JPH08201323A - Induction heating flaw detection method and apparatus for electrically conductive continuous cast pieces - Google Patents

Abstract

(57) [Summary] [Object] To provide an induction heating flaw detection method and apparatus capable of detecting a surface flaw existing in a continuously cast piece before rolling. In the heating step, the high-frequency power supply device 24 drives the induction coil 18 with a high-frequency current having a predetermined frequency, so that an induction current having a penetration depth smaller than the depth of the surface flaw is applied to the surface of the conductive inspection material 10. Then, the surface temperature of the conductive inspection material 10 is measured by the radiation temperature measuring devices 78a, 78b, 78c, 78d in the temperature measuring step. Then, in the calculation determining step, the calculation determining means 84 calculates the local temperature change amount signal SΔT based on the surface temperature, and
The temperature change amount signal SΔT has a negative first determination reference value Th ₁
The presence or absence of the pinhole 68 is determined by comparison with the above. Therefore, the pinhole 68 of the conductive inspection material 10 before rolling
The presence or absence of can be easily determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating flaw detection apparatus for flaw detection on a surface flaw based on the non-uniformity of the surface temperature when the surface of a conductive cast piece is induction heated.

[0002]

2. Description of the Related Art The surface of a conductive test material is heated by generating an induction current in the conductive test material by electromagnetic induction, and the surface temperature of the conductive test material is measured. An induction heating flaw detection device for a conductive inspection material has been proposed which detects a surface flaw in the conductive inspection material based on the uniformity. In such a flaw detector, when the eddy current generated by electromagnetic induction is concentrated on the surface by the skin effect, the surface of the conductive inspection material is heated by eddy current loss and the like, but the portion where the surface flaw exists is Since the flow of eddy current is changed more than other parts and the amount of heat generation of that part also changes, the part where the surface temperature changes locally compared to other parts is judged as a surface flaw. .

By the way, the above-mentioned induction heating flaw detector is also used, for example, for flaw detection of a cast piece such as a continuously cast steel material. In the continuous casting method, surface flaws such as pinholes (cylindrical minute holes) may occur in the surface layer of the cast piece that was in contact with the mold, but in general, the cast piece is variously deformed by the multi-step rolling process. Therefore, the surface flaw is spread over a wide area in the rolling process, the defect area is increased, and the process is wasted. Therefore, it is desirable that the surface defects existing from the time of casting be found and removed at the earliest possible stage.

[0004]

However, in the conventional induction heating flaw detector, the eddy current on the surface of the conductive material to be inspected is obstructed by the surface flaw so that it is diverted to the portion adjacent to the surface flaw. It is formed on the premise that the surface temperature of the surface flaw portion locally rises due to the formation of a current concentration region near the surface flaw (US Pat. No. 4,109,508). Therefore, when a high-frequency induction current is applied in the direction orthogonal to the longitudinal direction of the linear flaw formed in the billet after rolling and extending in the longitudinal direction of the steel material, the linear flaw (surface A flaw is detected, but in the case of a flaw such as the pinhole in which the length of the steel material in the longitudinal direction is relatively short, the current concentration region in the vicinity of the surface flaw is not clearly formed. Therefore, there is a problem that the surface flaw cannot be found even if the cast piece before rolling is flaw-detected.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an induction heating flaw detection method and apparatus capable of detecting a surface flaw existing in a continuously cast piece before rolling. To provide.

[0006]

In order to achieve such an object, the gist of the induction heating flaw detection method of the present invention is that an induction current is generated in a continuous cast piece having conductivity by electromagnetic induction. , The surface of the cast piece is heated by the electromagnetic induction, the surface temperature of the cast piece is measured, and the continuous cast piece having conductivity for flaw detection of the surface flaw of the cast piece based on the non-uniformity of the surface temperature Induction heating flaw detection method of, (a) a heating step of heating the surface of the casting piece by an induction current having a penetration depth smaller than the depth of the surface flaw,
(b) a temperature measuring step of measuring the surface temperature of the cast piece with a radiation thermometer, and (c) calculating a local temperature change amount of the surface of the cast piece based on the surface temperature, and locally And a calculation determination step of determining a pinhole when the temperature change amount exceeds a predetermined negative determination reference value,
To include.

