JPS60228943A - Inspection of surface state of stainless steel plate - Google Patents

Abstract

PURPOSE:To make it possible to easily perform the inspection of the surface state of a stainless steel plate by accurately detecting a partial worn-off flaw, by allowing light to be incident to a surface to be inspected at a large incident angle and observing the surface to be inspected from the direction almost same to the incident direction. CONSTITUTION:An illumination light source 2 is arranged so that illumination light 3 is allowed to obliquely irradiate the surface of a material 1 to be inspected being a stainless steel plate at a large incident angle theta and a light detector 4 is arranged so as to observe the surface of the material 1 to be inspected from the direction almost same to the irradiation direction by the light source 2. As the incident angle theta of the light 3 from the light source 2 to the surface of the material 1 to be inspected is made larger, the light 3 is reflected from the mirror surface of the material 1 to be inspected without receiving the influence by the surface roughness of said material 1 to obtain regularily reflected light 3' but, if there is a revealed partial worn-off flaw, diffused reflected light 7 is generated. Therefore, for example, if a TV camera is used as the light detector 4, the image of the partial worn-off flaw is brightly observed in the relatively dark image of the material 1 being inspected on the picture of a monitor TV receiver 5.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for inspecting the surface condition of a stainless steel plate. Specifically, a method for inspecting the degree of occurrence of minute scratches that may occur on the surface. Regarding.

(Prior art) A cold-rolled stainless steel plate has a thickness ranging from several micrometers to several micrometers on its surface.
Fine bald-like flaws of 0 μm may occur.

Since many uses of stainless steel sheets place emphasis on aesthetics, and because underflow can cause rust, materials with significant occurrence of such flaws are rejected.

As shown in Fig. 15+a), these minute sludge-like flaws 6 are usually in close contact with the surface of the steel plate 10 and have no special optical discontinuity, so they cannot be visually observed or It is not possible to detect defects by optical methods. However, many stainless steel sheets are coated with a thin film such as vinyl at the finish rolling stage to prevent surface damage due to contact, collision, friction, etc. with other steel sheets or machine tools during transportation, storage, or mechanical processing. In many products, the thin film is peeled off when it is attached to the final product and handed over to the user, and at this time, underflow 6 is caused, resulting in the problem as shown in Figure 15(b). manifest.

The planar shape of the underflow 6a is in the shape of a tongue as shown in FIG. ) only rises. However, when things like this happen, items that are noticeable, that is, items that have a large number of standing heges, can be seen at first glance to have flaws (flickering or sparkling) even if they are not so obvious. be evaluated.

Also, since rust will progress further than this, this is actually not preferable.

Although the cause of the occurrence of sludge defects is not clear, it is thought that the cause is minute holes (indentations) on the surface of the steel sheet or cracks along grain boundaries, which are deformed by rolling. If painted, these scratches would be hidden and would not be noticeable (but since the bare skin is made of stainless steel, it cannot be hidden by painting, etc.) Therefore, inspection for scratches is carried out. Conventionally, this inspection method has relied on visual inspection by inspectors.In other words, inspectors apply adhesive tape to the surface of the material to be inspected, then peel it off, visually inspect it to reveal any sagging defects, and identify significant ones. We use methods such as categorizing items that are almost non-existent into ranks A to D. However, this visual inspection is not always easy (some items cannot be seen clearly), and since it is a sensory test, quantitative analysis is not possible. There were disadvantages such as poor accuracy and individual differences.As a method to improve quantitativeness, it is possible to count the density of flaws using a microscope, but it is time consuming and impractical. .

Furthermore, automation using an image processing device for microscopic images can be considered, but it is not always easy to automatically select target flaws from the microscopic images.

(Object of the Invention) The purpose of the present invention is to solve the problems of the conventional method, to accurately detect sagging defects, and to easily inspect the quality of the surface condition of stainless steel sheets. It is.

(Structure and operation of the invention) The present invention irradiates an illumination light beam at a large angle of incidence onto the surface of a stainless steel plate to be inspected which may have underflow, and out of the reflected light reflected from the surface to be inspected, the illumination light beam is The reflected light returning to the incident side of the light beam is received by a photodetector, and mf! is determined by the number of bright spots in the output of the photodetector corresponding to the surface to be inspected. It is characterized by inspecting the quality of the surface condition.

The present invention will be explained below. FIG. 1 is an explanatory diagram showing an overview of the present invention, and FIGS. 2 to 4 are explanatory diagrams of its operation.

