Porous metal filter bag and preparation process thereof

Abstract

The invention relates to the technical field of high-temperature flue gas purification, in particular to a porous metal filter bag and a preparation process thereof. The preparation method comprises the following steps: firstly, directly preparing a cylindrical green body with porosity gradient (from high-precision filtering holes in a surface layer to large-flux supporting holes in an inner layer) and material gradient through a one-step forming technology; and then, a co-sintering process is adopted, so that the porous filter layer and the compact metal framework form firm metallurgical bonding through atomic diffusion at a high temperature, and a seamless and high-strength integral structure is obtained at a time. According to the method, traditional welding or splicing is abandoned, the filter bag with the integrated structure and function is directly prepared, the final product achieves high filtering precision, large treatment flux, excellent thermal shock resistance and excellent mechanical strength at the same time, the filtering efficiency under the harsh working conditions of high temperature, corrosion and the like is remarkably improved, and the service life of the filter bag under the harsh working conditions of high temperature, corrosion and the like is remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of high-temperature flue gas purification technology, and more specifically, to a porous metal filter bag and its preparation process. Background Technology

[0002] With increasingly stringent environmental standards (such as ultra-low emission requirements), the deep purification of particulate matter in industrial high-temperature flue gas (typically from cement kiln heads and tails, steel sintering and converters, waste incineration, coal-fired power plants, and non-ferrous metal smelting) has become a key technological challenge. Baghouse dust collectors have become the mainstream choice due to their high filtration accuracy, and the performance of their core component—the filter bag—directly determines the system's operating efficiency, energy consumption, and cost.

[0003] Currently, filter bags used in the above-mentioned working conditions mainly face the following technical bottlenecks: Traditional non-metallic filter bags (such as PPS and PTFE) have low temperature resistance limits (usually <260℃), are prone to chemical degradation, hardening and cracking under temperature fluctuations or acidic atmospheres, have short service life (1-2 years), and cannot meet the requirements of higher temperature working conditions.

[0004] Traditional metal filter media, such as sintered metal fiber felt, consist of three-dimensional pores formed by the disordered overlapping of metal fibers. They have high porosity (>80%) and good air permeability, but the pore size is uneven. To achieve high filtration accuracy (such as PM2.5 capture), extremely fine fibers (<8μm in diameter) must be used, leading to high costs, reduced strength, and a significant increase in resistance. Meanwhile, sintered metal powder plates / tubes are formed by the stacking and sintering of powder particles, resulting in uniform and controllable pore size and high filtration accuracy. However, the pores are tortuous and elongated, with poor air permeability and extremely high operating resistance (pressure drop), leading to high system energy consumption. Furthermore, the material is brittle and has poor resistance to thermal shock and mechanical impact.

[0005] Secondly, existing metal filter bags generally use external metal cages for support. During pulse cleaning, the filter bag surface expands instantaneously and then rebounds, resulting in violent collisions and friction with the rigid cage. This periodic mechanical action leads to two main failure points: first, stress concentration at the filter bag welds, making them prone to fatigue cracking; second, damage to the contact points between the filter bag and the cage due to repeated friction. Structural reliability becomes a key weakness limiting the filter bag's lifespan (typically <3 years). Summary of the Invention

[0006] The purpose of this invention is to provide a porous metal filter bag and its manufacturing process. The filter bag body is a self-supporting structure composed of a gradient composite of metal fibers and metal powder, with an integrated embedded support skeleton as the structural reinforcement. A continuous coating, rolling, and co-sintering process is used to integrally form the filter bag in one step, achieving both high filtration accuracy and high air permeability at high temperatures, and eliminating mechanical fatigue and wear caused by external support. This addresses the problems mentioned in the background art.

[0007] To achieve the above objectives, in one aspect, the present invention provides a porous metal filter bag, which is a cylindrical integral structure without longitudinal welds, comprising, from the outside to the inside: Firstly, the gradient composite metal filter layer: This is the core functional layer of the filter bag. It is a whole with continuously varying pores, consisting of a three-dimensional network of metal fibers as the main supporting skeleton and metal powder metallurgically bonded to the surface area of ​​the skeleton.