[0007]

According to this structure, when the surface of the continuously cast piece is heated by the induction current having a penetration depth smaller than the depth of the surface flaw in the heating step, the The surface temperature is measured, and in the calculation determination step, the local temperature change amount of the cast piece surface is calculated based on the surface temperature, and the temperature change amount exceeds a predetermined negative judgment reference value. Therefore, the pinhole is determined. If the penetration depth of the induced current is smaller than the depth of the surface flaw, if the surface flaw is such that the length of the casting piece in the longitudinal direction is short, such as a pinhole, then the eddy current will be lateral to the pinhole. By forming a non-conducting region directly under the bypass, the temperature rise in the pinhole portion locally decreases. Therefore, when the amount of temperature change exceeds a predetermined negative determination reference value, it is determined that there is a pinhole in that portion in the calculation determination step, and the pinhole of the continuous cast piece that has not been rolled is The presence / absence can be easily determined.

[0008] Here, preferably, (d) the calculation determination step is a negative first value in which the local temperature change amount is predetermined.
The pinhole is judged by exceeding the judgment reference value, and the bleeding or cracking is judged by the local temperature change amount exceeding the predetermined positive second judgment reference value. In this way, when the local temperature change is negative and exceeds the first determination reference value, the pinhole is determined as described above, while the local temperature change is positive. If the second judgment reference value is exceeded, bleeding or cracking is judged. Therefore, whether or not the surface flaw of the continuously cast piece is a pinhole or bleed or a crack is determined.

Incidentally, the bleed is a surface flaw that can be formed in a convex shape on the surface of a cast piece manufactured by continuous casting, and has foreign matter and bubbles inside. When the penetration depth of the induced current is smaller than the depth of the surface flaw in the area where such a bleed is present, a complicated current path is formed due to the uneven texture, and eddy currents are flowed randomly. As a result, the electrical resistance increases, and the temperature rise locally increases. Further, even in cracks and corner cracks, when an induced current having a penetration depth shallower than those depths flows, the current is closely diverted in accordance with the flaws, so that the temperature of these flaws and cracks also rises. That is, the surface temperature of the continuous cast piece measured in the temperature measuring step is changed by the existence of the surface flaw regardless of the shape of the surface flaw, and the positive or negative of the temperature change amount is determined by the shape of the surface flaw. Therefore, by comparing the amount of temperature change with the first judgment reference value or the second judgment reference value depending on whether the temperature change is positive or negative, the presence or absence and the shape of the surface flaw of the continuous cast piece can be judged.

[0010]

In order to achieve the above object, the gist of the induction heating flaw detector of the present invention is that an induction current is generated in a continuous slab having conductivity by electromagnetic induction. Then, the surface of the cast piece is heated by the electromagnetic induction, the surface temperature of the cast piece is measured, and continuous casting with conductivity is performed to detect the surface flaw of the cast piece based on the non-uniformity of the surface temperature. An induction heating flaw detection device for a piece, (e) a high-frequency heating device for heating the surface of the casting piece by generating an induction current having a penetration depth smaller than the depth of the surface flaw on the surface of the casting piece. , (F) a radiation thermometer for measuring the surface temperature of the cast piece, and (g) calculating a local temperature change amount of the surface of the cast piece based on the surface temperature measured by the radiation thermometer. , The local temperature change is And determining calculation determination means pinholes with a possible exceeding the negative determination reference value set is to contain.

[0011]

In this way, the induction heating flaw detection apparatus can generate the induced current of the penetration depth smaller than the depth of the surface flaw on the surface of the cast piece to heat the surface. A device, a radiation thermometer that measures the surface temperature, and a local temperature change amount is calculated based on the surface temperature, and a pinhole is determined when the temperature change amount exceeds a negative determination reference value. And a calculation determining unit for performing the calculation. If the penetration depth of the induced current is smaller than the depth of the surface flaw, if the surface flaw is such that the length of the casting piece in the longitudinal direction is short, such as a pinhole, then the eddy current will be lateral to the pinhole. By forming a non-conducting region directly under the bypass, the temperature rise in the pinhole portion locally decreases. Therefore, when the amount of temperature change exceeds a predetermined negative judgment reference value, it is judged by the calculation judging means that a pinhole exists in that portion, and the pinhole of the continuous cast piece that has not been rolled is determined. The presence / absence can be easily determined.

