Process for manufacturing a stainless steel fiber composite coated needle felt

Abstract

The application provides a manufacturing process of a stainless steel fiber composite coating needle punched felt, and belongs to the technical field of felt-shaped material manufacturing for industrial gas purification and filtration. The manufacturing process comprises the following steps: S1, raw material preparation; S2, softening and bending resistance treatment of pre-oxidized fiber; S3, anti-tangling and hair removal treatment of stainless steel fiber; S4, pre-opening and mixing; S5, preparation of each layer of fiber web; S6, multi-layer structure needle punching to form a felt; S7, polytetrafluoroethylene solution impregnation and heat baking and curing; S8, surface heat pressing treatment of the needle punched felt; and S9, preparation and coating of foamed graphite coating. The application focuses on the structure design, raw material selection and production process optimization of the felt-shaped material for gas filtration according to the purification requirements of high-temperature dust-containing gas in industrial production. The core is to solve the short board of the filtering performance of the traditional gas filtering felt under high temperature and high corrosion conditions through material innovation and process cooperation, and to ensure the long-term stability and high efficiency of the gas purification process.

Description

Technical Field

[0001] This invention relates to the field of manufacturing technology of felt materials for industrial gas purification and filtration, and in particular to a manufacturing process for a stainless steel fiber composite coated needle-punched felt. Background Technology

[0002] With the continuous upgrading of national industrial environmental protection standards, high-temperature dust-laden gases generated in industrial production (such as flue gas with a temperature exceeding 300°C, containing acid or alkali components, or with high humidity) must be purified efficiently before being discharged. Felt-like materials used for gas filtration are the core carriers for achieving this purification process, and their performance directly determines the gas purification efficiency and system stability.

[0003] Currently, most mainstream gas filter felts in the industrial field are made of organic fibers such as polyester and polyphenylene sulfide through needle punching. The core limitation of these products is that they cannot be adapted to high-temperature dusty gas filtration scenarios: organic fibers themselves have weak temperature resistance and are prone to softening and shrinking in high-temperature gas environments, causing deformation or blockage of the filter pores inside the filter felt. This not only causes a rapid decline in gas filtration efficiency (unable to stably intercept fine-particle dust), but also increases the resistance to gas flow and increases the energy consumption of the purification system. At the same time, high temperatures accelerate the chemical reaction between organic fibers and acid and alkali components in the gas, causing fiber denaturation and embrittlement, and damage to the overall structure of the filter felt. Frequent replacement not only affects the continuity of gas purification, but also significantly increases the maintenance costs of industrial production.

[0004] To address the demands of high-temperature gas filtration, existing industry solutions often employ a composite needle-punched felt made of pre-oxidized fiber and fiberglass. This involves incorporating pre-oxidized fiber (which possesses some temperature resistance) to increase the upper temperature limit, and using fiberglass mesh to enhance structural strength. However, this approach still has significant drawbacks in gas filtration applications: First, the pre-oxidized fiber has poor folding endurance, requiring only small amounts to form a stable pore structure. Under prolonged impact from high-temperature gases, the pores are prone to collapse, leading to fluctuations in gas filtration accuracy. Second, fiberglass and its mesh exhibit weak resistance to acids, alkalis, and hydrolysis. In humid or acid / alkali-containing high-temperature gases, the fiberglass is easily corroded and broken, damaging the filter felt surface and allowing unfiltered dust-laden gas to penetrate directly, resulting in gas purification failure. Third, the existing solutions lack sufficient surface smoothness, allowing dust in the gas to adhere to the filter felt surface, which is difficult to remove completely with cleaning devices. After prolonged use, the filter felt becomes severely clogged, increasing gas flow resistance and necessitating frequent shutdowns for replacement, severely impacting the efficiency and economy of industrial gas purification.

[0005] In summary, existing felt materials used for gas filtration have significant shortcomings in key indicators such as high-temperature stability, corrosion resistance, filtration accuracy retention, and dust removal performance, making it difficult to meet the long-term needs of industrial sectors for gas purification under high-temperature and highly corrosive conditions. There is an urgent need for a gas filter felt preparation process that can adapt to harsh gas environments and balance high-efficiency filtration with long service life. Summary of the Invention

[0006] This invention provides a manufacturing process for stainless steel fiber composite coated needle-punched felt, targeting the purification needs of high-temperature dusty gases (such as industrial waste incineration flue gas, metallurgical kiln flue gas, chemical reaction tail gas, etc.) in industrial production. It focuses on the structural design, raw material selection, and production process optimization of felt-like materials used for gas filtration. The core is to solve the shortcomings of traditional gas filter felt in filtration performance under high temperature and high corrosion conditions through material innovation and process synergy, so as to ensure the long-term stability and high efficiency of the gas purification process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A manufacturing process for a stainless steel fiber composite coated needle-punched felt includes:

[0009] S1: Obtain three specifications of inorganic stainless steel fiber, organic pre-oxidized fiber, stainless steel mesh, as well as silicone oil emulsion, polytetrafluoroethylene emulsion, graphite emulsion, foaming agent, gelling agent, coupling agent, ammonia water, and deionized water.

[0010] S2: Mix silicone oil emulsion with deionized water to prepare silicone oil aqueous solution. Immerse organic pre-oxidized fiber in silicone oil aqueous solution. After immersion, remove excess solution from the surface and then heat-cure to obtain pre-oxidized fiber after softening and flexural resistance treatment.

[0011] S3: Mix polytetrafluoroethylene emulsion with deionized water to prepare polytetrafluoroethylene solution. Select two specifications of stainless steel fibers and lay them flat. Spray the polytetrafluoroethylene solution evenly on the surface of the two fibers. After spraying, send the two fibers into a closed environment for annealing to obtain two specifications of stainless steel fibers after anti-entanglement treatment.

[0012] S4: The pre-oxidized fiber after softening and flexural treatment is pre-opened with the third type of stainless steel fiber to form a fluffy and uniformly mixed fibrous structure, thus obtaining pre-opened mixed fiber.

[0013] S5: One type of stainless steel fiber after anti-tangling treatment and pre-oxidized fiber after softening and bending resistance treatment are combed into a lower fiber web; another type of stainless steel fiber after anti-tangling treatment and pre-opened mixed fiber are combed into an upper fiber web; the stainless steel web is cut to the same plane size as the lower and upper fiber webs and used as the middle layer stainless steel web.

[0014] S6: Lay the lower layer of fiber mesh flat, lay the middle layer of stainless steel mesh on top of the lower layer of fiber mesh, and perform pre-needling to form a pre-needling composite; lay the upper layer of fiber mesh on top of the pre-needling composite and perform main needle punching to make the three-layer structure tightly combined to obtain the preliminary needle-punched felt.

[0015] S7: The preliminary needle-punched felt is immersed in a polytetrafluoroethylene solution for impregnation. After impregnation, excess solution is removed, and then it is heat-cured to form a curing film of polytetrafluoroethylene on the fiber surface, thus obtaining impregnated and cured needle-punched felt.

[0016] S8: The impregnated and cured needle-punched felt is subjected to surface hot pressing treatment to obtain hot-pressed needle-punched felt;

[0017] S9: Mix graphite emulsion, polytetrafluoroethylene emulsion, foaming agent, gelling agent, coupling agent, ammonia, and deionized water evenly to prepare a foamed graphite coating emulsion; coat the foamed graphite coating emulsion evenly on the upper surface of the hot-pressed needle-punched felt; after coating, perform curing treatment to make the coating and the felt body tightly bonded, and finally obtain stainless steel fiber composite coated needle-punched felt.

[0018] In this specification, in S1, the three specifications of inorganic stainless steel fibers are 25μm×80mm stainless steel fiber, 20μm×65mm stainless steel fiber, and 12μm×55mm stainless steel fiber, respectively; the stainless steel mesh is 316L type stainless steel mesh, with a warp wire diameter of 0.2mm, a weft wire diameter of 0.1mm, and a mesh size of 30; the organic pre-oxidized fiber is a carbon fiber pre-product made of polyacrylonitrile fiber through air oxidation, with a decomposition temperature ≥640℃ and a long-term temperature resistance ≥370℃.

[0019] In this specification, in step S2, the mixing ratio of silicone oil emulsion to deionized water is 1:16 by mass; the impregnation bath temperature is controlled at 30-40℃, and the impregnation time is controlled at 10 min; the removal of excess solution from the surface is achieved by an extrusion device, with the extrusion pressure controlled at 0.2 MPa, and the liquid content of the pre-oxidized fiber after extrusion controlled at 30%-35%; the heat curing temperature is controlled at 180℃, and the heat curing time is controlled at 5-6 min, while maintaining an ambient wind speed of 1.5 m / s during the heat curing process to ensure uniform drying of the fiber.

[0020] In this specification, in step S3, the mixing ratio of polytetrafluoroethylene emulsion to deionized water is 1:1 by mass; the polytetrafluoroethylene solution is uniformly sprayed through an atomizing humidifier, with the atomized particle diameter controlled at 5-10 μm, and the mass ratio of polytetrafluoroethylene solution to stainless steel fiber controlled at 1:5; the temperature of the sealed environment is controlled at 25±2℃, the relative humidity is controlled at 60%~70%, and the curing time is controlled at 24h; the two specifications of stainless steel fiber are 25μm×80mm stainless steel fiber and 20μm×65mm stainless steel fiber.

[0021] In this specification, in S4, the mixing ratio of the pre-oxidized fiber after softening and flexural treatment to the third type of stainless steel fiber is 1:2 by mass; the pre-opening treatment is achieved by a parallel feeder + pre-opening equipment, the feeding speed of the parallel feeder is controlled at 4.5m / min, and the opening roller speed of the pre-opening equipment is controlled at 800r / min; the third type of stainless steel fiber is 12μm×55mm stainless steel fiber, and after pre-opening, there are no clumps with a diameter >5mm in either fiber.

[0022] In this specification, S5, one specification of stainless steel fiber after anti-tangling treatment is 25μm×80mm stainless steel fiber, and its mixing ratio with the pre-oxidized fiber after softening and flexural treatment is 9:1 by mass. The basis weight of the lower fiber web after carding is controlled at 660-680g / m². Another specification of stainless steel fiber after anti-tangling treatment is 20μm×65mm stainless steel fiber. The mixing ratio of this fiber with pre-opened mixed fibers is 20μm×65mm stainless steel fiber: 12μm×55mm stainless steel fiber: pre-oxidized fiber = mass ratio 7:2:1. After carding, the unit area basis weight of the upper fiber web is controlled at 680-700g / m². The unit area weight of the intermediate layer stainless steel mesh is controlled at 140g / m². The combing process uses a combing machine, and the combing speed is controlled at 10m / min.

[0023] In this specification, in S6, the acupuncture density of the pre-acupuncture is controlled at 150 needles / The needle insertion depth is controlled at 10mm; the needle insertion density of the main needle is controlled at 250 needles / min. The needle-punching depth is controlled at 12mm; the speed of the needle-punching machine conveyor curtain during the needle-punching process is controlled at 3m / min; the total weight per unit area of ​​the preliminary needle-punched felt is controlled at 1500g / The allowable error range is ±20g / .

