DIES FOR EXTRUSION-SHAPING CERAMIC HONEYCOMB STRUCTURAL BODIES

Abstract: Ceramic honeycomb structural body-extruding dies are disclosed which each comprise a plurality of die-constituting members (2, 5). The die-constituting members are bonded together with a bonding layer (7). To avoid solution of the bonding layer (7) by acid used to remove plating layers applied to the die to control dimensions, the bonding layer is composed of an acid-resisting metal, e.g. Au.

Description: The present invention relates to dies for extrusion-shaping of ceramic honeycomb structural bodies (hereinafter referred to as "ceramic honeycomb structural body extruding dies"). Ceramic honeycomb structural bodies are used as catalyst carriers for purifying exhaust gases from internal combustion engines, filters for removing fine particles in exhaust gases, and heat exchangers for exhaust gases, and are produced by an extrusion-shaping process. However, in order to improve catalyst-purifying performance and filtering performance, there has recently been a demand for enlarging the surface area in ceramic honeycomb structural bodies. For this purpose, it is necessary that the number of cells per unit sectional area of the honeycomb structural body is increased, the thickness of the partition walls is reduced, and dimensional precision is increased. Therefore, the dies used in the extrusion-shaping process are required to have a decreased channel width, a decreased channel pitch, and a higher dimensional precision. In order to satisfy the above requirements, it is known that excellent dimensional precision extrusion-shaping dies with a channel width of not more than 0.3 mm are obtained by forming extrusion-shaping channels in the dies by plating (JP-A-55-140,514). It is also known that when the shaping channels of the die as obtained by the above method are abraded with a ceramic material, the desired shaping channels are regenerated by chemically dissolving off the abraded plated layer and plating them again (JP-A-55-140,515). EP 83850 discusses a method of making a composite type die plate for extruding honeycomb structures. A feed plate and a discharge plate are bonded by brazing or soldering, preferably with copper. As honeycomb structural body-extruding dies, there is also known an extrusion die with a structure having ceramic material-holding portions for temporarily holding the ceramic material therein provided between ceramic material-supply holes to which a ceramic material is first fed from an extrusion machine and the lattice-form shaping channels giving the shape of the desired ceramic honeycomb structural body (US-A-3,038,201). Further, in another die ceramic material-flowing sections are provided between the ceramic material-supply holes and the shaping channels for uniform flow of the ceramic material through the die (JP-A-54-8,661). JP-A-55-140,515 relates to an extremely excellent method of regenerating a die as mentioned above. However, this method has a drawback that since the plated layer of Ni or the like is dissolved off with an acid such as nitric acid, a bonding layer is partially or entirely corroded with the acid, when die-constituting members are bonded together with silver solder or the like. When the bonding layer is entirely corroded, the die is decomposed into, for instance, a member having the supply holes for a ceramic material to be extruded (hereinafter referred to as ceramic material-supply hole member), a member having extrusion-shaping ceramic material holding portions (hereinafter referred to as a ceramic material-holding member) and a member having shaping channels (hereinafter referred to as shaping channel member). Consequently, the die can no longer be regenerated again. Even if the bonding layer is partially corroded, uneven portions are formed in the corroded bonding layer, so that the flow of the ceramic material is disturbed by the unevenness. As a result, a strain remains in extrusion-shaped bodies, causing cracks therein during firing. In the die structure disclosed in US-A-3,038,201 or JP-A-54-8,661 in which the dimension of the shaping channels is made small and therefore the flow of the ceramic material needs to be improved, it is necessary from the standpoint of mechanical working that the shaping channel member, the ceramic material-supply hole member, and a member having the ceramic material-flowing sections provided between the shaping channel member and the ceramic material-supply hole member (hereinafter referred to as "ceramic material-flowing member") and/or the ceramic material-holding member are separatedly machined, and then bonded together. In this case, since the bonding area is small, even a small degree of the corrosion largely causes the deterioration of the bonding strength. Thus, there is a problem that the shaping channel member and the ceramic material-holding member are separated to disable the assembling