JPS6196104A - Coupling structure of steam turbine bucket - Google Patents

Abstract

PURPOSE:To prevent a tenon from being fractured by gradually reducing a cross-sectional area of a bucket coupling member in a width direction thereof from buckets adjoining circumferentially toward a central portion among the buckets, and reducing centrifugal force and stress applied to a bucket coupling member. CONSTITUTION:A shroud plate 4 is assembled onto the outer peripheral surface of a plurality of buckets 1 having a tenon 2 provided at an end part on the outer peripheral side thereof as a bucket coupling member having a hole fitting to the tenon 2. Thereupon, the shroud plate 4 is adapted to have a prescribed wall thickness and a width gradually reduced from the buckets 1 adjoining circumferentially toward a central portion 4a among the buckets forming a circular arc-shape. Namely, the shroud plate 4 has a maximum width B at their portions superposed on the end part 4b on the outer peripheral side thereof, the width being gradually reduced toward the central portion 4a among the buckets. In addition, the central portion 4a has an amount of indentation delta1 at the side of a steam inlet and an amount of indentation delta2 at the side of a steam outlet respectively being shortened, and has a minimum width A at the central portion 4a among the buckets.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a connection structure for steam turbine rotor blades, and particularly to a connection structure in which a plurality of rotor blades are connected around the outer periphery of a long low-pressure stage blade to form one group of blades. Regarding. [Background of the Invention] In general, if a steam turbine rotor blade is left as a single blade without a connecting structure, its strength against IWI force and complex steam excitation is not 1 minute, and in terms of performance, the shroud plate at the blade tip is A connection structure that connects with a connection member such as this is essential. Conventionally, there is a first-order type of connection structure for steam turbine rotor blades. (1) The most typical example is the shroud plate caulking structure shown in 1 Mechanical Engineering Handbook (Japan Society of Mechanical Engineers, July 15, 1972), Volume 13, 13-97, Figure 235. 2) As a connection structure used under high centrifugal forces such as low-pressure stage long blades,
A turbine rotor blade cover shown in Publication No. 44 is rotatably coupled through a projection and a fitting hole, and (3) a shelf is protruded in the circumferential direction at the tip of the rotor blade. , one type with a welded cover that connects multiple moving blades by welding the shelves together. etc. are known. In these conventional technologies, compared to the shroud plate caulking structure described in (1), the turbine rotor blade cover described in (2) is rotatably coupled, and the one-type welded cover described in (3) is used. However, the problem is that the structure is complicated and the number of man-hours required increases. In addition, for the one-type welding cover mentioned in (3) above, materials that are compatible with welding must be used.
There is also the issue of material constraints. Next, Figures 7 and 8 show a connection structure using shroud plates as a conventional technology that is widely applied from short blades used in high pressure stages to long blades used in low pressure stages. Indicates the condition. In the connection structure shown in these figures, a protrusion (hereinafter referred to as a tenon) 2 is provided at the outer peripheral end of each rotor blade 1, and a shroud plate 3 having a fitting hole that fits into the tenon 2 is connected to the tenon. 2 and the fitting hole, the tenon 2 is caulked on the outer circumferential side of the shroud plate 3, and the five rotor blades 1 are bound by the shroud plate 3, and are integrated into one blade group structure. There is. By the way, there are several reasons why a plurality of rotor blades are combined to form a group structure, but there are two main reasons. One of them is the front shoulder and vibration damping effect from the excitation frequency of blade vibration (excitation caused by rotor rotation, excitation caused by deviation of steam flow from the upstream nozzle, etc.), and the other one is This is to prevent steam leakage at the tips of rotor blades and to prevent drifting that can lead to performance degradation. For the above reasons, it is necessary to attach rotor blade connecting members such as a shroud plate and a turbine rotor blade cover to the tip of the rotor blade, but as the blade length increases, In the case of the shroud plate structure shown, centrifugal stress increases and effectively
For aircraft, the effective wing length is 600(1), 25Hz, and for 307 aircraft, the organic length is approximately 750R1. For those with a wing length exceeding this,
Either adopt the structure shown in Publication No. 54 or the one-type welded cover described in (3) above, or ignore its necessity and abandon the connection using the rotor blade connection member, and use only the tie wire that connects the intermediate part of the blade to achieve the load-bearing force. Either way will be taken to maintain the . By the way, the above-mentioned connection structure using shroud plates is the simplest, requires less man-hours to manufacture, and has excellent performance, but when it is applied to long wings. There is a strength problem around Tenon. In the connection structure shown in FIGS. 7 and 8, the width and thickness of the shroud plate 3 are made constant. The distribution of stress acting on this type of shroud plate 3 and problems with its structure will be explained below with reference to FIGS. 9 to 11. Figures 9 and 10 are the ■-■ line and X-X in Figure 8.
