METHOD OF PRODUCING CERAMIC HONEYCOMB STRUCTURAL BODIES

Abstract: A die for extruding a honeycomb structural body, which is produced by forming a lattice of slits (2) having a given depth in the front surface of the matrix (1) of the die in a shape corresponding to the geometrical shape of a honey­ comb structural body to be extruded, forming a plurality of independent feed inlets (3) for a ceramic batch and communicated to the slits in the rear surface of the matrix, and forming a metal film (4) on the surface of the slits (2) by plating so that the slits (2′) have a given width, can be easily recovered its original given slit width by forming again a metal film on the surface of the slits by plating after the original metal film has been worn due to the abrasion by the ceramic batch.

Description: TITLE: METHOD OF RECLAIMING A DIE FOR EXTRUDING A CERAMIC BATCH INTO A HONEYCOMB STRUCTURAL BODY AND A DIE RECLAIMED BY SUCH METHOD Background of the invention 1) Field of the Invention: The present invention relates to a method of reclaiming a die for extruding a ceramic batch into a honeycomb structural body. 2) Description of the Prior art: There has been known a ceramic honeycomb structural body having a large number of parallel cells1 which are confined by a relatively thin lattice-like partition wall and extend therethrough in its axial direction, and having an open frontal area of about 60-90%, preferably 65-85%. Such kind of honeycomb structural body has been used for the catalyst supports for the purpose of removing harmful CO, HC and NOX from the exhaust gas by passing the exhaust gas through the cells so as to react it with a catalyst supported on the surface of the partition wall. The honeycomb structural body is manufactured by a method, wherein a ceramic batch is extruded through the extrusion die into a ceramic green body, and the ceramic green body is dried and fired, as described in U.S. Patent Specification No. 3,824,196. In the die for extruding the ceramic honeycomb structural body, a large number of slits formed in the front surface of the die are worn rapidly due to the abrasion by the ceramic batch extruded through the slits, and as the result the slit width is enlarged. Therefore, when the extrusion die having such an enlarged slit width is used as such, the thickness of partition wall between adjacent cells in the resulting honeycomb structural body is larger than the given thickness. That is, when slits of a die are somewhat worn, the die can be no longer used, and moreover the die cannot be reclaimed. Accordingly, expensive dies have hitherto been always discarded wastefully. Further, a honeycomb structural body having a circular, race track or an oval cross-sectional shape must be produced depending upon the demand. In this case, a mask having an opening, whose shape corresponds to the above described cross-sectional shape of the aimed honeycomb structural body, is arranged on the front surface of the die. When a part of slits formed in the peripheral portion of the die are closed by the mask, only the slits in the closed peripheral portion of the die, are not worn due to the absence of extrusion of ceramic batch. As the result, the width of worn slits in the opening portion is naturally different from the width of closed and unworn slits in the peripheral portion of the die. Therefore, when the originally used mask is replaced by a mask, whose opening is different in the shape and dimension from the opening of the originally used mask, the slit width in the peripheral portion of the die is different from that in the centre portion thereof, and the extrusion rate and amount of ceramic batch are locally different, and a honeycomb structural body can not be formed. Further, even if a honeycomb structural body could be extruded, the resulting honeycomb structural body cracks or deforms during the drying step and firing step following to the extrusion, and moreover the resulting honeycomb structural body has not a satisfactory shape. Accordingly, it is impossible to produce proper honeycomb structural bodies having different cross-sectional shapes by varying only the mask of one extrusion die. When masks having openings different in the shape or in the dimension are used, even if the masks are used by a method, wherein slits wear substantially equally in the central portion and peripheral portion of a die, in order to obviate the above described phenomena, the die can not be reclaimed. Therefore, the dies must be always discarded wastefully. Summary of the Invention The object of the present invention is to obviate the above described wasteful discarding of a conventional die for extruding a honeycomb structural body. That is, the feature of the present invention is the provision of a method of reclaiming a die for extruding a honeycomb structural body, which is manufactured by forming a lattice of slits having a given depth in the front surface of the matrix of the die in a shape substantially corresponding