A method for manufacturing a high-air-tightness nickel-based gray cast iron sealing gasket

Abstract

The application discloses a manufacturing method of a high-airtightness nickel-based gray cast iron sealing gasket and belongs to the technical field of sealing gasket manufacturing. In the method, the gray cast iron raw material is subjected to composite deslagging and desulfurization treatment in a smelting stage, and a Bi-Zr-Ni alloy system is added to realize molten iron alloying modification; in a casting forming stage, vacuum filling is combined with a partition pulse micro-positive pressure nitrogen pressure maintaining process to eliminate internal shrinkage and edge deformation defects of the castings; in a nickel-based infiltration sintering stage, nano nickel-nano alumina composite powder is adopted, nano boron powder is added as a sintering activator, and solid phase sintering is completed through a pulse constant temperature process; in a finishing stage, normal temperature rolling and flattening treatment is adopted to optimize sealing surface precision, and the sealing gasket is prepared. Through the technical means of refining the cast iron matrix structure, blocking internal leakage channels and strengthening the combination effect of the nickel-based coating, the method effectively solves the problems of poor air tightness, low bonding strength and short service life of the traditional gray cast iron sealing gasket.

Description

Technical Field

[0001] This invention relates to the field of sealing component manufacturing technology, specifically to a method for manufacturing a high-airtightness nickel-based gray cast iron gasket. Background Technology

[0002] Gaskets are core sealing components for fluid transport and equipment connections under high-pressure conditions. Gray cast iron gaskets, due to their readily available raw materials, convenient casting and processing, and relatively low overall cost, are widely used in static sealing scenarios in mechanical equipment, fluid pipelines, and pressure vessels, making them a fundamental sealing component with a wide range of applications in industrial production. However, with the industry trend of gradually increasing operating pressure and extending service life of industrial equipment, sealing components need to simultaneously meet the requirements of high sealing reliability, high structural stability, and long service life. The performance shortcomings of traditional gray cast iron gaskets are becoming increasingly prominent, making them unsuitable for high-pressure, long-term service scenarios.

[0003] In existing technologies, gray cast iron gaskets are mostly manufactured using traditional smelting processes. The molten iron undergoes only basic melting and simple slag removal, lacking efficient methods for impurity removal, desulfurization, and deoxidation. This results in low purity of the molten iron, with harmful impurities such as sulfur and oxygen easily remaining at the grain boundaries of the matrix. This leads to poor uniformity of the cast iron matrix structure, coarse and randomly distributed graphite morphology, and a large number of naturally occurring micropores and loose structures within the matrix. These microscopic defects can form through-hole leakage channels under high-pressure media, directly causing sealing failure and failing to achieve a stable, high-airtightness seal. Furthermore, the existing forming process for gray cast iron gaskets mainly relies on conventional gravity casting, with some processes only using simple vacuum-assisted filling. No matching feeding methods are designed based on the solidification shrinkage characteristics of gray cast iron. During solidification, the casting is prone to internal shrinkage cavities, porosity, and other volume defects. Simultaneously, the cooling rates at the edges and center of the casting are inconsistent, easily leading to warping, deformation, and excessive dimensional deviations. Therefore, internal defects and insufficient dimensional accuracy of the blank directly affect the processing quality of the subsequent sealing surface, making it impossible to form a flat and continuous contact surface, further increasing the risk of seal failure. In addition, in the surface sealing strengthening and post-treatment stages, existing processes mostly use ordinary metal powder coating followed by direct isothermal sintering. The sintering process lacks activation mechanisms and stress control methods, resulting in low powder sintering density, poor adhesion between the coating and the substrate, and easy occurrence of peeling and cracking, making it difficult to effectively seal the micropores on the substrate surface.

[0004] Therefore, it is necessary to provide a method for manufacturing a high-airtightness nickel-based gray cast iron gasket to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for manufacturing a high-airtightness nickel-based gray cast iron gasket, so as to solve the technical problems of poor airtightness, low pressure resistance and short service life caused by the loose matrix structure, casting shrinkage deformation and weak sintering bonding of nickel-based coating of traditional gray cast iron gaskets.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for manufacturing a high-airtightness nickel-based gray cast iron sealing gasket, comprising the following steps: (1) Smelting: Gray cast iron raw materials are put into a smelting furnace for melting, followed by composite slag removal and desulfurization, and then an alloy system composed of Bi-Zr-Ni is added to the molten iron to obtain alloyed gray cast iron molten iron; (2) Casting and molding: The alloyed gray cast iron molten iron obtained in step (1) is injected into the mold. First, a vacuum is drawn to fill the mold with molten iron. Then, a slightly positive pressure nitrogen gas is introduced into the mold. After holding the pressure and cooling, the mold is demolded to obtain the sealing gasket blank. (3) Nickel-based infiltration sintering: Nano nickel-nano alumina composite powder is coated on the sealing surface of the gasket blank, and nano boron powder is added as a sintering activator. The coated gasket blank is then sent into a sintering furnace for solid-phase sintering. (4) Finishing: The sealing gasket after sintering in step (3) is subjected to room temperature rolling and leveling treatment to obtain a high airtightness nickel-based gray cast iron sealing gasket.

