Bearing steel ball production inspection and quality judgment method based on multi-node internal control indexes

Abstract

The invention discloses a bearing steel ball production inspection and quality judgment method based on a multi-node internal control index. The method comprises a wire in-factory inspection process, an inspection process after heat treatment, a hard grinding and fine grinding process monitoring process and a finished product final inspection process. The technical problems that the quality of the steel ball production process is out of control, the quality stability of a finished product is poor and the defective rate is high due to the fact that existing bearing steel ball production inspection only carries out tail end single index detection according to the national standard and lacks full-process quality control are solved.

Description

Technical Field

[0001] This invention relates to the field of bearing processing technology, specifically to a method for production inspection and quality judgment of bearing steel balls based on multi-node internal control indicators. Background Technology

[0002] Rolling bearings are key basic components in the equipment manufacturing industry, widely used in core fields such as high-end machine tools, new energy vehicle drive systems, wind power equipment, rail transportation, and aerospace. The bearing steel balls, as the core rolling elements of rolling bearings, directly determine the bearing's rotational accuracy, service life, operational reliability, and vibration and noise levels based on their material purity, structural stability, uniformity of mechanical properties, surface integrity, and dimensional accuracy. With the rapid development of high-end equipment towards higher speeds, higher loads, higher precision, longer lifespans, and higher reliability, stringent requirements have been placed on the quality consistency and performance redundancy of the supporting bearing steel balls, far exceeding general industry standards.

[0003] Currently, the production and quality inspection of bearing steel balls in China generally follow the national standard GB / T 308.1-2013 "Rolling Bearings - Steel Balls". This standard specifies the basic technical requirements and inspection methods for steel balls of different precision grades, including dimensional tolerances, hardness, crushing load, surface quality, and microstructure. It provides a universal basis for quality compliance in steel ball production within the industry and is the core quality judgment criterion implemented by the vast majority of steel ball manufacturers. However, in the existing conventional production model, steel ball quality control mainly focuses on "final inspection compliance of finished products". Sampling inspection is only carried out after the finished product is processed, according to national standard requirements. As long as all indicators meet the lower limit requirements of the national standard, the product is judged as qualified.

[0004] However, based on the above standards, long-term production practice and systemic failure analysis have revealed that existing technologies and general standards have inherent defects that make them difficult to adapt to the needs of high-end equipment: Firstly, in order to ensure the broad applicability of the entire industry, the general national standard sets a wide range of quality parameters, only stipulating the minimum threshold for qualified steel balls. It does not set performance redundancy and consistency control requirements for high-end and harsh working conditions. As a result, a large number of "qualified" steel balls that fully meet the national standard requirements are prone to failure problems such as early fatigue spalling, accelerated wear, and loss of precision under high speed and high cyclic contact stress service conditions, which has become the core shortcoming restricting the overall performance improvement of bearings. Secondly, the existing quality control model emphasizes the final product inspection while neglecting the whole process control. It has not established a systematic internal control system for the key nodes that determine the final performance in the entire steel ball production process, and ignores core influencing factors such as the purity of raw materials, the uniformity of heat treatment structure, and the quality fluctuations of intermediate processing steps. This not only easily leads to the waste of raw materials and processing costs in the production process, but also makes it impossible to fully identify some quality defects generated in the early stage through the final inspection of finished products. These defects may then flow into downstream applications and cause failure risks. Third, the existing quality judgment logic relies on independent judgment of a single indicator, requiring only that each inspection item meets the national standard requirements, without considering the synergistic matching of core parameters such as the microstructure, mechanical properties, and surface integrity of the steel ball. This cannot avoid the quality risk of "single indicator meeting the standard but overall performance being insufficient." At the same time, there is insufficient batch consistency control over key performances such as crushing load and hardness, which can easily lead to a few steel balls with performance deficiencies within a batch, resulting in a significant reduction in the service life of the entire bearing set. For example, when the hardness difference of five points on the surface of a single steel ball exceeds 1.5 HRC, it indicates that there are microscopic differences in its internal microstructure transformation or cooling uniformity, which can easily lead to deformation incoordination under cyclic contact stress, becoming the initiation source of micro-area fatigue cracks. When the hardness difference of steel balls in the same batch exceeds 3.0 HRC, it will directly lead to a significant increase in the overall vibration value after assembly into a bearing, producing abnormal noise.

