GB1595427A

GB1595427A - Method and apparatus for measuring and regulating the level of liquid metal within the mould of a continuous casting installation

Info

Publication number: GB1595427A
Application number: GB4505277A
Authority: GB
Original assignee: Arbed SA
Current assignee: Arcelor Luxembourg SA
Priority date: 1976-11-05
Filing date: 1977-10-28
Publication date: 1981-08-12
Also published as: BE860425A; LU76147A1; FR2369892A1; DE2748622A1; FR2369892B1

Description

(54) METHOD AND APPARATUS FOR MEASURING AND REGULATING THE LEVEL OF LIQUID METAL WITHIN THE MOULD OF A CONTINUOUS CASTING INSTALLATION (71) We, ACIÉRIES RÉUNIES DE BUR BACH-EICH-DUDELANGE S.A. ARBED, a So ciété anonyme organised under the laws of Luxembourg, of Avenue de la Liberty, Lux- embourg, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method and to an apparatus for measuring and regulating the level of liquid metal within the mould of a continuous casting installation.

The invention makes use of variations in the resonance frequency of an oscillating electrical circuit which are due to the movement of the liquid metal surface relative to a coil which is on of the active elements of the circuit .

In accordance with the invention, there is provided a device for monitoring the level of liquid metal within a mould in a continuous casting installation. the device comprising; a self-oscillating circuit having a capacitive element and a coil, the coil being concentric with, and inside, the mould and being formed by a rigid conducting tube wound in one or more turns, a fixed rigid support for mounting the coil above the liquid level in usen and means for monitoring the resonant frequency of the oscillating circuit and for detecting changes in that frequency caused by variations in the electrical characteristics of the coil as the liquid level moves relative to it.

Variation in the liquid level results in change in the resonant frequency of the oscillating circuit due to change in either the inductive or capacitive characteristics of the coil.

The coil is preferably horizontal and a little. e.g. 4 inches, above the liquid level in use.

Also in accordance with the invention is a method of monitoring the level of liquid metal within a mould in a continuous casting installation which includes using a selfoscillating circuit having a capacitive element and a coil which is disposed within the mould above the liquid level and concentric with the mould, and monitoring the resonant frequency of the oscillating circuit and de detecting changes in that frequency caused by variations in the electrical characteristics of the coil as the liquid level moves relative to it.

The capacitance of the oscillating circuit is suitably provided by a system formed by two coaxial elements, e.g. a flexible coaxial cable or two rigid concentric tubes. Such a coaxial cable can act both as a conductor and as part of the monitoring means.

In order to reduce external influences, e.g.

those due to vertical oscillatory movement of the mould or to the displacement of the liquid metal stream, the device may include an electrical static screen which surrounds the coil and is open at its end facing the liquid metal, one of the poles of the coil being connected to the screen. When the capacitance of the oscillating circuit is provided by a coaxial cable as described above, the external conductor of the coaxial cable, the reference voltage of which may be zero, can be connected to the screen.

The device preferably includes a thermocouple to determine the coil temperature and means connected to the thermocouple to compensate for frequency variations in the oscillating circuit caused by temperature changes in, and thermal deformation of, the coil.

Since the free surface of the liquid metal is in motion, the resonant frequency of the oscillating circuit will move around a reading corresponding to an average level. To stabilize the signal used to regulate the rate of feeding of metal into the mould, the circuit can include an averaging circuit.

An embodiment of the invention will now be described in detail by way of example only with reference to the accompanying drawings. in which: Fig I shows a monitoring device in accordance with the invention in use. and Fig. 2 shows a circuit for use in the device shown in Fig. 1.

Fig. I shows s a continuous casting installa- tion including a mould I which contains liquid steel 5 and which is fed by a stream of liquid steel 6. The installation is provided with a monitoring device according to the invention. the device has a coil 2. formed of four turns of diameter 4() inches mounted on a fixed support 7 so that it is disposed inside the mould l and above the surface of the liquid steel 5. The coil 2 is generally horizontal and concentric with the mould I. The support 7 is fixed to foundation X so that.

when the mould I oscillates up and down during the casting operation. the coil 2 remains stationary. One pole of the coil 2 is connected to a coaxial cable 3 of length 150 inches and having a capacitance of 240 pF.

