Steel plate hardness measuring device, measurement method using the same, and steel plate manufacturing method

Abstract

To obtain a steel plate hardness measuring device capable of measuring steel plate hardness with high precision without contact, a measurement method using the same, and a steel plate manufacturing method. [Solution] The steel plate hardness measuring device 1 of the present invention comprises an excitation coil 2 positioned opposite one surface La of the steel plate and applying a static magnetic field to the steel plate, a magnetic sensor 3 positioned opposite the other surface Lb of the steel plate with the steel plate between it and the excitation coil and measures the magnetic flux density leaking through the steel plate, an excitation power supply 4 that supplies an excitation current to the excitation coil, a current measuring instrument 5 that measures the excitation current supplied from the excitation power supply to the excitation coil, and a control device 6 that controls the excitation power supply. The control device controls the excitation current supplied from the excitation power supply to the excitation coil so that the magnetic flux density measured by the magnetic sensor becomes a constant value, and calculates the hardness based on the excitation current.

Description

Technical Field

[0001] The present invention relates to a steel plate hardness measuring device, a measuring method using the same, and a method for manufacturing a steel plate.

Background Art

[0002] Various magnetic hardness meters that can non-destructively and continuously measure the hardness of thin steel plates (strip steel) inline have been proposed. In Patent Document 1, a bar-shaped direct current electromagnet disposed above the strip steel applies a constant static magnetic field in a direction perpendicular to the measurement target with a constant direct current, and a leakage magnetic flux leaking to the lower part through the strip steel is detected by a magnetic sensor, and a technique for calculating the hardness of the strip steel from the leakage magnetic flux using a calibration curve method is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In conventional methods including Patent Document 1, variations in measurement accuracy occur depending on the material, so a measurement method with high accuracy has been demanded.

Means for Solving the Problems

[0005] As a result of intensive research, the inventor of the present invention has found a device, a measurement method, and a method for manufacturing a steel plate that can measure the hardness of a steel plate with high accuracy. The present invention has been made in view of the above points, and an object thereof is to provide a steel plate hardness measuring device capable of measuring the steel plate hardness with high accuracy non-contact, a measuring method using the same, and a method for manufacturing a steel plate.

[0006] (1) The steel plate hardness measuring device according to the present invention is a non-contact steel plate hardness measuring device that measures the hardness of a steel plate, comprising: an excitation coil positioned opposite one side of the steel plate and applying a static magnetic field to the steel plate; a magnetic sensor positioned opposite the other side of the steel plate between the excitation coil and the steel plate and measuring the magnetic flux density leaking through the steel plate; an excitation power supply that supplies an excitation current to the excitation coil; a current measuring device that measures the excitation current supplied from the excitation power supply to the excitation coil; and a control device that controls the excitation power supply, wherein the control device controls the excitation current supplied from the excitation power supply to the excitation coil so that the magnetic flux density measured by the magnetic sensor becomes a constant value, and calculates the hardness based on the excitation current. (2) The steel plate hardness measuring device according to the present invention is the steel plate hardness measuring device described in (1), wherein the control device calculates the hardness of the steel plate from the excitation current by utilizing the correlation between a plurality of steel plate samples whose hardness, composition and thickness are known and the excitation current in the plurality of steel plate samples. (3) The steel plate hardness measuring device according to the present invention is the steel plate hardness measuring device described in (1), characterized in that the excitation coil is a C-yoke type excitation coil or an H-yoke type excitation coil that applies a static magnetic field parallel to the steel plate. (4) The steel plate hardness measuring device according to the present invention is the steel plate hardness measuring device described in (1), characterized in that the excitation power supply is a DC power supply. (5) The steel plate hardness measuring device according to the present invention is the steel plate hardness measuring device described in (1), wherein the control device performs calibration to eliminate the influence of the Earth's magnetic field based on the magnetic flux density measured by the magnetic sensor with the steel plate removed from between the excitation coil and the magnetic sensor. (6) The steel plate hardness measurement method according to the present invention is a steel plate hardness measurement method for measuring the hardness of a steel plate in a non-contact manner using the steel plate hardness measuring device described in (1), and is characterized by comprising the steps of: supplying an excitation current to the excitation coil; measuring the magnetic flux density leaking through the steel plate using the magnetic sensor; controlling the excitation current so that the magnetic flux density measured by the magnetic sensor becomes a constant value; measuring the excitation current supplied from the excitation power source to the excitation coil; and converting the measured value of the excitation current into hardness using the calibration curve method. (7) The method for manufacturing a steel sheet according to the present invention is characterized by including a step of measuring the hardness of a steel sheet using a steel sheet hardness measuring device described in any one of (1) to (5). [Effects of the Invention]

