JPS5915738B2 - Method for measuring solidification thickness of continuously cast slabs - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the solidification thickness of a slab continuously drawn from a mold in a continuous casting method for molten metal (hereinafter simply referred to as molten metal).

Generally, in the continuous casting method of molten metal, as shown in FIG. 1, molten metal 3 is poured into a mold 2 having a predetermined cross-sectional shape through a tundish 1, and is continuously drawn out from below as a slab 4.

It is well known that the unsolidified molten metal 3 remains inside the slab 4 pulled out from the mold 2, and the entire slab gradually solidifies. Accurately detecting and measuring the complete solidification point of the slab 4 or the solidification thickness of the slab at a predetermined position prevents the so-called plague-out accident in which the molten metal inside ruptures the solidified shell and leaks to the outside. It is also well known that by optimizing so-called casting conditions such as cooling progress and drawing speed, information can be obtained that can greatly improve safety, productivity, and quality. Various methods using ultrasonic waves have been proposed and tested for the purpose of measuring the solidified thickness of slabs, but all of them have problems in terms of accuracy and in terms of application to actual equipment. The reality is that no definitive thickness measurement method has been developed yet.

For example, as shown in Fig. 2, a roll 5 containing a transmitter and a receiver inside is pressed against the slab, and the ultrasonic waves emitted from the transmitter 15 are transmitted between point b on the outside of the slab and c on the inside of the solidified shell. A method is known in which the coagulation thickness is measured from the time difference between the pulse reflection echo and the point.

In this method, reflection at point a of the inner shell of one roll accounts for approximately 94% of the total energy.

2. Also, the reflection at point b is large, so the reflected energy at point c is extremely small.

3 Furthermore, reflected waves occur at points a, b, c, d, and e, and the reflected energy at point c is extremely small. There is a huge problem in terms of sentiment.

Furthermore, as shown in Fig. 3, an ultrasonic transmitter is placed opposite to the slab 4, and the ultrasonic wave is transmitted through it, and the degree of change in the passage time of the sound wave is 30 degrees depending on the difference in solidification thickness. A so-called impulse transmission method for estimating the distance is also known. However,
In this method, as in the case of Fig. 2, the reflection on the outer surface of the slab is extremely large, and since it is estimated based on the transmission time, it is unclear how much unsolidified molten metal actually exists35. , so there is a drawback that the measurement error is larger than that of the reflection method in FIG. In addition, an impulse transmission method using transverse waves is disclosed in Japanese Patent Publication No. 48-3932, but this method detects that the sound wave is not being received due to the presence of an unsolidified portion, so it is completely solidified. However, it is not suitable for the purpose of measuring solidified thickness.

In addition, a method of measuring the solidification thickness by welding a delay rod to the slab is disclosed in No. 100349/1982, but this method has the disadvantage that the solidification thickness cannot be measured continuously. In view of these circumstances, and as a result of various studies, the present invention has developed an extremely accurate solidification thickness measurement system that utilizes electromagnetic force to inject ultrasonic waves into a slab and electrically detect the reflected echo at the solid-liquid phase boundary. This method has been discovered and will be described in detail below with reference to the drawings based on examples. FIG. 4 shows a principle diagram of the present invention. The outer wall of the molten metal 3 is cooled to form a slab 4, and a transmitter/receiver is placed near the slab 4.

A magnetic field generation power supply device 7 supplies a magnetic field generation current to the transceiver 6, an electrical signal is supplied to the transceiver 6 by a transmission circuit 8, and a received signal is supplied to the transceiver 6 by an amplifier 9. The measured results are displayed on the cathode ray tube display device 10. The feature of the present invention is that ultrasonic waves are transmitted through the slab using electromagnetic force without bringing the transceiver 6 into contact with the slab 4, and the reflected echo at the boundary between the solid phase of the slab 4 and the liquid phase of the molten metal 3 is detected. The purpose is to detect it electrically.

