JPS5993901A - Steam turbine moving blade - Google Patents

Abstract

PURPOSE:To make an accurate estimate of characteristic-frequency in time of rating on the basis of the characteristic-frequency of a moving blade at a standstill, by making a hook and a disc peripheral groove to be formed in an embedded part of the moving blade into a wedge type by the way of tilting them in an axial direction locking thereat with a clamping bolt. CONSTITUTION:A hook 10 projected from a embedded part 3 of a turbine moving blade 1 is tilted in the axial direction. Also a disc peripheral groove to be fitted in this embedded part 3 is made to be the same form. After the embedded part 3 is inserted into the disc peripheral groove, a clamping bolt 13 is tightened whereby both the moving blade 1 and disc are completely locked tight. In this way, in time of assembling, the moving blade and disc are secured tight enough so that accurate characteristic-frequency at the rating speed can be estimated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a steam turbine rotor blade having a Christmas tree-shaped implant for fixing the rotor blade to a disk.

[Technical background of the invention and its problems]

Generally, in a steam turbine plant, vibration management of turbine rotor blades is essential for safe and stable operation of the plant. This is because the steam turbine rotor blades are exposed to an excitation force with a frequency that is an integral multiple of the rotation speed caused by unbalanced vibrations of the turbine rotor, and an excitation force (hereinafter referred to as NPF) generated when the rotor blades cross the steam flow exiting the nozzle. If the natural frequency of the turbine rotor blade exists near the frequency of these excitation forces, the turbine rotor blade will resonate at the frequency of the excitation force, and the stress generated within the turbine rotor blade will become extremely large. This is because it causes cracks to occur in the turbine rotor blades. Once a crack occurs, it becomes larger and may eventually lead to a major accident in which the turbine rotor blades are blown off.

Therefore, when designing and assembling a turbine rotor blade, great care is taken to ensure that its natural frequency is sufficiently detuned from the frequency of the excitation force described above.

Its natural frequency is expressed by the following equation.

Nimoth Mishi Pi = Bi (ω)・Pot...I1) C, ω... Turbine rotation speed Pot... Primary surface vibration frequency at rest pi... Rotation speed ω i-th oscillation frequency Bi (ω2)
As is clear from equation (1), which is a function of the rotational speed with respect to the i-th natural frequency, there is a considerable difference between the natural frequency of the turbine rotor when it is stationary and the natural frequency when it is rotating. Measuring the natural frequency of a turbine rotor blade during rotation in a real-root plant requires a great deal of effort and is a very difficult problem. In addition, the natural frequency of the turbine rotor blade may differ from the predicted calculation performed at the time of design due to material inhomogeneities, manufacturing errors, and differences in the fixing conditions of the implanted part. Frequency analysis of the vibration at that time was performed to measure the natural frequency Poi at rest, and from equation (1) and the accumulated data, the natural frequency P1if at the rated rotation speed was calculated.
i-predictive and vibration management methods have been implemented.

Conventionally, because of its shape, the Christmas tree-shaped implanted portion has a larger load capacity against centrifugal force than other implanted portions, and thus has the characteristic that it can be made smaller in size. Therefore, it is very advantageous when designing a compact steam turbine. FIG. 1 shows an overall cross-sectional view when a turbine rotor blade having a Christmas tree-shaped implant is assembled into a turbine rotor. Moreover, FIG. 2 is a perspective view showing the details of the assembly part.

As shown in FIGS. 1 and 2, a turbine rotor blade 1 has a plate 2 at its root, and these are connected to a turbine rotor by an implant 3 shaped like a Christmas tree that protrudes from the plate 2. It is fixed to the disk 5 attached to the. That is, as shown in FIG. 2, the hook 6 provided on the Christmas tree-shaped implant 3 fits into the groove 8 provided in the implant 7 of the disk 5, so that the turbine rotor blade 1 is attached to the disk 5. installed. This assembly is performed using method 1, in which the turbine rotor blade 1 is inserted in the direction shown by the arrow in FIG. = It's on. By driving a key (not shown) into a key hole 9 formed in the center of the plate 2, removal in the direction of the arrow is prevented. In this way, the Christmas tree-shaped implanted part is formed of several stages of hooks (three stages shown), and there is an assembly gap between the hook 6 and the groove 8 for insertion in the direction of the arrow in Figure 2. . However, since the gap is very small, 0.05 m or less, the gaps between the upper row hooks become uneven due to manufacturing errors. Figure 3 shows an enlarged front view of the implanted part, showing the implanted part hooks 6.6', 6" and disk connections 8, 8', 8".
Let the gap between the two points be c,, cl, and c. At the time of design,
a CO= CI= C*TOL, the gap is determined so that each hook is in uniform contact. However, due to manufacturing errors)
Generally, Co'=Cx'=Cz.

