Apparatus for molding a honeycomb structure

Details Apparatus for molding a honeycomb structure Apparatus for molding a honeycomb structure

2002-03-22

2004-11-09

Heitbrink, Tim (Department: 1722)

Plastic article or earthenware shaping or treating: apparatus

Stock pressurizing means operably associated with downstream...

Plural orifices

C264S177120, C425S463000, C425S467000

Reexamination Certificate

active

06814562

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for molding a honeycomb structure, a spinneret for extrusion, and a method for molding a honeycomb structure.
Problems which become afresh are influences on earth environments and ecosystems of nitrogen oxides, sulfur oxides, hydrogen chloride, etc. contained in exhaust gases of automobiles in addition to carbon dioxide which warms the earth. It is said that, in the future, automobiles which utilize as energy source, for example, electricity, natural gas or methanol which have less influences on the ecosystem will be substituted for automobiles which utilize gasoline and gas oil as energy source. However, there are difficulties to overcome for practical use of these technologies, and tentative measures are reduction of cost of fuels and purification of exhaust gases. The honeycomb structures are used for exhaust gas purification apparatuses of automobiles as a technology for the solution of environmental problems.
For example, honeycomb structures made of ceramics materials or metallic materials as shown in
FIGS. 2-4
are used as catalyst carriers for exhaust gas purification apparatuses of automobiles.
FIG. 3
is an oblique view of a honeycomb structure
61
,
FIG. 4
is a front view of the honeycomb structure
61
, and
FIG. 2
is a partially enlarged view of the honeycomb structure
61
. This honeycomb structure
61
is generally columnar as shown in
FIG. 3
, and comprises partition walls
64
having a honeycomb structure which form many cells
63
and an outer wall
62
covering the outer periphery.
For making such honeycomb structure
61
, an apparatus for molding honeycomb structures, for example, as shown in
FIG. 5
, is used.
FIG. 5
is a vertical sectional view of an apparatus for molding honeycomb structure which is provided with back pores
53
from which a molding material is introduced, a spinneret
54
having slits
52
through which the molding material is extruded, and a press plate
55
provided downstream the spinneret
54
. Extrusion molding is carried out using this apparatus to make the honeycomb structure
61
.
In the honeycomb structure molding apparatus
50
, the spinneret
54
comprises an inner side part
71
and an outer periphery part
72
, and the inner side part
71
protrudes to downstream side to form a level difference part
75
between the inner side part
71
and the outer periphery part
72
. The inner side part
71
is provided with slits
73
by which a honeycomb structure is molded, and the outer peripheral part
72
is provided with slits
74
shorter than the slits
73
. Furthermore, a gap part
57
which molds the outer wall of the honeycomb structure is provided between the spinneret
54
and the press plate
55
. Press jig
58
and back press plate
59
are holders for setting the spinneret
54
and the press plate
55
.
In carrying out extrusion molding by the honeycomb structure molding apparatus
50
, the molding material is extruded from the upstream side of spinneret
54
to the downstream side through the spinneret
54
by an extruder (not shown) as shown in FIG.
5
. The molding material extruded from slits
73
provided in the inner side part
71
of the spinneret
54
which opens on the downstream side forms a honeycomb structure comprising many cells
63
.
On the other hand, the molding material extruded from slits
74
provided in the outer peripheral part
72
of the spinneret
54
flows with changing its running direction to the level difference part
75
from the extrusion direction with rupturing the honeycomb shape by the action of the gap part
57
, and again flows with changing its running direction to the extrusion direction at the position where the press plate
55
opens, thereby forming an outer wall
62
surrounding the cells
63
.
However, in such conventional honeycomb structure molding apparatus and molding method, there is the problem of failure in formation of cells.
As examples of failure in formation of cells, mention may be made of twist or rupture of cells as shown in FIG.
11
. In the honeycomb structure molding apparatus shown in
FIG. 5
, there are problems that when the molding material for forming an outer wall flows with changing its running direction to the extrusion direction at the opening of the press plate
55
, an excessive force is applied to the molding material for forming the cells in the outer peripheral part
72
to bring about twist of cells
94
or rupture of cells
93
. Another example is omission of cells as shown in
FIGS. 6 and 7
.
FIG. 6
is a front view of a honeycomb structure from which some cells are omitted, and
FIG. 7
is an enlarged view of the portion in which omission of cells occurred in FIG.
6
. Many cell omission portions
92
in the honeycomb structure
91
are seen in the direction of 90° in the vicinity of the outer wall
62
, and it is presumed that this phenomenon occurs because a molding material which is originally to form the partition wall
64
flows to the outer wall portion
62
at the time of being extruded from the spinneret.
The omission of cells means a phenomenon that one or more of partition walls which form cells
63
are not formed. The direction of 90° at the section of the honeycomb structure means a direction progressing along the crossing partition walls
64
from nearly the center of the section of the honeycomb structure.
If failure in formation of cells occurs, strength of the honeycomb structure is deteriorated, and this is not preferred. Furthermore, when cells are closed in the form of checks and the honeycomb structure is used as a filter for apparatus for purification of exhaust gas of automobiles, there are portions which do not have filtration function to cause deterioration of performance. Moreover, when the honeycomb structure is used as catalyst carriers of automobile exhaust gas purification apparatus, recently, not only the exhaust gas purification performance is required, but also it is demanded to make the cell density as small as possible and the partition walls forming the cells as thin as possible for inhibition of deterioration of horse-power of automobiles. A honeycomb structure composed of a small number of cells thin in wall thickness is apt to be low in strength from the point of structure, and hence occurrence of failure in formation of cells which causes further deterioration of strength must be prevented by any means.
For the purpose of improving the strength of honeycomb structures, measures have hitherto been proposed.
For example, JP-A-57-157706 discloses various dies for honeycomb molding.
FIGS. 8-10
are sectional views showing examples of the disclosed dies for honeycomb molding. Outer peripheral part of edge face of outlet side for a molding material of die
202
(spinneret) is cut out to form a step-like part
223
at the whole periphery, a level difference part
224
is provided between the central part of the edge face of outlet side for the molding material and the outer peripheral part of the die
202
, and a ring space
204
is provided between the level difference part
224
and an inner peripheral face
231
of a die mask
203
(press plate) opposing and surrounding the level difference part
224
.
In die
198
for honeycomb molding having a level difference part
224
of tapered angle as shown in
FIG. 8
, the molding material going in centripetal direction from molding channel
221
(slit) in the outer peripheral part of the die
202
is extruded after forcedly fed to the molding channel
221
in the central part of the die
202
, and, hence, no pressure is applied to the portion near the peripheral wall (outer wall) of the already molded honeycomb body and no distortion is caused at the partition walls near the peripheral wall of the resulting honeycomb molded body. Furthermore, since the molding material filled in the space
204
flows together with the molding material coming straight from the molding channel
221
below the space
204
and is extruded along the inner peripheral face
231
of the die mask
203
, a

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