Corrosion-resistant valve casting process for improving coating attaching and sealing performance

Abstract

The invention relates to the technical field of valves, and discloses a corrosion-resistant valve casting process for improving the fitting and sealing performance of a coating, and the corrosion-resistant valve casting process comprises the steps of S1, raw material selection and pretreatment, S2, casting mold manufacturing, S3, valve casting, S4, surface treatment, S5, coating preparation and spraying, S6, sealing rubber strip installation and S7, quality detection. According to the method, the corrosion resistance is remarkably improved, high-performance austenitic stainless steel containing 22-25% of chromium, 12-15% of nickel and 3-5% of molybdenum is selected as a main body material of the valve, the valve can show excellent corrosion resistance in different corrosion environments by accurately controlling the content of all alloy elements, the chromium element forms a compact oxidation film on the surface of the valve, and the corrosion resistance of the valve is improved. The invasion of external corrosive media is effectively prevented; the nickel element enhances the stability of the alloy and improves the corrosion resistance, and the molybdenum element further enhances the resistance to corrosive ions such as chloride ions.

Description

Technical Field

[0001] The invention relates to the technical field of valves, and in particular to a corrosion-resistant valve casting process for improving coating adhesion and sealing performance. Background Art

[0002] In many industrial fields, valves are key components for controlling the flow of fluid media, and their performance directly affects the safety and stable operation of the entire system. With the continuous development of industrial production, higher requirements are placed on the corrosion resistance, coating fit and sealing performance of valves.

[0003] Corrosive media are widely present in the chemical, petroleum, and marine industries. The corrosion resistance of valves produced by traditional valve casting processes is often difficult to meet the needs of long-term operation in highly corrosive environments. Ordinary metal materials are prone to corrosion and rust under the erosion of corrosive media, which not only shortens the service life of the valve, but also may cause safety hazards such as leakage. Some valves cast with ordinary stainless steel materials are prone to pitting and crevice corrosion in media containing chloride ions, which seriously affects the normal use of the valve.

[0004] Coating technology has been widely used in valve surface protection, but the adhesion between the coating and the valve substrate has always been a problem that has plagued the industry. The existing coating process is insufficient in the bonding strength between the coating and the substrate, which causes the coating to peel off and peel during use, and cannot effectively play the protective role of the coating. In some high-temperature and high-pressure working conditions, the adhesion problem of the coating is more prominent, which greatly reduces the protective effect of the valve.

[0005] The sealing performance of valves is crucial to prevent media leakage. However, traditional sealing structures and materials are difficult to ensure good sealing effects when facing complex working conditions. For example, in an environment with large temperature and pressure fluctuations, ordinary sealing strips are prone to aging and deformation, resulting in reduced sealing performance, which in turn causes media leakage, which not only wastes resources but may also pollute the environment.

[0006] The current valve casting process has many deficiencies in terms of corrosion resistance, coating adhesion and sealing performance in the face of increasingly stringent industrial demands. A new process is urgently needed to solve these problems. Summary of the invention

[0007] 1. Technical issues to be solved

[0008] In view of the deficiencies of the prior art, the present invention provides a corrosion-resistant valve casting process for improving the coating adhesion and sealing performance, which has the advantages of optimizing the coating adhesion effect, etc., and solves the problem that the existing coating process has deficiencies in the bonding force between the coating and the substrate, resulting in phenomena such as peeling and flaking of the coating during use, and the coating cannot effectively play its protective role.

[0009] (II) Technical Solution

[0010] To achieve the above object of optimizing the coating adhesion effect, the present invention provides the following technical solution: A corrosion-resistant valve casting process for improving the coating adhesion and sealing performance, including S1 raw material selection and pretreatment, S2 casting mold making, S3 valve casting process, S4 surface treatment, S5 coating preparation and spraying, S6 sealing strip installation, and S7 quality inspection. The S1 raw material selection and pretreatment:

[0011] Metal material: Select a high-performance austenitic stainless steel containing 22-25% chromium, 12-15% nickel, and 3-5% molybdenum as the valve body material. This material, while ensuring mechanical strength, has excellent corrosion resistance due to the synergistic effect of chromium, nickel, and molybdenum, and can effectively resist the erosion of various corrosive media. The purchased steel needs to be subjected to spectral analysis to ensure that the content of each element is within the specified range, and the deviation is controlled within ±0.5%;

[0012] Coating material: Adopt a nano-ceramic coating material, the main components of which are titanium dioxide (TiO2) and silicon dioxide (SiO2), where the content of TiO2 is 40-45%, the content of SiO2 is 50-55%, and 3-5% of nano-level zirconia (ZrO2) is added as a reinforcing agent. These components are specially proportioned to significantly improve the adhesion, hardness, and corrosion resistance of the coating. Before use, the coating material is dried in an oven at 120-150 °C for 2-3 hours to remove moisture and avoid affecting the coating quality;

