Low-pressure casting device and method for high-voltage GIS matching oil tank shell of oil pressure operator

Abstract

The application belongs to the technical field of low-pressure casting and particularly relates to a low-pressure casting device and method for a high-voltage GIS supporting oil pressure operator oil tank shell, the high-voltage GIS supporting oil pressure operator oil tank shell being a large-size thin-wall hollow cavity casting, designed with a boss and a reinforcing rib; the low-pressure casting device comprises a mold system, a sand core, a sand core positioning and supporting mechanism and a pouring system, double sprues are designed at the position of the reinforcing rib with large wall thickness, aluminum liquid enters from the sprues and fills the cavity through the sprue reinforcing rib; a riser is arranged above the opposite side of the surface where the sprue is located, the lower part of the riser is provided with a riser neck with a gradually reduced cross section, a side extraction insert block is arranged on the mold, and demolding, material removal and mold closing are realized through side extraction of the insert block driven by an oil cylinder, the application shortens the aluminum liquid filling distance and solidification time, improves the feeding capacity of the sprue, reduces the mold manufacturing and maintenance cost and the production instability problem caused by insufficient water cooling.

Description

Technical Field

[0001] This invention belongs to the field of low-pressure casting technology for large-size aluminum alloy structural parts, specifically relating to a low-pressure casting device and method for the oil tank housing of a high-pressure GIS supporting hydraulic operator. Background Technology

[0002] Large-size aluminum alloy housing structural components are widely used in aerospace, shipbuilding, and power equipment industries due to their lightweight, high strength and toughness, and excellent corrosion resistance. High-voltage electrical equipment, including high-voltage switchgear, transformers, surge arresters, and insulators, plays a crucial role in the transmission, distribution, and conversion of electricity. These components require special insulation properties, withstand voltage capabilities, and safety designs to ensure stable and reliable operation under high-voltage environments and guarantee the normal operation of the power system. The main functions of the hydraulic actuator tank in high-voltage GIS (Gas Insulated Switchgear) are to store hydraulic oil, dissipate heat, buffer, mount the base, and provide protection. Based on these requirements, aluminum alloys with good electrical and thermal conductivity are typically chosen. Aluminum alloys also possess high strength and light weight, which can improve equipment reliability and stability while reducing equipment weight and cost.

[0003] The hydraulic actuator tank for high-voltage GIS mainly houses a series of electrical components and contains insulating hydraulic oil to ensure effective isolation of the energized parts from the external environment, thus improving safety and reliability. Considering its operating environment and service life, its design requires a certain wall thickness and sealing performance; therefore, integral casting of aluminum alloy is the optimal process for mass production. Because the annual demand for hydraulic actuator tanks for high-voltage GIS (Gas Insulated Metal Enclosed Switchgear) is relatively small, a full sand casting process is typically used. While this process offers greater flexibility, it results in poor surface quality, inconsistent internal quality and external dimensions, and requires significant time for grinding, rework, and machining adjustments.

[0004] In the process design of all-sand casting of aluminum alloy parts, the gating and riser system is relatively complex and relies heavily on experience, lacking systematic theoretical support. Especially for thin-walled, large-cavity castings such as the oil tank of a high-pressure GIS hydraulic actuator, which has large height and lateral dimensions and extremely long molten metal flow, even slight design errors can easily lead to low process yield, pass rate, and production efficiency. Summary of the Invention

[0005] To address the technical problems of sand casting of aluminum alloy tank shells for high-pressure GIS hydraulic actuators, this invention provides a low-pressure casting device and method for tank shells of high-pressure GIS hydraulic actuators, wherein the outer surface is formed by a metal mold and the interior is formed by a sand core.

[0006] The complete technical solution of this invention includes:

[0007] Low-pressure casting device for the oil tank housing of high-pressure GIS supporting hydraulic actuator.

[0008] The oil tank shell of the high-pressure GIS hydraulic actuator is a hexahedral structure with a flange at the opening and holes of different diameters on both sides. The oil tank shell of the high-pressure GIS hydraulic actuator is provided with bosses and reinforcing ribs. The height of the oil tank shell of the high-pressure GIS hydraulic actuator is not less than 500mm, the length is not less than 550mm, the width is not less than 350mm, and the average wall thickness is 15~25mm.

