JPS6336268Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

This invention mainly relates to a magnetic saturation device for eddy current flaw detection using a through coil, and relates to a magnetic saturation device for eddy current flaw detection that can efficiently magnetize a material to be inspected with low power.

[Conventional technology]

Currently, various methods of eddy current flaw detection are applied in various fields, and among those methods in which inspection is carried out by magnetically saturating the material to be inspected, there is an eddy current flaw detection method using a through coil. Eddy current flaw detection is a flaw inspection method that focuses on the impedance of a detection coil. Eddy current is generated on the surface of the material to be inspected using a detection coil to which a high frequency voltage is applied, and the disturbance of the eddy current at the flaw is detected by the detection coil. It is detected as a change in impedance. However, factors that change the impedance of the detection coil include, in addition to flaws, the magnetic permeability of the material to be inspected. Normally, in carbon steel and alloy steel, the impedance change due to magnetic permeability change is much larger than the impedance change due to the flaw to be detected, and is the most harmful external factor for inspection. In the through-coil flaw detection method, in order to reduce changes in magnetic permeability in the material to be inspected, this external factor is eliminated by applying a large DC magnetic field to achieve magnetic saturation. Generally, the penetration depth of high-frequency eddy current is expressed by the following equation (1). Here, δ: Penetration depth: Frequency σ: Electrical conductivity μ: Magnetic permeability As shown in equation (1) above, the higher the magnetic permeability, the smaller the penetration depth, so the detection performance for subsurface flaws is will be lost. Therefore, a magnetic saturation device is used as a means to reduce the magnetic permeability value as well as to reduce the previous change in magnetic permeability. A commonly used method for applying a direct current magnetic field to a material to be inspected is to insert the material to be inspected inside a cylindrical coil having a multilayered winding structure and apply a direct current. FIG. 1 is a longitudinal sectional view showing an example of a conventional magnetic saturation device. 1 is a material to be inspected, and 2 is a cylindrical coil. That is, applying a direct current to the cylindrical coil 2,
The material to be inspected 1 is inserted into the coil to perform magnetic saturation. Note that 3 is a cooling oil, 4 is a cooling oil supply port, and 5 is a cooling oil discharge port.

[Problem that the idea aims to solve]

However, in the case of a method in which the material to be inspected is inserted inside a cylindrical coil with a multi-layered winding structure and a direct current is applied, a coil with tens of thousands of windings is used to obtain a large magnetization ability. However, since a current of several amperes is applied, a large amount of power is consumed, and while the necessary magnetization ability can be obtained, the heat generated by the power consumption in the coil section is the biggest negative factor. For this reason, the conventional magnetic saturation device consists of a cooling oil 3, a cooling oil supply port 4, and a cooling oil outlet 5 in order to prevent damage to the insulator due to heat generation of the coil when operated continuously for a long time. A cooling device is provided to perform forced cooling using a cooling medium such as oil. This invention was made to eliminate these drawbacks of the conventional technology, and its purpose is to create a cooling device that can magnetically saturate the material to be inspected with low power and does not generate heat. The purpose is to provide a magnetic saturation device that does not require.

[Means to solve the problem]

The gist of this invention is to apply direct current to a cylindrical coil with a multi-layered winding structure to magnetize a material to be inspected inserted into the cylindrical coil. A pair of cylindrical inner yokes made of a soft magnetic material with an inner diameter larger than the outer diameter of the material to be inspected is placed on the inner periphery of the shaped coil. A cylindrical material made of a soft magnetic material is provided on the same axis with a distance larger than the distance from the outer peripheral surface of the material, and surrounds the other end of each of the pair of inner yokes and the outer periphery of the cylindrical coil over the entire length in the axial direction. The device is characterized in that a pair of annular side yokes made of a soft magnetic material are integrally provided between both ends of the outer yoke to cover the side surfaces of the coil. That is, in this invention, a cylindrical coil having a multilayer structure is covered with an outer surface yoke, a pair of side yokes, and a pair of inner yokes, and each of the yokes is made of a soft magnetic material, such as low carbon steel, as a means of reducing magnetic resistance. The first characteristic is that In addition, inside the device, in order to magnetize the inserted material to be inspected, a gap (hereinafter referred to as a magnetic gap) is created between the opposing end surfaces of a pair of inner yokes that is larger than the distance between the inner surface of the inner yokes and the outer surface of the material to be inspected. call)
The second feature is that it has a structure that efficiently transmits through the material to be inspected when the material to be inspected is interpolated.

