Liquid-tight slip-casting molds and method for production thereof

Abstract: A mold (1) for cast-molding a slip under pressure is provided. The mold comprises a divisible casting mold (1) including at least two mold portions (8,9) to form a slip-­ depositing mold cavity (18) when mated together; a sealing material layer (11) attached onto at least the whole mating filter surface (16) of at least one mold portion to be mated; and a resilient material layer (10) attached onto one of the sealing material layer (11) and another mating filter surface (16), along slip-depositing divisible surfaces (12) of the filter layers (2); whereby the mold portions (8,9) mated together are provided with a resilient liquid-tight zone (14) between the mating filter surfaces (16). The mold is readily produced by coating at least the whole mating filter surfaces (16) of at least one mold portion (8,9) to be mated with a sealing compound; applying a releasing material between the mating mold portions (8,9), mating the mold portions, and hardening the sealing compound to provide a sealing material layer (11); and then bonding a resilient material sheet (10) onto one of the resulting sealing material layer (11) and another mating filter surface(16), along slip-depositing divisible surfaces (12) of the filter layers.

Description: This invention relates to a liquid-tight mold for cast-molding a slip under pressure to facilitate deposition of the slip, and a method for producing the mold. More particularly, this invention relates to improvement of conventional molds in increasing liquid-tight properties of the molds, enhancing performance of cast-molding operation, and preventing such molds from breaking. Cast-molding under pressure, wherein a slip is pressurized during deposition of the slip, has been widely used for producing green articles of sanitary ware such as stool ware, wash basin and the like. The molded articles are then fired into ceramic articles. According to a conventional method which uses a casting mold as shown in Fig. 2, there have been problems with respect to liquid-tight properties of the mold during cast-molding a slip under pressure. Such problems are markedly noted, when there is unevenness in the mating surfaces of the mold or when foreign matter enters between the mating surfaces. The conventional problems are further explained in detail in the comparative example of this specification. GB-A-792351 discloses a mold for casting a slip under pressure substantially as indicated in the preamble of claim 1. It also discloses a method for producing such a mold substantially as indicated in the preamble of claim 8. Thus, an object of the present invention is to provide a novel mold for cast-molding a slip under pressure, wherein the above-mentioned problems in conventional casting molds are eliminated by the use of both a resilient material layer and a sealing material layer in combination. Another object of the invention is to provide a method for producing the mold. The present inventors have found that such problems can be eliminated by providing the conventional divisible mold comprising mating filter layers with a sealing material layer at least on a mating filter surface of at least one mold portion to be mated and a resilient material layer at least on a part of the sealing layer or another mating filter surface. According to the invention there is provided a mold for cast-molding a slip under pressure which comprises a divisible casting mold including at least two mold portions to form a slip-depositing mold cavity when mated together; each mold portion comprising an air-tight housing and a filter layer of continuously porous structure inside of the housing; a slip supply duct being connected with said mold cavity and communicated with the outside of the housing; and wherein a sealing material layer is attached onto at least the whole mating filter surface of at least one mold portion to be mated: characterized in that a resilient material layer is attached onto one of the sealing material layer and another mating filter surface, along slip-depositing divisible surfaces of the filter layers, whereby the mold portions mated together are provided with a resilient liquid-tight zone between the mating filter surfaces. The invention also provides a method for producing a mold as defined above, which comprises coating at least the whole mating filter surfaces of at least one mold portion to be mated, with a sealing compound; applying a releasing material between the mating mold portions, mating the mold portions, and hardening the sealing compound to provide a sealing material layer; and characterized by then bonding a resilient material sheet onto one of the resulting sealing material layer and another mating filter surface, along slip-depositing divisible surfaces of the filter layers, whereby the mold portions mated together are provided with a resilient liquid-tight zone between the mating filter surfaces. Fig. 1 shows an enlarged cross-sectional view of the essential part of a mold according to the present invention. Fig. 2 shows a side cross-sectional view of a conventional