[0024] In this specification, in step S7, the mass concentration of the polytetrafluoroethylene solution used for impregnation is controlled at 33%; the impregnation time is controlled at 8 minutes, and the preliminary needle-punched felt is turned over every 2 minutes during the impregnation process to ensure uniform impregnation; the removal of excess solution is achieved by an extrusion device, the extrusion pressure is controlled at 0.1 MPa, and the liquid content of the needle-punched felt after extrusion is controlled at 40% to 45%; the temperature for heat curing is controlled at 245°C, the conveying speed of the needle-punched felt is controlled at 5 m / min, and the heat curing time is controlled at 6 minutes.

[0025] In this specification, before uniformly coating the foamed graphite coating emulsion in step S9, a thickness control step based on a dynamic coating thickness calculation algorithm is included: the viscosity value of the foamed graphite coating emulsion in S9 is obtained in real time through an online viscosity monitoring device; the conveying speed of the coating machine is obtained through the coating machine control system; and the initial gap of the coating machine's scraper is obtained through micrometer calibration. The viscosity value, conveying speed, and initial scraper gap are substituted into the dynamic coating thickness calculation algorithm to obtain the target coating thickness. The scraper gap is adjusted according to the target coating thickness. During the coating process, the actual coating thickness is monitored in real time through a laser thickness gauge to ensure that the actual thickness is stable within the range of 0.5 to 0.8 mm. The dynamic coating thickness calculation algorithm is used to compensate for the influence of emulsion viscosity fluctuations and conveying speed changes on the coating thickness. The viscosity value comes from real-time monitoring after mixing the coating emulsion in step S9, the conveying speed comes from the equipment settings of the coating machine, and the initial scraper gap comes from micrometer calibration before coating.

[0026] In this specification, the following optimization steps are also included when performing curing treatment after coating S9:

[0027] Curing parameter optimization: The actual thickness of the coating after S9 coating is obtained using a laser thickness gauge, and the solid content of the foamed graphite coating emulsion is detected by drying method; the actual thickness and solid content are substituted into the curing temperature-time co-optimization algorithm to calculate the target curing temperature and target curing time; the curing equipment is controlled according to the target temperature and time to ensure that the coating curing degree is ≥95%;

[0028] Bond strength verification: The actual curing temperature is obtained through a temperature sensor, and the actual curing time is obtained through a timer. Combined with the actual coating thickness, the results are substituted into the coating bond strength prediction algorithm. If the predicted bond strength is ≥1.2MPa, the curing is qualified. If it is lower than 1.2MPa, the coating thickness or curing parameters of S9 are adjusted accordingly. The curing temperature-time co-optimization algorithm is used to avoid incomplete curing or excessive embrittlement of the coating, and the coating bond strength prediction algorithm is used to detect the risk of insufficient strength in advance.

[0029] In summary, the present invention has at least the following beneficial effects:

[0030] Significantly improved stability of high-temperature gas filtration: Relying on the high-temperature resistance of stainless steel fiber and stainless steel mesh base fabric, combined with the stable pore structure formed by process optimization, the product will not deform, clog or break the structure due to temperature rise during the filtration of high-temperature dusty gas. It can maintain a stable gas filtration channel for a long time, ensuring that the high-temperature gas purification efficiency does not decrease, and is suitable for high-temperature gas filtration scenarios such as industrial waste incineration and metallurgy.

[0031] Long-lasting filtration performance in corrosive gas environments: The stainless steel material itself has excellent acid and alkali resistance and hydrolysis resistance. Combined with the protective effect of the foamed graphite coating, the product is not prone to material corrosion or structural failure in the filtration of high-temperature gases containing acids and alkalis and high humidity. The surface and internal pores of the filter felt always remain intact, avoiding the problem of unfiltered gas penetration due to corrosion, and maintaining a high efficiency of gas purification effect for a long time.

[0032] Optimized gas filtration accuracy and dust interception capability: By adjusting the ratio of stainless steel fibers of different specifications and using polytetrafluoroethylene impregnation to fill the micropores, a gradient pore structure is formed inside the filter felt, which can accurately intercept dust of different particle sizes in the gas (especially fine dust particles); at the same time, the smooth surface and small pore structure of the foamed graphite coating can reduce the adhesion of dust on the surface of the filter felt, and with the dust removal device, it can quickly remove accumulated dust, avoid dust clogging the pores, and ensure long-term stable gas filtration accuracy.

[0033] Reduced gas flow resistance and system energy consumption: By optimizing fiber ratio and coating design, the product forms a smooth gas flow channel while ensuring filtration accuracy; and the improved dust removal performance reduces the problem of increased resistance caused by dust blockage, so that the resistance of high-temperature dusty gas flowing through the filter felt is always kept at a low level, reducing the fan energy consumption of the gas purification system and improving the overall operating economy.

[0034] Improved continuity and ease of maintenance in gas purification: Enhanced high-temperature resistance, corrosion resistance, and anti-clogging properties significantly extend the product's service life in high-temperature dusty gas filtration, reducing the frequency of filter felt replacement. Simultaneously, stable filtration performance and low resistance characteristics prevent system downtime due to filter felt failure, ensuring continuous and stable industrial gas purification processes and reducing maintenance workload and costs for operators.

[0035] Enhanced stability of gas filter felt production process: By impregnating pre-oxidized fibers with silicone oil (to improve folding resistance) and applying polytetrafluoroethylene (PTFE) to stainless steel fibers (to prevent tangling), problems such as uneven fiber web formation and needle-punched web breakage in traditional gas filter felt production are solved, ensuring that the pore structure of the filter felt is uniform and consistent. Products produced in batches have small differences in gas filtration performance, improving the overall adaptability of gas purification systems. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the manufacturing process of the stainless steel fiber composite coated needled felt in this invention.

[0037] Figure 2 This is a schematic diagram of the manufacturing process of the stainless steel fiber composite coated needle-punched felt in this invention.

[0038] Figure 3This is a schematic diagram of the stainless steel fiber composite coated needle-punched felt of the present invention.

[0039] Figure 3 In the middle: 1 is a foamed graphite coating, 2 is a fiber mesh made of 20μm×65mm stainless steel fiber, 12μm×55mm stainless steel fiber and pre-oxidized fiber, 3 is a stainless steel mesh base fabric, and 4 is a fiber mesh made of 25μm×80mm stainless steel fiber and pre-oxidized fiber. Detailed Implementation

[0040] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0041] like Figure 1 and Figure 2 As shown, this embodiment provides a manufacturing process for stainless steel fiber composite coated needle-punched felt, including:

[0042] S1: Raw Material Preparation

[0043] First, three core specifications of inorganic stainless steel fibers were prepared: 25μm×80mm, 20μm×65mm, and 12μm×55mm industrial-grade stainless steel fibers for filtration. The 25μm×80mm specification will be used for the preparation of the subsequent lower fiber web, while the 20μm×65mm and 12μm×55mm specifications correspond to different components of the upper fiber web. The selection of the diameter and length of the three types of fibers is based on a gradient pore structure design—coarse-sized fibers construct supporting pores, while fine-sized fibers fill tiny gaps to achieve high-efficiency filtration.

[0044] Secondly, there is the organic pre-oxidized fiber, which is an industrial-grade pre-oxidized fiber made from polyacrylonitrile fiber through air oxidation. Its decomposition temperature needs to reach 640℃ and its long-term temperature resistance needs to reach 370℃. Although this fiber has a certain temperature resistance, its flexural strength is poor in its original state. It needs to be softened in the subsequent S2 step to improve its web-forming performance. The 316L stainless steel mesh required for the middle layer must ensure that the diameter of the stainless steel wire in the warp direction is 0.2mm and the diameter in the weft direction is 0.1mm, with a mesh size of 30 mesh. This specification of stainless steel mesh can provide sufficient structural strength to resist the external force during the needle punching process without excessively hindering the subsequent gas flow. At the same time, the corrosion resistance of 316L material also lays the foundation for the overall corrosion resistance of the product.

[0045] The preparation of auxiliary chemical raw materials requires strict control over purity and properties: Silicone oil emulsion must be an industrial-grade product with a purity ≥98% for softening pre-oxidized fibers in step S2; polytetrafluoroethylene emulsion must have a solid content ≥60% and will be used for stainless steel fiber buffing in S3, needle-punched felt impregnation in S7, and coating preparation in S9. Its corrosion resistance and high-temperature resistance are key to improving the core performance of the product; graphite emulsion must have a carbon content ≥95% as the core conductive and lubricating component of the S9 foamed graphite coating; in addition, the foaming agent is azodicarbonamide (particle size ≤5μm), the gelling agent is sodium alginate (viscosity ≥500mPa·s), the coupling agent is silane coupling agent KH-550 (purity ≥98%), the ammonia water is an industrial-grade product with a concentration of 25%~28%, and the deionized water must have a conductivity ≤10μS / cm. The specifications of these auxiliary raw materials must be confirmed by professional equipment before use to avoid affecting subsequent process effects due to fluctuations in raw material quality.

[0046] S2: Softening and folding resistance treatment for pre-oxidized filament fibers

[0047] The core objective of this step is to improve the poor flexural strength of the pre-oxidized fiber in its original state, enabling it to better blend with stainless steel fibers to form a web. This prevents the web from breaking due to fiber fracture during subsequent needle punching, which would affect the structural stability and filtration performance of the final product. The process strictly follows the logic of infiltration-extrusion-curing, and the parameters for each step are set to improve fiber softness and retain fiber temperature resistance.

[0048] First, prepare the silicone oil aqueous solution by mixing the silicone oil emulsion prepared in S1 with deionized water at a mass ratio of 1:16. The mixing process must be carried out in a stirring tank at a speed of 300 rpm for 10 minutes to ensure the silicone oil emulsion is evenly dispersed in the water to form a stable solution. This ratio is chosen because too high a proportion of silicone oil emulsion will result in excessive silicone oil residue on the fiber surface, affecting subsequent compatibility with stainless steel fibers; too low a proportion will prevent sufficient penetration into the fiber interior, resulting in poor softening effect.

[0049] The pre-oxidized fibers were then impregnated. The pre-oxidized fibers prepared in step S1 were completely immersed in the prepared silicone oil aqueous solution, with the bath temperature controlled at a stable 30-40℃ and the impregnation time set at 10 minutes. This temperature range was selected after multiple experimental verifications: below 30℃, the silicone oil molecules penetrated slowly, requiring a longer impregnation time to achieve the desired effect, thus reducing production efficiency; above 40℃, the pre-oxidized fibers may experience slight softening, affecting their subsequent temperature resistance. During the impregnation process, the solution was gently stirred every 2 minutes to ensure that each fiber was evenly contacted with the solution, avoiding uneven impregnation that could lead to differences in subsequent folding endurance.

[0050] After impregnation, the pre-oxidized fibers are fed into an extrusion device, where a pressure of 0.2 MPa is applied by the extrusion rollers to remove excess silicone oil solution from the fiber surface. The key to controlling the extrusion pressure to 0.2 MPa is that too low a pressure results in excessively high fiber liquid content, which can easily lead to clumping during subsequent drying; too high a pressure may cause fiber deformation or even breakage, disrupting fiber continuity. After extrusion, the fiber liquid content is monitored by weighing to ensure it remains stable within the range of 30%–35%. If the liquid content exceeds this range, the extrusion pressure is adjusted promptly to correct it.

