Ceramic fiber molding for manifold reactors

Ceramic fiber molding for manifold reactors in which Al.sub.2 O.sub.3 --SiO.sub.2 ceramic fibers or SiO.sub.2 ceramic fibers are employed to form a molded product having a hardness of 20.degree. - 55.degree., a tensile strength of 120 - 1500 g/cm.sup.2 and a molded density of 0.06 - 0.35 g/cm.sup.3.

In recent years research has been pursued with a view to developing a 
recombustion type exhaust gas purifier which reburns the carbon monoxide 
and hydrocarbons contained in automotive emissions and transforms them 
into harmless carbon dioxide and water; and as a result manifold reactors 
having heat-insulated construction has come into practical use. Such a 
manifold reactor, which serves to collectively transmit the emission from 
each cylinder to the exhaust pipe, reburns carbon monoxide and 
hydrocarbons which are among the harmful contents of the automotive 
emission and transforms them into harmless carbon dioxide and water.

As illustrated in the partial vertical sectional view of FIG. 1 and in the 
sectional view of FIG. 2, the manifold reactor is constructed so that the 
exhaust gas is introduced through the exhaust gas inlet pipe 1 and, after 
it has been reburned, it is discharged through the exhaust gas discharge 
pipe 2. A ceramic fiber molding 7 according to the present invention is 
packed as heat insulation material between the outer tube 5 (which holds 
the inner tube 3 of the recombustion chamber together with the inner core 
support 4) and the outer casing which is divisible into two parts 6, 6'. 
The manifold reactor can be heat insulated in various ways, for example: 
(1) A castable ceramic slurry may be poured into a heat-insulated space and 
permitted to dry and solidify. (By "castable ceramic slurry" is meant a 
refractory concrete which usually comprises alumina cement added to a 
refractory aggregate, such as alumina or clay.) 
(2) A packed foaming ceramic powder may be fired and solidified. 
(3) A ceramic fiber blanket may be vacuum-packed in a vacuum-resistant 
plastic bag. 
(4) A ceramic fiber blanket may be packed after impregnating it with water 
for better handling. 
(5) A ceramic fiber blanket may be impregnated with water and an inorganic 
binder, and then packed in to dry and solidify. 
(6) A ceramic fiber blanket may be packed in after cutting it into pieces. 
A molded product obtained by steps (1) or (2) is so poor in elasticity 
that, when packed into the inner and outer tubes of the manifold reactor, 
it cracks because the coefficient of heat expansion of the castable 
ceramic is lower than those of the inner and outer tubes. 
According to methods (3) or (6), when the ceramic fiber blanket in a 
vacuum-resistant plastic bag is vacuum-packed, the packability improves, 
but the special plastic bag which is used burns when heated, generating 
harmful gases. The plastic bag therefore has to be burned away and for 
this reason installation is expensive and vacuum-packing increases the 
production cost. Besides, the blanket used in these methods lacks tensile 
strength and soon breaks, turns to dust or leans to one side, thereby 
lowering the heat insulating effectiveness of the reactor. In methods (4) 
or (6) when the blanket is to be manually packed, a worker with allergies 
cannot be employed. Moreover, since the work is manual, a wide variation 
occurs in the packed state, resulting in low durability of the product. 
The method (5), in which the worker has to work with gloves on, acts just 
like the method (4), yielding products with a wide variation in quality 
and poor durability. 
As described above, various imperfections are noted in the methods of 
heat-insulating manifold reactors, while the molded ceramic fibers to be 
used for lining the manifold reactor leave much to be desired. 
Specifically, the manifold reactor should possess heat resistance, heat 
insulating properties, and vibration resistance, because it is exposed to 
heat as high as 1000.degree. C. in the recombustion chamber when in 
service at the cylinder head exhaust port of the engine. Meanwhile the 
molded ceramic fibers, which are to be packed into the manifold reactor, 
have to excel in packability. 
The moded ceramic fibers of the present invention can be used to form an 
improved catalytic converter which transforms the carbon monoxide and 
hydrocarbons of an engine exhaust into harmless carbon dioxide and water 
through chemical reaction. As illustrated in FIG. 5, i.e., a longitudinal 
perspective view including a partial section, a catalyst converter 
according to the present invention is constructed so that the exhaust gas 
is introduced from the joint 20 to the exhaust pipe through the inner tube 
18 into the catalyst chamber 19. The harmful exhaust gas thus introduced, 
after being converted to harmless carbon dioxide and water by chemical 
reaction with the catalyst, is discharged through the inner passage 18', 
the middle passage 17 and the exhaust pipe joint 21. The molded ceramic 
fibers 16, 16' according to the present invention are packed as heat 
insulation into the space between the inner tube formed by the members 18, 
18' and the casing halves 14, 14'. 