Here, in the first and second inventions, preferably, the cast piece is a continuously cast steel piece made of magnetic steel. In this case, in order to generate an induced current having a penetration depth smaller than the depth of the surface flaw, it is possible to use a high-frequency heating device having a frequency of several tens to 100 kHz which is relatively easy to use.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a plan view showing an induction heating flaw detector according to an embodiment of the present invention. In the figure, the conductive test material 10 is a cast piece which has a square cross section with a side of about several tens of cm and a length of about 10 m, and is a cast piece that has been cast by continuous casting and has not yet been rolled. It is made of a metal material or a non-magnetic metal material such as stainless steel, aluminum alloy, and copper alloy.

The conductive material 10 to be inspected is supported by a conveying roller (not shown) and two pinch roller units 12 and 14, and the pinch roller units 12 and 14 are rotatably driven by a driving device (not shown). It is conveyed at a constant speed in the longitudinal direction with the diagonals of the cross section being substantially vertical and horizontal, and in the course of the conveyance, it can be successively passed through the powder coating device 16, the induction coil 18, and the powder removing device 20. ing.

FIG. 2 is a perspective view of the powder coating device 16 as seen from its outlet side. The powder coating device 16 is provided with a through hole 22 having a larger cross section for allowing the conductive inspection material 10 to pass therethrough, and the high-frequency power supply device 24 is provided with the conductive inspection material from the through hole 22. Through hole 2 having a shape slightly larger than its cross section for passing the material 10
An induction coil 18 having 6 is erected. In this embodiment, the high frequency power supply device 24 and the induction coil 18 constitute a high frequency heating device. The pinch roller unit 14 is composed of a drive roller 28 that is rotationally driven by a drive device (not shown), and a pressing roller 30 that faces the drive roller 28 and presses the conductive inspection target material 10. The pinch roller unit 12 has the same structure as the pinch roller unit 14. Further, the powder removing device 20 is also provided with a through hole 32 like the powder applying device 16.

The powder coating device 16 is, for example, as shown in FIG. 3, a box-shaped main body 17 and powders directed toward the four side surfaces of the conductive inspection material 10 at a predetermined distance in the main body 17. 4 spray guns 3 for ejecting each body 34
6 is provided. The coating gun 36 is located at a fixed distance directly above the widthwise center of each side surface of the conductive inspection material 10. Also, this coating gun 36
4, is a powder supply port 38 connected to a hopper (not shown), a compressed air connection port 40 to which compressed air is supplied, and a discharge port 42 for discharging the powder 34.
And a high-voltage power supply 44 that outputs a negative high voltage of about 100 kV and an electrostatic electrode 46 that is electrically connected to the discharge port 42 and that ejects the negatively charged powder 34. Is configured. Since the material 10 to be inspected is grounded via the transport roller (not shown) and the two pinch roller units 12 and 14, etc., the powder 34 is attracted by the Coulomb force, and the material 34 is electrically conductive according to the principle of electrostatic coating. It is evenly adsorbed and applied to the surface of the material 10 to be inspected. Excess powder 34 in the powder coating device 16 is duct 48
It is designed to be collected via.

Further, the powder removing apparatus 20 is, for example, as shown in FIG. 5, a box-shaped main body 21 and four side surfaces of the conductive inspection material 10 which are separated by a predetermined distance in the main body 21. It is provided with four air injection guns 50 which each discharge compressed air of about 4 kg / cm ² . The air injection gun 50 is provided with a plurality of nozzles 52 arranged in the width direction of the side surface of the conductive inspection material 10 so as to project toward the side surface thereof. The powder 34 electrostatically applied to the surface of the conductive material 10 to be inspected is easily removed. The removed powder 34 is collected via the duct 54.

The duct 48 of the powder coating device 16 and the duct 54 of the powder removing device 20 are, as shown in FIG.
It is connected to the dust collector 56 so that the powder 34 remaining in the powder coating device 16 and the powder 34 removed in the powder removing device 20 can be collected in the dust collector 56 and reused. It has become.

That is, the dust collector 56 includes a cyclone type primary dust collector 58 connected to the ducts 48 and 54, and a filter type secondary dust collector 62 connected to the primary dust collector 58 via a duct 60. Through the primary dust collector 58 and the secondary dust collector 62, the powder coating apparatus 1
6 and a suction blower 6 for sucking air in the powder removing device 20
And 4. The primary dust collector 58 is of a type that removes the powder 34 continuously and efficiently in accordance with a centrifugal force by rotating the intake air in an inversely tapered space. The secondary dust collector 62 is of a type that removes the powder 34 having a relatively fine particle size mixed in the air by sucking the intake air through the filter cloth.
The powder 34 collected by the primary dust collector 58 and the secondary dust collector 62 is periodically taken out, cleaned, and then reused.