[0013] Sealing material: Select fluororubber with a Shore hardness of 70-80 HA, a tensile strength of not less than 12 MPa, and an elongation at break of not less than 300% as the sealing strip material. Its excellent chemical corrosion resistance, high temperature resistance, and good elasticity can ensure the sealing performance of the valve under different working conditions. The sealing strip needs to be subjected to surface grinding treatment before use, and the roughness is controlled at Ra0.8-1.6 μm to enhance the fit with the valve;

[0014] S2 casting mold making includes S201 mold design and S201 mold design;

[0015] S3 valve casting process includes S301 melting, S302 pouring, and S303 cooling;

[0016] The S4 surface treatment includes S401 machining, S402 cleaning and degreasing, and S403 surface activation;

[0017] The S5 coating preparation and spraying includes S501 coating material formulation, S502 spraying, and S503 curing;

[0018] The S6 sealing strip installation includes S601 strip pretreatment and S602 installation;

[0019] The S7 quality inspection includes S701 appearance inspection, S702 coating performance inspection, and S703 sealing performance inspection.

[0020] Preferably, for the S201 mold design: Use professional CAD / CAM software for three-dimensional mold design. According to the structure and size requirements of the valve, accurately design the cavity, core, runner, and riser parts of the mold to ensure that the dimensional accuracy of the mold is within ±0.05 mm, and avoid valve size deviation caused by mold accuracy problems;

[0021] The S202 mold processing: Select H13 hot work die steel as the mold material, which has good hot strength, thermal fatigue performance, and wear resistance. Use a CNC machining center for mold processing. During the processing, the cutting speed is controlled at 80 - 120 m / min, the feed rate is 0.1 - 0.2 mm / r, and the cutting depth is 0.5 - 1.0 mm. After processing, perform nitriding treatment on the mold surface. The nitriding temperature is 550 - 580 °C, and the nitriding time is 8 - 10 hours to form a nitrided layer with high hardness and good wear resistance on the mold surface, improving the service life of the mold.

[0022] Preferably, for the S301 melting: Put the selected stainless steel material into an intermediate frequency induction furnace for melting. During the melting process, control the temperature in the furnace at 1550 - 1600 °C, and add appropriate amounts of deoxidizer and refining agent, such as calcium silicate alloy (the addition amount is 0.1 - 0.2% of the mass of the molten metal), aluminum block (the addition amount is 0.05 - 0.1% of the mass of the molten metal), to remove impurities and gases in the molten metal, improve the purity of the molten metal. At the same time, stir the molten metal through an electromagnetic stirring device, and the stirring frequency is 30 - 50 Hz to make the composition of the molten metal uniform and the temperature distribution consistent.

[0023] Preferably, for the S302 pouring: When the molten metal reaches the appropriate pouring temperature (1500 - 1530 °C), use a bottom gating system for pouring, control the pouring speed to make the molten metal fill the mold cavity within 3 - 5 seconds, and avoid turbulence and oxidation of the molten metal. During the pouring process, introduce an appropriate amount of argon gas into the cavity, and the argon gas flow rate is 5 - 8 L / min to protect the molten metal from oxidation.

[0024] Preferably, for the cooling in S303: After pouring is completed, the valve is cooled in the mold. First, the water-cooling method is adopted, and the cooling rate is controlled at 5-10 °C / s to rapidly solidify the surface of the valve and form a certain strength. When the surface temperature of the valve drops to 800-900 °C, it is changed to air-cooling, and the cooling rate is controlled at 1-2 °C / s to reduce the stress concentration inside the valve and prevent crack defects.

[0025] Preferably, for the machining in S401: The cast valve is machined to remove the oxide scale and sand particle impurities on the surface and ensure the dimensional accuracy and surface roughness of the valve. The inner and outer surfaces of the valve are turned by a CNC lathe. The turning speed is 150-200 m / min, the feed rate is 0.1-0.2 mm / r, and the cutting depth is 0.2-0.5 mm. The surface roughness of the machined valve is controlled at Ra3.2-6.3 μm.

[0026] Preferably, for the cleaning and degreasing in S402: The machined valve is put into an alkaline cleaning solution for cleaning and degreasing treatment. The main components of the cleaning solution include 5-8% sodium hydroxide (NaOH), 3-5% sodium carbonate (Na2CO3), and 2-3% sodium phosphate (Na3PO4). The cleaning temperature is 60-70 °C, and the cleaning time is 15-20 minutes. Through cleaning and degreasing, the oil stains and impurities on the valve surface are removed, providing a good basis for subsequent coating treatment;

[0027] For the surface activation in S403: The chemical activation method is used to activate the valve surface. The valve is immersed in an activation solution containing 1-2% hydrofluoric acid (HF) and 3-5% nitric acid (HNO3) for 5-10 minutes. After activation treatment, a microscopically rough structure is formed on the valve surface, increasing the contact area between the coating and the valve surface and improving the adhesion of the coating.

