Preparation method of polyvinylidene fluoride-based composite material of key component of magnetic drive pump

Abstract

The invention discloses a preparation method of a polyvinylidene fluoride based composite material of a magnetic drive pump key component, and relates to the technical field of polymer composites.The preparation method comprises the specific steps of raw material modification treatment, component premixing, melt blending extrusion, mold pressing cooling forming and plasma aftertreatment. The PVDF resin is subjected to graft modification, the carbon fibers are sequentially subjected to oxidation and silane coupling agent dipping treatment, and the filler with the specific function is matched and premixed, so that bonding of adaptive interfaces of a matrix, a reinforced phase and the functional filler is promoted, and it is guaranteed that components are uniformly distributed and consistent with the internal structure; a compact structure is formed through melt blending, gradient pressure mold pressing and segmented cooling forming, and the surface state is optimized in combination with plasma aftertreatment, so that the material adapts to the stress requirement of key components of the magnetic drive pump and resists severe working conditions, performance fluctuation caused by environmental factors is reduced, and long-term stable operation of the components is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump. Background Technology

[0002] As a leak-free conveying device, magnetic pumps are widely used in chemical, pharmaceutical, and environmental protection fields due to their excellent sealing performance, and are used to convey corrosive, toxic and harmful media. The impeller, bushing and other key components are the core components of the magnetic pump, and their performance directly determines the equipment's operational stability, service life and applicable range. These components need to work under harsh conditions of corrosive media, mechanical stress and temperature fluctuations for a long time, which puts extremely high requirements on the comprehensive performance of the materials.

[0003] However, in the existing technology, polyvinylidene fluoride (PVDF) vinyl composite material is a commonly used material for key components of magnetic pumps, but it has some defects. The interfacial bonding stability between the PVDF matrix and the reinforcing phase is insufficient, the single carbon fiber treatment method leads to poor dispersion effect, material agglomeration is prone to occur during premixing, and improper moisture content control affects the effect of subsequent processes. There is a lack of targeted equipment pretreatment and impurity removal measures during melt blending, and unreasonable pressure and cooling control during molding leads to uneven internal structure of the material, accumulation of residual stress, and a lack of effective post-treatment processes to optimize the surface properties of the material, making it difficult to meet the comprehensive requirements of the working conditions. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing polyvinylidene fluoride (PVDF) composite materials for key components of magnetic pumps. This invention involves grafting and modifying PVDF resin, sequentially oxidizing and impregnating carbon fibers with silane coupling agents, and pre-mixing with specific functional fillers to promote a compatible interface between the matrix, reinforcing phase, and functional fillers, ensuring uniform component distribution and consistent internal structure. Further, through melt blending, gradient pressure molding, and segmented cooling, a dense structure is formed. Combined with plasma post-treatment to optimize the surface state, the material adapts to the stress requirements of key components of magnetic pumps, withstands harsh operating conditions, reduces performance fluctuations caused by environmental factors, and ensures long-term stable operation of the components.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump, the specific steps of which are as follows:

[0006] Raw material modification treatment: PVDF resin was selected and modified by maleic anhydride grafting to obtain modified PVDF matrix. Carbon fiber was selected as the reinforcing phase and then subjected to oxidation treatment and silane coupling agent impregnation treatment to obtain surface-treated carbon fiber. Nano Al2O3 was selected as functional filler.

[0007] Component premixing: Surface-treated carbon fibers and nano-Al2O3 are placed in a ball mill for premixing to obtain a premixed material;

[0008] Melt blending extrusion: The modified PVDF matrix and the premixed material are fed into a twin-screw extruder, melt blended and then extruded to obtain the extruded material;

[0009] Compression molding and cooling: The extruded material is transferred to a compression molding machine for gradient pressure molding. After molding, the material is cooled according to a segmented cooling rate to obtain the molded composite material.