Here, as an example, consider the case where Co<C1<02. That is, there is a normal gap between the hook 6 and the groove 80, but other gaps are large and there is almost no contact. In this case, the turbine rotor blade 1 is fixed to the disk 5 by only one hook. However, as the rotation of the turbine rotor increases, centrifugal force is applied to the implanted portion 3 in the direction of the arrow in FIG. Therefore, the implanted portion 3 moves in the direction of the arrow. This results in hooks 6', 6'' and groove 8'.

The gap with 8'' gradually decreases, and in order of decreasing gap (in this case CI<C2, hooks 6' and 8', hook 6''
and 8'I), the hooks make contact. In this way, as the rotation increases, the turbine rotor blade 1 is completely fixed to the disk 5. FIG. 4 shows the natural frequency of the turbine rotor blades relative to the rotational speed of the turbine rotor, where the horizontal axis is the rotational speed ω and the vertical axis is the natural frequency P.

All the thick solid lines show changes in the natural frequency when the hooks are in contact and the turbine rotor blade is completely fixed to the disk. Moreover, PR is the natural frequency at rest in that case. However, as mentioned above, the turbine rotor blades are not completely fixed due to the non-uniformity of each hook contact portion, so the natural frequency generally changes by one change as shown by the thin line. Also, for the same reason, the natural frequency at rest can be obtained as Pf, which can be measured much lower than PR. Then, as the rotation increases, the natural frequency changes along the thin line, but due to the centrifugal force mentioned above, the hooks start to come into contact with each other due to the increased assembly time. As shown, a discontinuous rise in the natural frequency occurs. Due to the change in part B, the implanted part is completely fixed and coincides with the thick solid line. As shown in an example in FIG. 4, a turbine rotor blade having a Christmas tree-shaped implanted portion generally has a natural frequency Pf obtained by striking the rotor blade when it is stationary, and a natural vibration with respect to the rotational speed. If the number change is predicted, it will be as shown by the dotted line, so the predicted natural frequency at the rated rotational speed ω1 will be a frequency different from the actual frequency (shown by the solid line).

Therefore, even if the natural frequency of the rated rotation speed predicted from Pf is detuned from the frequency of the excitation force mentioned above, the actual natural frequency may not be detuned, and accurate vibration management is not possible. Currently, this cannot be said to be the case, and the safe and smooth operation of turbine plants may be hindered.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned drawbacks, and the purpose of the present invention is to completely fix the Christmas tree-shaped implant to the disk so that the rated rotation speed is lower than the natural frequency of the turbine rotor blade when it is stationary. The object of the present invention is to provide a turbine rotor blade whose natural frequency can be accurately predicted at several times.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that the hook and the interlocking groove are inclined in the axial direction to form a wedge shape, and are fixed by tightening in the axial direction with a tightening bolt.

An embodiment of the present invention will be described below with reference to FIGS. 5 to 8. FIG. 5 is an assembled perspective view of the turbine rotor blade according to the present invention assembled into a disk. The structure is almost the same as a conventional Christmas tree-shaped implant, but the hook 10 protruding from the implant 3 and the groove 11 provided in the disk implant 7 have the same inclination with respect to the axis of the turbine rotor. When inserted, a 13 metal bolt is inserted into the bolt hole 12 provided in the implanted part 3 and tightened.

6 and 7 are a cross-sectional view of the assembled state and a view seen from the direction of the x arrow in FIG. 5, respectively. As shown in FIG. 6, the hooks lO of the implanted portion 3 are each inclined at an angle of θl with respect to the horizontal direction. Also, the implantation part 3
A gap C is provided between the disc 5 and the retaining disc 14 protruding from the disc 5.

Also, the fastening disk 14 has a screw hole 1 for the bolt 13.
5 is provided. Furthermore, as shown in FIG. 7, the turbine rotor is also tilted in the axial direction so as to have an angle of θ2. This inclination is the hook 10 and the hook 10' on the opposite side.
It is left-right symmetrical.

The grooves 11, 11' of the disk implant 7 also have a similar shape. FIG. 8 is a diagram showing the shape of the hook and groove in detail. As shown in FIG. 8, the width of the peak of the hook 10 of the implanted portion 3 is k dB, the height is hl, and that of the other end is 'ftd.
't, h7. Also, the length of the hook in the insertion direction is ft□. Similarly, the width of the valley of the groove 11 of the disc implantation part 7 is set to d2. d2', height is h2 t h, length is 4
shall be. Further, the arrows in FIG. 8 indicate the horizontal direction. Now the 6th
As shown in the figure, there is an angle θl between the horizontal direction and the insertion direction. In addition, since the hook 10 and the groove 11 are wedge-shaped, the width and height of the peaks and valleys are dl set.
1', h:)h', d2:)di, hz>M, so there is a relational expression expressed by equation (2).