[0009] The low-pressure casting device for the oil tank shell of the high-pressure GIS supporting hydraulic operator includes a mold system, sand core, sand core positioning and support mechanism and pouring system;

[0010] The gating system structure is as follows: at the reinforcing rib position of the oil tank shell of the high-pressure GIS matching hydraulic operator, there are bottom double gates at a certain distance. The aluminum liquid rises under the action of gas pressure, enters the bottom double gate through the riser pipe, and fills the cavity formed by the mold system and sand core through the reinforcing rib at the bottom double gate.

[0011] The oil tank housing casting of the high-pressure GIS matching hydraulic operator is provided with a riser at the top and a mold release part with a gradually narrowing cross section at the bottom of the riser;

[0012] The mold system includes a side-drawing insert, a side mold, a top mold, and a bottom mold. The side-drawing insert is driven by a side-drawing insert cylinder fixed on the top mold. After the high-pressure GIS matching hydraulic operator tank housing casting solidifies, the side-drawing insert is located at the mold-lifting part. Then the side mold begins to separate, at which time the side-drawing insert remains stationary.

[0013] After the side mold detaches from the high-pressure GIS hydraulic actuator tank housing casting, the side pull-out block remains stationary. Driven by the main hydraulic cylinder, the high-pressure GIS hydraulic actuator tank housing casting leaves the bottom mold along with the top mold. After reaching the height of the receiving tray, the side pull-out block detaches from the high-pressure GIS hydraulic actuator tank housing casting under the drive of the side pull-out block cylinder. At the same time, the ejector rod of the top mold ejects the high-pressure GIS hydraulic actuator tank housing casting, realizing material removal.

[0014] The sand core includes a main core head and an auxiliary core head. The sand core positioning support mechanism includes a support part and a tie rod. After the main core head contacts the bottom mold, one end of the sand core is a certain distance from the bottom mold and is in a suspended state. When the sand core is lowered, the support part is set in the suspended position of the sand core. Then the side mold corresponding to the auxiliary core head is closed. Then the support part is pulled away by the tie rod. Finally, the remaining side molds and the top mold are closed.

[0015] Furthermore, based on the height, maximum horizontal length, maximum horizontal width, and average wall thickness of the oil tank shell casting of the high-pressure GIS supporting hydraulic operator, the area of ​​the reinforcing ribs at the bottom double gate is designed.

[0016] Furthermore, the diameter of the bottom double gate is 60-70mm.

[0017] Furthermore, the riser is a cylindrical shape with a draft angle and a diameter of 50-65mm.

[0018] Furthermore, the sand core is a two-piece spliced ​​structure, and the interior of the sand core is hollow after splicing.

[0019] Furthermore, the sand core is equipped with reinforcing ribs.

[0020] Furthermore, the auxiliary mandrel includes a first auxiliary mandrel and a second auxiliary mandrel located on two opposite sides.

[0021] Furthermore, the distance between the two bottom gates shall not be less than 1 / 3 of the width of the oil tank housing of the high-pressure GIS matching hydraulic operator.

[0022] Furthermore, the core wall thickness is 20~30mm, and the joints of the core have a concave-convex structure.

[0023] Furthermore, the method for low-pressure casting of the oil tank shell of the high-pressure GIS matching hydraulic operator using the aforementioned low-pressure device includes the following steps:

[0024] 1) Liquid rising stage: Under the action of gas pressure, the aluminum liquid is raised through the riser pipe to the bottom double gating position;

[0025] 2) Filling stage: Continue to increase the gas pressure to fill the cavity formed by the mold system and the sand core with aluminum liquid. During the filling stage, the gas pressure increase rate is dynamically adjusted according to the height of the aluminum liquid level. After the filling stage, the gas pressure is 280mbar-300mbar.

[0026] 3) Shell formation and pressurization stage: After the aluminum liquid fills the cavity, the gas pressure continues to increase to 320mbar-350mbar at a pressurization rate of 15mbar / s-25mbar / s. The aluminum liquid at the contact surface with the cavity begins to solidify and form a shell.

[0027] 4) Solidification and pressure holding stage: Maintain a gas pressure of 300mbar-370mbar to completely solidify the aluminum liquid in the cavity. The solidification and pressure holding stage lasts for 400s-500s.

[0028] 5) Depressurization stage: After the solidification and pressure holding stage is completed, the gas pressure in the holding furnace is released, and the unsolidified aluminum liquid in the bottom double gating and riser pipe flows back into the holding furnace under the action of gravity.