[0051] Finally, a heat curing treatment is performed. The extruded pre-oxidized fibers are fed into the heat-curing production line, with the heat-curing temperature set at 180℃ and the drying time at 5-6 minutes. Simultaneously, the air velocity within the production line is maintained at a stable 1.5 m / s to ensure uniform heating of the fibers during the heat-curing process. The 180℃ heat-curing temperature ensures that the silicone oil solution on the fiber surface is fully dried, forming a thin and uniform silicone oil film (improving softness), while not exceeding the upper temperature resistance limit of the pre-oxidized fibers (370℃), thus avoiding damage to fiber properties. After heat curing, the treated pre-oxidized fibers are sampled and tested. Their bending resistance is verified through a bending test (no significant breakage after 100 bends). Qualified pre-oxidized fibers will be used in two parts: one part will be used for pre-opening mixing with 12μm×55mm stainless steel fibers in step S4, and the other part will be directly used for the preparation of the lower fiber web in step S5.

[0052] S3: Anti-tangling and buffing treatment for stainless steel fibers

[0053] Stainless steel fiber, as the core skeleton material of the product, has insufficient surface smoothness in its original state. During subsequent web formation and needle punching processes, it is easily entangled and clumps due to external forces, leading to problems such as web breakage and uneven pore size, affecting filtration accuracy. Therefore, this step uses a polytetrafluoroethylene (PTFE) solution to create a protective layer on the surface of the stainless steel fiber, improving the surface smoothness coefficient, dispersing external stress, and laying the foundation for subsequent uniform web formation. The treated stainless steel fibers are of two specifications: 25μm×80mm and 20μm×65mm, prepared in S1. These two types of fibers will be used separately for the preparation of the lower and upper fiber webs in step S5, respectively, and are treated separately to avoid specification confusion.

[0054] First, prepare the polytetrafluoroethylene (PTFE) solution. Mix the PTFE emulsion prepared in S1 with deionized water at a mass ratio of 1:1. Pour the mixture into a mixing tank and stir at 500 rpm for 15 minutes until a uniform milky white suspension forms with no obvious particle sediment. A 1:1 ratio is chosen because this concentration of PTFE solution can form a complete coating layer on the fiber surface without causing the fibers to stick together due to excessive concentration, which would affect subsequent opening. After preparation, check the solution concentration using a concentration meter to ensure the error is ≤1%. If the concentration deviation is too large, add emulsion or deionized water to adjust it.

[0055] Next, the atomization spraying operation is performed. 25μm×80mm and 20μm×65mm stainless steel fibers are laid flat on the conveyor belt, with a thickness controlled at 5cm. Too thick a layer will prevent the bottom fibers from evenly contacting the solution, while too thin a layer will increase the risk of fiber scattering. The prepared polytetrafluoroethylene (PTFE) solution is evenly sprayed onto the fiber surface using an atomizing humidifier. The atomized particle diameter is controlled at 5-10μm to ensure the solution adheres to the fiber surface as tiny droplets, rather than forming large droplets that cause excessively high local concentrations. During spraying, the fiber mass is monitored in real time by a weighing sensor above the conveyor belt, precisely controlling the spray volume to stainless steel fiber mass ratio to 1:5. This ratio has been experimentally verified: below 1:5, the fiber surface coverage is incomplete, resulting in poor anti-tangling effect; above 1:5, excess solution increases the subsequent annealing time, reducing production efficiency.

[0056] After spraying, the two specifications of stainless steel fibers were separately placed into sealed molding chambers for molding treatment. The molding environment was controlled at room temperature (25±2℃) and relative humidity of 60%~70%, with the molding time strictly maintained at 24 hours. A room temperature environment prevents excessively high temperatures from causing premature curing of the PTFE, which would affect the uniformity of coverage; controlling the relative humidity at 60%~70% prevents the solution from evaporating too quickly, ensuring that the PTFE components have sufficient time to penetrate and cover the fiber surface. During the molding process, the molding chamber was opened every 8 hours to observe the fiber condition. If clumping was found in some areas, the fibers were gently turned over to ensure uniform treatment.

[0057] After the initial coating process, samples of the two specifications of stainless steel fibers were tested. The PTFE coverage on the fiber surface was observed using an electron microscope to ensure a coverage area of ​​≥95%. Simultaneously, a tensile test was conducted to verify the fiber's flexibility (no breakage after 10% stretching). The qualified 25μm×80mm stainless steel fibers will be used for the preparation of the lower fiber web in step S5, while the 20μm×65mm stainless steel fibers will be used for the preparation of the upper fiber web in step S5.

[0058] S4: Pre-opened mixture

[0059] This step aims to thoroughly mix and pre-open the pre-oxidized fibers treated in S2 with the 12μm×55mm stainless steel fibers prepared in S1, forming a fluffy and uniform mixed fiber body. This mixed fiber will serve as the core component of the upper fiber web in step S5, and its mixing uniformity directly affects the pore structure and filtration accuracy of the upper fiber web. Since the two types of fibers differ in density and flexibility, direct mixing could easily lead to stratification. Therefore, a synergistic process of precise proportioning, parallel feeding, and pre-opening is employed to ensure effective mixing.

[0060] First, precise control of the raw material ratio is crucial. Pre-oxidized fiber (S2 treatment) and 12μm×55mm stainless steel fiber (S1) are weighed at a 1:2 mass ratio. An electronic scale with 0.5g accuracy is used for weighing. First, the pre-oxidized fiber is weighed, then the corresponding mass of 12μm×55mm stainless steel fiber is calculated and weighed according to the ratio. Data is recorded for each batch to ensure traceability. The 1:2 ratio is chosen because the addition of pre-oxidized fiber improves the web-forming properties of the mixed fibers, preventing web breakage when stainless steel fiber forms a web alone. A higher proportion of 12μm×55mm stainless steel fiber ensures the filtration accuracy and high-temperature resistance of the upper fiber web. An imbalance in the ratio would result in either poor web-forming properties or insufficient filtration accuracy.

[0061] Following this, a parallel feeding operation is performed, feeding the two proportioned fibers into the pre-opening equipment via a parallel feeder at a speed set at 4.5 m / min. The parallel feeder is designed to simultaneously and evenly feed both fibers into the equipment, avoiding fiber stratification caused by traditional single-feeding methods. The 4.5 m / min feeding speed was determined after multiple process verifications: too high a speed would cause fibers to accumulate at the feed inlet, affecting the uniformity of subsequent opening; too low a speed would reduce production efficiency and may cause fibers to clump together due to prolonged residence time in the feeder. To prevent fiber scattering during feeding, a sealing baffle is installed at the junction of the feeder and the pre-opening equipment. The gap between the baffle and the conveyor belt is controlled at 2 mm, ensuring smooth fiber passage while effectively preventing scattering.

[0062] Next, the pre-opening equipment is started for pre-opening treatment. The opening roller speed is set to 800 r / min, and the opening roller needle cloth is model AC2030. The tooth shape and density of this model of needle cloth can effectively break up the fiber clumps while avoiding damage to the fibers. During the opening process, the fiber mixing state is observed in real time through the observation window on the side of the equipment. If obvious fiber clumps (diameter > 5 mm) are still found, the opening roller speed is appropriately increased (not exceeding 900 r / min to prevent fiber breakage due to excessive speed); if the fibers are found to be excessively dispersed and scattered, the speed is reduced. The goal of the pre-opening treatment is to form a fluffy, free, and uniformly mixed fibrous structure. By sampling and testing the mixing uniformity, it is ensured that in any 10 g of mixed fibers, the mass deviation of the pre-oxidized fiber is ≤0.5 g, and the mass deviation of the 12 μm × 55 mm stainless steel fiber is ≤1 g.

[0063] After pre-opening, the mixed fibers are fed into a temporary storage chamber, which is kept dry (relative humidity ≤50%) to prevent the fibers from becoming damp and clumping. Simultaneously, a uniform discharge device is installed at the bottom of the temporary storage chamber to ensure continuous and uniform feeding when the mixed fibers are used in the subsequent S5 step, avoiding fluctuations in the basis weight of the upper fiber web due to uneven feeding. This pre-opened mixed fiber will be directly used in the preparation of the upper fiber web in the S5 step; its uniformity and bulkiness are key prerequisites for ensuring the high-precision filtration pores of the upper fiber web.

[0064] S5: Preparation of each layer of fiber web

[0065] This step is the core of constructing the three-layer composite structure of the product: bottom layer, middle layer, and top layer. The bottom and top fiber meshes are prepared separately, along with the middle layer stainless steel mesh. The selection of components, weight control, and structural design of each layer all revolve around the concept of gradient pore filtration—the bottom fiber mesh provides supporting coarse pores, the middle stainless steel mesh strengthens the structure, and the top fiber mesh forms high-precision filtration pores. These three layers work together to achieve highly efficient filtration. Strict parameter control is maintained throughout the preparation of each layer to ensure that the final needle-punched felt achieves a total basis weight of 1500g / m². The design requirements are met, and the layers are closely connected.

[0066] First, the lower fiber web is prepared. This layer serves as the supporting base of the product, possessing certain strength and air permeability. Therefore, 25μm×80mm stainless steel fibers treated with S3 (coarse gauge, providing support) and pre-oxidized fibers treated with S2 (to improve web formation) are mixed at a mass ratio of 9:1. The mixing process is carried out in a cotton blender with a speed set to 400 rpm and a mixing time of 15 minutes to ensure uniform dispersion of the two types of fibers. After mixing, the fibers are fed into a carding machine. The carding machine uses AC2030 carding cloth and a carding speed controlled at 10 m / min. Through the action of the rollers and carding cloth, the mixed fibers are carded into a continuous fiber web. During carding, the basis weight of the fiber web is monitored in real time by a basis weight detection device at the carding machine outlet to ensure it remains stable at 660–680 g / m². Within the specified range, if the basis weight is too high, reduce the feeding speed; if the basis weight is too low, increase the feeding speed. The carded lower fiber web is then wound up, with the winding tension controlled at 50N to avoid excessive tension causing stretching and deformation of the fiber web, which would affect subsequent laying accuracy. This lower fiber web corresponds to the support layer in the subsequent needle-punched structure; its coarse pore design can initially intercept large-diameter dust particles in the gas, while simultaneously providing stable support for the upper fiber web.

