JP2002235501A - Rotor of gas turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress bending deformation of a stacking bolt end due to a centrifugal force during an operation in a rotor of a gas turbine. SOLUTION: Counter boring holes 17 and 18 are formed coaxially around the opening of a bolt hole 16 in the side surfaces of disk-like members 2 and 7 on the most front side and most back side. All disk-like members are integrally interconnected by fastening bolt screw parts 8a and 8b projecting from the bottom surfaces of respective counter boring holes 17 and 18 with nuts 9 and 10. A bolt support member 12 is screwed with a bolt overhanging part 8c projecting long from the back end surface 10a of the back nut 10. The bolt support member 12 has at its end a cap member 12a with a diameter slightly smaller than that of the counter boring hole 18. When a centrifugal force is applied to the bolt overhanging part 8c in an operation, the cap member 12a is restricted on the inner peripheral surface of the counter boring hole 18 to restrict the bolt overhanging part 8c in the radial direction, so that the bending deformation of the bolt 8 can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas turbine rotor in which a plurality of disk members are fastened together by stacking bolts and integrally connected. The present invention relates to a rotor of a gas turbine performed inside a counterbore provided.

[0002]

2. Description of the Related Art A gas turbine is provided with a rotor such as a turbine rotor and a compressor rotor. Each of these rotors has a configuration in which a plurality of disk-shaped members each having a rotor blade mounted on the outer periphery are stacked in the axial direction, a plurality of stacking bolts (hereinafter, referred to as bolts) are passed through them, fastened with nuts, and integrally connected. Has become. In such a rotor structure, after the disc-shaped members are overlapped by passing through the bolts, in order to transmit torque between the disc-shaped members, the bolts are pulled at the time of assembling and the tension of the bolts is increased to increase the tension between the disc-shaped members. It is necessary to strengthen the conclusion. There are two methods for pulling a bolt during assembly, as described in JP-A-2000-161777.

A first method is to apply a large torque to a nut screwed to a bolt end and rotate the nut to screw the nut into the bolt and pull the bolt.

[0004] In the second method, a nut is mounted in advance so that a large tension is not applied to the bolt, the bolt end protruding from the end face of the nut is gripped by a tool such as a bolt jack and pulled, and the nut is tightened. It is a method of fixing.

Further, regarding the structure of the nut fastening portion, as described in Japanese Patent Application Laid-Open No. 2000-161777, for example, counterbore holes are provided on the side surfaces of disk-shaped members located at both ends to prevent windage damage. In some cases, nuts are fastened to bolts. This nut is usually
A single nut is used as described in US Pat. Also, there is an example in which a double nut is used as described in JP-A-10-121903.

[0006]

In the first method of pulling a bolt at the time of assembling the rotor, the bolt is pulled by rotating the nut. Therefore, the bolt has not only a pulling force but also a frictional force between the bolt and the nut. Thus, there is a problem that even the originally unnecessary torsional force is added, and the torsional force continues to be applied even during the operation after the assembly due to the frictional force of the nut seat surface, so that the stress generated inside the bolt increases.

In the second method, since no rotational force acts on the bolt, unnecessary torsional force does not act on the bolt and there is no increase in stress as compared with the first method. For this reason, the tension can be increased by an amount corresponding to no increase in the stress.

[0008] With the recent improvement in gas turbine performance, the output generated with respect to the size of the gas turbine has been increasing. Therefore, the amount of torque transmitted between the disk-shaped members is also increasing, and the pulling force of the bolt is also increasing. The second method is more advantageous than the first method in increasing the bolt pulling force.

[0009] However, in the second method, the bolt extension protruding from the end of the nut becomes longer by the amount of grip of the jack. Therefore, when the rotor rotates at a high speed, the centrifugal force acting on the bolt overhang increases, and the bolt overhang bends, generating a bending stress at the bolt located near the nut seat surface, which is caused by the originally required tensile force. There is a possibility that the bolt may be damaged by exceeding the allowable stress due to the superposition of the tensile stress and the bending stress.

In particular, in order to cope with an increase in torque transmission accompanying an increase in the output of a gas turbine in recent years, it has become necessary to increase the bolt mounting radius position so as to increase the number of bolts. Increasing the bolt mounting radius increases the centrifugal force acting on the bolt overhang during operation. For this reason, the stress state of the bolt portion located near the nut seat surface becomes increasingly severe.

