Preparation method of fusible polytetrafluoroethylene composite material for bearing

Abstract

The invention provides a preparation method of a fusible polytetrafluoroethylene composite material for a bearing, which comprises the following steps: by taking fusible polytetrafluoroethylene as a polymer matrix and carbon fibers, copper powder and graphite as reinforcing components, carrying out low-temperature liquid phase blending, crushing and drying processes to prepare the fusible polytetrafluoroethylene composite material for the bearing. The invention aims to control the moisture content and the uniformity of the composite material through low-temperature mixing and freeze-drying by taking a fusible polytetrafluoroethylene (PFA) agglomerated material obtained by polymerization as a raw material. Compared with the traditional composite material prepared by carrying out secondary mechanical blending on PFA resin, the composite material has the advantages that the moisture content can be controlled to be far lower than the existing level of 0.02%, and agglomeration during transportation and storage is avoided; and meanwhile, crushing, shaping and composite material extraction processes are adopted, so that the uniformity of the composite material is greatly improved, and the comprehensive performance of the composite material is enhanced. On the basis, the content of the modified monomer in the PFA resin is regulated and controlled, so that the mechanical property and the dimensional stability are improved; through synergistic modification of the carbon fibers, the copper powder and the graphite, the wear resistance and the thermal conductivity of the composite material are comprehensively improved.

Description

Technical Field

[0001] The invention belongs to the field of composite materials, relates to the preparation of fluoroplastics, and in particular to the preparation of fusible polytetrafluoroethylene composite material for bearings. Background Art

[0002] Polytetrafluoroethylene resin is one of the core materials for manufacturing wear-resistant and lubricating bearings. Its particle size and compound formula directly determine the performance, reliability and life of the bearings. Fusible polytetrafluoroethylene (PFA) is a new type of fluoroplastic copolymerized from tetrafluoroethylene and a small amount of perfluoroalkoxy-modified monomers. It is used in the field of bearings and has the characteristics of high temperature resistance, friction reduction, wear resistance, and corrosion resistance. In particular, it is easy to be compounded with metal parts by bonding, inlaying, or even welding.

[0003] After more than sixty years of development, the composite modification technology of polytetrafluoroethylene has become relatively mature. However, the development of low-melting-point, low-crystallinity fusible polytetrafluoroethylene lags far behind. At present, most existing PFA resins are commercially sold in the form of pure resins, and the grades are distinguished only by the resin particle size. The reason is that the compounding system of PFA resin is not perfect, and it is difficult to meet the comprehensive requirements of bearing applications for multiple performance dimensions of materials, resulting in a single variety and brand and unbalanced comprehensive performance. When developing bearing products, it is necessary to purchase PFA resins of different brands from upstream resin manufacturers, and then perform compound modification. This makes it difficult to meet the objective needs of the bearing field for complex material systems, diverse component specifications, and precise overall structures.

[0004] To this end, the present invention provides a PFA composite material and a preparation method thereof by regulating the content of modified monomers, designing a compounding system, and regulating the crushing, mixing, and drying processes. The developed composite material does not require secondary treatment and can be directly used for the molding and manufacturing of PTFE integral bearings, bonded bearings, and inlaid bearings. It has low water content, low shrinkage, high wear resistance, high thermal conductivity, and strong self-lubricating properties, meeting the application requirements in the field of wear-resistant and lubricating bearings. Summary of the invention

[0005] The purpose of the present invention is to disclose a method for preparing a fusible polytetrafluoroethylene composite material for bearings, so as to solve the problem that the existing PFA resin compounding system is imperfect and it is difficult to meet the requirements of bearing applications on multiple performance dimensions of materials.

[0006] 1. Preparation of Fusible Polytetrafluoroethylene Composites A method for preparing a fusible polytetrafluoroethylene composite material for a bearing comprises the following steps: 1) Raw material mixing: Add fusible polytetrafluoroethylene agglomerates, carbon fiber, copper powder and graphite into a mixing kettle, stir for 30 to 120 minutes in an ice-water medium (-5°C to -35°C), and remove the medium after filtering.