[0067] Next, the upper fiber web is prepared. This layer is the key to achieving high-precision filtration and has fine and uniform pores. Therefore, three components are selected for synergistic mixing: 20μm×65mm stainless steel fibers treated with S3 (medium size, for auxiliary filtration), and pre-opened mixed fibers treated with S4 (containing 12μm×55mm stainless steel fibers and pre-oxidized fibers, providing high-precision filtration and web formation). The three are mixed in a mass ratio of 7:2:1 (20μm×65mm stainless steel fibers: 12μm×55mm stainless steel fibers: pre-oxidized fibers). Because it involves three components, the mixing process is carried out in two steps: First, 20μm×65mm stainless steel fibers are mixed with pre-opened blended fibers (containing 12μm×55mm stainless steel fibers and pre-oxidized fibers, in a mass ratio of 1:2) at a ratio of 7:3 (corresponding to a final ratio of 7:2:1), and mixed in a blending machine at a speed of 450 rpm for 20 minutes. Second, samples are taken to test the content of each component, ensuring that the ratio of 12μm×55mm stainless steel fibers to pre-oxidized fibers conforms to 2:1. If the deviation is too large, the corresponding fibers are added for adjustment. After the mixing is qualified, the fibers are sent to a carding machine of the same model as the lower fiber web (with consistent parameters: AC2030 carding cloth, carding speed 10m / min), carded to a unit area weight of 680~700g / g / m². The upper fiber web has a slightly higher basis weight than the lower layer because it requires a finer fiber arrangement to achieve high-precision filtration. The basis weight is also monitored in real time during the combing process to ensure a deviation of ≤10g / L. After combing, the fibers are wound up again, with the winding tension consistent with the lower layer (50N) to avoid misalignment during subsequent needle punching due to tension differences between the two fiber webs.

[0068] Finally, the intermediate layer of stainless steel mesh is prepared. The core function of this intermediate layer is to enhance the overall tensile strength of the product and prevent deformation or damage to the fiber mesh due to gas impact under high-temperature conditions. Therefore, the 316L type stainless steel mesh (corrosion-resistant and high-temperature resistant) prepared in S1 is selected. First, based on the width of the lower and upper fiber meshes, the stainless steel mesh is cut to the same size using a laser cutting machine. During the cutting process, the dimensional error is controlled to ≤2mm to ensure complete alignment with the upper and lower fiber meshes during subsequent laying. After cutting, the edges of the stainless steel mesh are ground to remove burrs, preventing burrs from snagging fibers and causing mesh breakage during needle punching. Simultaneously, the basis weight of the stainless steel mesh is tested to ensure it remains stable at 140g / m². If the weight deviation is too large (exceeding ±5g / L), the design value will be affected. (This involves changing the batch number to avoid affecting the total weight of the final product.)

[0069] After each layer is prepared, sampling tests are conducted on the lower fiber mesh, upper fiber mesh, and middle stainless steel mesh: the porosity of the lower and upper fiber mesh is tested (lower layer ≥70%, upper layer ≥65%), and the tensile strength of the middle stainless steel mesh is tested (warp ≥200N / 5cm, weft ≥150N / 5cm). After all tests are passed, the materials of each layer are transferred to the needle punching machine in step S6 and stacked in the order of lower fiber mesh-middle stainless steel mesh-upper fiber mesh to prepare for subsequent needle punching and felting, ensuring that the performance and dimensions of each layer of material meet the process requirements of composite needle punching.

[0070] S6: Multi-layered needle-punched felt

[0071] This step employs a two-step needle-punching process—pre-needling and main needle-punching—to composite the lower fiber mesh, middle stainless steel mesh, and upper fiber mesh prepared from S5 into a preliminary needle-punched felt. The core objective of the needle-punching process is to ensure a tight bond between the three layers, forming a seamless, uniformly porous whole, while avoiding excessive needle-punching that could lead to fiber breakage or damage to the stainless steel mesh, affecting the product's structural strength and filtration performance. The entire needle-punching process is matched with the characteristics of each fiber mesh layer, and the parameter settings have undergone multiple experimental verifications to ensure that the final product's basis weight per unit area accurately reaches 1500g / L. (Minor errors are allowed), and the structural stability meets the requirements for subsequent processing.

[0072] First, the bottom layer is laid and positioned. The lower fiber web prepared by S5 is unwound from the winding device and laid flat on the conveyor curtain of the needle punching machine. The conveyor curtain speed is set to 3m / min, which matches the subsequent needle punching density to ensure uniform needle punching. During the laying process, the edge position of the fiber web is monitored in real time by positioning sensors on both sides of the conveyor curtain to ensure that the center line of the fiber web is aligned with the center line of the conveyor curtain, with a deviation of ≤1mm, to avoid misalignment when laying the intermediate and upper layers. After the lower fiber web is laid, it is gently compacted with a pressure roller (pressure 5N / m). This ensures that the fiber web fits tightly against the conveyor curtain, preventing the fiber web from shifting during the needle punching process.

[0073] Next, the intermediate layer of stainless steel mesh is laid. The intermediate layer of stainless steel mesh prepared in S5 is laid flat on top of the lower fiber mesh. During laying, manual positioning is used to ensure that the four sides of the stainless steel mesh are completely aligned with the four sides of the lower fiber mesh, with an alignment deviation ≤2mm. To prevent the stainless steel mesh from shifting during needle punching, biodegradable positioning adhesive dots (diameter ≤5mm, which will naturally decompose during subsequent heat treatment) are used to fix the four corners of the stainless steel mesh. The selection of positioning adhesive dots ensures that they will not affect the fiber bonding while providing sufficient temporary fixing force. After the intermediate layer is laid, check the surface of the stainless steel mesh for wrinkles. If wrinkles are present, gently stretch them to flatten them to avoid the problem of excessively high density in some areas after needle punching.

[0074] The pre-needling machine is then started for pre-needling assembly. The purpose of pre-needling is to initially fix the lower fiber mesh and the middle stainless steel mesh, laying the foundation for subsequent main needle punching. The needle density of the pre-needling machine is set to 150 needles / ... The needle-punching depth is controlled at 10mm. The needle-punching depth is strictly controlled: too deep, and the needle will excessively hook the lower layer of fibers after penetrating the stainless steel mesh, causing damage to the fiber mesh; too shallow, and the two layers cannot be effectively bonded, easily leading to delamination when the upper layer of fiber mesh is laid later. During the pre-needling process, the surface of the composite structure after needle-punching is observed in real time through a camera above the equipment. If damage to the stainless steel mesh or breaks in the fiber mesh are found, the machine is immediately stopped and the needle-punching depth is adjusted (0.5mm each time) until the problem is resolved. After pre-needling, the formed pre-needled composite is continuously conveyed to avoid prolonged contact with the conveyor curtain, which could cause the surface to become damp.

[0075] Next, the upper fiber mesh is laid. After unfolding the upper fiber mesh prepared by S5, it is laid flat on top of the pre-needle-punched composite. The laying method is similar to that of the middle layer: using a combination of positioning sensors and manual assistance, the four sides of the upper fiber mesh, the lower fiber mesh, and the middle stainless steel mesh are ensured to be completely aligned, with a deviation ≤2mm. Because the fibers of the upper fiber mesh are finer, avoid pulling it forcefully during laying to prevent stretching and deformation that could lead to uneven pores. After laying, it is also gently compacted with a pressure roller (pressure 3N / m²). (The pressure should be less than that of the lower layer to avoid damaging the fine fibers).

[0076] Finally, the main needle-punching machine is started to perform main needle-punching and felting. The function of main needle-punching is to tightly bond the three-layer structure (pre-needle-punched composite + upper fiber web) into a whole, forming a complete needle-punched felt. The needle-punching density of the main needle-punching machine is set to 250 needles / ... (Higher than pre-needling to ensure tight bonding), the needling depth is controlled at 12mm (slightly deeper than pre-needling to ensure the needling needle can hook three layers of fibers, forming a cross-layer bond). Triangular needles (model 15×18×35, strong hooking ability, and reduced fiber breakage) are used. During the main needling process, the weight per unit area of ​​the needle-punched felt is monitored in real time by a weighing device below the conveyor curtain to ensure it remains stable at 1500g / m². Design value, error ±20g / If the basis weight is too high, reduce the feeding speed of the upper fiber web; if the basis weight is too low, increase the feeding speed. Simultaneously, sample the needle-punched felt for testing its thickness (controlled between 5 and 6 mm) and tensile strength (warp ≥ 300 N / 5 cm, weft ≥ 250 N / 5 cm). Qualified preliminary needle-punched felt will be directly sent to step S7 for polytetrafluoroethylene (PTFE) solution impregnation to ensure the needle-punched felt enters subsequent processing stages in a compact structure and with satisfactory performance.

[0077] S7: Polytetrafluoroethylene solution impregnation and heat curing

[0078] Although the initial needle-punched felt has formed a three-layer composite structure, many tiny pores still exist between the fibers. If used directly for filtration, fine-particle dust can easily penetrate these pores, resulting in insufficient filtration accuracy. Simultaneously, the exposed fibers on the surface of the needle-punched felt are susceptible to corrosion in high-temperature environments. Therefore, this step utilizes a polytetrafluoroethylene (PTFE) solution impregnation followed by heat curing to form a thin, uniform PTFE membrane on the fiber surface. This membrane not only fills the tiny pores, improving filtration accuracy, but also enhances the product's acid and alkali resistance and hydrolysis resistance, laying the foundation for subsequent S8 hot-pressing treatment and S9 coating application. The entire process involves precise control of solution concentration, impregnation time, and heat curing parameters to avoid over-impregnation leading to pore blockage or incomplete curing that could affect performance.

[0079] First, the PTFE impregnation solution was prepared by mixing the PTFE emulsion prepared in S1 with deionized water to obtain a PTFE solution with a mass concentration of approximately 33%. The preparation process was carried out in a corrosion-resistant tank equipped with a stirrer. The stirring speed was set to 400 rpm for 20 minutes to ensure complete mixing of the emulsion and water without stratification. A mass concentration of 33% was chosen because this concentration effectively fills the tiny pores between fibers (diameter < 1 μm) without completely clogging the filter pores (diameter > 1 μm). If the concentration is too high, a dense layer may form after curing, increasing gas flow resistance; if the concentration is too low, the pores will not be fully filled, and the effect of improving filtration accuracy will be insignificant. After preparation, the solution concentration was checked with a concentration meter to ensure an error ≤ 1%. If the concentration deviation was too large, PTFE emulsion or deionized water was added to correct the error.

[0080] The needle-punched felt was then impregnated. The preliminary needle-punched felt prepared by S6 was completely immersed in the prepared polytetrafluoroethylene solution for 8 minutes. During impregnation, the needle-punched felt was turned up and down three times using a lifting device to ensure that the solution could penetrate evenly to the surface of every fiber inside the felt, avoiding uneven impregnation that could lead to performance differences after curing. To prevent deformation of the needle-punched felt during impregnation, it was fixed in a mesh frame with a pore size of 10mm (to not affect solution penetration). The frame size matched the needle-punched felt to ensure that the felt remained flat during impregnation. Controlling the impregnation time is crucial: less than 8 minutes results in insufficient solution penetration and incomplete coverage of the fiber surface; more than 8 minutes results in excessive liquid content in the felt, prolonging the subsequent drying time and increasing energy consumption.

[0081] After impregnation, the needle-punched felt, along with the mesh frame, is fed into an extrusion device. A pressure of 0.1 MPa is applied through the extrusion rollers to remove excess PTFE solution from the felt. The extrusion pressure was adjusted multiple times: too low a pressure resulted in a high liquid content (>45%), which could easily lead to clumping during drying; too high a pressure resulted in a low liquid content (<40%), which would not adequately cover the fiber surface. After extrusion, the liquid content of the felt was checked by weighing to ensure it remained stable within the range of 40%–45%. If the liquid content did not meet the requirements, the extrusion pressure was adjusted and the extrusion was repeated.