mold. Fig. 3 shows a side cross-sectional view of another mold according to the present invention. Fig. 4 is an enlarged cross-sectional view of the part IV in Fig. 3. In the mold according to the invention, the air-tight housing can comprise a reinforcing housing 4 for the mold and a supporting layer for the filter layer installed between the housing and the filter layer. The filter layer in each mold portion can include therein fluid-flowing conduits 7 connected with a fluid-flowing duct to communicate with the outside of the housing. The fluid-flowing conduits 7 normally comprise curved porous cords or tubes arranged along the shape of the mold cavity 18, and/or straight blind holes installed towards the mold cavity 18. The thin resilient material layer 10 employed in the present invention unexpectedly serves to give a durable liquid-tight zone 14 between the mated filter surfaces 16 of the mold, to hold and sink possible foreign matter pieces in the resilient layer, and to give a small clearance between the mated filter surfaces and protect the filter surfaces from fracture due to the foreign matter pieces. Thus, the thickness of the resilient layer 10 is generally selected to hold and sink possible foreign matter pieces therein and not to substantially deteriorate uniform filtering performance of the slip-depositing surfaces. The width and elasticity of the resilient layer is generally selected to be readily compressed by relatively weak clamping force of the mating mold portions. The thin sealing material layer 11 in the present invention serves to protect the mating filter surfaces, to correct the surface conditions of the mating mold portions, to give air-tight properties to the mating filter surfaces for facilitating suction and pressurization of the filter layers, and to give good bonding properties with the resilient layer 10 to the mating filter layer. The thickness of the sealing layer 11 is generally selected to firmly adhere to the mating filter layer and not to substantially deteriorate uniform filter performance of the slip-depositing surfaces 12. The sealing material layer 11 may be attached onto one or both of the whole mating filter surfaces 16 of the mold portions. The sealing layer may extend onto the mating supporting layer, as necessary. The thickness of the sealing layer is usually 0.1 to 8 mm, preferably 0.3 to 1 mm. As the sealing material, can be used ordinary sealing compounds and preferably resinous sealing compounds comprising epoxy, urethane, silicone, polyester, phenol resin components, etc. The sealing material may be a commercially available resinous putty compound comprising resin materials and fillers. The resilient material layer 10 is attached onto at least a part of the sealing layer or another mating filter surface 16 of a mold portion, along slip-depositing divisible surfaces 12 of the mated filter layers and preferably apart from the slip-depositing surface with a receding distance (a) of at least 1 mm. The distance (a) is usually 1 to 20 mm, preferably 3 to 10 mm. By installing the resilient layer apart from the slip-depositing surface to form a receding zone 13, the resilient layer is prevented from protruding from the mating surfaces of the mold portions into the mold cavity 18 when the mold portions are mated together with clamping force. Incidentally, even when foreign matter gets in the receding zone 13 between the mold cavity and the resilient layer installed apart from the cavity, the filter layer is prevented from breaking and sufficient liquid-tight properties of the mold is obtained. This is because the clearance formed between the mating filter surfaces of the mold portions works to decrease the repulsive pressure of the foreign matter exerted upon the mating filter surfaces. As the resilient material can be used resilient rubber-like or sponge-like sheets having elasticity to form a liquid-tight zone 14 when compressed, such as non-porous silicone or urethane rubber sheets as well as polyurethane sponge sheets. In the case of sponge materials, substantially closed cell sponge materials are used because a slip does not permeate into the porous cells and elasticity of the sponge material is maintained to provide sufficient liquid-tight properties of the mold. Polyurethane or other synthetic rubber sponge materials are exemplified as a preferred sponge material. The thickness of the resilient layer is usually 0.2 to 5 mm, and preferably 0.3 to 3mm. The width (b) of the resilient layer is usually about 3 to 100 mm, preferably 4 to 50 mm. Thus, the resilient layer may cover a mating mold surface ranging from a part of the mating filter surface to both the mating filter surface and mating supporting layer surface. The resilient layer 10 can be bonded onto the sealing layer 11 or another mating filter surface with an adhesive. Epoxy or urethane resin adhesives are generally used as a preferred adhesive. The present invention will be further explained by way of the following examples with reference to the drawings. Example 1 (Comparative): A cross-sectional view of a conventional casting mold is shown in FIG. 2. Mold 1 is for cast-molding