A method of pressurized solidification of aluminum alloy castings based on low pressure casting

Abstract

The application relates to a low-pressure casting-based aluminum alloy casting pressurized solidification method, and belongs to the technical field of aluminum alloy casting, which solves the problem that the top of a casting with a high height dimension is prone to loose defects in low-pressure casting, thereby affecting the casting quality and the yield of finished products. The pressurized solidification method increases the pressurizing mode from top to bottom on the basis of the traditional low-pressure casting mode of pressurizing from bottom to top, the upper and lower parts of the liquid casting are simultaneously pressurized during casting, effective feeding under pressure of the whole region of the casting can be realized, and the loose defects of the top of the casting are solved.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy casting technology, and in particular to a method for pressurized solidification of aluminum alloy castings based on low-pressure casting. Background Technology

[0002] Aluminum alloy castings are increasingly in demand in the aerospace industry due to their lightweight and high specific strength. Aerospace cabin castings are mostly load-bearing components with high performance requirements, necessitating excellent microstructure and high internal quality. Low-pressure casting is generally used in the research and production of these castings. In low-pressure casting, molten metal fills the mold cavity under pressure, which helps to form castings with smooth surfaces, high internal quality, and dense microstructure.

[0003] When using traditional low-pressure casting to produce large-sized castings, porosity defects are easily generated at the top of the casting, resulting in poor casting quality and yield. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a pressure solidification method for aluminum alloy castings based on low-pressure casting, which solves the problems of internal porosity, insufficient top mechanical properties, and low yield rate that are prone to occur in castings with high dimensions during low-pressure casting in the prior art.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] This invention provides a method for pressurized solidification of aluminum alloy castings based on low-pressure casting, comprising the following steps:

[0007] S1. Install the upper pressure device, and the top of the casting solidifies under the pressure of the upper pressure device during casting;

[0008] S2. Start pouring. Under the gas pressure of the lower pressurization device, the molten metal rises along the riser pipe to fill the mold cavity. After the molten metal has filled the mold, continue pouring and start the hydraulic system.

[0009] S3. After the molten metal has completely solidified, stop pouring and shut down the hydraulic system.

[0010] Furthermore, S1 specifically includes:

[0011] S01. Connect and fix the pressure plate to the hydraulic system via a connecting rod;

[0012] S02. Pass the horizontal plate of the sand mold locking mechanism through the hollow structure on the pressure plate to secure the sand mold, so that the sand mold is fixed during the pressurization process;

[0013] S03. Adjust the position of the pressure plate so that the protrusion of the pressure plate is inserted into the outer edge of the sand mold riser and fits tightly against the outer edge of the sand mold riser, so that the pressure plate and the molten metal in the sand mold riser come into contact and apply pressure when pressurizing.

[0014] Furthermore, in S2, the hydraulic system is started 10 to 20 seconds after the molten metal filling process is completed.

[0015] Furthermore, in S2, after the hydraulic system is started, the connecting rod of the hydraulic system drives the pressure plate to move downward, pressurizing the upper part of the molten metal in the sand mold riser at the top of the casting cavity.

[0016] Furthermore, in S2, the pressure plate moves downwards by 10-15mm and then stops moving while maintaining pressure.

[0017] Furthermore, in S2, the pressure is maintained at 500 kPa for 300–420 seconds.

[0018] Furthermore, in S2, the pouring temperature is 690–700℃, the filling pressure is 75 kPa, and the filling speed is 60 mm / s.

[0019] Furthermore, after S3, solidification, cooling, and depressurization are required for subsequent processing to finally obtain the aluminum alloy casting.

[0020] Furthermore, even when the aluminum alloy casting is large in size, the top structure of the casting remains dense.

[0021] Furthermore, in S1, the upper pressurizing device includes a pressurizing plate and a pressurizing plate driving mechanism; the lower end face of the pressurizing plate is provided with a protrusion of the pressurizing plate, and the protrusion of the pressurizing plate is inserted into the outer edge of the sand mold riser and fits tightly with the outer edge of the sand mold riser; the pressurizing plate driving mechanism includes a hydraulic system with connecting rods, one end of the hydraulic system is fixed on the low-pressure casting machine, and the other end of the hydraulic system is connected to the pressurizing plate through the connecting rods. Under the drive of the hydraulic system, the pressurizing plate moves downward, so that the protrusion of the pressurizing plate pressurizes the top molten metal from above.

[0022] The present invention also provides a pressure device for aluminum alloy castings, used to implement the above-described method, including a low-pressure casting machine, a sand mold disposed inside the low-pressure casting machine, and an upper pressure system.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] 1. During the pouring process of aluminum alloy castings, the molten aluminum fills the mold cavity under the pressure of both the upper and lower directions, ensuring that the entire area of ​​the casting is fed under pressure, effectively preventing the formation of porosity defects inside the casting, and improving the density of the internal structure of the casting.