[0007] As a preferred embodiment, in step (1): the composite slag removal and desulfurization step is as follows: after the gray cast iron raw material is melted, the temperature is raised to 1420~1480℃, and under nitrogen protection, calcium-based composite refining agent and rare earth deoxidizer are added and stirred and kept warm for 5~10 minutes. After slag removal and static impurity removal, pure molten iron is obtained.

[0008] Preferably, the calcium-based composite refining agent is a calcium-silicon alloy with a calcium content of 28-35 wt%, a silicon content of 55-65 wt%, and the balance being iron; the rare earth deoxidizer is a rare earth ferrosilicon alloy with a total rare earth content (RE) of 25 wt%-45 wt%, a silicon content of 30 wt%-45 wt%, and the balance being iron; the calcium-based composite refining agent and the rare earth ferrosilicon alloy are placed at the bottom of the ladle 5-8 minutes before the molten iron is tapped from the furnace, and then poured into the ladle after the molten iron is tapped to achieve uniform mixing.

[0009] As a preferred embodiment, in step (1), the amount of Bi-Zr-Ni alloy system added is: 0.6%~1.2% of the total mass of molten iron when nickel is added in nickel-iron alloy; 0.05%~0.15% of the total mass of molten iron when zirconium is added in silicon-zirconium alloy; and 0.01%~0.03% of the total mass of molten iron when bismuth is added in bismuth-iron alloy.

[0010] Preferably, in step (1): the gray cast iron raw material is HT250 or HT300 primary iron, mixed with carbon scrap steel, with carbon equivalent controlled at 3.2%~3.8%, sulfur content ≤0.08%, and phosphorus content ≤0.10%.

[0011] Preferably, in step (2): the vacuum degree for filling the mold with molten iron is -0.04~-0.06MPa, and the filling time is 3~8s; the micro-positive pressure nitrogen gas is introduced into the mold in a zoned pulse manner, and the zoned pulse parameters are: nitrogen pressure in the central zone is 0.04~0.05MPa, nitrogen pressure in the edge zone is 0.01~0.02MPa, the pulse pressure frequency is 3 times / 10s, and the pressure holding time is 10~20s.

[0012] Preferably, in step (2): the mold preheating temperature is 200~300℃, the molten iron casting temperature is 1380~1420℃, and the mold is demolded after cooling to below 300℃.

[0013] Preferably, in step (3): the nano-nickel-nanoalumina composite powder is composed of nano-nickel powder and nano-Al2O3 ceramic powder in a mass ratio of 92:8 to 95:5, and the particle size of the composite powder is 50 to 200 nm; the amount of nano-boron powder added is 0.5% to 1% of the total mass of the nano-nickel-nanoalumina composite powder, forming a mixed powder after addition; the mixed powder is made into a slurry and coated onto the gasket sealing surface, with a coating amount of 0.02 to 0.06 g / cm² per unit area of ​​the gasket sealing surface. 3 Before coating, the sealing surface of the gasket blank is shot-blasted to a roughness Ra≤3.2μm.

[0014] Preferably, in step (3), the solid-state sintering process parameters are as follows: the first stage is heated from room temperature to 300℃ at a rate of 3~5℃ / min; the second stage is heated from 300℃ to 720~740℃ at a rate of 8~10℃ / min; sintering is carried out at 720~740℃, and the holding temperature is maintained by pulse constant temperature method, with a 3min interval between every 8~10min of holding, and a total holding time of 1~1.5h; the sintering atmosphere is nitrogen protection, and the furnace is cooled to room temperature after sintering.

[0015] Preferably, in step (4): the room temperature rolling and leveling treatment uses a carbide rolling wheel, the rolling pressure is 0.5~1.5MPa, the rolling speed is 10~20mm / s, and the rolling times are 1~2 times; after rolling, the flatness of the sealing surface is ≤0.05mm and the roughness Ra≤0.8μm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a composite slag removal and desulfurization process combined with Bi-Zr-Ni alloying smelting. Under nitrogen protection, calcium-based composite refining agents and rare earth deoxidizers are used to thoroughly remove impurities, sulfur, and oxygen from the molten iron, reducing internal defects in the matrix. Bi-Zr-Ni alloying elements form stable segregated phases at the grain boundaries of cast iron, effectively refining the graphite morphology and matrix grains, sealing intergranular pores, and significantly improving the density of the cast iron matrix. This blocks fluid leakage channels from the root of the matrix, laying the microstructure foundation for the high airtightness of the sealing gasket.

[0017] 2. In the casting and forming stage of this invention, vacuum filling combined with zoned pulse micro-positive pressure nitrogen holding process is adopted. The vacuum environment can ensure the integrity of molten iron filling. The zoned pulse pressure matches the cooling rate difference between the center and the edge of the casting. The high pressure in the center area achieves sufficient feeding and eliminates shrinkage cavities and porosity defects. The low pressure in the edge area avoids flash and warping deformation of the casting. It can accurately control the size and shape accuracy of the blank, reduce the initial defects of the sealing surface, and improve the adaptability of subsequent coating and finishing processes.

