Filter element as well as preparation process and application thereof

Abstract

The invention provides a filter element as well as a preparation process and application thereof. The preparation process of the filter element comprises the following steps: S1, injecting an injection material into a mold to form a filter element blank, and performing first degreasing treatment on the filter element blank; the injection material comprises metal powder and an adhesive; s2, buckling the filter element blank on a gasket to form a filter mold blank; a boss part is arranged on one surface of the gasket; and S3, sintering the filter mold blank to obtain the filter element. The filter element prepared by the preparation process disclosed by the invention has good mechanical properties, and the bearable drawing strength reaches 20 MPa or above; in addition, the metal filter element with the complex internal structure and appearance can be manufactured through the method, the application range of the metal filter element is expanded, the production efficiency can be improved, and the production cost can be reduced.

Description

Technical Field

[0001] The invention relates to a filter element and a preparation process and application thereof. Background Art

[0002] Modern industrial production, such as semiconductor manufacturing, biopharmaceuticals, and aerospace, places extremely high demands on the filtration precision of liquids and gases. Currently, metal filter elements are manufactured using a variety of methods, including powder metallurgy, braiding, and winding. However, these traditional methods (powder metallurgy) have limitations when manufacturing complex metal filter elements, such as low production efficiency, poor product precision, and uneven porosity.

[0003] Metal Injection Molding (MIM) is a new near-net-shape forming technology that has the advantages of being able to manufacture parts with complex shapes, high production efficiency, and good product consistency. It has gradually been applied to the manufacture of metal filter elements. The existing metal filter element preparation process mainly includes the following steps: (1) preparing blank powder according to different product requirements; (2) loading the blank powder into the corresponding forming mold to form the desired shape. The process includes weighing the powder, loading the powder, pressing, holding the pressure, and demolding; (3) through high-temperature heating, atomic diffusion between the powder particles occurs, and the sintering temperature, time, and sintering atmosphere in the furnace chamber are adjusted to combine the contact surface of the powder particles in the blank to achieve the physical and mechanical properties required by the product; (4) by post-processing the sintered product, the stability of the product is improved; (5) welding the gasket to one end of the sintered filter element, and then welding the other end of the filter element to seal.

[0004] However, the existing metal injection process still has some problems when manufacturing metal filter elements. For example, the strength of the sintered filter element is difficult to meet the ideal requirements, and the welding process requirements are not high enough to meet the quality requirements. This makes it difficult to stably produce high-precision metal filter elements that meet the needs of high-end fields. Specifically, due to the low sintering temperature of traditional powder metallurgy, usually below 1050-1280℃, the filter element strength is insufficient. In addition, since welding only involves high-temperature fusion welding of the joint between the filter cartridge and the gasket, it is easy to cause carbonization and discoloration at the weld, resulting in product scrapping and failure to meet production needs. At the same time, the weld area is prone to stress due to high-temperature fusion. After cooling, the stress will cause the filter cartridge or gasket to deform due to the existence of stress, which is difficult to control. In addition, during the welding process, the weld is prone to defects such as empty welds and cold welds, which poses problems and hidden dangers. After welding, 100% leak detection is still required, which is inefficient and increases costs.

[0005] Therefore, it is necessary to develop a new method for manufacturing metal filter elements using a metal injection process to solve the above problems. Summary of the Invention

[0006] To overcome the problems of insufficient filter element strength and product defects caused by welding processes in existing metal injection processes, the present invention provides a filter element, a preparation process, and applications thereof. The filter element produced by the preparation process of the present invention exhibits excellent mechanical properties and can withstand a pull-out strength exceeding 20 MPa. Furthermore, this method can produce metal filter elements with complex internal structures and shapes, expanding the application range of metal filter elements, improving production efficiency, and reducing production costs.

[0007] The present invention solves the above technical problems through the following technical solutions.

