Spherical sealing body used for the exhaust pipe joints and a method of manufacturing thereof

A method of manufacturing a spherical sealing body for use in exhaust pipe joints, including the steps of; laminating a flexible refractory sheet and a flexible wire net with each other, winding the laminated refractory sheet and the wire net to thereby form a cylindrical member, laminating the other flexible refractory sheet and an unsintered tape or film made of a polytetrafluoroethylene resin to each other, compressing to integrate the laminated other refractory sheet and the unsintered tape or film in a direction of the thickness thereof to thereby form an sliding face member, winding the sliding face member to an outer circumferential surface of the cylindrical member to thereby form a cylindrical preform body, and applying compression to the preform body in an axial direction of the preform body, and a spherical sealing body for use in exhaust pipe joints manufactured by the method above mentioned.

BACKGROUND OF THE INVENTION 
The present invention relates to a spherical sealing body used for exhaust 
pipe joints in automobiles and a method of manufacturing thereof. 
A spherical sealing body used for exhaust pipe joints is disclosed, for 
example, in Japanese Patent Application Laying Open No. 54-76759 
(hereinafter referred to as "related art I"). The spherical sealing body 
disclosed in the related art I has heat resistance, excellent fitness with 
mating members and remarkably improved impact shock resistance but it 
involves, on the other hand, a drawback of often generating abnormal 
frictional noise during sliding movement under dry frictional conditions. 
It is considered that the above-mentioned drawback in the sealing body is 
due to the great difference between the static friction coefficient and 
the kinetic friction coefficient of heat resistance material constituting 
the sealing body (expansive graphite, etc.) and also to that the 
frictional resistance of the sealing body made of such heat resistance 
material relative to the sliding velocity shows a negative resistance 
(that is, a phenomenon in which the friction coefficient is reduced in 
accordance with the increase in the sliding velocity). 
In view of the above, the present applicant has already proposed a sliding 
(sealing) member which can overcome the foregoing drawback and suitably be 
used to exhaust pipe joints in Japanese Patent Application No. 56-120701 
(Japanese Patent Laying Open No. 58-24620) (hereinafter referred to as 
"related art II"). 
That is, the sealing body in the related art II is prepared by molding 
refractory material as a mixture of one or more of expensive graphite, 
mica and asbesto together with reinforcing material comprising metal 
fibers, fine metal wires or metal gages obtained by weaving or knitting 
them, in which a lubricant composition comprising a 
polytetrafluoroethylene resin or a copolymer of tetrafluoroethylene and 
hexafluoropropylene is deposited to the surface of the sealing body. 
In this sealing body, the lubricant composition deposited to the surface 
thereof can provide effects of reducing the friction coefficient, 
prevention of the refractory matrix material from transferring to mating 
members, reduction of the difference between the static friction 
coefficient and kinetic friction coefficient, etc., in addition, the 
tetrafluoroethylene resin does not show negative frictional resistance 
relative to the sliding velocity, consequently, there can be obtained an 
advantageous effect of suppressing the generation of self-excited 
vibrations due to "deposition-sliding", thereby contributing to the 
prevention for the generation of abnormal frictional noise in addition to 
the foregoing effect. 
Now it has been found that although the sealing body based on the related 
art II described above can overcome the drawbacks in the related art I in 
view of the performance, there is a problem in this case for the method of 
manufacturing the sealing body. 
The method of manufacturing the sealing body in the related art II is as 
described below. 
(1) A method of coating adhesives to the surface of a sealing body 
substrate obtained by molding refractory material and reinforcing material 
together, and then scattering and depositing a tetrafluoroethylene resin 
powder thereover, or (2) a method of properly diluting a mixture of a 
tetrafluoroethylene resin powder and adhesives with a volatile solvent, 
brush-coating or spraying the solution to the surface of the sealing body 
substrate, or 
(1) a method of coating adhesives to the surface of a sheet-like refractory 
material and then scattering and depositing a tetrafluoroethylene resin 
powder or (2) a method of properly diluting a mixture of a 
tetrafluoroethylene resin powder and adhesives with a volatile solvent and 
then brush-coating or spraying the solution to the surface of the 
sheet-like refractory material. 
Any of the former methods of depositing the tetrafluoroethylene resin to 
the surface of the sealing body substrate requires an additional step of 
compressing the sealing body substrate again in a mold for adjusting the 
size and smoothing the surface after the deposition. In the latter 
methods, the method (1) requires a step of coating adhesives and the 
method (2) of applying brush coating brings about a difficulty in thin and 
uniform coating on the surface of the sheet-like refractory material. 