In order to keep the exhaust gas supplied to the catalyst converter hot so 
that the catalytic converter can work effectively, the exhaust pipe has to 
be heat-insulated. This is done as seen in FIG. 6, showing an exploded 
view of the exhaust pipe dismantled, and FIG. 7 showing a longitudinal 
section of the exhaust pipe assembled, by conveying the harmful exhaust 
gas emitted from the engine (not shown) to the exhaust pipe joint 29 and 
discharging it, with its heat retained, through the catalytic converter 
joint 30. The space between the inner tube 24 and the outer tube 26 is 
packed with the heat insulating molded ceramic fibers 25 of to the present 
invention. 
As heat insulating material for such a catalytic converter and exhaust 
pipe, a blanket of Al.sub.2 O.sub.3 --SiO.sub.2 ceramic fibers or 
SiO.sub.2 ceramic fibers is commonly employed. In this case too, just as 
in the methods (4) or (6) of packing the blanket in the manifold reactor, 
the packing is done manually and accordingly a worker afflicted with 
allergies cannot be assigned to the job. This blanket is not strong enough 
and is so shaped that it does not fit the configuration of the catalytic 
converter or the exhaust pipe. Specifically, it is a flat plate which is 
liable to become defective when packed. Moreover, dust generated therefrom 
affects the other components of the vehicle. 
As seen from FIG. 8, which shows another example of the catalytic 
converter, cavities 23a, 23b left in the molded ceramic fibers 16, 16' 
after being packed (caused because the blanket is cut when packed) lead to 
a decline in the effectiveness of the heat insulation. 
Also, as seen from FIGS. 9 and 10 showing another example of the exhaust 
pipe, cavities 28a, 28b left in the heat insulator 25a, 25b after it has 
been packed lead to a decline in the effectiveness of the heat insulation. 
After an intensive search for a molded product which retains high 
elasticity even at high temperatures of 800.degree.-1000.degree. C. and 
excels in heat insulating ability, packability and durability, we have 
successfully developed, and describe herein, molded ceramic fiber 
compositions that are especially for use in manifold reactors. 
The molded ceramic fiber compositions of the present invention are 
characterized by being a molded product of Al.sub.2 O.sub.3 --SiO.sub.2 
ceramic fibers or SiO.sub.2 ceramic fibers having a hardness of 
20.degree.-55.degree., a tensile strength of 120-1500 g/cm.sup.2 and a 
molded density of 0.06-0.35 g/cm.sup.3. 
According to the present invention, the hardness of the molded Al.sub.2 
O.sub.3 --SiO.sub.2 ceramic fibers or SiO.sub.2 ceramic fibers is selected 
to fall within the range of 20.degree.-55.degree., because at less than 
20.degree. the product is brittle and at more than 55.degree. it is liable 
to break and lacks packability. 
The tensile strength is selected to fall within the range of 120-1500 
g/cm.sup.2, because at less than 120 g/cm.sup.2 the product lacks 
durability; at more than 1500 g/cm.sup.2 the product becomes poor in 
packability because it becomes too hard (more than 55.degree.) or turns to 
dust in service, resulting in poor durability. 
The molded density of the molded Al.sub.2 O.sub.3 --SiO.sub.2 ceramic 
fibers is selected to fall within the range of 0.15-0.35 g/cm.sup.3, 
because at less than 0.15 g/cm.sup.3 the product is brittle, and lacking 
in packability and durability, while at more than 0.35 g/cm.sup.3, it is 
unable to absorb the heat expansion and the product therefore turns to 
dust or causes a deformation of the outer tube 5, leading to poor 
durability. For the same reason the molded density of the molded SiO.sub.2 
ceramic fibers is selected to fall within the range of 0.06-0.2 
g/cm.sup.3. 
Several embodiments of the present invention will now be described. 
EXAMPLE 1 
Bulky Al.sub.2 O.sub.3 --SiO.sub.2 ceramic fibers having the composition as 
listed in Table 1, together with starch and water as an organic binder 
were stirred as shown in FIG. 3 with a stirring machine 8. A highly 
permeable mold 10 was introduced into the resulting mixed solution and 
connected to a vacuum pump. Thus said solution was vacuum-molded, dried 
and solidified to form a ceramic fiber molding 7 for a manifold reactor. 
