JPH0234292B2 - DEISHOIKOMISEIKEINOHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of casting a slurry of ceramic, metal, cermet, etc. into a water-absorbing mold and solidifying it.

[Conventional technology]

The cast molding method is a method of obtaining a molded article by pouring slurry into a water-absorbing mold to form an ink layer. This molding method has the characteristics of being able to mold products with complex shapes, and is suitable for small-scale production because the equipment cost for molding is low, and is suitable for molding clay-based materials such as ceramics and sanitary ware. It is widely used. Recently, it has also come to be used for non-clay ceramic bases such as alumina, magnesia, zirconia, ferrite, silicon carbide, and silicon nitride. Application to metal cermets has also been attempted.

Gypsum is generally used as a water-absorbing mold for cast molding. Plaster molds can accurately copy even the finest patterns on a model and have excellent water absorption properties, but they do have some problems. That is, (1) It takes a long time from pouring the slurry to taking it out as a molded body. It is also possible to increase the speed of dewatering by pressurized casting, but the plaster mold is so weak that applying pressure is almost impossible.

(2) For non-clay ceramics, metals, and cermets, there is little or no shrinkage due to dehydration, and fine particles enter the pores of the plaster mold, resulting in poor mold release. It is easy to cause

(3) It takes a long time to dry the plaster mold after it is released.

(4) Gypsum has poor wear resistance and dissolves in extremely acidic or alkaline slurry, resulting in a short mold life.

There are drawbacks such as. On the other hand, in order to improve the service life, it is known to use molds made of resin, calcium silicate, or fiber-reinforced composite materials, but these are expensive and inferior to plaster molds in both water absorption and mold release properties.

There is also known a method in which a mold is made by compacting dry powder, such as alumina powder, and after casting, the powder is broken down to take out the molded body, and the powder is dried and reused. According to this method, mold release is relatively easy, and drying of the mold is replaced with drying of the powder, so the drying time can be significantly shortened. However, on the other hand, there are severe restrictions on the properties of the powder. In other words, in order to create a firm mold that does not lose its shape, it is necessary to increase the particle size of the powder, but if the particle size is increased, not only will the slurry penetrate between the particles, causing poor mold release.
Water absorption rate decreases. For this reason, a compromise has been made by using powder having a particle size close to that of the powder constituting the slurry. Another problem lies in the mold manufacturing method.
That is, mold manufacturing by tamping has a limit to the shapes that can be manufactured, and cannot be applied to complex shapes.

[Problem that the invention seeks to solve]

The purpose of the present invention is to provide a slurry casting method that can solve the problems of the conventional casting method as described above, and enables a significant reduction in molding time and the repetition of a mold material with good mold releasability. It is something to do.

[Means for solving problems]

The present invention is a slurry casting method in which a mold is constructed from a swellable powder, slurry is poured into the mold, and the powder absorbs water in the slurry, thereby dehydrating and hardening the slurry to form a molded body. This is a method of molding the swellable powder into a desired mold shape. Further, a swellable powder is sealed in a closed space in a desired mold shape, the main part of which is a film and a filter, with at least the wall constituting the cavity being a water-soluble film, and the swelling powder is encapsulated by suction from the filter part. This is a slurry casting method that involves creating a mold by applying negative pressure to the closed space to maintain its shape.

[Effect]

The swelling powder in the present invention refers to acrylic acid,
Water-absorbing swelling powder or non-water-absorbing swelling powder selected from vinyl alcohol copolymer, sodium acrylate polymer, sodium acrylate/acrylamide copolymer, graft polymerization of acrylic acid based on starch, etc. Since it is a mixed powder with the above-mentioned water-absorbing and swelling powder, it becomes a filler with voids in a dry state, has water-absorbing properties, and the particles swell due to water absorption and are easily plastically deformed. is a powder that does not form chemical bonds between particles.
In addition, this powder has a water absorption capacity of 20 to 50 g (moisture)/g (gypsum), whereas the water absorption capacity of the resin powder is 50 to 1000 g (moisture)/g (resin powder).
It is characterized by being extremely large.

Although the particle size of the powder is not uniformly determined, it is desirable to select it as appropriate from the range of about 20 to 1000 μm in dry state.

Films must be thermoplastic, tear resistant, have appropriate elongation, high tensile strength, and have an appropriate thickness.Polyethylene film, polypropylene film, soft vinyl chloride film, vinylon film, water-soluble film, hydrochloric acid rubber film , polybutylene film, etc., and its thickness cannot be determined uniformly as it varies depending on the shape of the target mold, the place where the film is applied, etc., but it should be selected as appropriate from 20 to 200 μm. This is desirable.