This shows the stress distribution acting on the shroud plate as seen from the line, where (〉 represents surface tensile stress and (= represents compressive stress. Figure 11 shows the stress distribution that occurs around the caulked tenon. 9 indicates the maximum stress between the blades of the shroud plate, 9 in Figure 10 indicates the maximum stress around the tenon of the shroud plate, and 11 In the figures (R indicates the maximum shear stress of the Tenon caulking part. In these figures, the stress distribution of the shroud plate 3 is
As shown in FIG. 1 and FIG. 10, 1 usually reaches a maximum around the tenon 2, and then becomes large approximately in the center between the tenons 2 and 2. On the other hand, the shear stress of the caulked part of Tenon 2 is the 11th
As shown in the figure, the stress in the shroud plate 3 increases at the corners on the steam inlet side or the steam outlet side, and is often at almost the same level.Furthermore, the structure around the tenon 2 tends to cause stress concentration. In addition, since excessive stress is likely to occur during caulking, even slight vibrations may cause damage. In order to prevent the above-mentioned failure accidents, it is necessary to keep the overall applied stress level low. [Object of the Invention] The object of the present invention is to provide a steam turbine rotor blade that can prevent tenon breakage accidents and that does not cause performance deterioration even when applied to the connection of a plurality of long blades used in a low pressure stage. Provides a connection structure. [Summary of the Invention] A feature of the present invention is that the cross-sectional area of the rotor blade connecting member in the width direction gradually decreases from the rotor blades that meet in the circumferential direction toward the center between the blades. , the above objective can be achieved reliably. [Embodiments of the Invention] Examples of the present invention will be described below with reference to the drawings. FIGS. 1, 2(a) and 2(b) show a first embodiment of the present invention, in which the outer circumferential surface of a plurality of rotor blades 1 is provided with a tenon 2 at the outer circumferential end. , l! has a fitting hole that fits into the tenon 2! The shroud plate 4 as an IJ blade connecting member is assembled to the tenon 2 by fitting into the fitting hole, and the tenon 2 protrudes from the outer peripheral surface of the shroud plate 4°.
In this embodiment, five rotor blades 1 are bound to the shroud plate 4 through a joint structure in which the ends of the blades are caulked to form one group of clouds, which is electrodynamically operated. The shroud plate 4 has a constant wall thickness and a width extending from the circumferentially adjacent rotor blades 1.1 to the center portion 4a between the blades.
It gradually decreases in an arc shape towards the end. That is, the shroud plate 4 has a maximum width B at a portion 4b overlapping the outer circumferential end of the rotor blade 1, and gradually decreases toward the central portion 4a between the blades, and has a concave shape on the steam inlet side in the central portion 4a. δ1, the concave amount δ2 is shortened on the steam outlet side, and the minimum width A is at the center portion 4a between the blades. As a result, the cross-sectional area of the shroud plate 4 in the width direction gradually decreases from the circumferentially adjacent rotor blades 1 toward the center portion 4a. Next, Figure 3 shows the shroud plate in Figures 1 and 2 (a).
