U.S. patent application number 09/945641 was filed with the patent office on 2002-05-02 for production process of a hexagonal honeycomb structure.
Invention is credited to Andou, Yosiyasu, Obata, Takasi, Yasuda, Kazuhiko.
Application Number | 20020050669 09/945641 |
Document ID | / |
Family ID | 26472559 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020050669 |
Kind Code |
A1 |
Obata, Takasi ; et
al. |
May 2, 2002 |
Production process of a hexagonal honeycomb structure
Abstract
The present invention provides a production process of a
hexagonal honeycomb structure having low deformation of hexagonal
cells. This process comprises an extrusion step for obtaining
moldings (7) in which partitions (71) 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 moldings (7), and a baking step for baking moldings (7).
The extrusion step is performed such that c axis (700) parallel to
two parallel sides (702) and (705) of the six sides (701) through
(706) of each hexagon formed by partitions (71) of extruded
moldings (7) is substantially vertical relative to the horizontal
plane.
Inventors: |
Obata, Takasi; (Kariya-city,
JP) ; Andou, Yosiyasu; (Nagoya-city, JP) ;
Yasuda, Kazuhiko; (Oogaki-city, JP) |
Correspondence
Address: |
Intellectual Property Group
Pillsbury Winthrop LLP
1600 Tysons Boulevard
McLean
VA
22102
US
|
Family ID: |
26472559 |
Appl. No.: |
09/945641 |
Filed: |
September 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09945641 |
Sep 5, 2001 |
|
|
|
09372124 |
Aug 11, 1999 |
|
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|
6309590 |
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Current U.S.
Class: |
264/630 ;
264/177.12; 264/631; 264/671 |
Current CPC
Class: |
F01N 3/2828 20130101;
F01N 2330/34 20130101; B01J 35/04 20130101; B28B 3/269
20130101 |
Class at
Publication: |
264/630 ;
264/631; 264/671; 264/177.12 |
International
Class: |
B28B 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 1998 |
JP |
10-274680 |
May 20, 1999 |
JP |
11-139872 |
Claims
1. 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.
2. A production process of a hexagonal honeycomb structure
according to claim 1, wherein said c axis of moldings obtained in
said extrusion step is within the range of .+-.10.degree. from the
vertical direction.
3. A production process of a hexagonal honeycomb structure
according to claim 1, wherein in addition to at least one of either
of said drying step or said baking step being performed
horizontally while maintaining the lengthwise direction of said
moldings substantially in the horizontal direction, said c axis of
said moldings is facing in the substantially vertical direction
relative to the horizontal plane.
4. A production process of a hexagonal honeycomb structure
according to claim 1, wherein when transporting or storing said
moldings between any of said extrusion step, drying step or baking
step, together with placing the moldings horizontally so that the
lengthwise direction of said moldings is maintained substantially
in the horizontal direction, said c axis of said moldings is facing
in the substantially vertical direction relative to the horizontal
plane.
5. 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 an upright 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 vertical
direction, a drying step for drying said moldings, and a baking
step for baking said moldings, wherein in at least one of either
said drying step or said baking step, in addition to placing
horizontally so that the lengthwise direction of said moldings is
maintained substantially in the horizontal direction, two of the
six sides of each hexagon in a cross-section in which said
partitions of the extruded moldings are formed 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.
6. A production process of a hexagonal honeycomb structure
according to claim 5, wherein when transporting or storing said
moldings between any of said extrusion step, drying step or baking
step, together with placing the moldings horizontally so that the
lengthwise direction of said moldings is maintained substantially
in the horizontal direction, said c axis of said moldings is facing
in the substantially vertical direction relative to the horizontal
plane.
7. 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 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 the orientation of c axis
parallel to these sides is in a direction that differs by
60-120.degree. from the orientation of c axis of said moldings in
the case of placing said moldings horizontally in at least one of
either of said drying step or said baking step so that the
lengthwise direction of said moldings is maintained substantially
in the horizontal direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Description of the Related Art
[0004] 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.
