JPH04286951A - Hot eddy current flaw-detecting method for wire rod - Google Patents

Abstract

PURPOSE:To prevent non-detection and excessive detection of a large defect caused by change in permeability and then enable eddy current flaw detection to be made accurately by placing two intervals of coils for inspection in axial line direction. controlling a magnetic saturation coil based on a defect detection signal of a coil for No.1 detection, and performing flaw detection of a defective portion by a coil for No.2 detection. CONSTITUTION:A coil for No.1 inspection 2 and the eddy current flaw detector 3 checks presence or absence of a surface defect of a wire which is heated at 1000 deg.C, or higher and then a size and status of the defect are detected by a coil for No.2 inspection 4 and the eddy current flaw detector 5. When the defect of a wire surface is detected by the coil for inspection 2, the inspection command is input to a control device 8 by the eddy current flaw detector 3, where a required time, T for the surface defect to reach the coil for inspection 4 is calculated. After T time, a conduction command is fed from the control device 8 to a DC power supply device 7 and a magnetic saturation coil 6 is electrified. A defect portion is located at the coil for inspection 4 and eddy current flaw detection is performed by the coil for inspection 4 in a magnetically saturated state.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a method for hot eddy current flaw detection of wire rods (including steel bars), and in particular for detecting surface defects of high temperature wire rods of 1000°C or higher with high accuracy by eddy current flaw detection using a through-coil method. Regarding the method.

0002

2. Description of the Related Art Hot eddy current flaw detection using a through-coil method has hitherto been put to practical use as a means for automatically detecting surface defects in wire rods. In this through-coil method, two solenoid-shaped inspection coils are generally arranged coaxially, and a solenoid-shaped excitation coil is arranged concentrically with the inspection coils around the outer periphery of the two solenoid-shaped inspection coils. It is inspected by passing through the inside of the coil.

[0003] In cold eddy current testing, when the material to be tested is a magnetic material,
Stable flaw detection can be achieved by performing magnetic saturation to receive changes in magnetic permeability and making the apparent relative magnetic permeability 1. However, in the case of hot eddy current flaw detection, the temperature of the material to be tested is above the magnetic transformation point and is in a non-magnetic state, so there is no need for magnetic saturation and no magnetic saturation coil is installed. do not have. However, recently, while conducting controlled rolling,
When performing low-temperature rolling, there are cases where rolling is performed below the magnetic transformation point, and magnetic saturation may be performed in conjunction with cold flaw detection.

0004

[Problem to be solved by the invention] However, at 1000°C
In hot eddy current flaw detection at the above-mentioned high temperatures, there is no correlation between defect volume and output, regardless of the size of the defect, even though the material being tested is non-magnetic. Therefore, the normal 1000℃
In the hot eddy current flaw detection described above, for example, if a "heavy flaw" occurs on the material to be inspected, due to the characteristics of this flaw, when the surface of the flaw is lifted, that part will be more easily cooled and will be more magnetic than other parts. If the temperature is below the transformation point (768°C or below), it is magnetic. Therefore, in the normal hot eddy current flaw detection method, the magnetic permeability changes in the flawed part as a result, and instead of detecting the change in electrical resistance in the original defect part,
This means that a change in magnetic permeability is detected, resulting in a defect signal different from the actual defect, resulting in overestimation. In other words,
There is almost no correlation between the size (volume) of a defect and the output, so a large defect may be overlooked, or a small defect may be overdetected.

[0005] The present invention solves the aforementioned problems in hot eddy current flaw detection at temperatures of 1000°C or higher, that is, it prevents overlooking and over-detection of large defects caused by changes in magnetic permeability caused by the temperature drop in the defective part, and allows eddy current flaw detection to be carried out with high accuracy. This paper attempts to propose a possible hot eddy current flaw detection method for wire rods.

[0006]

[Means for Solving the Problems] The present invention is designed to magnetically remove a defective part such as a flaw in order to avoid the influence of changes in the magnetic permeability of a test material in hot eddy current flaw detection at a temperature of 1000°C or higher. This is a method of flaw detection in a saturated state, and its gist is that in hot eddy current flaw detection using a through-coil method, two test coils are arranged at intervals in the axial direction, and No. 2. Magnetic saturation coils were installed on both sides of the test coil, and No. The magnetic saturation coil is controlled based on the defect detection signal of the No. 1 inspection coil. There is a method of detecting the defective part using a second inspection coil.

[0007]

[Function] In this invention, the pass line of the wire has no. 1. An inspection coil is arranged, and the test material is flaw-detected using this inspection coil. This No. When a surface defect is detected in one inspection coil, this surface defect is detected in the next inspection coil. 2. At the point where the coil for inspection is located, the magnetic saturation coil attached to the coil is controlled to magnetically saturate the surface defect portion. Therefore, if the surface defect is a flaw and has a local temperature lower than the magnetic transformation point and is magnetic, the magnetism will be erased, so No. With the second inspection coil, changes in magnetic permeability are not detected, but changes in electrical resistance at the original defective portion can be detected. In other words, a defect signal of an actual flaw is detected.

