Composite protection and high-precision sealing preparation process of valve body of marine desulfurization and denitrification system

Abstract

The application discloses a composite protection and high-precision sealing preparation process of a valve body of a marine desulfurization and denitration system. The process comprises the following steps: after roughening treatment is performed on the surface of the valve body, a micro-nano-pore structure oxide film layer is formed through electrochemical oxidation; an interface transition layer is coated so as to penetrate into the micro-nano-pore to form an anchoring structure; a multilayer modified fluoropolymer coating with a decreasing filler content gradient is sprayed, and the filler is composed of calcined modified desulfurization gypsum, deactivated denitration catalyst micro powder and activated modified red mud in a specific proportion; after being cured through segmented temperature rising, the sealing surface is subjected to ultra-precision grinding and deposition of a corrosion-resistant film. Through the micro-nano-pore anchoring structure and the gradient coating design, the coating adhesion and the thermal cycle life are significantly improved; the desulfurization and denitration process solid waste is creatively converted into a functional filler, the active protection and self-repairing function of the coating are realized, and the recycling economic goal of 'waste treatment with waste' is realized.

Description

Technical Field

[0001] This invention relates to the field of marine equipment technology, and in particular to the composite protection and high-precision sealing process for valve bodies of marine desulfurization and denitrification systems. Background Technology

[0002] With increasingly stringent environmental protection requirements in the global shipping industry, marine desulfurization and denitrification systems have become an important component of modern ships in order to meet emission standards. Among them, the valve body, as a key control element of the system, is exposed to harsh conditions such as high-temperature flue gas, acidic condensate and frequent opening and closing, and faces serious corrosion and sealing failure problems.

[0003] Marine desulfurization and denitrification systems operate in environments with multiple corrosive characteristics. On one hand, flue gas temperatures typically fluctuate between 150-350℃ and contain large amounts of acidic gases such as SO2, SO3, and NOx. These gases condense upon cooling, forming highly corrosive media like sulfuric acid and nitric acid, causing severe chemical corrosion to the valve body surface. On the other hand, systems using seawater desulfurization introduce high concentrations of chloride ions, further exacerbating the risk of pitting and crevice corrosion. Furthermore, the frequent start-ups and shutdowns of the system cause temperature cycling, generating alternating thermal stress on the valve body surface, accelerating the cracking and peeling of the protective coating.

[0004] Currently, valve body corrosion protection mainly employs fluoropolymer coating technology, such as polytetrafluoroethylene (PTFE) coatings, which possess excellent chemical corrosion resistance and low surface energy. However, traditional fluoropolymer coatings have the following shortcomings: First, the adhesion between the coating and the metal substrate is limited, making it prone to peeling under thermal cycling and mechanical stress; second, the significant difference in thermal expansion coefficients between the coating and the substrate generates substantial thermal stress at the interface during temperature fluctuations, leading to coating cracking; furthermore, conventional coating fillers mostly utilize commercially available inorganic powders, resulting in high costs and a lack of specific functional designs tailored to desulfurization and denitrification conditions.

[0005] Regarding the bonding between coatings and substrates, existing technologies typically employ sandblasting and primer to improve adhesion. However, this purely mechanical anchoring method is still insufficient for long-term service. While some research has attempted to prepare anodic oxide films on metal surfaces to enhance coating adhesion, these efforts have primarily focused on aluminum alloys. The preparation of microporous oxide films for commonly used valve body materials such as stainless steel, and their synergistic anchoring technology with coatings, remains immature.

[0006] In terms of valve body sealing surface treatment, traditional processes typically only involve grinding and polishing. This leaves the sealing surface directly exposed to corrosive media, making it prone to pitting corrosion and surface roughness deterioration after long-term operation, leading to decreased sealing performance. Simultaneously, the potential difference between the sealing surface and the mating valve seat due to material differences can trigger galvanic corrosion, further accelerating seal failure.

[0007] Furthermore, desulfurization and denitrification processes generate a large amount of solid waste, such as desulfurization gypsum, deactivated denitrification catalysts, and fly ash. The disposal of these solid wastes has become a significant issue in the environmental protection field. Currently, desulfurization gypsum is mainly used in building material production, and deactivated catalysts are mostly disposed of through landfill or metal recycling, but the degree of resource utilization is limited. If these solid wastes could be transformed into functional coating fillers, not only could coating costs be reduced, but the circular economy goal of "treating waste with waste" could also be achieved, resulting in significant environmental and economic benefits.

