JPH0677795B2 - Pressure casting manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a cast product made of an aluminum alloy having a hollow portion by a pressure casting method such as a die casting method.

(Prior Art) Generally, when casting a cast product having a hollow portion by a pressure casting method such as a die casting method, the molten metal is inserted into the shell core by the hot water pressure, so that the inner wall of the hollow portion of the cast product is cast. There is a risk that some of the core sand that composes the shell core will be bitten. When a cast product in which a part of the core sand is bitten is used as a product, it is separated from the inner wall of the hollow part of the core sand during use and is mixed with liquid such as oil or water flowing in the hollow part. In order to prevent such a situation from occurring, for example, as disclosed in Japanese Patent Publication No. 60-15418, a powdered refractory and colloidal silica were mixed on the surface of the shell core. The slurry core is applied and dried to form a first coating layer, and then an aqueous solution of mica is applied onto the first coating layer to form a second coating layer, thereby forming a shell core with the first coating layer. It is known that the surface of the core is made smooth and the pressure of the molten metal acting on the surface of the core is made uniform, and the infiltration of the molten metal into the shell core is suppressed by the second coating layer. Has been.

(Problems to be Solved by the Invention) However, since the outermost surface layer (second coating layer) of the shell core formed as described above has poor dispersibility of mica particles in the aqueous solution of mica, Is difficult to be uniformly distributed in the layer, and since the particles are large, the liquid sagging phenomenon makes the distribution in the layer more uneven.

When the distribution state of the mica particles in the outermost surface layer (second coating layer) becomes non-uniform as described above, the degree of shrinkage due to heating during the layer formation, that is, during the drying of the entire layer varies, and There is a risk of cracks occurring in the layer, and when casting is performed using a shell core in which this crack has occurred, the molten metal is inserted from the crack occurrence point into the shell core, that is, the core body composed of resin coated sand. The problem occurs.

Further, as described above, even if no crack is generated in the mica layer on the outermost surface of the core body, the crack is likely to occur due to the action of the water pressure during casting, and a particularly concave surface is exhibited. In the above core, the mica layer is likely to be peeled off due to contraction. Therefore, when pressure casting is performed using the core in such a state, the occurrence frequency of cracks in the mica layer is further increased.

Then, when the core is removed from the cast product after casting under such circumstances, there is a possibility that a part of the mica layer or core sand may remain attached to the inner wall of the hollow part of the cast product, and this mica layer or When a cast product is used as a product with a part of the core sand remaining adhered, the core will not be used during use, just like the core made of only core sand that does not form the mica layer as the molten metal invasion suppression layer as described above. A part of the mica layer or core sand may be separated from the inner wall of the hollow portion and may be mixed with a liquid such as oil or water flowing in the hollow portion.

The present invention has been made in view of the above point, and the purpose thereof is to perform pressure casting of a cast product made of an aluminum alloy, and in this case, specify a component constituting the outermost surface layer of the core. In addition, by taking appropriate measures on the cast product prior to the core removal work performed after casting, the distribution state of the components that make up the outermost surface layer of the core is In addition, the outermost surface layer can be easily separated from the cast product when the core is removed, and the degree of shrinkage of the outermost surface layer of the core due to heating during layer formation, that is, during drying, can be improved. It is possible to eliminate the occurrence of cracks due to the dispersion of the heat and cracks due to the effect of the molten metal pressure during casting, and to prevent the molten metal from being inserted into the core body during casting, and to ensure a cast product with a good casting surface. Cast into It is to to so that.

(Means for Solving the Problems) In order to achieve the above object, the solution means of the present invention is as follows. First, a powdery refractory material, a slurry liquid in which a metal oxide is dispersed in a solvent is applied to the outer surface of the core body. A core having a first coating layer formed by coating and drying on a first coating layer, and a second coating layer formed by coating and drying a solution in which graphite particles are dispersed in a solvent on the first coating layer. prepare. Then, the core is placed in a mold and a molten aluminum alloy is injected and pressurized to cast a cast product, and aluminum carbide is formed by the reaction between the molten metal and the graphite particles of the second coating layer. It is formed on the surface of the second coating layer. Then, the cast product is taken out from the mold together with the core and then contacted with water to corrode the aluminum carbide layer thus produced. After that, the core is removed from the cast product.

(Operation) According to the method of the present invention having the above-described structure, in the method of the present invention, the core having the coating layer of graphite particles formed on the outermost surface is placed in the mold, and the molten aluminum alloy is injected and pressurized to form a hollow casting. The product is cast and then the core is removed from the cast product.