[0005] In summary, the industry currently lacks a sophisticated production inspection and quality assessment method that runs through the entire steel ball production process, is stricter than general national standards, and takes into account both performance redundancy and batch consistency. This makes it impossible to meet the high-quality and high-reliability requirements of high-end equipment for bearing steel balls. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for the production inspection and quality judgment of bearing steel balls based on multi-node internal control indicators. This method solves the problem that existing bearing steel ball production inspections only rely on national standards for end-point single indicator testing and lack full-process quality control, resulting in uncontrolled quality in the steel ball production process, poor finished product quality stability, and a high defect rate.

[0007] To achieve the above objectives, this invention provides a method for production inspection and quality judgment of bearing steel balls based on multi-node internal control indicators, including wire rod incoming inspection process, post-heat treatment inspection process, hard grinding and fine grinding process monitoring process, and finished product final inspection process. The incoming inspection process for wire rods includes random sampling of each batch of GCr15 wire rods and inclusion testing in accordance with GB / T10561-2005 "Determination of Non-metallic Inclusion Content in Steel - Standard Rating Chart Microscopic Examination Method". The internal control judgment index for inclusion testing is that the fineness of each type of inclusion, such as A (sulfides), B (alumina), and C (silicates), is ≤2.0, while the fineness of Ds (single-particle spherical oxides) is ≤1.5. If any inclusion fineness exceeds the standard, the batch of wire rods is deemed unqualified. The post-heat treatment inspection process includes conducting hardness uniformity and microstructure inspections on batches of steel balls after quenching and tempering. The hardness uniformity inspection involves taking sample balls and using a Rockwell hardness tester to uniformly test five points of hardness along the equator of each ball. The internal control criteria for hardness uniformity are: the hardness range of the five points on a single ball ≤ 1.5 HRC, and the overall hardness range of the batch of sample balls ≤ 3.0 HRC. If any one of the hardness internal control criteria fails to meet the internal control standard, the batch of hot-rolled steel balls is deemed unqualified. The microstructure sampling inspection involves taking sample balls, preparing metallographic specimens, and conducting the inspection. The internal control criteria for microstructure sampling inspection are: martensite grade 1-2, retained austenite ≤ 5%, uniform carbide distribution, and no obvious network or banded segregation. If any one of the internal control criteria for microstructure sampling inspection fails to meet the internal control standard, the batch of steel balls is deemed unqualified. The hard grinding and fine grinding process monitoring flow is to monitor the dimensional variation and surface roughness trend of each process and realize statistical process control; The final inspection process includes inspecting the finished steel balls after grinding, fine grinding, and cleaning processes. This includes crushing load and uniformity testing, surface quality testing, and final microstructure verification. The crushing load and uniformity testing involves sampling the finished steel balls and conducting crushing tests. The internal control criterion for crushing load is that the average crushing load is ≥ GB / T The minimum crushing load value specified in standard 308.1 is 120%. The internal control criterion for the uniformity test is that the coefficient of variation of the crushing load data is ≤8%. The surface quality test involves sampling and testing the final finished steel balls. The internal control criterion for the surface quality test is that the surface roughness Ra value is ≤0.020μm. The final microstructure verification involves sampling and testing the samples from the crushing load, uniformity test, and surface quality test. The internal control criterion for the final microstructure verification is that the martensite structure is grade 1-2 and the retained austenite is ≤5%. If the three tests of crushing load, uniformity test, surface quality test, and final microstructure verification are compliant, the batch of finished steel balls is deemed qualified.

[0008] The present invention further includes the following provision: the surface quality inspection uses an eddy current flaw detector to sample and inspect the final finished steel balls.