[0011] The above problems are caused by the use of a counterbored hole in a bolt fastening portion as disclosed in Japanese Patent Application Laid-Open No.
The same applies when the second method is applied to the method described in JP-A-121903. In particular, in the case of fastening with a double nut as in JP-A-10-121903, the bending stress generated in the bolt further increases because the weight of the outer nut is added.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a gas turbine rotor which can apply a tensile force to a bolt by gripping a bolt overhang portion with a tool at the time of assembling the rotor and can suppress bending deformation of the bolt overhang portion due to centrifugal force during operation. Is to provide.

[0013]

(1) In order to achieve the above object, the present invention provides a method of stacking a plurality of disk-shaped members having a plurality of bolt holes in a circumferential direction, passing bolts through the bolt holes and using nuts. In the gas turbine rotor integrally joined by fastening, in the plurality of disk-shaped members, a counterbore hole is provided around an opening of the bolt hole on at least one side surface of the disk-shaped member located at both ends, The nut is fastened to the bolt in the counterbore hole, and a bolt overhang portion is provided in the counterbore hole to protrude from an end face of the nut. At least one of the bolt overhang portion and the inner peripheral surface of the counterbore hole includes the bolt. It is assumed that a cap-shaped bolt support member for restraining bending deformation of the overhang portion is provided.

By providing the bolt extension projecting from the end face of the nut as described above, the bolt can be tensioned by gripping the bolt extension with a tool during assembly of the rotor. In addition, by providing a bolt support member on at least one of the bolt overhang portion and the inner peripheral surface of the counterbore hole, when the bolt overhang portion is to be bent by centrifugal force during operation, the bending deformation is caused by the bolt support member. As a result, the bending deformation of the bolt is suppressed, and as a result, the bending stress generated in the bolt portion located near the nut seat surface is reduced, and the possibility of the bolt being damaged can be reduced.

(2) In the gas turbine rotor according to the above (1), preferably, the bolt supporting member is provided on the bolt extension portion side, and an outer peripheral surface of the bolt supporting member and the counterbore hole are formed. A minute gap is set between the inner peripheral surface and the inner peripheral surface due to the centrifugal force at the time of operation so that the two are in contact with each other and the bending of the bolt extension is restricted.

Thus, the bolt supporting member restrains the bending deformation of the bolt extension.

(3) In the gas turbine rotor according to the above (1), preferably, the bolt support member is provided on the counterbore side, and an inner peripheral surface of the bolt support member and the bolt extension portion are provided. A small gap is set between the outer peripheral surface of the bolt and the outer peripheral surface thereof due to the centrifugal force during operation to restrict the bending deformation of the bolt extension.

[0018] This also allows the bolt supporting member to restrain the bending deformation of the bolt extension.

(4) In the gas turbine rotor according to the above (2) or (3), preferably, the minute gap is 0.1 mm to 1.0 mm.

Thus, the bolt supporting member can be incorporated even if there is a dimensional error or an assembly error between the plurality of disk-shaped members, and the bending deformation of the bolt extension can be restrained.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

In the following embodiments, the present invention is applied to a turbine rotor as a gas turbine rotor. First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an axial cross-sectional view of the turbine rotor according to the present embodiment in which an upper half rotor blade is omitted, and FIG. 2 is a side view as viewed from an arrow A in FIG.

In FIG. 1, reference numeral 1 denotes a turbine rotor, and the turbine rotor 1 has a first disk-shaped member 2,
The second disk-shaped member 3, the third disk-shaped member 4, ...
N disk-shaped members 5, (N-1) -th disk-shaped member 6, N-th disk-shaped member 7, and bolts 8 penetrating all of the disk-shaped members
And nuts 9 and 10 fastened to bolt screw portions 8a and 8b at both ends of the bolt 8, and a cap-shaped bolt support member 12 screwed to a bolt extension 8c protruding from an end face 10a of the nut 10. It has.

The combustion gas flows rightward as shown by arrow 13 in FIG. In this specification, the upstream side (the left side in the figure) is referred to as the front side, and the downstream side (the right side in the figure) is referred to as the rear side with reference to the flow direction 13 of the combustion gas.

