JPH069746B2 - Seam position detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a seam position detecting device for detecting a seam position of an electric resistance welded steel pipe or a steel plate having a welded seam (seam line) portion.

<Prior Art> In an electric resistance welded steel pipe or the like, detecting the position of a seam portion, particularly a seam line called a white line is a necessary item in quality inspection of the product. Especially in ultrasonic flaw detection and post annealing (local heat treatment), 0.1
Accurate position detection of the white line or seam in mm is required.

It is not easy to accurately detect the seam position after the seam is welded, especially when that part is machined so as not to cause a mechanical degree difference or appearance difference from other parts. Have difficulty. Therefore, conventionally, as a seam position detecting method, an optical detecting method, an electric resistance detecting method, an ultrasonic detecting method, a magnetic detecting method, and the like have been proposed.
However, in the optical detection method, the peripheral part of the seam may be less discolored due to mechanical processing.In the detection method by electric resistance, the electric resistance value change is not limited to only the seam part. In the method, the change in ultrasonic characteristics is not limited to the seam position, and in the magnetic detection method, the change in the magnetic force line density occurs not only in the seam portion, but
It was difficult to measure the seam position in units of 0.1 mm.

<Problems to be Solved by the Invention> In general, steel that is a material of a steel pipe or a steel plate that is a subject is
It contains a small amount of carbon and various other elements. For example, when the seam portion of the steel pipe is manufactured, the abutting surfaces are melted at high temperature from both sides by an electric current or the like to be united and cooled and solidified. At this time, it is the abutting surface that exceeds the melting temperature of iron,
That is, it is a seam, but at that time, carbon existing in the vicinity of the seam is oxidized and becomes a gas to escape. Further, since the cooling is delayed at the seam portion, an element having a melting temperature lower than that of iron is unevenly distributed and the phenomenon is reduced at the seam portion. It has been discovered that when such a seam portion is present in the subject, when the magnetic force lines are applied, the magnetic force lines concentrate around the seam portion and the magnetic force line distribution has a unique shape. The present invention focuses on the fact that the magnetic characteristics at the seam portion change uniquely with respect to the other portions, and aims to provide a device for detecting the seam position stably and accurately.

<Means for Solving the Problems> The present invention uses a material having a high magnetic permeability on the upper surface of one pole of a magnetic field source having a substantially uniform density placed at a position separated from the surface of a subject having a seam portion. A support member having a bent portion in which the left and right ends are bent downward, and a support made of a non-magnetic material is provided on the lower surface of the other pole of the magnetic force source.
A magnetic field line density detection element is attached to the lower surface of the support in contact with or close to the surface of the subject, and the change in magnetic field line density is detected by moving the detection element in the direction perpendicular to the seam line,
The detection output is input to an electrical determination circuit to detect the seam position.

Further, the present invention is configured such that the distance of the surface of the subject of the magnetic field source is equal to or larger than the width of the magnetic field source, and further, the side surface of the magnetic field source and the bent portion of the supporting member. Is larger than the distance between the pole surface of the magnetic field source and the surface of the subject, and the left and right lengths of the support member are larger than the radius of the object to be inspected and the thickness of the support member is At least the thickness of the subject is set.

<Operation> To detect the seam position, the magnetic field line density detector determines whether the seam position is fixed by rotating the subject and rotating the subject, or by fixing the subject and moving the detector coaxially. When applying a magnetic force line from the magnetic force source so that it passes through the upper part of the line,
The electrical output near the seam makes a unique change that is different from other parts, and by detecting this and inputting it to the electrical determination circuit, the seam position can be accurately detected.

<Example> The following will describe an example of the present invention with reference to the accompanying drawings.

FIG. 1 shows a schematic configuration of the present invention. Reference numeral 1 is a detection unit, 2 is an electronic circuit for accurately determining a seam position based on the output of the detection unit, and 3 is a cross section of an electric resistance welded steel pipe as a subject. ,
Reference numeral 4 indicates a seam position.

The details of the detection unit 1 are shown in FIG. 2, and a linear shape made of a material having high magnetic permeability (for example, electric iron) is formed on the upper surface of one pole (N pole in the drawing) of the wide permanent magnet 5 which is a magnetic field line source. The support member 6 is fixed by being provided with a bent portion 7 in which the left and right ends are bent downward, and the Hall element is connected to the lower surface of the other pole (S pole in the figure) through a support body 8 made of a non-magnetic material. The magnetic field line density detection element 9 is provided in contact with or close to the surface of the subject 3, and these detection units 1 are supported so as to straddle the subject 3 (not shown).
It has a mechanism to rotate or move around. These mechanisms can be implemented by known means and are not particularly limited in the present invention.

