Low pressure casting apparatus and method for high voltage GIS aluminum alloy mechanism chamber

Abstract

This invention belongs to the field of low-pressure casting technology, specifically relating to a low-pressure casting device and method for a high-pressure GIS aluminum alloy structural chamber. The high-pressure GIS aluminum alloy structural chamber includes a base flange, a hemispherical first shell, a left chamber, and a right chamber. The low-pressure casting device includes a mold system, a sand core system, a gating system, a chill system, and a mold release system. The gating system is as follows: a gate is arranged below the flange face of the high-pressure GIS aluminum alloy structural chamber, and a horizontal runner is set between the gate and the flange face. Molten aluminum is injected from the bottom gate and enters the cavity through the horizontal runner. The area of ​​the horizontal runner is designed based on the height of the casting, the maximum horizontal length, the maximum horizontal width, and the average wall thickness, eliminating internal defects in the casting, ensuring product consistency, improving the density of the casting and the process yield, forming a stable casting cycle, improving production efficiency and product qualification rate, and reducing production costs.

Description

Technical Field

[0001] This invention belongs to the field of low-pressure casting technology for large-size aluminum alloy structural components, specifically relating to a low-pressure casting device and method for high-pressure GIS aluminum alloy structural chambers. Background Technology

[0002] Large-size aluminum alloy housing components are widely used in aerospace, shipbuilding, and power equipment industries due to their lightweight, high strength and toughness, and excellent corrosion resistance. In the power equipment sector, the mechanism chamber, or crank arm box, in high-voltage switchgear (such as circuit breakers and disconnectors) is a crucial mechanical transmission component connecting the operating mechanism (spring, hydraulic, pneumatic, electric) to the switch body (arc chamber, contact system). Its core function is to accurately and reliably convert the linear or rotary motion output by the operating mechanism into the specific motion (usually rotary or linear) required to drive the switch's moving contacts for opening and closing operations. The mechanism chamber / crank arm box of a high-voltage switchgear is a critical structural component integrating high strength, high rigidity, precision transmission, reliable sealing, long-term lubrication, and excellent environmental resistance. Under extreme mechanical stress and harsh environmental conditions, it must reliably and accurately complete the tasks of motion conversion and position holding over a long period, and its performance directly affects the safe and stable operation of the entire high-voltage switchgear and even the power grid. Its design, manufacturing, and maintenance all require extremely high levels of expertise.

[0003] The sealing characteristics of the mechanism chamber are crucial to prevent the intrusion of external dust, moisture, salt spray, and corrosive gases, and to protect the internal precision moving parts and grease while preventing internal lubricant leakage. In GIS (Gas Insulated Metal Enclosed Switchgear), although the mechanism box is on the atmospheric side, the dynamic sealing structure between it and the gas chamber filled with SF6 gas (such as the passage of the operating rod) must withstand gas pressure or vacuum, requiring extremely high sealing reliability to prevent insulation gas leakage from causing equipment insulation failure.

[0004] Due to their complex structure and the need for small-batch production of various products, aluminum alloy mechanical chambers are commonly formed using sand casting or gravity casting. Both of these casting methods involve complex gating and riser systems, which rely heavily on experience for design. Mechanical chambers, being thin-walled and large-cavity castings with significant height and lateral distances, have extremely long molten metal flow paths, making their design very challenging and prone to flaws. This can lead to low yield, low pass rate, and low production efficiency. Furthermore, in sand casting or gravity casting, the aluminum alloy solidifies under atmospheric conditions, resulting in a less dense casting structure and increasing the risk of failure of the mechanical chamber under SF6 gas pressure.

[0005] Furthermore, for castings such as structural components of the mechanism chamber, which are relatively tall, the main hydraulic cylinder stroke must completely cover more than 2.5 times the height of the casting during the demolding process of traditional casting technology (i.e., stroke S≥2.5H). This results in the axial runout tolerance of the aforementioned hydraulic cylinder generally exceeding the standard under continuous high pressure conditions, leading to high costs and a risk of deterioration in mold closing accuracy due to the dynamic sag of the hydraulic cylinder, resulting in a large amount of mold misalignment and an increase in casting defects. Designing a reasonable demolding method to reduce the stroke of the main hydraulic cylinder is also an urgent problem to be solved in the production of large-size castings. Summary of the Invention

[0006] This invention addresses the structural components of high-pressure GIS aluminum alloy mechanical chambers. It designs a low-pressure casting process and mold using a metal outer mold combined with an internal sand core and local chills. Through the rational design of the gating system and the casting auxiliary demolding structure, internal defects in the castings are eliminated, product consistency is ensured, and the density of the castings and the process yield are improved. With the cooperation of low-pressure casting equipment, a stable casting cycle is formed, thereby improving production efficiency and product qualification rate, and reducing production costs.

