A Comprehensive Analysis of Bearing Models: Understand How to Select the Right Model in One Article

In the field of mechanical manufacturing and equipment operation, bearings, as key basic components, are known as the "mechanical joints". Their performance directly affects the stability, accuracy and lifespan of the equipment. However, in the face of a wide variety and complex-coded bearing models in the market, how to select the right model quickly and accurately has become a common challenge for engineers, equipment maintenance personnel and procurement professionals. Next, we will deeply analyze the bearing model system and, in combination with practical application scenarios, systematically explain the selection key points to help you become an expert in bearing selection. 

The bearing model, which appears to be a confusing combination of letters and numbers, is actually a rigorous and standardized information coding system consisting of three parts: the prefix code, the basic code, and the suffix code. Each part carries specific information about the bearing's attributes. 

The basic code is the core of the bearing model, which clearly defines the basic characteristics of the bearing and consists of three key elements: type code, size series code, and inner diameter code. The type code uses numbers or letters to visually distinguish the type of the bearing. For example, "6" represents a deep groove ball bearing. This type of bearing has a simple structure, a low friction coefficient, and can withstand both radial and relatively small axial loads. It is widely used in equipment such as motors and fans. Bearings starting with "3" are tapered roller bearings. Due to the conical contact between the rollers and the raceways, they can withstand large radial and unidirectional axial loads and are often used in parts of automotive gearboxes and machine tool spindles that need to withstand combined loads; "N" represents a cylindrical roller bearing. The rollers and raceways have a linear contact, with strong radial load capacity and is suitable for heavy-duty conditions, such as mining machinery and metallurgical equipment. 

The size series code is composed of the width series code and the diameter series code. These two codes work together to determine the outer diameter and width dimensions of the bearing. The width series code reflects the variation in the width direction of bearings with the same inner diameter and diameter series, while the diameter series code indicates the outer diameter dimension series corresponding to the same inner diameter. Through the size series code, engineers can, based on the inner diameter requirements and the installation space and structural requirements of the equipment, select the appropriate outer diameter and width bearings to ensure their perfect compatibility with other components. 

The inner diameter code is used to identify the inner diameter size of the bearing. The common rule is that the code multiplied by 5 equals the inner diameter in millimeters. For example, for the "6208" bearing, "08×5 = 40", so the inner diameter is 40mm; however, for inner diameters less than 10mm, 22 - 495mm that are not multiples of 5, and for special cases greater than 500mm, there are different representation methods. When the inner diameter is less than 10mm, it is directly represented by the number, such as "618/2", "/2" indicates an inner diameter of 2mm; when the inner diameter is within 22 - 495mm and not a multiple of 5 or greater than 500mm, the inner diameter code directly reflects the actual size, for example, "230/500", its inner diameter is 500mm. This diverse representation method precisely covers the inner diameter specification requirements of various bearings. 

The prefix code is mainly used to indicate the component features of bearings. However, not all bearing models have this feature. For example, "L" indicates the separable inner or outer ring of a separable bearing. This design is convenient for installation and disassembly and is commonly seen in some equipment that requires frequent maintenance; "R" indicates a bearing without a separable inner or outer ring, clearly defining the overall structure of the bearing. Although the prefix code is used relatively less frequently, it can provide important structural information references for bearing selection and application in specific scenarios. 

The post-code can be regarded as the "information treasure trove" of bearing models, covering a wide range of contents such as the internal structure of the bearing, dust-proof sealing, cage type, tolerance accuracy, clearance range, and adaptability to special working conditions. In terms of the internal structure, taking angular contact ball bearings as an example, "AC" indicates an 25° contact angle, "B" indicates a 40° contact angle. Different contact angles determine the bearing's ability to withstand axial loads. The larger the contact angle, the stronger the axial load-bearing capacity; "E" usually indicates an enhanced design. By optimizing the shape of the rollers and the structure of the raceways, it significantly enhances the bearing's load-bearing capacity and service life. 

The sealing and dust-proof codes clearly indicate the protective performance of the bearings. "RS" indicates that one side of the bearing is equipped with a skeleton-type rubber sealing ring, which is a contact seal. It can effectively prevent dust and impurities from entering the bearing interior and also prevent the leakage of lubricating oil. It is suitable for environments with a lot of dust. "2RS" indicates that both sides of the bearing are equipped with skeleton-type rubber sealing rings, providing better protection. "Z" indicates one side with a dust cover, and "2Z" indicates both sides with dust covers. The dust covers are non-contact seals and are suitable for situations where the friction requirement is low and the environmental dust is less. 