[0008] In summary, the development of a composite protection and high-precision sealing process for valve bodies in marine desulfurization and denitrification systems solves problems such as insufficient coating adhesion, thermal stress mismatch, and corrosion of the sealing surface. At the same time, it enables the resource utilization of desulfurization and denitrification solid waste. This has important practical significance for improving the service life of valve bodies, reducing maintenance costs, and promoting the development of green shipping. Summary of the Invention

[0009] To address the aforementioned problems in the existing technology, this invention provides a composite protection and high-precision sealing manufacturing process for valve bodies of marine desulfurization and denitrification systems.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: The composite protection and high-precision sealing manufacturing process for valve bodies of marine desulfurization and denitrification systems includes the following steps: S1. The surface of the valve body to be protected is degreased, cleaned, and roughened to obtain a roughened valve body surface. S2. Electrochemical oxidation treatment is performed on the non-sealing surface area of ​​the roughened valve body to form an oxide film layer with a micro-nano porous structure. S3. Coat the surface of the oxide film layer with an interface transition layer, so that the interface transition layer penetrates into the micro-nano pores to form an anchoring structure. S4. After shielding and protecting the sealing surface of the valve body, a composite protective coating is sprayed onto the surface of the interface transition layer; the composite protective coating includes at least two modified fluoropolymer layers, and the total mass fraction of fillers in each layer decreases from the inside to the outside; the modified fluoropolymer layer uses fluoropolymer as the matrix and calcined modified desulfurization gypsum, deactivated denitrification catalyst powder and activated modified red mud as fillers, with a mass ratio of (3-6):(1-3):(0.5-2); S5. Perform segmented heating and curing on the composite protective coating to remove the shielding protection of the sealing surface; S6. The sealing surface of the valve body is subjected to ultra-precision grinding and a corrosion-resistant film is deposited on the sealing surface.

[0011] Furthermore, the valve body substrate is duplex stainless steel, super austenitic stainless steel, or heat-resistant cast steel. Duplex stainless steel combines the advantages of both austenitic and ferritic materials, exhibiting high strength and excellent pitting corrosion resistance, making it suitable for desulfurization environments containing chloride ions. Super austenitic stainless steel contains a high level of molybdenum, providing good corrosion resistance to strong acid media such as sulfuric acid and nitric acid. Heat-resistant cast steel is suitable for high-temperature operating conditions.

[0012] Furthermore, the surface roughening treatment in S1 is sandblasting or shot peening, with the abrasive being alumina or silicon carbide with a particle size of 60-150 mesh, and the sandblasting pressure being 0.3-0.8 MPa. Sandblasting can form a uniform micro-rough structure on the valve body surface, increasing the surface area and mechanical anchoring points, providing a good adhesion foundation for subsequent oxide film layers and coatings. If the abrasive particle is too fine, the roughening effect will be insufficient; if the particle is too coarse, it may cause surface damage. If the sandblasting pressure is too low, the efficiency will be low; if the pressure is too high, it may cause deformation of the substrate.

[0013] Furthermore, prior to step S2, an activation treatment is performed on the roughened valve body surface using a 5-25% hydrochloric acid solution or a 2-10% hydrofluoric acid solution for 1-10 minutes. The purpose of this activation treatment is to remove the natural passivation film on the stainless steel surface, exposing a fresh metal surface so that subsequent electrochemical oxidation can proceed smoothly. Hydrochloric acid solution is suitable for the activation of general stainless steel, while hydrofluoric acid solution is more effective for molybdenum-containing stainless steel.

[0014] Furthermore, in step S2, the electrochemical oxidation treatment uses an electrolyte containing phosphoric acid or sulfuric acid, with a treatment voltage of 10-80V, a treatment time of 5-90min, and a treatment temperature of 5-40℃. The electrochemical oxidation treatment generates an oxide film with a micro-nano porous structure in situ on the valve body surface. This oxide film is generated in situ with the substrate, has a continuous interface with the substrate, and is firmly bonded, with a bonding strength far exceeding that of physically deposited coatings. The treatment voltage affects the growth rate and pore structure of the oxide film; too low a voltage results in slow film formation and low porosity, while too high a voltage may lead to film breakdown or surface ablation. The treatment time determines the film thickness; too short a time results in a thin film, while too long a time reduces efficiency and may cause the film to become brittle. The treatment temperature affects the activity of the electrolyte and the uniformity of the film; too high a temperature accelerates electrolyte decomposition, while too low a temperature decreases the reaction rate.