to the geometrical shape of a honeycomb structural body to be extruded, forming a plurality of independent inlets for feeding a ceramic batch and communicated to the slits in the rear surface of the matrix, and forming a metal film on the surface of at least-the slits by plating so that the slits have a given width, an improvement comprising recovering the original given width of the slits by forming again a metal film on the surface of at least the slits by plating after the original metal film has been worn up to improper shape for a further extrusion due to the abrasion by the ceramic batch at the extrusion. Brief Description of the Drawinqs Figure 1 is a vertical sectional view of an extrusion die according to the present invention: Figure 2 is a horizontal sectional view of the die shown in Figure 1: and Figure 3 is a plan view of the die shown in Figure 1 in reduced scale, illustrating the mode of mounting a mask having an oval opening. Description of the Preferred Embodiments The present invention will be explained in more detail referring to the drawings. In Figures 1 and 2, the numeral 1 represents a matrix of an extrusion die similar to the conventional extrusion die of this kind, which is provided at its front surface with a large number of slits 2 crossed at a right angle with each other in the form of lines of checkerboard and bored in the matrix towards its rear surface in a given depth, and at its rear surface with a large number of feed inlets 3, having a circular cross-sectional shape, which feed inlets are bored in the matrix towards its front surface and are communicated to the slit 2 so as to supply a ceramic batch into the slits 2 from the rear surface side of the matrix. Further, in the extrusion die of the present invention, a metal film 4 is plated on the surface of the slits 2 bored in the matrix 1 so as to form slits 2' having a given width. In the die shown in Figure 1, the metal film 4 is plated on both the surface of slits 2 and the surface of feed inlets 3, but the metal film 4 may be plated only on the surface of slits 2. When it is intended to produce a honeycomb structural body having a certain outer shape, for example, a circular cross-section, by the use of the above described extrusion die 1', a mask 5 having a circular opening confined by its lower edge 5' is arranged on the front surface of the die, and a ceramic batch is continuously supplied to the slits 2' through the feed inlets 3 in a conventional manner to extrude a long honeycomb structural body from the slits 2', and then the extruded honeycomb structural body is cut into a given length. In the extrusion die 1', since the width of a large number of the slits 2' is made into a given width by plating a metal film 4 on the slits 2, all the slits 2' have a uniform given width, and as the result the thickness of all partition walls between adjacent cells formed in the extruded honeycomb structural body is uniform, and the honeycomb structural body has a proper structure. However, when the metal film 4 plated on the surface of the slit 2 is worn due to the abrasion by the ceramic batch during the operation of the die to form a slit width larger than the given width of the slit 2', the die can be no longer used. The extrusion die 1' having such worn metal film 4 can be reclaimed in the following manner. That is, before the wear reaches the slit 2 of the matrix 1, the matrix is separated from the mask 5, and then, for example, immersed in an aqueous solution of nitric acid or other acid, which can dissolve the metal film, to remove the metal film 4 remaining in the slit 2 and to obtain the matrix 1. Then, a metal film 4 is again plated on the surface of at least the slit 2. As the result, a metal film 4 having a uniform thickness can be formed on the slit 2, and the width of slit-2' can be made into the original given width, and the die is reclaimed as an extrusion die. Of course, the step for removing the remaining metal film can be omitted occasionally. Further, as illustrated in Figure 3, when the above described mask 5 having a circular opening 20 is replaced by a mask 5 having an opening different from circular shape, for example, a mask 5 having an oval opening 21, slits 2' which have not passed the ceramic batch when the opening is circular, that is, slits 2' which are located near the peripheral portion 10 of the die and have not been worn by the ceramic batch are opened by the opening in the longitudinal direction of the oval. This fact means that the width of newly opened slits which are located near the peripheral portion 10 of the die and have not been worn by the ceramic batch is different from the width of slits, which are located at the centre portion 11 of the die and have been worn by the ceramic batch. That is, the slits 2' are not uniform in the width. Accordingly, when it is intended to produce a honeycomb structural body having a cross-sectional shape different from the original cross-sectional shape, the thicknesses of