[0008] Material composition: The metal fibers have an average diameter of 15-50μm (such as 310S, 316L, Inconel 601 alloy), forming a basic skeleton with high porosity (>75%). The metal powder is a spherical or near-spherical alloy powder with an average particle size of 2-20μm (the material is compatible with or the same as the fiber).

[0009] Gradient structure: By controlling the process, metal powder is mainly filled and solidified in a region of 30%-70% thickness along the fiber skeleton (measured from the outer surface), thus forming a gradient structure on the filter media cross-section. The outermost layer is the precision filtration zone: it is enriched with powder, with an average pore size of 0.5-3μm, and is responsible for the initial high-precision surface filtration. Intermediate transition zone: Powder and fiber interwoven, with a pore size of 3-15μm, which plays a role in stabilizing the surface and pre-filtration; The inner surface layer is a breathable support area: it is basically made of pure fiber with a pore size of 15-50μm and the highest porosity, mainly providing structural strength and low-resistance flow channels.

[0010] This gradient structure enables fine surface capture and smooth deep drainage; during filtration, most dust is intercepted by the precise outer layer; during cleaning, the pulsed airflow can easily penetrate the high-porosity inner layer and act evenly on the entire filter cake, causing it to peel off as a whole, thus significantly reducing cleaning resistance and the risk of dust embedding while ensuring high precision.

[0011] Secondly, the integrated embedded support frame: This is the core of the filter bag's structural reinforcement. It is a three-dimensional mesh metal structure (such as corrugated plate type or honeycomb type) of the same length as the filter bag. During the manufacturing process, it forms a comprehensive metallurgical bond with the inner surface of the gradient composite filter layer through high-temperature diffusion welding, becoming an inseparable part of the filter layer.

[0012] Mechanical reinforcement: The combination of the skeleton and the filter layer forms a composite beam structure, which greatly improves the overall radial bending stiffness and negative pressure collapse resistance of the filter bag, so that the filter bag only produces uniform elastic deformation during pulse cleaning, eliminating violent slapping.

[0013] Friction elimination: Since the frame is integrated with the filter layer, the relative movement and friction between the traditional external cage and the filter bag are eliminated.

[0014] Preferably, the regular channels of the skeleton can serve as guide channels for the pulsed airflow, promoting the uniform distribution of the cleaning airflow along the length of the filter bag and achieving flow field optimization.

[0015] Third, metal end caps and connecting flanges: welded to both ends of the filter bag for sealing and installation.

[0016] On the other hand, the present invention provides a process for preparing the porous metal filter bag described above, comprising the following steps: S1. Raw material preparation: Metal fibers with an average diameter of 15-50μm are opened and combed to form a fiber felt with a thickness of 3.0-8.0mm and a uniform surface density; Metal powder with an average particle size of 2-20μm is mixed with an organic binder (such as polyvinyl butyral) and a solvent to prepare a uniform slurry with a solid content of 55-75 wt%.

[0017] S2, Gradient Composite and Preforming: The above slurry is applied by slot coating or spraying at a concentration of 80-200 g / m². 2 The coating amount is precisely applied to one side of the moving fiber felt. It is then immediately rolled through one or more sets of precision rolls, with the roll linear pressure controlled at 2-10 kN / cm (this pressure range is sufficient to press the powder into the fiber network to form a gradient, but must avoid excessive pressure that would cause the fiber network to collapse completely and damage the pore structure), compacting the coated composite material to 1.2-2.5 times the final thickness (i.e., a green body thickness of 1.5-4.0 mm after compaction). The rolling process serves the purpose of: First, the surface powder is pressed into the fiber network to a predetermined depth to form a gradient profile. Second, the material is compacted to improve the strength of the green body. Third, the material is rolled thin and guided to be rolled into a cylindrical green body of a predetermined diameter. This achieves mechanical interlocking and shape shaping between the powder and the fiber.

[0018] S3. Skeleton Insertion: Insert the prefabricated three-dimensional mesh metal support skeleton (material thickness 0.3-1.0mm) into the cylindrical blank, ensuring that its outer surface fits tightly against the inner wall of the blank.

