JPH036881B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a slip casting molding method for producing a molded product by casting slips of particles such as ceramic grains and metal grains, and a mold for molding. In particular, the present invention relates to a molding method and mold suitable for producing molded products with complex shapes.

[Background of the invention]

The mold used for slip casting of ceramics is usually a split mold and a draft angle is added to separate the mold after slip casting from the solidified slip molded body (hereinafter referred to as "green body"). . The obtained green body is then sintered to produce a finished ceramic product.

When molding a molded product with a complex external shape and cavity shape and high dimensional accuracy using slip casting, the conventional method was to combine a large number of main molds and cores to form the desired mold. . but,
This method requires a large number of man-hours to manufacture and assemble a large number of main molds and cores, and the green body is likely to crack during the process of dehumidifying the green body and removing the mold and core.

Further, this method can only be applied when the core has a shape that allows it to be pulled out from the slip molded product after solidification.

Therefore, as a method for removing the mold after slip casting in such cases, for example,
As disclosed in Japanese Patent Publication No. 125658, there is a method in which sintering is performed with the mold installed, and then the mold is disintegrated and removed. However, with this method, the green body is dried by leaving it in the air with the mold installed, and the green body is sintered with the mold installed. Cracks occur in the molded product due to shrinkage and deformation of the green body. Also, judging from its structure, this reference does not assume the use of cores.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 57-176107, a slip is poured into a hydrothermally disintegrable gypsum mold,
After the slip hardens and becomes a green body,
There is a method to remove the plaster mold by immersing the (green body + mold) in hot water of approximately 85℃ or higher.

However, in this method, a relatively large amount (0.5-5%) of binder is added to the slip to prevent the green body from disintegrating due to water absorption during soaking, which affects the mechanical properties of the sintered product. influence
In addition, it may take a long time to disintegrate deep parts of the mold with hot water, and depending on the conditions, it may be extremely difficult to remove the mold.

In other words, when a long and slender core (i.e. a core with a large length/diameter value) is made using a hot water disintegrable mold and a slip is cast around it, the proportion of the hot water contact area to the total surface area of the core is small. The smaller the mold, the longer it takes to remove the mold.

[Purpose of the invention]

In view of the above, it is an object of the present invention to provide a slip casting molding method and a mold that are suitable for preventing cracking of molded products and for molding complex-shaped products by making it possible to remove the mold immediately after solidification of the slip. purpose.

[Summary of the invention]

The present invention is a molding method in which a slip using water or an organic solvent as a medium is cast into a mold and the mold is removed after the slip has solidified, characterized in that the mold is molded with a water-soluble organic binder. It is.

In this case, the mold aggregate is alumina (Al ₂ O ₃ ),
Use refractory particles such as magnesia (MgO), zircon sand, silica sand, or resin particles that are insoluble in the slip medium used.

Water-soluble synthetic organic binders include polyvinyl alcohol (PVA) and water-soluble isobutane.
Maleic anhydride copolymer, polyacrylamide (PAAm), polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), water-soluble vinyl acetate copolymer, acrylic copolymer, polyethylene glycol (PEG), methylcellulose (MC) ,
One or more organic substances such as carboxymethyl cellulose (CMC), hydroxypropyl cellulose (HPC), and water-soluble wax are used in the form of a solution in water. Alternatively, natural water-soluble binders such as starch, glue, and gum arabic may be used.

The mixing ratio of bone machine, binder, and water depends on the workability during mold making, mold dry strength, absorption of solvent (water or organic solvents such as ethanol, acetone) in the slip, and mold collapse after absorption of water. This value is determined on a case-by-case basis depending on gender, etc., and is not fixed uniformly.

However, for a rough estimate, aggregate particles: 100
Binder: 5 to 10 parts by weight, water: 20 parts by weight
~30 parts by weight.