partition walls between adjacent cells of the honeycomb structural body are not uniform, and the extrusion die 1' can be no longer used. However, according to the present invention, such extrusion die can be reclaimed in the same manner as described above, and the present invention can eliminate the drawback of conventional extrusion die, which is obliged to be discarded wastefully. The plating method carried out in the present invention is specifically disclosed in our copending E.P.C. Application entitled as "Method of producing a die for extruding a ceramic batch into a honeycomb structural body and a die produced by such method and filed on the same day as the present Application. The following examples are given for the purpose of illustration of this invention and are not intended as limitations thereof. Example 1 Nickel film having a thickness of 0.087 mm was plated on a matrix made of steel and having slits of 0.324 mm width formed on its surface by the electroless plating to produce an extrusion die having slits of 0.150 mm width. A honeycomb structural body was extruded through the extrusion die until the slit width became 0.172 mm due to the abrasion of the nickel film. Then, the worn die was immersed in a 65% aqueous solution of nitric acid for about 3 hours to dissolve and remove chemically the nickel film remaining in the slit, washed with water, and then subjected to an electroless plating of nickel in the commonly known method to reclaim an extrusion die having the same slit width as the originally given slit width. Example 2 Nickel film having a thickness of 0.087 mm was plated on a matrix made of steel and having slits of 0.324 mm width formed on its surface by the electroless plating to produce an extrusion die having slits of 0.150 mm width. A mask having a circular opening of 100 mm diameter was arranged on the front surface of the die. A honeycomb structural body was extruded through the extrusion die until the slit width became 0.163 mm due to the abrasion of the nickel film by a ceramic batch passed through the slits. Then, the extrusion was stopped, and a large size mask having oval opening, whose longitudinal diameter was 200 mm, was arranged on the front surface of the die in place of the above described mask having a circular opening, and a further extrusion was again started. In this case, the width of 0.150 mm of slits, whose metal film had not been worn due to the absence of passing through of the ceramic batch, was different from the width of 0.163 mm of the above described worn slits, and therefore there was a difference between the unworn slits and the worn slits in the extrusion rate and amount of a ceramic batch in the second extrusion, and a proper honeycomb structural body was not able to be obtained. Therefore, the die, after the first mask having a circular opening was removed from the die and before the second mask having an oval opening was arranged on the surface of the die, was immersed in a 65% aqueous solution of nitric acid for about 3.5 hours to dissolve and remove chemically the nickel film remaining in the slits, washed with water, and then subjected to an electroless plating by a commonly used method to reclaim an extrusion die having the same slit width as the original given slit width. When the reclaimed extrusion die was used, a honeycomb structural body having a proper oval shape was able to be obtained.

Claims: CLAIMS 1. In a method of reclaiming a die for extruding a honeycomb structural body, which is manufactured by forming a lattice of slits having a given depth in the front surface of the matrix of the die in a shape substantially corresponding to the geometrical shape of a honeycomb structural body to be extruded, forming a plurality of independent inlets for feeding a ceramic batch and communicated to the slits in the rear surface of the matrix, and forming a metal film on the surface of at least the slits by plating so that the slits have a given width, an improvement comprising recovering the original given width of the slits by forming again a metal film on the surface of at least the slits by plating after the original metal film has been worn up to improper shape for a further extrusion due to the abrasion by the ceramic batch at the extrusion. 2. A method according to claim 1, wherein the metal film remaining in the die is removed before a metal film is again plated. 3. A method according to claim 1, wherein said metal film is formed by an electroless plating. 4. A method according to claim 3, wherein said electroless plating is an electroless nickel plating. 5, A method according to claim 4, wherein the nickel film formed by the electroless plating and remaining in the die is removed by the use of nitric acid before a metal film is again formed. 6. A A die reclaimed by the method of any one of the preceding claims.

Inventors: SUZUKI, KAZUO
Applicants: NGK INSULATORS, LTD.
Application year: 1979
Main classification: B28B3
IPC codes: B23P6, B28B3, C23C18, C23C2