JPS61124882A - Method and apparatus for measuring level of molten metal in mold - Google Patents

Abstract

PURPOSE:To measure the level of the molten metal in a mold with good accuracy, by measuring a time during which an ultrasonic wave is transmitted and reflected from the surface of the molten metal to be received. CONSTITUTION:An ultrasonic transmitter-receiver 10 transmits an ultrasonic pulse toward the surface of molten steel 24A in a mold 22. This ultrasonic pulse is reflected from the surface of molten steel 24A to be returned to the ultrasonic transmitter-receiver 10 and received by a receiver 34 to be outputted to a time measuring device 36. The time measuring device 36 measures the time difference of a main bang echo and the reflected echo, which was reflected from the surface of molten steel 24A and returned to the ultrasonic transmitter- receiver 10, from the inputted signal not only to display the measured value but also to output the same to an operational processor 38 which, in turn, calculates the distance DELTAl between the ultrasonic transmitter-receiver 10 and the surface of molten steel 24A in the mold 22 on the basis of the inputted time difference.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method and apparatus for measuring the level of molten metal in a mold, and is particularly suitable for use in continuous steel casting equipment.
The present invention relates to improvements in a method and device for measuring the level of molten metal in a mold, which measures the level of molten metal by transmitting ultrasonic waves and receiving the reflected waves.

[Conventional technology]

In continuous casting of metals such as steel, accurately determining the level of molten metal in the mold is extremely important for stable casting and maintaining good quality of the cast slab, and various measurement techniques currently exist. are doing. Among the measurement techniques, the following are representative. (1) A method of embedding a plurality of thermocouples or temperature sensing elements in a mold and measuring the molten steel level from the concentration distribution above and below the mold as measured by the thermocouples or temperature sensing elements. -Measurement method shown in 147469. (2) A measuring method disclosed in, for example, Japanese Patent Application Laid-Open No. 58-3763, which measures using a distance measuring principle based on eddy currents. (3) A measuring method disclosed in, for example, JP-A-58-53363, in which an excitation coil and a detection coil are installed at l1wM of the mold, and the molten steel level is measured from the impedance change of the detection coil. (4) Immerse an electrode or resistance wire in molten steel to detect continuity between the electrode and the mold wall, or change in resistance of an electric circuit consisting of a constant current power source, resistance wire, molten steel, mold wall, etc. Measuring the molten steel level, for example, JP-A-57
-19137 and the measurement method shown in JP-A-57-169626. (5) A measuring method disclosed in, for example, JP-A-57-173722, in which a radiation source is placed on one side of the mold and a detector is placed on the other side, and the molten steel level is measured from the amount of transmission of the radiation rod. (6) Photograph the hot water level inside the mold from diagonally above.
For example, a measuring method disclosed in Japanese Patent Laid-Open No. 58-29558, in which a television camera is installed above the mold and the molten steel level is measured from the video signal captured by the television camera. (7) Multiple ultrasonic transmitters/receivers - Attach or embed them in the vertical direction of the mold, transmit ultrasonic waves toward the inside of the mold (V < molten steel side), reflect on the inner wall of the mold, and return the ultrasonic waves to the ultrasonic transmitters/receivers. The level of molten steel is measured by measuring the intensity of the sonic echo 1b or by measuring the amount of transmission of the ultrasonic echo to an ultrasonic transmitter/receiver attached to an opposing mold. 1812
3. Measuring method disclosed in JP-A-57-159251.

[Problems to be solved by the invention]