[0008] The present invention provides a preparation process of a filter element, which comprises the following steps:

[0009] S1. Injecting an injection material into a mold to form a filter element blank, and then performing a first degreasing process on the filter element blank; the injection material includes metal powder and a binder; the filter element blank is a circular ring structure with one end open and the other end closed;

[0010] S2. Buckle the filter element blank onto a gasket to form a filter mold; one side of the gasket is provided with a boss portion, and the difference between the outer diameter of the boss portion and the inner diameter of the open end of the filter element blank is less than or equal to 0.5 mm; the buckling method includes: placing the open end of the filter element blank onto the gasket and arranging it around the outer periphery of the boss portion;

[0011] S3, sintering the filter mold to obtain a filter element, wherein the sintering temperature is 1300-1400°C, the sintering holding time is 1.5-2.5h, and the vacuum degree of the sintering is 10 -3 -10 -4 Pa.

[0012] In some embodiments, in step S1, the metal powder includes stainless steel powder, nickel-based alloy powder, titanium alloy powder, or Hastelloy powder.

[0013] In a specific embodiment, the metal powder is 316L stainless steel powder, which ensures the corrosion resistance and mechanical strength of the prepared filter element.

[0014] In one embodiment, the purity of the stainless steel powder is greater than 99.95%; and the average particle size of the stainless steel powder is 35 μm.

[0015] In the present invention, by further optimizing the injection material and injection conditions, the fluidity and stability of the injection material can be improved, thereby overcoming the problem of uneven thickness of the filter element blank during the injection process and manufacturing a high-precision, high-performance metal filter element.

[0016] In some embodiments, in step S1, the adhesive includes modified polyolefin, paraffin wax, and zinc stearate.

[0017] In a specific embodiment, the content of the modified polyolefin is 50%-60%, the content of the paraffin is 30%-40%, and the content of the zinc stearate is 5%-10%, where % is the mass percentage of each component in the adhesive.

[0018] In a specific embodiment, the modified polyolefin includes modified polyethylene or modified polypropylene.

[0019] The modified polyethylene may be conventional ethylene-vinyl acetate copolymer (EVA) in the art, which is obtained by copolymerizing ethylene and vinyl acetate.

[0020] The modified polypropylene may be conventional modified polypropylene in the art, which is composed of polypropylene and EPDM rubber.

[0021] In a specific embodiment, the melting point of the paraffin wax is 48-60°C.

[0022] In some embodiments, in step S1, the mass ratio of the metal powder to the binder is (6-9):1.

[0023] In a specific embodiment, the mass ratio of the metal powder to the binder is (7-8):1.

[0024] In some embodiments, in step S1, the particle size of the injection material is 2-3 mm.

[0025] In the present invention, the preparation method of the injection material generally includes the following steps: mixing the metal powder and the binder at 160-180° C. for 3-5 hours through a twin-screw extruder.

[0026] In some embodiments, in step S1, the first degreasing treatment includes: immersing the filtration mold blank in an organic solvent.

[0027] In a specific embodiment, the soaking temperature is 60-70° C.; the soaking time is 3-5 hours; under these conditions, 70%-80% of the adhesive can be removed.

[0028] In a specific embodiment, the organic solvent includes chloroform and ethanol.

[0029] In one embodiment, the volume ratio of chloroform to ethanol in the organic solvent is 7:3.

[0030] In the present invention, the dimensional accuracy of the filter element blank can generally be made to reach ±0.005 mm through precision machining and heat treatment.

[0031] In the present invention, preferably, the injection material is injected into the mold via an injection molding machine and meets one or more of the following conditions: ① the injection temperature during the injection process is 200-220°C; ② the injection pressure during the injection process is 100-150 MPa; ③ after the injection process is completed, a holding pressure is performed at a pressure of 80-120 MPa; ④ after the injection process is completed, a holding pressure is performed for a time of 8-12 seconds; ⑤ the injection speed during the injection process is 40-60 mm / s; ⑥ the mold uses a hot runner system; and ⑦ the mold temperature is controlled at 50-60°C. This method can effectively reduce molding defects and ensure the dimensional accuracy and surface quality of the filter element blank.

[0032] In one embodiment, the injection material is injected into the mold via an injection molding machine under the following conditions: the injection material is heated to 200°C; the injection temperature is set to 210°C; the injection pressure is 120 MPa; the holding pressure is 100 MPa; the holding time is 10 seconds; the injection speed is 50 mm / s; the mold uses a hot runner system, and the mold temperature is controlled at 55°C. Furthermore, a multi-stage injection and holding pressure method can be used to ensure injection molding quality.

