High-performance carbon / carbon composite bearing cage with CVD coating and preparation method thereof

Abstract

The present invention discloses a high-performance carbon / carbon composite bearing retainer with a CVD coating and a method for preparing the same, relating to the technical field of bearing retainer preparation. The method first utilizes high-strength carbon fibers to penetrate a carbon fiber fabric preform. A high-density carbon / carbon composite retainer blank is then prepared using chemical vapor infiltration. After graphitization heat treatment and fine machining, the carbon / carbon composite retainer is obtained. An isotropic (ISO) pyrolytic graphite coating is then deposited on the retainer's surface using CVD technology to produce the final product. This retainer exhibits superior wear resistance and friction reduction, increasing the bearing's rotational speed and operating temperature, further extending the bearing's service life.

Description

Technical Field

[0001] The present invention relates to the technical field of bearing retainer preparation, and in particular to a high-performance carbon / carbon composite material bearing retainer with a CVD coating and a preparation method thereof. Background Art

[0002] The function of a bearing cage is to evenly separate the rolling elements in the bearing, preventing collision and friction, and ensuring that each rolling element bears the appropriate load in turn and evenly. Under high-temperature and high-speed operating conditions, the high centrifugal force exacerbates friction, wear, and heat generation. In severe cases, this can cause the cage to burn or break, resulting in bearing malfunction. Therefore, in addition to possessing a certain strength, the cage material must also have good thermal conductivity, a low coefficient of friction, excellent wear resistance, high impact toughness, and a low density. In extremely low or high temperature operating environments, lubricants cannot be used, so the cage material must have excellent self-lubricating properties and high-temperature strength.

[0003] Conventional engineering plastic cages have certain lightness and self-lubricating properties, but their low and high temperature strength is poor, making it difficult to meet the requirements of -150℃~300℃ and DN value (bearing diameter and speed product) greater than 3×10 6 mm.r / min working environment requirements. Carbon / carbon composite materials made from traditional needle-punched preforms suffer from weaknesses such as cracking in the cage pockets and low overall strength. Therefore, developing a cage material with high strength, a wide temperature range, corrosion resistance, and the ability to form a uniform lubricating film is crucial. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a high-performance carbon / carbon composite bearing cage with a CVD coating and a preparation method thereof, so as to prepare a cage with wide temperature range and high performance, which can realize oil-free self-lubrication under harsh conditions such as high temperature, low temperature and high speed, thereby achieving the purpose of wear resistance and friction reduction.

[0005] To achieve this technical purpose, the present invention adopts the following scheme:

[0006] A method for preparing a high-performance carbon / carbon composite bearing cage with a CVD coating comprises the following steps:

[0007] S1. Preform preparation: A cylindrical preform is obtained by alternately winding and laying the non-woven carbon cloth and the mesh layer, puncturing and suturing, and the density of the cylindrical preform is 0.75±0.05g / cm 3 ;

[0008] S2. Chemical vapor infiltration densification treatment: Place the cylindrical preform in a chemical vapor infiltration furnace, introduce natural gas and hydrogen to pressurize and densify it, then take it out and place it in a vacuum induction graphitization furnace, perform graphitization heat treatment in a protective gas to obtain a graphitized body, and continue to perform densification and graphitization heat treatment on the graphitized body in sequence until the density of the cylindrical preform reaches 1.70~1.75g / cm 3 Until a cylindrical preform body is obtained;

[0009] S3, machining and surface pretreatment: cutting the cylindrical preform obtained in S2 to obtain a bearing cage blank, and then machining it to obtain a carbon / carbon composite material bearing cage;

[0010] S4. CVD coating treatment: placing the carbon / carbon composite material bearing cage obtained in S3 in a chemical vapor deposition furnace to deposit a coating, and obtaining a carbon / carbon composite material bearing cage with a CVD coating after coating technology.

[0011] Furthermore, the Z-axis yarn pitch and row pitch of the cylindrical preform of S1 are 5.0±0.5 mm, respectively, and the layer density is 20 layers / cm; the weftless carbon cloth fiber used is T300 3K / 6K PAN (polyacrylonitrile) based fiber, where K represents the number of thousands of tows.

[0012] Furthermore, in S2, the temperature in the chemical vapor infiltration furnace is 1000℃~1030℃, the volume ratio of natural gas and hydrogen is 2~4:1, the pressure is 5~10KPa, the densification time is 150h, and the deposited pyrolytic carbon structure is a smooth layer structure. Figure 1 .

[0013] Furthermore, the protective gas in the vacuum induction graphitization furnace in S2 is argon, the temperature is between 1800°C and 2100°C, and the graphitization heat treatment is carried out and kept warm for 2 to 3 hours.