[0015] Furthermore, the pore size of the micro-nanopores is 10-300 nm, the oxide film thickness is 0.3-10 μm, and the porosity is 10-50%. The pore size and porosity of the micro-nanopores directly affect the penetration effect of the interface transition layer. If the pore size is too small, the interface transition layer will be difficult to penetrate; if the pore size is too large, the anchoring effect will be weakened. If the porosity is too low, there will be insufficient number of channels available for anchoring; if the porosity is too high, the mechanical strength of the oxide film layer will decrease.

[0016] Furthermore, the interfacial transition layer in S3 is a composite cured layer of silane coupling agent and nano-inorganic particles. One end of the silane coupling agent molecule contains an alkoxy group that can react with metal oxides, and the other end contains an organic functional group that can react with organic coatings, acting as a bridge connecting the inorganic oxide film layer and the organic coating. The nano-inorganic particles can fill the gaps between silane molecules, improving the density and mechanical strength of the interfacial transition layer. Simultaneously, the high specific surface area of ​​the nanoparticles enhances their adhesion to the coating.

[0017] Furthermore, the silane coupling agent includes one or more of fluorinated silanes, aminosilanes, and epoxysilanes, with a concentration of 0.5-8 wt%. Fluorinated silanes have good compatibility with fluoropolymer coatings and can improve interfacial adhesion; the amino groups of aminosilanes can react with a variety of organic groups, making them widely applicable; the epoxy groups of epoxysilanes have high reactivity and can form a cross-linked network structure. If the silane concentration is too low, the film formation will be discontinuous; if the concentration is too high, self-polymerization may occur, affecting the penetration effect.

[0018] Furthermore, the nano-inorganic particles are silicon dioxide, alumina, or titanium dioxide, with a particle size of 3-80 nm and a concentration of 0.2-6 wt%. Nano-silica has good dispersibility and reinforcing effect; nano-alumina has high hardness, which can improve the wear resistance of the interface layer; nano-titanium dioxide has certain photocatalytic activity, which can endow the interface layer with self-cleaning function. If the nanoparticle size is too large, it is difficult to penetrate into the micro-nano pores; if the particle size is too small, it is easy to agglomerate; if the concentration is too low, the reinforcing effect is not obvious; if the concentration is too high, it may affect the penetration and film formation of silane.

[0019] Furthermore, after coating, the mixture is cured at 60-200℃, with an interface transition layer thickness of 0.1-5μm. If the curing temperature is too low, the silane condensation reaction will be incomplete; if the curing temperature is too high, the silane may decompose. If the interface transition layer is too thin, the anchoring effect will be insufficient; if it is too thick, internal stress may be generated, leading to cracking.

[0020] Furthermore, the calcined modified desulfurized gypsum is prepared by calcining and dehydrating desulfurized gypsum at 120-200℃, followed by surface modification with a silane coupling agent, resulting in a particle size of 1-30 μm. The main component of the desulfurized gypsum is calcium sulfate dihydrate, which transforms into calcium sulfate hemihydrate after calcination and dehydration. This substance undergoes a hydration reaction upon contact with water or acidic media, expanding in volume to form a dense calcium sulfate layer, enabling self-sealing and repair of microcracks in the coating. If the calcination temperature is too low, dehydration will be incomplete; if the calcination temperature is too high, over-calcination may occur, forming anhydrous calcium sulfate and losing its hydration activity. Surface modification with a silane coupling agent can improve the compatibility and dispersibility of the desulfurized gypsum with the fluoropolymer matrix.

[0021] Furthermore, the deactivated denitrification catalyst micropowder is obtained by crushing and grinding the SCR denitrification catalyst, containing vanadium-tungsten-titanium oxide components, with a particle size of 1-15 μm. The main active component of the SCR denitrification catalyst is V2O5-WO3 / TiO2. Although the denitrification activity decreases after catalyst deactivation, it still retains some catalytic oxidation capacity. When microcracks appear in the coating and acidic gases infiltrate, the deactivated catalyst can catalytically oxidize SO2 to SO3. SO3 further reacts with water to generate sulfuric acid, which reacts with calcium ions in the desulfurization gypsum to generate calcium sulfate, achieving in-situ solidification and sealing. This synergistic effect of desulfurization gypsum and deactivated catalyst endows the coating with active protection and self-healing functions.

[0022] Furthermore, the activated and modified red mud is obtained by acid washing followed by calcination activation at 500-900℃, with a particle size of 1-25μm. Red mud is a solid waste generated during alumina production, mainly composed of iron oxide, alumina, and silicon dioxide. After acid washing and calcination activation modification, it exhibits excellent resistance to acid and alkali corrosion. Acid washing removes soluble alkali from the red mud, avoiding adverse effects on coating performance; calcination activation improves the activity of the red mud and its adhesion to the substrate. The activated and modified red mud plays a reinforcing and toughening role in the coating; its iron oxide and alumina components can form a corrosion-resistant skeleton, improving the mechanical strength and wear resistance of the coating.

