U.S. patent application number 10/383053 was filed with the patent office on 2003-09-18 for catalyst carrier holding mat and process for production of catalytic converter.
This patent application is currently assigned to HONDA GIKEN KOGYO KABUSHIKI KAISHA. Invention is credited to Sugiyama, Tomomi, Tosa, Shinichi.
Application Number | 20030175177 10/383053 |
Document ID | / |
Family ID | 28043710 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030175177 |
Kind Code |
A1 |
Tosa, Shinichi ; et
al. |
September 18, 2003 |
Catalyst carrier holding mat and process for production of
catalytic converter
Abstract
A catalyst carrier holding mat is rolled around a catalyst
carrier so as not to wrinkle when rolled, and the catalyst carrier
is thereby uniformly compressed. Furthermore, method of forming a
catalytic converter in this manner is also provided.
Inventors: |
Tosa, Shinichi; (Wako-shi,
JP) ; Sugiyama, Tomomi; (Wako-shi, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
Suite 600
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Assignee: |
HONDA GIKEN KOGYO KABUSHIKI
KAISHA
|
Family ID: |
28043710 |
Appl. No.: |
10/383053 |
Filed: |
March 7, 2003 |
Current U.S.
Class: |
422/179 ;
422/177; 428/920 |
Current CPC
Class: |
F01N 3/2857 20130101;
F01N 2350/02 20130101; F01N 3/2853 20130101; F01N 2350/04 20130101;
F01N 2450/02 20130101 |
Class at
Publication: |
422/179 ;
428/920; 422/177 |
International
Class: |
F01N 007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2002 |
JP |
2002-069842 |
Mar 14, 2002 |
JP |
2002-069844 |
Claims
What is claimed is:
1. A catalyst carrier holding mat rolled around an outer surface of
a catalyst carrier accommodated in a cylindrical casing along a
circumferential rolling direction, the mat holding the catalyst
carrier in the casing by being compressed between the catalyst
carrier and the casing, the mat comprising: a convex part formed on
one side of the rolling direction of the mat and projecting in the
rolling direction, a concave part formed on the other side of the
mat to fit with the convex part, the convex part and the concave
part extending parallel to the rolling direction in condition of
fitting together to enable control of the rolling diameter, and
corner parts included in the convex part and the concave part, the
corner part formed into an R shape with a radius of not less than 5
mm or a linear-chamfered shape.
2. A producing method for a catalytic converter comprising the
following steps: inserting a cylindrical catalyst carrier rolled by
a mat into a cylindrical casing, compressing the mat by reducing
the diameter of the casing so as to hold the catalyst carrier in
the casing, wherein calculating an inner diameter of the casing
after reducing diameter thereof based on a surface density of the
mat and an outer diameter of the catalyst carrier before the
reducing diameter and a predetermined filled density of the mat
after reducing diameter of these mat and catalyst carrier, and
reducing the casing until an inner diameter of the casing reaches
the calculated inner diameter of the casing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to a mat which holds a
catalyst carrier of a catalytic converter which cleans exhaust gas
exhausted from an engine of cars or the like in a casing by being
rolled around the catalyst carrier, and in particular, relates to a
process for production of the catalytic converter.
[0003] 2. Background Art
[0004] Generally, a three-way catalytic converter is arranged in
part of an exhaust duct and is used in a method of cleaning exhaust
gas. This three-way catalytic converter changes three noxious
ingredients contained in exhaust gas such as carbon monoxide (CO),
hydrocarbons (HC), and nitrogen oxides (NO.sub.X) into harmless
substances in the entirety by a catalyst in which a noble metal
such as platinum or rhodium is held by alumina or the like. A
catalyst carrier which holds the catalyst described above is
cylindrical in form, has numerous minute cells having honeycomb
shaped cross section formed thereinside, and catalyst is coated on
cell walls which form the cells. The three noxious ingredients
mentioned above flow through the catalyst carrier, which reaches
200 to 300.degree. C., in the exhaust gas, a chemical reaction
occurs on the coated catalyst to render these noxious ingredients
harmless, and thus exhaust gas can be cleaned.
[0005] FIG. 9 shows an example of a conventional catalytic
converter having such a catalyst carrier. A catalyst carrier 1 is
packed in a cylindrical casing 2, and a zonal mat 10 in which
ceramic fiber is bound by a binder is rolled singly along a
circumferential direction on the central part of the outer
circumference of the catalyst carrier 1. This inmat 10 has heat
resistance and cushioning performance because a catalyst carrier
which has relatively low strength must be fixed in the casing. The
mat 10 is packed in the casing 2 being compressed to hold the
catalyst carrier 1 in the casing 2. Arrows show the flow direction
of the exhaust gas in FIG. 9.
[0006] The mat 10 described above has a convex part 11 which is
projecting in the rolling direction on one side of the rolling
direction of the mat as shown in FIG. 10, and a concave part 12 is
formed on the other side of the rolling direction of the mat. In a
condition in which the mat 10 is rolled around the catalyst carrier
1, the convex part 11 is fitted into the concave part 12 and these
edge parts are facing each other. By fitting the convex part 11
into the concave part 12 in this way, not only is the flow of
exhaust gas through a clearance between these edge parts prevented
by blocking the clearance with the convex part 11, the shifting of
the edge parts in the axial direction is also prevented.
