JPS6350601A - Steam turbine - Google Patents

Abstract

PURPOSE:To prevent reduction in the coupling strength of a plantation section, by forming an oxide film on the surfaces of a rotor disk and a moving blade, prior to fixing the moving blade. CONSTITUTION:Prior to fixing a moving blade 7 to a rotor disk 6, the rotor disk 6 and the moving blade 7 are put in a thermostatic chamber at a temperature below transformation temperature for a given time. As a result, an oxide film 21 consisting of a layer free from thermal refining 23 and an oxide layer 24 are formed on the surfaces of the rotor disk 6 and the moving blade 7, thereby allowing the plantation section of the moving blade to be free from erosion and the coupling strength thereof to be maintained.

Description

Detailed Description of the Invention (Objective of the Invention) (Industrial Application Field) The present invention relates to a steam turbine, and is particularly suitable for protecting rotating bodies such as a rotor disk and rotor blades from a severe corrosive environment. Regarding air turbines.

(Prior Art) Generally, in a steam turbine, as shown in FIG. 4, both the inner and outer ends of a large number of nozzle blades 1 arranged sequentially in the circumferential direction are integrated into a nozzle inner ring 2 and a nozzle outer ring 3. This nozzle outer ring 3 is fixed to the casing 4 to form a stationary part, and also to the rotor disk 6 which is integrated with or fitted into the rotating shaft 5! J [7 is planted to constitute a rotating section, and this stationary section and rotating section form one stage. A steam turbine is constructed by combining a plurality of these stages in the axial direction.

In such a steam turbine, steam, which is a working fluid, flows approximately axially through an annular passage formed by a nozzle inner ring 2 and a nozzle outer ring 3, and passes through the nozzle blades 1 with sufficient swirling force. The swirling force of the steam enters the rotor blades 7, where the swirling force of the steam is converted through the rotor blades 7 into a rotational force of 1 rotation 5. The steam flowing out from the rotor blades 7 flows into the next stage and repeats the same three glue operations. Here, a space 8 surrounded by the nozzle inner ring 2 and the mouth disk 6 is filled with steam leaking from the labyrinth packing 9, and the steam pressure P1 in this space 8 is the steam downstream of the moving blade 7. pressure P2
It is higher than that.

As shown in FIGS. 5 and 6, a plurality of dynamic TAs 7 that convert the thermal energy of steam into rotational energy are installed in the circumferential direction of the rotation @ 5, and the installation method is as follows. The dub dill structure is adopted. This dovetail structure has two hooks on the outer periphery of the rotor disk 6.
A dove dill groove 12 that forms the dove dill 10 of the stage and engages with the dove dill 10 in the implanted portion 11 of the rotor blade 7.
, and in the notch formed in one place of the rotor disk 6!
J+m7 is inserted in the radial direction, and the rotor blades 7 are moved circumferentially from this notch along the dovetail 10 to be sequentially assembled. Therefore, when a gap 13 is formed between the implanted portions 11 of adjacent rotor blades 7, the tangential restraining force in the implanted portions 11 becomes weaker, causing variations in the natural frequency of the incorporated rotor blades 7. arise, this (i!a'
If the fiG frequency matches the auxiliary frequency due to fluctuations in the impulse force of the steam flowing at the nozzle blade 1 outlet, the rotor blade 7 may be damaged. The blade tips are connected by a shroud band 14, and the gap 13 is made as small as possible.

(Problems to be Solved by the Invention) However, with the current assembly technology, it is difficult to reduce the gap 13 to zero, and it is difficult to reduce the gap 13 to zero due to elastic deformation of the implanted portion 11 during turbine operation. Since this cannot be avoided, during turbine operation, steam enters through the gap 13 and flows out to the downstream side of the rotor blade A where the pressure is lower. Therefore, the steam that entered through the gap 13,
There has been a problem in that the impurities contained in the steam fill and remain in the gap 15 formed at the engaging portion between the dove dill 10 and the dove dill groove 12, and are deposited in the gap 15 at the engaging portion. In particular, in geothermal turbines that use geothermal natural air as the fluid, the geothermal steam contains a large amount of scale and corrosive substances, so a large amount of corrosive substances accumulate in the gap 15, and furthermore, the rotor circle Rotating bodies such as the plate 6 and rotor blades 7 have high relative speeds with the working fluid and are exposed to high stress conditions. The degree of erosion by the Il fluid increases, and the rotor disk 6 and rotor blades 7 around the engagement portion corrode, reducing the engagement strength, and in the worst case, cracks 16 may occur in the implanted portion 11. There was a problem that the rotor blades 7 were scattered.

Therefore, the purpose of the present invention is to solve the above-mentioned problems of the prior art. An object of the present invention is to provide a steam turbine that can maintain the engagement strength of an implanted part.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention forms an oxide film on the surfaces of the rotor disk and the rotor blade before assembling the rotor blade.

(Function) The present invention will be described in detail based on the above configuration. Since an oxide film is formed on the surfaces of the rotor disk and the rotor blade, the metal surfaces of the rotor disk and the rotor blade can be protected from a corrosive environment.

