Bearings are built into all kinds of products, from home appliances to automobiles, and are indispensable parts for the manufacture of machines. It is also called the “rice of the machinery industry”.

In this article, we will explain the importance of doing quality inspection for bearings by breaking down the role and types of bearings, manufacturing methods, possible defects, and inspection methods. If you want to better understand bearings, please read to the end.

Role of Bearings

A bearing is a part that smoothly rotates an axis inside the machine. Since it is subject to rotation of the shaft, it is sometimes called “bearing”.

The basic structure of the bearing is the inner ring, ball and outer ring. When the outer ring is fixed to the machine and the shaft is fitted into the inner ring, the shaft rotates smoothly and stably. The role of this rotation is to bring the friction between the parts closer to zero.

Bearings are used in various places and are also incorporated into products that are indispensable to our lives, such as wind power generators, airplanes, automobiles, trains, and personal computers.

For example, about 100-150 bearings are used in automobiles. Without bearings, wheels and transmission rattle and the car cannot run smoothly.

In addition, bearings are indispensable for the high functionality of machines. It can be said that it is a part that also affects the energy saving of products. Because without bearings, friction increases and energy consumption increases. Sometimes used in harsh environments, bearings are truly unsung heroes.

By the way, if we look back at the history of bearings, it goes back to BC. At that time, when building a huge building, it was necessary to carry huge stones, but naturally, there were no cranes or anything like that.

Therefore, cylindrical timber was laid out on the ground, and stones were placed on top of them to carry them. This became the starting point, and since then, bearings that utilize this action have become popular throughout the long history from ancient times to modern times. And now it is used in various products.

Main Types of Bearings

Here are the main types of bearings. Bearings can be mainly divided into rolling bearings and plain bearings and other types. Learn more about each type below.

Rolling bearings

In general, the friction of rolling when the machine rotates is less than the friction of sliding. Rolling bearings take advantage of this characteristic.

Structure of rolling bearings

Rolling bearings are composed of a ball (rolling element), an outer ring, and an inner ring, and have a structure that uses rolling to reduce friction.

In recent years, rolling bearings have been generally adopted. By the way, the aforementioned BC case also uses the principle of rolling bearings.

There are two types of rolling bearings: ball bearings and coro bearings. If the rolling element is in the shape of a ball, it is called a ball bearing. It is widely used, and when we say bearing, we often refer to ball bearings. Also, ball bearings can receive both axial and radial forces.

Coro bearings indicate that the rolling element is cylindrical. Due to the cylindrical shape of the rolling element, the area of receiving force is larger. As a result, it can withstand large loads.

Features of rolling bearings

Rolling bearings have different characteristics depending on the rolling element. Bearings with balls for rolling elements are used in a wide range of applications and are suitable for high-speed rotation.

Cylindrical roller bearings can withstand heavy impacts. Needle roller bearings with needle rollers can withstand large forces compared to the size of the bearings. As you can see, rolling bearings have a variety of characteristics.

Plain bearing

It is easy to understand if you imagine a structure that uses lubricating oil to slide a plain bearing. The specific features are explained below.

Structure of plain bearing

Unlike rolling bearings, plain bearings have a mechanism in which the shaft comes into direct contact with the bearing. The axis is supported by a surface when moving.

There are several types of plain bearings, such as oil-lubricated bearings and oil-lubricated bearings.

Oil-lubricated bearings are designed to withstand impacts by creating an oil film with lubricating oil in the gap between the shaft and the bearing. Oil-lubricated bearings are classified into hydrostatic bearings that pump oil and dynamic bearings that involve oil with the momentum of rotation of the rotating shaft.

Gas bearings, which float the shaft and support rotation, pump gas between the bearing and the shaft as a substitute for lubricating oil. It is an image that uses air to support the axis like air hockey.

There are also magnetic bearings that utilize magnetic force. It is a method of supporting rotation by arranging magnets above and below the axis to generate magnetic force.

Features of plain bearings

The characteristic of plain bearings is that there is no movement noise and the movement is performed relatively quietly, so there is little vibration and noise. Applications for plain bearings include engines such as automobiles and machinery.

It also benefits from low maintenance and high-speed performance. Depending on maintenance, it can be used semi-permanently. On the other hand, there are disadvantages such as low speed disadvantage and low compatibility because it is not standardized.

Other bearing types

Some types of bearings are not included in the previous chapter’s classification.

Angular contact ball bearings

This bearing is a type in which the rolling element, inner ring, and outer ring meet at the contact angle, and supports loads from the vertical and horizontal sides.

Thrust ball bearing

This type is resistant to longitudinal loads relative to bearings. It can withstand even large loads.

Spherical roller bearings

This bearing automatically adjusts the misalignment between the inner and outer rings during rotation.

Gauge & Roller

It is a bearing that is built into the transmission of a car. Higher durability is required.

There are various types of bearings, and they are used differently depending on the product to be incorporated.

Bearing Manufacturing Process

From here, we will explain the bearing manufacturing process. Bearings are made through the following eight processes:

  1. Forging

Forging is the process of making the ring part of a bearing. The tubular material is cut and pressure is applied with a press to create a circular plate. After that, we will use a mold to make a ring. If you stretch the ring and change it to the desired size, the inner and outer rings are ready.