[0010] Plasma post-treatment: The molded composite material is placed in a plasma treatment device and treated with a mixture of Ar and O2 gas to obtain a polyvinylidene fluoride composite material that is compatible with key components of a magnetic pump.

[0011] Furthermore, in the raw material modification process, the melt index of the PVDF resin is 10-14 g / 10 min, the grafting rate of the maleic anhydride graft modification is 1.3-1.7%, the carbon fiber is T700 grade with a diameter of 6-8 μm, and the particle size of the nano-Al2O3 is 40-60 nm.

[0012] Furthermore, in the raw material modification process, the carbon fiber oxidation treatment uses nitric acid as the treatment medium, with a nitric acid concentration of 65-70 wt%, an oxidation temperature of 60-70℃, and an oxidation time of 2.5-3.5 h; the silane coupling agent is KH-550, the solvent is ethanol, and the concentration of the silane coupling agent in the ethanol solution is 1.5-2.5 wt%. The impregnation process is assisted by ultrasound, with an ultrasound-assisted treatment power of 100-150 W and an ultrasound-assisted treatment time of 25-35 min.

[0013] Furthermore, in the component premixing, the mass ratio of surface-treated carbon fiber to nano-Al2O3 is 3:1-6:1; the ball mill speed is 280-320 rpm, the mixing time is 1.5-2.5 h, and the ball-to-material ratio is 4:1-6:1; during the mixing process, the machine is stopped for 5-10 minutes every 30-40 minutes, and the material in the ball mill is turned over during the stop. After the turning is completed, the mixing operation continues.

[0014] Furthermore, in the component premixing process, the surface-treated carbon fiber and nano-Al2O3 materials are dried separately before premixing at a temperature of 80-100℃ for 2-3 hours, and the moisture content of the dried materials is ≤0.02%. After premixing, the premixed materials are sieved with a screen mesh size of 80-120 mesh to remove unevenly mixed agglomerated particles.

[0015] Furthermore, in the melt blending extrusion, the mass ratio of modified PVDF matrix to premixed material is 3:1-5:1; the temperature of the twin-screw extruder is set in a gradient according to the feeding section, melting section, mixing section, and die head, with the temperatures of each section being 175-185℃, 190-200℃, 200-210℃, and 185-195℃, respectively; before melt blending extrusion, the barrel and screw of the twin-screw extruder are preheated at a temperature of 170-180℃ for a time of 30-45 minutes.

[0016] Furthermore, in the melt blending extrusion, the twin-screw extruder has a screw speed of 140-160 rpm, a vacuum level maintained between -0.07 and -0.09 MPa during operation, a vacuum devolatilization time of 10-15 min, and a three-stage filtration device with filter pore sizes of 4-6 μm, 1-3 μm, and 0.3-0.7 μm respectively. The feeding rate is 5-8 kg / h, the die diameter of the twin-screw extruder is 3-5 mm, and the traction rate of the extruded material is 0.8-1.2 m / min.

[0017] Furthermore, in the compression molding cooling process, the gradient pressure is as follows: 4-6 MPa in the preheating stage, 14-16 MPa in the holding stage, and 7-9 MPa in the slow-release stage. The preheating time is 4-6 min, the holding time is 18-22 min, and the pressure drop rate in the slow-release stage is 1.5-2.5 MPa / min. The segmented cooling rate is 8-12℃ / min in the 200℃-150℃ stage and 4-6℃ / min in the 150℃-80℃ stage. After cooling to 80℃, the molded composite material is placed in a clean room temperature environment to cool naturally to room temperature for no less than 2 hours.

[0018] Furthermore, in the compression molding process, the parallelism error of the press plate of the molding machine is ≤0.02mm, the mold temperature is 190-210℃, the inner wall of the mold cavity is polished and the surface roughness is ≤0.8μm; after obtaining the molded composite material, the edge is trimmed to remove the edge burrs.