[0018] 3. In the nickel-based infiltration sintering stage of this invention, nano-nickel-nano-alumina composite powder is used in combination with nano-boron powder as a sintering activator. Nano-boron powder can significantly reduce the sintering activation energy of nickel-based powder, promote the full penetration of nickel-based phase into the micropores of cast iron surface and form a metallurgical bond with the matrix. Combined with pulse isothermal sintering process, it effectively releases the thermal stress during sintering, avoids microcracks and warping deformation of coating, greatly improves coating density and bonding strength, and enhances surface sealing effect. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. 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.

[0020] Example 1 This embodiment provides a method for manufacturing a high-airtightness nickel-based gray cast iron gasket, specifically including the following steps: (1) Smelting: HT250 primary iron and clean carbon scrap steel were mixed according to the production ratio as raw materials for gray cast iron. The carbon equivalent of the raw materials was tested and controlled to be 3.5%, the sulfur content to be 0.06%, and the phosphorus content to be 0.08%. The mixed raw materials were put into a medium-frequency melting furnace and heated to be completely melted. After the molten iron was clear, the temperature was raised to 1450℃. Under the nitrogen protective atmosphere, calcium-based composite refining agent and rare earth deoxidizer were added to the molten iron. The calcium-based composite refining agent was a silicon-calcium alloy with a calcium content of 32%, a silicon content of 60%, and the balance being iron. The rare earth deoxidizer was a rare earth silicon-iron alloy with a total rare earth content of 35%, a silicon content of 40%, and the balance being iron. The two refining agents were placed at the bottom of the ladle 6 minutes before the molten iron was poured out of the furnace. After the molten iron was poured into the ladle, it was automatically mixed and stirred and kept at a constant temperature for 8 minutes. Then, slag was removed and the mixture was allowed to stand for 10 minutes to remove impurities and obtain pure molten iron. Bi-Zr-Ni composite alloy system was added to the pure molten iron. Nickel is added in the form of a nickel-iron alloy at a concentration of 0.9% of the total mass of the molten iron. Zirconium is added in the form of a silicon-zirconium alloy at a concentration of 0.10% of the total mass of the molten iron. Bismuth is added in the form of a bismuth-iron alloy at a concentration of 0.02% of the total mass of the molten iron. After complete melting and diffusion of the alloys, a homogeneous alloyed gray cast iron is obtained.

[0021] (2) Casting and Molding: Preheat the special sealing mold to 250℃, control the pouring temperature of the alloyed gray cast iron molten iron to 1400℃, and smoothly pour the molten iron into the mold cavity. First, evacuate the mold cavity and control the vacuum degree to -0.05MPa. Complete the molten iron filling under this vacuum degree, and the filling time is 5s. After the filling is completed, introduce zoned pulsed micro-positive pressure nitrogen into the mold. The nitrogen pressure in the middle area of ​​the gasket is 0.045MPa, and the nitrogen pressure in the outer peripheral area of ​​the gasket is 0.015MPa. The pulse charging frequency is 3 times / 10s, and the holding time is set to 15s. After the holding process is completed, allow the casting to cool naturally in the mold. When the casting temperature drops below 280℃, open the mold and demold to obtain a sealing gasket blank with complete dimensions and uniform structure.

[0022] (3) Nickel-based infiltration sintering: First, the sealing surface of the gasket blank is shot-blasted until the surface roughness Ra ≤ 3.2 μm. Nano-nickel powder and nano-alumina ceramic powder are weighed at a mass ratio of 93:7 and mixed to prepare nano-nickel-nano-alumina composite powder, controlling the composite powder particle size to be 100 nm. Nano-boron powder is added to the composite powder as a sintering activator, with the amount of nano-boron powder added being 0.8% of the total mass of the composite powder. After uniform mixing, a slurry is prepared. The mixed powder slurry is coated onto the gasket sealing surface, with a coating amount of 0.04 g / cm² per unit area of ​​the gasket sealing surface. 3The coated sealing gasket blank was fed into a sintering furnace for solid-state sintering. The first stage involved heating from room temperature to 300℃ at a rate of 4℃ / min. The second stage involved heating from 300℃ to 730℃ at a rate of 9℃ / min. Sintering was then carried out at 730℃ using a pulsed isothermal method, with a 3-minute pause after every 9 minutes of holding, for a total holding time of 1.2 hours. A nitrogen protective atmosphere was used throughout the sintering process, and the furnace was cooled to room temperature after sintering.

[0023] (4) Finishing: The sintered gaskets are then subjected to room temperature rolling and leveling. Carbide rolling rollers are used, with a rolling pressure of 1.0 MPa, a rolling speed of 15 mm / s, and one rolling cycle. After rolling, the flatness of the sealing surface is ≤0.05 mm and the roughness Ra is ≤0.8 μm, resulting in a high-airtightness nickel-based gray cast iron gasket.

