JPH0572181A - Magnetic-field inspection device - Google Patents

Abstract

PURPOSE:To remarkaly improve defect inspection ability of a device by performing computation of detected defect or estimation of harmfulness by means of a magnetizer for generating magnetic field in a metallic belt and magnetic sensors for detecting magnetism leak while being arranged in respective hollow rolls. CONSTITUTION:A metallic band 10 is run in the arrow mark direction, an under side hollow roll 1 is applied by downward force due to the tension of the metallic band 10 so as to rotate the roll 1 in the arrow mark direction, and hence an upper side hollow roll 1a is downward energized with a spring so as to rotate in the arrow mark direction. A magnetizing electric power source device 16 is started, exciting current is let flow in the exciting coil in the roll, and a magnetic path is formed with the iron core of an attached magnetizer and the metallic belt 10. If an injury is on the surface and the like of the metallic belt 10, the magnetic path is disturbed, it is detected with respective magnetic sensors in the rolls 1a, 1, and input to signal processing circuits 17, 17a. Defect scale (k) and a generation position (d) are computed in a computing circuit 18, and harmfulness (alpha) is computed in a harmfulness estimation circuit 20. When the harmfulness is over a limit value, an alarm 21 is actuated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic flaw detector for detecting defects in a running metal band by accommodating a magnetizer and a magnetic sensor in a rotating hollow roll, and particularly to a metal having a detected defect. The present invention relates to a magnetic flaw detector for evaluating the degree of harmfulness to a belt.

[0002]

2. Description of the Related Art As a magnetic detection device for detecting defects such as flaws and inclusions existing inside or on the surface of a metal strip by using magnetism, not only can the metal strip be measured in a stationary state, but also for example in a factory. A magnetic flaw detector which can continuously detect defects existing in a running metal strip in a production line etc. has been proposed (Japanese Utility Model Laid-Open No. 63-107849).
(Kaikai 61-170068).

FIG. 8 is a diagram showing a magnetic flaw detector for continuously detecting defects in a running metal strip disclosed in Japanese Utility Model Laid-Open No. 63-107849, and FIGS. 8 (a) and 8 (b) respectively. It is a cross-sectional schematic diagram seen from a different direction.

One end of a fixed shaft 2 penetrates the center of a hollow roll 1 made of a non-magnetic material. The other end of the fixed shaft 2 is supported by a frame of a building (not shown). The fixed shaft 2 is supported on the inner peripheral surfaces of both ends of the hollow roll 1 by a pair of rolling bearings 3a and 3b so as to be located at the center of the hollow roll 1. Therefore, the hollow roll 1 freely rotates about the fixed shaft 2 as the rotation center axis.

A magnetized iron core 4c having a substantially U-shaped cross section is provided in the hollow roll 1 with a magnetic pole 4a, 4b of each magnet pole 4a and 4b being close to the inner peripheral surface of the hollow roll 1, and a fixed shaft with a supporting member 5 interposed therebetween. It is fixed at 2. A magnetizing coil 6 is wound around the magnetized iron core 4c. Therefore, the magnetized core 4c and the magnetized coil 6 constitute the magnetizer 4. Magnetized iron core 4
A magnetic sensor group 7 in which a plurality of magnetic sensors 7a are linearly arranged in the axial direction between the magnetic poles 4a and 4b of c is also fixed to the fixed shaft 2.

A power cable 8 for supplying an exciting current to the magnetizing coil 6 and each magnetic sensor 7 of the magnetic sensor group 7.
The signal cable 9 for extracting the output signal of a is the fixed shaft 2
It is led to the outside via the inside. Therefore, the positions of the magnetizer 4 and the magnetic sensor group 7 are fixed, and the hollow roll 1 rotates around the outer circumference of the magnetizer 4 and the magnetic sensor group 7 with a minute gap.