[0082] Next, a heat curing process is performed. The extruded needle-punched felt is fed into a heat oven at a temperature of 245℃. The conveying speed of the needle-punched felt is controlled at 5 m / min, ensuring that the felt travel time within the oven is 6 minutes (the effective length of the oven is 30 m, 5 m / min × 6 min = 30 m). 245℃ is the optimal curing temperature for PTFE: below 240℃, PTFE cannot be fully cured, resulting in poor film adhesion; above 250℃, PTFE may undergo slight decomposition, affecting its corrosion resistance. Multiple temperature sensors (evenly distributed around the oven) are installed inside the heat oven to ensure that the temperature deviation in each area is ≤5℃, preventing uneven curing caused by excessively high or low temperatures. Simultaneously, ventilation is maintained within the heat oven at a wind speed of 1 m / s to promptly remove trace amounts of volatile substances generated during the curing process, preventing them from affecting the film quality.

[0083] After heat curing, the needle-punched felt is sampled and tested: first, the coverage of the polytetrafluoroethylene film on the surface is tested (observed using an electron microscope, coverage area ≥90%); second, the porosity is tested (controlled at 60%–65% to ensure a balance between filtration accuracy and air permeability); and third, corrosion resistance is tested (the sample is immersed in a 5% sulfuric acid solution for 2 hours, with no obvious corrosion marks on the surface). The qualified impregnated and cured needle-punched felt is then sent to step S8 for surface hot-pressing treatment. At this point, the needle-punched felt has acquired preliminary corrosion resistance and high filtration accuracy, preparing the surface for the subsequent foamed graphite coating in step S9.

[0084] S8: Hot pressing treatment of needle-punched felt surface

[0085] After impregnation and heat curing in S7, although a polytetrafluoroethylene (PTFE) film has formed on the surface of the needle-punched felt, the film layer still has some unevenness, and some tiny pores between fibers are not completely filled. Furthermore, the surface unevenness can lead to uneven coating thickness when the foamed graphite coating is applied in S9, affecting the filtration and dust removal performance of the final product. Therefore, this step uses hot pressing to pre-treat the surface of the needle-punched felt to make the PTFE film layer denser and smoother. This not only further optimizes the pore structure but also provides a uniform substrate for the S9 coating, ensuring a tight bond between the coating and the felt surface and preventing coating peeling.

[0086] First, the calendering equipment is debugged. A two-roll calender is selected, with the calendering rollers made of stainless steel (high temperature and corrosion resistant) and a surface roughness ≤0.1μm (to ensure a smooth surface of the needle-punched felt after hot pressing). The debugging process requires three steps: First, adjust the pressure of the calendering rollers to 7MPa. This pressure densifies the PTFE film layer on the surface without excessively compressing the felt and causing pore blockage. Second, adjust the surface temperature of the calendering rollers to 226℃. This temperature is slightly higher than the glass transition temperature of PTFE (200℃), allowing the film layer to soften and reshape, forming a smooth surface without causing film decomposition. Third, adjust the surface linear speed of the calendering rollers to 15m / min, ensuring that the linear speed of the calendering rollers perfectly matches the conveying speed of the needle-punched felt, avoiding scratches or tensile deformation on the surface of the needle-punched felt due to speed differences. After debugging, a temperature sensor is used to detect the surface temperature distribution of the calendering rollers, ensuring the deviation is ≤2℃; a pressure sensor is used to detect the inter-roller pressure, ensuring the deviation is ≤0.2MPa.

[0087] Following this, the needle-punched felt undergoes hot-pressing treatment. The impregnated and cured needle-punched felt prepared in S7 is fed into the calendering equipment at a conveying speed of 15 m / min, ensuring full contact between the upper surface of the needle-punched felt (the side to be coated later) and the calendering rollers. During the conveying process, guide rollers at the equipment inlet ensure the needle-punched felt enters the calendering rollers smoothly, avoiding wrinkles. Simultaneously, a cooling device (cooling air temperature ≤50℃) is installed at the equipment outlet to rapidly cool the hot-pressed needle-punched felt to room temperature, preventing residual heat from causing further deformation of the surface film. The goal of the hot-pressing treatment is to reduce the surface roughness of the needle-punched felt from ≥2 μm after heat drying to ≤0.5 μm, while increasing the density of the polytetrafluoroethylene film on the surface by 10%–15%, further filling the micropores.

[0088] After hot pressing, the needle-punched felt undergoes multi-dimensional testing: First, the surface roughness of the upper layer is measured using a surface roughness meter (≤0.5μm); second, the thickness of the felt body is measured using a laser thickness gauge (controlled between 4.5 and 5.5 mm to ensure uniform thickness after hot pressing, with a deviation ≤0.2 mm); third, the gas flow resistance is measured using an air permeability tester (resistance ≤150Pa at a wind speed of 1 m / min to ensure air permeability is not affected by excessive hot pressing). The hot-pressed needle-punched felt that passes the tests is immediately transferred to step S9 for the preparation and application of the foamed graphite coating. At this stage, the needle-punched felt surface is smooth and the film layer is dense, ensuring uniform thickness and tight bonding during subsequent coating application. This avoids missed coating or sagging due to uneven surface, guaranteeing the core performance of the final product (such as dust removal and corrosion resistance).

[0089] S9: Preparation and Coating of Foamed Graphite Coating

[0090] Foamed graphite coating is a stainless steel fiber composite coating needle-punched felt that achieves ultra-precise emissions (≤10mg / N). The coating, a core functional layer known for its high temperature and corrosion resistance (300-400℃) and long lifespan, determines dust interception accuracy (too thin and dust leakage is easy, too thick and sagging is easy). Curing parameters (temperature / time) determine the bonding stability between the coating and the substrate (incomplete curing leads to detachment, over-curing leads to brittleness). Bond strength determines the product's lifespan under high-temperature conditions. Therefore, this process involves eight consecutive sub-steps: precise raw material proportioning → coating mixing and preparation → coating thickness algorithm control → coating application → curing parameter algorithm optimization → coating curing → bonding strength algorithm prediction → quality inspection. Simultaneously, it incorporates a dynamic coating thickness calculation algorithm (A), a curing temperature-time co-optimization algorithm (B), and a coating bonding strength prediction algorithm (C) to ensure the coating performance meets standards.

[0091] S9-1: Preparation of coating raw materials; This step involves preparing the foamed graphite coating raw materials specified in S1 in advance and testing the key parameters to avoid deviations in algorithm calculations due to fluctuations in raw material parameters.

[0092] 1.1 Raw Material List and Specification Confirmation: The specifications and quality of the seven raw materials were checked one by one. The first was graphite emulsion, industrial grade with a carbon content ≥95%. The testing method was the ignition method (5g of emulsion, ignited at 800℃ for 2 hours, and the percentage of residual carbon by mass), tested once per batch. Its purpose was to ensure the conductivity and lubricity of the coating. The second was polytetrafluoroethylene emulsion, industrial grade with a solid content ≥60%. It was tested using the drying method (10g of emulsion, dried at 105℃ to constant weight, and the percentage of solids by mass), tested once per batch, to improve the corrosion resistance and surface smoothness of the coating. The third was foaming agent, industrial grade azodicarbonamide with a particle size ≤5μm, tested using a laser particle size analyzer (model LS-POP6), tested once per batch, to ensure that the coating forms a uniform microporous structure for easy dust removal. The fourth was a gelling agent. The first component is industrial-grade sodium alginate with a viscosity ≥500 mPa·s (25℃), tested with a rotational viscometer (model NDJ-8S) once per batch to ensure the stability of the coating emulsion and prevent stratification; the second component is a coupling agent, industrial-grade silane coupling agent KH-550 with a purity ≥98%, tested by gas chromatography (model GC-2014) once per batch to enhance the adhesion between the coating and the needle-punched felt substrate; the third component is industrial-grade ammonia with a concentration of 25%–28%, tested by acid-base titration (0.1 mol / L hydrochloric acid standard solution) once per batch to adjust the pH of the coating emulsion to ensure the compatibility of each component; the fourth component is deionized water with a conductivity ≤10 μS / cm, tested by a conductivity meter (model DDS-307) once before each preparation to avoid impurities affecting the stability of the coating emulsion.

[0093] 1.2 Key Parameter Detection and Recording: The parameters of the three core raw materials used subsequently were detected, and the data were recorded and used as input for the algorithm. The first parameter was the solid content of the coating emulsion. The solid content of the polytetrafluoroethylene (PTFE) emulsion and graphite emulsion was tested separately using a drying method. The theoretical solid content of the final coating emulsion was then calculated by weighting the results according to the subsequent mixing ratio. The measured value should be within ±2% of the theoretical value. If it exceeds this range, the raw material ratio should be adjusted. For example, if the graphite emulsion has a solid content of 95% (7 parts) and the PTFE emulsion has a solid content of 60% (21 parts), and other raw materials (foaming agent, gelling agent, etc.) are calculated as having a 100% solid content, the theoretical solid content of the coating emulsion should be... The calculation method is (7×95%+21×60%+1.5×100%+4×100%+1×100%+0.1×25%+60×0%) divided by the total number of parts (7+21+1.5+4+1+0.1+60), resulting in approximately 26.3%. Secondly, the viscosity of the gelling agent... The viscosity of the sodium alginate solution was measured using a rotational viscometer; it needed to be ≥500 mPa·s. If this standard was not met, the amount of gelling agent should be increased. Finally, the ammonia concentration was checked. The concentration should be within the range of 25% to 28% when tested by acid-base titration. If the concentration is not correct, dilute or add concentrated ammonia.

[0094] S9-2: Preparation of foamed graphite coating emulsion; This step strictly follows the mass ratio specified in S1 (graphite emulsion: polytetrafluoroethylene emulsion: foaming agent: gelling agent: coupling agent: ammonia: deionized water = 7:21:1.5:4:1:0.1:60) to mix the raw materials, and the mixing order and stirring parameters are precisely controlled to avoid component agglomeration. At the same time, the emulsion viscosity is monitored in real time. .

[0095] 2.1 Preparation of mixing equipment: A double planetary mixing tank (model SDF-50) was selected. The tank was pre-washed with deionized water three times and dried until no residue remained (to avoid impurities affecting the stability of the emulsion). An online viscosity monitoring probe (model VM-100, measurement range 0~10 Pa·s, accuracy ±0.001 Pa·s) was installed to collect the emulsion viscosity in real time. .

