Closed end sleeve producing method and core structure used in the method

A method for producing a sleeve having a closed end by extruding a forming material from a mouthpiece. A core member is arranged in position in the mouthpiece and has a piston member detachably provided in a tip end of the core member. The piston member has an air communication aperture. On the other hand, an outer die is arranged in the mouthpiece for forming an outer configuration of the closed end. As a result, an annular space is formed by the mouthpiece, core member and outer die. The forming material is then supplied into the annular space and extruded to form the closed end of the sleeve. After the outer die has been removed from the mouthpiece, the piston member is caused to slide relative to the mouthpiece and at the same time the air is blown into an inside of the closed end through the air communication aperture of the piston, while the forming material is further supplied and extruded from the mouthpiece to form the closed end sleeve.

BACKGROUND OF THE INVENTION 
This invention relates to a method of producing a closed end sleeve or a 
sleeve having a closed end, and more particularly to a core structure to 
be used in the method. 
In order to produce closed end sleeves, a pressforming method has been 
used. However, a long closed end sleeve cannot be produced by the method. 
It is possible to produce such a long sleeve by attaching an end portion 
and a sleeve portion of the sleeve separately formed. In this case, 
however, such an attached sleeve is poor in strength at the attached 
portion of the sleeve. In order to eliminate this disadvantage of the 
method, the assignee of this application has proposed in Japanese Patent 
Application Laid-open No. 62-85,906, a method of producing a closed end 
sleeve having a closed end by extruding. 
FIGS. 1a-1d illustrate the producing processes of the proposed method. As 
shown in FIG. 1a, a core member 23 having a paraffin tip 22 for forming an 
inner surface of an end or bottom of the sleeve to be produced is arranged 
in a mouthpiece 21, and an outer die 25 formed at its center with a 
through-aperture 24 for forming an outer surface of the end or bottom of 
the sleeve is arranged in a front end of the mouthpiece 21 to form an 
annular space by the mouthpiece 21, the core member 23 and the outer die 
25. Thereafter, as shown in FIG. 1b, a forming material, for example, a 
ceramic material for forming the sleeve is supplied into the annular space 
and slightly extruded. When a minor amount of the ceramic material is 
extended from the through-aperture 24, the extruding operation is stopped. 
During this extrusion, the paraffin tip 22 is held in contact with the 
core member 23 via suction within the core member. 
After the outer die 25 has been removed from the mouthpiece 21 as shown in 
FIG. 1c, the air is supplied into the core member 23 so as to extrude the 
ceramic material to obtain a cylinder or sleeve having a desired length as 
shown in FIG. 1d. The remaining paraffin tip at the end or bottom of the 
cylinder is removed when the cylinder is burned. 
In the method of the Japanese Patent Application Laid-open No. 62-85,906, 
the paraffin tip 22 is used in order to remove the tip used for forming 
the end of the sleeve when burning the sleeve. However, the paraffin tip 
22 is often collapsed by the forming pressure during the extruding process 
during the formation of the end of the sleeve or before the removal of the 
outer die 25. As a result, the inner configuration of the end or bottom of 
the sleeve is deviated from the required configuration. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a method of producing a sleeve 
having a closed end and a core structure preferably used in the method, 
which eliminate all the disadvantages in the prior art and obtain the 
sleeve whose inner configuration at the end does not detrimentally deform. 
In order to achieve this object, the method of producing a sleeve having a 
closed end by extruding a forming material from a mouthpiece according to 
the invention, comprises the steps of arranging a core member in position 
in the mouthpiece, said core member having a piston member detachably 
provided in a tip end of the core member, said piston member being formed 
with air communication apertures passing therethrough for forming an inner 
configuration of said closed end, while arranging an outer die in said 
mouthpiece for forming an outer configuration of said closed end to form 
an annular space by the mouthpiece, the core member and the outer die; 
supplying said forming material into the annular space and extruding the 
material therefrom to form the closed end; removing said outer die from 
the mouthpiece; and causing said piston member to slide relative to said 
mouthpiece and at the same time blowing the air into an inside of said 
closed end through said air communication aperture of the piston member, 
while further supplying the forming material to extrude the material from 
said mouthpiece. 
