A low-pressure casting die and low-pressure casting process for a high-speed rail motor front end cover

Abstract

The application relates to a low-pressure casting die and a low-pressure casting process for a high-speed rail motor front end cover. The front end cover comprises a side wall and a bottom wall, the inside of the side wall and the bottom wall forms an inner cavity with a certain height, the upper end of the side wall is provided with a flange face structure, a plurality of reinforcing ribs are arranged at the periphery in intervals, a plurality of heat dissipation grooves and weight reduction holes are arranged on the bottom wall, and a bearing hole is arranged at the center of the bottom wall. On the basis of the low-pressure metal mold casting process, a low-pressure casting die is designed according to the structural characteristics of the above-mentioned front end cover. The sand core with a combined structure is matched with the metal mold die to form the front end cover part. Meanwhile, the double-layer and multi-gate pouring system is designed by utilizing the combinable characteristics of the sand core. The pouring system can consider the thick area and the hot section area of the product, sequentially solidifies from the outer wall to the center of the relative end cover, eliminates the internal defects of the product, guarantees the consistency and the qualified rate of the product, reduces the labor intensity, and reduces the manufacturing cost.

Description

Technical Field

[0001] This application relates to the field of low-pressure casting technology, and in particular to a low-pressure casting mold and low-pressure casting process for a front end cover of a high-speed train motor. Background Technology

[0002] The front end cover of the motor used in high-speed trains has the following characteristics compared with the end cover of ordinary motors or new energy motors: (1) large size, usually with a diameter between 450-550mm; (2) a certain height of inner cavity to enclose part of the motor structure; (3) a large number of heat dissipation grooves on the end cover, and multiple reinforcing ribs arranged on the outer wall of the end cover. Due to its complex structure and wall thickness usually above 10mm, the product's structural design itself has many hot spots, which makes the design of the casting process more difficult.

[0003] In related technologies, sand casting or mortise casting processes are commonly used to manufacture these types of parts. To address internal defects in the castings, holes are drilled in the sand core to increase the gating system. While this method is highly adaptable, it is difficult to control the production process, results in poor product consistency, imposes a significant workload on subsequent processes such as sawing and grinding, and generates a high rework rate, severely impacting manufacturing costs.

[0004] It should be noted that the information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention, and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] Based on the low-pressure metal mold casting process, this application provides a low-pressure casting mold and low-pressure casting process for the front end cover of a high-speed train motor, tailored to the structural characteristics of the product. The mold is designed with a combined sand core structure to work with the metal mold to form the front end cover part. At the same time, taking advantage of the combinable characteristics of the sand core, a double-layer, multi-gating system is designed. This gating system can take into account both the thick and hot areas of the product, forming a sequential solidification of the end cover from the outer wall to the center, eliminating internal defects, ensuring product consistency and pass rate, reducing labor intensity and manufacturing costs.

[0006] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application provides a low-pressure casting mold for a front end cover of a high-speed train motor. The front end cover includes a side wall and a bottom wall. The lower end of the side wall is connected to the bottom wall. The interior of the side wall and the bottom wall forms an inner cavity with a certain height. The upper end of the side wall is provided with a flange structure. Multiple reinforcing ribs are arranged at intervals around the periphery of the side wall. Multiple heat dissipation grooves and weight reduction holes are provided on the bottom wall. An annular bearing hole for cooperating with a bearing is provided at the center of the bottom wall. The low-pressure casting mold includes: an upper metal mold, a lower metal mold, and a sand core. The upper metal mold, the lower metal mold, and the sand core form the front end cover. The cover has a cavity; the front cover is formed by inverted molding, and the outer side surface of the bottom wall, the outer side surface of the side wall and the reinforcing rib are formed by the upper metal mold, the sand core is supported and positioned by the bottom metal mold and the flange surface structure is formed by the sand core, and the inner cavity, the heat dissipation groove and the weight reduction hole are formed by the sand core; wherein, the sand core is a combined structure, including an upper sand core and a lower sand core, and the upper sand core and the lower sand core form a cavity after being combined, the cavity is used to reduce the wall thickness of the upper sand core and the lower sand core, and the wall thickness of the upper sand core and the lower sand core is ≥15mm at each point.

