Preparation method of silicon nitride bearing ball and online defect detection device
Through the gradient sintering process and composite coating process, combined with the online defect detection device, the problems of hard and brittle characteristics, coating performance attenuation and detection hysteresis of silicon nitride bearing balls during the preparation process are solved, and low-cost and efficient preparation of silicon nitride bearing balls are achieved, improving its insulation and mechanical strength.
Patent Information
- Application Number
- CN202510502524.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-22
- Publication Date
- 2025-07-25
AI Technical Summary
During the preparation process, existing silicon nitride bearing balls have problems such as hard and brittle characteristics that lead to processing damage, attenuation of coating performance, high preparation cost and detection hysteresis, which are difficult to meet the needs of extreme working conditions.
Gradient sintering process, composite coating process and online defect detection device are used to control grain growth through presintering, main sintering and annealing stages, combined with laser-ultrasonic joint detection, surface cracks and internal pores are identified in real time, and sintering parameters are optimized.
It reduces the preparation cost and energy consumption, improves the insulation and mechanical strength of the bearing ball, reduces the scrap rate, and improves the processing accuracy and coating performance.
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Figure CN120365086A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of silicon nitride bearing balls, and specifically relates to a preparation method of silicon nitride bearing balls and an on-line defect detection device. Background Art
[0002] Silicon nitride (Si3N4) ceramic bearing balls, as representatives of the third-generation engineering ceramic materials, rely on their Vickers hardness above HV 1500, dimensional stability at high temperatures of 1200 °C (thermal expansion coefficient 3.2×10 -6 / °C), and low density of 3.2 g / cm 3 (only 40% of that of steel bearing balls) to have become the core components of high-speed precision bearing systems. In the aerospace field, its heat-resistant characteristics can meet the requirements of super-high-speed operation of more than 8000 r / min for the main shaft of aero-engines; in the drive motors of new energy vehicles, the low-density characteristics can reduce the weight of the bearing system by 35%, significantly improving the energy efficiency conversion rate; while in the field of medical devices such as artificial joints, its bio-inert surface can reduce the risk of metal ion precipitation by 97%. However, with the extension of application scenarios to extreme working conditions, the existing preparation technologies have exposed systematic technical bottlenecks.
[0003] First, at the level of precision machining, the hard and brittle characteristics of silicon nitride (fracture toughness 6-7 MPa·m 1 / 2 ) lead to the easy induction of surface / subsurface damage in the traditional diamond grinding wheel grinding process. Research shows that when the feed rate exceeds 0.2 μm / r, the incidence rate of chipping defects suddenly increases to 78%, and existing precision machine tools often use parameters of 0.5-1 μm / r to control processing efficiency. The resulting microcrack depth can reach 20-50 μm, directly leading to a 60%-80% decrease in the rolling contact fatigue life. More intractably, the "snowflake-shaped" defects (size > 5 μm) formed by the abnormal growth of β-Si3N4 grains during the sintering process will become stress concentration sources in subsequent processing, and the on-line detection rate of such defects is less than 30%.
[0004] Secondly, in terms of functional modification, the Al2O3 insulation coating (thickness 2-5 μm) prepared by traditional physical vapor deposition (PVD) has significant performance degradation under high-temperature working conditions. Experimental data show that when the temperature exceeds 400 °C, the thermal stress at the coating interface reaches 1.2 GPa, resulting in the insulation resistance dropping from the initial 5×10 9 Ω to the order of 10 6 Ω, increasing the risk of shaft current corrosion in variable-frequency motors by 10 times. Although some studies have attempted to use multi-layer gradient coatings (such as Al2O3 / Si3N4 composite structures), the difference in thermal expansion coefficients between layers (ΔCTE = 1.8×10 -6 / °C) will still cause coating spalling under cyclic thermal shock.
[0005] The economic contradictions in the preparation process are equally prominent. The current mainstream hot-pressing sintering process requires a high temperature of 1650 - 1800 °C and a pressure of 20 - 30 MPa. The energy consumption per furnace is as high as 1200 kwh, and the output per furnace is very low. Moreover, it is extremely sensitive to the purity of raw materials. Statistics show that when the purity of α-Si3N4 powder decreases from 99.9% to 99.5%, the porosity of the sintered body surges by 3 times, resulting in a 40% decrease in the dynamic load rating (C value) of the bearing ball. Although the gas pressure sintering (GPS) technology can reduce the cost by about 25%, it requires precise control of the N2 partial pressure (0.5 - 1.0 MPa), and the equipment investment cost increases by 30% instead.