TABLE 1 
______________________________________ 
Properties of Ceramic Fiber 
Items Characteristic values 
Fiber diameter 
A B C 
True specific 
Average 2.5.mu. 
Average 2.8.mu. 
Average 4.5.mu. 
gravity 2.65 g/cm.sup.3 
2.56 g/cm.sup.3 
2.50 g/cm.sup.3 
Melting point 
1,800.degree. C 
1,760.degree. C 
1,750.degree. C 
______________________________________ 
Al.sub.2 O.sub.3 
53% 50.1% 47.9% 
Chemical 
SiO.sub.2 
46% 49.17 51.8% 
Fe.sub.2 O.sub.3 
0.15% 0.2% 0.1% 
components 
TiO.sub.2 
0.15% 0.2% Tr 
CaO 0.15% 0.1% Tr 
MgO 0.15% Tr Tr 
Na.sub.2 O 
0.4% 0.3% 0.2% 
______________________________________ 
A ... Product of Ibigawa Denki Kogyo K.K. 
B ... Product of Isolite-Babcock Refractory K.K. 
C ... Product of Nihon Asbestos K.K. 
Next, the organic binder content, the hardness, the average fiber length, 
the tensile strength, the molded density and the packed density of the 
above mentioned molded products were measured, their durability was tested 
by a hot-cold vibration test and a durability test in service in a 
reactor, and their packability was evaluated. 
(i) MEASUREMENT OF THE ORGANIC BINDER CONTENT 
A sample of about 10g each is taken from 5 spots in the molded product; 
dried for one hour at 100.degree.-110.degree. C.; and then cooled in a 
dessicator. After it has been cooled, the sample is measured (weight B) in 
a previously weighed crucible (weight A); heated to 
500.degree.-1000.degree. C. for complete dissolution of the organic 
binder; cooled to the room temperature in the dessicator; and weighed 
(weight C). The average organic binder content (% by weight) for the five 
samples is calculated by the following formula: 
##EQU1## 
(ii) MEASUREMENT OF HARDNESS 
The flat, smooth part of the molded product is measured at 10 spots by a 
hardness gauge (rubber tester type C manufactured by Kobunshi Keiki with a 
measurable range of 0.degree.-100.degree., measurable unit 1.degree.) in 
accordance with the Japan Rubber Association Standard SRIS-0101; and the 
average value is taken as its hardness. 
(iii) MEASUREMENT OF AVERAGE FIBER LENGTH 
A sample of about 5g each is taken from five spots in the molded product, 
heated to 500.degree.-1000.degree. C. for complete dissolution of the 
organic binder, and then cooled to room temperature. (When an inorganic 
binder is used, heating and cooling to the room temperature may be 
omitted.) The sample is dispersed in ethyl alcohol or in water. The 
ceramic fibers are picked up by a pincette and transferred to apparatus in 
which their length is measured using a slide caliper capable of measuring 
to 0.1 mm and a magnifying glass. The measured values of 100 ceramic 
fibers are average to give the average fiber length. 
(iv) MEASUREMENT OF TENSILE STRENGTH 
The flat part of the molded product is cut into five sample pieces having a 
width of 50 mm, length of 150 mm and thickness of t mm. Variation is 
allowed to a certain extent in sample sizes. These samples, after 2 hours 
of heat treatment at 500.degree. C., are measured for width by slide 
calipers and for thickness to 0.01 mm by a special dial gauge. 
Next, using a universal testing machine having a sensitivity higher than 
0.1 kg, a gauge length of over 50 mm, a tension speed of 30 mm/min and 
maximum tensile load of 0.1 kg, the tensile strength is found from the 
following formula: 
##EQU2## 
As indicated in FIG. 4, a dial gauge 13 (TECLOCK product, no spring) is 
fastened to the support rod 12 erected on the mount 11. With the measuring 
member 13a (50 mm carbon steel, about 40g) of the dial gauge lifted, a 
sample is placed between said measuring member 13a and the mount 11, and 
the gauge dial 13b is read. 
(v) MEASUREMENT OF MOLDED DENSITY 
The weight of the molded product is measured to the nearest 0.01g. The 
thickness of the molded product is measured at more than 10 spots to the 
nearest 0.01 mm. The measured values are averaged. Then the width and 
length of the molded product are measured to the nearest 0.01 mm and the 
molded density is calculated from the following formula: 
##EQU3## 
(vi) CALCULATION OF KED DENSITY 
What is called packed density in the present invention assumes that the 
heat-insulated space of the manifold reactor is packed with molded ceramic 
fibers. 