[0009] The present invention further specifies that the microscopic tissue sampling is performed and evaluated in accordance with GB / T 13298 and GB / T 34891 standards.

[0010] The advantages of adopting the above technical solution are as follows: This technology addresses the core pain points of existing national standards for bearing steel balls, which only set minimum acceptable levels and have broad controls on key performance aspects. These issues lead to premature failure, poor precision retention, insufficient operational stability, and short service life of the steel balls under demanding high-end operating conditions. By setting internal control indicators stricter than the GB / T 308.1 national standard for four key dimensions determining the core performance of the steel ball—hardness uniformity, crushing load, microstructure, material purity, and surface quality—this technology achieves refined quality control of the steel balls from all dimensions: material origin, matrix structure, mechanical properties, and surface integrity, resulting in the following significant technical effects: Firstly, this invention strictly controls the uniformity of steel ball hardness, limiting the hardness difference of multiple points on the surface of a single steel ball to within 1.5 HRC and the hardness difference of sampled steel balls in the same batch to within 3.0 HRC. This effectively avoids microscopic differences caused by internal structural transformation or insufficient cooling uniformity of the steel balls, fundamentally eliminating the micro-area fatigue crack initiation source caused by deformation incoordination under cyclic contact stress, and significantly reducing the risk of early fatigue spalling of the steel balls. At the same time, by strictly controlling the hardness fluctuation of steel balls within a batch, it effectively avoids the problem of increased overall bearing vibration and abnormal operating noise after steel ball assembly, significantly improving the bearing's operational stability and NVH performance.

[0011] Secondly, by optimizing the internal control requirements of crushing load, this invention increases the average crushing load of steel balls to more than 120% of the minimum crushing load value specified in the national standard, significantly increasing the overall strength margin of the steel ball material and fully ensuring the structural stability and deformation resistance of the steel balls under high load conditions. At the same time, the crushing load dispersion coefficient is strictly controlled within 8%, precisely constraining the fluctuation range of mechanical properties of steel balls in the same batch, completely avoiding the problem of a few low-strength steel balls becoming the shortcoming of the entire bearing life, realizing the uniform control of the performance of batch steel balls, and significantly extending the overall service life of the bearing.

[0012] Thirdly, by tightening the internal control standards of microstructure, this invention limits the martensite structure grade to level 1-2, effectively avoiding the defects of high micro-stress and low toughness caused by coarse acicular martensite in level 3 structure. This achieves the optimal match between strength and toughness of the steel ball matrix, significantly improving the impact resistance and fatigue resistance of the steel ball. At the same time, it reduces the retained austenite content from the industry-standard ≤8% to ≤5%, greatly enhancing the microstructure stability of the steel ball. This effectively prevents the loss of dimensional accuracy and the generation of additional internal stress caused by the phase transformation of retained austenite during long-term service, ensuring the accuracy retention and operational reliability of the bearing throughout its entire life cycle.

[0013] Fourth, this invention rigorously controls the purity and surface quality of materials, sets stricter rating requirements for non-metallic inclusions in bearing steel wire, and implements zero-tolerance control for defects such as cracks, pits, and slag inclusions on the surface of finished steel balls. This comprehensively eliminates known stress concentration sources and early fatigue crack initiation points inside and on the surface of the steel balls, blocking the core causes of fatigue failure of steel balls from the source, and significantly improving the contact fatigue life and wear resistance of steel balls. At the same time, by further reducing the surface roughness requirements of steel balls, the friction and wear between steel balls and bearing raceways are effectively reduced, further improving the operating accuracy and long-term service reliability of bearings.