[0024] Example 2 This embodiment provides a method for manufacturing a high-airtightness nickel-based gray cast iron gasket, specifically including the following steps: (1) Smelting: HT300 primary iron and clean carbon scrap steel were mixed according to the production ratio as raw materials for gray cast iron. The carbon equivalent of the raw materials was tested and controlled to be 3.2%, the sulfur content to be 0.07%, and the phosphorus content to be 0.09%. The mixed raw materials were put into a medium-frequency melting furnace and heated to be completely melted. After the molten iron was clear, the temperature was raised to 1420℃. Under the nitrogen protective atmosphere, calcium-based composite refining agent and rare earth deoxidizer were added to the molten iron. The calcium-based composite refining agent was a silicon-calcium alloy with a calcium content of 28%, a silicon content of 55%, and the balance being iron. The rare earth deoxidizer was a rare earth silicon-iron alloy with a total rare earth content of 25%, a silicon content of 30%, and the balance being iron. The two refining agents were placed at the bottom of the ladle 5 minutes before the molten iron was poured out of the furnace. After the molten iron was poured into the ladle, it was automatically mixed and stirred and kept at a constant temperature for 5 minutes. Then, slag was removed and the mixture was allowed to stand for 8 minutes to remove impurities and obtain pure molten iron. Bi-Zr-Ni composite alloy system was added to the pure molten iron. Nickel is added in the form of a nickel-iron alloy at a concentration of 0.6% of the total mass of the molten iron. Zirconium is added in the form of a silicon-zirconium alloy at a concentration of 0.05% of the total mass of the molten iron. Bismuth is added in the form of a bismuth-iron alloy at a concentration of 0.01% of the total mass of the molten iron. After complete melting and diffusion of the alloys, a homogeneous alloyed gray cast iron is obtained.

[0025] (2) Casting and Molding: Preheat the special sealing mold to 200℃, control the pouring temperature of the alloyed gray cast iron molten iron to 1380℃, and smoothly pour the molten iron into the mold cavity. First, evacuate the mold cavity and control the vacuum degree to -0.04MPa. Complete the molten iron filling under this vacuum degree, and the filling time is 8s. After the filling is completed, introduce zoned pulsed micro-positive pressure nitrogen into the mold. The nitrogen pressure in the middle area of ​​the gasket is 0.04MPa, and the nitrogen pressure in the outer peripheral area of ​​the gasket is 0.01MPa. The pulse charging frequency is 3 times / 10s, and the holding time is set to 10s. After the holding process is completed, allow the casting to cool naturally in the mold. When the casting temperature drops below 300℃, open the mold and demold to obtain the sealing gasket blank.

[0026] (3) Nickel-based infiltration sintering: First, the sealing surface of the gasket blank is shot-blasted until the surface roughness Ra ≤ 3.2 μm. Nano-nickel powder and nano-alumina ceramic powder are weighed at a mass ratio of 92:8 and mixed to prepare nano-nickel-nano-alumina composite powder, controlling the composite powder particle size to be 50 nm. Nano-boron powder is added to the composite powder as a sintering activator, with the amount of nano-boron powder added being 0.5% of the total mass of the composite powder. After uniform mixing, a slurry is prepared. The mixed powder slurry is coated onto the gasket sealing surface, with a coating amount of 0.02 g / cm² per unit area of ​​the gasket sealing surface. 3 The coated sealing gasket blank was fed into a sintering furnace for solid-state sintering. In the first stage, the temperature was increased from room temperature to 300℃ at a rate of 3℃ / min. In the second stage, the temperature was increased from 300℃ to 720℃ at a rate of 8℃ / min. Sintering and holding at 720℃ were performed using a pulsed constant-temperature method, with a 3-minute interval between every 8 minutes of holding, for a total holding time of 1 hour. A nitrogen protective atmosphere was used throughout the sintering process, and the furnace was cooled to room temperature after sintering.

[0027] (4) Finishing: The sintered gaskets are then subjected to room temperature rolling and leveling. Carbide rolling rollers are used, with a rolling pressure of 0.5 MPa, a rolling speed of 10 mm / s, and one rolling cycle. After rolling, the flatness of the sealing surface is ≤0.05 mm, and the roughness Ra is ≤0.8 μm, finally obtaining a high airtightness nickel-based gray cast iron gasket.

[0028] Example 3 This embodiment provides a method for manufacturing a high-airtightness nickel-based gray cast iron gasket, specifically including the following steps: (1) Smelting: HT250 primary iron and clean carbon scrap steel were mixed according to the production ratio as raw materials for gray cast iron. The carbon equivalent of the raw materials was tested and controlled to be 3.8%, sulfur content 0.06%, and phosphorus content 0.07%. The mixed raw materials were put into a medium-frequency melting furnace and heated to complete melting. After the molten iron was clear, the temperature was raised to 1480℃. Under a nitrogen protective atmosphere, calcium-based composite refining agent and rare earth deoxidizer were added to the molten iron. The calcium-based composite refining agent was a silicon-calcium alloy with a calcium content of 35%, a silicon content of 65%, and the balance being iron. The rare earth deoxidizer was a rare earth silicon-iron alloy with a total rare earth content of 45%, a silicon content of 45%, and the balance being iron. The two refining agents were placed at the bottom of the ladle 8 minutes before the molten iron was poured out of the furnace. After the molten iron was poured into the ladle, it was automatically mixed and stirred and kept at a constant temperature for 10 minutes. Then, slag removal was performed, and the mixture was allowed to stand for 12 minutes to remove impurities and obtain pure molten iron. Bi-Zr-Ni composite alloy system was added to the pure molten iron. Nickel is added in the form of a nickel-iron alloy at a concentration of 1.2% of the total mass of the molten iron. Zirconium is added in the form of a silicon-zirconium alloy at a concentration of 0.15% of the total mass of the molten iron. Bismuth is added in the form of a bismuth-iron alloy at a concentration of 0.03% of the total mass of the molten iron. After complete melting and diffusion of the alloys, a homogeneous alloyed gray cast iron is obtained.