[0014] Furthermore, the mechanical processing in S3 includes rough processing, fine processing, mechanical polishing, ultrasonic cleaning and drying.

[0015] Furthermore, the ultrasonic cleaning power is 100W, the cleaning time is controlled at 15 minutes, the medium is alcohol and water; the drying temperature is 100°C, and the drying time is 2 to 3 hours.

[0016] Furthermore, the deposition pressure in the S4 chemical vapor deposition furnace is slightly positive (0.12 MPa), the working gas is methane and nitrogen with a purity of ≥99.999%, the deposition temperature is 1500~1600℃, the coating thickness is 100μm, and the deposition time is 20h.

[0017] The high-performance carbon / carbon composite material bearing cage with CVD coating obtained by the above method.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The cylindrical preform is obtained by alternately laying the non-woven carbon cloth and the mesh tire layer and then continuously puncturing and stitching them. The puncture and stitching process improves the interlayer strength of the material, especially the strength of the pockets;

[0020] 2. The carbon / carbon composite body is prepared by chemical vapor infiltration, that is, a carbon source precursor is used to form pyrolytic carbon on the surface of the preform. The structure of pyrolytic carbon directly affects the performance of carbon-based composite materials. Among various types of pyrolytic carbon, smooth layer pyrolytic carbon has the advantages of high density and high strength.

[0021] 3. The densification process of carbon / carbon composite materials uses a single gas source as a precursor. Since natural gas molecules have a small volume and a large diffusion coefficient, they can easily penetrate into the preform, ultimately resulting in a material with high density and excellent performance. The present invention uses a mixture of natural gas and hydrogen to prepare carbon / carbon composite materials. Hydrogen has the highest diffusion rate and can inhibit surface crusting. This shortens the densification cycle and easily obtains a smooth layer of pyrolytic carbon with excellent performance.

[0022] 4. Isotropic pyrolytic carbon coating applied on the surface of carbon / carbon cage by CVD (see attached Figure 3 ), with the advantages of high density and low porosity, its surface is more likely to form a lubricating film, reducing the friction coefficient and wear rate, and improving the stability of bearing operation;

[0023] 5. The tensile strength of the carbon / carbon composite bearing cage of the present invention is ≥220MPa at room temperature (see attached Figure 2 ), impact strength ≥50KJ / m 2 , thermal conductivity ≥ 35W / mk (RT-200℃), thermal expansion coefficient -0.63*10 -6 / K (RT-200℃); sliding dry friction coefficient 0.06 (grinding with silicon nitride balls). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A sample image of a high-performance carbon / carbon composite bearing cage with a CVD coating provided by an embodiment of the present invention;

[0025] Figure 2 A tensile strength-displacement curve of a high-performance carbon / carbon composite bearing cage sample with a CVD coating provided in an embodiment of the present invention;

[0026] Figure 3 Metallographic image of an isotropic (ISO) pyrolytic carbon coating deposited on the surface of a high-performance carbon / carbon composite bearing cage with a CVD coating provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments, but the present invention is not limited thereto.

[0028] The present invention provides a method for preparing a high-performance carbon / carbon composite bearing retainer with a CVD coating. The method first uses long-fiber non-woven carbon cloth and short-fiber mesh tires to alternately wind into a cylindrical preform, then punctures and sews in the thickness direction to improve the interlayer bonding strength, and then uses a chemical vapor infiltration method to prepare a high-density carbon / carbon composite retainer blank. After graphitization heat treatment, fine processing, ultrasonic cleaning and drying, a carbon / carbon composite retainer is obtained, which has excellent strength. Subsequently, a pyrolytic graphite coating is deposited on its surface using chemical vapor deposition technology to obtain the final product. The retainer treated by this method has more excellent wear resistance and friction reduction characteristics, can increase the rotation speed and operating temperature of the bearing, and further improve the service life of the bearing.

[0029] The preparation process of the embodiment is as follows:

[0030] S1. Preform Preparation

[0031] First, long fiber carbon cloth and mesh layers are alternately laid, and then inoculated and sutured to obtain a cylindrical preform. The Z-axis yarn pitch and row spacing are 5.0±0.5mm respectively; the layer density is 20 layers / cm; and the preform density is 0.70±0.05g / cm 3 The fiber is T300 3K / 6K PAN (polyacrylonitrile) based fiber (K ​​represents the number of thousands of tows).

