JPS5934146A - Flaw detector for rotor blade - Google Patents

Abstract

PURPOSE:To detect the abnormality of a rotor blade by recording the acoustic wave generated when the rotor blade is hammered, measuring the frequency thereof and comparing the same with the frequency obtd. similarly with a normal blade. CONSTITUTION:A memory 11 is provided in an arithmetic section 10, and the reference frequency output of the intensity of sound at each frequency obtd. beforehand by a frequency analysis when a normal blade 2 is hammered, that is, a frequency distribution or average frequency, is stored in the memory 11. A certain blade 2 is hammered and if the frequency output thereof deviates from the range of the normal value obtd. by hammering the normal blade 2, said deviation is discriminated in the section 10 which determines the presence of abnormality in the blade 2 and supplies an abnormality signal to an abnormality announcing means 12 constituted of a lamp or buzzer, thereby announcing the abnormality.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotor blade flaw detection device, and more particularly to a flaw detection device capable of detecting cracks existing in a turbine rotor blade by simple hammering.

Non-destructive testing methods are widely used when inspecting materials such as metal parts and the scratches generated by them. It has also been widely used as a flaw detection method. However,
When detecting the presence of cracks in the blades of turbine rotors, transmission inspection using radiation such as X-rays and visual inspection using microscopes have traditionally been used as non-destructive inspection methods. It's coming.

However, with such conventional flaw detection methods, the blade must be disassembled from the rotor in any case, and especially when using radiographic inspection, it is necessary to project the entire surface in order to obtain a transmission image. Not only does equipment cost money, it also takes time. In addition, the use of a microscope is limited to detecting external injuries, and when detecting flaws, there is a risk of overlooking small wounds, so reliability is an issue.

The object of the invention is to eliminate the above-mentioned drawbacks and to make the blade four-
To provide a rotor blade flaw detection device capable of detecting cracks in individual blades by hammering the turbine rotor as it is without disassembling it.

In order to achieve this purpose, the present invention records the sound waves generated by rotor blade hammering, measures its frequency, and determines whether the plate is in good condition.

Abnormalities in the blade are detected by comparing the frequency with the frequency obtained in the same manner.

The present invention will be described in detail below with reference to the drawings. In a general axial flow coupin, the turbine blades are installed radially on the rotor and have a cantilever structure. When cracks form, the stiffness decreases and the natural frequency of the blade becomes lower than that of other normal blades.

Therefore, based on this principle, the present invention performs three hammering operations on each blade, causes other blades to resonate, collects these sound waves through a sound collector, and analyzes the frequencies. Characteristic curves as shown in Figure 1 (4) and ω) were obtained. Here, the horizontal axis shows the frequency @ (Hz), and the vertical axis shows the sound intensity (dB), and Figure 1 (A) shows the frequency distribution when a normal blade is hammered.
Figure (J3) shows the frequency distribution when a blade with abnormalities such as cracks is hammered.

In other words, the peak of the waveform that stands out at the low frequency A (Hz) is generated by the blade with the abnormality, and the peak between frequencies B and C (Hz) is generated from other blades without the abnormality. It has become clear that by comparing these characteristic curves, it is possible to detect whether or not cracks have occurred in the rotor blade, as well as to detect which blades have cracks.

The present invention has been made based on the above-mentioned principle, and FIG. 1 shows an embodiment of the present invention based on this principle. Here, l shown on the right side of the figure is the turbine rotor to be inspected, ko is the rotor blade, and blade J! - It detects cracks existing in the brake plate by hammering with a hammer 3, and the flaw detection equipment [, S- is a microphone 6°, a frequency analysis section 7y, an F/v converter, an A/p converter 9, and a calculation section. /θ. 1
The vibration sound that incorporates the resonance sound of other blades when hammering the blade s is collected by a microphone and supplied to the frequency analysis section, where the frequency distribution and the average frequency of the distribution are collected. Get a frequency output such as.

The frequency output obtained by the frequency analysis section 7 is supplied to the F/V converter t and converted into a voltage, and this voltage output is further supplied to the A/D converter 9 and converted into a digital quantity, from which the calculation section / Output to θ. The calculation unit IO is provided with a memory//, and this memory l/ stores the sound intensity at each frequency obtained through frequency microanalysis when a normal blade a is hammered, that is, the frequency distribution or average frequency, etc. Memorize the reference frequency output. Therefore, when a certain brake coil is hammered, if its frequency output deviates from the range of normal values obtained by hammering a normal brake coil, the arithmetic unit 10 determines this and determines that the brake coil is abnormal. An abnormality can be notified by supplying an abnormality signal to the abnormality notification means/2, which is comprised of a lamp, a buzzer, or the like.

Furthermore, the average frequency output obtained by the calculation unit 10 is calculated as the frequency 'II
It can also be supplied to a H indicator meter/3 and read its average frequency output. Note that the frequency display on the frequency display meter/J may be in either an analog or digital format.

Furthermore, a fast Fourier transform (FFT) is applied to the frequency distribution output obtained by the calculation unit io, and the output is displayed on a cathode ray tube display, as shown in FIGS. 1(A) and (B).
An abnormality may be detected by displaying a characteristic curve such as the one shown in FIG. 1 and comparing it with the normal characteristic curve.

As explained above, according to the present invention, only the seven blades installed in the sweater are hammered, and at that time, the resonance sound of the other blades is also captured, and the vibration sound is frequency-analyzed. , the blade is in a normal state and the blade is in a normal state with an abnormality such as a crack, and when the frequency obtained from the analysis exceeds the normal value limit by a predetermined value or more, it is determined to be abnormal. Therefore, flaw detection can be performed without disassembling the blade while it is still attached to the rotor, and cracks existing in the blade can be detected reliably and quickly simply by hammering. Furthermore, it is also possible to detect the average frequency by performing only one hammering.

[Brief explanation of the drawing]

Figures 1 (A) and ω) are frequency distribution diagrams obtained when hammering a normal blade and a blade with an abnormality, respectively, and Figure 2 is a diagram of the flaw detection device for rotor blades of the present invention. FIG. 2 is a block diagram showing an example of the configuration together with a rotor and a hammer. l... Turbine rotor, Co... Blade, 3... Hammer, 3... Flaw detection device, 6... Microphone, 7... Frequency analysis section, J... F/v converter, 7 ...A/D converter, lO...computation unit, //...memory, /2...abnormality reporting means, /3...frequency display meter, lri...cathode ray, tube display. Patent applicant Nissan Motor Co., Ltd.

Claims (1)

[Claims] a frequency analysis means for obtaining frequency outputs of the vibration sound and the resonance sound obtained from the sound collection means; 1. A rotor blade flaw detection device comprising: a calculation unit that detects the presence or absence of an abnormality by comparing it with a reference frequency output determined in advance.