The illumination light source 2 is arranged so that the illumination light beam 3 irradiates the surface of the stainless steel plate, that is, the material to be inspected 1 obliquely, that is, at a large incident angle θ, and the photodetector 4 is arranged so that the surface of the stainless steel plate, that is, the material to be inspected 1 is irradiated with the illumination light ray 3 obliquely, that is, at a large incident angle θ. They are arranged so that the surface of the material to be inspected 1 is observed from the same direction. The larger the incident angle θ of the illumination light beam 3 from the illumination light source 2 with respect to the surface of the inspected material 1, the more the illumination light beam 3 is specularly reflected without being affected by the surface roughness of the inspected material 1, as shown in FIG. The reflected light 3' is specularly reflected as shown in FIG.

Therefore, for example, if an image reader such as a television camera is used as the photodetector 4, as shown in FIG. Image 6' of the Hege underflow can be observed brightly.

If you look at this part of the television signal, as shown in FIG. 4, a signal 6'' of the undercurrent is detected in the signal 1'' indicating the material to be inspected. Although this represents one scanning line, other scanning lines within the Hege underflow also follow this.

Since the surface of the stainless steel plate is a mirror surface and the angle of incidence θ is large, most of the light from the light source 2 is specularly reflected and flies away to the side opposite to the light source with the normal N set at the point of incidence. Therefore, if the surroundings are darkened and a light-absorbing material such as a black body is placed on the side where the light flies away, and if the surface of the steel plate is free of defects, there will be almost no light received by the television camera 4, and the monitor television will receive almost no light. The screen of the John receiver 5 becomes so dark that the surface of the steel plate can be faintly recognized. When there is an underflow on the surface of the steel plate and there is diffuse reflected light 7, the television camera 4 receives it, and the screen of the monitor television receiver shows the dark underflow as a bright spot on the surface of the steel plate. is displayed.

Therefore, surface inspection by this method is very easy and accurate. The inspection range is the adhesive tape coverage area according to the conventional method. If you want to widen this, just move the steel plate.

As shown in FIG. 15 (C1), there are also stripes 1a on the steel plate surface caused by rolling, which are mutually parallel lines (low protrusions or shallow striations) running in the rolling direction.

The light irradiation direction may be selected in a direction parallel to the stripes 1a so as not to pick up the stripes 1a, but in order to clearly show the bald spots on the screen 1', the light irradiation direction may be selected perpendicular to the stripes 1a. It is better to choose in the direction (this gives better results). However, in this case, if the angle of incidence θ is not large, the stripes 1a will appear on the screen 1', so choose the angle of incidence θ so that the stripes 1a disappear (since the circumferential surface of the stripes 1a is gentle, they disappear when θ becomes larger than a certain degree). .

A preferable incident angle θ is in the range of 60 degrees or more and less than 90 degrees, and this can be fixed after setting the light source 2 in this manner.

There are no particular restrictions on the type of light source 2 to be used, and all common incandescent lamps, fluorescent lamps, mercury lamps, halogen lamps, xenon lamps, sodium lamps, and laser light sources can be used. Further, as the photodetector 4, a COD element, a silicon (St) cell, a photomultiplier, and other various detection elements in the visible range and infrared wavelength range can be used depending on the wavelength distribution of the light source 2. In order to inspect the surface using the method of the present invention, it is necessary that the hege underflow be made obvious, and methods for making it obvious include the conventional method of attaching and peeling adhesive tape, as well as the method shown in Fig. 5 ( As shown in FIG. 5 (bl
Any method can be applied, such as a method of attracting the magnet 10 to the surface of the material to be inspected and then separating it, as shown in FIG. .

FIG. 6 shows another embodiment of the invention, in which the beam splinter 11
This makes it possible to observe the surface of the steel plate from a direction completely equal to the direction of incidence of the illumination light beam 3. That is, the illumination light beam 3 from the illumination light source 2 is reflected by the beam splitter 11 and enters the surface of the inspected material 10, and most of it is specularly reflected and becomes reflected light 3', but the diffusely reflected light due to the underflow is The light returns along the incident optical path, passes through the beam splinter 11, and enters the photodetector 4. Even if the arrangement of the light source 2 and the photodetector 4 is reversed, the result is the same. The closer the incident direction and observation direction are, the higher the detection sensitivity for diffusely reflected light from flaws will be. However, because the incident angle is large, there is extremely little diffusely reflected light from areas other than the eaves, so detection is sufficient even if the direction is shifted by about 30 degrees. ability is obtained.

FIG. 7 shows another embodiment of the present invention, in which optical fibers 13-1
5 and the optical branching/coupling device 12, the incident direction and the observation direction can be perfectly matched.