An example of a method of transmitting and receiving ultrasonic waves within a slab using electromagnetic force (hereinafter simply referred to as electromagnetic ultrasonic waves) will be described below.

FIG. 5 shows a cross-sectional view of a transceiver having an axis of rotational symmetry.

Reference numeral 11 denotes a magnetic field coil connected to the power source 7.

12 is a transmitting coil connected to the transmitting circuit 8;

Reference numeral 13 denotes a receiving coil which is connected to a cathode ray tube display device 10 through an amplifier 9.

14 is an iron core for magnetic field.

For example, when a voltage (for example, DC 200) is applied from the magnetic field power source 7 to the magnetic field coil 11, a magnetic field (5 KG) is generated, and a magnetic path is created in the slab 4 as shown in the opening of FIG.

The transmitting coil 12 is connected to the transmitting circuit in which combination the oscillating current (for example, the damped vibration f?21VHD of the RLC resonance is applied to the fifth
When flowing as shown in the figure, eddy current 15 appears on the surface of slab 4.
is generated, and as a result of the interaction with the magnetic field, a kinetic force f is generated in the direction of the liquid phase 3 according to Fleming's left-hand law, and the electric vibration is converted into mechanical vibration, which propagates in the direction of the liquid phase 3 as an ultrasonic wave. The reflected echo at the boundary between the solid phase 4 and the liquid phase 3 reaches the surface of the slab as shown in Fig. 5C, and as a result of interaction with the magnetic field, an eddy current 16 is generated according to Fleming's right-hand rule.
Mechanical vibrations are converted into electrical vibrations, which are transmitted to the receiving coil 13.
detected.

Further, since the receiving coil also detects the current flowing through the transmitting coil, the transmitting signal T and the detection signal F amplified by the amplifier 9 are displayed on the cathode ray tube display device 10. The displayed contents are shown in FIG. 5A. That is, the difference TO is measured as the solidified thickness. In this way, electromagnetic ultrasonic waves can easily transmit and receive ultrasonic waves to the slab being cast in a method that is completely different from the conventional method described above, and therefore has the following advantages.

1 Since electromagnetic ultrasonic waves can transmit and receive ultrasonic waves without the transmitter/receiver 6 coming into contact with the slab, there is no need to use rolls, delay rods, or any couplant unlike the conventional ultrasonic method described above.

2 During casting, the slab is pulled out at a certain speed, but electromagnetic ultrasonic waves can be transmitted and received without coming into contact with the slab.
Measurements can be made stably and continuously without being affected by increases or decreases in the drawing speed.

In this embodiment, the magnetic field has been explained using a magnetic field caused by a direct current, but this may be a pulsed magnetic field induced by passing a large pulsed current through a permanent magnet or a coil, and is not particularly limited.

Further, although different coils are used as the electric signal transmitting coil and the receiving coil, it is also possible to use the same coil by taking advantage of the time difference.

[Brief explanation of drawings]

Figure 1 is a sectional view showing the principle of general continuous casting, Figure 2~
Fig. 3 is an explanatory diagram of the conventional method, Fig. 4 is a block diagram of the measuring device according to the present invention), and Figs. It is. 1: tandate, 2: mold, 3: molten metal, 4: mold,
5: Roll, 6: Transmitter/receiver, 7: Magnetic field generation power supply device,
8: transmitting circuit, 9: intensifier, 10: cathode ray tube display, 11: magnetic field coil, 12: transmitting coil, 13: receiving coil, 14: iron core.

Claims (1)

[Claims] 1 A magnetic field is created by applying ultrasonic waves to the slab by inducing eddy currents in the slab while a magnetic field is applied to the slab, and applying reflected ultrasound waves from the boundary between the solid phase and liquid phase of the slab to the slab. A method for measuring the solidification thickness of continuously cast slabs, which is characterized by electrically converting and detecting the solidified thickness.