CA2348613A1 - Vertical continuous casting installation with optimized measurement of the metal level - Google Patents
Vertical continuous casting installation with optimized measurement of the metal level Download PDFInfo
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- CA2348613A1 CA2348613A1 CA002348613A CA2348613A CA2348613A1 CA 2348613 A1 CA2348613 A1 CA 2348613A1 CA 002348613 A CA002348613 A CA 002348613A CA 2348613 A CA2348613 A CA 2348613A CA 2348613 A1 CA2348613 A1 CA 2348613A1
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- 229910052751 metal Inorganic materials 0.000 title claims abstract description 112
- 239000002184 metal Substances 0.000 title claims abstract description 112
- 238000009749 continuous casting Methods 0.000 title claims abstract description 42
- 238000009434 installation Methods 0.000 title claims abstract description 28
- 238000005259 measurement Methods 0.000 title claims description 200
- 238000005266 casting Methods 0.000 claims abstract description 42
- 230000036962 time dependent Effects 0.000 claims abstract description 22
- 238000000034 method Methods 0.000 claims description 90
- 230000008569 process Effects 0.000 claims description 90
- 230000003287 optical effect Effects 0.000 claims description 21
- 230000001939 inductive effect Effects 0.000 claims description 17
- 238000002604 ultrasonography Methods 0.000 claims description 16
- 238000012546 transfer Methods 0.000 claims description 9
- 229910001338 liquidmetal Inorganic materials 0.000 claims description 8
- 229910000838 Al alloy Inorganic materials 0.000 claims description 7
- 150000002739 metals Chemical class 0.000 claims description 3
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 claims 1
- 238000005429 filling process Methods 0.000 abstract description 2
- 239000000155 melt Substances 0.000 description 13
- 230000008859 change Effects 0.000 description 10
- 230000001419 dependent effect Effects 0.000 description 5
- 238000010521 absorption reaction Methods 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000001154 acute effect Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 239000003779 heat-resistant material Substances 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 235000012054 meals Nutrition 0.000 description 1
- 229910001092 metal group alloy Inorganic materials 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 230000010363 phase shift Effects 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 230000002123 temporal effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/18—Controlling or regulating processes or operations for pouring
- B22D11/181—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level
- B22D11/185—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level by using optical means
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/18—Controlling or regulating processes or operations for pouring
- B22D11/181—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level
- B22D11/186—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level by using electric, magnetic, sonic or ultrasonic means
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
- Continuous Casting (AREA)
Abstract
A vertical continuous casting installation comprising at least one ingot mould (10) with a bottom (14) that can be lowered onto a casting table (16), a launder system (20) for conveying molten metal from a furnace into individual ingot moulds (10) and a measuring device for each ingot mould (10) in order to determine a time-dependent level of said molten metal N(t), in addition to a flow control device (30) that controls the supply of metal that is fed into the individual ingot moulds (10) on the basis of the difference between a predetermined setpoint flow Nsoll(t) and a measured time-dependent level of molten metal N(t). The measuring device consists of two measuring systems (22, 26) that work in a different physical manner. Said systems are respectively provided with a sensor (24, 28). The sensors (24, 28) are placed at a predetermined fixed distance in relation to the ingot mould (10). The first measuring system (22) has a measuring accuracy of at least ~ 2 mm in a measuring range of at least 200 mm and is used to measure the level N(t) during a first filling phase of the ingot mould (10) and the second measuring system (26) has a measuring accuracy of at least ~ 0.1 mm in a measuring range of at least 20 mm and is used to measure the level N(t) during the final phase of the filling process and the lowering phase of the casting table (16).
Description
WO 00/24535 (AMENDE;D) - 1 -Vertical Continuous Casting Installation with Optimised Measurement of the Metal Level The invention concerns a vertical continuous casting installation, in particular a vertical continuous casting installation for automatic continuous casting of aluminium alloys, comprising a control unit, several ingot moulds with bases arranged on a lowerable casting table, a transfer trough system for conveying a molten metal from a furnace into the individual. ingot moulds, a measurement device for each ingot mould in order to determine the time-dependent level N(t) of the molten metal and a flow control device to control the supply of metal into the individual ingot moulds as a function of the difference between a predetermined nominal set-point curve Nsol1(t) and the measured time-dependent level N(t;l of the molten metal.