[0029] (2) Casting and Molding: Preheat the special sealing mold to 300℃, control the pouring temperature of the alloyed gray cast iron molten iron to 1420℃, and smoothly pour the molten iron into the mold cavity. First, evacuate the mold cavity and control the vacuum degree to -0.06MPa. Complete the molten iron filling under this vacuum degree, and the filling time is 3s. After the filling is completed, introduce zoned pulsed micro-positive pressure nitrogen into the mold. The nitrogen pressure in the middle area of ​​the gasket is 0.05MPa, and the nitrogen pressure in the outer peripheral area of ​​the gasket is 0.02MPa. The pulse charging frequency is 3 times / 10s, and the holding time is set to 20s. After the holding process is completed, allow the casting to cool naturally in the mold. When the casting temperature drops below 260℃, open the mold and demold to obtain the sealing gasket blank.

[0030] (3) Nickel-based infiltration sintering: First, the sealing surface of the gasket blank is shot-blasted until the surface roughness Ra ≤ 3.2 μm. Nano-nickel powder and nano-alumina ceramic powder are weighed at a mass ratio of 95:5 and mixed to prepare nano-nickel-nano-alumina composite powder, controlling the composite powder particle size to be 200 nm. Nano-boron powder is added to the composite powder as a sintering activator, with the amount of nano-boron powder added being 1% of the total mass of the composite powder. After uniform mixing, a slurry is prepared. The mixed powder slurry is coated onto the gasket sealing surface, with a coating amount of 0.06 g / cm² per unit area of ​​the gasket sealing surface. 3The coated sealing gasket blank was fed into a sintering furnace for solid-state sintering. The first stage involved heating from room temperature to 300℃ at a rate of 5℃ / min. The second stage involved heating from 300℃ to 740℃ at a rate of 10℃ / min. Sintering was then carried out at 740℃ using a pulsed constant-temperature method, with a 3-minute pause after every 10 minutes of holding, for a total holding time of 1.5 hours. A nitrogen protective atmosphere was used throughout the sintering process, and the gasket was cooled to room temperature with the furnace after sintering.

[0031] (4) Finishing: The sintered gaskets are then subjected to room temperature rolling and leveling. Carbide rolling rollers are used, with a rolling pressure of 1.5 MPa, a rolling speed of 20 mm / s, and two rolling cycles. After rolling, the flatness of the sealing surface is ≤0.05 mm and the roughness Ra is ≤0.8 μm, resulting in a high-airtightness nickel-based gray cast iron gasket.

[0032] Comparative Example 1 The only difference between this comparative example and Example 1 is that: in step (1), nickel, zirconium and bismuth are not added during the smelting process, and the Bi-Zr-Ni alloy system is not alloyed. All other aspects are consistent with Example 1.

[0033] Expected performance: The cast iron matrix cannot form effective grain boundary segregation strengthening phases, resulting in decreased graphite morphology regularity and significantly reduced matrix density. Microscopic shrinkage porosity and through-pores are prone to appear inside the sealing surface, greatly increasing the risk of gas and liquid leakage. The bonding force between the nickel-based sintered layer and the cast iron matrix is ​​weakened, making it prone to problems such as coating peeling and seal failure during use.

[0034] Comparative Example 2 The only difference between this comparative example and Example 1 is that: in step (2) during the casting process, the partitioned pulse nitrogen pressure holding process is not used, but instead the overall constant pressure holding is used. The pressure holding pressure is uniformly set to 0.03MPa, and the pressure holding time remains unchanged at 15s. All other aspects are consistent with Example 1.

[0035] Expected performance: The slow cooling rate in the central area of ​​the casting results in insufficient feeding, easily leading to concentrated shrinkage cavities and diffuse porosity. Excessive pressure in the edge areas easily causes flash, burrs, and localized deformation, resulting in severely substandard flatness of the blank. Subsequent rolling processes cannot fully correct dimensional deviations, leading to uneven contact of the sealing surfaces, localized stress concentration after assembly, and a significant decrease in sealing performance, making it difficult to meet high airtightness requirements.

[0036] Comparative Example 3 The only difference between this comparative example and Example 1 is that: in step (3) nickel-based infiltration sintering, no nano boron powder is added as a sintering activator, while the rest are consistent with Example 1.

