JPH0729490Y2 - DC magnetizer for eddy current flaw detection - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] This invention is an eddy current that enables flaw detection in the temperature range where it was difficult to apply eddy current flaw detection in steel, where the magnetic fluctuation is strong just below the Curie point. The present invention relates to a DC magnetizing device for flaw detection.

[Prior Art] The eddy current flaw detection method is a method for conducting flaw detection by focusing on the change in the impedance of the detection coil based on the properties of the material to be inspected. In the case of a body, the impedance of the detection coil fluctuates even if there is a local fluctuation in the magnetic permeability, and it cannot be distinguished from a flaw signal as it is.Therefore, direct current magnetization of the test material is performed to suppress fluctuations in the magnetic permeability μ. Therefore, a method of detecting a flaw signal has been adopted.

For direct current magnetization in this case, a solenoid type coil is used in the case of a through-type excitation coil, and the strength of direct current magnetization is slightly lower than magnetic saturation, and the SN ratio is better. Adjusted and set.

The SN ratio is better when the strength of the DC magnetization is slightly lower than the magnetic saturation, because the magnetic resistance based on the shape of the defect of the test material causes the magnetic permeability of the defective portion to be higher than that of the sound portion when the DC magnetization is performed. This is because local uneven distribution of magnetic permeability is also detected at the same time as defects, and if DC magnetization is too strong, this effect will weaken,
This is because the SN ratio deteriorates.

For this reason, the strength of the magnetization at the center of the DC magnetizing coil was set to about 1000 Erested, which is slightly lower than the magnetic saturation in view of the SN ratio of the defect signal.

[Problems to be Solved by the Invention] A method of performing eddy current flaw detection under such a DC magnetization is
There are application examples not only in the cold but also in the hot magnetic region, but from 650 ° C to 770 ° C below the Curie point in the hot magnetic region.
It has been considered that eddy-current flaw detection cannot be applied even by the DC magnetization method because the change in magnetic permeability μ is extremely large in the range up to ° C.

Since the present invention has a large magnetic fluctuation, it can be used for eddy current flaw detection to suppress eddy current flaw detection of pipes, steel bars, wires, etc. in the temperature range from 650 ℃ to 770 ℃ where conventional eddy current flaw detection cannot be applied. It is an object of the present invention to provide a DC magnetizing device.

[Means for Solving the Problem] As a result of investigations by the inventors, even in a temperature region where the magnetic fluctuation is intense just below the Curie point, the noise due to the magnetic fluctuation is suppressed by increasing the DC magnetization level to 3000 Erested or more, We obtained the knowledge that flaw detection is possible. The present invention relates to means for embodying this.

When a DC magnetic field is obtained by a solenoid type coil, it is necessary to pass a current of several amps to ten and several amps through a coil having a number of turns of several thousand to tens of thousands even in the conventional case of about 1000 Erested. Since a conductor is used and heat is generated, a cooling device is required, resulting in a considerably large device. In order to obtain 3000 Erested with the same configuration as before, the equipment must be made larger, the power consumption for magnetization increased, the capacity of the cooling pump increased, and the distance between the feed roll fulcrums due to the increase in the dimension in the coil length direction. As the distance becomes longer, backlash and runout during transportation of the material to be tested increase, and problems such as deterioration of the SN ratio occur.

Therefore, in the present invention, the DC magnetization level 30
As a means for obtaining more than 00 Erested, a plurality of multi-layer winding cylindrical coils arranged concentrically are provided with a space between each coil, and the ratio of the coil length to the average coil diameter of the coil group is provided. Is between 1 and 2, and a non-magnetic metal tube is passed between a soft magnetic metal drum covering the coil group and a side plate central hole of a housing formed of a soft magnetic metal perforated disc-shaped side plate, The coil group attached to this is hermetically sealed and liquid-cooled to enhance the magnetization efficiency, and it is a relatively small device, and the magnetic field of the central part of the coil center line at the time of air core is relatively low power. It is characterized in that it is configured so that an axial strength of 3000 Erested or more can be easily obtained.

[Operation] When an electric current of the same strength is applied to a cylindrical coil in which conductor wires of the same diameter are wound in the same number of layers, the coil length L and the average coil diameter D
The relationship between the ratio (hereinafter referred to as L / D) and the axial strength H of the central magnetic field is shown in equation (1) and FIG.

In equation (1), D is the average coil diameter, L is the coil length, i is the current, and K is
Is a constant of proportionality.

As shown in FIG. 1, the axial component of the coil central magnetic field increases sharply with an increase in L / D up to L / D of about 2, but the rate of increase above that decreases.

On the other hand, the ratio of the coil axis orthogonal component and the axial direction component of the magnetic field in the vicinity of both side surfaces of the coil increases as L / D decreases.