The first disk-shaped member 2 is a flange portion of the rotor intermediate shaft 14 located on the front side, and the N-th disk-shaped member 7 is a flange portion of the rotor rear shaft 15 located on the rear side. Further, the second disk-shaped member 3 and the (N-1) th
The disk-shaped member 6 is a turbine disk for extracting an output from the combustion gas, and has a plurality of moving blades (not shown) attached to an outer periphery thereof. The third disk-shaped member 4 and the (N-2) th disk-shaped member 5 are spacers.

Each of the above disk-shaped members is overlapped in the axial direction, and a plurality of bolt holes 16 are formed in the circumferential direction thereof so that bolts 8 can be inserted across all the disk-shaped members. . On the front side surface of the first disk-shaped member 2 and the rear side surface of the N-th disk-shaped member 7, a cylindrical counterbore hole 1 is formed coaxially around the opening of each bolt hole 16.
7 and 18 are formed, and bolt screw portions 8a and 8b at both ends of the bolt 8 project from the bottom surfaces of the counterbore holes 17 and 18 with the bolt 8 passed through the bolt hole 16, respectively. By fastening the nuts 9 and 10, all the disk-shaped members are integrally connected. These disc-shaped members apply a surface pressure to the contact surfaces of the disc-shaped members due to the pulling force of the bolts 8, and transmit torque by the frictional force of the contact surfaces.

When the nuts 9 and 10 are fastened, the nuts 9 and 10 are lightly fastened in advance, and then the bolt overhang 8c of the bolt screw portion 8b on the rear side is pulled with a bolt jack. Further, by tightening and fixing, an appropriate tension is applied to the bolt 8. For this reason, in particular, the bolt extension 8c of the bolt screw portion 8b of the bolt 8 protrudes from the rear end face 10a of the nut 10 by an amount for gripping the bolt jack. In this method, since the bolt 8 is not pulled by the rotation of the nut 10, there is no increase in stress generated in the bolt 8 due to twisting.
Also in the case of disassembly, the nut 10 can be loosened by pulling the bolt overhanging portion 8c of the bolt screw portion 8b, and there is no problem even if the nut seating surface 10b is contaminated due to a change over time in operation. Bolt support member 12 is nut 1
Screwed in after tightening 0.

The bolt 8 has an overall length slightly shorter than the overlapping length of all the disc-shaped members.
10, both ends of the bolt 8 including the bolt support member 12 are arranged to be accommodated in the counterbore holes 17 and 18, respectively. The nut 9 and the bolt screw portion 8a are located inside the counterbore hole 17 provided in the first disk-shaped member 2, that is, inside the side surface of the first disk-shaped member 2, and the nut 10, the bolt screw portion 8b, and the bolt support member 12 It is located in the counterbore hole 18 provided in the N-th disk-shaped member 7, that is, inside the side surface of the N-th disk-shaped member 7, thereby providing the nuts 9, 10; the bolt screw portions 8a, 8b;
Winding and noise rise due to the rotation of 2 are suppressed.

The bolt support member 12 is screwed to the bolt extension 8c of the bolt thread 8b so as to contact the rear end face 10a of the nut 10. The bolt support member 12 has a cap member 12a having a slightly smaller diameter than the counterbore hole 18 at one end, and a female screw hole 12b formed at the center of the cap member 12a.
It is screwed to the bolt overhang 8c at b.

The length of the bolt supporting member 12 in the axial direction is substantially the same as the length of the bolt projecting portion 8c protruding from the rear end face 10a of the nut 10. As a result, the bolt supporting member 12 is connected to the bolt projecting portion. In a state where the cap member 12a is attached to the rear end face 8c, the rear side surface of the cap member 12a substantially coincides with the rear end surface of the bolt extension 8c in the axial direction.