[0007] Furthermore, a concave-convex mating structure is provided between the upper sand core and the lower sand core. The concave-convex mating structure is provided on the outer wall surface of the upper sand core / lower sand core, and the mating surface of the concave-convex mating structure is designed to have three sides.

[0008] Furthermore, a junction box is provided on the side wall of the front cover, and the mold also includes a side mold. The junction box is formed by the cooperation of the side mold and the sand core.

[0009] Furthermore, the gating system of the mold includes a double-layer gating structure, wherein the upper gating structure is arranged corresponding to the bearing hole position of the front end cover, and the lower gating structure is arranged corresponding to the flange face structure position of the front end cover.

[0010] Furthermore, the lower casting structure includes multiple spaced-apart first ingates, and each reinforcing rib of the front end cap has a corresponding first ingate.

[0011] Furthermore, a support structure is provided on the casting at the position corresponding to the first ingate.

[0012] Furthermore, the inner cavity is formed by the cooperation of the upper and lower sand cores, the upper casting structure is formed by the cooperation of the lower sand core with the upper metal mold, and the lower casting structure is formed by the cooperation of the lower sand core with the bottom metal mold.

[0013] Furthermore, an anti-misalignment fitting structure is provided between the lower sand core and the metal mold bottom mold.

[0014] Secondly, this application provides a low-pressure casting process for the front end cover of a high-speed train motor. This process is based on the low-pressure casting mold described in the first aspect and includes the following steps: 1) Liquid riser: Under the action of high-pressure gas, the molten aluminum in the holding furnace of the low-pressure casting equipment is brought into the gate position of the low-pressure casting mold through the liquid riser pipe. 2) Filling: Continue to apply pressure to fill the mold cavity with molten aluminum. According to the direct proportional relationship between pressure and liquid height, the order in which molten aluminum fills the cavity is: bottom gate, first horizontal runner, first inner gate and the corresponding product cavity, second sprue, second horizontal runner, second inner gate and the corresponding product cavity, until the cavity of the low-pressure casting mold is completely filled. 3) Crystallization pressurization: After the filling is completed, a certain pressure is added on the basis of the current pressure to enhance the contact between the casting and the mold cavity, so that the product can solidify in a short time. At this time, the solidified metal structure is dense and the performance is better. 4) Crystallization and pressure holding: Maintain the current pressure until all the molten aluminum in the low-pressure casting mold has solidified; 5) Depressurization: The compressed gas inside the insulated aluminum is discharged through the equipment's exhaust valve, which is called depressurization. This allows the molten aluminum that has not solidified due to the insulation material in the gating and riser pipe to flow back into the insulated furnace under gravity for later use.

[0015] Furthermore, in the above process, the liquid metal rising rate is controlled at 15-20 mm / s. If the rate is lower than this, the temperature at the front edge of the liquid metal will drop significantly, increasing the risk of incomplete pouring, cold shut-off, and poor venting. If the rate is higher than this, the liquid metal is prone to gushing in areas with large changes in the product cross-section, causing local turbulence, gas entrapment, and increased secondary oxidation inclusions. In other words, both excessively high and low liquid rising rates can lead to product defects.

[0016] The beneficial effects of this application are: 1. By using a composite structure for the sand core, the interior of the sand core is designed to be hollow. This can save sand core material, reduce curing time during the core-making process, and shorten the cycle time. It can also facilitate demolding. 2. The double-layer, multi-gate gating system takes into account most of the hot spots in the casting structure, providing better molten metal filling and solidification feeding for thick areas of the casting, and significantly improving the internal quality of the casting. Attached Figure Description

[0017] Figure 1 According to some embodiments of this application, a structural schematic diagram of a low-pressure casting mold is shown; Figure 2 According to some embodiments of this application, it is shown that Figure 1 A sectional view; Figure 3 According to some embodiments of this application, a structural schematic diagram of a sand core is shown; Figures 4-5 According to some embodiments of this application, a schematic diagram of the combined structure of the sand core is shown; Figure 6 According to some embodiments of this application, cross-sectional views of sand cores are shown; Figure 7 A schematic diagram of the gating system is shown according to some embodiments of this application; Figure 8 According to some embodiments of this application, schematic diagrams of the structure of sand cores, gating systems, and castings are shown. Detailed Implementation

[0018] The technical features and advantages of this application will be described in more detail below with reference to the accompanying drawings, so that the advantages and features of this application can be more easily understood by those skilled in the art, thereby making a clearer and more explicit definition of the scope of protection of this invention.