[0023] Furthermore, the matrix resin of the modified fluoropolymer layer is polytetrafluoroethylene (PTFE) or meltable PTFE. PTFE possesses excellent chemical corrosion resistance, an extremely low coefficient of friction, and good high-temperature resistance, making it an ideal matrix material for protective coatings on valve bodies of marine desulfurization and denitrification systems. Meltable PTFE (PFA), while maintaining the excellent properties of PTFE, exhibits better melt flowability, which is beneficial for forming a dense coating structure.

[0024] Furthermore, the composite protective coating has a two- to four-layer gradient structure. The bottom modified fluoropolymer layer has a filler mass fraction of 25-55% and a thickness of 10-50 μm; the top modified fluoropolymer layer has a filler mass fraction of 5-25% and a thickness of 10-50 μm; the total thickness of the composite protective coating is 30-150 μm. The purpose of the gradient structure design is to achieve a gradual transition in the coefficient of thermal expansion of the coating, reducing thermal stress between the coating and the substrate, as well as between the layers. The bottom layer has a high filler content and a coefficient of thermal expansion close to that of a metal substrate, resulting in good thermal matching with the substrate; the top layer has a low filler content and a coefficient of thermal expansion close to that of pure fluoropolymer, resulting in a smooth and dense surface and excellent corrosion resistance.

[0025] Further, the segmented heating and curing in S5 includes: a first stage of heating to 100-180℃ at 0.5-5℃ / min and holding for 10-60min; a second stage of heating to 220-320℃ at 1-5℃ / min and holding for 10-50min; a third stage of heating to 340-390℃ at 0.5-4℃ / min and holding for 15-90min; followed by slow cooling to below 200℃ at a rate not exceeding 3℃ / min. The purpose of segmented heating and curing is to allow the solvent and moisture in the coating to gradually evaporate, and the fluoropolymer to gradually melt and level, ultimately forming a dense coating structure. The first stage mainly involves solvent evaporation and pre-drying; the second stage is coating pre-curing and residual solvent removal; the third stage is fluoropolymer melting and sintering to form a continuous and dense coating. Too rapid a heating rate will cause rapid solvent evaporation and bubble formation, while too slow a heating rate will result in low efficiency; too short a holding time will lead to incomplete curing, while too long a holding time may cause coating aging. Slow cooling can reduce thermal stress inside the coating and prevent cracking.

[0026] Furthermore, the ultra-precision grinding process in S6 employs cubic boron nitride or diamond abrasives with a grit size of W0.5-W10. Cubic boron nitride and diamond are superhard abrasives capable of efficiently and precisely machining stainless steel sealing surfaces. The grit size determines the surface roughness after machining; finer grit results in a smoother surface but lower machining efficiency, while coarser grit results in higher efficiency but poorer surface roughness. A grit size range of W0.5-W10 meets the precision requirements of the sealing surface.

[0027] Furthermore, the corrosion-resistant film is a chromium nitride film, a doped titanium oxide film, or a metal-doped diamond-like carbon film, with a thickness of 0.1-5 μm, deposited by magnetron sputtering or arc ion plating at a deposition temperature not exceeding 350℃. Chromium nitride films possess high hardness, good wear resistance, and corrosion resistance; doped titanium oxide films exhibit excellent chemical stability and certain electrical conductivity; metal-doped diamond-like carbon films combine the high hardness of diamond with the electrical conductivity of metals, wherein the metal can be one or more transition metals such as chromium, titanium, tungsten, and nickel. These films, deposited on the sealing surface, effectively protect the sealing surface from corrosive media. Simultaneously, by controlling the electrochemical properties of the film, the potential difference between the sealing surface and the mating valve seat is reduced, suppressing galvanic corrosion. A deposition temperature not exceeding 350℃ avoids adverse effects on the substrate performance.

[0028] The present invention also provides a marine desulfurization and denitrification system valve body prepared by the above-mentioned preparation process. The non-sealing surface area of ​​the valve body is provided with a micro-nano porous oxide film layer, an interface transition layer and a composite protective coating containing solid waste-derived functional filler in sequence from the inside to the outside. The interface transition layer is partially embedded in the micro-nano porous structure. The sealing surface of the valve body is provided with a corrosion-resistant film.

