Method for producing aluminum casting and hollow shell

Abstract

To provide a method for producing an aluminum casting by casting using a hollow shell obtained by efficiently manufacturing a hollow shell having strength suitable for casting.SOLUTION: A method for producing an aluminum casting includes: a first step of forming a hollow shell, the step including supplying a resin sand into a shell-forming mold; a second step of placing the hollow shell as a core in a casting mold, pouring a molten aluminum into the casting mold, solidifying it, and then taking an aluminum casting out of the casting mold; and a third step of discharging the hollow shell from the casting mold, wherein: the shell-forming mold has a curing-promoting part having a shape protruding toward an internal space in the vicinity of an inner surface; and, in the first step, a cured layer of the hollow shell is formed by the resin sand in contact with an inner surface of the shell-forming mold and a surface of the curing-promoting part.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an aluminum casting and a hollow shell used therein. [Background technology]

[0002] In the method of manufacturing aluminum or aluminum alloy castings (castings), a core is used to form recesses, hollows, etc. according to the shape of the casting. Casting is performed by pouring molten metal into the space (cavity) defined between the mold and the core. A "hollow shell" is sometimes used as a core for casting. A mold manufactured by the shell molding method is called a "shell." In this specification, a molded shell from which the unhardened layer has been expelled and which is hollow is called a "hollow shell."

[0003] The hollow shell is manufactured by feeding resin sand into a preheated shell mold, hardening the resin sand in contact with the mold using the heat of the shell mold, and then removing the unhardened excess resin sand to obtain a hollow shell. The resin sand may be resin-coated sand or a mixed sand of resin and silica sand.

[0004] When a hollow shell is placed in a casting mold for casting, if the hollow shell collapses due to the pouring of molten metal, this could lead to leakage of the molten metal or a defective casting shape, so the hollow shell needs to be strong enough to withstand the pouring of molten metal. On the other hand, after casting is completed, the hollow shell needs to be collapsed and discharged, so the hollow shell needs to have a moderate degree of collapsibility. From this perspective, a manufacturing method has been known in which the hollow shell is formed from two constituent layers (Patent Documents 1 and 2).

[0005] Patent Document 1 describes a two-layer shell mold manufacturing method in which a first shell mold layer is formed on the mold surface, and then a reinforcing second shell mold layer is formed on the first layer by scattering resin sand for the second layer onto the first layer through a shielded portion having a different degree of opening. Patent Document 2 describes a method for manufacturing a two-layer shell mold, which includes the steps of (a) filling the pattern space of a heated molding die with thermosetting resin-coated sand for the outer layer using an underblow method, then ejecting the uncured sand to form the outer layer on the pattern surface, and then inverting the molding die, and (b) filling the outer layer formed in the above step with thermosetting resin-coated sand for the inner layer using a topblow method to integrate the two layers, and returning the molding die to its original position as needed to eject the uncured sand. The outer layer has an integrated structure formed in at least a portion of the shell mold, and the outer layer is formed with a larger grain size index than the inner layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 57-175056 [Patent Document 2] Japanese Patent Application Publication No. 10-166106 Summary of the Invention [Problem to be solved by the invention]

[0007] When the thickness of the layers forming the mold structure of a shell is thin, the strength of the mold decreases. Patent Documents 1 and 2 propose a manufacturing method in which a second layer (inner layer) is overlaid on a first layer (outer layer) to form two layers in order to compensate for the lack of strength of the shell and ensure the necessary strength. However, in conventional manufacturing methods, the second layer is formed after the first layer is formed. The two layers are formed by repeating a series of steps, such as supplying resin-coated sand, hardening it, removing excess sand, and firing, twice. This increases the working time and work procedures, leading to higher manufacturing costs.

[0008] In view of the above problems, the present invention aims to efficiently produce a hollow shell having strength suitable for casting, and to provide a method for producing an aluminum casting by casting using the obtained hollow shell. [Means for solving the problem]

[0009] As a result of investigations to achieve the above object, the inventors discovered that the curing of the resin sand filled in the shell molding die can be accelerated by providing a protruding portion in the vicinity of the inner surface of the shell molding die, and thus completed the present invention. Specifically, the present invention includes the following aspects (1) to (5).