Furthermore, this mat keeps the catalyst carrier hot. Such a mat is
disclosed in Japanese Unexamined Patent Application Publication No.
217426/95. In this publication, clearance which exists at both
sides of a convex part are extending at different positions along
the rolling direction to prevent flowing out of fibers of a
mat.
[0007] In a conventional mat 10 shown in FIG. 10, a convex part 11
and a concave part 12 extend parallel to the rolling direction so
as to fit the convex part 11 and the concave part 12 to each other
in the case in which a catalyst carrier having different a diameter
is used, that is to say, so as to enable control of the rolling
diameter. Therefore, each of the corner parts 11a and 12a included
in the convex part 11 and concave part 12 are formed so as to be
almost right-angled, and slightly R-shaped. In the case in which
mat 10 is rolled around the catalyst carrier, rolling wrinkles
which extend along the axial direction inevitably occur on the
inner circumference of the mat 10, and such rolling wrinkles easily
occur partially from the convex corner parts 11a and 12a as
origins. FIG. 11 shows a condition in which a conventional mat such
as mat 10 mentioned above is rolled around a catalyst carrier, and
several rolling wrinkles partially occurred. These rolling wrinkles
occur as the mat is being bent at a corner part as an origin.
[0008] If the catalyst carrier 1 and the mat 10 are canned, in
other words, packed in the casing 2 as shown in FIG. 10 under the
conditions in which rolling wrinkles partially occur as described
above, surface pressure against the catalyst carrier 1 brought from
around the rolling wrinkles on compressed mat 10 is increased, and
the catalyst carrier may break in the case in which the surface
pressure exceeds the breaking strength. Therefore, it is desirable
that rolling wrinkles 13 occur equally along the circumferential
direction to reduce the surface pressure. However, this is
difficult because the corner parts 11a and 12a exist as described
above.
[0009] Furthermore, in a process for production of such a catalytic
converter, a technique in which a mat is compressed under a canning
condition as mentioned above is required. As a conventional example
of such a producing method, there is a method in which a catalyst
carrier having a mat on its outer circumference is set inside of a
pair of half members which compose a casing, and the half members
are joined together. However, in this producing method, although
the mat is compressed sufficiently along the joined direction of
the half members, compression along the vertical direction of the
joined direction is not sufficient. Therefore, there is a problem
in that holding ability of the catalyst carrier cannot be
stabilized. Therefore, a producing method in which a casing formed
by rolling a flat plate was put on a catalyst carrier rolled by a
mat, the diameter of the casing was shrunk by compressing the mat,
and edges of the casing were welded, and thus the mat can be
uniformly compressed along the whole circumference, was
suggested.
[0010] Such a producing method is disclosed in Japanese Unexamined
Patent Application Publication No. 291426/2000, and furthermore, in
the publication, a technique in which surface pressure of a mat
against a catalyst carrier is maintained constant by controlling
the degree of diameter shrinking (called the "degree of tightening
of outer shell" in the publication) of a casing depending on the
outer shape of the catalyst carrier. In addition, as a producing
method in which the diameter of a casing is reduced, there is also
a tube shrinking method in which a cylindrically formed casing is
shrunk. In this method, a process of welding each of the casings
after reducing the diameter can be omitted.
[0011] A mat used in catalytic converters is obtained by applying a
process of a kind of paper-production to ceramic fibers which
mainly contain alumina-silica, or to heat resistant fibers such as
alumina fibers or mullite fibers. Furthermore, it is common for
vermiculite to be added to make it have a characteristic of
expansion under high temperatures. There is also a mat in which
vermiculite is not contained. Because the mat is prepared by such
components and the producing process as described above, it is
difficult to reduce reduction of surface density of the mat.
Generally, it is said that there is a reduction in surface density
of 8 to 10% at most by weight ratio. Because of such reduction in
surface density, it is difficult to maintain surface pressure of a
mat against a catalyst carrier at a constant value even if the
diameter of the casing is reduced depending on the outer diameter
of the a catalyst carrier.
[0012] In particular, a recent catalyst carrier shows a tendency to
thin cell walls to increase the number of cells, so as to improve
cleaning ability and to reduce exhaust resistance by increasing
through cross section of exhaust gas. Therefore, breaking strength
of the catalyst carrier is deteriorated compared to a conventional
one. FIG. 12A shows an end face of a catalyst carrier of the thin
wall type in which cleaning ability is improved, and such a
catalyst carrier is usually produced by extrusion. In this
extruding process, deformation easily occurs at a cell wall because
of uniform flow of base material passing through a slit metallic
mold for extrusion. In particular, this deformation easily occurs
around the outer wall, and FIG. 12B shows an example of a catalyst
carrier in which a cell wall near the outer wall is deformed. The
strength may be further deteriorated because such a deformed cell
wall can be easily buckled if compressed.
[0013] Therefore, in a recent thin wall type catalyst carrier, it
is required that surface pressure which is brought by a mat under
canning condition not further exceed the minimum required surface
pressure to be held in the casing. To realize this, it is necessary
to prevent the occurrence of partial rolling wrinkles originating
from corner parts described above.
