Rolling bearings are indispensable key supporting components in various mechanical equipment. Their service life and load-carrying capacity directly determine the operational reliability, service cycle and maintenance cost of the entire machine. Whether it is precision machine tools, electrical equipment, or industrial transmission systems, the performance of bearings plays a decisive role. As a world-renowned manufacturer of high-precision bearings, Japan's EZO Bearings (a brand under Hokuyo Seiki Co., Ltd.) has made detailed specifications on the core principles and calculation methods of rolling bearing life and load rating in its official technical specifications, combined with the ISO 281 international standard. By integrating EZO Bearings' technical standards and production practices, we can systematically and in-depth understand the specific application of this knowledge in engineering practice. All content is based on EZO Bearings' industrial test data, rigorous scientific theories and practical experience, and has strong practicality and scientificity.

To understand bearing life, it is first necessary to clarify the core mechanism of its failure. When a bearing rotates under load, the raceways of the inner and outer rings and the surface of the rolling elements are continuously subjected to repeated contact loads. This long-term cyclic load causes rolling contact fatigue of the material. With the continuous accumulation of fatigue damage, pitting, flaking and other damages will eventually occur on the raceway or rolling element surface, which is also the most common failure mode of rolling bearings. It is worth noting that the fatigue life of bearings is not a fixed value. Even bearings of the same batch, same size, using the same material and heat treatment process will have significant differences in life when operating under exactly the same conditions. This discreteness determines that we must define and measure bearing life from a statistical perspective.

In industrial practice, the industry generally uses the basic rated life L₁₀ as the benchmark indicator of bearing life. Its scientific definition is: the total number of revolutions or working hours that 90% of a group of bearings of the same specification can avoid fatigue flaking damage when operating under the same operating conditions. This indicator corresponds to a reliability of 90%, which is the core basis for bearing life calculation and selection, and can provide a unified and practical reference standard for engineering design. Based on this standard and combined with its own high-precision processing technology, EZO Bearings has formulated clear L₁₀ ratings for its various bearings such as ultra-small, thin-walled and stainless steel bearings in its product technical documents, ensuring that the service life of products under different working conditions is predictable and controllable.

The core parameters closely related to bearing life are load ratings, which are mainly divided into basic dynamic load rating and basic static load rating. The two correspond to the load-carrying capacity of bearings under different operating states respectively. The basic dynamic load rating C is essentially the constant load that a bearing can bear when its basic rated life reaches 1 million revolutions. Its specific value varies according to the type of bearing—for radial bearings, it refers to the central radial load, denoted as Cᵣ; for thrust bearings, it refers to the central axial load, denoted as Cₐ. For its core products, such as ultra-small bearings with an inner diameter starting from 0.6mm and thin-walled flange bearings, EZO Bearings clearly marks the Cᵣ and Cₐ values of each model to facilitate engineers' selection and calculation. For EZO duplex bearings composed of two single-row radial bearings with adjusted clearance, the basic dynamic load rating is usually about 1.62 times that of a single single-row bearing. This conversion relationship is derived by EZO based on its own product structure and force characteristics, which can accurately reflect its actual load-carrying capacity. The core physical meaning of the basic dynamic load rating is to characterize the bearing's ability to resist rolling contact fatigue damage, and it is also the core parameter for EZO Bearings to carry out life calibration and product design.

Compared with the basic dynamic load rating, which is used to measure the fatigue resistance of bearings in dynamic operation, the basic static load rating C₀ is mainly used to check the load safety of bearings in static or extremely low-speed operation. Its scientific definition is: the static load when the contact stress between the rolling elements and the raceway reaches 4200MPa, and the total permanent deformation between them is about 1/10000 of the rolling element diameter. In the production process, EZO Bearings effectively improves the contact accuracy between the raceway and the rolling elements through ultra-precision processing of the raceway surface (surface roughness can reach 10nm level), making its C₀ value more stable, which can better avoid problems such as unsmooth rotation, increased noise and intensified vibration caused by plastic deformation when the bearing is in static, extremely low-speed operation or under impact load. For EZO duplex single-row radial bearings, the basic static load rating is twice that of a single single-row bearing. This conversion logic is similar to that of dynamic load, both based on the structure and force characteristics of EZO bearings, adapting to its multi-scenario application needs.

