JPS6232202A - Blade dove tail - Google Patents

Abstract

PURPOSE:To prevent fretting fatigue, by forming a clearance groove for preventing each rotor side dove tail and the associated blade side dove tail from making into contact with each other, in a turbine rotor at a position where each adjacent blades are opposed to each other. CONSTITUTION:A turbine impeller having several blades 2 assembled on the outer periphery of a rotor 1, is formed such that male dove tails 3' formed on the blades 2 are fitted in female dove tails 3 formed in the outer peripheral section of the rotor 1, and those in each group consisting of a predetermined number of the blades are coupled with each other by means of a shroud cover 8. In this arrangement, a clearance groove 11 is formed in the rotor at a position where a hook 10 of each wheel side tab tail is opposed to the adjacent sections of hooks 9 of two blade side dove tails. With this arrangement, is is possible to prevent a part in the vicinity of the round section of each hook 9 from butting the hook 10, thereby it is possible to surely prevent fretting fatigue.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a dovetail for attaching blades to a turbine rotor, and particularly to a blade dovetail improved to prevent fretting cracks that tend to occur in the dovetail. It is.

[Background of the invention]

Steam turbines use a method in which high-pressure, high-temperature steam is expanded and accelerated through a nozzle, and then flowed into blades attached to a rotating shaft to extract power. In an axial flow turbine, nozzles and blades are arranged radially around the circumference.

FIG. 4 shows a high-pressure first stage structure at the steam inlet of a turbine, in which blades 2 are installed on a rotor 1 in a dovetail 3 structure. After the steam S from the boiler flows into the nozzle box 4, it passes through the nozzle 5 and hits the blade 2. FIG. 5 shows the nozzle box 4 seen from the A-A plane in FIG. 4. The interior is divided into four sections by partition plates 68 to 6d, and steam from the boiler flows into each room from separate piping. The piping in front of the nozzle box is provided with Nα1 valves to Nn4 valves, respectively, and in order to adjust the load on the turbine, these valves are opened and closed to adjust the steam flow rate. Namely.

When the load increases, Lice 1 valve → Nα2 valve → Nα3 valve → Ha
The four valves are opened in order, and during partial load operation, only the &1 valve or only the Nα1 and 2 valves are open.

When only the &1 valve is open, steam flows to the nozzle 5 between the partition plate 6a or 66b, and steam does not flow to the other valve nozzles.

FIG. 6 shows a perspective view of the blade 2 shown in FIG.

A male dovetail 3 is machined all around the outer periphery of the rotor 1, and a female dovetail 3' that fits into the male dovetail 3 is attached to the blade 2 opposite to this.

The number of dovetail hooks is 3 in this diagram, but
Generally, there are about 1 to 4 hooks, and they are used depending on the size of the blade 2.

A plurality of blades 2 are set around the entire circumference of the rotor along the dovetail 3, and then a tenon 7 that is integrated with the blade 2 is set.
is inserted into the hole of the shroud cover 8, and the tenon 7 is caulked to form a plurality of blade group structures. Multiple sets of these blades are arranged around the entire circumference.

Steam enters from the direction shown, flows through the flow path of the blades 2, and rotates the rotor 1. Therefore, each blade 2 receives a propulsive force in the direction of rotation, and also receives a centrifugal force due to the rotation.

As explained with reference to FIG. 5, when the turbine is operated under partial load, steam flows through only one part of the nozzle around the entire circumference. The force that the blades receive at this time will be explained with reference to FIG. 7. For details, see the U.S. literature ``Turbine Blade Vibration Due to Partial Atomization''.
bration dua to PartialAdm
ission: Int, J, Mech).

A diagram (a) shows an expanded view of the nozzle and blade located on the entire circumference 3600. During partial injection, steam flows through only one part of the nozzles 5 provided around the entire circumference. The diagram (b) shows the force that one blade 2 receives at this time. When this force is further broken down, it becomes the force (C) and the force (d).

In particular, the force (c) is the impact force that the blade receives every rotation, and is unique to the first stage blade. The force (d) is a wake generated by the non-uniformity of the flow occurring downstream of the nozzle 5.

Therefore, the steam force (
It is used under severe conditions because it is subjected to the combined force of Q) and the steam force (d) exerted by 71 rotations of the nozzle, and is further subjected to centrifugal force and is at a high temperature. In recent years, large-capacity thermal power turbines have also been operated under a system of low load during the night and high load during the day, as nuclear power turbines are operated under base load conditions.

