A preparation process of ultra-clean fusible polytetrafluoroethylene joint

Abstract

The present invention relates to a preparation process of an ultra-clean fusible polytetrafluoroethylene joint, and belongs to the technical field of ultra-clean plastic joints. It mainly includes the following steps: S1, PFA material pretreatment; S2, mold surface treatment; S3, extrusion; S4, injection molding and rapid and uniform heating and rapid solidification through high-temperature and high-pressure steam treatment; S5, pressure holding; S6, demolding; S7, heat treatment to eliminate the internal stress caused by the PFA joint molding process and improve the mechanical properties of the PFA joint; S8, post-treatment. The preparation process of the present invention is simple, and the prepared fusible polytetrafluoroethylene joint has good cleanliness, low metal ion precipitation rate, low microparticle precipitation rate, and the joint has good hardness, dimensional precision, and anti-penetration performance.

Description

Technical Field

[0001] The invention belongs to the technical field of ultra-clean plastic joints and relates to a preparation process of an ultra-clean fusible polytetrafluoroethylene joint. Background Art

[0002] PFA (fusible polytetrafluoroethylene), also known as perfluoroalkoxy resin, is a special plastic with excellent chemical stability, corrosion resistance, and high and low temperature resistance. Ultra-clean PFA connectors make full use of these characteristics of PFA during design and manufacturing, and add special sealing and connection methods to achieve ultra-clean fluid transmission. Ultra-clean PFA connectors are an important component with a wide range of applications in specific application scenarios, such as occasions where high-purity fluid transmission is required.

[0003] Ultra-clean PFA connectors use advanced sealing technology to ensure tight connections between pipes and effectively prevent leakage of ultra-pure chemicals. This sealing technology not only ensures the stable operation of the system, but also avoids fluid contamination caused by leakage, ensuring the purity of the transmitted fluid. Secondly, during the manufacturing process of ultra-clean PFA connectors, precise processing technology and quality control are used to achieve smooth and impurity-free inside the connector. This further ensures that the fluid will not be contaminated during transmission, meeting the needs of ultra-clean applications.

[0004] In addition, the ultra-clean PFA fittings also have good corrosion resistance and can resist the erosion of most chemicals, which enables them to operate stably for a long time in various harsh environments and reduce the frequency of failures and repairs.

[0005] In general, ultra-clean PFA connectors provide reliable and efficient solutions for applications that require high-purity fluid transmission by utilizing the excellent properties of PFA materials and combining advanced sealing technology and precise manufacturing processes. This type of connector is widely used in industries such as semiconductor industry, pharmaceutical industry, electronics industry, medical and biotechnology, and food processing, providing important technical support for these industries. Summary of the invention

[0006] The object of the present invention is to provide a preparation process of an ultra-clean fusible polytetrafluoroethylene joint, which has the advantages of simple preparation process, good cleanliness of the prepared fusible polytetrafluoroethylene joint, low metal ion mobility in the material, and good hardness of the joint.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A preparation process of an ultra-clean fusible polytetrafluoroethylene joint, the preparation of the ultra-clean fusible polytetrafluoroethylene joint comprising the following steps:

[0009] S1. Pretreatment of PFA particles: In a Class 100 clean production workshop, the PFA particles were dried at 60°C for 30 minutes by laser drying method, where the laser power was 250W;

[0010] S2. Mould surface treatment: grind the PFA resin with a ball mill at a speed of 400r / min for 4-5h, pass through a 200-mesh sieve to obtain PFA powder, sandblast the mould surface with quartz sand as the spray material, and then use an electrostatic spray gun to evenly spray the PFA powder on the mould surface for the first coating, and then bake at high temperature in steps, first bake at 270-280℃ for 0.5h, then bake at 320-340℃ for 1-2h, and finally bake at 260-280℃ for 0.5h. After baking, cool to room temperature at a cooling rate of 5-8℃ / min; then slowly cool to room temperature to obtain the second A layer of coating, PFA powder is evenly dispersed in deionized water by ultrasonic treatment, and then a second coating is performed by ultrasonic spraying, and it is dried and cured by 250W laser for 30 minutes, and the mold is placed in a magnetron sputtering coating device, and chromium powder and nickel powder are loaded on the target holder as sputtering targets, and vacuum is evacuated, argon and nitrogen are introduced, and the chromium target power supply and the nickel target power supply are alternately turned on to form a composite coating on the mold surface, wherein the sputtering power of the chromium target is 250~280W, and the sputtering power of the nickel target is 300~340W, and the interval time for alternately turning on the chromium target power supply and the nickel target power supply is 5min, and it is turned off after the last nickel target sputtering is completed;