The water-soluble film applied to the walls constituting the cavity must, in addition to the above-mentioned properties, dissolve in water in a short period of time at a working temperature of about 10 to 35°C. Preferably, polyvinyl alcohol-based and methylcellulose-based water-soluble films are suitable. Film thickness is 20~
It is advisable to select an appropriate one from those with a diameter of 200 μm.

The filter is to prevent the powder that makes up the mold from scattering into the suction system, and it is desirable that it is resistant to clogging and has low pressure loss. For example, use a 200 to 250# wire mesh made of plain data weave. .

Examples of the present invention will be described below.

〔Example〕

FIGS. 1 to 9 are explanatory diagrams specifically showing the operation of an example of an embodiment of the method of the present invention.

First, as shown in FIG. 1, a surface plate 2 having a vent hole is installed above a suction box 1, and a model 3 is further installed at a predetermined position above the surface plate 2. Next, the second
As shown in the figure, a vacuum suction system consisting of a three-way switching valve 4, a dust filter 5, and a vacuum pump 6 is connected to the suction box 1, and above the model 3, a clamp frame 8 holding a water-soluble film 7 and an electric heater are connected. Install 9. In this case, the heater is not limited to an electric heater, but also a gas heater,
The vacuum pump 6 is operated while the water-soluble film 7 is heated, which may be a hot air heater. In order to promote the elongation of the water-soluble film 7, water vapor may be added in combination. When the water-soluble film 7 reaches the appropriate molding temperature, move the clamp frame 8 to the surface plate 2 as shown in FIG. Remove clamp frame 8.

Next, as shown in FIG. 4, a metal frame 11 having a filter 10 is placed on the surface plate 2, which is entirely fixed to a vibration table 17, so as to surround the model 3.
In addition to this, a three-way switching valve 12, a dust filter 13,
After connecting the vacuum suction system consisting of the vacuum pump 14 and placing the sleeve 15 covered with the film 7 on the model 3, the swellable powder 16 is introduced, and the vibration table 17 is operated to remove the swellable powder 16. is packed tightly inside the metal frame 11, and excess powder is removed by scraping. Afterwards, as shown in Figure 5, the gold frame 1
1, the film 18 is clamped onto the frame 8.
The film 18 is sandwiched between the film 18 and the electric heater 9 is installed.
is heated while the vacuum pump 14 is operated.
When the film 18 reaches the appropriate molding temperature, the clamp frame 8 is moved to the metal frame 11, the film 18 is brought into close contact with the swellable powder 16 by vacuum suction, and the clamp frame 8 is removed.
The metal frame 11 is covered with the film 18 and the metal frame 11 as shown in FIG. Then, as shown in FIG. 7, the metal frame 11 is moved upward to perform die cutting. The upper mold is molded using the metal frame 19 using the same procedure as the lower mold molding described above, and as shown in FIG. Break the hole and complete the cavity.

On the other hand, slurry 21 is charged into a closed type stirrer 20, and while stirring and mixing, the vacuum pump 22 is operated to defoam. When the defoaming is completed, the vacuum pump 22 is stopped. After connecting the slurry discharge pipe 23 to the sleeve 15, the air compressor 24 is operated to discharge the slurry under pressure and cast it into the cavity 25. After casting, the air compressor 24 is stopped, the three-way switching valve 26 is switched, atmospheric air is introduced, the pressure is maintained at atmospheric pressure, and the slurry is kept pressurized by the differential pressure with the negative pressure inside the mold. The pressure is important for preventing casting defects such as shrinkage and for promoting inkling, but it must not exceed atmospheric pressure to prevent damage to the mold. Cavity 25
Inside, the water in the slurry becomes water-soluble films 7 and 18.
When it penetrates and dissolves it and creates a hole, the cavity 25
The residual air escapes into the swellable powder layer, and the slurry completely fills the cavity. The swellable particles that come into contact with water swell and plastically deform, filling and closing the voids, so that the cast body is surrounded by a void-free swellable powder layer via the dissolved water-soluble films 7 and 18. In this way, the particles in the slurry are completely prevented from moving into the mold, and the water is absorbed into the swellable powder without relying on capillary forces, while being evaporated and removed by the suction of the vacuum pumps 6 and 14. . In this way, the cast body dehydrates and hardens to become a molded body, but during this time, even if it contracts during dehydration, the swollen powder follows and expands, so the mold does not separate and the cavity wall is always in contact with the infill layer, increasing water absorption. last.