[0007] 2) Freeze drying: drying the filtrate obtained in step 1) at a temperature of -80°C to -15°C for 45 to 240 minutes; 3) Crushing and shaping: Put the composite material obtained in step 2) into the ultra-fine airflow pulverizer at a pressure of 0.5~1.5MPa and an air compressor flow rate of 2~40m 3 / min for 1~3 times, and then put into the horizontal turbine classifier at an air compressor flow rate of 2~100m 3 / min, oxygen content 5~50ppm, shaping 2~8 times, extracting fine powder with particle size 20~60μm.

[0008] The fusible polytetrafluoroethylene mass described in step 1) has a size of 0.5-10 mm and a perfluorovinyl ether content of 0.01%-0.20%; the carbon fiber has a diameter of 5-8 μm and an aspect ratio of 3-6; the copper powder is pine cone-shaped, has a thermal conductivity of 200-750 W / (m·K), and a size of 5-60 μm; and the graphite has a size of 5-50 μm.

[0009] In parts by mass, the fusible polytetrafluoroethylene mass, carbon fiber, copper powder and graphite are 75-85 parts, 3-15 parts, 1-5 parts and 1-5 parts respectively.

[0010] 2. Properties of Fusible PTFE Composites 1. Moisture content The test was carried out in accordance with Section 5.7 of HG / T 2903-1997 “Fine-grained polytetrafluoroethylene resin for molding”.

[0011] 2. Shrinkage Take an appropriate amount of resin or compound material and pour it into the cavity of a cylindrical mold with an outer diameter of 52 mm, filling the entire cavity. After closing the mold, place it in a hydraulic press and slowly pressurize it to (34.5±2.0) MPa. After maintaining the pressure for 2 minutes, release the pressure and take out the preform with an outer diameter of about 50 mm and a thickness of 20 mm from the mold. According to Table 2 of HG / T 2903-1997 "Fine-grained polytetrafluoroethylene resin for molding", the outer diameter change rate is measured after sintering, which is the shrinkage rate of the compound material. The data are listed in Table 1.

[0012] 3. Tensile properties The composite material was filled into a mold with a cavity of φ120 mm×4 mm and pressed at 45 MPa for 5 min. After sintering at 360°C for 60 min, the dumbbell shape of 80 mm×10 mm×4 mm was punched and cut. The tensile strength was tested on a universal testing machine according to GB / T 1040.2-2022. The data are listed in Table 1.

[0013] 4. Thermal conductivity test The composite material was filled into a mold with a cavity of φ60 mm×2 mm, and after molding according to the conditions specified in HG / T 2903-1997 "Fine-grained polytetrafluoroethylene resin for molding", it was punched and cut into small discs of φ12.7 mm×2 mm. The thermal conductivity was tested on a thermal conductivity tester according to GJB / T 1201.1-91. The data are listed in Table 1.

[0014] 5. Friction and wear performance test The composite material was filled into a mold with a cavity of φ80 mm×10 mm, and after molding according to the conditions specified in HG / T 2903-1997 "Fine-grained polytetrafluoroethylene resin for molding", it was machined into a ring with an outer diameter of 31.7 mm, an inner diameter of 16 mm, and a height of 10 mm. The wear rate was measured on a friction and wear tester according to ASTM D3703. The data are listed in Table 1.

[0015] Table 1 Performance of PFA composites prepared in Examples 1 to 3 As shown in Table 1, the moisture content of the PFA composite prepared by the present invention is 0.005%~0.008%, the shrinkage is 0.8%~1.7%, the tensile strength is 28.7~33.0MPa, the thermal conductivity is (0.50~0.62)W / (m·K), and the wear rate is (0.8~2.5)×10 - 6 mm 3 / N·m. It can be seen that the PFA composite material developed in the present invention has an extremely low moisture content, which is far less than the average level of 0.02%, and can effectively avoid agglomeration due to water absorption during transportation and storage; it has a low shrinkage rate, indicating that the composite material has a high dimensional stability during pressing and sintering; at the same time, the tensile strength and thermal conductivity are high, and the wear rate is low, which can meet the core requirements of high-strength, high-thermal-conductivity and low-wear bearing applications. In contrast, Comparative Example 1 directly uses PFA resin powder instead of the aggregate obtained by polymerization as raw material, and adopts conventional mechanical blending, so a small amount of water that causes the resin to agglomerate is wrapped, which is difficult to remove through the subsequent drying process, resulting in a moisture content of 0.022% at the conventional level, which is not conducive to long-term transportation or storage, and the shrinkage rate, tensile strength, thermal conductivity and wear rate and other properties also have a slight decrease. Comparative Example 2 uses a conventional drying process to remove water, and the water content is at a high level of 0.039%, resulting in a significant decrease in comprehensive performance. Comparative Example 3 was not subjected to shaping treatment, resulting in insufficient uniformity of the composite material, causing the tensile strength to drop to 24.8 MPa and the wear rate to increase to 4.7×10 -6 mm 3 / N·m, which is not conducive to the long-term reliable use of bearings. DETAILED DESCRIPTION

[0016] The preparation and performance of the polytetrafluoroethylene bearing of the present invention are further described below through specific examples.

