A METHOD AND AN APPARATUS FOR EXTRUDING CERAMIC MULTI-LAYER STRUCTURAL BODIES

Abstract: A method and apparatus for shaping ceramic multi-layer structural bodies by extruding through a die. Ceramic layers (1,2) having different properties are fed under pressure, united and integrated in an extruding apparatus, while the thicknesses of the layers are controlled by adjusting extruding pressures. The extruding apparatus comprises a die (18) having a tip end opening of a given shape corresponding to the structural bodies to be extruded, a first extruding means (16) capable of feeding a ceramic molding compound to the die under a given pressure, and a second extruding means (17) for feeding another ceramic molding compound to the die. The second extruding means is provided separately from the first extruding means.

Description: The present invention relates to a method and an apparatus for extruding ceramic multi-layer structures, in which integral ceramic multi-layer structural bodies can be obtained from molding ceramic compounds having different compositions, grain sizes, color tones, etc. Two-layer structural bodies in which ceramics having different properties such as different compositions, grain sizes, water contents, viscosities, color tones, porosities, etc. are laminated in the form of two layers are employed for various uses. These multi-layer structural bodies are each integrally produced by forming a ceramic shaped body as a base layer, and then coating another ceramic layer on the ceramic shaped body. For instance, in order to produce a cylindrical two-layer structural body, a cylindrical ceramic shaped body is extruded or compression-molded as a base, and then another layer is formed on the thus shaped cylindrical ceramic body by dipping, brushing, or spraying a ceramic slurry. For example, depositing a slurry to make a thin electrode layer is mentioned on page 92 of "Fuel Cell Handbook", May 1988, DOE/METC-88/16096. For this purpose, at least two steps: an extrusion step or a compression molding step and a coating step are required to produce ceramic two-layer structural bodies, so that the number of the steps unfavorably increases. In addition, it is impossible to easily control the thickness of a coated layer in the coating step and a mixing state of a boundary layer. Furthermore, it is difficult to form a ceramic thin layer with a high viscosity slurry by dipping, brushing or spraying. It is an object of the present invention to solve the above-mentioned problems. The invention provides a method and an apparatus for extruding ceramic multi-layer structural bodies, in which multi-layer ceramic structural bodies can be obtained by a single extrusion step, and the thicknesses of layers and the state of a boundary layer can easily be controlled. The present invention provides a method for shaping a ceramic multi-layer structural body as set out in claim 1. The apparatus for extruding ceramic multi-layer structural bodies according to the present invention is set out in claim 6. In the invention, the moulding compounds having different compositions, grain sizes, water contents, viscosities, color tones, etc. are independently extruded, and united, laminated and integrated together inside the extruding apparatus, thereby obtaining the multi-layer structural bodies. Furthermore, by adjusting extruding pressures of the respective layers, the thicknesses of the layers are controlled. Thus, the multi-layer structural body in which the thickness of each of the layers is controlled can be obtained by a single extruding step. In addition, the mixed state of a boundary layer between the molding compounds can also be controlled by varying the uniting location of the molding compounds having different properties in the die. Moreover, according to the extruding apparatus of the present invention, the ceramic molding compounds having different properties are separately extruded under given pressures thereof by providing the first and second independent extruding means. Thus, the above-mentioned extruding method can favorably be achieved by this extruding apparatus. For a better understanding of the invention, reference is made to the attached drawings, wherein: Fig. 1 is a perspective view illustrating the structure of a two-layer ceramic structural body made according to the present invention; Fig. 2 is a view illustrating an embodiment of the extruding apparatus favorably used for extruding the ceramic multi-layer structural body having the shape shown in Fig. 1; Fig. 3 is a view illustrating a way of controlling a boundary face in the extruding apparatus shown in Fig. 2; Fig. 4 is a view illustrating the structure of another ceramic multi-layer structural body made according to the present invention; Fig. 5 is a view illustrating another embodiment of the extruding apparatus favorably used for extruding the ceramic multi-layer structural body having the