In this case, the graphite particles forming the outermost surface layer of the core have a property that the particle size is small and can withstand a relatively high casting pressure as compared with the mica particles, and therefore, with the mica layer. The distribution state in the outermost surface layer is as uniform as possible compared to the case where it is formed, and as a result, cracks due to variations in layer shrinkage due to heating of the outermost surface layer of the core during layer formation, that is, during drying. Occurrence of
The generation of cracks due to the action of the molten metal pressure during casting is eliminated, the insertion of the molten metal into the core body during casting is suppressed, and a cast product with a good casting surface is cast.

Also, during this pressure casting, aluminum in the molten metal reacts with the graphite particles in the coating layer of the core that come into contact with the molten metal to produce aluminum carbide. The aluminum carbide has a property of easily reacting with water, and when it comes into contact with water, the aluminum carbide layer corrodes to generate a corrosion product. This corrosion product is very brittle and subtle vibrations break the layer. Thereafter, the cast product taken out together with the core from the mold is once contacted with water prior to the removal of the core, so that this contact causes the aluminum carbide to react with water and corrode, so that the aluminum carbide The layer is easily broken, and the core is easily separated from the cast product, so that the cast product having a good casting surface in which the core-constituting substance does not remain on the inner wall of the hollow portion can be more reliably cast.

(Example) Hereinafter, the Example of this invention is described based on drawing.

First, before explaining the method of the present invention, the core 1 used in the method
The configuration will be described with reference to FIGS. 1 and 2. First
The core 1 shown in FIG. 2 and FIG. 2 is of a split type for rotor casting of a rotary engine of an automobile.
The core 2 and the second core 3 are vertically divided into two parts, and the first and second cores 2 and 3 are the same except that they have different shapes. The child 2 will be described, and the same components of the second core 3 will be denoted by the same reference numerals and detailed description thereof will be omitted.

4 is a core body of the first core 2,
Is molded by, for example, filling a resin-coated sand obtained by mixing 200 mesh sand with a phenol resin as a binder into a core molding die (not shown) heated and held at about 250 ° C.

The first coating layer 5 is formed on the outer surface of the core body 4.
The first coating layer 5 is formed on the outer surface of the core body 4 by applying a slurry liquid in which a powdery refractory material and a metal oxide are dispersed in a solvent, and then, for example, a drying temperature of 100
The layer is formed to have a layer thickness of, for example, 100 to 350 μm by undergoing a drying step under conditions of a temperature of 20 ° C. and a drying time of 20 minutes. The reason for setting the layer thickness of the first coating layer 5 in the above range is 10
If it is less than 0 μm, cracks may occur due to the molten metal pressure during casting, while if it exceeds 350 μm, the effect of preventing penetration that is proportional to the increase in the layer thickness of the molten metal on the core body 4 cannot be expected. This is because the accuracy may be adversely affected. The composition of the slurry liquid is, for example, SiO ₂ 57.5% by weight, Al ₂ O ₃ 2.0% by weight, Fe ₂ O ₃ 4.0% by weight, CaO 0.5% by weight, MgO 25.0%.
% By weight, 0.5% by weight of ZrO ₂ , 6.0% by weight of C, and others 4.
5% by weight dispersed in ethyl alcohol as a solvent and diluted to 50% is used.

Further, a second coating layer 6 is formed on the first coating layer 5 of the core body 4, and the second coating layer 6 is, for example, a solution in which graphite particles having an average particle size of 0.5 to 10 μm are dispersed in a solvent. Is applied on the first coating layer 5 and then a drying step is performed to form a layer thickness of 10 to 50 μm. The reason for setting the particle size of the graphite particles forming the second coating layer 6 in the above range is 0.5
If the thickness is less than 10 μm, it is difficult to manufacture. On the other hand, if the thickness exceeds 10 μm, it is difficult to densify the layer, and there is a risk of infiltration of the molten metal. The reason why the layer thickness of the graphite particles is set within the above range is that if the thickness is less than 10 μm, cracks may occur due to the water pressure during casting, while if it exceeds 50 μm, the core body 4
This is because the effect of preventing intrusion proportional to the increase in the layer thickness of the molten metal cannot be expected. The graphite particles may be spherical or flaky, but the flaky shape is particularly effective in preventing penetration. As the solution in which the above graphite particles are dispersed in a solvent, for example, a mixture of 50% by weight of graphite particles and 50% by weight of water as a solvent is used.