[0014] Furthermore, surface pressure against a catalyst carrier
caused by a mat in a canning condition must be set between a
pressure in which catalyst carrier does not shift if external force
such as vibration or pressure of exhaust gas is exerted and a
pressure which is lower than the breaking strength of the catalyst
carrier. However, this set range of surface pressure becomes small
because breaking surface pressure is decreased as breaking strength
of catalyst carrier is decreased. Therefore, if dispersion of
surface density of a mat is large as described above, surface
pressure of the mat against the catalyst carrier easily deviates
from the set range of surface pressures. In particular, in a tube
shrinking method in which the diameter of a cylindrical casing is
reduced, because the diameter of casing is slightly increased by
spring back if the diameter-shrinking load is released, the degree
of the diameter reduction must be decided by anticipating this
phenomenon. However, it is difficult to control the degree of
diameter reduction in which surface pressure is maintained constant
in consideration of the spring back together with the deterioration
of strength of a catalyst carrier.
SUMMARY OF THE INVENTION
[0015] Therefore, an object of the present invention is to provide
a catalyst carrier holding mat in which partial increasing of
surface pressure of the mat against a catalyst carrier under
canning condition can be prevented by preventing partial occurrence
of rolling wrinkles of the mat, and as a result, canning can be
reliably applied even to a catalyst carrier having low strength
without breaking. Furthermore, an object of the present invention
is to provide a process for production of a catalytic converter in
which under a tube shrinking method wherein a catalytic converter
is produced by canning, surface pressure of a mat against a
catalyst carrier can be controlled constantly for each pair of
casing and catalyst carrier depending on reduction of surface
density of the mat, and as a result, surface pressure of the mat
can be set within a set range of surface pressure even in the case
of a catalyst carrier having low strength.
[0016] Characteristics of the present invention are that in a
catalyst carrier holding mat which is rolled around the outer
circumference of a catalyst carrier along the circumferential
direction, and holds the catalyst carrier in a casing by being
compressed between the catalyst carrier and the casing, a convex
part which is directed in the rolling direction is formed on one
side of the rolling direction, a concave part in which the convex
part extends parallel to the rolling direction so as to fit
together to enable control of the rolling diameter, and a corner
part of the convex part and the concave part are formed into R
shapes of greater than 5 mm or a linear-chamfered shape.
[0017] In the present invention, bending of a mat originating from
corner parts and rolling wrinkles are difficult to occur because
corner parts included in a convex part and a concave part are not
conventional right angles but are R shaped or linear-chamfered
shapes. That is to say, partial occurring of rolling wrinkles
originated from corner parts can be prevented. Therefore, under
canning conditions, partial increase of surface pressure of a mat
against a catalyst carrier brought by partially occurred rolling
wrinkles can be prevented. As a result, canning can be reliably
applied to even a catalyst carrier having low strength without
breaking.
[0018] Furthermore, a process for production of a catalytic
converter of the present invention is a method in which the inner
diameter of a casing is calculated so as to maintain the filled
density of a mat to be constant by regarding the outer diameter of
a catalyst carrier which is a variable factor and surface density
of the mat as parameters, diameter of the casing is reduced to
obtain the calculated inner diameter of the casing, and a suitable
degree of diameter shrinking of the casing under the diameter
shrinking method is settled for each pair of the casing and the
catalyst carrier. That is to say, characteristics of the present
invention are that in a producing method of a catalytic converter
in which a cylindrical catalyst carrier rolled by a mat is inserted
into a cylindrical casing and the mat is compressed by reducing the
diameter of the casing so as to have the catalyst carrier held in
the casing, the inner diameter of the casing after diameter
reduction is calculated by a fixed filled density of the mat after
diameter reduction of the casing and surface density of a mat and
outer diameter of a catalyst carrier of a pair of the catalyst
carrier and the mat, and then the casing is shrunk until the inner
diameter of the casing becomes the calculated inner diameter of the
casing. As a casing of the present invention, a tube whose edges
are welded beforehand, a seamless tube, or a cylindrically formed
tube whose edge is not welded can be used. In the case of a tube
whose edges are not welded beforehand, the edges are tacked
temporarily if necessary after shrinking of diameter, and
welded.
[0019] Inner diameter D (mm) of a casing of the present invention
can be calculated by following formula (1). In the case in which
the outer diameter of a catalyst carrier is X (mm), surface density
of a mat is Y (g/m.sup.2), and filled density of a mat is GBD
(g/cm.sup.3),
D=X+2Y/(GBD.times.10.sup.3) (1)
[0020] In the present invention, the diameter of a casing is
reduced until the diameter becomes the calculated diameter of the
casing as described above, the calculated degree of diameter
shrinking can keep filled density of the mat constant with high
accuracy by settling the value of dispersion of plate thickness of
the casing before diameter reduction and the value of changing of
the plate thickness by diameter shrinking as corrective
parameters.
[0021] In the case in which plate thickness is set as a corrective
parameter is explained as follows.
