JPS58204352A - Method for detecting flaw on surface of metallic object - Google Patents

Abstract

PURPOSE:To enable the detection of the flaw on a surface with high S/N and with good accuracy by setting the angle between the incident angle of the irradiated light from forward and the surface of a specimen at 35 deg.-75 deg. and detecting the scattered and reflected light of <=20 deg. angle to the specular reflected light. CONSTITUTION:A laser light source 22 disposed forward in the traveling direction of a continuous casting slab 20 above the traveling line thereof irradiates external light in such a way that the angle theta1 between the surface of the slab 20 and the incident direction of the irradiated light attains 35 deg.-75 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 side opposite from the source 22 above the slab traveling line detects the scattered and reflected light of <=20 deg. angle theta2 to the specular reflection direction and a signal processing circuit 28 outputs a defect signal. The S/N of the defect signal is thus made >=2.0 and the defect detection with high accuracy is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface flaw detection of metal objects, and in particular,
Suitable for online detection of surface defects in moving steel products such as steel slabs, this method irradiates the surface of a moving object with light from the outside and receives the reflected light from the surface of the object. The present invention relates to an improvement in a surface flaw detection method for a metal object, which detects surface defects in a test object.

An optical surface flaw detection method is known in which surface defects on the test object are detected by shining light from outside onto the surface of the test object while it is running on a conveyance line, and receiving the light reflected by the surface of the test object. There is. This optical surface flaw detection method, for example, as shown in FIG. The object 10 is irradiated with external light and received by the light receiver 14, which is also placed directly above the object on the object travel line. It detects surface defects. For example, when a laser light source is used as the light projector 12, a spot-like light point is scanned in the width direction of the object 10 using a flying spot scanning method, and the reflected light from the object 1o is reflected by a photomultiplier tube or the like. A photoreceiver 14'c consisting of a series photocell or the like receives light, detects changes in the amount of light of each member, and detects the orientation caused by the defective portion. In addition, when a bar-shaped light beam of white light is used as the light projector 12, the reflected light from the subject 10 is transmitted to a light receiver 14 consisting of a -dimensional image sensor, one point per pixel, using a flying image scanning method. The light is received one after the other.

According to such an optical surface flaw detection method, surface defects of the moving object 10 can be measured online in a non-contact manner.
However, the degree of misdetection was high, which was a practical obstacle. In addition, as the test object 1o, a room temperature test object such as a cold-rolled steel plate is mainly used as the opposite edge, and it is not possible to use it as it is for surface Hl scratches on a Takaba material such as a continuous casting slab.
There were problems with heat resistance, etc. In history, part of the rotating mirror, etc.
It had a complicated mechanism, and the heat resistance measures and adjustments for the entire body were extremely complicated.

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and provides a method for scratching a surface of a metal object that can detect surface defects on a moving object with high precision and high S/N ratio. The purpose is to

The present invention provides a method for detecting surface flaws on 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. External light is irradiated onto the surface of the test object from a projector placed above the travel line in front or behind the test object in the direction of travel so that the angle between the surface of the test object and the direction of incidence of the irradiation light is 35 degrees to 75rIIL. , scattered reflected light that is received by a receiver located on the same side and/or opposite to the projector above the subject travel line and whose angle with the irradiation light incident direction and/or specular reflection direction is within 20 degrees. The above object is achieved by detecting surface defects of the object based on the changes.

Furthermore, the S/N ratio can be significantly increased by making the external light emitted from the projector a light having a predetermined polarization plane, and/or by making the light receiver receive a predetermined polarization component of the scattered reflected light. It is elevated.

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 a test object 10, the invention 1 and the like differs in various ways the incident direction of the irradiated light from the light projector 12 and the direction in which the reflected light is received by the light receiver 14 to determine the optimal positional relationship. This was done based on the results of experiments.