The invention slaw concerns a process for vertical continuous casting of meals, in particular aluminium alloys, in -a casting installation comprising several ingot moulds, i_n which process the liquid metal is supplied from a furnace by way of a transfer trough system to the individual ingot moulds and by way of a flow control devfce controlled by a control unit into the ingot moulds which are initially closed during a filling phase by bases arranged on a lowerable casting t=able, where starting from an initial level. Na of the molten metal at which the molten metal level control begins, up to a predetermined start level Ns at which the lowering of the casting table in order to generate the metal continuous casting begins, and during the entire lowering phase, the time-dependent metal level N(t) in each ingot mould is measured with a measurement device and compared with a time-dependent predetermined nominal set-point curve Nsoll(tv)~~ and the metal supply to the individual ingot moulds is controlled by a flow control device according to the mime-dependent difference between the actual and the nominal metal level.
' CA 02348613 2001-04-18 Such a process and such a vertical continuous casting installation containing several ingot moulds are known for example from DE-OS 32 05 480 A1. According to the doctrine described in DE-0;3 32 05 480 Al, the metal level is S determined using as a measurement sensor a float which lies on the surface of the metal column and is made of a heat-resistant material which must be selected so that absorption of molten metal or. .contaminants is avoided.
Patent specification EP-B 0 51? 629 also describes a device of the type described initially and a corresponding process for vertical continuous casting of metals, where a capacitative sensor is used to detect the time-dependent molten metal level in the individual ingot moulds.
Capacitative level measurement takes place between the surface of the molten metal and a plate at a predetermined distance from this, which in its distance to the metal surface is guided by means of a servo motor such that the capacitance remain: constant and equal to a reference capacitance.
In a multi-line continuous casting installation, for faultless operation it is essential in particular to control the starting process, i . e. the optimum control of the metal supply t:o the individual casting units until the actual casting start which is initiated by the lowering of the casting table. In order to adjust the metal level in the individual ingot moulds during the start-up phase as quickly as possible to a predetermined level for the start of lowering of the coating table, without risk of the metal cooling, WO 98/32559 describes a process according to which the metal level :in all ingot moulds is controlled simultaneously according to a set-point curve identical for all ingot moulds, the gradient of which at the start of control is greater than the mean gradient and at the end of the start:-up phase is less than the mean gradient.
The invention slaw concerns a process for vertical continuous casting of meals, in particular aluminium alloys, in -a casting installation comprising several ingot moulds, i_n which process the liquid metal is supplied from a furnace by way of a transfer trough system to the individual ingot moulds and by way of a flow control devfce controlled by a control unit into the ingot moulds which are initially closed during a filling phase by bases arranged on a lowerable casting t=able, where starting from an initial level. Na of the molten metal at which the molten metal level control begins, up to a predetermined start level Ns at which the lowering of the casting table in order to generate the metal continuous casting begins, and during the entire lowering phase, the time-dependent metal level N(t) in each ingot mould is measured with a measurement device and compared with a time-dependent predetermined nominal set-point curve Nsoll(tv)~~ and the metal supply to the individual ingot moulds is controlled by a flow control device according to the mime-dependent difference between the actual and the nominal metal level.
' CA 02348613 2001-04-18 Such a process and such a vertical continuous casting installation containing several ingot moulds are known for example from DE-OS 32 05 480 A1. According to the doctrine described in DE-0;3 32 05 480 Al, the metal level is S determined using as a measurement sensor a float which lies on the surface of the metal column and is made of a heat-resistant material which must be selected so that absorption of molten metal or. .contaminants is avoided.
Patent specification EP-B 0 51? 629 also describes a device of the type described initially and a corresponding process for vertical continuous casting of metals, where a capacitative sensor is used to detect the time-dependent molten metal level in the individual ingot moulds.
Capacitative level measurement takes place between the surface of the molten metal and a plate at a predetermined distance from this, which in its distance to the metal surface is guided by means of a servo motor such that the capacitance remain: constant and equal to a reference capacitance.
In a multi-line continuous casting installation, for faultless operation it is essential in particular to control the starting process, i . e. the optimum control of the metal supply t:o the individual casting units until the actual casting start which is initiated by the lowering of the casting table. In order to adjust the metal level in the individual ingot moulds during the start-up phase as quickly as possible to a predetermined level for the start of lowering of the coating table, without risk of the metal cooling, WO 98/32559 describes a process according to which the metal level :in all ingot moulds is controlled simultaneously according to a set-point curve identical for all ingot moulds, the gradient of which at the start of control is greater than the mean gradient and at the end of the start:-up phase is less than the mean gradient.