The metal strip 1 running on the outer peripheral surface of the hollow roll 1 of the magnetic flaw detector having such a structure in the direction of arrow a, for example.
0 against one side with a predetermined pressure, the fixed shaft 2
Is fixed to the frame, the hollow roll 1 rotates in the direction of arrow b.

In such a magnetic detector, when an exciting current is supplied to the magnetizing coil 6, a closed magnetic path is formed by the magnetic poles 4a and 4b of the magnetizing iron core 4c and the running metal strip 10. If there is a defect inside or on the surface of the metal strip 10, the magnetic path in the metal strip 10 is disturbed, and a leakage magnetic flux is generated. This leakage magnetic flux is detected by the magnetic sensor 7a facing the corresponding defect position forming the magnetic sensor group 7, and the magnetic sensor 7a outputs a signal corresponding to the corresponding defect.

Since the signal level of the detected signal corresponds to the size (size) of a defect inside or on the surface of the metal strip 10, the signal level of the output signal is measured to determine whether the signal is present inside or on the surface of the metal strip 10. It is possible to grasp the position where the defect is generated in the width direction and its approximate scale.

[0010]

However, the magnetic flaw detector shown in FIG. 8 still has the following problems to be solved.

That is, the signal level of the output signal of each magnetic sensor 7a corresponds to the size of the defect inside or on the surface of the metal strip 10. Strictly speaking, the signal level of the output signal is not only the size of the defect but also the defect position. Is also affected. That is,
Even if the defects are of the same scale, the value of the output signal is greatly different between the defect generated near the surface on the magnetic sensor 7a side and the defect generated near the surface on the opposite side to the magnetic sensor 7a side. Therefore, there is a problem that the defect occurrence position and the defect scale in the plate thickness direction cannot be accurately detected. On the other hand, even if the defect size is the same, the allowable limit of the defect size varies greatly depending on the position where the defect occurs in the thickness direction.

For example, comparing the bending strength of a metal strip having a defect on the surface or in the vicinity of the surface with the bending strength of a metal strip having a defect at a substantially central position in the plate thickness direction, a defect is found on the surface or in the vicinity of the surface. The bending strength of the existing metal strip is much smaller. Therefore, even if defects are of the same scale, the location of their occurrence is important.

Moreover, even if the defects are of the same scale,
The allowable limit varies depending on the position where the metal strip is finally processed, depending on what product is processed. For example,
When used as an edible can material, it is strict with respect to defects on the inner surface (back surface) of the can due to corrosion and the like, and strict with respect to surface defects for general steel materials.

In order to eliminate such a situation,
There has been proposed a method for detecting internal defects in a thin steel sheet, in which magnetic sensors are arranged on both sides of a running metal strip, and the defect occurrence position is detected from the sum and difference components of the output signals of the respective magnetic sensors (Japanese Patent Laid-Open Publication No. Sho. 57-108656).

Generally, a running metal strip travels while vibrating up and down greatly. Therefore, when this detection method is applied to a metal strip running while vibrating, the positions of the magnetic sensors arranged on both sides of the metal strip are fixed to, for example, the frame of the building, so that each magnetic sensor The distance called lift-off between the metal and the surface of the metal band fluctuates greatly. Therefore, the signal level of the output signal of the magnetic sensor fluctuates greatly. Therefore, the defect detection accuracy decreases.

The present invention has been made in view of the above circumstances, and a magnetic band is provided in each of a pair of hollow rolls which are in contact with the metal strip across the traveling path of the metal strip. To provide a magnetic flaw detector capable of accurately measuring the defect scale of defects existing on the surface and inside, the defect position, and the quantitative harmfulness of the defect to the metal band, and greatly improving the defect inspection capability of the entire device. To aim.