[0037] Expected performance: The sintering activation energy of the nano-nickel-based composite powder is increased, resulting in insufficient sintering driving force and difficulty in achieving sufficient densification of the coating. The penetration depth of nickel into the cast iron matrix is ​​insufficient, failing to effectively seal surface micropores. The coating exhibits high internal porosity, low bonding strength, and poor pressure resistance. Microcracks and leakage channels easily appear on the sealing surface, causing the airtightness to fail to meet design standards and significantly reducing product reliability.

[0038] Comparative Example 4 The only difference between this comparative example and Example 1 is that the pulse constant temperature process is cancelled in the heat preservation stage of solid phase sintering in step (3), and the continuous constant temperature heat preservation at 730℃ for 1.2h is adopted without intermittent pauses. The rest is consistent with Example 1.

[0039] Expected performance: Uneven heating between the coating and the substrate during sintering prevents timely release of thermal stress, easily leading to microcracks and warping deformation. The uniformity of the nickel-based phase distribution deteriorates, resulting in localized over-burning or incomplete sintering. The smoothness and density of the sealing surface decrease, weakening the coating's adhesion and making it prone to wear and leakage during use, resulting in poor long-term stability.

[0040] Comparative Example 5 The only difference between this comparative example and Example 1 is that the room temperature rolling and leveling treatment is cancelled in step (4), and the product is directly used after sintering. The rest is consistent with Example 1.

[0041] Expected performance: The surface roughness and flatness of the sealing surface fail to meet the requirements, and microscopic irregularities and machining marks are present. During assembly, a complete and uniform seal cannot be formed with the mating surfaces; excessive local contact pressure can easily lead to crushing and deformation, increasing the sealing gap. The product cannot achieve a high airtight seal, is prone to media leakage, and cannot meet the requirements for use under high-pressure conditions.

[0042] Comparative Example 6 The only difference between this comparative example and Example 1 is that in step (3), ordinary micron-sized nickel powder is used instead of nano-nickel-nano-alumina composite powder, and nano-alumina ceramic powder is not added. All other aspects are consistent with Example 1.

[0043] Expected performance: The powder sintering process has poor fluidity, making it difficult to fill the tiny pores on the cast iron surface, resulting in poor sealing performance. The coating lacks sufficient hardness, wear resistance, and corrosion resistance, making it prone to wear and scratches during use. The coating has low density and weak bonding strength, resulting in poor airtightness and structural stability, preventing the product from meeting the standards for high airtightness and long service life.

[0044] To compare the performance differences of the manufacturing methods of the high airtightness nickel-based gray cast iron gaskets provided in Examples 1-3 and Comparative Examples 1-6, the present invention provides the following test methods: 1. Air tightness test: The test was conducted using an automatic high-pressure gas leakage detection system, a dedicated sealing fixture, and a nitrogen supply device. The test medium was dry, pure nitrogen gas, the test pressure was 1.6 MPa, the ambient temperature was 23℃, the relative humidity was 50%, and the pressure holding time was 30 minutes. The sealing gasket was assembled into the dedicated sealing fixture, and the fixing bolts were tightened evenly to ensure a seal. The nitrogen supply device was turned on, and nitrogen was slowly introduced into the sealing cavity of the fixture to the set pressure. The inlet valve was closed, and the pressure was kept stable. The leakage detection system was activated to continuously collect gas leakage data of the sealed cavity within 30 minutes. The leakage value during the stable period was taken as the test result, with the unit being mL / min. The lower the leakage, the better the airtightness.

[0045] 2. Flatness inspection of sealing surface The test was conducted using a high-precision laser flatness measuring instrument and a horizontal testing platform. The ambient temperature was 23℃, and the horizontality error of the testing platform was no greater than 0.001 mm / m. The horizontal testing platform was calibrated to a level position, and the sealing gasket was placed stably on the platform, ensuring the sample was free from warping and shaking. The laser flatness measuring instrument was then turned on to perform a full-area scan of the gasket's sealing surface, covering both the central and outer peripheral areas. The maximum flatness deviation of the sealing surface was recorded as the test result, in mm. A smaller flatness deviation indicates a higher level of flatness of the sealing surface.

[0046] 3. Surface roughness inspection of sealing surface A portable surface roughness tester was used for testing at an ambient temperature of 23℃. Before testing, the sealing surface was wiped with anhydrous ethanol and the test was started after the surface was dry. Three test points were evenly selected radially along the sealing surface, and each test point was tested three times consecutively. The maximum and minimum values ​​were removed, and the average value was taken as the surface roughness result of the sample, in μm. The smaller the Ra value, the higher the smoothness of the sealing surface.

[0047] 4. Testing the bonding strength of nickel-based coatings The adhesion test was conducted using a pull-off method coating adhesion tester, a dedicated adhesive fixture, and high-strength structural adhesive. The ambient temperature was 23℃, the structural adhesive curing time was 24 hours, and the tensile rate was 1 mm / min. First, the surface of the sealing gasket coating was sanded. The adhesive fixture was then tightly bonded to the coating surface using structural adhesive. After curing at room temperature for 24 hours, the sample was mounted on the adhesion tester and stretched uniformly at a rate of 1 mm / min until the coating peeled off from the substrate. The tensile stress value at failure was recorded as the coating bond strength, in MPa. A higher value indicates a stronger bond between the coating and the substrate.