Typically, the fill level of the ingot moulds for the start of the lowering process is between 120 and 200 mm. Precise control of the metal level, in particular in the lowering phase, is of decisive importance for faultless operation of a casting installation. Precise control of the metal level in the individual ingot moulds requires a correspondingly precise measurement of the fill depth. Consequently, precise metal level control of a casting installation requires precise and reproducible level measurement over a large measurement range of typically 200 mm. The importance of precise metal. level determination is increased greatly, in particular, in the refined control systems of multi-mould continuous casting installations, such as for example control systems according to WU 9$/32559 in which level control takes place with non-linear nominal set -point curves.
To improve the measurement accuracy of the level measurement of a molten metal during the initial phase of ingot mould filling, ,1P--A-08019844 describes a measurement device with two sensors fitted above the ingot mould. During the start phase of casting the molten metal into the ingot moulds, to measure the molten metal level a laser beam or ultrasound sensor is us~ad where the corresponding measurement signal is used to monitor the metal melt level and determine the time for the addition of powder. As soon as the metal melt level reaches the measurement range of the second sensor, the metal level is monitored and the time for starting the lowering process of the ingot mould base determined on the basis of the molten metal level established using a sensor based on an eddy process.
For precise fil:1 level determination inductive or capacitati.ve sensors are suitable. The necessary precision can however only be achieved with inductive sensors within a measurement range ofd approximately 30 - 50 mm. Vertical continuous casting :installations known from the state of the art therefore normally use devices in which such sensors are guided by means of precision mechanics zn co-operation with a servo or stepped motor so that the measurement range permitted for the required measurement accuracy is not exceeded. Capacitat:ive sensors can be used for large measurement ranges .of for example up to 300 mm; however, they are greatly dependent on external measurement conditions sa frequent recalibration is required.
For fill, level and distance measurements, in principle laser optical, ultrasound and microwave processes are known, Laser optical processes can only be used within limits for fill level measurement oI highly reflective measurement products. Such procsases are therefore suitable mainly for level measurement of metal alloys, for example aluminium alloys, during the filling phase of the ingot moulds and at the start of the lowering phase. During the lowering phase, a few minutes after the start of the lowering phase, a highly reflective oxide layer forms - at least in aluminium alloys - which severely hinders or renders impossible the use of laser optical processes for level measurement, Ultrasound and microwave processes according to the radar principle have a large measurement range and allow contactless level measurement but do not however have the necessary measurement accuracy, at least not for the lowering phase of the continuous casting process. Ultrasound fill level measurement processes are also highly temperature-dependent: and microwave fill level measurement processes are influenced by the measurement environment.
The invention is therefore based on the task of providing a vertical continuous casting installation of the type described initially with a precise, reliable and low cost fill Ievel measurement and a process of the type specified initially in which metal level measurement can be performed in a simple manner with high precision.
_ According to the invention, the task on which the vertical continuous casting installation is based is solved in that the measurement de~~:ice consists of two measurement systems working physically differently, each with one sensor, where 5 the first measurement system is used to measure the time--dependent molten metal level N(t) during a first filling phase from an initial time to determined by the control unit until reaching a -time tw determined by the control unit, and the second measurennent system is used to measure the time-dependent molten metal level N(t) during the subsequent filling and lowering phase, the sensors of each measurement device are fixed at a predetermined and set distance from the ingot mould, the first. measurement system has a measurement accuracy of at least + 2 mm in a measurement range of at least 200 mm, and the second measurement system has a measurement accuracy of at least + 0.1 mm in a measurement range of at least 20 mm.
The solution according to the invention is based on the idea that at the start of the continuous casting process, i.e.
during the first filling phase of the ingot mould initially closed by the base" during the remaining filling phase and during the lowerin<t process of the casting table, various level measurement devices can be used which take optimum account of the specific requirements during the various principal phases.
The invention is a:Lso based on the knowledge that a large measurement range of approximately 200 mm is required only during the first filling phase of the ingot mould initially closed by the base, and in the subsequent filling and lowering phase of the casting table a smaller measurement range of for example 15 - 20 mm is sufficient. Also during the starting phase a lower measurement accuracy is required than in the subsequent filling and lowering phase as the fill level changes very quickly in the first filling phase.
During the subsequent: filling and lowering phase in contrast a very high measurement accuracy is required.
' , CA 02348613 2001-04-18 - 5a -The term measurement range means a measurement value range in which the value: can lie in the entire range between a maximum and a minimum measurement value, where the difference between the maximum and minimum value corresponds in amount to they measurement range. For example the measurement values in a measurement z~ange of 200 mm lie in a value range between 0 and 200 mm.
A measurement device is preferred in Which the first measurement system is based on an optical, capac:itative, ultrasound or microwave process, and the second measurement system on an inductive, capacitative or optical process.