That is, the projector 12 is placed above the test object travel line and in front of the test object travel direction, and the angle θ1 formed between the test object surface and the irradiation light incident direction is changed to be opposite to the projector 12 above the test object travel line. With the light receiver 14 placed on the side, the angle θ2 with the specular reflection direction is 101! When the scattered reflected light of [ was received and the Ti-plane defect of the object 10 was detected from it, the S'N ratio of the defect signal was as shown in FIG. As is clear from the figure, when the angle θ1 is within the range of 35 degrees to 7511 degrees, the S/N ratio of the defect signal is at a level S, , /N ratio 2.
0F or more, allowing highly accurate defect detection.

The angle θ1 formed between the irradiation direction 1147J- by the light projector 112 and the surface of the object to be examined is fixed at 45 degrees, and the angle θ2 formed between the direction in which the scattered reflected light is received by the light receiver 14 and the direction of specular reflection is varied. , investigate the change state of the S/N ratio of the defect signal detected from the scattered reflected light! In fact, the results shown in Figure 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.

Incidentally, if the angle θ1 is made too small, the distance between the light projector 12 and the light receiver 14 becomes large, which is disadvantageous as an installation condition on an actual operating line. On the other hand, the angle θ1
The larger the person is, the less affected by the vertical movement of the subject 10, but there is a risk that the emitter 12 and the receiver 14 will come into contact with each other. In particular, in practice, a range of 45 degrees to 75 degrees is more effective (-).

Moreover, in the above-mentioned angular range, when the polarization conditions were set appropriately, the S, -'N ratio of the defect signal was further improved. That is, the irradiation light emitted by the light projector 12 is l! II! 1 - light, and adjust its light plane so that it is parallel to the long side of the rod-shaped (band-shaped) field of view on the surface of the subject 10, that is,
The external light has a polarization plane parallel to the width direction of the subject 10,
When receiving the reflected light from the subject 10, only the light of the polarization plane is input to the light receiver 14.
When Toriya θ1 is 45 degrees, the change state of scattered reflected light due to vertical scraping of the signal received in the direction 10 degrees apart from the normal t#J/J' direction is as shown in Fig. 4 (B). The S/N ratio was significantly improved compared to the case where - light conditions were not set, which is also shown in FIG. 4(A). Figure 4 (A>, (
In B), beak A is a defective signal. Note that the polarization conditions are not limited to the above example, and for example, the polarization plane of the irradiated light is parallel to the short side of the bar-shaped (band-shaped) field of view on the surface of the subject 10,
That is, the same effect can be obtained even if the object 10 is parallel to the longitudinal direction and only the light with a scattered polarization plane that intersects the polarization plane, that is, the elliptical polarization component is received. .

The present invention has been made based on the above findings.

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

As shown in FIG. 5, the first embodiment of the present invention has a continuous casting slab 20 surface which is placed in front of the continuous casting slab 20 in the slab running direction above the running line of the continuous casting slab 20, and
, ♀ so that the angle θ1 is between 35 degrees and 75 degrees: 1
, a laser light source 22 that illuminates and extends external light onto the surface of the continuous casting slab 2o, and a cylindrical lens that spreads the laser light 22a oscillated by the laser light source 22 into a band shape to the required field width on the continuous casting slab 20. 24, a light-receiving camera 26 for receiving scattered reflected light having an angle θ2 with the specular reflection direction of 20 degrees or less, which is disposed on the side opposite to the laser light source 22 on the E side of the slab travel line; It is comprised of a signal processing circuit 28 for processing the output scattered N reflected light signal and outputting a defect signal.

In FIG. 5, reference numeral 30 indicates a laser beam 2 irradiated from a laser beam 1 m 22 disposed in the light receiving section of the light receiving camera 26.
This is an interference filter for eliminating the influence of self-luminous energy of the continuous casting slab 20 and improving detection accuracy by passing only the wavelength range used by the continuous casting slab 2a.