[0019] S4. Integrated Co-sintering: The assembled parts are fed into a controlled atmosphere (such as vacuum or high-purity argon, oxygen content <10ppm) sintering furnace, and the following sintering regime is performed: Increase the temperature to 300-500℃ at a rate of 1-5℃ / min and hold for 30-90 minutes to fully remove the organic binder; then increase the temperature to the main sintering temperature at a rate of 3-10℃ / min, which is 0.65-0.85 times the melting point of the filter bag metal material (for commonly used stainless steel or nickel-based alloys, this temperature range is about 1100-1300℃. This temperature can ensure that metal atoms diffuse fully to form a strong metallurgical bond, especially the interface bond between the skeleton and the filter layer, while avoiding excessive softening and deformation of fibers or coarse grains that affect material performance due to excessive temperature), and hold at this temperature for 60-180 minutes.

[0020] During this process, simultaneous metallurgical bonding occurs: between powder particles, between powder and fiber, and between the skeleton and the inner surface of the filter layer, a strong sintering neck and bonding interface are formed through atomic diffusion, permanently bonding them into a whole in one go.

[0021] S5. Post-processing: The sintered integral part is cut to a fixed length, the end is processed, and the end cap and flange are welded.

[0022] Furthermore, S2 and S4 are integrated into the production line control, and through closed-loop regulation of rolling pressure, sintering temperature and time, the consistency of product performance is ensured.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: In this porous metal filter bag and its preparation process... The gradient composite metal filter layer inherently unifies high precision and low resistance. Compared to homogeneous metal felt, while maintaining a filtration efficiency of ≥99.99%, it can increase initial air permeability by over 30% and reduce average resistance by 25%-40% during long-term operation, significantly reducing system energy consumption. Its easy-to-clean characteristics stabilize residual pressure and extend the high-efficiency filtration cycle. The integrated embedded support skeleton, through metallurgical bonding, forms the skeleton of the filter bag, resulting in a qualitative leap in its resistance to mechanical fatigue. Laboratory simulation tests show that its pulse cleaning fatigue life exceeds 2 million cycles, which is more than 4 times that of traditional external cage structure filter bags (typically <500,000 cycles). It eliminates the two major traditional failure modes of weld cracking and contact point wear, extending the expected service life to more than 5 years.

[0024] Secondly, by integrating multiple processes through continuous coating, rolling, and co-sintering, production efficiency is high and product quality is consistent. This process breaks through the length limitations of traditional seam welding, enabling the stable production of seamless integral filter bags with lengths of 8 meters and above, meeting the design requirements of modern large-scale dust collectors. By adjusting process parameters (such as slurry formulation, rolling pressure, and sintering curve), products with different filtration accuracies, diameters, and lengths can be flexibly customized, achieving flexible and large-scale manufacturing of high-performance filter bags. Simultaneously, the all-metal material and stable metallurgical interface ensure that the filter bags can operate stably for a long time in harsh flue gas environments ≤500℃, resist acid and alkali corrosion, and have a wide range of applications. Attached Figure Description

[0025] Figure 1 This is an overall flowchart of Embodiment 1 of the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1: This embodiment of the invention provides a 316L stainless steel gradient composite metal filter bag. This embodiment aims to prepare a filter bag suitable for flue gas dust removal scenarios in coal-fired power plants with temperatures ≤400℃ and ultra-low emission requirements.

[0028] In this embodiment, the filter bag is a cylindrical, one-piece structure without longitudinal welds, comprising, from the outside to the inside: Gradient composite metal filter layer: The total design thickness is 2.0 mm, and its cross-section exhibits a clear gradient structure: The outermost precision filtration zone is about 0.6 mm thick and is composed of a metal fiber skeleton and enriched spherical metal powder, with a target average pore size of 1.5 μm; the middle transition zone is about 0.8 mm thick, with fibers and powder interwoven, and a target average pore size of 8 μm; the innermost air-permeable support zone is about 0.6 mm thick and is basically composed of a pure metal fiber network, with a target average pore size of 35 μm and the highest porosity.

[0029] Integrated embedded support skeleton: Made of 0.5mm thick 316L stainless steel strip, pre-rolled into a corrugated plate with a wave height of 10mm and a wave pitch of 30mm, and then rolled and welded into a cylindrical three-dimensional mesh structure of the same length as the filter bag. During the manufacturing process, this skeleton achieves full metallurgical bonding with the inner surface of the filter layer (i.e., the air-permeable support area) through co-sintering, becoming the internal skeleton of the filter bag.