- g Particular preference is given to a measurement device in which the first measurement system is based on an optical or ultrasound or microwave process and the second measurement system on an i.nduct.i.ve or capacitative process.
The first filling phase of the ingot mould closed by the base is usually performed at the maximum possible speed so that the metal level. rises very quickly at the start of the ingot mould filling. As a result a turbulent flow is formed in the ingot mould .at the start of the filling phase sv that at the start of the filling process there is no flat melt surface so the reflection properties of the melt surface are substantially less than those of a flat surface of the same metal. For this reason, and because of the oxide skin not yet formed in this process phase, the first filling phase allows measurement: by means of laser optical processes. For the subsequent casting phase i.e, during the remaining filling phase and during the lowering process of the casting table, use of a laser optical level measurement process is not suitable for all alloys because of the'high reflection of the substantially flat molten metal surface.
According to the irwention the first measuring system can concern measuring recorders or sensors Which are based on one of the fill level measurement process described below:
a) ultrasound process b) optical process c) microwave process on the radar principle d) capacitative process.
A fill level measurement with ultrasound is based either on measurement of the run time of a sound pulse or on measurement of sound .absorption. Measurement of the run time of an ultrasound pula3e is preferred i.e. the distance of the melt surface is calculated from the run time between the signal being sent and received. The run time process normally works on t:he echo principle i.e. an electric pulse is converted into aui ultrasound pulse for example by a piezoelectric oscillator arranged on the base or the lower area of the ingot mould, where this pulse is emitted into the melt and partly reflected by the melt-air boundary layer, where the rE~flected ultrasound pulse (echo) meets a similar piezoelectric oscillator in which the echo is converted back into an electric pulse. The fill level is calculated from the run time of the sound pulse and the speed of sound. The fill level can be measured using the same echo principle: if the ultrasound emitter and receiver l0 are arranged in the air chamber above the melt surface. For ultrasound fill level measurement the temperature of the measurement media must be taken into account as the speed of sound is temperatur~a-dependent.
For fill level measurement with microwave using the radar principle, the microwave transmitter and receiver and an antenna are fitted .above the ingot mould. The surface of the molten metal partly reflects the usually frequency-modulated electromagnetic waves or pulses emitted by the microwave transmitter. The distance between antenna and melt surface is measured on t:he radar principle. In a preferred embodiment of this process, a microwave signal of constant amplitude is emitted and after reflection received again and mixed with part of the transmission signal: the frequency of the mixer output. signal is proportional to the run time and hence a measure of the distance between the transmitter and melt surface.
Optical fill level measurement processes can be interferametric distance measurement, a laser run time process or a triangulation process.
For interferometric distance measurement, the distance of the reflective melt surface from a sensox is measured. As a measurement signal either the phase angle difference between the reflected and x~on-reflected modulated laser beam is analysed or the displacement of the reflector surface (melt surface) is measured with a counter laser interferometer. In interferometric distance measurement suitably monochromatic laser beam is split on a semi-transmissive mirror into a measurement and a reference beam. The two beams are each reflected by a reflector, one fixed and one moving_ The reflecaed beams are overlaid on the semi-transmissive mirror causing interference stripes which lie transverse to the receiver and are analysed by this. A
distance change of the melt surface of ~,/4 (~, = wavelength of laser beam) causESS a maximum change in light intensity so that the change in melt level arises from the number of registered maxima ox' minima and the wavelength.
In laser run time processes, the fill level measurement can be carried out by a direct run time measurement of a light pulse or' by phase measurement_ In phase measurement the transmission signal is suitably modulated onto a carrier signal, for example in the MHz range, where measurement of the phase shift takes place after demodulation in the receiver. Direct run time measurement takes place on the radar principle where the smallest time difference is measured in the nano- to pico-second range.
In the triangulation process the fill Level measurement is traced back to an angle measurement. A tightly focussed light beam of a laser hits the melt surface at an acute angle and is reflected from this. Depending on the fill level the reflected light beam hits a certain point on the receiver i.e. for e~s;ample a position detector. The position detector can for example consist of a CCD line (charge-coupled device) which consists of a high number of light-sensitive elements (pixels) arranged in a line. with a CCD
line, this position can be detected and converted into the fill level by the angle or path difference. The place of breakdown of the reflected laser beam on the position detector moves as a function of the distance of the melt surface from the sensor.
- g _ in capacitativa fill level measurement, the capacitance is measured as a function of the melt level. The capacitance changes, for example due to the degree of cover or the distance between two given surfaces. The capacitance however also changes on a change in dielectric constant (e.g. of air) due to the introduction of molten metal. A change in capacitance is shown, for example, by the change in a capacitative resistor.