[0005] 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.
[0006] However, the production process of the above-mentioned
hexagonal honeycomb structure of the prior art has the problems
described below.
[0007] 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.
[0008] 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
[0009] 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:
[0010] 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,
[0011] a drying step for drying said moldings, and
[0012] a baking step for baking said moldings,
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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 1/2 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] Thus, according to the present invention, a production
process of a hexagonal honeycomb structure can be provided having
low deformation of hexagonal cells.
[0023] It is preferable that the above-mentioned c axis of moldings
obtained from the above-mentioned extrusion step be within the
range of .+-.10.degree. from the vertical direction. In the case of
exceeding .+-.10.degree. from the vertical direction, there is the
problem of the deformation inhibitory effect of the above-mentioned
cells not being effectively demonstrated.
[0024] 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.
[0025] 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.
[0026] When transporting or storing the above-mentioned moldings
between any of the above-mentioned extrusion step, drying step or
baking step, together with placing the moldings horizontally so
that the lengthwise direction of the above-mentioned moldings is
maintained substantially in the horizontal direction, it is
preferable that the above-mentioned c axis of the above-mentioned
moldings be facing in the substantially vertical direction relative
to the horizontal plane. In this case, cell deformation that occurs
during transport can be inhibited, and dimensional accuracy of the
hexagonal honeycomb structure can be further improved.
[0027] A second 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:
[0028] 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 an upright 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
vertical direction,
[0029] a drying step for drying said moldings, and
[0030] a baking step for baking said moldings,
[0031] wherein in at least one of either said drying step or baking
step, in addition to being placed horizontally so that the
lengthwise direction of said moldings is maintained substantially
in the horizontal direction, two of the six sides of each hexagon
in a cross-section in which said partitions of the extruded
moldings are formed 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.
[0032] What is most noteworthy in this aspect is that, in the case
of performing this extrusion step using the above-mentioned upright
extruder, the direction of disposition of the above-mentioned c
axis of the above- mentioned moldings in at least one of either of
the following drying step or baking step is limited to the
above-mentioned specific direction.
[0033] In this case, cell deformation, of which there is the risk
of occurring in the case of placing moldings horizontally following
the extrusion step, can be inhibited, thereby making it possible to
improve the dimensional accuracy of the hexagonal honeycomb
structure.
[0034] When transporting or storing the above-mentioned moldings
between any of the above-mentioned extrusion step, drying step or
baking step, together with placing the moldings horizontally so
that the lengthwise direction of the above-mentioned moldings is
maintained substantially in the horizontal direction, it is
preferable that the above-mentioned c axis of the above- mentioned
moldings be facing in the substantially vertical direction relative
to the horizontal plane. In this case as well, cell deformation
that occurs during transport can be inhibited in the same manner as
previously described, and dimensional accuracy of the hexagonal
honeycomb structure can be further improved.
[0035] A third 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:
[0036] 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,
[0037] a drying step for drying said moldings, and
[0038] a baking step for baking said moldings,
[0039] wherein two of the 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 the orientation of c axis parallel to these sides is in a
direction that differs by 60-120.degree. from the orientation of c
axis of said moldings in the case of placing said moldings
horizontally in at least one of either of said drying step or
baking step so that the lengthwise direction of said moldings is
maintained substantially in the horizontal direction.
[0040] What is most noteworthy in this third aspect of the present
invention is that the orientation of the above-mentioned c axis of
moldings obtained in the above-mentioned extrusion step, and the
orientation of c axis of the above-mentioned moldings in at least
one of either the above-mentioned drying step or baking step are
intentionally changed to different directions and intentionally
control cell deformation of the hexagonal honeycomb structure.