[0029] The beneficial effects of this invention are as follows:

[0030] 1) For the oil tank shell of the high-pressure GIS matching hydraulic operator with a large size and local thick reinforcing ribs on the outer surface, it is arranged horizontally, and a double gate is designed at the thick part of the side wall. This shortens the aluminum liquid filling and solidification distance and improves the feeding capacity of the gate.

[0031] 2) The process of horizontally arranging the oil tank shell of the high-pressure GIS-equipped hydraulic operator ensures that the area finally filled by the molten aluminum is the thickest part of the cavity. At the same time, the riser with a mold lifting part is used to replace the mold water cooling system, which not only achieves good internal quality, but also reduces mold manufacturing and maintenance costs and production instability caused by insufficient water cooling.

[0032] 3) The mold-lifting part is designed to fit the mold structure. The shape of the mold-lifting part is utilized to achieve an innovative demolding method for castings with difficult-to-demold structures, avoiding the risk of the high-pressure GIS hydraulic actuator tank housing remaining in the bottom mold after mold opening. A reasonable design was implemented for the sand core structure, positioning method, and sand core placement process under the horizontal casting process for the complex high-pressure GIS hydraulic actuator tank housing.

[0033] 4) During the filling stage, a dynamic filling method is adopted, which adjusts the filling pressure and speed in real time based on the real-time cross-sectional area change during the rise of the aluminum liquid. This avoids the problems of drastic changes in the flow velocity of the aluminum liquid in the existing large-size high-pressure GIS matching hydraulic operator oil tank shell casting with complex internal cavity shape and abrupt changes in cross-sectional area during the filling process, which can lead to air entrapment, porosity, oxide inclusions, and cold shuts. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the oil tank housing casting of the high-pressure GIS matching hydraulic operator of the present invention.

[0035] Figure 2 for Figure 1 Cross-sectional view.

[0036] Figure 3 This is a schematic diagram of the gate and riser.

[0037] Figure 4 This is a schematic diagram of the gate reinforcement.

[0038] Figure 5 This is a schematic diagram of the decomposed structure of a sand core.

[0039] Figure 6 This is a schematic diagram of the main core head.

[0040] Figure 7 This is a schematic diagram of the auxiliary core tip.

[0041] Figure 8This is a schematic diagram of the main core head and the bottom mold positioning part.

[0042] Figure 9 This is a schematic diagram of the overall casting equipment.

[0043] In the figure, 1-casting, 2-flange, 3-hole, 4-reinforcing rib, 5-bore, 6-gate, 7-gate reinforcing rib, 8-riser, 9-molding part, 10-sand core, 11-sand core reinforcing rib, 12-main core head, 13-first auxiliary core head, 14-second auxiliary core head, 15-main core head and bottom mold positioning part, 16-support part, 17-pull rod, 18-side pull insert, 19-side pull insert cylinder. Detailed Implementation

[0044] The present invention will now be described in detail with reference to embodiments and accompanying drawings. However, it should be understood that the embodiments and drawings are for illustrative purposes only and do not constitute any limitation on the scope of protection of the present invention. All reasonable modifications and combinations included within the inventive spirit of the present invention fall within the scope of protection of the present invention.

[0045] like Figures 1-2 As shown, the high-pressure GIS hydraulic actuator tank shell obtained by low-pressure casting of this invention has a hexahedral box structure with five sealed sides and one open side. A flange 2 is provided at the open side, and holes 3 with diameters of 42mm and 185mm are designed on both sides of the box. Other sides are designed with circular or elongated bosses 5 according to functional and assembly requirements. Based on the working strength requirements of the high-pressure GIS hydraulic actuator tank shell, the outer surface has locally increased wall thickness to form reinforcing ribs 4. The main body wall thickness of the high-pressure GIS hydraulic actuator tank shell is 12.5–15mm. The reinforcing ribs and bosses are areas where the wall thickness is increased during the filling process. The wall thickness at the reinforcing ribs is approximately 22.5mm, and the wall thickness at the locally independent bosses is approximately 25mm–30mm. The overall height of the high-pressure GIS hydraulic actuator tank shell is 512mm, the length is 597mm, the width is 401mm, and the average wall thickness is 15–25mm.

[0046] For castings with similar structures, existing traditional aluminum alloy sand casting processes typically design a single gating gate at the open flange of the casting, and risers at other thicker locations. However, because the castings involved in this invention are large in volume and weight, have a considerable amount of hollow space, and have multiple reinforcing ribs and bosses with abrupt changes in wall thickness, a single gating gate alone is insufficient to meet the requirements for filling and solidification feeding. Furthermore, the large lateral dimensions make them prone to casting defects such as cold shuts, shrinkage cavities, and porosity.

