JP2639250B2 - Magnetic flaw detector - Google Patents

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 a defect in a metal strip in a running state by housing a magnetizer and a magnetic sensor in a rotating hollow roll. The present invention relates to a magnetic flaw detector for evaluating the degree of harm to a band.

[0002]

2. Description of the Related Art As a magnetic detecting device for detecting defects such as flaws and inclusions present inside or on a metal strip using magnetism, not only a metal strip is measured in a stationary state but also a factory. A magnetic flaw detector capable of continuously detecting a defect existing in a traveling metal strip has been proposed in a production line or the like (Japanese Utility Model Laid-Open No. 63-107849,
Japanese Utility Model Laid-Open Publication No. 61-17068).

FIG. 8 is a view showing a magnetic flaw detector which continuously detects a defect of a running metal band disclosed in Japanese Utility Model Laid-Open Publication No. 63-107849, and FIGS. It is the cross section schematic diagram seen from a different direction.

[0004] One end of a fixed shaft 2 passes through the center of a hollow roll 1 formed 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 a rotation center axis.

A magnetized iron core 4c having a substantially U-shaped cross section is fixed in a hollow roll 1 via a support member 5 in such a manner that its magnetic poles 4a and 4b are close to the inner peripheral surface of the hollow roll 1. It is fixed to 2. A magnetizing coil 6 is wound around the magnetizing core 4c. Therefore, the magnetizer 4 is constituted by the magnetized iron core 4c and the magnetized coil 6. 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 taking out the output signal of the
It is led out through 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 periphery of the magnetizer 4 and the magnetic sensor group 7 with a small gap.

[0007] For example, the metal strip 1 running on the outer peripheral surface of the hollow roll 1 of the magnetic flaw detector having such a configuration in the direction of arrow a.
0 at 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 detecting device, when an exciting current is supplied to the magnetizing coil 6, a closed magnetic path is formed between the magnetic poles 4a and 4b of the magnetized iron core 4c and the moving metal band 10. If a defect exists inside or on the surface of the metal band 10, a magnetic path in the metal band 10 is disturbed, and a leakage magnetic flux is generated. The leakage magnetic flux is detected by the magnetic sensor 7a facing the position of the defect constituting the magnetic sensor group 7, and a signal corresponding to the defect is output from the magnetic sensor 7a.

Since the signal level of the detected signal corresponds to the size (magnitude) of the defect inside or on the metal band 10, the signal level of the output signal is measured to determine whether the signal exists inside or on the metal band 10. It is possible to grasp the occurrence position of the defect 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, although the signal level of the output signal of each magnetic sensor 7a corresponds to the size of a defect inside or on the surface of the metal strip 10, strictly speaking, the signal level of the output signal differs from the defect size in addition to the defect size. Is also affected. That is,
Even if the defect is of the same scale, the value of the output signal is significantly different between a defect generated near the surface on the magnetic sensor 7a side and a defect generated near the surface on the side opposite to the magnetic sensor 7a. Therefore, there is a problem that the defect occurrence position and the defect scale in the 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 of the defect in the thickness direction.

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

Further, even if the defects are of the same scale,
The allowable limit differs depending on the position where the metal strip is finally formed into what product is processed. For example,
When used as a food can, it is severe against defects on the inner surface (rear surface) of the can due to corrosion and the like, and severe against defects on the surface of general steel materials.

Incidentally, in order to solve such a situation,
There has been proposed a method of detecting an internal defect of a thin steel sheet in which a magnetic sensor is disposed on both sides of a traveling metal strip and a defect occurrence position is detected from a sum and a difference component of output signals of the respective magnetic sensors (Japanese Patent Application Laid-Open (JP-A) No. 2002-110630). 57-108656).

In general, a traveling metal strip travels while vibrating largely vertically. Therefore, when this detection method is applied to a metal band running while vibrating, the positions of the magnetic sensors disposed on both sides of the metal band are fixed to, for example, a frame of a building. The distance between the metal strip and the surface of the metal strip, called lift-off, varies greatly. Therefore, the signal level of the output signal of the magnetic sensor fluctuates greatly. Therefore, the accuracy of defect detection decreases.

