A gradient structure powder mesh composite membrane and a preparation method thereof

Abstract

The scheme discloses a gradient structure powder net composite membrane and a preparation method thereof. The composite membrane is integrally combined by a gradient type four-layer stainless steel sintered net substrate and a three-layer gradient coating. The four-layer sintered net is sequentially stacked by four layers of metal wire meshes with different mesh numbers. The metal wire meshes are arranged in the order of an inner strengthening layer, an intermediate strengthening / shunt layer, a control layer and a protection layer. The three-layer gradient coating is coated on the protection layer, uniformly penetrates and is fixed on the control layer. Each coating layer is formed by mixing a powder raw material and a binder. The particle size of the powder raw material is gradually reduced in the order of a gas permeation strengthening layer, a transition buffer layer and a dense functional layer. The scheme constructs a four-stage aperture gradient and a three-stage gradient particle size powder system, accurately matches the aperture of the control layer, optimizes the accurate penetration spraying and sintering process, improves the interfacial bonding strength between the powder and the substrate layer, simplifies the preparation process, reduces the production cost and realizes the industrialized batch production of the composite membrane.

Description

Technical Field

[0001] This solution relates to the field of filter material technology, and in particular to a gradient structure powder mesh composite membrane and its preparation method. Background Technology

[0002] As a high-end filtration material, gradient structure powder-mesh composite membranes must simultaneously meet the core requirements of high-precision filtration, high air permeability, and strong structural stability. Existing technologies for composite membrane preparation suffer from several defects: unreasonable matrix structure and pore size gradient design lead to chaotic pore size standards; lack of gradient matching in powder particle sizes results in insufficient adaptability, easily causing local pore blockage or loss, leading to uneven pore size distribution and frequent occurrences of abnormally large pore sizes; the spraying and sintering processes are not specifically optimized, resulting in insufficient interlayer bonding strength; some processes require complex pretreatment, making the process cumbersome, costly, and difficult to achieve industrial-scale mass production. Summary of the Invention

[0003] This solution aims to at least solve the technical problems existing in the prior art. To this end, the first aspect of the present invention proposes a gradient structure powder mesh composite film, wherein the composite film is integrally composed of a gradient four-layer stainless steel sintered mesh substrate and a three-layer gradient coating. The four-layer sintered mesh is composed of four layers of metal wire mesh with different mesh counts stacked sequentially. The metal wire mesh is arranged in the order of inner reinforcing layer, middle reinforcing / diversion layer, control layer, and protective layer. The inner reinforcing layer, the control layer, and the protective layer are square mesh, and the middle reinforcing / diversion layer is woven mesh. The mesh count of the control layer is greater than that of the other layers. The three-layer gradient coating is applied to the protective layer, uniformly penetrates and is fixed to the control layer; the three-layer gradient coating consists of a dense functional layer, a transition buffer layer and a breathable enhancement layer arranged sequentially in the direction away from the control layer, and the breathable enhancement layer is in contact with the control layer; each layer of the coating is made of powder raw material and binder, and the particle size of the powder raw material decreases in the order of the breathable enhancement layer, the transition buffer layer and the dense functional layer.

[0004] Optionally, the mesh size of the inner reinforcing layer is 10-35 mesh, the mesh size of the intermediate reinforcing / diversion layer is 80-160 mesh, the mesh size of the control layer is 325-600 mesh, the mesh size of the protective layer is 60-100 mesh, the total thickness of the four sintered mesh layers is 1.2-2.5 mm; the total thickness of the four sintered mesh layers is 1.6 mm, and the total thickness of the three gradient coating layers is 0.8-1.2 mm.

[0005] Optionally, the metal wire mesh is made of any one of 316L, 310S, or Inconel 600; the wire diameter deviation of the square mesh is ≤±5%, and the aperture deviation is ≤±10%; the wire diameter deviation of the woven mesh is ≤±3%, and the aperture deviation is ≤±8%; the overall porosity of the square mesh and the woven mesh is 37~41%.

[0006] Optionally, the powder raw material is one or more of 316L, 310S, Inconel 600 powder, FeAl3, and TiAl alloy powder; the dense functional layer is composed of 100% fine-particle-size powder; the transition buffer layer is composed of 68% medium-particle-size powder and 32% adaptive control layer particle-size powder; and the air permeability enhancement layer is composed of 72% adaptive control layer particle-size powder and 28% medium-particle-size powder.

[0007] A second aspect of this invention provides a method for preparing a gradient structure powder mesh composite film, the method comprising: The pre-prepared four-layer sintered mesh is sequentially degreased, pickled, and dried to obtain the sintered mesh to be processed. The four-layer sintered mesh consists of four layers of metal wire mesh with different mesh counts stacked sequentially. The metal wire mesh is arranged as an inner reinforcing layer, an intermediate reinforcing / diversion layer, a control layer, and a protective layer. The inner reinforcing layer, the control layer, and the protective layer are square-hole meshes, and the intermediate reinforcing / diversion layer is a woven mesh. The mesh count of the control layer is greater than that of the other layers. Using deionized water as a solvent, add the binder solution and dispersant, and stir to dissolve to obtain the binder solution; Three powder raw materials with different particle sizes were selected, and the binder solution was added to each powder raw material. The mixtures were then ball-milled to obtain coating slurries with three different particle sizes. The three coating slurries are injected into the three independent channels of the spraying machine. The spraying machine is used to spray the three coating slurries onto the protective layer of the sintering mesh to be processed in descending order of particle size, so that the powder of the coating slurry can be uniformly penetrated and fixed in the control layer, resulting in a blank including three gradient coatings. The green body is subjected to two-stage degreasing treatment at different temperatures to obtain a degreased green body; The degreased preform is sintered at high temperature and then slowly cooled to obtain a gradient structure powder mesh composite film.

