Casting method of servo valve body

Abstract

The invention relates to a marine machinery technology, and discloses a casting method of a servo valve body, which comprises the following steps: step S100, making casting equipment of a casting process through three-dimensional mapping design, casting simulation, optimization design and simulation verification in sequence, respectively placing patches, risers and chilling blocks on two sides of a valve core of a mold and the upper surface of the mold, and casting the valve body of the servo valve; a temperature gradient is formed through the synergistic effect of the patch, the riser and the chilling block so as to control and optimize the solidification process of the casting; s200, a series core frame used for connecting the resin chromite sand layer and the ester-hardened sodium silicate sand layer in series is placed in the mold, then the working faces of the mold and the core are filled with resin chromite sand, and the non-working faces are filled with ester-hardened sodium silicate sand; and S300, molten steel smelting is carried out, and the molten steel is prepared from, by percentage, 0.34%-0.35% of C, 0.45%-0.46% of Si, 0.70%-0.71% of Mn, 0.93%-0.95% of Cr, 0.20%-0.30% of Mo, smaller than or equal to 0.025% of S and smaller than or equal to 0.025% of P. The technical problems that in the prior art, a valve body is poor in performance and quality can be solved.

Description

Technical Field

[0001] The 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 hydraulic systems of ships. By accurately adjusting flow and pressure, servo valves can ensure the stable operation of hydraulic systems. Its working principle is based on the movement of liquid in a closed environment. The movement of the valve core changes the flow of liquid in the liquid circuit, thereby achieving precise control of the entire output. As a key component of the servo valve, the internal quality and inner cavity surface quality of the valve body are crucial, which directly affects the realization of the equipment function.

[0003] 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. 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, uneven distribution of thick and large areas, and often has shrinkage holes and shrinkage defects, which leads to poor density and low pressure bearing of the valve body. In addition, the valve body is usually made of low-alloy steel with high performance requirements. However, the existing casting methods often lead to unqualified casting performance and cannot meet the use requirements. (3) Sand problem: Traditional valve body molding sand generally uses ordinary water glass sand. This sand mold is very prone to sand sticking defects, which not only affects the surface quality of the casting, but also hinders the flow of liquid in 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 will affect 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 scheme:

[0006] Step S100: formulating casting equipment of the casting process through three-dimensional mapping design, casting simulation, optimization design and simulation verification in sequence, placing subsidies for compensating shrinkage, risers for controlling the solidification time of the casting and chills for controlling the cooling rate on both sides of the valve core of the mold and the upper surface of the mold respectively; the subsidies include a first subsidy and a second subsidy, 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 parts on the left and right sides of the upper surface of the mold, and cold irons for controlling the cooling speed 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 for connecting the resin chromite sand layer and the ester hardened water glass sand layer in series in the mold, wherein the series core frame prevents the resin chromite sand layer and the ester hardened water glass sand layer from being separated due to the difference in materials during the molding process; then filling the resin chromite sand on the working surfaces of the mold and the core to form the resin chromite sand layer, and filling the ester hardened water glass sand on the non-working surface to form the ester hardened water glass sand layer;

[0010] Step S300: smelting molten steel, 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, S, P≤0.025.

[0011] The principle of this scheme is:

[0012] First, a 3D model of the casting equipment and mold is made using 3D modeling software, and then the casting simulation software is used to verify and optimize the casting process to determine the optimal shrinkage compensation process. Through 3D mapping design, casting simulation, optimization design, and simulation verification design, this solution adopts a combination of "compensation + riser + chiller" in shrinkage compensation, and improves the molding sand material and smelting control components. When molding, it is first necessary to place a series core frame 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, avoid the separation of different sand layers during the casting process, and thus reduce the situation of sticky sand defects. Then, resin chromite sand is filled on the working surface of the mold and the core to form a resin chromite sand layer, and ester hardened water glass sand is filled on the non-working surface to form an ester hardened water glass sand layer; after the modeling is completed, ensure that the various parts of the mold and the core are tightly fitted without obvious gaps or defects, and then molten steel is smelted. When smelting molten steel, the smelting composition must be strictly controlled to meet the requirements (percentage) 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.