[0014] In summary, this invention breaks through the limitations of existing national standards that only specify the lower limit of qualified steel balls. Through multi-dimensional and refined internal control indicator design, it systematically solves the industry pain point of insufficient performance of qualified steel balls under high-end and harsh working conditions. It realizes the full-chain performance optimization of bearing steel balls from raw materials to finished products. The produced steel balls can fully adapt to the supporting needs of high-end equipment with high speed, high load, long life and high reliability requirements, and have significant technological progress and extremely high engineering application value. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the process for incoming inspection and post-heat treatment inspection of wire in this invention; Figure 2 This is a schematic diagram of the final inspection process for finished products in this invention. Detailed Implementation

[0016] Specific process of this invention (the test object is G5 grade GCr15 precision steel ball): Incoming inspection process for wire rod: Random samples are taken from each batch of GCr15 wire rod and the inclusions are inspected according to GB / T 10561-2005 "Determination of non-metallic inclusion content in steel - standard rating chart microscopic inspection method". The internal control judgment index for inclusion inspection is that the fineness of each type of inclusion, such as A (sulfides), B (alumina) and C (silicates), is ≤2.0, and the fineness of Ds (single particle spherical oxides) is ≤1.5. If any inclusion fineness exceeds the standard, the batch of wire rod is deemed unqualified. The post-heat treatment inspection process includes hardness uniformity testing and microstructure testing of steel ball batches (500kg per batch) after quenching and tempering. The hardness uniformity testing involves selecting 30 sample balls and using a calibrated Rockwell hardness tester to perform 5-point hardness tests evenly distributed near the equator of each ball. The internal control criteria for hardness uniformity testing are: the hardness range of a single ball at the 5-point test ≤ 1.5 HRC, and the overall hardness range of the batch of sample balls ≤ 3.0 HRC (e.g., hardness distribution concentrated in the 63.0-65.5 HRC range). If any test in the hardness internal control criteria fails to meet the internal control standard, the batch of hot-rolled steel balls is deemed unqualified. The microstructure sampling test involves taking 3 additional metallographic samples from the above sample balls and testing them according to GB / T 13298 and GB / T 34891 Observation and Evaluation: The internal control judgment index for the microstructure sampling inspection is that the martensite structure is grade 1-2, the retained austenite (XRD determination) is ≤5%, and the carbides are evenly distributed without obvious network (≤2 grade) or band (≤2 grade) segregation. If any of the internal control judgment indexes for the microstructure sampling inspection does not meet the internal control standard, the batch of steel balls is judged to be unqualified. The final inspection process includes inspecting the finished steel balls after grinding, fine grinding, and cleaning. This includes crushing load and uniformity testing, surface quality testing, and final microstructure verification. The crushing load and uniformity testing involves randomly selecting 25 finished steel balls and conducting a crushing test according to the method in Appendix GB / T 308.1-2013. The internal control criterion for the crushing load is that the average crushing load is ≥ 120% of the minimum crushing load value specified in GB / T 308.1 (approximately 38kN for a Φ9.525mm steel ball), i.e., ≥ 45.6kN. The internal control criterion for the uniformity testing is that the coefficient of variation of the crushing load data is ≤ 8%. The surface quality testing involves 100% automatic inspection of the finished steel balls using an eddy current flaw detector. The internal control criterion for the surface quality testing is that the surface roughness Ra value is higher than that specified in GB / T 308.1. The specified values ​​for G5 grade steel balls in 308.1 are reduced by more than 20%, i.e., surface roughness ≤ 0.020 μm, and no stress concentration sources such as cracks, pits, or inclusions. The final microstructure verification involves sampling and inspecting samples from the crushing load and uniformity test and surface quality inspection. The internal control criteria for the final microstructure verification are no grinding burn structures (e.g., white layer from secondary quenching), and the martensite structure in the core is grade 1-2, with retained austenite ≤ 5%. If the three tests of crushing load and uniformity test, surface quality inspection, and final microstructure verification are compliant, the batch of finished steel balls is deemed qualified.

[0017] By implementing the aforementioned sequential, high-threshold inspection and quality control process, it is possible to ensure synergistic optimization in material cleanliness, matrix microstructure, mechanical strength, and surface integrity of the steel balls leaving the factory. Production statistics show that the early failure rate of these steel balls in high-end precision bearings has been significantly reduced. This method, through rigorous data-driven standards, has achieved a quality leap from "meeting basic national standards" to "meeting the reliability requirements of extreme operating conditions."