[0008] Optionally, the adhesive solution is prepared as follows: Weigh the raw materials according to the following proportions: PVP 3wt%~7wt%, polyethylene glycol 1.2~1.7wt%, dispersant 0.15~0.25wt%, and deionized water balance. The raw materials are added to a mixing vessel and stirred at 800 rpm for 60 minutes at 60°C until a homogeneous and transparent solution is formed, thus obtaining the binder solution.

[0009] Optionally, the binder solution is added to each powder raw material, and the mixture is ball-milled separately to obtain coating slurries with three particle sizes, including: An equal amount of the binder solution was added to each powder raw material to obtain three solutions to be treated. Each of the solutions to be treated was poured into a planetary ball mill and milled at 220 rpm for 3 hours to obtain three kinds of ball mill slurries. The three ball mill slurries were allowed to stand for 30 minutes to degas, resulting in coating slurries with three different particle sizes.

[0010] Optionally, the step of spraying the three coating slurries onto the protective layer of the four-layer sintered mesh in descending order of particle size using the spraying machine includes: The three coating slurries are injected into the three independent channels of the spraying machine respectively; Start the spraying machine and apply the three coating slurries layer by layer to the four-layer sintered mesh protective layer in descending order of particle size through the three independent channels. During the process, control the wire mesh tube speed of the spraying machine to 10-15 rpm, the reciprocating speed of the spray gun to 330-630 mm / min, maintain the slurry temperature at 27-35℃, the spraying pressure at 0.19-0.27 MPa, and maintain the distance between the spray gun and the substrate surface at 10-14 cm to complete the layer-by-layer spraying operation.

[0011] Optionally, the step of subjecting the green body to two-stage degreasing treatment at different temperatures to obtain a degreased green body includes: The green body was placed in a degreasing device for two-stage degreasing treatment. First, the temperature was increased from room temperature to 300℃ at a heating rate of 2.9℃ / min and held for 0.8h. Then, the temperature was increased to 550℃ at a heating rate of 4.6℃ / min and held for 1.4h to finally obtain a degreased green body.

[0012] Optionally, the step of sintering the degreased preform at high temperature and then slowly cooling it to obtain a gradient structure powder mesh composite film includes: The degreased preform is placed in a sintering equipment for high-temperature sintering. The sintering temperature is controlled at 1100~1250℃ and held for 30~90 minutes. Then, the preform is slowly cooled at a cooling rate of 3.8℃ / min to finally form a gradient structure powder mesh composite film.

[0013] The embodiments of the present invention have the following beneficial effects: The gradient structure powder-mesh composite membrane provided in this invention is integrally formed by a gradient four-layer stainless steel sintered mesh substrate and a three-layer gradient coating. The four-layer sintered mesh consists of four layers of metal wire mesh with different mesh counts stacked sequentially, arranged as an inner reinforcing layer, an intermediate reinforcing / diversion layer, a control layer, and a protective layer. The inner reinforcing layer, the control layer, and the protective layer are square-hole meshes, while the intermediate reinforcing / diversion layer is a woven mesh. The mesh count of the control layer is greater than that of the other layers. The three-layer gradient coating is applied to the protective layer, uniformly penetrates, and is fixed to the control layer. In the direction away from the control layer, the three-layer gradient coating consists of a dense functional layer, a transition buffer layer, and a breathable enhancement layer arranged sequentially, with the breathable enhancement layer in contact with the control layer. Each layer of the coating is composed of a powder raw material and a binder, and the particle size of the powder raw material decreases in a gradient order from the breathable enhancement layer, the transition buffer layer, to the dense functional layer. This solution optimizes the gradient structure matrix design, constructs a "wide → narrow → even narrower → wide" pore size gradient to solve the problem of inconsistent pore size references; and designs a three-level gradient particle size powder system to precisely match the pore size of the control layer, eliminate abnormal maximum pore size, and ensure pore size uniformity. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of a gradient structure powder mesh composite film provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the steps of a method for preparing a gradient structure powder mesh composite film according to an embodiment of the present invention. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present solution, and not all embodiments. Based on the embodiments of the present solution, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present solution.

[0016] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0017] Figure 1 This is a schematic diagram of a gradient structure powder mesh composite membrane provided in an embodiment of the present invention.

[0018] like Figure 1 As shown, the gradient structure powder mesh composite film is composed of a gradient four-layer stainless steel sintered mesh substrate and a three-layer gradient coating integrated into one composite. The four-layer sintered mesh is composed of four layers of metal wire mesh with different mesh counts stacked sequentially. The metal wire mesh is arranged in the order of inner reinforcing layer, middle reinforcing / diversion layer, control layer, and protective layer. The inner reinforcing layer, the control layer, and the protective layer are square mesh, and the middle reinforcing / diversion layer is woven mesh. The mesh count of the control layer is greater than that of the other layers. The three-layer gradient coating is applied to the protective layer, uniformly penetrates and is fixed to the control layer; the three-layer gradient coating consists of a dense functional layer, a transition buffer layer and a breathable enhancement layer arranged sequentially in the direction away from the control layer, and the breathable enhancement layer is in contact with the control layer; each layer of the coating is made of powder raw material and binder, and the particle size of the powder raw material decreases in the order of the breathable enhancement layer, the transition buffer layer and the dense functional layer.