In a preferred embodiment, the method comprises steps of arranging a core 
member in position in said mouthpiece, said core member having at its tip 
end a tip die made of a porous body for forming an inner configuration of 
said closed end, while arranging an outer die made of a porous body at an 
outer end 1a of said mouthpiece for forming an outer configuration of said 
closed end to form an annular space by the mouthpiece, the core member and 
the outer die; supplying said forming material into the annular space and 
extruding the material therefrom, while applying suction to said outer die 
made of the porous body from its outside to form the closed end; removing 
said outer die from the mouthpiece by blowing the air against the outer 
die from its outside; and supplying the air through the tip die made of 
the porous body into a volume between the formed closed end and the tip 
die, while further supplying the forming material to extrude the material 
from said mouthpiece. 
In a particular embodiment of the invention, the method comprises steps of 
inserting a core member in the forming material being extruded in the 
mouthpiece, and continuing the extruding of the forming material, while 
blowing the air into the forming material through a through-aperture of 
the core member. 
A core structure to be used for producing a sleeve having a closed end 
according to the invention comprises a holder member, a cylinder member 
having a tapered portion at its front end and connected to the holder 
member, and a piston member having at its front end a hemispherical 
portion for forming an inner configuration of the closed end and a tapered 
portion to fit with said tapered portion of the cylinder member and having 
an air communication aperture, said piston member having at its rear end a 
stopper for stopping the piston member after its sliding movement through 
a predetermined distance. 
With the arrangement above described, the member for forming the inner 
configuration of the closed end of the sleeve is constructed by, for 
example, the piston member made of a metal or the porous body made of a 
ceramic material and the forming material is extruded by these members. 
Therefore, closed end sleeves can be reliably produced in predetermined 
shapes without deforming the inner configurations of the closed ends of 
the sleeves. 
Moreover, in the case where the outer die made of the permeable porous body 
is used, the outer die can be easily separated from the mouthpiece by 
blowing the air into the outer die from its outside in separating the 
outer die from the mouthpiece. Furthermore, the air can be sucked through 
the outer die in extruding the forming material, so that the aperture at 
the center of the outer die is not needed. As a result, a protrusion does 
not occur at the center on the outer surface of the closed end of the 
sleeve so that a process for amending the outer surface is not needed 
after the forming process. 
The invention will be more fully understood by referring to the following 
detailed specification and claims taken in connection with the appended 
drawings.

DETAILED EXPLANATION OF PREFERRED EMBODIMENTS 
FIGS. 2a-2e are sectional views illustrating one embodiment of the method 
of producing a sleeve having a closed end according to the invention. 
First, as shown in FIG. 2a, a core member 2 is arranged in position in a 
mouthpiece 1, while an outer die 3 is arranged at an outer end 1a of the 
mouthpiece 1 for forming an outer configuration of the end or bottom of 
the sleeve. A piston member 5 formed with an air communication aperture 4 
extending therethrough is detachably inserted into a tip end of the core 
member 2 for forming an inner configuration of the closed end of the 
sleeve. As a result, an annular space is formed by the mouthpiece 1, the 
core member 2, the piston member 5, and the outer die 3. 
Then, as shown in FIG. 2b, a forming material 7 of, for example, a ceramic 
material is supplied into the annular space 6 and slightly extruded 
through a through-aperture 8 formed at a center of the outer die 3 to an 
extent that a slight amount of the ceramic material 7 is extended out of 
the through-aperture 8 to form the end or bottom of the sleeve. During 
such an operation, the air is sucked from a through-aperture 9 of the core 
member 2 to prevent the piston member 5 from moving from the core member 
2. 
After the outer die 3 has been removed from the mouthpiece 1 as shown in 
FIG. 2c, the air is blown through the center through-aperture 9 of the 
core member 2, while the ceramic material 7 is further extruded so that 
the piston member 5 is slid until a stopper 5a of the piston member 5 
abuts against the inside of the tip end of the core member 2 as shown in 
FIG. 2d. 
Finally, as shown in FIG. 2e, the ceramic material 7 is further extruded so 
as to form a ceramic cylinder having a desired length to obtain a required 
closed end sleeve. 
FIGS. 3a-3d illustrate another embodiment of the method according to the 
invention, wherein like components are designated by the same reference 
numerals a those used in the first embodiment and will not be described in 
further detail. 
In this embodiment, first a core member 2 is arranged in position in a 
mouthpiece 1, and an outer die 3 is arranged at an outer end of the 
mouthpiece 1 as shown in FIG. 3a. A tip die 11 made of a porous body is 
provided on the tip of the core member 2 for forming an inner 
configuration of the closed end of the sleeve. The porous body may be made 
of a ceramic material. Moreover, the outer die 3 comprises an outer die 
member 12 made of a porous body and a holder 13 so that the air can be 
blown into and out of the annular space 6 through the outer die member 12. 