[0011] S3, extrusion: the pretreated PFA particles are passed into a high-temperature fluoroplastic extruder, the feed temperature is 80-100°C, the temperature is controlled in sections in the high-temperature fluoroplastic extruder, and the PFA particles are completely melted and extruded, wherein the high-temperature fluoroplastic extruder is divided into five sections for temperature control, wherein the rear temperature is 350-360°C, the middle temperature is 360-370°C, the front temperature is 370-380°C, the temperature of the die head is 380-390°C, and the temperature of the nozzle is 390-400°C;

[0012] S4, injection molding: After the completely molten PFA particles are extruded through the nozzle of a high-temperature fluoroplastic extruder and injected into the mold, the temperature of the mold is kept constant by high-temperature and high-pressure steam, wherein the temperature of the high-temperature and high-pressure steam is 150-200°C and the pressure is 0.4-0.8MPa. After the injection molding is completed, the supply of high-temperature and high-pressure steam is stopped after 5-8 minutes, and cooling water is introduced after the steam is emptied to quickly reduce the temperature of the mold for cooling and solidification molding;

[0013] S5, pressure holding: After complete cooling, the mold is pressure-held for 100-150 seconds, and the pressure is completely released to normal pressure after the pressure holding is completed;

[0014] S6, demoulding: taking the formed PFA joint out of the mold for demoulding;

[0015] S7. Heat treatment: After cooling and solidification, the PFA joint is placed in a tubular furnace under a nitrogen atmosphere, and the temperature is raised to 260-290°C at a rate of 3°C / min, and maintained for 4 hours, and then naturally annealed to room temperature;

[0016] S8, post-processing: put the heat-treated PFA joint into a freezing trimming machine for trimming.

[0017] As a preferred technical solution of the present invention, in step S2, the parameters of the ultrasonic spraying are: ultrasonic power of 40-60 W, ultrasonic frequency of 100-200 kHz, and spraying distance of 30-60 mm.

[0018] As a preferred technical solution of the present invention, in step S2, the thickness of the first coating layer is 0.5-1 mm, the thickness of the second coating layer is 0.5-1 mm, and the thickness of the PFA coating layer is 1-2 mm.

[0019] As a preferred technical solution of the present invention, in step S3, a nickel-plated layer is provided on the nozzle surface of the high-temperature fluoroplastic extruder.

[0020] As a preferred technical solution of the present invention, in step S4, the cooling and curing time is 140-200 s, and the flow rate of cooling water is 10-20 m 3 / h.

[0021] As a preferred technical solution of the present invention, in step S5, the pressure during pressure maintenance is 0.6-0.7 MPa, and the rate of pressure release is 0.1 MPa / min.

[0022] Beneficial effects of the present invention:

[0023] The present invention coats a layer of PFA on the surface of the mold. First, the PFA layer is sprayed on the surface of the mold in powder form by an electrostatic spray gun, so that the adhesion between the mold and the coating after surface sandblasting in the coating preparation process can be increased. The PFA powder attached to the surface of the mold can be heat-treated at 270-280° C. to remove volatile substances therein, and then baked at 320-340° C. for 1-2 hours to completely melt the PFA powder. Finally, the PFA powder is kept warm and baked at 260-280° C. for 0.5 hours. After the baking is completed, the temperature is cooled to room temperature to solidify. Then, the secondary spraying is performed by ultrasonic spraying, so as to make the coating thickness distribution more uniform, and the PFA joint can be effectively prevented from being corroded to the mold material or causing metal ions to migrate to the PFA joint due to excessively high temperature when the PFA joint is formed in the mold. Through the effect of the surface PFA layer, the surface smoothness can be enhanced, the strippability of the mold can be increased, and the migration of metal ions into the joint to affect the cleanliness can be avoided; because the PFA coating is applied first, the mold surface is smoother, avoiding uneven metal film or peeling due to the uneven mold base during subsequent metal plating, and PFA can help the metal film to be more tightly loaded on the mold, thereby improving the stability of the overall coating; using nickel and chromium as target materials and coating with magnetron sputtering technology at a higher power can form a metal film of uniform thickness on the surface, which can not only ensure the density of the coating, but also improve the hardness and wear resistance of the mold surface coating, and improve the preparation efficiency. Through the preparation of the composite coating, the mold has higher wear resistance, thereby effectively preventing the coating from falling off during frequent injection molding and demolding.

