JP2007278916A - Method and device for inspecting flaw of cast piece - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flaw inspection method of a cast piece, capable of increasing lift-off and capable of inspecting cracks of a cast piece in a high temperature state, immediately after casting without having to widen the observation range, and to provide a flaw inspection device therefor. <P>SOLUTION: The flaw inspection method of the cast piece has a radiation step of radiating an electromagnetic wave toward the surface of the cast piece, a step of measuring the reflection intensity of electromagnetic waves reflected from the surface of the cast piece and a step of detecting a crack flaw of the cast piece, on the basis of the reflection intensity. Furthermore, the flaw inspection device of the cast piece has a radiation means for radiating the electromagnetic waves toward the surface of the cast piece that they converge to the surface of the cast piece, a measuring means for measuring the reflection intensity of the electromagnetic waves reflected from the surface of the cast piece and a flaw detection means for detecting the crack flaw of the cast piece, on the basis of the reflection intensity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a defect inspection method and a defect inspection apparatus for a slab slab manufactured by continuous casting.

In continuous casting of steel, molten steel is poured into a water-cooled mold and cooled, and a solidified shell is formed on the contact surface with the mold, and this solidified shell is continuously drawn below the mold and solidified with cooling water on the way. The layer is developed and cut to a certain length after the whole solidifies to produce a slab.
In the cooling process of the slab, if the cooling rate is increased, the drawing speed of the slab can be increased. As a result, the manufacturing speed of the slab is increased, and the production amount can be increased.

  However, the slab has a thickness of 200 to 300 mm, and it is difficult to keep the same cooling state from the surface layer to the center. As a result, a temperature difference occurs between the surface layer and the inside. The low temperature portion shrinks in volume compared to the high temperature portion. When the shrinkage of the surface layer proceeds, stress is generated on the surface layer, and when it is large, surface layer cracking occurs. In particular, the corner portion of the square slab has a large surface area, so the temperature is low and cracking is likely to occur.

  When such a crack occurs and is found by inspection, an operation of grinding the surface layer portion and removing the crack portion in a later process is added. If it is overlooked in the inspection, the cracked part becomes a trigger, and the operation is greatly affected, such as breakage in a later process or remaining as a pattern defect on the surface. For this reason, a defect inspection device is required for finding cracks in the slab at an early point (immediately before and immediately after cutting).

  Conventionally, many inspections of slabs, including the method of installing and monitoring a camera, were visually. Some of them are automated by adding image processing, but these problems are that if the slab temperature is high, the influence of infrared rays in the background is large and cracks are difficult to see, and cracks with small openings are difficult to detect. , It becomes invisible when the scale is covered.

On the other hand, as shown in Patent Document 1, attempts have been made to detect defects such as cracks using electromagnetic waves. It is also conceivable to use eddy currents and ultrasonic waves, which are general non-destructive inspection methods.
JP 10-31804 A

However, when eddy current inspection or ultrasonic inspection is used, it is necessary to reduce the distance from the sensor to the object (hereinafter referred to as lift-off), and the surface temperature can be 800 ° C. or higher. It will increase in size. In addition, since it is greatly affected by the surface properties, the S / N of the signal is likely to deteriorate in a slab having poor surface properties immediately after casting.
If the lift-off is increased, the influence of surface properties and the influence of heat are considered to be reduced, but the observation range of the sensor on the slab is expanded, resulting in insufficient sensitivity to small cracks.

  The present invention has been made in view of the above circumstances. The object of the present invention is to increase the lift-off, inspect the crack of the slab in a high-temperature state immediately after casting, and inspect it without expanding the observation range. And to provide the device.

The slab defect inspection method according to the present invention includes:
A defect inspection method for detecting crack defects existing on the slab surface in a non-contact manner using electromagnetic waves,
A radiation process for radiating electromagnetic waves toward the surface of the slab;
Measuring the reflection intensity of the electromagnetic wave reflected on the slab surface;
And a step of detecting a crack defect based on the reflection intensity.

