JPH0464281B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is applicable to slip casting molds for making molded products by casting slips of refractory particles such as ceramic particles, metal particles, carbon particles, etc. In particular, the present invention relates to a mold suitable for making molded products with complex shapes.

[Background of the invention]

The green body obtained by the slip casting method has low strength, so it is difficult to release it from the mold. In particular, when it comes to obtaining a green body with a complex shape or molding a shaped product with an internal space, there are restrictions such as mold division and mold removal methods.

There is a method for removing the mold after slip casting, for example, as disclosed in Japanese Patent Publication No. 58-125658, in which the mold is sintered with the mold in place and then disintegrated and removed. Because the product is left to dry and is sintered with the mold still in place, if the shape is complex, shrinkage and deformation of the mold and molded product may occur during drying and sintering.
Cracks occur in the molded product. Furthermore, this reference does not assume the use of core molds.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 57-176107, a slip is poured into a hot water disintegrating plaster mold,
There is also a method of removing the plaster mold by immersing the solidified molded product and casting mold in warm water of approximately 85°C or higher, but a binder is added to prevent the molded product from collapsing during soaking, and this prevents the molding from collapsing. It affects the mechanical properties and requires a long time to disintegrate deep inside with hot water.

[Purpose of the invention]

In view of the above, an object of the present invention is to provide an optimal mold configuration that facilitates removal of the mold when molding a molded object with a complex shape by slip casting, and a binder used for molding the mold. .

[Summary of the invention]

The present invention provides a first surface layer formed of a mold material whose strength decreases due to absorption of solvent in the slip on the mold cavity side, and a second layer having higher strength than the first surface layer outside of the first surface layer. This is achieved by molding one surface layer using a binder soluble in an organic solvent or a binder soluble in water, depending on the solvent contained in the slip.

In slip casting, in order to easily remove the green body from the mold without damaging it, when the slip hardens and the green body is generated, it is necessary that the strength of the mold around the green body is reduced.

That is, (i) a mold whose strength decreases as the slip solidifies, and (ii) a mold whose strength is weak may be used.

On the other hand, in actual slip casting, when two or more molds are combined, the strength of the entire mold is reduced [(i)], or the mold with low strength [(ii)] is sufficient only in the vicinity of the green body. Therefore, it is desirable that the layers other than the first surface layer of the mold cavity have high strength.

That is, as shown in FIG. 1, there is a first surface layer 1 on the side of the mold cavity, and a second layer 2 having higher strength on the outside thereof.
A composite mold is effective as a slip casting mold. When such composite molds are combined, the slip is poured into the mold cavity, the slip is solidified (green body 4 is generated), and the mold is released, the strength near the surface of the green body has decreased. The mold will collapse and the green body will not.

The purpose of the second mold layer 2 is to reinforce the first surface layer 1, and a plaster mold, a ceramic mold, or a heat-resistant resin mold can be used, and these molds can be used repeatedly.

Therefore, it has been found that a mold in which the strength of the first surface layer of the mold decreases as the slip hardens is effective, and that this objective can be achieved by using a mold formed with a binder that dissolves in the solvent of the slip. Ta.

In the case of a slip using water as a solvent, a mold made of a water-soluble binder may be used, and water-soluble binders include organic and inorganic ones.

Possible inorganic water-soluble binders include carbonates (sodium carbonate, potassium carbonate), sulfates (ammonium sulfate, sodium hydrogen sulfate, potassium hydrogen sulfate, magnesium sulfate), and phosphates (trisodium phosphate, tripotassium phosphate). , chlorides (potassium chloride, magnesium chloride).

Examples of organic water-soluble binders include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, and ethyl cellulose.

These inorganic and organic water-soluble substances are dissolved in water and used as a binder, and mixed with mold aggregate to be used as a mold material.

In addition to alumina, magnesia, zircon sand, and silica sand, non-refractory particles can also be used as the mold aggregate.

The mechanism by which the mold aggregate binds when using inorganic and organic water-soluble binders, absorbs the solvent (water) in the slip, solidifies the slip, and at the same time reduces the strength of the mold itself is as follows. It is.

As shown in Figures 2a, b, and c, particles 5 in the mold aggregate are coated with water-soluble binder 6 in the wet state, but (see a) the particles 5 in the mold aggregate are coated with water-soluble binder 6 in the dried and hardened mold. evaporates to form fine pores 7 inside, and when a slip is cast into such a mold, the moisture in the slip (including other solutions) enters into the pores 7 and forms the water-soluble binder 6. Weakening the cohesive force of each particle 5
(see c). This results in a mold that is less strong and easier to remove, while the slip releases moisture and produces a green body.