[0028] Preferably, for the coating material preparation in S501: According to the selected coating material formula above, the TiO2, SiO2, and ZrO2 raw materials are fully mixed in a high-speed mixer. The stirring speed is 1000-1500 r / min, and the stirring time is 30-45 minutes to ensure the uniformity of the coating material. Then, an appropriate amount of organic binder and diluent are added to prepare a coating suitable for spraying. The addition amount of the organic binder is 5-8% of the total mass of the coating material, and the addition amount of the diluent is adjusted according to the viscosity of the coating to control the viscosity of the coating at 15-20 s (measured by a coating-4 cup viscometer);

[0029] S502 Spraying: Use a high-pressure airless spraying equipment to spray the coating on the valve surface. The spraying pressure is controlled at 15 - 20 MPa, the distance between the spray gun and the valve surface is maintained at 200 - 300 mm, the spraying angle is 90°. During the spraying process, follow the sequence of inner surface first and then outer surface. The thickness of each coating layer is controlled at 50 - 80 μm, and a total of 3 - 4 layers are sprayed, with the total coating thickness reaching 150 - 250 μm;

[0030] S503 Curing: After spraying, put the valve into a high-temperature curing furnace for curing treatment. The curing temperature is 350 - 400 °C, the heating rate is controlled at 5 - 10 °C / min, and the holding time is 2 - 3 hours. After curing, cool it in the furnace to room temperature to fully cure the coating and form a hard and dense protective film.

[0031] Preferably, for the S601 rubber strip pretreatment: Cut the sealing rubber strip according to the size of the valve sealing groove. The length of the cut rubber strip is slightly longer than the circumference of the sealing groove by 1 - 2 mm to ensure the sealing effect after the rubber strip is installed. Then, bevel the two ends of the rubber strip, and the bevel angle is 30 - 45° to enable better butt joint of the rubber strip during installation;

[0032] S602 Installation: Apply a layer of sealant evenly in the sealing groove. The application amount of the sealant is 0.5 - 1.0 g / m 2 , and slowly embed the pretreated sealing rubber strip into the sealing groove to ensure that the rubber strip fits tightly with the sealing groove without air bubbles and gaps. During the installation process, use a special tool to compact the rubber strip to make its fit degree with the sealing groove reach more than 95%.

[0033] Preferably, for the S701 Appearance inspection: Conduct a comprehensive inspection on the appearance of the valve. Observe whether there are sand holes, air holes, crack defects on the valve surface, whether the coating is uniform and smooth, and whether there are peeling and blistering phenomena. Adopt a combination of visual inspection and auxiliary inspection with a 5 - 10 times magnifying glass to ensure that the appearance quality meets the standard requirements;

[0034] S702 Coating performance inspection: Use a coating thickness gauge to detect the thickness of the coating to ensure that the coating thickness is within the specified range. Adopt the cross-cut test method to detect the adhesion of the coating, and conduct the test according to the GB / T 9286 - 1998 standard. The coating adhesion should reach level 0 - 1. Detect the hardness of the coating through a hardness tester, and the coating hardness should not be lower than 500 HV;

[0035] S703 Sealing performance inspection: Adopt the pressure test method to detect the sealing performance of the valve. Install the valve on the test device, introduce the medium into the valve, gradually increase the pressure to 1.1 times the nominal pressure of the valve, and the pressure holding time is 10 - 15 minutes. Observe whether there is any leakage at the sealing part of the valve. If there is no leakage during the pressure holding period, the sealing performance of the valve is qualified.

[0036] (III) Beneficial effects

[0037] Compared with the prior art, the present invention provides a corrosion-resistant valve casting process for improving the coating adhesion and sealing performance, having the following beneficial effects:

[0038] 1. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance significantly enhances the corrosion resistance: This process selects a high-performance austenitic stainless steel containing 22-25% chromium, 12-15% nickel, and 3-5% molybdenum as the main valve material. By precisely controlling the content of each alloy element, it can exhibit excellent corrosion resistance in different corrosion environments. The chromium element forms a dense oxide film on the valve surface, effectively preventing the intrusion of external corrosive media; the nickel element enhances the stability of the alloy and improves the corrosion resistance; the molybdenum element further enhances the resistance to corrosive ions such as chloride ions. In chemical production, the valves manufactured by this process have a service life 2-3 times longer than those manufactured by traditional processes in corrosive media containing a large amount of chloride ions, greatly reducing the equipment maintenance cost and replacement frequency.