[0010] (1) a first step of molding a hollow shell, including dispensing resin sand into a shell mold; a second step of placing the hollow shell as a core in a casting mold, pouring molten aluminum into the casting mold, solidifying the molten aluminum, and then removing the aluminum casting from the casting mold; a third step of collapsing the hollow shell contained in the aluminum casting and ejecting the hollow shell from the casting mold; A method for manufacturing an aluminum casting comprising: the shell molding die has a curing accelerating portion near the inner surface and having a shape that protrudes into the internal space, A method for manufacturing an aluminum casting, wherein in the first step, a hardened layer of the hollow shell is formed by the resin sand in contact with the inner surface of the shell molding die and the surface of the hardening accelerating portion.

[0011] (2) The method for producing an aluminum casting according to (1) above, wherein in the first step, the resin content of the resin sand is 2.0 mass% or less.

[0012] (3) A method for producing an aluminum casting according to (1) above, wherein the first step comprises placing a placing core in the shell molding die to form the hollow shell.

[0013] (4) The method for producing an aluminum casting according to (1) above, wherein in the second step, a load applied from the molten aluminum to one side surface of the hollow shell is 100 N or more.

[0014] (5) A hollow shell used in the method for producing an aluminum casting according to any one of (1) to (4) above, a recessed portion corresponding to the hardening accelerating portion; The hollow shell has a thickness of 5 mm or more around the recessed portion. [Effects of the Invention]

[0015] According to the present invention, hollow shells having strength suitable for casting can be efficiently produced, and therefore, in a method for producing aluminum castings in which the hollow shells are used for casting, casting defects and poor casting performance can be prevented, contributing to a reduction in production costs. [Brief explanation of the drawings]

[0016] [Figure 1] 1A and 1B are schematic diagrams illustrating the first step according to the present embodiment, in which (a) shows the arrangement of the molding die and resin sand, (b) shows the process of filling the molding die with resin sand, and (c) shows the process of forming a hardened layer of resin sand. [Figure 2] FIG. 10 is a schematic diagram for explaining a first step according to the present embodiment, showing a process of discharging an unhardened layer of the shell. [Figure 3] 1A is a schematic diagram illustrating a molding die and a shell according to the present embodiment, showing how the shell is produced in the molding die equipped with a curing-accelerating portion, FIG. 1B is a diagram showing how the shell is removed from the molding die, and FIG. 1C is a diagram showing the appearance of the molded shell. [Figure 4] FIG. 10 is a schematic diagram illustrating a second step according to the present embodiment. [Figure 5]1A and 1B are diagrams for explaining a method for measuring the pressure and load of molten aluminum acting on a hollow shell according to the present embodiment, in which (a) is a schematic diagram of the hollow shell as viewed from the X direction, and (b) is a schematic diagram showing the side region of the hollow shell. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments, and can be practiced with appropriate modifications within the scope of the object of the present invention. In this specification, the expression "X to Y" (X and Y are arbitrary numerical values) means "at least X and at most Y."

[0018] (Aluminum casting manufacturing method) The method for producing an aluminum casting according to this embodiment comprises the following steps: a first step of forming a hollow shell, which includes supplying resin sand into a shell-forming mold; a second step of placing the hollow shell as a core in a casting mold, pouring molten aluminum into the casting mold, allowing it to solidify, and then removing the aluminum casting from the casting mold; and a third step of collapsing the hollow shell contained in the aluminum casting and ejecting it from the casting mold.

[0019] A "casting" is a cast product manufactured by casting. The "aluminum casting" according to this embodiment refers to a cast product (casting) obtained by casting molten aluminum or aluminum alloy.

[0020] (1st step) The manufacturing method according to this embodiment includes a first step of molding a hollow shell, which involves supplying resin sand into a shell molding die. FIGS. 1(a) to 1(c) and 2 are schematic diagrams illustrating the first step. As shown in FIGS. 1(a) to 1(c) and 2, the hollow shell is manufactured using a molding device having a shell molding die and a raw material storage container containing resin sand. Hereinafter, the "shell molding die" may also be referred to as a "molding die."

