JPH0698458B2 - Core for pressure casting and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a core used for pressure casting such as a die casting method and a method for producing the same.

(Prior Art) Generally, when casting a casting 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 water pressure, so that the inner wall of the hollow portion of the casting after casting has a shell. Part of the core sand that composes the core may get caught. Then, when a casting in which a part of the core sand is bitten is used as a product, the core sand is separated from the inner wall of the hollow portion during use and is mixed with a liquid such as oil or water flowing in the hollow portion. Therefore, in order to prevent such a situation from occurring, for example, as disclosed in JP-B-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. To have.

(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 the liquid sagging phenomenon makes the distribution in the layer more uneven.

When the distribution state of the mica in the outermost surface layer (second coating layer) becomes non-uniform as described above, the degree of shrinkage due to the heating during the layer formation, that is, the drying during the formation of the entire layer varies, and the layer becomes uneven. There is a possibility that a crack will occur in the case, when casting is performed using the shell core in which this crack has occurred, there is a problem that the molten metal is inserted from the crack occurrence location into the core body composed of the shell core, that is, the resin coated side. Occurs.

The present invention has been made in view of the above points, and an object thereof is to specify the components constituting the outermost surface layer of the core to make the distribution state of the components uniform in the layer. In this way, a pressure casting core that can prevent the occurrence of cracks by eliminating the variation in the degree of shrinkage of the layer due to heating during layer formation, that is, during drying, and can suppress the insertion of the molten metal into the core body during casting. To provide.

Furthermore, the present invention is to provide a manufacturing method for efficiently manufacturing the above-mentioned core.

(Means for Solving the Problem) In order to achieve the above object, the solution means of the present invention is to provide a core body with a first coating layer made of powdered refractory and metal oxide on the outer surface thereof. Form. Further, a second coating layer made of powdered boron nitride is formed on the first coating layer.

Furthermore, the present invention, as a manufacturing method for manufacturing the above core, first, a powder 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, and then a drying step is performed. After that, the first coating layer is formed.
Then, a solution in which powdery boron nitride is dispersed in a solvent is applied on the first coating layer, and then a drying step is performed to form a second coating layer.

(Operation) With the above configuration, in the present invention, the outer surface of the core body is
The first coating layer is formed by applying and drying a slurry liquid in which powdered refractory and metal oxide are dispersed in a solvent,
Then, a solution in which powdery boron nitride is dispersed in a solvent is applied and dried on the first coating layer to form a second coating layer. The boron nitride forming the second coating layer has a property that it has good dispersibility and has a wettability (affinity) with respect to a molten metal such as an aluminum alloy that is not better than that of mica. Therefore, when the solution in which the boron nitride is dispersed in the solvent is applied on the first coating layer of the core body, the boron nitride is uniformly dispersed in the solvent and is formed through the subsequent drying process. Since the distribution state of boron nitride is made uniform in the second coating layer to be formed, the second coating layer does not have cracks due to the variation in the degree of shrinkage of the layer at the time of heating. Since the wettability with the molten metal is not good even when occurs, the degree of insertion of the molten metal from the cracked portion is small, and therefore the insertion of the molten metal into the core body during casting is reliably suppressed.

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

FIG. 1 and FIG. 2 show a two-division type of pressure casting according to an embodiment of the present invention including a first core 1 and a second core 2 applied when casting a rotor of an automobile rotary engine. 2 shows the child 3, and the first and second both of the core 3
Since the cores 1 and 2 have the same configuration except that the shapes are different, the first core 1 will be described below, and the same components of the second core 2 will be designated by the same reference numerals. The detailed description will be omitted.

Reference numeral 4 denotes a core body of the first core 1,
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 by applying a slurry liquid in which a powdery refractory material or a metal oxide is dispersed in a solvent to the outer surface of the core body 4 and then performing a drying process, for example, 100 It is formed to a layer thickness of ˜350 μm. This first
The reason for setting the layer thickness of the coating layer 5 in the above range is that if it is less than 100 μm, cracks may occur due to the water pressure during casting, while if it exceeds 350 μm, it is proportional to the increase in the layer thickness of the molten metal for the core body 4. This is because such an intrusion prevention effect cannot be expected and may adversely affect the dimensional accuracy of the first core 1. 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, Mg
O 25.0% by weight, ZrO ₂ 0.5% by weight, C 6.0% by weight and other 4.5% by weight are dispersed in ethyl alcohol as a solvent and diluted to 50%.

