Plastic and nonmetallic article shaping or treating: processes – Removal of liquid component or carrier through porous mold... – By direct application of vacuum or pneumatic pressure
Patent
1998-02-26
2000-12-26
Aftergut, Karen
Plastic and nonmetallic article shaping or treating: processes
Removal of liquid component or carrier through porous mold...
By direct application of vacuum or pneumatic pressure
425 84, 425 85, B28B 126
Patent
active
061653985
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of slip casting a powdery material such as an inorganic, organic, or metallic powdery material, a mold for use in a slip casting method, and a method of manufacturing an open porous body for use in a mold.
DESCRIPTION OF THE RELEVANT ART
Heretofore, molds for slip casting powdery materials have primarily been in the form of gypsum molds for various reasons. The gypsum molds are inexpensive, can easily be formed to shape, and, most importantly, have the following two superior properties for use as molds: (1) The gypsum molds have a self water absorption capability (Since some slurries used in the slip casting process employ an organic solvent rather than water, the term "water" used in the present invention should be interpreted as covering an organic solvent. Therefore, the water absorption capability is meant to include an ability to absorb an organic solvent.) (2) The gypsum molds allow molded products to be removed with good mold releasability.
A depositing step in a slip casting process causes water in a slurry to be absorbed by a porous mold. The water is absorbed by the porous mold under a differential pressure between a mold surface and a deposition surface (a boundary surface between a region where the slurry is deposited and a region where the slurry is not deposited). The differential pressure maybe developed by roughly two mechanisms, i.e., capillary attractive forces produced by the mold and an external pressure applied to the mold or the slurry, e.g., the gravity head pressure of the slurry, the forces applied to directly press the slurry, or the suction forces applied to evacuate the mold. The self water absorption capability, which is the first advantage of the gypsum molds, is produced by the capillary attractive forces, and allows a slurry to be deposited without applying an external pressure.
A mold releasing step of removing a molded product from a mold is important in the slip casting process. If the molded product is not smoothly released from the mold, the molded product will be deformed as it is soft. The reason why a gypsum mold provides good mold releasability is that since gypsum is poor in water resistance, the surface of the gypsum mold is dissolved into water little by little. Stated otherwise, the good mold releasability provided by the gypsum mold is achieved because the molding surface of the gypsum mold is peeled off together with the molded product.
As described above, the gypsum molds have two advantages, i.e., good mold releasability and self water absorption capability. These advantages, however, are associated with disadvantages. Because the self water absorption capability is achieved by the capillary attractive forces, the rate at which the slurry is deposited cannot be substantially increased, posing a limitation on efforts to increase the productivity. Inasmuch as the good mold releasability is provided by dissolving the molding surface of the mold, the molding surface will be greatly worn when the mold is used in many slip casting processes. The number of products that can be molded by one mold, i.e., the service life of one mold, is only in the range from 80 to 150.
In order to eliminate the above shortcomings of the gypsum molds, there has been used a mold of water-resistant resin. A slurry is deposited in the mold of water-resistant resin by directly applying a pressure to the slurry. Therefore, when the pressure applied to the slurry is increased, the rate at which the slurry is deposited is also increased. The mold of water-resistant resin provides mold releasability which is much lower than the gypsum molds. Therefore, it has been customary to deliver air under pressure to the mold of water-resistant resin, i.e., to apply a back pressure to the mold, for supplying water accumulated in the mold and the air to a boundary surface between the mold and the molded product thereby to release the molded product from the mold. Specifically, Japanese patent publication No. 2-15364 discloses an air gr
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Hasebe Katsuhiro
Hirayama Akira
Matsumoto Akio
Misumi Yoshifumi
Sato Takeshi
Aftergut Karen
Blackman William D.
Carrier Joseph P.
Toto Ltd.
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