JPS58179558A - Precision casting method using water-soluble casting mold - Google Patents

Abstract

PURPOSE:To cast a thin walled member having an intricate shape precisely by performing vacuum casting then pressure casting by using a water soluble casting mold which is produced from gypsum and hydrate of magnesium sulfate and removing the mold with water after the casting. CONSTITUTION:Hemihydrate gypsum and magnesium sulfate are mixed at about 3:2 ratio, and a powdery and granular refractory material and water are added thereto to prepare a slurry. The slurry is cast into a pattern and is solidified, whereby a molding is obtained. The molding is dried primarily at <=120 deg.C and is then dried secondarily at >=270 deg.C to remove crystal water. A water-soluble casting mold having high mechanical strength and having a dense layer consisting of the fine crystal particles of magnesium sulfate in the surface layer is thus obtained. Such mold 13 is installed in the case 2 of a precision casting device 1 and the inside is evacuated with a vacuum pump 10, whereafter molten metal M is charged into the cavity 15 and is cast under pressure by a compressed air source 8 successively. The mold 13 is dipped and dissolved in water upon solidification of the metal M whereby the casting which is a product is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a precision casting method using a water-soluble mold in which a dense layer in which many crystalline particles of magnesium sulfate are concentrated is formed in the surface layer.

Conventionally, in order to cast parts with thin walls and complex shapes such as turbocharger impellers and turbine impellers, α-type hemihydrate gypsum is generally used as the main material, and refractory powder or setting time or A slurry made by mixing cast river gypsum with additives to control the amount of expansion and water is poured onto a rubber model placed in a frame and allowed to harden.
The model was removed, a mold was formed, and the temperature was 250 to 55.
Molten metal is poured into the mold preheated to 0° C., and casting is performed by a vacuum casting method or a pressure casting method. After casting, the mold is disintegrated and removed by mechanical vibration or high-pressure water washing.

However, when casting a thin-walled member with a complicated shape as described above, significant restrictions are imposed on the shape of the casting because mold remains after collapse or deformation of the thin-walled portion occurs.

In addition, since conventional molds use α-Kate-sui gypsum as a coagulating material (binder), the composition is approximately uniform both on the surface and inside of the mold, and when heated to 100 to 120°C, the α-Kate-sui gypsum It becomes hemihydrate gypsum, and when heated to around 200℃, it becomes anhydrous gypsum.

Strength decreases. For this reason, a part of the mold breaks during vacuum casting or pressure casting, and sand encroachment causes rough casting surface.

The present inventors have accomplished the present invention in order to improve the above-mentioned conventional problems, and the purpose thereof is as follows.

By using a water-soluble mold that has excellent mechanical strength during casting and can be easily disintegrated and removed by water after casting, it is possible to obtain a product with a good casting surface and a sound interior. It is an object of the present invention to provide a casting method which is particularly suitable for precision casting thin-walled and complicatedly shaped members such as supercharger impellers and turbine impellers.

In order to achieve the above object, the present invention prepares a slurry by mixing gypsum, hydrated magnesium sulfate, water and, if necessary, a powdered or granular refractory material. A process of pouring the mold into a mold and hardening it, then removing the model to make a molded product, and heating and drying this molded product in two stages at a temperature of 120°C or higher and then at a temperature of 270°C or higher to produce a mold. The gist of the process is that molten metal is continuously cast using this mold, first under reduced pressure and then under increased pressure.

An example of the precision casting method according to the present invention will be explained in detail below in order of steps.

First, to describe the method for producing a water-soluble mold, the first step is to use hemihydrate gypsum (CaSO4'/!H,O
) to a hydrate of magnesium sulfate, for example 1°2, 3.4.
5.6.7 or a hydrate in which 12 water molecules are bonded.
For example, mix it so that the weight ratio is about the same as the amount of hemihydrate gypsum above.

A powdered refractory such as mullite flour and water are added to this mixture, and further a granular refractory such as silica sand is added and mixed to form a slurry.

This slurry is then poured under reduced pressure or other conditions with as few air bubbles as possible onto a product-shaped rubber model placed in a frame, left to stand for 5 to 10 minutes to solidify the plaster, and then the above-mentioned rubber The model is removed and a molded product that will later become a mold is manufactured.

Next, the molded product is dried in a drying oven at 120°C or lower for a predetermined time 1.
It is then dried, and then dried in a drying oven of 270 U or more to form a water-soluble mold.

In the above, the reason for adding hydrated magnesium sulfate instead of anhydrous magnesium sulfate is that when drying the molded product described in F, an aqueous solution of hydrated magnesium sulfate passes between the acicular crystals of gypsum on the surface. This is aimed at the so-called flotation phenomenon in which the crystalline fine particles of magnesium sulfate move toward the surface and form a dense layer on the surface. If added, the anhydrous magnesium sulfate will solidify before the gypsum, and the above-mentioned 70-tail/yon will not occur, so the entire mold will have a uniform composition similar to the conventional one, resulting in a decrease in strength.

The reason why the trench was first dried at a temperature below 120°C was because if it was heated and dried all at once above this temperature, the dehydration reaction of gypsum hydrate (CaSO+・zato) and magnesium sulfate hydrate would occur rapidly. This is because the dense layer on the surface of the mold created by the 70-tail 7 yen becomes poorly ventilated, causing the mold to partially rupture and no longer function as a mold.

Furthermore, secondary drying was carried out at a temperature of 270°C or higher because the hydrate of magnesium sulfate becomes anhydrous magnesium sulfate at 270°C or higher, which prevents cavities and blisters after casting, and also prevents water from forming. This is to make it easily soluble. By doing it like this.

The mold can be easily collapsed after casting.

The mold can be removed without deforming a thin-walled, complex-shaped product.