[0024] Similarly, the nozzle surface of the high-temperature fluoroplastic extruder is nickel-plated to prevent some components of the metal from seeping out and merging into the PFA material at high temperature when in contact with molten PFA, thereby causing the metal ion content to exceed the standard and affecting the performance of the finished workpiece.

[0025] During the injection molding process, the molten PFA material is injected into the mold. During the molding process, the PFA joint can be quickly and evenly solidified by high-temperature and high-pressure steam treatment at 150~200℃ and a pressure of 0.4~0.8MPa. Then it is cooled by cooling water to ensure that the PFA joint reaches sufficient strength and hardness before demolding. Through this process, the mold is easier to detach, and deformation or damage to the PFA joint during the demolding process can be avoided.

[0026] The purpose of heat treatment after cooling and solidification of PFA adapter is mainly to improve its material properties. After heat treatment, the grain size of PFA adapter products is reduced, the number of grain boundaries is reduced, and the surface internal stress is eliminated, so the product's penetration resistance can be improved; the heating rate is controlled at 3℃ / min, and the heat treatment temperature is 260~290℃, which can dissolve elements such as carbon and nitrogen into the matrix to form a solid solution, thereby improving the hardness and strength of the material; and can make elements such as carbon and nitrogen precipitate on the grain boundaries to form fine and evenly distributed particles, thereby improving the toughness of PFA materials; heat treatment can enhance the hardness and wear resistance of the material; by changing the crystal structure inside the material, reducing the grain size and the number of grain boundaries, thereby improving the dimensional stability of the material; internal stress may be generated during the cooling and solidification process, and heat treatment can eliminate these internal stresses and improve the mechanical properties and dimensional stability of PFA materials.

[0027] The heat-treated finished product together with the burrs are deburred under freezing conditions. Liquid nitrogen is used to make the burrs of the finished product brittle at low temperatures. Specific frozen particles are used to hit the burrs to quickly remove the burrs and reduce the powder and debris generated when removing the burrs. Impurities on the surface of the PFA joint are removed by cleaning and drying, thereby improving the cleanliness of the PFA joint. DETAILED DESCRIPTION

[0028] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0029] The inner surface of the material tube of the screw injection molding machine and the outer surface of the screw assembly and the nozzle are provided with a nickel-plated layer.

[0030] In the following examples and comparative examples:

[0031] The mold used: The manufacturer is Dalian Economic and Technological Development Zone Xinghai Mold Co., Ltd., product number / trademark number: XH2317, the specific material is S136 mold steel, the size is (length, width and height): 350ⅹ350ⅹ268mm, the shape is a square two-plate mold;

[0032] PFA particles and PFA coating on the mold surface were purchased from Daikin Fluorochemical (China) Co., Ltd., with the brand name AP-231SH;

[0033] Quartz sand: purchased from Shanghai Ziming Reagent Factory (Kramer), item number: 13081076711-25kg;

[0034] Chromium powder: purchased from Hubei Yongkuo Technology Co., Ltd., purity: 99%;

[0035] Nickel powder: purchased from Hubei Yongkuo Technology Co., Ltd., effective substance content: 99%.