[0019] It should be noted that in the description of this application, the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention.

[0020] The terms “first” and “second” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly indicating the importance of the technical features shown.

[0021] Furthermore, it should be noted that, in the description of this application, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] The front end cover of the high-speed train motor consists of side walls and a bottom wall. The upper end of the side wall has a flange structure, and the lower end connects to the bottom wall. The interior of the side wall and the bottom wall forms an inner cavity with a certain height to accommodate the motor. Several reinforcing ribs are arranged at intervals around the periphery of the side wall, and wiring grooves are also provided on the side wall. The bottom wall has multiple weight-reducing holes and heat dissipation grooves, and a bearing hole for mating with the bearing is located at the center of the bottom wall. The overall structure of this end cover is complex, with a wall thickness of over 10mm. The product design itself has many thick and hot areas, making the casting process design quite challenging.

[0023] In conventional technology, the casting process for this type of end cap part is usually formed with the opening facing upwards, mainly based on the product structure and the traditional process design considering the clamping force after solidification. However, the wall thickness at the flange and sidewall connection near the opening of this type of product suddenly increases, and it is furthest from the gate position in conventional processes. It cannot establish a good feeding channel with the gate during solidification, i.e., solidification sequence. The product's weight reduction hole design further exacerbates the risk of isolated liquid phase region, i.e., internal shrinkage cavity, in this area, resulting in excessive defect level, surface depression, high scrap rate, or increased rework and welding processes, ultimately seriously affecting product cost.

[0024] Based on low-pressure casting technology and considering the structural characteristics of the front end cap, the inventors of this application designed a low-pressure casting mold. The front end cap part is formed by combining a metal mold and a sand core. During casting, the front end cap is formed by inverted casting, and the sand core is designed with an upper and lower combined structure. This combined structure simplifies the core-making process and facilitates demolding. Furthermore, utilizing the combinable nature of the sand core, a double-layer, multi-gating system was designed. This system can accommodate both the thick area at the bearing hole location of the end cap and the hot spot area where the side wall meets the reinforcing rib, thus achieving sequential solidification of the end cap from the outer wall to the center of the bearing chamber, eliminating internal defects in the casting. Compared to traditional casting processes, there is no need to drill holes in the sand core to add runners, reducing the core-making process, shortening the cycle time and labor intensity. This mold enables mass production, ensuring uniform process standards and appearance requirements, reducing the difficulty of control during the casting process, guaranteeing product consistency and pass rate, and reducing manufacturing costs while lowering labor intensity.

[0025] To achieve the above objectives, the basic idea of ​​the embodiments of this application is as follows: Please see Figures 1-2The diagram below shows the structure of the low-pressure casting mold 1000, which includes: an upper metal mold 1100, a bottom metal mold 1200, a side puller 1300, and a sand core 1500. The metal mold, the side puller 1300, and the sand core 1500 form a cavity for forming the front end cap. Specifically, the upper metal mold 1100 forms the outer wall surface of the front end cap and prevents the sand core 1500 from floating; the sand core 1500 forms the weight-reducing holes and heat dissipation grooves on the bottom wall, as well as the inner cavity of the front end cap; the bottom metal mold 1200 supports and positions the sand core 1500 and forms the flange structure on the upper surface of the front end cap; and the sand core 1500, in conjunction with the metal mold, forms the gating system 1600 of the mold.