[0047] Invention patent CN111673072B discloses a wheel forming device and method based on multi-lift liquid pipe central pressurization, which solves the problems of long filling distance and difficult forming and feeding of aluminum alloy wheel castings by filling through multiple liquid pipes and gates. However, the aluminum alloy shell casting involved in this invention has a larger overall size and more complex internal structure, and cannot use an all-metal mold structure. It is necessary to form the internal cavity composite structure through sand cores. Therefore, the above-mentioned pouring method can no longer be used. Based on this, the casting mold method of this invention, which adopts low-pressure casting + metal mold outer mold + internal precision shaped sand core, is designed to abandon the traditional process of designing gates at the open flange of such castings. In order to obtain better solidification sequence and internal quality of castings, while taking into account feeding of all thick areas of the structure, a double gate is designed at the position of the thick reinforcing rib on the narrower side of the six-sided structure of the casting. The two gates are spaced a certain distance apart.

[0048] The process design of this invention involves horizontally arranging the casting. In this horizontal arrangement, the maximum lateral dimension is 597 mm, and the maximum longitudinal dimension is 512 mm. Figures 3-4 As shown, two gates 6 are designed at a certain distance at the bottom to better meet the process requirements. The gate diameter is 60-70mm, and the gate spacing is adjusted according to the width of the casting, not less than 1 / 3 of the casting width. Based on the external surface structure, the double gate design is on the casting body. The molten aluminum enters the gate reinforcement rib 7 at the gate from the bottom double gate and then fills the cavity. The gate reinforcement rib performs the function of a horizontal runner, which serves to receive the molten aluminum. Therefore, there is no need to design other runners and ingates, saving the amount of molten aluminum used and facilitating subsequent sawing and removal.

[0049] Simultaneously, the gating system is designed based on the shape characteristics of the casting, and a reasonable gating reinforcement structure is selected to achieve reasonable filling. For the large hollow castings produced by this invention, the structure of the gating reinforcement determines whether sufficient flow of molten aluminum can be provided, preventing the molten aluminum from solidifying prematurely due to excessive cooling before reaching the far end of the cavity, and achieving a reasonable balance between flow rate and cooling time, so that the molten aluminum maintains its liquid flow capability throughout the filling process, eliminating cold shut defects. Analysis revealed that if the area of ​​the gating reinforcement is too small, the flow rate of molten aluminum will not meet the filling requirements of castings with large transverse dimensions, forming cold shuts, and causing excessively rapid pressure decay, resulting in shrinkage cavities and porosity defects concentrated at the far end. It may also lead to unstable filling, scouring or air entrapment of the mold sand core. On the other hand, if the gating reinforcement is too large, the rising speed of the molten aluminum may be too slow, increasing the temperature difference between the top and bottom and the solidification time, resulting in excessive internal stress in the casting, and potentially forming dead water zones, increasing subcutaneous porosity defects, and causing unnecessary waste of molten aluminum. Therefore, this invention incorporates the transverse dimensional characteristics of the casting into the design for the first time, in order to solve the problem of unreasonable solidification during filling of large-span cavities. Specifically:

[0050]

[0051] In the formula, This represents the total area of ​​the gate reinforcement. This is an empirical coefficient, with a value range of 0.001–0.0025. This refers to the height of the casting (mm), applicable range 500–700mm. This is the maximum horizontal length of the casting. The maximum width of the casting in the horizontal direction. The equivalent (average) wall thickness (mm) of the casting is applicable to a range of 10–30 mm.

[0052] In the above formula, through The item takes into account the flow rate requirement of the casting volume, and This highlights the crucial impact of lateral dimensions, addressing the challenge of filling large spans. This is a wall thickness correction factor, meaning that the thinner the wall, the greater the flow resistance, and the larger the area of ​​the gate reinforcement is required.

[0053] When designing a casting system using the above principles, certain boundary conditions must also be imposed based on the actual spatial layout and the strength requirements of the sand core. Specifically:

[0054]

[0055] In the formula, The filling time is expressed in seconds (s).

[0056] The above formula ensures that the filling time is short enough by constraining the filling time, thus preventing the aluminum liquid from solidifying in the far cavity.

[0057] Based on the above principles and the specific dimensional parameters of the structural components of this invention, the casting height is 512 mm, the horizontal length is 597 mm, the maximum width is 401 mm, the average wall thickness is 19.5 mm, and the filling time should be less than 28 seconds. Based on the calculation results and practical considerations, the total area of ​​the gate reinforcing ribs designed for this invention is approximately 92000 mm². 2 .