Here, the powder 34 is carbon particles,
The emissivity equalizing powder is obtained by coating particles such as titanium particles having a particle size of about 40 to 100 μm with an insulating resin such as an epoxy resin or an acrylic resin. The resin-coated carbon particles are black, and the resin-coated titanium particles are white to gray, but all of them emit energy corresponding to the surface temperature to cause the surface state of the conductive inspection material 10. The variation of infrared emissivity is prevented and uniformized and the emissivity is increased. The insulating resin is for electrically insulating carbon particles, titanium particles, etc., but since it softens or starts melting at a relatively low temperature, the surface heating temperature of the conductive inspection material 10 is at maximum.
Limited to below 80 ℃.

In the powder coating device 16, the conductive test material 10 having a square cross section of 155 mm on one side is 40 m / m.
90g / min powder 34 while conveying at in speed
The amount of the powder 34 discharged from each coating gun 36 is set so that is applied to the surface of the conductive inspection material 10.
The powder 34 on the surface of the conductive inspection material 10 at this time
Since the average coating thickness of 7 is 7 μm, the thickness is about 1/6 of the average particle diameter of the powder 34. That is, the powder 34 is set so as to be sparsely attached on the surface of the conductive inspection material 10.

When the coating thickness of the powder 34 becomes too large and piles up on each other, the conductive material 10 to be inspected
The heat conduction from the surface to the outermost powder 34 is lowered, and infrared radiation of energy corresponding to the temperature of the conductive inspection material 10 cannot be performed. If the coating thickness of the powder 34 becomes too small, the coating effect of the powder 34, that is, the surface of the conductive inspection material 10 is glossy like rubbing traces against each other, and is caused by a portion having a low emissivity. Therefore, it becomes impossible to obtain the effect of increasing the emissivity at a place where the temperature is low and making the emissivity uniform by increasing the emissivity and increasing the emissivity of the whole.
From this point of view, it is desirable that the coating amount of the powder 34 be 1/15 to 1/3 of the average particle size.

As shown in FIGS. 6 and 7, the induction coil 18 is made of copper or the like having a width of about 20 to 40 mm so as to form a through hole 26 larger than the sectional shape of the conductive test material 10. An annular part 70 in which a strip-shaped metal member is bent in an annular shape
And a linear portion 74 in which both ends of the strip-shaped metal member are fixed to each other via an insulating plate 72 made of ceramic or resin.
It consists of and. Then, as shown in FIG. 8, the temperature of the pair of side surfaces of the conductive inspection material 10 at the outlet of the coil 18 is measured by the two radiation temperature measuring devices 78a and 78b supported by a frame (not shown). Along with the same, 2 supported by a frame (not shown)
The radiation temperature measuring devices 78c and 78d of the table allow the coil 1
The surface temperatures of the two corners of the conductive material to be inspected 10 at the outlet of 8 are measured. in this case,
The temperature of the upper half side surface of the conductive inspection material 10 is measured, but the remaining lower half side surface may be similarly processed further downstream to measure the temperature. Of course, the temperature may be measured on all side surfaces of the conductive inspection material 10 at the same time, or it may be inverted again by 180 ° in the above embodiment and re-conveyed to measure.

The radiation temperature measuring devices 78a, 78b, 7
Reference numerals 8c and 78d respectively collect infrared rays radiated from the surface of the conductive test material 10 on the detection surface of an infrared detection sensor in which a large number of detection elements are arranged in the detection surface in a one-dimensional direction (not shown) so as to be conductive. The surface temperature of the measurement point is measured by scanning at a frequency of about 200 Hz in the direction perpendicular to the longitudinal direction of the inspected material 10. FIG. 9A shows the temperature detection signal ST corresponding to the temperature distribution in the width direction of the side surface of the conductive inspection material 10 detected by the radiation temperature measuring devices 78a and 78b. As shown in FIG. 6, the induction coil 18 has a cooling liquid passage 7 communicating in the longitudinal direction thereof.
9 has a hollow structure inside, and is designed to cool the heat generated by the high frequency drive current.

