A lost-wax precision casting process suitable for impeller pumps with complex flow channel structure

Abstract

The present application relates to a kind of lost wax precision casting process suitable for complex flow channel structure impeller pump, the present application is implemented by the following innovative technical means, significantly improve the precision casting quality and efficiency of complex structure impeller pump: polyvinyl alcohol or paraffin-based composite material is used, and nano-silicon dioxide is added as wax mold material, combined with stearic acid and plasticizer, optimize physical property and demolding characteristic;Specific SiO2, viscosity and pH range of silica sol are used as binder, improve shell quality and mechanical strength;Shell is removed by vacuum and microwave waxing process, so that wax material is quickly and uniformly removed, prevent local overheating and bubble generation;Shell is baked after completing waxing, using specific time and gradient heating-holding process, to strengthen shell structure, and fully remove residual organic matter and carbon, improve the internal and external density and dimensional accuracy of casting;Finally, three-coordinate measuring instrument is used to monitor flow channel three-dimensional geometry, ensure structure consistency and casting tolerance.

Description

Technical Field

[0001] This invention relates to the field of lost-wax precision casting technology for manufacturing high-precision impeller pumps, and particularly to a lost-wax precision casting process suitable for impeller pumps with complex flow channel structures. Background Technology

[0002] Lost-wax casting, also known as investment casting, is a precision metal forming process. Its core process involves: first, creating a precise wax model using fusible wax, assembling it into a wax tree, repeatedly applying refractory slurry and sprinkling sand, then drying and solidifying to form a multi-layered ceramic shell; subsequently, heating to remove the wax, forming a hollow shell, which is then fired at high temperature before molten metal is poured in. After cooling, the shell is removed to obtain a high-precision casting. This process is particularly suitable for manufacturing metal parts with complex structures and high surface finish requirements. However, existing lost-wax casting techniques suffer from the following problems with complex flow channel impeller pump structures: due to the complex shape and structure of the impeller pump's flow channels, defects such as bubbles and shrinkage cavities are prone to occur during casting, affecting the quality and performance of the casting and resulting in poor casting quality and low efficiency. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a lost-wax precision casting process for manufacturing high-precision impeller pumps, which can solve the problems of casting defects such as bubbles and shrinkage cavities and unstable quality of finished products that are prone to occur during the casting process of the above-mentioned impeller pumps with complex flow channel structure.

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is: a lost-wax precision casting process suitable for impeller pumps with complex flow channel structures, the innovation of which is: including the following steps: Impeller wax molds are prepared using polyvinyl alcohol or paraffin-based composite materials; refractory materials are coated on the surface of the wax molds to form a ceramic shell, and the thickness of the ceramic shell is controlled to be 1.5–3 mm; the wax molds are removed by vacuum dewaxing or microwave dewaxing to obtain a hollow shell; the hollow shell is calcined and then molten metal is poured in to obtain an impeller casting with a complex flow channel structure; the three-dimensional morphology of the impeller pump flow channel is detected by a coordinate measuring machine and compared with the design model to ensure that the geometric consistency error does not exceed 70% of the design tolerance.

[0005] Furthermore, the polyvinyl alcohol or paraffin-based composite material is made by mixing polyvinyl alcohol, paraffin, stearic acid and plasticizer in a certain mass ratio.

[0006] Furthermore, the inner layer of the ceramic shell is made of mullite powder slurry bonded with silica sol, and the outer layer is formed by coating and drying bauxite sand layer by layer.

[0007] Furthermore, the silica sol The content is 25%–35%, the viscosity is 4–8 mPa·s, and the pH value is 9.0–10.5.

[0008] Furthermore, the vacuum dewaxing is carried out at a temperature of 80–95°C and an absolute pressure of 100°C for a duration of 30–60 minutes.

[0009] Furthermore, the microwave dewaxing process employs microwave radiation at a frequency of 915MHz or 2450MHz, with a power density of 2.0-3.5W / cm², to uniformly heat and melt the interior of the wax mold.

[0010] Furthermore, after dewaxing, the hollow shell is baked for 2–4 hours to completely remove residual organic matter and improve shell strength.

[0011] Furthermore, the temperature is first increased to 450°C at a rate of 10°C per minute and held for 2 hours to remove residual organic matter and enhance the primary strength of the shell; then the temperature is increased to 900°C at a rate of 5°C per minute and held for 1 hour to allow the residual carbon in the shell to fully volatilize and be removed.

