A casting method for a servo valve body

Abstract

The present invention relates to ship machinery technology and discloses a casting method for a servo valve body, comprising the following steps: step S100: formulating casting equipment for a casting process through three-dimensional mapping design, casting simulation, optimization design, and simulation verification in sequence, placing patches, risers, and chills on both sides of a valve core of a mold and on an upper surface of the mold, respectively, wherein the patches, risers, and chills synergistically form a temperature gradient to control and optimize the solidification process of the casting; step S200: placing a series core frame for connecting a resin chromite sand layer and an ester-hardened water glass sand layer in series in the mold, then filling the working surfaces of the mold and the core with resin chromite sand, and filling the non-working surfaces with ester-hardened water glass sand; and step S300: smelting molten steel, wherein the smelting controlled components (percentage) are: C: 0.34-0.35, Si: 0.45-0.46, Mn: 0.70-0.71, Cr: 0.93-0.95, Mo: 0.20-0.30, and S and P ≤ 0.025. The present invention can solve the technical problems of poor performance and poor quality of valve bodies in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of ship machinery, and in particular to a casting method for a servo valve body. Background Art

[0002] Servo valves are key components in industrial control and are widely used in ship hydraulic systems. By precisely adjusting flow and pressure, servo valves ensure stable operation of hydraulic systems. Their operating principle is based on the movement of liquid in a closed environment. The movement of the valve core changes the flow pattern of the fluid in the hydraulic circuit, thereby achieving precise control of the overall output. As a key component of the servo valve, the internal quality and surface quality of the valve body are crucial, directly affecting the function of the device.

[0003] However, the existing casting methods have the following problems: (1) Long R&D cycle and high R&D cost: At present, the development of casting technology mainly relies on the experience of technicians, and the optimal process parameters are determined through trial production and repeated verification, which makes its R&D cycle long and the R&D cost high. (2) Poor quality: The valve body casting has a complex structure, and the thick and large areas are unevenly distributed. Shrinkage holes and shrinkage defects often occur, resulting in poor density and low pressure bearing capacity of the valve body. In addition, the valve body is usually made of low-alloy steel and has high performance requirements. However, the existing casting methods often result in unqualified casting performance and cannot meet the use requirements. (3) Sand problem: Traditional valve body molding sand generally uses ordinary water glass sand. This type of sand mold is very prone to sand sticking defects, which not only affects the surface quality of the casting, but also hinders the liquid flow of the valve body during operation, reducing its performance and service life. (4) Material brittleness and cracks: The valve body material is relatively brittle and is very prone to crack defects during the thermal reaction process, which affects the service life and performance of the valve body. Summary of the Invention

[0004] The present invention aims to provide a casting method for a servo valve body to solve the technical problems of substandard valve body performance and poor quality in the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] Step S100: Developing casting equipment for the casting process through three-dimensional mapping design, casting simulation, optimization design, and simulation verification. Place shrinkage compensation pads on both sides of the valve core and on the upper surface of the mold, risers for controlling the solidification time of the casting, and chills for controlling the cooling rate. The pads include a first pad and a second pad, and the risers include a first riser, a second riser, a third riser, a fourth riser, and a fifth riser.

[0007] The second subsidy is located on both sides of the valve core, the second subsidy is used to compensate for shrinkage, the second riser is located above the second subsidy, and the second subsidy is connected to the valve core through a pouring system; a vertical upward pouring pipe is provided in the middle of the pouring system, and a pouring port for pouring molten steel is provided on the pouring pipe; the first subsidy is located in the middle of the upper surface of the mold away from the pouring system, the first riser is located above the first subsidy, the fourth riser is located on the side of the upper surface of the mold close to the pouring system, and the fifth riser is between the first riser and the fourth riser; the third riser is located at the outwardly protruding portions on the left and right sides of the upper surface of the mold, and chills for controlling the cooling rate are evenly provided around the third riser and the fourth riser;

[0008] The synergistic effect between the patch, riser and chill forms a temperature gradient to control and optimize the solidification process of the casting.

[0009] Step S200: Placing a series core frame in the mold for connecting the resin chromite sand layer and the ester-hardened water glass sand layer in series, the series core frame prevents the resin chromite sand layer and the ester-hardened water glass sand layer from separating during the molding process due to the different materials; then, filling the working surfaces of the mold and the core with resin chromite sand to form the resin chromite sand layer, and filling the non-working surfaces with ester-hardened water glass sand to form the ester-hardened water glass sand layer;

[0010] Step S300: smelting molten steel, wherein the smelting controlled composition (percentage) is: C: 0.34-0.35, Si: 0.45-0.46, Mn: 0.70-0.71, Cr: 0.93-0.95, Mo: 0.20-0.30, S, P ≤ 0.025.

[0011] The principles of this program are:

[0012] First, a 3D model of the casting equipment and mold was created using 3D modeling software. Casting simulation software was then used to verify and optimize the casting process to determine the optimal shrinkage feeding process. Through 3D mapping design, casting simulation, optimization design, and simulation verification, this solution adopted a combination of "feeding + riser + chill" for shrinkage feeding, as well as improvements to the molding sand material and smelting control components. During molding, a series of core frames were first placed at the intersection of the resin chromite sand layer and the ester-hardened water glass sand layer in the mold to strengthen the adhesion between the resin chromite sand layer and the ester-hardened water glass sand layer, preventing the different sand layers from separating during the casting process and thus reducing sand sticking defects. Then fill the working surfaces of the mold and core with resin chromite sand to form a resin chromite sand layer, and fill the non-working surfaces with ester-hardened water glass sand to form an ester-hardened water glass sand layer; after the molding is completed, ensure that the various parts of the mold and core are tightly fitted without obvious gaps or defects, and then carry out molten steel smelting. When smelting molten steel, the smelting composition must be strictly controlled to meet the requirements of: C: 0.34-0.35, Si: 0.45-0.46, Mn: 0.70-0.71, Cr: 0.93-0.95, Mo: 0.20-0.30, S, P ≤ 0.025 (percentage).

