JPH0229417B2 - - Google Patents

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. A filler made of heat-resistant particles is bonded and fixed inside the frame so that it does not lose its shape, and molten metal is injected into the cavity formed between the upper and lower molds to perform casting, eliminating the need for a binder. The flow of hot water is good, and the filler material can be used repeatedly with little modification, making it ideal for the mass production of cast products with flat shapes.

[Problem that the invention seeks to solve]

However, when casting is performed by applying the above molding method, _{the upper and lower molds M 1 and} M _{2 are}
After pulling out the model for forming the cavity 13 in between, the upper and lower molds M ₁ and M ₂ are matched, and after pouring is completed, until the molten metal solidifies,
The interiors of the upper and lower molds M ₁ and M ₂ are maintained in a final reduced pressure state by suction means. At that time, both molds M ₁ ,
Since the suction force acting on the mold matching surfaces P ₁ and P ₂ of M ₂ acts at right angles to the shielding sheet, both molds M ₁ ,
When the inside of M ₂ is suctioned with the same pressure, the periphery of the cavity 13 and the mold matching surface of the upper and lower molds M ₁ and M ₂
At the ridge line where P ₁ and P ₂ intersect, circular deformed parts 16 and 17 as shown in Fig. 3 are formed, and these deformed parts are caused by the lower surface of the upper mold M ₁ before mold matching.
Due to the fact that the weight of the filler 11 inside M ₁ is further superimposed, more damage occurs in the upper mold M ₁ than in the lower mold M ₂ as shown in FIG. Therefore, when the molds are matched, the cavities 1 of the upper and lower molds M ₁ and M ₂
A gap S having a wedge-shaped cross section is created between the mold mating surfaces P ₁ and P ₂ on the periphery of the mold, so when molten metal is injected into the cavity 13, the molten metal enters the gap S and creates a large casting on the periphery of the casting. It has the disadvantage that it can form tension, and this cast tension not only takes a lot of effort to remove using a chisel or a grinder in a later process, but also has the problem that it 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 objects in a simple manner, and consists of filling the inside of the frame with a filler made of heat-resistant particles and shielding the upper and lower open surfaces. In a casting method in which a pair of upper and lower molds are sealed with a sheet and kept under reduced pressure by internal suction means, and the casting is formed by pouring metal into the cavity formed between the upper and lower molds, the suction pressure inside the upper mold is It is characterized in that casting is carried out while reducing the suction pressure in the lower mold to be lower than the suction pressure in the lower mold to prevent 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 the drawings of the embodiment. FIG. 1 shows an example of a casting apparatus used in the method of the invention. In the case of this embodiment, vertically opposing molds M ₁ , M ₂ frames 1 and 2
Inside, a suitable number of suction pipes 3 and 4 are horizontally fixed and fixed, and a large number of suction holes 5 and 6 are bored at approximately equal intervals on the circumference of the suction pipes 3 and 4. A filter (not shown) is attached to the intake holes 5 and 6 to prevent the filler 11 from entering. Next, reference numerals 7 and 8 in the drawings indicate air guide tubes that are detachably connected to ports 9 and 10 provided at both ends of the suction tubes 3 and 4,
These air guide pipes 7 and 8 are used by connecting separate systems to a vacuum pump (not shown) for the upper mold M ₁ and the lower mold M ₂ . ₁ and the filler material 11,1 inside the lower mold _M2
In the case of the present invention, in particular, the suction pressure in the upper mold _M1 is set to be lower than the suction pressure in 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 shielding sheets 12 and 12. An upper mold M ₁ and a lower mold M ₂ are formed by covering and sealing the internal fillers 11 and 11, and the upper and lower molds M ₁ and M ₂ are matched to form both molds.
After forming the cavity 13 between M ₁ and M ₂ , if molten metal is injected into the cavity 13 through the sprue 14 and gas vent hole 15 provided in the upper mold M ₁ or through the feeder sprue, a cast molded product having the same shape as the model can be obtained. is obtained.

At that time, the upper and lower molds M ₁ , M ₂ are both molds M ₁ ,
After pulling out the model to form cavity 13 between M ₂ and until the molten metal hardens, the upper and lower molds
The suction tubes 3 and 4 inside M ₁ and M ₂ suck at a predetermined pressure from beginning to end, and the interior is at negative pressure, so it is pressed by atmospheric pressure via the upper and lower shielding sheets 12 and 12. In the case of the present invention, since the suction pressure in the upper mold M ₁ is lower than the suction pressure in the lower mold M ₂ , the lower surface of the upper mold M ₁ has the upper and lower molds M ₁ , M ₂ . Due to the difference in the internal pressure of the upper mold M ₁ and the adjustment of the dead weight and reduced pressure of the filler 11 inside the upper mold M ₁ , a force as shown by the arrow in _FIG . Mating face
Since P ₁ and P ₂ are in close contact with each other without any gaps, there is no wedge-shaped gap S between the mutual mold mating surfaces P ₁ and P ₂ as mentioned earlier, and the periphery of the cast product is formed along this gap. The phenomenon of large castings being formed is prevented.

In this case, the magnitude of the suction pressure applied to the upper and lower molds M ₁ and M ₂ 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 unconditionally, 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 of casting that can be removed is very small, so this type of casting This dramatically improves the quality of molded products and greatly contributes to their mass production.

[Brief explanation of drawings]

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. M ₁ ... Upper mold, M ₂ ... Lower mold, 1, 2 ... Frame body, 3, 4 ... Suction pipe, 5, 6 ... Intake hole, 7,
8... Air guide pipe, 9, 10... Port, 11... Filling material, 12... Shielding sheet, 13... Cavity, 14... Sprue, 15... Gas vent hole, 16,
17...Deformed part, S...Gap, _P1 , _P2 ...Mold matching surface.

Claims (1)

[Claims] 1 The inside of the frames 1 and 2 is filled with a filler 11 made of heat-resistant particles, and the upper and lower open surfaces are covered with shielding sheets 12,
A casting process in which a pair of upper and lower molds M ₁ and M ₂ whose interiors are kept in a vacuum state by suction means are sealed at 12 and poured into a cavity 13 formed between the upper and lower molds M ₁ and M ₂ to form a casting. In the method, the upper mold
The suction pressure in M ₁ is made smaller than the suction pressure in the lower mold M ₂ and the mold mating surface P ₁ at the periphery of the cavity 13 is
A casting method characterized by performing casting while preventing gaps from forming in _P2 .