[0019] Reference Figure 1 The four-layer sintered mesh is arranged as follows: inner reinforcing layer, intermediate reinforcing / diversion layer, control layer, and protective layer. The inner reinforcing layer is a square-pore mesh located on the innermost side, close to the support or raw material side, primarily providing mechanical strength and overall support. The intermediate reinforcing / diversion layer is a woven mat mesh with a twill weave and tortuous pores, serving to uniformly disperse the fluid, buffer pressure, and prevent powder penetration. The control layer is also a square-pore mesh with the highest mesh count and smallest pores, a crucial adhesion layer for subsequent powder coating, determining the final filtration accuracy and coating bonding strength. The outer protective layer is also a square-pore mesh located on the outermost side, primarily protecting the internal structure from damage during spraying and subsequent processing.

[0020] Specific reference Figure 1 The gradient structure powder mesh composite membrane is composed of a gradient four-layer stainless steel sintered mesh substrate and a three-layer gradient coating. The four layers of stainless steel sintered mesh substrate are: inner reinforcing layer, intermediate reinforcing / diversion layer, control layer, and protective layer. The three layers of gradient coating are: dense functional layer, transition buffer layer, and air permeability enhancement layer.

[0021] The composite membrane has a uniform pore size distribution and no abnormal maximum pore size. It has high-precision filtration performance, high air permeability, strong interlayer bonding strength and ≥210MPa bending strength, stable structure, and is suitable for high temperature, high pressure and high precision filtration conditions.

[0022] This solution optimizes the gradient structure matrix design, constructs a "wide → narrow → even narrower → wide" pore size gradient to solve the problem of inconsistent pore size references; and designs a three-level gradient particle size powder system to precisely match the pore size of the control layer, eliminate abnormal maximum pore size, and ensure pore size uniformity.

[0023] As an optional embodiment, the mesh size of the inner reinforcing layer is 10-35 mesh, the mesh size of the intermediate reinforcing / diversion layer is 80-160 mesh, the mesh size of the control layer is 325-600 mesh, the mesh size of the protective layer is 60-100 mesh, the total thickness of the four sintered mesh layers is 1.2-2.5 mm; the total thickness of the four sintered mesh layers is 1.6 mm, and the total thickness of the three gradient coating layers is 0.8-1.2 mm.

[0024] As an optional embodiment, the metal wire mesh is made of any one of 316L, 310S, and Inconel 600; the wire diameter deviation of the square mesh is ≤±5%, and the aperture deviation is ≤±10%; the wire diameter deviation of the woven mesh is ≤±3%, and the aperture deviation is ≤±8%; the overall porosity of the square mesh and the woven mesh is 37~41%.

[0025] As an optional embodiment, the powder raw material is one or more of 316L, 310S, Inconel 600 powder, FeAl3, and TiAl alloy powder; the dense functional layer is composed of 100% fine-particle-size powder; the transition buffer layer is composed of 68% medium-particle-size powder and 32% adaptive control layer particle-size powder; and the air permeability enhancement layer is composed of 72% adaptive control layer particle-size powder and 28% medium-particle-size powder.

[0026] In summary, the gradient structure powder-mesh composite membrane provided in this embodiment of the invention is composed of a gradient-type four-layer stainless steel sintered mesh substrate and a three-layer gradient coating integrally formed. The four-layer sintered mesh consists of four layers of metal wire mesh with different mesh counts stacked sequentially, arranged as an inner reinforcing layer, an intermediate reinforcing / diversion layer, a control layer, and a protective layer. The inner reinforcing layer, the control layer, and the protective layer are square-hole meshes, while the intermediate reinforcing / diversion layer is a woven mesh. The mesh count of the control layer is greater than that of the other layers. The three-layer gradient coating is applied to the protective layer, uniformly penetrates, and is fixed to the control layer. In the direction away from the control layer, the three-layer gradient coating consists of a dense functional layer, a transition buffer layer, and a breathable enhancement layer arranged sequentially, with the breathable enhancement layer in contact with the control layer. Each layer of the coating is composed of a mixture of powder raw material and a binder, and the particle size of the powder raw material decreases in a gradient order from the breathable enhancement layer, the transition buffer layer, to the dense functional layer. This solution optimizes the gradient structure matrix design, constructs a "wide → narrow → even narrower → wide" pore size gradient to solve the problem of inconsistent pore size references; and designs a three-level gradient particle size powder system to precisely match the pore size of the control layer, eliminate abnormal maximum pore size, and ensure pore size uniformity.

[0027] Figure 2 This is a flowchart illustrating the steps of a method for preparing a gradient structure powder mesh composite film according to an embodiment of the present invention.

[0028] like Figure 2 As shown, the method includes: Step 101: The pre-prepared four-layer sintered mesh is sequentially degreased, pickled, and dried to obtain the sintered mesh to be processed; the four-layer sintered mesh is composed of four layers of metal wire mesh with different mesh counts stacked sequentially, the metal wire mesh being arranged as an inner reinforcing layer, an intermediate reinforcing / diversion layer, a control layer, and a protective layer; the inner reinforcing layer, the control layer, and the protective layer are square-hole meshes, the intermediate reinforcing / diversion layer is a woven mesh; the mesh count of the control layer is greater than that of the other layers.