), (b) shows changes in stress generated in the shroud plate 4 and the tenon 2 when the shapes shown in FIG. This third
The figure shows the results of an experiment on a long blade with an effective length of about 600 m, and the amount of dent in the shroud plate 4 was set to 6 on the steam inlet side.
1. 62 on the steam outlet side, the maximum width B of the shroud plate 4
When, the dent size ratio of the shroud plate 4 (δ, +62
)/B on the horizontal axis and stress σ on the vertical axis. In Fig. 3, the curve t%lP indicates the maximum stress around the tenon of the shroud plate, the curve Q) indicates the maximum stress between the blades of the shroud plate, and the curve 1R· indicates the maximum shear stress at the tenon clamping part. , and Pa S represents the optimal point of the amount of dent in the shroud plate determined from the relationship with stress. From this Figure 7, the amount of dent in the shroud plate (δ1+62
) increases, mainly the centrifugal force of the shroud plate itself decreases, and as a result, the maximum stress tp around the tenon of the shroud plate and the maximum shear stress CRI at the caulked portion of the tenon decrease. Also, from Figure 7, it can be seen that as the width of the shroud plate decreases, the maximum stress between the blades of the shroud plate (9 N) increases. Judging comprehensively from these three stresses, the amount of dent in the shroud plate The optimal point r
When $r is selected, the dent size ratio (δ1+68)/B is approximately 0.
．． This results in a score of 6. When the amount of depression of the shroud plate is set to the optimum position), the stress acting on the shroud plate is also approximately 0.6 times the stress acting on the conventional shroud plate with the width constant. Although these values vary depending on the size of the rotor blade, tenon shape, thickness and material of the shroud plate, etc., the relationship between the applied stress and the amount of dent in the shroud plate follows the trend shown in Figure 3. Become. Next, FIG. 4 shows the steam drift situation at the tip of the rotor blade, and in relation to this, the above-mentioned FIGS. 1 and 2 (
The performance aspects of the embodiments shown in a) and (b) will be considered. As shown in FIG. 4, the main stream 5 of steam flows along the shape of the rotor blade 1, but the pressure on the ventral side 7 of the blade is higher than the pressure on the back side 8, so if there is no shroud plate 4, As shown in streamline 6, a secondary flow that wraps around the tip of the rotor blade occurs,
Not only does this increase the amount of steam leakage, but it also disrupts the flow of the main stream 5, resulting in a decrease in performance, which poses a serious problem.6 However, since this secondary flow occurs near the airfoil, the shroud plate prevents the entire blade span. It is not necessary to cover the shroud plate, and the shroud plate may have a shape that functions as a prevention plate to prevent steam from flowing around near the airfoil.6 Therefore, as shown in Fig. 1 and Fig. 2 (a) and (b). Thus, even if the shroud plate 4 has a shape that covers the entire blade span near the airfoil shape, and the width gradually decreases toward the center between the blades, there is hardly any adverse effect on performance and there is no problem. In the first embodiment, the recess may be provided only on the steam inlet side or the steam outlet side in the width direction of the shroud plate 4. Next, FIGS. 5 and 6 show a second embodiment of the present invention. In this embodiment, the width of the shroud plate 9 is constant, and the thickness of the shroud plate 9 is different. That is, the outer circumferential surface of the shroud plate 9 has a substantially concave shape, with the wall thickness gradually decreasing from the circumferentially adjacent rotor blades 1 toward the center between the blades, and the recess amount δ being subtracted from the overall wall thickness. An arc-shaped recess 10 is formed, and the cross-sectional area of the central portion is narrow. In this second embodiment as well, the centrifugal force acting on the shroud plate 9 can be reduced, and therefore the applied stress can be reduced. In addition, in one aspect of the present invention, the first aspect of the present invention. The second embodiment may also be used to narrow the width of the shroud plate at the center between the blades and reduce the wall thickness at the center between the blades). Furthermore, in the present invention, the shroud plate is formed using a material having a specific gravity lower than that of iron-based metal materials, such as tatan alloy or aluminum alloy, and as described above, the width of the central portion between the blades of the shroud is narrowed, The wall thickness in the center between the blades was made thinner, and the shroud plate was made of a material with lower specific gravity. The width between the blades in the shroud plate may be narrowed and the wall thickness may be thinned. [Effects of the Invention] According to the present invention described above, the cross-sectional area of the rotor blade connecting member in the width direction is gradually decreased from the circumferentially adjacent rotor blades toward the center between the blades. , it is possible to reduce the centrifugal force acting on the rotor blade connecting member, and therefore the stress acting on the rotor blade connecting member, which has the effect of preventing Tenon breakage accidents, and the long wing and group X
This effect can also be applied to the case of iW construction. Furthermore, according to the present invention, near the airfoil! ! It can be sufficiently covered by the llR connecting member and the flow of steam near the airfoil shape can be prevented, which has the effect of eliminating the problem of performance deterioration before it occurs.