The blades are therefore operated under considerable impact forces, which can lead to fatigue at the connection to the rotor.

FIG. 8 shows an example in which a crack has occurred in the dovetail wheel groove near the joint between the blades. In particular, since the blades 2 are connected by the shroud cover 8, there is a large relative movement between the adjacent blade groups B and C, and at this boundary, the male dovetail 3 provided on the wheel side It is thought that a crack occurred.

FIGS. 9 and 10 show the external forces that the blade receives from the group of wings. FIG. 9 shows the radial force due to centrifugal force. Since each blade has its own centrifugal force, an equal force Ft acts on the dovetail 3. Figure 10 shows the tangential force due to steam force. Since the group blades are connected by the shroud cover 8, if the rigidity is high, the blade will have an integral structure, and the external force Fs will act on the nearby redovetail as shown in the figure, and the largest force will act on the group blade tip. In addition to external forces,
The leading and trailing wings are free of circumferential restraint, making them easy to move.
At the dovetail, the relative movement between the wheel and blade is greatest.

FIG. 11 is a stress distribution diagram acting on the dovetail between the blades. The maximum stress is exerted at the contact end of the wheel and blade.

Figure 12 shows the blade side hook 9 and the wheel side hook 1.
It is a chart showing surface pressure distribution of o. The blade-side hook 9 has an R-shaped contact portion at both ends. The maximum surface pressure PMAχ acts on the root of this R. Therefore, the force that the wheel hook 10 receives is maximum at the R root of the blade hook 9, and this portion becomes the maximum stress portion. Further, the amount of relative movement of the contact portion is large in this portion, and there is a risk that fretting fatigue will occur.

[Purpose of the invention]

In view of the above-mentioned circumstances, the present invention provides a blade dovetail that can prevent fretting fatigue that tends to occur in dovetail hooks, thereby contributing to improving the reliability of steam turbines.

[Summary of the invention]

First, the basic principle of the blade dovetail of the present invention, which was created to achieve the above object, will be explained.

There is a variety of literature on fretting fatigue.

For example, as stated in the research on fretting fatigue in Proceedings of the Japan Society of Mechanical Engineers Vol. No fretting fatigue occurs in these areas.

Furthermore, even if a minute crack occurs on the very surface of the contact part due to fretting fatigue, if the crack does not propagate, it will not lead to a major damage accident. Therefore, to prevent crack propagation,
It is effective to reduce stress near areas where fretting is likely to occur.

As shown in Fig. 12, tensile stress σZ is generated in the wheel groove parallel to the contact surface due to the centrifugal force of the blade, but by lowering this stress, crack propagation from micro-cracks of fretting occurring near the contact edge PM^X can be prevented. can be prevented.

In order to achieve the above object (prevention of pretting cracks) based on the above-mentioned principle, the dovetail of the present invention provides a turbine rotor in which a large number of blades are engaged around the rotor by dovetails, in which adjacent blades are opposed to each other. A relief groove is provided to prevent the dovetail on the rotor side and the dovetail on the blade side from coming into contact near the location where the rotor side dovetail and the blade side dovetail come into contact.

[Embodiments of the invention]

Next, one embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG.

Figure 1 is an external view of a part of the rotor 1 in which blades 2 are arranged in a row, as seen in the axial direction of the rotor.Of the eight blades 2 depicted in this figure, the four on the left side and The four pieces on the right side are each connected by a shroud cover 8. FIG. 2 shows a cross section taken along the line ■-■ in FIG. 1, and this plane corresponds to the adjacent portions of the two blade groups.

Figure 3 shows the ■--■ cross section of Figure 2, and the ■-■ section shown in Figure 1.
The part corresponding to ′ is drawn.

An escape groove 11 is provided in a portion where a hook 10 of a wheel side dovetail faces adjacent parts of hooks 9 of two blade side dovetails. As a result, the vicinity of the R portion of the hook 9 of the blade side dovetail does not come into contact with the hook 10 of the wheel side dovetail.

As is clear from the comparison with the structure of the conventional example (Fig. 12),
By providing the relief groove, the contact area of both dovetail hooks 9 and 10 is reduced, and the surface pressure PMAX' at the maximum surface pressure point p1 is increased.

In this example, around the 21st point of the relief groove 11.

The distance between the groove bottoms is marked r.

FIG. 13 compares the state of stress at the contact end of the dovetail footer of the wheel and blade between the conventional example and the present example. Here, the conventional structure is named A shape and the shape of this example is shown as B shape. Further, the stress in the direction perpendicular to the contact surface is σR1, and the stress in the parallel direction is σR. In order to compare the magnitude of stress, the positions of the contact ends are aligned in the left and right direction.