[0013] The advantages of this solution are:

[0014] (1) This solution first places a series core frame in the mold, then fills the working surface of the mold and core with resin chromite sand, and fills the non-working surface with ester hardened water glass sand. The "resin chromite sand + ester hardened water glass sand" combined molding method adopted breaks the technical prejudice in the existing technology that ordinary water glass sand is prone to sand sticking defects when used for valve body molding. This combination method can greatly reduce the sand sticking defects on the surface of the valve body and ensure the smoothness and neatness of the casting surface. This solution adopts a layered filling method, that is, different molding sands are used on different working surfaces, which can improve the quality and performance of the casting, effectively control costs, improve production efficiency, and ensure the quality and performance of key parts (mold and core working surfaces).

[0015] (2) The series core frame used solves the problem of easy separation of resin chromite sand and ester hardened water glass sand, enhances the adhesion between the two, ensures the stability and integrity of the sand mold, and realizes the application effect of the two sand molds on different working surfaces, so as to solve the problems of different working surfaces in a targeted manner. Specifically, the resin chromite sand has good disintegration properties, which can reduce the sand sticking defects on the working surface, thereby improving the performance and quality of the key parts of the valve body; the ester hardened water glass sand has good yield properties, which can reduce the tendency to crack. Using ester hardened water glass sand on non-working surfaces can reduce the overall production cost and improve economic benefits; using resin chromite sand on the working surface can improve the performance and quality of key parts (such as the valve core), thereby improving the performance and quality of the overall casting. Through this optimized sand mold combination, the fire resistance and strength are guaranteed, and the environmental protection and air permeability are improved; and while solving the problem of sand sticking defects, the production cost is reduced.

[0016] (3) The improvement of smelting composition makes the mechanical properties data of castings more concentrated and stable, effectively reduces the carbon equivalent (CE) of steel castings, improves the welding performance of castings, and thus reduces the risk of welding cracks. At the same time, precise composition control reduces the risk of raw material waste and improves production efficiency and economic benefits.

[0017] (4) In terms of shrinkage compensation for castings, a combination of "subsidy + riser + chill" is adopted to effectively reduce shrinkage cavities and shrinkage porosity inside the castings and optimize the cooling process, thereby reducing defects in poor casting quality. Specifically, the combination of "subsidy + riser + chill" can effectively control the cooling process of the castings, ensure the expected sequential solidification of the castings, and ensure that the shrinkage compensation channel (i.e., the channel formed by the "subsidy + riser + chill" installation position) is unobstructed to form a temperature gradient, reduce shrinkage defects, and thus improve the quality and performance of the castings. Among them, the subsidy is used to compensate for the shrinkage of the castings during the cooling process, ensuring the dimensional stability and structural integrity of the castings; the riser slowly releases heat to prolong the solidification time of the molten steel, thereby improving the shrinkage compensation effect and reducing internal defects; the chill accelerates the cooling rate of the parts, prevents the formation of hot spots, reduces thermal stress and deformation, and promotes the flow of molten steel from other parts to the area that needs shrinkage compensation.

[0018] Preferably, as an improvement, the first riser and the fifth riser are heating and heat-insulating risers; the second riser is the first heating and heat-insulating component; the third riser is a necked heating and heat-insulating riser; the fourth riser is the second heating and heat-insulating component; the heating and heat-insulating component includes a heating and heat-insulating riser and a cover.

[0019] Beneficial effects: The exothermic riser is used to extend the solidification time of the molten steel in the middle of the upper surface of the mold, thereby improving the shrinkage feeding effect and reducing internal defects; the "exothermic riser + cover" can help control the solidification sequence of the casting, ensure uniform solidification from the outside to the inside, and reduce thermal stress and deformation; the necked exothermic riser allows the molten metal in the riser to flow more effectively to the area that needs to be fed, ensuring that the area that needs to be fed is fully fed.

[0020] Preferably, as an improvement, the pouring system adopts a side pouring or bottom pouring method, and the pouring system adopts a ceramic pouring pipe.

[0021] Beneficial effects: Side or bottom pouring can ensure the smooth rise of molten steel, avoiding scouring the cavity and forming defects such as sand sticking; ceramic pouring pipes can effectively reduce sand inclusion defects compared to sand runners.

[0022] Preferably, as an improvement, the step S200 further includes:

[0023] Step S210: Filling with molding sand

[0024] Step S220: opening the casting, removing the formed sand mold from the casting, and applying alcohol-based paint to the mold and core working surfaces;

[0025] Step S230: placing and assembling the core, and then filling the edge seam between the mold and the core;

[0026] Step S240: Before closing the box, use a vacuum hose to clean the cavity;

[0027] Step S250: closing the box

[0028] Beneficial effects: Applying alcohol-based paint to the working surfaces of the mold and core can reduce the adhesion between the molten steel and the sand mold, improve the surface finish of the casting, and at the same time, the alcohol-based paint can reduce the pores and inclusions on the surface of the mold, thereby improving the density and performance of the casting; filling treatment can reduce the leakage of molten steel during the pouring process, ensure the sealing of the mold, and avoid flash in the inner cavity of the casting; cleaning the mold cavity can remove dust, sand particles and other impurities in the mold cavity, and avoid sand inclusion defects caused by residual molding sand.