[0026] Please see Figures 3-5 The sand core 1500 in this embodiment is designed as a combined structure, including an upper sand core 1510 and a lower sand core 1520. The upper sand core 1510 includes: a first protrusion 1511 for forming a weight-reducing hole, a second protrusion 1512 for forming a heat dissipation groove, and a third protrusion 1513 for forming a wiring groove. The lower sand core 1520 includes: a first groove 1521 for forming a casting system 1600, a center hole 1522 and a second groove 1523, and a fourth protrusion 1524 for joining with the third protrusion 1513 to form a junction box. A convex-concave mating structure is provided between the upper sand core 1510 and the lower sand core 1520. This structure may include a protrusion 1514 on the upper sand core and a groove 1525 on the lower sand core 1520. Preferably, the mating surfaces of this convex-concave mating structure are designed to have three surfaces, which can reduce the sand and gravel falling off due to friction between the upper sand core 1510 and the lower sand core 1520 during assembly. The mating surfaces can be bonded together with an adhesive. At the same time, the convex-concave mating structure is located near the outer wall of the sand core 1500, which makes it convenient for the operator to observe and adjust when assembling the two sand cores.

[0027] For some preferred implementations, please refer to Figure 6 After the upper sand core 1510 and the lower sand core 1520 are assembled, a cavity 1530 is formed between them. The thickness of the sand core sidewalls on both sides of the cavity 1530 is approximately 15mm. The purpose of designing the interior of the assembled sand core as hollow is to: 1) save materials; 2) reduce the curing time during the core-making process and shorten the core-making cycle; 3) reduce the labor intensity of sand core assembly, transportation, and casting. At the same time, ensuring that the sand core wall thickness is not less than 15mm also guarantees that its strength meets the usage requirements. In this embodiment, the sand core 1500 is designed as an assembled structure, partly to facilitate the design of its interior as a hollow structure, thereby saving materials.

[0028] To position the sand core 1500 and the metal mold base 1200, an anti-misalignment mating structure can be provided between the lower sand core 1520 and the metal mold base 1200. For example, the aforementioned anti-misalignment mating structure can be a concave-convex mating mechanism; please refer to [reference needed]. Figure 5 Several anti-misalignment holes 1526 are designed at the bottom of the lower sand core 1520, and corresponding protrusions are provided on the metal mold 1200. During installation, the anti-misalignment holes 1526 are placed into the protrusions to achieve positioning between the lower sand core 1200 and the metal mold 1200.

[0029] In the structure of this front cover, the bearing hole area and the flange face area are both thick regions, and the intersection of the sidewall and the reinforcing rib structure forms a periodic hot spot area during casting. In view of this, please refer to... Figure 7 In this embodiment, the gating system 1600 of the mold is designed as a double-layer structure. The lower gating structure 1620 is arranged corresponding to the flange face of the front cover, providing molten metal filling and feeding during solidification for the side wall area of ​​the front cover. The upper gating structure 1630 is arranged corresponding to the bearing hole of the front cover, providing molten metal filling and feeding during solidification for the bottom wall area of ​​the front cover. This design allows the bottom wall and side wall of the casting to be filled with molten metal simultaneously during casting, thereby reducing internal quality defects in the casting.

[0030] For further details, please refer to Figures 7-8 The lower gating structure 1620 includes multiple first sprues 1621 extending radially and connected to them first ingates 1622. Each first ingate 1622 corresponds to a reinforcing rib of the front end cap, and the first ingate 1622 provides feeding for the hot spot area where the reinforcing rib meets the sidewall. The upper gating structure 1630 includes multiple second sprues 1631 extending radially and connected to them second ingates 1632. The multiple second ingates 1632 provide uniform circumferential feeding for the thick area at the bearing hole location. The double-layer multi-gate gating system 1600 is formed by sand core 1500. The multiple gates of the gating system 1600 take care of most of the hot spot areas on the casting structure, thereby significantly improving the internal quality of the casting.

[0031] Please see Figures 2-8 The gating system 1600 also includes a first sprue 1610 connected to the mold gate 1400 and a second sprue 1640 connected to the upper and lower gating structures. The first sprue 1610 is formed by the metal mold bottom mold 1200, and the second sprue 1640 is formed by the center hole 1522 of the lower sand core 1520.

