JPH0635808B2 - Turbin blade - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a turbine rotor blade, and in particular, it is intended to suppress wear of a joint surface between the rotor blade and the shroud and prevent damage to the shroud. Regarding turbine blades.

(Prior Art) Generally, in the first paragraph of a steam turbine, the pressure and temperature are higher than those in the other paragraphs, and the temperature change rate accompanying the load change rate is also large, so a nozzle box structure that can withstand harsh operating conditions is adopted. Has been done. As shown in FIG. 4, a steam turbine having this nozzle box structure has a container-shaped nozzle box 2 in which high-temperature, high-pressure steam generated in a boiler (not shown) passes through an inlet pipe 1 and is sealed except at an inlet and an outlet. Inside steam room 3
Flow out into the first stage nozzle 5 at the nozzle opening 4 which is the outlet of the nozzle box, and is discharged to the first stage moving blade 6, where the first stage moving blade 6 effectively absorbs the velocity energy of the steam. It drives the rotor 7. The nozzle box 2 is
As shown in FIG. 5, four steam chambers 3a to 3d are provided. The steam first flows into the first steam chamber 3a, is accelerated by the first stage nozzle 5 and flows out to the first stage moving blade 6. It When the turbine load is increased, the steam is generated in the second steam chamber 3b and the third steam chamber 3b.
The steam chamber 3c and the fourth steam chamber 3d sequentially flow into the steam chamber 3c and the fourth steam chamber 3d.

As described above, since the high-temperature and high-pressure steam that has flowed out of the first-stage nozzle 5 acts on the first-stage moving blades 6, normally, the shroud attached to the blade tips to maintain the inter-blade pitch is It has a double shroud structure to withstand high temperature and high pressure. FIG. 6 shows a double shroud structure in which a Christmas tree type rotor blade is used for the first stage rotor blade 6, and an inner shroud 10 is integrated with the blade at the tip of the blade effective portion 9 outside the implanting portion 8. The inner shroud 10, and a tenon 11 is projected on the outer surface of the inner shroud 10, and a thin plate-shaped outer shroud 12 is attached to the tenon 11.
By crimping 1, the double shroud 13 in which the inner shroud 10 and the outer shroud 12 are joined together is obtained.

However, it has become clear that the recent increase in the capacity of the turbine causes deformation of the shroud 13 having the double structure. The cause of this deformation will be described below. FIG. 7 shows the steam force acting on the first-stage rotor blade 6 for each load, and is a first valve of a steam control valve (not shown) for allowing steam to flow into the first steam chamber 3a of the nozzle box 2. Open 14
Has the largest steam power, and the second valve is opened 15 to allow steam to flow into the second steam chamber 3b, the third valve is open 16 to allow steam to flow into the third steam chamber 3c, and the fourth steam chamber 3d is It is shown that the steam force used for the rotor blade becomes smaller as the load increases sequentially when the fourth valve is opened 17 for allowing steam to flow in. This steam power P _U (Kg) is Required by. Here, K is an output conversion coefficient, KW is a paragraph output, D is a moving blade pitch diameter, n is the number of moving blades, θ is a nozzle opening angle, N is a rotor rotation number, and K, D, n, N Is constant regardless of the load. Therefore, it is known from the above formula (1) that the steam force P _U is affected by the paragraph output KW and the nozzle opening angle θ, and that the paragraph output KW does not change so much, so the nozzle opening angle θ Is 90 °, which is the smallest, and the steam power at the time of opening the first valve 14 is the maximum, and if the turbine is operated for a long time in this state, the condition becomes severe in terms of strength.

Further, FIG. 8 shows a steam flow in the first stage nozzle 5 and the first stage moving blade 6 at the time of partial load, for example, at the time of opening 14 of the first valve. The steam force P _U of the steam that has passed through the steam flow path of the first-stage nozzle 5 acts on the first-stage rotor blades 6 intermittently due to the rotation of the rotor blades. Vibration is generated, and the magnitude of the vibration is the steam force P _U as shown in the figure.
The bending force due to is as high as Q = Y _DY / Y _ST times.