As the mold absorbs moisture in the slip, it becomes a collapsible mold from the contact interface of the slip, but on the other hand, as the slip releases moisture, it shrinks.
The amount of deformation is increased, leading to the generation of a green body.
However, in the present invention, as the mold surface (interface with the slip) softens as moisture is absorbed, the mold does not inhibit shrinkage and deformation that occur during the green body production process. Therefore, a green body without any cracks can be obtained.

Furthermore, since the strength of the mold is reduced due to water absorption, it becomes extremely easy to remove the mold.

Further, depending on the material of the ceramic, a solvent other than water, such as an organic solvent, may be used as the slip medium. In this case, a binder soluble in the organic solvent used as the medium may be used as the binder for the mold aggregate of the first surface layer according to the above-mentioned mechanism. For example, when the slip medium is acetone or ethyl alcohol, the binder for the aggregate may include acrylonitrile, styrene polymer, polyvinyl acetate, cellulose acetate resin, polyvinyl chloride resin, etc.

[Embodiments of the invention]

[Example 1] An example in which the casing 8 shown in FIG. 3 is molded by slip casting using the composite mold of the present invention shown in FIG. 1 will be described.

The second layer 2 of the reinforcing mold shown in FIG. 1 was made by adding and mixing alumina sol to zircon and fused quartz, and molding and firing the mixture. Another model is installed in this second layer 2, a molding material containing potassium carbonate aqueous solution as a binder is put in the space, and after compacting, the model is demolded and the first surface layer 1 is hardened. , 2 at 200℃
Dry for an hour. The blending ratio of the first surface layer is water.
Add an aqueous solution of 80g of potassium carbonate to 100c.c. to 100g of alumina (250 mesh or less) to 25c.c.
It is added and mixed.

A core 3 made of the same composition as the first surface layer was placed in these composite molds, and silicon nitride slip (32 c.c. of water was added to 100 g of silicon nitride) was poured into the mold. After 2 hours, it was confirmed that each part had solidified, and the upper and lower reinforcing mold second layer 2 was released from the mold, and a small amount of water-soluble mold (mold first surface layer) was formed around the green body 4 of the solidified ceramic 2. The mold was released by leaving behind. Thereafter, the remaining portion of the first surface layer was removed with a soft brush to obtain the ceramic casing shown in FIG. 3.

[Example 2] A composite mold was produced in the same manner as in Example 1 using a plaster mold as the second layer 2 of the reinforcing mold and a mold material containing polyvinyl alcohol as a binder for the first surface layer of the mold.

The blending ratio of the first surface layer of the mold is to add 32 c.c. of an aqueous solution of 25 g of polyvinyl alcohol dissolved in 100 c.c. of water to alumina (250 mesh, 85 parts by weight, 125 mesh, 15 parts by weight). , and in order to dry the first surface layer, the composite mold is
It was kept at 60°C for 24 hours.

Add alumina strip (100g of alumina) to this mold.
35 c.c. of water was added), and as in Example 1, the ceramic casing shown in FIG. 3 was obtained easily and without any cracks in the green body.

〔Effect of the invention〕

As explained above, according to the present invention, when molding the first surface layer of a composite mold consisting of the first surface layer of the mold and the second layer reinforcing it, an organic solvent is used depending on the solvent contained in the slip. By using a soluble binder or a water-soluble binder, the first surface layer of the mold absorbs the slip solvent and softens to the extent that removal of the mold is extremely easy. The confinement speed becomes weaker, allowing for easier mold release and the molding of complex-shaped products.

Furthermore, shrinkage deformation of the green body is absorbed by the softened first surface layer of the mold, thereby preventing cracking during the production process of the green body.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a mold for forming a ceramic casing to explain the present invention, FIG. FIG. 3 is an external view of a ceramic casing molded for an embodiment of the present invention. 1... Mold first surface layer, 2... Mold second layer (reinforcing layer), 3... Core, 4... Ceramic green body,
5... Aggregate of mold, 6... Water-soluble binder, 7... Holes.

Claims (1)

[Claims] 1 Used in a molding method in which a slip is cast into a mold and the mold is removed after solidification of the slip, a first surface layer on the side of the mold cavity that is in contact with the slip, and a second surface layer having higher strength than the first surface layer on the outside of the first surface layer. In a slip casting mold comprising two layers, the first surface layer on the side of the mold cavity is made of a binder and a mold aggregate, and is softened by absorption of solvent in the slip; A slip casting mold, characterized in that the binder is selected from the group of inorganic water-soluble binders, organic water-soluble binders, and binders soluble in organic solvents.