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, flat boron nitride powder having an average particle diameter of 5 to 15 μm. A solution dispersed in a solvent is applied onto the first coating layer 5 and then dried to form a layer thickness of, for example, 10 to 50 μm in which boron nitride is uniformly distributed. The reason why the particle size of the boron nitride constituting the second coating layer 6 is set within the above range is that it is difficult to manufacture particles having a particle size of less than 5 μm, whereas if it exceeds 15 μm, it becomes difficult to densify the layer. This is because there is a risk of infiltration of molten metal. The reason for setting the layer thickness of boron nitride in the above range is that if it is less than 10 μm, cracks may occur due to the molten metal pressure during casting, whereas if it exceeds 50 μm, it is proportional to the increase in the layer thickness of the molten metal with respect to the core body 4. This is because the effect of preventing penetration cannot be expected. As the solution in which the above-mentioned boron nitride is dispersed in a solvent, for example, a mixture of 50% by weight of boron nitride and 50% by weight of ethyl alcohol 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 method for manufacturing the pressure casting core 3 according to the above embodiment will be described.

First, resin molding sand is filled in a molding die and then fired to mold each core body 4 of the first and second cores 1 and 2. Thereafter, the operation of immersing each core body 4 in the slurry liquid compounded as described above is repeated a suitable number of times to dip and coat the slurry liquid on the outer surface of the core body 4, and then the above-mentioned slurry liquid is coated. Each core body 4 is carried into a drying step, and dried, for example, under conditions of a drying temperature of 100 ° C. and a drying time of 20 minutes to form a first coating layer 5 of 150 μm on the outer surface of each core body 4.

Next, a solution in which boron nitride is dispersed in ethyl alcohol as described above is applied onto the first coating layer 5 by spray coating, or the core body 4 on which the first coating layer 5 is formed is immersed in the above solution. The second coating layer 6 having a thickness of 20 μm is formed on the first coating layer 5 by immersing it and drying it under the same drying conditions as those for forming the first coating layer 5.

In this way, the first and second cores 1 and 2 in which the first and second coating layers 5 and 6 are formed on the outer surfaces of the core bodies 4 and 4 in this manner are The core 3 is formed by interposing the reinforcing material 7 so that the first core 1 is on the upper side and the second core 2 is on the lower side. The core 3 is formed from the upper mold 8 and the lower mold 9. Is placed in a mold 10 and a 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, so that a rotor 12 of a rotary engine as shown in FIG. To cast. FIG. 5 shows the relationship between the penetration depth of the molten metal A into the core 3 and the layer thicknesses of the first and second coating layers 5 and 6 at this time.
This data shows that the casting pressure is 700 Kg / cm ² and the melt temperature is 730-75.
Comparative example (I) in which the second coating layer 6, that is, the layer of boron nitride is not provided and only the first coating layer 5 is provided,
What is indicated by the one-dot chain line is the layer thickness on the first coating layer 5.
Example (I) of the present invention in which the second coating layer 6 having a thickness of 10 μm is provided.
The embodiment (II) of the present invention in which the second coating layer 6 having a layer thickness of 50 μm is provided thereon, and the solid line shows the present invention in which the second coating layer 6 having a layer thickness of 20 μm is provided on the first coating layer 5. Example (III) of

According to this data, in the comparative example (I), unless the layer thickness of the first coating layer 5 is increased to about 250 μm, the penetration of the molten metal A into the core body 4 cannot be suppressed,
It can be seen that the penetration depth of the molten metal A reaches about 0.38 mm at the set layer thickness of 150 μm in this embodiment. On the other hand, in Example (I) of the present invention, the thickness of the first coating layer was about 180.
It can be seen that the effect of preventing the intrusion of the molten metal A into the core body 4 is obtained when the thickness is at least μm. In addition, in this Example (III), the thickness of the first coating layer is about 150 μm, and the penetration depth of the molten metal A is about 0.1.
2mm and total layer thickness of the first and second coating layers 0.1
It can be seen that the molten metal A has not reached the core body 4 below 7 mm. The same can be said for Example (II) of the present invention in which the second coating layer is thicker than that of Example (III). In Example (II), the second coating layer has a thickness of about 100 μm or less. It is understood that the molten metal A does not reach the core body 4 unless it becomes. Therefore, at the set layer thickness (150 μm) of the first coating layer 5, it is sufficient to secure a layer thickness of 20 μm or more as the layer thickness of the second coating layer 6 for suppressing the intrusion of the molten metal A into the core body 4. .