In the present invention, light is projected from an oblique direction and received in the same oblique direction. Therefore, when observing a relatively wide range at the same time using an optical device with a lens such as a television camera as a photodetector, as shown in FIG. As shown, when trying to obtain images of points Pa, PI, and P2 on the surface of the inspected material 1 on the imaging plane 17 using the lens 16, the distances an and a1 from the lens 16 to the points Po, PI, and P2 are ．． Due to the difference in a2, surface 17
There is no limit to the t at which a clear image can be obtained.

In order to solve this problem, as shown in FIG. 9, the focal length f of the lens 16 is set so that the imaging plane 17 is arranged obliquely with respect to the optical axis of the lens 16 according to the imaging holes @b+, b2. Alternatively, as shown in FIG. 10, points P'+ and Pθ on the surface of the material to be inspected 10 are measured using a diaphragm 18 having an aperture diameter.

Image formation positions P+' and Po' by the lens 16 of P2.

Is the image blurred due to the difference in P2'? 16 to b
It is preferable that the blurring δ1 and δ2 of the images P1'' and P2'' of the images P1 and P2 on the imaging plane 17 located at a distance of o be less than a permissible error. Further, by arranging the linear array photodetector 4 along a straight line where a clear image can be formed by the lens 16 as shown in FIG. 11, measurement without the above-mentioned problem is also possible. In order to give width to the surface of the material 1 to be inspected, the material 1 to be inspected is moved relative to the lens 16 and the photodetector 4.

Next, a method for evaluating the surface condition of a stainless steel plate based on the signal obtained by the above-mentioned optical method will be explained. There are basically two types of signals obtained.

That is, an image like the television screen 8 shown in FIG. 12(a) and a time series signal like the one shown in FIG. 12 (bl).

Of course, since images are also composed of time-series signals, there is no essential difference between the two. Based on the image shown in Figure 12(a),
By counting the number of bright spots corresponding to minute undercurrents over a predetermined surface area of the material to be inspected, a quantitative evaluation value regarding the surface condition of the steel plate can be immediately obtained. Furthermore, the 13th
As shown in Figure (al), it is possible to obtain more detailed information by measuring the size of the observed bright spots and counting the number of each size, or by measuring the brightness of the bright spots and counting the number of each brightness. Quantitative evaluation is also possible.

To measure the brightness, the video signal shown in Figure (b) can be used. However, in this case, in the case of a large bright spot detected across multiple scanning lines 82 to S5 as shown in FIG. 14, this is recognized as a single bright spot. It is necessary to perform image processing, which complicates the device configuration and increases processing time. Note that even if it is just one point in the image, if we count the large bright spot 6' detected in several screen scans each time it is detected, it is possible to achieve a one-to-one correspondence with the number of defects. However, if the bright spots are large, they can be counted several times and quantified, including size information, and can be used for some purposes. It is relatively inexpensive and the processing time is short.

In either case, it is important to evaluate the defect density in a fixed area on the surface of the material to be inspected, for example, 2 cA x 2 cIn.

(Effects of the Invention) As is clear from the above description, the present invention enables quantitative inspection of underflow on the surface of a stainless steel plate. In the present invention, light is incident at a large angle of incidence and the surface to be measured is observed from approximately the same direction as that direction, so unnecessary reflected light is removed and only scattered light due to flaws is detected.
A high test output of N can be obtained, and complicated signal processing can be made unnecessary.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the outline of the present invention, Figs. 2 to 4 are explanatory diagrams of each part thereof, Fig. 5 is an explanatory diagram of a method for making bald spots visible, Figs. FIG. 11 is a detailed explanatory diagram of the present invention, FIGS. 8 to 10 are explanatory diagrams of out-of-focus and its countermeasures,
FIGS. 12 to 14 are explanatory diagrams of the evaluation method, and FIG. 15 is an explanatory diagram of scab marks. In the drawing, 6 is the underflow, 6' is its image, 1 is a stainless steel plate, 3 is an illumination light beam, 3' is its reflected light, 2 is an illumination light source, and 4 is a photodetector. Applicant Minoru Aoyagi, Patent Attorney for Nippon M-Steel Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 9'1' Figure 4 Figure 5 Figure 6 ) Figure 14-1

Claims (1)

[Claims] (11) An illumination light beam is irradiated at a large angle of incidence on the surface of a stainless steel plate to be inspected that may have scalloped flaws, and the illumination light beam is A stainless steel plate characterized in that the reflected light returning to the incident side is received by a photodetector, and the quality of the surface condition of the steel plate is inspected based on the number of bright spots in the output of the photodetector corresponding to the surface to be inspected. Surface condition inspection method. (2) The surface of the stainless steel plate to be inspected is subjected to a treatment to make minute undercurrents apparent before being irradiated with illumination light. A method for inspecting the surface condition of a stainless steel plate as described in .