JPS58204350A - Method for detecting flaw on surface of metallic object - Google Patents

Abstract

PURPOSE:To enable the detection of the defect on a surface with high S/N ratio, by setting the angle between the normal on the surface of a specimen and the incident angle of irradiated light at 15-55 deg. and detecting the scattered light and specular reflected light of <20 deg. angle to the incident direction. CONSTITUTION:A laser light source 22 disposed in the diagonal direction intersecting orthogonally with the traveling direction of a continuous casting slab 20 on the lateral side of the traveling line of said slab irradiates external light in such a way that the angle theta1 between the normal on the surface of the slab 20 and the incident direction of the irradiated light attains 15-55 deg.. The laser light 22a is expanded to a belt shape up to the necessary visual field on the slab 20 by a cylindrical lens 24. On the other hand, a photodetection camera 26 disposed on the same lateral side as the light source 22 of the slab traveling line detects the scattered and reflected light of <20 deg. angle theta2 to the incident direction of the detected light. The outputs of the camera 26 and a camera 28 for detecting regular reflected light are compared in a comparator 34 via signal processing circuits 30, 32, and only the defect signal removed of the spurious defect signal by a scale, etc. is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting flaws on the surface of a metal object, and in particular, a method for detecting defects on the surface of a metal object during running 11, which is suitable for online detection of surface defects in a running high-temperature steel material such as a continuous express slab. The present invention relates to an improvement in a method for detecting defects on the surface of a metal object in which surface defects on the object are detected by irradiating light onto the surface of the object from the outside and receiving light reflected by the surface of the object.

An optical surface flaw detection method is known in which surface defects on the test object are detected by irradiating light from the outside onto the surface of the test object while it is running on a conveyance line, and receiving the reflected light from the test object surface. . This optical surface flaw detection method, for example, as shown in FIG. External light is irradiated, and the light receiver 1 is placed in the direction of the subject's weight on the subject's travel line.
Surface defects on the object 10 are detected from changes in the chain of reflected light (changes in light amount, diffraction pattern, etc.) received by the detector 4. For example, when a laser light source is used as the projector 12, a spot-like light spot is scanned in the width direction of the subject 10 using a flying spot scanning method, and the reflected light from the subject 10 is photoelectron multiplied by tR. The light is received by a light receiver 14 made of a photo cell or the like, and the position of the defective portion in the width direction is detected from the change in the amount of light at each point. When a bar-shaped white light source is used as the light projector 12, the light reflected from the subject 10 is sequentially received by the light receiver 14, which is a -dimensional image sensor, one pixel at a time, using a flying spot scanning method. do.

According to such an optical blush detection method, surface defects of the moving object 10 can be measured online in a non-contact manner. was high, which was an impediment to practical use.

In addition, the test object 10 is mainly a room-temperature test object such as a cold-rolled steel plate, and using it as it is for surface flaw detection of a hot material such as a continuous casting slab is difficult in terms of heat resistance. There was a problem. Furthermore, it has a complicated mechanism such as a part of the rotating mirror, and the heat resistance and adjustment of the entire device is difficult!
! It was rough.

The present invention was made in order to eliminate the above-mentioned conventional drawbacks, and it is possible to eliminate surface defects of a moving object by a high (XSN ratio: Ml).
It is an object of the present invention to provide a method for detecting flaws on the surface of a metal object that allows for good detection and allows easy heat resistance measures for a projector and a light receiver.

The present invention provides a method for imaging the surface of a metal object in which surface defects on the object are detected by irradiating light from the outside onto the surface of a moving object and receiving reflected light from the surface of the object. From a light projector placed on the side of the subject travel line in an oblique direction perpendicular to the subject travel direction, the subject is placed so that the angle between the normal to the subject surface and the incident direction of the irradiation light is 15 degrees to 55 degrees. External light is irradiated onto the surface, and the light is received by a scattered reflection light receiver placed on the same side of the object travel line as the projector or on the opposite side, and the angle made with the irradiation light incident direction or specular reflection direction is 20 Surface defects on the object to be inspected can be detected from changes in the scattered reflected light within a degree and changes in the specularly reflected light received by the specularly reflected light receiver placed on the opposite side of the object's travel line from the projector. The above objectives have been achieved.

The present invention will be explained in detail below.

The present invention, as shown in FIG. In a surface flaw detection method for detecting surface defects of the object 10, the inventors and others varied the incident direction of the irradiated light by the light emitting light 112 and the direction in which the reflected light was received by the light receiver 14 to find the optimal position. This was done based on the results of experiments on the relationship.