When a slip using water as a medium is cast into the above-mentioned mold, if the mold is thin, the mold can collapse with only the moisture in the slip, but if the mold is thick, enough moisture can be obtained from the slip to cause the slip to collapse. (i) It is preferable to reduce the mold wall thickness, and for this reason, in the case of thick-walled cores, a cavity is provided inside.
It is even more effective to employ methods such as (ii) adding moisture to the mold from the outside to improve the disintegration of the mold, and using (iii), (i) and (ii) together.

In other words, measures such as keeping the mold wall thickness as thin as possible, and providing one or more appropriate holes in the main mold or core to facilitate the addition of moisture are effective in eliminating mold collapse. It is effective for

Furthermore, as a method of adding water, it is also effective to add it in the form of a spray. Furthermore, leaving the mold (mold + green body) in a high-humidity chamber for a predetermined period of time to allow the mold to absorb moisture is also a method for removing mold collapse.

In the present invention, a slip using water as a medium is cast into a mold made by hardening aggregate particles with a water-soluble organic binder, and the slip is solidified as the mold absorbs water in the slip. The phenomena that make it easier to collapse are as follows.

As shown in Figure 1 a, b, and c, the aggregate particles 1 of the mold are coated with a water-soluble organic binder 2 in the undried state (see a), but in the dried and hardened mold, The water evaporates and a large number of fine pores 3 are formed inside, and when a slip is cast into such a mold, water, which is the medium in the slip, enters the pores 3 by capillary action and becomes water-soluble. Since the binder 2 is dissolved, its cohesive force is greatly weakened, and each aggregate particle 1
make independent. (see c).

Looking at this phenomenon from a macroscopic perspective, as the mold absorbs water from the slip, it gradually transitions to a state where it can collapse deeper than the interface with the slip, but on the other hand, as the slip releases water as a medium, As the density increases, the degree of solidification increases, eventually leading to the formation of a green body.

During the subsequent dehydration process, this green body
It shrinks little by little. On the other hand, since the mold absorbs moisture, it tends to swell, albeit slightly.

Normal gypsum molds do not lose their strength even if they absorb water in the slip, so the green body tends to crack due to the stress generated during the shrinkage of the green body and the swelling process of the mold.

However, in the present invention, since the mold softens as it absorbs water, the mold does not impede minute deformations such as shrinkage that occur during the green body production process. In other words, since the green body is not subjected to any external force from the mold (main mold or core), no stress is generated on the green body, and therefore no cracks occur at all.

Therefore, even if the mold is complex because the molded product is complex, or especially when a core is used, each part of the mold is equally disintegrated down to the depths, and each part of the mold can disintegrate evenly because it absorbs the moisture necessary for disintegration removal from the slip. becomes.

In addition, if the moisture content in the slip alone is insufficient to remove the mold, such as when the mold wall thickness is large,
As mentioned above, adding water from the outside is effective.

A mold is formed by compacting a mixture of aggregate particles, a water-soluble binder, and water, but the molding time can be shortened by imparting fluidity to the mold material.

Basically, to impart fluidity, it is sufficient to increase the water content. However, large amounts of water are not easy to evaporate.

Therefore, an alternative method is to prepare an alcoholic solution of a water-soluble binder that is stable in the form of a hydrate at room temperature, and add to this an amount of water necessary for fixation as crystal water, or a slightly smaller amount of water. It is good to give fluidity to the mold.

As mentioned above, since the softening of the mold progresses simultaneously with the solidification of the slip, complex-shaped ceramic molded products can be molded extremely easily without any cracks.

Furthermore, since the present invention uses an organic binder, as in the case of using a solid water-soluble binder (for example, K ₂ CO ₃ ), (i) when a water-soluble mold and a plaster mold are used in combination, (ii) The binder in the water-soluble mold diffuses into the green body, causing quality deterioration of the molded product; (iii) ) It does not have any problems such as reacting with the slip or affecting the pH of the slip.

Further, unlike other conventional methods, there is no need to immerse (mold + green body) in hot water before sintering, and a sintered product can be obtained by slip casting molding without any restrictions on shape.

