JP3854445B2 - Method and apparatus for measuring level of molten metal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a molten metal level measurement method and apparatus, and more particularly, to a molten metal level measurement method and apparatus in a mold having a molten metal forming coil.
[0002]
[Prior art]
In continuous casting of a slab, in order to improve the quality of the slab, the powder supplied on the molten metal surface is melted by the heat of the molten metal and flows between the mold and the solidified shell. That is, the melted powder flows between the mold and the solidified shell by the relative movement of the mold that vibrates up and down and the solidified shell that is pulled out from the bottom at a constant speed.
[0003]
The meniscus and the solidified tip shell are deformed by the dynamic pressure generated by the inflow of the melted powder, but this deformation is repeated every time the mold vibrates, so periodic ridges called oscillation marks are formed on the slab surface. Is done.
However, if the depth of the soot is too deep, not only will it become a mold surface soot defect, but depending on the steel type, certain elements may precipitate in the troughs, resulting in increased quality such as increased trapping of bubbles and inclusions. Become.
[0004]
On the other hand, in the continuous casting of billets and small cross-sectional area cast pieces, Repseed oil is used instead of powder. Although this rep seed oil burns in the meniscus and turns into graphite and prevents the solidified shell from seizing on the mold wall, it cannot form a clear oscillation mark, and the stability of operation or quality It is inevitable that it will be inferior to the case of use.
[0005]
For this reason, in order to further improve the quality of slabs cast by continuous casting, the hot water surface forming coil wound around the mold is excited with alternating current power, and the hot water surface is magnetized to bend the hot water surface. It has been proposed to improve the surface properties of the slab by JP-A-52-32824.
Furthermore, it has also been proposed to intermittently excite the coil with AC power and further improve the surface properties of the slab (Japanese Patent Laid-Open No. 64-83348).
[0006]
In addition, the amplitude of the AC power for exciting the coil is modulated with the vertical vibration frequency of the mold, and the relationship between the mold vibration frequency (fm) and the frequency (fp) of the coil excitation AC power is expressed as follows:
0.69 ≦ ln (fp / fm) ≦ 9.9
However, it has also been proposed to stabilize the molten metal surface shape and improve the surface properties of the slab by maintaining ln within a constant range (Republished Japanese Patent Application Laid-Open No. 8-805926).
[0007]
By the way, in order to improve the quality of the slab, it is also necessary to accurately measure the molten metal level of the molten metal in the mold. As an apparatus for measuring the level of molten metal, the eddy current type has advantages in accuracy and responsiveness in addition to a sensor using a thermocouple embedded in a mold and a transmission type sensor using γ rays. Sensors are also applied.
[0008]
However, in a mold having a molten metal surface forming coil, an induced current is induced in the eddy current sensor by an alternating magnetic field generated by the coil, and the molten metal surface cannot be detected accurately.
For example, when the coil is continuously excited with AC power having a frequency of 200 Hz and a magnetic flux density of 1,000 gauss is applied to the molten metal surface, the output signal of the eddy current sensor is saturated. Further, even when the coil is intermittently excited, it cannot be avoided that the output signal of the eddy current sensor is saturated during the supply of AC power.
[0009]
Therefore, when the coil is intermittently excited, a hot water level measuring device using an eddy current sensor that measures the hot water level during the AC power off period and stops the hot water level measurement during the AC power supply period has also been proposed. (Japanese Patent Laid-Open No. 11-188465).
In the hot water level measuring device according to the above proposal, it has also been proposed to provide a trigger pulse generator in the coil excitation power supply device and generate the trigger pulse based on the excitation power output from the power supply.
[0010]
The timing pulse generated based on this trigger pulse samples and holds the eddy current sensor output during the excitation power pause period, and outputs the hold value during the excitation power supply period, thereby eliminating the influence of excitation. Yes.
[0011]
[Problems to be solved by the invention]
However, in the hot water level measuring device according to the above proposal, the trigger pulse and the timing pulse are not generated when the coil excitation power source is not operating, and the hot water surface shape is not formed by magnetic force. The problem arises that the level meter cannot be calibrated.
