A precision casting process for a steam valve component
By using a self-made water-soluble wax core and a rotating cover mechanism, the problem of wax pattern manufacturing in the precision casting of steam valve parts was solved, reducing costs and improving casting quality, thus achieving a highly efficient casting process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FENGFAN
- Filing Date
- 2023-11-10
- Publication Date
- 2026-07-28
AI Technical Summary
In the existing precision casting process for steam valve parts, it is difficult to manufacture wax molds with an inner cavity width of 7mm annular groove structure, resulting in casting defects such as core breakage, internal leakage of castings, and pitting on the surface of castings. Moreover, the water-soluble wax core process is expensive.
A water-soluble wax core is made from a mixture of 40-60% polyethylene glycol, 40-60% sodium bicarbonate, and 0.2% nylon fiber. The wax core is then injected into the mold cavity of the steam valve mold using a molded wax rod. After the wax model is formed, the water-soluble wax core is dissolved, and multiple layers of refractory material are coated to form a shell. The shell is then sealed using a rotating cover mechanism, which reduces labor intensity.
It effectively solved the problem of water-soluble wax core breakage, reduced production costs, improved casting quality, ensured the density of refractory material in the annular groove, and reduced the labor intensity and health impact on operators.
Smart Images
Figure CN117620081B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of precision casting technology, and more specifically, relates to a precision casting process for steam valve parts. Background Technology
[0002] A steam valve precision casting, made of 2Cr13, a martensitic stainless steel, has a simple shape but an internal cavity with a 7mm wide annular groove structure. (See attached image.) Figure 1 The processes of wax model making, shell making, and casting are quite difficult.
[0003] Due to the special internal structure, the wax mold for precision casting cannot be manufactured using the core-pulling method to complete the annular flow channel. The ceramic core process is extremely expensive, so the water-soluble wax core process is generally used. However, during the shell-making and slurry-pouring process, casting defects such as core breakage, internal leakage of castings, and pitting on the surface of castings are very likely to occur. Summary of the Invention
[0004] The purpose of this invention is to provide a precision casting process for steam valve parts, which can be adapted to existing process conditions to reduce production costs and improve product quality.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a precision casting process for steam valve parts, comprising the following steps:
[0006] S1: A mixture is prepared by mass percentage of 40-60% polyethylene glycol, 40-60% sodium bicarbonate and 0.2% nylon fiber. The mixture is placed in a heating container and then poured into a wax press in liquid form to press a water-soluble wax core.
[0007] S2: The water-soluble wax core and the molded wax rod are assembled and placed in the cavity of the steam valve mold. After wax injection, a wax model with a water-soluble wax core is obtained. The wax model is placed in clean water to dissolve the water-soluble wax core and obtain the steam valve wax model.
[0008] S3: Weld the steam valve wax mold to the mold head assembly to form a mold with a casting system. Coat the inner and outer surfaces of the mold with multiple layers of refractory material. After drying, dewaxing and firing will form a shell with the same shape as the steam valve.
[0009] S4: Pour molten steel into the mold shell, and after the molten steel cools and solidifies, remove the mold shell to obtain a steam valve casting blank.
[0010] S5: After shot blasting, hydraulic sand removal, and sandblasting, the residual sand and oxide scale on the surface and inside the steam valve casting blank are removed. After annealing heat treatment, it is shot blasted again and inspected to obtain qualified steam valve castings.
[0011] In one possible implementation, in step S1, the mass percentage of the mixture is: 60% polyethylene glycol and 40% sodium bicarbonate + nylon fiber; or, 60% polyethylene glycol + nylon fiber and 40% sodium bicarbonate.
[0012] In one possible implementation, in step S1, after the mixture is placed into the heating container, the heating temperature of the heating container is set to 100°C, and the mixture is stirred until it melts into a liquid state. Then, the mixture is heated for 30 minutes, and the heating temperature of the heating container is set to 80°C and kept warm for 2 hours.