[0021] As shown in FIG. 1(a), the molding die 1 is composed of two shell molding die members 1a and 1b (hereinafter referred to as "molding die members"). The two molding die members 1a and 1b are joined together to form an internal space 4. The upper end of the molding die 1 has an opening 2 that leads to the internal space 4 of the molding die 1. The molding die 1 is heated to a predetermined temperature by a heating means (not shown). A raw material storage container 8 is placed on the upper surface of the molding die 1. The molding die 1 shown in FIG. 1(a) has a placement core 7 placed on its lower end. The placement core will be described later. After the two molding die members are joined and fixed, the molding die is heated to a predetermined temperature. Known conditions can be used for various parameters, such as the temperature, when heating the molding die. For example, the heating temperature can be selected from the range of 100°C to 500°C.

[0022] Next, as shown in FIG. 1(b), resin sand 9 is supplied from a raw material storage container 8 into the internal space 4 of the molding die 1 through the opening 2. When supplying the resin sand, for example, pressurized gas is introduced into the raw material storage container and the resin sand is blown into the internal space of the molding die, thereby filling the molding die with the resin sand. As shown in FIG. 1(c), the filled resin sand 9 hardens upon contact with the heated inner surface 5 of the molding die 1, forming a hardened layer 12. In this specification, the heat treatment in which the molding die is heated to harden the resin sand is referred to as a "baking treatment."

[0023] After the hardened layer 12 is formed, as shown in FIG. 2, the molding die 1 is inverted, and the unhardened resin sand 13 is discharged from the molding die 1 through the opening 2. This "discharging the resin sand" is sometimes referred to as "discharging sand." The hardened shell 10 is then removed from the molding die, yielding the desired hollow shell. Note that the sand discharge process may be performed without inverting the molding die. For example, the resin sand can be discharged through an opening provided separately from the opening for introducing the resin sand.

[0024] After the fired shell is removed from the mold, the mold members are closed. Because the mold is heated, resin sand can be introduced into the mold again and the firing process repeated to continuously produce shells. Therefore, it is preferable to continue heating the mold during the sand removal and removal steps.

[0025] The resin sand used in this embodiment may be resin-coated sand in which silica sand is coated with a thermosetting resin, or mixed sand in which a small amount of thermosetting resin is mixed with silica sand. The thermosetting resin contained in the resin sand comes into contact with the heated inner surface of the molding die and is thermally cured to form a cured layer. Examples of the thermosetting resin include phenolic resin, urea resin, melamine resin, unsaturated polyester resin, and epoxy resin. Phenolic resin is particularly preferred.

[0026] (shell molding mold) The shell molding die used in the manufacturing method according to this embodiment is characterized by having a curing-accelerating portion near its inner surface that protrudes into the interior space. Figure 3(a) is a schematic diagram showing how a shell is produced in the shell molding die according to this embodiment, and Figure 3(b) is a schematic diagram showing how the shell is removed from the molding die, with the uncured layer omitted. The molding die 1 is composed of a pair of mold members 1a and 1b, and an interior space 4 is formed by closing the molding die 1. The interior surface 5, which is the surface of the molding die facing the interior space, has a shape that matches the outer shape of the hollow shell to be produced. Resin sand 9 filled into the interior space 4 of the molding die 1 comes into contact with the heated interior surface 5 and hardens, forming a shell 10 of a predetermined shape.

[0027] However, depending on the shape of the internal space of the molding die, there may be areas where the thickness of the cured layer is thin. Therefore, as shown in Figures 3(a) and 3(b), by arranging a curing-accelerating portion 3 having a shape that protrudes into the internal space 4 in the region near the inner surface 5, the curing of the resin sand 9 is accelerated, and the thickness of the cured layer 12 in the shell 10 can be increased. A hollow shell 11 is obtained by removing the uncured resin sand 13 from the shell 10 obtained in Figure 3(b). Figure 3(c) is a schematic diagram showing the appearance of the hollow shell 11. The cross section in Figure 3(b) shows the shape located at cross section AA in Figure 3(c).