[0033] In the present invention, a gasket with a boss portion is used to replace the existing flat gasket, so that the boss portion of the gasket is combined with the filter element blank. After high-temperature integrated sintering, the boss portion and the filter element blank are tightly combined to form a special mortise and tenon structure, eliminating the difficult-to-control welding process.

[0034] In some embodiments, in step S2, the boss portion is in a hollow cylindrical structure to provide a flow channel for liquid or gas during actual filtration applications.

[0035] In some embodiments, the difference between the outer diameter of the boss portion and the inner diameter of the open end of the filter element body is less than or equal to 0.35 mm.

[0036] In the present invention, the material of the gasket may be stainless steel, such as SUS316L stainless steel.

[0037] In some embodiments, in step S2, the buckling method includes the following steps: placing the gasket on the ceramic fixture of the graphite disk with the boss portion facing upward, and then placing the open end of the filter element blank downward on the gasket and arranged on the periphery of the boss portion so that the boss portion is located inside the filter element blank.

[0038] In some embodiments, in step S2, the inner wall surface of the filter element blank has a stepped structure that gradually narrows from the open end to the closed end.

[0039] In a specific embodiment, the inner diameter of the open end side of the filter element blank is 5.8 mm, the inner diameter of the side away from the open end of the filter element blank is 5.5 mm, and the outer diameter of the boss portion is 5.5 mm.

[0040] In some embodiments, in step S2, after the filter mold base is formed, the filter mold base is subjected to a second degreasing treatment.

[0041] In a specific embodiment, the second degreasing treatment satisfies one or more of the following conditions: ① The second degreasing treatment is carried out in a vacuum sintering and degreasing integrated furnace; ② The vacuum degree of the second degreasing treatment is below 10Pa; ③ The second degreasing treatment is carried out under an inert atmosphere; ④ The temperature of the second degreasing treatment is 400-500°C; ⑤ The holding time of the second degreasing treatment is 2-3h; ⑥ The heating rate of the second degreasing treatment is 1-4°C / min.

[0042] In one embodiment, the conditions for the second degreasing treatment are as follows: under a nitrogen protective atmosphere, the vacuum sintering and degreasing integrated furnace is slowly heated to 400-500°C at a heating rate of 1-2°C / min, and kept warm for 2-3 hours. The vacuum degree of the vacuum sintering and degreasing integrated furnace is 10Pa; under this condition, the adhesive can be removed and deformation or cracking of the filter element blank can be avoided.

[0043] In the present invention, by optimizing the degreasing process and combining the first degreasing and the second degreasing, problems such as deformation and cracking of the filter element blank during the degreasing process can be solved, thereby ensuring the integrity of the filter element blank; specifically, in the above-mentioned degreasing process, since the adhesive has a certain lubricating effect, the metal powder undergoes plastic deformation under the action of the surface tension, and the powder particles move slowly under the action of the surface tension, which is similar to the creep of metal at high temperature, making the internal structure more isotropic, effectively improving the phenomenon of uneven pore distribution.

[0044] In the present invention, the welding step is omitted by sintering the filter mold in an integrated manner; compared with the existing welding process, it can not only improve efficiency and reduce costs, but also meet the requirements of high cleanliness and high flatness while meeting the filtration accuracy.

[0045] In some embodiments, in step S3, the sintering treatment is performed in a vacuum sintering and debinding integrated furnace.

[0046] In some embodiments, in step S3, before the sintering treatment, the filter preform is subjected to a third debinding treatment; the third debinding treatment comprises the following steps: heating at a temperature increasing rate of 10℃ / min for 20 minutes, stopping heating for 5 minutes, repeating 3 times, and then increasing the temperature to 800℃, and holding the temperature for 60min.

[0047] In the present application, the sintering treatment can adopt a pulse heating mode, i.e. heating for a period of time and then stopping heating for a short time, so as to make the temperature in the furnace uniformly distributed, promote atomic diffusion and metallurgical bonding between the metal powder particles, and improve the density and strength of the filter element.

[0048] In the present application, by controlling the vacuum degree of the system to be 10 -3 -10 -4 Pa, the oxidation of the metal is prevented, and the performance stability of the filter element is ensured.