[0017]

In order to solve the above-mentioned problems, in the magnetic flaw detector of the present invention, the magnetic belt is rotatably supported by a support shaft orthogonal to the traveling path of the metal strip, and the traveling path is sandwiched between the traveling axes. A pair of hollow rolls that rotate by contacting the upper surface and the lower surface of the metal strip traveling on the road, respectively,
A magnetizer that is disposed in one of the pair of hollow rolls and that generates a magnetic field in the metal strip, and that is disposed in each of the hollow rolls, is caused by defects inside or on the surface of the metal strip. A pair of magnetic sensors for detecting the leakage magnetic flux generated by the magnetic sensor, an arithmetic circuit for calculating the defect generation position and the defect scale in the thickness direction of the defective metal strip from the respective leakage magnetic flux values detected by the pair of magnetic sensors, and the metal strip. And a harmfulness evaluation circuit that evaluates the harmfulness of the defect to the metal band based on the plate thickness and the metal type information, and the calculated defect occurrence position and the defect scale.

[0018]

In the magnetic flaw detector constructed as described above,
A pair of hollow rolls are arranged opposite to each other with a metal strip interposed therebetween, and a magnetic sensor is arranged in each hollow roll. Further, since the pair of hollow rolls are in contact with the front surface or the back surface of the metal strip, the distance between each magnetic sensor and the front surface or the back surface of the metal strip is kept constant. Since a magnetic field is generated by the magnetizer inside the metal band, if there is a defect, each magnetic sensor detects the leakage magnetic flux corresponding to the defect. The output values Y ₁ and Y ₂ of the output signal (defect signal) of each magnetic sensor are, for example, as shown in the equations (1) and (2), for example, the defect size K expressed by the defect volume and the distance to the defect, that is, the corresponding magnetic field. It can be displayed as a function of the depths d ₁ and d ₂ from each surface on the sensor side. Y ₁ = F ₁ (d ₁ , K, D, Z) (1) Y ₂ = F ₂ (d ₂ , K, D, Z) (2) These functions F ₁ and F ₂ are, for example, As shown in Figure 4,
It can be approximated by a linear equation for each material of the metal strip. Further, since the plate thickness D of the metal strip is predetermined, D = d ₁ + d ₂ (3)

[0019] Z is a fixed correction value determined by the type of metal to be measured. Since Y ₁ and Y ₂ are the values measured by the respective magnetic sensors, by solving the simultaneous equations (1) to (3), the defect size K and the defect occurrence position d (= d ₁ ) is obtained.

Next, using the defect size K, the defect occurrence position d, the metal plate thickness D, and the type correction value Z as the metal type information calculated in this way, the degree of harmfulness of the defect to the metal band is determined. A procedure for evaluating α will be described.
That is, the degree of harmfulness α is K, d,
It is a function of D and Z. α = F ₃ (K, d, D, Z) (4)

As described above, the closer the defect is located on the surface or in the vicinity of the surface, the more easily cracks are generated due to bending stress during processing, and conversely, the defect is located in the center (d = D /
2) Time is the most difficult to damage.

This is apparent from the experimental results shown in FIG. 7 with respect to the reference sample performed by the drawing test apparatus of FIG. That is, a known reference scale K ₀ (= 7.8 × 10 ⁻³ m) on the hole 31 in the table 32 having the circular hole 31.
m ³ ) The reference defect 33 and the reference sample 34 having the reference plate thickness D ₀ are placed. A punch 35 having the same diameter as the hole 31 applies pressure downward from the upper surface to the reference sample 34. Then, the pressure P when the crack is generated in the reference sample 34 is measured.

An experiment was conducted on a plurality of reference samples 34 in which the position d of the reference defect 33 in the plate thickness direction was variously located from the upper surface (d = 0) to the lower surface (d = D ₀ ).
Then, the ratio of the crack pressure when the defects are located on the upper surface and the lower surface to the crack pressure P at each defect generation position d when the crack pressure is set to the reference pressure P ₀ is defined as the harmfulness α. α = (P ₀ / P) × 100 (%) (5) The measurement result shows that the central portion (d = D ₀ /
2) has the lowest harmfulness α, and the maximum value is 1 at the surface positions on both ends.
Indicates 00%.