Next, in the detection unit 1, in order that the magnetic field line density distribution on the surface of the subject 3 may change without being constrained by the permanent magnet 5, the distance L between the pole face of the permanent magnet 5 and the surface of the subject 3 is set to the permanent magnet 5. It is desirable that the width is equal to or larger than the width S of the above. Further, in order to reduce the leakage magnetic field lines that do not pass through the subject 3, the distance R between the side surface 5 ′ of the permanent magnet 5 and the bent portion of the support member 6 is set to the above-mentioned polar surface of the permanent magnet 5 and the surface of the subject 3. It is desirable that the distance L be larger than the distance L.

Further, since the magnetic field lines 10 are widely supplied to the subject 3 and the magnetic path makes the magnetic attenuation smaller than that of the subject 3, the lateral length (2 × w) of the support member 6 is larger than the radius of the subject 3. , Support member 6
As for the thickness T, it is desirable that T is at least not less than the thickness of the subject 3. Further, even if the support member 6 is not linear, as shown in FIG. 3, even if the support member 6 has a curved shape, there is no problem as a magnetic path, and bending of both ends of the support member 6 is performed to further reduce magnetic attenuation. The tip of the portion 7 may be shaped so as to follow the peripheral surface of the subject 3.

Next, the operation will be described. In the state of FIG. 2, assuming that the seam 4 is not present in the subject 3, the magnetic force lines 10 generated by the permanent magnet 5 are the magnetic flux, the supporting member 6, the bent portion 7, and the air. , Passes through the subject 3 and is distributed as shown in FIG. Here, since the surface of the permanent magnet 5 which is the magnetic field line source is wide and is separated from the subject 3, the magnetic field line density passing through the detection element 9 before and after the magnetic field line density detection element 9 at the tip of the support 8 is I don't concentrate. Further, there is no particular restriction on the concentration of the magnetic force lines 10 on the surface of the detection element 9 due to the inside of the subject 3.

Further, when the seam 4 portion is located at the position indicated by reference numeral 4 in FIG. 2 during the measurement, the magnetic force line concentration occurs around the portion, and the magnetic force line density distribution has the shape of Mt. Fuji shown in FIG. In FIG. 5, the vertical axis represents the magnetic permeability, and the horizontal axis represents the dimension perpendicular to the seam line. Further, the depressed portion indicated by the symbol M in FIG. 5 indicates the seam position, and H indicates the range of the heat-affected zone which has been melted to a high temperature during seam formation.

Now, in the state of FIG. 2, the detection unit 1 is fixed and the subject 3 is rotated leftward in the figure, or the subject 3 is fixed and the detection unit 1 and the subject 3 are coaxially moved rightward. It is moved so that the magnetic force line density detection element 9 passes above the seam line 4. In the measurement, this rotation and movement causes the detection element 9 to electrically detect the magnetic flux density penetrating therethrough. Therefore, the electrical output near the seam 4 accompanying the rotation or movement is the waveform shown in FIG. Becomes

Thus, it cannot be said that the electrical output detected by the magnetic force line density detection element 9 is always constant at a place other than the seam 4, and the partial change of the magnetic permeability inside the steel pipe material which is the subject 3 is caused when the steel material is processed. There may be a change in output due to partial magnetization generated, proximity of magnetic material in the periphery, or local processing scratches.

Here, FIG. 6 shows an example of the electrical output of the detection element 9 over the entire circumference of the subject 3 when the detection unit 1 and the subject 3 are relatively continuously rotated by the mechanical drive device. In FIG.
The waveform portion indicated by reference numeral 11 is the output at the seam portion, but it is found that this seam portion waveform 11 has a great difference in the morphological characteristics from the electrical output waveform in other cases. That is, the first feature is that 1 in the seam waveform 11
The amplitude A is the maximum, and the electric output is large in other places, but is smaller than the seam waveform 11 as one amplitude. The second characteristic is that the seam portion waveform 11 is generated locally at the seam portion, so that the seam portion waveform abruptly expands and changes from its periphery, and its inclination angle is large. The third feature is that the seam portion waveform 11 is symmetrical with the seam 4 line as the center, but the waveforms at other locations are indefinite. Therefore, as a result of extracting the output of the detection element 9 over the entire circumference of the subject 3,
The seam position is determined by finding a place having the above-mentioned first, second, and third features together.

In addition, after measuring the entire circumference of the subject 3 and detecting and storing the seam portion waveform 11 in advance, the location of the next stored seam portion waveform 11 is measured again and the seam position is designated with high accuracy. May be. As described above, when the seam waveform 11 is measured again after the entire circumference is measured once, the main body of the detection unit 1 is fixed substantially at the seam waveform 11, and the magnetic field line density detection element 9 is used. It is also possible to use a method in which the chisel is mechanically oscillated to the right and left by a minute dimension.