[0029] Compared with existing technologies, this invention provides a composite protection and high-precision sealing manufacturing process for valve bodies in marine desulfurization and denitrification systems, which has the following beneficial effects: (1) This invention forms a micro-nano porous oxide film layer on the surface of the valve body through electrochemical oxidation treatment, and allows the interface transition layer to penetrate into the micro-nano pores to form an anchoring structure, thus realizing the dual combination of chemical bonding and physical anchoring between the coating and the substrate; at the same time, the multi-layer coating structure design with a gradient decrease in filler content realizes the gradual transition of the coating thermal expansion coefficient from the substrate side to the surface side, effectively alleviating the thermal stress concentration between the coating and the substrate, improving the coating adhesion by 3-5 times compared with the traditional process, and increasing the thermal cycle life by more than 2 times, thus solving the problem of coating peeling failure under thermal cycling and acidic media.

[0030] (2) This invention creatively transforms solid waste from desulfurization and denitrification processes into functional fillers for coatings. Among them, calcined modified desulfurization gypsum has a self-sealing function when exposed to acid, and the deactivated denitrification catalyst retains some catalytic oxidation activity. The synergistic effect of the two can achieve active protection and self-repair of the coating. Activated modified red mud provides a corrosion-resistant skeleton and enhances toughness. The three solid waste fillers work together to give the coating excellent acid corrosion resistance. At the same time, the solid waste fillers are sourced from the desulfurization and denitrification site, which is inexpensive and has a stable supply. This achieves the circular economy goal of "treating waste with waste" and has significant economic and environmental benefits.

[0031] (3) The present invention deposits a corrosion-resistant film on the sealing surface, which not only improves the wear resistance and corrosion resistance of the sealing surface, but also reduces the potential difference between the sealing surface and the mating valve seat by regulating the electrochemical properties of the film, effectively inhibiting the occurrence of galvanic corrosion and significantly extending the service life of the sealing surface. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] I. Raw Material Sources and Pretreatment 1. Valve body base material The valve body substrate used in this embodiment of the invention is 2507 duplex stainless steel, 254SMO super austenitic stainless steel or ZG20CrMoV heat-resistant cast steel, and the valve body specification is DN100 butterfly valve body.

[0034] 2. Preparation of solid waste packing material (1) Preparation of calcined modified desulfurized gypsum The desulfurized gypsum produced by the wet flue gas desulfurization process is calcined at 120-200℃ for 2-4 hours to remove the water of crystallization and convert it into calcium sulfate hemihydrate. After cooling, 1-3% of the mass of the desulfurized gypsum is added with silane coupling agent KH-560, and the mixture is mixed in a high-speed mixer for 30 minutes to obtain calcined modified desulfurized gypsum with a particle size of 1-30μm.

[0035] (2) Preparation of deactivated denitration catalyst micro powder The deactivated catalyst (honeycomb V2O5-WO3 / TiO2 catalyst) replaced by the SCR denitrification system was coarsely crushed by a jaw crusher, finely ground by a ball mill, and passed through a 325-mesh sieve to obtain deactivated denitrification catalyst micro powder with a particle size of 1-15μm.

[0036] (3) Preparation of activated and modified red mud Red mud produced during alumina production was acid-washed with a 10% hydrochloric acid solution until the pH value reached 6-7. After washing with water and drying, it was calcined and activated at 700℃ for 2 hours. After cooling, it was ball-milled through a 400-mesh sieve to obtain activated modified red mud with a particle size of 1-25μm.

[0037] 3. Other raw materials Fluoropolymer dispersion: PTFE aqueous dispersion, solid content 60%; Silane coupling agents: KH-550 (aminosilane), KH-560 (epoxysilane), perfluorooctyltriethoxysilane (fluorinated silane); Nano-inorganic particles: Nano-silica, particle size 20nm, specific surface area 200m² 2 / g; all other reagents were commercially available. Example 1

[0038] The composite protection and high-precision sealing manufacturing process for valve bodies of marine desulfurization and denitrification systems includes the following steps: S1, Surface pretreatment The valve body of the DN100 butterfly valve is made of 2507 duplex stainless steel. First, it is ultrasonically cleaned with acetone for 15 minutes to remove surface oil stains. Then, it is sandblasted with 100-mesh alumina abrasive at a pressure of 0.5MPa to obtain a roughened valve body surface.

[0039] S2, electrochemical oxidation treatment The roughened valve body surface was activated with a 15% hydrochloric acid solution for 5 minutes, washed with water, and then placed in an electrolyte containing 10% phosphoric acid. The valve body was used as the anode and the stainless steel plate as the cathode. The treatment was carried out at 45V for 45 minutes, and the electrolyte temperature was controlled at 20℃. A microporous oxide film layer was formed in the non-sealing area. The microporous pore size was 100-180nm, the oxide film thickness was 5μm, and the porosity was 30%.