[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 prior art 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 castings, 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, which can reduce the sand adhesion 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 yielding property, which can reduce the crack tendency. The use of ester hardened water glass sand on the non-working surface can reduce the overall production cost and improve the economic benefits; the use of 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 adhesion 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 + chiller" is used 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 + chiller" can effectively control the cooling process of the castings, ensure the expected sequential solidification of the castings after installation, and ensure that the shrinkage compensation channel (i.e., the channel formed by the "subsidy + riser + chiller" installation position) is unobstructed to form a temperature gradient, reduce shrinkage defects, and thus improve the quality and performance of the castings. 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 chiller accelerates the cooling rate of the parts, prevents the formation of hot spots, reduces thermal stress and deformation, and at the same time 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 heat-generating and heat-insulating risers; the second riser is the first heat-generating and heat-insulating component; the third riser is a necked heat-generating and heat-insulating riser; the fourth riser is the second heat-generating and heat-insulating component; the heat-generating and heat-insulating component includes a heat-generating and heat-insulating riser and a cover.

[0019] Beneficial effects: The exothermic and insulating 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 and insulating 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 shrinking exothermic and insulating riser allows the molten metal in the riser to flow more effectively to the part that needs shrinkage-feeding, ensuring that the area that needs shrinkage-feeding 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 pouring or bottom pouring can ensure the smooth rise of molten steel and avoid scouring the cavity to form 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, taking out the formed sand mold from the casting, and applying alcohol 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 tube 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 molten steel and the sand mold and improve the surface finish of the casting. 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 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: 100mm-140mm makes the thickness of the resin chromite sand layer moderate, and 60mm-80mm makes the thickness of the ester hardened water glass sand moderate, that is, neither too thick nor too low. Too low thickness will lead to slow heat dissipation and the formation of iron sand inclusions, while too high thickness will increase production costs; the particle size of ester hardened water glass sand is 30-50 mesh, which has good air permeability and fluidity, and helps to reduce the pores and sand inclusions in the casting. The particle size of the resin chromite sand is 40-70 mesh, which can provide better surface finish and density, and help to reduce the roughness of the casting surface.

[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, the production cost can be reduced.

[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 molten steel fully filling the sand mold, reducing the cold shut and insufficient pouring during the pouring process, and can reduce the 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, and after the casting is naturally cooled, it is dropped into the sand box for treatment, the casting is taken out of the sand box and the sand is cleaned, and then, before gas cutting, the casting is preheated at a preheating temperature of 250-300°C.

[0036] Beneficial effects: The casting is cooled naturally in the molding sand. After 18-24 hours, the casting is placed in 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 method further includes: Step 500: the casting is subjected to quenching and tempering heat treatment, the quenching temperature is 850-890°C, and the temperature is kept for 3-6 hours. At the same time, a water quenching and oil cooling process is adopted, the water temperature is ≤45°C, and the oil temperature is 30-80°C.

[0038] Beneficial effects: The heat treatment quenching temperature is 850-890℃, and the heat preservation time is 3-6h. It solves the problem of product plasticity, toughness, and unqualified elongation due to excessive quenching temperature and long heat preservation time; water quenching and oil cooling process, water temperature ≤45℃, oil temperature 30-80℃, ensures that the casting obtains rapid and uniform cooling effect during the quenching process, improves its hardness, strength and surface quality, reduces the risk of deformation and cracking, optimizes the microstructure, and improves 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 resistance 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 the 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 castings, 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 castings, 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 and shorten the production cycle by one third. For example, if the existing production cycle is 3 months, the production cycle of this solution will be shortened to 2 months. While improving the production cycle, the production quality is also taken into account.