[0049] In some embodiments, in step S3, the sintering treatment further comprises vacuum inner sintering, and the conditions of the vacuum inner sintering comprise: controlling the temperature of the vacuum inner sintering to be 1050℃, and holding the temperature for 60min; the vacuum inner sintering stage can effectively remove other impurities or other oxides among the powder particles, so that the powder particles enter the high-temperature sintering stage under the condition of maintaining good purity precision, and the displacement change of the powder particles under the high-temperature state tends to be synchronous under the protection of the inert gas, and the pore size and distribution also tend to be uniform, thereby producing qualified products.

[0050] In some embodiments, in step S3, the temperature increasing rate of the sintering treatment is 5℃ / min, the temperature of the sintering treatment is 1350℃, the holding time of the sintering treatment is 2h, and the vacuum degree of the sintering treatment is 10 -3 Pa.

[0051] In some embodiments, in step S3, after the sintering treatment, a cooling treatment is performed; the conditions of the cooling treatment comprise: reducing the temperature in the system to 800℃, and holding the temperature for 30min.

[0052] In some embodiments, in step S3, after the sintering treatment, forced cooling is performed; the conditions of the forced cooling comprise: introducing argon into the system to increase the pressure, and cooling the system to below 60℃.

[0053] In some embodiments, after step S3, the preparation process of the filter element further comprises: S4, sequentially performing cleaning, polishing and packaging and warehousing on the filter element.

[0054] The cleaning polishing comprises one or more of the following conditions ①-④:

[0055] ① The cleaning polishing comprises a chemical polishing method;

[0056] ② The polishing solution of the cleaning polishing comprises phosphoric acid, sulfuric acid, nitric acid and corrosion inhibitor;

[0057] ③ The temperature of the cleaning polishing is 60-70 DEG C;

[0058] ④ The time of the cleaning polishing is 20-30 min.

[0059] In the application, after the filter element is cleaned and polished, the surface oxide layer and tiny defects are removed, and the surface smoothness is improved; then high-precision detection equipment is used to comprehensively detect the porosity, pore size distribution, filtration accuracy and mechanical strength of the filter element, so that the product quality meets high standards.

[0060] The packaging and warehousing generally comprises the following steps: the filter element is packed into a sealed bag, vacuumized, labeled and submitted to the warehousing process, and the finished product is delivered to the warehouse.

[0061] The application further provides a filter element prepared by the preparation process of the filter element.

[0062] In the application, the filter element can also be referred to as a filter.

[0063] The application further provides an application of the filter element in filtering nano-particles.

[0064] In the application, the filter element has ultra-high precision and can be used for filtering 3nm or 1nm particles.

[0065] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined arbitrarily, i.e. the preferred examples of the application are obtained.

[0066] The reagents and raw materials used in the application are commercially available.

[0067] The application comprises at least one of the following beneficial technical effects:

[0068] 1. The filter element prepared by the method of the application has good mechanical properties, and the withstanding tensile strength reaches more than 20MPa. Compared with the welding process in the prior art, the integrated sintering forming of the application can fundamentally and effectively solve the pain points in the welding process of the existing similar products, reduce the welding process link, optimize the gasket filter production process, improve the efficiency and the yield, and has the following effect advantages:

[0069] (a) Integrated sintering not only reduces production steps and improves efficiency, but also effectively prevents secondary contamination. (b) Integrated sintering eliminates undesirable phenomena such as blackening and discoloration. (c) Integrated sintering ensures uniform heating of the entire product, eliminating defects such as localized stress. (d) Due to the uniformity of the product after integrated sintering, 100% inspection is not required, saving costs and improving efficiency.

[0070] 2. This method can produce metal filter elements with complex internal structures and shapes, expand the application range of metal filter elements, and can improve production efficiency and reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 This is a schematic diagram of the exploded structure of the gasket and filter element blank of Example 1 of the present application;

[0072] Figure 2 This is the handle force test curve of the filter element with 1 / 2 specifications in Example 1;

[0073] Figure 3 This is the pull force test curve of the 1 / 4 specification filter element in Effect Example 1;

[0074] Figure 4 This is the flow and pressure difference effect diagram of the existing filter;

[0075] Figure 5 This is a flow rate and pressure difference effect diagram of the filter element of Example 1 of the present application;

[0076] Description of reference numerals:

[0077] Gasket 1; boss portion 101; filter element body 2; open end 201. DETAILED DESCRIPTION

[0078] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0079] Example 1

[0080] This embodiment discloses a filter element and a method for preparing the same.