[0012]
Furthermore, even if molding the melt surface shape by a magnetic force, intent, or accidentally but also Ru Ah when the coil excitation is interrupted, the measurement of the molten metal surface level is canceled during excitation suspended The problem of end up. Therefore, it is conceivable to provide a manual bypass switch to stop the sample and hold and output the output of the eddy current sensor as it is when the coil is not excited.
[0013]
However, there is no guarantee that the switching is performed reliably, and there is a possibility that the molten metal level control may be hindered when molten metal is injected.
The present invention has been made in view of the above problems, and not only can measure the molten metal level in synchronization with excitation of the molten metal forming coil, but also continuously adjust the molten metal surface level when not excited. An object of the present invention is to provide a hot water level measuring method and apparatus capable of measuring.
[0014]
[Means for Solving the Problems]
Melt surface level measuring method of molten metals according to the first invention, the mold comprising a wrapping coil and a power source for outputting intermittently turned on and off AC power at a predetermined period to excite the coil A molten metal surface level measuring method for measuring a molten metal surface level of a molten metal using an eddy current sensor, wherein the first logic level is output during an AC power output period when the power source is in operation. , and the during the output suspension period of the AC power is a second logic level, and the trigger pulse signal output step the power supply is stopped for outputting a trigger pulse signal to be continuously second logic level, the When the trigger pulse signal transits from the first logic level to the second logic level, the trigger pulse signal transits from the first logic level to the second logic level after a predetermined time elapses. Logical level Maintaining the second logic level for a period of time and for a first predetermined period and then returning to the first logic level so that the trigger pulse signal has a second logic level for a second predetermined period or more. The timing pulse signal output step for outputting the timing pulse signal to be shifted to and maintained at the second logic level when the current is maintained, and the output of the eddy current sensor as it is when the timing pulse signal is at the second logic level And a sample-and-hold step of sampling and holding the output of the eddy current sensor and outputting the held output of the eddy current sensor when it is at the first logic level .
[0015]
Melt surface level measuring device of the molten metal according to the second invention, the mold comprising a wrapping coil and a power source for outputting intermittently turned on and off AC power at a predetermined period to excite the coil the molten metal surface level of the molten metal, a molten metal surface level measuring apparatus for molten metal to be measured using an eddy current sensor, in the power supply is in operation, during the output period of the AC power first logic level , and the during the output suspension period of the AC power is a second logic level, and the trigger pulse signal output means and the power supply is stopped for outputting a trigger pulse signal to be continuously second logic level, the when the trigger pulse signal outputted from the trigger pulse signal output means transitions from a first logic level to a second logic level, the transition from the first logic level after the lapse a predetermined time to the second logic level Shi Trigger pulse signal maintaining and first pre-period determined second logic level while in the second logic level, and then return to the first logic level, advance the trigger pulse signal is in the second when maintaining the above-determined period the second logic level and the timing pulse signal output means for outputting a timing pulse signal to maintain the transition to the second logic level, said timing pulse signal is at a second logic level Sample-and-hold means for outputting the output of the eddy current sensor as it is, sampling and holding the output of the eddy current sensor, and outputting the output of the held eddy current sensor when at a first logic level. It is characterized by comprising.
[0016]
When the coil wound around the mold is intermittently excited by AC power, the output of the eddy current sensor is sampled and held during the power supply pause period, and the held output is output during the power supply period. The
When the excitation of the coil is stopped, the output of the eddy current sensor is output as it is.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view of a hot water level measuring device according to the present invention, and power is supplied to a mold unit 10 from a power supply unit 11. The molten metal level of the molten metal in the mold is measured by the molten metal level measuring unit 12.
Molten metal 103 is injected from the casting nozzle 102 into the mold 101 of the mold unit 10. The hot metal surface forming coil 104 is wound around the mold 101.
[0018]
The coil 104 is excited by the power supplied from the power supply unit 11 to form the meniscus of the molten metal 103 in a convex shape. The power supply unit 11 includes a trigger pulse signal generation unit in addition to the power supply 111 that generates excitation power. 112 is included. The trigger pulse signal generation unit 112 generates a trigger pulse signal synchronized with on / off of the pulsed AC power output from the power supply 111.