Further, as shown in FIG. 9, the steam temperature in the first paragraph of the turbine changes depending on the load and becomes higher as the valves are sequentially opened from the time of opening the first valve 14. However, since the absolute value of the temperature is not so different between the first valve open time 14 and the fourth valve open time 17, it can be said that the first valve open time 14 is under severe conditions of high temperature.

As described above, when the turbine is operated under the above-mentioned severe conditions of material strength, the double shroud 13 of the first stage rotor blade 6, particularly the outer shroud 12, has steam as shown in FIG. Since the bending force due to the steam force P _U and the centrifugal force due to the rotation of the rotor as shown in FIG. 11 act at the same time, there is a risk that the outer shroud 12 may be swollen outward or damaged. The double shroud 13 has been designed as a structure capable of sufficiently withstanding these severe conditions.

(Problems to be Solved by the Invention) However, when the total operating time of the steam turbine becomes long, the outlet end of the first stage nozzle 5 is corroded and the steam passage area changes from the design value, resulting in pressure changes before and after the paragraph. Since the difference tends to increase and the bending stress tends to increase, and the erosion of the outlet end of the nozzle does not always occur evenly around the entire nozzle opening, the direction of bending stress shown in FIG. In some cases, the fluctuations alternated from the top to the bottom and from the bottom to the top alternately. Then, under the situation where stress concentrates on the blade ventral side edge and the blade back side edge of such a moving blade, the double shroud 13 is
Performs repetitive movement with relatively small amplitude (hereinafter referred to as fretting) in a state where the inner shroud 10 and the outer shroud 12 are joined, causing fretting wear on the joint surface between the inner shroud 10 and the outer shroud 12, and this fretting Fretting fatigue accumulates due to repeated stress caused by wear force and external force, and even if the shroud is designed as a double shroud structure with a sufficient safety factor, cracks occur at the joint surface between the inner shroud 10 and the outer shroud 12. There was a problem.

Therefore, the present invention solves the problems of the above-mentioned conventional technology, prevents the shroud from being damaged by suppressing fretting of the joint surface of the inner shroud and the outer shroud that are machined integrally with the moving blade, and prevents damage to the shroud. It is an object of the present invention to provide a turbine rotor blade that enables a turbine to operate safely.

[Structure of Invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention forms an inner shroud at the tip of a blade effective portion of a moving blade, and mounts an outer shroud on the outer peripheral end of the inner shroud. In the turbine moving blade, the non-interference area is formed at the tip of the blade, except for the central joint between the inner shroud and the outer shroud, on the blade ventral edge and blade dorsal edge on both sides thereof. It was done.

(Operation) Since the non-interference zone forming part isolates the stress concentration area of the double structure shroud and the fretting occurrence area, the non-interference area suppresses the occurrence of fretting due to the contact between the inner shroud and the outer shroud. Further, as a result of acting as a space for reducing the repeated stress from the stress concentration portion acting on the fretting occurrence portion, the accumulation of fretting fatigue is suppressed.

(Embodiment) An embodiment of a turbine rotor blade according to the present invention will be described below with reference to FIGS. 1 to 3. The same parts as those in the conventional art are designated by the same reference numerals.

As shown in FIG. 1, a plurality of first-stage moving blades 6 provided at a predetermined distance in the axial direction from the first-stage nozzle of the first paragraph of the steam turbine are arranged in the circumferential direction of the rotor 7. There is. An inner shroud 10 is integrally carved at the tip of the blade effective portion 9 of each moving blade. A tenon 11 is provided on the outer surface of the inner shroud 10.
1, a thin plate-shaped outer shroud 12 that connects several moving blades as a set is mounted. Then, the outer shroud 12 is fixed to the outer peripheral end of the inner shroud 10 by caulking the tenon 11 to form a band-shaped double-structure shroud 13. Further, between the inner shroud 10 and the outer shroud 12, a wedge-shaped gap 18 as a non-interference area is formed on both sides thereof, that is, the blade ventral side edge and the blade dorsal side edge, except for the central joint portion by the tenon 11. The outer diameter R ₁ of the inner shroud 10 in the portion where the gap 18 is formed is smaller than the inner diameter R _{0 of the} outer shroud 12.

