JPS6128938B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting edge defects in metal plates.

Conventionally, optical surface flaw inspection devices have been used as methods for detecting surface defects on metal plates, such as thin steel plates.In principle, these methods are well-known as the flying spot method, flying image method, and flying spot flying image method. There is. However, all of the currently known detectors have some kind of edge dead zone, and in reality, defects in the edges cannot be detected. Furthermore, there is a pinhole detector as a detector for penetrating defects in thin steel sheets, but this is also an optical device, and it goes without saying that it cannot be detected unless the defect is optically penetrated.

Some pinhole detectors track edges and extract open crack defects from sudden changes in the edges, but since they are essentially optical, they cannot detect all edges. It is difficult to detect defects in parts, and the current situation is that it is not widely used.

However, edge defects are the starting point for sheet breakage on thin sheet production lines, and once a sheet breakage occurs in a continuous processing line, it takes a great deal of time and money to recover, and is the most important cause of production disruption. This is a serious problem. In addition, we have 1000~ thin plate manufacturing and surface treatment lines.
At a high speed of 2000 feet/min, it is difficult to visually detect these defects, which is an important problem in terms of quality assurance.

Eddy current flaw detection is known as a method for detecting defects that are not optically penetrating. This is because a coil is placed close to the material to be inspected, and when a high-frequency current is passed through it, an eddy current flows on the surface of the material to be inspected.If a defect exists on the surface layer of the material to be inspected, this eddy current is disrupted and the impedance of the coil increases. However, the drawback of this conventional method is that changes in the distance to the inspected material and changes in the shape of the edge directly cause large changes in impedance. It is to let Therefore, it is impossible to completely imitate materials such as thin plates that run at high speeds and generate edge shape defects and vibrations such as ear waves, and conventional eddy current flaw detection methods cannot be used. It cannot be applied to edge defect detection.

The present invention has been made in view of the above-mentioned background, and it is possible to remove defects in the edge portion of a thin plate at high speed and without contact, without being affected by vertical vibration of the plate, and to remove defective shapes and slight defects in the edge portion of the plate. To detect edge defects regardless of whether they are open or closed, without being affected by changes in the width of the board or even slight movement in the width direction of the board, and to make it possible to determine the degree of harmfulness of the defects. It is something.

The present invention will be described in detail below with reference to an embodiment shown in the drawings. Figure 1 shows the structure of the detection end, where 1 indicates the main core, and 2 is a high frequency excitation coil for causing a vortex to flow on the surface of the material to be inspected. It's wrapped.
3 is a detection coil for detecting a horizontal magnetic field component generated when a defect disturbs the eddy current on the surface of the material to be inspected. This is wound around the center of the main core 1 in the width direction, perpendicular to the high frequency excitation coil 2. 4-1 and 4-2 are magnetic field shape control cores, which are provided in front and behind the main core 1 so that the distance from the main core 1 can be freely adjusted, and controls the shape of the magnetic field to move it in the lateral direction of the material to be inspected. This is to suppress noise due to positional fluctuation or vertical movement of the inspection object 6, or angular fluctuation between the inspection object 6 and the detection end due to a defect in the shape of the inspection object 6.

Therefore, the main core 1, the high frequency excitation coil 2, the detection coil 3 and the magnetic field shape control core 4-
1 and 4-2 constitute a detection end 5.

In the drawing, reference numeral 6 indicates an edge portion of the material to be inspected, and the detection end 5 is placed close to the edge portion 6 of the material to be inspected so that the detection coil 3 is perpendicular to the edge portion 6 of the material to be inspected.
A feature of this method is that the overlap between the detection end 5 and the edge portion 6 of the material to be inspected can be arbitrarily set as long as it is larger than the defect to be detected.

FIG. 2 shows the principle of detection, with 7-1 and 7-2 showing the paths of eddy currents. 8 indicates the secondary magnetic flux generated by the eddy current 7-1. The detection coil 3 is on a plane perpendicular to the position indicated by the dotted line 9, and the distribution of the eddy current 7-1 on the left and right sides of the dotted line 9 is exactly the same, so the detection coil 3 has a secondary magnetic flux 8.
are not linked and no detection output is output. This relationship remains the same even if the gap between the material to be inspected and the detection side 5 changes, and furthermore, even if the amount of overlap between the detection end 5 and the material to be inspected changes, no voltage is induced. This is an important feature of the present invention.

Next, 10 indicates an edge cracking defect existing in the edge portion 6. In this case, an unbalance occurs in the distribution of the vortex flows 7-2 on the left and right sides of the dotted line 9, a horizontal magnetic field component is generated, and the detection coil 3 induces a voltage in

Figure 3 schematically shows how an output is generated at the detection end 5 when there is an ear split, where 11 is the eddy flow route when there is no defect, and 12 is a rectangular ear split. It shows the eddy current route in case. The latter eddy current route 12 can be replaced with a small current route 14 like 13 and a eddy current route 11 in the case where there is no defect. In other words, the difference from the eddy current route 11 when there is no defect is that the small current loop 1
Only 4 will be available. Therefore, it is sufficient to detect the influence of the magnetic field generated by this small current loop 14 on the detection coil 3.

FIG. 4 shows the relationship between the output of the detection end 5 and defects.
When the detection coil 3 is placed at the position indicated by the dotted line 15 and the edge portion 6 of the inspected material moves in the direction of the arrow 16, the detected value of the output of the detection end 5 becomes 17. That is, when the defect 10 comes directly under the detection coil 3, the left and right sides of the detection coil 3 are balanced and the output becomes zero, and the output shows a maximum and a minimum before and after that. That is, a defect is detected when the detected value changes from the minimum to the maximum.

