JPS61286039A - Casting method - Google Patents

Abstract

PURPOSE:To eliminate large casting flashes and to improve the quality of a casting by adjusting the suction pressure in an upper casting mold to the pressure smaller than the suction pressure in a lower casting mold and executing casting while preventing deformation of the mold mating surfaces at the peripheral edge of the cavity. CONSTITUTION:The open surfaces of flask bodies 1, 2 are coated with shielding sheets 12, 12. The upper casting mold M1 and the lower casting mold M2 which are hermetically sealed with internal heat insulating packing materials 11, 11 are formed. The upper and lower molds M1, M2 are mated and the cavity 13 is formed between both molds. A molten metal is thereafter poured into the cavity 13 by using the sprue 14 and vent hole 15 of the mold M1. The suction pressure in the mold M1 is acted smaller than the suction pressure in the mold M2 until the molten metal solidifies. More specifically, the downward pressure is always acted on the bottom surface of the mold M1 by adjusting the difference in the internal pressure between the upper and lower molds M1, M2, the own weight of the material 11 in the mold M1 and the pressure reducing power thereof, by which the mold mating surfaces P1, P2 of the molds M1, M2 are brought into tight contact with each other without space. The generation of a wedge-shaped space between the surfaces P1 and P2 is thus obviated and the generation of the flashes is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a casting method for forming a casting using a vacuum molding method.

[Conventional technology]

As is well known, in the vacuum molding method, the open surface of the frame is sealed with a shielding sheet made of vinyl acetate resin, etc., and the inside is kept in a reduced pressure state using suction means, while aggregate (equivalent to foundry sand) is molded under atmospheric pressure. The filling material (made of heat-resistant particles) is bonded and fixed in the frame so that it does not lose its shape, and the molten metal is poured into the cavity formed between the upper and lower molds to perform casting.
Since no binder is required, the flow of the hot water is good, and the filler can be used repeatedly without any modification, it is ideal for the mass production of cast products with flat shapes.

[Problem that the invention seeks to solve]

However, when casting using the above molding method,
For the upper and lower molds M1 and M2, after pulling out the model for forming the cavity 13 between both collar molds and 9M2, the upper and lower molds M1. After matching the molds of M2 and completing pouring,
Until the molten metal solidifies, the interiors of the upper and lower molds M1 and M2 are maintained in a final reduced pressure state by suction means. that time,
Both guard type M1. M2 mold matching surface P□.

Since the suction force acting on P2 acts at right angles to the shielding sheet, when the insides of both flanges M, M, are suctioned with the same pressure, the periphery of the cavity 13 and the upper and lower molds N□2M2
Mold matching surface P1. A circular deformed part 16, 17 as shown in Fig. 3 is formed at the ridge line where P2 intersects, and this deformed part is formed by the mold N and the internal filler 11 relative to the lower surface of the upper mold section before mold matching. Due to the additional weight of the
As shown in FIG. 4, this occurs more in the upper mold A than in the lower mold M2. Therefore, when performing mold matching, the mold matching surface p1. p,
Since a gap S having a wedge-shaped cross-section is created in the cavity 13, when molten metal is injected into the cavity 13, the molten metal enters the gap S, resulting in a large casting at the periphery of the casting. However, there are problems in that it takes a lot of effort to remove using a chisel, a grinder, etc. in a later process, and it also significantly impairs the appearance of the product.

The main purpose of the present invention is to create a casting in which there is almost no risk of large castings occurring in the product even when this type of molding method is used, and even if castings are formed, the amount of casting removal is very small. The goal is to establish a new and improved casting method.

[Means for solving problems]

The casting method according to the present invention was developed to achieve the above-mentioned object in a simple manner, and includes filling the inside of the frame with a filler made of heat-resistant particles.

In a casting method, a pair of upper and lower molds whose upper and lower open surfaces are sealed with a shielding sheet and maintained in a reduced pressure state by internal suction means are put together, and the mold is poured into a cavity formed between the upper and lower molds to form a casting. It is characterized in that the suction pressure in the upper mold is lower than the suction pressure in the lower mold to perform casting while preventing a gap from forming on the mold mating surface at the periphery of the cavity.