[0012] Furthermore, the molten metal is a nickel-based high-temperature alloy or stainless steel.

[0013] Furthermore, nano-silica particles with a particle size of [missing information] are added to the wax model material, and the amount added is 0.2%–0.8% of the total mass, in order to enhance the rigidity and surface smoothness of the wax model.

[0014] The advantages of this invention are: 1) In this invention, polyvinyl alcohol or paraffin-based composite materials with added nano-silica are used as wax model materials, combined with stearic acid and plasticizers to optimize the physical properties and release properties of the wax model; a multi-layer ceramic shell composed of an inner layer of silica sol combined with mullite powder and an outer layer of bauxite sand is coated on the surface of the wax model, with the thickness precisely controlled at 1.5–3 mm; vacuum dewaxing and microwave dewaxing processes are used to remove the wax material quickly and evenly, preventing local overheating and bubble formation; after dewaxing, the shell is fired using a specific time and gradient heating-holding process to strengthen the shell structure and fully remove residual organic matter and carbon, improving the internal and external density and dimensional accuracy of the casting; nickel-based high-temperature alloys or stainless steel are used for molten metal pouring, and the pouring temperature is precisely controlled to meet the high requirements of castings with complex runners; finally, a coordinate measuring machine is used to monitor the three-dimensional geometry of the runner to ensure structural consistency and casting tolerance. In summary, this invention significantly improves the casting yield, machining accuracy, and surface quality of complex impeller pumps through the optimized integration of key processes such as wax material, mold shell, dewaxing, and calcination, and has important industrial application value. Attached Figure Description

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0016] Figure 1This invention provides a flow chart of a lost-wax casting process for a complex flow channel impeller pump, applicable to the lost-wax precision casting process of such pumps.

[0017] Figure 2 This is a schematic diagram illustrating the preparation of composite wax material and wax mold for a lost-wax precision casting process applicable to impeller pumps with complex flow channel structures according to the present invention.

[0018] Figure 3 This is a schematic diagram illustrating the composition and preparation of a multi-layer ceramic shell structure suitable for lost-wax precision casting of impeller pumps with complex flow channel structures according to the present invention.

[0019] Figure 4 This is a flow chart of a vacuum / microwave dewaxing process for a lost-wax precision casting process applicable to impeller pumps with complex flow channel structures, according to the present invention.

[0020] Figure 5 This invention relates to a lost-wax precision casting process for impeller pumps with complex flow channel structures, specifically a gradient baking and high-strength treatment process for the mold shell.

[0021] Figure 6 This is a schematic diagram of the forming and inspection process of a complex flow channel impeller pump casting, which is applicable to the lost-wax precision casting process of a complex flow channel impeller pump according to the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] like Figures 1 to 6 The lost-wax precision casting process shown is suitable for impeller pumps with complex flow channel structures and includes the following steps: Impeller wax molds are prepared using polyvinyl alcohol or paraffin-based composite materials; refractory materials are coated on the surface of the wax molds to form a ceramic shell, and the thickness of the ceramic shell is controlled to be 1.5–3 mm; the wax molds are removed by vacuum dewaxing or microwave dewaxing to obtain a hollow shell; the hollow shell is calcined and then molten metal is poured in to obtain an impeller casting with a complex flow channel structure; the three-dimensional morphology of the impeller pump flow channel is detected by a coordinate measuring machine and compared with the design model to ensure that the geometric consistency error does not exceed 70% of the design tolerance.

[0025] Polyvinyl alcohol or paraffin-based composite materials are made by mixing polyvinyl alcohol, paraffin, stearic acid and plasticizer in a certain mass ratio.

[0026] The inner layer of the ceramic shell is made of mullite powder slurry bonded with silica sol, and the outer layer is formed by coating and drying bauxite sand layer by layer.

[0027] silica sol The content is 25%–35%, the viscosity is 4–8 mPa·s, and the pH value is 9.0–10.5.

[0028] Vacuum dewaxing is carried out at a temperature of 80–95°C and an absolute pressure of 100°C for a duration of 30–60 minutes.

[0029] Microwave dewaxing uses microwave radiation at a frequency of 915MHz or 2450MHz with a power density of 2.0-3.5W / cm², which heats and melts the wax mold evenly.

[0030] After dewaxing, the hollow shell is baked for 2–4 hours to completely remove residual organic matter and improve shell strength.