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

[0017]

In order to solve the above-mentioned problems, a magnetic flaw detector according to the present invention is rotatably supported on a support shaft orthogonal to a traveling path of a metal strip, and the traveling path is sandwiched between the traveling paths. A pair of hollow rolls that rotate by contacting the upper and lower surfaces of a metal strip traveling on a road, respectively,
A magnetizer that is disposed in one of the pair of hollow rolls and generates a magnetic field in the metal band, and is disposed in each of the hollow rolls and is caused by a defect inside or on the surface of the metal band. A pair of magnetic sensors for detecting a magnetic flux generated by the magnetic sensor, an arithmetic circuit for calculating a defect occurrence position and a defect size in the thickness direction of the metal strip of the defect from each of the magnetic fluxes detected by the pair of magnetic sensors, and a reference defect. The relationship between the defect location previously determined experimentally using the reference metal sample formed with the reference metal and the harmfulness of the reference indicating the ease of crack initiation when a bending stress is applied to the reference metal sample is shown. From the reference harmfulness characteristics, calculate the harmfulness of the reference at the calculated defect occurrence position, and calculate the harmfulness of the calculated reference based on the defect size, the thickness of the metal strip, and the metal determined by the purpose of use of the metal strip. Type information and Correcting the those having a deleterious evaluation circuit for obtaining the final hazardous degree for the metal strip.

[0018]

With the magnetic flaw detector configured as described above,
A pair of hollow rolls are disposed to face each other with a metal band therebetween, and a magnetic sensor is disposed 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 band, the distance between each magnetic sensor and the front surface or the back surface of the metal band is kept constant. Since a magnetic field is generated by the magnetizer inside the metal strip, if a defect exists, each magnetic sensor detects a leakage magnetic flux corresponding to the defect. As shown in equations (1) and (2), the output values Y ₁ and Y ₂ of the output signals (defect signals) of the respective magnetic sensors are, for example, the defect size K expressed by the defect volume and the distance to the defect, ie, 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 FIG.
It can be approximated by a linear equation for each material of the metal strip. Further, since the thickness D of the metal strip is predetermined, D = d ₁ + d ₂ (3)

## EQU1 ## Z is a constant correction value determined by the type of the metal to be measured. Since Y ₁ and Y ₂ are values measured by the respective magnetic sensors, by solving the simultaneous equations (1) to (3), the defect scale K and the defect occurrence position d (= d ₁ ) is obtained.

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

As described above, as the defect is located at or near the surface, cracks are more likely to occur due to bending stress during processing, and conversely, the defect is located at the center (d = D /
2) Time is most difficult to break.

This is evident from the results of the experiment shown in FIG. 7 for the reference sample performed by the drawing test apparatus shown in FIG. That is, a known reference scale K ₀ (= 7.8 × 10 ⁻³ m) is formed on the hole 31 in the table 32 having the circular hole 31.
m ³ Placing the reference sample 34 with a reference defect 33, and the reference thickness D ₀ of the). A punch 35 having the same diameter as the hole 31 applies a pressure to the reference sample 34 downward from the upper surface. Then, the pressure P when a crack occurs 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 thickness direction was variously located from the upper surface (d = 0) to the lower surface (d = D ₀ ).
The ratio of the crack pressure at each defect occurrence position d to the crack pressure P when the crack pressure when the defect is located on the upper surface and the lower surface is defined as the reference pressure P ₀ is defined as a harmfulness α. α = (P ₀ / P) × 100 (%) (5) As shown in FIG. 7, the measurement result is shown at the center (d = D ₀ /
2) has the lowest harmfulness α, and the maximum value is 1 at the surface positions at both ends.
00%.

As described above, the degree of harmfulness α of the reference defect 33 existing in the reference sample 34 is obtained. The reference harmfulness characteristic 36 indicating the harmfulness α changes depending on the previously calculated defect occurrence position d, defect size K, and plate thickness D. Further, it differs depending on the type correction value Z. Note that the type correction value Z changes according to the item used for the metal strip and the metal material.

[0025]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the entire system of the magnetic flaw detector of the embodiment. The metal strip 10 fed from the supply reel 12 is guided to a pair of hollow rolls 1 and 1a via front pressing rolls 13a and 13b, passes between the hollow rolls 1 and 1a, and then is pressed to the rear pressing rolls 14a and 1a.
4b, it is wound on the winding reel 15 at a constant speed.

The lower hollow roll 1 of the pair of hollow rolls 1 and 1a is connected to a magnetization power supply 16 via a power cable 8 and the upper hollow roll 1a is connected to a signal processing circuit 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 7 a 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-described method using the input signal values Y ₁ and Y ₂ and the thickness D of the metal strip 10 supplied from the host computer 20. I do. Calculated defect size K
The defect occurrence position d is sent to the next harm evaluation circuit 20.