[0040] S3, Interface transition layer coating Preparation of the interface transition layer solution: 4 wt% KH-550 silane coupling agent and 3 wt% nano-silica (particle size 40 nm) were added to an ethanol-water mixed solvent (volume ratio 4:1), and stirred for hydrolysis for 2 hours. The valve body was immersed in the above solution and coated by pull coating, allowing the interface transition layer solution to penetrate into the micro- and nano-pores. After removal, it was cured at 130°C for 60 minutes to form an interface transition layer with a thickness of 2.5 μm.

[0041] S4, Composite Protective Coating Spraying Use ceramic fiber tape with a temperature resistance of 450℃ to cover and protect the sealing surface.

[0042] Preparation of the base coat: Mix the PTFE dispersion with the filler, which consists of calcined modified desulfurized gypsum, deactivated denitrification catalyst powder and activated modified red mud in a mass ratio of 5:2:1, with a total filler mass fraction of 40%. After stirring evenly, spray the mixture onto the surface of the interface transition layer with a coating thickness of 45μm.

[0043] Preparation of surface coating: Mix PTFE dispersion with filler, the filler composition is the same as the base layer, the total mass fraction of filler is 15%, spray it on the surface of the base layer, the coating thickness is 45μm.

[0044] The total thickness of the composite protective coating is 90μm.

[0045] S5, Segmented Temperature Curing The coated valve body was placed in a programmable oven for staged temperature curing: the first stage was heated to 140℃ at 2℃ / min and held for 30 minutes; the second stage was heated to 270℃ at 3℃ / min and held for 30 minutes; the third stage was heated to 365℃ at 2℃ / min and held for 45 minutes; then it was slowly cooled to below 200℃ at a rate of 2℃ / min, removed and allowed to cool naturally, and the protective covering on the sealing surface was removed.

[0046] S6. Sealing surface treatment The sealing surface was subjected to ultra-precision grinding using a W3 diamond abrasive tool; then, a chromium nitride thin film was deposited on the sealing surface using magnetron sputtering at a temperature of 280℃ and a film thickness of 2.5μm. Example 2

[0047] The only difference from Example 1 is that the filler mass ratio is calcined modified desulfurization gypsum: deactivated denitrification catalyst powder: activated modified red mud = 4:1.5:1. The remaining steps and parameters are exactly the same as in Example 1. Example 3

[0048] The only difference from Example 1 is that the composite protective coating has a three-layer gradient structure: the bottom layer has a total filler mass fraction of 45% and a thickness of 25 μm; the middle layer has a total filler mass fraction of 28% and a thickness of 25 μm; the top layer has a total filler mass fraction of 12% and a thickness of 25 μm; and the total thickness of the composite protective coating is 75 μm. The remaining steps and parameters are exactly the same as in Example 1. Example 4

[0049] The difference from Example 1 is that the following parameters take the lower limit value: The electrochemical oxidation treatment voltage was 15V, the treatment time was 80 minutes, the micro-nano pore size was 30-60nm, the oxide film thickness was 1μm, and the porosity was 15%. The concentration of silane coupling agent is 1 wt%, the concentration of nano-inorganic particles is 0.5 wt%, and the thickness of the interfacial transition layer is 0.5 μm; The filler mass ratio is 3:1:0.5, the total mass fraction of the bottom filler is 28%, the total mass fraction of the surface filler is 8%, and the total thickness of the composite protective coating is 35μm; The curing temperature for the third stage is 345℃.

[0050] The remaining steps are the same as in Example 1. Example 5

[0051] The difference from Example 1 is that the following parameters take the upper limit value: The electrochemical oxidation treatment voltage was 70V, the treatment time was 15 minutes, the micro-nano pore size was 200-280nm, the oxide film thickness was 8μm, and the porosity was 45%. The concentration of silane coupling agent is 7 wt%, the concentration of nano-inorganic particles is 5 wt%, and the thickness of the interfacial transition layer is 4.5 μm; The filler mass ratio is 6:3:1.8, the total mass fraction of the bottom filler is 52%, the total mass fraction of the surface filler is 22%, and the total thickness of the composite protective coating is 140μm; The curing temperature for the third stage is 385℃.