[0041] More specifically, in the case of, for example, making the
orientation of the above-mentioned c axis of moldings obtained in
the extrusion step so that it is facing substantially in the
vertical direction, in the following drying step or baking step,
the direction of the above-mentioned c axis of the above-mentioned
moldings is made to be facing in a direction other than
substantially the vertical direction, for example, the
above-mentioned c axis is made to face in the horizontal direction
(the two sides are in the horizontal direction).
[0042] In addition, the orientation of the c axis of the
above-mentioned moldings in the above-mentioned extrusion step and
its following steps is made to be 60.degree.-120.degree.. If less
than 60.degree. or greater than 120.degree., there is the problem
of effects that correct cell deformation occurring during the
extrusion step not being fully demonstrated. The orientation is
most preferably 90.degree.. In this case, deformation in directions
that differ by 90.degree. can be made to occur in the case of the
extrusion step and following steps, which is extremely effective in
controlling cell deformation.
[0043] In the third aspect of the present invention, the
orientation of the above-mentioned c axis of the above-mentioned
moldings is changed within the range of 60.degree.-120.degree. in
the extrusion step and following steps as previously described.
Consequently, the directions of deformation that is able to occur
in the extrusion step and its following steps are such that they
mutually cancel out deformation. For this reason, deformation can
be applied in a direction in which cell deformation that occurs in
the extrusion step can be intentionally reduced.
[0044] As a result, instead of simply inhibiting the amount of
deformation, corrections can be made intentionally so that the
deformation is reduced in the case deformation occurs as a result
of the extrusion step.
[0045] Thus, according to this third aspect as well, the present
invention provides a production process of a hexagonal honeycomb
structure in which hexagonal cell deformation is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is an explanatory drawing showing the state of
hexagon deformation in the case of stress acting in parallel with c
axis (FIG. 1A) and the case of stress acting perpendicular to c
axis (FIG. 1B).
[0047] FIG. 2 is a perspective view of the hexagonal honeycomb
structure in Embodiment 1.
[0048] FIG. 3 is an explanatory drawing showing the constitution of
horizontal extruder 1 in Embodiment 1.
[0049] FIG. 4 is a cross-sectional view showing the arrangement of
slits in an extrusion die in Embodiment 1.
[0050] FIG. 5 is a cross-sectional view showing the arrangement of
partitions of moldings obtained in an extrusion step in Embodiment
1.
[0051] FIG. 6 is a cross-sectional view showing the arrangement of
slits in an extrusion die for molding of comparative article C1 in
Embodiment 2.
[0052] FIG. 7 is a cross-sectional view showing the arrangement of
partitions in moldings obtained in the extrusion step of
comparative article C1 in Embodiment 2.
[0053] FIG. 8 is an explanatory drawing respectively showing the
locations of outer diameter measurement from the side (FIG. 8A) and
from the front (FIG. 8B) in Embodiment 2.
[0054] FIG. 9 is an explanatory drawing showing the relationship
between measurement location and outer diameter dimensions of
embodiment E1 of the present invention in Embodiment 2.
[0055] FIG. 10 is an explanatory drawing showing the relationship
between measurement location and outer diameter dimensions of
comparative article C1 in Embodiment 2.
[0056] FIG. 11 is an explanatory drawing showing the shift angle
.theta. of the above-mentioned c axis from the vertical direction
in moldings obtained from an extrusion step in Embodiment 3.
[0057] FIG. 12 is a graph showing the relationship between shift
angle .theta. and the amount of cell deformation in Embodiment
3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] Embodiment 1
[0059] The following provides an explanation of the production
process of a hexagonal honeycomb structure in a first embodiment of
the present invention using FIGS. 2 through 5.
[0060] As shown in FIG. 2, this embodiment comprises a method of
producing hexagonal honeycomb structure 8 in which a large number
of hexagonal cells 80 are provided surrounded by partitions 81 in
the form of a hexagonal matrix. Furthermore, the cell size is
enlarged for the sake of explanation in FIG. 2 (and similarly
enlarged in FIGS. 4 through 7).