[0017] Example 1 (1) Raw material mixing: 16 kg of fusible polytetrafluoroethylene agglomerates (size 5 mm, perfluorovinyl ether content 0.02%), 2 kg of carbon fiber (diameter 6.5 μm, aspect ratio 6), 1 kg of copper powder (pine cone shape, thermal conductivity 215 W / (m·K), size 50 μm), and 1 kg of graphite (size 50 μm) were added to a mixing kettle, stirred in an ice-water medium for 30 min, and the medium was removed after filtration.

[0018] (2) Freeze drying: drying the filtrate obtained in step 1) at -80°C for 45 min; (3) Crushing and shaping: The composite material obtained in step 2) is crushed in an ultra-fine air flow mill at a pressure of 0.5 MPa and an air compressor flow rate of 4 m 3 / min, and then crushed once, and passed through a horizontal high-precision turbine classifier at an air compressor flow rate of 20m 3 / min, and an oxygen content of 20ppm, the shaping was performed twice to extract fine powder with a particle size of 60μm.

[0019] The performance data are listed in Table 1.

[0020] Example 2 (1) Raw material mixing: 85 kg of fusible polytetrafluoroethylene agglomerates (size 2 mm, perfluorovinyl ether content 0.15%), 15 kg of carbon fibers (diameter 7.2 μm, aspect ratio 4), 3 kg of copper powder (pine cone-shaped, thermal conductivity 600 W / (m·K), size 40 μm), and 2 kg of graphite (size 15 μm) were added to a mixing kettle, stirred in an ice-water medium for 60 min, and the medium was removed after filtration.

[0021] (2) Freeze drying: drying the filtrate obtained in step 1) at -60°C for 240 min; (3) Crushing and shaping: The composite material obtained in step 2) is crushed in an ultra-fine air flow mill at a pressure of 1.5 MPa and an air compressor flow rate of 40 m 3 / min, crushed 3 times, passed through a horizontal high-precision turbine classifier at an air compressor flow rate of 100m 3 / min, and an oxygen content of 8ppm, the shaping was performed 5 times to extract fine powder with a particle size of 55μm.

[0022] The performance data are listed in Table 1.

[0023] Example 3 (1) Raw material mixing: 17 kg of fusible polytetrafluoroethylene agglomerates (size 1 mm, perfluorovinyl ether content 0.10%), 1 kg of carbon fiber (diameter 7.5 μm, aspect ratio 3), 1 kg of copper powder (pine cone shape, thermal conductivity 450 W / (m·K), size 20 μm), and 1 kg of graphite (size 5 μm) were added to a mixing kettle, stirred in an ice-water medium for 40 min, and the medium was removed after filtration.

[0024] (2) Freeze drying: drying the filtrate obtained in step 1) at -20°C for 60 min; (3) Crushing and shaping: The composite material obtained in step 2) is crushed in an ultra-fine air flow mill at a pressure of 0.75 MPa and an air compressor flow rate of 10 m 3 / min, crushed twice, passed through a horizontal high-precision turbine classifier at an air compressor flow rate of 50m 3 / min, and an oxygen content of 40ppm were used for three times to extract fine powder with a particle size of 30μm.

[0025] The performance data are listed in Table 1.

[0026] Comparative Example 1 (1) Raw material mixing: 16 kg of fusible polytetrafluoroethylene (particle size 30 μm, perfluorovinyl ether content 0.02%), 2 kg of carbon fiber (diameter 6.5 μm, aspect ratio 6), 1 kg of copper powder (pine cone shape, thermal conductivity 215 W / (m·K), size 50 μm), and 1 kg of graphite (size 50 μm) were blended in a mechanical stirrer at a stirring speed of 400 rpm for 60 min.