Therefore, it is possible to prevent a decrease in the strength of the engagement portion between the rotor disk and the rotor blade due to corrosion, prevent cracks from occurring in the rotor blade implantation portion, and obtain a highly reliable steam bottle.

(Example) Hereinafter, an example of a steam turbine according to the present invention will be described with reference to FIGS. 1 to 3. Note that the same reference numerals are used for parts that are the same as in the prior art.

In FIG. 1A, reference numeral 7 indicates a rotor blade, and each J yellow 7 is incorporated into the rotor disc 6 by a dovetail structure, and the dovetail 10 formed on the outer periphery of the rotor disc 6 and each rotor blade 7 are A dovetail groove 12 formed in the implanted portion 11 is engaged. As shown in FIG. 1B, an oxide film 21 is formed on the surfaces of the rotor disk 6 on which the dovetail 10 is integrally formed and the rotor blade 7 on which the implanted portion 11 is formed integrally. This oxide film 21 is formed by leaving the rotor disk 6 and the dynamic cuff in a thermostatic chamber at a temperature below the A1 transformation temperature for a certain period of time before assembling the rib W, and is formed on the surface of the base steel 22. The non-tempered layer 2 is formed by Cr, P, etc. contained in the stone.
3 and an oxide layer 24 formed on top of the oxide layer 24. The temperature at which the oxide film is formed in the constant temperature bath has been determined empirically from a series of corrosion tests, and it has been found that 300°C or 400°C is preferable.

Figures 2 and 3 are rotor materials for geothermal turbines.
The results of a corrosion test of r-No-V steel in 3% saline solution are shown. In the figure, the symbol indicates that no oxide film was formed, and the symbol indicates that the steel was left in a constant temperature bath at 300'C for 10 hours. The WA symbol indicates that the product was left in a constant temperature bath at 400°C for 10 hours. As is clear from the above test results,
It can be seen that when the corrosion loss a of the metal with the oxide film formed is reduced, the fatigue life against corrosion is improved, and the oxide film is effective as a protective film for metal materials in a corrosive environment.

By forming the oxide film 21 on the surfaces of the rotor disc 6 and 1FJJH7 in this way and then incorporating the rotor A7, steam can enter from the gap 13 of the adjacent 8-tone implantation part 11 during operation, and the rotor Even if corrosive substances in the steam accumulate in the gap 15 formed at the engagement portion between the disk 6 and the rotor blade 7,
The metal surfaces of the rotor disk 6 and the dynamic W7 are not subject to corrosion. Therefore, the engagement strength of the implanted portion 11 of the rotor blade can be maintained, and it is possible to prevent the occurrence of cracks 16 in the implanted portion 110, which can directly lead to a serious accident such as flying off the rotor blade.

The oxide film 21 must be formed when a new turbine is installed or when new parts are installed due to repairs or the like.

In addition, instead of forming an oxide film in a constant temperature bath as described above, salt bath nitrocarburizing is performed in an atmosphere of cyanate (MCN) or cyanate (MCNO-1), or gas soft nitriding is performed in an atmosphere of N2-13 gas. A similar effect in terms of corrosion resistance can be obtained by avoiding hardening of the rotor disk and rotor blade surfaces by nitrocarburizing or various carburizing operations.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, since an oxide film is formed on the surfaces of the rotor disk and rotor blades before the rotor blades are assembled, a decrease in the engagement strength of the rotor blade implantation part due to corrosion is prevented. This makes it possible to prevent the occurrence of cracks in the rotor blade implant, which can directly lead to serious accidents. Therefore, a highly reliable steam turbine can be obtained.

[Brief explanation of drawings]

FIG. 1A is a perspective view showing the rotor disk and rotor blades of the steam turbine according to the present invention, and FIG. 1B is the △ portions d3 and 8 of FIG. 1A.
Figures 2 and 3 are diagrams showing the corrosion test results of the rotor shaft for a geothermal turbine. Figure 4 is a sectional view of one stage of the steam turbine. Figure 5 is the dovetail structure of the steam turbine. 6 is an exploded perspective view, and FIG. 6 is a front view showing a state in which the rotor blades are assembled into the rotor disk. 6... Rotor disk, 7... Moving blade, 10... Dovetail, 11... Implanted part, 12... Dovetail groove, 1
3.15... Gap, 21... Oxide film, 22...
Subway, 23...out of order? 1 layer, 24... oxidized layer. Applicant's agent Sato - Male muscle IA figure 5 Interval between eating days (days) Yu 2 Number of flat records N Muscle 3 Figure 4 Figure 5

Claims (1)

[Claims] A steam turbine in which a hook part is formed on the outer periphery of a rotor disk that is integrated with or fitted into the rotating shaft, and a plurality of moving blades are assembled around the rotating shaft by engaging the implanted part of the moving blade with the hook part. A steam turbine characterized in that an oxide film is formed on the surfaces of the rotor disk and the rotor blades before the rotor blades are assembled.