EXTRUDING DIE FOR FORMING FINNED CERAMIC HONEYCOMB STRUCTURES

Abstract: An extruding die for forming finned ceramic honeycomb structures has wall forming grooves (3) for extruding a ceramic material and a plurality of material supply apertures (5) for supply of the ceramic material into the extruding die. The wall forming grooves open at the front surface of the die and intersect to form of a mesh corresponding to the sectional configuration of the ceramic honeycomb structure. The material supply apertures communicate with the wall forming grooves at intersecting zones thereof. To form fins, the extruding die has fin forming grooves (4) branching from the wall forming grooves for forming fins, and the material supply apertures (5) communicate with at least parts of the fin forming rooves. In forming a ceramic honeycomb structure with this die, it is easily formed uniformly in density in its entirety including fins, thereby preventing the fins from falling off during extruding and preventing cracks occurring in drying or firing.

Description: This invention relates to an extruding die for forming finned honeycomb structures by extruding. Ceramic honeycomb structures have been widely used as catalyzer carriers for purifying exhaust gases from internal combustion engines, filters for removing fine particles in the exhaust gases and heat exchange elements for the exhaust gases, because they are superior in heat resistance and corrosion resistance and have large surfaces contacting combustion gases with low pressure losses. In general, the ceramic honeycomb structures are manufactured by forming with extruding dies. An extruding die for this purpose is known from, for example, JP-B-61,592/82 whose die is provided with tapered portions between honeycomb forming grooves and extruding supply apertures for forming raw material into a honeycomb structure. Another extruding die is known from JP-B-1,232/76, wherein a solid block is provided with first and second channels, and supplied material is extruded from the first channels to the second channels to form a module. Moreover, a further die is known from JP-A-54-8,661 (US-A-4 118 456), wherein a feed hole member and an extruding slot member are formed with feed holes and extruding slots, respectively and small apertures are provided therebetween. Furthermore, US-A-3,038,201 discloses a die which comprises forming material supply apertures into which a ceramic material is first supplied from an extruder, grid-shaped forming slots and pooling areas between the supply apertures and the forming slots or temporarily accumulating the ceramic material therein. With all these extruding dies, the supply apertures for the ceramic material open at intersections of the extruding slots and communicate therewith, and only partition walls of honeycomb structures are formed by the ceramic material supplied into the supply apertures. A die for forming finned ceramic honeycomb structures is not yet known. In recent years, an attempt has been made to enlarge surface area per unit volume of the ceramic honeycomb structures in order to improve the purifying performance of catalyzer and filtering performance. For this purpose, a finned ceramic honeycomb structure (JP-A-61-167798) has been proposed. The inventors of the present application attempted to produce the proposed finned ceramic honeycomb structure by applying the above described extruding dies of the prior art. If finned ceramic honeycomb structures are formed by the use of the extruding dies of the prior art, fins branched from partition walls forming the honeycomb structures are uneven in height and width and even if the formed fins are sound in appearance, they are uneven in density so that cracks may occur when drying or firing the honeycomb structures. With the extruding dies for producing finned ceramic honeycomb structures, moreover, it is needed to inspect whether branched forming grooves provided in surfaces of the dies on outlet sides for ceramic materials has been formed with required accuracy in dimension without any damage. Such an inspection is troublesome and time-consuming operation. The inventors of the present application have investigated the problems arising in forming finned ceramic honeycomb structure by means of the extruding dies of the prior art and ascertained that the problems result from the fact that, in the dies of the prior art only formed with branched forming grooves for fins, the relation between ceramic material supply holes and branched forming grooves for forming the fins is indefinite and therefore that the ceramic material is not supplied into the branched forming grooves sufficiently to form complete fins although the material is uniformly supplied to form the partitions of honeycomb structures. It is an object of the invention to provide an improved extruding die for forming finned ceramic honeycomb structures, which eliminates or reduces the disadvantages of the prior art and which is able to easily form fins and an entire structure uniformly in density, thereby preventing the fins from falling off during extruding and preventing cracks occurring in drying or firing. The invention provides an extruding die for forming finned ceramic honeycomb structures as set out in claim 1. In order that the invention may be more clearly understood, embodiments will be described, by way of example, with reference to the accompanying drawings. Fig. 1a is an end view of an embodiment of an