[0027] (2) Freeze drying: drying the composite material obtained in step 1) at -80°C for 45 min; (3) Crushing and shaping: The composite material obtained in step 2) is crushed in an ultra-fine air flow mill at a pressure of 0.5 MPa and an air compressor flow rate of 4 m 3 / min, and then crushed once, and passed through a horizontal high-precision turbine classifier at an air compressor flow rate of 20m 3 / min, and an oxygen content of 20ppm, the shaping was performed twice to extract fine powder with a particle size of 60μm.

[0028] The performance data are listed in Table 1.

[0029] Comparative Example 2 (1) Raw material mixing: 17 kg of fusible polytetrafluoroethylene agglomerates (size 1 mm, perfluorovinyl ether content 0.10%), 1 kg of carbon fiber (diameter 7.5 μm, aspect ratio 3), 1 kg of copper powder (pine cone shape, thermal conductivity 450 W / (m·K), size 20 μm), and 1 kg of graphite (size 5 μm) were added to a mixing kettle, stirred in an ice-water medium for 40 min, and the medium was removed after filtration.

[0030] (2) Drying: Dry the filtrate obtained in step 1) at 40°C for 240 min; (3) Crushing and shaping: The composite material obtained in step 2) is crushed in an ultra-fine air flow mill at a pressure of 0.75 MPa and an air compressor flow rate of 10 m 3 / min, crushed twice, passed through a horizontal high-precision turbine classifier at an air compressor flow rate of 50m 3 / min, and an oxygen content of 40ppm were used for three times to extract fine powder with a particle size of 30μm.

[0031] The performance data are listed in Table 1.

[0032] Comparative Example 3 (1) Raw material mixing: 17 kg of fusible polytetrafluoroethylene agglomerates (size 1 mm, perfluorovinyl ether content 0.10%), 1 kg of carbon fiber (diameter 7.5 μm, aspect ratio 3), 1 kg of copper powder (pine cone shape, thermal conductivity 450 W / (m·K), size 20 μm), and 1 kg of graphite (size 5 μm) were added to a mixing kettle, stirred in an ice-water medium for 40 min, and the medium was removed after filtration.

[0033] (2) Freeze drying: drying the filtrate obtained in step 1) at 40°C for 240 min; (3) Crushing and shaping: The composite material obtained in step 2) is crushed in an ultra-fine air flow mill at a pressure of 0.75 MPa and an air compressor flow rate of 10 m 3 / min for two times, and extract fine powder with a particle size of 30μm.

[0034] The performance data are listed in Table 1.

Claims

1. A method for preparing a fusible polytetrafluoroethylene composite material for bearings, characterized in that: The following steps are involved: 1) Raw material mixing: Add fusible polytetrafluoroethylene agglomerates, carbon fiber, copper powder and graphite into a mixing kettle, stir in ice water medium for 30-120 minutes, and remove the medium after filtering; 2) Freeze drying: drying the filtrate obtained in step 1) at a temperature of -80°C to -15°C for 45 to 240 minutes; 3) Crushing and shaping: Put the composite material obtained in step 2) into the ultra-fine airflow pulverizer at a pressure of 0.5~1.5MPa and an air compressor flow rate of 2~40m 3 / min for 1~3 times, and then put into the horizontal turbine classifier at an air compressor flow rate of 2~100m 3 / min, oxygen content 5~50ppm, shaping 2~8 times, extracting fine powder with particle size 20~60μm.

2. A fusible polytetrafluoroethylene composite material for bearings and a preparation method thereof as claimed in claim 1, characterized in that: The fusible polytetrafluoroethylene mass described in step 1) has a size of 0.5-10 mm and a perfluorovinyl ether content of 0.01%-0.20%; the carbon fiber has a diameter of 5-8 μm and an aspect ratio of 3-6; the copper powder is pine cone-shaped, has a thermal conductivity of 200-750 W / (m·K), and a size of 5-60 μm; and the graphite has a size of 5-50 μm.

3. A high PV polytetrafluoroethylene integral sliding bearing and a preparation method thereof as claimed in claim 1, characterized in that: In step 1), the fusible polytetrafluoroethylene mass, carbon fiber, copper powder and graphite are respectively 75-85 parts, 3-15 parts, 1-5 parts and 1-5 parts by mass.

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