[0029] After preparing the four layers of sintered mesh, degreasing, pickling, and drying are performed sequentially. Degreasing is used to remove any lubricant or organic matter that may have remained in the mesh during the previous sintering process; pickling is used to remove surface oxides and impurities, activate the metal surface, and enhance coating adhesion; drying is used to prevent moisture from affecting subsequent spraying and bonding, and the moisture content after drying is ≤0.5%.

[0030] Step 102: Using deionized water as a solvent, add the binder solution and dispersant, and stir to dissolve to obtain the binder solution.

[0031] Deionized water, as a solvent, has the advantages of being environmentally friendly, low-cost, and avoiding the toxicity of organic solvents.

[0032] The binder solution can be a water-soluble polymer solution, which serves to bind powder particles together and provide sufficient strength before sintering.

[0033] Dispersants, such as polyelectrolytes and surfactants, prevent powder from agglomerating in the slurry and ensure that the slurry is uniform and stable.

[0034] The solvent, binder solution, and dispersant are stirred and dissolved to obtain the binder solution, which serves as the binding system for the subsequent powder slurry. Stirring and dissolving ensures the formation of a homogeneous and stable solution, facilitating subsequent mixing with the powder.

[0035] As an optional embodiment, the adhesive solution is prepared as follows: Step 1021: Weigh the raw materials according to the following proportions: PVP 3wt%~7wt%, polyethylene glycol 1.2~1.7wt%, dispersant 0.15~0.25wt%, and deionized water balance.

[0036] PVP is the main binder, an excellent water-soluble polymer containing highly polar amide groups (-NC=O) in its molecular chain. Polyethylene glycol serves as a plasticizer and auxiliary binder. The dispersant stabilizes the slurry and prevents powder agglomeration; sodium dodecylbenzene sulfonate can be selected as the dispersant.

[0037] Deionized water is used to dissolve PVP and polyethylene glycol to form a homogeneous liquid medium.

[0038] Step 1022: Add the raw materials to the mixing vessel and stir at 800 rpm for 60 minutes at 60°C until a homogeneous and transparent solution is formed, thus obtaining the binder solution.

[0039] A mixing vessel is a mechanical stirring device with heating and precise speed control functions.

[0040] A temperature of 60°C, higher than room temperature but lower than the boiling point of water, significantly accelerates the dissolution of PVP and PEG. 800 rpm provides sufficiently strong shear force and mixing action. 60 minutes ensures complete dissolution and homogenization.

[0041] The surface tension of the adhesive solution is controlled at 29-35 mN / m.

[0042] Step 103: Select three powder raw materials with different particle sizes, add the binder solution to each powder raw material, and mix and ball mill them to obtain coating slurries with three particle sizes.

[0043] The powder raw materials are usually selected from metal or ceramic powders that are the same as or compatible with the wire mesh material, such as 316L stainless steel powder. The particle size relationship of the three powders is: coarse > medium > fine.

[0044] Each powder was mixed separately with a binder solution and then ball-milled to obtain coating slurries with three different particle sizes. The purpose of the ball milling was to fully disperse the powder, prevent agglomeration, ensure uniform mixing, and coat each powder particle with the binder.

[0045] As an optional embodiment, the binder solution is added to each powder raw material, and the mixture is ball-milled separately to obtain coating slurries with three particle sizes, including: Step 1031: Add an equal amount of the binder solution to each powder raw material to obtain three solutions to be treated.

[0046] For the three powder raw materials, the volume of binder solution added is the same.

[0047] This step is merely a premixing process, designed to initially wet all powder particles with the liquid, preventing dry powder from flying or clumping during subsequent high-energy ball milling. The resulting "solution to be processed" is actually a non-uniform mixture.

[0048] Step 1032: Pour each of the solutions to be treated into a planetary ball mill and ball mill at 220 rpm for 3 hours to obtain three ball mill slurries.

[0049] Planetary ball mills are ideal for processing fine powder slurries. The grinding jars revolve around the main shaft while also rotating on their own axis. This combined motion generates extremely high collision energy and shear force in the grinding balls, resulting in a dispersion efficiency far exceeding that of ordinary drum ball mills.

[0050] 220 rpm is a medium-high speed, which can provide enough centrifugal force to make the grinding balls and slurry move and collide fully.

[0051] The powders of the three particle sizes must be ball-milled separately and independently. This is because: The objectives differ: For coarse powders, the primary objective is wetting and light dispersion; for fine powders, the core objective is strong deagglomeration. Mixed ball milling can cause interference.

[0052] To prevent cross-contamination: If ball milling is mixed, the hardest or coarsest particles may wear down and produce finer impurities, contaminating other slurries and compromising the designed gradient purity.

[0053] The viscosities of the three ball milling slurries are as follows: Dense functional layer 21000-27000 mPa s, Transition buffer layer 16000-21000mPa s, breathable reinforcement layer 10000-16000mPa s.

[0054] Step 1033: Let the three ball mill slurries stand for 30 minutes to degas, and obtain coating slurries with three particle sizes.

[0055] The purpose of static degassing is to remove the tiny air bubbles introduced during ball milling, in order to obtain a dense, defect-free coating slurry.

[0056] After these three steps, three coating slurries with suitable solid content and viscosity, uniform particle dispersion, no bubbles, and good stability are finally obtained. They correspond to three gradient levels: coarse, medium, and fine.

[0057] Step 104: Inject the three coating slurries into the three independent channels of the spraying machine, and use the spraying machine to spray the three coating slurries layer by layer onto the protective layer of the sintering mesh to be processed in order of decreasing particle size, so that the powder of the coating slurry penetrates and is fixed in the control layer, and a blank including three gradient coatings is obtained.

