JPH0338692Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a defect detection sensor suitable for detecting defects such as non-metallic inclusions in a running steel plate.

[Conventional technology]

When a steel plate is magnetized, leakage magnetic flux is generated at the flawed portion, so by detecting this leakage magnetic flux, it is possible to detect flaws in the steel plate. To detect leakage magnetic flux, Hall elements, SMD magnetic diodes, thin film magnetoresistive elements, magnetic heads of tape recorders, etc. are used, but such sensors and steel plates need to be placed close to each other by about 0.2 mm, but If so, there is a problem that the steel plate is easily damaged when it breaks.

[Problem that the invention attempts to solve]

In thin plate manufacturing equipment, steel plates are run at high speeds such as 1200mpm, and there are many accelerations and decelerations, so accidents that break the steel plate are likely to occur.If the steel plate breaks, the sensor surface will be subjected to intense scratching or mechanical shock, and there is a risk of damage. be.

Therefore, the present invention aims to provide a detection sensor that is not easily damaged even when installed in a high-speed sheet threading line, is easy to manufacture, has excellent heat resistance, and has characteristics of uniform sensitivity.

[Means for solving problems]

The present invention is a sensor for detecting defects in steel plates using the magnetic flux leakage method, in which a coil is wound around a U-shaped core, both leg ends of the core are made to protrude from the coil, and the distance between the protruding leg ends is determined by the defect to be detected. A plurality of sensor elements whose lengths match the length of the sensor elements are inserted into a common space bar with both protruding ends inserted, and a plurality of such sensor element groups are arranged in parallel so that each sensor element is staggered. The sensor element is characterized in that it is molded in a case with open end faces, and the end faces are ground so that the end faces of both core legs of each sensor element are aligned on the same plane.

〔Example〕

To explain with reference to the drawings, FIG. 1 shows one element of a defect detection sensor according to the present invention, and 1 is a U-shaped core made by bending a single silicon steel plate.
2 and 3 are coils wound around both legs of core 1;
They have the same number of turns and are connected in series with polarity such that the induced voltage due to changes in magnetic flux passing through the core 1 is summed. The distance d between the legs of the core 1 is set to be small according to the length or width of the micro defect to be detected. Figure 3 shows that the length of defect DF to be detected in steel plate S is 0.5 to 2.5.
mm, so an example will be shown in which the interval d is set to the maximum distribution length accordingly. The core 1 is made to protrude from the coils 2 and 3 by a length L, and a nonmagnetic space bar 4 is inserted into this protruding portion.

A large number of cores 1 wound with coils 2 and 3, that is, sensor elements, are arranged in parallel, and a space bar 4 passes through the extensions of both legs of these cores 1, as shown in FIG. 2a.
1a, 1b, 1c, ... are core 1, and subscripts a, b,
c, . . . are used to distinguish them from each other. Coil-wrapped core 1 with such a space bar 4 inserted through it
Two sets of a, 1b, . . . are provided, and the core positions of each are staggered. FIG. 2b shows this, in which 1a', 1b', ... and 4' are the other core and space bar, and the cores 1a',
In this example, cores 1b', . . . are placed between cores 1a, 1b, . The cores and the like arranged in this manner are inserted into a non-magnetic case 5 with both ends open as shown in FIG. 4, and are injected with resin 6 and molded to be solidified into one piece. After that, the end surfaces (detection surfaces) are ground and flattened, so that the end surfaces of the cores 1 of all the sensors are exposed and can face the steel plate surface at uniform minute intervals.

Defect detection using this sensor 10 is performed, for example, as shown in FIG. 11 is a non-magnetic hollow roll, and 12 is an auxiliary roll, which hold down the traveling steel plate S from above and below as shown in the figure, and keep the position constant. By keeping the position constant in this way, it becomes easy to make the end face of the sensor 10 face the surface of the steel plate S with a small gap therebetween. Although not shown, the sensor 10 may be attached to a fluid floating boat that blows out fluid such as air to create a gap between the boat and the steel plate S. A magnetizing device 13 for the steel sheet S is housed inside the hollow roll 11 . The rolls 11 and 12 rotate as the steel plate S moves, but the magnetization device 13 does not rotate and maintains the state shown in the figure. That is, this magnetizing device has a pair of parallel N and S poles extending in the width direction of the steel sheet, and since these N and S poles are aligned in the length direction of the steel sheet, the steel sheet is magnetized in the length direction. Of course, the range of magnetization is the N,
This is the region in the width direction and length direction of the steel sheet where the S pole exists and its vicinity.