As the laser light source 22, for example, an argon laser with an output of 5 W can be used. Generally, when a high-temperature object is tested, the self-luminous energy of the test object has strong energy components on the long wavelength side of infrared and visible wavelengths, so when receiving reflected light and obtaining defect signals, it is necessary to It is more advantageous to project light with a short wavelength and less self-luminous components. The argon laser has the strongest output wavelength near 500u], so it can be used for continuous casting slab-like ll4a! This Yuzu laser corresponds to the relatively weak wave S region of the self-luminous component of steel materials, and it is effective as a light source for surface flaw detection because it can provide a continuous and relatively strong output. This laser beam 11
22 is arranged at the center position in the width direction of the continuous casting slab 20, or at a position within about ±10% therefrom, in order to address the customer group when processing the received light signal.

The light-receiving camera 26 C may be, for example, an electronic scanning image sensor using an i1 double-coupled device disposed on the focal plane. The lens of the light-receiving camera is selected to have an optimal aperture depending on the distance between the object and the light-receiving camera, the width of the band-shaped light projection surface, etc.Currently, when inspecting one field of view using a 2048Jl sensor, Its geometric resolution is about 0.5 decimals.

The light emitting wall including the laser beam 1122, the cylindrical lens 24, etc., and the light receiving device including the light receiving camera 26, interference filter 30, etc. are all equipped with heat-resistant gas or liquid heat-resistant counters so that they can be used continuously for a long time. It has a picture on it.

The action will be explained below.

The continuously cast slab 20 having a surface temperature of 500° C. or more is running on the production line at a substantially constant speed in the direction of arrow Ell 43, and is in a state where at least the surface to be inspected can be considered flat. Laser light 2
2a is projected onto the continuous casting slab 20 in a band shape by a cylindrical lens 24. The laser beam reflected by the test surface of the continuous casting slab 20 passes through an interference filter 30.
The edge of the band-shaped light is input to the focal plane of the light receiving camera 26 as one-dimensional information, converted into a defect signal by the signal processing circuit 28, and output.

In this example, since the laser beam 122 is used as the projector, the laser beam 1122 and the cylindrical lens 24 and the continuous casting slab 2 which is ^144 are
0 and the distance between the continuous casting slurry 720 and the light receiving camera 26, which is advantageous in terms of heat resistance. That is, laser light has strong directivity, the beam is very small, and the energy per degree is extremely high, so the distance is
There is no reduction in energy density, and even if it is spread laterally with the cylindrical lens 24, a high energy density can be obtained in 1 minute.

Also, as a characteristic of Ray IJ' light, its wavelength component is single (
Therefore, as in this embodiment, by attaching an interference filter 30 suitable for the laser to be used in front of the lens of the light-receiving camera 26, it is possible to extremely selectively receive only the laser light. Therefore, 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
Since 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, signal extraction scanning is much more efficient than conventional mechanical scanning. The speed can be increased to Therefore, it is possible to respond even if the running speed of the subject is 1000S/min. In addition, compared to a case where the light receiver is configured with a photomultiplier tube, a silicon photocell, an amplifier, etc., the light receiver is smaller, and it is easier to take measures for shielding such as moisture resistance, heat resistance, and acid resistance. History (The flaw detection device as a whole is easy to maintain as there are no rotating parts.

Next, the second embodiment of the present invention/! : Explain in detail.

The fourth embodiment has a laser light source 22, a cylindrical lens 24, and a cylindrical lens 24, which are similar to those of the first embodiment, as shown in FIG.
In the surface flaw detection device for continuous casting slurry 720, which includes a light receiving camera 26, a signal processing circuit 28, and an interference filter 30, the laser light source 22 is a linearly polarized laser light source having a predetermined light plane. With the laser beam 1122
A polarization plane rotator 32 for rotating the polarization plane is rotatably mounted around the optical axis on the front surface of the light projection lens of the light reception camera 26, and between the front surface of the light reception lens of the light reception camera 26 and the interference filter 30, One or more polarizing filters 34 are mounted rotatably around the optical axis. The other configurations and basic functions (A) are the same as those of the first embodiment, so their explanations will be omitted.

In this example, by appropriately setting the V(- light conditions) according to the defect pattern, it is possible to obtain a defect signal with an extremely good S,7N ratio. When detecting slab defects, the slab running speed is equal to the drawing speed of the casting machine, which is at a low speed of less than 2 mm/min, so the polarization conditions of the light emitting system and light receiving system are changed in sequence according to the pattern of the defect. Therefore, it is possible to detect almost the same field of view, and it is possible to detect several types of defects at the same time.