For the purpose of detecting flaws on the surface of the conductive material 10 to be inspected, the high-frequency power supply device 24 determines the depth of the surface flaw on the surface of the material 10 according to the magnetic permeability of the material 10 to be inspected. The induction coil 18 is supplied with a high frequency drive current having a predetermined frequency selected so that an induction current (eddy current) having a penetration depth smaller than the above is generated. For example, when the conductive inspection material 10 is a magnetic metal material (that is, when the magnetic permeability is large), the predetermined frequency is several tens to 100 k.
A relatively low value of about Hz is selected, and the surface is heated to about 50 to several hundred tens of μm due to eddy current loss.
On the other hand, in the case of a non-magnetic metal material (that is, when the magnetic permeability is small), a relatively high value of several hundred kHz is selected, so that the surface is heated to approximately 1 mm due to eddy current loss. That is, assuming that the eddy current on the surface of the conductive test material 10 is I ₀ , the frequency is f, the magnetic permeability is μ, and the conductivity is σ, the eddy current I generated in the conductive test material 10 is shown.
Is attenuated in relation to the distance x from the surface as shown in Equation 1, and the value of x at which the exponent of Equation 1 becomes -1 (penetration depth)
Is expressed as Mathematical Expression 2. in this way,
The eddy current I is concentrated on the surface layer due to the skin effect, so that the surface of the conductive inspection material 10 is heated.

[0026]

[Equation 1]

[0027]

[Equation 2]

The electronic control unit 66 for controlling flaw detection shown in FIG.
A well-known microcomputer having a PU, a ROM, a RAM and the like is provided, and by processing an input signal in accordance with a program stored in advance in the ROM, the radiation temperature measuring devices 78a, 78b, 78c and 78d output the signals. Based on the temperature detection signal ST, the surface flaws of the conductive test material 10 as shown in FIG. 10, that is, the pinholes 68 and the bleeds 69 of the continuously cast pieces are determined, and the flaw position is output and , Conductive material 1
A flaw marker (not shown) that displays the flaw position on the surface of 0 with ink is operated. The frequency of the high frequency drive current is set so that the penetration depth δ of the eddy current is smaller than the depth d of the surface flaw that may exist in the cast piece before rolling.

FIG. 11 is a functional block diagram showing the essential part of the control function of the flaw detection control device 66 and the relationship between the penetration depth δ and the surface flaw (pinhole 68) depth d.
In the figure, the averaging means 80 averages the temperature detection signal ST representing the surface temperature of the conductive test material 10 measured by the radiation temperature measuring devices 78a to 78d, and outputs the average temperature signal ST _AV . Surface temperature change amount calculation means 8
In 1, the average temperature signal ST _AV is subtracted from the temperature detection signal ST representing the surface temperature of the conductive test material 10 measured by the radiation temperature measuring devices 78a to 78d, whereby the surface of the conductive test material 10 is locally localized. The temperature change amount is calculated, and the temperature change amount signal SΔT indicating the temperature change amount is output. In the flaw determination means 82, the negative change amount of the surface temperature change exceeds the preset first determination reference value based on the local surface temperature change calculated by the surface temperature change amount calculation means 81. The presence or absence of a pinhole is determined based on the above, and the presence or absence of bleeding is determined based on the fact that the positive change amount of the local surface temperature change exceeds a preset second determination reference value. That is, in the present embodiment, the averaging processing means 80, the surface temperature change amount calculating means 81, and the flaw determining means 82 make the calculation determining means 84.
Is configured. In the figure, the pinhole 6
The size of 8 and the penetration depth δ are exaggeratedly drawn.

FIG. 12 is a flow chart for explaining the main part of the arithmetic control operation of the flaw detection control device 66, that is, the flaw detection operation while the conductive inspection material 10 is running.

First, by performing a start-up operation (not shown), the conductive material to be inspected 10 is conveyed at a constant speed in the direction of the arrow in FIG. 1, and at the same time, the powder coating device 16 is operated to operate the powder. 34 is applied to the side surface of the conductive inspection material 10, a high-frequency current is supplied to the induction coil 18, and the powder 34 is removed by the powder removing device 20. At this time, the surface of the conductive material 10 to be inspected is heated by about 20 to 50 ° C. from room temperature by the induction coil 18 to which the high frequency drive current of the predetermined frequency is supplied from the high frequency power supply device 24.