[0025] 2. The internal quality of the castings has been significantly improved. X-ray inspection showed a high pass rate, solving the problem that high-height castings are prone to porosity defects at the top during low-pressure casting in existing technologies.

[0026] 3. Effectively improves the mechanical properties of the top of the casting, enhancing the overall strength and durability of the casting. In this invention, the above-mentioned technical solutions can also be combined to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0028] Figure 1 This is a schematic diagram and cross-sectional view of the pressure casting device for aluminum alloy castings according to the present invention;

[0029] Figure 2 for Figure 1 Enlarged schematic diagram of the pressure plate area in the device;

[0030] Figure 3 This is a schematic diagram of the pressure plate structure;

[0031] Figure 4 Diagram of a device for removing the pressure plate (left) and having the pressure plate (right);

[0032] Figure 5 X-ray inspection image of the casting manufactured for Comparative Example 1;

[0033] Figure 6 The image shows an X-ray inspection image of the casting manufactured in Example 1.

[0034] Figure label:

[0035] 1-Low-pressure casting machine; 2-Partition plate; 3-Hydraulic system; 4-Sand mold; 5-Sand box; 6-Sand mold cover plate; 7-Pressure plate; 8-Support rod of sand mold locking mechanism; 9-Horizontal plate of sand mold locking mechanism; 10-Crucible; 11-Electric heating wire; 12-Liquid riser pipe; 13-Casting cavity; 14-Hollow structure of pressure plate; 15-Protrusion of pressure plate; 16-Sand mold riser; 17-Sand mold pressure plate. Detailed Implementation

[0036] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0037] In traditional low-pressure casting, gas pressure is applied to the molten metal from the bottom to the top of the casting cavity during pouring. However, when pouring castings with a high height, such as castings with a height of 1200 mm or more, the pressure applied to the liquid surface during solidification cannot be transmitted to the top of the casting due to the long flow path of the gating system. This greatly weakens the pressure feeding effect of low-pressure casting, and the top of the casting can only solidify under gravity conditions, which easily leads to porosity defects at the top of the casting.

[0038] The method of this invention adds upper pressure, i.e., upper pressure, to the traditional method of only lower pressure, i.e., gas pressure applied from bottom to top. During casting, the upper and lower parts of the molten metal are simultaneously pressurized, which can achieve effective feeding of the entire casting area under pressure, thereby solving the porosity defect at the top of large-scale castings.

[0039] A method for pressurized solidification of aluminum alloy castings based on low-pressure casting includes the following steps:

[0040] S1. Install an upper pressure device to ensure that the top of the casting solidifies under the pressure of the upper pressure device during casting, thus ensuring the metallurgical quality of the top of the casting.

[0041] S2. Start pouring. Under the gas pressure of the lower pressurization device, the molten metal rises along the riser pipe to fill the mold cavity. After the molten metal has filled the mold, continue pouring and start the hydraulic system.

[0042] S3. After the molten metal has completely solidified, stop pouring and shut down the hydraulic system.

[0043] Furthermore, S1 specifically includes:

[0044] S01. Connect and fix the pressure plate to the hydraulic system via a connecting rod;

[0045] S02. The horizontal plate of the sand mold locking mechanism is passed through the hollow structure on the pressure plate to secure the sand mold, so that the sand mold is fixed during the pressurization process, while the hollow structure of the pressure plate allows the pressure plate to move freely during the pressurization process.

[0046] S03. Adjust the position of the pressure plate so that the protrusion of the pressure plate is inserted into the outer edge of the sand mold riser and fits tightly against the outer edge of the sand mold riser, so that it can contact the molten metal in the sand mold riser and apply pressure to it during pressurization.

[0047] Specifically, before S01, the sand box 5 containing the sand mold 4 needs to be placed on the partition plate 2 in the low-pressure casting machine 1, and then the sand mold cover plate 6 is installed on the sand mold 4.

[0048] Furthermore, in S2, the molten metal is poured after it reaches the set temperature, and the hydraulic system is activated 10 to 20 seconds after the molten metal has filled the mold.

[0049] Specifically, the reason for starting the process 10-20 seconds after the filling is completed is that there is still gas that has not been discharged after the molten metal is filled. After 10-20 seconds, the gas is discharged, and then the hydraulic system 3 is started. The pressure plate acts directly on the surface of the molten metal, which can effectively feed the casting.

[0050] Furthermore, in S2, after the hydraulic system 3 is started, the connecting rod of the hydraulic system drives the pressure plate to move downward, pressurizing the upper part of the molten metal in the sand mold riser at the top of the casting cavity.