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of the present invention, which is a perspective view of a shroud plate serving as a rotor blade connecting member, viewed from the outer peripheral side;
Figures 2(a) and (b) are I[a-Ha in Figure 1, respectively.
3 is an enlarged cross-sectional view taken along the line II b-II b, FIG. 3 is a diagram showing the relationship between the dent size ratio in the width direction of the shroud plate and the applied stress in the first embodiment of the present invention, and FIG. A performance explanatory diagram of the first embodiment of the invention, and FIG.
Fig. 6 is an enlarged sectional view taken along line VI-VI in Fig. 5, and Fig. 7 is a conventional rotor blade connection structure using a shroud plate. FIG. 8 is a perspective view of the shroud plate seen from the outer circumferential side, and FIGS. 9 and 10 are [ of FIG.
FIG. 11 is an explanatory diagram of acting stress on the shroud plate viewed from the -1 X-ray and x-X-ray directions, and FIG. 11 is an explanatory diagram of acting stress around Tenon. DESCRIPTION OF SYMBOLS 1... Moving blade, 2... Tenon provided at the outer peripheral side end of the moving blade, 4... Shroud plate as a moving blade connecting member, 4
a...Central part between the blades on the shroud plate, 4b...
・The part of the shroud plate that overlaps the outer edge of the rotor blade,
δ□, δ2... Amount of dent in the width direction of the shroud plate, A
... Minimum width of the shroud plate, B... Maximum width of the shroud plate, 9... Shroud plate, 10... Indentation in the thickness direction of the shroud plate, δ3... Indentation in the wall thickness of the shroud plate amount.

Claims (1)

[Claims] 1. A protrusion for caulking is provided on the outer peripheral side end of the rotor blade, a rotor blade connecting member is assembled to the protrusion through a fitting hole, the protrusion is caulked, and a plurality of protrusions are attached. In the connection structure in which two rotor blades are connected to form a group of blades, the cross-sectional area in the width direction of the rotor blade connecting member is gradually decreased from circumferentially adjacent rotor blades toward the center between the blades. A steam turbine rotor blade connection structure characterized by: 2. In claim 1, the thickness of the rotor blade connecting member is constant, and the width of the rotor blade connecting member gradually decreases from the circumferentially adjacent rotor blades toward the center between the blades. A steam turbine rotor blade connection structure characterized by: 3. In claim 1, the width of the rotor blade connecting member is constant, and the thickness of the rotor blade connecting member gradually decreases from the circumferentially adjacent rotor blades toward the center between the blades. A steam turbine rotor blade connection structure characterized by: 4. In claim 1, the width of the rotor blade connecting member is gradually decreased from the circumferentially adjacent rotor blades toward the center between the blades, and the wall thickness of the rotor blade connecting member is increased. , a connection structure of steam turbine rotor blades, characterized in that the rotor blades that are adjacent to each other in the circumferential direction gradually decrease toward the center between the blades. 5. Claims 1, 2, 3, or 4
2. The steam turbine rotor blade connection structure according to item 1, wherein the rotor blade connection member is made of a material having a specific gravity smaller than that of an iron-based metal material.