[Embodiments of the invention]

Hereinafter, this invention will be specifically explained with reference to drawings of embodiments. Fig. 1 shows an example of a casting apparatus used in the method of the invention. A suitable number of suction tubes 3.4 are horizontally fixed and installed inside each of the frames 1 and 2 of tM2.
A large number of air intake holes 5,6 are formed at equal intervals on the circumferential surface of the cylinder, and each air intake hole 5,6 is provided with a filter (not shown) to prevent the filler 11 from entering. Next, code 7 in the drawing
, 8 are ports 9, 1 provided at both ends of the suction tubes 3, 4.
The air guide pipes 7 and 8 are separated into separate systems for the upper mold M1 and the lower mold M2, respectively, and are connected to vacuum pumps (not shown). Unlike conventional devices, it is configured to be able to suction the filler material 11.11 inside the upper mold N and the lower mold M2 at different set pressures, and in the case of the present invention, in particular, the suction pressure inside the upper mold M1 is is set to a pressure smaller than the suction pressure inside the lower mold M2.

The casting method uses, for example, the above-mentioned apparatus, performs mold filling and mold cutting operations in the same manner as the conventional vacuum molding method, and covers the open surfaces of the frames 1 and 2 with a shielding sheet 12.
After molding an upper mold M1 and a lower mold M2, which are covered with 12 and sealing the internal filler 11.11, and molding the upper and lower molds 1M2 together to form a cavity 13 between the two brim-shaped skins 2M2, By injecting the molten metal into the cavity 13 through the sprue 14 and gas vent hole 15 provided in the upper mold M1 or the feeder sprue, a cast molded product having the same shape as the model can be obtained.

At that time, the upper and lower mold towns tH2 are both flange type H works tl'lz
After the model for forming the cavity] 3 is pulled out until the molten metal solidifies, the suction pipes 3 and 4 in the upper and lower molds M, M2 are used to suck the mold at a predetermined pressure from beginning to end, creating a negative pressure inside. Therefore, it is pressed by atmospheric pressure through the upper and lower shielding sheets 12°12, but in the case of the present invention, the suction pressure in the upper mold 1 is lower than the suction pressure in the lower mold M2. Due to the relationship, the lower surface of the upper mold N
By adjusting the weight of the filler 11 inside and the reduced pressure, a force as shown by the arrow in FIG. Therefore, the wedge-shaped gap S as mentioned earlier is not formed between the mutual mold mating surfaces P1 and P2, and the phenomenon of large cast tension being formed at the periphery of the cast product along this gap is prevented. .

In this case, the magnitude of the suction pressure applied to the upper and lower molds M, , M varies slightly depending on conditions such as the area and shape of the cast molded product, the specific gravity and particle size of the filler, and the material and thickness of the shielding sheet. -Although it cannot be determined generally, the suction pressure inside the upper mold is approximately 65 to 80% of the suction pressure inside the lower mold in a practical range.

〔Effect of the invention〕

As described above, if the present invention is applied to the production of cast molded products by the reduced pressure molding method, the suction pressure in the upper mold is made smaller than the suction pressure in the lower mold to effectively deform the mold mating surface at the periphery of the cavity. Since it is possible to perform casting while preventing the casting from occurring, there is almost no risk of creating large castings on the product, and even if castings occur, the amount to be removed is very small. Dramatically improve the quality of cast molded products,
It makes a great contribution to mass production.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a casting apparatus used in carrying out the method of the present invention, FIG. FIG. 4 is a cross-sectional view showing the shape of the mating surface of a mold made by a conventional method.

Claims (1)

[Claims] A pair of upper and lower molds M_1 and M_2 are formed by filling the inside of the frames 1 and 2 with a filler 11 made of heat-resistant particles, sealing the upper and lower open surfaces with shielding sheets 12 and 12, and keeping the inside in a reduced pressure state by suction means. In a casting method in which a casting is formed by pouring metal into the cavity 13 formed between the upper and lower molds M_1 and M_2, the suction pressure in the upper mold M_1 is controlled by the lower mold M_
2. A casting method characterized in that casting is carried out at a pressure lower than the suction pressure in the cavity 13 to prevent gaps from forming between the mold mating surfaces P_1 and P_2 at the periphery of the cavity 13.