[0028] (hardening acceleration part) The first step involves forming a hardened layer on the hollow shell using resin sand in contact with the inner surface of the shell mold and the surface of the hardening accelerator. The "low shell strength area" shown in Figure 3(a) refers to an area where the shell mold or the core is not heated sufficiently, resulting in an insufficient hardened layer thickness to withstand the load applied by the molten metal during casting. Typically, the inner surface of the mold where the core is placed is more difficult to heat than the inner surface of other areas, making it difficult to form a hardened layer of sufficient thickness. Insufficient shell strength can lead to "sinking" during the casting of aluminum castings, impairing the function of the hollow shell. Sinking occurs when the wall of the hollow shell breaks during the pouring process, allowing molten metal to penetrate the shell through the break, forming a lump in the hollow portion of the casting and resulting in a defective product.

[0029] 3(a) and 3(b), when a first hardened layer 14 is formed by the resin sand 9 in contact with the inner surface 5 of the molding die 1, the hardening accelerating portion 3 arranged near the inner surface 5 is also heated in the same manner as the inner surface 5, and therefore a second hardened layer 15 is formed by the resin sand 9 in contact with the surface 6 of the hardening accelerating portion 3. As a result, the first hardened layer 14 and the second hardened layer 15 join together to form a third hardened layer 16 with an increased thickness.

[0030] By employing the first step according to this embodiment, the hardened layer formed around the protruding hardening-accelerating portion and the hardened layer of the thinner portion formed in contact with the inner surface of the molding die merge together to form a thick hardened layer, thereby obtaining a hollow shell exhibiting high strength. The hollow shell according to this embodiment can withstand the load applied from the molten aluminum during casting and easily collapses during the sand removal process after casting, thereby enabling the production of aluminum castings with excellent productivity and casting quality.

[0031] Regarding the location where the curing accelerating portion is provided, the distance between the tip of the protruding portion and the inner surface of the molding die closest to the protruding portion is preferably 3 to 15 mm. If this distance is less than 3 mm, there is a risk that the resin sand will not be filled sufficiently. If it exceeds 15 mm, there is a risk that the hardened layers will separate and will not contribute to increasing the strength of the hollow shell. In addition, it is preferable to provide the curing accelerating portion near a portion where it is expected that the resin sand will not be heated sufficiently during shell molding, or near a portion where it is expected that a large force will be applied during casting when the shell is used as a core.

[0032] (hollow shell) The hollow shell according to this embodiment can be used in the above-described method for manufacturing an aluminum casting. In the first step, the hollow shell is molded using a molding die having a hardening accelerating portion, so that a concave recessed portion 17 is formed in the shell portion corresponding to the protruding hardening accelerating portion. This recessed portion also needs to be strong enough to withstand the pouring of molten metal, so the periphery of the recessed portion preferably has a thickness of 5 mm or more.

[0033] (Resin amount in resin sand) The resin content of the resin sand can be selected depending on the shell shape, molding conditions, casting conditions, etc. As explained in the third step below, the hollow shell ejected from the casting mold together with the aluminum casting must be collapsed and removed from the casting. Efficient removal contributes to improving the productivity of aluminum castings. Therefore, it is preferable that the hollow shell has appropriate shell collapsibility. If the resin content of the resin sand is too high, the hardened layer will be too thick and have too much strength, making it difficult to collapse the shell after casting. From this perspective, in order to improve the shell's collapsibility, the resin content is preferably 2.0% by mass or less, and may be 1.5% by mass or less.

[0034] (Replaced core) In the first step, the hollow shell may be formed by placing a "placed core" in the shell molding die. A placed core is a core used mainly to create shapes for parts that cannot be formed using the mold's extraction mechanism, and in this specification, it refers to a core separate from the hollow shell. As shown in Figure 1, a "placed core" can be placed in the molding die 1, and molding can be performed to create a mold structure that combines a hollow shell 11 and a placed core 7. Such a mold structure makes it easy to create cast products with complex shapes.

[0035] When using a molding die with a mounting core, the filled resin sand is heated through the mounting core. Because heat from the inner surface of the molding die is difficult to transfer to the surface of the "mounting core," it is difficult to form a sufficiently thick hardened layer in the resin sand region in contact with the "mounting core." In the molding die according to this embodiment, the hardening accelerating portion is arranged within the molding die so that the hardened layer formed in contact with the surface of the mounting core and the hardened layer formed in contact with the hardening accelerating portion merge. The term "merging" as used above means that the two hardened layers are formed by joining together. Thus, the first step according to this embodiment is advantageous in that it can form a hollow shell strong enough to withstand the pouring of molten metal during casting.