[0043] (3) The combination of "subsidy + riser + chill" and the synergistic effect of 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 a reduction in 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. At the same time, it also has high practical value and market competitiveness, and can be suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0048] Figure 2 A schematic diagram of the structure of a mold in a casting method of 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 in 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 in an embodiment of the present invention.

[0052] Figure 6 A schematic structural diagram of a series of core frames in a casting method for a servo valve body provided in 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 in an embodiment of the present invention.

[0054] Figure 8 A logic frame 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 port 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] Embodiment 1:

[0058] The embodiment is basically as shown in the attached Figure 1 As shown: A method for casting a servo valve body, 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 solution achieves the best effect in shrinkage compensation.

[0061] Specifically, (1) 3D mapping design: First, a 3D model of the casting is made using 3D modeling software to accurately represent the geometric shape, size and details of the casting, including its complex internal structure and external features, and then the position and arrangement of the gating system 5 are designed. In this embodiment, the gating system 5 adopts a side injection or bottom injection method.

[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 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 according to 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, the present solution provides a casting device for a servo valve body. In this embodiment, the subsidy 4 includes a first subsidy 41 and a second subsidy 42, and the riser 3 includes a first riser, a second riser, a third riser, a fourth riser and a fifth riser, wherein the first riser and the fifth riser are combined to form a heat-generating and heat-insulating riser 31, the second riser is a first heat-generating and heat-insulating component 32, the third riser is a shrinking heat-generating and heat-insulating riser 33, and the fourth riser is a second heat-generating and heat-insulating component 34, and the heat-generating and heat-insulating component includes a heat-generating and heat-insulating riser and a cover. The subsidy 4 (i.e., the shrinkage subsidy) provides additional molten metal to compensate for the voids generated by the volume shrinkage of the casting during the solidification process. By providing the subsidy 4, it can be ensured that the casting has enough molten metal to fill these voids during the cooling process, thereby reducing or eliminating shrinkage cavities and shrinkage defects. The riser 3 generates heat through the heat-generating material (such as aluminum powder, iron powder, etc.) inside it, which can maintain the temperature of the riser 3 area, thereby extending the solidification time of the casting, and helping the molten metal and molten steel to have enough time to compensate for shrinkage during the cooling process, thereby reducing or eliminating shrinkage cavities and shrinkage defects.

[0065] Specifically, Figure 2 , Figure 3 , Figure 4As shown, the mold 1 is placed on the equipment in a horizontal manner. Second subsidies 42 for compensating shrinkage are installed on both sides of the valve core 12 in the mold 1. The second subsidies 42 are used to fill these cavities with enough molten metal during the cooling process of the casting, thereby reducing or eliminating shrinkage cavities and shrinkage defects. The second subsidies 42 are connected through the pouring system 5 and are connected to the mold 1 through the valve core 12, so that a circulation system is formed between the second subsidies 42, the pouring system 5 and the mold 1, which is convenient for the subsequent side injection of molten steel to inject molten steel into the mold 1 to form a casting. A first heating and heat preservation component 32 is installed above the second subsidy 42, and the first heating and heat preservation component 32 is a heating and heat preservation riser 31 and a cover, wherein the cover is used to reduce heat loss and maintain the high temperature state inside the riser 3 near the valve core 12, thereby ensuring that the temperature of the molten steel in the riser 3 is more uniform and stable, and improving the quality of the valve core 12. A vertical upward pouring pipe is installed in the middle position of the pouring system 5, and a pouring port 51 for pouring molten steel is provided on the pouring pipe. The mold upper surface 11 is provided with a first patch 41 in the middle position away from the pouring system 5, a heating and heat preservation riser 31 is installed above the first patch 41, and necked heating and heat preservation risers 33 are installed on the protruding parts on the left and right sides of the mold upper surface 11. A second heating and heat preservation component 34 is installed on the side of the mold upper surface 11 close to the pouring system 5, and its heating and heat preservation riser 31 also includes a fifth riser located between the first patch 41 and the second heating and heat preservation component 3. Cold irons 2 for controlling the cooling speed are evenly installed around the second heating and heat preservation component 34 and the necked heating and heat preservation 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 upper surface 11 of the mold, thereby improving the shrinkage compensation effect and reducing internal defects; the heat-insulating assembly 34 (i.e., "heat-insulating riser 31 + 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 shrinking heat-insulating riser 33 allows the molten metal in the riser 3 to flow more effectively to the part where the upper surface needs to be protruding, thereby ensuring that the area can be fully compensated. In this embodiment, there are 4 compensations 4, 8 risers 3, and 12 chillers 2.