[0029] Preferably, as an improvement, the thickness of the resin chromite sand is 100mm-140mm; the thickness of the ester hardened water glass sand is 60mm-80mm; the particle size of the ester hardened water glass sand is 30-50 mesh, and the particle size of the resin chromite sand is 40-70 mesh.

[0030] Beneficial Effects: A moderate thickness of 100mm-140mm for the resin-cured chromite sand layer, and 60mm-80mm for the ester-cured water glass sand layer, neither too thick nor too thin. A thin layer can slow heat dissipation and form iron inclusions, while a thick layer can increase production costs. The ester-cured water glass sand has a particle size of 30-50 mesh, offering excellent air permeability and fluidity, helping to reduce porosity and sand inclusions in castings. The resin-cured chromite sand has a particle size of 40-70 mesh, providing excellent surface finish and density, helping to reduce surface roughness in castings.

[0031] Preferably, as an improvement, the usage ratio of ester-hardened water glass sand to resin chromite sand is 5:1.

[0032] Beneficial effect: While ensuring the quality of castings, it can reduce production costs.

[0033] Preferably, as an improvement, the step 300 further includes: after the molten steel is smelted, pouring is performed, the pouring temperature is 1560±10° C., and the number of supplementary pouring is 4-6 times.

[0034] Beneficial effects: The pouring temperature range of 1560±10℃ can ensure that the molten steel has good fluidity, which is conducive to the full filling of the sand mold with molten steel, reducing cold shut and insufficient pouring during the pouring process, and can reduce casting defects caused by temperature fluctuations, and improve the surface quality and internal structure of the casting; 4-6 times of supplementary pouring can ensure that the casting always has sufficient molten steel supply during the solidification process, reduce defects such as shrinkage cavities and shrinkage, improve the density and performance of the casting, and at the same time extend the solidification time of the casting, so that the molten steel can be cooled more evenly in the sand mold, reducing thermal stress and deformation.

[0035] Preferably, as an improvement, step 400: after the molten steel is poured, the casting is naturally cooled in the molding sand for 18-24 hours. After the casting has cooled naturally, it is dropped into the sand box, the casting is taken out of the sand box and the sand is cleaned. Then, before gas cutting, the casting is preheated to a temperature of 250-300°C.

[0036] Beneficial effects: The casting is cooled naturally in the molding sand. After 18-24 hours, the casting is dropped into the molding sand and the sand is cleaned to avoid cracks caused by the casting not solidifying or cooling too quickly. The preheating treatment at 250-300℃ avoids cracks caused by rapid heating of the casting, thereby reducing the crack tendency on the valve body surface.

[0037] Preferably, as an improvement, the process further includes: Step 500: subjecting the casting to a quenching and tempering heat treatment at a quenching temperature of 850-890°C for 3-6 hours, and simultaneously adopting a water quenching and oil cooling process at a water temperature of ≤45°C and an oil temperature of 30-80°C.

[0038] Beneficial Effects: Heat treatment quenching temperature of 850-890°C, holding temperature for 3-6 hours, solves the problem of poor product plasticity, toughness, and elongation due to excessively high quenching temperature and excessively long holding time. The water quenching and oil cooling process, with water temperature ≤45°C and oil temperature between 30-80°C, ensures rapid and uniform cooling of castings during quenching, improving their hardness, strength, and surface quality, while reducing the risk of deformation and cracking, optimizing microstructure, and increasing production efficiency and yield rate.

[0039] Preferably, as an improvement, the method further includes: Step 600: performing ultrasonic and magnetic particle flaw detection on the casting, and performing a pressure test on the casting.

[0040] Beneficial effects: It can ensure the internal and external quality of castings, improve the reliability and safety of castings, reduce scrap rate, and improve production efficiency and economic benefits.

[0041] Beneficial effects of the present invention: (1) In the above steps, each step is closely linked and complements each other, so that the entire casting process can be optimized, thereby ensuring the high quality and high reliability of the casting, and solving the technical problems of substandard mechanical properties and poor quality of the valve body in the prior art. The importance of each step in this solution lies not only in its own function, but also in its coordination with other steps to jointly achieve the shrinkage compensation effect, cooling process, defect reduction, quality improvement and production efficiency of the casting. This comprehensive optimized process design not only improves the performance of the casting, but also reduces production costs and improves overall production efficiency.

[0042] (2) Compared with the existing valve body casting method, the servo valve body casting process provided by this solution can improve the production cycle, shortening its production cycle by one third. For example, the existing production cycle is 3 months, while the production cycle of this solution can be shortened to 2 months. While improving the production cycle, it also takes into account the production quality.

[0043] (3) The combination of “subsidy + riser + chill” and the synergistic effect of the quenching and tempering heat treatment make the internal structure of the valve body prepared by this scheme denser and able to withstand greater pressure.

[0044] (4) The improvement of the molding method and smelting composition makes the appearance quality of the prepared valve body better, solves the common defects of the valve body such as sand sticking and cracks, and improves the mechanical properties of the valve body.

[0045] (5) The use of ester-hardened water glass sand and resin chromite sand and the improvement of smelting composition have achieved the reduction of production costs without affecting the quality of the valve body.

[0046] In summary, the casting method adopted in this scheme enables the prepared valve body to perform excellently in terms of pressure bearing, performance, and surface quality. It also has high practical value and market competitiveness, and is suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A logic block diagram of a casting method for a servo valve body provided by an embodiment of the present invention Figure 1 .