[0013] In one possible implementation, during step S2, when the water-soluble wax core and the molding wax rod are assembled, the molding wax rod is supported on the free end of the water-soluble wax core. During the wax injection process, the molding wax rod fuses with the paste wax pressed into the mold cavity of the steam valve.
[0014] In one possible implementation, in step S3, when the refractory material is coated multiple times on the inner and outer surfaces of the module, the surface layer and the second layer of refractory material are coated with zircon powder coating and 100-mesh zircon sand. After drying, a skeleton structure is formed. Then, the third and fourth layers are coated with only 4# James cup mullite coating with a viscosity of 12-15S. Finally, mullite coating and 30-60 mesh mullite sand and 16-30 mesh mullite sand are coated once each.
[0015] In one possible implementation, in step S4, the mold shell, which is still red-hot after casting, is placed on a sand bed and wax chips or flammable hydrocarbons are sprinkled on the mold shell. Then, an iron cover with the opening facing downwards is quickly put on the outside of the mold shell.
[0016] In one possible implementation, the mold shell is placed in the middle of the sand bed, a fixed shaft is provided on one side of the sand bed along the length of the sand bed, a bushing is provided on the outer wall of the iron cover near its opening, the bushing is rotatably sleeved on the fixed shaft, a limiting stop is provided on the sand bed, the limiting stop is located on the side of the fixed shaft away from the mold shell, the height of the limiting stop is greater than the height of the upper arc surface of the fixed shaft, and a hopper is provided inside the iron cover;
[0017] The iron cover rotates outward around the fixed axis until the outer wall of the iron cover abuts against the top of the limiting stop post. Then the bottom plate of the hopper tilts upward from the inside out and fills the hopper with wax chips or flammable hydrocarbons.
[0018] The iron cover rotates inward around the fixed shaft, and the bottom plate of the hopper gradually changes from tilting upward to tilting downward. Wax chips or flammable hydrocarbons filled in the hopper are continuously sprinkled from the hopper onto the mold shell until the iron cover is completely fastened to the sand bed, sealing the mold shell inside.
[0019] The beneficial effects of the precision casting process for steam valve parts provided by this invention are as follows: Compared with existing technologies, the self-made water-soluble wax not only meets the usage requirements but also allows for adjustment of its strength as needed, resulting in better performance and reduced production costs. The method of combining molded wax rods with water-soluble wax cores effectively solves the problem of water-soluble wax core breakage or displacement during wax injection, ensuring the quality of the wax model and providing a reference for the production of wax models for other similar precision casting products. The third and fourth layers of the annular groove shell-making process for the steam valve inner cavity are coated with only a certain viscosity of paint, effectively ensuring the density of the refractory material within the annular groove. This method is also effective for castings with slender holes, blind holes, and deep, narrow grooves, and is worthy of promotion. The design of a rotating cover mechanism eliminates the need for manual movement of the iron cover to secure it to the mold shell, reducing labor intensity and minimizing the impact on the operator's health. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 This is a schematic diagram of the structure of a steam valve in the prior art;
[0022] Figure 2 A process diagram illustrating a precision casting process for a steam valve component provided in an embodiment of the present invention;
[0023] Figure 3 An assembly structure diagram of the molding wax rod and water-soluble wax core provided by the present invention within the mold cavity;
[0024] Figure 4 This is a schematic diagram of the iron cover provided by the present invention on a sand bed.
[0025] Explanation of reference numerals in the attached figures:
[0026] 100. Molded wax rod; 200. Water-soluble wax core; 300. Sand bed; 400. Iron cover; 500. Fixed shaft; 600. Limiting stop; 700. Hopper; 800. Force-bearing handle. Detailed Implementation
[0027] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.
[0028] Please see Figure 2 and Figure 3 The present invention will now describe a precision casting process for a steam valve part.