[0066] This solution achieves the best effect in shrinkage compensation of the casting through the layout of the above-mentioned chill 2, riser 3 and subsidy 4, thereby optimizing the solidification process of the casting, reducing shrinkage defects and ensuring the quality of the casting. Shrinkage refers to the volume shrinkage of the 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. Shrinkage is usually caused by the failure to fully compensate for the tiny volume shrinkage of the local area of ​​the molten metal during the solidification process. Specifically, if Figure 5As shown, in the shrinkage porosity simulation diagram, the occurrence of shrinkage porosity is represented by the color depth, where black represents the highest probability, followed by gray, and white (the lightest color) is the lowest. In this embodiment, the white area (i.e., the lightest color area) indicates that there is no shrinkage porosity phenomenon. In this embodiment, through the combination of "subsidy 4 + riser 3 + chill 2" in the above-mentioned casting equipment, the casting body appears white, and the shrinkage distance from the casting body is higher than 1 / 3 of the height of the riser 3, thereby achieving the optimization of the casting shrinkage compensation effect.

[0067] In summary, this solution uses the integrated setting of three-dimensional mapping design, casting simulation, optimization design and simulation verification. In the process of simulation optimization, the pouring position selection and casting shrinkage compensation improvement are carried out. Specifically, the pouring position selection: the mold 1 is placed on the equipment in a horizontal manner, 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 compensation distance, reduce the difficulty of modeling, and improve the shrinkage compensation effect and surface quality of the casting. Improvement of shrinkage compensation for castings: A combination of a patch 4 + riser 3 + chill 2 is used to ensure that the shrinkage compensation channel (i.e., the installation position of the 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 a riser 3 above the patch 4 can extend the solidification time of the molten steel, improve the shrinkage compensation effect, and reduce internal defects; at the same time, a 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 a side injection or bottom injection method to ensure that the molten steel rises steadily and avoids scouring the cavity to form defects such as sand sticking. The material of the pouring system 5 will use a ceramic pouring pipe to reduce sand sticking, improve the stability and reliability of pouring, and reduce defects during the pouring process.

[0068] Step S200: Modeling

[0069] During the casting process, the working surface of the mold and core is made of resin chromite sand, while the non-working surface is made of ester-hardened water glass sand. The resin chromite sand has good disintegration, which helps to reduce the sand sticking defects in the inner cavity and reduce the difficulty of cleaning the casting. The ester-hardened water glass sand has good yieldability during the solidification process of the casting, is not easy to produce crack defects, and can improve the integrity and surface quality of the casting. At the same time, the cost of ester-hardened water glass sand is low, which helps to reduce production costs and has good environmental protection, reducing the impact on the environment.