[0061] As shown in FIGS. 3 through 5, an extrusion step, in which
molding 7 is obtained provided with partitions in the form of a
hexagonal matrix by extrusion molding mixed raw materials using a
horizontal extruder 1 having extrusion die 2 provided with slits in
the form of a hexagonal matrix and in which the direction of
extrusion is substantially the horizontal direction, a drying step
for drying the above-mentioned molding 7, and a baking step for
baking the above-mentioned molding 7, were carried out.
[0062] As shown in FIG. 5, the above-mentioned extrusion step was
carried out with c axis 700, which is parallel with two parallel
sides 702 and 705 of the six sides 701 through 706 of each hexagon
formed by the above-mentioned partitions 71 of the resulting
molding 7, facing substantially in vertical direction V relative to
the horizontal plane.
[0063] The following provides a detailed explanation of this.
[0064] Hexagonal honeycomb structure 8 produced by the present
embodiment uses, as its main component, cordierite having a
theoretical composition represented by
2MgO.2Al.sub.2O.sub.3.5SiO.sub.2. Normally, cordierite contains
SiO.sub.2 in the ratio of 49.0-53.0 wt %, Al.sub.2O.sub.3 in the
ratio of 33.0-37.0 wt %, and MgO in the ratio of 11.5-15.5 wt
%.
[0065] A raw material in which molding assistant is added and mixed
with cordieriting raw material adjusted to have the desired
cordierite composition is used for the raw material of this
hexagonal honeycomb structure.
[0066] Examples of cordieriting raw materials include talc
(Mg.sub.3Si.sub.4O.sub.10(OH).sub.2), kaolin
(Al.sub.2Si.sub.2O.sub.5(OH)- .sub.4), alumina (Al.sub.2O.sub.3)
and aluminum hydroxide (Al(OH).sub.3). In addition, oxides,
hydroxides and chlorides that serve as sources of Mg, Al and Si can
also be used, examples of which include serpentine
(Mg.sub.3Si.sub.2O.sub.5(OH).sub.4), pyroferrite
(Al.sub.2Si.sub.4O.sub.1- 0(OH).sub.2) and brucite
(Mg(OH).sub.2).
[0067] In addition, normally used lubricants, moisture retention
agents and binders can be used for the molding assistants added to
the cordieriting raw materials.
[0068] Examples of lubricants and moisture retention agents include
wax, water-soluble polyvalent alcohol derivatives and surface
activators. Examples of the above-mentioned binders include
methylcellulose and polyvinyl alcohol.
[0069] Next, as shown in FIG. 3, the above-mentioned cordieriting
raw material and molding assistant are mixed by mixer 3 and
extruded in an extrusion step using horizontal extruder 1.
[0070] As shown in the same drawing, horizontal extruder 1 has raw
material loading port 11 in opposition to mixer 3 provided above,
along with upper stage screw 12 and lower stage screw 15 below.
Vacuum chamber 13 and toothed roller 14 are provided between upper
stage screw 12 and lower stage screw 15. Filtering mesh 16 is
provided in front of lower stage screw 15 to make the flow of raw
material uniform, and extrusion die 2 is arranged in front of
filtering mesh 16. Sponge receiving pads 17 are provided in front
of extrusion die 2 to support the sides of the extruded
moldings.
[0071] As shown in FIG. 4, extrusion die 2 in the present
embodiment has slits 21 in the form of a hexagonal matrix. As shown
in the same drawing, this extrusion die 2 was installed on
horizontal extruder 1 so that c axis 200 parallel to two parallel
sides 202 and 205 of the six sides 201 through 206 of each hexagon
formed by slits 21 faces substantially in the vertical
direction.
[0072] Width W of slits 21 was 0.15 mm, and pitch P of each hexagon
was 1.36 mm.
[0073] A guide ring (not shown) that defines the dimensions of
outer diameter of molding 7 was provided on extrusion die 2. Its
inner diameter was 138 mm in the present embodiment.