[0036] Example 1

[0037] S1. Pretreatment of PFA (fusible polytetrafluoroethylene) particles: In a Class 100 clean production workshop, the PFA particles were dried at 60°C for 30 minutes by laser drying method, where the laser power was 250W;

[0038] S2. Surface treatment of mold: grind PFA resin with a ball mill at a speed of 400r / min for 4h, pass through a 200-mesh sieve to obtain PFA powder, sandblast the mold surface with quartz sand as the spray material, and then use an electrostatic spray gun to evenly spray the PFA powder on the mold surface for the first coating. First, bake at 270℃ for 0.5h, then bake at 320℃ for 1-2h, and finally bake at 260℃ for 0.5h. After baking, cool to room temperature at a rate of 5℃ / min; then slowly cool to room temperature to obtain the first layer of coating, evenly disperse the PFA powder in deionized water through ultrasonic treatment, and then apply the second coating by ultrasonic spraying, and use a 250W laser to dry for 30mi n, thereby forming a PFA coating on the mold surface, the ultrasonic power is 40W, the ultrasonic frequency is 100kHz, the spraying distance is 30mm, wherein the thickness of the first coating layer is 0.5mm, the thickness of the second coating layer is 0.5mm, and the thickness of the PFA coating is 1mm. The mold is placed in a magnetron sputtering coating device, chromium powder and nickel powder are used as sputtering targets and loaded on the target holder, vacuumed, argon and nitrogen are introduced, and the chromium target power supply and the nickel target power supply are alternately turned on to form a composite coating on the mold surface, wherein the sputtering power of the chromium target is 250W, and the sputtering power of the nickel target is 300W. The interval time for alternately turning on the chromium target power supply and the nickel target power supply is 5min, and the power supply is turned off after the last sputtering of the nickel target is completed;

[0039] S3, extrusion: the pretreated PFA particles are introduced into a high-temperature fluoroplastic extruder, the feed temperature is 80°C, the temperature in the high-temperature fluoroplastic extruder is controlled in sections, and the PFA particles are completely melted and extruded, wherein the high-temperature fluoroplastic extruder is divided into five sections for temperature control, wherein the rear temperature is 350°C, the middle temperature is 360°C, the front temperature is 370°C, the die temperature is 380°C, and the nozzle temperature is 390°C;

[0040] S4, injection molding: After the completely molten PFA particles are extruded through the nozzle of the high-temperature fluoroplastic extruder and injected into the mold, the temperature of the mold is kept constant by high-temperature and high-pressure steam, wherein the temperature of the high-temperature and high-pressure steam is 150°C and the pressure is 0.4MPa. After the injection molding is completed, the supply of high-temperature and high-pressure steam is stopped after 5 minutes, and the flow rate of 10m is introduced again after the steam is emptied. 3 / h cooling water for 140s to quickly reduce the mold temperature and perform cooling and solidification molding;

[0041] S5, pressure holding: After complete cooling, the mold is pressure-held at 0.6 MPa for 100 seconds. After the pressure holding is completed, the pressure is completely released to normal pressure at a rate of 0.1 MPa / min;

[0042] S6, demoulding: taking the formed PFA joint out of the mold for demoulding;

[0043] S7. Heat treatment: After cooling and solidification, the PFA joint is placed in a tubular furnace under a nitrogen atmosphere, heated to 260°C at a rate of 3°C / min, and maintained for 4 hours, and then naturally annealed to room temperature;

[0044] S8, post-processing: put the heat-treated PFA joint into a freezing trimming machine for trimming.

[0045] Example 2

[0046] S1. Pretreatment of PFA particles: In a Class 100 clean production workshop, the PFA particles were dried at 60°C for 30 minutes by laser drying method, where the laser power was 250W;

[0047] S2. Surface treatment of mold: grind PFA resin with a ball mill at a speed of 400r / min for 4.5h, pass through a 200-mesh sieve to obtain PFA powder, sandblast the mold surface with quartz sand as the spray material, and then use an electrostatic spray gun to evenly spray the PFA powder on the mold surface for the first coating. First, bake at 275℃ for 0.5h, then bake at 330℃ for 1-2h, and finally bake at 270℃ for 0.5h. After baking, cool to room temperature at a rate of 7℃ / min; then slowly cool to room temperature to obtain the first layer of coating, evenly disperse the PFA powder in deionized water through ultrasonic treatment, and then apply the second coating by ultrasonic spraying, and use a 250W laser to dry for 30mi n, thereby forming a PFA coating on the mold surface, the ultrasonic power is 50W, the ultrasonic frequency is 150kHz, the spraying distance is 40mm, the thickness of the first coating layer is 0.8mm, the thickness of the second coating layer is 0.7mm, and the thickness of the PFA coating is 1.5mm. The mold is placed in a magnetron sputtering coating device, chromium powder and nickel powder are used as sputtering targets and loaded on the target holder, vacuumed, argon and nitrogen are introduced, and the chromium target power supply and the nickel target power supply are alternately turned on to form a composite coating on the mold surface, wherein the sputtering power of the chromium target is 260W, the sputtering power of the nickel target is 320W, the interval time of alternately turning on the chromium target power supply and the nickel target power supply is 5min, and the power supply is turned off after the last sputtering of the nickel target is completed;