[0029] A precision casting process for steam valve parts includes the following steps: Preparation of a water-soluble wax core 200: A mixture is prepared by mass percentage of 40-60% polyethylene glycol, 40-60% sodium bicarbonate, and 0.2% nylon fiber. The mixture is placed in a heating container, and the heated mixture is poured into a wax press to press the water-soluble wax core 200. Steam valve wax mold preparation: The water-soluble wax core 200 and a molded wax rod 100 are assembled and placed in the cavity of a steam valve mold. After wax injection, a wax mold with the water-soluble wax core 200 is obtained. The wax mold is placed in clean water to dissolve the water-soluble wax core 200. The process involves: obtaining a steam valve wax model; mold assembly and shell making: welding the steam valve wax model to the mold head assembly to form a mold assembly with a gating system; coating the inner and outer surfaces of the mold assembly with multiple layers of refractory material; drying; and then dewaxing and firing to form a shell with the same shape as the steam valve; melting and casting: pouring molten steel into the shell; removing the shell after the molten steel has cooled and solidified to obtain a steam valve casting blank; post-casting treatment: after shot blasting, hydraulic sand cleaning, and sandblasting, the residual sand and oxide scale on the surface and inside the casting blank are removed; after annealing heat treatment, shot blasting is performed again; and inspection is conducted to obtain a qualified steam valve casting.
[0030] This invention provides a precision casting process for steam valve parts. Compared with existing technologies, the self-made water-soluble wax, compared with imported commercial water-soluble wax, not only meets the usage requirements, but also allows for adjustment of the wax strength as needed, resulting in better performance and reduced production costs. The method of combining the molding wax rod 100 with the water-soluble wax core 200 effectively solves the problem of water-soluble wax core 200 breaking or displacing under stress during wax injection, ensuring the quality of the wax model. This method can serve as a reference for the production of wax models for other similar precision casting products.
[0031] Polyethylene glycol, a white, flaky solid, is an important chemical raw material; it is non-toxic and harmless. Sodium bicarbonate, a white, powdery solid, is also non-toxic and harmless. Nylon fibers provide reinforcement. The manufacturing process is as follows:
[0032] Based on the required shape, structure, and strength of the water-soluble wax core 200, the percentages of polyethylene glycol (PEG) and sodium bicarbonate (SB) are determined. A higher percentage of PEG results in a stronger water-soluble wax, while a lower percentage results in a weaker wax. Conversely, a higher percentage of SB results in a more hydrolyzable wax, while a lower percentage results in a less hydrolyzable wax. Different strengths and hydrolytic properties of water-soluble waxes are obtained by varying the PEG and SB ratios. The amounts of PEG and SB are then weighed according to the determined proportions. Considering the strength requirements of the steam valve water-soluble wax core, the mass percentage of the mixture is: 60% PEG and 40% SB + nylon fiber; or 60% PEG + nylon fiber and 40% SB.
[0033] The heating container is a stainless steel container heated by heat transfer oil. After the mixture is put into the heating container, the heating temperature of the heating container is set to 100℃, and the mixture is stirred until it melts into a liquid state. Then, the heating continues for 30 minutes, and the heating temperature of the heating container is set to 80℃ and kept warm for 2 hours.
[0034] When assembling the water-soluble wax core 200 and the molding wax rod 100, the molding wax rod 100 is supported on the free end of the water-soluble wax core 200, and the molding wax rod 100 plays a positioning and supporting role. This prevents the suspended water-soluble wax core from breaking or shifting due to the pressure of the liquid paste wax during the wax injection process. During the wax injection process, the molding wax rod 100 fuses with the paste wax pressed into the mold cavity of the steam valve. After wax injection, the resulting wax mold with the water-soluble wax core 200 is placed in clean water to dissolve the water-soluble wax core 200 completely. The steam valve wax mold is then obtained through trimming.
[0035] When the inner and outer surfaces of the module are coated with refractory material multiple times, the surface layer and the second layer of refractory material are coated with zircon powder paint and 100-mesh zircon sand, which form a skeleton structure with a certain strength after drying.