The harm evaluation circuit 20 stores a reference harm characteristic 36 of the reference sample 34 shown in FIG. Then, this harmfulness evaluation circuit 20 first obtains harmfulness α ₀ on the reference harmfulness characteristic 36 at the defect occurrence position d input from the arithmetic circuit 18. Next, the ratio (K) of the defect size K obtained for the degree of harmfulness α ₀ to the reference defect size K ₀
/ K ₀ ). Since the harmfulness α decreases as the plate thickness D increases, the harmfulness α is divided by the ratio (D / D ₀ ) of the reference sample 34 to the reference thickness D.

Further, correction is performed using the metal type correction value Z input from the host computer 19 to obtain the final harmfulness α. The type correction value Z ranges from d = 0 to d = D of the metal band 10.
Have different correction values depending on each position up to. For example, when the use of the metal band 10 is a food can, as shown in FIG. 5, the metal band 10 has a high correction value on the inside and a low correction value on the outside.
On the other hand, a general material has a high correction value on the outside.
Thus, each of these correction values Z has a correction characteristic according to the material of the metal band 10 and the application. These various correction values Z are supplied from the host computer 19. Therefore, the final degree of harmfulness α ₁ is given by equation (6). α ₁ = α ₀ · (K / K ₀ ) · (D ₀ / D) · Z (6)

Then, the finally obtained harmfulness α ₁ is sent to the alarm device 21. Alarm device 21 alarm output when the harmful degree alpha ₁ input becomes more predetermined limit harmful degree alpha _M at buzzer.

FIG. 2 (a) is a schematic cross-sectional view when the pair of hollow rolls 1 and 1a are cut along a plane parallel to the running direction of the metal strip 10 as indicated by an arrow, and FIG. FIG. 3 is a schematic cross-sectional view when cut along a plane perpendicular to the traveling direction. 8 (a) and 8 (b) are denoted by the same reference numerals. Therefore, the detailed description of the overlapping part will be omitted.

Each of the hollow rolls 1 and 1a is formed 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 is penetrated through each central shaft of each of the hollow rolls 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 building frame 22. The frame 23 is supported above the frame 23 via a support spring 24a. That is, the upper and lower fixed shafts 2 and 2 a
They are biasing each other at 4.24a.

Each of the fixed shafts 2 and 2a is connected to each of the hollow rolls 1 and 1a.
Are supported on the inner peripheral surfaces at both ends of each of the hollow rolls 1 and 1a via a pair of rolling bearings 3a and 3b, respectively, so as to be positioned on the respective central shafts. Therefore, each hollow roll 1,
1a rotates freely around the fixed shafts 2 and 2a as a rotation center axis.

In the upper hollow roll 1a, a group of magnetic sensors composed of a plurality of magnetic sensors 7b is fixed to the fixed shaft 2a via a supporting member in a posture facing downward. The tip of each magnetic sensor 7b is opposed to the inner peripheral surface of the upper hollow roll 1a with a small 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.

A calibration coil 25a is wound so as to cover the outer circumference of a magnetic sensor group including a plurality of magnetic sensors 7b. The calibration coil 25a is a coil for applying a current before the start of measurement, generating a pseudo leakage magnetic flux, and performing gain adjustment in the signal processing circuit 17a.

On the other hand, the structure inside the lower hollow roll 1 is shown in FIG.
Is substantially the same as the structure inside the hollow roll 1. However, a calibration coil 25 is wound around the magnetic sensor group 7 composed of a plurality of magnetic sensors 7a, similarly to the upper hollow roll 1a. And. The output signal of each magnetic sensor 7a is guided to the signal processing circuit 17 of FIG.

Therefore, each magnetic sensor 7b accommodated in the upper hollow roll 1a faces the magnetic sensor 7a accommodated in the lower hollow roll 1 at a predetermined interval via the metal band 10.

In the magnetic flaw detector having such a configuration,
When the metal band 10 travels at a constant speed in the direction of the arrow a shown in FIG. 2, a downward force due to the tension of the metal band 10 and a 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. The upper hollow roll 1a is also urged downward by a spring, and therefore rotates in the direction of arrow c.