a wash basin, and a blank portion 18 within the mold is a mold cavity for molding the basin. The mold 1 comprises a filter layer 2, a supporting layer 3, and a pressure-resistant reinforcing housing 4 in a pile from the mold cavity outwardly. The mold is divisible into an upper mold portion 5 and a lower mold portion 6. The filter layer 2 is generally composed of a porous synthetic resin or gypsum, the supporting layer 3 is generally composed of a non-porous synthetic resin or cement mortar containing sand, and the pressure-resistant reinforcing layer 4 is generally composed of iron plates or iron frames and paint. Incidentally, within the filter layer 2 are normally installed fluid-flowing conduits 7 such as porous tubes 7 for suction and drainage of water contained in a slip during cast-molding and for supplying water under pressure to form a water film on the slip-depositing surfaces 2a during demolding the molded article. According to the cast-molding using the mold 1, a slip (a slurry of mineral powder for molding green articles) is supplied via a slip-supply duct 17 to a mold cavity formed in a divisible casting mold and pressurized to drive unnecessary liquid (e.g. water) contained in the slip into the mold, whereby the mineral components deposit onto the inner surfaces 2a of the mold. Remaining excess slip is drained from the mold cavity via the slip-supply duct 17 by setting the duct 17 to a gravitationally low position, when a hollow article is to be obtained. Then, the mold is divided into mold portions to take out a molded green article. In the mold 1, it has been necessary to liquid-tightly contact the mating surfaces of the upper mold portion 5 and lower mold portion 6 mainly by tightly contacting the supporting layers 3,3 with each other, because the filter layers 2,2 are porous and do not have a mechanical strength sufficient to bear the load and pressure for clamping the mold portions. In such a mold, liquid-tight properties of the mold are sometimes lost to lead leaking of the slip in the case where (1) there is an uneven portion in the mating surfaces, (2) foreign matter such as hardened clods of the slip or fragments of the mold materials enter between the mating surfaces of the mold, or (3) the filter layer is chipped off, which sometimes occurs when the mold portions 5,6 are strongly pressed to each other with foreign matter sandwiched between the mating filter surfaces because the filter layers are porous, weak and fragile. Moreover, when a slip-depositing surface 12 of the filter layers along the mating surfaces is chipped off, the resulting molded article suffers from a flash-like projection having a shape similar to the chipped portion and is deteriorated in surface properties thereof. Example 2 (Working): FIG. 1 shows an enlarged cross-sectional view of the essential part of a mold for cast-molding a slip under pressure according to the present invention. The essential part corresponds to the part A in FIG. 2 showing a conventional mold. In FIG. 1, the mold is divided into an upper mold portion 8 (corresponding to the portion 5 in FIG. 2) and a lower mold portion 9 (corresponding to the portion 6 in FIG. 2), which comprise supporting layers 3 and filter layers 2 of a continuously porous epoxy resin material. In this example, a sealing resin layer 11 is attached onto the mating surface of the lower mold portion 9, and the sealing resin layer 11 is not provided on the mating surface of the upper mold portion 8. The sealing layer 11 is produced with an epoxy resin putty compound. The sealing layer 11 is formed, for example, by coating the mating surface of the lower mold portion 9 with the epoxy resin sealing compound about 0.6 mm in thickness and applying a release agent (e.g. silicone or wax) onto the mating surface of the upper mold portion 8, and then mating the mold portions 8 and 9 to harden the resinous compound. By mating the mold portions and hardening the resinous compound, the mating surface patterns of the upper mold portion 8 are transfered to the surface of the resulting hardened resin layer on the lower mold portion. After the resinous compound is substantially hardened, the mated mold portions, 8 and 9 are separated. Since a release agent has been applied only onto the mating surface of the upper mold portion 8, the resinous sealing layer about 0.5 mm thick can be readily separated from the mating surface of the upper mold portion 8 and is firmly adhered to that of the lower mold portion 9. The sealing compound somewhat permeates into the filter layer and supporting layer, and then hardens to firmly adhere thereto. When the resinous sealing compound comes out from the mating surface of the lower mold portion 9 during hardening of the compound under mating to form fins around the mold portion 9, the fins can be cut off after the resinous compound is hardened. Incidentally, in order to prevent the mating surfaces of the upper mold portion 8 and lower mold portion 9 from failing to mate each other upon mating the mold portions, it is possible to provide one or more projection(s) on one of the mating surfaces and corresponding mating depression(s) on