JPS6086809A - Demagnetizing method and device thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a demagnetization method and apparatus.

[Background of the invention]

In general, steel materials such as steel pipes and round steel are made of special nets, such as high carbon steel, manganese steel, chromium molybdenum steel, etc., and are used for important structures and high pressure piping materials, so they may have defects such as surface scratches, internal scratches, or external defects. Diameter.

Quality such as bending and wall thickness is inspected during the manufacturing process, and measurement equipment that uses magnetism is generally used. However, when a measuring device using magnetism is used, residual magnetism remains in the special mesh, causing problems in workability, weldability, etc. In addition, the plugs and mandrel bars used in the manufacturing process of high-quality seamless steel pipes, which are often used as materials for oil country tubular goods, line pipes, and important structures, are subject to residual magnetism by measuring devices that use magnetism. If the magnet is exposed to heat, scale from the surrounding area will adhere to it, causing scratches on the inner surface, causing problems in terms of product quality, and demagnetization during the manufacturing process and product shipping stage has become an essential need.

The residual magnetism ΔBr generated in the manufacturing process of steel materials is a sufficiently small value that causes no problem in the case of ordinary steel, but it becomes relatively large in the case of special steel. Generally, a through-type degaussing coil is provided in a series of lines to minimize ΔBr. but,
In the case of a through-type degaussing coil, an air-core coil applies an alternating magnetic field, so when the outer diameter of the steel material varies, the gap between the coil diameter and the steel material diameter creates a non-uniform magnetic field, which changes the demagnetizing ability, and the gap causes large power consumption. Requires. Furthermore, when the power of the AC magnetic field increases, a considerably large leakage magnetic field is generated in the surrounding area, so an electromagnetic shield is required to protect surrounding measurement equipment from noise.

In the case of special steel, it will become clear from the following explanation that the residual magnetism ΔBr is relatively larger than that of ordinary steel. In FIG. 1(a), the horizontal axis represents the carbon content (%) in the steel material, and the vertical axis represents the holding force Hc, and when the steel material is annealed and quenched, the curve ■ is plotted.

It becomes like U. That is, as the carbon content increases, the holding force H8 increases, and this is remarkable in hardened materials. In this way, the hysteresis curve of special steel with a high carbon content has a demagnetization curve of R5, which is significantly different from the demagnetization curve R of ordinary steel, as shown in Figure 1 (b). . That is, for ordinary steel, if holding forces -H and N are taken, B and N
In special steel, even if the coercive force -H68 is removed, the residual magnetism Brg remains, which becomes B, s) B, N. In order to reduce this 3rll, generally draw a hysteresis curve several times while decreasing the magnetomotive force.
It is demagnetized. However, the operating point changes as shown in Fig. 1(b) due to the gap g (g 1 < g 2 < g 3...) between the steel material l and the demagnetizing coil. Reverse magnetic field Hg,, Hg2. Hg3...
changes, and the desired demagnetization cannot be achieved without complex control.

As shown in FIG. 2, in general, when the steel material 1 already has an internal magnetomotive force H, an external magnetic field H.! effective magnetic field) (@ff is H-tt"14-knee H' because a demagnetizing field H' of the magnetic material is generated due to the local appearance of N and S poles on the surface of the composite material. =H,
,--J......(1) Represented by μO. Here, N is the demagnetizing field coefficient and J is the magnetization strength. This demagnetizing field coefficient N changes depending on the length-to-diameter ratio of the copper material. Therefore, even if an attempt is made to remove residual magnetism by an external magnetic field, if the demagnetizing field is large, it is necessary to add an external magnetic field commensurate with the large demagnetizing field. When residual magnetism Br occurs at the edge of a steel material and an external magnetic field is applied in the axial or longitudinal direction to remove it from the outside, the conventional demagnetization method using a through-type coil only demagnetizes the vicinity of the surface of the steel material. However, there is a drawback that the demagnetizing effect is weakened by the influence of the demagnetizing field coefficient N mentioned above.

[Purpose of the invention]

An object of the present invention is to provide a demagnetizing method and apparatus that can easily demagnetize the entire cross section of a steel material.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 3(a), (b) and FIGS. 4(a) and (b). FIG. 3(a) is a sectional view, and FIG. 3(b) is a front view. In Figure 3,
A penetrating magnet consisting of a yoke 2, magnetic poles 4 and 5, and an excitation coil 3 is attached to a frame (not shown) so as to penetrate the steel material 1. The steel material 1 is supported by, for example, a pinch roller 6, and is conveyed at a speed V in the direction of the arrow.

