Apparatus for pressure slip casting
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of and an apparatus for pressure slip casting of pottery articles such as sanitary ware. 
     2. Description of the Relevant Art 
     As disclosed in Japanese Laid-Open Patent Publication No. 63(1988)-31709, for example, there is known a pressure slip casting apparatus in which a slip is poured into a mold placed horizontally on a mold table, and after a desired shaped article is produced in the mold, the excess slip is discharged from the mold. According to the disclosed pressure slip casting apparatus, the assembled mold is clamped vertically and laterally and placed horizontally on the mold table, and then the slip is poured into the mold and the excess slip is poured from the mold after the desired product is formed in the mold. 
     The mold has a slip inlet/outlet hole defined in a lower portion thereof. When the slip is introduced through the slip inlet/outlet hole into the molding space or cavity in the mold, air in a region near the inlet/outlet hole tends to be trapped in the slip. Since the air trapped in the slip cannot easily escape from the slip, the article produced in the mold is highly likely to contain unwanted cavities therein. In order to prevent air from being trapped in the slip, the slip has to be poured into the mold at a low speed. Furthermore, if the bottom of the molding cavity in the mold is flat, then the excess slurry cannot easily be discharged from the mold and it takes a long period of time to pour the excess slurry from the mold after the desired ware is formed in the mold. Therefore, the time required to mold a desired shaped product is long and the rate of production of such shaped articles is low. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method of and an apparatus for pressure slip casting, which prevent air from being trapped in a slip when the slip is introduced into a mold, so that high-quality articles can be produced, and which can introduce a slip into a mold and discharge an excess slip from the mold in short periods of time, resulting in a high efficiency with which shaped articles can be produced. 
     According to the present invention, there is provided a method of forming a shaped article through pressure slip casting with a mold having a molding cavity defined therein and a slip inlet/outlet hole communicating with the molding cavity, and a tiltable mold table having a support surface on which the mold is to be mounted, the method comprising the steps of positioning the mold on the support surface while the mold table is being maintained horizontally, tilting the mold table through a first angle with respect to a horizontal plane so that an inner end of the slip inlet/outlet hole is positioned near a lowermost end of the molding cavity in the mold, introducing a slip into the molding cavity through the slip inlet/outlet hole, and thereafter discharging excess slip from the molding cavity through the slip inlet/outlet hole. 
     According to the present invention, there is also provided an apparatus for forming a shaped article through pressure slip casting, comprising a mold having a molding cavity defined therein and a slip inlet/outlet hole for supplying a slip into the molding cavity and discharging excess slip from the molding cavity, mold table means having a support surface for placing the mold thereon, the mold table means being tiltable about a central axis, tilting means for tilting the mold table means about the central axis, and positioning means for positioning the mold on the support surface of the mold table means so that an inner end of the slip inlet/outlet hole is positioned near a lowermost end of the mold cavity in the mold, when the mold table means is tilted through a first angle with respect to a horizontal plane. 
     The above and further objects, details and advantages of the present invention will become apparent from the following detailed description of preferred embodiments thereof, when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a pressure slip casting apparatus according to an embodiment of the present invention; 
     FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1; 
     FIG. 3 is a cross-sectional view of a mold in the pressure slip casting apparatus shown in FIG. 1; 
     FIG. 4 is a side elevational view of a pressure slip casting apparatus according to another embodiment of the present invention; and 
     FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 4. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 through 3 show a pressure slip casting apparatus according to an embodiment of the present invention. 
     As shown in FIG. 1, the pressure slip casting apparatus includes a mold table 3 having a flat upper support surface 3a for placing a mold 20 thereon, the mold table 3 being tiltably supported at one end thereof on bearing holders 2 through pivot shafts 12. The opposite end of the mold table 3, which is remote from the pivotally supported end, is connected to a cylinder unit 8 for tilting the mold table 3. Therefore, the mold table 3 can be tilted upwardly or downwardly when the cylinder unit 3 is expanded or contracted. The mold table 3 has four corner support posts 4 extending vertically upwardly from the support surface 3a, a top plate 5 mounted on the upper ends of the support posts 4, a vertical clamping cylinder unit 6 mounted on the top plate 5 and extensible and contractable perpendicularly with respect to the support surface 3a, and a presser plate 7 mounted on the lower distal end of the piston rod of the cylinder unit 6. 