[Embodiments of the invention]

Examples of the present invention will be described below.

Example 1 Al ₂ O ₃ (250-325 meshes); 100 parts by weight, aqueous solution of polyvinyl alcohol (PVA) with a concentration of 5%; 20 parts by weight were added and mixed uniformly to form a mold material.

The core 4 shown in FIG. 2 was molded from the above molding material using a wooden mold prepared separately, and main molds 5 and 6 made of plaster were also molded. Core 4 was sufficiently dried and hardened at 100°C. Furthermore, main molds 5 and 6 made of plaster were sufficiently dried at 60°C. Thereafter, these main molds and cores were assembled to form a predetermined mold cavity.

Next, Al ₂ O ₃ with an average particle size of 2 μm; 100 parts by weight, water;
An alumina strip 8 prepared by uniformly mixing 16 parts by weight of a peptizer and a pH adjuster was cast into the cavity 7 of the mold and left for one hour.

After the slip hardened, the plaster main molds 5 and 6 were removed. Since the core 4 had absorbed the moisture in the slip, its cohesive strength was extremely low, and it could be easily disintegrated and removed. Furthermore, no cracking was observed in the green body.

Example 2 A mold material was prepared by kneading 100 parts by weight of Al ₂ O ₃ (250-325 mesh) and 20 parts by weight of a 5% aqueous solution of polyacrylamide (PAAm), and prepared separately according to Example 1. The mold is made using a wooden mold, and then
A core was made by sufficiently drying and curing at 100°C, and assembled together with separately molded plaster main molds 5 and 6. Sialon slip 8, in which 100 parts by weight of Sialon powder, 40 parts by weight of water, peptizer, sintering aid, etc. were added and mixed uniformly, was cast into mold cavity 7 and left for one hour. As a result, as in Example 1, the core 4
could be easily removed, and no cracks were observed on the green body.

Example 3 A casing having the shape shown in FIG. 4 was created by slip casting using the method and mold of the present invention. Since this casing has an extremely complicated shape including a flange 9, a fastening groove 10, and a spiral flow passage 11 inside, it was impossible to mold it by the slip casting method using a conventional mold.

Zircon sand (250-325 powder); 100 parts by weight,
5% polyvinylpyrrolidone (PVP) aqueous solution; 15
Mix the weight parts uniformly to adjust the mold material, fill it into a separately prepared hard Si rubber core holder to create a spiral core, then thoroughly dry it at 100℃, and mold it into a separately molded plaster half. The mold was assembled along with the main mold for the split method. Thereafter, an alumina strip similar to that in Example 1 was cast and left for 2 hours.

Afterwards, the main plaster mold was removed. Since the water-disintegratable spiral core according to the present invention sufficiently absorbs the moisture in the slip, the cohesive force of the mold was significantly reduced and it could be easily disintegrated and removed.

This alumina green body is air-dried, then dried at 100℃ (completely removing free moisture), then slowly heated from room temperature and heated to 1700℃ for 2 hours to create an alumina sintered product with no cracks and good mechanical properties. A casing was obtained.

Example 4 The present invention was applied to molding a threaded rotor shown in FIG.

In the case of such a shape, it is extremely difficult to mold the mold using the conventional slip casting method using a plaster mold, which reduces dimensional accuracy due to the need to divide the mold into an extremely large number of pieces, and causes damage to the green body when removing the mold due to a large number of burrs. It was hot. Therefore, a screw-shaped model identical to that shown in FIG. 4 was separately foam-molded from expanded polystyrene using a mold. One-component RTV silicone rubber was applied to the entire surface of the model 12 except for the top 15 to a thickness of about 50 μm and cured to form an insoluble coating film 13.

