A mold for casting end caps of shell-type hydraulic valve bodies and its casting process

Abstract

This application relates to a mold and casting process for casting end caps of shell-type hydraulic valve bodies, belonging to the technical field of casting processing. The mold includes a mold body with a cavity formed within it. A runner sand core is disposed within the cavity and fixedly connected to the mold body. A gating port is provided at the bottom of the mold body and communicates with the cavity. The bottom gating assembly includes a sprue base plate and a vertical gating pipe. A horizontal runner is provided within the sprue base plate, with its length direction along the horizontal direction. The vertical gating pipe is vertically positioned above the sprue base plate, with its lower end connected to the sprue base plate and communicating with the horizontal runner. The mold body is fixed to the sprue base plate, and the gating port communicates with the horizontal runner. This application reduces the occurrence of splashing, turbulence, and air entrapment of molten metal within the cavity, thereby reducing the generation of secondary oxidation inclusions and porosity defects inside the casting, which improves the final casting quality.

Description

Technical Field

[0001] This application relates to the technical field of casting processing, and in particular to a mold and casting process for casting end caps of shell-type hydraulic valve bodies. Background Technology

[0002] Hydraulic valve body end caps are core components in the hydraulic systems of engineering machinery. They typically feature complex internal flow channels to guide and control the flow of hydraulic oil. In high-end hydraulic valve manufacturing, to meet the requirements of high strength and high pressure resistance, these end caps are usually made of QT500-7 (ductile iron) material and often employ shell casting processes to ensure dimensional accuracy and surface finish.

[0003] Currently, the common process for producing castings such as hydraulic valve body end caps is as follows: the casting mold is placed flat, and then the corresponding molten metal is poured into the gate at the top of the mold. Under the action of gravity, the molten metal flows into the cavity inside the mold and fills its space. At this time, the runner sand core inside the mold cavity is used to form the internal runner of the casting. After the molten metal cools and solidifies, the mold is opened and the internal runner sand core is cleaned, and then the cast product is taken out.

[0004] Regarding the aforementioned technologies, due to the significant differences in wall thickness and complex internal flow channels in castings such as hydraulic valve body end caps, the leading edge of the molten metal needs to flow from top to bottom to the bottom of the mold cavity during the pouring of molten metal. During this process, this leading edge of molten metal is accelerated by gravity and violently impacts the runner sand core, resulting in severe splashing, turbulence, and air entrapment. This turbulent filling state not only causes secondary oxidation of the molten metal, but also, the continuous scouring of the slender runner sand core by the high-temperature, kinetic-energy molten metal easily leads to thermal cracking, deformation, or even local collapse of the runner sand core due to thermal shock. This results in veins, excess material, and sand inclusions on the surface of the internal flow channels of the final casting, thereby reducing the dimensional accuracy and surface finish of the casting. Summary of the Invention

[0005] This application provides a mold and casting process for casting a shell-type hydraulic valve body end cap, the purpose of which is to improve the casting quality of the hydraulic valve body end cap.

[0006] Firstly, the mold for casting a shell-type hydraulic valve body end cap provided in this application adopts the following technical solution:

[0007] A mold for casting a shell-type hydraulic valve body end cap includes a mold body with a cavity formed therein. A runner sand core is disposed within the cavity and is fixedly connected to the mold body. A pouring port is provided at the bottom of the mold body and communicates with the cavity. A bottom pouring assembly includes a sprue base plate and a vertical gating pipe. A horizontal runner is provided within the sprue base plate, with its length direction along the horizontal direction. The vertical gating pipe is vertically disposed and located above the sprue base plate, with its lower end connected to the sprue base plate and communicating with the horizontal runner. The mold body is fixed to the sprue base plate, and the pouring port communicates with the horizontal runner.

[0008] By adopting the above technical solution, under the design of the bottom-pouring assembly, during the pouring process, the molten metal first enters the horizontal flow channel at the bottom through the vertical gating pipe. The horizontal flow channel buffers and rectifyes the high-speed falling molten metal, consuming its kinetic energy and transforming it from turbulent flow to stable laminar flow. Subsequently, the molten metal enters the mold cavity through the gating gate and gradually fills the cavity from bottom to top, thus realizing the bottom-pouring filling method.

[0009] This casting method effectively avoids the direct impact of molten metal falling onto the inner wall of the mold cavity and the runner sand core, thereby reducing the occurrence of splashing, turbulence and air entrapment of molten metal in the mold cavity. This reduces the risk of thermal cracking, deformation and collapse of the runner sand core, and further reduces the occurrence of secondary oxidation inclusions and porosity defects inside the casting, which can improve the final casting quality of the casting.

[0010] Optionally, the vertical gating pipe includes a gating cup and a plurality of straight runner cups. The gating cup is vertically arranged and located above the gating base plate. The plurality of straight runner cups are located vertically between the gating cup and the gating base plate. The plurality of straight runner cups are arranged coaxially in sequence along the vertical direction. The straight runner cups are bonded to adjacent straight runner cups, the gating cups, or the gating base plate. The gating cups are coaxially connected to adjacent straight runner cups. The lowest straight runner cup is connected to the horizontal flow channel.

[0011] By adopting the above technical solution, the vertical sprue, through the design of the sprue cup and several straight runner cups, enables the vertical sprue to have a modular adjustable height. In actual production, the number of straight runner cups can be freely selected according to the mold body of different heights, thereby changing the total height of the vertical sprue so that the height of the vertical sprue can meet the needs of mold bodies of different heights.

[0012] Optionally, the height of the vertical gating pipe in the vertical direction is greater than the height of the mold body.

[0013] By adopting the above technical solution, since the height of the liquid column in the vertical gating pipe is higher than that of the mold body, based on the principle of hydrostatics, this height difference can provide sufficient gravity static pressure head for the molten metal. Thus, during the pouring process, this static pressure can drive the molten metal to overcome the complex flow resistance and gas back pressure in the cavity, thereby forcing the molten metal to completely fill the cavity of the mold body. This effectively prevents molding defects such as incomplete filling or poor fusion of molten metal caused by insufficient filling power, which can improve the structural integrity of the final produced casting.