[0022] Because a method in which a jig or the like which is put on
an outer circumference of a casing are pushed to the inner
direction of diameter is conducted to reduce the diameter of a
casing, for example, the inner diameter of the casing is actually
controlled by the inner surface of the jig which is contacted to
the outer circumference of the casing, that is to say, the outer
diameter of the casing. Inner diameter D (mm) of the casing can be
calculated from the outer diameter Dout (mm) of the casing and
plate thickness T (mm) of the casing by applying the following
formula.
D=Dout-2T
[0023] Simultaneous equations of this formula and formula (1) are
solved about Dout, and formula (2) can be obtained as follows.
Dout=2T+X+2Y/(GBD.times.10.sup.3) (2)
[0024] By measuring the plate thickness beforehand before diameter
reduction of the casing and applying the formula (2), filled
density of a mat can be maintained constant at higher accuracy than
in the case in which formula (1) is applied.
[0025] Furthermore, in the case in which changing of plate
thickness is set as a corrective parameter is explained as
follows.
[0026] If a tube whose edges are welded beforehand before diameter
reduction or a seamless tube is used as a cylindrical casing,
length and plate thickness of the shrunk casing is generally larger
compared to the casing before diameter reduction. The reason for
this phenomenon is that even if the diameter is shrunk, plastic
deformation of lengthening and thickening occur to conserve the
volume. Therefore, by adding the predicted value of plate thickness
after diameter shrinking Tfrc as a corrective parameter to plate
thickness T which was measured before diameter shrinking, surface
density of the mat can be maintained constant at a high accuracy.
Because plate thickness is increased by a conservation of volume,
plate thickness after diameter reduction is increased as value of D
or Dout is decreased if the diameter of the casing before diameter
reduction is constant. This is expressed in a formula as
follows.
Tfrc-T=f(D) or f(Dout)
[0027] An experiment in which D or Dout was intentionally changed
to measure Tfrc and T was performed, a relationship between Tfrc-T
and D or Dout was solved, and f can be obtained as a regression
formula. If simultaneous equations of the relational expression of
Tfrc and D or Dout obtained in this way and the formula (1) or (2)
are solved about D or Dout, increasing of plate thickness by
diameter reduction is reflected and the filled density of the mat
can be maintained constant at a higher accuracy.
[0028] Next, an embodiment of the present invention is explained by
way of FIGS. 1 and 2.
[0029] FIG. 1 shows a catalytic converter in which a mat of the
embodiment is used. Reference numeral 20 is the mat, reference
numerals 1 and 2 are a catalyst carrier and a casing similar to the
ones shown in FIG. 9, respectively, and arrows show flow direction
of exhaust gas. The mat 20 is a zonal object in which ceramic fiber
is bound by a binder. This mat is singly rolled around the central
part of outer circumference of the catalyst carrier 1 along the
circumferential direction. The catalyst carrier 1 is canned in the
casing 2 with the mat 20 rolled therearound. The mat 20 is
compressed in this canning condition, and the catalyst carrier 1 is
held in the casing 2 by being brought into contact with the mat at
a fixed pressure.
[0030] As shown in FIG. 2, a convex part 21 which is directed in
the rolling direction (longitudinally) is formed on an edge of the
rolling direction of the mat 20, and a concave part 22 which is
fitting to the convex part 21 is formed on the other edge of the
rolling direction of the mat 20. The convex part 21 and the concave
part 22 are formed on the center of the width direction of the mat
20, and each width is set to be one-third of the width of the mat
20. The width of mat 20 can be suitably selected depending on the
length of the axial direction of the catalyst carrier 1, and is
usually about 45 to 120 mm. The length of mat 20 is set as a
suitable length relative to the circumference of the catalyst
carrier 1. The convex part 21 and the concave part 22 are extending
parallel to the rolling direction so as to fit each other even in
the case in which the diameter of a catalyst carrier 1 is
different, that is to say, so as to enable control of a rolling
diameter.
[0031] Concave parts 21a existing at both sides of the convex part
21, between the convex part 21 and a principal part 20A (a part in
which edge parts of the convex part 21 and the concave part 22 are
removed) of the mat 20, are formed into a quarter arc shape having
a radius R of 5 mm or more, respectively. Furthermore, convex
corner parts 21b existing on the tip of the convex part 21 are also
formed into the quarter arc shape having an R of 5 mm or more. On
the other hand, concave corner parts 22a existing at both side of
the concave part 22, between the back tip of the concave part 22
and the principal part 20A of the mat 20, are formed into the
quarter arc shape having an R or 5 mm or more. Furthermore, convex
corner parts 22b existing on the concave part 22-side of tips of a
pair of edge parts 22A on both sides of the concave part 22 are
also formed into the quarter arc shape having an R of 5 mm or
more.
[0032] The mat 20 mentioned above is rolled around the outer
circumference of the catalyst carrier 1 along the circumferential
direction, the convex part 21 is fitted into the concave part 22
while maintaining a condition of these edges facing each other as
shown in FIG. 2, and the mat 20 is canned in the casing 2 with the
catalyst carrier 1 as shown in FIG. 1. According to a catalytic
converter shown in FIG. 1, exhaust gas flows through numerous cells
in the catalyst carrier 1 under conditions in which the catalyst
carrier 1 is heated to more than activation temperature by exhaust
gas, noxious ingredients in the exhaust gas are rendered harmless
by chemical reaction, and thus exhaust gas is cleaned. Because the
convex part 21 is fitting to concave part 22, clearance between the
edge parts of the mat 20 is blocked to prevent exhaust gas from
flowing in the clearance, and furthermore, the edge part does not
shift in the axial direction.