[0048] S3, extrusion: the pretreated PFA particles are introduced into a high-temperature fluoroplastic extruder, the feed temperature is 90°C, the temperature in the high-temperature fluoroplastic extruder is controlled in sections, and the PFA particles are completely melted and extruded, wherein the high-temperature fluoroplastic extruder is divided into five sections for temperature control, wherein the rear temperature is 355°C, the middle temperature is 365°C, the front temperature is 375°C, the die temperature is 385°C, and the nozzle temperature is 395°C;

[0049] S4, injection molding: After the completely molten PFA particles are extruded through the nozzle of the high-temperature fluoroplastic extruder and injected into the mold, the temperature of the mold is kept constant by high-temperature and high-pressure steam, wherein the temperature of the high-temperature and high-pressure steam is 160°C and the pressure is 0.6MPa. After the injection molding is completed, the supply of high-temperature and high-pressure steam is stopped after 6 minutes, and the flow rate of 15m is introduced again after the steam is emptied. 3 / h cooling water for 180 s to quickly reduce the mold temperature and perform cooling and solidification molding;

[0050] S5, pressure holding: After complete cooling, the mold is pressure-held at 0.6 MPa for 140 seconds. After the pressure holding is completed, the pressure is completely released to normal pressure at a rate of 0.1 MPa / min;

[0051] S6, demoulding: taking the formed PFA joint out of the mold for demoulding;

[0052] S7. Heat treatment: After cooling and solidification, the PFA joint is placed in a tubular furnace under a nitrogen atmosphere, heated to 280°C at a rate of 3°C / min, and maintained for 4 hours, and then naturally annealed to room temperature;

[0053] S8, post-processing: put the heat-treated PFA joint into a freezing trimming machine for trimming.

[0054] Example 3

[0055] S1. Pretreatment of PFA particles: In a Class 100 clean production workshop, the PFA particles were dried at 60°C for 30 minutes by laser drying method, where the laser power was 250W;

[0056] S2. Surface treatment of mold: grind PFA resin with a ball mill at a speed of 400r / min for 5h, pass through a 200-mesh sieve to obtain PFA powder, sandblast the mold surface with quartz sand as the spray material, and then use an electrostatic spray gun to evenly spray the PFA powder on the mold surface for the first coating, first bake at 280℃ for 0.5h, then bake at 340℃ for 2h, and finally bake at 280℃ for 0.5h. After baking, cool to room temperature at a rate of 8℃ / min; then slowly cool to room temperature to obtain the first layer of coating, evenly disperse the PFA powder in deionized water through ultrasonic treatment, and then apply the second coating by ultrasonic spraying, and use a 250W laser to dry for 30m in, thereby forming a PFA coating on the mold surface, the ultrasonic power is 60W, the ultrasonic frequency is 200kHz, the spraying distance is 60mm, wherein the thickness of the first coating layer is 1mm, the thickness of the second coating layer is 1mm, and the thickness of the PFA coating is 2mm, the mold is placed in a magnetron sputtering coating device, chromium powder and nickel powder are used as sputtering targets and loaded on the target holder, vacuumed, argon and nitrogen are introduced, the chromium target power supply and the nickel target power supply are alternately turned on, and a composite coating is deposited on the mold surface, wherein the sputtering power of the chromium target is 260W, the sputtering power of the nickel target is 320W, the interval time of alternately turning on the chromium target power supply and the nickel target power supply is 5min, and it is turned off after the last nickel target sputtering is completed;