FIG. 1 shows a comparison of the strength of the water-soluble mold obtained as described above and a conventional mold.

As is clear from FIG. 1, the mold used for carrying out the method of the present invention has excellent strength, and there is no disadvantage that part of the mold breaks during pressure casting.

Next, a precision casting method using the above-mentioned water-soluble mold will be explained in detail with reference to FIG.

Figure 2 shows the precision casting device 1.
An opening 3 is formed on the top surface of the box-shaped case 2, and this opening 3 can be airtightly sealed with a lid 4, and two knobs 5 and 6 are connected to the bottom surface (7). , one pipe 5 is connected to an air source 8 via a pulp 7, and the other vibro is connected to a vacuum pump 10 via a pulp 9.

Inside the case 2 is an angled bracket 11i/
A flask 12 is supported by the shingle, and a water-soluble mold 13 manufactured by the method described above and a cold (7 gold 14) are placed in the flask 12.
is set. These molds 13 and chillers 1
4 and a cavity 15 in which the product is cast.
A sprue 16 is formed which is connected to the sprue.

To carry out precision casting using the casting apparatus 1 as described in 1- below, remove the lid 4, pour the molten metal M from the opening 3 into the preheated ladle 17, and close the opening 3 with the lid 4. 1. The vacuum pump 10 is driven to reduce the pressure inside the case 2. Thereafter, the ladle 17 is tilted to fill the cavity 15 with the molten metal M via the molten metal 1]16.

Then, at rt=l, the pulp 9 is closed to break the vacuum, and then the pulp 7 is opened before the molten metal M solidifies, and the case 2
Pressurized air is introduced into the mold, and the molten metal M is cast while being pressurized. After solidifying the molten metal M in this manner, the mold 13 is taken out from the casting apparatus 1 and immersed in a water tank to melt the mold 13 and obtain a cast product.

Next, specific examples of the present invention will be described.

(Example 1) 60 parts of gypsum, 40 parts of magnesium sulfate hydrate, and 50 parts of water are mixed to minimize the generation of air bubbles to form a slurry, and this slurry is installed in a frame to create a rubber model of a compressor wheel. After the plaster solidified, the rubber model was removed to create a mold. After that, this molded product was dried in a drying oven at 80°C for 4 hours.
Next, it was dried in a drying oven at 270°C for 3 hours to form a mold.

Then, preheat the mold to about 200°C, 20. ,l
Molten aluminum (equivalent to ACJC) with a melting temperature of 720°C was cast in a Hf reduced pressure chamber, and immediately after 9 hours of compressed air was fed into the machine for about 6 minutes to solidify it.

After exposing the mold to the atmosphere and leaving it to cool, the mold was immersed in a water tank for about 30 minutes.
The mold was completely eluted, and when the casting itself was washed with running water, a casting with an excellent cast surface was obtained.

(Example 2) Using a gypsum mouthpiece, 8 parts of magnesium sulfate hydrate, 20 parts of mullite flour, 60 parts of silica sand, and 20 parts of water as materials, a molded article was created in the same manner as in Example 1. After drying this at 100°C for 3 hours, it was dried at 270°C for 3 hours to form a mold, and molten aluminum was cast under the same conditions as in Example 1 without decreasing the temperature of this mold. . Immediately after the cast metal had solidified, it was immersed in a water bath, and the mold was completely dissolved.

FIG. 3 shows the surface roughness of the casting surface of the thus obtained casting product and the surface roughness of the casting surface when a conventional gypsum mold was used. That is, the surface roughness of the cast surface of the product obtained by the method of the present invention is excellent, approximately 15μ, as shown in FIG. As shown in Figure 3 (b), about 3. It is inferior to OP.

As is clear from the above description, according to the present invention, a mold is manufactured by forming a slurry containing gypsum, magnesium sulfate hydrate, and water into a mold shape, and then heating and drying the slurry in two stages. Because of this, a dense layer containing a large amount of crystalline fine particles of magnesium sulfate is formed on the mold surface due to flow fusion during the drying process.

The mold has excellent mechanical strength during casting, and at the same time is easily soluble in water after casting.

Therefore, products obtained by a precision casting method in which the mold is first cast in a reduced pressure state and then in a pressurized state have many advantages, such as high dimensional accuracy and an extremely excellent casting surface.

[Brief explanation of drawings]

The drawings show an example of implementation of the present invention. Fig. 1 is a diagram comparing the strength of the mold obtained by the method of the present invention with that of a conventional example, Fig. 2 is a longitudinal cross-sectional view of a casting device for carrying out the method of the present invention, and Fig. 3 (a) is a diagram comparing the strength of the mold obtained by the method of the present invention with that of a conventional example. A diagram showing the surface roughness of the casting surface of a product obtained by the inventive method, and FIG. 3 (b) is a diagram showing the surface roughness of the casting surface of the product obtained by the conventional method. In the drawing, 1 is a gluing device, 8 is a pressure source, 10 is a vacuum pump, 12 is a casting flask, 13 is a mold, 15 is a capacitance, and Mit molten metal. Patent Applicant Honda Motor Co., Ltd. Agent Patent Attorney 2 1) Co., Ltd.

Claims (1)

[Claims] A slurry made by mixing gypsum, magnesium sulfate hydrate, and water is poured into a model and allowed to harden.Then, the model is removed to form a molded product of a predetermined shape, and this molded product is heated at a temperature of 120°C or less. After drying, the mold is dried at a temperature of 270°C or higher to remove crystallization water in the molded product, and the molten metal is cast under reduced pressure using the mold that has been preheated by VC to room temperature or higher. A precision casting method using a water-soluble mold characterized by pressurizing molten metal with compressed gas before solidifying.