[0052] The remaining steps are the same as in Example 1. Comparative Example 1

[0053] The difference from Example 1 is that the S2 electrochemical oxidation treatment step is omitted, and an interface transition layer and a composite protective coating are directly applied to the roughened valve body surface after sandblasting. The remaining steps are the same as in Example 1. Comparative Example 2

[0054] The difference from Example 1 is that the S3 interface transition layer coating step is omitted, and the composite protective coating is directly sprayed after the electrochemical oxidation treatment. The remaining steps are the same as in Example 1. Comparative Example 3

[0055] The difference from Example 1 is that the composite protective coating uses a single-layer uniform structure instead of a double-layer gradient structure, the total coating thickness remains unchanged at 90 μm, the filler system and ratio are the same as in Example 1, and the total mass fraction of filler is 27.5% (consistent with the equivalent average filler content of the double-layer gradient structure in Example 1). The remaining steps are the same as in Example 1. Comparative Example 4

[0056] The difference from Example 1 is that the filler used is a conventional commercial filler, composed of silicon carbide micro powder, alumina micro powder and graphite powder in a mass ratio of 5:2:1. The total mass fraction of the filler and the coating structure are the same as in Example 1. The remaining steps are the same as in Example 1. Performance testing

[0057] The valve bodies prepared in the examples and comparative examples were subjected to the following performance tests: 1. Coating adhesion test: The adhesion between the coating and the substrate is determined by pull-out method according to GB / T 5210-2006 "Paints and Varnishes - Adhesion Test".

[0058] 2. Thermal cycling test: Referring to GB / T 1735-2009 "Determination of heat resistance of paints and varnishes", the valve body was placed in a high and low temperature cycling test chamber and tested according to the cycle system of "room temperature → 250℃ (holding for 30 min) → room temperature (holding for 30 min)". The number of cycles when the coating cracked or peeled off was recorded.

[0059] 3. Acid corrosion resistance test: Refer to GB / T 9274-1988 "Determination of resistance to liquid media for paints and varnishes", immerse the valve body in a sulfuric acid solution with a pH of 2 at a temperature of 50℃, and after soaking for 500 hours, evaluate the corrosion level of the coating according to GB / T 1766-2008. Test Results Table 1. Performance test results of the examples and comparative examples:

[0060] .

[0061] Results Analysis As shown in Table 1, Example 1, as the optimal example, exhibits the best performance across all indicators: coating adhesion reaches 18.5 MPa, thermal cycling count reaches 520 cycles, and acid corrosion resistance is grade 0. Example 2 changed the filler ratio, and Example 3 adopted a three-layer gradient structure; both showed performance close to Example 1, indicating that the process of this invention has a good process window and adaptability. Examples 4 and 5 used lower and upper limit parameters, respectively, resulting in a slight decrease in performance, but still superior to the comparative example. Example 4, due to its smaller micro-nano pore size and thinner coating, exhibited relatively weaker anchoring effect and protective capability; Example 5, due to its larger micro-nano pore size and thicker coating, showed relatively higher internal stress.

[0062] Comparative Example 1 omitted the electrochemical oxidation treatment step, and the coating adhesion was only 5.2 MPa, a decrease of 72% compared to Example 1. The number of thermal cycles was only 180, a decrease of 65% compared to Example 1, indicating that the micro-nano pore anchoring structure is a key technology for achieving high coating adhesion. Comparative Example 2 omitted the interface transition layer, and the coating adhesion was 8.6 MPa, a decrease of 54% compared to Example 1, indicating that the interface transition layer plays an important bridging role between the anchoring structure and the coating. Comparative Example 3 changed the double-layer gradient structure to a single-layer uniform structure, and the number of thermal cycles was 220, a decrease of about 58% compared to Example 1. This indicates that the gradient structure design, through the synergistic mechanism of providing thermal expansion transition with high filler content in the bottom layer and ensuring density with low filler content in the surface layer, has a significant effect on alleviating thermal stress and improving thermal cycle life. Comparative Example 4 used conventional filler instead of solid waste-derived filler, and the acid corrosion resistance level was 3, a significant decrease compared to Example 1, indicating that the solid waste-derived functional filler of the present invention has unique acid corrosion resistance performance, which cannot be achieved by conventional fillers.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A composite protection and high-precision sealing manufacturing process for valve bodies of marine desulfurization and denitrification systems, characterized in that, Includes the following steps: S1. The surface of the valve body to be protected is degreased, cleaned, and roughened to obtain a roughened valve body surface. S2. Electrochemical oxidation treatment is performed on the non-sealing surface area of ​​the roughened valve body to form an oxide film layer with a micro-nano porous structure. S3. Coat the surface of the oxide film layer with an interface transition layer, so that the interface transition layer penetrates into the micro-nano pores to form an anchoring structure. S4. After shielding and protecting the sealing surface of the valve body, a composite protective coating is sprayed onto the surface of the interface transition layer; the composite protective coating includes at least two modified fluoropolymer layers, and the total mass fraction of fillers in each layer decreases from the inside to the outside; the modified fluoropolymer layer uses fluoropolymer as the matrix and calcined modified desulfurization gypsum, deactivated denitrification catalyst powder and activated modified red mud as fillers, with a mass ratio of (3-6):(1-3):(0.5-2); S5. Perform segmented heating and curing on the composite protective coating to remove the shielding protection of the sealing surface; S6. The sealing surface of the valve body is subjected to ultra-precision grinding and a corrosion-resistant film is deposited on the sealing surface.

