Production process of a hexagonal honeycomb structure

Details Production process of a hexagonal honeycomb structure Production process of a hexagonal honeycomb structure

1999-08-11

2001-10-30

Fiorilla, Christopher A. (Department: 1731)

Plastic and nonmetallic article shaping or treating: processes

Outside of mold sintering or vitrifying of shaped inorganic...

Producing article having plural hollow channels

C264S177120, C264S631000, C264S671000

Reexamination Certificate

active

06309590

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a production process of a hexagonal honeycomb structure used as a catalyst support and so forth in, for example, an automobile emission purification device.
2. Description of the Related Art
Honeycomb structures made of ceramics having for their main component, for example, cordierite are widely used, for example, as a support for automobile emission purification catalysts. In recent years, the partition thickness of the honeycomb structure has been made thinner to reduce the thermal capacity of the support for the purpose of improving the emission purification performance. In order to maintain the durability of the overall honeycomb structure when reducing partition thickness, it is advantageous to make the cells that compose the honeycomb form hexagonal. Consequently, as shown in
FIG. 2
to be described later, development of a hexagonal honeycomb structure 8 in which the shape of cells
80
and partitions
81
is hexagonal has been proceeding.
This hexagonal honeycomb structure can be produced by extrusion molding mixed raw materials using an extruder followed by drying and baking in the same manner as the case of a conventional square honeycomb structure.
However, the production process of the above-mentioned hexagonal honeycomb structure of the prior art has the problems described below.
Namely, in the case of performing each of the above-mentioned production steps of extrusion molding, drying and baking in the state in which the lengthwise direction of the honeycomb structure is in the horizontal direction as has been done in the past, cell deformation in the case of a hexagonal shape is greater than in the case of a square shape. Consequently, the overall dimensional accuracy of the hexagonal honeycomb structure is decreased.
In consideration of the above-mentioned problems of the prior art, the object of the present invention is to provide a production process of a hexagonal honeycomb structure offering low deformation of the hexagonal cells.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a production process of a hexagonal honeycomb structure in which a large number of hexagonal cells are provided surrounded by partitions in the form of a hexagonal matrix comprising:
an extrusion step for obtaining moldings in which partitions are provided in the form of a hexagonal matrix by extrusion molding of a mixed raw material using a horizontal extruder having an extrusion die provided with slits in the form of a hexagonal matrix and in which the direction of extruding is substantially the horizontal direction,
a drying step for drying said moldings, and
a baking step for baking said moldings,
wherein two of the six sides of each hexagon in a cross-section, in which said partitions of the extruded moldings are formed in the above-mentioned extrusion step and which is perpendicular to said direction of extrusion of said honeycomb structure, are parallel, and c axis parallel to these sides is substantially vertical relative to the horizontal plane.
What is most noteworthy in this first aspect of the present invention is that the above-mentioned extrusion process limits the direction of the disposition of the above-mentioned c axis of the extruded moldings to be substantially in the vertical direction as described above.
In order to limit the direction of disposition of the partitions of the moldings in this extrusion step as described above, it is necessary to similarly limit the orientation of the extrusion die in the above-mentioned horizontal extruder. More specifically, the above-mentioned extruder is arranged so that the two sides that compose the hexagons of the above-mentioned slits are parallel and substantially directed in the vertical direction.
In the present invention, the direction of the above-mentioned c axis of the moldings obtained from the above-mentioned extrusion step is substantially the vertical direction. Consequently, the cell shape of moldings can be stabilized and deformation can be inhibited as compared with the case of performing extrusion molding without making the above limitation.
Namely, when considering the case of a force acting from the outside on the sides that composes the hexagons, it is thought that deformation of the hexagon takes place due to a change in the angle of the apex between two sides without hardly any deformation of the side itself. Consequently, as shown in
FIG. 1B
, in the case of force F acting on hexagon
6
in the direction perpendicular to two parallel sides
61
and
64
(direction perpendicular to the above-mentioned c axis
600
), the entire portion L1 between these two sides
61
and
64
is subject to deformation.
In contrast, as shown in
FIG. 1A
, in the case a force F parallel to two parallel sides
62
and
65
(parallel to the above-mentioned axis c
600
) acts on hexagon
6
, only the portion other than the above-mentioned two sides
62
and
65
, namely the portion equal to ½ the total length of the hexagon in the direction in which force acts (L2+L3) is subject to deformation. Consequently, the amount of deformation in the direction parallel to these two sides in this hexagon is considered to be smaller than in the case of that in other directions.
When this is applied to the above-mentioned moldings during extrusion molding, since moldings are extruded in the horizontal direction as previously mentioned, gravitational force acts in the direction perpendicular to the lengthwise direction (extruding direction), namely the direction that compresses the hexagon from the outside.
Here, in the present invention, the direction of disposition of the slits of the extrusion die is limited as described above, and the direction of the above-mentioned c axis of the resulting moldings is substantially the vertical direction relative to the horizontal plane.
Consequently, the partitions of the above-mentioned moldings are arranged in a state in which the amount of deformation is the lowest with respect to gravitational force. For this reason, a cell shape can be stabilized and deformation can be inhibited as compared with the case of not restricting the direction of disposition of partitions in the moldings. For this reason, the overall dimensional accuracy of the resulting hexagonal honeycomb structure can be stabilized.
Thus, according to the present invention, a production process of a hexagonal honeycomb structure can be provided having low deformation of hexagonal cells.
It is preferable that the above-mentioned c axis of moldings obtained from the above-mentioned extrusion step be within the range of ±10° from the vertical direction. In the case of exceeding ±10° from the vertical direction, there is the problem of the deformation inhibitory effect of the above-mentioned cells not being effectively demonstrated.
It is preferable that, in addition to at least one of either the above-mentioned drying step or baking step being performed horizontally while maintaining the lengthwise direction of the above-mentioned moldings substantially in the horizontal direction, the above-mentioned c axis of the above-mentioned moldings is facing in the substantially vertical direction relative to the horizontal plane.
Namely, among each of the production steps in the above-mentioned production process, the moldings are the softest in the above-mentioned extrusion step and there is the greatest susceptibility to deformation in this step. However, in the case of maintaining moldings so that their lengthwise direction is substantially in the horizontal direction (by being placed horizontally) in the following steps as well, there is an even greater risk of the occurrence of deformation. Consequently, in the case of placing moldings horizontally in the drying or baking step, it is preferable to limit the direction of the above-mentioned c axis of moldings to substantially the vertical direction as previously described. Doing so makes it possible to further inhibit the amount of cell deformation.
When tr

Affiliated with

Also associated with

Rating

Production process of a hexagonal honeycomb structure does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Production process of a hexagonal honeycomb structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production process of a hexagonal honeycomb structure will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2570193