However, the above conventional method has the problems described below. That is, in the method (1) of embedding multiple thermocouples or temperature sensing elements in the mold, the measurement accuracy is determined by the pitch at which the thermocouples or temperature sensing elements are installed. Thermocouples and temperature-sensing elements are required, and measurement equipment is large-scale, resulting in high installation and maintenance costs. or,
There is a considerable delay in the change in concentration distribution within the mold due to fluctuations in the molten steel level, resulting in a slow response speed. In addition, in the measurement method (2) using the eddy current, when a magnetic body approaches the surrounding area, disturbance occurs in the magnetic field, resulting in a large error in the measured value. Furthermore, in the measurement method (3) in which an excitation coil and a detection coil are installed on the side wall of the mold, the processing of the mold wall and its processing accuracy affect the detection accuracy. In addition, in the measurement method of (4) in which the electrode or resistor R1 is immersed in molten steel, since the electrode or resistance wire is directly immersed in molten steel, wear and tear on the probe is unavoidable, resulting in problems in maintainability. There is. Also, if mold powder is present on the surface of molten steel,
Its electrical characteristics affect detection accuracy. Furthermore, in the measurement method (5) in which the mold is sandwiched and a radiation source is placed on one side and a detector is placed on the other side, there is a possibility of radiation leakage, which poses a safety problem. In addition, in the measurement method (6) of photographing the molten metal surface in the mold from diagonally above, the image may be distorted by optical disturbances caused by flames of the molten steel, etc., resulting in large measurement errors. When there is unmelted mold powder on the surface, the amount of light emitted by this unmelted mold powder is extremely smaller than that of molten steel, so the unmelted mold powder is captured as a dark spot in the image. . If it exists near the boundary line between the mold and molten steel, the boundary between the mold and molten steel becomes uniform and cannot be identified. In addition, in the measurement method (7) in which a plurality of ultrasonic transceivers are attached or embedded in the vertical direction of the mold, it is necessary to attach or embed a large number of ultrasonic probes in the mold, making it difficult to measure. In addition to making the system complicated, it also has poor maintainability. [Objective of the Invention 1] The present invention has been made in view of the above-mentioned conventional problems, and is capable of measuring the molten metal level in a mold with a simple measurement system that is resistant to external disturbances, has a fast response speed, and has high accuracy. It is an object of the present invention to provide a method and apparatus for measuring the level of molten metal in a mold. [Means for Solving Problem 11m] The present invention provides a method for measuring the level of molten metal in a mold by emitting ultrasonic waves and receiving the reflected waves, as shown in FIG. As shown in Figure 2, ultrasonic waves are emitted from above the mold almost perpendicularly into the air toward the molten metal surface within the mold, and after the ultrasonic waves are emitted, they are reflected by the molten metal surface and received. The above objective is achieved by measuring the time until the mold melts and measuring the level of molten metal in the mold from the measured result. The present invention also provides an in-mold molten metal level measuring device that measures the level of molten metal by emitting ultrasonic waves and receiving the reflected waves. an ultrasonic transmitter that transmits ultrasonic waves into the air substantially perpendicularly toward a metal surface; an electric pulse transmitter that applies an electric pulse to the ultrasonic transmitter;
an ultrasonic receiving means for receiving ultrasonic waves reflected from the molten metal surface in the mold; a receiver for amplifying the signal received by the ultrasonic receiving means; and an ultrasonic transmitting means for transmitting ultrasonic pulses. The above object is also achieved by including a time measuring device that measures the time interval from when the ultrasonic waves are transmitted to when the ultrasonic waves are received by the ultrasonic receiving means. [Operation 1] The operation of the present invention will be explained in detail below with reference to the drawings. In FIG. 1 mentioned above, the ultrasonic pulses transmitted from the ultrasonic transceiver 10 are applied to the molten gold in the mold 22! It is reflected by the surface of a24, becomes a reflected echo 14, and is returned to and received by the ultrasonic transceiver 10. Note that 26 is a coagulation shell, 32 is an electric pulse transmitter, 34 is a receiver, and 36 is a time measuring device. At this time, the ultrasonic signal received by the ultrasonic transceiver 10 is
The waveform is shown in FIG. In FIG. 2, reference numeral 12 indicates a main bang echo, which occurs in the ultrasonic transducer in the ultrasonic transmitter/receiver 10 when transmitting an ultrasonic pulse, and 14 indicates a main bang echo that occurs when the transmitted ultrasonic wave melts. This is an ultrasonic echo that is broken on the surface of the gold 121124 and returned to the ultrasonic transmitter/receiver 10, that is, a reflected echo. Therefore, the time difference Δt between the main bang echo 12 and the reflected echo 14 is # required for the ultrasonic wave emitted by the ultrasonic transceiver 1o to travel back and forth between the ultrasonic transceiver 1o and the surface of the molten metal 24. It is between. Therefore, by dividing the time difference Δt by the speed of sound, the round trip distance 2Δβ between the ultrasonic transceiver 10 and the surface of the molten metal 24 can be determined. However, in reality, since the molten metal 24 is at a high temperature, a temperature gradient occurs on the propagation path of the ultrasonic pulse, and the sound velocity on the propagation path of the ultrasonic pulse also has a distribution as a function of temperature. is occurring. Therefore, when the distance between the ultrasonic transmitter/receiver 10 and the surface of the molten metal 24 changes as the molten metal level changes, the temperature near the surface of the molten metal 24 changes.
Although the concentration distribution in the dark part changes only slightly,
The proportion of the low-temperature portion near the ultrasonic transceiver 10 in the entire propagation path of the ultrasonic pulse changes. Therefore, the average sound velocity on the propagation path of the ultrasonic pulse changes, and if the vI difference Δt was always calculated using a constant sound velocity value, then the An error occurs in the distance Δβ from the surface of the molten metal 24. However, during normal operation, the molten metal 24
8i near the surface of the molten metal 24 as the level of
The fluctuations in the speed distribution are extremely small, and therefore the fluctuations in the sound speed distribution are also extremely small. That is, the change in the time difference Δt between the main bang echo 12 and the reflected echo 14 as the level of the molten gold 1124 changes is monotonous and smooth, as shown in FIG. 3, for example.
Moreover, the reproducibility is good. However, the time difference Δt increases monotonically with an increase in the distance Δβ between the ultrasonic transceiver 10 and the molten metal surface, but the molten metal level increases as the distance Δ(