[0058] Furthermore, due to the large volume of the castings of this invention, even when placed horizontally, the area to be filled is still far from the gate, making the gate insufficient to provide adequate feeding during the entire solidification process, especially in areas with external reinforcing ribs or bosses. In this case, if the wall thickness difference between the reinforcing and non-reinforcing areas is less than 1.5 times, a local water-cooling structure can be added to accelerate the cooling rate of the thicker areas. However, this would increase the cost of mold manufacturing and subsequent maintenance. If the wall thickness difference between the reinforcing and non-reinforcing areas is greater than 1.5 times, stronger water cooling is required, along with more water channels, making control more difficult. Therefore, to further avoid internal defects in the thicker areas, this invention designs a riser 8 in the thicker areas of the casting. The riser is located above and opposite the gate surface. Based on mold flow analysis, the riser of this invention is designed as a cylinder with a draft angle and a diameter of 50-65 mm.

[0059] Meanwhile, the lower part of the riser of the present invention is designed with a gradually narrowing mold-removing part 9. The design concept of the above-mentioned mold-removing part is primarily to avoid the problem of "backflow" during solidification and feeding at the connection between the riser and the casting, i.e., the product feeding aluminum liquid into the riser, which would lead to internal shrinkage defects in the casting body or the connection position. The mold-removing part 9, which is designed in the same direction as the mold opening, has been verified in production. When used in conjunction with an insulating riser sleeve, the riser feeding effect is better during the solidification process of the actual product.

[0060] Secondly, the present invention employs a movable platform during mold opening, allowing the bottom mold and a side mold to be located on the platform and moved to the casting station to complete mold closing and casting. After completion, each side mold is opened first, and the main hydraulic cylinder slightly lifts the top mold to separate the sprue from the bottom mold. Then, the ejector rod of the top mold is used to eject the casting from the top mold, allowing the casting to fall onto the bottom mold. Subsequently, the movable platform carries the casting away from the casting station to complete the part removal.

[0061] The above process involves the top mold lifting the casting and sand core from the bottom mold after the side molds are opened following casting completion. To achieve this, the top mold needs sufficient clamping force to support the weight of the casting and sand core. Therefore, if... Figure 9As shown, a corresponding side-pull insert 18 was specifically designed. Driven by a side-pull insert cylinder 19 fixed to the top mold, it is used to detach the casting and sand core from the bottom mold along with the top mold after mold opening, facilitating subsequent demolding and material receiving. The above design is due to the fact that the main body of the casting is a cuboid, and a metal outer mold design with mold opening on each plane is adopted. There is no obvious design structure that can be used to detach from the bottom mold. Therefore, the shape of the mold-lifting part is used to assist demolding. An independent side-pull insert is designed. After the casting solidifies, four side molds are opened first. At this time, the side-pull insert does not move and is located in the mold-lifting part position. After the side molds are detached, the side-pull insert remains stationary. Driven by the main cylinder, the casting and sand core leave the bottom mold with the top mold. After reaching the height of the receiving tray, the side-pull insert is detached from the casting by the side-pull insert cylinder. At the same time, the top mold ejector rod ejects the casting and sand core to achieve material removal.

[0062] Furthermore, due to the large volume of the inner cavity of the high-voltage electrical component casting of this invention, the sand core used is extremely heavy. During sand core handling and bottom mold preparation, the heavy weight leads to insufficient strength, making it highly susceptible to damage. This also increases the manufacturing cost of the sand core. Even if the weight of the sand core can be reduced by pouring out the incompletely solidified sand during the core-making process through an opening, the sand core size, sand injection weight, and required draft angle still challenge the limits of actual production equipment, and may even ultimately affect the draft angle of the casting cavity and the weight of the casting. Therefore, this invention designs the sand core used for forming the inner cavity of the casting as a two-piece spliced ​​design, such as... Figure 5 As shown, the sand core 10 has a hollow structure with a wall thickness controlled at approximately 25mm. The joint between the two sand cores is designed with a concave-convex structure to facilitate the subsequent sand core bonding process. Simultaneously, reinforcing ribs 11 are designed inside the sand core to increase its strength, significantly reducing its weight while ensuring its strength. Furthermore, when the sand core comes into contact with high-temperature molten aluminum and generates a large amount of gas, the hollow structure of the sand core can promptly expel the gas, preventing it from entering the casting and causing internal porosity defects.