[0048] Figure 2 A schematic structural diagram of a mold in a casting method for a servo valve body provided by an embodiment of the present invention

[0049] Figure 3 A schematic structural diagram of a casting device in a casting method for a servo valve body provided by an embodiment of the present invention.

[0050] Figure 4 A top view of a casting device in a casting method for a servo valve body provided by an embodiment of the present invention.

[0051] Figure 5 A simulation diagram of shrinkage cavities and porosity of a casting device in a casting method for a servo valve body provided by an embodiment of the present invention.

[0052] Figure 6 This is a structural schematic diagram of a series core frame in a casting method of a servo valve body provided by an embodiment of the present invention.

[0053] Figure 7 A cross-sectional view of a valve core in a casting method of a servo valve body provided by an embodiment of the present invention.

[0054] Figure 8 A logic block diagram of a casting method for a servo valve body provided by an embodiment of the present invention Figure 2 . DETAILED DESCRIPTION

[0055] The following is further described in detail through specific implementation methods:

[0056] The figure marks in the drawings of the specification include: mold 1, chill 2, riser 3, heating and heat-insulating riser 31, first heating and heat-insulating component 32, necked heating and heat-insulating riser 33, second heating and heat-insulating component 34, subsidy 4, first subsidy 41, second subsidy 42, pouring system 5, pouring gate 51, resin chromite sand layer 6, ester hardened water glass sand layer 7, series core frame 8, intersection layer of chromite sand and ester hardened water glass sand 9, mold surface 10, mold upper surface 11, valve core 12, working surface 13, non-working surface 14.

[0057] Example 1:

[0058] The embodiment is basically as shown in the attached Figure 1 A method for casting a servo valve body is shown, comprising the following steps:

[0059] Step S100: Formulate casting process

[0060] The casting process is formulated through 3D mapping design, casting simulation, optimization design and simulation verification to ensure that the final casting process plan achieves the best effect in terms of shrinkage compensation.

[0061] Specifically, (1) 3D mapping design: First, a 3D model of the casting is created using 3D modeling software to accurately represent the casting's geometry, dimensions, and details, including its complex internal structure and external features. The position and layout of the gating system 5 are then designed. In this embodiment, the gating system 5 employs side or bottom injection.

[0062] (2) Casting simulation: Set simulation parameters, place corresponding chill 2, riser 3, and patch 4 in the three-dimensional model, and simulate the pouring and solidification process of the casting.

[0063] (3) Design optimization and simulation verification: Analyze the results of the casting simulation, identify existing problems and potential risks, and then adjust the design of the pouring system 5, chill 2, riser 3, compensation 4 and sand mold based on the simulation results. Finally, re-simulate the optimized design scheme to verify the improvement effect, repeat the simulation and optimization process to ensure that the final casting process scheme achieves the best effect in terms of shrinkage compensation.

[0064] Specifically, this solution provides a casting device for a servo valve body. In this embodiment, the filler 4 includes a first filler 41 and a second filler 42, and the riser 3 includes a first riser, a second riser, a third riser, a fourth riser, and a fifth riser. The first and fifth risers combine to form a heat-insulating riser 31, the second riser is a first heat-insulating assembly 32, the third riser is a necked heat-insulating riser 33, and the fourth riser is a second heat-insulating assembly 34. The heat-insulating assembly includes a heat-insulating riser and a cover. The filler 4 (i.e., the shrinkage filler) provides additional molten metal to compensate for voids created by volumetric shrinkage during the solidification process of the casting. The provision of the filler 4 ensures that sufficient molten metal fills these voids during the cooling process, thereby reducing or eliminating shrinkage cavities and shrinkage defects. The riser 3 generates heat through its internal heat-generating material (such as aluminum powder, iron powder, etc.), which can maintain the temperature of the riser 3 area, thereby extending the solidification time of the casting. This helps ensure that the molten metal and molten steel have sufficient time to feed during the cooling process, reducing or eliminating shrinkage cavities and shrinkage defects.

[0065] Specifically, such as Figure 2 、 Figure 3 、 Figure 4As shown, the mold 1 is placed horizontally on the equipment. Secondary pads 42 are installed on either side of the valve core 12 in the mold 1 to compensate for shrinkage. These second pads 42 ensure sufficient molten metal to fill these cavities during the cooling process, thereby reducing or eliminating shrinkage cavities and porosity defects. The second pads 42 are connected to each other via the gating system 5 and to the mold 1 via the valve core 12. This forms a circulation system between the second pads 42, the gating system 5, and the mold 1, facilitating the subsequent side-injection of molten steel into the mold 1 to form the casting. A first heating and insulation assembly 32 is installed above the second pads 42. This first heating and insulation assembly 32 comprises a heating and insulation riser 31 and a cover. The cover is used to reduce heat loss and maintain a high temperature within the riser 3 near the valve core 12, thereby ensuring a more uniform and stable temperature for the molten steel within the riser 3 and improving the quality of the valve core 12. A vertical pouring pipe is installed in the middle of the pouring system 5, with a pouring port 51 for pouring molten steel. A first patch 41 is provided in the middle of the mold upper surface 11, away from the pouring system 5. A heating and insulation riser 31 is installed above the first patch 41. Neck heating and insulation risers 33 are installed on the protruding portions on the left and right sides of the mold upper surface 11. A second heating and insulation component 34 is installed on the side of the mold upper surface 11 close to the pouring system 5. The heating and insulation riser 31 also includes a fifth riser located between the first patch 41 and the second heating and insulation component 3. Chills 2 for controlling the cooling rate are evenly installed around the second heating and insulation component 34 and the neck heating and insulation riser 33. In this embodiment, the heat-insulating riser 31 is used to extend the solidification time of the molten steel in the middle of the mold's upper surface 11, thereby improving the shrinkage feeding effect and reducing internal defects. The heat-insulating assembly 34 (i.e., the heat-insulating riser 31 + cover) helps control the solidification sequence of the casting, ensuring uniform solidification from the outside inward and reducing thermal stress and deformation. The necking heat-insulating riser 33 allows the molten metal in the riser 3 to flow more effectively to the area where the upper surface protrusion is required, ensuring that this area is fully fed. In this embodiment, there are four feeding points 4, eight risers 3, and twelve chills 2.