In engineering design, we need to calculate the actual life of bearings through scientific formulas. For ball bearings, the industry has formed a mature and rigorous calculation system, which is derived based on rolling fatigue theory and a large number of industrial test data. EZO Bearings also clearly adopts this system as the calculation standard for its product life in its official technical documents. The most basic life calculations include three forms: total revolution life, working hour life and running distance life. Among them, the calculation of working hour life is the most commonly used, and its formula is L₁₀ₕ=(C/P)³×16667/n, where C is the basic dynamic load rating, P is the dynamic equivalent load, and n is the rotating speed of the bearing (unit: r/min). In its product samples, EZO Bearings marks the corresponding C value for each model and provides a coefficient method for rapid estimation, that is, using the relationship between the life factor fₕ and the speed factor fₙ, the life estimation value can be quickly obtained through the simultaneous calculation of L₁₀ₕ=500×fₕ³, fₕ=fₙ×C/P, and fₙ=(33.3/n)¹/³. This method is particularly practical in the initial selection stage of EZO bearings, which can help engineers quickly lock in the suitable model.

It is necessary to focus on explaining the meaning of the dynamic equivalent load P here. Because in practical applications, the load borne by the bearing is often not a single radial or axial load, but a composite load of the two. The dynamic equivalent load is to convert this composite load into a single constant load, so that the life of the bearing under this equivalent load is consistent with that under the actual composite load, thereby simplifying the calculation process. For radial bearings, the calculation formula of the dynamic equivalent load Pᵣ is Pᵣ=X·Fᵣ+Y·Fₐ, where Fᵣ is the actual radial load, Fₐ is the actual axial load, X is the radial factor, and Y is the axial factor. These two factors need to be determined by looking up the table according to the specific type of bearing and the ratio of the axial load to the bearing structural parameters. In its technical documents, EZO Bearings provides detailed X and Y coefficient comparison tables for different types of products such as deep groove ball bearings and angular contact ball bearings, facilitating engineers to make accurate calculations. For EZO thrust bearings with a contact angle of 90°, the dynamic equivalent load Pₐ is equal to the actual axial load Fₐ, which is determined by the force characteristics of the thrust bearing and is also consistent with the product design of EZO thrust bearings.

Corresponding to the dynamic equivalent load is the static equivalent load P₀, which is mainly used for the static strength check of bearings. Its calculation logic is similar to that of the dynamic equivalent load, which is also to convert the composite static load into a single load. For radial bearings, the static equivalent load P₀ᵣ needs to calculate the results of two formulas and take the larger value, namely P₀ᵣ=0.6Fᵣ+0.5Fₐ and P₀ᵣ=Fᵣ, which can ensure full coverage of static strength requirements under different load combinations; similarly, for EZO thrust bearings with a contact angle of 90°, the static equivalent load P₀ₐ is equal to the actual axial load Fₐ. To ensure the safe operation of the bearing under static load conditions, it is also necessary to introduce the safety factor fₛ, whose calculation formula is fₛ=C₀/P₀. According to different operating conditions, there are clear minimum requirements for the safety factor: not less than 1.0 under normal operating conditions, not less than 1.5 when there is impact load, and not less than 2.0 for scenarios requiring quiet and high-precision rotation. This requirement is not only an industry consensus, but also the core standard for EZO Bearings in product selection and safety check in high-end application scenarios such as medical equipment and precision instruments, which is consistent with its product positioning of high precision and high reliability.

It should be noted that the above basic life formula is derived based on the ideal conditions of standard materials, good lubrication and 90% reliability. In actual engineering, bearings often operate under harsher conditions, so it is necessary to correct the basic life. This correction method follows the ISO 281 international standard, and the correction formula is Lₙₐ=a₁·a₂·a₃·L₁₀, where Lₙₐ is the corrected rated life, L₁₀ is the basic rated life, and a₁, a₂, a₃ are the reliability correction factor, bearing characteristic correction factor and operating condition correction factor respectively. Combining with its own product characteristics, EZO Bearings has made clear regulations on the correction factors: for bearings produced with its standard materials, a₂=1; under good lubrication conditions (grease dynamic viscosity ≥13mm²/s), a₃=1; at the same time, EZO Bearings has effectively improved the life performance under high-temperature conditions through dimensional stabilization treatment (S0~S3 grades). When the operating temperature exceeds 120℃, the corresponding grade of treatment process can be used to suppress dimensional changes and hardness reduction, ensuring that the corrected life is more in line with actual operating needs. This is also an important reason why EZO Bearings can be widely used in harsh scenarios such as high temperature and high speed.