When magnetized in this way, the flaw DF shown in FIG. 3 becomes N and S poles at both ends in the length direction, causing leakage magnetic flux to the outside. This leakage magnetic flux is caused by the core 1 of the sensor 10.
When it comes directly below a or 1a', etc., it passes through the U-shaped core and induces a voltage in the coils 2a, 3a, etc., which becomes a defect detection signal. Core 1a,
If the cores 1a', . . . are arranged in a staggered manner, any one of the cores 1a, 1a', .

The S/N ratio of the U-shaped core 1 can be improved by reducing the distance d between both legs. In other words, the magnetic flux passing through the core 1 due to the leakage magnetic field due to the flaw DF is in the direction of the solid arrow in Fig. 3 (or the opposite direction), and when the magnetic flux passes in this direction, the voltages induced in the coils 2 and 3 are summed. Since the coil is connected,
For example, the voltages induced in the coils 2 and 3 by the external magnetic field Nφ in the direction indicated by the dotted arrow are differentially generated, so that the noise component becomes small. The external magnetic field Nφ is generally non-uniform and changes in direction, but the closer the legs of the core 1 are, the more the induced voltages in the coils 2 and 3 become the same as they receive the external magnetic field in the same direction and magnitude. They tend to cancel each other out.

Induced voltage in coils 2 and 3 due to flaw DF (signal S
component) is minute, so the induced voltage caused by an external magnetic field is a problem. For example, coils 2 and 3 due to external magnetic field
The induced voltage of is 10 mV, and the output voltage due to the flaw DF (the sum of the induced voltages of coils 2 and 3) is about 100 μV, and the induced voltage of coils 2 and 3 due to the external magnetic field is made differential to reduce this to almost 0. However, if there is a 1% imbalance and the induced voltage in coils 2 and 3 is 10.1 mV on one side and 10 mV on the other, the noise output will be 100 μV, which will be the same as the signal voltage. There is a great deal of awareness to bring the legs of core 1 closer together to minimize imbalance. Of course, if they are brought too close to each other so that the length of the flaw DF is less than the length of the flaw DF, the signal voltage will become small, so it is preferable that the distance d between both legs is tuned to the length of a minute specific flaw.

This sensor 10 has a core that protrudes from the coil by a length L, and the space bar 4 is inserted into this core protrusion, and the sensor 10 is placed in a case 5 and molded, so it is mechanically strong and is stable during driving. Even if a breakage accident occurs in a steel plate, there is little risk that it will become unusable. If the steel plate S is heated and the sensor is required to be heat resistant, the coils 2 and 3 wrapped around the core 1 should be heat resistant, and the molding material injected into the case 5 to fix the core group should be heat resistant. It is better to use the one from

If the length of the sensor 10 is less than or equal to the width of the steel plate S,
An appropriate circuit configuration may be used, such as using a plurality of sensors 10 arranged in the width direction of the steel plate, or using each coil of the sensor as one leg of a bridge. The width d of the core 1 is adjusted to the length (size) of the defect to be detected, which increases the sensitivity. If there are defects of various lengths, the spacing d
It is better to prepare multiple types of sensors with different values.

[Effects of the invention] As explained above, according to the invention, the sensor is strong, has high sensitivity, and is easy to process as a sensor for detecting defects in steel sheets using the leakage magnetic flux detection method, and can be combined with the magnetization device shown in Fig. 5. When combined, it is possible to provide a sensor that has various advantages such as uniform detection sensitivity over the entire width direction of the steel plate and easy provision of heat resistance.

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the structure of the sensor element according to the present invention, Figure 2 is a diagram explaining the arrangement of the sensor elements, where a is a side view, b is an end view, and Figure 3 is the core spacing of the sensor element. FIG. 4 is a perspective view showing a state in which the sensor element group is molded, and FIG. 5 is an explanatory view of the defect detection device.

Claims (1)

[Claims for Utility Model Registration] A sensor for detecting defects in steel plates using the magnetic flux leakage method, in which a coil is wound around a U-shaped core, both leg ends of the core protrude from the coil, and the distance between the two protruding leg ends is A plurality of sensor elements whose length matches the length of the defect to be detected are lined up by inserting both of the protruding ends into a common space bar, and a plurality of such sensor element groups are arranged so that each sensor element is staggered. A sensor for detecting defects in a steel plate, characterized in that the sensor elements are arranged in parallel, placed in a case with open ends and molded, and the end faces are ground so that the end faces of both core legs of each sensor element are aligned on the same plane.