That is, the projector 12 is placed on the side of the subject running line in an oblique direction orthogonal to the subject running direction, and the angle θ1 between the normal to the subject surface and the direction of incidence of the irradiation light is varied.
A light receiver 14 placed on the same side of the object travel line as the light projector 12 receives scattered reflected light having an angle θ2 of 10 degrees with the incident light direction, and surface defects on the object 10 are detected from this light. However, the S, -'N ratio of the defect (mainly vertical crack) signal was as shown in FIG. As is clear from the figure, when the angle θ1 is within the range of 15 degrees to 55y1, the S/N ratio of the defect signal is 2.0 or more, which is the level at which defect signals can be discriminated in practice. Then,
It is possible to detect defects as high as 11 degrees.

Also, projecting light! By fixing the angle θ1 between the incident direction of the irradiated light and the normal line of the object surface to 45 degrees,
14 and the direction of receiving the scattered reflected light and the above-mentioned light projection! The change in the S/N ratio of the defect signal detected from the scattered reflected light was investigated by changing the angle θ2 between the beam and the incident direction of the irradiated light by 112, and the results shown in FIG. 3 were obtained. As is clear from the figure, if the angle θ2 is within ±20 degrees, the S/N ratio of the defect signal is 2.0 or more, and highly accurate defect detection is possible.

Furthermore, the projector 12 is also placed on the side of the subject travel line.
It is arranged in a diagonal direction orthogonal to the subject running direction, and the angle θ1 between the normal to the subject surface and the irradiation light incident direction is changed by 1p1 degrees, so that the light on the side opposite to the projector 12 of the subject running line is The specularly reflected light was received by the light receiver 14 placed at the specularly reflected light receiving position where the angle between the normal to the surface of the subject and the direction of receiving the reflected light was equal to the angle θ1, and surface defects on the subject 1o were detected from this. However, the S y'N ratio of the defect signal was as shown in FIG. As is clear from the figure, for the defect signal obtained from specularly reflected light, the angle θ1 is 15 degrees to 5
If it is within the range of 5 degrees, the S/N ratio will be 2.0 or more, and highly accurate defect detection is possible.

Furthermore, when the incident direction of the light irradiated by the projector 12 is set to an oblique direction to the side of the line, the reflected light close to the regular reflected light from the shoulder of the vertical crack 10a is emphasized, as shown in FIG. In addition, the reduction rate of specularly reflected light due to the vertical crack 10a is also emphasized, so that the projector 1.
,・The method of placing 2 diagonally above the side of the line is especially useful for running,
This method is effective for detecting vertical cracks parallel to the row direction. or,
Even when the vertical distance from the subject is small, heat-resistant measures are advisable. Furthermore, there is no need to provide a large distance between the projector and the reflection point, and sufficient light reaches the reflection point regardless of the influence of dust that is abundant at the site.

Incidentally, if the angle θ is too small, the perspective of the projected field of view is forced, which may cause problems in addressing during focusing and signal processing.

-h, the larger the angle θ1 is, the less it will be affected by the upward movement of the subject 10, but since it will be closer to the top surface of the subject 10, this will be a problem, especially in terms of heat resistance of high-temperature materials. or,
When inspecting the lower surface of the object 10 without inverting it, it is also necessary to increase the depth T of the pit in which the light projector 12 is disposed. Therefore, as mentioned above, 15 degrees ~ 551! It is preferably within the range of [, and in particular, the range of 20 degrees to 50 degrees is more effective in practice.

Furthermore, as shown in FIG. 5 (A>), on the upper surface of the subject 10,
If there are sources of pseudo-defect signals such as vertical cracks 10.8 and scale 11, the light reception signal received by the scattered reflection light receiver will be as shown in FIG. 5(B).
The signal received by the specular reflection light receiver is shown in Figure 5 (C
), by comparing the output signals of the two, it is possible to detect surface defects with high precision without being influenced by sources of pseudo-defect signals such as scale.

In FIGS. 5(B) and 5(C), beak A is a pseudo defect signal and beak B is a defect signal.

The present invention has been made based on the knowledge as described in -F.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a continuous casting slab surface flaw detection apparatus employing a metal object surface flaw detection method according to the present invention will be described in detail below with reference to the drawings.