[0057] S3, extrusion: the pretreated PFA particles are introduced into a high-temperature fluoroplastic extruder, the feed temperature is 100°C, the temperature in the high-temperature fluoroplastic extruder is controlled in sections, and the PFA particles are completely melted and extruded, wherein the high-temperature fluoroplastic extruder is divided into five sections for temperature control, wherein the rear temperature is 360°C, the middle temperature is 370°C, the front temperature is 380°C, the temperature of the die head is 390°C, and the temperature of the nozzle is 400°C;

[0058] S4, injection molding: After the completely molten PFA particles are extruded through the nozzle of the high-temperature fluoroplastic extruder and injected into the mold, the temperature of the mold is kept constant by high-temperature and high-pressure steam, wherein the temperature of the high-temperature and high-pressure steam is 200°C and the pressure is 0.8MPa. After the injection molding is completed, the supply of high-temperature and high-pressure steam is stopped after 8 minutes, and the flow rate of 20m is introduced again after the steam is emptied. 3 / h cooling water for 200 s to quickly reduce the mold temperature and perform cooling and solidification molding;

[0059] S5, pressure holding: After complete cooling, the mold is pressure-held at 0.7 MPa for 150 seconds. After the pressure holding is completed, the pressure is completely released to normal pressure at a rate of 0.1 MPa / min;

[0060] S6, demoulding: taking the formed PFA joint out of the mold for demoulding;

[0061] S7. Heat treatment: After cooling and solidification, the PFA joint is placed in a tubular furnace under a nitrogen atmosphere, heated to 290°C at a rate of 3°C / min, and maintained for 4 hours, and then naturally annealed to room temperature;

[0062] S8, post-processing: put the heat-treated PFA joint into a freezing trimming machine for trimming.

[0063] Comparative Example 1

[0064] The difference between Comparative Example 1 and Example 1 is that step S2 is not subjected to PFA coating treatment, and the other operations are the same.

[0065] Comparative Example 2

[0066] The difference between Comparative Example 2 and Example 1 is that the metal film is not formed by magnetron sputtering coating equipment in step S2, and the other operations are the same.

[0067] Comparative Example 3

[0068] The difference between Comparative Example 3 and Example 1 is that the operation of step S4 is as follows: S4, cooling water is introduced to rapidly reduce the mold temperature, and the mold is cooled and solidified, wherein the cooling time is 200 s, and the flow rate of the cooling water is 20 m 3 / h; other operations are the same.

[0069] Comparative Example 4

[0070] The difference between Comparative Example 4 and Example 1 is that the S7 step is not performed, and the other operations are the same.

[0071] 1. Hardness: GB / T 2411-2008;

[0072] 2. Withstand voltage test: GB / T 15560-1995.

[0073] Table 1

[0074] Group Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Hardness (Shore D) 59 56 55 54 47 53 50 Pressure resistance / MPa 50 47 45 45 42 46 44

[0075] 3. The PFA joints prepared in each embodiment and comparative example were cleaned with ultrapure water for 10 times, and then injected with 5% nitric acid. The pipe opening of the PFA joint was blocked with an ultra-clean PFA plug. After soaking at room temperature for 24 hours, the plug was opened and the sample was tested. The metal ion content was tested by the test instrument: acid extraction combined with ICP-MS and the test standard: SEMI F57. The method detection limit (MDL) was 0.01, and the unit was ug / m 2 ND means not detected, the result is less than the detection limit, the results are shown in Table 2:

[0076] Table 2

[0077]

[0078] From the above performance test data, it can be seen that the PFA joint prepared by the present invention has higher hardness and better pressure resistance. At the same time, the metal ion content measured in the embodiment is lower, indicating that the PFA joint prepared by the present invention has good cleanliness.