[0036] Next, the third and fourth layers are coated only with mullite powder coating of 12-15S viscosity (using a #4 Jameson cup), without any additional sand. This ensures that the flowing mullite powder coating can fully enter and fill the annular groove inside the wax mold cavity. The third and fourth layers of the annular groove shell-making and slurry-coating process for the steam valve cavity, using only coatings of a certain viscosity, effectively ensures the density of the refractory material within the annular groove. This method is also effective for castings with slender holes, blind holes, and deep, narrow grooves, and is worthy of promotion.
[0037] Finally, apply a layer of mullite powder coating and 30-60 mesh mullite sand and 16-30 mesh mullite sand once each. After drying and dewaxing, a shell with high internal and external strength is obtained. The shell is dried in a sealed drying room.
[0038] The steam valve casting is made of 2Cr13. After pouring, it undergoes oxidation due to oxygen in the air during the cooling process, resulting in oxidation pitting defects. This is a key point in process control. Therefore, the mold shell, still red-hot after pouring, is placed on a sand bed 300, and wax shavings or flammable hydrocarbons are sprinkled on it. Immediately afterwards, an iron cover 400 with its opening facing downwards is quickly placed over the outside of the mold shell. This consumes oxygen to create a reducing atmosphere and prevents oxidation of the casting surface.
[0039] Please refer to Figure 4 A rotating cover mechanism was specifically designed for this purpose. The rotating cover mechanism includes a base and an iron cover 400. A sand bed 300 is laid on the base, and the mold shell is placed in the middle of the sand bed 300. The iron cover 400, with its opening facing downwards, is fastened onto the sand bed 300, enclosing the mold shell inside the iron cover 400. Multiple supports are provided on one side of the upper end face of the base, extending above the sand bed 300. These supports share a common mounting shaft 500. A bushing is provided on the lower part of the outer wall of the iron cover 400, and the bushing connects to the fixed shaft 500. A fixed shaft 500 is rotatably connected to the sand bed 300, which is located along the length of the sand bed 300 on one side. A bushing is provided on the outer wall of the iron cover 400 near its opening, and the bushing is rotatably fitted onto the fixed shaft 500. A limiting stop 600 is provided on the sand bed 300, located on the side of the fixed shaft 500 away from the mold shell. The height of the limiting stop 600 is greater than the height of the upper arc surface of the fixed shaft 500. A hopper 700 is provided inside the iron cover 400. The iron cover 400 rotates outward about the fixed shaft 500. When the outer wall of the iron cover 400 abuts against the top of the limiting stop 600, the bottom plate of the hopper 700 tilts upward from the inside out, and wax scraps or flammable hydrocarbons are filled into the hopper 700. The iron cover 400 rotates inward around the fixed shaft 500, and the bottom plate of the hopper 700 gradually changes from upward to downward. Wax chips or flammable hydrocarbons filled in the hopper 700 are continuously scattered from the hopper 700 onto the mold shell until the iron cover 400 is completely fastened onto the sand bed 300, sealing the mold shell inside.
[0040] Similarly, when the iron cover 400 needs to be opened, it can be quickly opened by rotating it in the opposite direction. There is no need to manually move the iron cover 400 and fasten it onto the mold shell, which reduces labor intensity and minimizes the impact on the operator's health.
[0041] In addition, the top of the iron cover 400 is equipped with a force-bearing handle 800. Using a special tool, such as a long-handled rod with a hook at the end, the handle 800 can be hooked to rotate the iron cover 400, allowing the operator to work away from the mold shell. The support extends out of the sand bed 300 and has a mounting groove. The fixing shaft 500 is located in the mounting groove and welded in place. The cross-sectional area of the iron cover 400 decreases from top to bottom. Without affecting the internal space for accommodating the mold shell, the weight of the iron cover 400 is minimized to facilitate operator work.
[0042] Preferably, there are multiple iron covers 400, which are equally spaced along the axial direction of the fixed shaft 500 and rotatably connected to the fixed shaft 500 through corresponding bushings. Multiple iron covers 400 can be used to enclose multiple mold shells at once, improving work efficiency.