[0066] This solution achieves the best effect in shrinkage compensation of castings through the layout of the above-mentioned chill 2, riser 3 and subsidy 4, thereby optimizing the solidification process of castings, reducing shrinkage defects and ensuring the quality of castings. Shrinkage refers to the volume shrinkage of molten metal during the solidification process. If certain parts of the casting (especially thick-walled parts or parts with complex structures) do not have enough molten metal to fill the gaps caused by shrinkage during solidification, shrinkage will be formed, and shrinkage is usually caused by the failure to fully compensate for the tiny volume shrinkage of the local area of ​​molten metal during the solidification process. Specifically, Figure 5As shown in the shrinkage porosity simulation diagram, the presence of shrinkage porosity is indicated by color depth, with black indicating the highest probability, gray the next highest, and white (the lightest color) the lowest. In this implementation, the white areas (i.e., the lightest areas) indicate the absence of shrinkage porosity. In this implementation, the combination of "pad 4 + riser 3 + chill 2" in the aforementioned casting equipment results in a white casting body, with shrinkage cavities located one-third higher than the riser 3, thus achieving optimal shrinkage feeding.

[0067] In summary, this solution uses an integrated setup of 3D mapping design, casting simulation, optimization design, and simulation verification. During the simulation optimization process, pouring position selection and casting shrinkage feeding improvements are performed. Specifically, in pouring position selection, the mold 1 is placed horizontally on the equipment, and a circulation system is formed between its second subsidy 42, the pouring system 5, and the mold 1, so that the pouring position of the casting will adopt a horizontal pouring method to shorten the shrinkage feeding distance, reduce the molding difficulty, and improve the shrinkage feeding effect and surface quality of the casting. Improvement of casting shrinkage compensation: A combination of patch 4 + riser 3 + chill 2 is adopted to ensure that the shrinkage compensation channel (i.e., the installation location of patch 4, riser 3, and chill 2) is unobstructed and a temperature gradient is formed. Different patches 4 and risers 3 are used in different parts of the mold 1 (valve core 12 and mold upper surface 11) to compensate for shrinkage to ensure the dimensional stability and structural integrity of the casting. Installing riser 3 above patch 4 can extend the solidification time of molten steel, improve the shrinkage compensation effect, and reduce internal defects. At the same time, chill 2 is placed on the upper surface of the casting to accelerate local cooling, prevent the formation of hot spots, and reduce thermal stress and deformation. Design of pouring system 5: The pouring system 5 will adopt side pouring or bottom pouring to ensure that the molten steel rises smoothly and avoids scouring the mold cavity to form defects such as sand sticking. The material of pouring system 5 will use ceramic pouring pipe to reduce sand sticking, improve the stability and reliability of pouring, and reduce defects in the pouring process.

[0068] Step S200: Modeling

[0069] During the casting process, resin-cured chromite sand is used for the working surfaces of molds and cores, while ester-cured water glass sand is used for the non-working surfaces. The resin-cured chromite sand has good disintegration properties, which helps reduce sand sticking defects in the inner cavity and makes cleaning castings easier. The ester-cured water glass sand has good yield properties during the solidification process, making it less prone to cracking defects, thereby improving the integrity and surface quality of the castings. Ester-cured water glass sand is also low-cost, which helps reduce production costs, and is environmentally friendly, minimizing impact on the environment.

[0070] Specifically, the mold 1 is placed horizontally on the casting equipment, and a riser 3 or a chill 2 is placed at the corresponding position of the mold 1 and fixed firmly, and the pouring system 5 is arranged at the same time. Then, the molding sand is filled at the position where the mold 1 is specially filled with molding sand. The resin chromite sand is filled into the mold and core working surfaces to form a resin chromite sand layer 6, and the ester hardened water glass sand is filled into the other non-working surfaces to form an ester hardened water glass sand layer 7. Figure 6 As shown, during the molding sand filling process, a series core frame 8 is first placed at the intersection layer 9 of the chromite sand and ester-hardened water glass sand within the casting. Resin chromite sand is then added to the working surfaces of the mold and core, and ester-hardened water glass sand is added to the non-working surfaces. The series core frame 8 connects the resin chromite sand layer 6 and the ester-hardened water glass sand layer 7 in series, strengthening the adhesion between the resin chromite sand layer 6 and the ester-hardened water glass sand layer 7, preventing separation during the casting process and thus reducing sand sticking defects. The thickness of the resin chromite sand layer 6 is 100mm-140mm, and the thickness of the ester-hardened water glass sand is 60mm-80mm. The thickness of the resin chromite sand layer 6 and the ester-hardened water glass sand layer should be moderate, neither too thick nor too thin. Too thin a thickness will result in slow heat dissipation and the formation of iron inclusions, while too thick a thickness will increase production costs. Specifically, in this example, the thickness of the resin chromite sand layer 6 is 100 mm, and the thickness of the ester hardened water glass layer is 60 mm, which can avoid the slow heat dissipation caused by too low thickness and the formation of iron sand, and avoid the increase in production cost caused by too high thickness.