[0051] In one possible implementation, an electric heating wire inside the low-pressure casting machine heats the molten metal in the crucible to a certain temperature. Once the temperature reaches the pouring temperature, the molten metal rises through a riser pipe into the casting cavity under a certain air pressure, filling the cavity. (See reference for details.) Figure 1 After the molten metal has filled the mold, the hydraulic system is activated. The connecting rod of the hydraulic system moves the pressure plate downward, pressurizing the upper part of the molten metal in the sand riser at the top of the casting cavity. At this time, the molten metal at the top of the casting will be subjected to pressure from both the upper and lower directions during the solidification process. This allows for full-area pressure feeding of the aluminum alloy casting, effectively feeding the casting and resulting in better internal quality.

[0052] Furthermore, in S2, the pressure plate moves downwards by 10-15mm and then stops moving while maintaining pressure.

[0053] Specifically, as the pressure plate 7 moves downwards, the molten metal in the casting cavity begins to solidify, reducing its fluidity and affecting pressure transmission efficiency. After moving 10-15 mm, it is sufficient to ensure that the pressure can be effectively transmitted to the entire surface of the molten metal. If the pressure plate continues to move downwards after the molten metal has partially solidified, it may put excessive pressure on the casting, causing deformation or damage.

[0054] Furthermore, in S2, the pressure is maintained at 500 kPa for 300–420 seconds.

[0055] Specifically, after the pressure plate 7 moves downward by 10-15mm, the molten metal has partially solidified and reached a relatively stable state. At this time, maintaining a pressure of 500kPa can achieve the best feeding effect of the molten metal. Pressure greater than 500kPa can easily damage the sand mold 4. The pressure holding time is selected as 300-420s because the molten metal has not completely solidified before 300s, and after 420s the molten metal has completely solidified, and further pressure will have no effect.

[0056] Furthermore, in S2, the pouring temperature is 690–700℃, the filling pressure is 75 kPa, and the filling speed is 60 mm / s.

[0057] Specifically, in S2, this temperature range is used because temperatures below 690℃ are not conducive to molten metal feeding, while temperatures above 700℃ will cause increased shrinkage during casting solidification, resulting in dispersed porosity. This filling pressure is used because it can ensure that the molten metal completely fills the mold cavity. This filling speed is used because it is the critical filling speed of the molten metal. Below this speed, the filling time is long, and there is a risk of incomplete pouring. Above this speed, the filling process of the casting will cause turbulence and slag inclusions.

[0058] Furthermore, after S3, solidification, cooling, and depressurization are required to obtain an aluminum alloy casting. Even when the casting is large in size, the top structure of the casting remains dense.

[0059] Furthermore, in S1, the upper pressurizing device includes a pressurizing plate 7 and a pressurizing plate driving mechanism;

[0060] The lower end face of the pressure plate is provided with a protrusion 15 of the pressure plate, and the protrusion 15 of the pressure plate is inserted into the outer edge of the sand mold riser 16 and fits tightly with the outer edge of the sand mold riser 16.

[0061] The pressure plate drive mechanism includes a hydraulic system 3 with connecting rods. One end of the hydraulic system 3 is fixed on the low-pressure casting machine 1, and the other end of the hydraulic system 3 is connected to the pressure plate 7 through the connecting rods. Under the drive of the hydraulic system 3, the pressure plate 7 moves downward, so that the protrusion 15 of the pressure plate pressurizes the top molten metal from the top.

[0062] During pressure casting, the molten metal rises along the riser pipe 12 under gas pressure to fill the casting cavity 13. During pouring, the protrusion 15 of the pressure plate, driven by the hydraulic system 3, pressurizes the molten metal at the top of the sand mold riser 16 from above. Based on this pressure casting method, aluminum alloy castings can be filled into the cavity simultaneously under pressure from both above and below during pouring, achieving full-area pressure feeding of the casting. This effectively feeds the casting, resulting in a dense internal structure and better internal quality. X-ray inspection of the castings shows a high pass rate. This method solves the problem of porosity defects easily occurring at the top of taller castings during low-pressure casting, affecting casting quality and pass rate, and also effectively improves the mechanical properties of the casting top.

[0063] Furthermore, the upper pressurization device also includes a partition plate 2, which is disposed on the upper surface of the low-pressure casting machine 1, and one end of the hydraulic system 3 is fixed to the low-pressure casting machine 1 through the partition plate 2.

[0064] Specifically, the pressure plate 7 is located at the top of the pressure device and is used to move downward under the drive of the hydraulic system 3 to apply pressure to the top molten metal; the protrusion 15 of the pressure plate is inserted into the outer extension of the sand mold riser 16, which can contain molten metal during pouring. During pouring, the protrusion 15 of the pressure plate directly contacts the molten metal and applies pressure to it; the hydraulic system 3 with connecting rod is used to perform pressure application, pressure holding, etc. in the casting process. After the hydraulic system 3 is started, the connecting rod drives the pressure plate 7 to move downward to apply pressure.