In this way, the harmfulness α of the reference defect 33 existing in the reference sample 34 is obtained. Then, the reference harmfulness characteristic 36 indicating the harmfulness α changes depending on the defect occurrence position d, the defect scale K, and the plate thickness D calculated previously. It also differs depending on the type correction value Z. The type correction value Z changes depending on the item used for the metal strip and the metal material.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the overall system of the magnetic flaw detector of the embodiment. The metal strip 10 fed out from the supply reel 12 is guided to the pair of hollow rolls 1 and 1b through the front holding rolls 13a and 13b, passes through between the hollow rolls 1 and 1a, and the rear holding rolls 14a and 1b.
After 4b, it is wound around the winding reel 15 at a constant speed.

A magnetizing power supply device 16 is connected to the lower hollow roll 1 of the pair of hollow rolls 1 and 1a via a power cable 8 and a signal processing circuit to the upper hollow roll 1a via a signal cable 9a. 17a is connected.
Further, a signal processing circuit 17 is connected to the lower hollow roll 1 via a signal cable 9. Each signal processing circuit 1
The signal values Y ₁ and Y ₂ output from 7a and 17 are input to the arithmetic circuit 18. The arithmetic circuit 18 calculates the defect scale K and the defect occurrence position d by the above-mentioned method using the input signal values Y ₁ and Y ₂ and the plate thickness D of the metal strip 10 supplied from the host computer 20. To do. Calculated defect scale K
The defect occurrence position d is sent to the next harmfulness evaluation circuit 20.

The harmfulness evaluation circuit 20 stores a reference harmfulness characteristic 36 in the reference sample 34 shown in FIG. Then, the harmfulness evaluation circuit 20 first obtains the harmfulness α ₀ on the reference harmfulness characteristic 36 at the defect occurrence position d input from the arithmetic circuit 18. Next, the defect size K obtained at this harmfulness α ₀ and the reference defect size K ₀ are compared (K
/ K ₀ ). Further, since the harmfulness α becomes small when the plate thickness D is large, it is divided by the ratio (D / D ₀ ) to the reference thickness D of the reference sample 34.

Further, the final harmfulness α is obtained by making a correction with the metal type correction value Z input from the host computer 19. The type correction value Z is from d = 0 to d = D of the metal strip 10.
Up to each position has a different correction value. For example, when the metal strip 10 is used for food cans, it has a high correction value on the inside and a low correction value on the outside, as shown in FIG.
On the other hand, general materials have a high correction value on the outside.
As described above, each of these correction values Z has a correction characteristic according to the material of the metal strip 10 and the intended use. The various correction values Z are supplied from the host computer 19. Therefore, the final hazard level α is given by Eq. (6). α = α ₀ · (K / K ₀ ) · (D ₀ / D) · Z (6)

Then, the finally obtained harmfulness α is sent to the alarm device 21. The alarm device 21 outputs a warning by a buzzer or the like when the inputted harmfulness α exceeds a predetermined limit harmfulness α _M.

FIG. 2 (a) is a schematic sectional view of the pair of hollow rolls 1 and 1a taken along a plane parallel to the traveling direction of the metal strip 10 indicated by an arrow, and FIG. It is a cross-sectional schematic diagram at the time of cutting in the surface orthogonal to the said running direction. 8 (a) and 8 (b) are designated by the same reference numerals. Therefore, detailed description of the overlapping portions will be omitted.

Each hollow roll 1, 1a is made of a non-magnetic material. The outer diameters are set equal to each other. One end of each of the hollow fixed shafts 2 and 2a passes through each central shaft of each hollow roll 1 and 1a. As shown in FIG. 3, the other end of the fixed shaft 2 of the lower hollow roll 1 is supported by a building frame 22 via a support spring 24, and the fixed shaft 2a of the upper hollow roll 1a is assembled on the frame 22 of the building. It is supported on the upper side of the frame 23 via a support spring 24a. That is, the upper and lower fixed shafts 2 and 2a are the support springs 2
4.24a biases each other.