     As shown in FIG. 2, the mold 20, which is of a box shape or rectangular parallelepiped, is positioned on the mold table 3 such that a horizontal central line l 1  of the rectangular parallelepiped of the mold 20 is inclined at an angle α to a central axis l of the pivot shafts 12 about which the mold table 3 can be tilted. On the mold table 3, there is also mounted a horizontal clamping cylinder unit 9 for pressing a side mold member 22 (FIG. 3) in a direction parallel to the support surface 3a, the horizontal clamping cylinder unit 9 having an axis aligned with the horizontal central line l 1  of the mold 20. 
     A plurality of rocket pins 10 for positioning and fixing the mold 20 are mounted on the mold table 3, the rocket pins 10 projecting upwardly from the support surface 3a. As shown in FIG. 3, the mold 20 has positioning recesses 23f defined in a lower surface thereof, for receiving the rocket pins 10 respectively in snugly fitting engagement. 
     In FIG. 3, the mold 20 comprises an upper mold member 21, the side mold member 22, and a lower mold member 23, which jointly define a molding space or cavity C of desired shape therebetween. The upper mold member 21 has a porous resin layer 21a, a water-impermeable back layer 21b, and an iron plate 21c, which are successively arranged outwardly from the molding cavity C. The porous resin layer 21a has a plurality of water passages 21d defined therein which are connected to a common water pipe 21e extending out of the upper mold member 21. Likewise, the side mold member 22 and the lower mold member 23 have porous resin layers 22a, 23a, respectively, water-impermeable back layers 22b, 23b, respectively, and iron plates 22c, 23c, respectively. The porous resin layers 22a, 23a have water passages 22d, 23d defined therein which are connected to common water pipes 22e, 23e extending out of the side and lower mold members 22, 23, respectively. The positioning recesses 23f for receiving the rocket pins 10 are defined in the lower surface of the lower mold member 23. 
     A slip inlet/outlet hole 24 extends through the iron plate 22c, the water-impermeable back layer 22b, and the porous resin layer 22a of the side mold member 22, thereby providing communication between the molding cavity C and the exterior of the mold 20. The slip inlet/outlet hole 24 has an inner end 24a positioned such that it is located in the lowermost end of the molding cavity C when the mold 20 is tilted through a predetermined angle in response to angular movement of the mold table 3 about the pivot shafts 12. The slip inlet/outlet hole 24 is connected to a slip discharge pipe 26 through a valve 25 outside of the mold 20 and also to a slip supply pipe 28 through a valve 27 outside of the mold 20. 
     The lower mold member 23 has an air hole 32 defined therein for supplying air under pressure into the molding cavity C in order to force excess slip out of the molding space C after a desired shaped product is formed in the molding cavity C. The air hole 32 is connected through a valve 30 to an air supply pipe 31 outside of the mold 20. 
     The pressure slip casting apparatus of the aforesaid construction operates as follows: 
     As shown in FIG. 1, the mold table 3 is maintained horizontally, and the mold 20 is placed on the mold table 3 with the rocket pins 10 fitted respectively in the positioning recesses 23f. At this time, the box-shaped mold 20 is positioned such that the horizontal central line l 1  of the mold 20 is inclined through the angle α to the central axis l about which the mold table 3 is tiltable, as shown in FIG. 2. The angle α is selected such that when the mold table 3 is tilted to tilt the mold 20 through a predetermined angle with respect to a horizontal plane, a slip can flow most efficiently into and out of the molding cavity C through the slip inlet/outlet hole 24. The inner end 24a of the slip inlet/outlet hole 24 is located at an end of the molding cavity C near a position closest to the central axis l. 