The cap member 12a of the bolt support member 12
Has a ring shape whose outer diameter is slightly smaller than the inner diameter of the counterbore hole 18, as shown in FIG. 2, and a gap δ1 is formed between the outer periphery of the cap member 12a and the inner peripheral surface of the counterbore hole 18. Is formed. The purpose of the cap member 12a is to restrain the bending deformation of the bolt extension 8c during rotation of the rotor. Therefore, the gap δ1 is set to be smaller than the bending deformation δ2 (described later) of the bolt 8. Here, in order to restrain the bending deformation of the bolt extension 8c, the gap δ1 should be as small as possible. However, in practice, when the bolt 8 is inserted into the bolt hole 16 due to a dimensional error in forming the bolt hole 16 or the counterbore hole 18 of each disk-shaped member or an assembly error when connecting the disk-shaped members. A certain amount of displacement occurs inevitably between the axial center position of the shaft 8 and the axial center position of the counterbore hole 18. The gap δ1 is set such that the displacement is allowed, and the cap member 12a of the bolt support member 12 screwed into the bolt screw portion 8b is securely fitted in the counterbore hole 18. As an example, δ1 = 0.5 mm.

On the end face of the cap member 12a, three grooves 20 are formed radially at regular intervals of about 120 degrees as shown in FIG. The bolt support member 12 is screwed to the bolt extension 8c by inserting a tool into the three grooves 20 and rotating the bolt.

Next, the operation of the bolt support member 12 will be described.

During operation of the gas turbine, the turbine rotor 1 rotates at a high speed by receiving the energy of the combustion gas, and a centrifugal force F acts on the bolt overhang 8c located in the counterbore holes 17, 18. At this time, if the bolt support member 12 is not attached to the bolt overhang 8c as in the prior art, there is nothing to restrict the bolt overhang 8c in the radial direction, and as shown in FIG. 8c causes a bending deformation of δ2, and the bending deformation δ2 generates bending stress in the X portion (the bolt 8 located near the nut seating surface 10b) in FIG. The bending stress generated in the X portion overlaps with the tensile stress due to the tensile force of the bolt 8 added in advance at the time of fastening the nut, and if it exceeds the allowable stress of the bolt 8, the bolt 8 may be damaged.

On the other hand, in the present embodiment, the bolt support member 12 is provided as described above, and the cap member 1 is provided.
A gap δ1 between the outer periphery of 2a and the inner periphery of the counterbore hole 18 is set smaller than the bending deformation δ2 of the bolt extension 8c. Therefore, when the bolt 8 is bent and deformed by the centrifugal force F acting on the bolt overhang 8c, the cap member 12a of the bolt support member 12 is moved to the inner peripheral surface of the counterbore hole 18 before the bolt overhang 8c bends by δ2. To restrain the bolt extension 8c in the radial direction. Thereby, the bending deformation of the bolt extension 8c caused by the centrifugal force F is reduced, and the bending stress generated in the X portion (the bolt portion located near the nut seating surface 10b) is also reduced.

The gap δ1 between the inner peripheral surface of the counterbore hole 18 and the cap member 12a is preferably 0.1 mm to
1.0 mm, and in the present embodiment, δ1 = 0.5 mm
It is.

As described above, the gap δ1 should be as small as possible in order to suppress the bending deformation of the bolt extension 8c. However, when the bolt 8 is inserted into the bolt hole 16 due to a dimensional error at the time of forming the bolt hole 16 or the counterbore hole 18 of each disk-shaped member or an assembly error at the time of coupling the disk-shaped member, the shaft of the bolt 8 is The center position and the axial center position of the counterbore hole 18 are inevitably displaced to some extent. If the gap δ1 is too small, the cap member 12a of the bolt support member 12 cannot enter the counterbore hole 18.
As a result of the study, it is possible to fit the cap member 12a of the bolt support member 12 in the counterbore hole 18 by increasing the processing accuracy of the bolt hole 16 and the counterbore hole 18 if the gap δ1 is at least about 0.1 mm. I got the confirmation. On the other hand, if the gap δ1 is too large, δ1> δ2, and the bending deformation of the bolt extension 8c cannot be restricted. Although it depends on the material of the bolt 8, the allowable maximum bending deformation of the bolt overhang 8c is about 1.0 mm, and if the gap δ1 is at most about 1.0 mm, the bolt overhang 8
It was found that c was effective in restraining bending deformation.

As described above, according to the present embodiment, the bending deformation of the bolt extension 8c is suppressed by the constraint of the cap member 12a of the bolt support member 12, the bending stress generated in the X portion is reduced, and the bolt 8 Can be reduced.