As shown in FIG. 7, since the hook is inclined by 02 in the axial direction of the turbine rotor, there is a relationship between the peak heights as expressed by equation (3).

In addition, in order to set the gap cl between the implantation part 3 and the retaining disc 14, dI < d/M <h1', and the hook 1
so that it stops midway through the inserted sowing groove 11, so that all the hooks and grooves have this shape.

Since the present invention has such a structure, tightening is done by tightening the bolt 13 during assembly and insertion, and the implanted part moves along the wedge of each hook, so that the contact gap between each hook gradually becomes smaller. Then, by further tightening the bolts, the unevenness of the gap CI C due to the manufacturing error shown in Figure 3 is eliminated, and each hook is in contact with the groove, and the turbine rotor blade and disk are completely connected. It will be firmly established.

Also, during rotation, centrifugal force acts upward in Figure 6, and the implant tries to move along the taper with the inclination angle θlk provided on the hook, so the wedge-shaped hook becomes even tighter and more complete. It is possible to create fixed conditions. The retaining disc 14 also serves to prevent steam leakage in the insertion direction.

As is clear from the above, according to the present invention, since the turbine rotor blades are completely fixed to the disk during assembly, the fourth
This prevents incorrect vibration management due to incomplete fixation as shown in the figure, and enables appropriate vibration management by obtaining the natural frequency PR at rest and the predicted natural frequency at the correct rated rotation speed. Become.

Next, another embodiment of the turbine rotor blade according to the present invention will be shown. FIG. 9 is a perspective view showing the method and state of assembly.

Implanted portion 3a of turbine rotor blade 1a.

The disk implantation portion 7a has hooks and grooves 10a and lla' having the same shape as those described above.

Further, the turbine rotor blade 1b is rotationally symmetrical with respect to 1a, and the insertion direction is opposite to that of the turbine rotor blade 1b. Arrows A and B shown in FIG. 9 are the respective insertion directions.

Further, there is a bolt hole 16 in the plate 2a on the turbine rotor blade 1a, and a plate 2 on the turbine rotor blade 1b.
A screw hole 17 is provided in b to match the bolt hole 16. The two rotor blades are then tightened using bolts 18. FIG. 10 is a cross-sectional view showing the assembled state. As can be seen, the hooks are tilted in opposite directions, giving them a wedge shape. Also, when inserting, there is a play in the bolt hole 16 and screw hole 17) 2a and 2.
b has a gap C'. With such a structure, by tightening the bolt 18, the turbine rotor blades 1a and 1b are attracted to each other, the hook portions move along the wedge-shaped slope, and all the hook portions come into contact with each other. In this way, by tightening one bolt, the two turbine rotor blades are completely fixed to the disk, and the same effect as described above can be obtained.

〔Effect of the invention〕

As described above, the turbine rotor blade with the Christmas tree-shaped embedded part according to the present invention can achieve complete fixation of the rotor blade and disk during assembly, making it possible to accurately predict the natural frequency at the rated rotation speed. . Since the detuning of the natural frequency of the rotor blade from the frequency that is the excitation source of the vibration of the turbine rotor blade can be confirmed during assembly, reliable vibration management is possible. This eliminates scattering accidents and enables safe and smooth long-term operation of turbine plants.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a turbine rotor incorporating a turbine rotor blade with a Christmas tree-shaped implant, Figure 2 is a perspective view showing the implanted state, and Figure 3 is an enlarged front view of the implant. 4
5 is an assembled perspective view showing an embodiment of the present invention; FIG. 6 is a partially enlarged sectional view of FIG. 5; FIG. is a plan view in the direction of the x arrow in FIG. 5, FIG. 8 is an enlarged perspective view of the hook portion in FIG. 5, FIG. 9 is a perspective view showing another embodiment of the present invention, and FIG. It is a partially enlarged front view. 1, la, lb... Turbine rotor blades 3.3a, 3b... Implanted portion 4... Turbine rotor 5... Disc 6.6', 6'', 10.
14) a - Hook 8.8', 8", 11.lla
...Groove 13.18...Tightening bolt (7317) Representative patent attorney Kensuke Chika (and 1 other person) Fig. 1 Fig. 2 Fig. 3 Fig. 4 (A) υ Nol Fig. 5 Figure 6 Figure 8/1 Figure 9

Claims (1)

[Claims] The leg has a chestnut-shaped implanted part formed by a plurality of hooks, and this implanted part is fixed to the disc by fitting into a groove of the same shape provided on the outer circumference of the rotor disk. A steam turbine rotor blade, characterized in that the hooks and grooves are axially inclined to form a wedge shape, and are fixed by tightening in the axial direction with tightening bolts.