shape shown in Fig. 4; Fig. 6 is a view illustrating a way of controlling a boundary face in the extruding apparatus shown in Fig. 5; and Fig. 7 is a view illustrating the structure of a further embodiment favorably used for extruding the ceramic multi-layer structural bodies shown in Fig. 1. In the two-layer structural body shown in Fig. 1, onto an outer peripheral surface of a cylindrical inner layer 1 is provided an outer layer 2 having a uniform thickness and different properties from those of the first layer. A dust-removing ceramic filter may be formed by varying porosity between the inner layer 1 and the outer layer 2. Fig. 2 is a view of illustrating the structure of an embodiment of an extruding apparatus favorably used for extruding the ceramic two-layer structural body having the shape shown in Fig. 1. In the extruding apparatus shown in Fig. 2, it is preferable that an inner cylinder 11 is provided concentrically with an outer cylinder 12. Ceramic molding compounds 14 and 15 having different properties are fed in the inner cylinder 11 and a space between the inner and outer cylinders 11 and 12, respectively. Pistons 16 and 17 are provided for extruding the ceramic molding compounds 14 and 15, respectively. A first extruding means is constituted by the inner cylinder 11 and the piston 16, while a second extruding means is constituted by the outer cylinder 12 and the piston 17. A die 18 having a tip end of a given cylindrical shape is connected to an end of the outer cylinder 12. The tip end of the inner cylinder 11 is arranged at a given location adjustable relative to the die 18. In this embodiment, since the inner layer 1 is made cylindrical, a core 19 is arranged in the center of the die 18 to obtain a cylindrical shape of products. In the extruding apparatus shown in Fig. 2, assume that pressures applied to the pistons 16 and 17 are taken as P₁ and P₂, respectively. When P₁ is made smaller than P₂, the thickness of the outer layer 2 can be made greater, while when P₁ is made greater than P₂, the thickness of the outer layer 2 can be made smaller. Fig. 3 is a view illustrating a way of controlling a boundary face between the inner layer 1 and the outer layer 2 for the extruding apparatus shown in Fig. 2. That is, when the end of the inner cylinder 11 is located nearer the die 18 in Fig. 2, the ceramic molding compound 14 is difficult to mix into the ceramic molding compound 15 at the boundary face. When the end portion of the inner cylinder 11 is located remoter from the die 18 in Fig. 2, the ceramic molding compound 14 is easily mixed into the ceramic molding compound 15 at the boundary face. By controlling the thickness of the outer layer 2 with the pressure of the piston and controlling the boundary face through adjusting the location of the end portion of the inner cylinder 11 as mentioned above, the thickness and the state of the boundary face can continuously be varied. Thus, the pressure and the location of the end portion can be determined depending upon the desired thickness and the state of the boundary face. In the two-layer structural body shown in Fig. 4, a surface layer 4 is provided on a surface of a planar base layer 3. The surface layer has a uniform thickness and properties, such as a grain size, a color tone, etc., different from those of the base layer 3. Fig. 5 is a view illustrating the structure of an extruding apparatus favorably used for extruding the ceramic multi-layer structural body shown in Fig. 4. In the extruding apparatus shown in Fig 5, a die 22 having a tip end of a given rectangular section is provided at an end portion of a base cylinder 21, and a side cylinder 23 is located at a side wall of the die 22. Ceramic molding compounds 24 and 25 having different properties are fed into the base cylinder 21 and the side cylinder 23, respectively. A first extruding means is constituted by providing a piston 26 in the base cylinder 21, while a second extruding means is constituted by providing a piston 27 in the side cylinder 23. In the extruding apparatus shown in Fig. 5, pressures applied on the pistons 26 and 27 are taken as P₃ and P₄, respectively. When P₃ is smaller than P₄, the surface layer 4 can be made thicker. When P₃ is greater than P₄, the surface layer 4 can be made thinner. Fig. 6 is a schematic view illustrating an example of controlling a boundary face between the base layer 3 and the surface layer 4 in the extruding apparatus shown in Fig. 5. That is, when the side cylinder 23 is positioned at a location nearer the tip end of the die 22, the ceramic molding compounds 24 and 25 are difficult to mix together at the boundary face. When the side cylinder 23 is located remoter from the tip end of the die 22, the ceramic molding compounds 24 and 25 are easily mixed at the boundary face. Fig. 7 is a view illustrating the structure of another embodiment of the extruding apparatus favorably used for extruding