This results in a resonance frequency Fu of approximately 4.6 MFlz.

The coil 2 is surrounded by an electrical static screen 4 which is open on the side facing the surface of the liquid steel 5. The second pole of the coil 2 is connected to the screen 4 so that both show a zero reference potential. The device also includes a thermocouple 9 which is used to monitor the temperature of the coil 2.

Using an oscillating circuit having a coil 2 and capacitance 3 as described above. a movement of the liquid level of 0.5 inches towards the coil 2 produces a change in the resonant frequency Fu of about 20 to 40 kHz.

The response is not linear.

Fig. 2 shows one embodiment of an electronic circuit in which the resonant frequency of the oscillating circuit is relatively high; in this case it may be appropriate to transpose the resonant frequency Fu of the signal into the range of acoustic frequencies, though this is not mandatory. Modulator (mod) provides at its output a signal representing the sum of and the difference between the frequency Fr of a reference signal Osc. ref. and that (Fu) of the coil signal Osc.

A band-pass filter Bp eliminates the sum of frequencies Fr and Fu. What is shown is an analogical treatment; a frequency-to-voltage converter immediately following Bp provides a voltage proportional to the input signal frequency (Fr Fti). Fu and thus (Fr Fu) are not linear functions of the distance between the coil and the liquid level, but linearity is not required for correct performance of the device.

(Fr Fu) is set to a minimum when the level of the liquid steel 5 is at its lowest or alternatively to a maximum. In this way a voltage reading provided by the converter F/V, which is in the middle of the voltage range of the device will correspond to the average level of the liquid within the mould I Since the frequency Fu which corresponds to the level of the free liquid surface varies around an average which in turn corresponds to an average level it is useful to eliminate these variations through an averager circuit AVE formed by a band-pass filter with a very low cutting frequency. Comparator (Comp) provides a signal proportional to the difference between the "average" voltage reading of circuit AVE and reference voltage reading Vr which is indicative of the liquid level and is used to drive a servo-engine which regulates the input of liquid steel into the mould For clarity Fig. I omits an indication of refractory block(s) on or in which the coil 2 is disposed.

WHAT WE CLAIM IS: I. A device for monitoring the level of liquid metal within a mould in a continuous casting installation, the device comprising, (a) a self-oscillating circuit having a capacitive element and a coil, the coil being concentric with, and inside, the mould and being formed by a rigid conducting tube wound in one or more turns (b) a fixed rigid support for mounting the coil above the liquid level in use, and (c) means for monitoring the resonant frequency of the oscillating circuit and for detecting changes in that frequency caused by variations in the electrical characteristics of the coil as the liquid level moves relative to it.

2. A device according to claim I in which the monitoring means produces signals in response to variations in the resonant frequency of the oscillating circuit, the signals being passed through a filter and used to regulate the flow of liquid metal into the mould.

3. A device according to claim 1 or 2 which comprises an electrical static screen which surrounds the coil and is open at its end facing the liquid metal, one of the poles of the coil being connected to the screen.

4. A device according to any of claims 1 to 3 in which the coil rests on or is embedded in one or more refractory blocks.

5. A device according to any of the preceding claims which includes a thermocouple to determine the coil temperature and means connected to the thermocouple to compensate for frequency variations in the oscillating circuit caused by temperature changes in and thermal deformation of the coil.

6. A method of monitoring the level of liquid metal within a mould in a continuous casting installation which includes using a self-oscillating circuit having a capacitive

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

only with reference to the accompanying drawings. in which: Fig I shows a monitoring device in accordance with the invention in use. and Fig. 2 shows a circuit for use in the device shown in Fig. 1.

Fig. I shows s a continuous casting installa- tion including a mould I which contains liquid steel 5 and which is fed by a stream of liquid steel 6. The installation is provided with a monitoring device according to the invention. the device has a coil 2. formed of four turns of diameter 4() inches mounted on a fixed support 7 so that it is disposed inside the mould l and above the surface of the liquid steel 5. The coil 2 is generally horizontal and concentric with the mould I. The support 7 is fixed to foundation X so that.

when the mould I oscillates up and down during the casting operation. the coil 2 remains stationary. One pole of the coil 2 is connected to a coaxial cable 3 of length 150 inches and having a capacitance of 240 pF.