In this embodiment, as shown in FIG. 6, the normal line of the surface of the continuous casting slab 20, which is disposed on the side of the running line of the continuous casting slab 20 in an oblique direction orthogonal to the slab running direction, and the irradiation light incident direction The laser beam 122 that irradiates the surface of the continuous casting slab 2° with external light so that the angle θ1 is 15 degrees to 5511 degrees, and the laser beam 22a oscillated by the laser light source 22 are applied to the continuous casting slab 20 as required. ! A cylindrical lens 24 for widening the field of view in a strip shape and a cylindrical lens 24 disposed on the same side of the slab running line as the laser light source 22 are arranged to suppress scattered reflected light whose angle θ2 with the irradiation light incident direction is within 20[1]. Scattered reflected light receiving camera 2 for receiving light
6, and is arranged at a specularly reflected light receiving position on the side opposite to the laser light source 22 of the slab traveling line, where the angle between the normal to the surface of the continuous casting slab 20 and the reflected light receiving direction is equal to the angle θ1. In addition, a specular reflection light receiving camera 28 for receiving specular reflection light, and a scattering reflection light signal 51 for processing the scattering reflection light signal output from the scattering reflection light receiving camera 26! l
a specular reflection light signal processing circuit 32 for processing the specular reflection light signal output from the specular reflection light receiving camera 28; and outputs of the scattering reflection light signal processing circuit 30 and the specular reflection light signal processing circuit 32. A comparison circuit 34 outputs only defect signals from which pseudo defect signals due to scale etc. have been removed.
It is composed of. In FIG. 6, 36 and 38 pass only the usable wavelength range of the laser beam 22a irradiated from the laser beam 22 disposed in the light receiving parts of the scattered reflection light receiving camera 26 and the specular reflection light receiving camera 28, respectively. This is an interference filter for removing the influence of self-luminous energy of the continuous casting slab 20 and improving detection accuracy.

As the laser beam ai22, for example, an argon laser with an output of 5 W can be used. Generally, when a high-temperature object is used as the test object, the self-luminous energy of the test object has a strong 1-energy component on the long wavelength side of infrared and visible wavelengths, so when obtaining a defect signal by receiving reflected light, It is advantageous to project light of a short wavelength with as few self-luminous components as possible. Since the wavelength component of the strongest output of the argon laser has a wavelength in the vicinity of 50011, it falls within the wavelength range where the self-luminous component of high-temperature steel materials such as continuous casting slabs is relatively weak. It is effective as a light source for surface flaw detection because it can provide a relatively strong output.

As the scattered reflection light receiving camera 26 and the specular reflection light receiving camera 28, for example, an electronic scanning image sensor using a charge-coupled device can be used, which is disposed on the focal plane. The lens of each light-receiving camera is selected to have an optimal aperture depending on the distance between the subject and the light-receiving camera, the width of the band-shaped light projection surface, and the like. Now, when inspecting the field of view width 1- using a sensor of 2048 @ child, its geometric resolution is approximately Q,
It becomes 5m.

A light projection device including the laser light source 22, the cylindrical lens 24, etc.; a scattering reflected light receiving device including the scattered reflected light receiving camera 26; an interference filter 36; a regular reflecting light receiving camera 28; All of the reflected light receivers are arranged at a sufficiently large distance in the diagonal direction of the continuous casting slab 20, and are heat-resistant with gas or liquid so that they can be used continuously for a long time.

The action will be explained below.

The continuous casting slab 20 with a surface concentration of 500° C. or more is running on the production line at a substantially constant speed in the direction of arrow C,
At least the surface to be inspected is in a state that can be considered flat. The laser beam 22a emitted from the laser light source 22 is applied to the continuous casting slab 2 in a strip shape by a cylindrical lens 24.
The light is projected onto 0. The laser light reflected by the surface to be inspected of the continuous casting slab 20 enters the scattered reflection light receiving camera 26 and the specular reflection light receiving camera 28, and a band-shaped light image is firstly focused on the focal plane of each light receiving camera 26, 28. After being input as original information and converted into defect signals by each signal processing circuit 30 and 32, a comparison circuit 34 also considers the address of each defect signal in the width direction of the object, removes false defect signals, and converts it into a genuine defect signal. Only defect signals are output.

In this embodiment, since the laser light source 22 is used as the projector, the laser light source 22 and the cylindrical lens 24 are connected to the continuous casting slab 20, which is the material.
It is possible to increase the distance between the pass line between the continuous casting slab 20 and each of the light receiving cameras 26 and 28, which is more advantageous in terms of heat resistance. That is, the laser beam has strong directivity, the beam is very small, and the energy density is extremely high, so there is almost no attenuation with distance, and the cylindrical lens 24
Even if it is spread horizontally, a sufficiently high energy density can be obtained.