the ceramic multi-layer structural body shown in Fig. 1. In the embodiment shown in Fig. 7, a reservoir section 32 is formed in a base cylinder 31. A first extruding means is constituted by connecting a screw feeder 34 to the base cylinder 31 for extruding the ceramic molding compound 33. A second extruding means is constituted by connecting a feeder 36 to the reservoir section 32 for continuously feeding the ceramic molding material 35 into the reservoir section under a given pressure. In the extruding apparatus shown in Fig. 7, as is the same with the above-mentioned embodiments, it is not only possible to control the thickness of the outer layer 1 due to the extruding pressure but also to control the mixed state in the boundary layer by varying the location of the end portion of the reservoir section 32. Thus, ceramic two-layer structural bodies can continuously be obtained. The present invention is not limited to the above-mentioned embodiments only, and various modifications, variations and changes could be made. Although tubular or planar two-layer structural bodies have been explained by way of examples in the above-mentioned embodiments, the invention is not limited to production of such bodies. It goes without saying that the present invention can favorably be applied to two-layer structural bodies having different shapes, and also to three-layer structural bodies and the like in addition to the two-layer structural bodies. As is clear from the above-detailed explanation, according to the method and the apparatus for extruding the ceramic multi-layer structural bodies in the present invention, the multi-layer structural bodies are obtained by independently extruding, uniting, laminating and integrating molding compounds having different properties, and the thicknesses of the ceramic shaped layers having the different properties can be adjusted by controlling the extruding pressures of them. Thereby, the multi-layer structural bodies in which the thicknesses of the respective layers are controlled can be obtained by a single extruding operation.

Claims: A method for shaping a ceramic multi-layer structural body by extruding ceramic molding compounds (1,2;3,4) through a die, said method comprising the steps of separately feeding said ceramic molding compounds (1,2;3,4) having respectively different properties under pressure, uniting and integrating the ceramic molding compounds in an extruding apparatus, characterised by controlling thicknesses of layers of the respective ceramic molding compounds (1,2;3,4) by adjusting extruding pressures (P₁ ,P₂ ) of the respective ceramic molding compounds. The method claimed in claim 1, wherein the ceramic molding compounds are separately fed into and extruded through an inner cylinder (11) of a multiple wall-structural pipe constituted by the inner cylinder (11) and an outer cylinder (12), and a space between the inner cylinder and the outer cylinder, respectively. The method claimed in claim 2, wherein the mixing state of the ceramic molding compounds (1,2) in a boundary layer between the ceramic molding compounds is controlled by varying the location of a tip end of the inner cylinder (11) in the extruding apparatus. The method claimed in claim 1, wherein one of the ceramic molding compounds having the respective different properties is fed and extruded through a side wall of the extruding apparatus. The method claimed in claim 4, wherein the mixing state of the boundary layer between the ceramic molding compounds is adjusted by varying a location where one of the ceramic molding compounds having the different properties is fed through the side wall of the extruding apparatus. An apparatus for extruding ceramic multi-layer structural bodies, said apparatus comprising a die having a tip end opening of a given shape corresponding to the structural bodies to be extruded, a first extruding means (11,16) capable of feeding a ceramic molding compound to the die under a given pressure, and a second extruding means (11,15,17) for feeding another ceramic molding compound to the die, said second extruding means being provided separately from the first extruding means, characterised in that said first extruding means is formed by an inner cylinder (11) and a piston (16) arranged in the inner cylinder, and said second extruding means is formed by a space defined by the inner cylinder (11) and an outer cylinder (15) arranged around an outer periphery of the inner cylinder and a piston (17) placed in said space. The apparatus claimed in claim 6, wherein the inner cylinder (11) is movable inside the outer cylinder (15) in the extruding direction in order to adjust the end location of the space defined between the inner and the outer cylinders (11,15) relative to the tip end opening of the die.

Inventors: MISAWA, HIDENOBU
Applicants: NGK INSULATORS, LTD.
Application year: 1989
Main classification: B28B3
IPC codes: B28B3