[0007] The complete technical solution of this invention includes:

[0008] Low-pressure casting device for high-pressure GIS aluminum alloy mechanical chamber.

[0009] The high-pressure GIS aluminum alloy mechanism chamber includes a base flange, a hemispherical shell, a left chamber, and a right chamber.

[0010] The base flange is frustum-shaped, with a thickness of 25~35mm, an outer diameter of not less than 450mm, and an inner diameter of not less than 320mm.

[0011] The wall thickness of the hemispherical shell is no more than 25mm, the outer diameter is no less than 190mm, and the inner diameter is no less than 175mm;

[0012] The wall thickness of the left and right chambers is 10-15mm, and the height of the high-pressure GIS aluminum alloy mechanism chamber is not less than 500mm;

[0013] The low-pressure casting device includes a mold system, a gating system, conformal aluminum alloy chills, and a mold release system. The gating system is structured as follows: a gate is set below the flange face of the base flange, and a horizontal runner is set between the gate and the flange face. The molten aluminum rises under the pressure of compressed air, is injected from the gate through the liquid riser channel, and enters the mold cavity through the horizontal runner.

[0014] The mold-lifting system includes a first riser, a second riser, and a mold-lifting groove located at the top of the high-pressure GIS aluminum alloy mechanism chamber. After the casting solidifies, the side mold of the mold system is opened first, and the main hydraulic cylinder group lifts the top mold of the mold system to a certain height. Through the clamping force between the mold-lifting system and the casting, the casting is driven to rise, causing the sprue to separate from the bottom mold of the mold system. Then, the ejection hydraulic cylinder is used to eject the casting from the top mold, causing the casting to fall to the bottom mold.

[0015] Furthermore, the area of ​​the horizontal runner is designed based on the height of the casting, the maximum horizontal length, the maximum horizontal width, and the average wall thickness.

[0016] Furthermore, the outer side of the horizontal runner is offset from the outer side of the base flange. The width of the horizontal runner on both sides is 0.8 times the width of the base flange, and the width of the central part of the horizontal runner is 1.5 times the width of the base flange. The horizontal runner is symmetrically arranged on both sides with the gate as the center.

[0017] Furthermore, the mold system includes a bottom mold, side molds, a top mold, and a sand core. The bottom mold is used to fix the sprue cup and the insulated cup, support and position the sand core, and form the sprue and runner. The side molds are used for forming the overall outer side of the high-pressure GIS aluminum alloy chamber and provide support and positioning for the sand core. The top mold is used for forming the top surface of the high-pressure GIS aluminum alloy chamber.

[0018] Furthermore, the sand core is used for the inner cavity forming of the high-pressure GIS aluminum alloy mechanism chamber. The bottom surface of the sand core cooperates with the bottom mold, and the side surface of the sand core cooperates with the side mold to achieve the fixation, anti-rotation and anti-floating of the sand core.

[0019] Furthermore, side risers are provided at the side mold positions to compensate for the excessive thickness of the high-pressure GIS aluminum alloy mechanism chamber.

[0020] Furthermore, the draft angle of the side riser is 2°-3°, and the draft angle of the top riser is 1°.

[0021] Furthermore, the depth of the mold release groove is 40mm.

[0022] Furthermore, a conformal aluminum alloy chill is placed on the sand core, the conformal aluminum alloy chill has a thickness of 20mm, and a cooling system is provided within the mold system.

[0023] Furthermore, the method for low-pressure casting of high-pressure GIS aluminum alloy mechanism chambers using the aforementioned low-pressure casting apparatus includes the following steps:

[0024] 1) Liquid rising stage: Under the pressure of compressed air, the molten aluminum in the holding furnace enters the gate through the liquid rising channel;

[0025] 2) Filling stage: The pressure of compressed air is continuously increased to fill the mold cavity with molten aluminum. The filling pressure is dynamically adjusted according to the height of the molten aluminum to complete the filling of the mold cavity.

[0026] 3) Shell Formation and Pressurization Stage: After the filling stage is completed, the compressed air pressure is increased to allow the casting to form a shell within a certain time.

