly, which helps prevent overheating.
Summary: Bearings that support our lives
The machines used to manufacture energy, materials and products may seem unusual in our daily lives; however, as we have seen, many bearings support the operation of these machines. These bearings not only support the rotation of the machine, but also provide valuable support for our daily activities.
Class 7: Special Bearings with Special Materials and Lubricants for Specific Environments
1. What are bearings with special materials and lubricants for special use environments?
Common bearing components are made of metallic materials and use lubricating oil or grease as lubricants. However, if these common bearings are used in environments where electricity is generated, magnetism is generated, and are susceptible to acid and alkali corrosion, they will be quickly damaged and unable to rotate smoothly.
To guarantee their use under the above conditions, bearings are developed with special materials and lubricants for special use environments.
2. Providing Support for “A Better Life” – Air Conditioning Bearings.
The outdoor unit of the air conditioner is equipped with a fan that sends air out and the bearings support this fan. In recent years, motors that can control fan rotation speed (frequency conversion) have become increasingly prevalent. However, due to its characteristics, the motor can generate voltage from high frequency current during operation.
When voltage builds up to a certain level, current flows through the inside of the bearing, which can cause bearing failure. This phenomenon is called “electrical erosion”. Therefore, ceramic bearings with excellent insulation performance (not easily conductive) are required as rolling elements of the bearing.
Furthermore, ceramic bearings are also used in critical equipment such as mechanical motors for infrastructure-related facilities and hospitals to prevent sudden equipment failures.
3. Providing Support for “Healthy Living” – Bearings for Medical Equipment
Image 3 – MRI (Magnetic Resonance Imaging Device)
As aging becomes more severe, people's attention to health increases and medical equipment increases constantly around the world. MRI (magnetic resonance imaging device) uses strong magnetic force to capture organs and blood vessels for internal examination.
If ordinary bearings are used under the strong magnetism of MRI, it will interfere with the magnetic field and an accurate examination cannot be performed. Furthermore, the bearings cannot rotate smoothly.
Therefore, when used for MRI, bearings that are not affected by strong magnetism are required.
The raceway ring and rolling elements of the bearing sleeve use ceramics, which are not easily affected by magnetism. The cage uses resin with excellent lubrication performance, contributing to accurate medical examinations.
4. Providing Support for a “Full Life” – Skateboard Bearings
In the skateboards used by Olympic athletes, the bearings were developed according to the athletes' expectations. Each of the skateboard's four wheels uses two bearings (a total of eight).
The skateboard is equipped with bearings that use ceramic balls and have a special surface treatment on the ring and track cage, enhancing the sensation of “light and smooth rotation” and “comfortable ride”.
Additionally, it allows athletes to maintain speed until the end of the race, allowing them to challenge more difficult skills. Therefore, it contributes to successfully completing difficult skill movements such as the “heel turn”.