The cage plays a crucial role in guiding and separating the rolling elements during the operation of the bearing. Different cage codes correspond to different materials and structures. "M" represents a brass solid cage, which has high strength and good wear resistance and can work stably under high-speed and heavy-load conditions; "J" is a steel plate stamping cage, which has a lower cost and is often used in ordinary bearing applications; "TN" is an engineering plastic injection-molded cage, which is lightweight and has good self-lubrication properties, and is suitable for some equipment with strict requirements for noise and friction. 

The tolerance and clearance codes are related to the accuracy and operational performance of bearings. The tolerance grades range from low to high as P0, P6, P5, P4, P2, etc. P0 is the ordinary grade, which can meet the usage requirements of most general machinery; while in precision machine tools, aerospace and other fields with extremely high precision requirements, high-precision bearings of grades P5, P4 or even P2 should be selected. The clearance codes include C0 (standard clearance, usually omitted from the notation), C1, C2, C3, C4, C5, etc. The larger the clearance value, the greater the radial clearance of the bearing. Large clearance bearings (such as C3) are suitable for working conditions with large temperature variations and significant deformation of the shaft or housing, which can prevent the bearing from getting stuck due to thermal expansion or installation errors; small clearance bearings (such as C2) are suitable for scenarios with high rotational accuracy requirements and stable loads. 

Special working condition codes are set for specific working environments such as high temperature, low temperature, and severe corrosion. "S1" indicates that the bearing can operate normally at a temperature of 200℃. By using special materials, heat treatment processes, and suitable high-temperature lubricating grease, the bearing's performance is ensured to be stable at high temperatures; "S2" corresponds to 250℃, "S3" to 300℃, and "S4" to 350℃, meeting the requirements of different high-temperature working conditions. For harsh conditions such as low temperature, high humidity, and strong acids and alkalis, there are also corresponding special designs and code markings to ensure the reliable operation of the bearing in extreme environments. 

The selection of bearings is not merely a matter of matching the model; it is a systematic project that requires comprehensive consideration of various factors. During the actual selection process, in-depth analysis and weighing need to be conducted from the following key dimensions. 

Load is the primary factor influencing the selection of bearings, covering three aspects: load size, direction, and nature. From the perspective of load size, in light-load conditions, ball bearings, due to their point-contact characteristics between the rolling elements and the raceways, have low friction and are flexible in operation, making them an ideal choice. For example, the 6000 series deep groove ball bearings are commonly used in small motors and office equipment. In heavy-load scenarios, the line-contact design of roller bearings enables them to withstand greater pressure. Components such as self-aligning roller bearings and cylindrical roller bearings are widely used in mining machinery and heavy machine tools.

The direction of the load is also crucial. Pure axial loads should be given priority to thrust bearings, such as thrust ball bearings and thrust roller bearings, which are specifically designed to withstand axial forces and ensure the stability of the equipment's axial operation. When both radial and axial combined loads exist, angular contact ball bearings and tapered roller bearings can distribute the combined loads reasonably and effectively handle complex force conditions. For example, in automotive wheel hub bearings, they need to withstand the radial loads caused by the vehicle's own weight and also deal with the axial forces during braking and steering. Double-row angular contact ball bearings or tapered roller bearings can well meet these requirements. 

Furthermore, the nature of the load cannot be ignored. Impact loads and vibration loads can cause instantaneous high stress and fatigue damage to the bearings. At this time, it is necessary to select a bearing type with strong impact resistance, such as reinforced roller bearings, and appropriately increase the safety factor to extend the service life of the bearings. 

Speed is another important factor in determining the type of bearing to be selected. There are significant differences in the maximum operating speed of different types of bearings. Ball bearings are more suitable for high-speed operation scenarios because the friction resistance between the rolling elements and the raceways is small and the heat generation is low. In the field of high-speed electric spindles, to achieve speeds of tens of thousands of revolutions or even higher, high-precision angular contact ball bearings are often used. Through optimized design and manufacturing processes, the internal friction of the bearings is reduced, improving the rotational accuracy and stability. However, roller bearings have a certain limitation in terms of speed because the contact area between the rolling elements and the raceways is large and the friction is relatively high. Nevertheless, they can perform outstanding load-bearing performance in low-speed and heavy-load conditions. For example, in the rotating mechanism of port cranes, where the rotation speed is low and the load is huge, cylindrical roller bearings or self-aligning roller bearings become reliable choices. 