[0019]
The hot water surface level measuring unit 12 is an eddy current sensor 121 installed on the upper part of the mold 101, a preprocessing unit 122 for amplifying, detecting and filtering the output of the eddy current sensor 121, and an output of the preprocessing unit 122. A sample-and-hold unit 123 that samples and holds, a low-pass filter 124 that removes high-frequency components from the output of the sample-and-hold unit 123, a linearizer 125 that linearizes the output of the low-pass filter 124, and a mode switch that controls the sample-and-hold unit 123 Part 126.
[0020]
FIG. 2 is a circuit diagram of an example of the sample and hold unit 123, and the input terminal 31 of the sample and hold unit 123 is connected to the non-inverting input terminal of the first operational amplifier 32. The output of the first operational amplifier 32 is connected to the common terminal of the switch 33. The break terminal of the switch 33 is connected to one terminal of the hold capacitor 34 and the non-inverting input terminal of the second operational amplifier 35. The other terminal of the hold capacitor 34 is grounded.
[0021]
The output of the second operational amplifier 35 is connected to the output terminal 36 of the sample and hold unit 123. Further, the output of the second operational amplifier 35 is fed back to the inverting terminal of the first operational amplifier 32 and the inverting terminal of the second operational amplifier 35.
When the timing pulse signal supplied from the mode switching unit 126 is “low level” and the switch 33 is closed, the signal supplied to the input terminal 31 is output as it is from the output terminal 36. When the timing pulse signal is “high level” and the switch 34 is opened, the voltage held in the hold capacitor 34 is output from the output terminal 36.
[0022]
FIG. 3 is an output waveform diagram of the trigger pulse signal generator, where (a) shows the output waveform when the power supply 111 is operating and (b) shows the output waveform when the power supply 111 is stopped. That is, the trigger pulse signal is “high level” during the period when the excitation power is on during operation, and the trigger pulse signal is “low level” during the period when the excitation power is on. Further, the trigger pulse signal is maintained at “low level” while the power source 111 is stopped.
[0023]
FIG. 4 is a circuit diagram illustrating an example of the mode switching unit, which includes a timing pulse generation circuit 41, a timing pulse switching circuit 42, an oscillator 43, and a timer circuit 44.
That is, the trigger pulse signal is supplied from the trigger pulse signal generation unit 112 to the input terminal 40 of the mode switching unit 126. Then, the timing pulse generation circuit 41 generates a timing pulse signal that becomes “low level” only for a predetermined period from “high level” with the falling timing of the trigger pulse signal as a trigger. The timing pulse signal is output from the output terminal 45.
[0024]
The timer circuit 44 counts the predetermined time by counting the number of level transitions of the square wave output from the oscillator 43. When the timing pulse generation circuit 41 does not detect the falling edge of the trigger pulse signal timed by the timer circuit 44, the timing pulse switching circuit 42 operates to maintain the timing pulse signal at "low level". .
[0025]
FIG. 5 is an output waveform diagram of the timing pulse switching circuit. (A) shows an output waveform when the power supply 111 is operating, and (b) shows an output waveform when the power supply 111 is stopped.
That is, while the power supply 111 is operating, the timing pulse is maintained at “high level” while the excitation power is on, and the timing pulse for a predetermined period within the period when the excitation power is off transitions to “low level”. Therefore, during operation of the power supply 111, the output of the eddy current sensor 121 is sampled and output as it is during the off period of the excitation power, and the value held in the sample and hold unit 123 is output during the other period.
[0026]
Conversely, while the power supply 111 is stopped, the timing pulse signal is maintained at the “low level”, so that the sample and hold unit 123 operates in the continuous sample mode, and the output of the eddy current sensor 121 is output as it is.
In the above embodiment, the mode switching circuit is configured using a logic integrated circuit, but it is obvious that the mode switching circuit can be configured using a programmable element such as a microcomputer.
[0027]
【The invention's effect】
According to the molten metal surface level measuring method and measuring instrument according to the present invention, when the coil wound around the mold is intermittently excited by AC power, the molten metal surface is not affected by the excitation of the coil. Not only can the level be measured, but also the molten metal level can be continuously measured when the coil is not energized.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a hot water level measuring device according to the present invention.
