Plastic article or earthenware shaping or treating: apparatus – Stock pressurizing means operably associated with downstream... – Including auxiliary shaping means associated with molding...
Reexamination Certificate
2002-06-24
2003-11-04
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Stock pressurizing means operably associated with downstream...
Including auxiliary shaping means associated with molding...
C264S177120, C425S461000, C425S467000
Reexamination Certificate
active
06641385
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a metal mold for molding a honeycomb structure that is used as a catalyst carrier or the like in, for example, a device for cleaning the exhaust gas from an automobile, and to a method of producing the metal mold.
2. Description of the Related Art
A ceramic honeycomb structure comprising, for example, cordierite as a chief component is produced by extrusion-molding a material by using a metal mold. The honeycomb structure constitutes a number of cells by forming the partitioning walls in the form of a lattice, and the cells assume, for example, a hexagonal shape.
To produce a honeycomb structure having cells of the hexagonal shape (hereinafter referred to as hexagonal honeycomb), a metal mold having slit grooves of the shape of a hexagonal lattice must be used and the partitioning walls must be formed in the shape of a hexagonal lattice.
A conventional metal mold for producing a hexagonal honeycomb structure has, as shown in
FIGS. 1A and 1B
, feed holes
11
for feeding a material and slit grooves
3
formed in the shape of a hexagonal lattice and communicated with the feed holes
11
.
To produce this metal mold
1
, the feed holes
11
are formed by drilling from one surface of the metal mold blank, and the slit grooves are formed in the shape of a hexagonal lattice from the other surface thereof by such machining means as electric discharge machining. Then, as shown in
FIG. 1
, the intersecting points of the slit grooves of the shape of a hexagonal lattice are communicated with the feed holes
11
to thereby obtain the metal mold
1
.
However, the conventional metal mold
1
for producing the hexagonal honeycomb structure has problems as described below.
That is, in order to uniformly form the partitioning walls of the hexagonal honeycomb structure by using the above-mentioned conventional metal mold
1
, the depth of the slit grooves of the shape of a hexagonal lattice must be selected to be not smaller than 10 times as great as the width of the grooves. Therefore, an extended period of time is required for forming the slit grooves.
Furthermore, when it is attempted to form the slit grooves relying upon, for example, the electric discharge machining, the electrodes are worn out during the machining often causing a dispersion in the depth of the slit grooves. In this case, therefore, the partitioning walls of the obtained hexagonal honeycomb structure loses uniformity.
To produce the metal mold
1
, furthermore, a metal mold blank
4
is prepared having a hole-forming surface
41
in which the feed holes
11
will be formed and having a groove-forming surface
43
in which the slit grooves
3
will be formed (see FIG.
14
). The feed holes
11
are formed by drilling in the hole-forming surface, the slit grooves
3
of the shape of a hexagonal lattice are formed by the electric discharge machining in the groove-forming surface, and the slit grooves
3
and the feed holes
11
are communicated with each other thereby to obtain the metal mold
1
.
Referring to
FIG. 2
, the electric discharge machining is carried out by using an electrode
81
for the electric discharge machining provided with a working surface
80
of the shape of a lattice corresponding to the whole surfaces of the slit grooves
3
that are to be formed, and repeating the electric discharge between the electrode
81
for the electric discharge machining and the groove-forming surface
43
of the metal mold blank
4
in a working solution. The working solution is fed from a working solution-feeding pipe
95
of a working solution-feeding jig
9
disposed on the back surface side of the electrode
81
for the electric discharge machining.
However, the above-mentioned conventional method of producing the metal mold for forming a honeycomb structure has problems as described below.
That is, the slit grooves
3
have heretofore been formed by the electric discharge machining by using an electrode for the electric discharge machining having the shape of a lattice corresponding to the whole slit grooves that are to be formed. During the electric discharge machining, the electrode for the electric discharge machining is often distorted or worn out in varying amounts and is deformed. In such a case, the depth of the slit grooves varies causing a problem from the standpoint of quality.
On the other hand, the electrode for the electric discharge machining is made of a very hard material such as a tungsten alloy or the like, and is produced requiring a long period of time of, for example, several tens of days. When it is attempted to newly produce a metal mold for molding a honeycomb structure, therefore, several tens of days are, first, required for producing the electrode for the electric discharge machining and, then, another several tens of days are required for forming the slit grooves by the electric discharge machining, which is a very long lead time.
SUMMARY OF THE INVENTION
The present invention was accomplished in view of the above-mentioned problems inherent in the prior art, and its object is to provide a metal mold for molding a honeycomb structure, capable of precisely and efficiently forming the slit grooves within a short lead time and exhibiting good moldability, and a method of producing the same.
A first invention is concerned with a metal mold for molding a hexagonal honeycomb structure, having feed holes for feeding a material, pool grooves formed in the shape of a triangular lattice and communicated with the feed holes, and slit grooves formed in the shape of a hexagonal lattice and communicated with the pool grooves.
In this invention, the most important point is that the pool grooves of the shape of a triangular lattice are formed between the feed holes and the slit grooves.
The pool grooves are formed in the shape of a triangular lattice by, for example, regularly and alternatingly arranging equilateral triangles in the opposing directions.
It is further desired that the pool grooves and the feed holes are communicated with each other at the intersecting points of the triangular lattices of the pool grooves. This permits the material to smoothly flow from the feed holes to the pool grooves. In this case, the feed holes need not necessarily be communicated at every intersecting point of the pool grooves, but many be constituted in various ways by taking into consideration the size of the honeycomb structure that is to be molded and the moldability. For example, the feed holes may be communicated with every second intersecting point or with every third intersecting point.
It is desired that each hexagonal lattice of the slit grooves is so formed as to come into agreement with a hexagon shaped by combining six triangular lattices of the pool grooves.
In this case, it is possible to more uniformly and smoothly move the material during the extrusion molding.
Here, the hexagon shaped by combining six triangular lattices of the pool groups stands for the one formed as an outer shape of when six triangles are viewed as a unit, the six triangles being radially arranged neighboring each other about an intersecting point of the pool grooves.
In this case, therefore, when the slit grooves and the pool grooves are viewed from the front, the pool grooves are located at portions overlapped on the hexagonal slit grooves and on the boundary portions of the six triangles formed by connecting the vertexes thereof and the centers thereof.
A second invention is concerned with a method of producing a metal mold for molding a hexagonal honeycomb structure, having feed holes for feeding a material, pool grooves formed in the shape of a triangular lattice and communicated with the feed holes, and slit grooves formed in the shape of a hexagonal lattice and communicated with the pool grooves, each hexagonal lattice of the slit grooves being so formed as to come into agreement with a hexagon shaped by combining six triangular lattices of the pool grooves;
wherein a metal mold base for forming the feed holes, and a groove-forming membe
Andou Yosiyasu
Fujita Masayoshi
Miyazaki Mitsutoshi
Denso Corporation
Leyson Joseph
Mackey James P.
Nixon & Vanderhye PC
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