In addition, the slab defect inspection method according to the present invention,
In the radiation step,
The radiating electromagnetic wave is radiated so as to be focused on the surface of the slab.

In addition, the slab defect inspection method according to the present invention,
In the radiation step,
The electromagnetic field is emitted so that the electric field excited on the surface of the slab is perpendicular to the cracking direction of the crack defect.

In addition, the slab defect inspection method according to the present invention,
The size of the focusing point for focusing the electromagnetic wave on the surface of the slab is set to be twice or less the shortest defect length to be detected.

In addition, the slab defect inspection method according to the present invention,
An electromagnetic wave having a wavelength of the electromagnetic wave that is not more than twice the shortest defect length to be detected is used.

Moreover, the slab defect inspection apparatus according to the present invention is:
Radiation means for radiating electromagnetic waves toward the slab surface so as to focus the electromagnetic wave on the slab surface;
Measuring means for measuring the reflection intensity of the electromagnetic wave reflected by the slab surface;
Defect detecting means for detecting crack defects in the slab based on the reflection intensity.

According to the present invention, since the electromagnetic wave is focused so as to coincide with the inspection target point, the propagation path can be lengthened, and the lift-off can be increased while suppressing the reduction in sensitivity.
In addition, by concentrating electromagnetic waves on a small area of the observation range on the slab, inspection with reduced sensitivity to small defects can be performed.

Embodiment 1 FIG.
Hereinafter, the present invention will be specifically described by using an example applied when casting molten steel with a slab continuous casting machine.
In continuous casting of steel, molten steel is poured into a water-cooled mold and cooled, and a solidified shell is formed on the contact surface with the mold, and the solidified shell is continuously drawn below the mold to produce a continuous cast slab. is doing. At the end of the continuous caster, the slab is cut to a predetermined length.

FIG. 1 shows a structure of a slab defect inspection apparatus that realizes a slab defect inspection method according to Embodiment 1 of the present invention.
The slab defect inspection apparatus shown in FIG. 1 includes an electromagnetic wave generator 101, a waveguide 102, a dielectric lens 104, and a horn antenna 106.
The electromagnetic wave generator 101 is realized by a network analyzer, for example, and generates millimeter waves (1 GHz to several hundreds GHz).
The electromagnetic wave generated by the electromagnetic wave generator 101 is radiated from the horn antenna 106 via the waveguide 102.
The electromagnetic wave 103 ′ radiated from the horn antenna 106 reaches the slab surface. Thereby, the strength of the electromagnetic wave is kept high, and it is possible to inspect with high sensitivity even if the distance from the cast slab which is the subject is increased. In addition, the size of the focused point of the focused electromagnetic wave is preferably not more than twice the length of the crack defect to be detected.

FIG. 2 is a schematic view of the slab defect inspection apparatus 205 according to the first embodiment when the slab defect inspection apparatus 205 according to the first embodiment is installed at the end of the continuous casting machine.
The slab 201 is cut immediately after the machine end to become a slab 202 having a predetermined length.
If the non-uniformity of the cooling state is large at the stage of the slab 201, a crack 203 occurs in the slab 201. At this time, the slab defect inspection apparatus 205 according to the first embodiment is installed in order to inspect for cracks.
When a defect is detected by the slab defect inspection device 205, the slab 201 is cut to a predetermined length to form a slab 202, and then partially ground. When the defective part is large, an area of about 50 cm to 1 m including the defective part may be cut and discarded.

Here, the polarized wave of the electromagnetic wave 103 ′ radiated from the slab defect inspection apparatus 205 is radiated so that the electric field excited on the slab 201 is perpendicular to the crack 203. The reason for this will be described with reference to FIG.
The emitted electromagnetic wave 103 ′ is set so as to be focused at the inspection target point on the surface of the slab 201.