[0063] Regarding the positioning of sand cores, the first step is to consider the structural characteristics of the casting, such as... Figure 6 – Figure 8 As shown, after the casting is placed horizontally in the mold, the main core head 12 for supporting the sand core used for internal forming is located on one side of the casting. The main core head on the bottom mold and the bottom mold positioning part 15 contact the bottom mold to achieve positioning and support. However, the main core head is insufficient within the designed size range to maintain its balance and stability in the mold. In the prior art, castings of this structure usually have openings on two corresponding sides away from the opening for mounting matching electrical components. In this invention, the above-mentioned openings are used as the first auxiliary core head 13 and the second auxiliary core head 14, as follows. Figure 7 As shown, the sand core is supported when the corresponding side mold is closed, which ultimately enables the entire sand core to be precisely positioned and stabilized in the mold.

[0064] Regarding the mold closing sequence, based on the aforementioned sand core positioning and support method, auxiliary tools are needed in actual operation to achieve the "lowering sand core" action. After the main core head contacts the bottom mold, the other end of the sand core is still a certain distance from the bottom mold and is in a suspended state. Based on this suspended height, a support part 16 is designed. Before placing the sand core, the support part is placed in the corresponding position to support the sand core to prevent it from being suspended. Then, the two side molds corresponding to the auxiliary core head are closed first. As the mold is closed, the sand core can be stably placed in the mold through one main core head and two auxiliary core heads. At this time, the support part is pulled away from the sand core by the pull rod 17. Finally, the other two side molds and the top mold are closed to complete the entire process of lowering the sand core and closing the mold.

[0065] The method for low-pressure casting of the oil tank shell of a high-pressure GIS-equipped hydraulic actuator using the above-mentioned device includes the following steps:

[0066] (1) Liquid rising stage: The aluminum liquid is raised to the bottom double gating position through the liquid rising pipe. At this time, the gas pressure value is 110mbar-130mbar;

[0067] (2) Filling stage: continuously increase the gas pressure to fill the mold cavity with aluminum liquid. According to the liquid level, realize the dynamic adjustment of the gas pressure increase rate so that the aluminum liquid fills the gate and gate reinforcing rib in sequence, and further fills the remaining area until the mold cavity is completely filled. After the filling stage, the gas pressure is 280mbar-300mbar.

[0068] In low-pressure casting, existing technologies typically employ a fixed pressure increase rate during filling. However, large-sized castings often have complex internal cavity shapes with multiple abrupt changes in cross-sectional area and relatively thin walls. As the molten aluminum rises, its flow velocity changes drastically at these abrupt changes in cross-section. A rapid, short-term increase in velocity can impact the cavity interior and sand core, easily causing air entrapment, porosity, sand holes, or rupture of the oxide film on the liquid surface, leading to oxide inclusions. Conversely, when the molten aluminum enters a cavity with a suddenly enlarged cross-section, the flow velocity drops rapidly, resulting in excessively slow flow and temperature decreases, potentially leading to cold shut defects.

[0069] To address the above problems, the low-pressure casting apparatus of this invention achieves stable and rapid filling by dynamically controlling the gas pressure rise rate during filling through its control system. First, a reasonable reference gas pressure rise rate, i.e., the reference filling pressure rise rate, is determined based on the casting process conditions. Then, the filling pressure rise rate is dynamically adjusted based on the real-time cross-sectional area change during the actual aluminum melt rise process. Specifically, this includes:

[0070] 1) Determination of reference filling pressure and rate of increase

[0071] First, based on process conditions such as pouring temperature, mold preheating temperature, and thermal properties of molten aluminum, simulation and experimental verification were conducted. Combined with the minimum wall thickness of the casting, the minimum flow rate of molten aluminum to avoid cold shuts and the maximum flow rate to prevent air entrapment were determined. Based on this, a baseline filling pressure rise rate of 8 mbar / s to 12 mbar / s was obtained to ensure stable filling.

[0072] 2) Real-time dynamic adjustment during the filling process

[0073] This process is the core step in dealing with sudden changes in the filling cross section and achieving flow stability. It identifies sudden changes in the cross section by the real-time height position of the molten aluminum and dynamically adjusts the gas pressure rise rate.