The smaller the value, the larger the time difference Δt becomes, so as shown in FIG. 3, the time difference Δt monotonically decreases as the molten metal level increases. Therefore, if the time difference Δt is measured in advance for several values of the distance Δb, and the relationship between the level of the molten metal 1i124 and the time difference Δt as shown in FIG. , the distance Δp can be determined from the time difference Δ[. Furthermore, instead of the relationship between the distance Δ and the time difference Δ, the relationship between the average sound speed on the ultrasonic pulse propagation path and the time difference Δ may be determined in advance and used to measure the distance Δ. However, when determining the relationship between the distance ΔC and the time difference Δt, the distance Δ° C. may be continuously changed to determine the time difference Δt. Note that when the relationship between the distance Δ°C and the time difference Δt is determined in advance, a means different from the means using ultrasonic waves is used to measure the distance Δ. On the other hand, when using the measured value of the molten metal level in the mold as a control signal to maintain a constant molten metal level in the mold, the absolute value of the molten metal level in the mold is determined as described above. 1. without carrying out the procedure. It is also possible to use the measured value of the time difference Δ(, which is the propagation time of an ultrasonic pulse) as is. Since the present invention uses ultrasonic waves, it is resistant to electromagnetic disturbances. It is determined by the pulse transmission interval, which is usually about 0.01 sec to 0.0 O1 sec, and it is possible to measure very fast response speed.Furthermore, an ultrasonic transmitter/receiver is installed above the mold. This method has the advantage that the measurement system is less likely to be worn out due to the high heat of the molten metal.Therefore, continuous casting equipment can operate stably and produce slabs of good quality. [Example] Examples of the present invention will be described in detail below. Figure M4 is a diagram showing an example to which the present invention is applied. Body 201.
: an ultrasonic transmitter/receiver 10 which is installed and fixed and transmits ultrasonic waves to the surface of the molten steel 24A and receives reflected echoes 14; an electric pulse transmitter 32 which applies electric pulses to the ultrasonic transmitter/receiver 10; A receiver 34 amplifies the signal received by the ultrasonic transceiver 10, and after the ultrasonic transceiver 10 emits an ultrasonic pulse, the ultrasonic pulse is reflected on the surface of the mold self-fusing IM 24A and the ultrasonic pulse is A time measuring device 36 that measures and outputs or displays the time interval until the sound wave is returned to the ultrasonic transmitting/receiving element 10, and from the output of the time measuring device 36, the ultrasonic transmitting/receiving element 10 and the molten steel in the mold 24A.
Arithmetic processor 38 that calculates and outputs or displays the distance to the surface
It is composed of. The operation of this embodiment will be explained in detail below. The electric pulse transmitter 10 transmits the molten steel 24 in the mold 22.
In order to measure the level of A, the electric pulse input to the ultrasonic transmitter/receiver 10 is transmitted with a constant repetition, and the force receiver 34 is also connected to one ultrasonic transmitter/receiver 10 along with the electric pulse transmitter 32. Therefore, the ultrasonic transmitter/receiver 10 serves both as a transmitter and a receiver. Upon receiving the electric pulse from the electric pulse transmitter 32, the ultrasonic transceiver 10 transmits the ultrasonic pulse toward the surface of the molten steel 24A in the mold 22. This ultrasonic pulse is reflected on the surface of the molten steel 24A and is returned to the ultrasonic transceiver 10. The ultrasonic pulses returned to the ultrasonic transmitter/receiver 10 are again converted into electrical signals, received by the receiver 34, and amplified. The amplified signal is outputted from the receiver 34 to a time measuring device 36, and the time measuring device 36 reflects the input signal from the main bang echo 12 and the surface of the molten steel 24A and transmits the signal to the ultrasonic transmitter/receiver. The time difference Δt of the reflected echo 14 returned to the echo 10 is measured, this value is displayed, and the performance n! I! output to the processor 38. The arithmetic processor 38 calculates the input time difference Δ[
Based on the ultrasonic transmitter/receiver 10 and the melt 1m2 in the mold 22.
4A to the surface is determined, and the value of the distance Δβ is displayed and this value is recorded on a suitable recording medium. FIG. 5 shows an in-mold molten metal level measuring device to which the present invention is applied. An example of the results of actually measuring the molten steel level is shown below. It can be seen that fluctuations in the molten steel level are measured with an accuracy of 1n or less. In the above example, one ultrasonic wave is used for both transmission and reception. Although the transmitter/receiver is illustrated, the ultrasonic transmitter and the ultrasonic receiver are not limited to this, and an ultrasonic transmitter/receiver that transmits and receives separately may be used. The fraud processor 38 is used to calculate the distance between the transmitter/receiver 10 and the surface of the mold inner layer steel 24A.
However, the method is not limited to this, as long as the distance Δβ between the ultrasonic transceiver 10 and the surface of the molten metal in the mold can be determined. If the distance between and the surface of the molten metal in the mold is determined, the calculation process M63B is not required. Further, although the above embodiments relate to a method and apparatus for measuring the surface level of molten steel, the method and apparatus are not limited to molten steel, and may be applied to other molten metals. [Effects of the Invention] As described above, according to the present invention, the level of molten metal in a mold can be measured with a simple measurement system that is resistant to external disturbances, has a fast response speed, and has high accuracy. Therefore, when casting molten metal, stable operation is possible, and excellent effects such as being able to produce slabs of good quality are achieved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view, including a partial block diagram, showing a state in which ultrasonic waves are transmitted from an ultrasonic transmitter/receiver to measure the level of molten metal in a mold, for explaining the present invention in detail. , FIG. 2 is a diagram showing an example of the waveform of an ultrasonic signal transmitted from an ultrasonic transceiver and received by the ultrasonic transceiver, and FIG. , FIG. 4 is a vertical cross-sectional view 1 including a partial block diagram showing an embodiment to which the present invention is applied, and FIG. Mold inner layer 1 measured in Example
It is a diagram showing an example of n levels. DESCRIPTION OF SYMBOLS 10... Ultrasonic transmitter/receiver, 12... Main bang echo, 14... Reflected echo, 22... Mold, 24... Molten metal, 2
4A... Molten steel, 32... Electric pulse transmitter, 34... Receiver, 36... Time measuring device,
38... Arithmetic processor, Δbu...-Distance between the ultrasonic transceiver and the molten metal surface, Δ
t: Time difference between transmitting and receiving ultrasonic waves.