FIG. 3 illustrates a state of reflection of electromagnetic waves radiated to the slab 201 by the slab defect inspection apparatus 205 of FIG.
The slab defect inspection apparatus 205 radiates the electromagnetic wave 103 ′ to the slab 201 and scans the surface of the slab 201 for cracks (upper view in FIG. 3).
The lower diagram of FIG. 3 shows how the intensity of the reflected wave varies depending on the presence or absence of the crack 203. The direction of the arrow represents the propagation direction of the electromagnetic wave, and the length of the arrow represents the intensity of the electromagnetic wave.
When scanning the portion without the crack 203 (lower diagram (1) in FIG. 3), the electromagnetic wave 103 ′ is almost reflected on the slab 201, but when scanning the crack 203 portion (lower diagram in FIG. 3 ( In 2)), since the electric field propagates along the crack 203 and the electromagnetic wave 103 ′ is attenuated in the crack 203, the reflection intensity is reduced.

  The reflected wave is received by an antenna (not shown) provided separately or used for radiation (horn antenna 106 in FIG. 1) and analyzed by a network analyzer (electromagnetic wave generator 101 in FIG. 1). Equivalent to the measurement means and defect detection means described).

FIG. 4 shows the relationship between the intensity of the reflected wave in FIG. 3 and the scan position of the slab 201. FIG. 4 shows a measurement example when scanning is performed in a direction substantially perpendicular to the direction of defect cracking in the surface of the slab.
When the crack 203 is scanned, the reflected wave is attenuated as described above. By analyzing the reflection intensity, it is possible to detect the presence of a crack in a portion where the reflection intensity is greatly attenuated. Become.

When an oxide or the like is present on the surface, depending on the electrical characteristics of the oxide, there is a case where reflection on the oxide surface is large and a change in intensity signal due to cracking is small.
In this case, even if a crack exists on the surface, the intensity of the reflected wave does not become small enough to be detected, so that it is difficult to detect the crack.
In this case, the detection accuracy can be increased by reducing the frequency or the like to increase the permeability of the oxide and reduce the reflection on the oxide surface.

The reason why the electric field is made perpendicular to the cracking direction is that the electric resistance is increased and the loss of electrolysis is increased. Furthermore, since a part goes into the crack depth direction, the loss becomes larger. As the loss increases, it becomes easier to detect a change in the intensity of the reflected wave, so that the crack detection accuracy also increases.
If the electric field is parallel to the crack, the resistance is small, and hence the loss is small. Therefore, the signal change of the reflected wave is small, and the crack detection accuracy is low.

Next, the wavelength of the electromagnetic wave radiated from the slab defect inspection apparatus will be described.
The minimum size of the focusing point that can be focused is determined by the wavelength of the electromagnetic wave used, and as a result, the size of the detectable crack is determined. This is because it can be detected if it is a crack having a length of 1/2 or more with respect to the wavelength of the electromagnetic wave used.
For example, in the first embodiment, the electromagnetic wave generation device 101 of FIG. 1 generates millimeter waves, but when the wavelength of this electromagnetic wave is 3 mm and the frequency is 100 GHz, the detectable crack has a length of 1. .5 mm or more.
If the minimum length of a crack to be detected is 1 mm, the wavelength needs to be 2 mm or less. In this case, it is necessary to use a frequency of 150 GHz or more.

Generally, cracks that are a problem on the slab are several millimeters or more in length, and the use range is 10 GHz to 300 GHz. If the target is longer than 10 mm, 15 GHz may be used. If another expression is used, it is preferable that the wavelength of the electromagnetic wave is not more than twice the shortest defect length to be detected.
This is because the waveguide does not transmit electromagnetic waves when the size of the waveguide is smaller than the half-wave size of the electromagnetic waves.
If the crack defect part is regarded as a waveguide, the electromagnetic wave emitted by the slab defect inspection device will not enter the crack defect part, so that reflection becomes dominant and loss is reduced. The signal change of the reflected wave becomes smaller.
Then, it becomes difficult to detect a crack by analyzing the intensity of the reflected wave, and the detection accuracy is lowered.
Therefore, the frequency of the electromagnetic wave is set so that the wavelength of the electromagnetic wave radiated from the slab defect inspection apparatus is not more than twice the shortest detection target defect length.