[0074] Using a 3D CAD model of the casting, the casting is sliced ​​along its height and discretized into n height steps, preferably n = 50–120. The real-time equivalent cross-sectional area is obtained by dividing the volume within each step by its height, and a lookup table corresponding to the filling height h and the cavity cross-sectional area A is established. During the actual filling process, a baseline filling pressure is initially used for increasing the filling rate. Simultaneously, the control system interpolates the real-time equivalent cross-sectional area A(h) from this table based on the real-time h(t) (which can be obtained through multiple pre-installed non-contact liquid level sensors in the mold or through pressure feedback calculation). An area change rate threshold is defined. =20%. The rate of change of the equivalent cross-sectional area between two adjacent step sizes (height intervals). , For the next step, the equivalent cross-sectional area, This is the equivalent cross-sectional area of ​​the current step size. When this threshold is exceeded, dynamic adjustments are made.

[0075]

[0076] To accelerate the gas pressure increase in the next step, The gas pressure is increased at the current step size. This is an adjustment coefficient, with a value range of 0.5–0.7.

[0077] The filling method of this invention, compared to the prior art, first predicts the shape of the cavity ahead through a pre-stored lookup table, and then combines this with real-time liquid level for feedforward-feedback composite control. This achieves a shift from passive execution to active adaptation, allowing for pre-adjustment of gas pressure before the molten aluminum reaches the abrupt change region, rather than post-adjustment, thus greatly improving control accuracy.

[0078] Secondly, a balance between rapid and stable filling was achieved. By setting a reasonable baseline filling pressure and rate of increase, safety was ensured at the thinnest wall thickness. In areas with wide cross-sections, the allowable gas pressure rate of increase was appropriately increased through dynamic adjustment to compensate for the filling time, thereby optimizing the overall filling speed and efficiency while ensuring no air entrapment or scouring.

[0079] Furthermore, the filling method described above can be pre-calibrated and optimized through numerical simulation, reducing the cost and risk of on-site trial and error. It achieves complete digitization of the filling process. Once successfully debugged for a certain type of casting, the method can be quickly replicated in the development of similar new products, significantly improving the level of process standardization. Through the above filling method, under stable pressure, molten aluminum fills the entire mold cavity in a laminar flow manner. Precise filling speed control yields castings with clear contours and smooth surfaces, preventing casting defects.

[0080] (3) Shell formation and pressurization stage: After the aluminum liquid fills the cavity, the gas pressure is increased to 320mbar-350mbar at a pressurization rate of 15mbar / s-25mbar / s. This stage increases the pressure on the contact surface between the aluminum liquid and the cavity, which can make the aluminum liquid at this point start to solidify and form a shell in a shorter time.

[0081] (4) Solidification and pressure holding stage: During the solidification of the casting, a constant pressure is maintained, i.e., 300mbar-370mbar, for 400s-500s.

[0082] (5) Pressure relief: After the solidification and pressure holding period ends, the pressure in the holding furnace is released, and the unsolidified aluminum liquid in the gating and riser pipe flows back into the holding furnace under the action of gravity.

[0083] The foregoing has only described preferred embodiments of the present invention in detail and is not intended to limit the invention. Those skilled in the art will readily conceive of other embodiments of this disclosure upon considering the disclosure in the specification and embodiments. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

Claims

1. A low-pressure casting device for the oil tank housing of a high-pressure GIS-equipped hydraulic actuator, characterized in that, The oil tank shell of the high-pressure GIS hydraulic actuator is a hexahedral structure with a flange at the opening and holes of different diameters on both sides. The oil tank shell of the high-pressure GIS hydraulic actuator is provided with bosses and reinforcing ribs. The height of the oil tank shell of the high-pressure GIS hydraulic actuator is not less than 500mm, the length is not less than 550mm, the width is not less than 350mm, and the average wall thickness is 15~25mm. The low-pressure casting device for the oil tank shell of the high-pressure GIS supporting hydraulic operator includes a mold system, sand core, sand core positioning and support mechanism and pouring system; The gating system structure is as follows: at the reinforcing rib position of the oil tank shell of the high-pressure GIS matching hydraulic operator, there are bottom double gates at a certain distance. The aluminum liquid rises under the action of gas pressure, enters the bottom double gate through the riser pipe, and fills the cavity formed by the mold system and sand core through the reinforcing rib at the bottom double gate. The oil tank housing casting of the high-pressure GIS matching hydraulic operator is provided with a riser at the top and a mold release part with a gradually narrowing cross section at the bottom of the riser; The mold system includes a side-drawing insert, a side mold, a top mold, and a bottom mold. The side-drawing insert is driven by a side-drawing insert cylinder fixed on the top mold. After the high-pressure GIS matching hydraulic operator tank housing casting solidifies, the side-drawing insert is located at the mold-lifting part. Then the side mold begins to separate, at which time the side-drawing insert remains stationary. After the side mold detaches from the high-pressure GIS hydraulic actuator tank housing casting, the side pull-out block remains stationary. Driven by the main hydraulic cylinder, the high-pressure GIS hydraulic actuator tank housing casting leaves the bottom mold along with the top mold. After reaching the height of the receiving tray, the side pull-out block detaches from the high-pressure GIS hydraulic actuator tank housing casting under the drive of the side pull-out block cylinder. At the same time, the ejector rod of the top mold ejects the high-pressure GIS hydraulic actuator tank housing casting, realizing material removal. The sand core includes a main core head and an auxiliary core head. The sand core positioning support mechanism includes a support part and a tie rod. After the main core head contacts the bottom mold, one end of the sand core is a certain distance from the bottom mold and is in a suspended state. When the sand core is lowered, the support part is set in the suspended position of the sand core. Then the side mold corresponding to the auxiliary core head is closed. Then the support part is pulled away by the tie rod. Finally, the remaining side molds and the top mold are closed.