[0030] Metal end caps and connecting flanges: Made of 304 stainless steel, machined and welded to both ends of the sintered filter bag for sealing and installation.

[0031] Preparation process (see) Figure 1 ): S1. Raw material preparation: Fiber felt preparation: 316L stainless steel fibers with an average diameter of 30μm were selected. The fiber bundles were dispersed by an opening machine and then carded and stacked by a cross-laying machine to form a surface density of (1200±50)g / m². 2 A continuous fiber felt tape with an initial loose thickness of approximately 5.0 mm and a width of 500 mm is formed. This step ensures a uniform three-dimensional fiber network, providing a high-porosity substrate for subsequent gradient composites.

[0032] Slurry preparation: Spherical 316L stainless steel powder with an average particle size (D50) of 8 μm (obtained by gas atomization) was selected. The raw materials were weighed according to the mass ratio of metal powder: polyvinyl butyral (PVB) binder: anhydrous ethanol = 65:5:30, placed in a planetary ball mill, and ball-milled at 200 r / min for 4 hours to obtain a uniform suspension slurry with a solid content of 65 wt% and a viscosity of approximately 3500 mPa·s (25℃). The uniformity and viscosity of the slurry are crucial to ensuring the quality of subsequent coating.

[0033] S2, Gradient Composite and Preforming: Slot coating: A continuous fiber felt is fed through the coating machine at a constant speed of 0.5 m / min. The slot width of the coating head is set to 0.3 mm, and the slurry supply pressure is precisely controlled to ensure a flow rate of (150 ± 10) g / m. 2 The coating is applied evenly to the upper surface of the fiber felt (i.e., the outer surface of the future filter bag). This unilateral coating is the starting point for forming an axial gradient.

[0034] Precision rolling and coil forming: The wet composite material coated with slurry immediately enters a three-roll precision rolling mill, with the linear pressure applied by the rolls set to 6 kN / cm. The rolling process achieves: Mechanical interlocking and gradient forming: The pressure of the rollers forces the metal powder in the surface slurry into the fiber network. However, due to the resistance of the fiber network and the viscosity of the slurry, the powder mainly fills within a depth of about 1.2 mm from the surface, while the inner fiber remains basically pure. Thus, a gradient prototype with enriched outer powder and pure inner fiber is formed in the greening stage.

[0035] Compaction and thickness setting: The loose composite material is compacted to the target green body thickness (approximately 2.4 mm, which is 1.2 times the final sintered thickness), which improves the strength of the green body and facilitates subsequent operations.

[0036] Shape shaping: With the help of guide rollers, the thinned and plasticized green strip is automatically guided and rolled into a continuous cylindrical blank with an inner diameter of about φ154mm.

[0037] S3. Skeleton Placement: The prefabricated corrugated metal support skeleton (outer diameter φ154mm) is synchronously conveyed with the cylindrical green billet belt and precisely fitted into its interior, ensuring that the outer surface of the skeleton fits tightly against the inner wall of the green billet without any visible gaps.

[0038] S4. Integrated co-sintering: The assembled green parts are sent into a horizontal vacuum sintering furnace.

[0039] Degreasing stage: The temperature is programmed to rise to 400°C at a rate of 3°C / min and held at this temperature for 60 minutes. During this process, the PVB binder and solvent are fully pyrolyzed and volatilized, and discharged through the furnace exhaust system to avoid carbon residue. The heating rate and holding time are optimized to prevent cracking of the green body.

[0040] High-temperature sintering stage: After degreasing, the temperature is further increased to 1180℃ (approximately 0.84 times the melting point of 316L stainless steel (~1400℃)) at a rate of 5℃ / min, under a vacuum degree better than 1.0×10⁻⁶. -2 Keep warm for 120 minutes under the condition of Pa.

[0041] At this high temperature, metal atoms acquire sufficient diffusion kinetic energy, resulting in simultaneous metallurgical bonding at three levels: The powder particles bond together to form a strong sintered neck, which constitutes a dense porous skeleton for the precision filtration zone.

[0042] The powder particles and the adjacent metal fiber surfaces form a strong metallurgical bonding interface through atomic diffusion, achieving a strong anchoring between the powder layer and the fiber skeleton.

