[0001] The present invention relates to extruding dies and a method of extruding ceramic
honeycomb structural bodies by using such extruding dies. More specifically, the invention
relates to extruding dies to be used in extruding ceramic honeycomb structural bodies
having partition walls of different wall thicknesses, such as catalyst carriers for
purifying waste gases from internal combustion engines, heat exchangers, and rotors
for pressure wave type superchargers, and to a method of extruding ceramic honeycomb
structural bodies by using such extruding dies.
[0002] Hereinafter, the term "ceramic honeycomb structural bodies" is used to mean structural
bodies having a plurality of through holes defined by partition walls.
[0003] In order to increase mechanical strength of an outer peripheral edge portion of a
honeycomb structural body which comprises partition walls having at least two different
thicknesses and is used as a catalyst carrier for purifying waste gases from an internal
combustion engine, it is known that the thickness of the outermost peripheral wall
of the honeycomb structural body is increased (see Japanese patent publication No.
54-28,850), and that the thickness of partition walls at an outer peripheral portion
of the honeycomb structural body is made greater than that of partition walls at an
inner portion thereof (see Japanese patent publication No. 57-50,170).
[0004] As dies for extruding such ceramic honeycomb structural bodies, there have been proposed
dies in which a hold plate is provided above an outer peripheral portion of shaping
channels corresponding to the sectional configuration of the honeycomb structural
bodies to unit partition walls extruded through the shaping channels at the outer
peripheral portion, and dies in which ceramic body feed holes are provided at an interval
corresponding to the width of shaping channels.
[0005] However, the dies of such constructions can be used for extruding honeycomb structural
bodies in which through holes are shaped in a relatively simple geometrical sectional
shape such as a triangular or rectangular section and the thickness of partition walls
does not largely vary. However, ceramic honeycomb structural bodies, such as supercharger
rotors, which contain partition walls having two or more different thicknesses and
through holes of a complicated section cannot be shaped through extrusion by these
dies, because of a non-uniform extruding speed of the body.
[0006] In order to eliminate the above drawbacks, NGK Insulators, Ltd. have formerly proposed
a novel die for extruding ceramic honeycomb structural bodies as shown in Figs. 6
and 7 (Japanese patent application Laid-open No. 60-67,111). This die comprises shaping
channels 2 (2a,2b, 2c, 2d, and 2e) corresponding to the sectional configuration of
the ceramic honeycomb structural body and ceramic body feed holes 3 (3a, 3b, 3c, 3d,
and 3e) communicating with the shaping channels at intersecting portions or annular
shaping channel portions, wherein the hydraulic diameter of the ceramic body feed
holes 3b, 3c and 3d communicating with the shaping channels 2b, 2c and 2d giving thinner
partition walls is made greater than that of the ceramic body feed holes 3a, and 3e
communicating with the shaping channels giving thicker partition walls.
[0007] Since this novel ceramic honeycomb structural body-extruding die has the above-mentioned
construction, the thicker partition walls and the thinner partition walls are shaped
at an equal extruding speed by using it. Thus, mechanically strong ceramic honeycomb
structural bodies can be obtained.
[0008] However, in this extruding die, while the ceramic body is being extruded, it is rapidly
spread at transitional locations between the ceramic body feed holes 3a and 3e and
the wider shaping channels 2a and 2e to form the thicker partition walls. Consequently,
adhesion in the body becomes weaker when the partition walls are being formed from
the body passing through the ceramic body feed holes, and ceramic grains are roughly
and non-uniformly charged into an outer peripheral wall and an inner peripheral wall.
Accordingly, fine cracks very often occur at inner portions of the partition walls
due to the rough charging. When the outer and inner peripheral walls are ground after
firing, defects such as scratches or patterns appear and cracks are formed in parallel
with an extruding direction.
[0009] Under the circumstances, the present inventors have strenuously made studies to solve
the problems encountered by the prior art, and found out that the problems can be
solved by bending communicating paths of ceramic body feed holes, which communicate
with the shaping channels giving thicker partition walls. The present invention has
been accomplished based on this discovery.
[0010] According to a first aspect of the present invention, there is provided a die for
extruding ceramic honeycomb structural bodies having at least two through holes with
partition walls having a plurality of different thicknesses, said extruding die comprising
shaping channels corresponding to a sectional configuration of the ceramic honeycomb
structural bodies, and ceramic body feed holes communicating with the shaping channels
at intersecting portions or annular shaping channel portions, wherein a hydraulic
diameter of the ceramic body feed holes communicating with the shaping channels giving
the thinner partition walls is made greater than that of the ceramic body feed holes
communicating with the shaping channels giving the thicker partition walls, and communicating
paths of the ceramic body feed holes, which communicate with the shaping channels
giving the thicker partition walls are bent.