[0036] (2nd process) The method for producing an aluminum casting according to this embodiment includes a second step of placing the hollow shell as a core in a casting mold, pouring molten aluminum into the casting mold, solidifying it, and then removing the aluminum casting from the casting mold. A known casting method can be applied to the casting mold depending on the desired shape of the casting. For example, gravity casting, die casting, etc. may be used. In this embodiment, "molten aluminum" refers to molten aluminum or an aluminum alloy.

[0037] FIG. 4 is a schematic diagram illustrating the casting mold, hollow shell, and aluminum casting in the second step. As shown in FIG. 4, a casting mold 20 is used by combining a pair of casting mold members 20a and 20b. After the hollow shell is placed in the casting mold, molten aluminum is poured into the internal space formed between the inner surface 21 of the casting mold 20 and the hollow shell 11, producing an aluminum casting 22. During this process, the load of the molten aluminum is applied to the side surface of the hollow shell. If the hollow shell is damaged by this load, it can cause casting defects in the resulting casting. Therefore, the hollow shell needs to be strong enough to withstand the pouring of molten aluminum.

[0038] The hollow shell formed in the first step has a strength that can withstand pouring, and therefore can be cast satisfactorily in the second step even if the load applied to one side of the hollow shell from the molten aluminum during casting is 100 N or more. This is therefore preferable in terms of improving the degree of freedom in designing the feeder means during casting, the shape of the casting, etc.

[0039] (3rd step) The method for manufacturing an aluminum casting according to this embodiment includes a third step of disintegrating the hollow shell contained in the aluminum casting and removing the sand. After casting is completed, the hollow shell is incorporated into the aluminum casting. The hollow shell is then disintegrated by any disintegrating means and removed from the casting mold. A device called a shell breaker can be used as the disintegrating means. [Example]

[0040] Examples of the present invention will be described below, but the present invention is not limited to the following description.

[0041] (Aluminum casting manufacturing) In the first step, a preheated core (made of spheroidal graphite cast iron) was placed in a shell molding die (hereinafter referred to as the "molding die"), which was made by combining a pair of mold members. The mold members were then fixed, and the molding die 1 was heated to 300°C and maintained at that temperature. Resin-coated sand was then blown into the molding die. The resin-coated sand hardened by contact with the inner surface of the molding die. The resin-coated sand was held in the molding die and subjected to a baking treatment, after which the molding die was released and opened. The unhardened resin-coated sand was then ejected from the molding die, and the hardened shell was removed from the molding die to obtain a hollow shell. The distance between the preheated core and the hardened layer formed by the hardening-accelerating portion of the molding die was set to 8 mm during the molding die design stage so that they would merge.

[0042] Next, the second step was performed to obtain an aluminum casting by gravity casting. Specifically, molten aluminum in which an aluminum alloy was melted was prepared, and the hollow shell obtained in the first step was placed as a core in a casting mold. The molten aluminum was then poured into the internal space formed by the casting mold and the hollow shell. After the molten aluminum was solidified, the aluminum casting was removed from the casting mold.

[0043] Next, the third step was carried out, in which the hollow shell contained in the aluminum casting was broken down by a shell breaker, and the sand was discharged (sand discharged) from the casting mold.

[0044] The appearance of the obtained aluminum casting was visually observed. No casting defects such as submersion were visible in the aluminum casting, and it was found to have good properties. From this, it was confirmed that the hollow shell of the example had strength suitable for casting.

[0045] (Pressure and load of molten aluminum applied to hollow shell) Here, we investigated the pressure and load of the molten aluminum (hereinafter simply referred to as "molten metal") applied to the hollow shell in the second casting step. As shown in FIG. 5(a), we measured the depth H of the molten metal applied to the hollow shell as viewed in the X direction shown in FIG. 4, and the area A of region 26 on the side of the hollow shell when viewed in cross section in the X direction. Region 26 is the portion shown in FIG. 5(b). Using these measured values, we calculated the pressure and load of the molten metal applied to the side of the hollow shell. This is explained below.