FIG. 5 is for explaining the function of the magnetic field shape control cores 4-1 and 4-2. Reference numeral 18 shows the case without the magnetic field shape control core, and 19 shows the case of the present invention in which the magnetic field shape control cores 4-1 and 4-2 are provided. 18-1 and 19-1 indicate the strength of the respective magnetic fields on the surface of the material to be inspected.
Although the strength of the lower magnetic field of main core 1 does not change much,
When there are magnetic field shape control cores 4-1 and 4-2, a sharp peak is also seen below the magnetic field shape control cores 4-1 and 4-2, whereas the magnetic field shape control core 18-1 If there is no curve, it will be a gentle curve. For this reason, the density of the eddy current flowing on the surface of the material to be inspected also causes a difference as seen in 18-2 and 19-2, and when the magnetic field shape control cores 4-1 and 4-2 are provided, the density of the eddy current changes. is sharp, and it is confirmed that defects can be detected with high accuracy. Main core 1
This tendency becomes stronger as the distance between the magnetic field shape control cores 4-1 and 4-2 is narrowed, but the amount of magnetic flux directly leaking between the cores gradually increases, and the magnetic field on the plate surface becomes weaker. Therefore, the optimum distance between the main core 1 and the magnetic field shape control cores 4-1, 4-2 is determined by the material of the material to be inspected and the gap between the material to be inspected and the detection end 5. This value is preferably determined experimentally.

FIG. 6 illustrates the effect when the detection end 5 does not touch the edge of the material to be inspected at right angles.
In FIG. 6, 20 is the main route of the vortex, and 21 is its equivalent route. The magnetic field generated by the small current loop 14 induces a voltage in the detection coil 3. 22
23 is the eddy current when there is no magnetic field shape control core 4-1, 4-2, and 23 is the magnetic field shape control core 4-1, 4-
2 shows the eddy current in the case of the present invention. In the former case, the magnetic flux 24 is drawn toward the main core 1 and almost entirely interlinks with the detection coil 3, whereas in the latter case of the present invention, the entire top of the small current loop 14 is covered by the core. Therefore, the magnetic flux 24 spreads in all directions, and its output could be reduced to about 1/6. In a similar experiment, while maintaining the same detection power for defects, the influence of the gap between the detection end 5 and the inspected material was reduced to 1/2 or less, and the influence of the overlap between the detection end 5 and the edge portion 6 was reduced to 1/2. It was confirmed that the magnetic field shape control cores 4-1 and 4-2 functioned extremely well.

As mentioned above, the detection end 5 of the present invention is overwhelmingly superior to conventional methods in detecting defects in edge portions of objects such as thin plates that run at high speed and cannot be imitated due to vertical vibration or poor shape. It has characteristics.

FIG. 7 shows an example of a detection signal processing device. 7th
In the figure, 2 is a high frequency excitation coil wound around the main core 1, and 3 is a detection coil. The detection end 5 is the first
As shown in the figure, they are arranged at intervals above the edge of the material to be inspected. 25 is an oscillator for causing a high frequency current to flow through the high frequency excitation coil 2, and 26 is an amplifier for the detected voltage. This amplifier 26 amplifies the signal by about 100 times and sends it to a synchronous detector 27 . A phase shifter 28 sends a signal delayed by an arbitrary phase from the voltage phase of the oscillator 25 to generate a synchronous detection signal for the synchronous detector 27. The signal synchronously detected by the synchronous detector 27 is sent to the low-pass filter 29,
The signal component of the edge defect is extruded. 30 is a comparator, which judges the amplitude of the defect signal and sends the alarm 3
Activate 1. 32 is a recorder that records analog signals and the presence or absence of defects.

Since the present invention is as described above, defects in the edge portion of a metal plate can be detected with high accuracy without being affected by vertical movement of the test material, defective shape of the test location, or movement in the width direction of the test material. .

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the main parts of an embodiment of the present invention, Fig. 2 is a perspective view showing eddy currents in a material to be inspected, Fig. 3 is a plan view showing eddy current distribution, and Fig. 4 is a perspective view showing defects and defects. An explanatory diagram showing the relationship between the detection coil induced voltage, Fig. 5 is an explanatory diagram showing the configuration of the defect detection end and magnetic flux distribution, Fig. 6 is an explanatory diagram showing the correlation between the attitude of the defect detection end and eddy current, and Fig. 7 FIG. 2 is a block diagram showing the configuration of a processing device that energizes a defect detection terminal and processes a defect signal. 1...Main core, 2...High frequency excitation coil, 3...
...detection coil, 4-1, 4-2...magnetic field shape control core, 5...detection end (defect detection device), 6...material to be inspected (edge part), 7-1, 7-2, 11~ 1
4... Eddy current, 8... Secondary magnetic flux, 9, 15... Projection position of detection coil 3, 10... Defect, 16...
Movement direction of inspected material, 17...Detection signal, 24...
magnetic flux.

Claims (1)

[Claims] 1. A high-frequency excitation coil that is wound around the horizontal outer circumference of the main core in parallel to the surface of the material to be tested and generates eddy currents in the material to be tested, and a high-frequency excitation coil that is perpendicular to the high-frequency excitation coil,
Wound vertically around the widthwise center of the main core,
A detection coil for detecting a horizontal magnetic field component generated when a defect in the material to be inspected disturbs the eddy current; A metal plate edge defect detection device comprising a magnetic field shape control core.