[0096] 2.2 Step-by-step mixing operation (execute in sequence, do not reverse): The first step is to dissolve the gelling agent. Add 60 parts of deionized water to the mixing tank, start stirring (300 r / min), slowly add 4 parts of gelling agent (sodium alginate), and stir for 15 minutes until completely dissolved to form a transparent gelling solution. At this time, use an online viscometer to measure the viscosity. The initial pressure needs to be ≥500 mPa·s; if this is not met, add more gelling agent. The second step is to add functional components. Maintaining a stirring speed of 300 rpm, add 7 parts graphite emulsion, 21 parts polytetrafluoroethylene emulsion, 1.5 parts foaming agent, and 1 part coupling agent sequentially. Stir for 5 minutes after each addition to ensure uniform mixing. At this point, the solution should be a milky white suspension without obvious particle agglomeration. The third step is to adjust the pH value. Reduce the stirring speed to 200 rpm and add 0.1 parts ammonia water in three portions (1 / 3 of the total amount each time, 5 minutes apart). After each addition, use a pH meter (model PHS-3C) to monitor the solution's pH value in real time until pH=9 (an alkaline environment can prevent graphite oxidation and improve the dispersibility of polytetrafluoroethylene). The fourth step is viscosity adjustment and stabilization. Maintain a stirring speed of 200 rpm and continue stirring for 10 minutes. Read the emulsion viscosity using an online viscometer. (Recorded as) (Requires a range of 0.8–1.5 Pa·s) If If the emulsion concentration is >1.5 Pa·s (the emulsion is too thick, which can easily lead to uneven coating), add a small amount of deionized water (0.5 parts each time, stir for 3 minutes, and then measure again). );like If the emulsion is too thin (causing sagging after coating), add a small amount of gelling agent (0.1 parts each time, stir for 3 minutes, and then measure again). The fifth step is to allow the emulsion to stand and degas. Turn off the stirring and let the mixed foamed graphite coating emulsion stand for 10 minutes to naturally remove the air bubbles generated during stirring. If there are many air bubbles, vacuum degassing can be used (vacuum degree -0.09 MPa, time 5 minutes). Finally, a uniform, bubble-free, and viscosity-stable foamed graphite coating emulsion is obtained. Record the final viscosity at this point. (As input parameters to algorithm A, denoted as...) ).

[0097] S9-3: Dynamic control of coating thickness; This step is based on the equipment parameters of the coating machine and the viscosity of the coating emulsion. The required coating thickness is accurately calculated using the dynamic coating thickness calculation algorithm A. And adjust the scraper gap to avoid the deviation caused by traditional manual thickness estimation (traditional deviation ±0.15mm, algorithm A can control the deviation within ±0.03mm).

[0098] 3.1 Basic definition of Algorithm A: This is the target coating thickness output by Algorithm A, in mm. It refers to the thickness that the coating needs to achieve after application (process requirement: 0.5-0.8 mm), calculated and output by Algorithm A. This is the viscosity of the coating emulsion, measured in Pa·s. It refers to the final viscosity of the foamed graphite coating emulsion obtained in step S9-2, measured by an online viscometer (output from S9-2). It is the conveyor speed of the coating machine, in m / min, which refers to the speed at which the needled felt moves on the conveyor belt of the coating machine (adjustable range 1-3 m / min), and is set by the coating machine equipment. This is the initial gap of the scraper, in mm. It refers to the initial distance between the scraper of the coating machine and the conveyor curtain (the theoretical gap without considering the viscosity of the emulsion), calibrated by a micrometer (measured before coating). It is a viscosity correction coefficient used to compensate for the effect of emulsion viscosity on coating thickness (the higher the viscosity, the larger the coefficient, and the greater the thickness correction), and is fitted by experimental training (value is 0.18). It is a speed correction coefficient used to compensate for the effect of conveying speed on coating thickness (the higher the speed, the larger the coefficient, and the greater the thickness correction), and is fitted by experimental training (value is 0.25). This is the actual coating thickness, in mm. It refers to the actual coating thickness measured after coating, which is measured by a coating thickness gauge (to verify the accuracy of algorithm A).

[0099] 3.2 Model Construction for Algorithm A: During the coating process, the flow of the foamed graphite coating emulsion on the surfaces of the doctor blade and needle-punched felt conforms to the laminar boundary layer theory (based on precise calculations using fluid mechanics): emulsion viscosity The larger the gap, the worse the flowability, and the actual coating thickness will be less than the initial gap of the scraper. Transmission speed The larger the size, the shorter the residence time of the emulsion under the doctor blade, and the smaller the actual coating thickness will be. Therefore, by using viscosity correction terms and velocity correction terms... The model formula has been adjusted and is as follows:

[0100] ;In the formula, The core of the viscosity correction term is the logarithmic function, which is used because the effect of emulsion viscosity on thickness decreases marginally. When the pressure increases from 0.8 Pa·s to 1.5 Pa·s, The correction value increased slowly from 0.588 to 0.916, which is consistent with actual fluid characteristics. It is the core of the speed correction item, which will adjust the transmission speed. Normalized to the range of 0-1 ( When the maximum speed is 3 m / min, this item is 1) to avoid the influence of speed units on the calculation results; coefficient =0.18、 The value of 0.25 was obtained through 15 sets of experimental training to ensure the goodness of fit between the calculated and measured values. ≥0.96.

[0101] 3.3 Model Training for Algorithm A

[0102] 3.3.1 Training Experiment Design: To ensure the coefficients , To ensure versatility, a full factorial experiment was designed with 5 groups of viscosity and 3 groups of speed (a total of 15 groups, covering practical processes). , (All possible ranges), each experiment was repeated 3 times, and the average value was taken as the measured data. For example, when =0.8 Pa·s =1m / min When =0.6mm, the actual measurement The average value is 0.51 mm; =0.8 Pa·s =2m / min The average value is 0.55 mm; =0.8 Pa·s =3m / min The average value is 0.59 mm; =1.0 Pa·s When = 1 m / min, The average value is 0.49mm, and so on, until coverage is achieved. (0.8, 1.0, 1.2, 1.4, 1.5 Pa·s) and All combinations of (1, 2, 3 m / min).

[0103] 3.3.2 Training process: Calculated using Algorithm A Compared with actual measurement ( The objective function is constructed to minimize the sum of squared residuals (the average of the values). Fitting using MATLAB's lsqcurvefit function The constraint is 0.1 ≤ ≤0.3, 0.2≤ ≤0.3, finally obtained =0.18, =0.25, at which point the sum of squared residuals is... =0.0008, goodness of fit =0.97 (indicating that the model can accurately predict the coating thickness).

[0104] 3.4 Application of Algorithm A: The first step is to collect input parameters, obtaining the viscosity of the coating emulsion from S9-2. (like =1.2Pa·s), setting the conveyor speed of the coating machine. (Based on production efficiency, take) =2.5m / min), calibrate the initial gap of the scraper with a micrometer. (like =0.6mm). The second step is to calculate the target coating thickness. Substitute the parameters into the formula: The third step is verification and adjustment. Within the range of 0.5-0.8mm (e.g., 0.64mm meets the requirements), then maintain... =0.6mm, start coating; if <0.5mm (e.g.) =1.5 Pa·s When = 1 m / min, =0.44mm), then increase (If adjusted to 0.65mm, recalculate) =0.65×[1-0.18×0.916+0.25×0.333]=0.65×0.92=0.6mm, which meets the requirements); if If the value is >0.8mm (the dependent variable range has been covered, but this situation does not actually exist), then decrease the value. .

[0105] S9-4: Coating application implementation; this step is based on calculations using algorithm A. The foamed graphite coating emulsion is uniformly coated onto the upper surface of the hot-pressed needle-punched felt obtained from S8 using a coating machine, ensuring the actual coating thickness. and The deviation is ≤ ±0.03mm.

[0106] 4.1 Coating Equipment Debugging: A doctor blade coating machine (model TC-1600) was selected. The debugging steps are as follows: The first step is conveyor belt calibration. The hot-pressed needle-punched felt (S8 output) is laid flat on the conveyor belt, and the conveyor belt level is adjusted (deviation ≤ 0.1mm / m) to avoid uneven thickness during coating; the second step is doctor blade positioning, calculated according to algorithm A. Adjust the gap between the scraper and the conveyor belt (i.e.) The first step is to check the uniformity of the gap using a feeler gauge (deviation at both ends ≤ 0.02mm); the third step is to debug the emulsion feeding system. Pour the foamed graphite-coated emulsion prepared in S9-2 into the feeding tank, start the feeding pump, and adjust the feeding speed (to match the emulsion feed rate). Matching, such as When the flow rate is 2.5 m / min, the feed rate is 1.2 L / min to ensure that the emulsion continuously covers the scraper.

[0107] 4.2 Coating process monitoring: The first step is real-time thickness detection. A laser thickness gauge (model LK-G80, accuracy ±0.001mm) is installed at the coating machine exit, and data is collected every 10 seconds. and with Comparison: If and Deviation ≤ ±0.03mm (e.g.) When =0.64mm, If the deviation is 0.63-0.65mm, continue coating; if the deviation is > ±0.03mm (e.g., ... If the thickness is less than 0.61 mm, the system will automatically send feedback to the coating machine control system for adjustment. (For example, increase by 0.02mm) until the deviation is acceptable. The second step is surface quality monitoring. Operators are instructed to check the surface of the coated needle-punched felt every 5 minutes, ensuring there are no runs, missed areas, or bubbles. If runs occur (because...), If the value decreases, then retest. And adjust (add gelling agent).

[0108] 4.3 Post-coating output: Obtain needle-punched felt coated with foamed graphite coating, and record the actual coating thickness. (like =0.64mm), which serves as the core input parameter for subsequent algorithm B.

[0109] S9-5: Curing temperature-time synergistic optimization; after coating application, curing allows moisture in the emulsion to evaporate, polytetrafluoroethylene to crosslink, and graphite to bond with the substrate. If the curing temperature... Too low or time If the coating is too short, it will not cure completely (and may peel off at high temperatures); if Too high or If the curing time is too long, the coating will over-cured (making it brittle and prone to breakage during cleaning). Therefore, an optimization algorithm B based on curing temperature and time is used to address this issue. and coating emulsion solid content Calculate the optimal and .

[0110] 5.1 Basic definition of Algorithm B: This is the target curing temperature output by Algorithm B, in °C, indicating the temperature required for coating curing (process requirement 110℃ ≤). (≤300℃, to avoid decomposition of polytetrafluoroethylene), output calculated by algorithm B; This is the target curing time output by Algorithm B, in minutes, indicating the time it takes for the coating to cure. Time required to reach 95% curing degree (process requirement ≤ 20min) (≤40min), the output is calculated by algorithm B; The actual coating thickness, in mm, is the input to Algorithm B. It refers to the coating thickness measured in step S9-4 and is output by S9-4. ); This is the coating emulsion solid content input to Algorithm B, expressed as a percentage (%). It refers to the coating emulsion solid content calculated in step S9-1 and output by S9-1. ); It is the curing reaction rate constant, in units of This reflects the speed of the coating curing reaction (and) (Positive correlation), calculated by the Arrhenius equation; It is the pre-exponential factor of the curing reaction, in units of , is an inherent parameter of the curing reaction (related to the reaction type), which is fitted by experimental training; It is the activation energy of the curing reaction, expressed in J / mol, and is the minimum energy required for the curing reaction (related to the raw material composition), which is fitted by experimental training. It is the gas constant, with units of J / (mol·K), and is a universal physical constant with a value of 8.314; This refers to the degree of curing of the coating, expressed as a percentage, indicating the completeness of the coating curing reaction (requirements). ≥95% (measured by differential scanning calorimetry (DSC)).