[0006] In the dimension of quality monitoring, the existing off-line detection methods mainly rely on manual inspection with a microscope, which has significant lag and high eye strain. Summary of the Invention
[0007] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art, and provide a preparation method of silicon nitride bearing balls with low cost, good insulation and strong mechanical properties; the present invention also provides an on-line defect detection device, which can detect the defects of bearing balls in real time during the polishing process of the ball mill, timely adjust the sintering process parameters, and efficiently reduce the rejection rate.
[0008] The preparation method of the silicon nitride bearing balls described in the present invention includes a gradient sintering process, a composite coating process, and on-line defect detection;
[0009] The gradient sintering process successively includes three stages: pre-sintering, main sintering, and annealing. The temperature in the pre-sintering stage is 1200 - 1400 °C; the temperature in the main sintering stage is 1600 - 1800 °C, and the temperature in the annealing stage is 1350 - 1450 °C.
[0010] Furthermore, the gradient sintering process successively includes three stages: pre-sintering, main sintering, and annealing. In the pre-sintering stage, it is heated to 1200 - 1400 °C at a rate of 8 - 15 °C / min and kept in an N2 atmosphere for 1 - 2 h; in the main sintering stage, it is heated to 1600 - 1800 °C at a rate of 2 - 5 °C / min and kept in an N2 atmosphere for 2 - 3 h; in the annealing stage, it is cooled to 1350 - 1450 °C at a rate of 1.5 - 2.5 °C / min and kept for 2.5 - 3.5 h, and then cooled to room temperature. The grain growth is controlled by the temperature gradient to reduce internal stress and cracks.
[0011] The preparation method of the silicon nitride bearing balls also includes raw material treatment and forming processes.
[0012] The raw material treatment process is as follows: mix silicon nitride powder with Al2O3, Y2O3, and TiC additives, and ball mill until the average particle size D50 is 0.5 μm. The purity of the silicon nitride powder is ≥99.5%.
[0013] The total mass of Al2O3 and Y2O3 is 5-10% of the silicon nitride powder, and the mass ratio of Al2O3 to Y2O3 is 7:3-6:4. TiC is 1-2% of the silicon nitride powder, which improves the relative density (>99.5%) and thermal shock resistance.
[0014] Forming process: The processed raw materials are cold isostatically pressed at a pressure of 180-220 MPa.
[0015] The coating process is to first form an Al2O3 coating with a thickness of 10-20 μm on the surface of the bearing ball by plasma spraying to improve the high-temperature insulation performance (DC impedance ≥ 10 GΩ), and then form a 2-5 μm SiC coating outside the Al2O3 layer by chemical vapor deposition to reduce the friction coefficient (≤0.05) and enhance wear resistance.
[0016] The on-line detection of defects is carried out by laser-ultrasonic combined screening, with the accuracy of real-time identifying surface cracks being 0.1 μm and the resolution of internal pores being 50 μm, further controlling the dynamic adjustment parameters of the sintering furnace.
[0017] The on-line defect detection device used in the preparation method of the silicon nitride bearing ball: It includes an on-line defect detection body, a laser scanning module and an ultrasonic detection module are installed inside the on-line defect detection body, and a reject discharge hole is arranged on the body of the on-line defect detection body. A laser scanning and ultrasonic combined detection module is set at the post-sintering station to real-time identify surface cracks (accuracy 0.1 μm) and internal pores (resolution 50 μm).
[0018] The on-line defect detection body is installed between the upper grinding disc and the lower grinding disc and fixed to the upper grinding disc. The on-line defect detection body is fixed to the upper grinding disc by bolts or other means.
[0019] Specifically, the preparation method of the silicon nitride bearing ball includes the following steps:
[0020] (1) Raw material treatment: Mix silicon nitride powder (purity 99.5%) with 5-10% of Al2O3-Y2O3 (mass ratio 7:3-6:4) additives based on the mass of the silicon nitride powder, and TiC accounts for 1-2% of the mass of the silicon nitride powder, and ball mill to an average particle size D50 of 0.5 μm.
[0021] (2) Forming and sintering: The processed raw materials are cold isostatically pressed at a pressure of 180 - 220 MPa; then gradient sintering is carried out. The gradient sintering process consists of three stages: pre-sintering, main sintering, and annealing. In the pre-sintering stage, the temperature is raised to 1200 - 1400 °C at a rate of 8 - 15 °C / min and maintained for 1 - 2 h in an N2 atmosphere; in the main sintering stage, the temperature is raised to 1600 - 1800 °C at a rate of 2 - 5 °C / min and maintained for 2 - 3 h in an N2 atmosphere; in the annealing stage, the temperature is lowered to 1350 - 1450 °C at a rate of 1.5 - 2.5 °C / min, maintained for 2.5 - 3.5 h, and then cooled to room temperature. The sintering procedure is as Figure 2 shown. The gradient sintering process reduces energy consumption by 20% and increases the raw material utilization rate to 95%.