Claims (2)

[Claims] (1) In a method for measuring the level of molten metal in a mold, in which the level of molten metal is measured by transmitting ultrasonic waves and receiving the reflected waves, a method for measuring the level of molten metal in a mold is performed from above the mold, approximately perpendicularly to the surface of the molten metal in the mold. emit ultrasonic waves into the air, measure the time from when the ultrasonic waves are emitted until they are reflected and received by the molten metal surface, and measure the level of the molten metal in the mold from the measured results. A method for measuring the level of molten metal in a mold. (2) In a device for measuring the level of molten metal in a mold, which measures the level of molten metal by emitting ultrasonic waves and receiving the reflected waves, the molten metal level in the mold is provided above the mold. an ultrasonic transmitting means for transmitting ultrasonic waves substantially vertically into the air; an electric pulse transmitter for applying an electric pulse to the ultrasonic transmitting means; and an ultrasonic wave reflected from the surface of the molten metal in the mold. an ultrasonic receiving means for receiving the ultrasonic pulse; a receiver for amplifying the signal received by the ultrasonic receiving means; and a receiver for amplifying the signal received by the ultrasonic receiving means, from when the ultrasonic transmitting means transmits an ultrasonic pulse to when the ultrasonic pulse is received by the ultrasonic receiving means. A device for measuring the level of molten metal in a mold, comprising: a time measuring device for measuring a time interval;