Pipe joints or couplings – Packed – Screw thimble-gland
Reexamination Certificate
2000-10-23
2003-12-16
Sandy, Robert J. (Department: 3677)
Pipe joints or couplings
Packed
Screw thimble-gland
C285S148260, C285S235000, C285S253000, C285S322000, C285S328000, C285S420000, C285S903000
Reexamination Certificate
active
06663146
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a single flare tube and to a joint structure of the single flare tube. The single flare tube includes a tubular portion and a flare portion attached to the front end of the tubular portion. The joint structure of the single flare tube includes the single flare tube, a flare nut and a union. The joint structure of the single flare tube can be used, for example, in a fluid circuit in order to connect one part of the fluid circuit to another part of the fluid circuit.
2. Description of Related Art
A joint structure of a single flare tube is well known among several kinds of joint structures of tubes. One example of a joint structure of a single flare tube is shown in FIG.
6
. With reference to
FIG. 6
, a cylindrical hole
101
a
is drilled into a union
101
, and an internal thread
101
b
is cut in a part of the cylindrical hole
101
a
. An external thread
102
b
is cut in an outer peripheral surface of a flare nut
102
, and the flare nut
102
is connected with the union
101
by screwing together the external thread
102
b
and the internal thread
101
b
. The flare nut
102
has a longitudinal through-hole
102
a
. A single flare tube
103
has a longitudinal through-hole
105
a
for flowing fluid, and includes a flare
104
and a tube
105
. The tube
105
passes through the through-hole
102
a
of the flare nut
102
. The flare
104
is positioned at the front end part of the single flare tube
103
, and an outer peripheral circumference of the flare
104
extends radially outward. The outer diameter of the flare
104
progressively decreases closer to the front end of the flare
104
, and thus a front slanting surface
104
b
of the flare
104
is nearly slant-shaped.
The flare nut
102
with the single flare tube
103
positioned in the through-hole
102
a
is inserted into the cylindrical hole
101
a
. When the flare nut
102
is tightened at the thread
101
b
of the union
101
and the thread
102
b
of the flare nut
102
, the flare
104
is located between a front surface
102
c
of the flare nut
102
and a slant shaped inner wall
101
c
of the union
101
, and the single flare tube
103
is coupled to the union
101
.
In the above-mentioned joint structure of the single flare tube, the conventional type flare
104
has a longitudinal section shaped like &Lgr;, and is elastically longitudinally deformed by tightening the threads of the flare nut
102
and the union
101
. It had been thought that by this elastic deformation, the front surface
104
b
of the flare
104
could be tightly fitted to the interior wall
101
c
of the union
101
.
In actual practice, however, the flare
104
can be plastically deformed by excessive tightening of the flare nut
102
, as illustrated in FIG.
7
. An inner circumferential groove
104
a
of the flare
104
then becomes out of shape, and not only the front end of the front surface
104
b
, but also the whole slanted, front surface
104
b
could contact the interior wall
101
c
of the union
101
. In this case, since the contact area between the flare
104
and the interior wall
101
c
increases, the contact pressure between both parts is reduced. Then, the sealability of this area also decreases.
Furthermore, a phenomenon by which the flare
104
rotates together with the flare nut
102
(called dual-rotation) could happen in the condition where the flare
104
is sandwiched and pushed between the front end of the flare nut
102
and the inner wall
101
c
of the union
101
. If the flare nut
102
continues to be tightened until the flare
104
becomes out of shape completely and the gap of the inner circumferential groove
104
a
becomes substantially zero (as shown in FIG.
7
), a rotation angle of the flare
104
by this dual-rotation could become a non-negligible level. As a consequence, the single flare tube
103
could twist by an amount that can not be neglected.
In order to prevent the single flare tube
103
from rotating with the flare nut
102
, low friction oil (for example, vegetable-based rust preventive oil) could be placed on the external thread
102
b
and the front surface
102
c
of the flare nut
102
. In this case, however, an oil coating process is necessary which increases the cost. If the low friction oil accidentally happens to be placed on the front surface
104
b
, the friction between the front surface
104
b
and the inner wall
101
c
is lowered. Then, the flare
104
could be slippery to the inner wall
101
c
, which results in the dual-rotation of the flare
104
and the flare nut
102
. Consequently, the twisting angle of the single flare tube
103
could become higher.
Furthermore, in the case where the union
101
is surface-coated, the inner wall
101
c
must be masked in order to avoid being surface-coated and to prevent the friction between the slanting surface
104
b
and the inner wall
101
c
from becoming lower, and to prevent the flare
104
from rotating with the flare nut
102
. Since the masking process is necessary, it causes the cost to increase and the reliability to be lowered.
On the other hand, a curvature of an outer (radially outward facing) corner
103
a
located between the front end of the tube
105
and the rear end of the flare
104
is constant and high. In the case that the curvature of the outer corner
103
a
is high, a high tensile stress P is loaded to the surface of the outer corner
103
a
when the flare nut
102
is tightened firmly, and the tensile stress P on the outer corner
103
a
remains after fastening the single flare tube
103
to the union
101
with the nut
102
. At the outer corner
103
a
the fatigue strength of the single flare tube
103
becomes lower when the tensile stress P remains.
In addition, if the curvature of the outer corner
103
a
of the single flare tube is high, tensile stress tends to concentrate on the outer corner
103
a
when an external force places a further load on the single flare tube
103
.
As mentioned above, if the curvature of the outer corner
103
a
is high, the tensile stress P tends to remain and concentrate. Consequently, if a vibration adds to the single flare tube
103
, for example, it is not easy to ensure the durability of the single flare tube
103
at the outer corner
103
a.
SUMMARY OF THE INVENTION
It is thus one object of the present invention to solve the aforementioned problem. Another object of the invention is to provide a single flare tube and a joint structure of the single flare tube in which a flare is not easily plastically deformed and a tensile stress does not easily remain.
According to one aspect of the invention, a joint structure of a single flare tube includes a single flare tube, a first connector member and a second connector member. The single flare tube includes a tube and a flare, and the flare is coupled with the tube at the front end of the tube. The flare extends radially outward relative to a longitudinal axis of the tube. The first connector member can be, for example, a flare nut that has a through-hole for receiving the tube of the single flare tube. The second connector member can be, for example, a union that is connectable with the first connector member. The flare nut and the union can have, for example, threads that engage each other. A width of a narrow inner circumferential groove of the outer radially extending part of the flare does not substantially change when the single flare tube is pushed and coupled with the union by coupling the flare nut with the union.
Since the width of the narrow inner circumferential groove formed inside of the flare is not substantially changed when the single flare tube is pushed against the union by the flare nut, according to the present invention, the flare does not deform plastically, and a contacting area between a front slanting surface of the flare and an inner wall formed inside of the union does not increase. Accordingly, the contacting pressure between the slanting surface of the flare and the inner wall of the union does not decrease aft
Iguchi Hiroyuki
Sakai Tomotsugu
Tanaka Toshihide
Lugo Carlos
Sandy Robert J.
LandOfFree
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