A sample of 40 mm in diameter is taken from more than five spots in the 
molded product. The sample weight is measured to the nearest 0.01 g and 
using the average value of the measurements, the packed density is 
calculated from the following formula: 
##EQU4## 
(vii) MEASUREMENT BY HOT-COLD VIBRATION TEST 
The molded product packed into the manifold reactor is subjected to 100 
cycles of heating at 950.degree.-1050.degree. C. for 10 minutes in the 
inner tube while simultaneously subjected to 1600 vibrations per minute 
with a vibrational acceleration of 4.0-5.0 (980 cm/sec.sup.2) and a total 
amplitude 3.0-4.0 mm, followed by air cooling for 10 minutes. Before and 
after this hot-cold vibration test the change in weight of the molded 
product is measured and the results are rated as follows: 
Rating standard of hot-cold vibration test results: 
.circle. . . . good (change less than 10.0% by weight) 
.increment. . . . fair (change 10.0-20.0% by weight) 
X . . . poor (change more than 20.0% by weight) 
(viii) MEASUREMENT BY DURABILITY TEST IN SERVICE 
The molded product is housed in a manifold reactor and the manifold reactor 
mounted in an engine is subjected to a durability test under the following 
operating conditions: 
Operating conditions: 
Engine exhaust volume . . . 1600 cc 
Combustion chamber exhaust gas temperature . . . 900.degree.-1000.degree. 
C. 
Engine drive conditions: 
After (1) 6000 rpm .times. 100 hours and (2) (6000 rpm + 1000 rpm) .times. 
100,000 cycles, the state of the molded product within the manifold 
reactor (dusting or dispersion of molded product) is checked and the state 
rated as follows: 
Rating standard of durability test: 
.circle. . . . no dust, no dispersion 
.increment. . . . a little dust and dispersion (to an extent which causes 
practically no trouble) 
X . . . greater part dusted and dispersed 
(ix) MEASUREMENT OF KABILITY 
The time required for the molded product to be packed into the manifold 
reactor is measured and the results are rated as follows: 
Rating standard for packability 
.circle. . . . packing time required for one reactor less than 20 sec. 
.increment. . . . packing time required for one reactor 20-60 sec. 
X . . . packing time required for one reactor more than 60 sec. 
(x) OVERALL EVALUATION 
When either packability or durability is insufficient, in the overall 
evaluation the product is rated poor (X). 
The test results are summarized in Table 2. 
Table 2 
__________________________________________________________________________ 
Test results of molded products of Al.sub.2 O.sub.3 -SiO.sub.2 ceramic 
fibers 
using organic binder (starch) 
Example 1 ... by vacuum-molding 
Test Binder Average 
items 
content fiber 
Tensile Durability test 
Product 
(weight 
Hardness 
length 
strength 
Density (g/cm .sup.3) 
Hot-cold Pack- 
Overall 
No. % (.degree.) 
(mm) (g/cm.sup.2) 
Molded 
Packed 
vibration 
Service 
ability 
rating 
__________________________________________________________________________ 
1 0.5 7 3.5 80 0.06 0.08 
X .times. 
.times. 
.times. 
2 0.7 12 27.0 230 0.16 0.18 
.circle. 
.circle. 
.times. 
.times. 
3 1.0 27 4.0 125 0.10 0.12 
.times. 
.times. 
.circle. 
.times. 
4 2.0 38 2.3 95 0.18 0.22 
.times. 
.times. 
.circle. 
.times. 
5 2.0 37 6.0 210 0.12 0.14 
.DELTA. 
.DELTA. 
.circle. 
.DELTA. 
6 2.0 38 15.5 535 0.23 0.25 
.circle. 
.circle. 
.circle. 
.circle. 
7 4.0 47 30.0 980 0.31 0.32 
.circle. 
.circle. 
.circle. 
.circle. 
8 5.0 50 21.3 740 0.26 0.28 
.circle. 
.circle. 
.circle. 
.circle. 
9 6.0 52 12.5 478 0.21 0.22 
.circle. 
.circle. 
.circle. 
.circle. 
10 6.0 51 5.7 135 0.15 0.17 
.circle. 
.circle. 
.circle. 
.circle. 
11 7.0 68 10.5 425 0.18 0.20 
.circle. 
.circle. 
.times. 
.times. 
