JP3301187B2 - Induction heating 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 an induction heating flaw detector. More specifically, the present invention relates to an induction heating flaw detection device capable of performing flaw detection with high accuracy even if a long steel material to be inspected is bent or twisted.

[0002]

2. Description of the Related Art Conventionally, in order to detect a flaw generated on the surface of a steel material, the surface of the steel material is detected by an induction heating flaw detection method. In this induction heating flaw detection method, FIG.
As shown in FIG. 13 and FIG. 13, in the induction heating coil 1 having a similar shape to the cross-sectional shape of the steel
Of the induction heating coil 1 is aligned with the center of
Then, the steel material W to be inspected is heated by the induction heating coil 1, and the surface temperature of the heated steel material W is measured by a radiation thermometer. A portion (non-magnetic steel material) showing a lower temperature is detected as a flaw.

In the case where the steel to be inspected W is not bent or twisted, if the steel to be inspected W is arranged so that the center of the steel to be inspected W coincides with the center of the induction heating coil 1, the steel to be inspected W The distance from each surface of W to the induction heating coil 1 becomes equal, and as a result, the steel material W is uniformly heated. Therefore, if there is no bend in the inspected steel material W,
No problem arises with the measuring method.

[0004] However, if the steel to be inspected W is bent, the distance from the steel to be inspected W to the induction heating coil 1 is not constant, as shown in FIG. For this reason, a portion where the distance to the induction heating coil 1 is short is heated strongly, and the temperature is increased to be higher than the average temperature (see (b)). Conversely, since the portion far from the induction heating coil 1 is weakly heated, the temperature is raised below the average temperature (see (b)). Therefore, at a location near the induction heating coil 1, the temperature difference between the healthy part and the flaw part increases (see (c)). Conversely, at a location far from the induction heating coil 1, the temperature difference between the healthy part and the flaw part becomes small (see (c)). Therefore, in the case where a flaw is detected using a certain threshold value, if the inspected steel material W has a bend or the like, accurate flaw detection cannot be performed. That is, at locations near the induction heating coil 1, noises (hereinafter simply referred to as “noise”) such as flaws and handling marks in the threshold value are detected as flaws. Even a flaw exceeding this will not be detected as a flaw.

[0005] Incidentally, it is a fact that bending and the like do not occur so much in a short steel material, but it is inevitable that bending and the like occur in a long steel material. Therefore, the appearance of an induction heating flaw detector capable of accurately detecting a surface flaw of a long steel material has been eagerly desired.

In addition, although the temperature difference between a healthy part and a damaged part is generally small, the area of temperature rise (magnetic steel material) or temperature decrease (nonmagnetic steel material) of the wound part is much larger than the width of the wound. When a rising degree curve is generated by a moving average method or the like as a conventional technique, the rising degree curve fluctuates depending on a flaw part signal value, and there is a problem that a temperature difference between a healthy part and a flaw part becomes smaller than actual.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems of the prior art, and provides an induction heating flaw detector capable of accurately detecting a bent or twisted steel material. It is intended to be.

[0008]

According to a first aspect of the present invention, there is provided an induction heating flaw detector including an arithmetic processing unit, wherein a reference temperature rise of a surface temperature determined by a material and a heating power of a member to be inspected and the like. The reference threshold value at that time is given in advance, and it is compared with the measured rise curve of the inspected member,
It is characterized in that a threshold value generating means for obtaining a difference or a ratio, correcting a reference threshold value in accordance with the difference or the ratio, and generating an actually used threshold value is provided.

Further, a rising curve to be compared may be approximated by a simple function such as a straight line or a low-order polynomial by a least square method or a spline approximation method, and a threshold value may be generated using the approximate curve. .

A second aspect of the present invention is to provide a method for measuring a surface temperature of a member to be inspected in which the surface temperature rise curve has a slope.
Characterized in that a curve correcting means for correcting the inclination to eliminate the inclination and to make the degree of rise constant is provided. In this case, a reference threshold value is used as the threshold value for the scratch determination.

The third aspect of the present invention is directed to the first aspect or the second aspect.
In an aspect, a rise degree curve generation is obtained by performing an operation such as a weighted average using a plurality of surface temperature rise values at a desired position and a plurality of surface temperature measurement values separated by a predetermined distance or more from a temperature change range due to a flaw with the position as a center. It is characterized in that means are provided.

[0012]

In the first embodiment of the induction heating flaw detector according to the present invention, if there is a slope in the rise curve of the surface temperature of the member to be inspected, a threshold is generated in accordance with the slope. Even if the temperature of the inspection surface is not uniformly increased due to the bending or twisting of the steel material, noise and the like are not erroneously detected as flaws. Therefore, accurate flaw detection can be performed.

In the second aspect of the induction heating flaw detector of the present invention, contrary to the first aspect, since the measurement data is corrected so that the degree of rise is constant, the slope of the rise degree curve has a slope. Even if there is such an effect, the flaw detection can be performed with high accuracy as in the first embodiment.

