Preparation method of casting

Abstract

The invention discloses a preparation method of a casting. The preparation method of the casting comprises the steps that surface layer slurry and back layer slurry are prepared, the surface layer slurry contains additives, and the additives comprise fused quartz powder, dispersions, bonding substances and solvents; designing and manufacturing a model, and cleaning, airing and inspecting the model; immersing the model into the surface layer slurry to form a coating on the surface of the model, and drying; carrying out sand spraying and shell making on the model, and drying; immersing the model into silica sol, and then immersing the model into back layer slurry to form a back layer; roasting the model to obtain a shell and cleaning the shell; roasting the shell at a preset temperature; and metal is smelted and then cast in a mold shell to prepare a casting, shelling and cleaning are conducted, and the casting is inspected and detected. According to the preparation method of the casting, the problem that in the prior art, due to the fact that the refractoriness of a common surface layer molding material is not enough, the quality of a casting product is low can be at least solved.

Description

Technical Field

[0001] The invention relates to the technical field of precision casting, and in particular to a method for preparing a casting. Background Art

[0002] Precision casting can obtain relatively accurate shapes and high casting accuracy. In the field of precision casting technology, silica sol type membrane shell is the best process solution. The casting surface quality of silica sol type membrane shell is high, the rework rate is low, the scrap rate is low, the quality stability is good, and the material applicability is wide. The cost performance of precision castings depends largely on the quality and cost of the "shell", which is not only determined by the binder but also closely related to the refractory materials (sand, powder) in the shell material.

[0003] At present, the surface slurry used in investment casting is mainly prepared from surface powder and silica sol. However, the surface slurry in the prior art has insufficient refractoriness, which leads to problems such as sand sticking, pores on the surface, and difficulty in shell cleaning during the casting process, resulting in substandard casting product quality and increased production costs. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for preparing a casting, which at least solves the problem of low quality of casting products caused by insufficient refractoriness of ordinary surface molding materials in the prior art.

[0005] According to one aspect of the present invention, there is provided a method for preparing a casting, comprising:

[0006] Step S1: preparing a surface layer slurry and a back layer slurry, wherein the surface layer slurry contains additives, and the additives include fused silica powder, a dispersant, a binder, and a solvent;

[0007] Step S2: designing and making a model, and cleaning, drying and inspecting the model;

[0008] Step S3: immersing the model that meets the requirements into the surface slurry for slurrying, so that a coating is formed on the surface of the model, and drying;

[0009] Step S4: spraying sand on the dried model to make a shell and drying it;

[0010] Step S5: immersing the dried model into silica sol, and then immersing the model into the back layer slurry to form a back layer;

[0011] Step S6: calcining the mold to obtain a shell mold, and cleaning the shell mold;

[0012] Step S7: calcining the cleaned shell at a predetermined temperature;

[0013] Step S8: After smelting the metal, pouring it into the mold shell to prepare a casting, deshelling and cleaning the casting after it is formed, and inspecting and testing the casting.

[0014] Furthermore, the surface layer slurry also includes surface layer powder, binder, polymer glue, wetting agent and defoaming agent, wherein, in the surface layer slurry, the mass percentage of the additive is 9.5%-15%, the mass percentage of the surface layer powder is 60%-70%, the mass percentage of the binder is 18%-24%, the mass percentage of the polymer glue is 2.0%-2.4%, the mass percentage of the wetting agent is 0.02%-0.10% and the mass percentage of the defoaming agent is 0.02%-0.10%.

[0015] Furthermore, the surface layer powder includes at least one of zircon powder, mullite powder and corundum powder.

[0016] Furthermore, the binder includes at least one of silica sol, water glass and ethyl silicate.

[0017] Furthermore, the viscosity V of the surface layer slurry satisfies the relationship: 20 seconds ≤ V ≤ 45 seconds.

[0018] Furthermore, in the additive, the mass percentage of the fused silica powder is 64%-68%; the mass percentage of the binder is 21%-25%; the mass percentage of the dispersed material is 0.5%-0.7%; and the mass percentage of the solvent is 8%-12%.

[0019] Furthermore, in the additive, the particle size of the fused silica powder is 2.55 μm-2.65 μm.

[0020] Furthermore, in the additive, the mass fraction of silicon dioxide in the fused quartz powder is greater than or equal to 99.5%.

[0021] Further, in the additive, the dispersant includes at least one of bentonite, palygorskite and rectorite.

[0022] Furthermore, among the additives, the binder includes at least one of silica sol, water glass and ethyl silicate.