[0065] Specifically, the partition 2 is used to divide the upper surface of the device into different functional areas to facilitate the installation and layout of the hydraulic system 3 and components such as connecting rods.

[0066] Furthermore, the lower part of the upper pressurizing device also includes a sand mold locking mechanism, which includes a support rod 8 and a horizontal plate 9. One end of the support rod 8 is fastened to the middle partition 2, and the other end of the horizontal plate 9 and the support rod 8 are fastened to the middle partition 2 by a nut.

[0067] Furthermore, to avoid interference between the sand mold locking mechanism and the pressure plate 7, a hollow structure 14 for the pressure plate is radially provided on the upper part of the protrusion 15 of the pressure plate; the horizontal plate 9 of the sand mold locking mechanism can pass through the hollow structure 14 of the pressure plate to fasten the sand mold 4.

[0068] Specifically, the protrusion 15 of the pressure plate matches the outer extension of the sand mold riser 16. The sand mold riser 16 is annular, and the protrusion 15 of the pressure plate is an annular protrusion. The hollow structure consists of square holes radially opened on the annular protrusion 15 of the pressure plate. These holes allow the pressure plate 7 to move within a certain range during the pressurization process without interfering with the horizontal plate 9 of the sand mold locking mechanism or other fixed structures.

[0069] Furthermore, the upper pressurization device also includes a sand mold cover plate 6, a sand mold pressure plate 17, a sand box 5, a casting cavity 13, a riser pipe 12, a crucible 10, and an electric heating wire 11;

[0070] The sand box 5 is movably placed on the middle partition plate 2 to fix the sand mold 4 inside it; the sand mold 4 includes a core and a shell, and the space between the core and the shell is the casting cavity 13, and the upper part of the casting cavity 13 is the sand mold riser 16.

[0071] The sand mold cover plate 6 includes a core upper cover plate and a shell upper cover plate. When both parts are installed on the sand mold 4, the top edge of the sand mold 4 extends outward from the two parts, forming the outer extension of the sand mold riser 16. This part can accommodate excess molten metal during pouring, ensuring that the molten metal can fully fill the sand mold and form a complete casting. To facilitate the fit between the sand mold cover plate 6 and the sand mold 4, the lower surface of the sand mold cover plate 6 is provided with a protrusion, and the upper surface of the sand mold 4 is provided with a groove. The protrusion of the sand mold cover plate 6 and the groove of the sand mold 4 cooperate to achieve accurate positioning of the two.

[0072] The sand mold pressure plate 17 is disposed on the upper surface of the sand mold cover plate 6. The sand mold pressure plate 17 is designed to pass through the hollow structure 14 of the pressure plate, with one end connected to the upper cover plate of the core and the other end fixed to the support rod 8 of the sand mold locking mechanism. It is used to press the sand mold 4 to ensure the stability of the sand mold 4 during the casting process. In some cases, the sand mold pressure plate 17 can be omitted to simplify the structural design, but this may affect the stability of the sand mold 4 during casting.

[0073] The sand mold 4 has a casting cavity 13 inside, and the bottom of the casting cavity 13 is connected to the upper end of the riser pipe 12.

[0074] The low-pressure casting machine contains a crucible for holding molten metal. Electric heating wires are arranged around the crucible along the inner wall of the low-pressure casting machine to heat and melt the molten metal. A riser pipe is installed inside the crucible, and the lower end of the riser pipe is inserted into the molten aluminum inside the crucible.

[0075] Furthermore, the hydraulic system 3 with connecting rods has ≥4 components.

[0076] Furthermore, the height of the sand box 5 is higher than that of the sand mold 4; the height of the sand mold 4 is 1200-2000mm, and the height of the sand box 5 is 1600-2400mm.

[0077] Specifically, the sand box 5 is a container used to fix the molding sand and form the sand mold 4. It is cylindrical in shape and has a height of 1600-2400mm. The sand mold 4 is made of molding sand and is used to form the outer shape and part of the inner cavity of the casting. The sand mold 4 has a circular cross-section with a diameter of 800-1500mm and a height of 1200-2000mm.

[0078] Specifically, the diameter of most cabin-type castings is between 800 and 1500 mm. In order to meet the needs of most cabin-type castings, the diameter of sand mold 4 is set to 800 to 1500 mm in this invention.

[0079] Specifically, when the casting height is below 1200mm, qualified castings can be produced using traditional low-pressure casting methods, which is not of much significance to this invention; however, when the height is above 2000mm, the filling of the mold with molten metal is difficult due to the pressure limitation of the gas source in low-pressure casting. Therefore, this invention sets the height of the sand mold 4 at 1200-2000mm to suit this pressurized solidification method.

