One end-sealed ceramic double wall-structural tubes

One end-closed ceramic double wall-structural tubes are disclosed, which each include inner and outer tube members, and plural supporting portions integrating the outer and inner tube members. One end of the outer tube member only is sealed. A process for producing such tubes is also disclosed, which include the steps of extruding a green ceramic double wall-structural tube comprising inner and outer tube members, and a plurality of supporting portions integrating the outer and inner tube members; drying the green ceramic tube; grinding off the inner tube member and the supporting portions in a given depth from an end face of the dried tube, inserting a porous member made of an organic material into the ground-off portion of the tube inside the outer tube member; pouring and depositing a slurry into the tube on an axially outer side of the porous member; and drying and firing the thus one end-sealed ceramic tube. The porous member is shaped to meet an inner periphery of an end portion of the tube to be sealed, and the coefficient of thermal expansion of the slurry is the same as that of the ceramic tube during firing.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to one end-sealed ceramic double 
wall-structural tubes in which inner and outer tube members are integrally 
connected with each other by means of a plurality of supporting portions, 
and to a process for producing the same. 
(2) Related Art Statement 
When double wall-structural tubes in which an outer tube member and an 
inner tube member are integrally connected with each other through 
supporting portions are to be extruded, it has been impossible to obtain, 
by a single extrusion step, a double wall-structural tube in which an end 
of the tube, particularly an end of the outer tube member only is sealed. 
For this reason, when an end face of an integrally extruded ceramic double 
wall-structural tube, particularly an end portion of its outer tube member 
only needs to be sealed, it is a conventional practice that a dried member 
having a peripheral edge of the same shape as that of an end portion of 
the tube to be sealed and the same composition as that of the tube is 
separately formed, and is fixed to the end face of the dried tube, which 
is fired to effect integration at the end portion of the tube. 
However, the above-mentioned conventional end face-sealing process requires 
use of a member having the same composition as that of a double 
wall-structural tube and exhibiting, when dried, a given shape to seal an 
end of the tube. As a result, a gap is formed between the end of the tube 
and the sealing member in the tubular product integrated by firing. Thus, 
this unfavorably hinders complete integration. Consequently, ceramic 
double wall-structural tubes having such ends are likely to be broken, and 
are low in reliability. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to solve the above-mentioned 
problems, and to provide one end-sealed ceramic double wall-structural 
tubes and production thereof, in which complete integration can be made 
between an end-sealing member and a wall of the tube when the tube is 
sealed with the sealing member to offer a highly reliable end structure of 
the ceramic tube. 
It is another object of the present invention to provide a process for 
producing such ceramic double wall-structural tubes. 
According to a first aspect of the present invention, there is a provision 
of the one end-sealed ceramic double wall-structural tubes which each 
comprise inner and outer tube members integrated by means of a plurality 
of supporting portions and which each have only one end of the outer tube 
member of the integral double wall-structural tube sealed. 
According to a second aspect of the present invention, there is a provision 
of the process for producing one end-sealed ceramic double wall-structural 
tubes, which comprises the steps of: extruding a green double 
wall-structural tube having inner and outer tube members and integrated by 
means of a plurality of supporting portions, drying the green tube, 
grinding off the inner tube and a plurality of the supporting portions in 
a given depth measured from an end of the tube, inserting a porous member 
made of an organic material into the thus ground-off portion of the tube 
inside the outer tube member, the porous member being shaped to meet an 
inner shape of an end portion to be sealed, and pouring and depositing a 
slurry into the tube on an axially outer side of the porous member, the 
slurry exhibiting the same coefficient of thermal expansion as that of the 
tube during firing, followed by drying and firing. 
In the above construction, the double wall-structural tubes are extruded 
such that the inner and outer tube members are connected and integrated 
together by means of a plurality of supporting portions, the inner tube 
and the supporting portions are ground off by a specified depth, and then 
a bottom portion of the tube is formed by inserting the porous member made 
of an organic material into the thus ground-off potion of the tube. Thus, 
the inserted organic material porous member is burnt off during the firing 
of the tube. Further, the inner end shape of the sealed portion can freely 
be selected by varying the shape of the porous member. In addition, since 
the slurry exhibiting the same coefficient of thermal expansion as that of 
the ceramic tube during firing is directly poured and deposited into the 
dried ceramic tube, the tissue at the joint end face becomes homogeneous. 
Accordingly, the same quality as that of products integrally shaped can be 
obtained. Moreover, the density of the deposited portion can be controlled 
by adjusting the slurry with an organic additive such as a binder or a 
dispersant. In addition, the inner and outer tube members are preferably 
made concentric with each other. 