[0011] According to a second aspect of the present invention, there is provided a method
for extruding ceramic honeycomb structural bodies from a ceramic body, while thinner
and thicker partition walls of the ceramic body honeycomb structural bodies are extruded
at an equal extruding speed, by using a die for extruding ceramic honeycomb structural
bodies having at least two through holes with partition walls having a plurality of
different thicknesses, said extruding die comprising shaping channels corresponding
to a sectional configuration of the ceramic honeycomb structural bodies, and ceramic
body feed holes communicating with the shaping channels at intersecting portions or
annular shaping channels portions, wherein a hydraulic diameter of the ceramic body
feed holes communicating with the shaping channels giving the thinner partition walls
is made greater than that of the ceramic body feed holes communicating with the shaping
channels giving the thicker partition walls, and communicating paths of the ceramic
body feed holes, which communicate with the shaping channels giving the thicker partition
walls are bent.
[0012] These and other optional features and advantages of the invention will be appreciated
upon reading of the following description of the invention when taken in conjunction
with the attached drawings, with the understanding that some modifications, variations,
and changes of the same could be made by the skilled person in the art to which the
invention pertains.
[0013] For a better understanding of the invention, reference is made to the attached drawings,
wherein:
Fig. 1 is a front view of an embodiment of the extruding die according to the present
invention as viewed from an extruding side thereof;
Fig. 2 is a front view of another embodiment of the extruding die according to the
present invention as viewed from an extruding side thereof;
Fig. 3 is a sectional view of Fig. 2 taken along a line III-III of Fig. 2;
Fig. 4 is a sectional view of a further embodiment of the extruding die according
to the present invention attached with a metallic plate;
Fig. 5 is a sectional view of Fig. 1 taken along a line V-V;
Fig. 6 is a sectional view of a conventional extruding die;
Fig. 7 is a sectional view of Fig. 6 taken along a line VII-VII, as attached with
a cylinder and a fitting frame;
Fig. 8 is a front view of a ceramic honeycomb structural body shaped according to
the present invention; and
Figs. 9 and 10 are examples of pressure wave type supercharger ceramic rotors produced
by using honeycomb structural bodies extruded according to the present invention,
Figs. 9 and 10 being a perspective view and a front view thereof, respectively.
[0014] In the following, the present invention will be explained in more detail with reference
to embodiments shown in the attached drawings.
[0015] As shown in Figs. 1, 2, 3, 4, and 5, a die 1 for extruding ceramic honeycomb structural
bodies (hereinafter referred to briefly as "die") according to the present invention
mainly comprises ceramic body feed holes (hereinafter referred to briefly as "feed
holes") 3: 3a, 3b, 3c, 3d, and 3e arranged on a side of an extruding machine, and
shaping channels 2: 2a, 2b, 2c, 2d, and 2e connected to the feed holes and adapted
to shape a ceramic body fed through the feed holes in the form of a desired ceramic
honeycomb structure. That is, the shaping channels form partition walls, an inner
peripheral wall, and an outer peripheral wall of the ceramic honeycomb structural
body. Thus, for instance, depending upon the partition walls having different thicknesses,
the shaping channels 2a and 2e having a greater shaping width and the shaping channels
2b, 2c and 2d having a smaller shaping width are provided corresponding to thicker
partition walls and thinner partition walls, respectively.
[0016] The above-constituted die according to the present invention is characterized in
that communicating paths of the feed holes 3a and 3e, which communicate with the shaping
channels 2a and 2e giving the greater partition wall thickness are bent.
[0017] By bending the communicating paths like this, shearing force is applied to the ceramic
body fed through the feed holes and at the same time the body is laterally forced
out. Consequently, adhesion in the ceramic body becomes greater. Therefore, the thus
obtained ceramic honeycomb body is free from defects seen in the above-mentioned conventional
techniques.
[0018] From the standpoint of adhesion in the body, it is preferable to bend the communicating
paths at an angle of 30° or more in an extruding direction. More preferably, the bending
angle is 90°. The communicating paths may be bent once, and more preferably twice
or more.
[0019] As shown in Fig. 3, it may be that the outer peripheral wall of the honeycomb structural
body is partially formed by an inner peripheral face of a die-fitting frame 5 for
fitting the die 1 to a cylinder 4 of the extruding machine, while the inner peripheral
wall is partially formed by an outer peripheral face of a ring piece 5' constituting
a part of the die 1.