[0019] Furthermore, in the plasma post-treatment, the volume ratio of Ar to O2 in the mixed gas is 2.5:1-3.5:1, the flow rate of the mixed gas is 20-30 sccm; the vacuum degree of the plasma treatment equipment is 0.05-0.07 MPa, the processing power is 110-130 W, the processing time is 4-6 min, after the treatment is completed, the mixed gas is continued to be introduced for 4-6 min and then the gas supply is stopped, and the equipment is kept in a vacuum state for 10-15 min after the gas supply is stopped.

[0020] Compared with existing technologies, this method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump has the following advantages:

[0021] I. This invention involves grafting and modifying PVDF resin, sequentially oxidizing and impregnating carbon fibers with silane coupling agents, selecting specific functional fillers, and then premixing the surface-treated carbon fibers with the functional fillers. This process creates a suitable interfacial bond between the modified PVDF matrix, the reinforcing phase, and the functional fillers. The premixing process ensures full contact between the materials, preventing agglomeration and resulting in a more uniform component distribution in the composite material. This ensures the consistency of the internal structure of the material and makes the properties of each part of the material more uniform, thus meeting the stress requirements of key components in magnetic pumps.

[0022] II. This invention involves melt-blending a modified PVDF matrix with a premixed material, followed by preheating and devolatilization filtration to remove impurities and volatiles. The material is then subjected to gradient pressure molding and segmented cooling to ensure full fusion and uniform internal stress distribution, resulting in a dense material structure. Finally, plasma post-treatment optimizes the surface condition of the material, enabling it to withstand harsh working conditions, reducing performance fluctuations caused by environmental factors during use, and ensuring the long-term stable operation of key components of the magnetic pump.

[0023] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0025] Figure 1 A flowchart illustrating a method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump;

[0026] Figure 2 A framework diagram of a method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump;

[0027] Figure 3 This is a flowchart of a melt blending extrusion process in the preparation method of polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump. Detailed Implementation

[0028] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0029] Example 1:

[0030] In the preparation of composite materials for the impeller of a magnetic pump for conveying 30% sulfuric acid in the chemical industry, a PVDF resin with a melt index of 12 g / 10 min suitable for strong acid media was selected. Maleic anhydride grafting modification was performed using a melt grafting method, controlling the grafting rate at 1.5% to strengthen the bonding ability with the reinforcing phase, thus obtaining a modified PVDF matrix. Figure 1 As shown, carbon fiber was selected as the reinforcing phase, specifically T700 grade carbon fiber with a diameter of 7μm. It was placed in a 68wt% nitric acid solution and oxidized at 65℃ for 3h to increase surface active groups. After removal, it was repeatedly rinsed with deionized water until the rinsing solution was neutral. After drying, it was immersed in a 2wt% silane coupling agent KH-550 ethanol solution and impregnated with a 130W ultrasonic device for 30min to improve the interfacial bonding stability. After drying, surface-treated carbon fiber was obtained. Nano-Al2O3 with a particle size of 50nm was selected as a functional filler to avoid the introduction of impurities that would affect the acid resistance.

[0031] Surface-treated carbon fiber and nano-Al2O3 were selected at a mass ratio of 4:1. Considering the influence of material uniformity on corrosion resistance under strong acid environment, the two materials were placed separately in a forced-air drying oven and dried at 90℃ for 2.5h before mixing to reduce the moisture content to 0.015% and prevent residual moisture from causing internal pores. The two materials were then put into a horizontal ball mill, with a speed of 300rpm, a mixing time of 2h, and a ball-to-material ratio of 5:1. During the mixing process, the mill was stopped for 8 minutes every 35min, and the material adhering to the cylinder wall was turned over with a sterile scraper to ensure that the reinforcing phase and functional filler were evenly dispersed. After mixing, the mixture was sieved through a 100-mesh stainless steel screen to remove agglomerated particles to avoid stress concentration during impeller operation, thus obtaining a premixed material.