[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A precision casting process for a steam valve part, characterized in that, Includes the following steps: S1: A mixture is prepared by mass percentage of 40-60% polyethylene glycol, 40-60% sodium bicarbonate and 0.2% nylon fiber. The mixture is placed in a heating container and heated in liquid form and poured into a wax press to press a water-soluble wax core (200). After the mixture is placed in the heating container, the heating temperature of the heating container is set to 100℃ and the mixture is stirred until it melts into a liquid state. Then, the mixture is heated for 30 minutes and the heating temperature of the heating container is set to 80℃ and kept warm for 2 hours. S2: The water-soluble wax core (200) and the molding wax rod (100) are assembled and placed in the cavity of the steam valve mold. After wax injection, a wax mold with the water-soluble wax core (200) is obtained. The wax mold is placed in clean water to dissolve the water-soluble wax core (200) and obtain the steam valve wax mold. S3: Weld the steam valve wax mold to the mold head assembly to form a mold with a casting system. Coat the inner and outer surfaces of the mold with multiple layers of refractory material. After drying, dewaxing and firing will form a shell with the same shape as the steam valve. S4: The molten steel is poured into the mold shell. After the molten steel cools and solidifies, the mold shell is removed to obtain a steam valve casting blank. The mold shell, which is still red-hot after pouring, is placed on a sand bed (300), and wax or flammable hydrocarbons are sprinkled on the mold shell. Then, an iron cover (400) with the opening facing down is quickly put on the outside of the mold shell. The mold shell is placed in the middle of the sand bed (300). A fixed shaft (500) is provided on one side of the sand bed (300) along the length of the sand bed (300). A bushing is provided on the outer wall of the iron cover (400) near its opening. The bushing is rotatably sleeved on the fixed shaft (500). A limiting stop (600) is provided on the sand bed (300). The limiting stop (600) is located on the side of the fixed shaft (500) away from the mold shell. The height of the column (600) is greater than the height of the upper arc surface of the fixed shaft (500). The iron cover (400) is provided with a hopper (700) inside. The iron cover (400) rotates outward with the fixed shaft (500) as the axis of rotation. When the outer wall of the iron cover (400) abuts against the top of the limiting column (600), the bottom plate of the hopper (700) tilts upward from the inside to the outside, and wax chips or flammable hydrocarbons are filled into the hopper (700). The iron cover (400) rotates inward with the fixed shaft (500) as the axis of rotation. The bottom plate of the hopper (700) gradually changes from tilting upward to tilting downward. The wax chips or flammable hydrocarbons filled in the hopper (700) continuously fall from the hopper (700) onto the mold shell until the iron cover (400) is completely fastened to the sand bed (300) and the mold shell is sealed inside. S5: After shot blasting, hydraulic sand removal, and sandblasting, the residual sand and oxide scale on the surface and inside the steam valve casting blank are removed. After annealing heat treatment, it is shot blasted again and inspected to obtain qualified steam valve castings.
2. The precision casting process for a steam valve part as described in claim 1, characterized in that, In step S1, the mass percentage of the mixture is: 60% polyethylene glycol and 40% sodium bicarbonate + nylon fiber; or 60% polyethylene glycol + nylon fiber and 40% sodium bicarbonate.
3. The precision casting process for a steam valve part as described in claim 1, characterized in that, In step S2, when the water-soluble wax core (200) and the molding wax rod (100) are assembled, the molding wax rod (100) is supported on the free end of the water-soluble wax core (200). During the wax injection process, the molding wax rod (100) and the paste wax pressed into the mold cavity of the steam valve are integrated.
4. The precision casting process for a steam valve part as described in claim 1, characterized in that, In step S3, when the refractory material is coated multiple times on the inner and outer surfaces of the module, the surface layer and the second layer of refractory material are coated with zircon powder coating and 100-mesh zircon sand. After drying, a skeleton structure is formed. Then, the third and fourth layers are coated with only 4# James cup mullite powder coating with a viscosity of 12-15S. Finally, mullite powder coating and 30-60 mesh mullite sand and 16-30 mesh mullite sand are coated once each.