[0048] 5. Density testing of cast iron matrix The density was tested using an electronic precision densitometer, distilled water, and degreased cotton, following Archimedes' principle of water displacement. The ambient temperature was 23℃, and the sample surface was free of oil and internal pores. First, the dry mass of the sample was measured using the electronic densitometer. Then, the sample was completely immersed in distilled water, and the immersion mass was measured. The bulk density was calculated based on the measured data, using the theoretical density of gray cast iron as 7.2 g / cm³. 3 The matrix density is calculated based on the measured density and the theoretical density. The higher the value, the fewer defects in the matrix and the denser the structure.

[0049] 6. Pressure resistance and durability simulation test The test was conducted on a high and low temperature cyclic sealing durability test bench and pressure control system. The test pressure was 1.6 MPa, the temperature cycling range was -40℃ to 120℃, the single cycle was 60 minutes, and the total number of cycles was 10,000. The sealing gasket was assembled into the fixture of the durability test bench. After setting the pressure and temperature cycling parameters, the equipment was started. After every 1000 cycles, the machine was stopped for inspection to observe for leakage, deformation, coating damage, sealing failure, etc. The number of cycles at which the sample failed was recorded as the simulated service life. The higher the effective number of cycles, the better the long-term stability and lifespan of the product. The experimental data are as follows: Table 1 Performance test results of the examples and comparative examples

[0050] Based on the experimental data in Table 1, the leakage rate of the examples was only maintained at 0.12-0.18 mL / min, which is significantly different from the comparative examples. Among them, Comparative Example 1, which did not add the Bi-Zr-Ni alloy system, had the highest leakage rate, reaching 12.65 mL / min. Comparative Example 2, which did not use partitioned pulse pressure holding, and Comparative Example 3, which did not add nano-boron powder, also showed a significant increase in leakage rate. Behind this result is the synergistic effect of multiple factors. The Bi-Zr-Ni alloy system can form segregated phases at the grain boundaries of cast iron, refine the graphite morphology, and close the leakage channels between grains. Partitioned pulse nitrogen pressure holding can match the cooling difference between the center and the edge of the casting, eliminating defects such as central shrinkage porosity and edge voids. Nano-boron powder can reduce the sintering activation energy of nickel-based composite powder, allowing the nickel-based phase to fully penetrate and seal the micropores on the surface of cast iron. These three effects work together to block the leakage path, which fully demonstrates that alloying modification, partitioned pulse feeding, and nano-boron activation sintering are the core means to improve the airtightness of gaskets.

[0051] Looking at the flatness and roughness of the sealing surface, the example shows that the flatness can be controlled within 0.032-0.041 mm, and the roughness Ra is stable within 0.62-0.75 μm, which is significantly higher than the comparison ratio. Comparative Example 5, which omits rolling and leveling, has the worst flatness and roughness performance. Comparative Example 2, which does not use zoned pressure holding, also shows particularly obvious dimensional deviations. Zoned pulse casting can precisely control the forming dimensions of the casting and reduce initial defects such as blank warping and deformation. Room temperature rolling and leveling can repair the microscopic unevenness of the sealing surface through micro-plastic deformation and optimize the surface morphology. These two processes work together to give the sealing surface high-precision fitting characteristics, which is enough to prove that zoned pulse casting and room temperature rolling and leveling processes are the key to ensuring high-precision fitting of the sealing surface.

[0052] Regarding coating adhesion strength and matrix density, the coating adhesion strength of the embodiments reached 24.3-28.6 MPa, and the matrix density reached 95.8%-97.2%. The comparative examples, lacking the core process, showed a significant decline in all data. Comparative Example 1, without the Bi-Zr-Ni alloy, had the lowest matrix density, and Comparative Example 3, without nano-boron powder, also exhibited significantly low coating adhesion strength. Bi-Zr-Ni alloying refines the cast iron matrix structure, reduces internal porosity defects, and significantly improves matrix density. Nano-boron powder strengthens the interfacial bonding between nickel-based powder and the cast iron matrix, promoting the diffusion of the nickel-based phase into the matrix to form a metallurgical bond. Pulse isothermal sintering effectively releases thermal stress during sintering, preventing microcracks and warping in the coating and ensuring the strong bond between the coating and the matrix. This demonstrates that alloy system optimization can strengthen the matrix structure, and the combined use of nano-boron powder and pulse isothermal sintering effectively improves the adhesion between the coating and the matrix.