[0032] S2. Chemical vapor infiltration densification treatment

[0033] The cylindrical preform is placed in a chemical vapor infiltration furnace, and natural gas and hydrogen are introduced at a ratio of 2:1 at 1030°C and a pressure of 5KPa. After densification for 150 hours, it is taken out and placed in a vacuum induction graphitization furnace. Under argon protection, a high-temperature graphitization heat treatment of 1800°C to 2100°C is carried out and kept warm for 2 to 3 hours. After the graphitization heat treatment, the green body continues to undergo densification and graphitization heat treatment in sequence until the density of the cylindrical preform reaches 1.70~1.75g / cm 3 until.

[0034] S3. Machining and surface pretreatment

[0035] The cylindrical preform of S2 that has reached the required density is cut to produce the bearing cage blank. It is then machined according to the finished cage drawing to produce a carbon / carbon composite bearing cage. After rough and fine machining, it undergoes mechanical polishing, ultrasonic cleaning, and drying. The ultrasonic cleaning power is controlled at 100W for 15 minutes using an alcohol-water medium. Finally, it is dried in an oven at 100°C for 2-3 hours.

[0036] S4, CVD coating treatment

[0037] The cage treated as above is placed in a chemical vapor deposition furnace with a slightly positive deposition pressure (0.11-0.13 MPa), high-purity methane and nitrogen (purity ≥ 99.999%), a deposition temperature of 1500-1600°C, a coating thickness of 100 μm, and a deposition time of 20 h. After the coating is completed, a high-performance carbon / carbon composite bearing cage with a CVD coating is obtained.

[0038] The tensile strength test of the product obtained in the embodiment was carried out (implementation standard GJB6475-2008), and the results are as follows Figure 2 As shown, the tensile strength of the product is 220Mpa and the impact strength is ≥50KJ / m 2 , thermal conductivity ≥ 35W / mk (RT-200℃), thermal expansion coefficient -0.63*10 -6 / K (RT-200℃); sliding dry friction coefficient 0.06 (grinding with silicon nitride balls).

[0039] The isotropic pyrolytic graphite coating deposited on the surface of the product obtained in the embodiment was detected under a microscope, and the results were as follows: Figure 3 As shown, this product has the advantages of high density and low porosity. It is easier to form a lubricating film on its surface, reducing the friction coefficient and wear rate, and improving the stability of bearing operation.

[0040] Comparative Example 1

[0041] S1. Preform Preparation

[0042] First, long fiber carbon cloth and mesh layers are alternately laid, and then inoculated and sutured to obtain a cylindrical preform. The Z-axis yarn pitch and row spacing are 5.0±0.5mm respectively; the layer density is 20 layers / cm; and the preform density is 0.70±0.05g / cm 3 The fiber is T300 3K / 6K PAN (polyacrylonitrile) based fiber (K ​​represents the number of thousands of tows).

[0043] S2. Chemical vapor infiltration densification treatment

[0044] The cylindrical preform is placed in a chemical vapor infiltration furnace, and natural gas and hydrogen are introduced at a ratio of 2:1 at 1030°C and a pressure of 5KPa. After densification for 150 hours, it is taken out and placed in a vacuum induction graphitization furnace. Under argon protection, a high-temperature graphitization heat treatment of 1800°C to 2100°C is carried out and kept warm for 2 to 3 hours. After the graphitization heat treatment, the green body continues to undergo densification and graphitization heat treatment in sequence until the density of the cylindrical preform reaches 1.70~1.75g / cm 3 until.

[0045] S3. Machining and surface pretreatment

[0046] The cylindrical preform of S2 that has reached the required density is cut to produce the bearing cage blank. It is then machined according to the finished cage drawing to produce a carbon / carbon composite bearing cage. After rough and fine machining, it undergoes mechanical polishing, ultrasonic cleaning, and drying. The ultrasonic cleaning power is controlled at 100W for 15 minutes using an alcohol-water medium. Finally, it is dried in an oven at 100°C for 2-3 hours.

[0047] Comparative Example 2

[0048] S1. Preform Preparation

[0049] First, long fiber carbon cloth and mesh layers are alternately laid, and then inoculated and sutured to obtain a cylindrical preform. The Z-axis yarn pitch and row spacing are 5.0±0.5mm respectively; the layer density is 20 layers / cm; and the preform density is 0.70±0.05g / cm 3 The fiber is T300 3K / 6K PAN (polyacrylonitrile) based fiber (K ​​represents the number of thousands of tows).

[0050] S2. Chemical vapor infiltration densification treatment

[0051] The cylindrical preform is placed in a chemical vapor infiltration furnace, and natural gas and hydrogen are introduced at a ratio of 2:1 at 1010°C and a pressure of 5KPa. After densification for 150 hours, it is taken out and placed in a vacuum induction graphitization furnace. Under argon protection, a high-temperature graphitization heat treatment of 1800°C to 2100°C is carried out and kept warm for 2 to 3 hours. After the graphitization heat treatment, the green body continues to undergo densification and graphitization heat treatment in sequence until the density of the cylindrical preform reaches 1.70~1.75g / cm 3 until.