[0014] Optionally, a compensation allowance groove is provided inside the mold body, and the compensation allowance groove is provided on the inner wall of the top of the cavity.

[0015] By adopting the above technical solution, the molten metal gradually fills the cavity from bottom to top, which causes the gas originally present in the cavity and the floating slag that may be generated to float on the surface of the molten metal in the cavity, and then gradually push it into the compensation allowance tank as the molten metal level rises.

[0016] After the molten metal solidifies in the mold cavity to form a casting, a metal layer will form on the top of the casting at the position corresponding to the compensation allowance groove. This metal layer will collect any micro-shrinkage, porosity, and floating non-metallic inclusions that may appear on the top of the casting.

[0017] Based on this, by removing the excess metal layer through subsequent processing, the defects on the top of the casting can be effectively removed, exposing the dense matrix structure on the top of the casting, thereby improving the density and surface quality of the casting.

[0018] Optionally, a self-heating riser is provided above the mold body. The self-heating riser is vertically arranged, and its lower end is connected to the mold body and communicates with the cavity.

[0019] By adopting the above technical solution, a self-heating riser is set at the top of the mold. By utilizing the heating and heat preservation characteristics of the self-heating riser, the solidification time of the molten metal in the self-heating riser can be delayed, so that the molten metal overflowing into the self-heating riser in the cavity remains in a liquid state.

[0020] Based on this, during the cooling and solidification process of the molten metal in the mold cavity, the liquid metal in the self-heating riser can act as a feeding liquid source, continuously feeding into the mold cavity under the action of gravity, in order to make up for the deficit caused by the volume shrinkage of the molten metal in the mold cavity during the solidification process.

[0021] Meanwhile, the self-heating riser has a high temperature, which creates a temperature gradient on the mold body, causing the molten metal to solidify in a bottom-up order. This means that when the lower layer of molten metal in the cavity solidifies and shrinks first, the adjacent molten metal above it is still in a liquid state. Under the action of gravity, it can immediately flow downward to fill the shrinkage gap. This process of molten metal filling the shrinkage gap is passed from bottom to top layer by layer until the solidification and shrinkage of the molten metal at the top of the cavity is finally filled by the molten metal in the self-heating riser. This can establish a continuous feeding channel and avoid shrinkage porosity and shrinkage cavities inside the casting.

[0022] Optionally, an overflow groove is provided through the top of the self-heating riser.

[0023] By adopting the above technical solution, the overflow channel, acting as a drainage channel on the self-heating riser, allows the molten metal at the initial pouring stage, which is at a lower temperature and may contain oxide scale and slag, to overflow outside the self-heating riser. This ensures that the molten metal ultimately remaining in the self-heating riser for feeding is high-temperature, pure molten metal, which helps activate the heating agent inside the self-heating riser and improves feeding efficiency. Furthermore, the overflow of molten metal from the overflow channel is also a direct signal that the mold cavity is full, allowing workers to know when to stop pouring.

[0024] Optionally, an inertial slag collection cavity is provided in the bottom plate of the gating system, and the horizontal flow channel is connected sequentially to the vertical gating pipe, the pouring port and the inertial slag collection cavity along its own length direction.

[0025] By adopting the above technical solution, in the initial stage of pouring, the first stream of molten metal entering the horizontal flow channel is fast, cold, and contaminated. Due to its enormous inertia, this fluid rushes past the side-opened gating gate and directly into the inertial slag collection chamber located at the end of the flow channel, where it is captured. After the slag collection chamber is filled, the subsequent stream of molten metal, with a more stable flow rate, higher temperature, and greater purity, will then be redirected and enter the mold cavity through the gating gate. Therefore, the design of the inertial slag collection chamber effectively blocks the initial entry of cold slag into the mold cavity, which reduces the probability of slag inclusions and cold shut defects in the casting.

[0026] Optionally, it also includes a sand box, in which a fast heat conduction layer, a medium heat conduction layer and a slow heat conduction layer are arranged sequentially from bottom to top, and the thermal conductivity of the fast heat conduction layer, the medium heat conduction layer and the slow heat conduction layer decreases sequentially; the mold body is located in the sand box, and the fast heat conduction layer, the medium heat conduction layer and the slow heat conduction layer all wrap around the mold body.

[0027] By employing the above technical solution, a physical thermal conductivity gradient environment is artificially constructed outside the mold body by filling the sand box with media of different thermal conductivity. The bottom rapid heat conduction layer accelerates heat dissipation from the lower part of the casting, allowing it to solidify preferentially; the middle medium-speed heat conduction layer follows; and the top slow heat conduction layer delays heat dissipation from the upper part. This layered heat conduction structure ensures that the molten metal in the cavity follows a bottom-up solidification path, guaranteeing that while the lower part of the casting solidifies and shrinks, the upper part always has a continuous supply of liquid metal for gravity-assisted shrinkage, thereby further eliminating the potential for shrinkage porosity and thermal spots inside the casting.

[0028] Optionally, the flow channel sand core is prepared by mixing abrasive sand and silica sand, wherein the abrasive sand accounts for 20% to 40% of the mass, and the remainder is silica sand, and both the abrasive sand and the silica sand have a mesh size of 70-140 mesh.

[0029] By employing the above technical solution, the low thermal expansion coefficient of the abrasive sand is utilized to neutralize the volume expansion of the silica sand upon heating. This allows for control of the abrasive sand's mass ratio, resulting in excellent volume stability of the mixed sand core surrounded by molten metal. This effectively prevents thermal cracking due to excessive expansion of the sand core and avoids dimensional deviations caused by excessive shrinkage. Simultaneously, the selection of a 70-140 mesh particle size balances the permeability of the sand core with the surface finish of the casting's internal flow channels. This ensures the stability of the mold body, reduces defects such as veins, excess material, and sand inclusions on the surface of the final casting's internal flow channels, thereby improving the casting's dimensional accuracy and surface finish.