[0080] Specifically, a sand mold cover plate 6 needs to be installed on sand mold 4, so the height of sand box 5 needs to be higher than the height of sand mold 4. After installing sand mold cover plate 6, the outer extension of sand mold riser 16 can reach 400mm, which is sufficient to feed the upper casting with molten metal during pressurized solidification. Therefore, the height of sand box 5 is 400mm higher than the height of sand mold, that is, within the range of 1600-2400mm.

[0081] Specifically, the casting cavity is the space inside the sand mold, and its shape corresponds to the shape of the desired casting. During the casting process, molten metal is introduced into the cavity, and after cooling and solidification, a casting is formed.

[0082] Specifically, the sand mold cover plate is made of steel, such as H13 steel, with a thickness of ≥400mm, for example, 400mm, and the shape of the middle part of the cover plate is consistent with the shape of the riser in the casting.

[0083] Specifically, the cover plate is made of steel such as H13 steel, which can withstand multiple high-temperature impacts, as well as the force applied to the pressure plate by the hydraulic system and molten metal, forming greater pressure at the outer edge of the riser, thus better feeding the casting.

[0084] Furthermore, during casting, the electric heating wire 11 heats the molten metal in the crucible 10 to a certain temperature. After the temperature reaches the pouring temperature, the molten metal rises into the casting cavity 13 through the riser pipe 12 under a certain air pressure.

[0085] At this time, the upper pressure plate 7 moves downward under the drive of the hydraulic system 3 linkage, so that the protrusion 15 of the pressure plate applies pressure to the molten metal inside the sand mold riser 16.

[0086] At this time, the molten metal at the top of the casting fills the cavity under the combined action of upper and lower pressures and enters the part of the casting that needs to be fed, thus achieving effective feeding and making the internal structure of the casting dense.

[0087] Compared with existing technologies, this embodiment provides a pressure solidification method for aluminum alloy castings based on low-pressure casting. This method applies pressure to both the upper and lower parts of the molten casting during casting, ensuring that the top of the casting solidifies under external force during low-pressure pouring of large castings. This guarantees the metallurgical quality of the top of the casting and improves the overall performance of the casting. Characterization results show that castings produced by this method exhibit improved tensile strength, ductile elongation, and elongation after fracture, indicating an effective improvement in the mechanical properties of aluminum alloy castings.

[0088] On the other hand, the present invention also provides a pressure device for aluminum alloy castings, including a low-pressure casting machine 1, a sand mold 4 disposed inside the low-pressure casting machine 1, and an upper pressure system; the upper pressure system includes a pressure plate 7 and a pressure plate driving mechanism; the lower end face of the pressure plate 7 is provided with a pressure plate protrusion 15, the protrusion 15 of the pressure plate is inserted into the outer edge of the sand mold riser 16 and tightly fits against the outer edge of the sand mold riser 16; the pressure plate driving mechanism includes a hydraulic system 3 with connecting rods, one end of the hydraulic system 3 is fixed to the low-pressure casting machine 1, and the other end of the hydraulic system is connected to the pressure plate 7 through the connecting rods. The upper pressure system also includes a partition plate 2, which is disposed on the upper surface of the low-pressure casting machine 1, and one end of the hydraulic system 3 is fixed to the low-pressure casting machine 1 through the partition plate 2.

[0089] Furthermore, the pressurizing device also includes a sand mold locking mechanism, which includes a support rod 8 and a horizontal plate 9. One end of the support rod 8 is fastened to the partition plate 2, and the other end of the horizontal plate 9 and the support rod 8 are fastened to the partition plate 2 by a nut. The upper part of the protrusion 15 of the pressure plate has a radially open perforated structure 14; the horizontal plate 9 of the sand mold locking mechanism can pass through the perforated structure 14 of the pressure plate to fasten the sand mold 4.

[0090] Furthermore, the pressurizing device also includes a sand mold cover plate 6, a sand mold pressure plate 17, a sand box 5, a casting cavity 13, a riser pipe 12, a crucible 10, and an electric heating wire 11; the sand box 5 is movably placed on the partition plate 2 to fix the sand mold 4 inside; the sand mold 4 includes a core and a shell, with the casting cavity 13 between the core and the shell, and the upper part of the casting cavity 13 is the sand mold riser 16; the sand mold cover plate 6 includes an upper cover plate for the core and an upper cover plate for the shell, and when both parts are installed on the sand mold 4, the outer edge of the sand mold riser 16 will be formed between the two parts. The sand mold pressure plate 17 is set on the upper surface of the sand mold cover plate 6, with one end connected to the upper cover plate of the core and the other end fixedly connected to the support rod 8 of the sand mold locking mechanism, for pressing the sand mold 4; the sand mold 4 is provided with a casting cavity 13 inside, and the bottom of the casting cavity 13 is connected to the upper end of the riser pipe 12; a crucible 10 is placed inside the low-pressure casting machine 1, and an electric heating wire 11 is arranged around the crucible 10 along the inner wall of the low-pressure casting machine 1. A riser pipe 12 is arranged inside the crucible 10, and the lower end of the riser pipe 12 is inserted into the aluminum liquid inside the crucible 10.