In this state, step SS in FIG.
1, the radiation temperature measuring devices 78a, 78b, 78c, 7
1 which is one unit of the temperature detection signal ST output from 8d
It is determined whether or not signals for scanning have been input. Of FIG.
(a) illustrates the temperature detection signal ST for one scan on the predetermined side surface of the conductive inspection material 10. If the determination in step SS1 is negative, the signal for one scan is made to wait until it is input, but if the determination is affirmative, the averaging process of step SS2 and below is executed. In the radiation temperature measuring devices 78a, 78b, 78c, 78d, the processings of step SS2 and thereafter are executed in synchronization with the scanning cycle of the temperature measurement points electrically determined. The step SS1 corresponds to a temperature detection signal reading means or a temperature detection signal reading step.

In step SS2, the average value of the input temperature detection signals ST is subjected to well-known moving average calculation processing within a suitable section, low-pass filter calculation processing having a suitable cutoff frequency, or the like. Is converted into the average temperature signal ST _AV . This average temperature signal ST _AV is treated as the surface temperature of a place where no flaw exists, and FIG. 9B shows the average temperature signal ST _AV .
_AV is illustrated. This step SS2 corresponds to the average processing means 80 or the average processing step.

At the following step SS3, the temperature detection signal is sent.
No. ST to the above average temperature signal ST_AVSubtraction subtraction
Is executed, the surface of the conductive inspection material 10 is
A temperature change amount signal indicating the local temperature change amount in
Defect signal SΔT (ST-ST _AV) Is calculated. Of FIG.
 (c) illustrates this flaw signal SΔT. This step
SS3 is the surface temperature change amount calculation means 81 or the temperature change amount.
It corresponds to the process of calculating the amount of chemicals.

Next, at step SS4, it is judged whether or not the flaw signal SΔT exceeds a preset first judgment reference value Th ₁ (whether SΔT <Th ₁ or not).
The first determination reference value Th ₁ is a negative value experimentally obtained in advance for determining the pinhole 68 of the conductive inspection material 10, and a value of about −5 ° C. is adopted, for example.

If the determination in step SS4 is affirmative, the process proceeds to step SS6, but if the determination is negative, it is determined in step SS5 whether the flaw signal SΔT exceeds the preset second determination reference value Th _2. Or (SΔT> Th
₂ or not) is determined. This second judgment reference value T
h ₂ is a positive value experimentally obtained in advance for determining the bleed 69 or the like of the conductive inspection material 10, and for example, a value of about + 5 ° C. is adopted.

If the determination in step SS5 is negative, this routine is terminated and steps SS1 and subsequent steps are executed again, but if affirmative, step S5 is executed.
Similar to the case where the determination in S4 is affirmative, the process proceeds to step SS6, in which the flaw determination signal is output to a flaw marker (not shown) and the flaw position is stored at the same time, and then this routine is ended. Note that FIG.
Indicates, for example, one scan on the broken line A in FIG.
A low temperature portion that exceeds the first judgment reference value Th ₁ is formed at a position in the width direction corresponding to the pinhole 68. Therefore, when such a temperature detection signal ST is input, the determination at step SS4 is affirmative and the routine proceeds to step SS6 where it is determined that there is a pinhole 68. In this embodiment, the steps SS4 and SS5 correspond to the flaw determining means 82 or the flaw determining step,
The steps SS2 to SS5 correspond to the calculation determining means.

Here, according to the present embodiment, in the heating step, the high frequency power supply device 24 drives the induction coil 18 with a high frequency current of a predetermined frequency, so that the penetration depth smaller than the depth d of the surface flaw. When the induced current of δ is generated on the surface of the conductive inspection material 10 and the surface is heated, the radiation temperature measuring devices 78a, 78b, 7 are generated in the temperature measuring step.
The surface temperature of the conductive inspection material 10 is measured by 8c and 78d. Then, in the calculation determining step, the local temperature change amount signal SΔT is calculated by the calculation determining means 84 based on the surface temperature, and the temperature change amount signal SΔT is the first determination reference value Th ₁ having a negative value. The presence or absence of the pinhole 68 is determined by comparison with the above.