[0020] As shown in Fig. 5, it may be that the outer and inner peripheral walls of the honeycomb
structural body are formed by the die by itself, respectively. In addition, as shown
in Fig. 4 as a further embodiment, a metal plate 7, which is provided with openings
6a and 6e having a smaller hydraulic diameter and openings 6b, 6c and 6d corresponding
to the shaping channels 2a and 2e, and 2b, 2c and 2d having the greater shaping width
and smaller shaping width, respectively, may be attached, on a side of the cylinder
4, to the body feed holes 3 having substantially the same hydraulic diameter, that
is, to the ceramic body in flow portion of the feed holes 3. The die for controlling
the flowing of the ceramic body with the metallic plate is effectively used when various
shaping channel-provided section and feed hole-provided section are separately formed
and an appropriate combination thereof is selected depending upon the shape of desired
ceramic honeycomb structural bodies or when the flowing of the ceramic body is desired
to be partially controlled at the shaping channels and/or the feed holes.
[0021] As shown in Figs. 3, 4 and 5, the shaping channels may be designed in various sectional
shapes and in various arranging manners depending on the shape of the ceramic honeycomb
structural bodies. The shaping channels may be formed by a conventional technique
such as discharge working taking the dimension and material thereof into consideration.
[0022] The ratio between the maximum width T₂ and the minimum width T₂ of the shaping channels
may be set in a range of 1 < T₁/T₂ ≦ 300. If the ratio exceeds 300, it is necessary
to greatly reduce the dimension of the feed holes corresponding to the wider shaping
channels. This renders mechanical working difficult.
[0023] The feed holes are formed in the die on the cylinder side of the extruding machine
such that they may be located corresponding to intersections or annular portions of
the shaping channels. It is necessary to make the hydraulic diameter of the feed holes
correspond to the width of the shaping channels.
[0024] That is, as shown in Figs. 3 through 5, the feed holes 3a and 3e having the smaller
hydraulic diameter connect with the shaping channels 2a and 2e having the greater
shaping width, respectively, while the feed holes 3b, 3c and 3d having the greater
hydraulic diameter connect with the shaping channels 2b, 2c and 2d having the smaller
shaping width, respectively.
[0025] The connection of the feed holes to the shaping channels means herein that the ceramic
body coming from the extruding machine is fed into the feed holes through the cylinder
4 and flows inside the shaping channels at right angles relative to the extruding
direction, and the body is united inside the shaping channels. In order to unit the
ceramic body inside the shaping channels, it is necessary to appropriately select
the dimension, number and arrangement of the feed holes such that the shaping channels
may fully be filled with the ceramic body. On the other hand, the depth of the shaping
channels needs to be large enough to fully charge the body thereinto.
[0026] Next, steps of forming ceramic honeycomb structural bodies having partition walls
of plural different thicknesses by using the die according to the present invention
will be explained.
[0027] The ceramic body inside the cylinder 4 is press fed into the feed holes 3 of the
die 1 by the extruder. At that time, since the ceramic body undergoes greater resistance
from the inner wall faces of the fed holes 3a and 3e having a smaller hydraulic diameter
than from those of the feed holes 3b, 3c and 3d having the greater hydraulic diameter,
the ceramic body flows more slowly inside the former. On the other hand, as to the
shaping channels 2, the shaping speed of the ceramic body in the shaping channels
2a and 2e having the larger shaping width is greater than in the shaping channels
2b, 2c and 2d having the smaller shaping width. That is, the extruding speed of the
ceramic body at the front face of the die is complementally controlled by the dimensions
of the feed holes and the shaping channels so that the thinner and thicker partition
wall portions of the honeycomb structural body may be extruded at the same shaping
speed.
[0028] Furthermore, since the communicating paths of the feed holes 3a and 3e, which connect
and communicate to the shaping channels 2a and 2e giving the thicker partition walls
are bent, the ceramic body laterally flows in the shaping channels so that the ceramic
body ceramic body is united together with great adhesion. Thus, a mechanically strong
green ceramic honeycomb structural body as shown in Fig. 8 can be obtained. Then,
the green body is fired, thereby obtaining a crack-free pressure wave type supercharger
ceramic rotor shown in Figs. 9 and 10.
[0029] Next, more specific examples of the present invention will be explained.
Examples
[0030] Five parts by weight of powdery magnesium oxide, 4.2 parts by weight of powdery cerium
oxide, and 0.8 parts by weight of powdery strontium oxide were added, as a sintering
aid, to 90 parts by weight of powdery silicon nitride having the average particle
diameter of 5.0 µm, thereby obtaining 100 parts by weight of a ceramic powder. The
thus obtained ceramic powder was kneaded with 6 parts by weight of an organic binder
mainly consisting of methyl cellulose as a shaping aid and 23 parts by weight of water.
