JPS61284657A - Crack inspecting method - Google Patents

Abstract

PURPOSE:To exactly evaluate the presence or absence of crack generation and the magnitude thereof by using two pieces a set of acoustic emission (AE) sensors and space filters. CONSTITUTION:The AE sensors 1A and 1C and sensors 1B and 1D are mounted to the two points each in the upper and lower parts of an upper metallic mold 22 in such a manner that the former are positioned on the upper side to face each other and that the latter are positioned on the lower side to face each other. The output signals from the sensors 1A-1D are fed via preamplifiers 2A-2D to a signal processing circuit 3 and the input signal in the circuit 3 is removed of noise through a filter and is inputted as the AE pulse to the space filters 4A, 4B. The AE appearing within the set time among the AE pulses from the sensors 1A-1D is selected as the effective pulse by the filters 4A, 4B and is inputted via an OR circuit 5 to a count circuit 6. The number of the input pulses per unit time and total cumulative number are counted in the circuit 6 and are recorded 7. On the other hand, the count result of the circuit 6 is applied to a comparator 8 by which the result is compared with the reference value for comparison determined by the press load from a control panel. An alarm is triggered if the result exceeds said value. Only the AE generated from the crack is thus detected effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for inspecting cracks in a press device or the like using acoustic emission.

[Prior art]

The UO method is a method for manufacturing large diameter steel pipes. In this method, the ends of the steel plate in the width direction are slightly bent upward, then press-formed into a U-shape with the ends facing each other, and the joining edges are welded to form a tube. Since the press equipment used for such processing is a welded structure, cracks may occur due to repeated loads. Therefore, periodic diagnostics are performed to detect abnormalities in the press equipment at an early stage, and one method for doing so is to utilize acoustic emissions.

[Problem that the invention seeks to solve]

This method is a method that attempts to acoustically detect cracks or their precursor phenomena, but in press equipment, there are sounds emitted by the moving parts or sounds of sliding contact between the workpiece and the contact part, and these noises and cracks can be detected acoustically. There was a problem in that the acoustic emissions from the other parts were mixed together, making it impossible to make an accurate diagnosis.

[Means for solving problems]

The present invention has been made to solve these problems, and uses a set of 21 acoustic emission sensors and a spatial filter to monitor a defined monitoring area where there is a high possibility of crack occurrence. The object of the present invention is to provide a crack inspection method that can accurately evaluate the presence or absence of crack occurrence, size, etc., by eliminating noise.

A crack inspection method according to the present invention detects acoustic emissions occurring in an object to be inspected, and based on this, inspects cracks occurring in the object to be inspected, in which a set of two sensors for detecting acoustic emissions is used. The sensor is attached to an object to be inspected, inputs the signal output from the sensor to a spatial filter, and extracts acoustic emissions from a one-dimensional monitoring space defined by the spatial filter.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof.

As shown in FIG. 1, the press device 20 includes a lower mold 21 that is fixedly installed, and an upper mold 22 that is raised and lowered by a hydraulic cylinder (not shown), and has semicircular groove-shaped dies formed on each opposing surface. A U-shaped tube material 30 is inserted between the portions 21a and 22a with opposing edges facing upward.

Acoustic emission (hereinafter referred to as AH) sensors 1^ and IB are installed at two locations on the upper and lower sides of the upper mold on opposite sides.
, IC, LD, IA and IC are located above and face each other directly, and I
It is installed so that the B and ID are located at the bottom and face each other directly. Although the mounting position and number of sensors are not limited to those mentioned above, two sensors are used as a set, and the one-dimensional monitoring area defined by the position and the setting of the spatial filter described later is a possible place where cracks may occur. Make it a place with high sexual quality. In this embodiment, sensors IA and IB are used as one set, and sensors Ic and ID are used as one set.

Output signals from the respective AE sensors IA, 1B, 1c, and LD are amplified by preamplifiers 2A, 2B, 2C, and 2D and input to the signal processing circuit 3.

The signal processing circuit 3 passes the preamplifier output through a filter to remove noise, amplifies and detects the preamplifier output, converts it into a pulse, and outputs an AE pulse. This circuit is provided for four channels depending on the number of AE sensors or preamplifiers. The AE pulse outputs of the signal processing circuit 3 are inputted from sensors IA and IB to a spatial filter 4A, and those from sensors IG and 10 are inputted to a spatial filter 4B.

The spatial filters 4A and 4B are well-known filters that output only those signals that appear during a set time out of the input signals as valid signals. Now, the setting time for the input signals from the sensor l^ and IB will be explained based on FIG. 2.

FIG. 2 represents a plane including a line segment connecting the sensors IA and IB (hereinafter referred to as the X axis) and a line segment connecting the sensors IC and 10 (hereinafter referred to as the Y axis, see FIG. 4).