Furthermore, as a characteristic of laser light, its wavelength component is single, so as in this embodiment, an interference filter 36, 38 suitable for the laser to be used is attached to the front surface of the lens of each light receiving camera 26, 28. Therefore, it is possible to receive only the laser beam extremely selectively, and it is easy to effectively eliminate the influence of self-luminous energy. Note that the type of projector is not limited to this, and for example, a mercury lamp that projects white light can also be used.

Furthermore, in this embodiment, the light from the laser light source 22 is
Light is projected in a band shape onto the surface of the continuous casting slab 20, and the reflected light is received by an electronic scanning image sensor to obtain an output signal, so signal extraction scanning is easier than conventional mechanical scanning. It is extremely transparent. Therefore, it is possible to respond even when the traveling speed of the object is above 10001/min. Also, it is possible to respond by using a photomultiplier tube, silicon photocell, amplifier, etc. Compared to the case where the flaw detection device is configured, the light receiver is smaller, and it is easier to take shielding measures such as moisture resistance, heat resistance, acid resistance, etc.Furthermore, since there are no rotating parts in the flaw detection device as a whole, maintenance is easy.

In the above embodiment, the scattered reflected light receiving camera 26
was arranged on the same side of the slab running line as the laser light source 22, and the light receiving camera 26 was configured to receive scattered reflected light having an angle of 20 It or less with respect to the incident direction of the irradiated light. However, the 15 method for receiving scattered reflected light is
However, the scattered reflection light receiving camera 26 is arranged on the side h opposite to the laser beam m22 of the slab traveling line, that is, on the same side as the specular reflection light receiving camera 28,
The light receiving camera 26 makes an angle of 2 with the direction of specular reflection.
It is also capable of receiving scattered reflected light within 0 degrees.

In the above embodiments, the present invention was applied to flaw detection on continuously cast slabs, which are high-temperature materials. It is clear that the present invention can be similarly applied to online flaw detection of hot rolled steel strips, online flaw detection of pickling lines, online flaw detection of cold rolled steel strips, steel plates, etc.

As explained below, according to the present invention, it is possible to detect surface defects on an object to be inspected during running, such as continuous casting snow 1, with a high signal-to-noise ratio (accuracy), and moreover, It is easy to take measures against heat resistance.It also has excellent effects such as not suffering from pseudo-defects such as scale.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a state in which a conventional surface flaw detection method is being performed, and FIG. 2 is a perspective view showing the principle of the present invention. i1! Figure 3 shows an example of the relationship between the angle between the normal to the specimen surface and the incident direction of the irradiated light and the S/N ratio of the defect signal detected from changes in the scattered reflected light. FIG. 4 is a diagram showing an example of the relationship between the angle between the incident direction and the scattered reflected light receiving direction and the S,'N ratio of the defect signal detected from the change in the scattered reflected light. A diagram showing an example of the relationship between the angle between the normal line and the incident direction of the irradiated light and the S,/N ratio of the defect detected from the change in specularly reflected light, W
Figure 4b (A) is a cross-sectional view showing the state in which the irradiation light is directed diagonally to the surface of the subject that also has vertical prints and scales, and Figures 5 (B) and (C) are respectively FIG. 6 is a diagram showing the state of change of scattered reflected light and specular reflected light. FIG. FIG. 2 is a perspective view partially including a block diagram. 10... Subject, 10a... Vertical crack, 11.
...Scale, 12... Emitter, 14... Light receiver, 20... Continuous casting slab, 22... Laser light source, 24... Cylindrical lens, 26...
Scattered reflected light receiving camera, 28...Specular reflected light receiving camera, 30...Scattered reflected light target N circuit, 32...Specular reflected light signal processing circuit, 34...Comparison circuit, 36.38...・Interference filter. Agent Takaya Ron (and 1 other person) Figure 1 Figure 2 - Single degree θC

Claims (1)

[Claims] (1) A metal object surface flaw detection method in which external light is directed onto the surface of a moving object, and the reflected light from the surface of the object is received to detect surface defects on the object. , from a projector placed on the side of the subject running line in an oblique direction orthogonal to the subject running line, so that the angle between the line on the subject's surface and the direction of incidence of the irradiated light is 15 degrees to 55 degrees. External light is irradiated onto the surface of the test object, and the light is received by a scattered reflection light receiver placed on the same side of the test object travel line as the projector or on the opposite side. Changes in scattered reflected light within a dimension angle of 20 degrees,
A surface of a metal object, characterized in that surface defects on the object to be inspected are detected from changes in specularly reflected light received by a specularly reflected light receiver placed on the opposite side of the object's travel line to the projector. Detecting damage.