     The vertical clamping cylinder unit 6 (FIG. 1) is actuated to cause the presser plate 7 to press the mold 20 downwardly, and the horizontal clamping cylinder unit 9 (FIG. 2) is actuated to press the side mold member 22. The upper, side, and lower mold members 21, 22, 23 of the mold 20 are now clamped together, with the molding cavity C tightly defined therebetween. 
     Then, the cylinder 8 is actuated to tilt the mold table 3 into a tilted position indicated by the imaginary line D in FIG. 1, and then inactivated to hold the mold table 3 in the tilted position. At this time, the mold table 3 is tilted through a certain angle with respect to the horizontal plane, with the inner end 24a of the slip inlet/outlet hole 24 being at the lowermost position in the molding cavity C. 
     The valve 25 is closed and the valve 27 is opened. A slip is then supplied under pressure from the slip supply pipe 28 through the valve 27 and the slip inlet/outlet hole 24 into the molding cavity C. 
     The slip as it is introduced into the molding cavity C goes upwardly from the lowermost position in the molding cavity C, forcing air upwardly and out of the molding cavity C through the air hole 32 and the valve 30, until finally the slip fills up the molding cavity C. Therefore, the air in the molding cavity C is prevented from being trapped in the slip when it is poured into the molding cavity C. 
     The water contained in the slip which has been introduced into the molding cavity C passes through the porous resin layers 21a, 22a, 23a and through the water passages 21d, 22d, 23d, and is then discharged out of the mold 20 through the common water pipes 21e, 22e, 23e. At the same time, the clay in the slip is deposited on the surfaces of the porous resin layers 21a, 22a, 23a which face the molding cavity C. 
     After the clay has been deposited to a desired thickness, the valve 27 is closed and the valve 25 is opened. Then, the valve 30 is opened and air under pressure is supplied from a pressurized air source (not shown) through the air supply pipe 31 into the molding cavity C. The excess slip in the molding cavity C is thus forcibly discharged out of the mold 20 through the slip inlet/outlet hole 24. 
     When the excess slip is discharged, the cylinder unit 8 may be actuated again to change the angle at which the mold table 3 is tilted, or may be reciprocally extended and contracted to swing the mold 20, for thereby discharging the slip at a higher speed. 
     In the above embodiment, the mold 20 is positioned on the mold table 3 by the rocket pins 10 and the positioning recesses 23f. However, the mold 20 may be positioned on the mold table 3 by a positioning block, a jack bolt, a positioning cylinder unit, or the like. 
     In the above embodiment, the present invention is applied to the pressure slip casting apparatus in which the excess slip has to be discharged out of the mold. However, the principles of the present invention are also applicable to a solid slip casting apparatus in which no excess slip is introduced and discharged. 
     A pressure slip casting apparatus according to the present invention will be described below with reference to FIGS. 4 and 5. Those parts show in FIGS. 4 and 5 which are identical to those of the previous embodiment are denoted by identical reference numerals, and will not be described in detail. 
     As shown in FIG. 5, the mold 20 has a horizontal central line l 2  extending parallel to a central line of the mold table 3 which is rectangular in shape, and the cylinder unit 8 for tilting the mold table 3 is connected to one corner of the mold table 3. The horizontal central line l 2  is inclined at an angle β to the axis l about which the mold table 3 is tiltable by the cylinder unit 8. When the mold table 3 is tilted through a predetermined angle, the slip inlet/outlet hole 24 is also in the lowermost position according to this embodiment. The other structural details of the pressure slip casting apparatus shown in FIGS. 4 and 5 are identical to those of the pressure slip casting apparatus shown in FIGS. 1 through 3. 
     According to the present invention, as described above, when the slip is poured into the molding cavity, air is prevented from being trapped into the slip. Therefore, any shaped pottery products formed according to the present invention are of high and stable quality. Furthermore, the slip can be introduced into the molding cavity at high speed, and the excess slip can be discharged out of the molding cavity in a short period of time. As a result, pottery articles can be manufactured at an increased rate according to the present invention. 
     Although there have been described what are at present considered to be the preferred embodiments of the present invention, it will be understood that the invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments are therefore to be considered in all aspects as illustrative, and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description.