[0039] 2. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance optimizes the coating adhesion effect: It uses a nano-ceramic coating material and strictly pre-treats the valve surface, including steps such as cleaning and degreasing, surface activation, etc., effectively improving the adhesion between the coating and the valve substrate. The nano-scale coating material can better fill the micro-pores on the substrate surface, increasing the contact area between the coating and the substrate. Combining with special spraying processes and curing conditions, a strong chemical bond is formed between the coating and the substrate. After testing, the coating adhesion prepared by this process reaches level 0-1, far higher than the adhesion level of coatings by traditional processes, effectively avoiding the peeling and flaking of the coating during use and ensuring the long-term protection effect of the coating.

[0040] 3. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance enhances the sealing performance: It selects fluororubber with a Shore hardness of 70-80 HA, a tensile strength of not less than 12 MPa, and an elongation at break of not less than 300% as the sealing strip material, and optimizes the special pre-treatment and installation process of the sealing strip. The excellent elasticity and chemical corrosion resistance of fluororubber enable it to maintain good sealing performance under different working conditions. The special installation process ensures that the sealing strip fits tightly with the valve sealing groove, with a fitting degree of more than 95%, effectively preventing medium leakage. Under high-temperature, high-pressure and corrosive medium working conditions, the valves manufactured by this process have stable and reliable sealing performance, and the leakage rate is far lower than the industry standard, effectively ensuring the safety and environmental protection requirements of industrial production.

[0041] 4. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance, which improves product quality and stability: from the strict screening and pretreatment of raw materials, to the high-precision production of casting molds, and then to the precise control and quality inspection of each production link, this process has established a complete quality control system. By precisely controlling key parameters such as melting temperature, pouring speed, and cooling method, the defects inside the valve are effectively reduced, and the product quality and stability are improved. According to statistics, the qualified rate of the valves produced by this process reaches over 98%, which is 10 - 15 percentage points higher than that of the traditional process, providing more reliable valve products for industrial production. Detailed implementation manners

[0042] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0043] S1 Raw material selection and pretreatment:

[0044] Metal materials: Select high-performance austenitic stainless steel containing 22 - 25% chromium, 12 - 15% nickel, and 3 - 5% molybdenum as the main material for the valve body. While ensuring mechanical strength, this material has excellent corrosion resistance due to the synergistic effect of chromium, nickel, and molybdenum, and can effectively resist the erosion of various corrosive media. The steel purchased needs to be subjected to spectral analysis to ensure that the content of each element is within the specified range, and the deviation is controlled within ±0.5%;

[0045] Coating materials: Adopt nano-ceramic coating materials, the main components of which are titanium dioxide (TiO2) and silicon dioxide (SiO2), with the TiO2 content being 40 - 45% and the SiO2 content being 50 - 55%, and 3 - 5% of nano-level zirconia (ZrO2) is added as a reinforcing agent. These components are specially proportioned to significantly improve the adhesion, hardness, and corrosion resistance of the coating. Before use, the coating materials are dried in an oven at 120 - 150 °C for 2 - 3 hours to remove moisture and avoid affecting the coating quality;

[0046] Sealing materials: Select fluororubber with a Shore hardness of 70 - 80 HA, a tensile strength of not less than 12 MPa, and an elongation at break of not less than 300% as the sealing strip material. Its excellent chemical corrosion resistance, high temperature resistance, and good elasticity can ensure the sealing performance of the valve under different working conditions. Before use, the sealing strip needs to be surface polished, and the roughness is controlled at Ra0.8 - 1.6 μm to enhance the fit with the valve;

[0047] S2 Foundry Mold Making:

[0048] S201 Mold Design: Use professional CAD / CAM software for 3D mold design. According to the structure and size requirements of the valve, accurately design the cavity, core, runner, and riser parts of the mold to ensure that the dimensional accuracy of the mold is within ±0.05 mm, and avoid valve size deviation caused by mold accuracy problems.

[0049] S202 Mold Machining: Select H13 hot work die steel as the mold material, which has good hot strength, thermal fatigue performance, and wear resistance. Use a CNC machining center for mold machining. During the machining process, control the cutting speed at 80 - 120 m / min, the feed rate at 0.1 - 0.2 mm / r, and the cutting depth at 0.5 - 1.0 mm. After machining, perform nitriding treatment on the mold surface. The nitriding temperature is 550 - 580 °C, and the nitriding time is 8 - 10 hours to form a nitrided layer with high hardness and good wear resistance on the mold surface, thereby increasing the service life of the mold.