That is, when the penetration depth δ of the induced current is smaller than the depth d of the surface flaw, in the case of the surface flaw such as the pinhole 68 in which the length of the conductive inspection material 10 in the longitudinal direction is short, The eddy current is diverted to the side of the eddy current, and a non-conducting region is formed immediately below it. For this reason, the temperature rise in that portion is locally reduced, and at the widthwise position corresponding to the pinhole 68 in FIG.
Exceeds the negative first judgment reference value Th ₁ and it is judged that the pinhole 68 exists. Therefore, according to the present embodiment, it is possible to easily determine the presence or absence of the pinhole 68 in the conductive test material 10 that is a continuously cast piece that has not been rolled.

FIG. 13 shows a temperature detection signal S corresponding to one scan of the conductive inspection material 10 on the one-dot chain line B in FIG.
FIG. 3 shows T, and a locally high temperature portion is formed at a position in the width direction corresponding to the bleed 69.
Therefore, when such a temperature detection signal ST is processed according to each step of FIG. 11 and converted into the temperature change amount signal SΔT as in the case of FIG. 9 described above, the determination in step SS4 is denied. The determination in step SS5 that determines whether the second determination reference value Th ₂ shown in (c) of 9 is exceeded (whether SΔT> Th ₂ or not) is affirmative, and it is determined that there is a bleed 69 or the like. The Rukoto.

That is, according to the present embodiment, when the pinhole 68 exists on one scanning line which is one unit of the temperature detection signal ST output from the radiation temperature measuring devices 78a, 78b, 78c and 78d, As shown in FIG. 9, the portion where the temperature change amount signal SΔT is low is locally formed and the determination in step SS4 is affirmed, so that the pinhole 6
On the other hand, when the bleed 69 exists on one scanning line while the determination of 8 is made, a portion where the temperature change amount signal SΔT is high is locally formed, and the determination of step SS5 is affirmed. The decision is made. Therefore, the presence of the surface flaw of the conductive inspection material 10 cast by the continuous casting is detected regardless of its type.

Next, another embodiment of the present invention will be described. FIG. 14 is a flowchart for explaining a main part of the control operation of the flaw detection control electronic control unit 66, and shows a part different from FIG. In this embodiment, steps SS7 and SS8 are provided instead of steps SS4 and SS5 of FIG. In step SS7 of the figure, the absolute value | SΔT | of the temperature change amount signal SΔT is calculated. In step SS8, this absolute value | SΔ
It is determined whether or not T | exceeds a preset determination reference value Th, and if the determination is negative, this routine is ended and steps SS1 and subsequent steps are executed again. Outputs the flaw determination in step SS6. In this embodiment, the step SS8 corresponds to the flaw determination means or the flaw determination step, and steps SS2 and SS are performed.
3, SS7, SS8 correspond to the calculation determination means or the calculation determination step.

The absolute value | SΔT | is calculated in order to facilitate the flaw determination, and therefore, regardless of whether the temperature change amount signal SΔT is positive or negative, the absolute value | SΔT | It becomes possible to make a judgment. In the case where the surface flaw of the conductive inspection material 10 is any of the pinhole 68, the bleed 69 and the crack, if the temperature change amount signal SΔT having a sufficiently large absolute value is obtained, the absolute value is the same. Since the judgment reference value can be used, the absolute value | SΔT | may be configured to be compared with the judgment reference value Th as described above when the output of the type of surface flaw is not particularly required. Of. With this configuration, the defect determination is performed as in the above-described embodiment, and since the determination only needs to be performed once, there is an advantage that the determination algorithm is simple.

Although one embodiment of the present invention has been described above with reference to the drawings, the present invention can be applied to other modes.

For example, although the conductive material 10 to be inspected in the above-described embodiment has a rectangular cross section, it may have a circular cross section or may not be a long material.

Further, although the powder 34 of the above-mentioned embodiment is the one in which carbon particles or titanium particles are insulatingly coated with resin, other particles may be used as long as they are particles of a substance having a relatively high emissivity. The effect of the present invention can be obtained even if the powder 34 is not used.