As shown in FIG. 3b, the ceramic material 7 is then supplied into the 
annular space 6 and extruded to form an end or bottom of the sleeve. At 
the same time as the extrusion of the ceramic material, the air in the 
annular space 6 is removed, through suction, through the tip die 11 and a 
through-aperture of the core member 2 as shown by the arrow on the left 
side in FIG. 3b and the air in the annular space 6 is also removed through 
suction, through the outer die member 12 as shown by the arrow on the 
right side in FIG. 3b. After a lapse of a predetermined time, the 
extrusion and the suction are completed. 
Thereafter, the outer die 3 is removed from the mouthpiece 1 as shown in 
FIG. 3c. At the same time as the removal of the outer die 3, the air in 
the annular space 6 is removed, through suction, through the tip die 11 
and the air in the atmosphere is blown through the outer die member 12 
into the annular space 6. Therefore, the removal of the outer die 3 from 
the mouthpiece 1 can be easily and rapidly effected. 
Finally, the air is blown into the annular space 6 through the 
through-aperture, while the ceramic material 7 is further extruded so as 
to form a cylinder having a predetermined length to obtain a required 
closed end sleeve having a closed end. 
The invention is not limited to the embodiments above described and various 
changes and modifications can be made in the invention. For example, the 
outer die in the first embodiment shown in FIGS. 2a-2e may be made of a 
porous body having at its center a through-aperture which can obtain a 
closed end sleeve of good quality. The porous body may be made of a 
ceramic material. Moreover, by applying the method shown in FIGS. 2a-2e a 
hollow body can be obtained on the way of the extrusion of a solid body. 
This method will be explained in more detail by referring to FIGS. 4a-4c. 
As shown in FIG. 4, a core member 2 is arranged into a mouthpiece 1 during 
extrusion of the ceramic material. After the piston member 5 has arrived 
at a predetermined position as shown in FIG. 4b, the extrusion of the 
ceramic material 7 is continued, while air is blown into the core member 2 
through a through-aperture of the piston member 5, thereby obtaining a 
required closed end sleeve. 
FIG. 5 is a sectional view illustrating one example of a core structure 
comprising a core member 2 and a piston member 5 preferably used in the 
method shown in FIGS. 2a-2e. In this embodiment, the core member 2 
comprises a holder member 15 and a cylinder member 16 connected to the 
holder member 15 and having at its front end an inner tapered portion. The 
piston member 5 is formed at its one end with a tapered portion 18 having 
an air communication aperture 17 and adapted to fit in the inner tapered 
portion of the cylinder member 16 and with a hemispherical portion 19 for 
forming the inner configuration of the end of the sleeve. The piston 
member 5 has substantially the same diameter as the cylinder member 16. 
Moreover, the piston member 5 is formed at the other end with a stopper 20 
for stopping a further movement of the piston member 5 after its sliding 
movement of a constant distance. 
The respective members are made of a metal, for example, a hard steel such 
as S45C (Japanese Industrial Standard). Outer surfaces of the holder 
member 15 and the cylinder member 16 and the hemispherical portion 19 of 
the piston member 5 which are adapted to be in contact with the moving 
ceramic material are plated by, for example, chromium plating. Moreover, 
Teflon (trade name) is more preferable for the coating on the 
hemispherical portion 19 of the piston member 5. 
With the core member 2 and the piston member 5 explained with reference to 
FIG. 5, when the air is sucked through the air communication aperture 17, 
the tapered portions of the cylinder member 16 and the piston member 5 are 
maintained in close contact with each other. On the other hand, when the 
air is blown into through the air communication aperture 17, the air is 
jetted through a clearance between the tapered portions so that the piston 
member 5 is slidable until the stopper 20 abuts against the cylinder 
member 16 through the core member 2. 
As can be seen from the above description, according to the invention, the 
member for forming the inner configuration of the closed end of the sleeve 
is constructed by, for example, the piston member made of a metal or the 
porous body made of a ceramic material for extruding the forming material. 
Therefore, closed end sleeves can be reliably produced in predetermined 
shapes without deforming the inner configurations of the closed ends of 
the sleeves. 
Moreover, in case that the outer die made of the permeable porous body is 
used, the outer die can be easily separated from the mouthpiece and a 
protrusion does not occur at a center on an outer surface of the closed 
end of the sleeve so that a post-process for amending the outer surface is 
not needed. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details can be made therein without departing from the spirit and scope of 
the invention.