Here, in order to detect a crack with high sensitivity, it is necessary to change the polarization of the electromagnetic wave depending on the direction of the crack.
For this purpose, two slab defect inspection apparatuses with 90 ° polarized waves may be installed, or a single slab defect inspection apparatus may be rotated.
Actually, it seems that there are relatively many vertical cracks that break in the longitudinal direction of the slab (drawing direction in continuous casting). In such a case, the slab defect inspection device is set so that the electric field polarization is in the slab width direction. Should be installed.
On the other hand, in the center of the slab, there are cases where vertical cracks and lateral cracks that break in the width direction increase in the vicinity of the corner portion. In such a case, the electric field polarization may be set in the longitudinal direction of the slab. As described above, since the cracking direction of the defect changes depending on the part, it is necessary to change the polarization according to the inspection object.

In FIG. 2, the slab defect inspection device 205 may be installed on the cut slab 202, or may be installed on a cooling floor of the slab.
In addition, once the slab has been shaved, the surface properties may be stabilized and the crack detection sensitivity may be improved. Therefore, even if the slab defect inspection device 205 is attached at the position to be inspected after cutting. good.

FIG. 5 explains peripheral devices and the like of the continuous casting machine in FIG.
Depending on the position and number of defects in one slab, there are cases in which measures such as changing the initially planned manufactured product or changing the shipping destination are taken.
Therefore, the slab defect position / number can be output from the slab defect inspection apparatus 205 to the recording system 206, recorded in the system, and communicated to the lower process.
In addition, when there are many defects, the cooling process may be inappropriate. Therefore, it is possible to provide feedback to the upper process and optimize the cooling water control of the slab cooling device 207.
In this way, defect information on the slab is made into a database and optimal measures are taken to avoid the occurrence of defects in the lower process, production of products that are inappropriate in quality, and continuation of inappropriate operations. be able to.

  In the first embodiment, a network analyzer is used as the electromagnetic wave generator 101. However, an oscillator such as a GUN type and a receiver such as a power meter may be used.

  As described above, according to the slab defect inspection apparatus according to the first embodiment, the radiation means (horn antenna 106 and dielectric lens 104) that radiates electromagnetic waves toward the inspection target point of the slab, and the inspection Since it has a measurement means (network analyzer 101) for measuring the reflection intensity of the electromagnetic wave reflected at the target point, and a defect detection means (also used by the network analyzer 101) for detecting a defect at the inspection target point based on the reflection intensity. Since the lift-off can be increased while suppressing the reduction in sensitivity, the slab defect inspection apparatus can be installed in an environment where the slab is at a high temperature.

  Further, since the radiating means (horn antenna 106 and dielectric lens 104) focuses the radiated electromagnetic wave so that the focal point of the radiated electromagnetic wave coincides with the point to be inspected, the propagation path of the electromagnetic wave can be lengthened, and the slab By concentrating electromagnetic waves in a small area of the observation range, inspection with reduced sensitivity to small defects can be performed.

  Further, the radiation means (horn antenna 106 and dielectric lens 104) radiates electromagnetic waves so that the electric field excited on the upper surface of the slab is perpendicular to the direction of cracks existing in the slab. Since the electrical resistance increases and the loss of electrolysis increases, it becomes easier to detect the intensity change of the reflected wave when scanning for cracks, and the crack detection accuracy increases.

  In addition, the radiating means (horn antenna 106 and dielectric lens 104) uses an electromagnetic wave such that the wavelength of the electromagnetic wave reaching the inspection target point is not more than twice the shortest detection target defect length. The incident wave easily propagates along the crack of the crack, and the intensity change of the reflected wave in the crack increases, so that the crack detection accuracy increases.