[0071] For example, Figure 7 As shown, the working surface 13 inside the valve core 12 will be filled with resin chromite sand for molding sand, while the non-working surface 14 outside the valve core will be filled with ester hardened water glass sand for molding sand. The working surface 13 and the non-working surface 14 will be connected by a series core frame 8 to avoid separation of the resin chromite sand layer 6 and the ester hardened water glass sand layer 7. The thickness of the resin chromite sand layer 6 along the direction of the non-working surface 14 of the working surface 13 is 100 mm, while the thickness of the ester hardened water glass sand layer 7 along the direction of the working surface 13 of the non-working surface 14 is 60 mm.

[0072] In this solution, the series core frame solves the problem of easy separation of resin chromite sand and ester hardened water glass sand, enhances the adhesion between the two, ensures the stability and integrity of the sand mold, and at the same time achieves the effects of the two sand molds on different working surfaces, so that the problems of different working surfaces are solved in a targeted manner.

[0073] Step 300: Smelting and pouring

[0074] In this embodiment, an electric arc furnace is used to smelt molten steel. The smelting process consists of three steps: a melting phase, an oxidation phase, and a reduction phase. The melting phase involves adding raw materials (i.e., steel) to the electric arc furnace and applying high temperatures thereto, completely melting the raw materials into molten metal. An oxidation phase is then performed to remove impurities and non-metallic inclusions from the liquid, thereby purifying the molten metal. Finally, a reduction phase is performed to remove oxides from the liquid metal and restore its chemical composition, thereby forming molten steel. The final molten steel composition (%) is controlled by the following: C: 0.34-0.35; Si: 0.45-0.46; Mn: 0.70-0.71; Cr: 0.93-0.95; Mo: 0.20-0.30; and S and P ≤ 0.025.

[0075] After molten steel is smelted, it is poured at a temperature of 1560±10°C, with 4-6 additional pours. Specifically, a pouring temperature range of 1560±10°C ensures good fluidity of the molten steel, allowing it to fully fill the sand mold, reducing casting defects caused by temperature fluctuations and improving the surface quality and internal structure of the casting. 4-6 additional pours ensure a constant supply of molten steel during the solidification process, reducing defects such as shrinkage cavities and porosity, and improving the density and performance of the casting.

[0076] Step 400: Insulation and gas cutting

[0077] Specifically, after the molten steel is poured, the casting is naturally cooled in the molding sand for 18-24 hours to avoid cracks caused by the casting not solidifying or cooling too quickly. After the casting has cooled naturally, it is dropped into the sand box, and the casting is removed from the sand box and the sand is cleaned to remove the molding sand and residues on the surface of the casting to ensure that the surface of the casting is clean and no sand remains. Then, before gas cutting, the casting is preheated at a temperature of 250-300°C to ensure a uniform preheating process and avoid local overheating. The purpose of preheating is to reduce the thermal stress inside the casting and avoid cracks in the casting due to rapid heating. When the casting is preheated to the specified temperature, the gas cutting operation is started to remove the patch 4 and riser 3 on the casting.

[0078] Step 500: Heat treatment

[0079] Specifically, the castings undergo quenching and tempering heat treatment, with a quenching temperature of 850-890°C and a holding time of 3-6 hours. A water quenching and oil cooling process is also used, with a water temperature of ≤45°C and an oil temperature of 30-80°C. Specifically, quenching and tempering heat treatment solves the problem of excessively high quenching temperatures and long holding times, which can affect product plasticity and toughness, leading to substandard elongation.

[0080] Step 600: Inspection and testing

[0081] Castings are tested according to national and technical standards to ensure they meet the JB / T6402-2018 standards for yield strength ReH ≥ 510 MPa, tensile strength Rm ≥ 830 MPa, and impact energy (AKU2) ≥ 31 J. Castings are also tested for ultrasonic and magnetic particle flaw detection in accordance with GB / T7233.1-2023 to ensure they meet the corresponding quality grade requirements. Castings are also pressure tested to ensure they meet the designed pressure requirements.

[0082] In this example, after the above casting process steps, the mechanical properties of the casting of this solution meet the requirements of tensile strength of 932MPa, yield strength of 680MPa, impact energy Aku2 of 52J, and compressive pressure of 25MPa. Specifically, as shown in the following table:

[0083] Mechanical properties:

[0084]

[0085]

[0086] Pressure:

[0087] method Pressure value Existing technology 16MPa This program 25MPa

[0088] In summary, the casting process of this solution improves the mechanical properties and pressure bearing capacity of the castings. Furthermore, according to the JB / T6402-2018 standard: yield strength ReH ≥ 510 MPa; tensile strength Rm ≥ 830 MPa; impact energy (AKU2) ≥ 31 J, the performance of the castings produced by this solution exceeds the standard values. Furthermore, according to the inspection and testing in step 600, the qualified rate of the castings in this solution is 100%, while the qualified rate of the existing technology is only 85%. In comparison, this solution significantly improves the quality of the castings.

[0089] In the above steps, each process step in this solution is closely linked and complementary to each other, so that the entire casting process can be optimized, thereby ensuring the high quality and high reliability of the castings, and solving the technical problems of substandard mechanical properties and poor quality of the valve body in the existing technology.