Besides, a material constituting the slurry is preferably the same as that 
of the ceramic tube, because there exists no difference in thermal 
expansion between them. 
These and other objects, features, and advantages of the invention will be 
appreciated upon reading 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 without 
departing from the spirit of the invention or the scope of claims appended 
hereto.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to a longitudinal sectional view of an embodiment of a one 
end-sealed ceramic double wall-structural tube according to the present 
invention shown in FIG. 1(a), the double wall-structural tube 1 comprises 
an outer tube 2 and an inner tube 3. As is seen in an A--A line cross 
sectional view of FIG. 1(b), the outer tube 2 and the inner tube 3 are 
connected and integrated with each other by a plurality of supporting 
portions 4-1 through 4-3. At one tip end 5 of the double wall-structural 
tube 1, the outer tube 2 only is sealed in the form of a test tube, 
whereas a tip end of the inner tube 3 is open within the tip end 5. 
FIGS. 2(a) through (f) are views showing the sequence of steps for 
producing a double wall-structural tube according to the second aspect of 
the present invention. As is shown in FIG. 2(a), a double wall-structural 
tube 11 in a green state comprises an outer tube member 12, an inner tube 
member 13, and a plurality of supporting portions 14-1 and 14-2 is shaped 
by extrusion and dried. Next, as shown in FIG. 2(b), the inner tube 13 and 
the supporting portions 14-1 and 14-2 are ground off in a given depth by 
using a diamond grinding stone 15 having substantially the same diameter 
as the inner diameter of the outer tube member 12. Then, as shown in FIG. 
2(c), a porous member 16 made of an organic material is inserted inside 
the outer tube member 12 of the dried ceramic double wall-structural tube. 
When the porous member 16 is inserted, it needs to be shaped such that a 
contact face 17 at which the porous member contacts with the slurry may 
conform with an inner end of a sealed portion. As the organic material 
porous member 16, use may be made of a water-absorbable filter paper or 
the like. Then, as shown in FIG. 2(d), a slurry 18 is poured inside the 
outer tube member 12 of the ceramic double wall-structural tube 11. This 
slurry exhibits the same coefficient of thermal expansion as that of the 
ceramic double wall-structural tube 11, or preferably is made of the same 
material as that of the ceramic tube 11. Water contained in the slurry is 
absorbed into the outer tube member 12 and the porous member 16 of the 
organic material to deposit the slurry. Then, as shown in FIG. 2(e), the 
thus obtained one end closed tube is dried, which is fired to burn off the 
porous member 16 of the organic material. Thereby, a one end-sealed 
ceramic double wall-structural tube as shown in FIG. 2(f) having a 
predetermined sealed shape is obtained. When in practical use, an outer 
end portion is removed along a broken line as shown in FIG. 2(f). 
FIG. 3 shows application of a ceramic double wall-structural tube according 
to the present invention as a reaction tube. In FIG. 3, in order to obtain 
a C-liquid on reaction between an A-liquid and a B-liquid, the A-liquid is 
fed inside an inner tube member 21, and the B-liquid is fed outside an 
outer tube member 22. The outer tube member is made of a porous ceramic 
material. When the A-liquid flows back from the tip edge of the inner tube 
member 21 between the outer surface of the inner tube member 21 and the 
inner surface of the outer tube member 22, the A-liquid reacts with the 
B-liquid penetrating inside the tube through the outer tube member 22. 
Then, the C-liquid is taken out from an end of a space between the outer 
surface of the inner tube member 21 and the inner surface of the outer 
tube member 22. 
Besides the above-mentioned application, the ceramic double wall-structural 
tubes according to the present invention can favorably be applied as a 
variety of filters, heat exchangers, concentrators, etc. 
The present invention is not limited to the above-mentioned embodiments, 
but various modifications, variations, and changes can be made. For 
instance, in the above-mentioned embodiments, two or three supporting 
portions are provided between the inner tube member and the outer tube 
member. The number of the supporting portions is not limited to two or 
three, but any number of supporting portions may clearly be used so long 
as sufficient supporting strength can be obtained. 
As is evident from the aforegoing detailed explanation, according to the 
one end-sealed ceramic double wall-structural tubes and the producing 
process therefor in the present invention, the double wall-structural tube 
comprising the outer tube member, the inner tube member and the supporting 
portions is extruded, the inner tube member and the supporting portions 
are ground off in a specific depth from an end face of the tube, a porous 
member of organic material is inserted inside the outer tube member, and a 
given slurry is poured and deposited inside the tube on the axially outer 
side of the porous member, followed by drying and firing. No joining trace 
is seen and the same quality as that of products integrally shaped can be 
obtained.