[0032] Modified PVDF matrix and premixed material were fed into a twin-screw extruder at a mass ratio of 4:1. To prevent residual impurities in the barrel from contaminating the material and affecting its corrosion resistance, the barrel and screw were preheated to 175℃ for 40 minutes before extrusion. Temperature gradients were set: 180℃ for the feeding section, 195℃ for the melting section, 205℃ for the mixing section, and 190℃ for the die head. The screw speed was 150 rpm, and the vacuum degree of the twin-screw extruder was maintained at -0.08 MPa. Volatile matter was removed from the material through 12 minutes of vacuum devolatilization. During the devolatilization process, impurities of different particle sizes were sequentially filtered through a three-stage filtration device with filtration pore sizes of 5μm, 2μm, and 0.5μm to ensure material purity. A stable feeding rate of 6 kg / h was maintained, and the material was extruded through a 4mm diameter die head at a traction rate of 1.0 m / min to obtain a uniform strip-shaped extruded material suitable for impeller forming. Figure 2 As shown.

[0033] The extruded material is cut into blocks that fit the shape of the impeller and transferred to a molding press. The mold cavity is designed according to the impeller contour to give the composite material a suitable shape. The inner wall of the mold cavity is polished to a surface roughness of 0.6μm, and the parallelism error of the pressure plate is controlled within 0.015mm. A gradient pressure is set: 5MPa for 5min preheating, 15MPa for 20min holding, and 8MPa for slow release. The pressure drop rate in the slow release stage is 2MPa / min. During the molding process, the mold temperature is maintained at 200℃ to ensure that the material is fully fused. During cooling, the temperature is reduced at a rate of 10℃ / min from 200℃ to 150℃ and 5℃ / min from 150℃ to 80℃. After cooling to 80℃, the molded composite material is placed in a clean room temperature environment to cool naturally for 3 hours. After cooling, the edges are trimmed to remove excess material, resulting in a molded composite material that fits the shape of the impeller.

[0034] The molded composite material adapted to the impeller shape was placed in a plasma treatment device, and a mixed gas of Ar and O2 in a volume ratio of 3:1 was introduced, with the gas flow rate controlled at 25 sccm. The vacuum degree of the plasma treatment device was maintained at 0.06 MPa, and the treatment power was set to 120 W and the treatment time to 5 min. After the treatment was completed, the mixed gas was introduced for another 5 min, and then the gas supply was stopped and the device was kept in a vacuum state for 12 min to ensure the surface modification effect was stable. Finally, a polyvinylidene fluoride composite material adapted to the impeller of a magnetic pump for conveying 30% sulfuric acid in the chemical industry was obtained.

[0035] In summary, to meet the impeller adaptation requirements of magnetic pumps for conveying 30% sulfuric acid in the chemical industry, a modified PVDF matrix was obtained by grafting maleic anhydride onto PVDF resin suitable for strong acid media. Surface-treated carbon fibers were obtained by ultrasonic impregnation with nitric acid oxidation and a silane coupling agent using carbon fiber as the reinforcing phase. These fibers were then combined with nano-Al2O3 functional fillers, pre-mixed at a mass ratio of 4:1, dried, and sieved. Finally, the mixture was melt-blended with the modified PVDF matrix at a 4:1 ratio using a twin-screw extruder. The resulting composite material was then subjected to gradient pressure molding, trimming, and plasma post-treatment to obtain a high-temperature resistant, strong acid-resistant, and structurally uniform polyvinylidene fluoride composite material that perfectly meets the impeller's operating requirements.