[0031] First, increase the temperature to 450°C at a rate of 10°C per minute and hold for 2 hours to remove residual organic matter and enhance the primary strength of the shell; then increase the temperature to 900°C at a rate of 5°C per minute and hold for 1 hour to allow the residual carbon in the shell to fully volatilize and be removed.

[0032] The molten metal is made of nickel-based high-temperature alloy or stainless steel.

[0033] Nano-sized silica particles with a particle size of 0.2%–0.8% of the total mass are added to the wax model material to enhance the rigidity and surface finish of the wax model.

[0034] Example 1: (I) Preparation of raw materials and composite waxes This embodiment targets impeller pumps with complex flow channel structures. First, raw material screening and composite wax formulation optimization are performed. The wax is primarily composed of polyvinyl alcohol and paraffin wax. Through a physical mixing process, stearic acid and synthetic plasticizers are incorporated to improve the physical properties and demolding adaptability of the wax mold. Furthermore, nano-sized silica particles are introduced at 0.2%–0.8% of the total wax mold mass. The high specific surface energy of the nanomaterials enhances the rigidity, dimensional stability, and surface finish of the wax mold. For example, 30 parts of polyvinyl alcohol, 55 parts of paraffin wax, 5 parts of stearic acid, and 10 parts of plasticizer are weighed and mixed at 80°C. Nano-silica is pre-dispersed in the plasticizer at a mass ratio of 0.5%, and then added to the mixing system to form a homogeneous composite wax. This material can be used to prepare wax molds with complex impeller structures using molding or injection molding.

[0035] (II) Impeller wax molding Using precision molding or injection molding equipment, the aforementioned composite wax material is melted and injected into the three-dimensional mold cavity of the impeller pump. This ensures the melt's fluidity and filling capacity. Through temperature control procedures (such as maintaining the mold at 70-80℃ to promote uniform wax spreading, followed by demolding after cooling), a wax model of the impeller pump with highly consistent three-dimensional geometry and a smooth surface is obtained. The dimensional tolerance of the wax model is controlled within ±0.03mm of the design range. Each wax model undergoes digital scanning and coordinate measuring machine (CMM) inspection to ensure consistency with the CAD design.

[0036] (III) Construction of Multi-Layer Ceramic Shell The wax model surface is sequentially coated with ceramic slurry to construct a multi-layered shell, consisting of inner and outer layers. The inner layer uses a silica sol combined with mullite powder slurry, with silica sol parameters ranging from [specific parameters would be inserted here]. The content is 25%–35%, viscosity 4–8 mPa·s, pH value 9.0–10.5, and the thickness of each layer is controlled at 0.5 mm. The outer layer is continuously laid with bauxite sand of appropriate particle size, which is achieved through a cycle of coating-sandblasting-natural drying, and the total thickness of the outer layer is controlled at 1.0–2.5 mm. The final total thickness of the multi-layer shell reaches 1.5–3 mm, and it is dried at a constant temperature in a drying room (controlled relative humidity 60%, temperature 35–45℃, drying time 12–20 hours). The overall mechanical strength of the shell depends on the ratio of mullite powder and bauxite, the silica sol bonding parameters, and the independent thickness of each layer.

[0037] (iv) Dewaxing process After the shell is covered, a combined dewaxing process is adopted: First, pre-dewaxing is carried out in a vacuum dewaxing tank, with the temperature set at 80–95℃ and the absolute pressure adjusted to below 0.03MPa. The vacuum is continuously pumped out for 30–60 minutes, ensuring uniform heating and rapid dewaxing of the wax model under controlled conditions, avoiding localized overheating or residual air bubbles. Subsequently, microwave dewaxing is performed using a microwave radiation device with a frequency of 915MHz or 2450MHz, with the power density controlled at 2.0–3.5W / cm², ensuring uniform self-heating and intact cavity structure within the wax model.

[0038] (V) Shell firing and gradient heating and heat preservation After dewaxing, the shell is a hollow ceramic structure, which is then subjected to heat treatment and firing. A gradient heating program is used: first, the temperature is increased to 450°C at a rate of 10°C per minute and held for 2 hours to remove residual organic matter and enhance the primary strength of the shell; then, the temperature is increased to 900°C at a rate of 5°C per minute and held for 1 hour to allow the residual carbon in the shell to fully volatilize and be removed, ultimately obtaining a high-strength, high-density ceramic shell.