Accordingly, a method of depositing by means of spraying has been 
recommended in view of practical use. 
However, although the method of depositing the solution by means of 
spraying to the surface of the sheet-like refractory material enables thin 
and uniform deposition on the surface, it has been found that a 
considerably great amount of the tetrafluoroethylene resin scatters around 
the sheet-like refractory material to cause loses in the 
tetrafluoroethylene resin, that is, poor material yield. 
SUMMARY OF THE INVENTION 
The first object of the present invention is to provide a method of 
manufacturing a spherical sealing body for use in exhaust pipe joints 
capable of improving the material yield and remarkably improving the 
operation-ability while keeping advantages of the related art II in view 
of the performance as they are. 
The second object of the present invention is to provide a spherical 
sealing body for use in exhaust pipe joints causing less self-excited 
vibrations and, thus, less generation of abnormal frictional noise. 
According to the present invention, the foregoing first object can be 
attained by the following methods, that is, 
a method of manufacturing a spherical sealing body for use in exhaust pipe 
joints, comprising the steps of; 
laminating a first flexible refractory sheet and a flexible wire net to 
each other, 
winding said laminated first refractory sheet and said wire net such that 
said wire net is situated at the outermost circumference to thereby form a 
cylindrical member, 
laminating a second flexible refractory sheet and an unsintered tape or 
film made of a polytetrafluoroethylene resin to each other, 
compressing to integrate said laminated second refractory sheet and said 
unsintered tape or film in a direction of the thickness thereof to thereby 
form a sliding face member, 
winding said sliding face member to an outer circumferential surface of 
said cylindrical member such that said unsintered tape or film is situated 
to an outside to thereby form a cylindrical preform body, and 
applying compression to said preform body in an axial direction of said 
preform body so as to form a main body of said sealing body by entangling 
to integrate said first refractory sheet and said wire net and so as to 
form a surface layer made of said resin to a spherical portion of said 
main body by integrating said cylindrical member with said sliding face 
member, or 
a method of manufacturing a spherical sealing body for use in exhaust pipe 
joints, comprising the steps of; 
laminating an unsintered tape or film made of a tetrafluoroethylene resin 
over a predetermined length at one end on one surface of a flexible 
refractory sheet, 
compressing to integrate said laminated refractory sheet and said 
unsintered tpe or film in the direction of thickness thereof, 
laminating a flexible wire net to the other surface of said refractory 
sheet integrated with said unsintered tape or film, 
winding said laminated refractory sheet and said wire net such that said 
unsintered tape or film integrated with said refractory sheet is situated 
to an outermost circumference thereof to thereby form a cylindrical 
preform body and 
applying compression to said preform body in an axial direction of said 
preform body so as to form a main body of said sealing body, and form a 
surface layer made of said resin to a spherical portion of said main body, 
by entangling to integrate said first refractory sheet and said wire net. 
According to the method of the present invention, since the 
polytetrafluoroethylene resin is used in the form of unsintered tape or 
film, the handling is facilitated and the material yield can be improved 
remarkably. 
Since the unsintered tape or film and the flexible refractory sheet, or the 
unsintered tape or film, the flexible refractory sheet and the flexible 
wire net are press-bonded and integrated by the compression in the 
direction of the thickness, firm bonding can be obtained without using 
adhesives as in the related art and, since the sliding face member can be 
handled as a unitary member, the operationability can be improved. 
In a casee where the wire net and the flexible refractory sheet are 
compressed in adjacent with each other, since the meshes of the wire net 
are filled with the refractory sheet by its easy flexibility, both of them 
can be integrated firmly. Further, in a case where the wire net and the 
unsintered tape or film are compressed in adjacent with ether other, since 
the surface of the unsintered tape or film is press-bonded in an unevenned 
state due to the flexibility of the unsintered tape or film, both of them 
can be integrated firmly. Accordingly, if the wire net, the refractory 
sheet and the unsintered tape or film are laminated in this order and 
compressed, an unevenned surface is formed, in which the refractory sheet 
fills the meshes of the wire net and the wire net is partially exposed, 
and the unsintered tape or film is press-bonded to the unevenned surface. 
Accordingly, they are integrated by press-bonding more firmly than the 
case without using the wire net. Particularly, in the case of laminating 
and compressing the refractory sheet, the unsintered tape or film and the 
wire net in this order, since the refractory sheet and the unsintered tape 
or film form an unevenned press-bonded surface, integration under stronger 
press-bonding can be attained as compared with the case of not using the 
wire net. 