[0058] The spraying machine adopts "low-pressure atomization + axial powder feeding" and sprays layer by layer through three independent channels. The process parameters are controlled to make the powder penetrate evenly and fix it in the control layer.

[0059] Each of the three independent channels can be fed independently, allowing for precise control of the conveying and spraying parameters of each slurry layer. After the three coating slurries are sprayed, they form a dense functional layer, a transition buffer layer, and a breathable enhancement layer on the sintering mesh, respectively, according to their particle size from fine to coarse.

[0060] The breathable reinforcement layer is sprayed first, adhering to the large pores of the control layer to form the bottom layer. It has low resistance and primarily serves as a pre-filter and support. The transition buffer layer is sprayed after the breathable reinforcement layer, filling the large pores of the coarse powder layer to form a transition layer. The dense functional layer is sprayed last, forming the outermost layer with the finest pores, undertaking the main separation or filtration functions.

[0061] By controlling the slurry viscosity, spraying pressure, and time, the slurry is made to penetrate and fix evenly in the control layer without over-penetrating into the internal distribution layer or reinforcement layer, thus ensuring a strong bond between the gradient coating and the metal mesh substrate.

[0062] As an optional embodiment, the step of spraying the three coating slurries onto the protective layer of the four-layer sintered mesh in descending order of particle size using the spraying machine includes: Step 1041: Inject the three coating slurries into the three independent channels of the spraying machine.

[0063] Each of the three independent channels can be fed independently, allowing for precise control of the delivery and spraying parameters of each layer of slurry.

[0064] Step 1042: Start the spraying machine and apply the three coating slurries layer by layer to the protective layer of the four-layer sintered mesh in descending order of particle size through the three independent channels. During the process, control the wire mesh tube speed of the spraying machine to 10-15 rpm, the reciprocating speed of the spray gun to 330-630 mm / min, maintain the slurry temperature at 27-35℃, the spraying pressure at 0.19-0.27 MPa, and maintain the distance between the spray gun and the substrate surface at 10-14 cm to complete the layer-by-layer spraying operation.

[0065] The coarsest slurry is sprayed first. These coarse particles initially enter and partially fill the large pores of the screen's "protective layer" and "control layer," forming a porous underlying support structure. The medium-sized slurry, then sprayed, deposits on top of and within the pores of the coarse powder layer, further refining the pores. Finally, the finest slurry is sprayed, forming a precision filter layer on the outermost surface.

[0066] This gradient structure, with coarser layers at the bottom and finer layers at the top, conforms to the principle of deep filtration. It has a large dust holding capacity, is not prone to clogging, and has a slow increase in pressure drop. At the same time, the finest layer ensures the final filtration accuracy.

[0067] Step 105: The blank is subjected to two-stage degreasing treatment at different temperatures to obtain a degreased blank.

[0068] The first stage is low-temperature degreasing, and the second stage is high-temperature degreasing, which can thoroughly and gently remove all organic components in the green body, such as binders and dispersants.

[0069] As an optional embodiment, the step of subjecting the green body to a two-stage degreasing process at different temperatures to obtain a degreased green body includes: The green body was placed in a degreasing device for two-stage degreasing treatment. First, the temperature was increased from room temperature to 300℃ at a heating rate of 2.9℃ / min and held for 0.8h. Then, the temperature was increased to 550℃ at a heating rate of 4.6℃ / min and held for 1.4h to finally obtain a degreased green body.

[0070] In this embodiment of the invention, the first stage is a low-temperature slow-release stage, involving very slow heating. This ensures that the temperature inside and outside the billet rises uniformly, avoiding thermal stress cracking caused by temperature differences.

[0071] 300℃ is the temperature range within which the backbone of most organic binders (especially PEG and PVP) begins to undergo significant thermal decomposition. Holding the binder at 300℃ for 0.8 hours allows the decomposition reaction to proceed fully. This provides time for the gaseous products to exit, forming initial pore channels.

[0072] The second stage is a high-temperature purification section with a faster heating rate. The target temperature is 550℃, which ensures that all organic matter is completely oxidized or decomposed.

[0073] This step, through precise control of temperature and time, allows the organic matter to leave the preform in a stepwise and gradual manner, thereby obtaining a pure porous metal skeleton while protecting the delicate and fragile gradient structure from damage.

[0074] Step 106: The degreased preform is sintered at high temperature and then slowly cooled to obtain a gradient structure powder mesh composite film.

[0075] High-temperature sintering temperatures are typically close to but below the melting point of the base metal. At this temperature, the necks of the metal powder particles grow, the pores become spherical, and the powder layer itself becomes denser. Simultaneously, atomic interdiffusion occurs at the interface between the powder and the wire mesh, forming a strong metallurgical bond.

[0076] Slow cooling usually occurs within the furnace, specifically by controlling the cooling rate. The purpose is to reduce thermal stress and prevent cracking or deformation caused by uneven thermal shrinkage of different materials (coarse and fine powder layers, powder and wire mesh).

[0077] As an optional embodiment, the step of sintering the degreased preform at high temperature and then slowly cooling it to obtain a gradient structure powder mesh composite film includes: The degreased preform is placed in a sintering equipment for high-temperature sintering. The sintering temperature is controlled at 1100~1250℃ and held for 30~90 minutes. Then, the preform is slowly cooled at a cooling rate of 3.8℃ / min to finally form a gradient structure powder mesh composite film.

