Fluid reaction surfaces (i.e. – impellers) – Multiple axially spaced working members
Reexamination Certificate
2000-05-22
2002-08-20
Kwon, John (Department: 3754)
Fluid reaction surfaces (i.e., impellers)
Multiple axially spaced working members
C416S20400A
Reexamination Certificate
active
06435831
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas-turbine rotor. More specifically, the present invention relates to a gas-turbine rotor constructed by assembling a plurality of rotor discs.
2. Description of the Related Art
In a gas turbine, high pressure, high temperature combustion gas generated by burning fuel in high pressure combustion air is used for driving a turbine through which the energy of the combustion gas is converted into a mechanical output. Usually, combustion air is supplied by an axial-flow compressor driven by the turbine. Thus, usually the rotors of the axial-flow compressor and the output turbine are combined together to form an integral gas-turbine rotor. Further, the axial-flow compressor portion of the gas-turbine rotor is usually constructed by placing a number of rotor disks one next to another and by fastening the rotors in the axial direction using through bolts. Rotor blades of the axial-flow compressor are embedded on the outer peripheries of the respective rotor disks. In other words, an assembled gas-turbine rotor is used in the gas turbine.
FIG. 7
illustrates a general construction of an assembled rotor of a gas turbine. In
FIG. 7
, a gas-turbine rotor
1
is composed of a turbine rotor assembly
20
which generates rotary mechanical power from the flow of combustion gas and a compressor rotor assembly
10
connected to, and driven by, the turbine rotor assembly
20
through an intermediate shaft
25
. The gas-turbine rotor
1
in
FIG. 7
is a “cold end drive type” in which rotary mechanical power for driving an external load is taken from the compressor rotor assembly side end
15
.
As can be seen from
FIG. 7
, both of the turbine rotor
20
and compressor rotor
10
are composed of rotor disks. The rotor disks are placed one next to another in the axial direction and fastened together by through bolts. For example, in the compressor rotor
10
, rotor disks
50
having compressor rotor blades embedded on the outer peripheries thereof are placed one next to another in the axial direction, and all the rotor disks
50
are fixed together by spindle bolts
51
piercing through the rotor disks
50
in the axial direction.
As explained later, on the side faces of the respective rotor disks
50
, at the portions where the rotor disk abuts to adjoining rotor disk, grooves
33
having semicircular cross sections are formed in the radial direction. When the adjoining rotor disks are assembled together in such a manner that the grooves
33
of both rotor disks align, the pairs of semicircular grooves form circular holes
35
extending in radial directions. As explained later, torque pins
40
are inserted into the circular holes
35
.
FIG. 8
is a perspective view illustrating the grooves
33
and torque pins
40
of the compressor rotor disk
50
in detail. As can be seen from
FIG. 8
, an annular protrusion
53
concentric with the center of the rotor disk is formed on each of the side faces
50
a
of the rotor disc
50
. The annular protrusion
53
has a generally rectangular cross section. The inner periphery (i.e., the inner side wall)
53
a
and the outer periphery (i.e., the outer side wall)
53
b
of the annular protrusion
53
are formed as cylindrical surfaces concentric with the center of the rotor disk
50
. The top face
53
c
of the annular protrusion is formed a flat plane perpendicular to the center axis of the rotor disk
50
.
When the rotor disks
50
are assembled, the top face
53
c
of the annular protrusion
53
of the rotor disk
50
abuts the top face
53
c
of the annular protrusion of the adjoining rotor disk. Thus, the top faces
53
c
of the annular protrusions
53
of the adjoining rotor disks closely contact to each other when the spindle bolts
51
are fastened.
51
a
in
FIG. 8
designates bolt holes piercing through the respective rotor disks
50
for receiving the spindle bolts
51
.
As shown in
FIG. 8
, grooves
33
having semicircular cross sections are formed on the respective top faces
53
a
and extending in the radial direction. The grooves
33
, together with the grooves
33
on the top face
53
a
of the annular protrusion
53
of the adjoining rotor disk, form circular torque pin holes
35
which penetrate the annular protrusions
53
in the radial direction when the annular protrusions of the adjoining rotor disks are joined.
When the rotor disks
50
are assembled, a cylindrical pin (a torque pin)
40
is fitted into each of the torque pin holes
35
. The torque pins
40
function as keys for transmitting rotation torque between the adjoining rotor disks
50
and prevents relative angular movement between the rotor disks.
As can be seen from
FIG. 7
, since the number of the rotor disks
50
(i.e., the compression stages) of the compressor rotor assembly
10
is larger than the number of the rotor disks of the turbine assembly
20
, the axial length of the compressor rotor assembly
10
is larger than that of the turbine rotor assembly
20
. Further, in the cold end drive type gas-turbine rotor in
FIG. 7
, rotary torque is transmitted to an external load (such as a generator) from the turbine rotor assembly
20
via the compressor rotor assembly
10
. Therefore, the torque required for driving the external load, in addition to the torque required for driving compressor assembly
10
, must be transmitted from one rotor disk to the adjoining rotor disk during the operation of the gas turbine.
Further, a relatively steep temperature gradient along the axial direction is generated in the compressor rotor assembly during the operation of gas turbine. This causes the radial clearances of the bolt holes
51
a
relative to the spindle bolts
51
to change in accordance with the temperature gradient. Therefore, the radial clearances of the bolt holes
51
a
relative to the spindle bolts are different in the respective rotor disks
50
. Thus, though the spindle bolts
51
fasten the rotor disks
50
to each other in the axial direction, they cannot transmit a large torque between the rotor disks. Therefore, torque pins
40
are required for transmitting torque between the rotor disks.
During the operation of the gas turbine, centrifugal force due to the rotation of the gas-turbine rotor is exerted on the torque pins
40
. In order to prevent the torque pins
40
from coming out from the torque pin holes
35
due to the centrifugal force, a stopper flange
40
a
is formed on each of the torque pins
40
at the inner end thereof (i.e., the end of the torque pin located nearer the center of the rotor disk). Further, in order to prevent the torque pins
40
from falling out from the torque pin holes
35
due to their own weight when the gas-turbine rotor is at rest, another flange
40
b
is formed on each of the torque pins
40
at the outer end thereof (i.e., the end of the torque pin located far from the center of the rotor disk).
Usually, the stopper flange
40
a
is formed as a disk plate having flat faces on both sides thereof while the inner side wall
53
a
is formed as a cylindrical surface. Therefore, in order to ensure uniform contact between the flanges
40
a
and the inner side wall
53
a
when the centrifugal force is exerted on the torque pins
40
, the inner face
53
a
of the annular protrusion
53
must be machined flat, i.e., spot facing must be formed on the surface of the inner side walls
53
a
at the portion around the torque pin holes
35
where the flanges
40
a
contact the inner face.
However, since the spot facings must be formed on the inner side walls
53
a
of both annular protrusions
53
of the adjoining rotor disks continuously, the machining of the spot facings requires elaborate machining work.
In order to ensure uniform contact between the stopper flange
40
a
and both inner side walls
53
a
of adjoining rotor disks, the accuracy of the machining of the spot facings must be high. In order to obtain a high accuracy of the machining, the inner side walls
53
a
of the adjoining rotor disks must be machined to form spot facings in the c
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