[0074] In the carrying out of an extrusion step using this
horizontal extruder 1, raw material is loaded into raw material
loading port 11 from the above-mentioned mixer 3. This is then fed
to lower stage screw 15 by way of vacuum chamber 13 and toothed
roller 14 by the driving force produced by rotation of upper stage
screw 12. Finally, molding 7 is extruded from extrusion die 16 by
the driving force produced by rotation of lower stage screw 15. The
extruded molding 7 is fed towards the front while being supported
by the above-mentioned sponge receiving pads 17.
[0075] Here, molding 7, extruded in this extrusion step, is in a
form to which the shape of the slits of extrusion die 2 have been
transcribed. Consequently, the c axis parallel to two parallel
sides 702 and 705 of the six sides 701 through 706 of each hexagon
formed by the formed partitions 71 is facing in substantially
vertical direction V.
[0076] Next, after the extrusion step, the above-mentioned molding
7 is cut to a prescribed length while still held on the
above-mentioned sponge receiving pads 17. Each separated molding 7
was allowed to stand for 1 hour while still held on sponge
receiving pads 17. Namely, in addition to placing molding 7
horizontally such that the lengthwise direction of molding article
7 was maintained in substantially the horizontal direction, a
drying step was carried out for 1 hour with the above-mentioned c
axis 700 of molding 7 facing in substantially the vertical
direction V.
[0077] Next, after completion of the drying step, molding 7 placed
on sponge receiving pads 17 was transported to a baking oven were
baking was carried out. Baking was carried out under conditions of
holding at a temperature of 1400.degree. C. for 5 hours.
[0078] Furthermore, although the above-mentioned transport and
baking steps were carried out horizontally, the orientation of the
hexagons formed by partitions 71 was not controlled and left to be
random. In addition, the orientation of the partitions of molding 7
after the baking step was also not controlled and left to be
random.
[0079] Following completion of the baking step, a finishing step
was carried out involving, for example, removing the cut ends of
each molding 7 to obtain hexagonal honeycomb structure 8.
[0080] In the production process of the present embodiment, the
direction of disposition of c axis 700 of molding 7 supplied to the
above-mentioned extrusion and drying steps is limited to
substantially vertical direction V. Namely, in these two steps, two
sides 702 and 705 of the six sides 701 through 706 of each hexagon
formed by partitions 71 of molding 7 are facing substantially in
the vertical direction V.
[0081] Consequently, during extrusion molding, work is carried out
in the state in which the amount of cell deformation with respect
to gravitational force acting on molding 7 is the lowest. For this
reason, cell deformation in the extrusion step can be reliably
inhibited in comparison to the case of not restricting the
direction of disposition of the partitions of the molding in any
way.
[0082] Next, cell deformation can be stabilized and deformation can
be inhibited in comparison to the case of not restricting the
direction of disposition of the partitions of the molding in any
way in the drying step as well for the same reasons as in the case
of the above-mentioned extrusion step.
[0083] As a result of intentionally managing the direction of
placement of the molding, the resulting hexagonal honeycomb
structure 8 had less deformation in comparison with the prior
art.
[0084] Furthermore, the direction of disposition of partitions of
moldings in steps following the drying step was not controlled in
the present embodiment. However, since these steps were carried out
after the moldings had solidified in the above-mentioned drying
step, this is not considered to have much effect.
[0085] Embodiment 2
[0086] In this embodiment, a hexagonal honeycomb structure 8
(embodiment E1 of the present invention) was fabricated in the same
manner as Embodiment 1, comparative article Cl, in which a portion
of the production process was changed, was fabricated, and the
dimensions of each part were measured to quantitatively evaluate
the effects of Embodiment 1.
[0087] With respect to comparative article C1, as shown in FIG. 6,
extrusion die 2 in horizontal extruder 1 was fabricated by changing
by 90.degree. the direction of disposition of the c axis 200 of
slits 21 in the form a hexagonal matrix. More specifically,
extrusion die 2 in the case of comparative article C1 was installed
in horizontal extruder 1 so that two parallel sides 201 and 204 of
the six sides 201 through 206 of each hexagon formed by slits 21
are facing in the substantially horizontal direction as shown in
FIG. 6.