[0111] 5.2 Model Construction for Algorithm B: The core of coating curing is the cross-linking reaction of polytetrafluoroethylene (PTFE), which is a thermally driven reaction, and the reaction rate conforms to the Arrhenius equation; simultaneously, the coating thickness... The larger the solid content, the slower the heat transfer within the coating, requiring a longer time to reach 95% curing. The larger the value, the less moisture evaporates, and the shorter the curing time can be. Therefore, Algorithm B's model consists of two steps:

[0112] 5.2.1 First step: Reaction rate constant based on the Arrhenius equation calculate

[0113] The Arrhenius equation describes the effect of temperature on the reaction rate, and the formula is as follows:

[0114] ;In the formula, +273.15 converts Celsius temperature to absolute temperature (K) to ensure unit consistency; The higher the temperature, The larger the size, the faster the reaction.

[0115] 5.2.2 Second step: Time based on curing requirements calculate

[0116] Coating curing degree With time The relationship conforms to the first-order reaction kinetic model: ;

[0117] To ensure coating performance, ≥95%, substituting, we get: ;

[0118] Then introduce a thickness correction term ( ) and solids content correction item ( ), to compensate for the effects of thickness and solid content, ultimately formula: In the formula, ln(20)≈3 is... =95% corresponds to the constant term; It is the thickness correction factor ( The larger, The larger, (The longer the length), the value is 0.8; It is the solid content correction factor ( The larger, The larger, (The shorter the value), the value is 0.02; Obtained through experimental training.

[0119] 5.3 Model Training for Algorithm B

[0120] 5.3.1 Training Experiment Design: A total of 36 experiments were designed, consisting of 3 sets of thickness × 3 sets of solid content × 4 sets of temperature. The degree of curing in each experiment was monitored using a DSC (model DSC-60), and the results were recorded upon reaching the specified temperature. =95% of the time For example, when =0.5mm =24%, =150℃, actual measurement The average time was 28 minutes. =0.5mm =24%, At 180℃, The average time was 22 minutes. ==0.5mm、 =24%, At 210℃, The average time was 17 minutes. ==0.5mm、 =24%, At 240℃, The average is 13 minutes, and so on, covering... = (0.5, 0.65, 0.8mm) (24%, 26%, 28%) All combinations of (150, 180, 210, 240℃).

[0121] 5.3.2 Training process: The first step is fitting. , ,fixed =0.65mm =26%, 4 groups and Substituting the average value into the formula yields a system of equations, which are then fitted using the nonlinear least squares method to obtain... , =45000 J / mol (goodness of fit) =0.97). The second step is fitting. Substitute The data was fitted using 36 sets of experimental data, with the constraint 0.5 ≤ ≤1.0, 0.01≤ ≤0.03, finally obtained =0.8, =0.02 (goodness of fit) =0.95).

[0122] 5.4 Application of Algorithm B: The first step is input parameter acquisition, obtained from S9-4. =0.64mm, obtained from S9-1 =26.3%. The second step is to set the initial temperature and calculate the time, setting the initial curing temperature. =200℃ (within the range of 110-300℃, balancing efficiency and safety), substituting into the formula: ;

[0123] The calculation process is as follows: the denominator is 1 + 0.512 - 0.526 = 0.986; the exponent term is... , ; molecules are ;final min (within the range of 20-40 min). The third step is parameter verification and adjustment. If the timeframe is within 20-40 minutes (e.g., 23.6 minutes meets the requirement), then output... =200℃ =23.6min; if <20min (e.g.) At 220℃, (≈18min), then decrease Recalculate at 210℃. ≈20.5min (meets requirements); if >40min (e.g.) At 170℃, (≈42min), then the elevation Recalculate at 175℃. ≈39min (meets requirements).

[0124] S9-6: Coating curing implementation; This step is calculated based on algorithm B. and The coating is cured in a curing oven to ensure the degree of curing. ≥95%, and the coating is free from cracking and peeling.

[0125] 6.1 Curing Oven Commissioning: A hot air circulating curing oven (model RXH-45) was selected. The commissioning steps are as follows: The first step is temperature calibration. Five temperature sensors (model PT100, accuracy ±0.5℃) are evenly arranged inside the curing oven, and the target temperature is set. =200℃, wait for the temperature to stabilize, and then check the temperature deviation of each sensor (≤±2℃, otherwise adjust the hot air volume); the second step is to set the conveyor speed of the curing oven. Equal to the effective length of the curing oven divided by For example, if the effective length of the curing oven is 12m, =23.6min, then =12 / 23.6≈0.508m / min (ensuring the needle-punched felt stays in the furnace for exactly the required time). The third step is to adjust the airflow speed, setting the hot air speed to 2m / s (to ensure uniform surface temperature of the coating and avoid local over-curing).

[0126] 6.2 Curing process monitoring: The first step is to sample and test the degree of curing. Every 30 minutes, one piece of coated needle-punched felt is sampled and the degree of curing is measured using DSC. (Requires ≥95%), if <95% (e.g.) =92%$), then extend (e.g., increasing from 23.6 min to 25 min); the second step is coating appearance inspection. After curing, operators are arranged at the needle-punched felt outlet to inspect the coating surface (no cracks, no bubbles, no peeling). If cracks appear (because...) If it is too high, then lower it. (e.g., from 200℃ to 195℃).

[0127] 6.3 Output after curing: Obtain the stainless steel fiber composite coated needle-punched felt after curing the foamed graphite coating, and record the actual curing parameters. =200℃ =23.6min, which is used as the input parameter for subsequent algorithm C.

[0128] S9-7: Prediction and Verification of Coating Bond Strength; Coating Bond Strength It is a key indicator for the product to operate at high temperatures of 300-400℃ for extended periods (requirement) (≥1.2MPa), traditional methods require sampling and testing after curing (destructive testing, unable to achieve 100% coverage), while the coating bonding strength prediction algorithm C can be based on... , , Predict in advance This avoids mass rework.

[0129] 7.1 Basic Definitions of Algorithm C: This is the predicted bond strength output by Algorithm C, in MPa, referring to the predicted bond strength between the coating and the needle-punched felt substrate (requirements). (≥1.2MPa), calculated and output by algorithm C; The actual coating thickness, measured in mm, is the input to Algorithm C, referring to the thickness measured in step S9-4. Output from S9-4; This is the actual curing temperature input to algorithm C, in °C, referring to the temperature measured in step S9-6. Output from S9-6; This is the actual curing time input to Algorithm C, in minutes, referring to the time measured in step S9-6. Output from S9-6; It is the thickness weight coefficient, which refers to the weight of the coating thickness on the bonding strength (the weight is the largest when the optimal thickness is 0.65mm), and is fitted by experimental training (0.45). It is the temperature weighting coefficient, which refers to the weight of the effect of curing temperature on the bonding strength (the weight decreases when the temperature is too high or too low), and is fitted by experimental training (0.25). It is the time weight coefficient, which refers to the weight of the effect of curing time on the bonding strength (the weight decreases if the time is too long or too short), and is fitted by experimental training (0.20). It is the temperature-time interaction coefficient, with units of MPa·10000 / (℃·min), used to compensate for the synergistic effect of temperature and time (avoiding the single parameter being optimal but the synergy being poor), and is fitted by experimental training (0.08). It is the actual bond strength, measured in MPa. It refers to the actual bond strength of the coating after curing, measured by a tensile testing machine.

[0130] 7.2 Model Construction for Algorithm C: Combination Strength Coating thickness is affected by the combined effects of thickness, temperature, and time. The optimal value is 0.65mm (too thick and it's prone to delamination, too thin and the bonding area is small), using a quadratic function. Description; Curing temperature Within the temperature range of 110-250℃, the higher the temperature, the greater the bonding strength (but it is prone to brittleness above 250℃), using the normalized term. Description; Curing time Within the range of 20–40 minutes, shorter time results in lower bonding strength (but curing is incomplete for <20 minutes), using the normalization term. Description; Temperature-time interaction (e.g., the binding strength at 200℃+25min is better than that at 220℃+20min), using interaction terms Description. Final model formula: ;

[0131] 7.3 Model Training for Algorithm C

[0132] 7.3.1 Training Experiment Design: Design a full factorial experiment with 3 sets of thickness × 4 sets of temperature × 3 sets of time (36 sets in total). Each set of experiments will be tested using a tensile testing machine (model WDW-10). (Maximum tensile force / peeling area during coating peeling). For example, when =0.5mm =150℃ =20min, actual measurement The average value is 1.0 MPa; =0.5mm =150℃ =30 minutes, The average value is 1.1 MPa; =0.5mm =150℃ =40 minutes, The average value is 1.05 MPa; =0.5mm =180℃ =20min, The average value is 1.2 MPa, and so on, covering... = (0.5, 0.65, 0.8mm) (150, 180, 210, 240℃) All combinations of (20, 30, 40 min).

[0133] 7.3.2 Training Process: The first step is to initialize the coefficients and set... =0.4、 =0.3、 =0.2、 =0.1 (weight sum is 0.9, reserving space for interaction terms); the second step is to construct the objective function. (Mean squared error); the third step is gradient descent optimization, with a learning rate of 0.01, iterating 1000 times, updating the coefficients each time (e.g., ...). The fourth step is the training results, which yield... =0.45、 =0.25、 =0.20、 =0.08, at this time =0.0012, goodness of fit =0.94.

[0134] 7.4 Application of Algorithm C in Models

[0135] The first step is to collect input parameters and obtain them. =0.64mm (S9-4 output) =200℃ (S9-6 output) =23.6min (S9-6 output); the second step is to calculate Substitute into the formula: ;

[0136] Calculation process: Thickness term: 0.45×(1-0.0001)=0.44995; Temperature term: 0.25×90 / 140≈0.1607; Time term: 0.20×16.4 / 20≈0.164; Interaction term: 0.08×4720 / 10000≈0.0378; Total ≈0.44995+0.1607+0.164+0.0378≈1.81MPa (≥1.2MPa, meets the requirements); the third step is actual verification, sampling and testing. =1.78MPa, and A deviation ≤ ±0.05MPa indicates that the model prediction is accurate; if <1.2MPa (e.g.) =0.5mm =150℃ =20min, =1.0MPa), then the feedback is sent to Algorithm A (if adjusted). (up to 0.65mm) or Algorithm B (such as adjustment) Up to 180℃ (Up to 30 minutes), then repeat the coating and curing process.

[0137] S9-8: Post-Cure Quality Inspection; This step involves a comprehensive inspection of the cured needle-punched felt with the foamed graphite coating to ensure all performance indicators meet the standards. The first item is coating thickness inspection, using a laser thickness gauge to randomly select 10 points on the needle-punched felt for measurement. The average value is within the range of 0.5 to 0.8 mm, with a deviation of ≤ ±0.03 mm; the second item is the degree of cure test, which is measured by DSC. ≥95%; the third item is to combine strength testing, using a tensile testing machine to measure... ≥1.2MPa; the fourth item is surface resistance testing, using a surface resistance meter (model ST-302) to measure the coating surface resistance ≤1× Ω (Ensure conductivity and meet high-temperature antistatic requirements); the fifth item is acid and alkali resistance test, where the needle-punched felt is immersed in 5% sulfuric acid solution (80℃) and 5% sodium hydroxide solution (80℃) for 24 hours, and the coating shows no peeling or discoloration (ensure high-temperature corrosion resistance at 300-400℃); the sixth item is filtration efficiency test, using a dust filtration efficiency tester (model TSP-100), with 0.3μm talc powder as the test dust, and a wind speed of 1m / min, the filtration efficiency is measured to be ≥99.99% (ensure ≤10mg / N). (Ultra-precision emissions).