The frequency of the high-frequency drive current supplied from the high-frequency power supply device 24 to the induction coil 18 is such that the penetration depth δ of the induction current generated in the conductive test material 10 is a surface flaw (pinhole 68 or crack). If it is set to be smaller than the depth d of), the effect of the present invention can be obtained.
The penetration depth δ, that is, the frequency of the high frequency drive current is appropriately changed depending on the material of the conductive inspection material 10 and the depth d of the surface flaw that may occur. The smaller the penetration depth δ, the better. For example, if the depth d of the pinhole 68 or the like is about 1 mm, and the conductive material 10 to be inspected is a non-magnetic metal material, a high-frequency driving current of a relatively high frequency is used, so that the magnetic metal Penetration depth δ as for material
Is preferably about several tens of μm.

The above description is merely one embodiment of the present invention, and the present invention can be variously modified without departing from the gist thereof.

[Brief description of drawings]

FIG. 1 is a plan view showing an induction heating flaw detector according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a powder coating device and an induction coil shown in FIG.

FIG. 3 is a diagram illustrating an internal structure of the powder coating apparatus of FIG.

FIG. 4 is a diagram illustrating a coating gun in the powder coating apparatus of FIG. 1 and a powder coating operation thereof.

5 is a diagram illustrating an internal structure of the powder removing apparatus of FIG.

FIG. 6 is an enlarged front view showing a part of a main part of the induction coil shown in FIG.

FIG. 7 is a side view of FIG. 6;

FIG. 8 is a view showing a radiation temperature measuring device provided in the induction heating flaw detection device of FIG. 1.

9 is a diagram showing a temperature detection signal waveform obtained from the radiation temperature measuring device of FIG. 8 and a waveform signal-processed by the operation of FIG. 11, respectively.

FIG. 10 is a perspective view showing an example of a surface flaw generated in a conductive inspection material.

FIG. 11 is a functional block diagram illustrating a control function of a flaw detection control device provided in the induction heating flaw detection device of FIG. 1.

FIG. 12 is a flowchart illustrating an essential part of the operation of a flaw detection control device provided in the induction heating flaw detection device of FIG. 1.

13 is a diagram showing another example of a temperature detection signal obtained from the radiation temperature measuring device of FIG.

FIG. 14 is a main part of a flowchart for explaining the operation of the flaw detection control device according to another embodiment of the present invention.

[Explanation of symbols]

10: Conductive material to be inspected {18: Induction coil, 24 high frequency power supply device} (high frequency heating device) 68: Pinhole (surface flaw) 78: Radiation temperature measuring device (radiation thermometer) 84: Calculation determining means

Claims (3)

[Claims] 1. A continuous cast piece having electrical conductivity is caused to generate an induction current by electromagnetic induction, the surface of the cast piece is heated by the electromagnetic induction, the surface temperature of the cast piece is measured, and the surface temperature of the cast piece is measured. A method for inductive heating flaw detection of a continuous cast piece having conductivity for flaw detection on the surface flaw of the cast piece based on uniformity, the surface of the cast piece by an induction current having a penetration depth smaller than the depth of the surface flaw. A heating step of heating the cast piece, a temperature measuring step of measuring the surface temperature of the cast piece with a radiation thermometer, and calculating a local temperature change amount of the surface of the cast piece based on the surface temperature, A method for induction heating flaw detection of a continuous cast piece having conductivity, which comprises a calculation determination step of determining a pinhole when the amount of local temperature change exceeds a predetermined negative determination reference value. . 2. The calculation determination step determines a pinhole when the local temperature change amount exceeds a predetermined negative first determination reference value, and the local temperature change amount is determined in advance. The bleeding or cracking is judged by exceeding the defined positive second judgment reference value.
Induction heating flaw detection method for continuous cast pieces having electrical conductivity. 3. A continuous cast piece having electrical conductivity is caused to generate an induction current by electromagnetic induction, the surface of the cast piece is heated by the electromagnetic induction, the surface temperature of the cast piece is measured, and the surface temperature is not measured. An induction heating flaw detector for a continuous cast piece having conductivity for flaw detection on the surface flaw of the cast piece based on uniformity, and an induction current having a penetration depth smaller than the depth of the surface flaw on the surface of the cast piece. A high-frequency heating device that heats the surface of the cast piece by generating, a radiation thermometer that measures the surface temperature of the cast piece, and the surface of the cast piece based on the surface temperature measured by the radiation thermometer While calculating the local temperature change of
Induction heating flaw detection of a continuous cast piece having conductivity, which comprises a calculation determination means for determining a pinhole when the local temperature change amount exceeds a predetermined negative determination reference value. apparatus.