JPS6261761B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a structure for attaching and fixing blades to a rotor by fitting the root portion of the blade into a groove provided in the rotor, and particularly relates to a structure for attaching and fixing blades to a rotor. The present invention relates to a blade mounting structure suitable for a turbine.

[Prior art]

The blade attachment part of conventional turbomachinery is
Reliability Gas Turbine Combined Cycle Development Program;
January 1980 issue, pp. 4-15 to 4-16, published by Electric Power Research Institute (High-Reliabilty Gas Turbine
Combined-Cycle Development Program, 4-
15-4-16, Jan.1980, Electric Power
Research Institute, this will be explained with reference to FIG. 1. 1 is a rotor, 2 is a blade, which rotates in the direction of the arrow. Reference numeral 3 denotes a blade root portion, which generally has a dovetail shape in cross section, and is inserted into a blade fixing groove 4 on the outer periphery of the rotor to be restrained in the radial direction (direction of centrifugal force). Reference numeral 5 denotes a piece for restraining the blade root portion 3 in the axial direction, and its cross section has the same shape as the blade root portion 3. This piece 5 is fixed by caulking 6 provided at the bottom of both ends of the fixing groove 4 so as not to come off in the axial direction. FIG. 2 is a detailed sectional view of this blade attachment part, and the same reference numerals as in FIG. 1 indicate the same parts. As can be seen from this figure, there is a gap of δ between the upper shoulder 9 of the dovetail-shaped blade root 3 and the groove shoulder 7.
When a bending moment ±M is alternately applied to the blade 2 as an excitation force, relative sliding is enabled at the contact surface between the blade root portion 3 and the fixing groove 4,
It is designed to absorb vibrational energy.
Figure 3 shows the contact pressure and surface stress distribution on the blade root side near the upper end of the contact surface between the blade root 3 and groove shoulder 7, which is a problem area in terms of strength when a bending moment is applied in this way. shows. As described above, when relative slip occurs on the contact surface, the end of the contact surface 10 on the blade root side, where the surface pressure is high, becomes rough and presents a fretting damaged surface with minute cracks. If an external force is applied to the surface where such microcracks have occurred, the cracks will propagate and there is a risk of fatigue failure. However, as shown in FIG. 3, in the conventional structure, the end of the contact surface 10 on the blade root side It had the disadvantage that surface stress was concentrated in the vicinity, making it easy for microcracks to grow, making it susceptible to fatigue failure.

[Purpose of the invention]

The present invention has been made based on the above-mentioned matters, and has a structure that prevents microcracks from growing into large cracks even if they occur due to fretting.
It is an object of the present invention to provide a blade mounting structure for a turbomachine that prevents damage that would impede the functionality of the machine.

[Summary of the invention]

The present invention is characterized by a turbo machine in which the blade root section has a dovetail shape, and the blade root portion is fitted into a blade fixing groove provided in the rotor, thereby attaching and fixing the blade to the rotor. In this blade mounting structure, the dovetail-shaped blade root portion is configured so that the point where fretting occurs and the point where high stress occurs are separated.

[Embodiments of the invention]

A fourth embodiment of the blade attachment part of the present invention will be described below.
This will be explained with reference to FIG. Figure 4 shows a cross-sectional view of the blade attachment part, and Figures 1, 2, and 3.
The same reference numerals as in the figures indicate the same parts. The dovetail-shaped blade root portion 3 is constructed by connecting the end surface portion 9a of the upper shoulder portion 9 and the end portion of the contact surface 10 with a discontinuous curved surface portion 11. In this way, as shown in FIG. 5, at the contact surface between the blade root 3 and the groove shoulder 7, the end surface of the groove shoulder 7 overhangs upward from the contact surface. As a result, the curved surface portion 11 of the blade root portion 3 has the function of alleviating stress concentration on the contact surface 10, and therefore, the fretting damaged portion and the maximum stress portion generated at the bottom of the curved surface portion 11 can be separated. .

6 and 7 show other examples of the blade mounting structure of the present invention. In the example shown in FIG. 6, the radius of curvature of the curved surface portion 11 is made sufficiently large for the purpose of reducing stress concentration on the curved surface portion 11 and further improving fatigue strength.

In the example shown in FIG. 7, the curved surface portion 11 has a large radius of curvature, and a convex portion is provided on the upper shoulder portion 9 of the blade root portion 3. With this structure, stress concentration on the curved surface portion 11 is reduced. can improve fatigue strength,
In addition, since the gap δ between the upper shoulder 9 and the groove shoulder 7 can be reduced, even if an excessive bending moment (vibration force) is applied to the blade 2, the blade 2 will tilt excessively and will not connect to the adjacent stator blade. There is no danger of contact.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to shift the fretting damage part at the blade root and the position where the surface stress is maximum, so that even if microcracks occur due to fretting, they will not grow significantly. Therefore, a blade mounting structure with high fatigue strength can be obtained.

[Brief explanation of the drawing]

Figure 1 is a partial perspective view of the blade mounting structure of a conventional turbomachine, Figure 2 is a cross-sectional view of the blade mounting structure in Figure 1, and Figure 3 is the end of the contact surface between the blade root and the groove in Figure 2. Diagram showing nearby surface pressure and stress distribution,
FIG. 4 is a sectional view of an embodiment of the blade mounting structure of a turbomachine according to the present invention, and FIG. 5 is a diagram showing surface pressure and stress distribution near the end of the contact surface between the blade root and the groove in FIG. 4. 6 and 7 show cross-sectional views of other embodiments of the blade mounting structure of the present invention. DESCRIPTION OF SYMBOLS 1... Rotor, 2... Blade, 3... Blade root part, 4... Blade fixing groove, 7... Groove shoulder part, 9... Upper shoulder part of blade root part, 10... Blade root part contact surface, 11... curved surface part.

Claims (1)

[Claims] 1 The blade root has a dovetail-shaped cross section, has an upper shoulder at the same height as the groove shoulder of the rotor, and the blade root is fitted into a blade fixing groove provided on the rotor. In a blade mounting structure for a turbomachine in which a blade is attached and fixed to a rotor by inserting the blade into the rotor, a discontinuous curved surface portion connects the contact surface portion of the blade root portion with the groove and the upper shoulder end surface portion of the blade root portion. A blade mounting structure for a turbomachine, characterized in that a blade root portion is configured to separate a point where fretting occurs and a point where high stress occurs.