When the magnetizing power supply 16 is activated to supply an exciting current to the exciting coil 6, a closed magnetic path is formed between the magnetizing core 4c of the magnetizer 4 and the running metal band 10. If a defect such as a flaw or a bubble exists inside or on the surface of the metal band 10, a magnetic path in the metal band 10 is disturbed, and a leakage magnetic flux is generated. This leakage magnetic flux causes the upper and lower hollow rolls 1a,
The signals are detected by the magnetic sensors 7b and 7a housed in the device 1 and input to the signal processing circuits 17a and 17 respectively.

Then, 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 ₁ by the above-described procedure. The warning device 21 was calculated harmful degree alpha ₁ is alarm output by a buzzer or the like becomes more than the limit harmful degree alpha _M.

According to the magnetic flaw detector configured as described above, the magnetic sensors 7a and 7b provided in the pair of hollow rolls 1 and 1a opposed to each other with the metal band 10 to be flawed interposed therebetween are used. From the detected defect signals Y ₂ , Y _{1 of} the metal band 10, the generation position d of the defect existing on the surface and inside of the metal band 10 and the defect size K are calculated by a simple calculation formula.
Can be accurately grasped.

The defect occurrence position d and the defect scale K
If, from the thickness D and the type correction value Z, quantitatively calculates a harmful degree alpha ₁ due to a defect in the relevant metal strip 10 is present, this harmful degree alpha ₁ is detrimental degree alpha _M or higher limit , Has output an alarm. The degree of harmfulness α ₁ is a quantitative value in which the metal strip 10 is actually processed into a product or corrosion after processing is taken into consideration. Thus, by quantitatively grasping a harmful degree alpha ₁ which was considered as a conventional qualitative concept, it is more realistic defect inspection.

FIG. 5 shows the same defect size (K = 2.8 × 10 ^−2).
mm ³⁾ is a be defect position d, the plate thickness D, Different types correction value D, a measured value indicating that the final hazardous degree alpha ₁ greatly varies. FIG. 5A shows the harmfulness characteristics when the condition for using the metal band 10 as a material for a can is set as the type correction value Z. As shown in the figure, the degree of harm when a defect exists is higher on the inner side than on the outer side. Naturally, the harmfulness increases when the plate thickness D is small.

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

The magnetic sensors 7a and 27b are housed in the hollow rolls 1 and 1a, respectively. Each of the hollow rolls 1 and 1a is constantly pressed against the upper and lower surfaces of the metal band 10 with a constant urging 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 band 10 vibrates up and down during the traveling process, the distance is maintained at a constant value, so that the accuracy of defect measurement can be further improved.

[0046]

As described above, according to the magnetic flaw detector of the present invention, the magnetic sensors are respectively disposed in a pair of hollow rolls in contact with the metal band with the running path of the metal band interposed therebetween. Therefore, the defect scale and defect position of the defects existing on the surface and inside of the metal strip can be accurately measured.

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

[Brief description of the drawings]

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

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

FIG. 3 is a schematic view showing the installation of the apparatus of the 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 embodiment,

FIG. 6 is a schematic view showing a drawing test apparatus for obtaining basic harmfulness characteristics,

FIG. 7 is a diagram showing basic harmfulness characteristics 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 strip, 17,
17a: signal processing circuit, 18: arithmetic circuit, 19: host computer, 20: harmfulness evaluation circuit, 21: alarm device.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Maki 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) References JP-A-3-175352 (JP, A) JP-A-57 -108656 (JP, A) JP-A-61-62816 (JP, A)

Claims (1)

(57) [Claims] 1. A pair of hollows rotatably supported on a support shaft orthogonal to a traveling path of a metal strip and rotating by contacting the upper and lower surfaces of the metal strip traveling on the traveling path with the traveling path interposed therebetween. A roll, a magnetizer disposed in one of the pair of hollow rolls to generate a magnetic field in the metal band; and a magnetizer disposed in each of the hollow rolls, inside the metal band or A pair of magnetic sensors for detecting a leakage magnetic flux generated due to a surface defect, and a defect occurrence position and a defect size in the thickness direction of the metal band of the defect from each leakage magnetic flux value detected by the pair of magnetic sensors. Using an arithmetic circuit to calculate and a reference metal sample on which a reference defect has been formed,
The defect generation position required in
Shows the ease of crack initiation when a shear stress is applied
From the reference hazard characteristics showing the relationship with the reference hazard,
Calculates the reference hazard at the calculated defect occurrence position
Then, the calculated reference harmfulness is calculated as the calculated defect.
It depends on the scale, the thickness of the metal strip and the purpose of use of the metal strip.
To the metal band
A magnetic flaw detector including a harm evaluation circuit for obtaining harm.