[0091] The present invention will be further described below with reference to the embodiments in conjunction with the specification, but the embodiments are only for the purpose of using the present invention and are not intended to limit the present invention.

[0092] Example 1

[0093] A method for pressurized solidification of aluminum alloy castings based on low-pressure casting includes the following steps:

[0094] (1) Install the pressurization device, specifically including the following steps:

[0095] 1. Place the sand box 5: Place the sand box 5 containing the sand mold 4 on the partition plate 2 of the low-pressure casting machine 1, ensuring that the sand box 5 is placed stably and in an accurate position.

[0096] 2. Install the sand mold cover plate 6: Install the sand mold cover plate 6 on the sand mold 4, ensuring that the sand mold cover plate 6 and the sand mold 4 are tightly connected and well sealed.

[0097] 3. Connect the pressure plate 7: Connect and fix the pressure plate 7 to the hydraulic system 3 through four connecting rods to ensure a firm connection and that the hydraulic system 3 can drive the pressure plate 7 normally.

[0098] 4. Install the sand mold locking mechanism: Install the support rod 8 of the sand mold locking mechanism at an appropriate position in the sand box 5, ensuring that the support rod is vertical and stable.

[0099] 5. Install the pressure plate 7: Adjust the position of the pressure plate 7 so that the protrusion 15 of the pressure plate is aligned with the sand mold riser 16, ensuring that the pressure plate 7 can apply pressure evenly.

[0100] 6. Install the sand mold pressure plate 17: Pass the sand mold pressure plate 17 through the hollow structure 14 of the pressure plate, so that one end of the sand mold pressure plate 17 is connected to the top of the support rod 8 of the sand mold locking mechanism, and the other end is installed in an appropriate position on the sand mold cover plate 6, so as to ensure that the sand mold pressure plate 17 can evenly press the sand mold 4 to prevent the sand mold 4 from loosening or deforming during the pouring process.

[0101] 7. Pass the horizontal plate 9 of the sand mold locking mechanism through the hollow structure 14 of the pressure plate and tighten the sand mold 4 to ensure that the sand mold 4 will not move or deform during the pressurization process.

[0102] (2) Preheating equipment: Start the electric heating wire 11 to preheat the aluminum alloy in the crucible and ensure that the aluminum alloy reaches the appropriate temperature before pouring.

[0103] (3) After the aluminum liquid reaches the required temperature, the casting begins. The casting temperature is 695℃, the filling pressure is 75Kpa, and the filling speed is 60mm / s.

[0104] (4) After the aluminum liquid filling is completed for 10 seconds, start the hydraulic system 3. After the hydraulic system 3 is started, it drives the pressure plate to apply pressure to the top metal liquid. The pressure plate 7 moves 10mm and then stops moving. Maintain the pressure. The pressure holding pressure is maintained at 500Kpa and the pressure holding time is 300s. Finally, the top of the casting solidifies under pressure during the solidification process.

[0105] (5) Solidification, cooling, depressurization and other subsequent treatments are carried out to finally obtain an aluminum alloy casting with a height of 1200mm.

[0106] The above method is achieved by using an aluminum alloy casting pressure casting device, which includes a hydraulic system and connecting rods, sand mold, sand mold cover plate, pressure plate, sand mold locking mechanism, and sand mold pressure plate.

[0107] The lower end face of the pressure plate 7 is provided with a pressure plate protrusion 15, which is inserted into the outer edge of the sand mold riser 16 and fits tightly against the outer edge of the sand mold riser 16. Figure 3 and Figure 4 As shown;

[0108] The pressure plate 7 is connected to the connecting rod of the hydraulic system. Driven by the hydraulic system 3, the pressure plate 7 moves downward, so that the protrusion 15 of the pressure plate pressurizes the top molten metal from above.

[0109] The sand mold locking mechanism includes a support rod 8 and a horizontal plate 9; the horizontal plate 9 and the support rod 8 of the sand mold locking mechanism are fastened to the sand mold by means of a nut.

[0110] To avoid interference between the sand mold locking mechanism and the pressure plate 7, a hollow structure for the pressure plate is radially provided on the upper part of the protrusion; the horizontal plate of the sand mold locking mechanism can pass through the hollow structure of the pressure plate to fasten the sand mold.

[0111] The sand mold cover plate 6 includes a core upper cover plate and a shell upper cover plate. When both parts are installed on the sand mold 4, an extension of the sand mold riser 16 will be formed between the two parts.

[0112] The sand mold pressing plate 17 is disposed on the upper surface of the sand mold cover plate 6. The sand mold pressing plate 17 passes through the hollow structure 14 of the pressure plate, one end is connected to the upper cover plate of the core, and the other end is fixedly connected to the support rod 8 of the sand mold locking mechanism, and is used to press the sand mold 4.