FIG. 2 is a circuit diagram of an example of a sample and hold unit.
FIG. 3 is an output waveform diagram of a trigger pulse signal generator.
FIG. 4 is a circuit diagram of an example of a mode switching circuit.
FIG. 5 is an output waveform diagram of a timing pulse switching circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Mold part 101 ... Mold 102 ... Casting nozzle 103 ... Molten metal 11 ... Power supply part 111 ... Power supply 112 ... Trigger-pulse signal generation part 12 ... Hot water level measurement part 121 ... Eddy current sensor 122 ... Pre-processing part 123 ... Sample and hold unit 124 ... low pass filter 125 ... linearizer 126 ... mode switching unit

Claims (4)

And wrapping the coil, the molten metal surface level of molten metal in the mold having a power supply for outputting intermittently turned on and off AC power at a predetermined period to excite the coil, using the eddy current sensor A molten metal level measurement method for measuring a molten metal,
While the power supply is operating, it is at the first logic level during the AC power output period, at the second logic level during the AC power output pause period, and continuously when the power supply is stopped . A trigger pulse signal output step of outputting a trigger pulse signal having a logic level of 2 ,
When the trigger pulse signal transits from the first logic level to the second logic level, the trigger pulse signal transits from the first logic level to the second logic level after elapse of a predetermined time. The second logic level is maintained during the first predetermined period and then returned to the first logic level for a first predetermined period or more during the second predetermined period. A timing pulse signal output step of outputting a timing pulse signal that is transitioned to and maintained at the second logic level when the logic level of 2 is maintained;
When the timing pulse signal is at the second logic level, the output of the eddy current sensor is output as it is, and the output of the eddy current sensor is sampled and held, and when the timing pulse signal is at the first logic level, the output is held. A method for measuring a molten metal level, comprising a sample-and-hold step for outputting an output of an eddy current sensor . And wrapping the coil, the molten metal surface level of molten metal in the mold having a power supply for outputting intermittently turned on and off AC power at a predetermined period to excite the coil, using the eddy current sensor A molten metal level measuring device for measuring a molten metal,
While the power supply is operating, it is at the first logic level during the AC power output period, at the second logic level during the AC power output pause period, and continuously when the power supply is stopped. a trigger pulse signal output means for outputting a trigger pulse signal which becomes the second logic level,
When the trigger pulse signal outputted from the trigger pulse signal output means transitions from a first logic level to a second logic level, the first logic level after the lapse of a predetermined time to a second logic level transition to the trigger pulse signal is maintained and the first pre-period determined second logic level while in the second logic level, and then return to the first logic level, said trigger pulse signal is first when maintaining the second predetermined period or more second logic level and the timing pulse signal output means for outputting a timing pulse signal to maintain the transition to the second logic level,
When the timing pulse signal is at the second logic level, the output of the eddy current sensor is output as it is, and the output of the eddy current sensor is sampled and held, and when the timing pulse signal is at the first logic level, the output is held. An apparatus for measuring a molten metal level, comprising: sample-and-hold means for outputting an output of an eddy current sensor. Pre-processing means for amplifying and detecting the output of the eddy current sensor in the previous stage of the sample and hold means, and removing high-frequency components;
The low-pass filter means for removing high-frequency components contained in the output of the sample-and-hold means, and the linearization means for linearizing the output of the low-pass filter means are further provided downstream of the sample-and-hold means. Molten metal level measuring device. The sample and hold signal output means comprises:
When the trigger pulse signal outputted from the trigger pulse signal output means transitions from a first logic level to a second logic level, the first logic level after the lapse of a predetermined time to a second logic level Timing to generate a timing pulse signal that transitions and maintains the second logic level while the trigger pulse signal is at the second logic level and for a first predetermined period of time and then returns to the first logic level A pulse generator ;
A timer unit for outputting a switching signal when the trigger pulse signal outputted from the trigger pulse signal outputting means maintaining the second logic level or a second predetermined time period,
When the switching signal is not output from the timer unit, the output of the timing pulse generation unit is output as it is, and when the switching signal is output from the timer unit, a switching unit that continuously outputs the second logic level; An apparatus for measuring a molten metal surface level according to claim 2 or 3 .

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