[0018] The GB / T 308.1-2013 standard "Rolling Bearing Steel Balls" referenced in the above technology is a general recommended basic national standard in my country for the production, inspection, and quality judgment of steel balls for rolling bearings. It is applicable to bearing steel ball products of various precision grades and materials, and is the minimum quality compliance standard generally implemented by domestic bearing steel ball manufacturers. This standard comprehensively specifies the basic specifications for the entire process of bearing steel ball production, including terminology definitions, classification and precision grades, technical requirements, inspection methods, inspection rules, marking, and packaging. The core technical requirements that directly correspond to the internal control indicators of this invention are all normative contents disclosed in this standard and are existing technologies known to those skilled in the art.

[0019] Regarding the control of non-metallic inclusions in bearing steel ball raw materials in the aforementioned technology, Clause 5.1 "Materials" of GB / T 308.1-2013 clearly stipulates that the bearing steel used to manufacture steel balls should comply with the corresponding bearing steel material standard, and the inspection of non-metallic inclusions in the steel shall be carried out in accordance with GB / T 10561 "Determination of Non-metallic Inclusion Content in Steel - Standard Rating Chart Microscopic Examination Method". The industry's general requirements based on this standard are: the fine series rating of Class A sulfides, Class B alumina, and Class C silicates should not exceed 2.5, and the fine series rating of Class Ds single-particle spherical oxide inclusions should not exceed 2.0. This requirement is the industry's general minimum threshold for incoming raw material inspection and is also the benchmark content for the internal control indicators of this invention.

[0020] Regarding the hardness and microstructure requirements of steel balls after heat treatment, Clause 5.3 "Hardness" in GB / T 308.1-2013 clearly stipulates that steel balls made of high-carbon chromium bearing steel (such as GCr15) with a diameter not exceeding 25.4 mm should have a finished product hardness of 60~66 HRC. This clause only specifies the lower and upper limits of the acceptable range for steel ball hardness, without making clear quantitative requirements for the hardness difference at multiple points on the surface of a single steel ball or the overall hardness difference of sampled steel balls in the same batch. Regarding the microstructure, Clause 5.4 "Microstructure" of the same standard clearly stipulates that the martensite structure of the steel ball after quenching and tempering should be grade 1~3, the network carbides should not exceed grade 3, the residual austenite content of the finished steel ball should not exceed 8%, and the carbide distribution should be uniform. This content serves as the benchmark requirement for the internal control indicators of the microstructure in this invention.

[0021] Regarding the crushing load requirements for finished steel balls in the aforementioned technology, Clause 5.5 "Crushing Load" of GB / T 308.1-2013 clearly stipulates that the crushing load of the steel ball should not be less than the minimum crushing load value for the corresponding specification of steel ball specified in Appendix B (normative appendix) of the standard. Appendix B specifies the calculation formula and numerical comparison table for the minimum crushing load of steel balls of different diameters. For example, the minimum crushing load specified for a Φ9.525mm steel ball is approximately 38kN. This standard only sets a minimum requirement for the single minimum value of the crushing load of the steel ball, without making any quantitative provisions for the average value or batch dispersion coefficient of the crushing load of steel balls in the same batch. This content serves as the benchmark comparison requirement for the internal control index of crushing load in this invention.

[0022] Regarding the surface quality and roughness requirements of the finished steel balls in the aforementioned technology, Clause 5.2 "Surface Quality" of GB / T 308.1-2013 clearly stipulates that the surface of the steel ball should be smooth and clean, and defects such as cracks, pits, rust, and burrs that affect its use are not allowed. Minor surface defects not exceeding dimensional tolerances are permitted. Regarding surface roughness, the standard table clearly specifies the upper limit value of surface roughness Ra for steel balls of different precision grades. For example, the upper limit value of surface roughness Ra for G5 precision steel balls is 0.025μm, and the upper limit value of surface roughness Ra for G10 precision steel balls is 0.032μm. This content serves as the benchmark comparison requirement for the internal control index of surface quality in this invention.