This results in a resonance frequency Fu of approximately 4.6 MFlz.

The coil 2 is surrounded by an electrical static screen 4 which is open on the side facing the surface of the liquid steel 5. The second pole of the coil 2 is connected to the screen 4 so that both show a zero reference potential. The device also includes a thermocouple 9 which is used to monitor the temperature of the coil 2.

Using an oscillating circuit having a coil 2 and capacitance 3 as described above. a movement of the liquid level of 0.5 inches towards the coil 2 produces a change in the resonant frequency Fu of about 20 to 40 kHz.

The response is not linear.

Fig. 2 shows one embodiment of an electronic circuit in which the resonant frequency of the oscillating circuit is relatively high; in this case it may be appropriate to transpose the resonant frequency Fu of the signal into the range of acoustic frequencies, though this is not mandatory. Modulator (mod) provides at its output a signal representing the sum of and the difference between the frequency Fr of a reference signal Osc. ref. and that (Fu) of the coil signal Osc.

A band-pass filter Bp eliminates the sum of frequencies Fr and Fu. What is shown is an analogical treatment; a frequency-to-voltage converter immediately following Bp provides a voltage proportional to the input signal frequency (Fr Fti). Fu and thus (Fr Fu) are not linear functions of the distance between the coil and the liquid level, but linearity is not required for correct performance of the device.

(Fr Fu) is set to a minimum when the level of the liquid steel 5 is at its lowest or alternatively to a maximum. In this way a voltage reading provided by the converter F/V, which is in the middle of the voltage range of the device will correspond to the average level of the liquid within the mould I Since the frequency Fu which corresponds to the level of the free liquid surface varies around an average which in turn corresponds to an average level it is useful to eliminate these variations through an averager circuit AVE formed by a band-pass filter with a very low cutting frequency. Comparator (Comp) provides a signal proportional to the difference between the "average" voltage reading of circuit AVE and reference voltage reading Vr which is indicative of the liquid level and is used to drive a servo-engine which regulates the input of liquid steel into the mould For clarity Fig. I omits an indication of refractory block(s) on or in which the coil 2 is disposed.

WHAT WE CLAIM IS: I. A device for monitoring the level of liquid metal within a mould in a continuous casting installation, the device comprising, (a) a self-oscillating circuit having a capacitive element and a coil, the coil being concentric with, and inside, the mould and being formed by a rigid conducting tube wound in one or more turns (b) a fixed rigid support for mounting the coil above the liquid level in use, and (c) means for monitoring the resonant frequency of the oscillating circuit and for detecting changes in that frequency caused by variations in the electrical characteristics of the coil as the liquid level moves relative to it.
2. A device according to claim I in which the monitoring means produces signals in response to variations in the resonant frequency of the oscillating circuit, the signals being passed through a filter and used to regulate the flow of liquid metal into the mould.
3. A device according to claim 1 or 2 which comprises an electrical static screen which surrounds the coil and is open at its end facing the liquid metal, one of the poles of the coil being connected to the screen.
4. A device according to any of claims 1 to 3 in which the coil rests on or is embedded in one or more refractory blocks.
5. A device according to any of the preceding claims which includes a thermocouple to determine the coil temperature and means connected to the thermocouple to compensate for frequency variations in the oscillating circuit caused by temperature changes in and thermal deformation of the coil.
6. A method of monitoring the level of liquid metal within a mould in a continuous casting installation which includes using a self-oscillating circuit having a capacitive

element and a coil which is disposed within the mould above the liquid level and concentric with the mould, and monitoring the resonant frequency of the oscillating circuit and detecting changes in that frequency caused by variations in the electrical characteristics of the coil as the liquid level moves relative to it.
7. A monitoring device substantially as hereinbefore described with reference to the accompanying drawing.
8. A monitoring method substantially as hereinbefore described with reference to the accompanying drawing.