12 8.0 73 7.6 270 0.15 0.18 
.DELTA. 
.DELTA. 
.times. 
.times. 
13 9.0 82 3.2 95 0.20 0.21 
.times. 
.DELTA. 
.times. 
.times. 
14 10.0 89 2.5 88 0.11 0.12 
.times. 
.times. 
.times. 
.times. 
15 7.0 760 11.5 350 0.12 0.21 
.circle. 
.circle. 
.times. 
.times. 
16 0.5 7 13.0 180 0.14 0.26 
.circle. 
.circle. 
.times. 
.times. 
17 4.0 46 33.0 1470 0.34 0.35 
.circle. 
.circle. 
.circle. 
.circle. 
18 7.0 70 31.5 1250 0.33 0.34 
.circle. 
.circle. 
.times. 
.times. 
19 7.0 72 38.5 1650 0.39 0.40 
.DELTA. 
.DELTA. 
.times. 
.times. 
20 9.0 96 40.5 1710 0.42 0.43 
.DELTA. 
.DELTA. 
.times. 
.times. 
__________________________________________________________________________ 
As seen from Table 2, the products Nos. 1, 2 and 16 with a hardness of less 
than 12.degree. or more than 68.degree. L were definitely poor in 
packability, while Nos. 1-5 and 11-16 with a tensile strength less than 
120 g/cm.sup.2 and a molded density less than 0.15 g/cm.sup.3 had their 
heat-insulating effect decreased during the durability test because the 
fibers became embrittled, turned to dust, or became dispersed or became 
concentrated at one side in the heat-insulating space. 
In Nos. 12 and 13 with an increased hardness, packability dropped though 
durability improved; and in Nos. 15 and 16 with a decreased molded 
density, packability improved but durability dropped. 
In Nos. 19 and 20 with a tensile strength of more than 1,500 g/cm.sup.2, 
packability became extremely poor. For these reasons, the molded product 
according to the present invention has to meet the conditions that the 
hardness is 20.degree.-55.degree., tensile strength is 120-1500 g/cm.sup.2 
and molded density is 0.15-0.35 g/cm.sup.3 to assure both high packability 
and high durability. 
EXAMPLE 2 
Molded ceramic fibers for a manifold reactor were produced using Al.sub.2 
O.sub.3 --SiO.sub.2 ceramic fibers as in Example 1 and a phenol resin as 
the organic binder by the following molding processes. 
Molding processes: 
Special molded blanket process . . . A mat impregnated with phenol resin as 
the organic binder is taken from the ceramic fiber blanket manufacturing 
process, and dried to solidify in a mold. 
Molded blanket process . . . A ceramic fiber blanket impregnated with 
phenol resin as the organic binder is dried to solidify in a mold. 
Special vacuum-molding process . . . A ceramic fiber blanket is impregnated 
with phenol resin as the organic binder, and molded and dried in a highly 
permeable vacuum-mold. 
Thereafter, in the same way as in Example 1, the resulting products were 
subjected to various tests for physical properties and durability. In 
Example 1, the hot-cold vibration test and the service test yielded nearly 
identical results with no problem in their evaluation, but in Example 2 
some of the tests were limited to hot-cold vibration. The results are 
summarized in Table 3. 
Table 3 
__________________________________________________________________________ 
Test results of molded products of Al.sub.2 O.sub.3 -SiO.sub.2 ceramic 
fibers using organic binder (phenol resin) 
Example 2 . . . by various molding processes 
Test Binder Average 
items content 
Hard- 
fiber 
Tensile Durability test 
Product (weight) 
ness 
length 
strength 
Density (gm/cm.sup.3) 
Hot-cold Pack- 
Overall 
No. Processes % (.degree.) 
(mm) (g/cm.sup.2) 
Molded 
Packed 
vibration 
Service 
ability 
rating 
__________________________________________________________________________ 
101 Special vacuum-mold 
0.5 13 2.4 75 0.08 0.10 
.times. 
.times. 
.times. 
.times. 
102 " 2.0 29 8.5 130 0.12 0.13 
.DELTA. 
-- .circle. 
.DELTA. 
103 " 2.0 30 20.4 235 0.15 0.17 
.circle. 
-- .circle. 
.circle. 
104 Molded blanket 
3.0 35 3.0 84 0.10 0.11 
.times. 
-- .circle. 
.times. 
105 " 3.0 37 12.5 126 0.08 0.10 
.times. 
.times. 
.circle. 
.times. 