2. The preparation process according to claim 1, characterized in that, The valve body substrate is made of duplex stainless steel, super austenitic stainless steel, or heat-resistant cast steel.

3. The preparation process according to claim 1, characterized in that, The surface roughening treatment in S1 is sandblasting or shot peening, with the sandblasting abrasive being alumina or silicon carbide with a particle size of 60-150 mesh, and the sandblasting pressure being 0.3-0.8 MPa; before S2, the roughened valve body surface is further activated by treating it with a hydrochloric acid solution with a mass fraction of 5-25% or a hydrofluoric acid solution with a mass fraction of 2-10% for 1-10 minutes.

4. The preparation process according to claim 1, characterized in that, The electrochemical oxidation treatment in S2 uses an electrolyte containing phosphoric acid or sulfuric acid, with a treatment voltage of 10-80V, a treatment time of 5-90min, and a treatment temperature of 5-40℃. The micro-nano pores formed by the electrochemical oxidation treatment have a pore size of 10-300nm, an oxide film thickness of 0.3-10μm, and a porosity of 10-50%.

5. The preparation process according to claim 1, characterized in that, The interface transition layer in S3 is a composite cured layer of silane coupling agent and nano-inorganic particles; the silane coupling agent includes one or more of fluorinated silane, aminosilane, and epoxysilane, with a concentration of 0.5-8wt%; the nano-inorganic particles are silicon dioxide, aluminum oxide, or titanium oxide, with a particle size of 3-80nm and a concentration of 0.2-6wt%; after coating, it is cured at 60-200℃, and the thickness of the interface transition layer is 0.1-5μm.

6. The preparation process according to claim 1, characterized in that, The calcined modified desulfurized gypsum is obtained by calcining and dehydrating desulfurized gypsum at 120-200℃ and then surface-modifying it with a silane coupling agent, with a particle size of 1-30μm; the deactivated denitrification catalyst micro powder is obtained by crushing and grinding SCR denitrification catalyst, containing vanadium, tungsten, and titanium oxide components, with a particle size of 1-15μm; the activated modified red mud is obtained by acid washing of red mud and then calcining and activating it at 500-900℃, with a particle size of 1-25μm.

7. The preparation process according to claim 1, characterized in that, The base resin of the modified fluoropolymer layer is polytetrafluoroethylene or fusible polytetrafluoroethylene; the composite protective coating has a two- to four-layer gradient structure, the filler mass fraction of the bottom modified fluoropolymer layer is 25-55%, and the thickness is 10-50μm; the filler mass fraction of the top modified fluoropolymer layer is 5-25%, and the thickness is 10-50μm; the total thickness of the composite protective coating is 30-150μm.

8. The preparation process according to claim 1, characterized in that, The segmented heating and curing process in S5 includes: a first stage where the temperature is increased to 100-180℃ at a rate of 0.5-5℃ / min and held for 10-60 min; a second stage where the temperature is increased to 220-320℃ at a rate of 1-5℃ / min and held for 10-50 min; a third stage where the temperature is increased to 340-390℃ at a rate of 0.5-4℃ / min and held for 15-90 min; and then slowly cooled to below 200℃ at a rate not exceeding 3℃ / min.

9. The preparation process according to claim 1, characterized in that, The ultra-precision grinding process in S6 uses cubic boron nitride or diamond abrasives with a particle size of W0.5-W10; the corrosion-resistant film is a chromium nitride film, a doped titanium oxide film, or a metal-doped diamond film with a thickness of 0.1-5μm, deposited by magnetron sputtering or arc ion plating, with a deposition temperature not exceeding 350℃.

10. A marine desulfurization and denitrification system valve body prepared using the preparation process described in any one of claims 1-9, characterized in that, The non-sealing surface of the valve body is provided with a microporous oxide film layer, an interface transition layer and a composite protective coating containing solid waste-derived functional filler in sequence from the inside to the outside. The interface transition layer is partially embedded in the microporous structure. The sealing surface of the valve body is provided with a corrosion-resistant film.