[0079] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A process for preparing an ultra-clean fusible polytetrafluoroethylene joint, characterized in that: The preparation of the ultra-clean fusible polytetrafluoroethylene joint comprises the following steps: S1. Pretreatment of fusible polytetrafluoroethylene (PFA) particles: PFA particles were dried at 60°C for 30 minutes by laser drying in a Class 100 clean production workshop, where the laser power was 250W; S2. Mould surface treatment: grind the PFA resin with a ball mill at a speed of 400r / min for 4-5h, pass through a 200-mesh sieve to obtain PFA powder, sandblast the mould surface with quartz sand as the spray material, and then use an electrostatic spray gun to evenly spray the PFA powder on the mould surface for the first coating, and then bake at high temperature in steps, first bake at 270-280℃ for 0.5h, then bake at 320-340℃ for 1-2h, and finally bake at 260-280℃ for 0.5h. After baking, cool to room temperature at a cooling rate of 5-8℃ / min; then slowly cool to room temperature to obtain the second A layer of coating, PFA powder is evenly dispersed in deionized water by ultrasonic treatment, and then a second coating is performed by ultrasonic spraying, and it is dried and cured by 250W laser for 30 minutes, and the mold is placed in a magnetron sputtering coating device, and chromium powder and nickel powder are loaded on the target holder as sputtering targets, and vacuum is evacuated, argon and nitrogen are introduced, and the chromium target power supply and the nickel target power supply are alternately turned on to form a composite coating on the mold surface, wherein the sputtering power of the chromium target is 250~280W, and the sputtering power of the nickel target is 300~340W, and the interval time for alternately turning on the chromium target power supply and the nickel target power supply is 5min, and it is turned off after the last nickel target sputtering is completed; S3, extrusion: the pretreated PFA particles are passed into a high-temperature fluoroplastic extruder, the feed temperature is 80-100°C, the temperature is controlled in sections in the high-temperature fluoroplastic extruder, and the PFA particles are completely melted and extruded, wherein the high-temperature fluoroplastic extruder is divided into five sections for temperature control, wherein the rear temperature is 350-360°C, the middle temperature is 360-370°C, the front temperature is 370-380°C, the temperature of the die head is 380-390°C, and the temperature of the nozzle is 390-400°C; S4, injection molding: After the completely molten PFA particles are extruded through the nozzle of a high-temperature fluoroplastic extruder and injected into the mold, the temperature of the mold is kept constant by high-temperature and high-pressure steam, wherein the temperature of the high-temperature and high-pressure steam is 150-200°C and the pressure is 0.4-0.8MPa. After the injection molding is completed, the supply of high-temperature and high-pressure steam is stopped after 5-8 minutes, and cooling water is introduced after the steam is emptied to quickly reduce the temperature of the mold for cooling and solidification molding; S5, pressure holding: After complete cooling, the mold is pressure-held for 100-150 seconds, and the pressure is completely released to normal pressure after the pressure holding is completed; S6, demoulding: taking the formed PFA joint out of the mold for demoulding; S7. Heat treatment: After cooling and solidification, the PFA joint is placed in a tubular furnace under a nitrogen atmosphere, and the temperature is raised to 260-290°C at a rate of 3°C / min, and maintained for 4 hours, and then naturally annealed to room temperature; S8, post-processing: put the heat-treated PFA joint into a freezing trimming machine for trimming.

2. The preparation process of the ultra-clean fusible polytetrafluoroethylene joint according to claim 1, characterized in that: In step S2, the parameters of the ultrasonic spraying are: ultrasonic power of 40-60 W, ultrasonic frequency of 100-200 kHz, and spraying distance of 30-60 mm.

3. The preparation process of the ultra-clean fusible polytetrafluoroethylene joint according to claim 1, characterized in that: In step S2, the thickness of the first coating layer is 0.5-1 mm, the thickness of the second coating layer is 0.5-1 mm, and the thickness of the PFA coating layer is 1-2 mm.

4. The preparation process of the ultra-clean fusible polytetrafluoroethylene joint according to claim 1, characterized in that: In step S3, a nickel plating layer is provided on the nozzle surface of the high-temperature fluoroplastic extruder.

5. The preparation process of the ultra-clean fusible polytetrafluoroethylene joint according to claim 1, characterized in that: In step S4, the cooling and curing time is 140-200 seconds, and the flow rate of cooling water is 10-20m 3 / h.

6. The preparation process of the ultra-clean fusible polytetrafluoroethylene joint according to claim 1, characterized in that: In step S5, the pressure during the pressure maintenance is 0.6-0.7 MPa, and the rate of pressure release is 0.1 MPa / min.

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