JPS58204348A - 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 incident direction of the irradiated light from the lateral side and the normal of the surface of a specimen at 15-55 deg. and detecting the scattering light of <20 deg. the angle to the incident direction of the irradiated light. 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 angle of the irradiated light and a signal processing circuit 28 outputs a defect signal. The S/N ratio 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 detecting flaws on the surface of a metal object, and particularly to a method for detecting flaws on the surface of a metal object, which is suitable for online detection of surface defects in a high-grade steel material such as a continuously cast slab. I of the subject of
! This invention relates to an improvement in a method for detecting defects on the surface of a metal object by irradiating the surface with light from the outside and receiving light reflected by the surface of the object to detect surface defects on 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. There is. In this optical surface flaw detection method, for example, as shown in FIG. 1, a projector 12 placed directly above the object 10 above the travel line of the object 10 is used to simultaneously irradiate the surface of the object 10 with external light spread in a fan shape. Alternatively, using external light that can scan flying spots, reflected light received by the light receiver 14, which is also placed in the direction of the subject's weight on the subject's travel line (D. For example, when a laser light source is used as the projector 12, a spot-shaped light point is scanned in the width direction of the object 100 using a spot scanning method. The reflected light from the specimen 10 is received by a light receiver 14 made of a photomultiplier tube, a silicon photocell, etc., and the widthwise position tt of the defective portion is detected from the change in the amount of light at each point.

When a bar-shaped light source of white light is used as the light projector 12, the light reflected from the object 10 is sequentially received one point (one pixel) at a time by a light receiver 14, which may also be a -dimensional image sensor, using a flying scanning method. do.

This optical surface flaw detection method has the feature of being able to measure surface defects on the moving object 100 without contact, but conventionally, a noise signal is interpreted as a defect signal and the number of false detections is reduced. was high (and had become an obstacle in practical use).

In addition, the test object 10 is mainly a room-temperature test object such as a cold-rolled steel plate, and it is difficult to use it for surface flaw detection of high-temperature materials such as continuous casting slabs due to its heat resistance. There was a problem. Furthermore, it has a complicated mechanism such as a part of the rotating mirror, and the heat resistance measures and adjustments for the entire device are extremely complicated.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional art. The purpose of this invention is to provide a method for detecting flaws on the surface of a metal object that allows easy heat resistance measures.

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. A light projector placed on the side of the travel line in an oblique direction perpendicular to the travel direction of the test object is used to illuminate the surface of the test object such that the angle between the normal to the test surface and the incident direction of the irradiated light is between 15 degrees and 55 degrees. External light is irradiated and received by a light receiver placed on the same side and/or opposite to the projector of the subject travel line, and the angle between the irradiated light incident direction and/or specular reflection direction is 20 degrees. This object has been achieved by detecting surface defects on the object from changes in the scattered reflected light within a range of 1.

The present invention will be explained in detail below.

The present invention, as shown in FIG. In a surface flaw detection method for detecting defects on the II surface of a test object 10, the inventors determined the optimum position by varying the incident direction of the irradiated light from the light projector 12 and the direction of the reflected light received by the light receiver 14. This was based on the results of my dormitory experience regarding the relationship.

That is, the projector 12 is placed on the side of the subject running line in an oblique direction perpendicular to the subject running direction, and the angle R'+ between the normal to the subject surface and the incident direction of the irradiation light is varied. The light receiver 14 arranged on the same side of the subject travel line as the light emitter 12 allows the angle 0.00000000000 to be made with the direction of incidence of the irradiated light. is 1
After receiving the scattered reflected light at 0 degrees and detecting surface defects on the object 10, the S/N ratio of the defect (mainly vertical cracks) signal is clear from the 0 degree diagram shown in Figure 2. As shown, when the angle θ is within the range of 15Jf to 5b degrees, the 8/N ratio of the defect signal becomes 2.0 or more, which is a level that can practically discriminate the defect signal, Highly accurate defect detection is possible.