[0033] In the mat 20 of the embodiment, each concave corner parts
21a and 22a which is included in the convex part 21 and the concave
part 22 are formed into semi-circular arc shapes having an R of 5
mm or more. Although these corner parts 21a and 22a cause origins
of rolling wrinkles in the condition in which the mat is rolled
around the catalyst carrier 1 if they are formed into right angles
as conventionally, the rolling wrinkles which are originated from
the corner parts 21a and 22a are difficult to occur if the corner
parts are formed into an R shape. That is to say, partial occurring
of rolling wrinkles which are originated from the corner parts 21a
and 22a can be prevented. Therefore, in the canning condition,
partial increasing of surface pressure of the mat 20 against the
catalyst carrier 1 by partial rolling wrinkles can be prevented,
and as a result, canning can be certainly performed without
breaking even if strength of the catalyst carrier 1 is low.
[0034] In other words, canning can be performed by using the mat 20
of the embodiment even if a wall which is forming cells of the
catalyst carrier 1 is thinned and its strength is reduced.
Therefore, engine output can be improved as pressure loss in the
passing of exhaust gas is reduced, and the catalyst carrier 1 can
be quickly activated as heat capacity is decreased to enable
reducing amount of exhaust gas at engine starting which
is.containing noxious ingredients.
[0035] Next, another embodiment of the present invention is
explained by way of FIG. 3.
[0036] In a mat 30 shown in FIG. 3, each of the corner parts 21a,
21b, 22a, and 22b which are formed into semicircular arc shapes in
the embodiment mentioned above are formed into linear-chamfered
shapes by 5 mm or more. The linear-chamfered shape is a shape whose
two edges forming the corner part are connected by line to fill in
the corner in the case of concave corner parts 21a and 22a, and a
shape whose two edges forming the corner are connected by a line to
cut off the corner in the case of convex corner parts 21b and 22b.
Furthermore, the size of 5 mm is equivalent to the filled part of
concave corner parts 21a and 22a, or length of a base of an
isosceles triangle removed from concave corner parts 21b and 22b as
shown L in FIG. 3.
[0037] Also, in another embodiment shown in FIG. 3, similar to the
embodiment mentioned above, partial occurring of rolling wrinkles
which are originated from the concave corner parts 21a and 22a can
be prevented when the mat 30 is rolled around the catalyst carrier
1, partial increasing of surface pressure of the mat 30 against the
catalyst carrier 1 by the rolling wrinkles can be prevented under
canning condition, and as a result, even a catalyst carrier having
low strength can be certainly canned without breaking.
[0038] In addition, it is more desirable that plural grooves
extending in width direction be formed beforehand on the inner
circumference of the mat 20 at a constant interval to make rolling
wrinkles occur uniformly in the circumferential direction, so as to
prevent partial occurring of rolling wrinkles. FIG. 4 shows the
inside of such a processed catalyst carrier.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0039] FIG. 1 is a drawing showing a cross section of a catalytic
converter applied by a mat of an embodiment of the present
invention.
[0040] FIG. 2 is a plane drawing showing both edges of a mat of an
embodiment of the present invention.
[0041] FIG. 3 is a plane drawing showing both edges of a mat of
another embodiment of the present invention.
[0042] FIG. 4 is a photograph showing the inside of a mat of
another embodiment of the present invention.
[0043] FIG. 5 is a graph showing the result of measurement of
breaking strength of the catalyst carrier (thick wall type).
[0044] FIG. 6 is a graph showing the result of measurement of
breaking strength of the catalyst carrier (thin wall type).
[0045] FIG. 7 is a photograph showing the result of measurement of
surface pressure distribution of a mat of an Example.
[0046] FIG. 8 is a photograph showing the result of measurement of
surface pressure distribution of a mat of a Comparative
Example.
[0047] FIG. 9 is a drawing showing a cross section of a
conventional catalytic converter.
[0048] FIG. 10 is a plane drawing showing both edges of a mat of a
conventional catalytic converter.
[0049] FIG. 11 is a photograph showing a cross section of a
conventional catalytic converter.
[0050] FIG. 12A is a photograph showing an edge of a catalytic
converter of the thin type, and FIG. 12B is a photograph showing an
edge of a catalytic converter of the thin type whose cell walls are
deformed.
[0051] FIG. 13A is a drawing showing a side cross section of a tube
shrinking device used in an Example, and FIG. 13B is a cross
section B-B line arrow along in FIG. 13A.
[0052] FIG. 14 is a graph showing the relationship of filled
density of mat and surface pressure measured in an Example.
[0053] FIG. 15 is a graph showing the relationship of surface
density of mat and surface pressure of mat measured in an
Example.