[0022] (3) Coating processing: First, a 10 - 20 μm thick Al2O3 coating is formed on the surface of the bearing ball by plasma spraying, and then a 2 - 5 μm thick SiC coating is formed outside the Al2O3 layer by chemical vapor deposition, as Figure 3 shown.
[0023] (4) Online detection: Through laser - ultrasonic combined screening, the accuracy of real - time identifying surface cracks is 0.1 μm and the resolution of internal pores is 50 μm. The rejection rate of manual inspection is reduced to <1%. The diameter of the silicon nitride bearing ball is 3 - 40 mm. Online detection reduces the manual sorting cost by 30%.
[0024] Compared with the prior art, the beneficial effects of the present invention are:
[0025] (1) The preparation method of the silicon nitride bearing ball of the present invention, compared with the traditional grinding process, greatly saves labor costs and has low energy consumption. The surface roughness and error of the prepared bearing both meet the GB / T31703 - 2015 standard.
[0026] (2) The preparation method of the silicon nitride bearing ball of the present invention, after two - layer coating, the impedance retention rate of the prepared bearing is ≥90% at 300 °C, and the wear resistance is increased by more than 3 times.
[0027] (3) By using the online detection and defect device of the present invention, intelligent detection of the preparation of silicon nitride bearing balls is realized, and the qualified rate is improved. Brief Description of the Drawings
[0028] Figure 1 is a schematic diagram of the online detection and defect device of the present invention.
[0029] Figure 1 In the figure: 1. Online detection and defect main body; 2. Laser scanning module; 3. Ultrasonic detection module; 4. Rejected product discharge hole; 5. Upper grinding disc; 6. Lower grinding disc.
[0030] Figure 2 This is a graph showing the variation of temperature with time in the gradient sintering process of the present invention.
[0031] Figure 3 This is a schematic diagram of two layers of the bearing coating prepared by the present invention. Specific embodiments
[0032] The present invention will be further described below in conjunction with specific embodiments.
[0033] The raw materials and auxiliaries used in the following examples and comparative examples are all commercially available products. The chemical deposition method and plasma spraying method described in the present invention are existing processes and will not be elaborated too much. In addition, the on-line defect detection device is installed at the ball mill station and detects defects at any time during the polishing process of the ball mill.
[0034] Such as Figure 1 As shown, the on-line defect detection device used in the preparation method of the silicon nitride bearing balls includes an on-line defect detection body 1. A laser scanning module 2 and an ultrasonic detection module 3 are installed inside the on-line defect detection body 1, and a non-conforming product discharge hole 4 is provided on the body of the on-line defect detection body 1. A combined laser scanning and ultrasonic detection module is set at the sintering post-station to identify surface cracks (accuracy 0.1 μm) and internal pores (resolution 50 μm) in real time.
[0035] The on-line defect detection body 1 is installed between the upper grinding disc 5 and the lower grinding disc 6 and is fixed to the upper grinding disc 5. The on-line defect detection body 1 is fixed to the upper grinding disc 5 by means of bolts or the like.
[0036] The usage steps of the on-line defect detection device are as follows:
[0037] (1) Load into the ball mill according to the requirement of the number of balls per tray for different specifications of bearing balls.
[0038] (2) Start the ball mill, and the ball blanks roll and grind repeatedly in the grinding discs.
[0039] (3) When approaching the end of this process, turn on the on-line defect detection device. When defective products are detected, they will be automatically discharged from the square hole of the lower non-conforming product discharge hole 4.
[0040] Example 1
[0041] The preparation method of the silicon nitride bearing balls includes the following steps:
[0042] (1) Raw material treatment: Mix silicon nitride powder (purity 99.5%) with 8% of Al2O3 - Y2O3 (mass ratio 7:3) auxiliary agent based on the mass of the silicon nitride powder, and TiC accounts for 1% of the mass of the silicon nitride powder, and ball mill until the average particle size D50 is 0.5 μm.