[0046] As shown in FIG. 5(a), the casting mold 20 has a gate 23 at its top for pouring molten metal into the casting mold. The molten metal poured through the gate 23 descends and fills the interior space of the casting mold 20. The load of the molten metal presses against the inner surface 21 of the casting mold 20 and one side surface 24 and the opposite side surface 25 of the hollow shell 11. The filled molten metal then solidifies to produce a casting 22 of a predetermined shape. Here, focusing on the one side surface 24 and the opposite side surface 25 of the hollow shell that are pressed by the load of the molten metal (hereinafter, these side surfaces will be referred to as the "pressing surfaces"), the pressure and load of the molten aluminum acting on the pressing surfaces of the hollow shell were determined.

[0047] The pressure of the molten metal applied to the pressing surface of the hollow shell (hereinafter referred to as "molten metal pressure") varies depending on the depth of the molten metal, so the molten metal pressure at the center of the hollow shell was calculated as the average molten metal pressure. The above molten metal pressure was used to evaluate the load applied to the hollow shell. As shown in Figure 5(a), the distance from the sprue to the center of the pressing surface was defined as "depth H." The mass of the molten metal at depth H is expressed as mass per unit area M by the following formula: M (kg / m 2 ) = H (m) × molten aluminum density (kg / m 3 )

[0048] The molten metal pressure P (unit: Pa, unit: kg / m s) acting on the hollow shell 2 ) is the mass per unit area M (kg / m 2 ) to the gravitational acceleration of 9.80 (m / s 2 ) and calculated using the following formula (1). P (Pa) = H (m) × density of molten aluminum (kg / m 3 )×9.80(m / s 2 )...Equation (1)

[0049] The load of the molten metal applied to the hollow shell is the area A (m 2 ) by the molten metal pressure P (Pa). In this example, the calculation results for the molten metal pressure P on the hollow shell and the load F (unit: N) applied to one pressing surface of the hollow shell are shown in Table 1.

[0050] [Table 1]

[0051] As shown in Table 1, the hollow shell according to this embodiment was able to be cast properly without breakage even when a load F of 100 N or more was applied to one side surface. From the above, it was confirmed that the method for manufacturing an aluminum casting according to this embodiment has a useful effect in preventing casting defects and poor casting. [Explanation of symbols]

[0052] 1. Shell molding mold 1a, 1b Shell molding die members 2 Opening 3 Hardening acceleration part 4. Interior space 5. Inner surface of shell molding die 6 Surface of the hardening accelerating part 7 Placed core 8 Raw material storage container 9 Resin Sand 10 shells 11 Hollow Shell 12 Hardened layer 13 Uncured resin sand 14 First hardened layer 15 Second hardened layer 16 Third hardened layer 17 Recessed part 20 Casting mold 20a, 20b Casting mold members 21 Inner surface of casting mold 22 Aluminum Castings 23 Spout 24 One side of the hollow shell 25 Opposite side of hollow shell 26 Side area of ​​a cross-section of a hollow shell H Depth

Claims

1. a first step of forming a hollow shell, the first step including dispensing resin sand into a shell mold; a second step of placing the hollow shell as a core in a casting mold, pouring molten aluminum into the casting mold, allowing it to solidify, and then removing the aluminum casting from the casting mold; a third step of collapsing the hollow shell contained in the aluminum casting and ejecting the hollow shell from the casting mold; A method for manufacturing an aluminum casting comprising: the shell molding die has a curing accelerating portion near the inner surface and having a shape that protrudes into the internal space, In the first step, a hardened layer of the hollow shell is formed by the resin sand in contact with the inner surface of the shell molding die and the surface of the hardening accelerating portion.

2. 2. The method for producing an aluminum casting according to claim 1, wherein the resin content of the resin sand in the first step is 2.0 mass % or less.

3. 2. The method for manufacturing an aluminum casting according to claim 1, wherein the first step comprises placing a place core in the shell molding die to form the hollow shell.

4. 2. The method for manufacturing an aluminum casting according to claim 1, wherein in the second step, a load applied from the molten aluminum to one side surface of the hollow shell is 100 N or more.

5. A hollow shell used in the method for producing an aluminum casting according to any one of claims 1 to 4, a recessed portion corresponding to the hardening accelerating portion; The hollow shell has a thickness of 5 mm or more around the recessed portion.

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