It is worth noting that the actual operating speed of the bearing is also affected by various factors such as the lubrication method, cooling conditions, and installation accuracy. In high-speed applications, in addition to choosing the appropriate type of bearing, it is also necessary to adopt efficient lubrication methods (such as oil-air lubrication, oil mist lubrication) and a good heat dissipation structure design to ensure that the bearing operates normally in high-temperature and high-speed environments. 

Installation space is a strict constraint for bearing selection. The size of the shaft determines the inner diameter of the bearing, while the overall structure of the equipment limits the outer diameter and width of the bearing. During the design stage, engineers need to initially determine the range of the bearing's inner diameter based on the shaft diameter, and then, in combination with the internal space layout of the equipment, select the appropriate outer diameter and width dimensions. When the radial space is extremely compact, needle roller bearings, with their extremely small outer diameter size, become the ideal choice. For example, in the crank connecting rod mechanism of an automotive engine, needle roller bearings can achieve reliable support in a narrow space; if the axial space is limited, then the type of bearing with a smaller width should be prioritized to ensure that the installation of the bearing does not affect the normal operation of other components of the equipment. 

For some special-structured equipment, such as circular guides and robot joints, the shape and installation method of the bearings also need to be considered. Special types like flange bearings and thin-walled bearings should be selected to meet the unique space and functional requirements. 

In equipment with extremely high requirements for rotational accuracy, the selection of bearing precision grades is of crucial importance. Ordinary grade (P0) bearings have relatively larger manufacturing tolerances and can meet the daily operation needs of most general machinery, such as agricultural machinery and general mechanical equipment; however, in high-end fields such as precision machine tools, semiconductor manufacturing equipment, and aircraft engines, in order to ensure processing accuracy, product quality, and equipment stability, high precision grade bearings must be selected. P5 and P4 grade bearings significantly improve rotational accuracy by strictly controlling dimensional tolerances, shape and position tolerances, and surface roughness; in ultra-precision processing equipment, even P2 grade bearings are used, with their precision reaching the micrometer level, ensuring the stability and reliability of the equipment during high-speed rotation. 

The manufacturing process of high-precision bearings is complex and costly. Therefore, when selecting them, it is necessary to make a reasonable choice based on the actual precision requirements of the equipment to avoid excessive pursuit of high precision, which may lead to cost waste. At the same time, high-precision bearings have stricter requirements for installation, lubrication and maintenance. Only under good usage conditions can their high-precision advantages be fully exerted. 

Work environment factors have a direct impact on the performance and lifespan of bearings. When selecting the type, environmental conditions such as temperature, humidity, corrosive media, and dust impurities must be fully considered. In high-temperature environments, ordinary bearing materials and lubricants will soften and oxidize due to high temperatures, resulting in a decline in performance. At this time, high-temperature-resistant bearings, such as those with the "S1 - S4" special codes, need to be selected. These bearings are made of high-temperature-resistant alloy steel and are combined with high-temperature lubricants, which can operate stably at temperatures ranging from 200°C to 350°C. In low-temperature environments, the bearing materials need to have good low-temperature toughness to prevent cold brittleness. At the same time, lubricants with excellent low-temperature performance should be selected to ensure that the bearings can start and operate normally at low temperatures. 

For environments that are damp and contain corrosive gases or liquids, such as in chemical production and marine engineering, corrosion-resistant bearings should be selected. Stainless steel bearings have excellent corrosion resistance, and bearings with special surface coating treatments (such as nickel plating, zinc plating, or Dacromet coating) can also effectively resist corrosion. At the same time, the choice of sealing structure is also crucial. Double-sided rubber sealing rings (2RS) or sealing structures made of special sealing materials can prevent corrosive media from entering the interior of the bearings, thereby extending the service life of the bearings. 

In environments with a high concentration of dust, sand particles and other impurities, such as in mining operations and construction equipment, the dust-proof performance becomes the key factor in selecting bearings. Bearings equipped with dust covers (Z, 2Z) or contact-type rubber sealing rings (RS, 2RS) can effectively prevent dust and impurities from entering, protecting the rolling elements and raceways from wear and tear, and ensuring the normal operation of the bearings. 

