JPH0685975B2 - Manufacturing method of core for pressure casting - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a method for manufacturing a core used for pressure casting such as a die casting method.

(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 separates 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, a powdered refractory and colloidal silica were mixed on the surface of the shell core as disclosed in, for example, Japanese Patent Publication No. 60-15418. The slurry liquid is applied and dried to form a first coating layer, and then the first coating layer is formed.
By applying the aqueous solution of mica on the coating layer to form the second coating layer, the surface of the shell core is smoothed by the first coating layer, and the water pressure acting on the surface of the core is made uniform. It is known that the second coating layer is used to suppress the infiltration of the molten metal into the shell core.

(Problems to be Solved by the Invention) However, in the above-described conventional one, since the method of sequentially applying the slurry liquid and the aqueous solution of mica to the surface of the shell core, the slurry liquid applied to the surface of the shell core and The aqueous solution of mica drips during drying, resulting in non-uniform thickness of the formed first and second coating layers, resulting in a non-smooth outermost surface of the shell core. As a result, the shell core is used in combination. In this case, there is a problem in that a gap is formed in the mating surface portions of both shell cores and molten metal is inserted from this gap.

The present invention has been made in view of the above points, and an object thereof is to take appropriate means for smoothing the coating layer formed on the outermost surface of a core such as a shell core as described above. Therefore, when the cores are used in combination, a gap does not occur in the mating surface portions of both cores, and thus it is possible to reliably suppress the insertion of the molten metal from the core mating surface portions, and It is to be able to cast a casting with good skin.

(Means for Solving the Problem) In order to achieve the above object, the solution means of the present invention is as follows. First, a solution in which fine particles or flat particles of graphite or mica are dispersed in a solvent is applied to the molding surface of the core molding die. After coating, a volatile component in the solution is evaporated by a drying process to form a first coating layer. Next, a powdery refractory material and a metal oxide are dispersed in a solvent to apply a slurry solution on the first coating layer, and then the molding die is filled with core sand. After that, the core body is molded by firing the core sand by passing through a heating step,
Volatile components in the slurry liquid are evaporated to form a second coating layer. After that, the core molded by the above firing is taken out from the mold.

(Operation) With the above configuration, in the method of the present invention, since the first coating layer forming the outermost surface layer of the core is applied and formed on the molding surface of the core molding die, the first coating layer is applied and formed. Even if dripping occurs during the process, this dripping occurs not on the outermost surface of the core, but on the side of the second coating layer that is subsequently formed on the surface, so that the outermost surface of the finally molded core is According to the shape of the molding surface, it will be finished in the desired smooth state.

Therefore, when using cores in combination, no gap is created in the mating surface portions of both cores, and the insertion of the molten metal from the core mating surface portions is reliably suppressed, and a casting with good casting surface is cast. Will be done.

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

FIG. 1 shows a manufacturing process of a core manufacturing method for pressure casting according to an embodiment of the present invention. First, a core molding die 1 as shown in FIG. 1 (a) is prepared. Then, as shown in FIGS. 1B and 1C, a solution in which fine particles or flat particles of graphite or mica are dispersed in a solvent (hereinafter, referred to as the first coating template 2
That is, the operation of injecting into the core molding die 1 and then discharging the core molding die 1 is repeated a suitable number of times to form a first coating die material layer 3 having a predetermined thickness on the formation surface thereof. In this case, when the first coating material 2 is a coating material of graphite particles, for example, the average particle size is 0.
Water as a solvent is added to 5 parts by weight of 5 to 10 μm graphite particles.
In the case of a coating material for mica particles, for example, 80 parts by weight of mica particles having an average particle diameter of 2 to 10 μm and 20 parts by weight of water glass (sodium silicate) as a solvent are used. The mixture is used in each proportion. The reason why the particle diameters of graphite and mica particles are set in the above ranges is that the lower limit is a manufacturing problem, and the upper limit is the densification of the first coating layer 3'formed by the subsequent drying process. This is difficult to do and there is a risk of molten metal infiltration during casting.

Next, the mold 1 coated with the first coating material layer 3 is carried into a drying step, and the first coating material layer 3 is dried under the conditions of a drying temperature of 100 ° C. and a drying time of 30 minutes, for example. As shown in FIG. 1 (d), the volatile components of the first coating material layer 3 are evaporated to form a first coating layer 3 '. By drying in this manner, the influence of the application of the second coating material to be applied later, that is, the second coating material is mixed into the first coating material layer 3 and the thickness of the first coating material layer 3 becomes uneven. Can be prevented. This first coating layer 3 '
The layer thickness of the graphite layer is, for example, 10 to 50 μm.
In the case of a mica layer, the thickness is, for example, 50 to 150 μm. In this way, the reason why the layer thickness of graphite and mica is set in the above range is that when the graphite layer is less than 10 μm, cracks may occur due to hot water pressure during casting.
This is because if it exceeds 50 μm, the effect of preventing intrusion in proportion to the increase in the layer thickness of the molten metal on the core body 6 ′ to be molded thereafter cannot be expected, and in the case of the mica layer, it is less than 50 μm like the above graphite layer. In this case, cracks may occur due to the melt pressure during casting, but if it exceeds 150 μm, an effect of preventing penetration that is proportional to the increase in the layer thickness of the melt with respect to the core body 6 ′ that is subsequently molded cannot be expected.