[0070] Specifically, the mold 1 is placed horizontally on the casting equipment, a riser 3 or a chiller 2 is placed at the corresponding position of the mold 1 and fixed firmly, and a pouring system 5 is arranged. Then, the molding sand is filled at the position where the mold 1 is specially filled with molding sand, and resin chromite sand is filled on the mold and core working surfaces to form a resin chromite sand layer 6, and ester hardened water glass sand is filled on other non-working surfaces to form an ester hardened water glass sand layer 7. Figure 6 As shown, in the process of filling the molding sand, firstly, a series core frame 8 is placed at the intersection layer 9 of the chromite sand and the ester hardened water glass sand in the casting, and then the resin chromite sand is filled on the working surface of the mold and the core, and the ester hardened water glass sand is filled on the non-working surface. The series core frame 8 connects the resin chromite sand layer 6 and the ester hardened water glass sand layer 7 in series, strengthens the adhesion between the resin chromite sand layer 6 and the ester hardened water glass sand layer 7, and avoids the separation of the two during the casting process, thereby reducing the situation of sticking sand 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 layer needs to be moderate, neither too thick nor too low. Too low thickness will lead to slow heat dissipation and the formation of iron sand inclusions, while too high 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 and iron inclusion caused by too low thickness, and avoid the increase of 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, while the non-working surface 14 outside the valve core will be filled with ester hardened water glass 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 realizes the effects of the two sand molds on different working surfaces, so as to solve the problems of different working surfaces in a targeted manner.

[0073] Step 300: Smelting and pouring

[0074] In this embodiment, an electric arc furnace is used to smelt molten steel, and the smelting process is divided into three steps: melting period, oxidation period, and reduction period. The melting period treatment is to add raw materials (i.e., steel materials) into the electric arc furnace and provide high temperature through the electric arc furnace to completely melt the raw materials into molten metal, and then an oxidation period treatment will be carried out to remove impurities and non-metallic inclusions in the liquid, thereby purifying the molten metal, and finally a reduction period treatment will be carried out to remove oxides in the molten metal and restore the chemical composition of the molten metal, thereby forming molten steel, so that the molten steel finally reaches the requirements of smelting control composition (%): 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.

[0075] After the molten steel is smelted, it will be poured at a temperature of 1560±10℃ and 4-6 times of supplementary pouring. Specifically, the pouring temperature range of 1560±10℃ can ensure that the molten steel has good fluidity, which is conducive to the molten steel fully filling the sand mold, reducing casting defects caused by temperature fluctuations, and improving 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, and improve the density and performance of the casting.

[0076] Step 400: Insulation and gas cutting

[0077] Specifically, after pouring the molten steel, the casting is naturally cooled in the sand for 18-24 hours to avoid cracks due to the casting not solidifying or cooling too quickly. After the casting is naturally cooled, it is dropped into the sand box, and the casting is taken out of the sand box and the sand is cleaned to remove the sand and residues on the surface of the casting to ensure that the surface of the casting is clean and free of sand particles. 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 subsidies 4 and risers 3 on the casting.

[0078] Step 500: Heat treatment

[0079] Specifically, the castings are subjected to quenching and tempering heat treatment, with a quenching temperature of 850-890℃ and a heat preservation period of 3-6h. At the same time, a water quenching and oil cooling process is adopted, with a water temperature of ≤45℃ and an oil temperature of 30-80℃; specifically, the quenching and tempering heat treatment solves the problem of excessive quenching temperature and long heat preservation time, which affects the plasticity and toughness of the product and causes unqualified elongation.

[0080] Step 600: Testing and experimentation

[0081] According to national and technical standards, the performance of casting products is tested to ensure that they meet the requirements of JB / T6402-2018 standard, namely, yield strength ReH ≥ 510MPa; tensile strength Rm ≥ 830MPa; impact energy (AKU2) ≥ 31J. According to GB / T7233.1-2023 standard, castings are tested by ultrasonic and magnetic particle inspection to ensure that they meet the requirements of corresponding quality grades. Pressure resistance tests are carried out on castings to ensure that they meet the designed pressure.