[0032] Based on the aforementioned low-pressure casting mold, the low-pressure casting process for this front end cap includes the following steps: 1) Liquid riser: Under the action of high pressure gas, the aluminum liquid in the holding furnace of the low pressure casting equipment enters the gate (1400) position of the low pressure casting mold through the liquid riser pipe located in the center of the holding furnace. 2) Filling: The equipment continues to pressurize, so that the molten aluminum fills the cavity of the gating system (1600) and the front end cover. According to the direct proportional relationship between pressure and liquid height, the order of molten aluminum filling the mold cavity is: bottom gate (1400), first horizontal runner (1621), first inner gate (1622) and the product cavity at the corresponding height, second sprue (1640), second horizontal runner (1631), second inner gate (1632) and the product cavity at the corresponding height, until the mold cavity is completely filled. 3) Crystallization pressurization: After the filling is completed, the pressure is increased by 50mbar in 5 seconds on the basis of the current pressure to enhance the contact between the product and the cavity of the low-pressure casting mold, thereby improving heat exchange and allowing the product to start to solidify in a shorter time. At this time, the solidified metal structure is dense and has better performance. 4) Crystallization and holding pressure: Maintain the current pressure until all the molten aluminum in the low-pressure casting mold has solidified, holding pressure for 600 seconds; 5) Depressurization: The compressed gas inside the insulating aluminum is discharged through the equipment's exhaust valve, i.e., depressurization, so that the molten aluminum that has not solidified due to the insulation material in the gating and riser pipes flows back into the insulation furnace under the action of gravity, for later use.

[0033] Please see Figures 1-2 In this embodiment, when the low-pressure casting mold is closed, the operator first uses an air gun to blow away the metal bottom mold 1200 to remove impurities such as sand; then, the assembled sand core 1500 is placed into the metal bottom mold 1200 according to the anti-misalignment structure at the bottom, and then the side oil cylinder 1700 of the equipment is started to push the side mold 1300 into place; then, under the drive of the main oil cylinder of the equipment, the metal upper mold 1100 is pushed into place, and the mold closure is completed, and the casting can be started.

[0034] After the casting solidifies, the mold opening process is as follows: First, the side mold 1300 moves horizontally away from the casting under the action of the side oil cylinder 1700. Then, the upper mold frame 1800 connected to the equipment moves vertically upward along the direction of the metal upper mold 1100 fixed on the upper mold frame 1800, driven by the main oil cylinder of the equipment. At the same time, under the action of solidification clamping force, the front end cover casting, the gating system 1600 and the sand core 1500 are lifted. Finally, the equipment receiving tray enters below the housing casting, the mold ejection system 1900 moves downward, and the product is successfully ejected and falls into the receiving tray.