[0027] 4) Crystallization and pressure holding stage: Maintain the compressed air pressure of the shell-forming and pressurizing stage until all the aluminum liquid in the cavity has solidified;

[0028] 5) Depressurization stage: The compressed gas in the holding furnace is discharged to relieve the pressure, allowing the unsolidified aluminum liquid in the gating and rising channel to flow back into the holding furnace.

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

[0030] 1. Optimized Design of the Gating System: For large, hollow, thin-walled castings with complex internal structures, a gating system design method based on actual production processes is proposed. This method utilizes a gating system design on the flange surface, offering versatility applicable to the rational design of gating systems for various castings. Specifically for the casting in this invention, a reasonable pouring area for the horizontal runner is defined, employing a horizontal runner structure that is staggered from the base flange to avoid heat points, and a symmetrical layout with a span of 60°-90° around the gate. Simultaneously, the design principle of dynamically adjusting the draft angle of the riser position according to the mold opening direction (2°-3° for side risers, approximately 1° for top risers) is implemented. This optimized gating system design reduces heat points, improves process yield (metal utilization), and optimizes process efficiency and economy.

[0031] 2. Innovative Mold Structure: A unique composite low-pressure casting solution combining a metal outer mold, sand core, and localized chills systematically solves the key challenges in manufacturing the aluminum alloy chamber of a high-voltage switch. The five-element synergistic mold configuration—bottom mold, side mold, top mold, sand core, and riser sleeve—integrates the following: the bottom mold fixes the gating system, supports and positions the sand core, and forms the runner; the side molds function as both external casting forming and sand core support / positioning; the top mold integrates top surface forming, riser fixing, and a release groove (approximately 40mm deep) for reliable demolding; a thin-walled (approximately 5mm) sealable riser sleeve design; and a precise anti-rotation and anti-floating mechanism between the sand core and the metal mold ensures the consistency and integrity of the complex structure. Coupled with the automation characteristics of low-pressure casting, this creates a stable production cycle. The coordinated design of the sand core and metal molds (bottom mold and side molds) (positioning, anti-rotation, and anti-floating) guarantees high-precision replication of the chamber's shape. The introduction of the mold release groove structure cleverly utilizes the top mold to reliably remove the casting and sand core during mold opening, avoiding the risk of the casting accidentally falling off and damaging or remaining in the mold, and ensuring that the casting demolding process is controllable and the structure is intact.

[0032] 3. Key technologies for defect control: combining conformal aluminum alloy chills (approximately 20mm thick) on the sand core to eliminate internal thermal defects, and the process of directionally controlling the solidification sequence through the mold's built-in cooling system (water / air cooling).

[0033] 4. Low-pressure casting process parameters and flow: Protect the five-stage operation flow of the mold system, especially the key steps of the "shelling and pressurization" stage, which involves additional pressurization after filling to enhance the contact between the casting and the mold and accelerate the shelling, as well as the complete pressure control logic for each stage of liquid raising, filling, shelling and pressurization, crystallization and pressure holding, and pressure release.

[0034] 5. The overall process significantly improves the density and reliability of castings: Utilizing the continuous pressure feeding characteristics of low-pressure casting, combined with a precisely arranged riser system (outer side and top) and the active intervention of conformal aluminum alloy chills on hot spots, the molten aluminum is forced to solidify in a preset sequence, effectively eliminating shrinkage cavities and porosity defects that are difficult to avoid in traditional processes. The increased density of the casting directly enhances the sealing reliability of the mechanism chamber under SF6 gas pressure, significantly reducing the risk of high-pressure gas leakage. While ensuring high quality (dense, precise, and low-defect), this process, through modular mold design (such as the number of side molds and riser sleeve configuration) and flexible process control (pressure curves and conformal aluminum alloy chill arrangement), can adapt to the diverse, small-batch production needs of high-voltage switch mechanism chambers, balancing quality and adaptability, and providing an efficient and high-quality solution for the manufacturing of complex aluminum alloy structural components.

[0035] 6. 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 aluminum liquid during the filling process of large-sized construction castings with complex internal cavity shapes and abrupt changes in cross-sectional area, which can lead to air entrapment, porosity, oxide inclusions, and cold shuts. Attached Figure Description

[0036] Figure 1 This is a cross-sectional view of the low-pressure casting device provided by the present invention.

[0037] Figure 2 This is a structural diagram of the casting.