[0053] Simulated service life test results show that the tested examples can complete 10,000 cycles without failure, while the comparative examples exhibit problems such as leakage, deformation, and coating damage within 1260-6890 cycles. The reason for this is that the process of this invention allows the gasket to simultaneously possess a dense matrix, a highly adhesive sealing coating, and a high-precision sealing surface, maintaining structural stability and effective sealing even under high and low temperature cycling and high pressure conditions. This fully demonstrates that the synergistic process of melting alloying, partitioned pulse casting, nickel-based infiltration sintering, and room-temperature rolling leveling of this invention can improve the overall performance and reliability of the sealing gasket.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for manufacturing a high-airtightness nickel-based gray cast iron sealing gasket, characterized in that, Includes the following steps: (1) Smelting: Gray cast iron raw material is put into a smelting furnace for melting, followed by composite slag removal and desulfurization, and then an alloy system composed of Bi-Zr-Ni is added to the molten iron to obtain alloyed gray cast iron molten iron; (2) Casting and molding: The alloyed gray cast iron molten iron obtained in step (1) is injected into the mold. First, a vacuum is drawn to fill the mold with molten iron. Then, a slightly positive pressure nitrogen gas is introduced into the mold. After holding the pressure and cooling, the mold is demolded to obtain the sealing gasket blank. (3) Nickel-based infiltration sintering: Nano nickel-nano alumina composite powder is coated on the sealing surface of the gasket blank, and nano boron powder is added as a sintering activator. The coated gasket blank is then sent into a sintering furnace for solid-phase sintering. (4) Finishing: The sealing gasket after sintering in step (3) is subjected to room temperature rolling and leveling treatment to obtain a high airtightness nickel-based gray cast iron sealing gasket.

2. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 1, characterized in that, In step (1): the composite slag removal and desulfurization steps are as follows: after the gray cast iron raw material is melted, the temperature is raised to 1420~1480℃. Under nitrogen protection, calcium-based composite refining agent and rare earth deoxidizer are added and stirred and kept warm for 5~10 minutes. After slag removal and static impurity removal, pure molten iron is obtained.

3. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 2, characterized in that, The calcium-based composite refining agent is a silicon-calcium alloy with a calcium content of 28-35 wt%, a silicon content of 55-65 wt%, and the balance being iron. The rare earth deoxidizer is a rare earth ferrosilicon alloy, wherein the total rare earth content (RE) in the rare earth ferrosilicon alloy is 25wt% to 45wt%, the silicon content is 30wt% to 45wt%, and the balance is iron. The calcium-based composite refining agent and rare earth ferrosilicon alloy are placed at the bottom of the ladle 5-8 minutes before the molten iron is tapped from the furnace, and then poured into the ladle after the molten iron is tapped to achieve uniform mixing.

4. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 1, characterized in that, In step (1), the amount of Bi-Zr-Ni alloy system added is as follows: the amount of nickel added in the nickel-iron alloy is 0.6% to 1.2% of the total mass of the molten iron; the amount of zirconium added in the silicon-zirconium alloy is 0.05% to 0.15% of the total mass of the molten iron; and the amount of bismuth added in the bismuth-iron alloy is 0.01% to 0.03% of the total mass of the molten iron.

5. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 4, characterized in that, In step (1): the gray cast iron raw material is HT250 or HT300 virgin iron, mixed with carbon scrap steel, with carbon equivalent controlled at 3.2%~3.8%, sulfur content ≤0.08%, and phosphorus content ≤0.10%.

6. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 3, characterized in that, In step (2): the vacuum degree for filling the mold with molten iron is -0.04 to -0.06 MPa, and the filling time is 3 to 8 seconds; The micro-positive pressure nitrogen gas is introduced into the mold using a zoned pulse method. The zoned pulse parameters are: nitrogen pressure in the central zone is 0.04~0.05MPa, nitrogen pressure in the edge zone is 0.01~0.02MPa, pulse pressurization frequency is 3 times / 10s, and pressure holding time is 10~20s.

7. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 6, characterized in that, In step (2): the mold preheating temperature is 200~300℃, the molten iron casting temperature is 1380~1420℃, and the mold is demolded when cooled to below 300℃.

8. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 1, characterized in that, In step (3): the nano-nickel-nano-alumina composite powder is composed of nano-nickel powder and nano-Al2O3 ceramic powder in a mass ratio of 92:8~95:5, and the particle size of the composite powder is 50~200nm; The amount of nano-boron powder added is 0.5% to 1% of the total mass of the nano-nickel-nano-alumina composite powder, and a mixed powder is formed after the addition. The mixed powder is prepared into a slurry and coated onto the gasket sealing surface, with a coating amount of 0.02~0.06 g / cm² per unit area of ​​the gasket sealing surface. 3 Before coating, the sealing surface of the gasket blank is shot-blasted to a roughness Ra≤3.2μm.

9. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 8, characterized in that, In step (3), the solid-state sintering process parameters are as follows: The first stage involves heating from room temperature to 300℃ at a rate of 3~5℃ / min. The second stage involves heating from 300℃ to 720~740℃ at a rate of 8~10℃ / min. Sintering and holding were carried out at 720~740℃ using a pulse constant temperature method, with a 3-minute interval between every 8~10 minutes of holding, and a total holding time of 1~1.5 hours. The sintering atmosphere is nitrogen protection, and the furnace is cooled to room temperature after sintering.

10. The method for manufacturing a high-airtightness nickel-based gray cast iron gasket according to claim 1, characterized in that, In step (4): the room temperature rolling and leveling treatment uses a carbide rolling roller with a rolling pressure of 0.5~1.5MPa, a rolling speed of 10~20mm / s, and 1~2 rolling times; after rolling, the flatness of the sealing surface is ≤0.05mm and the roughness Ra≤0.8μm.

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