Place the top of this model on a surface plate (not shown),
Set up a wooden frame around it. Then Al ₂ O ₃ particles;
40 parts by weight of 100 parts by weight, 5% vinyl acetate emulsion aqueous solution were added and mixed uniformly to prepare a mold material 14, which was filled around the rotor model. Next, acetone was sprayed from the top 15 of the model 12 to shrink the volume of the sprayed Styrofoam model to about 1/30, and the mold was dried and hardened at 100°C.
Acetone was again sprayed onto the styrene model and removed from the mold together with the rubber film applied to the surface, followed by drying and hardening at 100C.

A Sialon slip 17 similar to that of Example 2 was cast into the mold cavity 16 thus formed, and the moisture in the slip was absorbed into the mold and solidified. At this time, the mold according to the present invention had extremely good disintegration properties because the caking force of the mold was drastically reduced due to absorption of water, and a green body could be obtained without damaging the threaded portion of the rotor.

This sialon green body was gradually dried in the air, then dried in a 100℃ oven to completely remove free moisture, and then slowly heated from room temperature to 1800℃
A homogeneous sialon rotor sintered product was obtained by pressureless sintering for 2 hours.

〔Effect of the invention〕

As explained above, according to the present invention, a water-soluble organic binder is mixed with insoluble aggregate particles, such as Al ₂ O ₃
The mold is mixed with powder, etc. to make a mold, and a slip of water or water-based ceramics is used as the medium, so the mold absorbs water from the slip and becomes soft and easily disintegrates. increases its density over time and solidifies, eventually becoming a green body.

Therefore, according to the present invention, the following effects are brought about when molding ceramic products.

(i) Since the mold softens as the slip hardens, no cracks will occur in the green body even when using a main mold or core with a complex shape.

(ii) Since the mold softens by absorbing moisture from the slip, it is possible to easily mold even complex-shaped molded products that require a highly uneven main mold and core.

[Brief explanation of the drawing]

Figures 1a, b, and c are explanatory diagrams showing the principle of the mold used for molding of the present invention, Figure 2 is an explanatory diagram of an embodiment of the molding method of the present invention, and Figures 3 and 4 are illustrations of the mold to which the present invention is applied. The external view of the molded product and FIGS. 5 to 7 are explanatory diagrams of the molding method of the present invention. DESCRIPTION OF SYMBOLS 1...Mold aggregate particles, 2...Water-soluble organic binder, 3...Void, 4...Water-disintegratable core, 14...
...Water-disintegratable main mold, 5,6...Main mold made of plaster,
7, 16... Mold cavity, 8, 17... Ceramic strip, 13... Insoluble coating film.

Claims (1)

[Scope of Claims] 1. In a slip casting molding method in which a slip is cast into a mold and the mold is removed after the slip has solidified, the mold is molded with an organic water-soluble binder, and the mold absorbs moisture in the slip. 1. A slip casting molding method, characterized in that the slip is solidified by absorbing water, and the mold is made to easily collapse due to water absorption. 2. The slip casting molding method according to claim 1, wherein after the slip has solidified to form a green body, moisture is added to the mold from the outside to promote disintegration of the mold. 3. A slip casting mold made of a mold aggregate and a binder, wherein the binder is a water-soluble organic binder. 4. The slip casting mold according to claim 3, wherein the mold aggregate is refractory particles. 5 Organic binders include polyvinyl alcohol, isobutane-maleic anhydride copolymer, polyacrylamide, polyethylene oxide, polyvinylpyrrolidone, vinyl acetate copolymer, acrylic copolymer, polyethylene glycol, methylcellulose, carboxymethylcellulose, hydroxy 4. The slip casting mold according to claim 3, wherein one or more of propylcellulose and water-soluble wax are dissolved in water. 6. The slip casting mold according to claim 3, wherein the organic binder is one or more of starch, glue, and gum arabic dissolved in water. 7. The mold for slip casting molding according to claim 5 or 6, characterized in that alcohol is added to the organic binder to impart fluidity to the mold. 8. The slip casting mold according to claim 3, further comprising a cavity for promoting collapsibility.