The refractory sheet used in the method according to the present invention 
is preferably made of expansive graphite, mica or asbesto and, more 
specifically, suitable expansive graphite is "Grafoil (trade name)", 
manufactured by Union Carbide Co. in U.S.A. as disclosed in Japanese 
Patent Publication No. 44-23966, or "Nicafilm (trade name)" manufactured 
by Nippon Carbon Co. As the mica, mica paper bonded with silicon is 
suitable and, as asbesto, chrysotile or amosite type asbesto paper or 
sheet is suitable. 
A step of compressing the refractory sheet made of expansive graphite and 
the wire net in the direction of the thickness thereby integrating them in 
the method according to the present invention is preferably carried out by 
using calendering or pressing. 
Preferred wire nets used in the present invention, are those prepared by 
weaving or knitting metal fibers or fine metal wires such as of stainless 
steels, for example, austenite SUS 304, SUS 316 (corresponding to 
JIS-G-430g: AISI-304, 316 respectively) and ferrite SUS 430 (corresponding 
to JIS-G-430g: AISI-430), iron wire, zinc plated iron wire (JIS G-3532: 
corresponding to ASTM A641) having mesh size preferably from 3 to 5 mm. 
As the resin sheet made of the tetrafluoroethylene resin used in the 
present invention, unsintered films or tapes of about 0.05-0.5 mm 
thickness are preferred and there can be mentioned, for example, 
unsintered films or unsintered tapes of polytetrafluoroethylene resin 
manufactured by the paste extrusion molding method from fine powder of 
tetrafluoroethylene resin (Teflon 6J, Polyflon F101, Fluon CD1: all in 
trade name) as suitable sheet. 
According to the present invention, the foregoing second object can be 
attained by a spherical sealing body for use in exhaust pipe joints 
manufactured by any one of the methods according to the present invention 
described above. 
In the spherical sealing member for use in an exhaust pipe joint according 
to the present invention, since a surface layer made of the 
tetrafluoroethylene resin or a composite surface layer comprising the 
tetrafluoroethylene resin and the wire net is formed at the spherical 
portion of the sealing, the frictional coefficient at the spherical 
portion of the sealing body can be reduced, transfer of the refractory 
material constituting the main body of the sealing body to the abutting 
portion of the exhaust pipe can be prevented and difference between the 
static friction coefficient and the kinetic friction coefficient can be 
reduced. In addition, since the tetrafluoroethylene resin does not show a 
negative frictional resistance relative to the sliding velocity, it is 
possible to suppress the generation of self-excited vibrations due to 
"deposition-sliding" and, accordingly, to prevent the generation of 
abnormal frictional noise. 
Particularly, in the spherical sealing body for use in exhaust pipe joints 
according to the present invention in which the composite surface layer 
comprising the tetrafluoroethylene resin and the wire net is formed to the 
spherical portion, when it is used for exhaust pipe joints, after the 
tetrafluoroethylene resin of the composite surface layer has been abrased 
to such an optimal shape as fitting the shape of the mating portion of the 
exhaust pipe, since the wire net in the composite surface layer inhibits 
the further development of the abrasion in the tetrafluoroethylene resin, 
it can improve and maintain the effect of sealing, as well as an effect of 
preventing the generation of abnormal frictional noise. 
Further objects and advantages of the present invention will be apparent 
from the following description, reference being had to the accompanying 
drawings wherein preferred embodiments of the present invention are 
clearly shown.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is to be described by way of its examples referring 
to the drawings. 
EXAMPLE I 
a. First Step 
A knitted wire net 1 of 3 mm mesh size is prepared by using SUS 403 fine 
metal wire having 0.28 mm wire diameter. Further, an expansive graphite 
sheet of 0.5 mm thickness ("Nicafilm", manufactured by Nippon Carbon Co.) 
is used as an expansive graphite sheet 2. 
Then, after laminating the refractory sheet 2 to the wire net 1, they are 
wound such that the refractory sheet 2 is situated at the inside and the 
wire net 1 is situated at the outermost circumference to prepare a 
cylindrical member 3 (FIG. 1). 
b. Second Step 
An unsintered tape 5 of a tetrafluoroethylene resin with 0.1 mm thickness 
is laminated on an expansive graphite sheet 4 with 0.5 mm thickness, they 
are passed between rollers 6, 6 in the direction of an arrow A to thereby 
prepare a sliding face member 7 in which the unsintered tape 5 of the 
tetrafluoroethylene resin is press-bonded to integrate to one surface of 
the expensive graphite sheet 4 (FIG. 2). 
c. Third Step 
The sliding face member 7 obtained in the second step described above is 
wound around the outer circumferential surface of the cylindrical member 3 
obtained in the first step with the tetrafluoroethylene resin layer being 
situated to the outside to prepare a preform member 8 (FIG. 3). 
d. Fourth Step 
The preform member 8 is tightly fitted over the outer circumferential 
surface of a core 11 in a mold 10 having a partial spherical surface 
portion 9 at the inner side thereof, and the preform member 8 is 
compressed in the axial direction thereof to obtain a spherical sealing 
body (FIG. 4). 