The fixed shafts 2 and 2a are hollow rolls 1 and 1a, respectively.
Are supported on the inner peripheral surfaces of both ends of each hollow roll 1, 1a via a pair of rolling bearings 3a, 3b so as to be located on each central axis. Therefore, each hollow roll 1,
1a is free to rotate with the fixed shafts 2 and 2a as the central axes of rotation.

In the upper hollow roll 1a, a magnetic sensor group consisting of a plurality of magnetic sensors 7b is fixed to the fixed shaft 2a via a supporting member in a posture in which it faces downward. The tip of each magnetic sensor 7b faces the inner peripheral surface of the upper hollow roll 1a with a minute gap. The output signal of each magnetic sensor 7b is guided to the signal processing circuit 17a of FIG. 1 by the signal line cable 9a passing through the inside of the fixed shaft 2a.

Further, the calibration coil 25a is wound so as to cover the outer circumference of the magnetic sensor group including the plurality of magnetic sensors 7b. It should be noted that the calibration coil 25a is a coil for causing a current to flow before the start of measurement to generate a pseudo leakage magnetic flux and for adjusting the gain in the signal processing circuit 17a.

On the other hand, the structure inside the lower hollow roll 1 is shown in FIG.
The structure is substantially the same as that inside the hollow roll 1. However, like the upper hollow roll 1a, the calibration coil 25 is rotated with respect to the magnetic sensor group 7 including a plurality of magnetic sensors 7a. And. The output signal of each magnetic sensor 7a is led to the signal processing circuit 17 of FIG.

Therefore, the magnetic sensors 7b housed in the upper hollow roll 1a oppose the respective magnetic sensors 7a housed in the lower hollow roll 1 at a predetermined interval via the metal strip 10.

In the magnetic flaw detector having such a structure,
When the metal strip 10 is run at a constant speed in the direction of the arrow a shown in FIG. 2, since the downward force due to the tension of the metal strip 10 and the downward force due to gravity are applied to the lower hollow roll 1, The lower hollow roll 1 rotates in the direction of arrow b. Further, since the upper hollow roll 1a is also urged downward by the spring, it rotates in the direction of arrow c.

When the magnetizing power supply device 16 is activated and an exciting current is supplied to the exciting coil 6, a closed magnetic path is formed by the magnetized iron core 4c of the magnetizer 4 and the running metal strip 10. When defects such as flaws and bubbles are present on the inside or the surface of the metal strip 10, the magnetic path inside the metal strip 10 is disturbed and leakage magnetic flux is generated. This leakage magnetic flux causes the upper and lower hollow rolls 1a,
It is detected by the magnetic sensors 7b and 7a housed in the unit 1 and input to the signal processing circuits 17a and 17.

Then, according to the procedure described above, the arithmetic circuit 18 calculates the defect scale K and the defect occurrence position d, and the harmfulness evaluation circuit 20 calculates the final harmfulness α. Then, the alarm device 21 outputs an alarm with a buzzer or the like when the calculated harmfulness α becomes equal to or higher than the limit harmfulness α _M.

According to the magnetic flaw detector constructed as described above, the magnetic sensors 7a and 7b are provided in the pair of hollow rolls 1 and 1a which are arranged opposite to each other with the metal strip 10 as the flaw detection target interposed therebetween. From the detected defect signals Y ₂ and Y _{1 of} the metal band 10, the generation position d and the defect size K of the defects existing on the surface and inside of the metal band 10 are calculated by a simple calculation formula.
And can be grasped accurately.

Further, the defect occurrence position d and the defect scale K
Then, the harmfulness α due to the presence of a defect in the metal strip 10 is quantitatively calculated from the plate thickness D and the type correction value Z, and when the harmfulness α becomes the critical harmfulness α _M or more, an alarm is issued. Is being output. The degree of harmfulness α is a quantitative value in which the metal strip 10 is actually processed into a product, and corrosion after processing is also taken into consideration. In this way, a more realistic defect inspection can be performed by quantitatively grasping the harmfulness α which was conventionally considered as a qualitative concept.