Further, the third aspect of the induction heating flaw detector of the present invention is as follows.
In the embodiment, even if a concave portion or a convex portion exists on the surface temperature curve due to a flaw or the like, the average value is obtained from the temperature at a point away from the concave portion or the convex portion. Therefore, unlike the prior art, the average value becomes convex or concave, and the temperature difference between the convex portion or concave portion and the healthy portion does not decrease. Therefore, accurate flaw detection can be performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments with reference to the attached drawings, but the present invention is not limited to only such embodiments.

Embodiment 1 An induction heating flaw detector according to Embodiment 1 of the present invention is shown in FIG. 1. An induction heating flaw detector according to Embodiment 1 includes an induction heating coil 1, a radiation thermometer 2, an arithmetic processing unit 10, and an output. The device 20 is a main component.

Although detailed descriptions of the configurations of the induction heating coil 1, the radiation thermometer 2, and the output device 20 are omitted, those conventionally used in induction heating flaw detectors can be suitably used.

The arithmetic processing unit 10 has a configuration similar to that of the conventional one, and also has a threshold generation means 11. The threshold value generating means 11 has a function of generating a threshold value corresponding to the slope when the surface temperature distribution of the steel material to be inspected W measured by the radiation thermometer 2 has a slope. That is, if the rise curve of the surface temperature of the steel material to be inspected having a slope as shown in FIG. 2 is obtained, for example, by the least square method, the deviation ε of each point with respect to the reference rise degree is obtained, and the deviation ε The threshold value of each point is calculated by correcting the given reference value.
For example, the threshold value at a point where the increase is 20% higher than the standard increase is, for example, 20% higher than the reference threshold. Here, the correction ratio is not limited to the above, but is appropriately selected according to the material and size of the member to be inspected.

Hereinafter, a case where induction heating flaw detection is performed on the non-magnetic square steel W by the apparatus of the first embodiment will be described with reference to the flowchart shown in FIG. In addition,
In FIG. 3, reference numerals S1 to S11 indicate step numbers.

Step 1: The steel material W to be inspected is heated by induction heating with the induction heating coil 1.

Step 2: The surface temperature of the steel material W to be inspected and heated by the radiation thermometer 2 is measured (see FIG. 4).

Step 3: The surface temperature before the induction heating is subtracted from the measured data, and the result is converted into the temperature rise data (FIG. 5).
reference). As the surface temperature before induction heating, a measured value is used, or a value previously obtained by an experiment or the like is used.

Step 4: Based on the data, a rise curve of the measured surface temperature is created by the least square method (FIG. 6).
reference).

Step 5: Calculate the deviation from the reference rise at a plurality of predetermined positions on the rise curve.

Step 6: Generate a threshold curve based on the deviation.

Step 7: A portion where a concave portion is formed on the rise degree curve is extracted from the rise temperature data.

Step 8: The lowest position of the recess is detected.

Step 9: The minimum temperature of the concave portion is evaluated based on the threshold value at the minimum position.

Step 10: If a flaw is recognized, a flaw signal is output, and the process proceeds to the next step. If not, proceed to the next step.

Step 11: It is determined whether or not all the concave portions have been evaluated. If all the concave portions have not been evaluated, the process returns to step 7. On the other hand, if all the concave portions have been evaluated, the flaw detection for that surface is terminated.

Thereafter, flaw detection of the remaining surface is performed in the same manner.

As described above, even when the test steel has a bend or torsion, the surface temperature rise curve of the test steel measured by the radiation thermometer has a slope. Is generated and flaw detection is performed, so that accurate flaw detection can be performed. That is, a harmful flaw as a product is reliably detected, and noise or the like is not erroneously detected as a flaw.

Embodiment 2 An induction heating flaw detector according to Embodiment 2 of the present invention is shown in FIG. 7, and the induction heating flaw detector of Embodiment 2 is the same as the induction heating flaw detector of Embodiment 1, The radiation thermometer 2, the arithmetic processing device 10, and the output device 20 are main components.

The arithmetic processing unit 10 has a configuration similar to the conventional one, and also has a curve correcting means 12. The curve correction means 12 calculates the degree of rise from the temperature rise data of the inspection target steel material W measured by the radiation thermometer 2 (see FIG. 8A), for example, based on a rise degree curve created by the least square method. To a constant value, that is, a reference rise degree, is applied to the rise temperature data to generate a correction curve (see (b)). By performing such processing on the flaw signal curve measured by the radiation thermometer 2, even if the measured flaw signal curve has a slope, as is clear from FIG.
The correction curve has no slope. For this reason, according to this correction curve, even if a certain threshold value is used, noise or the like is not erroneously detected as a flaw. Therefore, accurate flaw detection can be performed. That is, in the second embodiment, instead of generating the threshold value curve in step 6 in the flowchart shown in FIG. It is.

