JPS58204354A - 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 by setting the angle between the indicent direction of the irradiated light having a prescribed plane of polarization and the normal on the surface of a specimen at 15 deg.-55 deg. and detecting the scattered 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 the external light having a linear polarization characteritic 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 deg.-55 deg.. The laser light 22a is expanded to a belt shape up to the necessary visual field on the slab 20 by a cylidrincal lens 26 through a rotator 24 for the plane of polarization. On the other hand, a photodetection camera 30 which is disposed on the same side as the light source 22 in the slab traveling line and has a polarization filter 28 detects the prescribed polarization complent of the scattered and reflected light of <=20 deg. angle theta2 to the irradiation direction, and a signal processing circuit 32 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 detecting flaws on the surface of a metal object, and in particular, the present invention relates to a method for detecting flaws on the surface of a metal object, and in particular, to detect surface flaws in running high-temperature steel materials such as continuous casting slabs.
An all-woven fabric that is suitable for use in detecting defects on the surface of a moving object by irradiating light from the outside onto the surface of the object and receiving the reflected light from the surface of the object. Concerning improvements in body surface flaw detection methods.

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 surface of the test object. ing. This optical surface flaw detection method, for example, as shown in FIG. irradiated with external light, and received by the light receiver 14 placed just above the subject on the subject travel line, the reflected light is received by the light receiver 14. , which detects defects on the surface of the object 100. For example, when a laser light source is used as the light 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 reflected by the photomultiplier tube 10. The light is received by a light receiver 14 made of silicon photocells, and the position of the defective portion in the width direction is detected from changes in the light cover at each point. In addition, when a white S-shaped light k is used as the light projector 12, the reflected light from the object 10 is sent to one point (- Both plans) will receive the light.

Such an optical surface flaw detection method has the feature of being able to measure surface defects on a moving object 1O in a non-contact manner. Frequency 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-pressed copper plate, and it is difficult to use it for surface detection of continuous-temperature materials such as continuous pillow casting stubs.
1) There was some confusion regarding fever and other issues. In addition, we will ML complex mechanisms such as a part of the rotating mirror, heat resistance measures for the entire device, and 1Iil.
li was very complicated.

The present invention solves the above-mentioned conventional drawbacks. M should be used to detect surface defects on moving objects with an extremely high S/N ratio.
Good accuracy (can be detected and detected).

The overall purpose of the present invention is to provide a method for detecting flaws on the surface of a metal object in which heat resistance measures for a projector and a light receiver can be easily taken.

The present invention provides an external bl! to the surface of a running subject. Karakohi・
7, and detect the surface defects of the specimen by receiving the reflected light from the surface of the specimen. The angle between the normal to the surface of the object and the direction of incidence of the irradiated light is 15 degrees to 5 degrees from the projector placed diagonally perpendicular to the traveling direction.
External light that commands a predetermined polarization plane or that does not have a kl polarization characteristic is irradiated onto the surface of the subject so that the angle is 5 degrees. □The incident direction of the irradiated light and/or the specular reflection direction, which is received by the receiver placed on the opposite side] Scattered reflected light at an angle of 20 degrees or less, or a change in its constant polarization component from,
The above object has been achieved by detecting surface defects on the object.

The present invention will be explained in detail below.

The present invention provides a system 2 for irradiating light from the outside onto the surface of a running subject 10 using a projector 12, as shown in Figure 1.
In a surface flaw detection method ff: in which surface defects of the test object 10 are detected by receiving the reflected light from the surface area K1 of the test object 100 by the light receiver 14, the inventor Gin describes The temperature was determined based on the results of experiments to determine the optimum positional relationship between the incident direction and the direction in which the light receiver 14 receives the reflected light depending on the structure.

That is, the light projector 12 is placed on the side of the object traveling line in an oblique direction orthogonal to the object traveling direction, and the angle a1 between the normal to the object surface and the incident direction of the irradiated light is varied, and the object is moved. The light receiver 14 is placed on the same side as the projector 12 of the line, and the scattered reflected light with a corner angle θ of 10 degrees from the direction of incidence of the irradiated light is transmitted as shown by A in Figure 2. became. - As is clear from (, angle 0. is 15 degrees to 55 degrees
If the S/N ratio of the defect signal is within the range of 2.0, the S/N ratio of the defect signal is approximately 2.0
As described above, it is possible to detect defects with high accuracy.