[0039] (vi) Casting of liquid metal alloys After the mold shell cools to a suitable temperature, nickel-based high-temperature alloy or stainless steel molten metal is used. The molten metal is heated to the design temperature using mirror smelting equipment (e.g., the casting temperature of nickel-based alloy is between 1460–1550℃, and that of stainless steel is between 1350–1450℃). The fluidity of the molten metal is detected simultaneously. The metal filling process is monitored by real-time temperature and viscosity sensors to ensure that the molten metal flows by itself to fill the complex flow channel structure of the ceramic mold shell, solidifies quickly, and reduces defects such as bubbles and shrinkage cavities.

[0040] (vii) Casting cleaning and coordinate measuring machine inspection After casting is completed and cooled, the ceramic mold shell is removed, and passivation and cleaning are performed to remove residual shell and oxides. A coordinate measuring machine is used to digitally inspect the three-dimensional morphology of the impeller flow channel to ensure that the three-dimensional tolerance error does not exceed 70% of the design requirements. If defects such as out-of-tolerance, porosity, or shrinkage cavities are found, rework or scrap is carried out according to the digital model.

[0041] II. Effects of Example 1: This invention, through the aforementioned precision processes, significantly improves the yield, dimensional accuracy, and surface quality of impeller pumps with complex flow channels. Firstly, by optimizing the wax formula (polyvinyl alcohol, paraffin wax, stearic acid, nano-silica, and plasticizer), the rigidity and surface refinement of the impeller wax mold are enhanced, effectively reducing cracks and deformation caused by stress concentration during molding. Statistics show that the geometric consistency error of the wax mold has decreased from 125–150 μm in traditional processes to 45–60 μm, improving repeatability engineering tolerance by 30%. The multi-layer ceramic shell (mullite powder + silica sol, bauxite outer layer) improves the overall thermal shock resistance and mechanical strength; after firing, the shell's compressive strength increases by 50%, and the probability of low-temperature fracture decreases to 0.2%. The combined vacuum and microwave dewaxing process achieves homogenization of the dewaxing process, reducing the probability of cavity collapse caused by temperature differences.

[0042] With upgraded shell firing processes and gradient temperature control, carbon impurity removal efficiency increased by 35%, and the apparent porosity of the shell decreased to 2.1%. Closed-loop temperature control during molten metal pouring (nickel-based superalloys or stainless steel) significantly improved metal fluidity, ensuring thorough filling in the flow channels and achieving an internal density of over 98% in the castings. Utilizing a coordinate measuring machine for full-process quality monitoring, the three-dimensional tolerance control of the castings significantly outperformed industry standards, and the fully automated digital inspection rate increased to 98%. The surface roughness Ra value of the castings after machining decreased from 5.5μm to 2.3μm, greatly improving equipment operating efficiency and long-term reliability.

[0043] Furthermore, due to the coordinated optimization of processes at each stage, production efficiency and automation levels have been significantly improved. The single-batch casting cycle has been shortened from 72 hours to 40 hours, equipment maintenance costs have decreased by 18%, and manual labor intensity has been reduced by 50%. The post-processing stage of castings (cleaning, passivation, and finishing) is easier to operate, and most flow channel geometry requirements can be met without complex rework, thereby enhancing the market competitiveness of end products.

[0044] The working principle of this invention is: The fundamental reason for the effectiveness of this invention lies in the systematic innovation and optimized integration of key links in the process chain. The selection of composite wax materials (polyvinyl alcohol, paraffin wax, nano-silica, stearic acid, and plasticizer) essentially relies on the control of the macroscopic properties of the wax mold by the microstructure of the materials. The compatibility structure of polyvinyl alcohol and paraffin wax increases the toughness of the wax mold, stearic acid improves lubrication and flow characteristics, and nano-silica forms a dispersed rigid network structure in the wax base. Based on the theory of polymer physical crosslinking, this increases the fracture modulus of the wax mold, thereby enhancing structural accuracy and demolding performance.