[0007] According to the present invention, a steel plate hardness measuring device capable of measuring the hardness of a steel plate with high precision without contact can be obtained. [Brief explanation of the drawing]

[0008] [Figure 1] An overall view of the steel plate hardness measuring device according to the first embodiment. [Figure 2] Functional block diagram of a steel plate hardness measuring device according to the first embodiment. [Figure 3] A diagram showing the excitation coil and magnetic flux of a steel plate hardness measuring device according to the first embodiment. [Figure 4] A diagram illustrating the measurement principle of a steel plate hardness measuring device according to the first embodiment. [Figure 5] A flowchart illustrating a measurement method using the steel plate hardness measuring device according to the first embodiment. [Figure 6] A diagram showing a comparative example of an excitation coil, which serves as a premise for explaining the first embodiment. [Modes for carrying out the invention]

[0009] Next, we will explain one embodiment of the present invention using drawings. Figure 1 is an overall view of the steel plate hardness measuring device according to the first embodiment, and Figure 2 is a functional block diagram of the steel plate hardness measuring device according to the first embodiment. The steel plate hardness measuring device 1 can measure the hardness of steel plates and steel strips. Steel plates include long steel strips. The details of the device are described below, using steel strip L as an example, but the device can be used similarly by substituting steel strip for steel plate.

[0010] The steel plate hardness measuring device 1 is a device that measures the hardness of a steel strip L that is moving in the longitudinal direction without contact, and as shown in Figures 1 and 2, it comprises an excitation coil 2, a magnetic sensor 3, an excitation power supply 4, a current measuring instrument 5, and a control device 6.

[0011] The excitation coil 2 is positioned opposite one surface of the steel strip L, for example, the upper surface La, and applies a static magnetic field to the steel strip L being measured. The excitation coil 2 has a magnetic circuit configuration that generates magnetic field lines B (see Figure 3) parallel to the steel strip L. The excitation coil 2 can be any coil that generates magnetic field lines B parallel to the steel strip L, and a C-yoke type excitation coil or an H-yoke type excitation coil can be used. In this embodiment, the excitation coil 2 is a C-yoke type excitation coil that applies a static magnetic field parallel to the steel strip L.

[0012] The magnetic sensor 3 is positioned opposite the other surface of the steel strip L, for example, the lower surface Lb, via a steel strip L between it and the excitation coil 2, and detects the magnetic flux density leaking through the steel strip L. The magnetic flux density signal detected by the magnetic sensor 3 is supplied to the control device 6 via the signal amplification board 7. The magnetic sensor 3 is composed of a Hall IC with a compensation circuit that minimizes temperature drift. The excitation coil 2 and the magnetic sensor 3 are fixed in positions facing each other with a predetermined distance between them, and the steel strip passes between them non-contact in the direction indicated by the arrow in Figure 1. The steel strip L is transported such that the lift-off distance between it and the magnetic sensor 3 is always constant. In other words, the magnetic sensor 3 is positioned so that the lift-off distance between it and the lower surface Lb of the steel strip L is always constant.

[0013] As shown in FIG. 2, the signal amplification substrate 7 is composed of a signal amplification unit 71 that amplifies the signal of the detected magnetic flux detected by the magnetic sensor 3, and a preamplifier substrate having an input filter 72 that removes signal noise.