[0138] If all test items meet the standards, step S9 is completed, and qualified stainless steel fiber composite coated needle-punched felt is obtained; if any item fails to meet the standards, trace back to the previous sub-step (e.g., if the filtration efficiency fails to meet the standards, check algorithm A). (Check if it's too thin), readjust the parameters and execute. Stainless steel fiber composite coated needle-punched felt, such as... Figure 3 As shown, Figure 3 In the middle: 1 is a foamed graphite coating, 2 is a fiber mesh (i.e., upper fiber mesh) made of a mixture of 20μm×65mm stainless steel fiber, 12μm×55mm stainless steel fiber and pre-oxidized fiber, 3 is a stainless steel mesh base fabric (i.e., middle layer stainless steel mesh), and 4 is a fiber mesh (i.e., lower layer fiber mesh) made of a mixture of 25μm×80mm stainless steel fiber and pre-oxidized fiber.

[0139] The core contributions of the algorithms are as follows: Algorithm A solves the problem of large coating thickness deviation (±0.15mm→±0.03mm) caused by traditional manual adjustment of the scraper gap, ensuring dust interception accuracy and laying the foundation for ultra-precise emissions; Algorithm B solves the problem of incomplete (or over-curing) curing caused by traditional curing temperature / time settings based on experience, increasing the curing pass rate from 85% to 99.5% and ensuring coating stability at high temperatures; Algorithm C solves the problem that traditional post-destructive testing of bonding strength cannot provide full coverage, predicting the pass rate in advance and reducing the rework rate from 12% to <1%, thus reducing production costs.

Claims

1. A manufacturing process for stainless steel fiber composite coated needle-punched felt, characterized in that, include: S1: Obtain three specifications of inorganic stainless steel fiber, organic pre-oxidized fiber, stainless steel mesh, as well as silicone oil emulsion, polytetrafluoroethylene emulsion, graphite emulsion, foaming agent, gelling agent, coupling agent, ammonia water, and deionized water. S2: Mix silicone oil emulsion with deionized water to prepare silicone oil aqueous solution. Immerse organic pre-oxidized fiber in silicone oil aqueous solution. After immersion, remove excess solution from the surface and then heat-cure to obtain pre-oxidized fiber after softening and flexural resistance treatment. S3: Mix polytetrafluoroethylene emulsion with deionized water to prepare polytetrafluoroethylene solution. Select two specifications of stainless steel fibers and lay them flat. Spray the polytetrafluoroethylene solution evenly on the surface of the two fibers. After spraying, send the two fibers into a closed environment for annealing to obtain two specifications of stainless steel fibers after anti-entanglement treatment. S4: The pre-oxidized fiber after softening and flexural treatment is pre-opened with the third type of stainless steel fiber to form a fluffy and uniformly mixed fibrous structure, thus obtaining pre-opened mixed fiber. S5: One type of stainless steel fiber after anti-tangling treatment and pre-oxidized fiber after softening and bending resistance treatment are combed into a lower fiber web; another type of stainless steel fiber after anti-tangling treatment and pre-opened mixed fiber are combed into an upper fiber web; the stainless steel web is cut to the same plane size as the lower and upper fiber webs and used as the middle layer stainless steel web. S6: Lay the lower layer of fiber mesh flat, lay the middle layer of stainless steel mesh on top of the lower layer of fiber mesh, and perform pre-needling to form a pre-needling composite. A top layer of fiber mesh is laid on top of the pre-needled composite, and the main needle punching is performed to tightly combine the three-layer structure, thus obtaining the preliminary needle-punched felt. S7: The preliminary needle-punched felt is immersed in a polytetrafluoroethylene solution for impregnation. After impregnation, excess solution is removed, and then it is heat-cured to form a curing film of polytetrafluoroethylene on the fiber surface, thus obtaining impregnated and cured needle-punched felt. S8: The impregnated and cured needle-punched felt is subjected to surface hot pressing treatment to obtain hot-pressed needle-punched felt; S9: Mix graphite emulsion, polytetrafluoroethylene emulsion, foaming agent, gelling agent, coupling agent, ammonia water, and deionized water evenly to prepare a foamed graphite coating emulsion; coat the foamed graphite coating emulsion evenly on the upper surface of the hot-pressed needle-punched felt; after coating, perform curing treatment to make the coating and the felt body tightly bonded, and finally obtain stainless steel fiber composite coated needle-punched felt. The organic pre-oxidized fiber is a precursor product of carbon fiber made from polyacrylonitrile fiber through air oxidation.

2. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 1, characterized in that, In S1, the three specifications of inorganic stainless steel fibers are 25μm×80mm stainless steel fiber, 20μm×65mm stainless steel fiber, and 12μm×55mm stainless steel fiber, respectively; the stainless steel mesh is 316L type stainless steel mesh, with a warp wire diameter of 0.2mm, a weft wire diameter of 0.1mm, and a mesh size of 30; the organic pre-oxidized fiber has a decomposition temperature ≥640℃ and a long-term temperature resistance ≥370℃.

3. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 1, characterized in that, In S2, the mixing ratio of silicone oil emulsion to deionized water is 1:16 by mass; the impregnation bath temperature is controlled at 30-40℃, and the impregnation time is controlled at 10min; the removal of excess solution from the surface is achieved by an extrusion device, with the extrusion pressure controlled at 0.2MPa, and the liquid content of the pre-oxidized fiber after extrusion controlled at 30%-35%; the temperature for heat curing is controlled at 180℃, and the heat curing time is controlled at 5-6min, while maintaining an ambient wind speed of 1.5m / s during the heat curing process to ensure uniform drying of the fiber.

4. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 1, characterized in that, In S3, the mixing ratio of polytetrafluoroethylene emulsion to deionized water is 1:1 by mass; the polytetrafluoroethylene solution is uniformly sprayed through an atomizing humidifier, with the atomized particle diameter controlled at 5-10 μm, and the mass ratio of polytetrafluoroethylene solution to stainless steel fiber controlled at 1:5; the temperature of the sealed environment is controlled at 25±2℃, the relative humidity is controlled at 60%~70%, and the curing time is controlled at 24h; the two specifications of stainless steel fiber are 25μm×80mm stainless steel fiber and 20μm×65mm stainless steel fiber.

5. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 1, characterized in that, In S4, the mixing ratio of the pre-oxidized fiber after softening and flexural treatment to the third type of stainless steel fiber is 1:2 by mass. The pre-opening treatment is achieved by a parallel feeder and a pre-opening device. The feeding speed of the parallel feeder is controlled at 4.5 m / min, and the opening roller speed of the pre-opening device is controlled at 800 r / min. The third type of stainless steel fiber is 12 μm × 55 mm stainless steel fiber. After pre-opening, there are no clumps with a diameter > 5 mm in either fiber.

6. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 1, characterized in that, In S5, one specification of stainless steel fiber after anti-tangling treatment is 25μm×80mm stainless steel fiber. Its mixing ratio with pre-oxidized fiber after softening and flexural treatment is 9:1 by mass. The basis weight of the lower fiber web after carding is controlled at 660-680g / m². Another specification of stainless steel fiber after anti-tangling treatment is 20μm×65mm stainless steel fiber. The mixing ratio of this fiber with pre-opened mixed fibers is 20μm×65mm stainless steel fiber: 12μm×55mm stainless steel fiber: pre-oxidized fiber = mass ratio 7:2:

1. After carding, the unit area basis weight of the upper fiber web is controlled at 680-700g / m². The unit area weight of the intermediate layer stainless steel mesh is controlled at 140g / m². The combing process uses a combing machine, and the combing speed is controlled at 10m / min.

7. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 1, characterized in that, In S6, the acupuncture density of the pre-needle acupuncture is controlled at 150 needles / The needle insertion depth is controlled at 10mm; the needle insertion density of the main needle is controlled at 250 needles / min. The needle-punching depth is controlled at 12mm; the speed of the needle-punching machine conveyor curtain during the needle-punching process is controlled at 3m / min; the total weight per unit area of ​​the preliminary needle-punched felt is controlled at 1500g / The allowable error range is ±20g / .

8. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 1, characterized in that, In S7, the mass concentration of the polytetrafluoroethylene solution used for impregnation is controlled at 33%; the impregnation time is controlled at 8 minutes, and the preliminary needle-punched felt is turned over every 2 minutes during the impregnation process to ensure uniform impregnation; the removal of excess solution is achieved by an extrusion device, the extrusion pressure is controlled at 0.1 MPa, and the liquid content of the needle-punched felt after extrusion is controlled at 40% to 45%; the temperature of the heat curing is controlled at 245℃, the conveying speed of the needle-punched felt is controlled at 5 m / min, and the heat curing time is controlled at 6 minutes.

9. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 8, characterized in that, Before uniformly coating the foamed graphite coating emulsion in step S9, a thickness control step based on a dynamic coating thickness calculation algorithm is also included: the viscosity value of the foamed graphite coating emulsion in S9 is obtained in real time through an online viscosity monitoring device, the conveying speed of the coating machine is obtained through the coating machine control system, and the initial gap of the coating machine's scraper is obtained through micrometer calibration; the viscosity value, conveying speed, and initial scraper gap are substituted into the dynamic coating thickness calculation algorithm to obtain the target coating thickness; the scraper gap is adjusted according to the target coating thickness, and the actual coating thickness is monitored in real time through a laser thickness gauge during the coating process to ensure that the actual thickness is stable within the range of 0.5 to 0.8 mm; the dynamic coating thickness calculation algorithm is used to compensate for the influence of emulsion viscosity fluctuations and conveying speed changes on the coating thickness, wherein the viscosity value comes from the real-time monitoring after mixing the coating emulsion in S9, the conveying speed comes from the equipment setting of the coating machine, and the initial scraper gap comes from the micrometer calibration before coating.

10. The manufacturing process of stainless steel fiber composite coated needle-punched felt according to claim 9, characterized in that, When S9 is coated and then cured, the following optimization steps are also included: Curing parameter optimization: The actual thickness of the coating after S9 coating is obtained by laser thickness gauge, and the solid content of foamed graphite coating emulsion is obtained by drying method; the actual thickness and solid content are substituted into the curing temperature-time co-optimization algorithm to calculate the target curing temperature and target curing time. The curing equipment is controlled according to the target temperature and time to ensure that the coating curing degree is ≥95%; Bond strength verification: The actual curing temperature is obtained through a temperature sensor, and the actual curing time is obtained through a timer. Combined with the actual coating thickness, the results are substituted into the coating bond strength prediction algorithm. If the predicted bond strength is ≥1.2MPa, the curing is qualified. If it is lower than 1.2MPa, the coating thickness or curing parameters of S9 are adjusted accordingly. The curing temperature-time co-optimization algorithm is used to avoid incomplete curing or excessive embrittlement of the coating, and the coating bond strength prediction algorithm is used to detect the risk of insufficient strength in advance.

Images