[0113] Sand mold 4 has a circular cross-section with a diameter of 800mm and a height of 1200mm; sand box 5 has a height of 1600mm; casting cavity 13 has a height of 1200mm; sand mold cover plate 6 is made of H13 steel with a thickness of 400mm.

[0114] Example 2

[0115] A method for pressurized solidification of aluminum alloy castings based on low-pressure casting includes the following steps:

[0116] Steps (1) and (2) are the same as those in Example 1;

[0117] (3) After the aluminum liquid reaches the required temperature, the casting begins. The casting temperature is 690℃, the filling pressure is 75Kpa, and the filling speed is 60mm / s.

[0118] (4) After the aluminum liquid filling is completed for 15 seconds, start the hydraulic system 3. After the hydraulic system 3 is started, it drives the pressure plate to apply pressure to the top metal liquid. The pressure plate 7 moves 12mm and then stops moving to maintain the pressure. The pressure holding pressure is maintained at 500Kpa and the pressure holding time is 360s, so that the top of the casting solidifies under pressure during the solidification process.

[0119] (5) Solidification, cooling, depressurization and other subsequent treatments are carried out to finally obtain an aluminum alloy casting with a height of 2000mm.

[0120] The above method is achieved by using an aluminum alloy casting pressure casting device. The only difference between this device and the device used in Example 1 is that the height of the sand mold 4 is 2000 mm, the height of the sand box 5 is 2400 mm, and the height of the casting cavity 13 is 2000 mm.

[0121] Example 3

[0122] A method for pressurized solidification of aluminum alloy castings based on low-pressure casting includes the following steps:

[0123] Steps (1) and (2) are the same as those in Example 1;

[0124] (3) After the aluminum liquid reaches the required temperature, the casting begins. The casting temperature is 700℃, the filling pressure is 75Kpa, and the filling speed is 60mm / s.

[0125] (4) After the aluminum liquid filling is completed for 20 seconds, start the hydraulic system 3. After the hydraulic system 3 is started, it drives the pressure plate to apply pressure to the top metal liquid. The pressure plate 7 moves 15mm and then stops moving. The pressure is maintained at 500Kpa and the pressure holding time is 420s. Finally, the top of the casting solidifies under pressure during the solidification process.

[0126] (5) Solidification, cooling, depressurization and other subsequent treatments are carried out to finally obtain an aluminum alloy casting with a height of 1500mm.

[0127] The above method is achieved by using an aluminum alloy casting pressure casting device. The only difference between this device and the device used in Example 1 is that the height of the sand mold 4 is 1500 mm, the height of the sand box 5 is 1900 mm, and the height of the casting cavity 13 is 1500 mm.

[0128] Comparative Example 1

[0129] A method for pressurizing and solidifying aluminum alloy castings based on low-pressure casting includes the following steps: filling the mold, bottom pressurization, solidification, cooling, depressurization, and post-processing, ultimately obtaining an aluminum alloy casting with a height of 1200mm.

[0130] The difference from Example 1 is that it is carried out using a traditional method, which utilizes a traditional low-pressure casting aluminum alloy casting device, including a low-pressure casting machine 1, a sand mold 4, a sand box 5, and a sand mold cover plate 6 (lacking an upper pressure device).

[0131] Comparative Example 2

[0132] A method for pressurizing and solidifying aluminum alloy castings based on low-pressure casting includes the following steps: filling the mold, bottom pressurization, solidification, cooling, depressurization, and post-processing, ultimately obtaining an aluminum alloy casting with a height of 2000 mm.

[0133] The difference from Example 2 is that it is carried out by a conventional method, using a conventional low-pressure casting aluminum alloy casting device. The only difference between this device and the device in Comparative Example 1 is the height of the casting cavity. The final product is an aluminum alloy casting with a diameter of 2000 mm.

[0134] Comparative Example 3

[0135] A method for pressurizing and solidifying aluminum alloy castings based on low-pressure casting includes the following steps: filling the mold, bottom pressurization, solidification, cooling, depressurization, and post-processing, ultimately obtaining an aluminum alloy casting with a height of 1500mm.

[0136] The difference from Example 3 is that it is carried out by a conventional method, using a conventional low-pressure casting aluminum alloy casting device. The only difference between this device and the device in Comparative Example 1 is the height of the casting cavity. The final product is an aluminum alloy casting with a diameter of 1500 mm.

[0137] Comparative Example 4

[0138] A method for casting aluminum alloy parts based on low-pressure casting, the only difference between this method and Example 1 is that, in S2, the hydraulic system 3 is started 30 seconds after the filling is completed.

[0139] Comparative Example 5

[0140] A method for casting aluminum alloy parts based on low-pressure casting, the only difference between this method and Example 4 is that, in S2, the pressure plate moves downward by 30mm and then stops moving while maintaining pressure.