The drying conditions for forming the first and second coating layers 5 and 6 are, for example, a drying temperature of 100 ° C. and a drying time of 20 minutes, but are not limited thereto. Any drying temperature and drying time may be used as long as they can vaporize the volatile components in the respective constituent solutions.

Next, a case will be described in which a rotor of a rotary engine of an automobile is cast using the pressure casting core 1 configured as described above.

First, a first coating layer 5 having a thickness of 150 μm is formed on the outer surface of the core body 4, and a second coating layer 6 having a thickness of 30 μm and made of graphite particles having a particle size of 1 μm and having a flake shape is laminated on the first coating layer 5. The first and second cores 2, 3
As shown in FIG. 3, the core 1 is assembled by interposing the reinforcing member 7 so that the first core 2 is on the upper side and the second core 3 is on the lower side.
To form. The core 1 is placed in a mold 10 composed of an upper mold 8 and a lower mold 9, and the molten metal A of an aluminum alloy is injected into the mold 10 at a pressure of 700 kg / cm ² by the operation of a plunger 11. The rotor 12 of the rotary engine as shown in FIG. 4 is cast. The relationship between the penetration depth of the molten metal A into the core 1 and the casting pressure at this time is shown in FIG.
In the figure, what is indicated by a broken line is a comparative example (I) in which a second coating layer made of mica particles having an average particle diameter of 3 μm is formed on the first coating layer 5 so that the layer thickness is 100 μm Shown is an embodiment (I) of the present invention in which a second coating layer 6 made of flaky graphite particles having an average particle size of 1 μm is formed on the first coating layer 5 so that the layer thickness is 10 μm, and further, What is indicated by the solid line is a second graph made of graphite particles having an average particle size of 1 μm, which is the same as in the above-mentioned Example (I).
This is Example (II) of the present invention in which the coating layer 6 is formed on the first coating layer 5 so that the layer thickness is 30 μm. The first coating layer 5 is set to the same layer thickness as 150 μm in each example.

According to this data, in Comparative Example (I) above, when the casting pressure was about 600 kg / cm ² , the penetration depth of the molten metal A was 0.3 mm, and the total layer thickness of the first and second coating layers was 0.25 mm.
It can be seen that the molten metal A has reached the core body 4 beyond. Further, in the above-mentioned embodiment (I), when the casting pressure is about 700 kg / cm ² which is the set pressure in this embodiment, the molten metal A is
Has not yet reached the core body 4, and has a thinner layer thickness than Comparative Example (I) and has an effect of preventing the intrusion of the molten metal A. In addition, since the layer thickness is thin, the dimensional accuracy of the core is good. Further, in the present embodiment (II), the penetration depth of the molten metal A is about 1st and ^2nd up to about 950kg / cm ² which is far higher than the set pressure (700kg / cm ² ).
The total thickness of the coating layer exceeds 0.18 mm, and therefore, at the above set pressure, no insertion into the core body 4 of the molten metal A is observed as in Example (I), but in this Example (II) It can be seen that the insertion of the molten metal A can be suppressed more reliably than in Example (I).

As another experimental data, the maximum fluctuation value of the layer thickness before and after the formation of the second coating layer 6, that is, before and after the drying process, was obtained.
In Example (I) of the present invention, the variation of the layer thickness is larger in Example (I) using a graphite layer having a thinner layer thickness than in Comparative Example (I) using a mica layer having a large layer thickness of 5 μm. It was found that the use of graphite particles rather than mica particles can withstand a high casting pressure with a smaller layer thickness, and a stable core 1 with less dimensional accuracy and less cracking can be obtained. Further, this shows that the radius of curvature can be made smaller in the thin graphite layer of the coating layer than in the thick mica layer of the coating layer at the same pressure resistance, and the present invention can be carried out more than the comparative example (I). The example (I) has an advantage that the effect of suppressing the insertion of the molten metal A from the joint can be further improved when, for example, a core is used in combination.

Further, as another experimental data, the comparative example (I) and the example (II) of the present invention were applied to a core having a concave surface with a radius of curvature of 50 mm, and each second coating layer 6, 6 in the drying process was applied. When the presence or absence of peeling was examined, peeling was observed in the second coating layer 6 in Comparative Example (I), but no peeling was observed in Example (II) of the present invention. Therefore, when pressure casting is performed in such a state, in Comparative Example (I), the frequency of cracks in the second coating layer 6 becomes high and the molten metal A is inserted into the core body 4. In the case of the example (II), the frequency of cracks in the second coating layer 6 can be suppressed to a low level, and the molten metal A can be suppressed from being inserted into the core body 4 as much as possible.

