JPS58220903A - Turbine movable blade made of ti-alloy - Google Patents

Abstract

PURPOSE:To prevent reduction of the intrinsic vibration frequency of a movable blade made of Ti-alloy by increasing the thickness of the movable blade which is made of Ti-alloy and used for low-pessure step by 5% than that of the blade which is made of 12Cr-steel and possesses an ordinary profile. CONSTITUTION:The section shown by the dotted line denotes the section of a movable blade 2 made of Ti-alloy, and the belly-side shape 4 is formed thicker by A corresponding to nearly 5% of the average thickness of the vane, in comparison with the section of the movable blade 1 which is shown by the solid line and made of 12Cr-steel.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a titanium alloy turbine rotor blade.

It has long been recognized that it is necessary to use titanium alloy rotor blades in the low-pressure final stage (hereinafter referred to as the final stage) in order to cope with the increase in the single machine capacity of steam turbines. There is also a trend toward using titanium alloy rotor blades.This is due to the three major properties of titanium alloys: high specific strength (tensile strength/density) and high corrosion resistance. Focusing on the latter, we used rotor blades made of titanium alloy in the first stage of the steam turbine, which is in the vicinity of the so-called Wilson line and is the most corrosive, to reduce rotor blade accidents. By the way, according to the statistics of steam turbine rotor blade accidents, the ratio of rotor blades in the previous paragraph is the highest, and many of the causes are due to environmental factors such as stress corrosion cracking (SCC). It is considered a thing.

When using titanium alloy rotor blades, the most common method is to use a conventional 12Cr steel rotor blade and a titanium alloy rotor blade with the same geometry (identical shape replacement).
. This is a very advantageous method in terms of economic efficiency in design and production, and ease of replacement with conventional blades, and is supported by the following properties of titanium alloy.

Generally, the natural frequency f of the rotor blades in a steam turbine is
If Young's modulus is E1 and specific weight is r, then /= K JT7
It is given by r (where +:, K is a proportionality constant). Here, the ratio of W of titanium alloy (take Ti-6A/-4J as a representative) and 12Cr steel is given by Held. This means that if a titanium alloy rotor blade is manufactured to have the same geometrical shape as a 12Cr steel rotor blade, it will exhibit nearly the same vibration characteristics despite the difference in material properties.

However, as is clear from the above, the specific motion number of titanium alloy rotor blades tends to decrease, although it is only about 5 inches.This is a fact confirmed by various experiments. .

However, in designing the rotor blades of a group turbine, it is important to design the rotor blades' natural frequency f and the turbine rotational speed N and its integral multiple as far as possible, and this is It is well known to those in the industry that this is the basis of vibration design. Therefore, there are cases where the above-mentioned drop in frequency of about 5 inches can be ignored, but there are many cases where it cannot be ignored. In particular, regarding the moving blades used in the final stage and immediately preceding stage of the low-pressure stage, the centrifugal force exerted on the moving blades is extremely severe, and the long tail length tends to cause vibration-related troubles. is also bad, so the reduction in natural vibration of about 5% mentioned above cannot be ignored in many cases.

The present invention is intended to solve the above problems,
It is an object of the present invention to provide a titanium alloy turbine rotor blade that corrects the above-mentioned decrease in frequency in an economical manner, rather than simply replacing the conventional titanium alloy with the same shape.

An embodiment of the present invention will be described below with reference to FIG.

Same shape replacement (1) In order to make the vibration characteristics of the titanium alloy rotor blade the same as the conventional 12Cr steel cracked rotor blade, the natural frequency of the titanium alloy rotor blade should be raised by about 5 cm. That's a good explanation.

The natural frequency f of a relatively long rotor blade, such as the rotor blade used in the final stage and the immediately preceding stage, is determined by the following formula: %f-=-h (where K: proportionality constant, b: blade Therefore, to increase f by about 5 inches, h needs to be increased by about 5 inches. However, as is well known, the rotor blade is generally
It has a profile as shown in the figure, its length and radius)
The cross section is not necessarily uniform in direction either.

FIG. 1 shows the rotor blade profile represented by the horizontal axis X and the vertical axis y. The rotor blade cross section indicated by the solid line in the figure is that of a conventional 12C steel rotor blade.

The cross section shown by the dotted line shows the cross section of the rotor blade 2 made of titanium alloy according to the present invention (2). In this case, the dorsal side shape 3 is the same for both, and the ventral side shape 4 is the same according to the present invention. The rotor blade 2 is made uniformly thick by A in the y direction.As shown in Figure 2, A and the rate of increase in the natural frequency of the rotor blade are approximately directly proportional to each other. We can now conclude that the above formula holds true for wings as well.

Therefore, processing of the titanium alloy turbine rotor blade of the present invention is easy. That is, when processing the dorsal side shape 3 in Fig. 1, it is processed in exactly the same way with the general milling cutter used when machining the dynamic R1 made of 12Cr steel, and when processing the ventral side shape 4, the 12Cr8! In other words, it is sufficient to use the general milling cutter used when processing the rotor blade 1 made of li1 by offsetting it in the y direction by A (corresponding to about the fifth factor of the blade average thickness). Other than this point, there is no difference in the processing of the two.

As described above, the same-shape replacement titanium alloy turbine rotor blade of the present invention has exactly the same vibration characteristics as the conventional 12CRFI rotor blade, and its processing method is also extremely economical.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the profile of a titanium alloy turbine rotor blade according to the present invention, and FIG. 2 is a diagram showing the relationship between the cutter offset processing amount and the natural frequency change of the rotor blade.

Claims (1)

[Claims] Low-pressure stage 1 of a steam turbine: Used for the blades, especially the last stage or the preceding stage, including the stop blades, as opposed to the blades C=, such as 12Cr steel, which usually have a profile. A titanium alloy turbine rotor blade characterized by an increase in thickness of approximately 5 inches.