Lip seal

Details Lip seal Lip seal

2001-05-01

2003-02-11

Knight, Anthony (Department: 3676)

Seal for a joint or juncture

Seal between relatively movable parts

Circumferential contact seal for other than piston

C277S559000

Reexamination Certificate

active

06517083

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a lip seal for sealing a shaft in various rotary machines, more particularly, a technology for improving a pressure resistance and a sealing capability under a condition that a pressure of sealing object fluid becomes high prominently.
DESCRIPTION OF THE RELATED ART
Conventionally, as a lip seal, there was one shown in
FIG. 4
or
FIG. 5. A
lip seal
100
of this kind has a structure that an elastomer lip member
102
, a pressure resisting reinforcement ring
103
which supports the elastomer lip member
102
from its rear side (a side opposite to an inner space of machine S
1
of a sealing object), a resin lip member
104
arranged on the rear side of the pressure resisting reinforcement ring
103
, and a back-up ring
105
which is additionally provided on the rear of the resin lip member
104
support their each outer diameter portion in a state closely adhered with each other on an inner circumference of a case
101
which is closely inserted and fixed in an inner circumference of an housing
1
through an O-ring
106
or a gasket portion
107
.
In the lip seal
100
of this kind, the elastomer lip member
102
has pumping threads
102
b
for lubrication which cause a pumping action in a leakage direction according to the rotation of a rotating shaft
2
and are formed on an inner circumferential surface of a seal lip portion
102
a
of an inner diameter side extending to the inner space of machine S
1
side, thereby, a leaking of high pressure fluid in the inner space of machine S
1
side is prevented when the shaft stops, that is, said leakage direction pumping is not performed. On the other hand, the resin lip member
104
has pumping threads
104
b
which cause a pumping action in a direction which pushes and backs fluid toward the elastomer lip member
102
side when the shaft rotates and are formed on the inner circumferential surface of its seal lip portion
104
a,
that is, the leaking of a sealing object fluid in the inner space of machine S
1
which has passed a sliding portion of the elastomer lip member
102
toward an atmosphere S
2
side is prevented mainly when the shaft rotates.
The pumping threads
104
b
in the seal lip portion
104
a
of the resin lip member
104
are formed at only around a front end of a sliding surface with the rotating shaft
2
. This is because that there is need to prevent the fluid from leaking toward the atmosphere S
2
side after passing the pumping threads
104
which lose the pumping action in a leakage blocking direction when the shaft stops.
In the lip seal
100
of this kind, in high pressure condition which the pressure of the inner space of machine S
1
is at least 1 MPa [gage], the resin lip member
104
receives an influence of said pressure, thus its section is deformed into approximately L-shape. And, in prior art, a stress of front end portion of the seal lip portion
104
a
in said deformation process is relatively small by the presence of the pumping threads
104
b,
and a stress generated in the vicinity of a bent portion
104
c
in which the pumping threads
104
b
are not formed is relatively large, thus a maximum portion of a surface pressure to the outer circumferential surface of the rotating shaft
2
is locally distributed toward said bent portion
104
c
side. Accordingly, the inner circumferential surface in the vicinity of the bent portion
104
c
is easily worn, and as a result, the front end portion in which the pumping threads
104
b
are formed causes a floating deformation on the outer circumferential surface of the rotating shaft
2
. And, if this floating is caused, there has been a problem that a sealing function is lowered when the shaft stops because the pumping action in the leakage blocking direction by said pumping threads
104
b
is damaged.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a lip seal which can prevent a front end portion of a resin lip member from being floating deformed on an outer circumferential surface of a rotating shaft, so that an excellent sealing function could be maintained for a long time.
A lip seal according to the present invention comprises an elastomer lip member which has a seal lip portion at an inner side, extending to a sealed space, the seal lip portion being brought into close contact with an outer circumferential surface of a rotating shaft; a first resin lip member which has a seal lip portion at an inner side and is arranged at a rear side of the elastomer lip member and has a bent portion at the inner side and extends to a sealed space, which is brought into close contact with an outer circumferential surface of the rotating shaft; and a second resin lip member having a seal lip portion of an inner side, which is arranged at a rear side of the first resin lip member and has a bent portion at the inner side, extending to a sealed space, which is brought into close contact with an outer circumferential surface of the rotating shaft. First pumping threads generate a pumping action in a leakage direction when the shaft rotates, which are formed on an inner circumferential surface of the seal lip portion of the elastomer lip member. Second pumping threads generate a pumping action in a direction opposite to the leakage direction when the shaft rotates, which are formed on the first resin lip member from an inner circumferential surface of the seal lip portion to a rear portion of a bent portion thereof. An inner circumferential surface of the second resin lip member is formed smoothly. And, the “rear” portion stated herein is a portion or surface opposite to the sealed space.


REFERENCES:
patent: 4336945 (1982-06-01), Christiansen et al.
patent: 4623153 (1986-11-01), Nagasawa
patent: 4834397 (1989-05-01), Shimasaki et al.
patent: 5149106 (1992-09-01), Takenaka et al.
patent: 6102409 (2000-08-01), Furuyama et al.
patent: 6199869 (2001-03-01), Furuyama et al.
patent: 6336638 (2002-01-01), Guth et al.

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