EXAMPLES
(1) Test for occurrence of rolling wrinkles
[0054] Four kinds of mats of the same shape as in FIG. 2 having
dimensions of width 60 mm, length 365 mm, and thickness 11 mm,
whose widths of convex parts and concave parts were 20 mm, whose
lengths of convex parts and concave parts were 65 mm, and whose R
(radius) of each corner parts were 5 mm, 7 mm, 10 mm and 15 mm,
were prepared as Example 1 to 4. On the other hand, a mat in which
the R of each corner part was 2 mm was prepared as a Comparative
Example. These mats of the Examples and Comparative Example were
rolled around a catalyst carrier having a diameter of 106 mm and
the convex parts and concave parts were joined together. This
rolling operation was repeated 5 times for each mat, and the
occurrence of rolling wrinkles at corner parts were observed
visually in each operation. Results are shown in Table 1.
1 TABLE 1 R size Test number (mm) 1 2 3 4 5 Comparative 2 Occurred
Occurred Occurred Occurred Occurred Example Example 1 5 Occurred
Did not occur Occurred Did not occur Did not occur Example 2 7 Did
not occur Did not occur Did not occur Did not occur Did not occur
Example 3 10 Did not occur Did not occur Did not occur Did not
occur Did not occur Example 4 15 Did not occur Did not occur Did
not occur Did not occur Did not occur
[0055] As shown in Table 1, occurring of rolling wrinkles can be
certainly prevented when the radius of corner parts are 7 mm or
more, and there were cases in which occurrence of rolling wrinkles
were prevented even in the case in which the radius of corner parts
were 5 mm. Rolling wrinkles certainly occurred in the case in which
the radius of corner parts were 2 mm. Therefore, it was confirmed
that the occurrence of rolling wrinkles can be prevented in the
case in which the radius of corner parts were 5 mm or more.
(2) Evaluation of effects of breaking of a catalyst carrier due to
increase of surface pressure due to occurrence of rolling
wrinkles
[0056] Breaking strength of two kinds of catalyst carriers in which
thickness of walls forming each cell was 110 m and 65 m were tested
by compressing. The catalyst carrier of the thick wall type having
a wall thickness of 110 1 m was a conventional product whose
cleaning ability was relatively low, and the number of samples used
in the breaking strength test was 497. On the other hand, the
catalyst carrier of the thin wall type having a wall thickness of
65 m was a recent product whose cleaning ability was higher than
that of the conventional product, and the number of samples applied
to the breaking strength test was 720. The results of the tests of
the thick wall type are shown in FIG. 5, and the results of the
tests of the thin wall type are shown in FIG. 6. As shown in FIG.
5, the catalyst carrier of the thick wall type was not broken until
a pressure of 20 kgf/cm.sup.2, and the average breaking strength
was 74.9 kgf/cm.sup.2. On the other hand, as shown in FIG. 6, the
catalyst carrier of the thin wall type was not broken until a
pressure of 6 kgf/cm.sup.2, and the average breaking strength was
23.2 kgf/cm.sup.2.
[0057] Next, a process in which a sheet shaped tactile sensor of a
surface pressure distribution measuring device (produce by the
Unitta Company) was rolled around a catalyst carrier before a mat
was rolled therearound, it was put into a cylindrical casing, and
canning (reduction of diameter of casing) was performed, was
applied to the mat of Example 3 mentioned above whose R of the
corner parts was 10 mm and to the mat of the Comparative Example
mentioned above whose R of the corner parts was 2 mm. In these two
cases, pressure of diameter reduction was the same. FIGS. 7 and 8
show the measured points including the corner parts of the mats of
Example 3 and the Comparative Example, and show the surface
pressure distribution data measured by the tactile sensors of the
measured points. If these figures are compared, although the
surface pressure of the mat against the catalyst carrier was in a
range of 5.5 to 6.0 kgf/cm.sup.2 at the most, surface pressure of
the mat of the Comparative Example was in a range of 7.5 to 8.0
kgf/cm.sup.2 at the most. Therefore, the mat of the Comparative
Example cannot be used for the thin wall type catalyst carrier
which exhibits the breaking strength shown in FIG. 6. On the other
hand, the mat of Example 3 can be used for the thin wall type
catalyst because the surface pressure against the catalyst carrier
was low.
(3A) Experiments for determining the relationship between filled
density of a mat and surface pressure of a mat
[0058] First, the relationship between the filled density of a mat
for a catalyst converter and surface pressure of this mat was
determined beforehand by experiment. FIGS. 13A and 13B show a tube
shrinking device used in the experiment. The structure of this tube
shrinking device is as follows. A fixed ring 2 is fixed on one edge
of the inside of a cylindrical housing 1, a shift ring 3 which can
shift freely along axial direction is put on the other edge, and
numerous pieces 4 are put inside the fixed ring 2 and the shift
ring 3 along the circumferential direction at a constant interval.