Next, the slurry discharge valve 27 is closed, the slurry discharge pipe is removed, and the metal frames 11 and 19 are placed on the screen 28 shown in FIG. Return the upper mold to atmospheric pressure. Subsequently, the vacuum pump 6 is stopped and the three-way switching valve 4 is switched to return the lower mold to atmospheric pressure.
Through this operation, the swellable powder in the metal frames 11 and 19 collapses under its own weight, breaks the water-soluble films 7 and 18, passes through the screen 28, and falls, and the water-soluble film 7 adheres to the surface. A molded body 29 left on the screen. The water-soluble film 7
can be easily wiped off. Note that the number of cavities in the mold is not limited to one, but it is also possible to increase productivity by forming multiple cavities at the same time.

Next, in the method of the invention described above, an α-alumina slurry consisting of 68.0% by weight of α-alumina powder (particle size 0.1 μm to 2 μm), 31.7% by weight of water, and 0.3% by weight of carboxymethyl cellulose was prepared, and vinyl acrylate was prepared as a water-absorbing and swelling powder. Alcohol copolymer (average particle size: 200 μm), film, and water-soluble film were both polyvinyl alcohol (thickness: 50 μm). The cavity consists of a shaft with a diameter of 20 mm and a length of 60 mm, and a disk with a diameter of 80 mm and a thickness of 15 mm attached 20 mm from one end of the shaft. When the negative pressure for holding the mold was set at -400 mmHg and the mold was released after 3 hours of dehydration after casting, there was no problem with mold release and a sound molded product could be obtained.
The water-absorbing swelling powder that absorbed water could be regenerated into dry powder by vacuum drying at 80°C and 2 Torr for 3 hours. 10 times water absorption,
Repeated drying did not change the water absorption performance at all; by the way, the water absorption performance of plaster decreases after it is used several times after being molded.

〔Effect of the invention〕

The slurry casting method of the present invention enables a significant reduction in molding time, good mold releasability, and a significant reduction in the required time by replacing drying of the mold with powder drying, allowing easy production of molds and use as a mold material. By repeatedly using the water-absorbing swelling powder, the problem of longevity can be solved and the drawbacks of the gypsum method can be overcome.

[Brief explanation of drawings]

FIGS. 1 to 9 are explanatory diagrams of the operating method in an embodiment of the method of the present invention. In the figure, 1: suction box, 2: surface plate,
3: Model, 4, 12, 26: Three-way switching valve, 5, 1
3: Dust filter, 6, 14, 22: Vacuum pump, 7: Water-soluble film, 8: Clamp frame, 9: Heater, 10: Filter, 11, 1
9: Metal frame, 15: Sleeve, 16: Swellable powder,
17: Vibration table, 18: Film, 20: Closed stirrer, 21: Slurry, 23: Slurry discharge pipe, 2
4: Air compressor, 25: Cavity, 28: Screen, 29: Molded body. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. Slurry casting characterized by casting slurry into a mold made of swellable powder, allowing the powder to absorb water in the slurry, and dehydrating and hardening the slurry to form a molded body. Method of molding. 2. A swellable powder is sealed in a closed space in a desired mold shape consisting of a film and a filter, the walls of which constitute at least the cavity are made of a water-soluble film, and the swelling powder is swelled by suction from the filter section. 2. The slurry casting method according to claim 1, wherein the mold is formed by maintaining the shape by applying negative pressure to the closed space. 3. The water-absorbing swelling powder is selected from acrylic acid/vinyl alcohol copolymer, sodium acrylate polymer, sodium acrylate/acrylamide copolymer, graft polymerization of acrylic acid based on starch, etc. 2. The method of slurry casting according to claim 1, wherein the slurry is a mixture of one type of water-absorbing swelling powder, a non-water-absorbing swelling powder, and the water-absorbing swelling powder. 4. The slurry casting method according to claim 3, wherein the particle size of the swollen powder is 20 to 1000 μm. 5. Claims characterized in that the film is one type of thermoplastic film selected from polyethylene, polypropylene film, soft vinyl chloride film, vinylon film, water-soluble film, hydrochloric acid rubber film, polyethylene film, etc. The method of slurry casting according to item 2. 6. The slurry casting method according to claim 5, wherein the film has a thickness of 20 to 200 μm. 7. The slurry casting method according to claim 2, wherein the water-soluble film applied to the wall constituting the cavity is soluble in water at a working temperature of about 10 to 35°C. Method. 8. The slurry casting method according to claim 7, wherein the water-soluble film is a polyvinyl alcohol-based or methylcellulose-based water-soluble film.