[0052] S3. Machining and surface pretreatment

[0053] The cylindrical preform of S2 that has reached the required density is cut to produce the bearing cage blank. It is then machined according to the finished cage drawing to produce a carbon / carbon composite bearing cage. After rough and fine machining, it undergoes mechanical polishing, ultrasonic cleaning, and drying. The ultrasonic cleaning power is controlled at 100W for 15 minutes using an alcohol-water medium. Finally, it is dried in an oven at 100°C for 2-3 hours.

[0054] In order to further study and evaluate the mechanical properties and friction and wear properties of the materials prepared in the examples and comparative examples, the materials prepared in the examples and comparative examples were subjected to performance tests, and the strength and test results were compared as shown in Table 1 below.

[0055] Example Comparative Example 1 Comparative Example 2 Tensile strength (MPa) 220 180 165 Dry friction coefficient (grinding with silicon nitride balls) 0.06 0.15 0.13

[0056] The pyrolytic carbon structure prepared in Comparative Example 1 has a smooth layer, while Comparative Example 2 has a rough layer. Neither layer has an ISO coating applied. This comparison shows that the composite material with the smooth layer exhibits higher tensile strength than the composite material with the rough layer. Applying a surface coating significantly improves the coefficient of friction while increasing tensile strength.

[0057] Finally, it should be noted that the above-listed embodiments are merely preferred embodiments of the present invention. Of course, those skilled in the art may make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should be considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance carbon / carbon composite bearing cage with a CVD coating, characterized in that: The steps include: S1. Preform preparation: A cylindrical preform is obtained by alternately winding and laying the non-woven carbon cloth and the mesh layer, puncturing and suturing, and the density of the cylindrical preform is 0.75±0.05g / cm 3 ; S2. Chemical vapor infiltration densification treatment: Place the cylindrical preform in a chemical vapor infiltration furnace, introduce natural gas and hydrogen to pressurize and densify it, then take it out and place it in a vacuum induction graphitization furnace, perform graphitization heat treatment in a protective gas to obtain a graphitized body, and continue to perform densification and graphitization heat treatment on the graphitized body in sequence until the density of the cylindrical preform reaches 1.70~1.75g / cm 3 Until a cylindrical preform body is obtained; S3, machining and surface pretreatment: cutting the cylindrical preform obtained in S2 to obtain a bearing cage blank, and then machining it to obtain a carbon / carbon composite material bearing cage; S4, CVD coating treatment: placing the carbon / carbon composite material bearing cage obtained in S3 in a chemical vapor deposition furnace to deposit a coating, and obtaining a carbon / carbon composite material bearing cage with a CVD coating after the coating process; The Z-axis yarn pitch and row pitch of the cylindrical preform of S1 were 5.0 ± 0.5 mm, and the layer density was 20 layers / cm. The weftless carbon cloth fiber was T300 3K / 6K PAN (polyacrylonitrile) based fiber, where K represents the number of thousands of tows. The deposition pressure in the S4 chemical vapor deposition furnace is slightly positive, the working gas is methane and nitrogen with a purity of ≥99.999%, the deposition temperature is 1500~1600℃, the coating thickness is 100μm, and the deposition time is 20h.

2. The method for preparing a high-performance carbon / carbon composite bearing cage with a CVD coating according to claim 1, characterized in that: The temperature in the chemical vapor infiltration furnace in S2 is 1000℃~1030℃, the volume ratio of natural gas and hydrogen is 2~4:1, the pressure is 5~10KPa, and the densification time is 150h.

3. The method for preparing a high-performance carbon / carbon composite bearing cage with a CVD coating according to claim 1, characterized in that: In the vacuum induction graphitization furnace S2, the protective gas is argon, the temperature is 1800℃~2100℃, and the graphitization heat treatment is carried out and kept warm for 2~3h.

4. The method for preparing a high-performance carbon / carbon composite bearing cage with a CVD coating according to claim 1, characterized in that: The machining in S3 includes rough machining, fine machining, mechanical polishing, ultrasonic cleaning and drying.

5. The method for preparing a high-performance carbon / carbon composite bearing cage with a CVD coating according to claim 4, characterized in that: The ultrasonic cleaning power is 100W, the cleaning time is controlled at 15 minutes, the medium is alcohol and water; the drying temperature is 100℃, and the drying time is 2~3 hours.

6. A high-performance carbon / carbon composite material bearing cage with a CVD coating obtained by the method for preparing a high-performance carbon / carbon composite material bearing cage with a CVD coating according to any one of claims 1 to 5.

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