A casing 10 is inserted through these pieces 4, and by sliding the
shift ring 3 toward the fixed ring 2 to compress the pieces 4, each
piece is shifted to the inside of the diameter direction, and as a
result, the diameter of the casing 10 is reduced by compression of
the pieces 4. In FIG. 13, reference numeral 11 indicates a catalyst
carrier, and reference numeral 12 indicates a mat. The center of
the axial direction of the outside surface of the pieces 4 is
thickest, and the outside surface is inclined in a tapered shape
from the central part toward both ends. The inner surface of the
fixed ring and the shift ring are also formed in a tapered shape so
as to come into contact with the outside of the pieces. The degree
of diameter reduction of the casing can be controlled by the degree
of sliding of the shift ring. In this case, the gradient of
tapering of the shift ring is 5:1; therefore, the degree of sliding
of the shift ring is five times as much as the degree of diameter
reduction.
[0059] In the experiment, desired values of filled density of the
mat were determined to be 0.500 g/cm.sup.3, 0.450 g/cm.sup.3, 0.400
g/cm.sup.3, and 0.350 g/cm.sup.3 as shown in Table 2, and three
values of the surface pressure of the mat as experiment data for
each desired value of filled density were measured, and thus twelve
values of surface density were measured in total (Experiments No. 1
to 12). As shown in Table 2, three kinds of catalyst carrier having
different outer diameters corresponded to each filled density, and
furthermore, the surface density of the mat which was put together
with each catalyst carrier. It should be noted that the outer
diameter of the catalyst carrier was measured by calipers or laser
dimension measuring apparatus, and that surface density of the mat
was calculated by measuring the weight of the mat with electronic
force balance, the measured weight was divided by the area of the
mat.
2TABLE 2 Experiment No. 1 2 3 4 5 6 7 8 9 10 11 12 Filled density
of mat 0.500 0.500 0.500 0.450 0.450 0.450 0.400 0.400 0.400 0.350
0.350 0.350 (g/cm.sup.3) Outer diameter of 105.71 105.43 105.55
105.71 105.43 105.55 105.71 105.43 105.55 105.71 105.43 105.55
catalyst carrier: X (mm) Surface density of mat: 2682 2388 2454
2662 2575 2510 2647 2629 2485 2700 2502 2605 Y (g/m.sup.2) Degree
of sliding of 31.29 38.56 36.64 25.77 29.11 29.95 18.75 20.62 23.60
7.78 14.86 11.29 shift ring (mm) Surface pressure of mat 3.61 4.88
4.05 2.38 3.06 3.27 1.29 1.56 2.02 0.69 1.12 0.64
(kgf/cm.sup.2)
[0060] Next, the degree of diameter reduction of the casing in
which the determined filled density of the mat can be found was
calculated by the formula of degree of diameter reduction (3) as
follows. The results are shown in Table 2.
Z=a+bX+cY (3)
[0061] (Z: Degree of diameter reduction of a casing (mm); X: Outer
diameter of a catalyst carrier (mm); Y: Surface density of mat
(g/m.sup.2); a, b, c: constants)
[0062] The formula mentioned above can be determined as
follows.
[0063] First, correlation between filled density and surface
pressure of the mat was determined by experiments, and surface
density of the mat of desired value was calculated from the results
as follows.
[0064] GBD: Filled density of the mat of desired value
[0065] Y: Surface density of the mat (g/cm.sup.2)
[0066] X: Outer diameter of the catalyst carrier (mm)
[0067] Z: Degree of reduced diameter of the casing (mm)
[0068] Db: Inner diameter of the casing before compression (mm)
[0069] Da: Inner diameter of the casing after compression (mm) Each
of GBD to Da are defined as above, and two formulas can be
established as follows.
GBD=2Y/(Da-X)
Z=Db-Da
[0070] Simultaneous equations of these two formulas are solved by
substituting actual numerical values into GBD and Db which are
constants, and constant terms a, b, and c in the formula (3)
mentioned above can be obtained.
[0071] Next, as shown in Table 2, the degree of sliding of the
shift ring in the tube shrinking device was calculated by
multiplying calculated degree of diameter shrinking in each of
experiment Nos. 1 to 12 by 5 times. Furthermore, in each experiment
Nos. 1 to 12, a tactile sensor of surface pressure distribution
measuring device (produced by the Unitta Company) was rolled around
the catalyst carrier before the mat was rolled therearound, it was
put into a casing prepared separately, and this casing was put into
the tube shrinking device shown in FIG. 13. Next, the shift ring
was shifted for calculated degree of sliding, and thus the diameter
of the casing was reduced to perform canning. At the time, data of
surface pressure distribution which were output from the tactile
sensors were analyzed, and the average value as the surface
pressure of the catalyst carrier brought by the mat was calculated.
These surface pressure data are shown in Table 2, and a
relationship between filled density of the mat and surface pressure
is described in a graph shown in FIG. 14. The relationship between
filled density of the mat and surface pressure became clear by this
graph.
(3B) Canning test
[0072] Next, to obtain surface pressure of the mat of desired
value, filled density of the mat which can obtain the surface
pressure was decided based on FIG. 14. Inner diameter of the casing
to be reduced was calculated from this filled density, measured
outer diameter of the catalyst carrier, and surface density of the
mat by the formula (1) mentioned above, and canning test in which
the diameter of the casing was reduced was performed based on this.