[0030] Secondly, the casting process for casting the end cap of a shell-type hydraulic valve body provided in this application adopts the following technical solution:

[0031] A casting process for casting a shell-shaped hydraulic valve body end cap, utilizing the aforementioned mold for casting a shell-shaped hydraulic valve body end cap, includes the following steps:

[0032] Mold preparation: Prepare the mold body, the sprue base plate, and the vertical sprue;

[0033] Mold assembly: Fix the mold body and the vertical sprue to the sprue base plate, and connect the vertical sprue, the horizontal runner and the pouring gate in sequence;

[0034] Bottom pouring: Molten metal is poured into the vertical gating pipe from the top end, so that the molten metal enters from the pouring port and fills the cavity from bottom to top;

[0035] Molding and demolding: After the casting has completely solidified and cooled, remove the mold body, the sprue base plate and the vertical sprue, and take out the casting.

[0036] By adopting the above technical solution, this process achieves bottom-pouring casting through standardized preparation and assembly steps. The bottom-pouring step, in conjunction with the mold structure, ensures stable molten metal filling and avoids damage to the runner sand core; the molding and demolding steps ensure smooth removal of the casting. The overall process is standardized and controllable, effectively guaranteeing the consistency and stability of the quality of hydraulic valve body end cap castings in mass production.

[0037] In summary, this application includes at least one of the following beneficial technical effects:

[0038] 1. This application utilizes the cooperation between the bottom gating assembly and the mold body to allow molten metal to gradually fill the mold cavity from bottom to top, thus achieving a bottom-filling casting method. This casting method effectively avoids the direct impact of molten metal falling onto the inner wall of the mold cavity and the runner sand core, thereby reducing the occurrence of splashing, turbulence, and air entrapment of molten metal within the mold cavity. This, in turn, reduces the risk of thermal cracking, deformation, and collapse of the runner sand core, which can reduce the generation of secondary oxidation inclusions and porosity defects inside the casting, thereby improving the casting quality.

[0039] 2. This application utilizes the synergistic effect of the inertial slag collection chamber and the overflow channel at the top of the self-heating riser. In the initial stage of pouring, the inertia of the bottom horizontal flow channel allows cold, dirty molten metal to be stored in the inertial slag collection chamber. In the final stage of pouring, the overflow channel at the top discharges the slag and low-temperature waste liquid floating on the surface of the molten metal in the mold cavity. This design ensures that the final material remaining in the mold cavity and the self-heating riser is high-temperature, pure molten metal, thereby improving the density and purity of the final casting.

[0040] 3. This application utilizes the combined design of self-heating risers and compensation allowance grooves. On the one hand, the heat-generating and heat-insulating effect of the self-heating risers, combined with the wide feeding channel formed by the compensation allowance grooves, effectively prevents the feeding path from being cut off due to premature solidification at the connection between the top of the casting and the self-heating riser, ensuring the long-term unobstructed flow of the feeding channel. On the other hand, during the pouring process, the gas and slag floating on the surface of the molten metal in the mold cavity are orderly pushed to the compensation allowance groove at the top as the liquid level rises, and some are pushed into the self-heating riser. Thus, after the casting cools and solidifies, these impurities and the micro-shrinkage porosity generated at the end of solidification are enriched in the metal layer formed in the compensation allowance groove and the metal column formed in the self-heating riser, thereby ensuring the purity and density of the matrix structure at the top of the casting. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the overall structure of the mold in Embodiment 1 of this application.

[0042] Figure 2 This is a cross-sectional structural schematic diagram of the mold of Embodiment 1 of this application.

[0043] Figure 3 This is a cross-sectional view of another location of the mold in Embodiment 1 of this application.

[0044] Figure 4 This is a schematic diagram of the overall structure of the mold in Embodiment 2 of this application.

[0045] Figure 5 This is a schematic diagram of the internal structure of the sand box in Embodiment 2 of this application.

[0046] Figure 6 This is a cross-sectional structural schematic diagram of the mold of Embodiment 2 of this application.

[0047] Figure 7 This is a cross-sectional view of another location of the mold in Embodiment 2 of this application.

[0048] In the diagram, 1. Mold body; 11. Cavity; 12. Runner sand core; 13. Sprue; 14. Overflow port; 15. Compensation allowance groove; 2. Bottom gating assembly; 21. Sprue base plate; 211. Horizontal runner; 212. Inlet; 213. Outlet; 214. Inertial slag collection chamber; 22. Vertical gating pipe; 221. Sprue cup; 222. Straight runner cup; 3. Self-heating riser; 31. Overflow groove; 32. Self-welding cover plate; 4. Sand box; 41. Fast heat conduction layer; 42. Medium heat conduction layer; 43. Slow heat conduction layer. Detailed Implementation

[0049] The following is in conjunction with the appendix Figure 1 - Appendix Figure 7 This application will be described in further detail below.

[0050] Example 1: A mold for casting end caps of a shell-type hydraulic valve body, referring to... Figure 1 and Figure 2 The system includes a mold body 1, a bottom gating assembly 2, and a self-heating riser 3. The bottom gating assembly 2 is connected to the bottom of the mold body 1, and the self-heating riser 3 is connected to the top of the mold body 1. During casting, molten metal is introduced through the bottom gating assembly 2, enters the mold body 1 from the bottom, and gradually fills the mold body 1 from bottom to top, thus achieving the bottom-filling casting method.

[0051] Reference Figure 2 and Figure 3 The mold body 1 has a cavity 11, and a runner core 12 is installed inside the cavity 11. The runner core 12 is integrally formed with the mold body 1. The mold body 1 has a pouring gate 13 on the lower side and an overflow port 14 on the upper side, and the pouring gate 13, the cavity 11, and the overflow port 14 are connected in sequence. Furthermore, the bottom gating assembly 2 is connected to the pouring gate 13, and the self-heating riser 3 is connected to the overflow port 14.