  • Turning

Turning is the process of making a rough shape of a bearing. The wheel finished by forging is machined and processed into a large frame shape. This process also creates a path for the ball.

  • Heat Treatment

In heat treatment, the shaped object is heated. When heated at a temperature of 800 ° C or higher, and cooled with oil, the metal structure becomes stronger.

  • Grinding

Grinding is a process of shaving and shaping in extremely fine units of micrometers, which is 1/1,000 of 1 millimeter. Processing is carried out using a machine called a grinding machine. The width, outer diameter, inner diameter, groove, etc. of the outer and inner rings are finished to the size as designed with high precision. The raceway through which the ball passes is carefully polished so that it is easy to rotate.

  • Assembly

In the assembly process, the ball is placed between the outer ring and the inner ring to make the ball evenly spaced. If the cage is fixed from above and below in that state, the bearing is complete.

  • Washing

This is the process of cleaning foreign matter and dirt adhering to assembled bearings. An ultrasonic cleaner is used to thoroughly wash the bearings.

  • Inspection

This is a process for inspecting the accuracy of bearings that have been cleaned. We will check the specified inspection items and see if there are any problems as a product. We inspect not only the function and accuracy, but also the appearance.

  • Packaging & Shipping

Bearings that have cleared the inspection are packaged and boxed. It is stored in a warehouse and shipped according to the number of orders.

Main Quality Inspection of Bearings and Defects that Can Be Detected

Bearing inspections include vibration inspection, visual inspection, and dimensional inspection. We will explain the contents of each inspection and the defects that can be found.

Vibration Inspection

Vibration inspection is an inspection that measures the vibration of a bearing when it is rotating to confirm its quality. Since the unit of vibration when the bearing is rotating is called “anderon”, vibration inspection is sometimes called “anderon meter”.

Vibration inspection can detect waviness of the inner and outer rings, waviness of rolling objects such as balls, scratches on cages and seals, adhesion of foreign matter, etc. For inner rings, outer rings, and rolling elements, roughness of the machined surface can also be detected. In other words, comprehensive quality inspection can be performed by performing vibration inspection.

Visual Inspection

Visual inspection inspects the appearance of finished products and assemblies. Inspections are mainly performed using cameras to check for defects such as rust, corrosion, scratches, dents, foreign matter, dirt, and air pores on the bearings.

In particular, visual inspection using a camera is characterized by the ability to instantly determine various defects.

By the way, images taken by the camera are processed in three flows: pre-processing, measurement processing, judgment and output. Pre-processing reduces noise in captured images to make them easier to inspect. The measurement process measures the dimensions of the image processed by preprocessing. In the judgment and output, the tolerance set by the image processing device is compared with the measurement result to determine whether the user passes or fails.

Dimensional Inspection

Dimensional inspection uses displacement sensors to inspect the dimensions of finished products and assemblies, such as outer and inner diameters, widths, and track grooves. A displacement sensor is a sensor that measures the amount of movement of an object when it moves to a predetermined position, but it is also used to measure not only the amount of movement but also the dimensions. There are various types of displacement sensors, and the most suitable equipment is selected according to the application and required accuracy.

Use Inspection Equipment To Find Defective Bearings

For bearing inspection, it is recommended to install inspection equipment. By introducing inspection equipment, it is possible to improve inspection accuracy and quality, and to reduce inspection costs.

Dimensional tolerances are stipulated in international standards for bearing accuracy, and accuracy in microns is required. Therefore, there is a limit to inspection methods that rely on humans, such as visual inspection.

In addition, inspection can be automated by introducing inspection equipment. The accuracy of inspections by inspectors tends to vary depending on individual experience and skills, and the inspection system may change depending on the physical condition of the inspectors.

When inspection is automated, inspection accuracy can be improved and stabilized. In addition, it will solve the labor shortage that plagues the manufacturing industry and reduce labor costs.

Third-Party Quality Inspection Service Help You Save Costs

Using inspection tools to check bearings is the best way to avoid making bad products and improve the quality of production. However, the introduction of bearing inspection equipment requires a lot of cost, especially the equipment with high accuracy and automation. Therefore, the third-party quality inspection service is a cost-effective and efficient way of carrying out quality inspection.

The third-party quality inspection company has professional tools to help with the first inspection of the first product of your bearing, the sampling inspections during production, and the final inspection before shipping!

The third-party testing company has rich testing experience and well-trained staff to carry out testing tools, so you do not need to spend the cost and energy training quality inspectors.

The third-party testing company cooperates with many suppliers and buyers, and has authoritative and reliable knowledge in import and export quality inspection, which will definitely help you improve the efficiency of the entire production and export!


Bearings are indispensable parts for the operation of various mechanical products. If a bearing breaks, the whole machine won’t work as well, so it’s especially important to keep quality high. Various inspections, such as visual inspections, are done to stop the flow of bad products. However, labor shortages and the difficulty of inspections have made it hard for inspectors to do accurate inspections. If you want to know more about bearing quality inspection or third-party quality inspection services, please contact us, you will get more professional guidance!