106 Special molded blanket 
0.5 13 3.5 86 0.08 0.07 
.times. 
-- .times. 
.times. 
107 " 0.5 14 4.6 120 0.24 0.25 
.DELTA. 
-- .times. 
.times. 
108 Special vacuum-mold 
2.0 30 14.7 385 0.30 0.31 
.circle. 
-- .circle. 
.circle. 
109 " 2.0 23 27.0 450 0.21 0.22 
.circle. 
.circle. 
.circle. 
.circle. 
110 Molded blanket 
3.0 35 15.5 335 0.18 0.20 
.circle. 
.circle. 
.circle. 
.circle. 
111 " 3.0 38 8.7 274 0.31 0.32 
.circle. 
.circle. 
.circle. 
.circle. 
112 Special molded blanket 
4.0 44 7.5 240 0.30 0.32 
.circle. 
-- .circle. 
.circle. 
113 " 4.0 42 6.7 255 0.20 0.22 
.circle. 
.circle. 
.circle. 
.circle. 
114 " 4.0 45 26.3 280 0.18 0.19 
.circle. 
-- .circle. 
.circle. 
115 Special vacuum-mold 
7.0 74 8.2 167 0.18 0.20 
.circle. 
.circle. 
.times. 
.times. 
116 " 7.0 76 4.0 96 0.10 0.12 
.circle. 
-- .times. 
.times. 
117 Molded blanket 
7.0 72 10.7 115 0.16 0.17 
.times. 
.circle. 
.times. 
.times. 
118 " 7.0 74 4.5 85 0.13 0.13 
.times. 
-- .times. 
.times. 
119 Special molded blanket 
8.0 83 19.5 218 0.17 0.19 
.DELTA. 
.DELTA. 
.times. 
.times. 
120 " 8.0 80 3.7 70 0.10 0.11 
.times. 
-- .times. 
.times. 
121 " 4.0 45 32.8 1450 0.34 0.356 
.circle. 
.circle. 
.circle. 
.circle. 
122 " 8.0 83 30.5 1100 0.32 0.33 
.circle. 
-- .times. 
.times. 
123 Molded blanket 
8.0 82 37.5 1590 0.38 0.39 
.DELTA. 
-- .times. 
.times. 
__________________________________________________________________________ 
As is evident from Table 3, there is no difference in packability and 
durability depending on the molding process and the overall rating depends 
on the characteristic values of the molded product. For instance in Nos. 
101, 106, 107 and 115-120, 122 with hardness values other than 
20.degree.-55.degree., packability is poor; in the products with a tensile 
strength of less than 120 g/cm.sup.2 or a molded density of less than 0.15 
g/cm.sup.3, durability is poor; and in No. 123 with a tensile strength of 
more than 1500 g/cm.sup.2, packability is poor. 
From these examples it is confirmed that, regardless of its molding 
process, a molded product with a hardness of 20.degree.-55.degree., a 
tensile strength of 120-1500 g/cm.sup.2 and a molded density of 0.15-0.35 
g/cm.sup.3 excels in packability and durability. 
Similar results were obtained when the organic binder was starch or 
polyvinyl alcohol. 
EXAMPLE 3 
Using a mixed solution of Al.sub.2 O.sub.3 --SiO.sub.2 ceramic fibers 
according to Example 1 and either Al.sub.2 O.sub.3 sol as an inorganic 
binder or starch as an organic binder, molded ceramic fibers for a 
manifold reactor were produced according to the vacuum-molding process of 
Example 1. 
The molded products thus obtained were subjected to various tests for 
physical properties and durability in the same way as in Example 1. Just 
as in Example 2, in some cases with the reactor test omitted, evaluation 
was made of the results of hot-cold vibration tests alone, the results 
being summarized in Table 4. 
Table 4 
__________________________________________________________________________ 
Test results of molded products of Al.sub.2 O.sub.3 -SiO.sub.2 ceramic 
fibers 
using inorganic binder (Al.sub.2 O.sub.3 sol) and organic binder 
(starch) 
Example 3 . . . by vacuum-molding process 
Test Binder content 
Average 
items 
(weight %) 
Hard- 
fiber 
Tensile 
Density (g/cm.sup.3) 
Durability test 
Product 
Al.sub.2 O.sub.3 
ness 
length 
strength Hot-cold Pack- 
Overall 
No. sol starch 
(.degree.) 
(mm) (g/cm.sup.2) 
Molded 
Packed 
vibration 
service 
ability 
rating 
__________________________________________________________________________ 
201 0.5 -- 11 2.3 62 0.07 0.09 
.times. 