Further, the angle t between the incident direction of the light emitted by the light projector 12 and the normal to the surface of the subject is fixed at 45 degrees, and the angle t between the incident direction of the light emitted by the light projector 12 and the normal line to the surface of the subject is fixed at 45 degrees, and the direction in which the scattered reflected light is received by the light receiver 14 and the light projector 12 are fixed.
When the change in the S/N ratio of the defect signal detected from the scattered reflected light was investigated by changing the angle QttX with the incident direction of the irradiated light, the results shown in FIG. 3 were obtained.

As is clear from the figure, if the domestic signal # is within 20 f, 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 light irradiated by the projector 12 is set diagonally to the side of the line, as shown in Fig. 4 (a), the reflected light close to the regular reflected light from the shoulder of the 10 m vertical crack is The light is emphasized and becomes scattered reflected light, so in this way, the light emitter 1
The method of placing it diagonally above the lateral side of the 2f line is particularly effective for detecting vertical cracks parallel to the running direction. FIG. 4 shows the received light waveform when the incident angle is 45 degrees, and beak B is a defect signal. Further, even when the vertical distance from the subject 10 is small, heat resistance measures can be easily taken.

Furthermore, there is no need to increase the distance between the projector and the reflection point.
Sufficient light reaches the reflection point regardless of the influence of dust on the site.

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

On the other hand, the closer the angle θ1 is, the less it is affected by the vertical movement of the subject 10 (although it is closer to the top surface of the subject 10, which is disadvantageous especially in terms of the four heats of high-temperature materials. ,
When inspecting the lower surface of the object 10 without inverting it, it becomes necessary to increase the depth of the bit for arranging one projector 12. Therefore, as described above, The angle is preferably within the range, and in particular, the range of 20 degrees to 50 degrees is more effective for practical use.

Furthermore, in the above-mentioned angle range, when the polarization conditions were set appropriately, the S/N ratio of the defect signal was further improved. That is, the irradiation light irradiated by the light projector 12 is linearly polarized light, the plane of polarization is adjusted 1ll11, and the object 10 is
Rod-like (band-like) on the surface? Jl! The external light has a polarization plane that is parallel to the short side of the field, that is, parallel to the running direction of the object 100. When receiving reflected light from the object 10, only the light with this polarization plane is sent to the receiver 14. When V was turned for input, under the same angle conditions as above, the S/N ratio was significantly improved as shown by center NC in FIG. 2 (and as shown by Q in FIG. 4). Even when the tube and polarization conditions were not limited to those in the previous example, and only one beam of light with a scattering polarization plane perpendicular to the incident polarization plane was received, an effect similar to 11y1 was obtained.

The present invention has been made based on the above-mentioned knowledge υ.

Hereinafter, an embodiment of a continuous casting slab V surface detection apparatus employing the metal object surface flaw detection method according to the present invention will be described with reference to the drawings.

In this example, #! As shown in Figure 5, continuous casting slab 20
The angle 11'+ between the normal to the surface of the continuous casting slab 20 and the incident direction of the irradiation light, which is arranged in an oblique direction perpendicular to the slab traveling direction on the side of the traveling line, is 15 degrees to 55 degrees. A laser light source 22 irradiates the surface of the continuous casting slab 20V with external light having linear polarization characteristics, and the laser light source 22 also converts the polarization plane of the emitted laser light into a predetermined polarization plane, for example, the rod shape of the continuous casting slab 20. (band-shaped) parallel to the short side of the field of view (i.e. parallel to the 200 travel direction of the continuous cast slab)
A polarization plane rotator 24 is used to generate a laser beam 22m having a polarization plane, and a laser beam 22m that commands a predetermined polarization plane of the polarization plane rotator 24 is formed into a strip shape up to the required field width on the continuous casting slab 20. A widening cylindrical lens 26,
J? is placed on the same side of the slab traveling line as the laser light source 22; 1 for receiving a predetermined polarized light component of scattered reflected light having an angle θ2 of 20 degrees or less in the direction of incidence of the irradiated light;
A receiver is constructed in which one or more polarizing filters 28 are installed. In FIG. 5, 34 is the light receiving camera 30
(By passing only the wavelength range used by the laser light 22av irradiated from the laser light source 22, the shadow Iw of the spontaneous energy of the continuous slab 20v is removed, and the detection accuracy is improved. Interference to enhance) Zurta.