[0014] The excitation power supply 4 has an excitation coil 2 connected to its output side, and supplies an excitation current to the excitation coil 2 in response to a control command from the control device 6. The excitation power supply 4 is composed of a DC power supply 41, and flows a current through the excitation coil 2 according to the operation amount. A DC amplifier can be used for the DC power supply 41. For example, by using a four-quadrant bipolar power supply, it is possible to make a device with a good response speed for sucking in current against the back electromotive force acting on the excitation coil 2.

[0015] The current measuring device 5 is interposed between the excitation power supply 4 and the excitation coil 2, and has a measuring unit 51 that measures the excitation current supplied from the excitation power supply 4 to the excitation coil 2. The measured value of the excitation current measured by the measuring unit 51 is input to the control device 6 as a hardness conversion target value.

[0016] The control device 6 controls the excitation power supply 4 to adjust the excitation current supplied from the excitation power supply 4 to the excitation coil 2. The control device 6 is composed of, for example, a PLC (Programmable Logic Controller). The control device 6 includes a CPU (Central Processing Unit), a storage device (not shown), an A / D converter 62 that inputs an amplified signal from the signal amplification substrate 7, an A / D converter 63 that inputs an excitation current from the current measuring device 5, and a D / A converter 64 that outputs a control signal from the CPU 61 to the excitation power supply 4. The control device 6 controls the excitation current supplied from the excitation power supply 4 to the excitation coil 2 so that the magnetic flux density measured by the magnetic sensor 3 becomes a preset constant value, and performs an arithmetic process of calculating the hardness using the measured value of the excitation current measured by the measuring unit 51 of the current measuring device 5 as a hardness conversion target value.

[0017] FIG. 3 is a diagram showing the structure of the excitation coil of the steel plate hardness measuring device according to the first embodiment. The exciting coil 2 has a rod-shaped iron core 21, a coil 22 in which a conducting wire is wound around the iron core 21, and a pair of yokes 23 and 24 arranged at both axial ends of the iron core 21. The exciting coil 2 is arranged such that the axis of the iron core 21 extends parallel to the steel strip L, and the pair of yokes 23 and 24 face the upper surface La of the steel strip L.

[0018] When the exciting coil 2 receives a direct current supply from the exciting power source 4 to the coil 22, it generates magnetic flux lines B that are output from the lower end of one yoke 23, travel parallel along the steel strip L, and enter the lower end of the other yoke 24. The exciting coil 2 applies a static magnetic field having the magnetic flux lines B to the steel strip L, and the magnetic sensor 3 detects the magnetic flux density that leaks through the steel strip L.

[0019] FIG. 4 is a diagram for explaining the measurement principle of the steel plate hardness measuring device according to the first embodiment. The leakage magnetic flux that leaks through the steel strip L changes according to the internal crystal grain size (= the size of magnetic walls) of the steel strip L. It is known that the internal crystal grain size of the steel strip L has a correlation with the hardness. The relationship between the magnetic field and the leakage magnetic flux is called magnetic characteristics. Assuming that there is a linearity in the relationship between the magnetic characteristics obtained from the leakage magnetic flux detected by the magnetic sensor 3 and the hardness, the control device 6 can calculate the unknown steel plate hardness (calibration curve method).

[0020] The control device 6 converts the magnetic field force when controlling the leakage magnetic flux density to a preset constant value in a static magnetic field environment into hardness. The preset constant value of the leakage magnetic flux density is determined based on a characteristic quantity that depends on the steel plate. When using magnetic characteristics, the sensitivity is good when measuring near the large change width (maximum magnetic permeability) of the BH curve shown in FIG. 4. The optimal leakage magnetic flux density to be controlled is determined by conditions such as the plate thickness and composition of the steel strip and the lift-off distance.

[0021] The control device 6 controls the exciting power source 4 to adjust the exciting current output from the exciting power source 4 to the exciting coil 2. Then, the measured value of the exciting current measured by the current measuring device 5 is converted into hardness using the calibration curve method.