In the embodiment described in fMj, the polarization plane rotator 32 was provided for the rape light 822, and the polarization shifter 34 was disposed in front of the light receiving (J) cod 26, but the laser light source 22 In some cases, it is possible to omit the optical plane rotator 32 by changing the position of the direct polarizing laser light source.

Furthermore, if the laser light source 22 is a randomly polarized 1f light source or a white light source, it is also possible to add one or more polarizing filters in front of the projector.

In history, the light emitted by the projector is treated as external light without polarization characteristics, and a polarizing filter is disposed in front of the light receiver so that only a predetermined light component of the scattered reflected light is received by the light receiver. It is also possible to configure - (Yes.

Incidentally, in each of the above embodiments, the light receiving camera 26
was disposed on the opposite side of the laser light source 22 up the slab running line, and the light receiving camera 26 was designed to receive scattered reflected light with an angle of 20 degrees or less relative to the specular direction. The method of receiving the scattered reflected light is not limited to this, but the scattered reflected light receiving camera 26 is placed above the slab traveling line on the same side as the laser light source 22, and the light receiving camera 26 detects the incident direction of the irradiated light. The angle made is 20...
It is also possible to receive scattered reflected light within ρ degrees.

In all of the above embodiments, the present invention was applied to flaw detection of continuously cast slabs, which are high-temperature materials, but the scope of application of the present invention is not limited to this. The same applies to 4-line flaw detection of hot-rolled steel strips on the exit side, online flaw detection of pickling lines, online flaw detection of cold-rolled copper strips, steel plates, etc. (obviously there is C).

As explained above, the present invention has the excellent effect of accurately detecting and detecting fi-plane defects in a running object such as continuous casting fabric 1 with a high signal-to-noise ratio.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a state in which the conventional surface detection 1h-method is performed, and FIG. 2 is a perspective view showing the principle of the present invention. Figure 3 is a miniature diagram showing an example of the relationship between the defect signal detected from the change in the scattered reflected light and the N ratio. Figures 4 (A) and (B) are diagrams showing an example of the relationship between the S/N ratio and the S/N ratio of the defect signal detected from the change in the polarization condition. FIG. 5, which is a miniature diagram showing a comparison of the state of change of scattered reflected light, is a partial diagram showing the configuration of a first embodiment of a continuous casting slab surface flaw detection apparatus in which the metal object surface flaw detection method according to the present invention is adopted. Perspective view including block diagram, No. 6
The figure is a perspective view partially including block lines, showing the configuration of the second embodiment. 10... Subject, 12... Floodlight, 14...
・Receiver, 20...Continuous casting 1.22...
- Rape light source, 24... Cylindrical lens, 26... Light receiving camera, 28... Signal processing circuit, 30... Interference filter, 32... - Optical surface rotator, 34... polarizing filter. Agent ^ Arrow Theory (1 idiot)

Claims (3)

[Claims] (1) In a metal object surface flaw detection method in which the surface of a moving object is irradiated with light from the outside and the reflected light from the surface of the object is received to detect surface defects on the object, the object is External light is irradiated onto the surface of the object from a projector placed above the line in front or behind the object in the direction of movement of the object so that the angle between the surface of the object and the direction of incidence of the irradiated light is 35 degrees to 75 fi. Same as the floodlight above the travel line.
Surface defects on the object to be inspected are detected from changes in scattered reflected light within 20 degrees with respect to the direction of incidence of irradiation light and/or the direction of specular reflection, which is received by a light receiver placed on the side and/or the opposite side. A method for detecting flaws on the surface of a metal object. (2) The metal object surface flaw detection method according to claim 1, wherein the external light emitted from the projector is light having a predetermined narrow optical surface. (3) The metal object surface flaw detection method according to claim 1, wherein the light receiver receives a predetermined polarized light component of the scattered reflected light.