In order to detect the seam position in the seam portion waveform 11 by taking out the electrical output of the magnetic force line density detection element 9 over the entire circumference of the subject 3 as described above, the electronic circuit 2 shown in FIG.
Is used. The operation of the electronic circuit 2 is shown in FIG. 7, which shows the judgment operation divided into individual parts.
The order of each operation is not limited. In some cases, it may be ineffective or may be excluded.

In this way, the first, second, and
After finding the waveform 11 having the third characteristic, if the position M of the minimum value of the decrease occurring in the central portion is detected, this indicates the seam position. The maximum value may indicate the seam position depending on the material and type of the object 3 to be measured, but the maximum value may indicate the seam position. It suffices to have a function for determining whether or not Further, the position and width of the heat-affected zone can be known from the positions of the maximum value H on both sides of the waveform.

Thus, the storage of the detected seam position, display, or command to the driving portion to stop at that position can be easily embodied by an electronic circuit or computer software together with the operation of the judgment detecting circuit. it can.

<Effects of the Invention> As described above, according to the present invention, a material having a high magnetic permeability is formed on the upper surface of one pole of the magnetic field source having a substantially uniform density placed at a position separated from the surface of the subject having the seam portion. Therefore, a supporting member whose right and left ends are bent downward is provided, and the magnetic force line is applied to the subject from the magnetic force source, and is attached to the surface of the subject where the magnetic force line exists or close to the surface and the lower surface of the non-magnetic support. The magnetic field line density detection element is moved in the direction perpendicular to the seam line to detect changes in the magnetic field line density and input it to the electrical judgment circuit to detect the seam position, ensuring accurate seam position. Can be detected. By providing the bent portion on the support member of the magnetic field source, the magnetic field can be widely supplied to the subject, and the seam position can be accurately detected.

Furthermore, by setting the distance between the polar surface of the permanent magnet, which is the magnetic field source, and the surface of the subject to be equal to or greater than the width of the permanent magnet, the magnetic flux density distribution on the surface of the subject is constrained by the permanent magnet. Can be changed without.

In addition, the distance between the side surface of the permanent magnet, which is the source of magnetic force, and the bent portion of the support member is set to be larger than the distance between the pole surface of the permanent magnet and the surface of the subject, thereby reducing leakage magnetic field lines that do not pass through the subject. Can be made.

In addition, the left and right length of the support member is larger than the radius of the subject,
In addition, by setting the thickness of the support member to be at least the thickness of the subject, magnetic lines of force can be widely supplied to the subject, and magnetic attenuation can be reduced.

Moreover, in the present invention, the magnetic field line density distribution at the seam can be detected as a unique Mt.Fuji waveform, and this waveform has a feature that it can be distinguished from waveforms at other locations.
It is possible to detect the position and width of the heat-affected zone, which is generated during the production of the electric resistance welded steel pipe, and the correct position of the seam.

[Brief description of drawings]

The drawings show an embodiment of the present invention. FIG. 1 is an explanatory view showing a schematic configuration of the present invention, FIG. 2 is an enlarged front view of a detecting portion, and FIG. 3 is another embodiment of the detecting portion. FIG. 4 is an explanatory diagram showing a magnetic field line distribution, FIG. 5 is an explanatory diagram showing a seam waveform, and FIG. 6 is an explanatory diagram showing an electric output waveform over the entire circumference of the subject, The figure is an explanatory view showing the operation of the electronic circuit. 1. ． ． Detector 2. ． ． Electronic circuit 3. ． ． Subject 4. ． ． Seam position 5. ． ． Permanent magnet 6. ． ． Support member 8. ． ． Support 9. ． ． Magnetic field density detector 11. ． ． Seam waveform 12,13. ． ． permanent magnet.

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Claims (4)

[Claims] 1. An upper surface of one pole of a magnetic field source having a substantially uniform distribution, which is placed at a position separated from the surface of a subject having a seam portion, is made of a material having high magnetic permeability, and its right and left ends are directed downward. A support member having a bent portion is provided, a support made of a non-magnetic material is provided on the lower surface of the other pole of the magnetic field source, and the magnetic field line density is detected by contacting or approaching the surface of the subject on the lower surface of the support. A seam position characterized by mounting an element, detecting the change in the magnetic force line density by moving the detection element in a direction perpendicular to the seam line, and inputting the detection output to an electrical determination circuit to detect the seam position. Detection device. 2. The distance between the polar surface of the magnetic field source and the surface of the subject is
The seam position detecting device according to claim 1, wherein the width is equal to or larger than the width of the magnetic field source. 3. The seam position detection according to claim 1, wherein the distance between the side surface of the magnetic field source and the bent portion of the support member is larger than the distance between the polar surface of the magnetic field source and the surface of the subject. apparatus. 4. The seam according to claim 1, wherein the lateral length of the support member is larger than the radius of the non-inspection body, and the thickness of the support member is at least the thickness of the inspection body or more. Position detection device.