Embodiment 3 An induction heating flaw detector according to Embodiment 3 of the present invention is shown in FIG. 9, and the induction heating flaw detector of Embodiment 3 has an induction heating coil 1 and a radiation thermometer 2 as in Embodiment 1. And arithmetic processing unit 1
0 and the output device 20 are main components.

The arithmetic processing unit 10 has a configuration similar to that of the conventional one, and further includes a rising degree curve generating means 13 and a threshold value correcting means 14 provided as required. The rise degree curve generating means 13 performs a rise degree generation process described later on a temperature curve including a flaw signal obtained by the radiation thermometer 2 (hereinafter, flaw signal curve). Further, the threshold value correcting means 14 corrects the threshold value in accordance with the rising degree curve.

Next, the ascending curve degree generation processing performed here will be described.

It is assumed that induction heating flaw detection is performed on the non-magnetic steel material W, and a measurement result (elevation degree data) as shown in FIG. 10, for example, is obtained. In this state, when the average value is calculated in the range from -M to M, the average value becomes lower due to the influence of the scratches O. So (In FIG. 10, n to m) right predetermined range of recesses is a temperature drop range due to a scratch and the left a predetermined range (in FIG. 10, -N~-M) to determine the average temperature T _R, T _L in To calculate the average temperature T _{M of} both. This average temperature T _M is defined as a necessary increase at the point O. This operation is performed as a whole to generate a rising degree curve.
By performing such an operation, the difference between the degree of rise of the flaw and the degree of rise curve becomes large, and the flaw detection performance is improved.

Although the present invention has been described based on the embodiment, the present invention is not limited to the embodiment, and various modifications can be made. In this embodiment, each unit is configured by software using an arithmetic processing unit, but each unit may be configured by a wired logic circuit. FIG. 11 shows a configuration in which the curve correction means is constituted by a wired logic circuit. Further, in the above embodiment, the rise degree curve is obtained by the least square method, but may be obtained by the spline interpolation method.

[0040]

As described above, according to the present invention, since the member to be inspected has a bend or a twist, even if the temperature rise curve measured by the radiation thermometer has a slope, a harmful flaw as a product is produced. It is possible to obtain an excellent effect that detection can be performed with high accuracy and noise and the like are not erroneously detected as flaws.

[Brief description of the drawings]

FIG. 1 is a block diagram of an induction heating flaw detector according to Embodiment 1 of the present invention.

FIG. 2 is a graph of a temperature rise curve of a surface of a member to be inspected.

FIG. 3 is a flowchart illustrating a flaw detection procedure performed by the induction heating flaw detection apparatus according to the first embodiment.

FIG. 4 is a graph schematically showing a measurement result of a surface temperature of a member to be inspected by a radiation thermometer.

FIG. 5 is a graph in which unnecessary parts are deleted from the graph.

FIG. 6 is a graph of a temperature rise curve obtained by applying the least squares method to the graph.

FIG. 7 is a block diagram of an induction heating flaw detector according to Embodiment 2 of the present invention.

FIG. 8 is an explanatory diagram of an example of a procedure for eliminating a tilt from a measurement result in the second embodiment.

FIG. 9 is a block diagram of an induction heating flaw detector according to Embodiment 3 of the present invention.

FIG. 10 is a graph showing a measurement result of a surface temperature of a member to be inspected by a radiation thermometer.

FIG. 11 is a block diagram of a temperature pattern correction means for induction heating flaw detection according to the second embodiment which is configured by a wired logic circuit.

FIG. 12 is a diagram illustrating a case where a square-shaped member to be inspected is induction-heated.

FIG. 13 is an explanatory diagram in the case of induction heating a round member to be inspected.

FIG. 14 is an explanatory diagram of an induction heating state when a member to be inspected has a bend;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Induction heating coil 2 Radiation thermometer 10 Arithmetic processing unit 11 Threshold generation means 12 Curve correction means 13 Ascent curve generation means 14 Threshold correction means 20 Output device W Inspection member (work)

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Taizo Yano 4-3-2 Izuraku-dori, Minami-ku, Nagoya-shi, Aichi (56) References JP-A-54-40685 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 25/72 B21C 51/00 G01J 5/00

Claims (3)

(57) [Claims] In an induction heating flaw detector including an arithmetic processing unit, when there is a slope in a measured rise degree curve of the surface temperature of a member to be inspected, a threshold value is generated to generate a threshold value corresponding to the rise degree. An induction heating flaw detector characterized by comprising means. 2. In an induction heating flaw detector equipped with an arithmetic processing unit, if there is a slope in a measured rise curve of the surface temperature of a member to be inspected, the slope is eliminated to make the rise constant. An induction heating flaw detector comprising a curve correcting means for performing correction. 3. An induction heating flaw detector according to claim 1 or 2, wherein a surface temperature increase at a desired position is obtained by using a plurality of surface temperature measurement values separated by a predetermined distance from the position. An induction heating flaw detector characterized by comprising means.