FIG. 5 shows the same defect scale (K = 2.8 × 10 ^-2).
mm ³ ), Even if the defect occurrence position d, the plate thickness D, and the type correction value D are different, the final harmfulness α changes greatly. FIG. 5A shows a harmfulness characteristic when the condition for using the metal strip 10 as a food can material is set as the type correction value Z. As shown in the figure, the degree of harm is higher when there are defects inside than outside. Of course, if the plate thickness D is thin, the degree of harmfulness is high.

On the other hand, FIG. 5B shows the harmfulness characteristic when the condition that the metal strip 10 is used as the general-purpose material is set as the type correction value Z. As shown in the figure, the degree of harm becomes higher when the defect exists on the outside than on the inside.

The magnetic sensors 7a and 27b are housed in the hollow rolls 1 and 1a, respectively. The hollow rolls 1 and 1a are constantly pressed against the upper surface and the lower surface of the metal strip 10 with a constant biasing force. Therefore, each magnetic sensor 7a. The distance between 7b and the upper and lower surfaces of the metal strip 10 can always be kept constant. Therefore, even if the metal strip 10 vibrates vertically during the traveling process, the distance is maintained at a constant value, so that the defect measurement accuracy can be further improved.

[0046]

As described above, according to the magnetic flaw detector of the present invention, the magnetic sensors are respectively arranged in the pair of hollow rolls which are in contact with the metal strip across the traveling path of the metal strip. Therefore, the defect size and the defect position of the defects existing on the surface and inside of the metal band can be accurately measured.

Further, the harmfulness of the defect to the metal band is calculated from the measured defect size, defect occurrence position, plate thickness, and metal type information. Therefore, it is possible to quantitatively grasp the degree of harmfulness of the defect to the metal band, which has been conventionally qualitatively evaluated, and to further improve the defect detection function.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an overall system of a magnetic flaw detector according to an embodiment of the present invention,

FIG. 2 is a schematic sectional view of the apparatus of the embodiment,

FIG. 3 is a schematic diagram of installation of the apparatus of the same embodiment,

FIG. 4 is a diagram showing a relationship between a defect signal level and a defect occurrence position;

FIG. 5 is a harmfulness characteristic diagram obtained by the apparatus of the same embodiment,

FIG. 6 is a schematic diagram showing a squeeze test device for obtaining basic harmfulness characteristics,

FIG. 7 is a basic harmfulness characteristic diagram obtained by the drawing test apparatus,

FIG. 8 is a schematic sectional view of a conventional magnetic flaw detector.

[Explanation of symbols]

1, 1a ... Hollow roll, 2, 2a ... Fixed axis, 4 ... Magnetizer, 7a, 7b ... Magnetic sensor, 10 ... Metal band, 17,
Reference numeral 17a ... Signal processing circuit, 18 ... Arithmetic circuit, 19 ... Host computer, 20 ... Harmfulness evaluation circuit, 21 ... Alarm device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Maki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (1)

[Claims] 1. A pair of hollows, which are rotatably supported by a support shaft orthogonal to the running path of the metal belt, and rotate by contacting the upper surface and the lower surface of the metal belt running on the running path while sandwiching the running path. A roll and a magnetizer that is disposed in one of the pair of hollow rolls and that generates a magnetic field in the metal strip, and that is disposed in each of the hollow rolls, inside the metal strip or A pair of magnetic sensors for detecting the leakage magnetic flux generated due to the surface defect, and the defect occurrence position and the defect scale in the thickness direction of the metal strip of the defect from the respective leakage magnetic flux values detected by the pair of magnetic sensors. A magnetic circuit comprising a calculation circuit for calculating, and a harmfulness evaluation circuit for evaluating the degree of harmfulness of the defect to the metal band from the thickness and metal type information of the metal band and the calculated defect occurrence position and defect size. Pneumatic flaw detector.