[0035] In the description of this specification, references to terms such as "some embodiments," "some examples," "exemplarily," "example," "preferred," or "further" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0036] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made based on the content of this specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A low-pressure casting mold (1000) for a front end cover of a high-speed train motor, the front end cover comprising a side wall and a bottom wall, the lower end of the side wall being connected to the bottom wall, the interior of the side wall and the bottom wall forming an inner cavity of a certain height, the upper end of the side wall being provided with a flange structure, and multiple reinforcing ribs being arranged at intervals around the periphery of the side wall; the bottom wall being provided with multiple heat dissipation grooves and weight reduction holes, and an annular bearing hole for mate with a bearing being provided at the center of the bottom wall, characterized in that, The low-pressure casting mold (1000) includes: an upper metal mold (1100), a bottom metal mold (1200), and a sand core (1500). A cavity for forming the front end cap is formed between the upper metal mold (1100), the bottom metal mold (1200), and the sand core (1500). The front end cap is formed by inverted molding. The upper metal mold (1100) forms the outer surface of the bottom wall, the outer surface of the side wall, and the reinforcing rib. The bottom metal mold (1200) supports and positions the sand core (1500) and forms the flange surface. The structure utilizes the sand core (1500) to form the inner cavity, the heat dissipation groove, and the weight reduction hole; wherein, the sand core (1500) is a combined structure, including an upper sand core (1510) and a lower sand core (1520). After the upper sand core (1510) and the lower sand core (1520) are assembled, a cavity (1530) is formed between them. The cavity (1530) reduces the wall thickness of the upper sand core (1510) and the lower sand core (1520). The wall thickness of the upper sand core (1510) and the lower sand core (1520) at each point is reduced. ; A concave-convex mating structure is provided between the upper sand core (1510) and the lower sand core (1520). The concave-convex mating structure includes a protrusion (1514) provided on the upper sand core (1510) and a groove (1525) provided on the lower sand core (1520). The mating surfaces of the concave-convex mating structure are designed to be three-sided. The gating system (1600) of the low-pressure casting mold (1000) includes a double-layer gating structure, wherein the upper gating structure (1630) is arranged corresponding to the bearing hole position of the front end cover, and the lower gating structure (1620) is arranged corresponding to the flange face structure position of the front end cover. The lower gating structure (1620) includes multiple first sprues (1621) extending radially and connected to them, and a first ingate (1622). Each reinforcing rib of the front end cap is provided with a corresponding first ingate (1622). The first ingate (1622) is used to compensate for the heat-congestion area at the junction of the reinforcing rib and the side wall. The upper gating structure (1630) includes multiple second sprues (1631) extending radially and connected to them, and a second ingate (1632). The multiple second ingates (1632) provide uniform circumferential compensation for the thick area at the bearing hole location. The double-layer multi-gate gating system (1600) is formed by a sand core (1500).

2. The low-pressure casting mold (1000) according to claim 1, characterized in that, The front end cover is also provided with a junction box on its side wall. The mold (1000) also includes a side mold (1300). The junction box is formed by the cooperation of the side mold (1300) and the sand core (1500).

3. The low-pressure casting mold (1000) according to claim 1, characterized in that, A support structure is provided on the casting at the position corresponding to the first ingate (1622).

4. The low-pressure casting mold (1000) according to claim 1, characterized in that, The inner cavity is formed by the cooperation of the upper sand core (1510) and the lower sand core (1520); the upper casting structure (1630) is formed by the cooperation of the lower sand core (1520) and the upper metal mold (1100); and the lower casting structure (1620) is formed by the cooperation of the lower sand core (1520) and the bottom metal mold (1200).

5. The low-pressure casting mold (1000) according to claim 1, characterized in that, An anti-misalignment fitting structure is provided between the lower sand core (1520) and the metal mold bottom mold (1200).

6. A low-pressure casting process for preparing the front end cover of a high-speed train motor based on the low-pressure casting mold (1000) according to any one of claims 1 to 5, characterized in that, Includes the following steps: 1) Liquid riser: Under the action of high-pressure gas, the aluminum liquid enters the gate (1400) position of the low-pressure casting mold (1000) through the liquid riser pipe; 2) Filling: Continue to pressurize so that the molten aluminum fills the gating system (1600) and the cavity. According to the direct proportional relationship between pressure and liquid height, the order in which the molten aluminum fills the gating system (1600) is as follows: bottom gate (1400), first sprue (1621), first ingate (1622) and the product cavity at the corresponding height, second sprue (1640), second sprue (1631), second ingate (1632) and the product at the corresponding height, until the cavity of the low-pressure casting mold (1000) is completely filled. 3) Crystallization pressurization: After filling, pressurize rapidly on the basis of the current pressure to enhance the contact between the product and the cavity to improve heat exchange, so that the product can solidify and form a shell in a short time. 4) Crystallization and pressure holding: Maintain the current pressure until all the molten aluminum in the low-pressure casting mold (1000) has solidified; 5) Depressurization: The compressed gas in the holding furnace is discharged through the equipment exhaust valve, which is called depressurization. The unsolidified aluminum liquid in the pouring gate (1400) and the riser pipe flows back into the holding furnace under the action of gravity for subsequent use.

7. The low-pressure casting process according to claim 6, characterized in that, in, The liquid flow rate of the molten metal in the filling section of the casting is 15–20. .

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