Specifically, a desired value of the surface pressure of the mat
was set at 2.6 kgf/cm.sup.2, and the filled density of the mat was
calculated as 0.44 g/cm.sup.3 from FIG. 14. Canning tests were
performed in the same manner as the experiment described above
(3A), in which tactile sensors of a surface pressure distribution
measuring device (produced by the Unitta Company) was rolled around
the catalyst carrier and then the mat was rolled therearound, and
the average of surface pressure on the catalyst carrier caused by
the mat was calculated after canning. Number of specimens of the
Examples was 18 (Specimens No. 1 to 18), and these data are shown
in Table 3. On the other hand, as the Comparative Examples, canning
tests in which the diameter of the casing was reduced so as to
maintain the inner diameter constant were performed. Number of
specimens was 5 (Specimens Nos. 19 to 23), and these data are also
shown in Table 3. Furthermore, based on Table 3, the relationship
between surface density of the mat and surface pressure of the mat
after diameter reduction in each of the Examples and the
Comparative Examples are described in a graph shown in FIG. 15.
3 TABLE 3 Desired surface Outer diameter of Surface Inner Filled
Surface Difference of Specimen pressure of mat catalyst carrier
density of casing density of pressure surface pressure No.
(kgf/cm.sup.2) (mm) mat (g/m.sup.2) (mm) mat (g/cm.sup.3)
(kgf/cm.sup.3) (kgf/cm.sup.2) Examples 1 2.6 105.37 2417 116.36
0.44 3.15 0.56 2 2.6 105.60 2548 117.19 0.44 2.92 0.33 3 2.6 105.58
2595 117.38 0.44 2.33 0.25 4 2.6 105.61 2460 116.80 0.44 3.31 0.72
5 2.6 105.58 2582 117.32 0.44 2.57 0.02 6 2.6 105.62 2446 116.75
0.44 3.04 0.46 7 2.6 105.58 2649 117.62 0.44 2.60 0.02 8 2.6 105.63
2546 117.21 0.44 2.73 0.14 9 2.6 105.60 2401 116.52 0.44 2.61 0.03
10 2.6 105.63 2440 116.72 0.44 2.98 0.40 11 2.6 106.29 2662 118.39
0.44 2.50 0.08 12 2.6 106.29 2605 118.14 0.44 2.42 0.16 13 2.6
106.34 2656 118.41 0.44 2.47 0.11 14 2.6 106.33 2624 118.27 0.44
2.48 0.10 15 2.6 104.83 2347 115.50 0.44 2.71 0.13 16 2.6 104.93
2370 115.70 0.44 3.17 0.59 17 2.6 104.94 2433 116.00 0.44 2.84 0.26
18 2.6 104.89 2382 115.72 0.44 2.91 0.33 Average 2.76 0.18 0.288
0.288 Comparative 19 2.6 106.33 2688 117.06 0.501 4.24 1.65
Examples 20 2.6 104.83 2330 117.06 0.381 1.32 1.26 21 2.6 105.60
2541 117.06 0.443 2.67 0.08 22 2.6 105.58 2496 117.06 0.435 2.46
0.12 23 2.6 105.63 2466 117.06 0.431 2.38 0.20 Average 2.55 0.03
0.783 1.046
[0073] According to Table 3, the average value of surface pressure
of the mat is relatively close to the desired value in both the
Examples and the Comparative Examples. However, large variations in
the surface density of the mat were observed in the Comparative
Examples, and the differences of surface pressure (desired surface
pressure of mat) was about 3.6 times as great as in the Examples.
Therefore, it was confirmed that even if there was variation in
surface density of a mat or outer diameter of a catalyst carrier,
the surface pressure can be controlled to be constant depending on
the variation in the process for production of the present
invention. In addition, because surface pressure of a mat can be
controlled as described above, breaking of catalyst carrier can be
prevented by controlling the surface pressure of the mat within a
set range even in the case of a catalyst carrier having low
breaking strength. Furthermore, as is obvious from FIG. 15, it is
confirmed that there is a correlation between surface density of a
mat and surface pressure of a mat after the diameter was reduced.
Therefore, in a mat which is compressed in a constant filled
density, surface pressure changes occurred correlating with surface
density before the mat was compressed. Therefore, the surface
pressure can be stabilized further by calculating the filled
density which is corrected depending on the surface density of the
mat before compression by making this correlation as an index, and
then reducing the diameter of the casing.
[0074] As explained above, in the catalyst carrier holding mat of
the present invention, partial occurrence of rolling wrinkles can
be prevented and partial increasing of surface pressure of the mat
against the catalyst carrier under canning condition can be also
prevented by this because corner parts included in convex part and
concave part fitted to each other when rolled around the catalyst
carrier are formed into an R shape having a radius of 5 mm or more,
or formed into a linear-chamfered shape, and as a result, even a
catalyst carrier having low strength can be reliably canned without
breaking.
[0075] Furthermore, in the process for production of the catalytic
converter of the present invention, the filled density of a mat
having correlation with the surface pressure of the mat against a
catalyst carrier is calculated for each catalytic converter which
is produced, and the degree of diameter reduction of the casing is
controlled depending on this, and a catalytic converter in which
surface pressure of the mat against the catalyst carrier is
constant can be produced.
* * * * *