[0043] Significant mutual diffusion occurs between the contact points such as the crests of the corrugated plate skeleton and the metal fibers on the inner surface of the filter layer, forming a continuous metal bond, making the skeleton and the filter layer an inseparable whole.

[0044] Cooling: Remove from the furnace when cooled to below 200°C.

[0045] S5. Post-processing: The continuous sintered tube is cut to a fixed length of 6000mm using a diamond wheel cutting machine. Both ends are machined to ensure that the end face is flat and perpendicular to the axis. Finally, the machined end caps and flanges are welded to both ends of the filter bag using argon arc welding.

[0046] Example 2: Inconel 600 nickel-based alloy gradient composite filter bag This embodiment aims to demonstrate the requirements for higher corrosion resistance (such as those containing Cl). - SOx Preparation of filter bags under acidic atmosphere conditions.

[0047] The following is a brief description of the differences from Example 1: Materials: Both the filter layer and the skeleton are made of Inconel 600 nickel-based alloy, with an average fiber diameter of 20μm and an average powder particle size of 5μm.

[0048] Gradient structure: total thickness 1.8 mm, outer surface pore diameter 1.0 μm, inner surface pore diameter 30 μm.

[0049] Skeleton: A three-dimensional honeycomb grid skeleton (5 mm side length) woven and welded from Inconel 600 alloy wire with a diameter of 0.4 mm provides a higher specific surface area and better airflow distribution.

[0050] Slurry binder: an acrylic resin system was used instead to adapt to different degreasing profiles.

[0051] Sintering atmosphere: To prevent oxidation of active elements in the alloy, high-purity argon gas (oxygen content <5ppm) is used for sintering protection. The main sintering temperature is 1250℃ and the holding time is 90 minutes.

[0052] Product dimensions: outer diameter φ130mm, length 8000mm, demonstrating the ability of this process to produce ultra-long seamless filter bags.

[0053] Comparative Example 1: Traditional metal fiber felt filter bags Commercial 316L metal fiber sintered felt (average fiber diameter 30μm, average pore size 25μm, porosity ~85%) was directly purchased, rolled into cylinders, and longitudinal welded to make φ160×6000mm filter bags. These bags were then used in conjunction with standard external 316L cages (φ152mm, 24 longitudinal ribs, thickness 2.0mm, galvanized surface). This comparison represents the current mainstream non-gradient, external support technology.

[0054] Comparative Example 2: Traditional Metal Powder Sintered Plate Filter Bag Using 316L stainless steel powder with an average particle size of 15μm, tubular green bodies were formed by dry molding and then sintered in a vacuum furnace at 1200℃ for 2 hours to produce rigid porous sintered tubes with an average pore size of 5μm, requiring no external cage. This comparative example has high precision but also high resistance and brittleness.

[0055] Comparative Example 3: Gradient-free composite filter bag Except for step S2, the remaining processes are the same as in Example 1. In S2, the slurry is uniformly penetrated throughout the thickness of the fiber felt using an impregnation method, followed by rolling. In the resulting green body and final product, the metal powder is uniformly distributed within the cross-section of the filter layer without any gradient change.

[0056] Comparative Example 4: Gradient Composite and External Cage Filter Bag Using the same raw materials and steps S1 and S2 as in Example 1, a green blank of an unsupported filter layer cylinder with a gradient structure was prepared. It was then sintered separately in step S4 (with the same parameters) to obtain a gradient metal filter cylinder. Finally, it was assembled and used with a conventional external cage (same as Comparative Example 1).

[0057] Test Examples: Performance Testing and Comparison. To ensure the fairness and repeatability of the tests, all filter bag samples (Examples 1 and 2, Comparative Examples 1-4) were tested in accordance with the same or equivalent national or industry standards.

[0058] Test Method 1: Filtration Performance and Air Permeability Test Testing standards: Refer to the relevant principles of GB / T 6719 "Technical Requirements for Bag Filters" and ISO 11057 "Test Methods for Cleanable Filter Media".

[0059] Testing equipment: Fully automatic filter media performance testing bench (including dust generation, filtration, pulse cleaning, differential pressure and flow monitoring system).

[0060] Test dust: ISO 12103-1 Class A2 fine test dust (Arizona Road Dust), of which PM2.5 accounts for approximately 15% by mass.