[0036] Example 2:

[0037] In the preparation of composite materials for the bushing of magnetic pumps used in the pharmaceutical industry for transporting chlorine-containing corrosive and toxic media, a PVDF resin with a melt index of 13 g / 10 min that meets the cleanliness standards of the pharmaceutical industry was selected. The resin was modified with maleic anhydride grafting, controlling the grafting rate at 1.6%, to obtain a modified PVDF matrix. Carbon fiber was selected as the reinforcing phase, specifically T700 grade carbon fiber with a diameter of 6.5 μm. This carbon fiber was oxidized at 68°C with 67 wt% nitric acid for 3.2 h to improve the bonding force between the surface and the matrix. After rinsing and drying, it was immersed in a 2.2 wt% silane coupling agent KH-550 ethanol solution and impregnated for 32 min with the assistance of a 140W ultrasonic device. After drying, surface-treated carbon fiber was obtained. Nano-Al2O3 with a particle size of 55 nm and no heavy metal impurities was selected as the functional filler, meeting the material safety requirements of the pharmaceutical industry.

[0038] Surface-treated carbon fiber and nano-Al2O3 were selected at a mass ratio of 5:1. Considering the requirement for material uniformity in the bushing sealing performance, the two materials were dried in a 100℃ forced-air drying oven for 2.8 hours before mixing to ensure that the moisture content was ≤0.01% to prevent internal pores from affecting the seal. The two materials were then put into a ball mill, with a speed of 310 rpm, a mixing time of 2.2 hours, and a ball-to-material ratio of 5.5:1. During the mixing process, the mill was stopped for 9 minutes every 38 minutes to manually stir the mixture to ensure that the reinforcing phase and functional filler were evenly dispersed. After mixing, the mixture was sieved through a 110-mesh sieve to remove undispersed agglomerated particles, resulting in a high-purity premixed material.

[0039] The modified PVDF matrix and premixed material are mixed at a mass ratio of 3.5:1 and fed into a twin-screw extruder; to ensure material cleanliness, such as Figure 3As shown, the barrel and screw were preheated to 178℃ and held for 42 minutes before extrusion. The temperature gradient was set to 182℃ for the feeding section, 198℃ for the melting section, 208℃ for the mixing section, and 192℃ for the die head. The screw speed was 155 rpm, and the vacuum degree was maintained at -0.085 MPa. Volatile matter was removed by vacuum de-idleization for 13 minutes. Impurities were intercepted by a three-stage filtration device during the de-idleization process. The filter pore sizes were 5.5μm, 2.5μm, and 0.6μm, respectively. A stable feeding rate of 7 kg / h was controlled, and the material was extruded through a 4.5 mm diameter die head at a traction rate of 1.1 m / min to obtain extruded material with a uniform diameter.

[0040] The extruded material is cut into blocks that fit the shape of the bushing and placed into a custom molding press. The mold cavity is designed according to the bushing contour. The inner wall of the mold cavity is polished to a surface roughness of 0.7μm, and the parallelism error of the pressure plate is ≤0.018mm. A gradient pressure is set: 4.5MPa for 4.5min during the preheating stage, 14.5MPa for 19min during the holding stage, and 7.5MPa for the slow release stage. The slow release pressure decrease rate is 1.8MPa / min. The mold temperature is maintained at 205℃ during molding to ensure that the material is fully leveled. The cooling process is carried out at a rate of 9℃ / min from 200℃ to 150℃ and 4.5℃ / min from 150℃ to 80℃. After cooling to 80℃, it is allowed to cool naturally for 2.5h to ensure dimensional stability. After cooling, the edges are trimmed to remove burrs, resulting in a molded composite material that fits the shape of the bushing.

[0041] The molded composite material adapted to the bushing shape was placed in a plasma treatment device, and a mixed gas of Ar and O2 in a volume ratio of 3.2:1 was introduced. The gas flow rate was controlled at 28 sccm, and the vacuum degree of the plasma treatment device was 0.055 MPa. The treatment power was set to 125W and the treatment time to 5.5 min. The surface smoothness of the material was optimized through plasma treatment to reduce the risk of residual toxic media. After the treatment was completed, the mixed gas was introduced for another 5.5 min. After the gas supply was stopped, the vacuum state of the device was maintained for 13 min before the vacuum was broken and the material was removed. This yielded a polyvinylidene fluoride composite material adapted to the bushing of a magnetic pump for conveying chlorine-containing corrosive and toxic media in the pharmaceutical field.