[0081] Preparation before implementing the preparation method of the filter element:

[0082] 1. The structure design of the gasket: the SUS316L stainless steel plate material is processed into the pre-designed size and shape. The outer diameter of the gasket is 19.8mm, the inner diameter is 5.5mm, and the gasket upper part retains a hollow cylindrical boss part with a height of 2mm±0.02mm, an outer diameter of 5.5mm±0.01mm, and a wall thickness of 0.6mm±0.01mm. It can be sintered with the filter core riveted together. Since the gasket boss part has almost no shrinkage at high temperature, while the filter core wall will shrink by 8%-12%, the shrinkage rates of the two are different, causing them to stick together at a certain temperature, firmly adhering together to achieve the required bonding strength and meet the product application requirements.

[0083] 2. The structure design of the filter core: the filter core structure is designed with one end closed and the other end open. The outer diameter of the filter core is 7.05mm±0.02mm, the inner diameter is 5.5mm±0.01mm, and the open end retains a bite step structure (groove) that matches the gasket boss part with an inner diameter of 5.85mm±0.01mm and a depth of 2mm.

[0084] The preparation method of the filter element includes the following steps:

[0085] 1) Raw material preparation: select 316L stainless steel powder with an average particle size of 35μm and a purity of 99.95%. The binder is a multi-component composite system composed of 55% modified polyethylene (EVA, which is obtained by copolymerization of ethylene and vinyl acetate), 35% low-melting-point paraffin, and 10% zinc stearate; through a twin-screw extruder, mix at 160-180℃ for 3-5 hours, with a mass ratio of metal powder to binder of 88:12, so that the metal powder is uniformly dispersed in the binder to form injection material with good flowability and stability. The mixed injection material is processed into injection material particles with a particle size of 2-3mm by a granulator for standby use.

[0086] 2) Injection molding: put the injection material particles prepared in step 1) into the barrel of an injection molding machine, heat the injection material particles to 200℃, and inject them into the mold. Set the injection temperature to 210℃, the injection pressure to 120MPa, the holding pressure to 100MPa, the holding time to 10 seconds, and the injection speed to 50mm / s. The mold uses a hot runner system, and the mold temperature is controlled at 55℃. Use multi-stage injection and holding pressure to ensure the quality of injection molding. The filter core blank after injection molding is subjected to preliminary appearance inspection, and the products with obvious defects are removed to obtain the filter core blank.

[0087] 3) First debinding treatment: (solvent debinding and placement)

[0088] 3.1) Solvent degreasing: The filter element blank after injection molding in step 2) is immersed in a 65° C. chloroform solution (composed of chloroform and ethanol in a volume ratio of 7:3) for 5 hours. At this time, the residual binder content in the filter element blank is about 12%.

[0089] 3.2) Ornaments: Figure 1 This is a schematic diagram of the exploded structure of the gasket and filter element blank of this embodiment. Specifically, the stainless steel gasket 1 prepared before implementation is placed on the ceramic jig of the graphite disk with the boss portion 101 facing upward. Then, the open end 201 of the filter element blank 2, which has been solvent-degreased in step 3.1), is buckled downward onto the gasket 1 and positioned around the boss portion 101. The boss portion 101 of the stainless steel gasket 1 is riveted together with the open end 201 of the filter element blank 2, thus obtaining a single, unsintered gasket filter blank. The ceramic jig is also a specialized ceramic jig designed based on the shape and structure of the injection molded blank.

[0090] 4) Second degreasing treatment: After the above-mentioned ornament steps, the filter element body and the gasket have been combined into a filter mold as a whole. Then the filter mold is placed on a special carrier and moved into a vacuum sintering and degreasing integrated furnace. The vacuum sintering and degreasing integrated furnace is evacuated to below 10Pa, and nitrogen is introduced. Under the protection of nitrogen atmosphere, the temperature is increased to 450℃ at a rate of 2℃ / min and kept warm for 150min. At this stage, catalytic degreasing can be completed to obtain a degreased part.