2. The low-pressure casting device for the oil tank shell of the high-pressure GIS supporting hydraulic operator according to claim 1, characterized in that, Based on the height, maximum horizontal length, maximum horizontal width, and average wall thickness of the oil tank shell casting of the high-pressure GIS supporting hydraulic operator, the area of ​​the reinforcing ribs at the bottom double gate is designed.

3. The low-pressure casting device for the oil tank shell of the high-pressure GIS matching hydraulic operator according to claim 2, characterized in that, The diameter of the bottom double gate is 60-70mm.

4. The low-pressure casting device for the oil tank shell of the high-pressure GIS supporting hydraulic operator according to claim 3, characterized in that, The riser is a cylindrical shape with a draft angle and a diameter of 50-65mm.

5. The low-pressure casting device for the oil tank shell of the high-pressure GIS matching hydraulic operator according to claim 4, characterized in that, The sand core is a two-piece spliced ​​structure, and the interior of the sand core is hollow after splicing.

6. The low-pressure casting device for the oil tank shell of the high-pressure GIS supporting hydraulic operator according to claim 5, characterized in that, The sand core is equipped with reinforcing ribs.

7. The low-pressure casting device for the oil tank shell of the high-pressure GIS matching hydraulic operator according to claim 6, characterized in that, The auxiliary mandrel includes a first auxiliary mandrel and a second auxiliary mandrel located on two opposite sides.

8. The low-pressure casting device for the oil tank shell of the high-pressure GIS supporting hydraulic operator according to claim 7, characterized in that, The distance between the two bottom gates shall not be less than 1 / 3 of the width of the oil tank housing of the high-pressure GIS matching hydraulic operator.

9. The low-pressure casting device for the oil tank housing of the high-pressure GIS supporting hydraulic operator according to claim 8, characterized in that, The core wall thickness is 20~30mm, and the joints of the core have a concave-convex structure.

10. A method for low-pressure casting of the oil tank shell of a high-pressure GIS-compatible hydraulic actuator using the low-pressure casting apparatus of claim 9, characterized in that, Includes the following steps: 1) Liquid rising stage: Under the action of gas pressure, the aluminum liquid is raised through the riser pipe to the bottom double gating position; 2) Filling stage: Continue to increase the gas pressure to fill the cavity formed by the mold system and the sand core with aluminum liquid. During the filling stage, the gas pressure increase rate is dynamically adjusted according to the height of the aluminum liquid level. After the filling stage, the gas pressure is 280mbar-300mbar. 3) Shell formation and pressurization stage: After the aluminum liquid fills the cavity, the gas pressure continues to increase to 320mbar-350mbar at a pressurization rate of 15mbar / s-25mbar / s. The aluminum liquid at the contact surface with the cavity begins to solidify and form a shell. 4) Solidification and pressure holding stage: Maintain a gas pressure of 300mbar-370mbar to completely solidify the aluminum liquid in the cavity. The solidification and pressure holding stage lasts for 400s-500s. 5) Depressurization stage: After the solidification and pressure holding stage is completed, the gas pressure in the holding furnace is released, and the unsolidified aluminum liquid in the bottom double gating and riser pipe flows back into the holding furnace under the action of gravity.

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