[0052] Based on the structural design of the mold body 1, during casting, the molten metal is introduced through the bottom pouring component 2 and enters the cavity 11 through the pouring port 13 on the lower side of the mold body 1. Then, the molten metal gradually fills the cavity 11 from bottom to top. This causes the gas originally present in the cavity 11 and the floating slag that may be generated to float on the surface of the molten metal in the cavity 11. As the surface of the molten metal rises, it is gradually pushed into the self-heating riser 3 of the mold body 1.

[0053] Under this design, on the one hand, the molten metal fills the cavity 11 gradually from bottom to top, which makes the fluctuation of the molten metal in the cavity 11 smaller, thereby reducing the occurrence of splashing, turbulence and air entrapment caused by the molten metal falling directly and impacting the flow channel sand core 12, thus reducing the risk of secondary oxidation inclusions and porosity defects inside the casting; on the other hand, since the gas and slag in the cavity 11 are always confined to the surface of the continuously rising molten metal, these impurities are physically isolated from the pure molten metal body below, and cannot be carried into the casting. They can only enter the top self-heating riser 3 in an orderly manner, thereby improving the purity and density of the casting.

[0054] In this embodiment, refer to Figure 1 and Figure 2 The mold body 1 has a shell-shaped structure, comprising an upper mold and a lower mold. The upper mold and the lower mold are bonded and fixed together using a refractory adhesive, and the mold body 1 is formed by curing coated sand. This design facilitates the shaping of the mold body 1 and the positioning and assembly of the internal flow channel sand core 12. Furthermore, the use of the refractory adhesive ensures the sealing of the mating surfaces of the upper and lower molds, effectively preventing high-temperature molten metal from leaking from the parting surface during pouring, thus guaranteeing the safety of the casting process and the dimensional accuracy of the castings.

[0055] In this embodiment, refer to Figure 2 The flow channel sand core 12 inside the cavity 11 is prepared by mixing silica sand and pearl sand, wherein the mass percentage of pearl sand is 20% to 40%, preferably 30%, and the remainder is silica sand, and the mesh size of both silica sand and pearl sand is 70-140 mesh, preferably 70 mesh or 140 mesh.

[0056] This formula design utilizes the low thermal expansion coefficient of the silica sand to counteract the expansion of the silica sand after heating, thereby effectively preventing the flow channel core 12 from cracking or deforming under the impact of high-temperature molten metal. This reduces the appearance of veins, excess material, and sand inclusions on the inner wall of the corresponding flow channel of the casting, thereby improving the dimensional accuracy and surface finish of the casting.

[0057] In this embodiment, refer to Figure 3A compensation allowance groove 15 is provided inside the mold body 1. The compensation allowance groove 15 is located on the inner wall of the top of the cavity 11. The self-heating riser 3, the compensation allowance groove 15, and the cavity 11 are connected in sequence along the vertical direction. Specifically, the depth of the compensation allowance groove 15 is preferably 3mm.

[0058] During the casting process, after the molten metal fills the compensation allowance tank 15, a metal layer forms within the compensation allowance tank 15 after the molten metal cools. This metal layer acts as a wide feeding channel connecting the casting body and the self-heating riser 3, accommodating shrinkage porosity, gas holes, and inclusions that may appear at the top of the casting body. This improves the density of the main structure of the casting body located below this metal layer. Furthermore, this metal layer can be removed through subsequent machining, ensuring the final casting quality.

[0059] Reference Figure 1 and Figure 2 The bottom pouring assembly 2 includes a gating base plate 21, which is horizontally arranged and has a horizontal flow channel 211 inside it. The length of the horizontal flow channel 211 is along the length of the gating base plate 21. An inlet 212 and several outlets 213 are provided on the upper side of the gating base plate 21. Both the inlet 212 and the outlets 213 are connected to the horizontal flow channel 211, and the inlet 212 and the several outlets 213 are spaced apart along the length of the horizontal flow channel 211. One end of the horizontal flow channel 211 is connected to the inlet 212.

[0060] Reference Figure 1 and Figure 2 The bottom pouring assembly 2 also includes a vertical pouring pipe 22, which is vertically arranged and located above the pouring channel bottom plate 21. The bottom of the vertical pouring pipe 22 is bonded and fixed to the pouring channel bottom plate 21 by a refractory adhesive, and the lower end of the vertical pouring pipe 22 is directly connected to the inlet 212.

[0061] Reference Figure 1 and Figure 2 The mold body 1 is stacked on the sprue base plate 21, and the mold body 1 and the vertical sprue 22 are spaced apart along the length of the horizontal runner 211. The bottom of the mold body 1 is bonded and fixed to the sprue base plate 21 with refractory adhesive. Several pouring gates 13 are provided on the lower side of the mold body 1, and the pouring gates 13 and the outlets 213 are arranged in a one-to-one correspondence, with the pouring gates 13 and the corresponding outlets 213 directly facing and communicating.

[0062] With the structural design of the bottom gating assembly 2, during casting, molten metal flows in from the upper end of the vertical gating pipe 22, which then guides the molten metal into the inlet 212. The molten metal then flows within the horizontal flow channel 211. This process effectively consumes the kinetic energy of the molten metal, stabilizing its flow rate. Subsequently, the molten metal enters the cavity 11 of the mold body 1 through the outlet 213. This establishes a stable bottom-pouring flow field outside the gating port 13 of the mold body 1, ensuring that the molten metal enters the cavity 11 in a stable laminar flow state. This further reduces the scouring of the flow channel sand core 12 within the cavity 11 by the molten metal, thereby improving the forming quality of the casting.

[0063] In this embodiment, refer to Figure 2 The vertical gating pipe 22 includes a pouring cup 221 and several straight runner cups 222. The pouring cup 221 is vertically arranged and located directly above the runner base plate 21. The straight runner cups 222 are vertically arranged, and several straight runner cups 222 are connected coaxially in sequence in the vertical direction. The several straight runner cups 222 are located vertically between the pouring cup 221 and the runner base plate 21, and the pouring cup 221 is coaxially connected to the adjacent straight runner cup 222. The lowest straight runner cup 222 is connected to the runner base plate 21 and communicates with the inlet 212. Specifically, the straight runner cups 222 are all bonded and fixed to the adjacent pouring cups 221, straight runner cups 222, or runner base plate 21 with refractory adhesive.