-- .times. 
.times. 
202 0.5 0.3 14 3.1 67 0.08 0.13 
.times. 
.times. 
.times. 
.times. 
203 0.5 0.5 16 4.8 108 0.15 0.15 
.times. 
-- .times. 
.times. 
204 1.0 0.5 22 5.0 116 0.15 0.16 
.DELTA. 
.DELTA. 
.DELTA. 
.DELTA. 
205 1.0 1.0 30 5.6 162 0.17 0.20 
.circle. 
.circle. 
.circle. 
.circle. 
206 2.0 1.0 38 12.3 340 0.11 0.12 
.times. 
-- .circle. 
.times. 
207 2.0 1.0 39 15.6 557 0.21 0.23 
.circle. 
.circle. 
.circle. 
.circle. 
208 3.0 -- 43 13.3 725 0.22 0.26 
.circle. 
.circle. 
.circle. 
.circle. 
209 4.0 1.0 49 10.1 830 0.20 0.22 
.circle. 
-- .circle. 
.circle. 
210 5.0 0.5 52 19.3 912 0.17 0.19 
.circle. 
.circle. 
.circle. 
.circle. 
211 6.0 0.5 53 3.4 941 0.11 0.14 
.times. 
.DELTA. 
.circle. 
.times. 
212 6.0 -- 50 2.3 936 0.15 0.16 
.times. 
-- .circle. 
.times. 
213 6.0 1.0 58 9.8 1150 0.17 0.18 
.circle. 
.circle. 
.DELTA. 
.DELTA. 
214 8.0 1.0 76 7.1 1325 0.20 0.21 
.DELTA. 
.DELTA. 
.times. 
.times. 
215 10.0 
-- 82 8.5 1470 0.11 0.11 
.DELTA. 
-- .times. 
.times. 
216 10.0 
0.5 89 3.3 1416 0.10 0.13 
.times. 
-- .times. 
.times. 
217 3.0 1.0 45 32.0 1480 0.33 0.34 
.circle. 
-- .circle. 
.circle. 
218 4.0 -- 44 3.5 1370 0.32 0.33 
.DELTA. 
.DELTA. 
.circle. 
.DELTA. 
219 8.0 1.0 78 20.5 1720 0.36 0.37 
.times. 
.times. 
.times. 
.times. 
220 10.0 
-- 85 12.5 1870 0.38 0.38 
.times. 
-- .times. 
.times. 
__________________________________________________________________________ 
As seen from Table 4, molded products using either an inorganic binder or 
an organic binder and meeting the conditions of the present invention for 
hardness, tensile strength and molded density, excel in both durability 
and packability. For instance in Nos. 206 and 211, which meet the hardness 
and tensile strength requirements of the present invention, but are as low 
as 0.11 g/cm.sup.3 in molded density, durability is inferior. In Nos. 203 
and 204 which meet the hardness and molded density requirements of the 
present invention but are as low as 108 g/cm.sup.2 in tensile strength, 
both durability and packability are poor. And in Nos. 219 and 220, with 
tensile strength higher than 1500 g/cm.sup.2, both durability and 
packability are also poor. 
EXAMPLE 4 
SiO.sub.2 ceramic fibers of the composition shown in Table 5 and starch as 
an organic binder were placed in water, and molded ceramic fibers for 
manifold reactor were then produced according to the vacuum-molding 
process of Example 1. 
TABLE 5 
______________________________________ 
Properties of SiO.sub.2 fibers 
Characteristic 
Items Values 
______________________________________ 
Fiber diameter 0.5 - 2.0.mu. 
True specific gravity 
2.6 g/cm.sup.3 
Melting point 1685.degree. C 
Chemical SiO.sub.2 98.1% 
Composition NaO, etc. 1.9% 
______________________________________ 
Note: SiO.sub.2 ceramic fibers manufactured by Nihon Glass Fiber Co. were 
used. 
The molded products thus obtained were, as in Example 1, subjected to 
various tests for physical properties and durability, the results being 
summarized in Table 6. 
Table 6 
__________________________________________________________________________ 
Test results of molded products of SiO.sub.2 ceramic fibers 
using organic binder (starch) 
Example 4 . . . by vaccum-molding process 
Test Binder Average 
items 
content fiber 
Tensile Durability test 
Product 
(weight 
Hardness 
length 
strength 
Density (g/cm.sup.3) 
Hot-cold Pack- 
Overall 
No. %) (.degree.) 