In the case of a magnetizing coil consisting of a cylindrical coil and a soft magnetic metal housing that covers it, the strength of the axial magnetic field at the center of the coil is the strength of the magnetic field generated by the cylindrical coil and the strength of the soft magnetic metal housing. It is the sum of the strengths of the magnetic fields. Of these, the former is preferably around 1.5 in consideration of the fact that if the L / D is too large, the distance between the fulcrum of the feed roll becomes longer, which causes troubles due to the runout of the material to be inspected, and the latter is near the coil side surfaces. The larger the component orthogonal to the coil axis of the magnetic field at, the larger.

The ratio of the coil axis orthogonal component and the axial direction component is as described above,
The smaller the L / D is, the larger the axial component is.The larger the L / D is, the larger the magnetic field added by the housing is. About 20% increase.

After all, by setting L / D to be between 1 and 2, it is possible to optimize the value of the sum of the two and to increase the strength of the direct current magnetization of the test material as necessary and sufficient.

Furthermore, in order to obtain a high magnetic field of 3000 Erested or more, the winding diameter should be as large as possible and the number of windings should be large, so the weight of the coil should be increased. However, since the current is increased and heat is generated, it is necessary to devise measures for cooling the coil.

The soft magnetic metal housing in the present invention also serves as a cooling container. A non-magnetic metal tube is passed through the center of the housing, which is hermetically sealed and cooled by a liquid, but the cylindrical coil is attached to the non-magnetic metal tube. , Solved the problem on strength,
The multi-layer winding cylindrical coil is configured such that a cooling liquid is passed through the coils with a space provided between the coils to cool the inside of the coil.

[Embodiment] FIG. 2 is a vertical sectional view of a DC magnetizing coil according to the present invention. The multi-layered cylindrical coil group 1 has a combination of five coils each having a different diameter, a cooling passage for the cooling liquid 4 is provided between the coils, and the ratio of the coil length L to the average coil diameter D is
It was set to 1.5.

This cylindrical coil group 1 is attached to a non-magnetic metal tube 3,
The surroundings are covered with a soft magnetic metal housing 2 composed of a soft magnetic metal drum and a perforated disc-shaped side plate, the cylindrical coil group 1 is sealed, and a transformer oil or the like is cooled via a radiator and a circulation pump (not shown). Circulate the liquid 4. The soft magnetic metal housing 2 is made of soft steel, and it is necessary to consider the thickness so as not to cause magnetic saturation in the housing.

In Fig. 2, the coil winding is 6000
Turned, coil length L is 405 mm, average coil diameter D is 27
The length of the soft magnetic metal housing 2 is 0 mm and 480 mm.
The strength of the magnetic field in the central axial direction of 3000 was obtained at a direct current of 15 amperes, which enabled eddy current flaw detection in the temperature range of 650 ℃ to 770 ℃ where conventional eddy current flaw detection could not be applied.

In this case, a cooled detection coil (not shown) is set in the non-magnetic metal tube 3. And pipes, steel bars,
When the test material made of wire is passed through the non-magnetic metal tube 3,
The flaw detection is performed by reading the impedance change generated in the detection coil (not shown).

Thus, according to the present invention, it is possible to obtain a predetermined high magnetic field with relatively small size and low power consumption.

[Effect of the Invention] As described above, the present invention enables eddy current flaw detection in the sudden magnetic fluctuation region just below the Curie point, from 650 ° C to 770 ° C, and is effective for online quality control and quality compensation in this temperature region. It becomes an effective inspection means.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the coil length and the average coil diameter in a cylindrical coil, that is, the relationship between L / D and the strength of the axial magnetic field at the coil center, and FIG. 2 is an eddy current showing an embodiment of the present invention. It is a vertical side view of the principal part of the DC magnetizing device for flaw detection. In the figure, 1: Cylindrical coil group 2: Soft magnetic metal housing 3: Non-magnetic metal tube 4: Coolant 5: Coolant inlet 6: Coolant outlet

Claims (1)

[Scope of utility model registration request] 1. A dc magnetizing device for eddy current flaw detection, in which dc magnetization is performed by a dc magnetizing coil to perform eddy current flaw detection. Is provided so that the ratio of the coil length to the average coil diameter of the coil group is between 1 and 2, and the soft magnetic metal housing and the soft magnetic metal perforated disc-shaped side plate covering the coil group are provided. A non-magnetic metal tube is passed between the side plate center holes of the housing, the coil group attached to this is sealed, and liquid cooling is performed, and the strength of the axial magnetic field at the center of the coil center line at the time of air core is 3000 Erested A DC magnetizing device for eddy current flaw detection, which is configured as described above.