[0064] For the structural design of the vertical sprue 22, the length of the vertical sprue 22 can be extended by bonding the straight runner cup 222. This allows for the free selection of the number of straight runner cups 222 to ensure that the final height of the vertical sprue 22 can meet the height requirements of different mold body 1.

[0065] In this embodiment, refer to Figure 2 The vertical height of the vertical gating pipe 22 is greater than the sum of the heights of the mold body 1 and the self-heating riser 3. Since the height of the liquid column in the vertical gating pipe 22 is higher than that of the mold body 1 and the self-heating riser 3, based on the principle of hydrostatics, this height difference can provide sufficient gravity static head for the molten metal. Thus, during the pouring process, this static pressure can drive the molten metal to overcome the complex flow resistance and gas back pressure in the cavity 11, thereby forcing the molten metal to fill the cavity 11 of the mold body 1 and the self-heating riser 3 at the top as much as possible. This effectively prevents molding defects such as incomplete filling or poor fusion of the molten metal in the cavity 11 due to insufficient filling power, which can improve the integrity of the final casting structure.

[0066] Reference Figure 1The self-heating riser 3 is prepared using an exothermic agent, insulating material, and refractory aggregate. It is bonded to the top of the mold body 1 using a refractory adhesive. During the casting process, when the high-temperature molten metal fills the cavity 11 and enters the self-heating riser 3, the molten metal contacts the inner wall of the riser 3, instantly triggering a strong exothermic reaction in the exothermic agent within the riser 3. This exothermic reaction significantly increases the temperature of the molten metal within the riser 3. Combined with the insulation effect of the insulating material within the riser 3, the molten metal within the riser 3 remains liquid for a prolonged period, and its solidification time is significantly later than that of the casting body within the cavity 11. This not only serves as a feeding liquid source but also as a heat source to heat the top of the casting, helping to establish a temperature gradient that is colder at the bottom and hotter at the top.

[0067] The implementation principle of this application embodiment is as follows: During the casting operation, molten metal is poured from the upper end of the vertical gating pipe 22 into the vertical gating pipe 22, and the vertical gating pipe 22 guides the molten metal into the bottom horizontal flow channel 211; the horizontal flow channel 211 plays a buffering and rectifying role for the high-speed falling molten metal, so that the flow rate of the molten metal tends to be stable and turns into a laminar flow state, thereby making the final molten metal smoothly fill the cavity 11 from bottom to top from the pouring port 13.

[0068] As the liquid level of the molten metal in the cavity 11 rises steadily, the gas and floating slag in the cavity 11 are pushed in an orderly manner to the top compensation allowance tank 15 and the self-heating riser 3, which avoids the slag and gas from being trapped in the casting body.

[0069] After the molten metal fills the cavity 11, the self-heating riser 3 at the top is activated to generate heat and maintain the temperature, thereby making the upper part of the mold body 1 have a high temperature and the lower part have a low temperature, thus establishing a temperature gradient of lower cold and upper hot.

[0070] Under this temperature gradient, the molten metal in cavity 11 gradually cools and solidifies from bottom to top. During solidification, since the cooling and solidification process strictly proceeds from bottom to top, when the molten metal at the bottom of the casting solidifies and shrinks, the molten metal directly above it remains liquid. At this time, this portion of molten metal can flow downwards to compensate for the shrinkage, thus forming a liquid phase compensation channel inside the casting. This allows the molten metal in the self-heating riser 3 to flow back into cavity 11 under gravity, replenishing the molten metal deficit caused by the overall solidification shrinkage of the casting.

[0071] Meanwhile, the self-heating riser 3 continuously supplies molten metal, ensuring that the final solidification area at the top of the cavity 11 still has sufficient molten metal for feeding, thereby ensuring that the entire casting has a dense structure and is free of shrinkage defects.

[0072] This embodiment also discloses a casting process for casting end caps of shell-type hydraulic valve bodies, including the following steps:

[0073] S1. Mold preparation: Prepare the mold body 1, the sprue base plate 21, and the vertical sprue 22.

[0074] Specifically, the preparation method of the mold body 1 is as follows: Silica sand and abrasive sand are mixed, wherein the mass percentage of abrasive sand is controlled at 20%–40%, preferably 30%, with the remainder being silica sand. Furthermore, both silica sand and abrasive sand are selected with a mesh size of 70–140 mesh. The mixed sand is then mixed with phenolic resin or other binders to prepare a coated sand. The prepared coated sand is used to manufacture the upper mold, lower mold, and internal flow channel sand core 12 of the shell mold body 1. The flow channel sand core 12 is then assembled and positioned within the corresponding upper mold and / or lower mold of the mold body 1. Subsequently, the upper mold and lower mold of the mold body 1 are bonded and fixed together.

[0075] The method for preparing the sprue base plate 21 is as follows: the sprue base plate 21 is prepared by integral molding using high-strength resin sand or coated sand through a core-making mold.

[0076] The vertical gating pipe 22 is prepared by pre-molding it using high-refractory ceramic material or coated sand to produce a smooth-walled gating cup 221 and several standard-length straight-line cups 222, in order to reduce the frictional resistance and temperature drop when the molten metal flows through it. The prepared gating cup 221 and several straight-line cups 222 are then bonded and fixed together in sequence using a refractory adhesive.

[0077] S2. Mold assembly: Fix the mold body 1 and the vertical sprue 22 to the sprue base plate 21, and connect the vertical sprue 22, the horizontal runner 211 and the pouring port 13 in sequence; fix the self-heating riser 3 to the mold body 1, and connect the self-heating riser 3 to the overflow port 14.

[0078] Specifically, the bottom of the vertical sprue 22 and the bottom of the mold body 1 are bonded to the upper side of the sprue base plate 21 using a refractory adhesive, and then the self-heating riser 3 is bonded to the top of the mold body 1 using a refractory adhesive.