[0078] In this embodiment of the invention, for a gradient structure composed of powders of different particle sizes, it is necessary to select a temperature that can ensure the full sintering of each layer. The fine powder layer, due to its large surface area and strong sintering driving force, begins to densify rapidly at a lower temperature; the coarse powder layer, on the other hand, requires a higher temperature to ensure bonding strength. The range of 1100-1250℃ provides the operational space for this balance.

[0079] After reaching the set sintering temperature, it needs to be maintained for 30 to 90 minutes to allow the atomic diffusion process to proceed fully and uniformly.

[0080] Slow cooling at 3.8℃ / min can minimize thermal stress and prevent cracking and deformation.

[0081] Example 1 A functionally graded four-layer sintered mesh made of 316L was selected. This sintered mesh consists of an inner reinforcing layer (plain weave 10-mesh square hole mesh), a middle reinforcing / diversion layer (sheet mesh), a control layer (plain weave 500-mesh square hole mesh), and an outer protective layer (plain weave 80-mesh square hole mesh), with a total thickness of 1.6 mm. The square hole mesh has a wire diameter deviation of ±3% and a pore size deviation of ±8%, while the sheet mesh has a wire diameter deviation of ±2% and a pore size deviation of ±6%, with an overall porosity of 39%.

[0082] The sintered mesh was degreased and acid-washed sequentially, then dried in a drying device until the moisture content was 0.3%. The raw materials were weighed as follows: PVP 5wt%, polyethylene glycol (PEG-6000) 1.5wt%, dispersant (sodium dodecylbenzenesulfonate) 0.2wt%, with the balance being deionized water. These raw materials were added to a stirred tank and stirred at 800 rpm for 60 minutes at 60°C to form a homogeneous and transparent binder solution. The surface tension of this solution was measured to be 32 mN / m.

[0083] 316L powder was selected as the raw material, with three particle size gradients: 20μm for fine particles, 50μm for medium particles, and 75μm for the adaptive control layer. The powder was mixed in the following proportions: dense functional layer: 100% fine particle size powder; transition buffer layer: 68% medium particle size powder + 32% adaptive control layer particle size powder; air permeability enhancement layer: 72% adaptive control layer particle size powder + 28% medium particle size powder.

[0084] The three mixed powders with the above proportions were added to equal amounts of the prepared binder solution, poured into a planetary ball mill, and ball-milled at 220 rpm for 3.0 h (ball-to-powder ratio 3:1). After ball milling, the mixtures were allowed to stand for 30 min to degas. The viscosities of the three coating slurries were measured as follows: dense functional layer 24000 mPa. s, Transition buffer layer 18000mPa s, breathable reinforcement layer 13000mPa The coating process employs a low-pressure atomization + axial powder feeding sprayer, applying the coating layer by layer through three independent channels. The process parameters are set as follows: wire mesh rotation speed 12 rpm, spray gun reciprocating speed 480 mm / min, slurry temperature 30℃, spraying pressure 0.23 MPa, and spray gun distance 12 cm from the substrate surface, ensuring uniform powder penetration and fixation to the control layer.

[0085] The dried green body was placed in a sintering furnace for two-stage degreasing and sintering: heating from room temperature to 300℃ at a rate of 2.9℃ / min and holding for 0.8 h; heating from 300℃ to 550℃ at a rate of 4.6℃ / min and holding for 1.4 h; and heating from 550℃ to 1180℃ at a rate of 5℃ / min and holding for 1 h, followed by slow cooling at a rate of 3.8℃ / min to obtain a gradient structure powder mesh composite film. The total thickness of the composite film substrate was 1.6 mm, and the total thickness of the coating was 0.8 mm.

[0086] Testing revealed that the pore size distribution is uniform, with no abnormal maximum pore size and an average pore size of 10μm; the interlayer bonding is tight, and it has been running continuously for 1000 hours without structural failure under simulated high-temperature flue gas filtration conditions (350℃, 2MPa), making it suitable for high-temperature and high-pressure filtration scenarios.

[0087] Example 2 A functionally graded four-layer sintered mesh made of 310S material was selected. This sintered mesh consists of an inner reinforcing layer (plain-weave 10-mesh square-hole mesh), a middle reinforcing / diversion layer (woven mesh), a control layer (plain-weave 500-mesh square-hole mesh), and an outer protective layer (plain-weave 80-mesh square-hole mesh), with a total thickness of 1.6 mm. The square-hole mesh has a wire diameter deviation of ±4% and a pore size deviation of ±9%, while the woven mesh has a wire diameter deviation of ±3% and a pore size deviation of ±7%, with an overall porosity of 41%. After degreasing and pickling, the sintered mesh was dried in a drying equipment until the moisture content reached 0.4%.

[0088] Weigh the raw materials by weight percentage: PVP 7wt%, polyethylene glycol (PEG-6000) 1.7wt%, dispersant (sodium dodecylbenzenesulfonate) 0.25wt%, with the balance being deionized water. Add the above raw materials to a stirred tank and stir at 800 rpm for 60 min at 60°C to form a homogeneous and transparent binder solution. The surface tension of this solution was measured to be 35 mN / m (within the range of 29-35 mN / m).

[0089] 310S powder was selected as the raw material, with three particle size gradients: fine particle size 18μm, medium particle size 60μm, and adaptive control layer particle size 96μm. The powder was mixed in the following proportions: dense functional layer: 100% fine particle size powder; transition buffer layer: 68% medium particle size powder + 32% adaptive control layer particle size powder; air permeability enhancement layer: 72% adaptive control layer particle size powder + 28% medium particle size powder.