[0050] S3 Valve Casting Process:

[0051] S301 Melting: Put the selected stainless steel material into an intermediate frequency induction furnace for melting. During the melting process, control the temperature in the furnace at 1550 - 1600 °C, and add appropriate amounts of deoxidizer and refining agent, such as calcium silicate alloy (the addition amount is 0.1 - 0.2% of the mass of the molten metal) and aluminum block (the addition amount is 0.05 - 0.1% of the mass of the molten metal), to remove impurities and gases in the molten metal and improve the purity of the molten metal. At the same time, stir the molten metal through an electromagnetic stirring device with a stirring frequency of 30 - 50 Hz to make the composition of the molten metal uniform and the temperature distribution consistent.

[0052] S302 Pouring: When the molten metal reaches the appropriate pouring temperature (1500 - 1530 °C), use a bottom - pouring gating system for pouring, control the pouring speed, and make the molten metal fill the mold cavity within 3 - 5 seconds to avoid turbulence and oxidation of the molten metal. During the pouring process, introduce an appropriate amount of argon gas into the cavity, with an argon gas flow rate of 5 - 8 L / min, to protect the molten metal from oxidation.

[0053] S303 Cooling: After pouring, the valve cools in the mold. First, use the water - cooling method with a cooling speed controlled at 5 - 10 °C / s to quickly solidify the valve surface and form a certain strength. When the valve surface temperature drops to 800 - 900 °C, switch to air - cooling with a cooling speed controlled at 1 - 2 °C / s to reduce stress concentration inside the valve and prevent crack defects.

[0054] S4 Surface Treatment:

[0055] S401 Machining: The cast valve is machined to remove the oxide scale and sand impurities on the surface, and ensure the dimensional accuracy and surface roughness of the valve. A CNC lathe is used to turn the inner and outer surfaces of the valve. The turning speed is 150 - 200 m / min, the feed rate is 0.1 - 0.2 mm / r, and the cutting depth is 0.2 - 0.5 mm. The surface roughness of the machined valve is controlled within Ra3.2 - 6.3 μm.

[0056] S402 Cleaning and Degreasing: The machined valve is put into an alkaline cleaning solution for cleaning and degreasing treatment. The main components of the cleaning solution include 5 - 8% sodium hydroxide (NaOH), 3 - 5% sodium carbonate (Na2CO3), and 2 - 3% sodium phosphate (Na3PO4). The cleaning temperature is 60 - 70 °C, and the cleaning time is 15 - 20 minutes. Through cleaning and degreasing, the oil stains and impurities on the valve surface are removed, providing a good foundation for subsequent coating treatment.

[0057] S403 Surface Activation: The chemical activation method is used to activate the valve surface. The valve is immersed in an activation solution containing 1 - 2% hydrofluoric acid (HF) and 3 - 5% nitric acid (HNO3) for 5 - 10 minutes. After activation treatment, a microscopically rough structure is formed on the valve surface, increasing the contact area between the coating and the valve surface and improving the adhesion of the coating.

[0058] S5 Coating Preparation and Spraying:

[0059] S501 Coating Material Preparation: According to the selected coating material formula above, the TiO2, SiO2, and ZrO2 raw materials are fully mixed in a high-speed mixer. The mixing speed is 1000 - 1500 r / min, and the mixing time is 30 - 45 minutes to ensure the uniformity of the coating material. Then, an appropriate amount of organic binder and diluent are added to prepare a coating suitable for spraying. The addition amount of the organic binder is 5 - 8% of the total mass of the coating material, and the addition amount of the diluent is adjusted according to the viscosity of the coating to control the viscosity of the coating within 15 - 20 s (measured by a coating - 4 cup viscometer).

[0060] S502 Spraying: A high - pressure airless spraying device is used to spray the coating on the valve surface. The spraying pressure is controlled at 15 - 20 MPa, the distance between the spray gun and the valve surface is maintained at 200 - 300 mm, and the spraying angle is 90°. During the spraying process, it is carried out in the order of the inner surface first and then the outer surface. The thickness of each layer of the coating is controlled at 50 - 80 μm, and a total of 3 - 4 layers are sprayed, with the total coating thickness reaching 150 - 250 μm.