[0079] S3, Bottom pouring: The molten metal is poured into the vertical gating pipe 22 from the top, so that the molten metal enters from the pouring port 13 and fills the cavity 11 from bottom to top until the molten metal fills the cavity 11 and then the pouring stops.

[0080] Specifically, the molten metal that has passed the smelting process is poured into the pouring cup 221. The molten metal then falls rapidly through the vertical gating pipe 22 into the horizontal runner 211. The horizontal runner 211 acts as a buffer to dissipate kinetic energy, allowing the poured molten metal to smoothly enter the mold cavity 11 until it is full and overflows into the self-heating riser 3 at the top. At this point, the mold cavity 11 is full, pouring is stopped, and the casting is left to cool and solidify naturally.

[0081] S4. Molding and Demolding: After the casting has cooled and solidified, remove the mold body 1, the sprue base plate 21 and the vertical sprue 22, and take out the casting.

[0082] S5. Post-processing: The excess material on the casting is removed by machining to obtain the final product.

[0083] Specifically, the removed casting is clamped and fixed, and the top of the casting is cut to completely remove the excess metal layer formed by the compensation allowance groove 15 in the mold body 1 and the excess metal column formed in the self-heating riser 3, thereby removing the excess metal layer and the micro-shrinkage and non-metallic inclusions enriched inside the metal column, revealing the dense casting matrix structure of the lower layer, and obtaining the final product.

[0084] The implementation principle of this application embodiment is as follows: During the process, the low expansion coefficient of the silica sand is first utilized to counteract the thermal expansion of the silica sand at high temperatures, thereby ensuring that the slender flow channel sand core 12 maintains dimensional stability during casting and does not experience thermal cracking or vein formation. During casting, a bottom-pouring method is adopted, utilizing the buffering effect of the horizontal flow channel 211 to allow the molten metal to gradually fill the cavity 11 from bottom to top in a stable laminar flow state, avoiding the molten metal falling and impacting the flow channel sand core 12, thus eliminating splashing and air entrapment. During the solidification stage, the active heating effect of the top self-heating riser 3 is used to establish a temperature gradient of lower cooling and upper heating within the cavity 11, thereby allowing the molten metal within the cavity 11 to gradually cool and solidify from bottom to top, ensuring that the shrinkage deficit of the casting body is promptly replenished by the liquid metal above. Finally, the excess material on the casting is removed by machining, resulting in higher surface precision of the casting and thus improving the quality of the final product.

[0085] Example 2: A mold for casting end caps of shell-type hydraulic valve bodies, referring to... Figure 4 and Figure 5 The difference between this embodiment and Embodiment 1 is that the mold further includes a sand box 4, which is filled from bottom to top with a fast heat conduction layer 41, a medium heat conduction layer 42, and a slow heat conduction layer 43, with the thermal conductivity of the fast heat conduction layer 41, the medium heat conduction layer 42, and the slow heat conduction layer 43 decreasing sequentially. Furthermore, the mold body 1 is located within the sand box 4, and the fast heat conduction layer 41, the medium heat conduction layer 42, and the slow heat conduction layer 43 all enclose the mold body 1.

[0086] Specifically, a fast-conducting heat layer 41 wraps around the bottom and lower sidewalls of the mold body 1, a medium-conducting heat layer 42 wraps around the middle sidewalls of the mold body 1, and a slow-conducting heat layer 43 wraps around the top sidewalls of the mold body 1. This layered design artificially creates a physical thermal gradient environment outside the mold body 1, ensuring that the bottom of the mold body 1 dissipates heat the fastest, followed by the middle, and the top the slowest. This forces the solidification path of the molten metal to strictly proceed from bottom to top, ensuring a continuous feeding channel from top to bottom within the casting. This allows the volume deficit caused by solidification shrinkage in the lower part of the casting to be promptly replenished by the gravity of the molten metal above, thereby improving the final density of the casting.

[0087] In this embodiment, refer to Figure 5 The fast-conducting heat conduction layer 41 is made of steel shot or iron shot, the medium-conducting heat conduction layer 42 is made of quartz sand or ordinary molding sand, and the slow-conducting heat conduction layer 43 is made of perlite insulating sand or vermiculite powder. Because steel shot or iron shot has a high thermal conductivity and high bulk density, it can adhere tightly to the outer wall of the lower part of the mold body 1, thereby quickly dissipating the heat from the bottom of the mold body 1, which promotes the preferential solidification of the bottom of the casting; while the slow-conducting heat conduction layer 43 at the top plays a role in heat insulation, delaying the heat loss of the molten metal at the top of the mold body 1.

[0088] Based on this, in order to ensure that the fast heat conduction layer 41, the medium heat conduction layer 42 and the slow heat conduction layer 43 can be repeatedly recycled, a thin layer of fire-resistant paper or fiberglass cloth will be laid between adjacent layers during the laying process.

[0089] In this embodiment, refer to Figure 5 The vertical sprue 22 and the sprue base plate 21 are both located inside the sand box 4, with the sprue base plate 21 situated within the fast heat conduction layer 41, while the upper end of the vertical sprue 22 extends above the slow heat conduction layer 43. This design serves two purposes: firstly, the gravity and lateral pressure generated by the high packing density of the bottom fast heat conduction layer 41 effectively press and fix the sprue base plate 21 and the mold body 1, resisting the enormous buoyancy generated by the molten metal during pouring and preventing the mold body 1 from shifting; secondly, the extension of the upper end of the vertical sprue 22 into the slow heat conduction layer 43 prevents impurities from falling into the sprue cup 221 during the filling of the heat-conducting material, and also facilitates the pouring operation.

[0090] Reference Figure 6 An inertial slag collection chamber 214 is also provided inside the bottom plate 21 of the gating system. The inlet 212, the outlet 213, and the inertial slag collection chamber 214 are arranged sequentially at intervals along the length of the horizontal flow channel 211, and one end of the horizontal flow channel 211 is connected to the inertial slag collection chamber 214. This makes the outlet 213 and the corresponding connected pouring port 13 located between the inlet 212 and the inertial slag collection chamber 214 along the length of the horizontal flow channel 211.