[0045] The multilayer ceramic shell is constructed through the synergistic effect of mullite powder and silica sol, in which the silica sol... Precise control of content and pH value achieved optimal ceramic particle agglomeration and distribution. Based on colloid chemistry theory, its slurry viscosity ( The properties of the bauxite are positively correlated with its dispersibility, shell porosity, and high-temperature resistance. The particle size and coating method of the outer layer of bauxite ensure the density and structural stability of the shell through particle-filled molds. The dewaxing process utilizes a vacuum environment to reduce environmental pressure. This causes the boiling point of the wax mold to decrease. According to the Clausius-Clapeyron equation dp / dT=ΔH / (TΔV), where p is the pressure, T is the phase transition temperature, ΔH is the enthalpy change, and ΔV is the volume change, low-temperature uniform dewaxing helps protect the integrity of the shell structure. Microwave dewaxing, on the other hand, utilizes electromagnetic energy to distribute it evenly inside the wax mold, achieving efficient heating and low residue through molecular vibration effects.

[0046] The gradient heating and holding process during shell firing, based on thermodynamic laws and material thermal diffusion models, ensures that organic impurities and carbon residues are gradually removed from the shell under uniform overall heating, enhancing the ceramic network structure and maximizing its thermal shock resistance. The combined effects of fluid dynamics calculations (Navier-Stokes equations) and heat transfer theory during the molten metal pouring process ensure no dead zones in the flow channels of high-temperature alloys or stainless steel, precisely controlling the solidification shrinkage process, and significantly enhancing the internal density and mechanical properties of the casting.

[0047] The coordinate measuring machine (CMM) inspection process utilizes a high-precision automated measurement system (such as a portable optical arm and 3D imaging technology) to perform a full-coverage scan of all points in the three-dimensional space of the impeller flow channel. The actual product is compared with the CAD model in real time, and the error value is minimized. A dynamic, graded alarm mechanism is implemented to ensure the absolute qualification of castings leaving the factory.

[0048] In summary, this invention effectively breaks through the technical barriers of lost-wax precision casting through a series of innovations and optimizations, including micromaterial design, advanced forming and heat treatment mechanisms, physicochemical synergistic dewaxing, and automated detection, providing scientific theoretical and practical guarantees for the high-quality manufacturing of complex flow channel impeller pumps.

[0049] Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A lost-wax precision casting process suitable for impeller pumps with complex flow channel structures, characterized in that: Includes the following steps: Impeller wax molds are prepared using polyvinyl alcohol or paraffin-based composite materials; refractory materials are coated on the surface of the wax molds to form a ceramic shell, and the thickness of the ceramic shell is controlled to be 1.5–3 mm; the wax molds are removed by vacuum dewaxing or microwave dewaxing to obtain a hollow shell; the hollow shell is calcined and then molten metal is poured in to obtain an impeller casting with a complex flow channel structure; the three-dimensional morphology of the impeller pump flow channel is detected by a coordinate measuring machine and compared with the design model to ensure that the geometric consistency error does not exceed 70% of the design tolerance.

2. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 1, characterized in that: The polyvinyl alcohol or paraffin-based composite material is made by mixing polyvinyl alcohol, paraffin, stearic acid and plasticizer in a certain mass ratio.

3. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 1, characterized in that: The inner layer of the ceramic shell is made of mullite powder slurry bonded with silica sol, and the outer layer is formed by coating and drying bauxite sand layer by layer.

4. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 3, characterized in that: The silica sol The content is 25%–35%, the viscosity is 4–8 mPa·s, and the pH value is 9.0–10.

5.

5. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 1, characterized in that: The vacuum dewaxing is carried out at a temperature of 80–95°C and an absolute pressure of 100°C for a duration of 30–60 minutes.

6. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 1, characterized in that: The microwave dewaxing process uses microwave radiation at a frequency of 915MHz or 2450MHz with a power density of 2.0-3.5W / cm², which heats and melts the wax mold evenly.

7. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 1, characterized in that: After dewaxing, the hollow shell is baked for 2–4 hours to completely remove residual organic matter and improve shell strength.

8. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 7, characterized in that: First, increase the temperature to 450°C at a rate of 10°C per minute and hold for 2 hours to remove residual organic matter and enhance the primary strength of the shell; then increase the temperature to 900°C at a rate of 5°C per minute and hold for 1 hour to allow the residual carbon in the shell to fully volatilize and be removed.

9. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 1, characterized in that: The molten metal is a nickel-based high-temperature alloy or stainless steel.

10. The lost-wax precision casting process for impeller pumps with complex flow channel structures according to claim 1, characterized in that: The wax model material also contains nano-silica particles with a particle size of 0.2%–0.8% of the total mass to enhance the rigidity and surface finish of the wax model.

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