As a control system for eddy current flaw detection by applying magnetic saturation to surface defects, No. 1. At the time of detection by the inspection coil, the rolling speed of the material to be inspected and the No. 1 inspection coil and No. Based on the distance between the two inspection coils, the surface flaw is No. 2. A method can be adopted in which the time taken to reach the test coil is measured and the magnetic saturation coil is energized after that time.

[0009] In the method of this invention, the temperature of the material to be tested is 100
Even though it is in a non-magnetic state at 0°C or above, which is above the magnetic transformation point, only the actual defect signal can be detected even if only the defect area has decreased in temperature and becomes magnetic. , high-precision flaw detection becomes possible.

0010

[Example] Fig. 1 is a schematic diagram showing an example of the configuration of an apparatus for carrying out the method of the present invention.
．． 1 is the test coil, 3 is No. 1 eddy current flaw detector, 4 is No
．． 2 test coil, 5 is No. 2 is an eddy current flaw detector, 6 is a magnetic saturation coil, 7 is a DC power supply, 8 is a control device, 9 is a finishing stand, and 10 is a rolling speed detector.

[0011] Here, No. 1. The inspection coil 2 and its eddy current flaw detector 3 are used to confirm the presence or absence of surface defects in a wire that is heated to a temperature of 1000° C. or higher, and are not intended to detect the size or form of defects. The size and shape of the defects are No. 2. Detection is performed using the inspection coil 4 and its eddy current flaw detector 5. The magnetic saturation coil 6 is No. 2 are arranged close to each other on both sides of the inspection coil 4, and are configured to be supplied with direct current by a direct current power supply device 7. The control device 8 is No. 1. In response to the detection command of the eddy current flaw detector 3, the rolling speed v input from the rolling speed detector 10 and the No. 1 input in advance are input. 1 Inspection coil 2 and No. 2 Inspection coil 4
The timing ΔT for energizing the magnetic saturation coil 6 is calculated from the distance L between them, and the energization command is given to the DC power supply device 7.

[0012] That is, No. 1 When a defect on the wire surface is detected by the inspection coil 2, No. The detection command is input from the eddy current flaw detector 3 to the control device 8, and the surface defect is detected as No. 1. The time ΔT required to reach the second inspection coil 4 is calculated. Then, after ΔT time, the control device 8
An energization command is sent to the DC power supply device 7, and the magnetic saturation coil 6 is energized. At this time, the defective part is No. 2 It is located at the inspection coil 4, so it is magnetically saturated and No.
．． 2. Eddy current flaw detection is performed using the inspection coil 4.

[0013]

[Example 1] A 5.5 mmφ Hi-C material (surface temperature 1100°C
) is shown in Figs. 2 and 3 in comparison with the defect output of a flaw (about 2 mm in length) with no magnetic saturation. That is, FIG. 2 shows the defect output with magnetic saturation (invention), and FIG. 3 shows the defect output with no magnetic saturation (conventional). As is clear from the results in Figures 2 and 3,
It can be seen that when there is no magnetic saturation, a large amount of magnetic noise is generated due to the generation of magnetic permeability, whereas when there is magnetic saturation, there is very little magnetic noise, indicating that it is possible to properly detect flaws.

[0014]

As explained above, according to the method of the present invention, magnetic saturation is applied to the defective part of the material to be inspected which is at a high temperature of 1000°C or more. Since it is possible to obtain a detection signal proportional to the size (volume) of the defect even when the temperature has decreased and it becomes magnetic, it is possible to overlook large defects such as scratches caused by foreign objects and to avoid errors caused by small defects such as dented scratches. This has the great effect of eliminating detection and enabling accurate quality assurance.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an apparatus configuration for implementing the method of the present invention.

FIG. 2 is a diagram showing defect output in the case of magnetic saturation in the embodiment of the present invention.

FIG. 3 is a diagram showing defective output in the case of no magnetic saturation in the same example.

[Explanation of symbols]

1 Pass line of wire rod 2 No. 1 inspection coil 3 No. 1 Eddy current flaw detector 4 No. 2 Inspection coil 5 No. 2 Eddy current flaw detector 6 Magnetic saturation coil 7 DC power supply 8 Control device 9 Finishing stand 10 Rolling speed detector

Claims (1)

[Claims] Claims: 1. In a method of eddy current flaw detection of a wire rod at a temperature of 1000° C. or higher using a through-coil method, two test coils are arranged at intervals in the axial direction, and a No. 1 test coil is placed on the downstream side. 2. Magnetic saturation coils were provided on both sides of the test coil. The magnetic saturation coil is controlled based on the defect detection signal of the No. 1 inspection coil. 1. A hot eddy current flaw detection method for wire rods, characterized in that the defective portion is detected using two inspection coils.