[0141] Characterization test

[0142] Comparative Examples 1-3 represent aluminum alloy castings obtained using conventional low-pressure casting methods, while Examples 1-3 represent aluminum alloy castings obtained using the improved method of this invention. The mechanical property test results of the castings are shown in Table 1.

[0143] Table 1 Comparison of mechanical properties of aluminum alloy castings obtained by traditional and improved methods

[0144]

[0145]

[0146] After conducting three sets of comparisons, it was found that the improved method resulted in castings with higher tensile strength, ductile strength, and elongation after fracture compared to the traditional method. This demonstrates that the improved method of this invention can effectively improve the mechanical properties of aluminum alloy castings.

[0147] Comparative Example 1 was examined by X-ray, and the results were as follows: Figure 5 The casting showed grade 5 porosity at the top. Comparative Examples 2 and 3 also showed grade 5 porosity at the top of the casting. Example 1 underwent X-ray inspection, and the results were as follows... Figure 6 The top of the casting showed grade 2 porosity. The test results for Examples 2 and 3 also showed grade 2 porosity at the top of the casting. These results indicate that the improved method reduces the porosity level of the final casting compared to the traditional method.

[0148] Comparative Example 4, as determined by X-ray inspection, showed grade 5 porosity at the top of the casting. This is likely because the hydraulic system was activated too late, after which the molten metal inside the casting cavity had solidified and lost its fluidity. Even if the hydraulic system was activated subsequently, the pressure could not be transmitted to the solidified area, failing to compensate for the solidified metal. Comparative Example 5 was found to have casting deformation, possibly because the pressure plate moved too far downwards, causing excessive pressure on the casting and resulting in deformation. These results indicate that the optimal parameters for this method are: activating the hydraulic system 10–20 seconds after filling is complete; and stopping the pressure plate movement 10–15 mm downwards while maintaining pressure.

[0149] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for pressurized solidification of aluminum alloy castings based on low-pressure casting, characterized in that, Includes the following steps: S1. Install the upper pressure device, and the top of the casting solidifies under the pressure of the upper pressure device during casting; S2. Start pouring. Under the gas pressure of the lower pressurization device, the molten metal rises along the riser pipe to fill the mold cavity. After the molten metal has filled the mold, continue pouring and start the hydraulic system. S3. After the molten metal has completely solidified, stop pouring and shut down the hydraulic system.

2. The method according to claim 1, characterized in that, S1 specifically includes: S01. Connect and fix the pressure plate to the hydraulic system via a connecting rod; S02. Pass the horizontal plate of the sand mold locking mechanism through the hollow structure on the pressure plate to secure the sand mold, so that the sand mold is fixed during the pressurization process; S03. Adjust the position of the pressure plate so that the protrusion of the pressure plate is inserted into the outer edge of the sand mold riser and fits tightly against the outer edge of the sand mold riser, so that the pressure plate and the molten metal in the sand mold riser come into contact and apply pressure when pressurizing.

3. The method according to claim 1, characterized in that, In S2, the hydraulic system is started 10 to 20 seconds after the molten metal filling is completed.

4. The method according to claim 3, characterized in that, In S2, after the hydraulic system is started, the connecting rod of the hydraulic system drives the pressure plate to move downward, pressurizing the upper part of the molten metal in the sand mold riser at the top of the casting cavity.

5. The method according to claim 4, characterized in that, In S2, the pressure plate moves downwards by 10-15mm and then stops moving while maintaining pressure.

6. The method according to claim 5, characterized in that, In S2, the pressure is maintained at 500 kPa for 300–420 seconds.

7. The method according to claim 1, characterized in that, In S2, the pouring temperature is 690-700℃, the filling pressure is 75Kpa, and the filling speed is 60mm / s.

8. The method according to claim 1, characterized in that, After S3, solidification, cooling, and depressurization are required to obtain the final aluminum alloy casting.

9. The method according to claim 1, characterized in that, In S1, the upper pressurizing device includes a pressurizing plate and a pressurizing plate driving mechanism; The lower end face of the pressure plate is provided with a protrusion of the pressure plate, and the protrusion of the pressure plate is inserted into the outer edge of the sand mold riser and fits tightly with the outer edge of the sand mold riser; The pressure plate drive mechanism includes a hydraulic system with connecting rods. One end of the hydraulic system is fixed on the low-pressure casting machine, and the other end of the hydraulic system is connected to the pressure plate through the connecting rods. Under the drive of the hydraulic system, the pressure plate moves downward, so that the protrusion of the pressure plate pressurizes the top molten metal from above.

10. A pressure device for aluminum alloy castings, used to implement the method described in any one of claims 1-9, characterized in that, It includes a low-pressure casting machine, a sand mold installed inside the low-pressure casting machine, and an upper pressurization system.

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