[0090] The importance of each process step in this solution lies not only in its own function, but also in its coordination with other steps to achieve the shrinkage compensation effect, cooling process, defect reduction, quality improvement and production efficiency of the casting. This comprehensive and optimized process design not only improves the performance of the casting, but also reduces production costs and improves overall production efficiency. Specifically, the adopted molding method of combining "resin chromite sand + ester hardened water glass sand" breaks the technical prejudice in the prior art that ordinary water glass sand is prone to sand sticking defects when used for valve body molding sand. It can greatly reduce the sand sticking defects on the surface of the valve body and ensure the smoothness and neatness of the casting surface. The series core frame 8 adopted combines the advantages of the two sand molds, which not only ensures the fire resistance and strength, but also improves the environmental protection and air permeability. At the same time, it takes into account the relationship between quality and cost in the project where it is used, and reduces production costs while improving quality. Improvements in the melting composition can make the mechanical properties of castings more concentrated and stable with less fluctuation, thereby improving the consistency and reliability of castings. It can also reduce the carbon equivalent (CE) of steel castings. A lower carbon equivalent helps reduce hot and cold cracks generated during welding, improving the strength and toughness of welded joints, thereby improving the welding performance of castings and reducing the risk of weld cracking. At the same time, precise control of the amount of alloy added during the melting process effectively reduces the risk of raw material waste, improves production efficiency, and reduces production costs. The combination of "4-subsidy + 3-riser + 2-chill iron" ensures that the shrinkage feeding channel is unobstructed and forms a temperature gradient. Subsidy 4 is installed in key parts of the casting (the valve core and the upper surface) to compensate for shrinkage, thereby reducing shrinkage porosity.

[0091] Thanks to improvements in feeding methods, molding techniques, and smelting composition, this solution significantly improves the overall quality and mechanical properties of castings, reduces the risk of sand adhesion and weld cracks, and simultaneously reduces production costs and improves efficiency. These improvements not only enhance overall product quality but also significantly shorten production cycles by one-third. This improvement maintains high production quality standards while improving cycle time.

[0092] Example 2:

[0093] The difference between this embodiment and the first embodiment is that, in this embodiment, step 200 also includes: mold turning processing, filling processing and cleaning processing. In addition, during the molding process, the molding sand covers the mold 1 with a thickness of 280mm-320mm, and the amount of molding sand used is about 2400kg.

[0094] Specifically, such as Figure 8 As shown:

[0095] Step S210: Filling with molding sand

[0096] The working surfaces of the mold and core are made of resin-hardened chromite sand, while the non-working surfaces are made of ester-hardened water glass sand. In other words, the thickness of the resin-hardened chromite sand near the surface of the working surface is 100 mm, and ester-hardened water glass sand is used throughout the entire working surface except for this area. In this embodiment, the ester-hardened water glass sand has a particle size of 30-50 mesh, while the resin-hardened chromite sand has a particle size of 40-70 mesh. Specifically, the ester-hardened water glass sand has a particle size of 40 mesh, which provides good air permeability and fluidity, helping to reduce porosity and sand inclusions in the casting. The resin-hardened chromite sand has a particle size of 60 mesh, which provides good surface finish and density, helping to reduce surface roughness of the casting. The ratio of ester-hardened water glass sand to resin-hardened chromite sand is 5:1.

[0097] This solution reduces the sand sticking rate of castings to 5% by adjusting the particle size, dosage and application location of ester-hardened water glass sand and resin chromite sand, thereby significantly reducing the sand sticking phenomenon of castings.

[0098] Step S230: mold remodeling

[0099] The mold is turned over, the formed sand mold is removed from the mold 1, and the mold and core working surfaces are coated with alcohol-based paint. Specifically, the thickness of the alcohol-based paint is 0.8-1.2 mm. This can reduce adhesion between the molten metal or molten steel and the sand mold, improve the surface finish of the casting, and reduce pores and inclusions on the mold surface, thereby improving the density and performance of the casting. Filling can reduce leakage of molten metal or molten steel during the pouring process, ensure the sealing of the casting, and prevent flash in the casting cavity. Cleaning the mold cavity can remove dust, sand particles, and other impurities in the mold cavity, while preventing sand inclusion defects caused by residual molding sand.

[0100] Step S240: Filling process

[0101] The core is set and assembled, and then the edge gap between the mold and the core is filled. Specifically, filling can reduce the leakage of molten metal or molten steel during the pouring process, ensure the sealing of the casting mold, and avoid flashing in the casting cavity.

[0102] Step S250: Cleaning

[0103] Before closing the mold, use a vacuum cleaner to clean the mold cavity. Specifically, cleaning can remove dust, sand particles and other impurities in the mold cavity, while preventing residual molding sand from forming sand inclusions.

[0104] Step S260: closing the box

[0105] In this embodiment, the molten metal refers to the liquid supplemented by the "subsidy + riser + chill" for shrinkage feeding, and the molten steel refers to the liquid with the smelting controlled composition (percentage) as follows: C: 0.34-0.35, Si: 0.45-0.46, Mn: 0.70-0.71, Cr: 0.93-0.95, Mo: 0.20-0.30, S, P ≤ 0.025.

[0106] This solution incorporates a series of treatments during the molding process, improving the surface quality of the castings, reducing defects, and enhancing the integrity and sealing of the castings. This improves overall casting quality and production efficiency, while also reducing the scrap rate. The molding step not only optimizes the casting process but also provides a reliable guarantee for the production of high-quality castings. By adjusting the particle size, dosage, and application location of ester-hardened water glass sand and resin chromite sand, the sand sticking rate of the castings is reduced to 5%, significantly reducing the phenomenon of sand sticking to the castings.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 1 is that the existing valve body molding sand generally adopts ordinary water glass sand, which is very prone to sand sticking defects and affects the liquid flow when the valve body is working.