extruding die according to the invention on a ceramic material supply side; Fig. 1b is an end view of the die shown in Fig. 1a on a ceramic material exit side; Fig. 1c is a sectional view of the die shown in Fig. 1b taken along a line IC-IC in Fig. 1b; Fig. 2a is an enlarged view of a main part of the die on a front side; Fig. 2b is an enlarged view of a main part of another die according to the invention of a front side; Figs. 3a-3g illustrate various shapes of extruding forming grooves applicable to the die according to the invention; Fig. 4a is an enlarged view of a main part of a die manufactured in the Example of the specification on a material supply side; Fig. 4b is an enlarged view of a main part of the die on a material exhaust side; Fig. 4c is a partial sectional view taken along a line IVC-IVC in Fig. 4a; Fig. 5 is an enlarged sectional view illustrating a further embodiment of a die according to the invention; Figs. 6a and 6b are enlarged sectional views illustrating main parts of dies according to the invention; and Figs. 7a-7h illustrate various fin forming grooves for dies according to the invention. Figs. 1a, 1b and 1c illustrate an extruding die for finned honeycomb structures as a preferred embodiment of the invention in end views on material supply and exhaust sides and a sectional view taken along a line IC-IC in Fig. 1b. The extruding die consists of a first metal member 1 and a second metal member 2. The second metal member 2 is formed with forming grooves 3 for forming partition walls of the ceramic honeycomb structure and with fin forming grooves 4 branched from the forming grooves 3. The first metal member 1 is formed with material supply apertures 5 for supplying the ceramic forming material. The forming grooves 3 intersect with each other to form a mesh corresponding to a sectional configuration of the ceramic honeycomb structure to be formed. In this manner, this extruding die for finned ceramic honeycomb structures is formed with the forming grooves 3 and the fin forming grooves 4 branched therefrom which have predetermined depths from the material exit side to the material supply side or from the second metal member 2 toward the first metal member 1, respectively, and with a plurality of independent material supply apertures 5 from the material supply side to the material exit side or from the first metal member 1 toward the second metal member 2. The material supply apertures 5 form passages for causing to flow the ceramic forming material (ceramic batch) supplied from an extruder. The material supply apertures 5 are aligned with intersections of the forming grooves 3 and communicate with at least parts of or all the fin forming grooves 4 (Fig. 1a). According to the invention, one of the material supply aperture 5 communicates with at least part of each fin forming groove 4. The relation between the material supply apertures and the fin forming grooves 4 are shown in Figs. 2a and 2b. It is important to design the material supply apertures 5 with suitable opening diameters as shown by A, B and C in these drawings. Unsuitable openings are shown in broken lines. In Fig. 2a, each material supply aperture 5 opens substantially in alignment with an intersection of the forming grooves 3 and within a circle inside the four fin forming grooves about the intersetion. In Fig. 2b, each the material supply aperture opens substantially in alignment with a fin forming groove and within a circle inside one fin forming groove. In this embodiment of the die for extruding finned ceramic honeycomb structures, the fin forming grooves 4 are arranged only in the proximity of a center of the group of extruding forming grooves 3 (Fig. 1b). However, the fin forming grooves 4 may be provided over a wider zone from the center of the grooves 3 toward their outer circumference in order to obtain surface areas of the structure required for properties of a catalyzer. Although one embodiment of the dies according to the invention has been explained by referring to Figs. 1a, 1b and 1c, the present invention can be applicable to various extruding dies having particular configurations of the mesh formed by the intersections of the extruding forming grooves, which are polygonal in section such as triangular or hexagonal or circular, and having fin forming grooves 4 provided at mid portions or intersections of the extruding forming grooves 3 as shown in Figs. 3a-3g. The extruding die for finned ceramic honeycomb structures comprises the material supply apertures 5 for supplying the forming material (ceramic batch), which communicate with at least parts of the fin forming grooves 4 formed in the forming grooves 3. In extruding the material to form the ceramic honeycomb structure, therefore, fins of the structure can be easily formed uniformly in density as well as the entire structure, thereby completely preventing fins from falling off during extruding or preventing cracks occurring in drying or firing. With the extruding die according to the invention, the forming grooves 3 and the fin forming grooves 4 can be directly observed through the material supply apertures 5 so that clogging and other troubles of the grooves 3 and 4 can be easily inspected. Example Extruding dies according to the invention were made for forming finned ceramic honeycomb structures which had an outer diameter of 100 mm, height of 127 mm, a partition wall thickness of 0.2 mm, a cell pitch of 1.47 mm and a cell density of 300 