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

[0083] Mechanical properties:

[0084]

[0085]

[0086] Pressure:

[0087] method Pressure value Prior art 16MPa This program 25MPa

[0088] In summary, through the casting process of this scheme, the mechanical properties and pressure bearing pressure of the castings are improved. At the same time, according to the JB / T6402-2018 standard: yield strength ReH ≥ 510MPa; tensile strength Rm ≥ 830MPa; impact energy (AKU2) ≥ 31J, the performance of the castings made by this scheme is higher than the standard value. In addition, according to the inspection and test in step 600, the qualified rate of the castings in this scheme is 100%, while the qualified rate of the prior art is only 85%. In comparison, this scheme significantly improves the quality of the castings.

[0089] In the above steps, each process step in this scheme 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 castings, and solving the technical problems of substandard mechanical properties and poor quality of the valve body in the prior art.

[0090] The importance of each process step in this scheme 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 and optimized process design not only improves the performance of the casting, but also reduces the production cost and improves the overall production efficiency. Specifically, the molding method of "resin chromite sand + ester hardened water glass sand" combined with the adopted "resin chromite sand + ester hardened water glass sand" breaks the technical prejudice of the prior art that the valve body molding sand using ordinary water glass sand is prone to sand sticking defects, and can greatly reduce the sand sticking defects on the surface of the valve body, ensuring 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 in which it is used, and reduces the production cost while improving the quality. Improvements in smelting composition can make the mechanical properties of castings more concentrated and stable with less fluctuation, thereby improving the consistency and reliability of castings, and at the same time reducing the carbon equivalent (CE) of steel castings. Lower carbon equivalent helps reduce hot cracks and cold cracks generated during welding, improves the strength and toughness of welded joints, thereby improving the welding performance of castings and reducing the risk of welding cracks. At the same time, during the smelting process, precise control of the amount of alloy added can effectively reduce the risk of raw material waste, improve production efficiency, and reduce production costs. The combination of "subsidy 4 + riser 3 + chiller 2" ensures that the shrinkage compensation channel is unobstructed and forms a temperature gradient. Subsidy 4 (valve core and upper surface) is installed at key parts of the casting to compensate for shrinkage, thereby reducing shrinkage and shrinkage holes.

[0091] It is precisely because of the improvements in the shrinkage feeding method, molding method and smelting composition that this solution can significantly improve the overall quality and mechanical properties of castings, reduce the risk of sand adhesion defects and welding cracks, and at the same time reduce production costs and improve production efficiency. These improvements not only improve the overall quality of the product, but also greatly shorten the production cycle, which can be shortened by one third. While improving the production cycle, it ensures high standards of production quality.

[0092] Embodiment 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 thickness of the molding sand covering the mold 1 is 280mm-320mm, and the amount of molding sand used is about 2400kg.

[0094] Specifically, Figure 8 As shown:

[0095] Step S210: Filling with molding sand

[0096] The working surface of the mold and core adopts resin chromite sand, and the non-working surface adopts ester hardened water glass sand. In other words, the thickness of the resin chromite sand near the surface of the working surface is 100mm, and ester hardened water glass sand is used except for this area. In this embodiment, 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. Specifically, in this example, the particle size of the ester hardened water glass sand is 40 mesh, which has good air permeability and fluidity, and helps to reduce the pores and sand inclusions in the casting. The particle size of the resin chromite sand is 60 mesh, which can provide better surface finish and density, and helps to reduce the roughness of the casting surface. The dosage ratio of ester hardened water glass sand to resin chromite sand is 5:1.

[0097] This solution makes the sand adhesion rate of the casting 5% by setting the particle size, dosage and use position of ester-hardened water glass sand and resin chromite sand, which significantly reduces the sand adhesion phenomenon of the casting.