FIG. 6 shows the relationship between the penetration depth of the molten metal A into the core body 4 and the casting pressure when the second coating layer 6 is composed of mica and boron nitride.
What is indicated by the broken line is a second coating layer composed of mica particles having an average particle diameter of 3 μm, and the first coating layer having a thickness of 100 μm.
Comparative example (II) formed on the coating layer 5, the solid line indicates that the second coating layer 6 made of boron nitride having an average particle diameter of 10 μm is formed on the first coating layer 5 so that the layer thickness becomes 50 μm. It is the embodiment (IV) of the present invention. The first coating layer 5 is set to the same layer thickness as 150 μm in each example.

According to this data, in the comparative example (II), 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. On the other hand, in Example (IV), the casting pressure is set to the set pressure (70
The penetration depth of the molten metal A does not exceed the total layer thickness of 0.25 mm of the first and second coating layers until it becomes more than 0 kg / cm ² ) and becomes approximately 850 kg / cm ^2.
No insertion into the core body 4 was observed. Further, in Example (IV), the wettability (affinity) of the boron nitride layer forming the outermost surface layer of the core 3 to the molten metal A is not as good as in the case of forming the mica layer. 1 and 2
Even if cracks occur in the coating layers 5 and 6, the core body 4
There is also an advantage that the degree of insertion of the molten metal A from the above-mentioned crack occurrence location with respect to is smaller than that in the case of the mica layer. Further, since the boron nitride layer may be thinner than the mica layer, there is also an effect that the dimensional accuracy of the core is good.

Further, in the above manufacturing method, only boron nitride is used as the second coating layer 6 forming the outermost surface of the core 3, and there is no need to employ a special means for forming the second coating layer 6, and the molten metal is not required. The insertion into the core body 4 of A can be efficiently suppressed.

In the above embodiment, the core bodies 4, 4 are shown to be made of resin coated sand, but not limited to this, it is also possible to adopt self-hardening sand such as cement sand or fine plaster of particles. This is possible, and the core 3 need not be limited to the split type. And, apart from this embodiment,
When the core body 4 is made of gypsum having fine particles as described above, the first coating layer 5 may be omitted and the second coating layer 6 may be directly formed on the core body 4. In this case, even if a crack is generated in the second coating layer 6, the wettability thereof is not good, so that the penetration of the molten metal A into the core body 4 can be suppressed as much as possible.

Further, in the above embodiment, the case of casting the rotor 12 of the rotary engine of the automobile is shown, but the present invention is not limited to this.
It is needless to say that the present invention can be applied to the case where casting products other than cylinder blocks, cylinder heads, and other automobile parts are cast.

(Effects of the Invention) As described above, according to the present invention, attention is paid to characteristics such as good dispersibility of boron nitride in a solution, and the outermost core of the core is prepared by a solution in which this boron nitride is dispersed in a solvent. Since the second coating layer forming the surface is formed, it is possible to form a second coating layer in which boron nitride is evenly distributed, and in addition to the poor wettability of boron nitride with respect to the molten metal, the formation of the molten metal during casting The insertion into the core body can be reliably suppressed.

Further, according to the manufacturing method of the present invention, it is possible to efficiently manufacture a core having the above-described effect of suppressing the insertion of the molten metal into the core body without using any special means.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a pressure casting core according to an embodiment of the present invention of a two-division type applied when casting a rotor of a rotary engine of an automobile, and FIG. 2 is an enlarged vertical front view of the same. The figure is a vertical sectional front view showing the casting state of the rotor,
FIG. 4 is a perspective view of the cast rotor, FIG. 5 is data showing the layer thickness of the first and second coating layers and the penetration depth of the molten metal, and FIG. 6 is the second coating layer composed of a mica layer. 3 is data showing the penetration depth of the molten metal into the core of the molten steel and that of boron nitride. 4 ... core body, 5 ... first coating layer, 6 ... second coating layer.

Claims (2)

[Claims] 1. A core body, a powdery refractory formed on the outer surface of the core body, a first coating layer made of a metal oxide, and a powdery layer formed on the first coating layer. And a second coating layer made of boron nitride. 2. A first coating layer is formed by applying a slurry liquid in which a powdery refractory material and a metal oxide are dispersed in a solvent to the outer surface of a core body and then performing a drying step. A method for producing a core for pressure casting, comprising forming a second coating layer by applying a solution in which powdery boron nitride is dispersed in a solvent onto the first coating layer and then performing a drying step.