The X axis is on the side surface of the upper mold 22. The perpendicular line H passing through the center of the X-axis represents the plane of the AH source trajectory (the plane perpendicular to the plane in Figure 2 including the X and Y axes) when there is no time difference between the AE multiplied signals captured by both sensors IA and IB. There is.

Now, as shown in Figure 3 (a) and (b), the time difference between the AE pulse captured by sensor IA and the AE pulse captured by sensor IB is ΔT (assuming that sensor IA detects it quickly).
If the corresponding AE propagation distance is ΔL, then the AE source in this case is on a hyperboloid (shown as a line in Figure 2) passing through a point on the X-axis whose distance from the perpendicular H is ΔL. .

The spatial filter 4^ uses the AE multiplied signal pulse from the sensor IA as a reference, and from a point delayed by ΔT (ΔL+ in terms of propagation distance) to a point further delayed by ΔT2 (ΔL2 in terms of propagation distance) from that point. time, ΔT1. This allows ΔT2 to be set as variable. In other words, the signals that appeared within this time, in other words, the AE from the area ΔL1 to ΔL1 + ΔL2 from the perpendicular H (the area surrounded by the curved surfaces of both stations) shown by hatching in Figure 2, are output as valid. It will be done.

FIG. 3 is an explanatory diagram showing the function of the circuit within the spatial filter that makes this possible. With the AE pulse from sensor IA, a pulse circuit cuts out a pulse with a set time width ΔT1 as shown in FIG.
As shown in Figure (e), there is a pulse circuit that cuts out a pulse with a set time ΔT2, and as shown in Figure 3 (d), there is a pulse circuit that cuts out a pulse with a set time width ΔT2 using the ^E pulse from sensor IB. provided in the spatial filter. Therefore, the time ΔT2 shown in FIG. 3(e) becomes the monitoring period, and when the AH pulse of sensor IB is input during this period, the corresponding pulse in FIG. 3(d) appears, and (d).

The pulse shown in FIG. 3(e) is obtained as an output signal from the AND circuit that performs the logical product of (e). That is, only when there is an AE generation source in the hunting area shown in FIG. 2, a pulse as shown in FIG. 3 is output.

Although the above explanation was made using sensor IA as a reference, the monitoring area can be similarly set using sensor IB as a reference (
Figure 2 right). Also, when setting ΔT, = O, ΔT2
It is possible to set a monitoring space centered on the perpendicular line H by using a chisel (center of Figure 2).These monitoring areas can be selected selectively, so that areas with a high possibility of crack occurrence are included in the monitoring area. You can set it to .

Setting of such a monitoring area is performed by Y related to the sensor IC, 10.
This can also be done for the axis. Although the monitoring areas of the spatial filters 4A and 4B are determined one-dimensionally on the X and Y axes, it goes without saying that the area actually monitored is a three-dimensional space surrounded by two hyperboloids. stomach.

The outputs of the spatial filters 4A and 4B are input to an OR circuit 5, and the output thereof is input to a count circuit 6.

The counting circuit 6 counts the number of input pulses and the cumulative total number per unit time, and causes the recorder 9 to record this.

On the other hand, the count result of the count circuit 60 is given to the comparator 8,
It is compared with a comparison reference value determined by the press load given from the control panel, and if it exceeds this value, an alarm (not shown) is activated.

In the case of a press machine, the crack occurs in the upper mold 22, where the maximum stress is exerted.
Most of the noise is concentrated on the die part 21a.
, 22a, and because they are sudden signals, noise can be removed by spatial filtering. In Figure 4, the monitoring area of spatial filters 4A and 4B is set at the top of the upper mold, and only 8E, which occurred due to cracks, was effectively detected in the hunting area, and the noise was suppressed. You will be freed from influence.

〔effect〕

Since the present invention uses a spatial filter one-dimensionally to set the monitoring area as described above, the monitoring area is set so as to avoid positions where noise is likely to occur and include positions where cracks are likely to occur. By setting this, highly accurate monitoring can be performed without being affected by noise, and the occurrence of cracks can be detected early before the press equipment breaks down, making it possible to prevent unexpected situations from occurring.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the apparatus used to carry out the method of the present invention, and FIG. 3. FIG. 4 is an explanatory diagram of the spatial filter. IA, IB, IC, 10...Sensor 3...Signal processing circuit 4A, 4B...Spatial filter 6...Count circuit 7...Recording section 8...Comparator patent Applicant Sumitomo Metals 1 person outside Kogyo Co., Ltd.

Claims (1)

[Claims] 1. In a method of detecting acoustic emissions generated in an inspected object and inspecting cracks occurring in the inspected object based on this, a set of two sensors for detecting acoustic emissions is attached to the inspected object. ,
A crack inspection method comprising inputting a signal output by the sensor to a spatial filter and extracting acoustic emissions from a one-dimensional monitoring space defined by the spatial filter.