Also, the angle between the direction of incidence of the irradiated light from the projector 12 and the normal to the surface of the subject is 0. is fixed at 45 degrees, and the receiver 1
When the angle between the receiving direction of the scattered reflected light by 4 and the incident direction of the irradiated light by the projector 12 was varied by t, and the variation lII of the defect signal O8/N ratio detected from the scattered reflected light was investigated, The results shown in Figure 3 were obtained. As is clear from the figure, if the angle f1 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, when the incident direction of the irradiated light from the projector 12 is set to the diagonal direction to the side of the line, as shown in FIG.
Since the reflected light close to the specular reflected light from the shoulder of the 10m vertical crack is emphasized and becomes scattered reflected light, the projector '1
2t - above the diagonal village on the side of the line (the method is particularly effective for detecting longitudinal cracks parallel to the running direction. Fig. 4 (
B) shows a received light waveform when the incident angle is 45 degrees, and beak A is a defect signal. Further, even when the vertical distance between the object 10 and the object 10 is small, heat resistance measures can be easily taken. Furthermore, there is no need to increase the distance M between the projector and the reflection point (
, Sufficient light reaches the reflection point, regardless of the influence of dust that is abundant at the site.

However, if the angle 01 is made too small, the perspective of the projected field of view will be emphasized, which may cause problems in addressing during focusing and signal processing.

On the other hand, the angle is 0. The thicker it is, the less it will be affected by vertical movement of the subject 10, but since it will be closer to the top surface of the subject 10, this will be disadvantageous, especially in terms of heat resistance of high-temperature materials. or,
When inspecting the lower surface of the object 10 without inverting it, it becomes necessary to increase the depth of the bit for arranging the projector 12. Therefore, as mentioned above, within the range of 15 degrees to 551 Preferably, a range of 20 degrees to 50 degrees is particularly effective for dormitory use.

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

Hereinafter, with reference to the drawings, an embodiment of a continuous casting slab surface flaw detection apparatus employing the metal object surface flaw detection method according to the present invention will be described in detail. (The angle θ1 between the webbing on the surface of the continuous casting slab 20, which is arranged in an oblique direction orthogonal to the slab running direction on the side of the continuous casting slab 20υ running line, and the irradiation light incident direction is,
A laser light source 22 irradiates external light onto the surface of the continuous casting slab 200 at an angle of 15 degrees to 55 degrees, and 22 m of laser light oscillated by the laser light source 22 is applied to the required viewing width on the continuous casting slab 20. A cylindrical lens 24 for spreading it into a band shape, and a cylindrical lens 24 disposed on the same side of the slab running line as the laser light source 22, for receiving scattered reflected light within 20 f of the stratum corneum θ which forms the incident direction of the irradiated light. The light receiving power is made up. In FIG. 5, 30 is disposed in the light receiving part of the light receiving camera 26, and allows only the usable wavelength range of the laser light 22m irradiated from the laser light source 22 to pass fC.Therefore, the self-luminous energy of the continuous casting slab 20 is This is an interference filter that removes the influence of noise and improves detection accuracy.

As the laser light source 22, for example, an argon laser with an output of 5 W can be used. In general, ′i! 6 When the object is t-object, the self-luminous energy of the object is:
Since it has strong energy components on the long wavelength side of infrared and BJ views, it is better to project short wavelength light with as few self-luminous components as possible in order to receive the reflected light and obtain a defect signal. be. The strongest wavelength component of the argon laser is 500 nm.
Since it has a wavelength near m, i# like a continuous casting slab
This type of laser corresponds to a wavelength range in which the self-luminous component of ib steel is relatively weak, and since this type of laser can continuously obtain a relatively strong output, it is effective as a light source for surface flaw detection.

As the light-receiving camera 26, it is possible to use, for example, one in which an electron beam sensor using a charge-coupled device is disposed on the focal plane. The lens of the light-receiving camera is selected to have a diameter of 47.0% based on the distance between the subject and the light-receiving camera, the width of the band-shaped light projection surface, etc. 4. When inspecting a field of view width of 1 mi using a sensor with 2048 elements, the geometric resolution is approximately 0.5 mm. , the light receiving device including the interference filter 30, etc., 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. It's broken.

The effect will be explained below.

The continuous casting slab 20 with a surface temperature of Hsoo°C or higher is running on the production line at a constant speed in the direction of arrow B.
At least the surface to be inspected is in a state that can be considered flat. Laser light 22& oscillated from the laser light source 22 is continuously cast into a strip-shaped slab 2 by a cylindrical lens 24.
The light is projected onto 0. The laser beam reflected by the test surface of the continuous casting slab 20 enters the light receiving camera 26 through the interference filter 301, and an image of the band-shaped light is displayed on the light receiving camera 26.
The information is input to the 6ρ focal plane as one-dimensional information, converted into a defect signal by the signal processing circuit 28, and output.

