Seal for a joint or juncture – Seal between relatively movable parts – Brush seal
Reexamination Certificate
2002-07-18
2004-09-07
Stodola, Daniel P. (Department: 3677)
Seal for a joint or juncture
Seal between relatively movable parts
Brush seal
C277S412000, C277S415000, C277S421000
Reexamination Certificate
active
06786488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a seal structure which is favorable for a rotating shaft of a steam turbine and relates to a turbine using the same.
2. Description of Related Art
Around a rotating shaft of gas turbine and a steam turbine, a seal structure for rotating shaft is employed so as to prevent gas from leaking from the high pressure region to a low pressure region. As an example of the seal structure for a rotating shaft, a brush seal
1
can be mentioned as shown in FIG.
6
.
The brush seal
1
comprises a ring
3
which is disposed around the outer periphery of a rotating shaft
2
and a brush
4
made of a plurality of wires disposed on the inner surface of the ring
3
. The ring
3
is fixed on the stator
5
, such as casing, which surrounds an outer periphery of the rotating shaft
2
. The brush
4
has appropriate rigidity and is disposed densely in a rotational direction of the rotating shaft
2
as shown in FIG.
7
. Also, a brush
4
is disposed so as to form an acute angle with the rotational surface of the rotating shaft
2
, and the brush
4
is disposed in slanted form in a rotational direction of the rotating shaft
2
(in a direction of an arrow d in the drawing). Between the tip of the brush
4
and a rotational surface
6
of the rotating shaft
2
, a space is provided.
This space becomes gradually smaller when the rotating shaft
2
rotates and a diameter of the rotating shaft
2
increases due to centrifugal force. The tip of the brush
4
contacts the rotational surface
6
of the rotating shaft
2
with a predetermined pressure before a turbine operates in a load condition as shown in
FIG. 8
(during low speed rotation of the rotating shaft
2
). By this contact, a brush seal
1
prevents gas from passing between the rotating shaft
2
and the stator
5
and leaking from a high pressure region to a low pressure region.
When a turbine operates in a load condition (in high speed rotation of the rotating shaft
2
), high temperature gas flows in between the rotating shaft
2
and the stator
5
from the combustor. Also, cooling air flows to the rotating shaft
2
so as to restrict heat due to this gas. For that purpose, the temperature of the rotating shaft
2
is maintained to almost the same temperature as the temperature of the cooling air. In contrast, because cooing air does not flow to the stator
5
, the temperature of the stator
5
and the ring
3
become nearly the same as the temperature of the gas. Therefore, the temperature of the stator
5
and the ring
3
become higher than the temperature of the rotating shaft
2
. Thus, the enlargement of the diameter of the stator
5
and the ring
3
due to thermal expansion becomes larger than the enlargement of the diameter of the rotating shaft
2
due to thermal expansion and centrifugal force. As a result, the ring
3
expands in outer radial direction so as to depart from the rotating shaft
2
. When the ring
3
departs from the rotating shaft
2
, the tip of the brush
4
departs from the rotational surface
6
of the rotating shaft
2
, and a space g is generated between the brush
4
and the rotational surface
6
as shown in FIG.
9
.
As described above, in brush seal
1
, gas passes through the space g and leaks to the low pressure region; thus, the function of sealing effect decreases because the space g is generated between the brush
4
and the rotational surface
6
when a turbine
22
operates in a load condition. When the seal effect decreases, driving force loss is generated in a turbine.
Also, the tip of the brush
4
of the above brush seal
1
slides on the rotational surface
5
of the rotating shaft
2
when a turbine
22
operates in a non-load condition. Therefore, the friction between the brush
4
and the rotational surface
6
of the rotating shaft
2
is large; thus, the service life of the brush seal is shortened.
SUMMARY OF THE INVENTION
The present invention was made in consideration of the above situation. An object of the present invention is to decrease the amount of gas leaking from high pressure region to a low pressure region when a turbine operates in a load condition, and another object of the present invention is to provide a seal structure for a rotating shaft and a turbine which is provided with such a seal structure.
In order to achieve the above objects, a seal structure for a rotating shaft according to a first aspect of the present invention is characterized in comprising a stator section, a rotating shaft, a groove formed on an inner surface of the stator section, a ring made of a plurality of portions formed in a circle and disposed in the groove, a brush composing a plurality of wires adhered on an inner surface of the ring and tips of the wires are disposed toward the surface of the inner surface, a spring member which pushes the ring in a direction in which the ring departs from the rotating shaft so as to float the brush from the inner surface of the stator and a connecting hole inducts fluid pressure which presses the ring in a direction in which the ring approaches to the rotating shaft so as to be against the spring force of the spring member and make the brush contact the inner surface of the stator wherein the sealing structure prevents the fluid from passing between the rotating shaft and the stator having a clearance from the surface of the rotating shaft and flowing in an axial direction of the rotating shaft.
In this seal structure for a rotating shaft, when the space between the rotating shaft and the stator does not need to be sealed (for example, before a turbine operation reaches its load condition), the brush and the rotational surface are maintained uncontacted by separating the ring from the rotating shaft with a spring force of the spring member so as to float the brush from the rotational surface of the rotating shaft. By doing this, when sealing effect is not necessary, the friction between the brush and the rotating shaft is prevented. When the space between the rotating shaft and the stator must be sealed (for example when a turbine operates in a load condition), the tip of the brush contacts the rotational surface of the rotating shaft by inducting a fluid pressure from connecting holes so as to be against the spring force of the spring member and by moving the ring with such fluid pressure in a direction in which the ring approaches to the rotating shaft. By doing this, when sealing effect is necessary, the fluid is prevented from flowing through the rotating shaft and the stator and leaking from an upstream region (high pressure region) to a down stream region (low pressure region).
A sealing structure for a rotating shaft according to a second aspect of the present invention is characterized in having a pressure inducting device which inducts the fluid pressure to the connecting hole.
In such a seal structure for a rotating shaft, features such as restricting the friction between the brush and the rotating shaft and the leak of the fluid from the upstream region to the downstream region are the same as the features described above.
A sealing structure for a rotating shaft according to a third aspect of the present invention, in a sealing structure for a rotating shaft in the first or the second aspect of the present invention, is characterized in that the spring member is disposed separately near the upstream of the fluid and near the downstream of the fluid so as to position the brush therebetween.
In such a seal structure for a rotating shaft, the spring member supports the ring at two points in the upstream region and the downstream region while having the brush therebetween. Therefore, no force other than the spring force by the spring member is given to the ring from the upstream region or from the downstream region; thus, inclination of the ring in the groove is prevented and the ring floats stably in the groove. When sealing effect is not necessary, the contact between the brush and the rotating shaft is avoided, and also the friction between the brush and
Laurello Vincent
Yuri Masanori
Lugo Carlos
Mitsubishi Heavy Industries Ltd.
Stodola Daniel P.
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