The laser beam #22 may be, for example, a 5WO output argon laser tM. In general, 1IIl, r
When an M object is used as the test object, the self-luminous energy of the test object has a large energy component on the long wavelength side of infrared and visible, so when receiving reflected light and obtaining a defect signal, it is necessary to It is more advantageous to project a short wavelength optical sound with less self-luminous components. The maximum @Takata wavelength is 500 when using argon laser.
Since it has a wavelength in the vicinity of nm, it corresponds to the wavelength range where the self-luminous component of m-copper materials such as continuous casting slabs is relatively weak.
In addition, since this laser beam produces a continuous and relatively strong output, it is suitable as a light source for surface flaw detection.

As the first light-receiving camera 30, for example, one in which an electronic scanning image sensor using an electric shock coupling system is disposed on the focal plane can be used. The lens of the light receiving camera is ζ
Depending on the distance between the object and the light-receiving camera, the width of the band-shaped light emitting surface, etc.
The optimum diameter has been selected. Now, when inspecting a field of view of 1 m1 using a sensor with a 204 g element, its geometric resolution is about G, 5 dragons.

The light projecting device including the laser light source 22, polarization plane rotator 24, cylindrical lens 26, etc., and the light receiving device including the front self-polarizing filter 28, light receiving camera 30, interference filter 34, etc. are all made of continuous casting slabs. It is arranged at a sufficiently large distance in the diagonal direction of 20, and is heat-resistant with gas or liquid so that it can be used continuously for a long time.

The action will be explained below.

The continuous casting slab 20 with a surface temperature of 500° C. or more is running on the production line at a speed of one foot in the direction of the arrow.
At least the test subject @J is in a state that can be considered as flat ground. The laser light 22m oscillated by the laser light source 22 is
After the polarization plane is made into a PA constant polarization curve by the polarization plane rotator 24, the light is projected onto the continuous casting slab 20 in a band shape by the cylindrical A lens 26. The laser beam reflected by the test surface of the continuous slab 20 passes through an interference filter 34.
and polarizing filter 281! : The image of the band-shaped light is inputted to the focal plane of the light receiving camera 30 as one-dimensional information, converted into a defect signal by the signal processing N path 32, and output.

In this embodiment, a laser beam @22' is used as a projector.
f (Since the laser light source 22 and the cylindrical lens 26 and the continuous casting slab 20 which is a high temperature material are used)
It is possible to increase the distance between the pass line between the casting slab 20 and the light receiving camera 30, and this is more advantageous in terms of heat resistance. In other words, the laser beam has strong directivity, the beam is very small, and the energy density is extremely direct, so the distance is 1li11t.
There is almost no attenuation for C, and the cylindrical lens 26
Even if the machine number is increased, a sufficiently high energy density can be obtained.

Furthermore, since the physical property of laser light is that its wavelength component is single, as in this embodiment, by attaching the interference filter 34t to the front surface of the lens of the light-receiving camera 30, which is suitable for the laser used, only the laser light can be isolated. It is possible to receive light extremely selectively, and it is easy to effectively remove shadows of self-luminous energy. Same, the types of floodlights are:
The present invention is not limited to this, and for example, it is also possible to use a mercury lamp that projects white light.

In addition, in this embodiment, a laser light source 22 emits light in a band shape onto the surface of the slab 20, and the reflected light is received by an electronic scanning image sensor. Since the output signal f: is obtained, the signal extraction set meal is
It can be significantly faster than conventional mechanical scanning. Therefore, even if the running speed of the object is 1000-/-, it is possible to respond by 5J. In addition, compared to the case where the receiver is composed of a photomultiplier tube, a silicon photocell, an amplifier, etc., the fluorescent lamp is smaller, and the fluorescent lamp is smaller than the one in which the receiver is composed of a photomultiplier tube, a silicon photocell, an amplifier, etc. It is easy to take safety measures such as l, r#, etc. Furthermore, since there are no rotating parts in the flaw detection device as a whole, maintenance is easy.