[0038] Figure 3 for Figure 1 The bottom view.

[0039] Figure 4 This is a diagram of the riser system.

[0040] Figure 5 This is a schematic diagram of a dual-gating system.

[0041] In the diagram, 1-bottom mold, 2-lower mold plate, 3-side mold, 4-top mold, 5-upper mold plate, 6-sand core, 7-gate, 8-sprue, 9-side riser, 10-first top riser, 11-second top riser, 12-riseer sleeve, 13-molding groove, 14-first chill, 15-second chill, 16-third chill, 17-casting, 18-base flange. Detailed Implementation

[0042] 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.

[0043] A low-pressure casting device for a high-pressure GIS aluminum alloy mechanism chamber, such as Figures 1-5 As shown, the casting 17 of the high-pressure GIS aluminum alloy mechanism chamber includes a base flange 18, a hemispherical shell, a left chamber, and a right chamber. The base flange is approximately frustum-shaped, with a thickness of 25-35 mm, an outer diameter of approximately 450-600 mm, and an inner diameter of approximately 320-400 mm. The hemispherical shell has a wall thickness of 5-25 mm, an outer diameter of 190-210 mm, and an inner diameter of 175-185 mm. The left and right chambers are approximately rectangular or trapezoidal cavities with a wall thickness of 10-15 mm. The height of the entire mechanism chamber is approximately 500-700 mm.

[0044] The inventors of this invention previously disclosed 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 using multiple lift pipes and gates for filling. However, the casting involved in this invention is a large hollow casting with larger dimensions, larger internal space and complex structure, and relatively thin wall thickness. The aluminum liquid flow path is long, which makes it very easy to have problems such as excessively rapid cooling and delayed filling. Furthermore, it is impossible to use an all-metal mold structure. It is necessary to form the internal cavity composite structure through sand cores. Therefore, the casting method of the aforementioned prior application cannot be used. In addition, the internal cavity of the casting of this invention has an irregular shape and a large variation in cross-sectional area. Therefore, it is impossible to use the method of entering the cavity through the internal gating channel. The aluminum liquid can only be injected from the bottom gate and enter the cavity through the horizontal gating channel, which further increases the design difficulty of the gating system.

[0045] Based on the above problems, the gating system designed in this invention has a gating gate 7 arranged below the downward flange face of the base flange of the mechanism chamber, and a horizontal runner 8 set between the gating gate and the flange face. The gating system is designed based on the shape characteristics of the casting, and a reasonable horizontal runner structure is selected to achieve reasonable filling. For the large hollow castings of this invention, the design of the horizontal runner determines whether sufficient flow can be provided to prevent the molten aluminum from solidifying too quickly before reaching the far end of the cavity, and to achieve a reasonable balance between flow rate and cooling time, so that the molten aluminum maintains its liquid flow capacity throughout the filling process, eliminating cold shut defects. If the horizontal runner area is too small, the flow rate of molten aluminum will not be able to 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 at the far end. It may also lead to unstable filling, scouring or air entrapment of the mold core. If the horizontal runner is too large, the rising speed of the molten aluminum may be too slow, increasing the temperature difference and solidification time, resulting in excessive internal stress in the casting, potentially forming dead water zones, increasing subcutaneous porosity defects, and causing unnecessary waste. Therefore, this invention incorporates the transverse dimension characteristics of the casting into the design for the first time to solve the problem of unreasonable filling and solidification of large-span cavities. Specifically:

[0046]

[0047] In the formula, The area of ​​the horizontal pouring channel. This is an empirical coefficient, with a value range of 0.001-0.0025. The height of the casting (mm) ranges from 500 to 700 mm. 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 ranges from 12 to 25 mm.

[0048] 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. The wall thickness factor means that the thinner the wall, the greater the flow resistance, and the larger the cross-sectional area of ​​the gating system is required.

[0049] 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:

[0050]

[0051] In the formula, The filling time is expressed in seconds (s).

[0052] 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.

[0053] Based on the above principles and the specific dimensional parameters of the mechanism chamber of this invention, the casting height is 531mm, the horizontal length is 619mm, the maximum width is 275mm, and the average wall thickness is 18mm. The filling time should be less than 29 seconds. Based on the calculation results, the horizontal runner structure of this invention is designed, specifically, a single gate / horizontal runner mode or a double gate / horizontal runner mode can be adopted.