[0109] In this comparative example, ordinary water glass sand is not easy to remove from the surface of the casting after the casting cools down. It is difficult to remove the sand, and the workload of subsequent cleaning and polishing is large. In addition, it has poor disintegration and is very easy to adhere to the surface of the casting, thereby causing surface defects. After testing, its sand adhesion rate is 50%.

[0110] Comparative Example 2

[0111] The difference between this comparative example and Example 1 is that the valve body molding sand adopts a mixture of resin chromite sand and ester hardened water glass sand, that is, the resin chromite sand and ester hardened water glass sand are mixed, and then the mixed sand is used for filling. Although the effect is improved, there is still sand sticking, which does not meet the expected requirements. After testing, the sand sticking rate is 30%.

[0112] According to Example 1, Example 2 and Comparative Example 1, Comparative Example 2, different sand materials were used to perform molding, and the sand bonding ratios thereof were as shown in the following table:

[0113]

[0114]

[0115] In summary, the improved shaping process in this solution significantly reduces the sand sticking rate compared to the prior art.

[0116] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A method for casting a servo valve body, characterized in that: The following steps are involved: Step S100: Developing casting equipment for the casting process through three-dimensional mapping design, casting simulation, optimization design, and simulation verification. Place shrinkage compensation pads on both sides of the valve core and on the upper surface of the mold, risers for controlling the solidification time of the casting, and chills for controlling the cooling rate. The pads include a first pad and a second pad, and the risers include a first riser, a second riser, a third riser, a fourth riser, and a fifth riser. The second subsidy is located on both sides of the valve core, the second subsidy is used to compensate for shrinkage, the second riser is located above the second subsidy, and the second subsidy is connected to the valve core through a pouring system; a vertical upward pouring pipe is provided in the middle of the pouring system, and a pouring port for pouring molten steel is provided on the pouring pipe; the first subsidy is located in the middle of the upper surface of the mold away from the pouring system, the first riser is located above the first subsidy, the fourth riser is located on the side of the upper surface of the mold close to the pouring system, and the fifth riser is between the first riser and the fourth riser; the third riser is located at the outwardly protruding portions on the left and right sides of the upper surface of the mold, and chills for controlling the cooling rate are evenly provided around the third riser and the fourth riser; The synergistic effect between the patch, riser, and chill forms a temperature gradient to control and optimize the solidification process of the casting; Step S200: Placing a series core frame in the mold for connecting the resin chromite sand layer and the ester-hardened water glass sand layer in series, the series core frame prevents the resin chromite sand layer and the ester-hardened water glass sand layer from separating during the molding process due to the different materials; then, filling the working surfaces of the mold and the core with resin chromite sand to form the resin chromite sand layer, and filling the non-working surfaces with ester-hardened water glass sand to form the ester-hardened water glass sand layer; Step S300: smelting molten steel, wherein the smelting controlled composition (percentage) is: C: 0.34-0.35, Si: 0.45-0.46, Mn: 0.70-0.71, Cr: 0.93-0.95, Mo: 0.20-0.30, S, P ≤ 0.

025.

2. The casting method of a servo valve body according to claim 1, characterized in that: The first riser and the fifth riser are heating and heat-insulating risers; the second riser is the first heating and heat-insulating component; the third riser is a necked heating and heat-insulating riser; the fourth riser is the second heating and heat-insulating component; the heating and heat-insulating component includes a heating and heat-insulating riser and a cover.

3. The casting method of a servo valve body according to claim 1, characterized in that: The step S100 further includes: the pouring system adopts a side pouring or bottom pouring method, and the pouring system adopts a ceramic pouring pipe.

4. The method for casting a servo valve body according to claim 1, characterized in that: The step S200 further includes: Step S210: filling molding sand; Step S220: Open the mold, take out the formed sand mold, and apply alcohol-based paint to the mold and core working surfaces; Step S230: placing and assembling the core, and then filling the edge seam between the mold and the core; Step S240: Before closing the box, use a vacuum hose to clean the cavity; Step S250: closing the box.

5. The method for casting a servo valve body according to claim 1, characterized in that: The thickness of the resin chromite sand is 100mm-140mm; the thickness of the ester hardened water glass sand is 60mm-80mm; the particle size of the ester hardened water glass sand is 30-50 meshes, and the particle size of the resin chromite sand is 40-70 meshes.

6. The method for casting a servo valve body according to claim 1, characterized in that: The dosage ratio of ester-hardened water glass sand to resin chromite sand is 5:

1.

7. The method for casting a servo valve body according to claim 1, characterized in that: The step 300 further includes: after the molten steel is smelted, pouring is performed, the pouring temperature is 1560±10° C., and the number of re-pouring is 4-6 times.

8. The method for casting a servo valve body according to claim 1, characterized in that: Also includes: Step 400: After pouring the molten steel, the casting is naturally cooled in the molding sand for 18-24 hours. After the casting has cooled naturally, it is dropped into the sand box. The casting is taken out of the sand box and the sand is cleaned. Before gas cutting, the casting is preheated to 250-300°C.

9. The method for casting a servo valve body according to claim 1, characterized in that: Also includes: Step 500: The casting is subjected to quenching and tempering heat treatment, with a quenching temperature of 850-890°C and a heat preservation period of 3-6 hours; at the same time, a water quenching and oil cooling process is adopted, with a water temperature of ≤45°C and an oil temperature of 30-80°C.

10. The method for casting a servo valve body according to claim 1, characterized in that: Also includes: Step 600: Perform ultrasonic and magnetic particle inspections on the casting, and perform a pressure test on the casting.

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