[0061] Test process: Initial air permeability: Under clean conditions, the air permeability of the filter media is measured under a fixed pressure difference of 200 Pa and converted into air permeability per unit area.

[0062] Filtration efficiency: Start dust generation, control the filtration velocity to 1.0 m / min, and after the outlet concentration stabilizes, use a photometer or particulate counter to measure the upstream and downstream concentrations and calculate the mass filtration efficiency of the filter bag for total dust and PM2.5.

[0063] Operating resistance and cleaning characteristics: During continuous operation, when the filter resistance reaches 1000Pa, pulse jet cleaning is triggered (pressure 0.5MPa, pulse width 100ms). The average operating resistance during a stable operating cycle (e.g., from cleaning to the next cleaning) and the stable residual resistance after cleaning are recorded.

[0064] Test Method 2: Pulse Cleaning Fatigue Life Test Testing standards: Refer to the industry-standard filter bag life simulation test method.

[0065] Testing equipment: High-frequency pulse cleaning fatigue testing machine.

[0066] Test conditions: The filter bags were installed in the test chamber, and a fixed negative pressure (-2000Pa) was applied to simulate the working condition. Pulse cleaning at a frequency of 0.5MPa was continuously applied at a frequency of 60 times / hour.

[0067] Termination Criteria: Failure is determined when any of the following conditions occur, and the number of pulses is recorded: (a) the filter bag has visible cracks or perforations; (b) the seal at the connection between the filter bag and the tube sheet fails; (c) under standard dust load, the residual resistance continues to rise abnormally after cleaning (exceeding 300% of the initial value), which is determined to be structural damage causing cleaning failure.

[0068] The performance comparison test results are shown in Tables 1 and 2.

[0069] Table 1: Comparison of Filtration Performance and Operating Resistance As shown in Table 1, Examples 1 and 2 achieved filtration efficiencies (>99.99%) comparable to Comparative Example 2 (powder sintering), but with initial air permeability 7-8 times higher and operating resistance reduced by 60-70%. This directly demonstrates that the fine powder enriched in the outer layer of the gradient composite metal filter layer ensures the high precision required for surface filtration, while the pure, high-porosity fiber network in the inner layer provides the low-flow-resistance channels required for deep filtration.

[0070] The resistance of Comparative Example 3 (without gradient) was significantly higher than that of Example 1, indicating that while uniformly distributed powder also improves precision, it blocks deep airflow channels, failing to achieve optimal air permeability and dust removal effect. The data demonstrates that gradient design is a necessary condition for achieving performance breakthroughs.

[0071] The embodiment exhibits the lowest residual resistance after dust removal, indicating that its gradient structure not only facilitates filtration but also enables the overall peeling of the filter cake under pulse action, preventing dust from embedding deep within the filter cake and maintaining long-term low-resistance operation.

[0072] In summary, while Comparative Example 1 (homogeneous fiber felt) exhibits excellent air permeability, its filtration accuracy (99.5%) is insufficient to meet ultra-low emission requirements. Comparative Example 2 (powder sintering), while possessing extremely high accuracy, suffers from poor air permeability, significant resistance, and brittle texture. This invention, through a unique gradient composite structure, successfully integrates high-precision filtration (achieved by powder enrichment in the outer layer) with low-flow-resistance guiding function (achieved by a pure fiber network in the inner layer). This allows it to maintain excellent air permeability similar to Comparative Example 1 while achieving the same level of extreme filtration accuracy (99.99%) as Comparative Example 2, achieving a technical effect that traditional technologies cannot simultaneously achieve.

[0073] Table 2: Comparison of Mechanical Reliability and Fatigue Life As shown in Table 2, the fatigue life of Examples 1, 2, and Comparative Example 3 (which also includes an integrated frame) far exceeds 2.5 million cycles, which is more than 5 times that of the traditional external cage structure (Comparative Example 1, 450,000 cycles). This irrefutably proves that the integrated embedded support frame eliminates relative motion and friction through metallurgical bonding and transforms impact loads into overall elastic deformation, thereby solving the two major mechanical failure modes of traditional filter bags.