After that, a slurry liquid in which powdery refractory and metal oxide are dispersed in a solvent (not shown, hereinafter referred to as second coating material)
In a manner similar to that shown in FIGS. 1 (b) and 1 (c), the operation of injecting into the core molding die 1 having the first coating layer 3'formed thereon and then discharging it is repeated a suitable number of times to obtain the first As shown in FIG. 6E, the second coating material layer 5 having a predetermined thickness is applied and formed on the first coating layer 3 '. In addition, the second
As the combination composition of the mold coating material, for example, 55.5 parts by weight of SiO ₂ , A
lO ₃ 2.0 parts by weight, Fe ₂ O ₃ 4.0 parts by weight, CaO 0.5 parts by weight, MgO
25.0 parts by weight, ZrO ₂ 0.5 parts by weight, C 6.0 parts by weight, others 4.
5 parts by weight dispersed in ethyl alcohol as a solvent and diluted to 50% are used.

Then, as shown in FIG. 1 (f), after the core sand 6 is filled in the molding die 1, the heating step is performed under the conditions of a heating temperature of 250 ° C. and a heating time of 20 minutes. As shown in (g), the core sand 6 is fired to form a core body 6 '.
And the volatile component, that is, ethyl alcohol, in the second mold coating material layer 5 is evaporated and, for example, 100 to 350
A second coating layer 5 ′ having a layer thickness of μm is formed, and the shell core 7 is molded. As the core sand 6 used for molding the core 7, for example, resin coated sand obtained by mixing 200 mesh sand with a phenol resin as a binder is used.
The reason why the layer thickness of the second coating layer 5'is set within the above range is that if the thickness is less than 100 μm, cracks may occur due to the water pressure during casting, while if it exceeds 350 μm, the molten metal for the core body 6 ' This is because the effect of preventing penetration that is proportional to the increase in layer thickness cannot be expected, and the dimensional accuracy of the shell core 7 may be adversely affected.

Thereafter, the molding die 1 is opened and the shell core 7 molded by the firing is taken out from the molding die 1.

In the shell core 7 molded in this way, since the first coating layer 3'is in contact with the molding surface of the molding die 1 when the first coating layer 3'that is the outermost surface layer thereof is formed, No liquid dripping occurs during the drying process of the first coating material 2 on the molding surface side, so that the outer surface of the first coating layer 3 ', that is, the outermost surface of the shell core 7 is formed into the shape of the molding surface. By doing so, the desired smoothness can be achieved.

Therefore, when casting the rotor 8 of a rotary engine of an automobile as shown in FIG. 2, as shown in FIG. 3 for casting the rotor 8, the split type cores 7a, 7b which are divided into upper and lower parts are used. Molded as described above, the cores 7
As shown in FIG. 4, the combination of a and 7b is arranged in a mold 11 composed of an upper mold 9 and a lower mold 10, and the molten metal A is injected into the mold 11 by the operation of a plunger 12.
In this case, the two cores 7a, 7b are combined in a normal state so that no gap is generated in the mating surface portions thereof, so that the insertion of the molten metal from the core 7a, 7b mating surface portions can be reliably suppressed. In addition to this, it is possible to cast a casting having a good casting surface.

In the above embodiment, the core body 6'is made of resin coated sand. However, the core body 6'is not limited to this and may be made of self-hardening sand such as cement sand. In (1), a molding die made of plastic is used to cure the self-hardening sand by microwave heating to mold the core body.

(Effects of the Invention) As described above, according to the method of the present invention, first, the first coating layer forming the outermost surface layer of the core is formed on the molding surface of the molding die, and then the first coating layer is formed. A second coating layer was formed on the top, and then the core sand was filled in the mold. Therefore, even if dripping occurs in the process of forming the first and second coating layers, the dripping occurs not on the mold side but on the second coating layer side, and finally the core of the molded core is formed. The outer surface will be finished to the desired smooth state, so when using the cores in combination, there will be no gap between the mating surface parts of both cores, and this will result in It is possible to reliably prevent the molten metal from being inserted, and it is possible to cast a casting having a good casting surface.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram showing a method for manufacturing a core for pressure casting according to an embodiment of the present invention, FIG. 2 is a perspective view showing a state in which a rotor of a rotary engine of an automobile is taken out from a mold, and FIG. 3 is a rotor. FIG. 4 is an exploded perspective view showing a split type core for casting, and FIG. 4 is a vertical sectional front view showing a cast state of the rotor. 1 ... Mold, 2 ... First coating material, 3 ... First coating material layer, 3 '... First coating layer, 5 ... Second coating material layer, 5' ... Second coating layer, 6 ... Core sand, 6 '
...... Core body, 7 ... Shell core.

Claims (1)

[Claims] 1. A solution in which fine particles or flat particles of graphite or mica are dispersed in a solvent is applied to a molding surface of a core molding die, and then a drying step is performed to evaporate volatile components in the solution. 1 coating layer is formed, and then, a powdery refractory material, a slurry liquid in which a metal oxide is dispersed in a solvent is applied on the first coating layer, and then core sand is filled in the mold. After that, the core sand is baked by a heating process to form the core body, and the volatile components in the slurry liquid are evaporated to form the second coating layer. A method for producing a core for pressure casting, which comprises taking out a molded core from a molding die.