[0023] In the present invention, in the preparation process of the casting, when using mullite powder or corundum powder to prepare the surface slurry, an additive prepared from 5000 mesh fused quartz powder, silica sol, bentonite and pure water with a particle size of 2.55μm to 2.65μm is added, which can improve the refractoriness and strength of the shell prepared by the surface slurry, and make the shell surface smoother. After strictly controlling parameters such as temperature and pressure during the casting process, the casting obtained by casting is not prone to sand sticking, no pores are generated on the surface of the casting, and the casting is not difficult to clean the shell. The surface of the casting prepared after adding the additive to the surface slurry forms an easily peelable surface dense ceramic layer, which improves the surface quality of the shell and the quality of the casting; after the casting is cast and cooled, it is easy to clean the shell when vibrating the shell, which reduces the operation of subsequent processing of the casting and reduces the production cost. Relevant experimental data show that adding additives to the surface slurry can reduce the overall cost of precision casting by about 30%. In addition, adding this additive to ordinary surface powder can replace expensive zircon powder and reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0025] Figure 1 The present invention is a flowchart of a method for preparing a casting disclosed in an embodiment of the present invention;

[0026] Figure 2 A scanning electron microscope image (left) of a mold shell prepared with a surface layer slurry (containing zircon powder) disclosed in an embodiment of the present invention and a scanning electron microscope image (right) of a mold shell prepared with a surface layer slurry (containing mullite powder and additives) disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0030] As mentioned in the background technology, at present, the surface slurry used in investment casting is mainly prepared from surface powder and silica sol. However, the model prepared by the surface slurry in the prior art has insufficient refractoriness, which leads to problems such as sand sticking, pores on the surface, and difficulty in shell cleaning during the casting process, thereby causing problems such as substandard product quality of the casting and increased production costs. For this reason, the present application provides a method for preparing a casting, in which an additive is added to the surface slurry to improve the refractoriness of the surface material, thereby improving the product quality of the casting.

[0031] like Figure 1 and Figure 2 As shown, according to an embodiment of the present application, a method for preparing a casting is provided.

[0032] Specifically, the preparation method of the casting includes:

[0033] Step S1: preparing a surface layer slurry and a back layer slurry, wherein the surface layer slurry contains additives, and the additives include fused silica powder, a dispersant, a binder and a solvent.

[0034] In this embodiment, the surface layer slurry also includes surface layer powder, binder, polymer glue, wetting agent and defoamer. Among them, in the surface layer slurry, the mass percentage of the additive is 9.5%-15%. For example, the mass percentage of the additive can be 9.5%, 10.5%, 12.5%, 15%, etc. The additive in the surface layer slurry can improve the refractoriness of the surface layer material and prevent the occurrence of sand sticking to the casting during the preparation of the casting, thereby improving the quality of the casting. When the mass percentage of the additive in the surface layer slurry is less than 9.5%, the effect of improving the refractoriness of the surface layer material is not obvious, and the surface of the casting produced in the end is not smooth and the time spent on shell vibration is long, and the casting still has the problem of sand sticking; when the mass percentage of the additive in the surface layer slurry is greater than 15%, the shell prepared using the surface layer slurry will be too dense, the air permeability is poor, and the problem of pore shrinkage is easy to occur. During the casting process, the gas in the metal liquid cannot be removed in time, which will cause defects such as pores to form on the casting, causing the casting to fail to meet the standards.

[0035] Furthermore, the additives include fused silica powder, dispersions, binders and solvents. Among them, the fused silica powder can further improve the strength and refractory properties of the shell, improve the surface finish, optimize the thermal expansion coefficient and improve the demolding performance. And in this embodiment, the fused silica powder is an ultrafine powder with a particle size of 2.55μm to 2.65μm, and the mass fraction of silicon dioxide in the fused silica powder is greater than or equal to 99.5%; in this way, the silicon dioxide content in the fused silica powder is high and the particle size is small, which can be evenly distributed in the surface slurry, thereby forming a denser and smoother surface; it can also help to reduce bubbles and impurities in the surface slurry, thereby reducing the problem of pores and sand adhesion on the surface. The additive also includes a dispersion, which can be bentonite, palygorskite, or rectorite. Among them, the network structure formed by bentonite in water can not only ensure the uniformity of dispersion and suspension stability of the surface improver, but also improve its bonding performance; rectorite has excellent thermal stability and high temperature resistance, is very easy to disperse in water, and has high plasticity. The presence of rectorite can improve the surface quality of the product. In this application, the preferred dispersion bentonite can make the fused quartz powder better dispersed and increase the viscosity, and can also reduce the risk of cracks in the shell and maintain the integrity and dimensional accuracy of the shell. The binder in the additive can be silica sol, water glass, and ethyl silicate. In this embodiment, the preferred binder is silica sol. The casting in this embodiment is precision cast by silica sol. The liquid in the surface slurry is mainly silica sol, which reduces the influence of other components; in addition, silica sol has high purity and good chemical stability, excellent thermal stability and fire resistance, high strength and good mechanical properties, improves the surface finish of the shell, and is environmentally friendly and healthy and safe. In this embodiment, the solvent is pure water.

[0036] Specifically, the mass percentage of the fused silica powder is 64%-68%. For example, the mass percentage of the fused silica powder can be 64%, 65%, 67%, 68%, etc. Since the particle size of the fused silica powder is very small, if the content of the fused silica powder is too much, it is not easy to form a uniform paste, and finally the quality of the surface slurry is affected when preparing the surface slurry, which will eventually affect the quality of the casting. In this embodiment, the mass percentage of the binder is 21%-25%. For example, the mass percentage of the binder can be 21%, 22%, 23.5%, 25%, etc. When the mass percentage of the binder is within the above range, it is conducive to uniformly distributing the binder between the fused silica powders to form a continuous bonding network; it can also make the nano-scale silica particles in the binder fill the tiny gaps between the fused silica powders, which is conducive to improving the surface finish of the casting. The mass percentage of the dispersed material is 0.5%-0.7%. For example, the mass percentage of the dispersed material can be 0.5%, 0.6%, 0.7%, etc. Excessive amounts of dispersants may increase the viscosity of the slurry, making the additive too thick, which is not conducive to the dispersion of ultrafine fused quartz powder; insufficient dispersants may result in insufficient adhesion of the additive. In this embodiment, the solvent is pure water, and the mass percentage of the solvent is 8%-12%. The mass percentage of the solvent can be 8%, 9%, 10%, 12%, etc. In this embodiment, the mass percentage of each component in the additive is not specifically limited. In actual production, it is adjusted according to actual process requirements. When the components in the additive are respectively within the above-mentioned ranges, adding the additive to the surface slurry of precision casting can significantly improve the strength, refractory properties, surface finish and chemical corrosion resistance of the shell, while also optimizing the fluidity of the surface slurry.

[0037] In this embodiment, the additive is first prepared and then added to the surface layer slurry. With this arrangement, the amount of additive in the surface layer slurry can be precisely controlled. Since the particle size of the fused quartz powder is very small, specific equipment is required to stir the fused quartz powder with the silica sol and pure water during the preparation process so that the fused quartz powder can be fully mixed with the silica sol and pure water to obtain a paste-like additive. If the components of the additive are directly added to the surface layer slurry, due to the limitations of the equipment used in the preparation of the surface layer slurry and the small amount of the additive added to the surface layer slurry, it is not easy to precisely control the components of the additive directly added to the surface layer slurry, thereby affecting the surface quality of the mold shell prepared using the surface layer slurry, and further affecting the quality of the casting.

[0038] Further, in the surface layer slurry, the mass percentage of the surface layer powder is 60%-70%. For example, the mass percentage of the surface layer powder can be 60%, 61.5%, 62.5%, 63%, 70%, etc. In this embodiment, the specific mass percentage of the surface layer powder is not limited. The surface layer powder in the surface layer slurry has a great influence on the surface layer of the mold shell. In this embodiment, the surface layer powder can be zircon powder (mainly composed of ZrO2 and SiO2), mullite powder (mainly composed of Al2O3 and SiO2) and corundum powder (mainly composed of Al2O3 and SiO2). Among them, zircon powder is superior to mullite powder and corundum powder in terms of refractoriness, thermal expansion coefficient and chemical stability, but the price of zircon powder is higher than that of mullite powder and corundum powder, which is 11 times that of mullite powder and 2.5 times that of corundum powder. The use of zircon powder in the surface layer slurry greatly increases the production cost of castings. Therefore, the mold shell prepared by adding additives to mullite powder or corundum powder in the present application has a compact and smooth surface, which is similar to the effect of the mold shell prepared by using the surface layer slurry prepared by zircon powder.

[0039] Further, in the surface layer slurry, the mass percentage of the binder is 18%-24%. For example, the mass percentage of the binder can be 18%, 22.5%, 23%, 23.5%, 24%, etc. The content of the binder affects the strength, thermal stability, surface finish, fluidity, drying and curing time of the surface layer slurry. When the mass percentage of the binder in the surface layer slurry is less than 18%, the surface layer slurry may have insufficient adhesion, resulting in a decrease in the strength of the shell. If the mass percentage of the binder is higher than 24%, the drying and curing speed of the shell may be slowed down, thereby extending the production cycle. In this embodiment, the binder can be silica sol, water glass, ethyl silicate, etc. In this embodiment, the binder is preferably silica sol (for example, S-830 silica sol), because silica sol has high purity and good chemical stability, excellent thermal stability and fire resistance, high strength and good mechanical properties, improved surface finish, environmental protection and health and safety.

[0040] Furthermore, in the surface layer slurry, the mass percentage of the polymer glue is 2.0%-2.4%. For example, the mass percentage of the polymer glue can be 2.0%, 2.25%, 2.3%, 2.4%, etc. Adding an appropriate amount of polymer glue can accelerate the drying speed of the mold shell and improve its strength and heat resistance. In this embodiment, the mass percentage of the polymer glue is not specifically limited. In actual production, a suitable addition ratio can be selected according to the process. Exemplarily, the polymer glue can be polyvinyl alcohol, polyacrylate, etc. Specifically, adding a polymer glue to the surface layer slurry can significantly improve the adhesion, fluidity and water resistance of the surface layer slurry, thereby ensuring the quality and production efficiency of the casting.

[0041] Further, in the surface slurry, the mass percentage of the wetting agent is 0.02%-0.10%. For example, the mass percentage of the wetting agent can be 0.02%, 0.015%, 0.03%, 0.05%, 0.10%, etc. In this embodiment, the main function of the wetting agent is to reduce the surface tension of the surface slurry and improve the coating property of the surface slurry. In the actual working process, the model is immersed in the surface slurry with the wetting agent, the hydrophilic group is easy to combine with the water molecules, and is attracted by the water molecules and remains on the surface of the surface slurry. The lipophilic end is attracted by the model and arranged in a directional manner, forming a monomolecular film composed of surfactant molecules, which changes the surface properties of the model and reduces the interfacial tension therebetween, so it can be well wetted, thereby improving the coating property of the surface slurry. In this embodiment, the wetting agents used are mainly medium-temperature wax wetting agent and low-temperature wax wetting agent. These two wetting agents have good wetting and penetration abilities, less foam and low stability, are easy to defoam, do not chemically react with the coating components, and do not affect the stability of the coating.

[0042] Further, the mass percentage of the defoamer is 0.02%-0.10%. For example, the mass percentage of the defoamer can be 0.02%, 0.03%, 0.08%, 0.10%, etc. In this embodiment, the defoamer can quickly eliminate the foam in the slurry and suppress the appearance of foam for a long time. When the mass percentage of the defoamer is less than 0.02%, the bubbles cannot be completely eliminated, resulting in a large number of pores and voids in the shell, affecting the strength and surface finish of the shell; when the mass percentage of the defoamer exceeds 0.1%, it will affect the adhesion and fluidity of the surface slurry and affect the surface quality of the final casting.

[0043] Specifically, the preparation method of the surface layer slurry includes the following:

[0044] First, add silica sol to the container, and then add an appropriate amount of additives. During the process, stirring needs to be continued until there is no particle agglomeration. Continue to add the surface powder and continue stirring for 24 to 48 hours to ensure that the surface powder, silica sol and additives are fully mixed. After the slurry is prepared, use a No. 5 Zahn cup to test the viscosity of the slurry. When the viscosity remains within the process requirements, continue to add polymer glue, wetting agent and defoaming agent, and stir to obtain the surface slurry. Finally, after the slurry has stabilized for a period of time, a wax mold test block is used to test the slurry hanging property of the surface slurry. It is worth noting that the viscosity needs to be strictly maintained in accordance with the process requirements throughout the production process.

[0045] Furthermore, the viscosity V of the surface slurry satisfies the relationship: 20 seconds ≤ V ≤ 45 seconds. The viscosity V can be 20 seconds, 25 seconds, 30 seconds, 40 seconds, or 45 seconds. In this way, the surface slurry can be coated on the wax mold, which is beneficial to improving the surface quality of the casting.

[0046] Step S2: Design and make a model, clean, dry and inspect the model. Set the three-dimensional model of the casting and make a wax mold according to product requirements. Complex castings can be completed by splicing multiple wax molds. Clean and dry the model and inspect and trim the wax tree to improve the preparation of subsequent castings.

[0047] Step S3: Dip the model that meets the requirements into the surface slurry to form a coating on the surface of the model, and dry it. Dip the wax tree into the surface slurry containing additives to coat and dry it. A dense and smooth shell is formed on the outer surface of the model. This process can be performed multiple times to increase the thickness of the shell.

[0048] Step S4: The dried model is sanded and dried. The model coated with the surface slurry is sanded so that the sand particles are evenly attached to the model to enhance the thickness and strength of the model, and then dried to form a hard shell.

[0049] Step S5: After the dried model is immersed in silica sol, the model is immersed in the back layer slurry to form a back layer. The model is immersed in silica sol so that the back layer slurry can be better bonded to the shell, and then the model is immersed in the back layer slurry to form a back layer. Repeat the process of making the back layer to increase the thickness of the shell and improve the strength and fire resistance of the model.

[0050] Step S6: The mold is fired to obtain a shell, and the shell is cleaned. This process is also called a dewaxing process. The hardened model is placed in a high-temperature furnace to melt the wax and flow out to form a shell. After ensuring that the inside of the shell is completely empty, a high-pressure water gun or chemical cleaning can be used to clean the residue.

[0051] Step S7: calcining the cleaned shell at a predetermined temperature. The cleaned shell is placed in a high temperature furnace for calcination, and the temperature is usually 800°C-1200°C to remove moisture and organic matter in the shell, making the shell stronger and more fire-resistant. During the calcination process, the silicon dioxide and other components in the shell will crystallize and sinter to form a denser structure, thereby improving the strength and fire resistance of the shell. Specifically, in this embodiment, no specific requirements are made on the temperature, and a suitable temperature can be selected according to the casting requirements.

[0052] Step S8: After the metal is melted, it is cast into the mold shell to prepare a casting. After the casting is formed, it is shelled and cleaned, and the casting is inspected and tested. According to the requirements of the casting, a suitable metal material is selected for smelting, and the molten metal solution is poured into the mold shell after roasting. During the pouring process, it is necessary to pay attention to controlling the temperature, speed and pressure to ensure that the metal solution can evenly fill the mold shell to avoid defects in the casting. After the casting is cooled, the mold shell is broken to take out the casting, and the casting is cleaned and polished to ensure that the appearance and size of the casting meet the requirements. If necessary, subsequent processing such as heat treatment can also be carried out. Finally, the casting is subjected to a comprehensive quality inspection, including dimensional accuracy, surface finish, internal defects, etc.

[0053] In order to verify the technical effect of the additive of the present invention, the present invention provides the following specific examples and comparative examples:

[0054] Example 1

[0055] Preparation of additives: pure water and silica sol are added to a fixed container, and then fused quartz powder and bentonite are added to the container, and an instrument is used for stirring so that the fused quartz powder and bentonite can be fully mixed with the silica sol and pure water to prepare a paste additive.

[0056] In this embodiment, the mass percentage of pure water is 10%, the mass percentage of silica sol is 23.3%, the mass percentage of fused silica powder is 66%, the particle size of the fused silica powder is 2.55 μm to 2.65 μm, and the mass percentage of bentonite is 0.7%.

[0057] Prepare the surface slurry: add silica sol to another fixed container, then add the additives prepared above, and continue to stir to mix the solution evenly, then add mullite, and continue to stir for 24h-48h to mix the slurry evenly; use No. 5 Zahn cup to test the viscosity of the mixed solution; finally, add polymer glue, wetting agent, and defoaming agent to obtain the surface slurry.

[0058] In this embodiment, the mass percentage of silica sol in the surface slurry is 24%, the mass percentage of additives is 9.9%, the mass percentage of mullite is 64%, the mass percentage of high molecular polymer glue is 2.0%, the mass percentage of wetting agent is 0.02%, and the mass percentage of defoaming agent is 0.02%. The viscosity of the surface slurry is 35.5 seconds.

[0059] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 2.9, and the time required for the casting to vibrate the shell is 30 seconds.

[0060] Example 2

[0061] The contents of the components in the surface slurry of Example 2 are substantially the same as those in Example 1, except that in this example, the mass percentage of pure water in the additive is 8.9%, the mass percentage of silica sol is 23.5%, the mass percentage of fused quartz powder is 67%, and the mass percentage of bentonite is 0.6%. The viscosity of the surface slurry is 35.8 seconds.

[0062] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 2.8, and the time required for the casting to vibrate the shell is 28 seconds.

[0063] Example 3

[0064] The contents of the components in the surface slurry of Example 3 are substantially the same as those in Example 1, except that in this example, the mass percentage of pure water in the additive is 10.6%, the mass percentage of silica sol is 24%, the mass percentage of fused quartz powder is 65.4%, and the mass percentage of bentonite is 0.5%. The viscosity of the surface slurry is 35.5 seconds.

[0065] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 3.0, and the time required for the casting to vibrate the shell is 30 seconds.

[0066] Example 4

[0067] The content of the components of the additives in Example 4 is substantially the same as that in Example 1, except that in this example, the mass percentage of silica sol in the surface slurry is 22%, the mass percentage of the additive is 12%, the mass percentage of mullite powder is 63.96%, the mass percentage of high molecular polymer glue is 2.0%, the mass percentage of the wetting agent is 0.02%, and the mass percentage of the defoaming agent is 0.02%. The viscosity of the surface slurry is 36 seconds.

[0068] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 1.8, and the time required for the casting to vibrate the shell is 24 seconds.

[0069] Example 5

[0070] The content of the additive components of Example 5 is substantially the same as that of Example 1, except that in this example, the mass percentage of silica sol in the surface slurry is 21%, the mass percentage of the additive is 14%, the mass percentage of mullite powder is 62.96%, the mass percentage of high molecular polymer glue is 2.0%, the mass percentage of the wetting agent is 0.02%, and the mass percentage of the defoaming agent is 0.02%. The viscosity of the surface slurry is 36 seconds.

[0071] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 1.2, and the time required for the casting to vibrate the shell is 22 seconds.

[0072] Example 6

[0073] The content of the components of the additives in Example 4 is substantially the same as that in Example 1, except that in this example, the mass percentage of silica sol in the surface slurry is 20%, the mass percentage of the additive is 15%, the mass percentage of mullite powder is 62.96%, the mass percentage of high molecular polymer glue is 2.0%, the mass percentage of the wetting agent is 0.02%, and the mass percentage of the defoaming agent is 0.02%. The viscosity of the surface slurry is 36.5 seconds.

[0074] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 0.8, and the time required for the casting to vibrate the shell is 20 seconds.

[0075] Comparative Example 1

[0076] No additives are added to the surface layer slurry in Comparative Example 1, and the surface layer powder in the surface layer slurry is zircon powder.

[0077] In the surface slurry of this embodiment, the mass percentage of zircon powder is 79.96%, the mass percentage of silica sol is 18%, the mass percentage of high molecular polymer glue, wetting agent and defoaming agent is 2.04% in total. The viscosity of the surface slurry is 45 seconds.

[0078] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 3.2, and the time required for the casting to vibrate the shell is 30 seconds.

[0079] Comparative Example 2

[0080] Comparative Example 2 is basically the same as Example 1, except that no additive is added to the surface layer slurry.

[0081] In this embodiment, in the surface layer slurry, the mass percentage of mullite powder is 76.96%, the mass percentage of silica sol is 21%, the mass percentage of high molecular polymer glue, wetting agent and defoaming agent is 2.04% in total, and the viscosity of the surface layer slurry is 35 seconds.

[0082] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 5.0, and the time required for the casting to vibrate the shell is 60 seconds.

[0083] Comparative Example 3

[0084] The contents of the components in the surface slurry of Comparative Example 3 are substantially the same as those in Example 1, except that in this example, the mass percentage of pure water in the additive is 12%, the mass percentage of silica sol is 24%, the mass percentage of fused quartz powder is 63.2%, and the mass percentage of bentonite is 0.8%. The viscosity of the surface slurry is 36 seconds.

[0085] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 3.5, and the time required for the casting to vibrate the shell is 30 seconds.

[0086] Comparative Example 4

[0087] The contents of the components in the surface slurry of Comparative Example 4 are substantially the same as those in Example 1, except that in this example, the mass percentage of pure water in the additive is 8.4%, the mass percentage of silica sol is 22%, the mass percentage of fused quartz powder is 69%, and the mass percentage of bentonite is 0.6%. The viscosity of the surface slurry is 37 seconds.

[0088] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 3.3, and the time required for the casting to vibrate the shell is 30 seconds.

[0089] Comparative Example 5

[0090] The contents of the components in the surface slurry of Comparative Example 5 are substantially the same as those in Example 4, except that in this example, the mass percentage of silica sol in the surface slurry is 20%, the mass percentage of additives is 9%, the mass percentage of mullite powder is 68.96%, the mass percentage of polymer glue is 2.0%, the mass percentage of wetting agent is 0.02%, and the mass percentage of defoaming agent is 0.02%. The viscosity of the surface slurry is 35.5 seconds.

[0091] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 3.8, and the time required for the casting to vibrate the shell is 31 seconds.

[0092] Comparative Example 6

[0093] The contents of the components in the surface slurry of Comparative Example 6 are substantially the same as those in Example 4, except that in this example, the mass percentage of silica sol in the surface slurry is 18%, the mass percentage of additives is 20%, the mass percentage of mullite powder is 59.96%, the mass percentage of polymer glue is 2.0%, the mass percentage of wetting agent is 0.02%, and the mass percentage of defoaming agent is 0.02%. The viscosity of the surface slurry is 35.5 seconds.

[0094] When the surface layer slurry in this embodiment is used to produce castings, the surface roughness Ra of the casting is 3.2, and the time required for the casting to vibrate the shell is 27 seconds.

[0095] Table 1:

[0096]

[0097]

[0098] Note: The table does not list the mass percentages of polymer glue, wetting agent and defoaming agent.

[0099] According to Table 1: By comparing Example 1, Example 2 and Example 3, it can be seen that when the mass percentage of each component in the surface layer slurry remains unchanged, as the sum of the mass percentages of the medium silica sol and fused quartz powder in the additive increases, the surface roughness of the prepared casting becomes smaller and the time required for shell vibration becomes shorter.

[0100] By comparing Example 1, Example 4, Example 5, and Example 6, it can be seen that as the mass percentage of the additive in the surface layer slurry increases, the surface roughness of the prepared casting becomes smaller and the time required for shell vibration becomes shorter.

[0101] By comparing Comparative Example 1 with Examples 1, 2, 3, 4, 5 and 6, it can be seen that the surface layer material used in the surface layer slurry is mullite powder, and the addition of additives can make the surface of the casting smooth. Adding additives to ordinary surface layer powder can achieve the same effect as the casting prepared with expensive zircon powder.

[0102] By comparing Comparative Example 2, Example 1, Example 2 and Example 3, it can be seen that adding additives to the surface layer slurry can make the surface of the casting smoother, so that the time required for shell vibration is shorter.

[0103] By comparing Comparative Example 3, Comparative Example 4 and Example 1, it can be seen that when the proportion of each component in the surface layer slurry does not change, when the fused quartz powder in the additive is insufficient or excessive, the surface roughness of the prepared casting increases.

[0104] By comparing Example 4, Comparative Example 5 and Comparative Example 6, it can be seen that when the composition of the additive and the mass percentage of the additive in the additive do not change, when the amount of the additive is insufficient or excessive, the surface roughness of the prepared casting will also increase.

[0105] Specifically, the above situation occurs mainly because the additive contains fused quartz powder, and the particle size of the powder is very small. It is used to prepare the surface slurry, which is smoother. When the surface slurry is used to make the shell, the strength and refractoriness of the shell are increased. The shell is relatively smooth, and it is not easy to stick to the sand during the casting process, thereby improving the surface finish of the casting. When the shell needs to be vibrated to remove the casting, the time required is shorter. However, when the amount of additives in the surface slurry is insufficient, the surface of the shell prepared is not smooth enough, and the refractoriness of the surface slurry is not enough, and it is easy to stick to the sand during the casting process, thereby reducing the surface finish of the casting, making the casting not meet the quality requirements. When excessive additives are added to the surface slurry, the surface of the shell will be too dense, the air permeability is poor, and the problem of pore shrinkage will easily occur. During the casting process, the gas in the metal liquid cannot be removed in time, which will cause defects such as pores to form on the casting, causing the casting to fail to meet the standards. In addition, adding a certain amount of additives to ordinary surface powder can improve the refractoriness of ordinary surface powder, so that the prepared castings also meet the quality requirements.

[0106] In summary, in the preparation process of the casting of the present invention, when using mullite powder or corundum powder to prepare the surface slurry, an additive prepared by 5000 mesh fused quartz powder, silica sol, bentonite and pure water with a particle size of 2.55μm to 2.65μm is added, which can improve the refractoriness and strength of the shell prepared by the surface slurry, and make the shell surface smoother. After strictly controlling the temperature, pressure and other parameters during the casting process, the casting obtained by casting is not prone to sand sticking, no pores will be generated on the surface of the casting, and the casting will not be difficult to clean the shell. The surface of the casting prepared by adding the additive to the surface slurry forms an easily peelable surface dense ceramic layer, which improves the surface quality of the shell and the quality of the casting; after the casting is cast and cooled, the shell is easy to clean when vibrating, which reduces the operation of subsequent processing of the casting and reduces the production cost. Relevant experimental data show that adding additives to the surface slurry can reduce the overall precision casting shell making cost by about 30%. In addition, adding this additive to ordinary surface powder can replace expensive zircon powder and reduce production costs.

[0107] like Figure 2 As shown in the left figure, the shell mold made of surface slurry (without additives) prepared with zircon powder is not smooth enough when observed at 50μm, and there are certain gaps between the materials. In the right figure, after adding additives to ordinary surface materials, the surface of the shell mold with additives is smoother and tighter at the same observation angle. The SEM image shows that the additive helps to improve the refractoriness of the surface material.

[0108] It can be seen from the above embodiments that the present invention can at least achieve the following technical effects:

[0109] (1) By adding an additive prepared from fused quartz powder, silica sol, bentonite and pure water to the surface layer slurry, the refractoriness of the surface layer material can be improved, and the problems of sand adhesion and pore generation of castings can be solved;

[0110] (2) By adding an additive prepared from fused quartz powder, silica sol, bentonite and purified water to the surface slurry, an easily peelable surface dense ceramic layer can be formed on the surface of the casting, thereby improving the surface quality of the shell and the quality of the casting;

[0111] (3) By adding an additive prepared from fused quartz powder, silica sol, bentonite and purified water to the surface slurry, the prepared casting is easy to clean, and the subsequent processing steps and production costs can be reduced;

[0112] (4) By adding an additive prepared from fused quartz powder, silica sol, bentonite and pure water to the surface slurry, expensive zircon powder can be replaced, thereby reducing production costs.

[0113] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0114] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0115] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a casting, characterized in that: The method for preparing the casting comprises: Step S1: preparing a surface layer slurry and a back layer slurry, wherein the surface layer slurry contains additives, and the additives include fused silica powder, a dispersant, a binder, and a solvent; Step S2: designing and making a model, and cleaning, drying and inspecting the model; Step S3: immersing the model that meets the requirements into the surface slurry for slurrying, so that a coating is formed on the surface of the model, and drying; Step S4: spraying sand on the dried model to make a shell and drying it; Step S5: immersing the dried model into silica sol, and then immersing the model into the back layer slurry to form a back layer; Step S6: calcining the mold to obtain a shell mold, and cleaning the shell mold; Step S7: calcining the cleaned shell at a predetermined temperature; Step S8: After smelting the metal, pouring it into the mold shell to prepare a casting, deshelling and cleaning the casting after it is formed, and inspecting and testing the casting.

2. The method for preparing a casting according to claim 1, characterized in that: The surface layer slurry also includes surface layer powder, binder, polymer glue, wetting agent and defoaming agent, wherein, in the surface layer slurry, the mass percentage of the additives is 9.5%-15%, the mass percentage of the surface layer powder is 60%-70%, the mass percentage of the binder is 18%-24%, the mass percentage of the polymer glue is 2.0%-2.4%, the mass percentage of the wetting agent is 0.02%-0.10% and the mass percentage of the defoaming agent is 0.02%-0.10%.

3. The method for preparing a casting according to claim 2, characterized in that: The surface layer powder includes at least one of zircon powder, mullite powder and corundum powder.

4. The method for preparing a casting according to claim 2, characterized in that: The binder includes at least one of silica sol, water glass and ethyl silicate.

5. The method for preparing a casting according to claim 2, characterized in that: The viscosity V of the surface layer slurry satisfies the relationship: 20 seconds ≤ V ≤ 45 seconds.

6. The method for preparing a casting according to claim 1, characterized in that: In the additive, the mass percentage of the fused silica powder is 64%-68%; the mass percentage of the binder is 21%-25%; the mass percentage of the dispersed material is 0.5%-0.7%; and the mass percentage of the solvent is 8%-12%.

7. The method for preparing a casting according to claim 1, characterized in that: In the additive, the particle size of the fused silica powder is 2.55 μm-2.65 μm.

8. The method for preparing a casting according to claim 1, characterized in that: In the additive, the mass fraction of silicon dioxide in the fused quartz powder is greater than or equal to 99.5%.

9. The method for preparing a casting according to claim 1, characterized in that: Among the additives, the dispersant includes at least one of bentonite, palygorskite and rectorite.

10. The method for preparing a casting according to claim 1, characterized in that: Among the additives, the binder includes at least one of silica sol, water glass and ethyl silicate.

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