[0023] All contents of the aforementioned GB / T 308.1-2013 "Rolling Bearing Steel Balls" and its supporting reference standards are existing technologies that were publicly published in China before the application date and are generally known to those skilled in the art. The national standard basic requirements mentioned in this invention shall be based on the published contents of the aforementioned standard clauses.

[0024] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

Claims

1. A method for production inspection and quality judgment of bearing steel balls based on multi-node internal control indicators, characterized in that: This includes the incoming inspection process for wire, the post-heat treatment inspection process, the hard grinding and fine grinding process monitoring process, and the final inspection process for finished products. The incoming inspection process for wire rods includes random sampling of each batch of GCr15 wire rods and inclusion testing in accordance with GB / T 10561-2005 "Determination of Non-metallic Inclusion Content in Steel - Standard Rating Chart Microscopic Examination Method". The internal control judgment index for inclusion testing is that the fineness of each type of inclusion, such as A (sulfides), B (alumina), and C (silicates), is ≤2.0, while the fineness of Ds (single-particle spherical oxides) is ≤1.

5. If any inclusion fineness exceeds the standard, the batch of wire rods is deemed unqualified. The post-heat treatment inspection process includes conducting hardness uniformity and microstructure inspections on batches of steel balls after quenching and tempering. The hardness uniformity inspection involves taking sample balls and using a Rockwell hardness tester to uniformly test five points of hardness along the equator of each ball. The internal control criteria for hardness uniformity are: the hardness range of the five points on a single ball ≤ 1.5 HRC, and the overall hardness range of the batch of sample balls ≤ 3.0 HRC. If any one of the hardness internal control criteria fails to meet the internal control standard, the batch of hot-rolled steel balls is deemed unqualified. The microstructure sampling inspection involves taking sample balls, preparing metallographic specimens, and conducting the inspection. The internal control criteria for microstructure sampling inspection are: martensite grade 1-2, retained austenite ≤ 5%, uniform carbide distribution, and no obvious network or banded segregation. If any one of the internal control criteria for microstructure sampling inspection fails to meet the internal control standard, the batch of steel balls is deemed unqualified. The hard grinding and fine grinding process monitoring flow is to monitor the dimensional variation and surface roughness trend of each process and realize statistical process control; The final inspection process includes inspecting the finished steel balls after grinding, fine grinding, and cleaning. This includes crushing load and uniformity testing, surface quality testing, and final microstructure verification. The crushing load and uniformity testing involves sampling the finished steel balls and conducting crushing tests. The internal control criterion for crushing load is that the average crushing load is ≥ 120% of the minimum crushing load value specified in GB / T 308.

1. The internal control criterion for uniformity testing is that the coefficient of variation of the crushing load data is ≤ 8%. The surface quality testing involves sampling the finished steel balls and conducting tests. The internal control criterion for surface quality testing is that the surface roughness Ra value is ≤ 0.020 μm. The final microstructure verification involves sampling and testing the samples from the crushing load and uniformity test and the surface quality test. The internal control criterion for final microstructure verification is that the martensite structure is grade 1-2 and the retained austenite is ≤ 5%. If the crushing load meets the requirements of the three tests—uniformity test, surface quality test, and final microstructure verification—then the batch of finished steel balls is deemed qualified.

2. The method for production inspection and quality judgment of bearing steel balls based on multi-node internal control indicators according to claim 1, characterized in that: The surface quality inspection uses an eddy current flaw detector to sample and inspect the final finished steel balls.

3. The method for production inspection and quality judgment of bearing steel balls based on multi-node internal control indicators according to claim 1, characterized in that: The microscopic tissue sampling was conducted and evaluated in accordance with GB / T 13298 and GB / T 34891 standards.

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