[0091] 5) High temperature sintering:

[0092] The specific steps include:

[0093] 5.1) Vacuum degreasing (third degreasing): After degreasing in step 4), continue to introduce nitrogen into the vacuum sintering and degreasing integrated furnace, heating at a heating rate of 10°C / min for 20 minutes, then stopping heating for 5 minutes. Repeat this three times, then raise the temperature to 800°C and hold for 60 minutes to complete the vacuum degreasing.

[0094] 5.2) Vacuum firing: After the above steps are completed, the furnace is evacuated and the temperature inside the furnace is maintained at 1050°C for 60 minutes to complete the vacuum firing.

[0095] 5.3) Partial pressure sintering: After vacuum sintering, argon gas was introduced and the temperature was raised to 1350°C at a heating rate of 5°C / min. The vacuum degree was controlled at 10 -3 Pa, keep warm for 2 hours, then reduce the furnace temperature to 800℃ and keep warm for 30 minutes.

[0096] 5.4) Forced cooling: After completing step 5.3), stop heating and continue to introduce argon to increase the pressure. Cool the furnace to below 60°C, open the furnace door and take out the product. The sintering process is now complete to obtain a sintered part.

[0097] 6) Cleaning and polishing: Polish and clean the sintered parts obtained in the above steps

[0098] 6.1. Use chemical polishing process and a specific polishing liquid (phosphoric acid, sulfuric acid, and nitric acid mixed in a volume ratio of 6:3:1). Place the sintered gasket filter in the chemical polishing liquid and treat it at 60-70℃ for 25 minutes to remove the surface oxide layer and minor defects and improve the surface finish of the product.

[0099] 6.2) Ultrasonic cleaning: After polishing, take out the polished product and place it in an ultrasonic cleaning tank. Add pure water to the cleaning tank and clean it for 20 minutes. Drain the water and then pour in clean water to clean it. Repeat this cleaning process 3 times.

[0100] 6.3) Drying: Place the cleaned product in an oven, heat to 80°C for 1.5 hours, and dry to obtain the final product.

[0101] 7) Packaging and storage: Take out the products after drying in the above steps, put each product in a plastic bag and vacuum seal it, and hand it over to the warehouse manager to complete storage.

[0102] The filter element prepared by the above preparation method has the following effects:

[0103] 1. Excellent filtration accuracy: By precisely controlling the metal powder particle size, injection material formula and sintering process, the filter element porosity can be precisely controlled within the range of 15%-45%, the pore size distribution is uniform, and the filtration accuracy reaches the nanometer level of 0.001 micron, which can effectively intercept tiny particle impurities and meet the strict requirements of high-end industry for high-precision filtration.

[0104] 2. Excellent mechanical properties: The optimized sintering process and post-processing procedures give the filter element excellent mechanical properties. It can withstand a tensile strength of more than 20MPa. When subjected to high working pressure and fluid impact, it is not easy to deform or damage, ensuring the long-term stable operation of the filter element.

[0105] 3. Complex structure manufacturing capability: The metal injection process combined with innovative mold design can produce metal filter elements with complex internal structures and shapes, such as those with microporous arrays, three-dimensional flow channels, etc., which makes it possible to meet diverse filtration needs and expand the application range of metal filter elements.

[0106] 4. Efficient and low-cost production: While ensuring product quality, the present method improves production efficiency and reduces costs by optimizing process parameters and adopting a batch production approach. Compared with traditional manufacturing methods, material utilization is increased by 40%-50%, effectively more than doubling production efficiency, resulting in significant economic benefits and market competitiveness.

[0107] 5. The sintering temperature of traditional powder metallurgy is relatively low, usually below 1050-1280°C. By optimizing the molding and sintering process, the sintering temperature can be increased to above 1300°C, thereby enhancing the strength of the filter element.

[0108] Effect Example 1

[0109] This embodiment examines the integrated sintering pull force effect of the filter element, potential defects such as empty welding, flow pressure difference effect, and filtering effect.

[0110] 1. Integrated sintered handle force effect:

[0111] The center of the gasket is designed with a cylindrical boss of specific dimensions, which can be riveted to the inner wall of the filter element blank after sintering. Because the gasket and filter element shrink differently during heating, the high-temperature sintering ensures a tight bond between them, achieving the required pull force required for product use.