[0098] Step S230: mold remodeling

[0099] The mold is turned over, the formed sand mold is taken out from the mold 1, and the mold and core working surfaces are coated with alcohol paint. Specifically, the thickness of the alcohol paint is 0.8-1.2mm, which can reduce the adhesion between the molten metal or molten steel and the sand mold, improve the surface finish of the casting, and the alcohol paint can reduce the pores and inclusions on the surface of the mold, thereby improving the density and performance of the casting; the filling treatment can reduce the leakage of the molten metal or molten steel during the pouring process, ensure the sealing of the mold, and avoid the flash in the inner cavity of the casting; the cleaning treatment of the mold cavity can remove dust, sand and other impurities in the mold cavity, and avoid the formation of sand inclusion defects due to residual molding sand.

[0100] Step S240: Filling process

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

[0102] Step S250: Cleaning

[0103] Before closing the mold, use a vacuum tube to clean the mold cavity. Specifically, cleaning can remove dust, sand and other impurities in the mold cavity, while preventing the 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 compensation, 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 carries out a series of treatments in the molding process, which improves the surface quality of the casting, reduces the defects of the casting, and improves the integrity and sealing of the casting, thereby improving the overall casting quality and production efficiency, and reducing the scrap rate of the casting. 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 use location of ester-hardened water glass sand and resin chromite sand, the sand sticking rate of the casting is reduced to 5%, which significantly reduces the sand sticking phenomenon of the casting.

[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 will affect 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 is cooled. The sand removal is difficult, the subsequent cleaning and grinding workload is large, and the collapsibility is poor. It is very easy to adhere to the surface of the casting, thereby causing surface defects. The sand adhesion rate is 50% after testing.

[0110] Comparative Example 2

[0111] The difference between this comparative example and Example 1 is that the valve body molding sand is a mixture of resin chromite sand and ester hardened water glass sand, that is, resin chromite sand and ester hardened water glass sand are mixed and then filled with the mixed sand. 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 and Comparative Example 2, different sand mold materials are used for molding respectively, and the sand bonding ratios thereof are shown in the following table:

[0113]

[0114]

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

[0116] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is 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 modifications and improvements can be made, which should also be regarded as the protection scope 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 specification 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: formulating casting equipment of the casting process through three-dimensional mapping design, casting simulation, optimization design and simulation verification in sequence, placing subsidies for compensating shrinkage, risers for controlling the solidification time of the casting and chills for controlling the cooling rate on both sides of the valve core of the mold and the upper surface of the mold respectively; the subsidies include a first subsidy and a second subsidy, 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 parts on the left and right sides of the upper surface of the mold, and cold irons for controlling the cooling speed are evenly provided around the third riser and the fourth riser; The synergistic effect between the said 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 for connecting the resin chromite sand layer and the ester hardened water glass sand layer in series in the mold, wherein the series core frame prevents the resin chromite sand layer and the ester hardened water glass sand layer from being separated due to the difference in materials during the molding process; then filling the resin chromite sand on the working surfaces of the mold and the core to form the resin chromite sand layer, and filling the ester hardened water glass sand on the non-working surface to form the ester hardened water glass sand layer; Step S300: smelting molten steel, 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, S, P≤0.

025.

2. A method for casting a servo valve body according to claim 1, characterized in that: The first riser and the fifth riser are heat-generating and heat-insulating risers; the second riser is a first heat-generating and heat-insulating component; the third riser is a necked heat-generating and heat-insulating riser; the fourth riser is a second heat-generating and heat-insulating component; the heat-generating and heat-insulating component includes a heat-generating 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 also includes: the pouring system adopts a side pouring or bottom pouring method, and the pouring system adopts a ceramic pouring pipe.

4. The casting method of 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 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 tube to clean the cavity; Step S250: closing the box.

5. The casting method of 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 casting method of 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 casting method of a servo valve body according to claim 1, characterized in that: The step 300 also includes: after the molten steel is smelted, pouring is carried out, the pouring temperature is 1560±10°C, and the number of supplementary 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 is naturally cooled, 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 at a temperature of 250-300°C.

9. The casting method of 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 oil 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 flaw detection on the casting, and perform a pressure test on the casting.

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