[0022] The calibration curve method calculates the hardness of a steel strip from its excitation current by utilizing the correlation between the excitation current of multiple steel strip samples with known hardness, composition, and thickness. Specifically, several standard samples (samples with known hardness) of steel strip whose hardness has been accurately measured by hardness testing are prepared, and a static magnetic field is applied to each of them from the excitation coil 2, and the leakage magnetic flux density near the maximum permeability is obtained in advance. The obtained leakage magnetic flux density is set to a predetermined constant value. The excitation current at which this obtained leakage magnetic flux density is obtained is measured by the current measuring instrument 5, and the hardness of the steel strip is calculated from the excitation current (see, for example, the linear calibration curve graph shown in Figure 4). For steel strips L with unknown hardness, the leakage magnetic flux density is measured in a static magnetic field environment, and the excitation current is adjusted so that the measured leakage magnetic flux density becomes a predetermined constant value. The excitation current when the leakage magnetic flux density reaches a predetermined constant value is measured using the current measuring instrument 5, and the measured excitation current is applied to the calibration curve graph to calculate the unknown hardness.

[0023] Figure 5 is a flowchart showing a measurement method using the steel plate hardness measuring device according to the first embodiment.

[0024] The control device 6 initializes the magnetic sensor 3 (S101) and waits until the output stabilizes (S102). Then, the leakage flux density measured by the magnetic sensor 3 (S103) is converted by A / D conversion using A / D62 (S104) to obtain the leakage flux density (PV) (S105). Then, the target value (SV) set in S106 is compared with the leakage flux density (PV) to perform feedback control (S107), feedforward control is performed using a disturbance element (S108) (S109), and the manipulated variable is output to the excitation power supply 4 (S110). In S106, the target value (SV) is set so that the leakage flux density (PV) is near the maximum permeability. The maximum permeability is determined based on conditions such as the thickness and composition of the steel strip and the lift-off distance.

[0025] The excitation power supply 4 outputs an excitation current to the excitation coil 2 based on the manipulated variable calculated by the control device 6 (S111). The excitation current measured by the current measuring instrument 5 (S112) is then converted by A / D conversion using A / D 63 (S113) to obtain the measured value of the excitation current (S114). The measured value of the excitation current is then converted to hardness using the calibration curve method (S115). It is determined whether the measurement is complete or not (S116). If it is complete (Yes in S116), the measurement is stopped. If it is not complete (No in S116), the process is restarted from S103.

[0026] Furthermore, the control device 6 can perform calibration to eliminate the influence of the Earth's magnetic field. For example, calibration is performed based on the magnetic flux density measured by the magnetic sensor 3 with the steel strip L removed from between the excitation coil 2 and the magnetic sensor 3.

[0027] Figure 6 shows a comparative example illustrating the configuration of the excitation coil in the first embodiment. The comparative example excitation coil 102 is a solenoid-type electromagnet having a rod-shaped iron core 121, a coil 122 with a conductor wound around the iron core 121, and a pair of non-magnetic materials 123 and 124 positioned at both ends of the iron core 121 in the axial direction. In the excitation coil 102, the axis of the iron core 121 extends perpendicularly to the steel strip L to be measured, with one non-magnetic material 123 positioned close to and facing the steel strip L, and the other non-magnetic material 124 positioned at a distance from the steel strip L. The excitation coil 102 has a magnetic circuit configuration that generates magnetic field lines perpendicular to the steel strip L.

[0028] The magnetic field lines B of the excitation coil 102 gradually diffuse once the number of magnetic field lines per unit area in the air becomes saturated. The magnetic field lines B diffuse as they enter the steel strip L, and most of them are attracted to the steel strip L, which has high magnetic permeability. The magnetic field lines B that have passed through the steel strip L further diffuse in the air before being input to the magnetic sensor 3. In the comparative example, the excitation coil 102 is in an open state as a magnetic circuit, making it difficult to control the application of the optimal magnetic force to the steel strip L.

[0029] In contrast, the excitation coil 2 of this embodiment has a magnetic circuit configuration that generates magnetic field lines B parallel to the steel strip L, as shown in Figure 3. Therefore, by controlling the leakage flux to a constant value, it is possible to measure the optimal magnetic characteristics corresponding to the steel strip L within the dynamic range, and to measure while avoiding the magnetic saturation region which changes depending on the composition of the steel strip.