[0054] The specific structure of the horizontal runner is as follows: the outer side of the horizontal runner is offset from the outer side of the base flange, leaving a certain distance. The width of the horizontal runner on both sides is 0.8 times the width of the base flange. To ensure sufficient pouring area, the width of the horizontal runner in the center is increased to 1.5 times the width of the base flange. In the single horizontal runner mode, the area is approximately 47,000 mm². 2 In the double horizontal runner configuration, the area is approximately 94000 mm². 2 Its thickness is referenced to the thickness of the base flange, and the thickness of the horizontal runner is approximately 1.5 times the thickness of the base flange to avoid the formation of hot spots. The span of the horizontal runner is 60°-90° symmetrical on both sides of the gate.

[0055] The mold structure of this invention includes a bottom mold 1, side molds 3, a top mold 4, and a sand core 6. The bottom mold 1 is used to fix the pouring cup and the insulated cup, support and position the sand core, and form the sprue and runner. The bottom mold is connected to the lower template 2 by bolts and other connecting parts, and is fixed to the lower platform of the low-pressure casting equipment by the lower template 2, while also connecting to the liquid lifting system of the low-pressure equipment. The side molds 3 are designed according to the structure of the mechanism chamber and the mold opening requirements of the metal mold. The side molds are first used for forming the outer side of the mechanism chamber as a whole, and provide support or positioning for the sand core formed in the inner cavity of the mechanism chamber. The top mold 4 is connected to the upper template 5 by bolts and other connecting parts, and is used for forming the top surface of the process position of the mechanism chamber, fixing the riser sleeve and forming the riser. Finally, it is used to pull up the casting and sand core through the mold release groove structure after the mold is opened, so that it is separated from the bottom mold 1. The sand core 6 is used for forming the inner cavity of the mechanism chamber. The bottom surface of the sand core mates with the bottom mold 1, and the side surface of the sand core mates with the side mold, thereby fixing, preventing rotation, and preventing floating of the sand core.

[0056] Next is the riser and mold-opening design of the present invention. As mentioned above, the present invention uses a movable platform when opening the mold, so that the bottom mold and a side mold are located on the platform and can be moved to the casting station to complete the mold closing and casting. After completion, each side mold is opened first, and the top mold is slightly lifted upward by the main hydraulic cylinder group to separate the sprue from the bottom mold. Then, the casting on the top mold is ejected by the ejection hydraulic cylinder so that the casting falls to the bottom mold. Then, the movable platform carries the casting away from the casting station to complete the part removal.

[0057] The above process involves the top mold lifting the casting and sand core from the bottom mold after the side mold is opened following casting completion. To achieve this, the top mold and casting need sufficient clamping force to support the weight of the casting and sand core. Regarding the risers, a first top riser 10 and a second top riser 11 are designed on the top side of the chamber, while a side riser 9 is provided at the side mold location for feeding the thicker areas of the chamber. Since both the outer and top sides of the chamber are formed using metal molds, the draft angle of the risers is adjusted according to the mold opening direction. The draft angle of the side risers is 2°-3°, while the draft angle of the top risers is reduced to approximately 1°. Meanwhile, since the outer side of the mechanism chamber is formed by the side mold, and the top mold is only used for forming the top surface of the mechanism chamber and the riser, the clamping force between the casting and the top mold is insufficient after the casting solidifies. Therefore, in order to prevent the casting from being uncontrolled to demold after the mold is opened, causing the casting to remain in the mold or fall off before ejection, a mold release groove 13 is designed on the top surface of the casting, with a depth of about 40mm. This is beneficial for the top mold to drive the casting and sand core to detach from the bottom mold after the mold is opened.

[0058] It also includes a riser sleeve 12, which is made according to the shape of the outer side of the riser in the casting, with a wall thickness of about 5mm. The material can be the same as the mold or other metal materials. The top of the riser sleeve is sealed with a cover plate connected by bolts to prevent the molten aluminum from overflowing the mold under pressure.

[0059] Cooling system: Based on the above structure and in combination with the casting process, water cooling or air cooling is designed on the metal mold corresponding to the first and last solidification areas of the casting to promote the solidification of the casting in the process sequence and shorten the casting cycle.