[0042] In summary, for the application scenarios of magnetic pump bushings used in the pharmaceutical field for conveying chlorine-containing corrosive and toxic media, a matrix is ​​prepared by modifying PVDF resin to meet cleanliness standards. T700 grade carbon fiber is used as the reinforcing phase, which is oxidized and coupled, premixed with nano-Al2O3 at a ratio of 5:1, dried and sieved, and then preheated and blended with the matrix at a ratio of 3.5:1 using an extruder. Finally, it is molded with gradient pressure using a customized mold, trimmed by segmented cooling, and surface modified by plasma to meet the requirements of the bushing.

[0043] Example 3:

[0044] In the application of composite materials for sealing rings of magnetic pumps used in the environmental protection field for transporting high-salt corrosive wastewater, a PVDF resin with a melt index of 11 g / 10 min and excellent salt corrosion resistance was selected. The resin was modified with maleic anhydride grafting, controlling the grafting rate at 1.4%, to obtain a modified PVDF matrix. Carbon fiber was selected as the reinforcing phase, specifically T700 grade carbon fiber with a diameter of 7.5 μm. This carbon fiber was oxidized at 63℃ for 2.8 h with 66 wt% nitric acid to increase surface roughness. After rinsing and drying, it was immersed in a 1.8 wt% silane coupling agent KH-550 ethanol solution and impregnated for 28 min with 120W ultrasonic equipment to improve the bonding strength with the matrix. After drying, surface-treated carbon fiber was obtained. Nano-Al2O3 with a particle size of 45 nm and good dispersibility was selected as a functional filler to enhance the material's wear resistance.

[0045] Surface-treated carbon fiber and nano-Al2O3 were mixed at a mass ratio of 3.5:1. Considering that the wear resistance of the sealing ring depends on the dispersibility of the material, the two materials were dried separately in a 95℃ forced-air drying oven for 2.2 hours before mixing to reduce the moisture content to 0.018% and prevent micropores from appearing after molding. The two materials were then put into a horizontal ball mill, with a speed of 290 rpm, a mixing time of 1.8 hours, and a ball-to-material ratio of 4.5:1. During the mixing process, the mill was stopped for 7 minutes every 32 minutes to stir the material in the mill and prevent the reinforcing phase from agglomerating and affecting the wear resistance uniformity. After mixing, the mixture was sieved through a 90-mesh sieve to remove agglomerated particles and obtain a uniformly dispersed premixed material.

[0046] Modified PVDF matrix and premixed material were mixed at a mass ratio of 4.2:1 and fed into a twin-screw extruder. To avoid residual impurities in the barrel affecting material purity, the barrel and screw were preheated to 172℃ and held for 35 minutes before extrusion. A temperature gradient was set at 178℃ for the feeding section, 193℃ for the melting section, 203℃ for the mixing section, and 188℃ for the die head. The screw speed was 145 rpm, and the equipment vacuum was maintained at -0.075 MPa. Volatile matter and trace impurities in the material were removed by vacuum devolatilization for 11 minutes. During the devolatilization process, impurities of different particle sizes were successively intercepted by a three-stage filtration device with filter pore sizes of 5μm, 2μm, and 0.4μm, respectively. A stable feeding rate of 5.5 kg / h was controlled, and the material was extruded through a 3.5 mm diameter die head at a traction rate of 0.9 m / min to obtain strip-shaped extruded material with uniform diameter.