[0043] (2) Forming and sintering: The processed raw materials are formed by cold isostatic pressing with a pressure of 200 MPa; then gradient sintering is carried out. The gradient sintering process includes three stages: pre-sintering, main sintering, and annealing. In the pre-sintering stage, the temperature is raised to 1350 °C at a rate of 10 °C / min and maintained for 1.5 h in an N2 atmosphere; in the main sintering stage, the temperature is raised to 1700 °C at a rate of 4 °C / min and maintained for 2.5 h in an N2 atmosphere; in the annealing stage, the temperature is lowered to 1400 °C at a rate of 2 °C / min, maintained for 3 h, and then cooled to room temperature. The sintering procedure is as Figure 2 shown.
[0044] (3) Coating processing: First, a 15-μm-thick Al2O3 coating is formed on the surface of the bearing ball by plasma spraying, and then a 3-μm-thick SiC coating is formed outside the Al2O3 layer by chemical vapor deposition, as Figure 3 shown.
[0045] (4) On-line inspection: During the grinding and polishing process, through the combined laser-ultrasonic screening of the on-line inspection defect device, the accuracy of real-time identification of surface cracks is 0.1 μm and the resolution of internal pores is 50 μm. The average diameter of the silicon nitride bearing ball is 5 mm.
[0046] Example 2
[0047] The preparation method of the silicon nitride bearing ball described above includes the following steps:
[0048] (1) Raw material treatment: Silicon nitride powder (purity 99.5%) is mixed with 10% of the mass of silicon nitride powder of Al2O3-Y2O3 (mass ratio 6:4) additive, and TiC accounts for 2% of the mass of silicon nitride powder, and ball-milled to an average particle size D50 of 0.5 μm.
[0049] (2) Forming and sintering: The processed raw materials are formed by cold isostatic pressing with a pressure of 180 MPa; then gradient sintering is carried out. The gradient sintering process includes three stages: pre-sintering, main sintering, and annealing. In the pre-sintering stage, the temperature is raised to 1200 °C at a rate of 8 °C / min and maintained for 2 h in an N2 atmosphere; in the main sintering stage, the temperature is raised to 1600 °C at a rate of 2 °C / min and maintained for 2 h in an N2 atmosphere; in the annealing stage, the temperature is lowered to 1350 °C at a rate of 1.5 °C / min, maintained for 3.5 h, and then cooled to room temperature. The sintering procedure is as Figure 2 shown.
[0050] (3) Coating processing: First, a 10-μm-thick Al2O3 coating is formed on the surface of the bearing ball by plasma spraying, and then a 2-μm-thick SiC coating is formed outside the Al2O3 layer by chemical vapor deposition, as Figure 3 shown.
[0051] (4) On-line detection: During the grinding and polishing process, through the combined laser-ultrasonic screening of the on-line defect detection device, the accuracy of real-time identification of surface cracks is 0.1 μm and the resolution of internal pores is 50 μm. The average diameter of the silicon nitride bearing balls is 15 mm.
[0052] Example 3
[0053] The preparation method of the silicon nitride bearing balls described above includes the following steps:
[0054] (1) Raw material treatment: Mix silicon nitride powder (purity 99.5%) with 5% of Al2O3-Y2O3 (mass ratio 7:3) of the mass of the silicon nitride powder, and 1% of TiC of the mass of the silicon nitride powder, and ball mill to an average particle size D50 of 0.5 μm.
[0055] (2) Molding and sintering: Cold isostatic pressing is carried out on the treated raw materials at a pressure of 220 MPa; then gradient sintering is carried out. The gradient sintering process includes three stages: pre-sintering, main sintering and annealing. In the pre-sintering stage, the temperature is raised to 1400 °C at a rate of 15 °C / min and kept for 1 h in an N2 atmosphere; in the main sintering stage, the temperature is raised to 1800 °C at a rate of 5 °C / min and kept for 2 h in an N2 atmosphere; in the annealing stage, the temperature is lowered to 1450 °C at a rate of 2.5 °C / min, kept for 2.5 h, and then cooled to room temperature. The sintering procedure is as Figure 2 shown.
[0056] (3) Coating processing: First, an Al2O3 coating with a thickness of 20 μm is formed on the surface of the bearing balls by plasma spraying process, and then a 5-μm SiC coating is formed outside the Al2O3 layer by chemical vapor deposition, as Figure 3 shown.
[0057] (4) On-line detection: During the grinding and polishing process, through the combined laser-ultrasonic screening of the on-line defect detection device, the accuracy of real-time identification of surface cracks is 0.1 μm and the resolution of internal pores is 50 μm. The diameter of the silicon nitride bearing balls is 30 mm.