[0030] In the comparative example shown in Figure 6, a constant excitation current is applied to the excitation coil 102, and the fluctuations in the magnetic field lines B transmitted through the steel strip L are measured by the magnetic sensor 3.

[0031] In contrast, in this embodiment, an excitation current is applied to the excitation coil 2 that fluctuates so that the magnetic field lines B (leakage magnetic flux density) passing through the steel strip L remain constant. Therefore, the effect of permeability, which changes depending on the magnitude of the excitation current, is taken into account, making it possible to measure magnetic properties according to hardness.

[0032] Furthermore, the steel sheet hardness measuring device of this embodiment may be used to measure the hardness of steel sheets manufactured in the steel sheet manufacturing process. By using the present invention, for example, after annealing in the steel sheet annealing process, the annealing conditions can be strictly adjusted, thereby preventing over-annealing and enabling the production of steel sheets with energy savings and high yield. The present invention can also be used in the hardness measurement process, which is part of the steel sheet manufacturing process. By using the present invention in the hardness measurement process, hardness measurement by sample sampling becomes unnecessary, reducing measurement time and manual labor, and enabling the efficient provision of steel sheets.

[0033] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various design modifications can be made without departing from the spirit of the invention as described in the claims. [Explanation of Symbols]

[0034] 1. Steel plate hardness measuring device, 2. Excitation coil, 3. Magnetic sensor, 4. Excitation power supply, 5. Current measuring instrument, 6. Control device, 7. Signal amplification board, 41. DC power supply, 51. Measuring unit, B. Magnetic field lines, L. Steel strip

Claims

1. A steel plate hardness measuring device that measures the hardness of a steel plate without contact, An excitation coil is positioned opposite one side of the steel plate and applies a static magnetic field to the steel plate, A magnetic sensor is positioned between the excitation coil and the other side of the steel plate, with the steel plate in between, and measures the magnetic flux density leaking through the steel plate. An excitation power supply that supplies excitation current to the excitation coil, A current measuring instrument for measuring the excitation current supplied from the excitation power supply to the excitation coil, A control device for controlling the excitation power supply, A steel plate hardness measuring device comprising: The control device is A steel plate hardness measuring device characterized by controlling the excitation current supplied from the excitation power supply to the excitation coil so that the magnetic flux density measured by the magnetic sensor becomes a constant value, and calculating the hardness based on the excitation current.

2. The control device is The steel plate hardness measuring device according to claim 1, characterized in that it calculates the hardness of the steel plate from the excitation current by utilizing the correlation between a plurality of steel plate samples, each of which has known hardness, composition, and thickness, and the excitation current in the plurality of steel plate samples.

3. The steel plate hardness measuring device according to claim 1, characterized in that the excitation coil is a C-yoke type excitation coil or an H-yoke type excitation coil that applies a static magnetic field parallel to the steel plate.

4. The steel plate hardness measuring device according to claim 1, characterized in that the excitation power supply is a DC power supply.

5. The steel plate hardness measuring device according to claim 1, characterized in that the control device performs calibration to eliminate the influence of the Earth's magnetic field based on the magnetic flux density measured by the magnetic sensor with the steel plate removed from between the excitation coil and the magnetic sensor.

6. A method for measuring the hardness of a steel plate in a non-contact manner using the steel plate hardness measuring device described in claim 1, The steps include supplying an excitation current to the excitation coil, The steps include measuring the magnetic flux density leaking through the steel plate using the magnetic sensor, The steps include controlling the excitation current so that the magnetic flux density measured by the magnetic sensor becomes a constant value, The steps include measuring the excitation current supplied from the excitation power supply to the excitation coil, A step of converting the measured value of the excitation current into hardness using the calibration curve method, A method for measuring the hardness of a steel plate, characterized by including the following:

7. A method for manufacturing a steel sheet, characterized by including a step of measuring the hardness of a steel sheet using a steel sheet hardness measuring device described in any one of claims 1 to 5.

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