As a result, the steel material advances while passing through the through-type magnet symmetrically throughout the entire cross section, and it becomes possible to demagnetize each point in the length direction of the steel material, that is, in the axial direction. The demagnetizing field shown in FIG. 2 is not necessarily in the opposite direction to the demagnetizing field applied from the outside in the longitudinal direction or radial direction of the steel material 1, but its vectors have various directions. Therefore, in the axial direction, that is, in the length direction, of the steel material 1, the 1-penetration magnet ~ is, for example,
Independent magnetic poles are formed such that the magnetic pole 4 is the north pole and the magnetic pole 5 is the south pole, and the copper material 1 is made to correspond to the iron core of a plunger type magnet, and the magnetic flux Φ is the middle between the two magnetic poles 4 and 5. The component is configured such that the component in the same direction as the axial direction of the steel material is maximum at , and the component perpendicular to the axial direction of the steel material is maximum immediately below the two magnetic poles 4 or 5 . That is, the continuous magnet has magnetic poles 4 and 5 parallel to each other formed in concentric circles surrounding the steel material 1 along the length direction of the steel material, and these are connected by a yoke 2, which is a groove in which almost no leakage magnetic flux is generated. It is constructed. This magnetic pole has a length Ω along the length direction of the steel material, and the distance between the two magnetic poles 4 and 5 is QP. Sufficient length in the longitudinal direction and approximately magnetic pole spacing A
Providing the yoke 2 of P) is convenient because a sufficient dynamic demagnetization cycle can be applied to the steel material 1 being conveyed at the speed V. In experiments conducted by the inventors, when the steel material 1 is made of special steel, the demagnetization curve becomes R6, as shown in Fig. 1(b), so that the demagnetization curve is , 1 / can be relatively effectively demagnetized by flowing one to several cycles of demagnetizing current. The demagnetizing device proposed in Fig. 3 is in a state close to contact with the steel material 1, and the air gap is small, so the holding force is 1.For example, Hgx in Fig. 1 (b) is used. Compared to a through-type demagnetizing coil that applies an alternating magnetic field using a coil, it is relatively easy to demagnetize with significantly less power.

The steel material 1 in FIG. 3 is N and S in FIG. 3 having different polarities.
Considering the mesh to be demagnetized corresponding to the magnetic pole spacing ap, the maximum magnetic flux density generated between the N and S magnetic poles is B1 at the transport speed v of the steel material 1, and the angular frequency of the forward/reverse switching excitation shown in Fig. 4(b) is Let W be an arbitrary point X on the moving steel material 1. The magnetic flux density Bx (Xo + i) after t seconds from the position is expressed as.

In order to obtain sufficient demagnetization performance, steel material 1 must have Q p /
2 <x<Q p / 2, that is, when passing between the magnetic poles of the demagnetizing device, it is important to undergo a large number of temporary demagnetizations, especially in the demagnetizing region shown in Figure 1 ('b'). In order to do so, make ■ small and 5w large.

The pitch Qp between the two magnetic poles 4 and 5 has no relation to the demagnetization period; the larger the magnetic pole pitch, the greater the number of repeated demagnetization cycles, and the better the demagnetization performance. The demagnetization pattern shown in FIG. 4(b) is a pattern in which excitation is equally reversed from positive to negative in each cycle. Therefore, in each cycle,
In the first half cycle, for example, the magnetic pole 4 becomes the north pole and the magnetic pole 5 becomes the south pole, and in the second half cycle, on the contrary, the magnetic pole 4 becomes the south pole and the magnetic pole 5 becomes the north pole. If the speed V of the steel material 1 is slow enough to allow a sufficient demagnetization pattern time of one cycle or more, each demagnetization mesh (
The mesh can take more than two demagnetization cycles as planned for the magnetic pole spacing QP), and can achieve sufficient demagnetization, but if the leading edge V of the steel material I is made faster, the next mesh will be removed before one demagnetization cycle is completed. As a result, there will be parts that are not demagnetized, resulting in imperfections. In order to compensate for this imperfection, the distance UP between the two magnetic poles is sufficiently set, and the speed V in which the steel material 1 advances in the axial direction per mesh is small, so that the steel material 1 passes through the effective magnetic pole spacing 12P of the demagnetizing device according to the present invention. This can be improved by subjecting it to several demagnetization cycles.

〔Effect of the invention〕

According to the present invention, continuous demagnetization can be performed while penetrating the steel material and moving the steel material from one direction.

[Brief explanation of drawings]

Figure 1 (a) is the holding force of the steel material, (b) is a hysteresis curve diagram, Figure 2 is a diagram explaining the principle of the present invention, Figure 3 is a configuration diagram of an embodiment of the present invention, and Figure 4 is demagnetization. It is a characteristic diagram. Kaya 19 (Ku) <b) (F) No ¥74 Continuation of page 1 [phase] Inventor Kazuji Tadashi 1-1 Kokubun-cho, Hitachi City

Claims (1)

[Claims] (1) A magnetic flux is applied to the demagnetized material that is linearly moved in the axial direction, and the magnetic flux acting on the demagnetized material is 1
A demagnetizing method characterized by demagnetizing a material to be demagnetized by repeatedly applying a demagnetizing pattern of positive to negative reversal over a cycle in accordance with the movement of the material to be demagnetized. 2. An electromagnet disposed around the outer periphery of the material to be demagnetized that is linearly moved in the axial direction and having a plurality of magnetic pole axes spaced apart at a predetermined distance in the direction of the demagnetized material; A demagnetizing device comprising means for repeatedly generating a demagnetizing pattern in which the magnetic flux acting on the demagnetized material is reversed from positive to negative over at least one cycle in accordance with the movement of the material to be demagnetized. 3. The two magnetic poles have a predetermined length in the axial direction of the material to be demagnetized, and the ratio of the axial movement speed to the switching frequency of the predetermined positive-negative reversal demagnetization pattern is set to a sufficiently small value. A demagnetizing device according to claim 2, characterized in that: