Method for manufacturing castings, molds, and coating agents for molds
The method of forming a coating layer with 500 nm or less silica particles and refractory particles on sand molds effectively addresses veining defects, enhancing casting quality and reducing costs in casting processes.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- KOMATSU LTD
- Filing Date
- 2025-10-15
- Publication Date
- 2026-05-13
AI Technical Summary
Existing methods for manufacturing castings using sand molds suffer from veining defects, which are burr-like defects caused by cracks in the mold surface allowing molten metal penetration, and there is a demand for improved quality and cost reduction by eliminating these defects.
A method involving the formation of a coating layer on the sand mold surface containing silica particles with an average size of 500 nm or less and refractory particles, which enhances adhesiveness and suppresses veining defects during casting.
The method effectively suppresses veining defects, improving casting quality and reducing costs by using a coating layer that includes fine silica particles and refractory particles.
Smart Images
Figure 2026077591000001_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a method for manufacturing a casting, a mold, and a coating agent for a mold.
Background Art
[0002] Castings made of metals such as cast steel and cast iron can be manufactured by casting using a mold such as a sand mold. A sand mold is prepared by mixing sand (natural silica sand or artificial sand) as an aggregate and a binder such as a clay component or resin, forming a cavity having a desired shape, and bonding the sand and the binder by pressure or a chemical reaction. The cavity is a space formed in the mold for filling molten metal to form a casting.
[0003] In the manufacture of castings using a sand mold, a defect called a veining defect may occur. A veining defect is a burr-like defect generated when cracks occur on the surface of the sand mold facing the cavity and molten metal penetrates into these cracks. The cracks on the surface of the sand mold are generated by thermal stress due to heat transfer when the cavity is filled with molten metal.
[0004] As a countermeasure for suppressing veining defects, a measure of forming a coating layer (coated mold) having a specific configuration on the surface of the sand mold facing the cavity has been proposed (see, for example, Patent Documents 1 and 2).
Prior Art Documents
Patent Documents
[0005]
Patent Document 1
Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[0006] The formation of the coating layer disclosed in the above-mentioned Patent Documents 1 and 2 has a certain effect in suppressing vaning defects. However, there is a demand for further improvement in the quality of castings and a demand for further cost reduction by eliminating the process of removing vaning defects.
[0007] One of the objectives of this disclosure is to provide a method for manufacturing castings, a mold, and a mold coating agent that can effectively suppress baining defects. [Means for solving the problem]
[0008] A method for manufacturing a casting according to this disclosure comprises the steps of: preparing a sand mold having a cavity; forming a coating layer on the surface of the sand mold facing the cavity, the coating layer containing silica particles with an average particle size of 500 nm or less and refractory particles; filling the cavity of the sand mold on which the coating layer has been formed with molten metal; and forming a casting by solidifying the molten metal.
[0009] A mold according to this disclosure comprises a sand mold having a cavity, and a coating layer disposed to cover the surface of the sand mold facing the cavity, and containing silica particles with an average particle size of 500 nm or less and refractory particles.
[0010] A mold coating agent according to this disclosure comprises silica particles with an average particle size of 500 nm or less, refractory particles, and a liquid portion in which the silica particles and refractory particles are dispersed. [Effects of the Invention]
[0011] According to the above-described method for manufacturing castings, mold, and mold coating agent, baining defects can be effectively suppressed. [Brief explanation of the drawing]
[0012] [Figure 1] Figure 1 is a schematic cross-sectional view showing the structure of the mold. [Figure 2] Figure 2 is a schematic cross-sectional view showing the structure near the surface of the sand mold facing the cavity. [Figure 3] Figure 3 is a flowchart showing the general procedure for manufacturing castings. [Figure 4] Figure 4 is a flowchart showing an example of the procedure for the coating layer formation process. [Figure 5] Figure 5 is a flowchart showing another example of the procedure for the coating layer formation process. [Figure 6] Figure 6 is a photograph of the surface of a casting corresponding to an experiment in which a cast iron casting was produced using a sand mold without forming a coating layer. [Figure 7] Figure 7 is a photograph of the surface of a casting corresponding to an experiment in which a cast iron casting was produced using a sand mold on which a coating layer was formed in the first procedure. [Figure 8] Figure 8 is a photograph of the surface of a casting corresponding to an experiment in which a cast iron casting was produced using a sand mold employing silica particles with an average particle size of more than 500 nm in the first procedure. [Figure 9] Figure 9 is a photograph of the surface of a casting corresponding to an experiment in which a cast iron casting was produced using a sand mold on which a coating layer was formed in the second procedure. [Figure 10] Figure 10 is a photograph of the surface of a casting corresponding to an experiment in which a cast iron casting was produced using a sand mold employing silica particles with an average particle size of more than 500 nm in the second procedure. [Figure 11] Figure 11 is a photograph of the surface of a casting corresponding to an experiment in which a casting made of cast steel was produced using a sand mold in which the addition of silica particles to the coating layer was omitted. [Figure 12] Figure 12 is a photograph of the surface of a casting corresponding to an experiment in which a casting made of cast steel was produced using a sand mold on which a coating layer was formed in the third step. [Figure 13] Figure 13 is a photograph of the surface of a casting corresponding to an experiment in which a casting made of cast steel was produced using a sand mold employing silica particles with an average particle size of more than 500 nm in the third step. [Figure 14]FIG. 14 is a photograph of the surface of a casting corresponding to an experiment of producing a steel casting using a sand mold employing silica particles having an average particle size exceeding 500 nm in the first procedure.
Embodiments for Carrying Out the Invention
[0013] [Summary of the Embodiment] The method for manufacturing a casting of the present disclosure includes a step of preparing a sand mold having a cavity, a step of forming a coating layer containing silica particles having an average particle size of 500 nm or less and refractory particles on the surface of the sand mold facing the cavity, a step of filling the cavity of the sand mold having the coating layer formed therein with molten metal, and a step of forming a casting by solidifying the molten metal.
[0014] The present inventors have studied measures for effectively suppressing veining defects. As a result, it has been clarified that by forming a coating layer containing fine silica (silicon dioxide; SiO2) particles having an average particle size of 500 nm or less in addition to refractory particles on the surface of the sand mold facing the cavity, veining defects can be effectively suppressed. The mechanism for suppressing veining defects is not particularly limited, but for example, it can be considered that when fine particles having an average particle size of 500 nm or less are adopted as silica particles, the molten metal is filled into the cavity, and the adhesiveness when the silica particles are vitrified is greatly improved. In the method for manufacturing a casting of the present disclosure, by forming a coating layer containing such fine silica particles on the surface of the sand mold facing the cavity, veining defects can be effectively suppressed.
[0015] In the above method for manufacturing a casting, the sand mold may contain a synthetic resin as a binder. As the binder of the sand mold used in the method for manufacturing a casting of the present disclosure, a synthetic resin is suitable. Examples of the adoptable synthetic resin include furan resin, phenol resin, alkaline phenol resin, urethane resin, and the like.
[0016] In the above-described method for manufacturing castings, the sand mold may contain furan resin as a binder. In furan self-hardening sand molds, which contain furan resin as a binder and harden through a chemical reaction, baing defects are prone to occur. The method for manufacturing castings of this disclosure, which can effectively suppress baing defects, is particularly suitable for manufacturing castings using a mold containing furan resin as a binder.
[0017] In the above-described method for manufacturing castings, the sand mold may contain natural silica sand as aggregate. While natural silica sand has the advantage of being less expensive than artificial sand, it has the disadvantage of being prone to baining defects. The method for manufacturing castings of this disclosure, which can effectively suppress baining defects, is particularly suitable for manufacturing castings using a mold containing natural silica sand as aggregate.
[0018] In the above method for manufacturing castings, the average particle size of the silica particles may be 100 nm or less. By using such fine silica particles, vaning defects can be suppressed even more effectively. The average particle size of the silica particles may be 5 nm or more.
[0019] In the above-described method for manufacturing a casting, the step of forming a coating layer may include the steps of applying a suspension in which silica particles and refractory particles are dispersed in a liquid to the surface of a sand mold facing the cavity, and drying the suspension to obtain a coating layer. By forming a coating layer using a suspension in which silica particles and refractory particles are dispersed in a solvent in this way, the method for manufacturing a casting according to this disclosure can be carried out while suppressing an increase in the number of steps.
[0020] In the above-described method for manufacturing a casting, the step of forming a coating layer may include the steps of forming a refractory layer containing refractory particles on the surface of a sand mold facing the cavity, applying a suspension in which silica particles are dispersed in a liquid to the surface of the refractory layer, and obtaining a coating layer by drying the suspension. Thus, the method for manufacturing a casting according to this disclosure can also be carried out by a process in which a refractory layer is formed and then a suspension containing silica particles is applied to form the coating layer.
[0021] The mold of this disclosure comprises a sand mold having a cavity, and a coating layer disposed to cover the surface of the sand mold facing the cavity, the coating layer containing silica particles with an average particle size of 500 nm or less and refractory particles. In the mold of this disclosure, a coating layer containing fine silica particles in addition to refractory particles is formed on the surface of the sand mold facing the cavity. As a result, according to the mold of this disclosure, baining defects can be effectively suppressed.
[0022] The mold coating agent of this disclosure comprises silica particles with an average particle size of 500 nm or less, refractory particles, and a liquid portion in which the silica particles and refractory particles are dispersed. By applying the mold coating agent of this disclosure to the surface of a sand mold facing the cavity and drying it, a coating layer containing fine silica particles in addition to refractory particles can be formed. As a result, the mold coating agent of this disclosure can effectively suppress baining defects.
[0023] [Specific examples of embodiments] Next, an example of a specific embodiment of the casting manufacturing method, mold, and mold coating agent of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals, and their descriptions will not be repeated.
[0024] First, a mold in one embodiment of the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is a schematic cross-sectional view showing the structure of the mold in this embodiment. Figure 2 is a schematic cross-sectional view showing the structure near the surface of the sand mold facing the cavity.
[0025] Referring to Figure 1, the mold 1 in this embodiment comprises a casting frame 10, a sand mold 20, and a coating layer 30. The sand mold 20 has a cavity 40, which is an internal space for filling with molten metal to form a casting (e.g., a machine part). The mold 1 is used, for example, to manufacture a component made of cast steel or cast iron.
[0026] The casting frame 10 is, for example, a wooden or metal frame. The casting frame 10 supports the sand mold 20 from the outer periphery. The sand mold 20 contains sand as aggregate and a binder. Artificial sand may be used as the sand, but in this embodiment natural silica sand is used. The binder is not particularly limited, but in this embodiment furan resin is used. The sand mold 20 in this embodiment is a furan self-hardening sand mold. The sand mold 20 includes a lower mold 21 and an upper mold 22. The lower mold 21 is positioned vertically below the upper mold 22 when the mold 1 is in use. The upper mold 22 is positioned vertically above the lower mold 21 when the mold 1 is in use.
[0027] The coating layer 30 is positioned to cover at least a portion of the cavity surface 20A, which is the surface of the sand mold 20 facing the cavity 40. In this embodiment, the coating layer 30 is positioned to cover the entire cavity surface 20A. The coating layer 30 may also be positioned to cover only a portion of the cavity surface 20A. The cavity 40 is formed when the upper mold 22 and the lower mold 21 are combined within the casting frame 10. The coating layer 30 may also be positioned only in areas where there is a risk of the casting and the mold 1 sticking together during casting.
[0028] The mold 1 has a flow path 50 formed therein, which serves as a communication passage connecting the outside of the mold 1 to the cavity 40. The flow path 50 has an opening on the surface of the upper mold 22 and is connected to the cavity 40 at the end opposite the opening. The flow path 50 functions as a supply route for molten metal to the cavity 40.
[0029] Referring to Figure 2, the coating layer 30 includes a surface layer 31 made of a mold coating composition containing silica particles and refractory particles, and a penetration layer 32 in which the mold coating composition has penetrated into the gaps 28 of the sand grains 29 constituting the sand mold 20. As the refractory particles, for example, at least one selected from the group consisting of oxide ceramics such as alumina, nitride ceramics such as silicon nitride, and graphite can be used. The silica particles have an average particle size of 500 nm or less. The average particle size of the silica particles may be 100 nm or less, 50 nm or less, 30 nm or less, or even 15 nm or less. The coating layer 30 is arranged to cover the cavity surface 20A, which is the surface of the sand mold 20 facing the cavity 40. The coating layer 30 contains silica particles with an average particle size of 500 nm or less and refractory particles. The average particle size of the refractory particles can be, for example, 10 μm or more and 30 μm or less.
[0030] In the mold 1 of this embodiment, a coating layer 30 containing fine silica particles in addition to refractory particles is formed on the cavity surface 20A. As a result, the mold 1 of this disclosure is a mold that can effectively suppress vaning defects.
[0031] Next, the general outline of the method for manufacturing castings in this embodiment will be described. Figure 3 is a flowchart showing the general procedure of the method for manufacturing castings. Figure 4 is a flowchart showing an example of the procedure for the coating layer formation process. Figure 5 is a flowchart showing another example of the procedure for the coating layer formation process. In the method for manufacturing castings in this embodiment, castings such as machine parts are manufactured by casting using the mold 1 of this embodiment described above.
[0032] Referring to Figure 3, in the casting manufacturing method of this embodiment, the first step (S10) is a sand mold preparation step. In this step (S10), referring to Figure 1, natural silica sand (aggregate) to which a binder, such as furan resin, and a hardening agent have been added in a predetermined ratio is kneaded to prepare the casting sand. A model having a shape corresponding to the cavity 40 (the shape of the casting product) is embedded in this casting sand. If left undisturbed, the furan resin dehydrates and condenses due to the action of the hardening agent, and the casting sand hardens. Subsequently, the casting sand is separated into a lower mold 21 and an upper mold 22, and the model is removed to obtain a sand mold 20 (lower mold 21 and upper mold 22) having a cavity 40. At this time, a model corresponding to the flow channel 50 can be embedded together and then removed to form the flow channel 50. The sand mold 20 may be manufactured using additive manufacturing technology.
[0033] Next, referring to Figure 3, a coating layer formation process is carried out as step (S20). In this step (S20), a coating layer 30 is formed on the lower mold 21 and the upper mold 22. Specifically, referring to Figure 4, a suspension coating process is first carried out as step (S21). In step (S21), a mold coating agent in the form of a suspension is used. The mold coating agent contains silica particles with an average particle size of 500 nm or less, refractory particles, and a liquid portion in which the silica particles and refractory particles are dispersed. The average particle size of the silica particles may be 100 nm or less. The mold coating agent can be made, for example, by adding refractory particles to colloidal silica containing silica particles with an average particle size of 500 nm or less. The colloidal silica may contain, for example, only 30% by mass or more and 50% by mass or less of silica particles. The average particle size of the refractory particles can be, for example, 10 μm or more and 30 μm or less. The dispersion medium constituting the liquid portion is not particularly limited, but for example, water or isopropyl alcohol can be used. The mold coating agent, which is a suspension prepared in this manner, is applied to the cavity surface 20A of the sand mold 20.
[0034] Next, a drying process is carried out as step (S22). In this step (S22), the mold coating agent applied in step (S21) is dried. By following the above steps (S21) to (S22), a coating layer 30 containing silica particles with an average particle size of 500 nm or less and refractory particles can be formed on the cavity surface 20A of the sand mold 20.
[0035] Step (S20) may be carried out by the following steps (S25) to (S27) instead of the above steps (S21) to (S22). Referring to Figure 5, first, a refractory layer formation step is carried out as step (S25). In this step (S25), for example, a suspension in which refractory particles of 10 μm to 30 μm in size are dispersed in water or ethanol is applied to the cavity surface 20A of the sand mold 20. A refractory layer is obtained by drying this suspension.
[0036] Next, a colloidal silica coating process is carried out as step (S26). In this step (S26), colloidal silica containing silica particles with an average particle size of 500 nm or less is coated onto the refractory layer formed in step (S25). As the dispersion medium for the colloidal silica, for example, water or isopropyl alcohol can be used.
[0037] Next, a drying process is carried out as step (S27). In this step (S27), the colloidal silica applied in step (S26) is dried. By following the above steps (S25) to (S27), a coating layer 30 containing silica particles with an average particle size of 500 nm or less and refractory particles can be formed on the cavity surface 20A of the sand mold 20. Note that steps (S25) and (S26) may be carried out in reverse order. That is, after colloidal silica containing silica particles with an average particle size of 500 nm or less is applied to the cavity surface 20A of the sand mold 20 (step (S26)), step (S25), which is the refractory layer formation step, may be carried out.
[0038] After process (S20) is carried out as described above, process (S30) is performed as the molten metal supply process. In this process (S30), referring to Figure 1, first the lower mold 21 and upper mold 22, on which a coating layer 30 is formed on the cavity surface 20A, are combined within the casting frame 10 to complete the mold 1. Next, molten metal is filled into the cavity 40 through the flow path 50. The molten metal can be, for example, molten cast steel or cast iron.
[0039] Next, referring to Figure 3, a solidification step is carried out as step (S40). In this step (S40), the molten metal filled into the cavity 40 in step (S30) is cooled and solidified. Cooling can be carried out, for example, by air cooling. This allows, for example, cast steel or cast iron to be formed into the desired shape.
[0040] Next, referring to Figure 3, the removal process is carried out as step (S50). In this step (S50), the product (casting) formed by the solidification of the molten metal in step (S40) is removed from the mold 1. Specifically, for example, the casting is removed from the inside by destroying the sand mold 20. After that, machining such as cutting, cutting, and grinding is carried out as needed to complete the casting, such as a machine part. Heat treatment may be carried out on the obtained casting as needed.
[0041] In the manufacturing method of mechanical parts according to this embodiment, a coating layer 30 containing fine silica particles is formed on the cavity surface 20A of the sand mold 20 in step (S20). As a result, the occurrence of vaning defects in steps (S30) to (S40) can be effectively suppressed. [Examples]
[0042] Experiments were conducted to confirm the effectiveness of the casting manufacturing method, mold, and mold coating agent described herein. The experimental procedure is as follows.
[0043] Multiple sand molds were prepared, each with the same shape and made of the same material. Additive-type sand molds were used. As a result, variations in shape and other characteristics between the multiple sand molds were reduced. Next, a coating layer containing silica particles with an average particle size of 500 nm or less and refractory particles was formed on the cavity surface of the sand mold. The coating layer was formed by one of the following procedures: the first procedure, performing steps (S21) and (S22) of the above embodiment in that order; the second procedure, performing steps (S25), (S26), and (S27) in that order; or the third procedure, performing steps (S26), (S25), and (S27) in that order. Afterward, molten cast iron or cast steel was supplied into the cavity of the sand mold and solidified to produce a casting. The casting was then removed from the sand mold. The surface of the casting was then observed to confirm the occurrence of baining defects (Example). For comparison, we prepared sand molds using silica particles with an average particle size exceeding 500 nm (specifically, an average particle size of 30 μm, with a particle size range of approximately 1 μm to 100 μm) instead of silica particles with an average particle size of 500 nm or less, sand molds without the addition of silica particles to the coating layer, and sand molds without the formation of a coating layer, and similarly produced castings, and conducted experiments to observe the surface of these castings (Comparative Example).
[0044] Figures 6 to 14 are photographs showing the surface observation results of the castings in the above experiment. Of these, Figures 6 to 10 are photographs of the surface of castings corresponding to the experiment in which molten cast iron was supplied into the cavity of a sand mold to produce a cast iron casting. Figures 11 to 14 are photographs of the surface of castings corresponding to the experiment in which molten cast steel was supplied into the cavity of a sand mold to produce a cast steel casting. The experimental results will be explained below with reference to Figures 6 to 14.
[0045] (1) Experiment to produce cast iron castings Figure 6 is a photograph of the surface of a casting corresponding to an experiment (comparative example) in which a cast iron casting was produced using a sand mold in which the formation of a coating layer was omitted. Figure 7 is a photograph of the surface of a casting corresponding to an experiment (example) in which a cast iron casting was produced using a sand mold in which a coating layer was formed in the first step. Figure 8 is a photograph of the surface of a casting corresponding to an experiment (comparative example) in which a cast iron casting was produced using a sand mold in which silica particles with an average particle size of more than 500 nm were used in the first step. Figure 9 is a photograph of the surface of a casting corresponding to an experiment (example) in which a cast iron casting was produced using a sand mold in which a coating layer was formed in the second step. Figure 10 is a photograph of the surface of a casting corresponding to an experiment (comparative example) in which a cast iron casting was produced using a sand mold in which silica particles with an average particle size of more than 500 nm were used in the second step.
[0046] Referring to Figure 6, when a sand mold without the formation of a coating layer is used, numerous baing defects A are observed on the surface of the casting. In contrast, as shown in Figure 7, when a sand mold (the sand mold in the embodiment of this disclosure) is used in which a coating layer containing silica particles with an average particle size of 500 nm or less is formed in the first step, the occurrence of baing defects is significantly suppressed. On the other hand, referring to Figure 8, when a sand mold using silica particles with an average particle size exceeding 500 nm is used in the first step, the effect of suppressing baing defects is not clear.
[0047] Furthermore, referring to Figure 9, it can be seen that when a sand mold (the sand mold in the embodiment of this disclosure) is used in which a coating layer containing silica particles with an average particle size of 500 nm or less is formed in the second step, the occurrence of vaning defects is significantly suppressed. On the other hand, when a sand mold is used in which silica particles with an average particle size exceeding 500 nm are employed in the second step, the effect of suppressing vaning defects is not clear.
[0048] As described above, in experiments to produce cast iron castings, it was confirmed that when a sand mold with a coating layer containing silica particles with an average particle size of 500 nm or less was used, the occurrence of vaning defects was significantly suppressed, regardless of the procedure for forming the coating layer.
[0049] (2) Experiment to produce a casting made of cast steel Figure 11 is a photograph of the surface of a casting corresponding to an experiment (comparative example) in which a casting made of cast steel was produced using a sand mold in which the addition of silica particles to the coating layer was omitted. Figure 12 is a photograph of the surface of a casting corresponding to an experiment (example) in which a casting made of cast steel was produced using a sand mold in which the coating layer was formed in the third step. Figure 13 is a photograph of the surface of a casting corresponding to an experiment (comparative example) in which a casting made of cast steel was produced using a sand mold in which silica particles having an average particle size of more than 500 nm were used in the third step. Figure 14 is a photograph of the surface of a casting corresponding to an experiment (comparative example) in which a casting made of cast steel was produced using a sand mold in which silica particles having an average particle size of more than 500 nm were used in the first step.
[0050] Referring to Figure 11, when a sand mold is used in which the addition of silica particles to the coating layer is omitted, numerous baing defects A are observed on the surface of the casting. In contrast, as shown in Figure 12, when a sand mold (the sand mold in the embodiment of this disclosure) is used in which a coating layer containing silica particles with an average particle size of 500 nm or less is formed in the third step, the occurrence of baing defects is significantly suppressed. On the other hand, referring to Figure 13, when a sand mold is used in which silica particles with an average particle size exceeding 500 nm are used in the third step, the effect of suppressing baing defects is not clear. Similarly, when a sand mold is used in which silica particles with an average particle size exceeding 500 nm are used in the first step, the effect of suppressing baing defects is not clear.
[0051] As described above, in experiments to produce castings made of cast steel, it was confirmed that the occurrence of baing defects was significantly suppressed by using a sand mold with a coating layer containing silica particles with an average particle size of 500 nm or less.
[0052] (3) Summary As described in (1) and (2) above, it has been confirmed that the method for manufacturing a casting using a sand mold (the sand mold of the embodiment of this disclosure) on which a coating layer containing silica particles with an average particle size of 500 nm or less is formed can effectively suppress the occurrence of baing defects, regardless of the procedure for forming the coating layer and regardless of whether the casting is made of cast iron or cast steel.
[0053] The embodiments and examples disclosed herein are illustrative in all respects and should be understood not to be restrictive in any way. The scope of the present invention is defined by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of Symbols]
[0054] 1 mold, 10 casting frame, 20 sand mold, 20A cavity surface, 21 lower mold, 22 upper mold, 29 sand grains, 30 coating layer, 31 surface layer, 32 permeation layer, 40 cavity, 50 flow path, A vaning defect.
Claims
1. The process of preparing a sand mold with a cavity, A step of forming a coating layer on the surface of the sand mold facing the cavity, the coating layer containing silica particles with an average particle size of 500 nm or less and refractory particles, A step of filling the cavity of the sand mold on which the coating layer is formed with molten metal, A method for manufacturing a casting, comprising the step of forming a casting by solidifying the molten metal.
2. The method for manufacturing a casting according to claim 1, wherein the sand mold contains a synthetic resin as a binder.
3. The method for manufacturing a casting according to claim 1, wherein the sand mold contains furan resin as a binder.
4. The method for manufacturing a casting according to claim 1, wherein the sand mold contains natural silica sand as aggregate.
5. The method for manufacturing a casting according to claim 1, wherein the average particle size of the silica particles is 100 nm or less.
6. The step of forming the aforementioned coating layer is: A step of applying a suspension in which the silica particles and the refractory particles are dispersed in a liquid to the surface of the sand mold facing the cavity, A method for producing a casting according to any one of claims 1 to 5, comprising the step of drying the suspension to obtain the coating layer.
7. The step of forming the aforementioned coating layer is: A step of forming a refractory layer containing the refractory particles on the surface of the sand mold facing the cavity, The process involves applying a suspension in which the silica particles are dispersed in a liquid to the surface of the refractory layer, A method for producing a casting according to any one of claims 1 to 5, comprising the step of drying the suspension to obtain the coating layer.
8. A sand mold with a cavity, A mold comprising a coating layer disposed to cover the surface of the sand mold facing the cavity, and containing silica particles with an average particle size of 500 nm or less and refractory particles.
9. Silica particles with an average particle size of 500 nm or less, Refractory particles and A mold coating agent comprising a liquid portion in which the silica particles and the refractory particles are dispersed.