Embodiment 2. FIG.
FIG. 6 explains electromagnetic wave generation means in the slab defect inspection apparatus according to Embodiment 2 of the present invention.
In the first embodiment, as shown in FIG. 1, the electromagnetic wave 103 is focused on a focusing point using a dielectric lens 104.
As a focusing method, a parabolic antenna shown in FIG. 6 can be used in addition to the dielectric lens.
In FIG. 6, an electromagnetic wave generator 601 generates an electromagnetic wave having a predetermined wavelength and radiates it by a radiator 602.
The radiated electromagnetic wave is reflected by the parabolic reflector 603 and the hyperboloidal mirror 604 and is focused at the focal point 606 via the propagation path 605.
The reflected wave reflected from the surface of the slab to be inspected is received by an antenna (not shown) or the like provided separately, and the strength is analyzed by an analysis device (not shown) to detect cracks.

FIG. 7 explains another method of realizing the electromagnetic wave generating means in the slab defect inspection apparatus according to Embodiment 2 of the present invention.
As a method of focusing electromagnetic waves, a phased array antenna using a plurality of antennas as shown in FIG. 7 can be used.
The antenna group 701 is an array of antennas having a phase difference.
The phase shifter group 702 is a set of phase shifters provided for each antenna of the antenna group 701.
Since the electromagnetic wave phase of each antenna is converted by a phase shifter, the electromagnetic wave can be generated in an arbitrary direction. Therefore, the electromagnetic wave of each antenna can be focused at the focusing point. 1 can achieve the same focusing effect as the dielectric lens 104 in FIG.

1 shows a structure of a slab defect inspection apparatus that realizes a slab defect inspection method according to Embodiment 1 of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The schematic before and after a machine end at the time of installing the slab defect inspection apparatus 205 which concerns on this Embodiment 1 in the machine end of a continuous casting machine is shown. The state of reflection of electromagnetic waves radiated to the slab 201 by the slab defect inspection apparatus 205 of FIG. 2 will be described. FIG. 4 shows the relationship between the intensity of the reflected wave in FIG. 3 and the scan position of the slab 201. FIG. The peripheral equipment of the continuous casting machine in FIG. 2 will be described. The electromagnetic wave generation means in the slab defect inspection apparatus according to Embodiment 2 of the present invention will be described. Another realization method of the electromagnetic wave generation means in the slab defect inspection apparatus according to Embodiment 2 of the present invention will be described.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Electromagnetic wave generator, 102 Waveguide, 103 Electromagnetic wave, 103 'Electromagnetic wave, 104 Dielectric lens, 106 Horn antenna, 201 Slab, 202 Slab (after cutting), 203 Crack, 205 Defect inspection apparatus, 206 Recording system, 207 Slab Cooling device, 208 roll, 601 electromagnetic wave generator, 602 radiator, 603 parabolic reflector, 604 hyperboloid mirror, 605 propagation path, 606 focal point, 701 antenna group, 702 phaser group.

Claims (6)

A defect inspection method for detecting crack defects existing on the slab surface in a non-contact manner using electromagnetic waves,
A radiation process for radiating electromagnetic waves toward the surface of the slab;
Measuring the reflection intensity of the electromagnetic wave reflected on the slab surface;
A slab defect inspection method comprising: detecting a crack defect based on the reflection intensity. In the radiation step,
The slab defect inspection method according to claim 1, wherein the radiated electromagnetic wave is radiated so as to be focused on the slab surface. In the radiation step,
The slab defect inspection method according to claim 1 or 2, wherein an electromagnetic wave is radiated so that an electric field excited on a slab surface is in a direction perpendicular to a crack direction of the crack defect. .   The slab defect inspection method according to any one of claims 1 to 3, wherein the size of the focusing point for focusing the electromagnetic wave on the slab surface is set to be twice or less the shortest detection target defect length. .   The slab defect detection method according to any one of claims 1 to 4, wherein the electromagnetic wave is used such that the wavelength of the electromagnetic wave is not more than twice the shortest detection target defect length. Radiation means for radiating electromagnetic waves toward the slab surface so as to focus the electromagnetic wave on the slab surface;
Measuring means for measuring the reflection intensity of the electromagnetic wave reflected by the slab surface;
A slab defect inspection apparatus comprising defect detection means for detecting a crack defect in a slab based on the reflection intensity.

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