[Effect]

A cylindrical coil with a multilayer structure is covered with an inner yoke, an outer yoke, and a pair of side yokes that have a predetermined distance between opposing surfaces in the axial direction, and the yokes are connected. The magnetic flux transmitted through each yoke in one direction,
Magnetic resistance decreases. In addition, when the material to be inspected is inserted into the cylindrical coil, most of the magnetic flux passes through the material through the space between the inner yoke and the material to be inspected, which is smaller than the magnetic cap, resulting in high magnetization. ability is obtained.

【Example】

FIG. 2 is a longitudinal sectional view showing an embodiment of the device of this invention. In this invention, a cylindrical coil having a multi-layered winding structure consists of two coils 2 and 2' spaced apart in the axial direction. A magnetic field is generated by passing a direct current through the cylindrical coils 2, 2'. The cylindrical coils 2, 2' are continuously covered with an outer yoke 6, a pair of side yokes 7, 7', and a pair of inner yokes 8, 8' made of a soft magnetic material, except for the magnetic gap. Since the magnetic flux φ generated by the cylindrical coils 2 and 2' passes in one direction through each yoke made of these soft magnetic materials, the magnetic resistance is significantly reduced. Therefore, each yoke should have a sufficient cross-sectional area so that the magnetic resistance does not become large. The two cylindrical coils 2, 2' are spaced apart by spacers 9, 9' made of non-magnetic material and an intermediate spacer 10. A magnetic gap is provided with a distance greater than the distance between the inner surface of the test material 1 and the outer surface of the material 1 to be inspected. If the material to be inspected is not inserted, the magnetic flux passing in one direction through each yoke will pass almost straight through the magnetic gap, but if the material to be inspected 1 is inserted, most of the magnetic flux will pass through the magnetic gap at intervals smaller than the magnetic gap. Since the light passes through the material to be inspected through the space between the inner yokes 8, 8' and the material to be inspected 1, it has a high magnetization ability. In addition, by interpolating the material 1 to be inspected, the magnetic flux passes through each yoke and the material 1 to be inspected in a loop shape as shown by the dotted line arrow in Figure 2, reducing magnetic resistance and providing more effective magnetization. This is possible. The reason why the inner diameter of the intermediate spacer 10 is made larger than the inner diameter of the inner yoke is to ensure a space for inserting the detection coil into this portion. Table 1 shows the results of implementing this invention in comparison with the conventional device. From Table 1, it can be seen that this device can magnetically saturate the material to be inspected with significantly lower power than conventional devices, and power consumption is significantly reduced.

【table】

[Effect of the idea]

As mentioned above, this invention has a structure in which a pair of inner yokes, a pair of side yokes, and an outer yoke, which have a predetermined distance between opposing surfaces in the axial length direction, are integrally connected so as to surround a cylindrical coil.
It is possible to magnetically saturate the material being inspected with low power consumption, resulting in a significant reduction in power consumption.Due to the low power consumption, there is no heat generation from the cylindrical coil, and there is no need for a cooling device that uses media such as oil. This has great effects such as equipment simplification. It goes without saying that this invention is not limited to the through-coil eddy current flaw detection device, but can also be applied to a probe rotation type eddy current flaw detection device by saturating the magnetization of the material to be inspected in the axial direction.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing an example of a conventional magnetic saturation device, and FIG. 2 is a vertical cross-sectional view showing an example of the configuration of the device of this invention. 1... Material to be inspected, 2... Cylindrical coil, 3...
...Cooling oil, 4...Cooling oil supply port, 5...Cooling oil discharge port, 6...External yoke, 7...Side yoke,
8...Inner yoke, 9...Spacer, 10...
intermediate spacer.

Claims (1)

[Claims for Utility Model Registration] In a magnetic saturation device that applies a direct current to a cylindrical coil having a multilayered winding structure to magnetize a material to be inspected inserted into the cylindrical coil, the inner periphery of the cylindrical coil A pair of cylindrical inner yokes made of a soft magnetic material with an inner diameter larger than the outer diameter of the material to be inspected is arranged such that the distance between the opposing end surfaces in the axial direction is such that the inner circumferential surface of the inner yoke and the outer circumferential surface of the material to be inspected are and the other end of each of the pair of inner yokes, and both ends of a cylindrical outer yoke made of a soft magnetic material that surrounds the outer periphery of the cylindrical coil over the entire length in the axial direction. 1. A magnetic saturation device for eddy current flaw detection, characterized in that a pair of annular side yokes made of a soft magnetic material are integrally provided between the coil side surface and the coil side surface.