thereof. Beside the case where, as mentioned above, the plated layer in the shaping channels is dissolved off with acid and the die is regenerated through plating, there is a problem that the use life becomes shorter because the die is corroded with the ceramic material during the extrusion-shaping process. Thus, the composition of the ceramic material needs to be selected to cause no corrosion of the die. Other background art is given in two US documents; US 2195314 discusses a method of joining a pair of metallic objects by assembling the objects with the surfaces to be united in contact with opposite faces of a sheet of an alloy containing some gold or silver, and cadmium, applying heat and pressure until the cadmium has substantially entirely escaped from the sheet, and then melting the gold or silver to unite the objects. US 3283616 relates to a process for producing composite spinnerettes; bonding is effected by providing a very thin bonding layer to raise the accuracy of the spun yarns. The bonding layer may be gold. Therefore, the present invention seeks to to eliminate or reduce at least some of the above problems. The present invention is set out in claim 1. According to the present invention, since the ceramic honeycomb structural body-extruding die can be produced by separately machining each of a plurality of the die-constituting members, for instance, a shaping channel member, etc., and subsequently bonding them together, a complicated configuration of honeycomb structural dies or dies having thin partition walls constituting a honeycomb structure can be easily obtained. Further, since the bonding layer is corrosion-resistant and will not be corroded with a material being extruded, the use life is long. In addition, since the bonding layer withstands the corroding action of an acid used to dissolve off a plated layer which is applied to narrow the width of the shaping channels, a plated layer giving a uniformly narrow shaping channel width can be restored over the whole of the shaping channels easily by removing the plated layer after the plated layer is abraded and plating the shaping channels again. Therefore, expensive dies having a large size and a complicated configuration can be repeatedly used through regeneration. Embodiments of the invention will be given by way of example in the following description of the invention. For a better understanding of the invention, reference is made to the attached drawings, wherein: Fig. 1 is a sectional view illustrating an embodiment of one die embodying the present invention; Fig. 2 is a front view of Fig. 1 as viewed from an extruding face of the die; Fig. 3 is a front view of Fig. 1 as viewed from an extruding machine side; and Fig. 4 is a sectional view illustrating another embodiment of the die according to the present invention. In Figs. 1 to 3, as illustrated in JP-A-54-8,661, a ceramic honeycomb structural body-extruding die 1 comprises a first metallic member 2 and a second metallic member 5. Shaping channels 3 and flow paths 4 communicating therewith are formed in the first metallic member 2 by machining. The flow paths 4 are each designed in a form of a hole, and have selected intersection points of the lattice of the shaping channels 3 as their centers. In the second metallic member 5 are provided ceramic material-supply holes 6 to which a ceramic material is fed by an extruding machine. The ceramic material-supply holes 6 are through holes having a diameter larger than that of the flow path 4, and also have selected intersection points of the lattice of the shaping channels 3 as their centers. The first metallic member 2 and the second metallic member 5 are bonded together by a bonding layer 7 to form the ceramic honeycomb structural body-extruding die 1. The bonding layer 7 is made of a metal which will not be corroded with a plated layer-removing acid. Any metal having an arbitrary purity or an alloy can be used as the metallic material of the bonding layer so long as it will not be corroded by the extruded ceramic material and withstands the corroding action of the acid used for dissolving off the plated layer which adjusts or narrows the width dimension of the shaping channels, and it is able to bond the die-constituting members through fusion. A metal composition mainly consisting of gold is preferable. In a preferred embodiment according to the present invention, the bonding layer is a gold brazing layer. A gold brazing process is carried out, for instance, by a method specified in JIS Z 3266. A brazing temperature may be determined depending upon a kind of the brazing material, and selected at a temperature from about 400 to about 800°C in view of the brazing strength. In another preferred embodiment according to the present invention, a gold layer which is provided on one member through gold plating, gold foil deposition, gold vapor deposition, etc. is sandwiched between the