[0112] Industry norms and standard test methods were used to test the pull-out force and pull-out strength of filter elements with 1 / 2 inch and 1 / 4 inch gaskets, respectively. The measured results are shown in Table 1, which shows the pull-out force test of filter elements of different specifications.

[0113] Table 1

[0114]

[0115] Figure 2 and Figure 3 The pull force test curves of filter elements with specifications of 1 / 2 inch and 1 / 4 inch are respectively; read the maximum pull force (N) that can be sustained from the curve, and divide it by the force-bearing area (mm 2 ) can obtain the tensile strength (MPa), and the filter element of the present application can withstand a tensile strength of more than 20MPa.

[0116] 2. Test for potential defects such as empty welding:

[0117] The conventional testing methods in the art were used to test the filter obtained by welding using the traditional process and the integrated sintered filter element of Example 1.

[0118] Specifically, the weld is irradiated with X-rays or gamma rays, and internal defects (such as incomplete penetration, slag inclusions, and pores) are observed through film or digital imaging.

[0119] Traditional filters utilize welding, a process that can result in hollow welds. A hollow weld in argon arc welding occurs when an effective molten pool or weld seam is not formed. Hollow welds can occur for a variety of reasons and are unavoidable. However, the integrated sintered structure at the junction of the gasket and filter element reduces the welding process and eliminates defects such as hollow welds, cold welds, and discoloration.

[0120] 3. Flow pressure difference effect:

[0121] The nitrogen source gas was passed through the existing filter and the filter element of Example 1 at different flow rates and pressures to test the flow rate and pressure difference effects of the different filter elements.

[0122] Figure 4 This is a flow rate and pressure difference effect diagram of an existing product (MOTT, USA, model GSG-V4-3-S filter); Figure 5 This is a flow rate and pressure difference effect diagram of the filter element of Example 1;

[0123] Depend on Figure 4-5 It can be clearly seen that under a pressure of 90psi, the pressure loss change rates of flow rates of 10slm and 20slm are compared respectively: the pressure loss of the GSG-V4-3-S filter changes from 12kPa to 50kPa, with a change rate of 416.667%; while the pressure loss of the filter element of Example 1 changes from 9kPa to 18kPa, with a change rate of 200%, which is significantly better than similar products on the market, and the pressure loss change rate is only half of that of similar products on the market.

[0124] And, by Figure 4-5 It can be seen that under the conditions of 90 psi pressure and 20 slm nitrogen source flow rate, the pressure loss of the GSG-V4-3-S filter is about 7.5 psid, while the pressure loss of the filter element of Example 1 is close to 3 psid, which is only 40% of similar products, meaning that the flow rate can be more than doubled (under the same flow rate, the smaller the pressure difference, the better the product quality).

[0125] 4. Filtering effect:

[0126] The filtration effect of the filter element of Example 1 was tested using a PSMPS test system; wherein the PSMPS test system is a 1 nm particle generation and measurement system of GRIMM Aerosol Technology Co., Ltd. of Germany.

[0127] The object of the filtration efficiency test is an aerosol source gas, wherein the particle size is in the range of 1-55 nm. The aerosol source gas is passed through the filter element of Example 1 at a flow rate of about 1 slm.

[0128] According to the particle distribution of aerosol, the gas filtration accuracy of the filter reaches >0.001μm (i.e. >1nm), and the filtration efficiency can reach 99.99999%, which fully meets the product design goals.

[0129] Since the product is a porous metal product, it is required to achieve a certain filtration accuracy and filtration efficiency. According to the results of this experimental verification, the expected effect has been fully achieved.

Claims

1. A preparation process for a filter element, characterized in that: It includes the following steps: S1. Injecting an injection material into a mold to form a filter element blank, and then performing a first degreasing process on the filter element blank; the injection material includes metal powder and a binder; the filter element blank is a circular ring structure with one end open and the other end closed; S2. Buckle the filter element blank onto a gasket to form a filter mold; one side of the gasket is provided with a boss portion, and the difference between the outer diameter of the boss portion and the inner diameter of the open end of the filter element blank is less than or equal to 0.5 mm; the buckling method includes: placing the open end of the filter element blank onto the gasket and arranging it around the outer periphery of the boss portion; S3, sintering the filter mold to obtain a filter element, wherein the sintering temperature is 1300-1400°C, the sintering holding time is 1.5-2.5h, and the vacuum degree of the sintering is 10 -3 -10 -4 Pa.