[0090] The three mixed powders with the above proportions were added to equal amounts of the prepared binder solution, poured into a planetary ball mill, and ball-milled at 220 rpm for 3.0 h (ball-to-powder ratio 3:1). After ball milling, the mixture was allowed to stand for 30 min to degas. The viscosities of the three coating slurries were measured as follows: dense functional layer 27000 mPa. s, Transition buffer layer 21000mPa s, breathable reinforcement layer 16000mPa s.

[0091] A low-pressure atomization + axial powder feeding sprayer is used to spray layer by layer through three independent channels. The process parameters are set as follows: wire mesh rotation speed 15 rpm, spray gun reciprocating speed 630 mm / min, slurry temperature 35℃, spraying pressure 0.27 MPa, and spray gun distance from the substrate surface 14 cm, so that the powder can penetrate evenly and be fixed in the control layer.

[0092] The dried green body was placed in a sintering furnace and treated according to the following parameters: First stage degreasing: heating from room temperature to 300℃ at a heating rate of 2.9℃ / min, holding for 0.8h; Second stage degreasing: heating from 300℃ to 550℃ at a heating rate of 4.6℃ / min, holding for 1.4h; Sintering: heating from 550℃ to 1250℃ at a heating rate of 6℃ / min, holding for 90min, followed by slow cooling at a cooling rate of 3.8℃ / min, to obtain a gradient structure powder mesh composite film. The obtained gradient structure powder mesh composite film has a total substrate thickness of 1.6mm and a total coating thickness of 1.2mm.

[0093] Testing revealed that the pore size distribution is uniform, with no abnormal maximum pore size and an average pore size of 12μm; the interlayer bonding strength is excellent, with no delamination or cracking, making it suitable for high-precision filtration conditions and high-temperature, high-pressure fluid separation scenarios in the biomedical field.

[0094] The beneficial effects of this invention are: 1. Excellent pore size uniformity: Through the dual adaptation design of gradient matrix and three-stage powder, the abnormal maximum pore size is completely eliminated, and the pore size distribution is uniform, meeting the stringent requirements of high-precision filtration for pore size consistency. 2. High interlayer bonding strength: Precise penetration spraying ensures that the powder adheres tightly to the substrate, and subsequent optimized sintering forms a metallurgical bond, significantly improving the interlayer bonding strength and structural stability; 3. Balanced filtration performance: The gradient coating structure achieves a perfect balance between high-precision filtration and high air permeability, reducing pressure loss during filtration and improving filtration efficiency. 4. Simple and controllable process: No complicated pretreatment steps are required, the process is simplified, the parameters are stable, the production cost is reduced, and industrialized mass production can be achieved.

[0095] In summary, the method for preparing a gradient structure powder mesh composite membrane provided in this embodiment of the invention includes: sequentially degreasing, acid washing, and drying a pre-prepared four-layer sintered mesh to obtain a sintered mesh to be processed; the four-layer sintered mesh is composed of four layers of metal wire mesh with different mesh counts stacked sequentially, the metal wire mesh being arranged as an inner reinforcing layer, an intermediate reinforcing / diversion layer, a control layer, and a protective layer; the inner reinforcing layer, the control layer, and the protective layer are square-hole meshes, and the intermediate reinforcing / diversion layer is a woven mesh; the mesh count of the control layer is greater than that of the other layers; using deionized water as a solvent, a binder solution and a dispersant are added, and stirred to dissolve to obtain a binder solution. Three powder raw materials with different particle sizes were selected, and the binder solution was added to each powder raw material. The mixtures were then ball-milled to obtain coating slurries with three different particle sizes. The three coating slurries were injected into three independent channels of a spraying machine. The spraying machine was used to spray the three coating slurries onto the protective layer of the sintering mesh to be processed in descending order of particle size, so that the powder of the coating slurry could be uniformly penetrated and fixed in the control layer, resulting in a blank containing three gradient coatings. The blank was then subjected to two-stage degreasing treatments at different temperatures to obtain a degreased blank. The degreased blank was then sintered at high temperature and slowly cooled to obtain a gradient structure powder mesh composite film. This solution optimizes the gradient structure matrix design, constructing a "wide → narrow → even narrower → wide" pore size gradient to solve the problem of inconsistent pore size references; it designs a three-level gradient particle size powder system to precisely match and control the pore size of the control layer, eliminate abnormal maximum pore size, and ensure pore size uniformity; it optimizes the precision penetration spraying and sintering process to improve the bonding strength between the powder and the matrix layers; it simplifies the preparation process, reduces production costs, and enables the industrial-scale mass production of composite membranes.

[0096] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0097] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A gradient structure powder mesh composite film, characterized in that, The composite membrane is integrally formed by a gradient four-layer stainless steel sintered mesh substrate and a three-layer gradient coating. The four-layer sintered mesh is composed of four layers of metal wire mesh with different mesh counts stacked sequentially. The metal wire mesh is arranged in the order of inner reinforcing layer, middle reinforcing / diversion layer, control layer, and protective layer. The inner reinforcing layer, the control layer, and the protective layer are square mesh, and the middle reinforcing / diversion layer is woven mesh. The mesh count of the control layer is greater than that of the other layers. The three-layer gradient coating is applied to the protective layer, uniformly penetrates and is fixed to the control layer; the three-layer gradient coating consists of a dense functional layer, a transition buffer layer and a breathable enhancement layer arranged sequentially in the direction away from the control layer, and the breathable enhancement layer is in contact with the control layer; each layer of the coating is made of powder raw material and binder, and the particle size of the powder raw material decreases in the order of the breathable enhancement layer, the transition buffer layer and the dense functional layer.