members, and is heated at about 1,050 to about 1,080°C to fuse the gold and bond the members together. In order to increase the bonding strength, the thickness of the gold layer is preferably from about 5 to 30 µm. The width of the shaping channels may be machined in the same thickness of the partition wall of the extrusion-shaped bodies. However, as described in JP-A-55-140,514, when the former is made larger than a desired dimension through the machining and then adjusted to the desired dimension through a non-electrolytic plating, the desired small width channels can be attained. When the channel width becomes wider than an allowable dimension through abrasion, etc., the die can be regenerated by plating it again as described in JP-A-55-140,514. The present invention is not restricted to the structure of the bonding layer as shown in Figs. 1 to 3, but an extruding die 1 may be constituted as shown in Fig. 4 such that bonding layers 7 are interposed between a first metallic member 2 in which ceramic material-supply holes 6 and ceramic material-holding portions 8 communicating therewith are machined, a second metallic member 5 with shaping channels 3, and a third metallic member 9 provided with shaping channels 3'. This embodiment is extremely effective in the case that the depth of the shaping channels is required to be increased to make the dimension of the partition walls of the honeycomb structural body extremely small and to make uniform the density of the extrusion-shaped bodies. In addition, although not shown, the bonding layer may be provided between the ceramic material-supply hole member, the ceramic material-holding member and the shaping channel member, or inside these members. According to the present invention, the following effects can be attained. Since the shaping channels having a uniform and narrow channel width can be maintained at a high precision for a long time period over the entire die, high quality and thin wall ceramic honeycomb structural bodies can be stably produced. In addition, cracking does not occur due to an non-uniform shaping density during firing. Furthermore, since the die can easily and simply be regenerated, expensive dies having a large size and a complicated shape can be inexpensively and precisely regenerated and need not be disposed of. For this reason, the dies according to the present invention enable the mass and inexpensive production of ceramic honeycomb structural bodies for the purification of exhaust gases from automobiles, catalyst carriers, filters, and rotary type heat exchangers in gas turbines, etc. and are extremely industrially useful.

Claims: An extrusion die for ceramic honeycomb structural bodies, comprising a plurality of die-constituting members (2,5;2,5,9,) bonded together with a metal bonding layer (7), said die-constituting members (2,5) being a first metallic member (2) having shaping channels (3) and flow paths (4) communicating therewith, and a second metallic member (5) having ceramic material-supply holes (6) communicating with said flow paths, characterised in that said shaping channels (3) in the die have wall surfaces formed by acid-soluble plating metal and in that said metal bonding layer (7) is composed of an acid-resistant metal, such that an acid treatment for removing the plating metal layer of the shaping channels (3) will not corrode the metal bonding layer (7). A ceramic honeycomb structural body-extruding die according to claim 1 wherein the metal bonding layer (7) has a thickness in the range 5 to 30µm. A ceramic honeycomb structural body-extruding die according to claim 1 or claim 2, wherein the metal bonding layer (7) is a metal composition mainly consisting of gold. A method of regenerating the extrusion die according to claim 1, wherein the method includes the steps of acid-treating the die to dissolve the acid-soluble metal plating of the shaping channels (3) and replating the shaping channels (3) with an acid-soluble metal. A method of manufacture of an extrusion die for ceramic honeycomb structural bodies, wherein the method includes the steps of bonding together a first metallic member (2) having shaping channels (3) and flow paths (4) communicating therewith and a second metallic member (5) having ceramic material-supply holes (6), such that the material-supply holes (6) communicate with the flow paths (4); characterised by plating the shaping channels (3) with acid-soluble metal, and by bonding together said first and second metallic members (2,5) with an acid-resistant metal bonding layer (7). A method according to claim 5 wherein said acid-resistant metal bonding layer (7) is formed to a thickness in the range 5 to 30 µm.

Inventors: FUTAMURA, SHOJI INSTITUTE OF TECHNOLOGY PRECISION, OZAKI, SEI
Applicants: INSTITUTE OF TECHNOLOGY PRECISION ELECTRICAL DISCHARGE WORKS, NGK INSULATORS, LTD.
Application year: 1987
Main classification: B28B3
IPC codes: B28B3