[0061] S503 Curing: After spraying is completed, place the valve in a high-temperature curing furnace for curing. The curing temperature is 350 - 400 °C, the heating rate is controlled at 5 - 10 °C / min, and the holding time is 2 - 3 hours. After curing is completed, cool it in the furnace to room temperature to fully cure the coating and form a hard and dense protective film;

[0062] S6 Sealing Strip Installation:

[0063] S601 Sealing Strip Pretreatment: Cut the sealing strip according to the size of the valve sealing groove. The length of the cut strip is slightly longer than the circumference of the sealing groove by 1 - 2 mm to ensure the sealing effect after installation. Then, bevel the two ends of the strip. The bevel angle is 30 - 45° to enable better butt joint during installation;

[0064] S602 Installation: Apply a layer of sealant evenly in the sealing groove. The application amount of the sealant is 0.5 - 1.0 g / m 2 , slowly embed the pretreated sealing strip into the sealing groove, ensuring that the strip fits tightly with the sealing groove without air bubbles and gaps. During installation, use a special tool to compact the strip to make its fit with the sealing groove reach over 95%;

[0065] S7 Quality Inspection:

[0066] S701 Appearance Inspection: Conduct a comprehensive inspection of the valve's appearance. Observe whether there are sand holes, air holes, crack defects on the valve surface, whether the coating is uniform and smooth, and whether there are peeling and blistering phenomena. Use a combination of visual inspection and 5 - 10 times magnifying glass assisted inspection to ensure that the appearance quality meets the standard requirements;

[0067] S702 Coating Performance Inspection: Use a coating thickness gauge to detect the thickness of the coating to ensure that the coating thickness is within the specified range. Use the cross - cut test method to detect the adhesion of the coating, and conduct tests according to the GB / T 9286 - 1998 standard. The coating adhesion should reach level 0 - 1. Detect the hardness of the coating through a hardness tester, and the coating hardness should not be lower than 500 HV;

[0068] S703 Sealing Performance Inspection: Use the pressure test method to detect the sealing performance of the valve. Install the valve on the test device, introduce the medium (such as water or gas) into the valve, gradually increase the pressure to 1.1 times the nominal pressure of the valve, and hold the pressure for 10 - 15 minutes. Observe whether there is any leakage at the sealing part of the valve. If there is no leakage during the pressure holding period, the sealing performance of the valve is qualified.

[0069] Furthermore, this method significantly improves the corrosion resistance: This process selects high-performance austenitic stainless steel containing 22-25% chromium, 12-15% nickel, and 3-5% molybdenum as the main material for the valve body. By precisely controlling the content of each alloy element, it can exhibit excellent corrosion resistance in different corrosion environments. Chromium forms a dense oxide film on the valve surface, effectively preventing the intrusion of external corrosive media; nickel enhances the stability of the alloy and improves corrosion resistance; molybdenum further enhances the resistance to corrosive ions such as chloride ions. In chemical production, the valves manufactured by this process have a service life 2-3 times longer than those manufactured by traditional processes in corrosive media containing a large amount of chloride ions, greatly reducing the equipment maintenance cost and replacement frequency.

[0070] Furthermore, this method optimizes the coating adhesion effect: It uses nano-ceramic coating materials and conducts strict pretreatment on the valve surface, including steps such as cleaning and degreasing, surface activation, etc., effectively improving the adhesion between the coating and the valve substrate. The nano-scale coating material can better fill the microscopic pores on the substrate surface, increasing the contact area between the coating and the substrate. Combining with special spraying processes and curing conditions, a strong chemical bond is formed between the coating and the substrate. After testing, the adhesion of the coating prepared by this process reaches level 0-1, far higher than the adhesion level of coatings prepared by traditional processes, effectively avoiding peeling and flaking of the coating during use and ensuring the long-term protection effect of the coating.

[0071] Furthermore, this method enhances the sealing performance: It selects fluororubber with a Shore hardness of 70-80 HA, a tensile strength of not less than 12 MPa, and an elongation at break of not less than 300% as the sealing strip material, and optimizes the special pretreatment and installation process of the sealing strip. The excellent elasticity and chemical corrosion resistance of fluororubber enable it to maintain good sealing performance under different working conditions. The special installation process ensures that the sealing strip fits tightly with the valve sealing groove, with a fit degree of over 95%, effectively preventing medium leakage. Under high-temperature, high-pressure and corrosive medium working conditions, the valves manufactured by this process have stable and reliable sealing performance, and the leakage rate is far lower than the industry standard, effectively ensuring the safety and environmental protection requirements of industrial production.

[0072] Furthermore, this method improves the product quality and stability: From the strict screening and pretreatment of raw materials, to the high-precision production of casting molds, and then to the precise control and quality inspection of each production link, this process has established a complete quality control system. By precisely controlling key parameters such as melting temperature, pouring speed, and cooling method, internal defects of the valve are effectively reduced, improving the product quality and stability. According to statistics, the qualified rate of valves produced by this process reaches over 98%, which is 10-15 percentage points higher than that of traditional processes, providing more reliable valve products for industrial production.