Comparing the stress on the wheel surface, in the σ8 stress distribution (surface pressure distribution), the stress at the contact end is higher in the B shape (this example) than in the A shape (conventional). That is, even if the blade receives external force, the pressure on one surface is high, so the relative slip between the wheel and the blade is reduced. Furthermore, when comparing the σZ stress distributions, the stress in the B shape (this example) is smaller than that in the A shape (conventional) at the contact end. This is because the B shape has a higher surface pressure than the A shape and the resulting secondary stress is higher, but since there is a groove on the wheel side and it is processed R, stress is released at one end in the σ2 direction. σZ becomes smaller.

That is, in the B shape (this example), the surface pressure is increased to reduce the relative deviation between the wheel and the blade contact portion, thereby preventing fretting fatigue. Furthermore, even if a small crack occurs, the circumferential stress σ2 is small, so the crack will not propagate and a major accident will not occur.

FIGS. 14 to 16 show embodiments different from those described above. In this example, the hook 9 of the blade side dovetail is also provided with an escape groove 12. ri indicates a radius attached to the cut-up portion of the groove 12 described above. This releases stress in the circumferential direction.

The circumferential stress on the blade side is reduced, and the progression of cracks is prevented.

By configuring the circumferential dimension Q1 of the blade-side relief groove 12 to be smaller than the circumferential dimension (one side) Ω2 of the wheel-side relief groove 11, the wheel-side dovetail can be made safer.

Common to the two embodiments described above, the amount of opposing burr is reduced by increasing the surface pressure on the end of the dovetail hook groove, which is connected by the contact structure between the rotor wheel dovetail and the blade dovetail. Since stress in the direction parallel to the contact surface can be released and lowered, fretting fatigue and crack propagation can be prevented.

The hook groove described above may be provided at the end of the group wing, may be provided on each wing, may be provided on each of the upper, middle, and lower row hooks, or may be provided at only one location.

〔Effect of the invention〕

As explained above, when the dovetail of the present invention is applied, it has an excellent practical effect of preventing fretting fatigue, and greatly contributes to improving the reliability of steam turbines.

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention. Figure 1 is an external view of the mounting part of the blades arranged in a row on the rotor, Figure 2 is a cross-sectional view taken along the line ■-■ in Figure 1, and Figure 3 is the ■-■ in Figure 2.
−■ It is a sectional view. Fig. 4 is a sectional view of the first stage of a conventional steam turbine, Fig. 5 is a sectional view taken along line A-A in Fig. 4, Fig. 6 is a perspective view of the blade, Fig. 7 is a diagram explaining the steam force exerted on the blade, and Fig. 8 is an explanatory diagram of dovetail hook cracks, Figures 9 and 10 are explanatory diagrams of external forces applied to the group blade, Figure 11 is a stress distribution diagram of the dovetail hook contact end, Figure 12 is a diagram of contact surface pressure distribution of the dovetail hook, Figure 13 shows the stress distribution at the dovetail contact end. 14 to 16 show an embodiment different from the above, FIG. 14 is an external view, and FIG. 15 is a 14th embodiment.
xv-xv sectional view of the figure, Fig. 16 is XVI of Fig. 15
-XVI sectional view. 1... Turbine rotor, 2... Blade, 3...
・Dovetail, 4... Nozzle box, 5... Nozzle, 6a-6d... Partition section, 7... Tenon, 8...
・Shroud cover, PH^xe PH^X'...
Maximum surface pressure at hook contact end, 9...blade side hook,
10... Wheel side hook, 11... Relief groove, σR
...Stress in the surface pressure direction, σ2...Stress in the local direction.

Claims (1)

[Claims] 1. In a turbine rotor in which a large number of blades are engaged around the rotor by dovetails, a dovetail on the rotor side and a dovetail on the blade side are arranged in the vicinity of a point where adjacent blades face each other. A blade dovetail characterized by an escape groove to prevent contact. 2. The plurality of blades are connected in groups to form a group of blades, and the relief groove is provided at a location where adjacent blades of the group face each other. A blade dovetail according to claim 1. 3. The blade according to claim 1 or 2, wherein the relief groove is formed in at least one of the dovetail on the rotor side and the dovetail on the blade side. Dovetail. 4. The escape groove is characterized in that it has a shape with an R provided at its end.
or the blade dovetail according to item 3 of the same.