In this embodiment, a laser light source 22t is used as a projector.
- The distance between the pass line between the laser light source 22 and the cylindrical lens 24 and the continuous casting slab 20, which is a high-temperature material, and the distance between the pass line between the continuous casting slab 20 and the light receiving camera 26. It is possible to take a large value, which is more advantageous in terms of countermeasures against copper heat. In other words, the laser beam has strong directivity, the beam is very small, and the energy density is extremely high, so there is almost no attenuation over distance, and even if it is spread horizontally with the cylindrical lens 24, it has a sufficiently high energy density. Energy density is obtained.

Furthermore, since the characteristic of laser light is that its wavelength component is single, as in this embodiment, by attaching an interference filter 301 suitable for the laser used to the front of the lens of the light receiving camera 26, only the laser light can be filtered. It is possible to receive light 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, it is also possible to use a water chain lamp that projects white light.

In addition, in the main dormitory example, 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 200 and the reflected light is received by an electronic scanning image sensor to obtain an output signal, signal ejection scanning is much more effective than conventional mechanical scanning. The speed can be increased to Therefore, it is possible to respond even when the traveling speed of the subject is 1000 intervals/minute or more.

In addition, compared to a case where the light receiver is configured with a photomultiplier tube, a silicon photocell, or an amplification device, the light receiver is smaller, and it is easier to take measures against humidity, heat resistance, #I4wI, etc.

Furthermore, since there are no rotating parts in the scratching device as a whole, maintenance is easy.

In the above embodiment, the light receiving camera 26 is placed on the same side of the slab running line as the laser light source 22, and the light receiving camera 26 detects scattered reflected light within 20 m at an angle with the incident direction of the irradiated light. However, the method of receiving scattered reflected light is not limited to this method.
The light receiving camera 26 is connected to the laser light source 2 of the slab running line 1.
It is also possible to arrange the light receiving camera 26 on one side opposite to the light receiving camera 26 to receive scattered reflected light having an angle of 20 m or less with respect to the specular reflection direction.

In 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, and is applicable to hot rolling on the exit side of finishing rolling mills running at higher speeds. It is clear that the present invention can be similarly applied to online flaw detection of steel strips, online flaw detection of pickling lines, online flaw detection of cold rolled steel strips, steel plates, etc.

As explained above, according to the present invention, it is possible to accurately detect surface defects on a moving object such as a continuously cast slab with a high S/N ratio. It also has the excellent effect of being easy to use.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing a state in which a conventional surface flaw detection method is performed. Figure 3 is a diagram showing an example of the relationship between the angle and the S/N ratio of a defect signal detected from changes in scattered reflected light. , a diagram showing an example of the relationship between the defect signal and the S/N ratio detected from the change in scattered reflected light; FIG. Fig. 4 (8) is a cross-sectional view showing the state in which light is incident, and Fig. 4 (8) is a line diagram showing the changing state of scattered reflected light. FIG. 1 is a perspective view showing the entire configuration of an embodiment of a surface probing device for continuous casting slabs, including a partial block diagram. 10...Object to be inspected, 10m...Vertical division γL, 12...
- Emitter, 14... Light receiver, 20... Continuous casting slab, 22... Laser light source, 24... Cylindrical lens, 26... Light receiving camera, 28... Signal processing circuit, 30...・Interference filter. Agent Takaya Ron (and 1 other person)

Claims (1)

[Claims] (In a metal object surface flaw detection method in which light is irradiated from the outside onto the surface of a moving object and the reflected light from the surface of the object is received to detect all surface defects on the object. Nine projectors are placed on the side in a diagonal direction perpendicular to the running direction of the subject, and external light is applied to the subject's surface so that the angle between the normal to the subject's surface and the direction of incidence of the irradiated light is 15 degrees to 55 degrees. Light is irradiated and received by a light receiver placed on the same side of the subject travel line as the projector and/or on the opposite side. : From the change in scattered reflected light within
A method for detecting surface flaws on a metal object, characterized by detecting surface defects on the object.