[0074] Secondly, while Comparative Example 4 (using only gradient materials but with an external cage) showed a slight improvement in lifespan (520,000 cycles) compared to Comparative Example 1 (thanks to the better toughness of the gradient materials), it remained on the same order of magnitude as the traditional structure, and the failure mode reverted to wear. This indicates that simply improving the filter bag's lifespan with gradient materials while retaining the traditional external support structure cannot fundamentally solve the problem of mechanical fatigue life. Only by combining the gradient materials with an integrated embedded skeleton and fusing them together through a co-sintering process can an order-of-magnitude improvement in lifespan be achieved.

[0075] All samples with fiber networks as the main load-bearing structure (Examples, Comparative Examples 3 and 4) did not exhibit the brittle fracture problem found in Comparative Example 2, confirming that the present invention inherits and enhances the impact resistance and thermal shock resistance of metal fiber materials.

[0076] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A porous metal filter bag, characterized in that, It is a cylindrical, monolithic structure without longitudinal welds, comprising, from the outside to the inside: The gradient composite metal filter layer is formed by a three-dimensional network of metal fibers forming the main framework and metal powder that is metallurgically bonded to its surface area. The filter layer has a gradient structure in the thickness direction with the pore size continuously increasing from the outside to the inside. An integrated embedded support frame, which is a three-dimensional mesh metal structure of the same length as the filter bag, is formed integrally with the inner surface of the gradient composite metal filter layer through metallurgical bonding. It is used to provide anti-collapse support and convert the impact load during pulse cleaning into the overall elastic deformation of the filter bag.

2. The porous metal filter bag according to claim 1, characterized in that, The gradient structure of the gradient composite metal filter layer specifically includes: The outermost precision filtration zone is enriched with metal powder, with an average pore size of 0.5-3μm; The intermediate transition zone is characterized by an interweaving of powder and fibers, with a pore size of 3-15 μm. The breathable support area of ​​the inner surface layer is a metal fiber network with a pore size of 15-50μm.

3. The porous metal filter bag according to claim 1, characterized in that, The regular mesh channels of the integrated embedded support frame are configured as guide channels for the pulse cleaning airflow to promote uniform distribution of airflow along the length of the filter bag.

4. The porous metal filter bag according to claim 1, characterized in that, The metal fibers have an average diameter of 15-50 μm, forming a basic network with a porosity greater than 75%; the metal powder is a spherical or near-spherical alloy powder with an average particle size of 2-20 μm.

5. The porous metal filter bag according to claim 1, characterized in that, The metal powder mainly fills and solidifies in the region of 30%-70% of the thickness direction of the metal fiber network.

6. A process for preparing a porous metal filter bag according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Raw material preparation: Metal fibers with an average diameter of 15-50μm are opened and combed to form fiber mats; Metal powder with an average particle size of 2-20μm is mixed with organic binders and solvents to form a uniform slurry. S2. Gradient compounding and preforming: The slurry is precisely applied to one side of the moving fiber felt by slit coating or spraying, and then rolled by rollers to compact and guide the coated composite material into a cylindrical blank of a predetermined diameter. S3. Skeleton insertion: The prefabricated three-dimensional mesh metal support skeleton is inserted into the cylindrical blank; S4. Integrated co-sintering: The assembly is fed into the sintering furnace and degreased and sintered at high temperature in sequence, so that a strong metallurgical bond is formed between powder particles, between powder and fiber, and between the three-dimensional mesh metal support skeleton and the inner surface of the filter layer through atomic diffusion.

7. The preparation process of the porous metal filter bag according to claim 6, characterized in that, In step S2, the rolling linear pressure is controlled at 2-10 kN / cm to compact the composite material to 1.2-2.5 times its final thickness.

8. The preparation process of the porous metal filter bag according to claim 6, characterized in that, In step S4, the sintering temperature is controlled at 0.65-0.85 times the melting point of the filter bag metal material, and the holding time is 60-180 minutes.

9. The preparation process of the porous metal filter bag according to claim 6, characterized in that, The coating amount of the slurry in S2 is 80-200 g / m. 2 The solid content of the slurry is 55-75 wt%.

10. The preparation process of the porous metal filter bag according to claim 6, characterized in that, In step S4, the degreasing is carried out at 300-500°C and kept at that temperature for 30-90 minutes.

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