The kneaded material to be extruded was extruded by a die 1 shown in Fig. 3, thereby
obtaining an extruded body having an outer diameter of 140 mm and a length of 200
mm. In this die, the width of the shaping channels 2a, 2e giving the outer and inner
peripheral partition walls was 5 mm, and that of the shaping channels 2b, 2c and 2d
giving the partition walls constituting cells was 2b=2d=0.7 mm, and 2c=1.0 mm. A body
having a length of 10 mm in an extruding direction was cut from the thus extruded
body. Although defects contained in the outer and inner peripheral walls were checked
by an X-ray radiographic inspection, no such defects were found out.
[0031] Next, after 30% of water was removed from the remaining extruded ceramic body by
using an electric range, water was completely removed by blowing hot air at 70°C through
holes.
[0032] Thereafter, the dried body was calcined at 500°C in air to remove the organic binder,
which was fired at 1,750°C for 2 hours in a nitrogen atmosphere, thereby obtaining
a sintered body.
[0033] By using a diamond wheel, this sintered body was machined at the outer and inner
peripheral portions and the end faces thereof to attain a desired shape, thereby obtaining
a pressure wave type supercharger ceramic rotor.
[0034] Although occurrence of defects such as cracks was visually checked, almost no defects
were found out in this rotor.
[0035] For comparison purpose, a ceramic body was extruded under the same conditions as
mentioned above by using the conventional die shown in Figs. 6 and 7, thereby obtaining
an extruded body having an outer diameter of 140 mm. A body having a length of 10
mm in an extruding direction was cut from the thus extruded body, and the outer and
inner peripheral walls were inspected as to their inner detects by the X-ray radiographical
inspection. Consequently, such inner detects were found out in both the outer and
inner peripheral walls. A ceramic rotor was obtained by drying, firing and grinding
the remaining extruded body. It was revealed that scratch-like cracks parallel in
the extruding direction and arcuate cracks representing flow of the body occurred
in the rotor.
[0036] As detailed above, in the extruding die according to the present invention, the hydraulic
diameter of the ceramic body feed holes communicating with the shaping channels giving
the smaller partition wall thickness is made greater than that of the ceramic body
feed holes communicating with the shaping channels giving the greater partition wall
thickness, and the communicating paths of the ceramic body feed holes, which connect
to and communicate with the shaping channels giving the thicker partition walls are
bent. Thereby, shearing force is applied to the ceramic body there so that the ceramic
body is united with great adhesion. Thus, the invention has a great advantage that
mechanically strong ceramic honeycomb structural bodies can be obtained.
1. A die for extruding ceramic honeycomb structural bodies having at least two through
holes with partition walls having a plurality of different thicknesses, said extruding
die comprising shaping channels (2) corresponding to a sectional configuration of
the ceramic honeycomb structural bodies, and ceramic body feed holes (3) communicating
with the shaping channels (2) at intersecting portions or annular shaping channel
portions, wherein the hydraulic diameter of the ceramic body feed holes (3b,3c,3d)
communicating with the shaping channels (2b,2c,2d) providing the thinner partition
walls is greater than that of the ceramic body feed holes (3a,3e) communicating with
the shaping channels (2a,2e) providing the thicker partition walls, and communicating
paths of the ceramic body feel holes which communicate with the shaping channels providing
the thicker partition walls are bent.
2. A die according to claim 1 wherein said bent communicating paths comprise path
portions extending at an angle to the respective shaping channels.
3. A die according to claim 1 wherein said bent communicating paths comprise path
portions extending at right angles to the respective shaping channels.
4. A die according to any one of claims 1 to 3 wherein said body feed holes communicating
with the shaping channels providing the thicker partition walls are parallel to and
laterally offset relative to their respective shaping channels.
5. A method for extruding ceramic honeycomb structural bodies from a ceramic body,
while thinner and thicker partition walls of the ceramic honeycomb structural bodies
are extruded at an equal extruding speed, by using a die for extruding ceramic honeycomb
structural bodies having at least two through holes with partition walls having a
plurality of different thicknesses, said extruding die comprising shaping channels
corresponding to a sectional configuration of the ceramic honeycomb structural bodies,
and ceramic body feed holes communicating with the shaping channels at intersecting
portions or annular shaping channel portions, wherein a hydraulic diameter of the
ceramic body feed holes communicating with the shaping channels giving the thinner
partition walls is made greater than that of the ceramic body feed holes communicating
with the shaping channels giving the thicker partition walls, and communicating paths
of the ceramic body feed holes which communicate with the shaping channels giving
the thicker partition walls and the ceramic body feed holes communicating therewith
are bent.