(mm) (g/cm.sup.2) 
molded 
packed 
vibration 
service 
ability 
rating 
__________________________________________________________________________ 
301 0.5 8 2.0 65 0.04 0.05 
.times. 
-- .times. 
.times. 
302 1.0 25 5.5 180 0.05 0.08 
.DELTA. 
-- .circle. 
.DELTA. 
303 2.0 36 8.8 455 0.08 0.08 
.circle. 
.circle. 
.circle. 
.circle. 
304 3.0 43 13.0 690 0.09 0.10 
.circle. 
-- .circle. 
.circle. 
305 4.0 48 26.0 1405 0.18 0.20 
.circle. 
-- .circle. 
.circle. 
306 5.0 52 24.5 1380 0.16 0.17 
.circle. 
.circle. 
.circle. 
.circle. 
307 5.0 50 4.0 135 0.05 0.06 
.DELTA. 
-- .circle. 
.DELTA. 
308 6.0 54 4.7 128 0.05 0.05 
.times. 
-- .times. 
.times. 
309 8.0 75 11.5 830 0.11 0.12 
.circle. 
-- .times. 
.times. 
310 10.0 90 7.0 140 0.04 0.04 
.times. 
-- .times. 
.times. 
311 8.0 77 30.5 1570 0.20 0.21 
.DELTA. 
-- .times. 
.times. 
312 10.0 92 33.0 1310 0.21 0.22 
.DELTA. 
-- 3 .times. 
__________________________________________________________________________ 
As seen from Table 6, even when satisfactory in hardness at 
20.degree.-55.degree. and in tensile strength at 120-1500 g/cm.sup.2, a 
molded product such as No. 302 with a molded density less than 0.06 
g/cm.sup.3 is poor in durability and packability, while products such as 
Nos. 309, 310, which are satisfactory as to molded density at 0.06-0.20 
g/cm.sup.3 molded density and in tensile strength at 120-1500 g/cm.sup.2, 
are inferior in packability. In Nos. 311, 312 with a tensile strength 
higher than 1500 g/cm.sup.2, packability drops. 
A molded product of over 0.20 g/cm.sup.3 in molded density could not absorb 
deformation of the material due to thermal expansion in the durability 
test and failed. In the present example, starch was employed as the 
organic binder, but polyvinyl alcohol, C.M.C. etc. may also be used. 
From the results of the present example it is confirmed that the molded 
SiO.sub.2 ceramic fibers should meet the conditions that they have a 
hardness of 20.degree.-55.degree., tensile strength of 120-1500 
g/cm.sup.2, and molded density of 0.06-0.20 g/cm.sup.3. 
REFERENCE EXAMPLE 1 
Molded ceramic fiber products with excellent packability and durability, 
Nos. 8, 9, 113, 208, 306 as obtained in Examples 1, 2, 3 and 4, after 
having been subjected to a durability test in service in a catalytic 
converter and exhaust pipe (the test conditions being the same as in 
viii), were taken out for observation of dusting and dispersion. The 
results show that, with no cavity in the packing, no dusting and no 
dispersion the products excel in packability and durability in the same 
way as when in service in a manifold reactor. And unlike the case of 
blanket packing, no complaint was made by the worker and no adverse effect 
on the working environment was observed. 
REFERENCE EXAMPLE 2 
When in Example 4, molded products of ceramic fibers with a hardness of 
40.degree., an average fiber length of 12.5 mm, a tensile strength of 550 
g/cm.sup.2, molded density of 0. 21 g/cm.sup.3 and a packed density of 
0.23 g/cm.sup.2, using an organic binder (starch 1.0%) and an inorganic 
binder (silica sol 2.0%) were submitted to a durability test in service in 
a catalytic converter and exhaust pipe (the test conditions being the same 
as in viii), both packability and durability turned out to be excellent. 
And unlike the blanket packing process no worker's complaint was heard and 
no adverse effect on the working environment was noted. 
As described above, the molded ceramic fibers for a manifold reactor 
according to the present invention are characterized by high elasticity at 
high temperatures, excellent heat insulating ability, excellent 
packability and durability, no dusting, no dispersion, no concentration at 
one side in the heat insulated space during use, and accordingly they 
preserve a high temperature in the manifold, reburn carbon monoxide and 
hydrocarbons, make the catalytic converter action more efficient, and 
render the emission gases harmless. Thus the present invention is highly 
valuable from the standpoint of industry and pollution control.