[0047] The extruded material is cut into blocks that fit the shape of the sealing ring and placed into a custom molding press. The mold cavity is designed according to the contour of the sealing ring. The inner wall of the mold cavity is polished to achieve a surface roughness of 0.75μm, and the parallelism error of the pressure plate is controlled within 0.017mm to ensure uniform material thickness. A gradient pressure is set: 4.8MPa for 4.8min during the preheating stage, 15.2MPa for 21min during the holding stage, and 7.8MPa during the slow release stage. The pressure drop rate during the slow release stage is 2.2MPa / min. The mold temperature is maintained at 195℃ during the molding process to ensure full material fusion. During cooling, the temperature is reduced at a rate of 11℃ / min from 200℃ to 150℃ and 5.5℃ / min from 150℃ to 80℃. After cooling to 80℃, the molded composite material is placed in a clean room temperature environment to cool naturally for 2.5h to avoid dimensional deformation caused by rapid cooling. After cooling, the edges are trimmed to remove burrs and ensure a smooth sealing surface, resulting in a molded composite material that fits the shape of the sealing ring.

[0048] The molded composite material adapted to the sealing ring shape was placed in a plasma treatment device, and a mixed gas of Ar and O2 in a volume ratio of 2.8:1 was introduced. The gas flow rate was controlled at 23 sccm, and the vacuum degree of the device was maintained at 0.058 MPa. The treatment power was set to 115W and the treatment time was 4.5 min. The plasma treatment improved the surface density and wear resistance of the material and reduced the channels for salt spray corrosion. After the treatment was completed, the mixed gas was introduced for another 4.5 min, and then the gas supply was stopped and the vacuum state of the device was maintained for 11 min to ensure the stability of the surface modification effect. Finally, a polyvinylidene fluoride composite material adapted to the sealing ring of a magnetic pump for transporting high-salt corrosive wastewater in the environmental protection field was obtained.

[0049] In summary, to meet the sealing ring requirements of magnetic pumps for conveying high-salt corrosive wastewater in the environmental protection field, a matrix was obtained by modifying salt-resistant PVDF resin. Carbon fiber was used as the reinforcing phase and subjected to oxidative coupling treatment. After premixing and drying with nano-Al2O3 at a ratio of 3.5:1 and sieving, the carbon fiber was preheated and blended with the matrix at a ratio of 4.2:1 using an extruder. Then, the mixture was subjected to gradient pressure molding with a sealing ring contour mold, segmented cooling trimming, and plasma treatment to finally obtain a wear-resistant, salt spray-resistant, and dimensionally stable polyvinylidene fluoride composite material, which meets the sealing ring usage requirements under wastewater conveying conditions.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump, characterized in that, The specific steps of this preparation method are as follows: Raw material modification treatment: PVDF resin was selected and modified by maleic anhydride grafting to obtain modified PVDF matrix. Carbon fiber was selected as the reinforcing phase and then subjected to oxidation treatment and silane coupling agent impregnation treatment to obtain surface-treated carbon fiber. Nano Al2O3 was selected as functional filler. Component premixing: Surface-treated carbon fibers and nano-Al2O3 are placed in a ball mill for premixing to obtain a premixed material; Melt blending extrusion: The modified PVDF matrix and the premixed material are fed into a twin-screw extruder, melt blended and then extruded to obtain the extruded material; Compression molding and cooling: The extruded material is transferred to a compression molding machine for gradient pressure molding. After molding, the material is cooled at a segmented cooling rate to obtain the molded composite material. Plasma post-treatment: The molded composite material is placed in a plasma treatment device and treated with a mixture of Ar and O2 gas to obtain a polyvinylidene fluoride composite material that is compatible with key components of a magnetic pump.

2. The method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 1, characterized in that, In the raw material modification process, the melt index of PVDF resin is 10-14 g / 10 min, the grafting rate of maleic anhydride graft modification is 1.3-1.7%, the carbon fiber is T700 grade with a diameter of 6-8 μm, and the particle size of nano Al2O3 is 40-60 nm.