[0091] With the design of the inertial slag collection cavity 214, in the initial stage of pouring, the leading edge of the molten metal entering the horizontal flow channel 211 often has a high flow rate, low temperature, and contains slag. When this part of the molten metal flows through the horizontal flow channel 211, it will directly rush past the lateral outlet 213 due to the huge flow inertia and directly rush into and stay in the inertial slag collection cavity 214 at the end. After the molten metal fills the inertial slag collection cavity 214, the molten metal will continue to fill the horizontal flow channel 211 and then overflow into the mold cavity 11 through the outlet 213. This ensures that the molten metal entering the mold cavity 11 is a pure molten metal with a uniform and slow flow rate, a high and constant temperature, and few impurities, which can further reduce the probability of defects such as slag inclusions, porosity, and cold shuts inside the casting.

[0092] In this embodiment, refer to Figure 6 The inertial slag collection chamber 214 is located vertically below the horizontal flow channel 211, and one end of the horizontal flow channel 211 is connected to the top of the inertial slag collection chamber 214. This height difference design serves two purposes: firstly, it utilizes gravity to retain the pre-captured low-temperature molten metal and heavy slag within the inertial slag collection chamber 214, preventing them from flowing back into the horizontal flow channel 211 and mixing into the mold cavity 11 during subsequent pouring process; secondly, the downward design of the inertial slag collection chamber 214 ensures that the horizontal flow channel 211 must be filled with the inertial slag collection chamber 214 before overflowing into the mold cavity 11, which further slows down the flow rate of the molten metal, allowing the molten metal to maintain a stable pressure and flow rate.

[0093] Reference Figure 7 An overflow groove 31 is provided through the top of the self-heating riser 3, which makes the overflow groove 31 connected to the internal space of the self-heating riser 3.

[0094] During the pouring process, the gases and any floating slag present inside the mold cavity 11 float on the surface of the molten metal. This means that the molten metal that first reaches the self-heating riser 3 is usually a low-temperature waste liquid mixed with slag. The overflow trough 31 serves as a drainage channel, allowing this waste liquid to drain outside the self-heating riser 3, ensuring that only high-temperature, pure molten metal remains inside. This facilitates the rapid activation of the exothermic agent in the self-heating riser 3. Simultaneously, this also ensures the quality of the molten metal subsequently added to the mold cavity 11, thereby improving the purity and density of the final casting. Furthermore, when some waste liquid is discharged from the overflow trough 31, it indicates that the mold cavity 11 is full, thus reminding the workers to stop pouring.

[0095] In this embodiment, refer to Figure 7 The self-heating riser 3 is topped with a self-welding cover plate 32, which seals the overflow groove 31.

[0096] For the design of the self-welding cover plate 32, when the molten metal fills to the top of the self-heating riser 3, the rising molten metal can push the self-welding cover plate 32 open, allowing the waste liquid to automatically overflow through the overflow tank 31. After the waste liquid is discharged, the worker stops pouring. The self-welding cover plate 32 falls back to its original position or is manually reset by the worker. The molten metal remaining on the top of the self-heating riser 3 has not completely solidified. This part of the molten metal can use its own heat and surface tension to weld and seal the self-welding cover plate 32 to the top of the self-heating riser 3.

[0097] Therefore, this enables a special design that first vents and discharges slag, and then automatically seals, which not only removes impurities but also ensures that the self-heating riser 3 in the feeding stage has good airtightness and heat preservation, preventing heat loss through radiation.

[0098] The implementation principle of this application embodiment is as follows: Before the casting operation, the mold body 1, the bottom pouring component 2 and the self-heating riser 3 are bonded and fixed and put into the sand box 4. Then, the sand box 4 is filled with a fast heat conduction layer 41, a medium heat conduction layer 42 and a slow heat conduction layer 43 from bottom to top.

[0099] At the start of casting, molten metal is injected into the vertical gating pipe 22 and rushes into the horizontal flow channel 211 at high speed. At this time, the leading molten metal with high flow rate and low temperature rushes directly into the inertial slag collection chamber 214 due to inertia and is left in the inertial slag collection chamber 214. After the inertial slag collection chamber 214 is full, the subsequent pure and stable molten metal enters the mold cavity 11.

[0100] As the molten metal fills the cavity 11, the waste liquid containing impurities and at a lower temperature at the top of the molten metal pushes open the self-welding cover plate 32 and is discharged outside the self-heating riser 3 through the overflow trough 31. After the waste liquid is discharged, the self-welding cover plate 32 falls back to its original position and automatically seals the overflow trough 31.

[0101] During the solidification stage, the molten metal in the cavity 11 is cooled and solidified sequentially in a bottom-up path.

[0102] Finally, after the casting has cooled and been removed, the metal layer formed by the compensation allowance groove 15 at the top and the metal pillar formed by the self-heating riser 3 are removed by machining to obtain the corresponding complete casting.

[0103] This embodiment also discloses a casting process for casting the end cap of a shell-type hydraulic valve body. The difference between this embodiment and Embodiment 1 is that it includes the following steps:

[0104] Steps S2 and S3 also include the following steps:

[0105] Mold embedding box: Place the assembled mold body 1, vertical gating pipe 22 and self-heating riser 3 into the sand box 4, and fill the sand box 4 with a fast heat conduction layer 41, a medium heat conduction layer 42 and a slow heat conduction layer 43 from bottom to top.

[0106] Specifically, the filling steps for the fast heat conduction layer 41, the medium heat conduction layer 42, and the slow heat conduction layer 43 are as follows: Filling the fast heat conduction layer 41: Fill the bottom of the sand box 4 and the lower side wall of the mold body 1 with steel shot or iron shot, covering 1 / 3 to 1 / 2 of the height of the mold body 1. During the filling process, vibration compaction is performed. The large bulk density of the steel shot and the lateral pressure generated are used to press and fix the sprue bottom plate 21 and the mold body 1 tightly to prevent buoyancy from lifting the box during subsequent pouring.

