Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Specific casing or vane material
Reexamination Certificate
1998-12-14
2001-11-27
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Specific casing or vane material
C416S24100B
Reexamination Certificate
active
06322323
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a movable blade of a turbine and in particular, to a turbine movable blade having a leading edge of an improved structure.
Normally, a steam turbine comprises a plurality of stages each provided by combining a turbine stationary blade, which may be called turbine nozzle, and a turbine movable blade, which may be called turbine bucket. A plurality of stages are arranged on a turbine shaft (rotor) along the stream of a turbine driving steam (main stream) and the turbine stationary and movable blades are arranged as an annual sequence along the circumferential direction of the turbine shaft.
Among the plural stages arranged on the turbine shaft, the final stage is driven by wet steam which has lost thermal energy and contains large quantity of droplets, and there may cause a problem of an erosion. The movable blade, in particular, directly receives droplet containing wet steam splashed from the stationary blade arranged upstream thereof. The wet steam may cause erosion to the leading edge thereof, i.e. front side edge with respect to a turbine steam flow. Since the movable blade in the final stage is as long as about 1 m compared with those in the remaining stages and has a greater centrifugal force and vibration stress, if an erosion occurs, there is a fear that a stable operation may be badly affected by the synergistic effect thereof.
FIG. 7
shows a perspective view of a conventional steam turbine, partially cut away, having a plurality of pressure stages to which the present invention is applicable. The shown steam turbine includes a turbine rotor as a rotational shaft
100
around which a plurality of pressure stages such as high pressure stage
101
and low pressure stage
102
(
103
) are formed. As is generally known in this art field, each pressure stage includes stationary and movable blade unit which are mounted circumstantially to the turbine rotor. The details of the arrangement of these members are well known in the art and detail description thereof is omitted herein.
FIG. 5
shows a conventional movable blade of a turbine, such as shown in
FIG. 7
, under the strict environment as stated above has been intended to prevent erosion caused by the wet steam, by attaching, for example, welding an erosion shield plate
3
made of high erosion protective material such as, for example, cobalt group alloy steel onto a leading edge
2
of the main body of the movable blade
1
(called hereinlater movable blade body
1
or merely blade body
1
) with silver brazing or welding. That is, a portion of the leading edge of the movable blade body is formed to have a recessed portion into which the erosion shield piece is welded as a separate member.
However, when such silver brazing or welding is applied, a connection defect occurs to or a residual stress remain in the base material of the blade body
1
. After the movable blade has been used for a long period of time, the erosion shield plate
3
may be peeled off. Besides, if the erosion shield plate is replaced repeatedly, various problems including occurrence of fatigue to the base material of the blade body I are caused due to a thermal effect. Considering this, the following measures have been taken for the recent movable blade as shown in
FIG. 6
, which is also applicable to a steam turbine of FIG.
7
. When the erosion shield piece
3
a
is attached to the leading edge
2
of the blade body
1
, surface flame hardening is locally conducted to the blade body
1
and the erosion shield piece
3
a
to maintain high strength, thereby preventing erosion by the wet steam.
As described above, in the recent turbine movable blade, the surface flame hardening is conducted instead of junction means such as welding when the erosion shield piece
3
a
is attached to the leading edge
2
of the blade body
1
. Accordingly, welding defects, liftoff and the like can be suppressed and the movable blade can be thus operated while maintaining the quality thereof in a stable condition even under the severe circumstances.
Normally, 12-chromium alloy steel is often used for the base material of the blade body
1
in the movable blade. In that case, since there are portions subjected to flame hardening and portions not subjected to the flame hardening between the erosion shield piece
3
a
and the 12-chromium alloy steel, a residual tensile force might sometimes occur. For this reason, the portions of the movable blade body subjected to the flame hardening are often cracked by stress corrosion crack or fatigue, which has made it difficult to maintain the quality of the movable blade in a stable condition.
To suppress the residual tensile stress generated at the 12-chromium alloy steel, there is proposed, for example, conducting of a shot peening to portions subjected to the flame hardening. This, however, is not a durable measure to maintain stable quality of the movable blade body.
SUMMARY OF THE INVENTION
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a movable blade of a turbine having an improved structure capable of further reducing a residual tensile stress generated at a base material of a movable blade main body and maintaining the quality of the movable blade in a stable condition, even if an erosion protective piece is attached to the blade body and surface hardening is conducted.
This and other objects can be achieved according to the present invention by providing, in one aspect, a movable blade of a turbine, which has a plurality of stages each provided with movable and stationary blades mounted to a turbine rotor, comprising a movable blade body having a leading edge portion on an upstream side with respect to a turbine steam flow and an erosion protective piece which is formed to be continuously integrally with the movable blade body so as to be protruded from the blade body, wherein the leading edge portion and the erosion protective piece are subjected to a surface hardening treatment such as flame hardening treatment.
In a preferred embodiment of this aspect, the erosion protective piece has a length in a longitudinal direction of the movable blade body in a range of 10% to 45% of an effective length of the movable blade body and a depth in a width direction thereof is set to be at least 1 mm or more.
In another aspect, there is provided a movable blade of a turbine, which has a plurality of stages each provided with movable and stationary blades mounted to a turbine rotor, comprising a movable blade body having a leading edge portion on an upstream side with respect to a turbine steam flow and an erosion protective piece which is formed to be continuously integrally with the movable blade body, wherein the erosion protective piece is protruded, in the upstream of the turbine steam f low, over a segment cover provided between a top portion of one of movable blade body and a top portion of another one of movable blade body adjacent to the one movable blade body.
In a further aspect, there is provided a movable blade of a turbine, which has a plurality of stages each provided with movable and stationary blades mounted to a turbine rotor, comprising a movable blade body having a leading edge portion on an upstream side with respect to a turbine steam flow and an erosion protective piece which is formed to be continuously integrally with the movable blade body so as to be protruded from the leading edge of the blade body, wherein the erosion protective piece has a base edge portion from which the erosion protective piece is protruded from the movable blade body, and a distance between the base edge portion and an outside edge portion of a tenon hole formed so as to join a blade cover disposed between a top portion of one of the movable blade body and a top portion of another one of the movable blade body adjacent to the one movable blade body is set at least 2 mm or more.
In a preferred embodiment of this aspect, the erosion protective piece is protruded over the location
Komiyama Manabu
Murata Yoriharu
Suzuki Toshio
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Look Edward K.
McAleenan James M
LandOfFree
Turbine movable blade does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Turbine movable blade, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Turbine movable blade will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2613647