[0088] In the extrusion step, extrusion was performed such that the
above-mentioned c axis 700 of extruded molding 7 is facing in the
substantially horizontal direction as shown in FIG. 7. In addition,
accompanying this change, the following drying step was also
performed so that c axis 700 of molding 7 is facing in
substantially the horizontal direction. Other matters were the same
as in Embodiment 1 (embodiment E1 of the present invention).
[0089] The results of measuring the dimensions of embodiment E1 of
the present invention and comparative article C1 are shown in FIGS.
9 and 10.
[0090] FIGS. 8A and 8B show the locations where the above-mentioned
dimensions were measured. As shown in FIG. 8A, measurements were
made at three locations (front portion, center portion and rear
portion) in the direction of extrusion (lengthwise direction) of
hexagonal honeycomb structure 1. In this drawing, reference numbers
F, C and R indicate the front, center and rear portions,
respectively. As shown in FIG. 8B, measurements were made at four
locations in the direction of circumference in the horizontal
direction A, vertical direction B, in the direction 45.degree. to
the right C as viewed from the front, and in the direction
45.degree. to the left D as viewed from the front based on the
arranged state in the extrusion step.
[0091] 20 samples each of embodiment E1 of the present invention
and comparative article C1 were prepared, and each measurement was
made 20 times.
[0092] The mean of measurement results (n=20) is shown in FIG. 9
for embodiment E1 of the present invention, and in FIG. 10 for
comparative article C1. In these drawings, measurement location is
plotted on the horizontal axis, while outer diameter (mm) is
plotted on the vertical axis. Reference numerals (F), (C) and (H)
on the horizontal axis represent the front portion, center portion
and rear portion, respectively, in the same manner as previously
described.
[0093] As can be determined from these drawings, the difference in
outer diameter between horizontal direction A and vertical
direction B is smaller for embodiment E1 of the present invention
than comparative article C1.
[0094] As shown in Table 1, the difference in mean values between
horizontal direction A and vertical direction B is considerably
smaller in the case of the embodiment of the present invention. The
deformation ratio (%) in Table 1 shows the deformation ratio (%)
which is mean value of the amount of deformation A to the inner
diameter of 138 mm of the guide ring in extrusion die 2-mean value
of the amount of deformation B to the inner diameter of 138 mm of
the guide ring in extrusion die 2.
1 TABLE 1 Mean value of A- Mean value of B Deformation ratio (mm)
(%) Embodiment E1 1.87 1.36 Comparative 2.88 2.09 Article C1
[0095] On the basis of the above results, embodiment E1 of the
present invention, in which c axis 700 of molding 7 obtained in the
above-mentioned extrusion step and drying step is facing in
substantially the vertical direction V, was determined to
significantly inhibit the amount of cell deformation in comparison
with comparative article C1, in which c axis 700 of molding 7 is
facing in substantially the horizontal direction.
[0096] Embodiment 3
[0097] In the present embodiment, as shown in FIG. 11, the
deformation ratio of cell form was measured relative to a shift
angle 0 in the case of shifting the direction of c axis 700 of the
hexagon formed by partitions 71 of the above-mentioned molding 7
(same direction as side 705) in the extrusion step and drying step
of Embodiment 1 from the vertical direction V.
[0098] Measurement results are shown in a graph in FIG. 12. In this
graph, the above-mentioned shift angle .theta. (.degree.) was
plotted on the horizontal axis, while the above-mentioned
deformation ratio (%) was plotted on the vertical axis. The
measured values of deformation ratio are shown by curve H.
[0099] As can be seen from the above graph, in the case of the
above-mentioned shift angle of .+-.10.degree., cell deformation
remains stable and at a low level.
* * * * *