2. The composite membrane according to claim 1, characterized in that, The inner reinforcing layer has a square mesh size of 10-35 mesh, the intermediate reinforcing / diversion layer has a woven mesh size of 80-160 mesh, the control layer has a square mesh size of 325-600 mesh, the protective layer has a square mesh size of 60-100 mesh, the total thickness of the four sintered mesh layers is 1.2-2.5 mm; the total thickness of the four sintered mesh layers is 1.6 mm, and the total thickness of the three gradient coating layers is 0.8-1.2 mm.

3. The composite membrane according to claim 1, characterized in that, The metal wire mesh is made of any one of 316L, 310S, or Inconel 600; the wire diameter deviation of the square mesh is ≤±5%, and the aperture deviation is ≤±10%; the wire diameter deviation of the woven mesh is ≤±3%, and the aperture deviation is ≤±8%; the overall porosity of the square mesh and the woven mesh is 37~41%.

4. The composite membrane according to claim 1, characterized in that, The powder raw material is one or more of 316L, 310S, Inconel 600 powder, FeAl3, and TiAl alloy powder; the dense functional layer is composed of 100% fine-particle-size powder; the transition buffer layer is composed of 68% medium-particle-size powder and 32% adaptive control layer particle-size powder; the air permeability enhancement layer is composed of 72% adaptive control layer particle-size powder and 28% medium-particle-size powder.

5. A method for preparing a gradient structure powder mesh composite film, characterized in that, The method includes: The pre-prepared four-layer sintered mesh is sequentially degreased, pickled, and dried to obtain the sintered mesh to be processed. The four-layer sintered mesh consists of four layers of metal wire mesh with different mesh counts stacked sequentially. The metal wire mesh is arranged as an inner reinforcing layer, an intermediate reinforcing / diversion layer, a control layer, and a protective layer. The inner reinforcing layer, the control layer, and the protective layer are square-hole meshes, and the intermediate reinforcing / diversion layer is a woven mesh. The mesh count of the control layer is greater than that of the other layers. Using deionized water as a solvent, add the binder solution and dispersant, and stir to dissolve to obtain the binder solution; Three powder raw materials with different particle sizes were selected, and the binder solution was added to each powder raw material. The mixtures were then ball-milled to obtain coating slurries with three different particle sizes. The three coating slurries are injected into the three independent channels of the spraying machine. The spraying machine is used to spray the three coating slurries onto the protective layer of the sintering mesh to be processed in descending order of particle size, so that the powder of the coating slurry can be uniformly penetrated and fixed in the control layer, resulting in a blank including three gradient coatings. The green body is subjected to two-stage degreasing treatment at different temperatures to obtain a degreased green body; The degreased preform is sintered at high temperature and then slowly cooled to obtain a gradient structure powder mesh composite film.

6. The method according to claim 5, characterized in that, The adhesive solution is prepared as follows: Weigh the raw materials according to the following proportions: PVP 3wt%~7wt%, polyethylene glycol 1.2~1.7wt%, dispersant 0.15~0.25wt%, and deionized water balance. The raw materials are added to a mixing vessel and stirred at 800 rpm for 60 minutes at 60°C until a homogeneous and transparent solution is formed, thus obtaining the binder solution.

7. The method according to claim 5, characterized in that, The binder solution is added to each of the powder raw materials, and the mixtures are ball-milled separately to obtain coating slurries with three particle sizes, including: An equal amount of the binder solution was added to each powder raw material to obtain three solutions to be treated. Each of the solutions to be treated was poured into a planetary ball mill and milled at 220 rpm for 3 hours to obtain three kinds of ball mill slurries. The three ball mill slurries were allowed to stand for 30 minutes to degas, resulting in coating slurries with three different particle sizes.

8. The method according to claim 5, characterized in that, The process of spraying the three coating slurries onto the protective layer of the four-layer sintered mesh in descending order of particle size using the spraying machine includes: The three coating slurries are injected into the three independent channels of the spraying machine respectively; Start the spraying machine and apply the three coating slurries layer by layer to the four-layer sintered mesh protective layer in descending order of particle size through the three independent channels. During the process, control the wire mesh tube speed of the spraying machine to 10-15 rpm, the reciprocating speed of the spray gun to 330-630 mm / min, maintain the slurry temperature at 27-35℃, the spraying pressure at 0.19-0.27 MPa, and maintain the distance between the spray gun and the substrate surface at 10-14 cm to complete the layer-by-layer spraying operation.

9. The method according to claim 5, characterized in that, The process of subjecting the green body to two-stage degreasing treatment at different temperatures to obtain a degreased green body includes: The green body was placed in a degreasing device for two-stage degreasing treatment. First, the temperature was increased from room temperature to 300℃ at a heating rate of 2.9℃ / min and held for 0.8h. Then, the temperature was increased to 550℃ at a heating rate of 4.6℃ / min and held for 1.4h to finally obtain a degreased green body.

10. The method according to claim 5, characterized in that, The process of sintering the degreased preform at high temperature and then slowly cooling it to obtain a gradient structure powder mesh composite film includes: The degreased preform is placed in a sintering equipment for high-temperature sintering. The sintering temperature is controlled at 1100~1250℃ and held for 30~90 minutes. Then, the preform is slowly cooled at a cooling rate of 3.8℃ / min to finally form a gradient structure powder mesh composite film.

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