[0107] First layer of insulating paper: A thin layer of fire-resistant paper or fiberglass cloth is laid on top of the rapid heat conduction layer 41.

[0108] Fill the medium-speed heat conduction layer 42: Above the fast heat conduction layer 41, continue to fill with quartz sand or ordinary molding sand until it covers the middle area of ​​the mold body 1.

[0109] Second layer of insulating paper: A thin layer of fire-resistant paper or fiberglass cloth is laid on top of the medium-speed heat-conducting layer 42.

[0110] Fill the slow heat conduction layer 43: Fill perlite insulation sand or vermiculite powder on top of the medium heat conduction layer 42 until it completely covers the top of the mold body 1.

[0111] In step S3, the pouring is stopped after the molten metal overflows from the overflow groove 31 at the top of the self-heating riser 3.

[0112] Specifically, when workers observe molten metal flowing out of the overflow tank 31 and the color of the flowing liquid brightens, it indicates that the pure molten metal has filled the cavity 11. This allows workers to intuitively understand the situation and immediately stop pouring.

[0113] In step S4, before removing the mold body 1, the sprue base plate 21 and the vertical sprue 22, the sand box 4 is tilted to pour out the slow heat conduction layer 43, the medium heat conduction layer 42 and the fast heat conduction layer 41 filled inside in sequence.

[0114] The implementation principle of this application embodiment is as follows: by forcing the molten metal to strictly follow the solidification path from bottom to top through this process, the potential hot spot in the middle of the casting is eliminated, ensuring that the feeding channel is unobstructed, thereby improving the density and purity of the final casting.

[0115] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. A mold for casting end caps of shell-type hydraulic valve bodies, characterized in that, include: The mold body (1) has a cavity (11) formed inside it. A runner sand core (12) is provided inside the cavity (11). The runner sand core (12) is fixedly connected to the mold body (1). A pouring port (13) is provided at the bottom of the mold body (1). The pouring port (13) is connected to the cavity (11). The bottom pouring assembly (2) includes a gating base plate (21) and a vertical pouring pipe (22). A horizontal flow channel (211) is provided in the gating base plate (21). The horizontal flow channel (211) is arranged in the horizontal direction along its length. The vertical pouring pipe (22) is arranged vertically and located above the gating base plate (21). The lower end of the vertical pouring pipe (22) is connected to the gating base plate (21) and communicates with the horizontal flow channel (211). The mold body (1) is fixed on the sprue base plate (21), and the pouring port (13) is connected to the horizontal runner (211); An inertial slag collection cavity (214) is provided in the bottom plate (21) of the gating channel. The horizontal flow channel (211) is connected to the vertical gating pipe (22), the pouring port (13) and the inertial slag collection cavity (214) in sequence along its own length direction. It also includes a sand box (4), in which a fast heat conduction layer (41), a medium heat conduction layer (42) and a slow heat conduction layer (43) are arranged sequentially from bottom to top, and the thermal conductivity of the fast heat conduction layer (41), the medium heat conduction layer (42) and the slow heat conduction layer (43) decreases sequentially. The mold body (1) is located inside the sand box (4), and the fast heat conduction layer (41), the medium heat conduction layer (42) and the slow heat conduction layer (43) all wrap the mold body (1).

2. The mold for casting a shell-type hydraulic valve body end cap according to claim 1, characterized in that, The vertical gating pipe (22) includes a pouring cup (221) and a plurality of straight runner cups (222). The pouring cup (221) is vertically arranged and located above the gating bottom plate (21). A plurality of straight runner cups (222) are located vertically between the pouring cup (221) and the runner base plate (21). The plurality of straight runner cups (222) are arranged coaxially in sequence in the vertical direction. The straight runner cups (222) are bonded to adjacent straight runner cups (222), the pouring cups (221), or the runner base plate (21). The pouring cups (221) are coaxially connected to adjacent straight runner cups (222). The lowest straight runner cup (222) is connected to the horizontal runner (211).

3. The mold for casting a shell-type hydraulic valve body end cap according to claim 1, characterized in that, The vertical gating pipe (22) is higher in the vertical direction than the height of the mold body (1).

4. The mold for casting a shell-type hydraulic valve body end cap according to claim 1, characterized in that, The mold body (1) is provided with a compensation allowance groove (15), which is located on the inner wall of the top of the cavity (11).

5. A mold for casting a shell-type hydraulic valve body end cap according to claim 1, characterized in that, A self-heating riser (3) is provided above the mold body (1). The self-heating riser (3) is vertically arranged, and the lower end of the self-heating riser (3) is connected to the mold body (1) and communicates with the cavity (11).

6. A mold for casting a shell-type hydraulic valve body end cap according to claim 5, characterized in that, An overflow groove (31) is provided through the top of the self-heating riser (3).

7. A mold for casting a shell-type hydraulic valve body end cap according to claim 1, characterized in that, The flow channel sand core (12) is prepared by mixing abrasive sand and silica sand. The abrasive sand accounts for 20% to 40% of the mass, and the remainder is silica sand. Both the abrasive sand and the silica sand have a mesh size of 70-140 mesh.

8. A casting process for casting a shell-type hydraulic valve body end cap, utilizing a mold for casting a shell-type hydraulic valve body end cap as described in any one of claims 1-7, characterized in that, Includes the following steps: Mold preparation: Prepare the mold body (1), the sprue base plate (21) and the vertical sprue (22); Mold assembly: Fix the mold body (1) and the vertical sprue (22) on the sprue base plate (21), and connect the vertical sprue (22), the horizontal runner (211) and the pouring port (13) in sequence; Bottom pouring: Molten metal is poured into the vertical gating pipe (22) from the top end, so that the molten metal enters from the pouring port (13) and fills the cavity (11) from bottom to top until the molten metal fills the cavity (11) and then the pouring stops. Molding and demolding: After the casting has cooled and solidified, remove the mold body (1), the sprue bottom plate (21) and the vertical sprue (22) and take out the casting.

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