[0073] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A corrosion-resistant valve casting process for improving the coating adhesion and sealing performance, including S1 raw material selection and pretreatment, S2 casting mold production, S3 valve casting process, S4 surface treatment, S5 coating preparation and spraying, S6 sealing strip installation, and S7 quality inspection, characterized in that: The selection and pretreatment of the S1 raw materials: Metal materials: A high-performance austenitic stainless steel containing 22 - 25% chromium, 12 - 15% nickel, and 3 - 5% molybdenum is selected as the main material for the valve body. While ensuring mechanical strength, this material has excellent corrosion resistance due to the synergistic effect of chromium, nickel, and molybdenum, and can effectively resist the erosion of various corrosive media. The steel purchased needs to be subjected to spectral analysis to ensure that the content of each element is within the specified range, with the deviation controlled within ±0.5%; Coating materials: Nano-ceramic coating materials are used, with the main components being titanium dioxide (TiO2) and silicon dioxide (SiO2). Among them, the content of TiO2 is 40 - 45%, the content of SiO2 is 50 - 55%, and 3 - 5% of nano-scale zirconia (ZrO2) is added as a reinforcing agent. Before use, the coating materials are dried in an oven at 120 - 150°C for 2 - 3 hours to remove moisture and avoid affecting the coating quality; Sealing materials: Fluororubber with a Shore hardness of 70 - 80 HA, a tensile strength of not less than 12 MPa, and an elongation at break of not less than 300% is selected as the sealing strip material. Its excellent chemical corrosion resistance, high temperature resistance, and good elasticity can ensure the sealing performance of the valve under different working conditions. Before use, the sealing strip needs to be surface polished, and the roughness is controlled within Ra0.8 - 1.6 μm to enhance the fit with the valve; The production of the S2 casting mold includes S201 mold design and S201 mold design; The S3 valve casting process includes S301 melting, S302 pouring, and S303 cooling; The S4 surface treatment includes S401 machining, S402 cleaning and degreasing, and S403 surface activation; The S5 coating preparation and spraying include S501 coating material formulation, S502 spraying, and S503 curing; The S6 sealing strip installation includes S601 strip pretreatment and S602 installation; The S7 quality inspection includes S701 appearance inspection, S702 coating performance inspection, and S703 sealing performance inspection.

2. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, wherein: The S201 mold design: Use professional CAD / CAM software for three-dimensional mold design. According to the structure and size requirements of the valve, accurately design the cavity, core, runner, and riser parts of the mold to ensure that the dimensional accuracy of the mold is within ±0.05 mm, and avoid valve size deviation caused by mold accuracy problems; S202 mold processing: Select H13 hot work die steel as the mold material, which has good hot strength, thermal fatigue performance, and wear resistance. Use a CNC machining center for mold processing. During the processing, the cutting speed is controlled at 80 - 120 m / min, the feed rate is 0.1 - 0.2 mm / r, and the cutting depth is 0.5 - 1.0 mm. After processing, the mold surface is nitrided at a temperature of 550 - 580°C for 8 - 10 hours to form a nitrided layer with high hardness and good wear resistance on the mold surface, improving the service life of the mold.

3. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, characterized in that: The S301 melting: Put the selected stainless steel material into an intermediate frequency induction furnace for melting. During the melting process, control the temperature in the furnace at 1550 - 1600 °C, and add appropriate amounts of deoxidizer and refining agent, such as calcium silicate alloy (the addition amount is 0.1 - 0.2% of the mass of the molten metal) and aluminum block (the addition amount is 0.05 - 0.1% of the mass of the molten metal), to remove impurities and gases in the molten metal and improve the purity of the molten metal. At the same time, stir the molten metal through an electromagnetic stirring device, with a stirring frequency of 30 - 50 Hz, to make the composition of the molten metal uniform and the temperature distribution consistent.

4. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, characterized in that: The S302 pouring: When the molten metal reaches the appropriate pouring temperature (1500 - 1530 °C), use a bottom - pouring gating system for pouring, control the pouring speed so that the molten metal fills the mold cavity within 3 - 5 seconds, to avoid turbulence and oxidation of the molten metal. During the pouring process, introduce an appropriate amount of argon gas into the cavity, with an argon gas flow rate of 5 - 8 L / min, to protect the molten metal from oxidation.

5. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, characterized in that: The S303 cooling: After pouring is completed, the valve is cooled in the mold. First, use the water - cooling method, with the cooling speed controlled at 5 - 10 °C / s, to quickly solidify the surface of the valve and form a certain strength. When the surface temperature of the valve drops to 800 - 900 °C, switch to air - cooling, with the cooling speed controlled at 1 - 2 °C / s, to reduce the stress concentration inside the valve and prevent crack defects.

6. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, characterized in that: The S401 machining: Machine the cast valve, remove the scale and sand impurities on the surface, and ensure the dimensional accuracy and surface roughness of the valve. Use a CNC lathe to turn the inner and outer surfaces of the valve, with a turning speed of 150 - 200 m / min, a feed rate of 0.1 - 0.2 mm / r, and a cutting depth of 0.2 - 0.5 mm. The surface roughness of the machined valve is controlled at Ra3.2 - 6.3 μm.

7. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, characterized in that: The S402 cleaning and degreasing: Put the machined valve into an alkaline cleaning solution for cleaning and degreasing treatment. The main components of the cleaning solution include 5 - 8% sodium hydroxide (NaOH), 3 - 5% sodium carbonate (Na2CO3), and 2 - 3% sodium phosphate (Na3PO4). The cleaning temperature is 60 - 70 °C, and the cleaning time is 15 - 20 minutes. Through cleaning and degreasing, remove the oil and impurities on the valve surface and provide a good foundation for subsequent coating treatment; The S403 surface activation: Use the chemical activation method to activate the surface of the valve. Immerse the valve in an activation solution containing 1 - 2% hydrofluoric acid (HF) and 3 - 5% nitric acid (HNO3) for 5 - 10 minutes. After activation treatment, a micro - rough structure is formed on the valve surface, increasing the contact area between the coating and the valve surface and improving the adhesion of the coating.

8. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, characterized in that: Preparation of the S501 coating material: According to the selected coating material formula above, the raw materials of TiO2, SiO2 and ZrO2 are fully mixed in a high-speed mixer. The stirring speed is 1000 - 1500 r / min, and the stirring time is 30 - 45 minutes to ensure the uniformity of the coating material. Then, an appropriate amount of organic binder and diluent are added to formulate a paint suitable for spraying. The addition amount of the organic binder is 5 - 8% of the total mass of the coating material, and the addition amount of the diluent is adjusted according to the viscosity of the paint to control the viscosity of the paint within 15 - 20 s (measured by a cup-4 viscometer). S502 Spraying: A high-pressure airless spraying device is used to spray the coating on the valve surface. The spraying pressure is controlled at 15 - 20 MPa, the distance between the spray gun and the valve surface is maintained at 200 - 300 mm, and the spraying angle is 90°. During the spraying process, it is carried out in the order of the inner surface first and then the outer surface. The thickness of each coating layer is controlled at 50 - 80 μm, and a total of 3 - 4 layers are sprayed, with the total coating thickness reaching 150 - 250 μm. S503 Curing: After spraying, the valve is placed in a high-temperature curing furnace for curing treatment. The curing temperature is 350 - 400 °C, the heating rate is controlled at 5 - 10 °C / min, and the holding time is 2 - 3 hours. After curing, it is cooled to room temperature with the furnace to fully cure the coating and form a hard and dense protective film.

9. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, characterized in that: Pretreatment of the S601 rubber strip: The sealing rubber strip is cut according to the size of the valve sealing groove. The length of the cut rubber strip is slightly longer than the circumference of the sealing groove by 1 - 2 mm to ensure the sealing effect after the rubber strip is installed. Then, the two ends of the rubber strip are bevelled, and the bevel angle is 30 - 45° to enable better butt-joint of the rubber strip during installation. Installation of S602: Apply a layer of sealant evenly in the sealing groove, and the application amount of the sealant is 0.5 - 1.0 g / m 2 , slowly embed the pre-treated sealant strip into the sealing groove, ensure that the strip fits tightly with the sealing groove without air bubbles and gaps. During the installation process, use a special tool to compact the strip so that its degree of fit with the sealing groove reaches more than 95%.

10. The corrosion-resistant valve casting process for improving the coating adhesion and sealing performance according to claim 1, characterized in that: S701 Appearance inspection: The appearance of the valve is comprehensively inspected. Observe whether there are sand holes, air holes, crack defects on the valve surface, whether the coating is uniform and smooth, and whether there are peeling and blistering phenomena. A combination of visual inspection and auxiliary inspection with a 5 - 10 times magnifying glass is used to ensure that the appearance quality meets the standard requirements. S702 Coating performance inspection: Use a coating thickness gauge to detect the thickness of the coating to ensure that the coating thickness is within the specified range. The cross-cut test method is used to detect the adhesion of the coating, and the test is carried out according to the GB / T 9286 - 1998 standard. The coating adhesion should reach level 0 - 1. The hardness of the coating is detected by a hardness tester, and the coating hardness should not be lower than 500 HV. S703 Sealing performance inspection: The pressure test method is used to detect the sealing performance of the valve. The valve is installed on the test device, and the medium is introduced into the valve. The pressure is gradually increased to 1.1 times the nominal pressure of the valve, and the pressure holding time is 10 - 15 minutes. Observe whether there is any leakage at the sealing part of the valve. If there is no leakage during the pressure holding period, the sealing performance of the valve is qualified.