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

Abstract

The present invention addresses the problem of providing: a steel plate hardness measurement device that can measure steel plate hardness with high accuracy in a non-contact manner; a measurement method using the same; and a method for manufacturing a steel plate. A steel plate hardness measurement device (1) according to the present invention comprises: an excitation coil (2) that is disposed facing one surface (La) of a steel plate and applies a static magnetic field to the steel plate; a magnetic sensor (3) that is disposed facing the other surface (Lb) of the steel plate with the steel plate interposed between the magnetic sensor (3) and the excitation coil, and measures the magnetic flux density permeating and 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 such that the magnetic flux density measured by the magnetic sensor is a constant value, and calculates hardness on the basis of the excitation current.

Description

Steel Plate Hardness Measuring Device, Measuring Method Using the Same, and Steel Plate Manufacturing Method

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

[0002] Various magnetic hardness meters that can nondestructively and continuously measure the hardness of thin steel plates (strip steel) inline have been proposed. In Patent Document 1, a rod-shaped direct current electromagnet arranged above the strip steel applies a constant static magnetic field in the direction perpendicular to the measurement object by 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.

[0003] Japanese Patent Publication No. 50-21869

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

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

[0006] (1) The steel plate hardness measuring device according to the present invention is a steel plate hardness measuring device for measuring the hardness of a steel plate in a non-contact manner, 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 between the excitation coil and the other side of the steel plate via 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), wherein 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), wherein 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 that measures the hardness of a steel plate non-contact using the steel plate hardness measurement 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 steel plate manufacturing method according to the present invention is characterized by comprising the step of measuring the hardness of a steel plate using the steel plate hardness measurement device described in any one of (1) to (5).

[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.

[0008] An overall diagram of the steel plate hardness measuring device according to the first embodiment. A functional block diagram of the steel plate hardness measuring device according to the first embodiment. A diagram showing the excitation coil and magnetic flux of the steel plate hardness measuring device according to the first embodiment. A diagram explaining the measurement principle of the steel plate hardness measuring device according to the first embodiment. A flowchart showing a measurement method using the steel plate hardness measuring device according to the first embodiment. A diagram showing a comparative example of the excitation coil that serves as a premise for explaining the first embodiment.

[0009] Next, one embodiment of the present invention will be described with reference to the 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 will be described below, using a steel strip L as an example, but the steel strip can be replaced with a steel plate and used in the same way.

[0010] The steel plate hardness measuring device 1 is a device that measures 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 that is to be 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 made up 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 in such a way 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 Figure 2, the signal amplification board 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 board having an input filter 72 that removes noise from the signal.

[0014] The excitation power supply 4 has an excitation coil 2 connected to its output side and supplies excitation current to the excitation coil 2 in response to control commands from the control device 6. The excitation power supply 4 is composed of a DC power supply 41 and supplies current to the excitation coil 2 according to the manipulated variable. 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 create a device with a good response speed by drawing in current in response to 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 value to be converted to hardness.

[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 memory device (not shown), an A / D converter 62 that receives an amplified signal from the signal amplification board 7, an A / D converter 63 that receives an excitation current from the current measuring instrument 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 calculation processing to calculate hardness using the measured value of the excitation current measured by the measurement unit 51 of the current measuring instrument 5 as the hardness conversion target value.

[0017] Figure 3 shows the structure of the excitation coil of a steel sheet hardness measuring device according to the first embodiment. The excitation coil 2 has a rod-shaped iron core 21, a coil 22 in which a conductor is wound around the iron core 21, and a pair of yokes 23 and 24 arranged at both ends in the axial direction of the iron core 21. The excitation coil 2 has the axis of the iron core 21 extending parallel to the steel strip L, and the pair of yokes 23 and 24 are positioned facing the upper surface La of the steel strip L.

[0018] When the excitation coil 2 receives a DC current from the excitation power supply 4 to the coil 22, it generates magnetic field lines B that are output from the lower end of one yoke 23, move parallel to the steel strip L, and are input to the lower end of the other yoke 24. The excitation coil 2 applies a static magnetic field with magnetic field lines B to the steel strip L, and the magnetic sensor 3 detects the magnetic flux density leaking through the steel strip L.

[0019] Figure 4 is a diagram illustrating the measurement principle of the steel sheet hardness measuring device according to the first embodiment. The leakage magnetic flux that permeates and leaks through the steel strip L changes according to the internal grain size (= size of the magnetic domain wall) of the steel strip L. It is known that the internal grain size of the steel strip L is correlated with hardness. The relationship between the magnetic field and the leakage magnetic flux is called the magnetic property. Assuming that there is linearity between the magnetic property obtained from the leakage magnetic flux detected by the magnetic sensor 3 and the hardness, the control device 6 can calculate the unknown steel sheet hardness (calibration curve method).

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

[0021] The control device 6 controls the excitation power supply 4 to adjust the excitation current output from the excitation power supply 4 to the excitation coil 2. Then, the measured value of the excitation current measured by the current measuring instrument 5 is converted to 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 of steel strip (samples with known hardness) 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 by 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 the A / D converter 62 (S104) to obtain the leakage flux density (PV) (S105). Then, the control device 6 compares the target value (SV) set in S106 with the leakage flux density (PV) and performs feedback control (S107), performs feedforward control (S109) using a disturbance element (S108), and outputs the manipulated variable 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 the A / D converter 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 of the first embodiment. The excitation coil 102 of the comparative example 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 arranged 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 approaching 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.

[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... Measurement unit, B... Magnetic field lines, L... Steel strip

Claims

1. A steel plate hardness measuring device for measuring the hardness of a steel plate in a non-contact manner, 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 between the excitation coil and the other side of the steel plate via 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 instrument 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 claim 1, characterized in that 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 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, comprising: a step of supplying an excitation current to the excitation coil; a step of measuring the magnetic flux density leaking through the steel plate using the magnetic sensor; a step of controlling the excitation current so that the magnetic flux density measured by the magnetic sensor becomes a constant value; a step of measuring the excitation current supplied from the excitation power source to the excitation coil; and a step of converting the measured value of the excitation current into hardness using the calibration curve method.

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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