[0060] Simultaneously determine the location of the hot spot within the internal cavity of the mechanism. If feeding cannot be achieved through risers on the outside or top, design a conformal aluminum alloy chill at the thickest location. The conformal aluminum alloy chill is 20mm thick and made of aluminum alloy. Before casting, it is combined with the sand core to generate extreme cooling effect on the designated area of ​​the casting, thereby eliminating internal defects in the casting. Figure 1 As shown, it includes a first chill 14, a second chill 15, and a third chill 16 disposed at the thickest part of the casting.

[0061] Operation process:

[0062] 1) Liquid Lifting Stage: In the low-pressure casting equipment, molten aluminum in the holding furnace is lifted into the gate location through the lifting channel under the pressure of compressed air. Specifically, the equipment steadily increases the pressure inside the sealed holding furnace to 180-220 mbar within 10-15 seconds at a rate of 15-25 mbar / s. Driven by this pressure, the molten aluminum rises steadily along the lifting channel until it completely fills the bottom gate of the mold, preparing for subsequent filling. The key to this stage is controlling the lifting speed to avoid turbulence and air entrapment.

[0063] 2) Filling stage: Continuous pressurization causes the molten aluminum to fill the mold cavity. According to the liquid height, the order in which the molten aluminum fills the cavity is: gate, runner, mechanism chamber and side risers, top riser;

[0064] 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.

[0065] Based on the above problems, the device of the present invention adopts a dynamic control filling method through the control system.

[0066] First, based on the casting process conditions, a reasonable baseline filling pressure rise rate is determined. Then, based on the real-time changes in the cross-sectional area of ​​the molten aluminum during the actual filling process, the filling pressure rise rate is dynamically adjusted. Specifically, this includes:

[0067] (1) Determination of reference filling pressure and rate of increase

[0068] First, based on process conditions such as pouring temperature, mold preheating temperature, and thermal properties of molten aluminum, simulation and experimental verification were conducted. Considering 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 flow rate that ensures smooth mold filling was obtained. Subsequently, based on the pressure balance of low-pressure casting filling: the pressure inside the crucible needs to overcome the static pressure of the molten aluminum and the flow resistance, the reference pressure increase rate is obtained: 8mbar / s-12mbar / s.

[0069] (2) Real-time dynamic adjustment during the filling process

[0070] 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 pressurization rate.

[0071] 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.

[0072]

[0073] To accelerate the pressure in the next long period, The pressure increase rate is set for the current step size. This is an adjustment coefficient, with a value range of 0.5–0.7.

[0074] 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 pressure adjustment before the molten aluminum reaches the abrupt change region, greatly improving control accuracy.

[0075] Secondly, a balance between rapid and stable filling was achieved. By setting a reasonable baseline flow rate, safety was ensured at the thinnest wall thickness. In areas with wide cross-sections, the allowable pressure rise rate 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.

[0076] Furthermore, by combining query statements and model adjustments, the filling process scheme was fully digitized. 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. This reduces the cost and risk of on-site trial and error.

[0077] Through the above-mentioned filling method, under stable pressure, the aluminum liquid fills the entire mold cavity in a laminar flow manner. Precise filling speed control is used to obtain castings with clear contours and smooth surfaces, and to prevent casting defects.

[0078] 3) Shell Formation and Pressurization Stage: After filling, the pressure is appropriately increased based on the current pressure to enhance the contact between the casting and the mold cavity, allowing the product to solidify and form a shell within a shorter time. Specifically, within 10-15 seconds, the pressure is rapidly increased to 500-600 mbar at a rate of 15-20 mbar / s. This pressurization operation aims to effectively act on the solidifying metal, forcibly compensating for shrinkage defects and porosity caused by solidification shrinkage, especially ensuring the density of the microstructure in thicker areas or the first solidified regions.

[0079] 4) Crystallization and Pressure Holding Stage: Maintain the current pressure until all the molten aluminum in the mold cavity solidifies; specifically: after pressurization, the system will maintain a pressure of 500mbar-600mbar for 500s-600s. During this period, the casting solidifies sequentially from far to near under constant pressure, allowing the molten aluminum in the holding furnace to continuously replenish the solidification shrinkage until the casting is completely solidified, thus ensuring the overall density and mechanical properties of the structure.

[0080] 5) Depressurization Stage: Depressurization is achieved by controlling the discharge of compressed gas from the holding furnace, allowing the molten aluminum that has not yet solidified in the gating and rising channels to flow back into the holding furnace. Specifically: after the holding time ends and the casting has completely solidified, the equipment control system opens the exhaust valve to release the compressed gas in the holding furnace, allowing the system pressure to steadily drop to atmospheric pressure. Subsequently, the molten aluminum that has not yet solidified in the gating and rising channels automatically flows back into the holding furnace under gravity, preparing for the next casting cycle.

[0081] 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 a high-pressure GIS aluminum alloy mechanism chamber, characterized in that, The high-pressure GIS aluminum alloy mechanism chamber includes a base flange, a hemispherical shell, a left chamber, and a right chamber. The base flange is frustum-shaped, with a thickness of 25~35mm, an outer diameter of not less than 450mm, and an inner diameter of not less than 320mm. The wall thickness of the hemispherical shell is no more than 25mm, the outer diameter is no less than 190mm, and the inner diameter is no less than 175mm; The wall thickness of the left and right chambers is 10-15mm, and the height of the high-pressure GIS aluminum alloy mechanism chamber is not less than 500mm; The low-pressure casting device includes a mold system, a gating system, conformal aluminum alloy chills, and a mold release system. The gating system is structured as follows: a gate is set below the flange face of the base flange, and a horizontal runner is set between the gate and the flange face. The molten aluminum rises under the pressure of compressed air, is injected from the gate through the liquid riser channel, and enters the mold cavity through the horizontal runner. The mold-lifting system includes a first riser, a second riser, and a mold-lifting groove located at the top of the high-pressure GIS aluminum alloy mechanism chamber. After the casting solidifies, the side mold of the mold system is opened first, and the main hydraulic cylinder group lifts the top mold of the mold system to a certain height. Through the clamping force between the mold-lifting system and the casting, the casting is driven to rise, causing the sprue to separate from the bottom mold of the mold system. Then, the ejection hydraulic cylinder is used to eject the casting from the top mold so that the casting falls to the bottom mold. The area of ​​the horizontal runner is designed based on the height of the casting, the maximum horizontal length, the maximum horizontal width, and the average wall thickness. The outer side of the horizontal runner is offset from the outer side of the base flange. The width of the horizontal runner on both sides is 0.8 times the width of the base flange, and the width of the central part of the horizontal runner is 1.5 times the width of the base flange. The horizontal runner is symmetrically arranged on both sides with the gate as the center. The mold system includes a bottom mold, side molds, a top mold, and a sand core. The bottom mold is used to fix the sprue cup and the insulated cup, support and position the sand core, and form the sprue and runner. The side molds are used to form the overall outer side of the high-pressure GIS aluminum alloy chamber and provide support and positioning for the sand core. The top mold is used to form the top surface of the high-pressure GIS aluminum alloy chamber. Side risers are set at the side mold position to compensate for the large thickness of the high-pressure GIS aluminum alloy mechanism chamber; The depth of the mold release groove is 40mm; The conformal aluminum alloy chill is placed on the sand core. The conformal aluminum alloy chill is 20mm thick. The mold system is equipped with a cooling system.

2. The low pressure casting apparatus for high voltage GIS aluminum alloy mechanism chamber according to claim 1, characterized by, The sand core is used for the inner cavity forming of the high-pressure GIS aluminum alloy mechanism chamber. The bottom surface of the sand core is matched with the bottom mold, and the side surface of the sand core is matched with the side mold to achieve the fixation, anti-rotation and anti-floating of the sand core.

3. The low pressure casting apparatus for high voltage GIS aluminum alloy mechanism chamber according to claim 2, characterized by, The draft angle of the side riser is 2°-3°, and the draft angle of the top riser is 1°.

4. A method for low-pressure casting of high-pressure GIS aluminum alloy mechanical chambers using the low-pressure casting apparatus described in claim 3, characterized in that, Includes the following steps: 1) Liquid rising stage: Under the pressure of compressed air, the molten aluminum in the holding furnace enters the gate through the liquid rising channel; 2) Filling stage: The pressure of compressed air is continuously increased to fill the mold cavity with molten aluminum. The filling pressure is dynamically adjusted according to the height of the molten aluminum to complete the filling of the mold cavity. 3) Shell Formation and Pressurization Stage: After the filling stage is completed, the compressed air pressure is increased to allow the casting to form a shell within a certain time. 4) Crystallization and pressure holding stage: Maintain the compressed air pressure of the shell-forming and pressurizing stage until all the aluminum liquid in the cavity has solidified; 5) Depressurization stage: The compressed gas in the holding furnace is discharged to relieve the pressure, allowing the unsolidified aluminum liquid in the gating and rising channel to flow back into the holding furnace.

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