the other mating surface. These projection(s) and depression(s) are usually located at the four corners of the mating surfaces of the upper mold portion 8 and lower mold portion 9. A resilient material layer 10 is attached onto the resinous sealing layer 11 installed on the mating filter surface 16 of the lower mold portion 9. A polyurethane sponge sheet is used as the resilient material. The resilient material layer 10 is about 15 mm in width (b) and about 1.5 mm in thickness. The resilient material layer 10 is adhered onto the sealing layer 11 with an epoxy resin adhesive at a position about 6 mm apart from the slip-depositing surfaces 12 of the mold portions. In the casting mold thus produced, the both mold portions 8 and 9 mated together may provide some liquid-tight properties of the mold because the resinous sealing layer 11 is sandwiched between the mating surfaces 15,16 of the mold portions 8 and 9. Moreover, since the resilient material layer 10 is provided on one of the mating surfaces, the mating surfaces of the mold portions 8 and 9 mate together to form a liquid-tight zone 14, even when the mating position of these mold portions 8 and 9 is slightly slipped off. Example 3 (Working): FIGS. 3 and 4 show another embodiment of the present invention, in which a supporting layer 3 is not employed and a filter layer 2 directly contacts a pressure-resistant reinforcing housing 4. The materials of the sealing layer 11 and resilient layer 10 used herein are the same as in Example 2. The resilient layer 10 is about 20 mm in width (b) and about 2 mm in thickness, and is installed at a position about 6 mm apart from a slip-depositing surface of the mold (a = 6 mm). The sealing layer 11 is about 0.5 mm thick. The casting mold according to Example 3 brings about substantially the same effects as in Example 2, because the mold does not need a large clamping force when mating the mold portions and the filter layers are durable without the supporting layers. Although a sealing layer 11 is attached onto the whole mating surface of a mold portion in Examples 2 and 3, it is possible to form a sealing layer 11 only on the mating surface of the filter layer 2 or on the whole mating filter layer surface and a part of the supporting layer surface. Moreover, a sealing layer 11 may be attached onto the both mating surfaces of the mold portions, as necessary. The present invention is explained by way of examples for molding a wash basin to be built in a washing stand, which employ an upper mold portion and a lower mold portion. The invention, however, is not restricted to such a mold including two mold portions, and is applicable, for example, to a mold for cast-molding other articles such as stool sanitary ware which employs an upper mold portion, a lower mold portion and a side mold portion(s), and as necessary core mold pieces. In such cases, the sealing layers and resilient layers are provided between the respective mating surfaces of these mold portions. By using a casting mold according to the invention, there is no leaking of pressurized slip and water from the mating surfaces of the mold portions. Incidentally, pressurization of the slip is generally at least 0.5 Kg/sq.cm (5MPa) and normally 1 Kg/sq.cm (10MPa) of gauge or more. For example, the slip is pressurized to 10 ∼100 MPa to facilitate deposition thereof. In addition, even when foreign matter gets in between the mating surfaces 15,16 of the mold portions, the repulsive pressure of the foreign matter exerted upon the mated filter layers 2 will be decreased by the resilient layer 10 sandwiched between them, thereby preventing the mating filter surfaces from breaking. Namely, in the case where the foreign matter is located on the resilient layer 10, the foreign matter sinks in the resilient layer 10 upon mating the mold portions 8 and 9. Thus, by the elasticity of the resilient layer 10, liquid-tight properties at the mating surfaces of the mold portions 8 and 9 can be retained and the repulsive pressure of the foreign matter upon the mated filter layers 2 will be decreased. On the other hand, in the case where the foreign matter is located on a part of the mating surfaces 15,16 other than on the resilient layer 10, the repulsive pressure of the foreign matter exerted upon the mated filter layers 2 will be decreased by a clearance between the mating surfaces formed by the resilient layer 10 having thin thickness, whereby the mating filter surfaces will be prevented from breaking. Typical effects of the present invention are summarized below: (1) liquid-tight properties of a casting mold are enhanced to prevent a slip from leaking; (2) flash-like portions in the molded articles are eliminated and removal of the flash before drying the articles is not needed, whereby working efficiency of cast-molding is increased; (3) it is not necessary to precisely finish the mating surfaces of the mold portions to give even or smooth mating surfaces, because such surfaces are corrected by the sealing layer and resilient layer; and (4) adverse effects of foreign matter pieces present between mating filter layers are substantially eliminated.