Therefore, when pressure-casting the second coating layer 6 in which the thickness of the second coating layer 6 fluctuates greatly and is peeled off as in the comparative example (I), cracks are easily generated in the second coating layer 6 and the molten metal A becomes the core body. However, in the present embodiment, since the variation in the thickness of the second coating layer 6 is small and the second coating layer 6 does not peel off as described above, the intrusion of the molten metal A can be reliably suppressed, and therefore the casting The rotor 12 with good skin can be cast.

In the pressure casting, the aluminum of the molten metal A,
The second coating layer 6 of the core 1 in contact with the molten metal A
The aluminum carbide is generated by the reaction with the graphite particles. This aluminum carbide has the property of easily reacting with water. Moreover, upon contact with water, the aluminum carbide layer corrodes, producing corrosion products. This corrosion product is very brittle and subtle vibrations break the layer.

Then, after pressure casting the rotor 12 as described above,
The rotor 12 is taken out of the mold 10 together with the core 1 and then immersed in water for about 1 to 2 hours. At this time, the aluminum carbide is corroded by the reaction with water,
Rotor with fragile layers of aluminum carbide
The detachment of the core 1 from the 12 is facilitated.

Then, the core 1 is disintegrated by the action of external force such as vibration and water injection and removed from the hollow portion of the rotor 12. As a result, the second coating layer 6, that is, the graphite particles, do not remain on the inner wall of the hollow portion of the rotor 12 and are removed so that the rotor 12 having a good casting surface can be obtained more reliably.

In the above embodiment, the core bodies 4 and 4 are shown to be made of resin coated sand, but the present invention is not limited to this, and it is possible to adopt self-hardening sand such as cement sand or plaster. Yes, and the core 1 need not be limited to the split type.

Further, in the above embodiment, the rotor 12 of the rotary engine of the automobile is shown as a pressure casting product, but the present invention is not limited to this.
Needless to say, the present invention is also applicable to the case of casting a cylinder block, a cylinder head, or other cast products other than automobile parts.

(Effect of the Invention) As described above, according to the method of the present invention, first, the core having the coating layer of graphite particles formed on the outermost surface of the core body is placed in the mold, and then the core is placed in the mold. A cast product is cast by pouring and pressurizing a molten aluminum alloy, and at the same time, the molten metal and graphite particles in the coating layer react with each other to generate aluminum carbide on the surface of the coating layer. Subsequently, the cast product was taken out from the mold together with the core, and was then contacted with water to corrode the aluminum carbide layer thus produced, and then the core was removed from the cast product.
Therefore, compared with the case where the outermost surface layer of the core is composed of a mica layer, the distribution state in the outermost surface layer is as uniform as possible, which allows the core to be formed during layer formation, that is, during drying. It is possible to cast a product with good casting surface by eliminating the occurrence of cracks caused by the variation in the layer shrinkage due to the heating of the outer surface layer, and reliably suppressing the insertion of the molten metal into the core body during casting. .

Also, aluminum carbide produced by the reaction of the molten aluminum during the pressure casting with the graphite particles of the coating layer of the core that comes into contact with the molten metal, and the water produced by the subsequent contact with water. Since it reacts and corrodes, it is possible to destroy the aluminum carbide layer with a slight vibration, which facilitates the removal of the core from the cast product and ensures a cast product with a good casting surface. Can be cast into.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a two-division type pressure casting core applied when casting a rotor of an automobile rotary engine, FIG. 2 is an enlarged front view of the same longitudinal section, and FIG. 3 is a rotor casting state. FIG. 4 is a perspective view of the rotor which is cast, and FIG. 5 is data showing the depth of penetration of the molten metal into the core during casting. 1 ... Core, 4 ... Core body, 5 ... First coating layer, 6
… Second coating layer, 10… Mold, 12… Rotor, A…
Molten metal.

Claims (1)

[Claims] 1. A first coating layer formed by coating and drying a slurry liquid in which a powdery refractory material and a metal oxide are dispersed in a solvent on the outer surface of a core body, and graphite particles are dispersed in the solvent. A core having a second coating layer formed by applying the dried solution onto the first coating layer and drying is prepared, the core is placed in a mold, and a molten aluminum alloy is injected and pressurized. By casting the cast product by
Forming aluminum carbide on the surface of the second coating layer by the reaction between the molten metal and the graphite particles of the second coating layer, and then removing the cast product together with the core from the mold and then contacting it with water. A method for producing a pressure cast product, comprising: corroding the aluminum carbide layer produced as described above, and then removing the core from the cast product.