FIG. 2 shows a method for forming the gap 18,
When shaving from the blade, the center O ₁ of the inner shroud 10, which is formed so as to be almost joined to the outer shroud 12, is offset from the center O ₀ of the outer shroud 12 by x ₁ , and the central joint around the tenon 11 is removed. The outer surface of the inner shroud 10 on both sides of the blade, that is, the ventral side and the blade back side, is arc-shaped from the center toward the blade belly and the blade back with a radius R ₁ .

Therefore, according to the turbine rotor blade of the present invention, the inner shroud 10 and the outer side are provided at the stress concentration points of the blade ventral edge and blade back edge where bending stress due to steam force and centrifugal force are overlapped and stress is particularly concentrated. Since the gap 18 of the shroud 12 is formed, the gap 18 acts as a non-interference area that separates the stress concentration part and the fretting occurrence part, and the relative sliding at the joint surface between the inner shroud 10 and the outer shroud 12 due to stress. Therefore, it is possible to suppress the accumulation of fretting fatigue due to the repeated stress acting on the portion where the inner shroud 10 and the outer shroud 12 contact each other with a relatively small amplitude. Therefore, due to fretting fatigue, the inner shroud 10 and the outer shroud 12 are
It is possible to prevent cracks from occurring on the joint surface of the turbine and to operate the turbine safely.

FIG. 3 shows another embodiment of the turbine rotor blade according to the present invention, in which the blade ventral side edge and the blade dorsal side edge of the inner shroud 10 facing the outer shroud 12 side are curved to form a gap. 19 is formed. This is to form the gap 19 as a non-interference area in the minimum necessary area where stress is concentrated, and the fretting suppressing effect is slightly inferior to the above-mentioned embodiment, but the processing is easy. Therefore, this embodiment is preferably used in a place where the stress level is not so severe.

〔The invention's effect〕

As is apparent from the above description, the present invention is a blade tip portion, except for the central joint between the inner shroud and the outer shroud, the blade ventral edge portion and the blade dorsal edge portion on both sides of the blade. Since the interference area is formed, the area where stress is concentrated and the area where fretting occurs are separated, and the accumulation of fretting fatigue at the joint surface can be suppressed, and the shroud is prevented from being damaged due to fretting fatigue and the turbine is safe. You can drive to.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a turbine rotor blade according to the present invention, FIG. 2 is a partially enlarged front view of FIG. 1, and FIG. 3 is a front view showing another embodiment of the turbine rotor blade according to the present invention. 4 and 5 are schematic cross-sectional views showing a steam turbine having a nozzle box structure, FIG. 5 is a schematic cross-sectional view showing a steam chamber of a nozzle box, and FIG. 6 is a vertical cross-section showing a double shroud of a blade tip. Fig. 7 is a schematic view of the surface, Fig. 7 is a diagram showing the relationship between the load and steam force acting on the blade, Fig. 8 is a diagram showing the vibration state of the blade due to steam force, and Fig. 9 is a graph showing the relationship between the load and steam temperature. Shown, No. 10
FIG. 11 is a diagram showing a distribution state of bending stress due to a steam force acting on the outer shroud, and FIG. 11 is a diagram showing a distribution state of stress due to a centrifugal force acting on the outer shroud. 2 ... Nozzle box, 3 ... Steam chamber, 5 ... First stage nozzle, 6 ... First stage moving blade, 7 ... Rotor, 9 ... Blade effective part, 10 ... Inner shroud, 11 ... Tenon, 12
... outer shroud, 13 ... double shroud, 14 ...
… When the first valve is open, 15 …… When the second valve is open, 16 …… When the third valve is open, 17 …… When the fourth valve is open, 18, 19 …… Gap.

Claims (3)

[Claims] 1. A turbine moving blade in which an inner shroud is formed at a tip of a blade effective portion of the moving blade, and an outer shroud is attached to an outer peripheral end portion of the inner shroud, the tip portion of the blade comprising: A turbine rotor blade, characterized in that a non-interference area is formed on the blade ventral edge and blade dorsal edge on both sides of the blade except for the central joint between the inner shroud and the outer shroud. 2. The turbine moving blade according to claim 1, wherein the non-interference area is formed by subjecting the blade ventral side edge and the blade back side edge to arc processing. 3. The turbine rotor blade according to claim 1, wherein the non-interference area is formed by subjecting a blade ventral edge portion and a blade dorsal end portion to curved surface processing.