cells/in². Fins having a height of 0.3 mm and a width of 0.2 mm were provided on partition walls within a circle having a diameter of 50 mm at a center of the honeycomb structure. Figs. 4a, 4b and 4c illustrate principal parts of the die in end views on its material exhaust and supply sides and a sectional view taken along a line IVC-IVC in Fig. 4a. As shown in the drawings, the extruding die comprises a die member 6 formed with forming grooves 7 for forming partition walls of the structure, fin forming grooves 8 for forming fins and material supply apertures 9 for supplying the material. Finned ceramic honeycomb structures were formed by the use of this extruding die. The material was prepared by kneading and conditioning a material containing cordierite crystal consisting of 25% of kaolin, 22% of calcined kaolin, 38% of talc and 15% of alumina, and 3.5% of an organic extruding aid and 30% of water. Fins of honeycomb structures were inspected during extruding. There was no damage or defect of the fins. The extruded honeycomb structures were fired at 1,400°C. The fired structures were observed for faults and cracks. There were no fault or crack in the structures. In this Example, the extruding die disclosed in the JP-B-61,592/82 was applied to the invention. However, the extruding dies disclosed in the JP-B-1,232/76 and US-A-3,038,201 may be applied to the invention. Fig. 5 and Figs. 6a and 6b illustrate extruding dies in cross-section which have been modified from dies of the prior art in order to apply them to the invention. Although the fin forming grooves for forming the fins on the partition walls of the ceramic honeycomb structures have been shown rectangular in the above example, the fin forming grooves may be circular, spherical, triangular, trapezoid grooves or chamfered rectangular grooves in section as shown in Figs. 7a-7h. Moreover, Figs. 7a, 7b and 7c illustrate relations between thicknesses of extruding forming grooves for partitions and diameters of circular or spherical grooves. Diameters D of the circular grooves are D=2T, D=T and D=0.6T in Figs. 7a, 7b and 7c, where T is a width of the extruding forming grooves. According to the invention, it is possible to advantageously prevent defective fins and cracks which otherwise unavoidably occur due to unevenness in density of extruded honeycomb structures. Moreover, the extruding die according to the invention is easy to manufacture. It is simple to inspect whether the extruding forming grooves and the fin forming grooves are formed with required dimensions by directly observing these grooves through the material supply apertures or to inspect whether any damage of these grooves occurs in use.

Claims: An extruding die for forming ceramic honeycomb structures, including wall forming grooves (3;7) for extruding a ceramic material opening at a front surface of the extruding die and intersecting with each other in the form of a mesh corresponding to the sectional configuration of the ceramic honeycomb structure, and a plurality of material supply apertures (5;9) for supply of the ceramic material into the extruding die, opening at a rear surface of the extruding die and communicating with said wall forming grooves, characterised in that, for forming finned ceramic honeycomb structures, said extruding die has fin forming grooves (4;8) branching from said wall forming grooves, said material supply apertures (5,9) communicating directly with at least parts of said fin forming grooves. An extruding die as set forth in claim 1, wherein each said fin forming groove (4;8) is provided substantially at a mid portion of a wall forming groove (3;7) between two adjacent intersections of that wall forming groove with other wall forming grooves. An extruding die as set forth in claim 2, wherein as seen in the extrusion direction each said material supply aperture (5;9) communicating with a fin-forming groove opens substantially in alignment with an intersection of the wall forming grooves (3;7) and within a circle circumscribing four fin forming grooves (4;8) located around said intersection. An extruding die as set forth in claim 2, wherein as seen in the extrusion direction each said material supply aperture (5;9) communicating with a fin-forming groove opens substantially in alignment with a fin forming groove (4;8) and within a circle circumscribing that fin forming groove. An extruding die as set forth in any one of claims 1 to 4, wherein said fin forming grooves (4;8) are arranged only at a central region of the extruding die. An extruding die as set forth in any one of claims 1 to 5, wherein said mesh formed by said wall forming grooves (3;7) has a cell configuration in section selected from triangular, square, hexagonal and circular configurations. An extruding die as set forth in claim 1, wherein said fin forming grooves (4) are provided at intersections of the wall forming grooves (3). An extruding die as set forth in any one of claims 1 to 7, wherein said fin forming grooves (4;8) are of a shape in section selected from circular, spherical, triangular, rectangular, trapezoid and chamfered rectangular shapes. An extruding die as set forth in claim 8, wherein said fin forming grooves (8) are circular in section with diameter D within the range 0.6T-2T, where T is the width of the wall forming grooves.

Inventors: INOUE, SATORU, MIZUNO, HIROSHIGE
Applicants: NGK INSULATORS, LTD.
Application year: 1987
Main classification: B28B3
IPC codes: B28B3, F01N3