Cost is an important factor that enterprises must consider during the selection process of bearings. It not only includes the purchase cost of the bearings, but also covers the full life cycle costs, such as maintenance costs, replacement costs, and equipment downtime losses. Different types, brands, and precision grades of bearings have significant price differences. Bearings made of ordinary chromium steel have lower costs and are suitable for general working conditions with low performance requirements; while high-performance bearings made of special materials (such as ceramics, special alloy steel) often cost several times or even dozens of times more than ordinary bearings. However, in special working conditions such as high speed, high precision, and heavy load, their excellent performance can significantly improve equipment operation efficiency, reduce the frequency of failures, and in the long run, may actually lower the overall cost. 

For instance, in semiconductor manufacturing equipment, although the purchase cost of ceramic bearings is high, their characteristics of low friction, high temperature resistance, and long lifespan can ensure the continuous and stable operation of the equipment, preventing production line shutdowns due to bearing failures, thereby reducing the huge economic losses caused by production interruptions. Therefore, when selecting the type, the purchase cost and the total life cycle cost need to be comprehensively considered. Based on the equipment's usage frequency, importance, and expected service life, the most cost-effective bearing solution should be chosen. 

To better understand the process of bearing selection, we conduct a detailed analysis through several typical application scenarios. 

In the field of industrial fans, the working characteristics of the fans are high-speed rotation and relatively light load, but they are usually located in environments with a lot of dust, such as factory workshops. Based on these conditions, we prefer to choose deep groove ball bearings, such as the 6206 - 2RS/P6 model. Here, "6206" determines the basic size and type of the bearing, with an inner diameter of 30mm, suitable for most fan shaft diameters; "2RS" indicates double-sided rubber sealing rings, which can effectively prevent dust from entering the bearing interior in the workshop, preventing contamination and wear; "P6" ensures the stability and low vibration performance of the fan during high-speed operation, reducing noise and improving the efficiency and lifespan of the fan. 

The spindle of a machine tool is the core component of the machine, and it has extremely high requirements for rotational accuracy, bearing capacity and stability. Taking the spindle of a medium-sized machining center as an example, during the processing, it not only needs to withstand the radial cutting force generated by the cutting tool, but also the axial force generated when the workpiece rotates. At the same time, it must ensure a high rotational speed (usually several thousand revolutions per minute) to achieve efficient processing. For such a complex working condition, we select high-precision angular contact ball bearings, such as 7015C/P4. "7015" determines the bearing size, with an inner diameter of 75mm; "C" indicates an angular contact of 15°, this design of the contact angle can better balance the radial and axial loads, adapting to the force characteristics of the spindle; "P4" ensures the positioning accuracy of the spindle at high-speed rotation, meeting the strict requirements of precision processing for dimensional accuracy and surface quality. In addition, to further improve the rigidity and stability of the spindle, multi-group angular contact ball bearings are often installed in pairs, and the internal clearance of the bearings is eliminated through pre-tightening technology to enhance the overall performance of the spindle. 

In the field of construction machinery, taking the walking mechanism of an excavator as an example, this mechanism needs to withstand huge weights and complex ground impact loads. The working environment is harsh, filled with dirt, sand, and other impurities. Under such conditions, self-aligning roller bearings become the preferred choice, such as 22320E. "22320" corresponds to the bearing size, with an inner diameter of 100mm; "E" indicates an enhanced design, which improves the bearing's load-bearing capacity and impact resistance through optimizing the roller and raceway structures. The spherical raceway design of the self-aligning roller bearings enables them to have an automatic alignment function, which can compensate for the effects caused by equipment installation errors or the deflection deformation of the shaft during operation, ensuring the stable operation of the walking mechanism. At the same time, to cope with harsh environmental conditions, this bearing is usually equipped with a dust-proof cover or sealing ring with good sealing performance, and uses lubricating grease with excellent anti-wear properties to reduce the intrusion of impurities and wear, thereby extending the service life of the bearing. 

Interpreting and selecting bearing models is a highly specialized and comprehensive task that requires a deep understanding of the coding rules of bearing models, as well as comprehensive consideration of the equipment's operating conditions, installation requirements, and cost factors. Through the detailed analysis and case sharing in this article, we hope to help you grasp the core points of bearing selection and make more scientific and reasonable selection decisions in practical work. If you encounter any problems during the bearing selection process, please feel free to visit our bearing website. Our professional technical team will be more than happy to provide you with consultation and solutions, helping your equipment operate efficiently and stably.