In this step, the wire net 1 and the refractory sheet 2 of the cylindrical 
member 3 are entangled to form an integrated sealing main body and the 
sliding face member 7 integrated with the main body is formed to the 
spherical sliding surface of the main body with the tetrafluoroethylene 
resin as the surface layer. 
FIG. 5 is a logitudinal cross sectional view illustrating a spherical 
sealing body 12 obtained by way of the first through fourth steps, in 
which there are shown an inner hole 13 along which the refractory sheet 2 
is exposed, an end face 14 and a spherical sliding face 15 made of the 
tetrafluoroethylene resin layer. 
EXAMPLE II 
a. First Step 
A knitted wire net 1 of 3 mm mesh size is prepared by using SUS 430 fine 
metal wire having 0.28 mm wire diameter. Further, an expansive graphite 
sheet of 0.5 mm thickness ("Nicafilm", manufactured by Nippon Carbon Co.) 
is used as an expansive graphite sheet 2. 
Then, after laminating the refractory sheet 2 to the wire net 1, they are 
wound such that the refractory sheet 2 is situated at the inside and the 
wire net 1 is situated at the outermost circumference to prepare a 
cylindrical member 31 (FIG. 6). 
b. Second Step 
After laminating an expansive graphite sheet 4 of 0.5 mm thickness over a 
separately prepared wire net 1' of a predetermined length, and an 
unsintered tape 5 of a tetrafluoroethylene resin of 0.1 mm thickness 
further over the expansive graphite sheet 4 (FIG. 7), they are passed 
between rollers 6, 6 in the same manner as in Example I to prepare a 
sliding face member 71, in which the wire net 1' and the expansive 
graphite sheet 4 and the tetrafluoroethylene resin unsintered tape 5 are 
integrated with each other (FIG. 8). 
In this step, since the expansive graphite sheet 4 fills the meshes of the 
wire net 1 by means of easy moldability and flexibility of the sheet 
itself and the wire net 1 is partially exposed to form an unevenned 
surface at the boundary after press-bonding the expansive graphite sheet 4 
and the wire net 1, the tape 5 of the tetrafluoroethylene resin disposed 
over the expansive graphite 4 is press-bonded to this unevenned surface to 
attain more firm integration. 
c. Third Step 
The sliding face member 71 obtained in the second step is wound over the 
outer circumferential surface of the cylindrical member 31 obtained in the 
first step with the tetrafluoroethylen resin layer being situated to the 
outside to prepare a preform member 81. 
d. Fourth Step 
A spherical sealing body is obtained in the same procedures as in Example I 
fro the preform member 81. 
EXAMPLE III 
a. First Step 
An expansive graphite sheet of 0.5 mm thickness ("Nicafilm", manufactured 
by Nippon Carbon Co.) is used as the refractory sheet 2 and, after 
laminating an unsintered tape 5 of tetrafluoroethylene resin of 0.1 mm 
thickness on the surface at one end of the refractory sheet 2, they are 
press-bonded to integrate by being passed between rollers (FIG. 10, FIG. 
11). 
b. Second Step 
A knitted wire net 1 of 3 mm mesh size is prepared by using SUS 403 as fine 
metal wire having 0.28 mm wire diameter. Then, after laminating the wire 
net 1 over the refractory sheet 2, they are wound with the refractory 
sheet 2 being at the inside and the unsintered tape 5 of 
tetrafluoroethylene press-bonded and integrated with the refractory sheet 
material 2 being situated to the outermost circumference to prepare a 
preform member 82 (FIG. 12). 
c. Third Step 
From the preform member 82, a spherical sealing body is obtained in the 
same procedures as in Example I. 
The spherical sealing body obtained through the manufacturing steps in 
Example I through Example III described above show the same effects as 
those in the spherical sealing body in the prior art II, regarding 
frictional characteristics, prevention for the generation of unpleasant 
sounds and tightly sealing function. 
Many widely different embodiments of the present invention may be 
constructed without departing from the spirit and scope of the present 
invention. It should be understood that the present invention is not 
limited to the specific embodiments described in this specification, 
except as defined in the appended claims.