Claims: A mold (1) for cast-molding a slip under pressure which comprises a divisible casting mold (1) including at least two mold portions (5,6) to form a slip-depositing mold cavity (18) when mated together; each mold portion comprising an air-tight housing (4) and a filter layer (2) of continuously porous structure inside of the housing (4); a slip supply duct (17) being connected with said mold cavity and communicated with the outside of the housing (4); and wherein a sealing material layer (11) is attached onto at least the whole mating filter surface (15) of at least one mold portion to be mated: characterized in that a resilient material layer (10) is attached onto one of the sealing material layer (11) and another mating filter surface (16), along slip-depositing divisible surfaces (12) of the filter layers (2), whereby the mold portions (8,9) mated together are provided with a resilient liquid-tight zone (14) between the mating filter surfaces (15,16). The mold according to Claim 1, in which the resilient material layer (10) is attached onto a sealing material layer (11) provided on the mating surface of the mold portion, along slip-depositing divisible surfaces (12) of the filter layers. The mold according to Claim 1 or 2, in which the airtight housing (4) comprises a reinforcing housing for the mold and a supporting layer (3) for the filter layer installed between the housing and the filter layer (2). The mold according to Claim 1, 2 or 3, in which each filter layer (2) includes therein fluid-flowing conduits (7), and a fluid-flowing duct is connected with the conduits and communicated with the outside of the housing (4). The mold according to any one of the Claims 1 - 4, in which the resilient material layer is provided at a receding distance (a) of at least 1 mm from the slip-depositing divisible surfaces (12) of the filter layers. The mold according to any one of Claims 1 - 5, in which the thickness of the resilient material layer (10) is substantially in the range of 0.2 - 5 mm and the width (b) of the resilient material layer is substantially in the range of 3 - 100 mm. The mold according to any one of Claims 1 - 6, in which the thickness of the sealing material layer (11) is substantially in the range of 0.1 - 8 mm. A method for producing a mold (1) as defined in Claim 1, which comprises coating at least the whole mating filter surfaces (15) of at least one mold portion (8) to be mated, with a sealing compound; applying a releasing material between the mating mold portions (8,9), mating the mold portions, and hardening the sealing compound to provide a sealing material layer (11); and characterized by then bonding a resilient material sheet (10) onto one of the resulting sealing material layer (11) and another mating filter surface (16), along slip-depositing divisible surfaces (12) of the filter layers (2), whereby the mold portions (8,9) mated together are provided with a resilient liquid-tight zone (14) between the mating filter surfaces (15,16). The method according to Claim 8, in which the resilient material layer (10) is attached onto a sealing material layer (11) provided on the mating surface of the mold portion, along slip-depositing divisible surfaces (12) of the filter layers. The method according to Claim 8 or 9, in which the air-tight housing (4) comprises reinforcing housing for the mold and a supporting layer (3) for the filter layer installed between the housing and the filter layer (2).

Inventors: ITO TAKESHI C O ENOKIDO KOJO, KOHMURA KUNIYOSHI C O ENOKIDO, MURATA KAZUSHIGE C O ENOKIDO K, ITO, TAKESHI, KOHMURA, KUNIYOSHI, MURATA, KAZUSHIGE, ITO, TAKESHI, C/O ENOKIDO KOJO, KOHMURA, KUNIYOSHI, C/O ENOKIDO KOJO, MURATA, KAZUSHIGE, C/O ENOKIDO KOJO
Applicants: INAX CORP, INAX CORPORATION
Application year: 1990
Main classification: B28B1
IPC codes: B28B7, B28B1