Further, since the bolt support member 12 is brought into contact with the rear end face 10a of the nut 10 and screwed, the loosening of the nut 10 is suppressed by the action of the double nut, and there is an effect that the nut 10 is more securely fastened.

Further, since the bolt supporting member 12 is installed so as to cover most of the opening of the counterbore hole 18 except that it has a gap δ1 on its outer periphery, even when the turbine rotor 1 is rotating at high speed, the counterbore hole 18 is provided. Ambient air can be prevented from entering the interior of the vehicle. Therefore, the turbine rotor 1 hardly receives the air resistance due to the counterbore hole 18, and the loss (windage loss) of the power of the gas turbine and the noise can be reduced.

A second embodiment of the present invention will be described with reference to FIG. In the figure, parts that are the same as the parts shown in FIG.

In FIG. 4, a groove 21 is formed on the end face of the bolt extension 8Ac of the bolt 8A. The vicinity of the inner periphery of the bolt support member 12A is caulked and fixed so as to bite into the groove 21. This makes it possible to prevent the bolt support member 12A from becoming loose. After swaging the cap support member 12A into the bolt overhang portion 8Ac, the caulking of the cap member 12Aa is performed.
Position 22 near groove 21 on end face of cap member 12Aa
It can be performed by driving a tool such as a center punch into the center.

According to the present embodiment, the fastening of the nut 10 is further ensured in combination with the action of the double nut,
The reliability of the bolt 8A can be improved.

The bolt extension 8A near the groove 20
By loosening the end face c and the counterbore hole 18 into the groove 20, the loosening of the bolt supporting member 12A can be similarly prevented.

A third embodiment of the present invention will be described with reference to FIG. In the figure, parts that are the same as the parts shown in FIGS. 2 and 4 are given the same reference numerals, and descriptions thereof will be omitted. In the present embodiment, a bolt support member for restraining bending deformation of the bolt extension is provided on the counterbore hole side.

In FIG. 5, a female screw is formed on the inner peripheral surface of the counterbore hole 18A, and a cap-shaped bolt support member 23 is screwed into the counterbore groove 18A.

The bolt support member 23 has a bolt through hole 23b having a diameter slightly larger than the outer diameter of the bolt extension 8c.
Has a ring-shaped cap member 23a formed at one end thereof, and has a male screw cut on the outer periphery thereof and is screwed to a female screw on the inner circumferential surface of the counterbore hole 18A. A gap δ1A is formed between the inner periphery of the bolt through hole 23b of the cap member 23a and the bolt extension 8c, and the rear side surface of the cap member 23a is substantially aligned with the rear end face of the bolt extension 8c in the axial direction. I have.

The gap δ1A in the present embodiment can also be used without disturbing the reliable installation of the bolt support member 23 and at the bolt extension 8 by the cap member 23a.
As in the first embodiment, it is desirable to set the thickness to 0.1 mm to 1.0 mm in order to fulfill the bending deformation restraining function of c.

The bolt supporting member 23 constructed as described above
According to the above, when the bolt 8 is bent and deformed by the centrifugal force F acting on the bolt overhang 8c, the bolt overhang 8c
Before the second bending deformation occurs, it contacts the inner periphery of the bolt through hole 23b of the cap member 23a and restrains the bolt extension 8c in the radial direction, so that the bending stress generated in the X portion as in the first embodiment. And the possibility of the bolt 8 being damaged can be reduced.

Further, according to the present embodiment, similarly to the first embodiment, the effect of reducing windage and noise of the power of the gas turbine can be obtained.

The bolt support member 23 can be caulked and fixed by driving the vicinity of the inner periphery of the counterbore hole 18A into the groove 20 of the cap member 23a.

In the above embodiment, the flanges of the rotor intermediate shaft 14 and the rotor rear shaft 15 constitute the disk members on the frontmost and rearmost sides, respectively, and the bolt holes 16 provided on the respective side surfaces are formed. The present invention is applied to a structure in which a counterbore hole 18 is formed around the periphery, but a counterbore hole is formed in a turbine disk provided with a rotor blade located at the forefront side or the rearmost side, and a nut is fastened. The present invention can be similarly applied to a device.