2. The process for preparing the filter element according to claim 1, wherein: In step S1, the injection material satisfies at least one of the following conditions ① to ⑤: ① The metal powder includes stainless steel powder, nickel-based alloy powder, titanium alloy powder or Hastelloy powder; ② The adhesive comprises modified polyolefin, paraffin wax and zinc stearate; ③ The mass ratio of the metal powder to the binder is (6-9):1; ④ The particle size of the injection material is 2-3 mm; ⑤ The first degreasing process includes: soaking the filter element blank in an organic solvent.

3. The preparation process of the filter element according to claim 2, characterized in that: In step S1, the injection material satisfies at least one of the following conditions ① to ④: ① The content of the modified polyolefin is 50%-60%, the content of the paraffin is 30%-40%, and the content of the zinc stearate is 5%-10%, where % is the mass percentage of each component in the adhesive; ② The modified polyolefin includes modified polyethylene or modified polypropylene; ③ The mass ratio of the metal powder to the binder is (7-8):1; ④ The organic solvent includes chloroform and ethanol.

4. The process for preparing the filter element according to claim 1, wherein: Step S2 satisfies at least one of the following conditions ① to ③: ① The boss portion is a hollow cylindrical structure; ② The difference between the outer diameter of the boss portion and the inner diameter of the opening end of the filter element body is less than or equal to 0.5 mm; ③ After the filter mold base is formed, the filter mold base is subjected to a second degreasing treatment.

5. The process for preparing the filter element according to claim 4, wherein: Step S2 satisfies at least one of the following conditions ① and ②: ① The buckling method includes the following steps: placing the gasket on a ceramic jig of a graphite disc with the boss facing upward, and then placing the open end of the filter element blank downward on the gasket and arranged on the periphery of the boss so that the boss is located inside the filter element blank; ② The inner wall surface of the filter element blank is in a step-like structure that gradually narrows from the open end to the closed end.

6. The process for preparing the filter element according to claim 5, wherein: When the inner wall surface of the filter element blank is in a stepped structure, the inner diameter of the open end side of the filter element blank is 5.85 mm, and the inner diameter of the side away from the open end of the filter element blank is 5.5 mm; the outer diameter of the boss portion is 5.5 mm.

7. The process for preparing the filter element according to claim 1, wherein: In step S3, the sintering process satisfies at least one of the following conditions ① to ⑥: ① The sintering process is carried out in a vacuum sintering and degreasing integrated furnace; ② Before the sintering process, the filter mold base is subjected to a third degreasing process; the third degreasing process comprises the following steps: heating at a heating rate of 10°C / min for 20 minutes, then stopping heating for 5 minutes, repeating this process three times, then raising the temperature to 800°C and holding the temperature for 60 minutes; ③ The sintering treatment further includes vacuum firing, and the conditions of the vacuum firing include: controlling the vacuum firing temperature at 1050° C. and maintaining it for 60 minutes; ④ The heating rate of the sintering process is 5℃ / min, the temperature of the sintering process is 1350℃, the holding time of the sintering process is 2h, and the vacuum degree of the sintering process is 10 -3 Pa; ⑤ After the sintering treatment, a cooling treatment is performed; the cooling treatment conditions include: lowering the temperature in the system to 800° C. and holding the temperature for 30 minutes; ⑥ After the sintering treatment, forced cooling is performed; the conditions for the forced cooling include: introducing argon gas into the system to increase the pressure and cooling the system to below 60°C.

8. The process for preparing the filter element according to claim 1, wherein: After step S3, the preparation process of the filter element further includes: S4, cleaning, polishing, packaging and storing the filter elements in sequence; The cleaning and polishing includes at least one of the following conditions ① to ④: ① The cleaning and polishing includes chemical polishing; ② The polishing solution for cleaning and polishing includes phosphoric acid, sulfuric acid, nitric acid and corrosion inhibitor; ③ The temperature of the cleaning and polishing is 60-70°C; ④ The cleaning and polishing time is 20-30 minutes.

9. A filter element, characterized in that: The filter element is prepared by the preparation process of the filter element according to any one of claims 1 to 8.

10. Use of the filter element according to claim 9 in filtering nano-sized particles.

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