JPS5924244B2 - Tie wire mounting structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tie wire attachment structure in which a tie wire is passed through a tie wire hole formed in a row of rotor blades of a turbine to connect the rotor blades.

Conventionally, in a steam turbine, tie wires are attached to the long rotor blades of the final stage and the final stage in order to suppress resonance with respect to the operating cycle and adjust the vibration frequency.

There are two types of tie wires, a silver solder type and a loose type, and in the former type, when the stress acting on the tie wire increases, the tie wire itself may be damaged or broken due to a decrease in the fatigue strength of the silver solder itself.

In order to prevent such accidents, the latter type of loose tie wire has come to be used, but even this type of tie wire has had accidents in which it has been damaged or broken.

As shown in FIGS. 1 and 2, this type of tie wire attachment device connects a rotor blade 2 attached to a turbine shaft 1.
Tie bosses 3 are welded and connected in groups of an arbitrary number and arranged in a circular shape, and tie wires 4 are passed through these rotor blades 2 to adjust the vibration frequency using the tie wires 4. .

When the tie wire 4 is attached to the rotor blade 2 and in a stationary state, it is held parallel to the tie wire hole 5 as shown in FIG. is deformed as shown by the solid line in FIG.

That is, when the rotor blade 2 is at rest, it is in the state shown by the dashed line, but when it is rotating, it is deformed into the state shown by the solid line.
Slightly deformed.

Since a bending stress corresponding to this amount of deformation acts on the tie wire 4, the tie wire 4 may be damaged or broken during long-term use.

The cause of this damage or breakage is that excessive stress is generated in the vicinity of the tie wire hole 5 due to the deformation of the rotor blade 2 during rotation, and this becomes repetitive stress that acts on the tie wire 4 itself, causing the tie wire 4 to break or break. It is thought that it will break.

Conventionally, consideration has been given to only two types of stress acting on tie wires: bending stress due to steam and stress due to the centrifugal force of the tie wire itself.

However, in view of the fact that breakage accidents have occurred even with loose type tie wires as mentioned above, in addition to the above two types of stress, bending stress due to deformation of the rotor blades during rotation acts with the vicinity of the tie wire hole as a fulcrum, and the stress was found to be excessive.

Moreover, in the case of loose tie wires, dozens of rotor blades are connected by a single tie wire, so if the tie wire is damaged or broken, it goes without saying that a great deal of effort and expense is required to repair it.

In view of the above, it is an object of the present invention to provide a tie wire attachment device that suppresses the bending stress generated by the deformation of rotor blades during rotation from acting on tie wires. The deformation of the rotor blade is taken into consideration in advance and the shape is formed to accommodate that deformation.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 5, reference numeral 2 denotes a rotor blade having a tie wire hole 6 provided inclined in a certain direction, and 4 denotes the tie wire hole 6.
This is a tie wire that passes through the.

As shown in FIG. 6, the tie wire hole 6 is provided to be inclined at an angle θ with respect to the original center line 7, and the diameter D2 of the tie wire hole 6 is determined by the following equation.

D2= (DI+T

When the tie wire 4 passes through the tie wire hole 6, among the gaps formed by both 4 and 6, on one side (the left side in FIG. 5) is a gap C1 between the tie wire 4 and the tie wire hole 6 on the rotation direction side 8. is the same gap C2 on the opposite rotation direction side
At the same time, on the other side (right side in FIG. 5), the gap C3 between the tie wire 4 and the tie wire hole 6 on the rotation direction side 8 is larger than the same gap C4 on the counter rotation direction side. (C3>C4).

As a result of an experiment conducted by rotating a turbine rotor blade to which the tie wire attachment device configured as described above is applied, it was found that the amount of deformation θ of the rotor blade changes as the rotation speed increases, as shown by curve 9 in Figure 8. It was confirmed that the amount increases.

From this, the appropriate value of the deformation amount θ is at least 8 degrees or less for a 3,600 rpm turbine, at least 6 degrees or less for a 3,000 rpm turbine, at least 3 degrees or less for a 1,800 rpm turbine, and at least 2 degrees for a 1,800 rpm turbine. It is understood that the optimum value is less than or equal to °.

As explained above, according to the present invention, it is possible to suppress the bending stress acting on the tie wire and reduce the bending deformation thereof, thereby making it possible to prevent damage and breakage of the tie wire.

[Brief explanation of drawings]

Figures 1 and 2 are front and side views of a rotor blade showing a conventional tie wire mounting structure, Figure 3 is a sectional view taken along the line ■-■ in Figure 1, and Figure 4 is a conventional tie wire mounting structure. 5 is a sectional view showing an embodiment of the tie wire mounting structure of the present invention, and FIGS. 6A and B are cross sections of the rotor blade used in the present invention. FIGS. 7A and 7B are a sectional view and a front view of a conventional rotor blade, and FIG. 8 is an explanatory diagram. 2... Moving blade, 4... Tie wire, 6... Tie wire hole, θ... Inclination angle, C1 to C4... Gap.

Claims (1)

[Claims] 1. In a loose tie wire mounting structure in which the rotor blades are connected by passing the tie wire through a tie wire hole provided in a row of rotor blades of a turbine, the tie wire hole is inclined in the same direction with respect to the center line of the tie wire. The tie wire mounting structure is characterized in that the inclination direction of the tie wire hole is set so that the tie wire hole and the center line of the tie wire are parallel to each other due to the twisting of the turbine rotor blade during turbine operation.