In the above embodiment, the structure in which the bolt supporting members 12, 12A or 23 are provided is applied to the turbine rotor 1, but may be applied to the compressor rotor.

[0054]

According to the present invention, it is possible to apply a tension to the bolt by gripping the bolt overhang portion with a tool at the time of assembling the rotor, and to bend the bolt overhang portion due to centrifugal force during operation. When bending, the bending deformation is constrained by the bolt support member and bending deformation of the bolt is suppressed. As a result, bending stress generated in the bolt portion located near the nut seating surface is reduced, and the possibility of bolt damage is reduced. it can.

[Brief description of the drawings]

FIG. 1 is an axial cross-sectional view of a turbine rotor according to a first embodiment of the present invention, in which an upper half rotor blade is omitted.

FIG. 2 is a side view of the turbine rotor viewed from an arrow A (rear) in FIG.

FIG. 3 is a diagram for explaining that bending deformation occurs in a bolt overhang due to centrifugal force.

FIG. 4 is a side view of a turbine rotor according to a second embodiment of the present invention as viewed from behind, and is an enlarged view of one counterbore;

FIG. 5 is a side view of a turbine rotor according to a third embodiment of the present invention as viewed from behind, and is an enlarged view of one counterbore;

DESCRIPTION OF THE REFERENCE NUMERALS 1 Turbine rotor 1A according to first embodiment 1A Turbine rotor 1B according to second embodiment 1B Turbine rotor according to third embodiment 2 First disk-shaped member 3 Second disk-shaped member 4 Third Disc-shaped member 5 No. (N-2) Disc-shaped member 6 No. (N-1) Disc-shaped member 7 N-th disc-shaped member 8, 8A Bolt (stacking bolt) 8a, 8b Bolt thread 8c, 8Ac Bolt overhang 9, DESCRIPTION OF SYMBOLS 10 Nut 10a Nut rear end surface 10b Nut seat surface 12, 12A Bolt support member 12a, 12Aa Cap member 12b Screw hole 13 Combustion gas flow direction 14 Rotor intermediate shaft 15 Rotor rear shaft 16 Bolt hole 17, 18, 18A Counterbore hole 20 Groove 21 Groove 22 Position near Groove 23 Bolt Support Member 23a Cap 23b bolt holes F centrifugal force δ1, δ1A gap δ2 bending deformation amount

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Manabu Matsumoto 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Power & Electric Development Laboratory, Hitachi, Ltd. 7-2-1, Hitachi, Ltd. Power and Electricity Development Laboratory (72) Inventor Tsuyoshi Takano 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture F-term (Hitachi, Ltd. Electric Power and Electricity Development Laboratory) Reference) 3G002 AA05 AB00

Claims (4)

[Claims] 1. A gas turbine rotor comprising: a plurality of disk-shaped members having a plurality of bolt holes arranged in a circumferential direction; a bolt being inserted through the bolt holes and fastened by a nut; A counterbore hole is provided around the opening of the bolt hole on at least one side surface of the disc-shaped member located at both ends of the shape member, and the nut is fastened to the bolt in the counterbore hole, and the counterbore is formed in the counterbore hole. A bolt overhang protruding from an end face of the nut is provided, and at least one of the bolt overhang and the inner peripheral surface of the counterbore hole is provided with a cap-shaped bolt support member that restrains bending deformation of the bolt overhang. Characteristic gas turbine rotor. 2. The gas turbine rotor according to claim 1, wherein the bolt support member is provided on the bolt extension portion side, and between an outer peripheral surface of the bolt support member and an inner peripheral surface of the counterbore hole. A small gap that is set in such a manner that the two parts come into contact with each other due to centrifugal force during operation and restrict the bending of the bolt extension. 3. The gas turbine rotor according to claim 1, wherein the bolt supporting member is provided on the counterbore side, and between an inner peripheral surface of the bolt supporting member and an outer peripheral surface of the bolt extension. A small gap which is set in such a manner that the two parts come into contact with each other by centrifugal force during operation and restrain bending deformation of the bolt overhang portion. 4. The gas turbine rotor according to claim 2, wherein said minute gap is 0.1 mm to 1.0 mm.