3. The method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 1, characterized in that, In the raw material modification process, the carbon fiber oxidation treatment uses nitric acid as the treatment medium, with a nitric acid concentration of 65-70 wt%, an oxidation temperature of 60-70℃, and an oxidation time of 2.5-3.5 h; the silane coupling agent is KH-550, the solvent is ethanol, and the concentration of the silane coupling agent in the ethanol solution is 1.5-2.5 wt%. The impregnation process is assisted by ultrasound, with an ultrasound-assisted treatment power of 100-150 W and an ultrasound-assisted treatment time of 25-35 min.

4. The method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 1, characterized in that, In the premixing of the components, the mass ratio of surface-treated carbon fiber to nano-Al2O3 is 3:1-6:1; the speed of the ball mill is 280-320 rpm, the mixing time is 1.5-2.5 h, and the ball-to-material ratio is 4:1-6:1; during the mixing process, the machine is stopped for 5-10 minutes every 30-40 minutes, and the material in the ball mill is turned over during the stop. After the turning is completed, the mixing operation continues.

5. The method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 1, characterized in that, In the component premixing process, the surface-treated carbon fiber and nano-Al2O3 materials are dried separately before premixing. The drying temperature is 80-100℃ and the drying time is 2-3h. The moisture content of the dried materials is ≤0.02%. After premixing, the premixed materials are sieved with a screen aperture of 80-120 mesh to remove unevenly mixed agglomerated particles.

6. The method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 1, characterized in that, In the melt blending extrusion, the mass ratio of modified PVDF matrix to premixed material is 3:1-5:1; the temperature of the twin-screw extruder is set in a gradient according to the feeding section, melting section, mixing section, and die head, with the temperatures of each section being 175-185℃, 190-200℃, 200-210℃, and 185-195℃, respectively; before melt blending extrusion, the barrel and screw of the twin-screw extruder are preheated at a temperature of 170-180℃ for 30-45 minutes.

7. The method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 5, characterized in that, In the melt blending extrusion, the twin-screw extruder has a screw speed of 140-160 rpm, a vacuum level maintained between -0.07 and -0.09 MPa, a vacuum devolatilization time of 10-15 min, and a three-stage filtration system with pore sizes of 4-6 μm, 1-3 μm, and 0.3-0.7 μm respectively. The feed rate is 5-8 kg / h, the die diameter of the twin-screw extruder is 3-5 mm, and the traction rate of the extruded material is 0.8-1.2 m / min.

8. A method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 1, characterized in that, In the compression molding process, the gradient pressure is as follows: 4-6 MPa in the preheating stage, 14-16 MPa in the holding stage, and 7-9 MPa in the slow-release stage. The preheating time is 4-6 min, the holding time is 18-22 min, and the pressure drop rate in the slow-release stage is 1.5-2.5 MPa / min. The segmented cooling rate is 8-12℃ / min in the 200℃-150℃ stage and 4-6℃ / min in the 150℃-80℃ stage. After cooling to 80℃, the molded composite material is placed in a clean room temperature environment to cool naturally to room temperature for no less than 2 hours.

9. A method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 1, characterized in that, In the compression molding process, the parallelism error of the press plate of the molding machine is ≤0.02mm, the mold temperature is 190-210℃, and the inner wall of the mold cavity is polished with a surface roughness of ≤0.8μm. After obtaining the molded composite material, trimming is performed to remove edge burrs.

10. A method for preparing polyvinylidene fluoride vinyl composite material for a key component of a magnetic pump according to claim 1, characterized in that, In the plasma post-treatment, the volume ratio of Ar to O2 in the mixed gas is 2.5:1-3.5:1, and the flow rate of the mixed gas is 20-30 sccm; the vacuum degree of the plasma treatment equipment is 0.05-0.07 MPa, the processing power is 110-130 W, the processing time is 4-6 min, and after the treatment is completed, the mixed gas is continued to be introduced for 4-6 min before the gas supply is stopped. After the gas supply is stopped, the equipment is kept in a vacuum state for 10-15 min.

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