[0058] Comparative Example 1
[0059] This comparative example is the same as Example 1. In the coating process of step (3), "and then a 3-μm SiC coating is formed outside the Al2O3 layer by chemical vapor deposition" is deleted, and only the Al2O3 coating is carried out.
[0060] Comparative Example 2
[0061] This comparative example is the same as Example 1. In the coating process of step (3), "first, an Al2O3 coating with a thickness of 10 μm is formed on the surface of the bearing balls by plasma spraying process" is deleted, and only the SiC coating is carried out.
[0062] For the bearing balls prepared in the above embodiments and comparative examples, after final grinding, the surface roughness Ra of the above bearing balls is 0.014 nm, and the spherical error is 0.13 μm. Performance testing is carried out according to industry standards, and the test results are shown in Table 1.
[0063] Table 1 Test Results
[0064] Item DC Impedance / GΩ Coefficient of Friction Impedance Retention Rate at 300°C / % Example 1 15 0.043 90 Example 2 13 0.042 85 Example 3 17 0.040 87 Comparative Example 1 16 0.048 75 Comparative Example 2 8 0.038 60
[0065] Of course, the above content is only the preferred embodiment of the present invention and cannot be considered as limiting the scope of the embodiments of the present invention. The present invention is not limited to the above examples. Equivalent changes and improvements made by those of ordinary skill in the art within the scope of the essence of the present invention shall fall within the scope covered by the patent of the present invention.
Claims
1. A method for preparing silicon nitride bearing balls, characterized in that: Including gradient sintering process, composite coating process, and on-line defect detection; The gradient sintering process includes three stages: pre-sintering, main sintering, and annealing. The temperature in the pre-sintering stage is 1200 - 1400 °C; the temperature in the main sintering stage is 1600 - 1800 °C, and the temperature in the annealing stage is 1350 - 1450 °C.
2. The preparation method of the silicon nitride bearing ball according to claim 1, characterized in that: The gradient sintering process includes three stages: pre-sintering, main sintering, and annealing. In the pre-sintering stage, it is heated to 1200 - 1400 °C at a rate of 8 - 15 °C / min and held for 1 - 2 h in an N2 atmosphere; in the main sintering stage, it is heated to 1600 - 1800 °C at a rate of 2 - 5 °C / min and held for 2 - 3 h in an N2 atmosphere; in the annealing stage, it is cooled to 1350 - 1450 °C at a rate of 1.5 - 2.5 °C / min, held for 2.5 - 3.5 h, and then cooled to room temperature.
3. The preparation method of the silicon nitride bearing ball according to claim 1, characterized in that: It also includes raw material treatment and forming processes.
4. The preparation method of the silicon nitride bearing ball according to claim 3, characterized in that: The raw material treatment process is: mixing silicon nitride powder with Al2O3, Y2O3, and TiC additives, and ball milling to an average particle size D50 of 0.5 μm.
5. The preparation method of the silicon nitride bearing ball according to claim 4, wherein: The sum of the masses of Al2O3 and Y2O3 is 5 - 10% of the silicon nitride powder, the mass ratio of Al2O3 to Y2O3 is 7:3 - 6:4, and TiC is 1 - 2% of the silicon nitride powder.
6. The preparation method of the silicon nitride bearing ball according to claim 3, wherein: Forming process: subjecting the treated raw materials to cold isostatic pressing with a pressure of 180 - 220 MPa.
7. The manufacturing method of the silicon nitride bearing ball according to claim 1, characterized in that: The coating process is to first form an Al2O3 coating with a thickness of 10 - 20 μm on the surface of the bearing ball by plasma spraying, and then form a 2 - 5 μm SiC coating outside the Al2O3 layer by chemical vapor deposition.
8. The manufacturing method of the silicon nitride bearing ball according to claim 1, characterized in that: The on-line defect detection is through laser-ultrasonic combined screening, with a real-time surface crack recognition accuracy of 0.1 μm and an internal pore resolution of 50 μm, and further controlling the dynamic adjustment parameters of the sintering furnace.
9. An on-line defect detection device used in the preparation method of the silicon nitride bearing balls as described in claim 1, characterized in that: It includes an on-line defect detection body (1). Inside the on-line defect detection body (1), a laser scanning module (2) and an ultrasonic detection module (3) are installed. On the body of the on-line defect detection body (1), there is a defective product discharge hole (4).
10. The on-line defect detection device used in the preparation method of the silicon nitride bearing balls according to claim 9, characterized in that: The on-line defect detection body (1) is installed between the upper grinding disc (5) and the lower grinding disc (6) and fixed to the upper grinding disc (5).