In this embodiment, the light-receiving camera 30 is placed on the same side as the laser light source 22 of the slab running line, and the light-receiving camera 30 allows the light-receiving camera 30 to detect an angle within 20 Although the scattered reflected light is received, the method of receiving the scattered reflected light is not limited to this.
It is also possible to arrange the light receiving camera 30 on the side opposite to the specular reflection direction to receive scattered reflected light having an angle of less than 20 degrees with respect to the specular reflection direction.

Furthermore, in the embodiment described above, the laser light source 22 was provided with the polarization plane rotator 24 and the polarization filter 28 was provided in front of the light receiving camera 30.
is a linearly polarized laser light source, it is also possible to omit the polarization plane rotator 24i by changing its arrangement position tM to 1. Further, the laser light source 22 is
If it is a randomly polarized laser light source or a white light source,
It is also possible to add one or more polarizing filters to the front circle of the projector. Furthermore, the irradiated light from the front 1 floodlight is polarized by 8. It is also possible to configure the receiver to receive only a predetermined polarized component of the scattered reflected light by disposing a polarizing filter on the s'lI plane of the receiver. .

In the previous 811 example, the present invention was applied to the flaw detection of continuously cast slabs, which are high-temperature materials. It is clear that the present invention can be similarly applied to online flaw detection of side hot rolled 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 of a continuously cast slab while it is being inspected with a significantly high S/N ratio. It has an excellent effect in that it is easy to take measures against Th heat in the vessel.

[Brief explanation of drawings]

Figure 1 shows a situation where the conventional surface flaw detection method is being used! i
'lr: Perspective view shown, Figure 2 shows the principle of the present invention,
Figure 3 is a miniature diagram showing the relationship between the angle made when the polarization condition is set and when it is not set, and the S/N ratio of the defect signal detected from the change in the scattered reflected light. FIG. 4(A) is a miniature diagram showing an example of the relationship between the angle formed by the direction and the direction of receiving the scattered reflected light, and the S/N ratio of the defect signal detected from the change in the scattered reflected light. FIGS. 4(B) and 4(C) are cross-sectional views showing a state in which irradiation light is incident obliquely on the surface of a subject with polarization conditions, and when polarization conditions are not set and when polarization conditions are set.
Fig. 5 is a miniature map showing the state of change of scattered reflected light in comparison.
1 is a perspective view, including a partial block diagram, showing the configuration of a theoretical example of a continuous casting slab surface flaw detection apparatus in which the metal object surface detection method according to the present invention is adopted; FIG. 10... Subject, 10a... Vertical crack, 12
... Emitter, 14... Light receiver, 20...
Continuous casting slab, 22... Laser light source, 24... Polarization rotator, 26... Cylindrical lens, 28... - Optical filter, 3o... Light receiving camera, 3
2... Signal processing circuit, 34... Interference filter. Agent Takaya Ron (and 1 other person) Fig. 1 Fig. 2 14 degrees θ1 Fig. 3 Fig. 4 (A) (B) (C)

Claims (1)

[Claims] (1) In a metal object different surface flaw detection method in which surface defects on the object are detected by irradiating light from the outside onto different surfaces of the object being inspected while the object is moving and receiving reflected light from the surface of the object, Specimen running line From the projector placed in the diagonal direction perpendicular to the running direction of the specimen, move the specimen so that the angle between the normal to the surface of the specimen and the incident direction of the irradiated light is 15 degrees to 55 degrees. Polarization plane t-' on the surface! irradiated with external light or external light without polarization characteristics, and received by a light receiver placed on the same side and/or on the opposite side of the subject travel line as the projector, in the incident direction of the irradiated light or/and A method for detecting defects on a different surface of a metal object, characterized in that a surface defect of the object to be inspected is detected from a change in the scattered reflected light or its polarized light component at an angle of 20 degrees or less with the direction of specular reflection.