According to the invention the second measurement system concerns measurement recorders or sensors which are based on one of the fill level measurement processes described below:
e) capacitative f) inductive g) optical.
Inductive sensors are preferably based on measurement of the change in inductive resistance XL with:
XI. _ ~L, where L = N2 . p . A
S
and N = number of windings S = path length of magnetic flux lines A = area crossed by magnetic flux lines ~ = permeability of material.
According to the invention the sensors are arranged at a predetermined and fixed distance from the ingot mould, i.e.
the two measurement systems have no device for height adjustment of the sensors.
Preferably also, measurement systems are used Which have no mechanically moving parts, and in particular no mechanical precision parts. Measurement systecus which work contactless in relation to the triolten metal are also preferred.
A measurement device for each casting unit (ingot mould) is preferred in which the first measurement system is based on an optical process, in particular a triangulation process, and the second measurement system on an inductive process.
Particularly preferred is a first measurement system with a measurement range of up to 200 mm, where an accuracy of _+ i mm is achieved over the entire measurement range, The measurement accuracy of the first measurement system is typically between ~ 0.1 mm and + 2 mm, preferably between +
0.1 mm and + 1 mm.
The measurement range of the second measurement system is typically 20 to 50 mm where the measurement accuracy is typically between + 0.01 ncn~ and + 0.1 mm, preferably between + 0.01 mm and + 0.013 mm.
The combination of an optical sensor with an inductive sensor allows the provision of a compact and efficient measurement device which firstly has no expensive, sensitive and complex mechanic: al sensor guidance devices and secondly, because of the sensor properties adapted fn measurement range and precision to the individual casting phases, allows an efficient level measurement of the molten metal with sufficiently high precision. The continuous casting installation according to the invention is particularly suitable for a control algorithm for introduction of metal into the individual .ingot moulds in which non-linear nominal set-point curves are: used to control the molten metal level.
By avoiding mechanical sensor guidance devices, for level measurement conside:viably less space is required with regard to the vertical dimensions, so the casting system can be constructed more compactly.
To solve the task according to the invention with regard to the process, the measurement of the time-dependent metal level N(t) is performed by a measurement device consisting of two measurement systems working physically differerntly, ' CA 02348613 2001-04-18 where starting from an initial time to determined by the control unit until reaching a time tw determined by the control unit, a first measurement system with a first sensor is used which has an accuracy of at least _+ 2 mm in a measurement range of at least 200 mm, and for further measurement of the time-dependent metal level N(t) during the subsequent filling and lowering phase a second measurement system with a second sensor (28) is used which has an accuracy o~ at least + 0.1 mm in a measurement range of at least 20 mm, and the sensors of the two measurement systems assume a fixed position in relation to the ingot mould which is constant throughout the entire continuous casting process.
The fill phase beq.ins on introduction of the liquid metal onto the base and ends at the start of lowering of the base i.e. when the start level Ns is reached at time ts. The metal level control normally only begins when a certain metal level Na is reached at time to in the ingot mould initially closed by the base. The first fill phase indicates the period from thE: start of introduction of liquid metal into the ingot mould until time tw at which the system switches to the second measurement system for determining the metal level, where tw indicates the time at which the metal level in the :ingot mould initially closed by the base reaches a predeterm:W ed height Nw. The time between tw and is describes the second or further fill phase, or the first subsequent fill phase. The lowering phase begins on reaching the start level Ns at time is and lasts until the end or interruption of the continuous casting process.
The flow control device is controlled as a function of the difference of the measured metal level N(t) from the nominal set-point curve Nsoil(t) using a control unit where the flow control device determines the quantity of molten metal flowing into the izxg~ot mould. The control unit, for example, determines the initial time to of ingot mould filling, time tw for the change of measurement system, start time is of - ila -the lowering proce:as, the filling of the ingot mould or the quantity of the metal to be introduced into the ingot mould per time unit during the filling phase and during the lowering process, t:he lowering rate of the casting table and the control of the measurement system responsible for level measurement N(t). The control unit is also however sometimes used for monitoring and control of further process parameters e.g. coolant water supply, COx supply, supply of grain refining agents, EMC power supply, and for example automatically initiates the lowering process of the casting table.
In a preferred embodiment of the process according to the invention, the metal supply in the individual ingot moulds is controlled only until start time is directly by the time-dependent difference between the actual and nominal values of the metal level.. Thereafter, direct control of the metal supply after the start. of the lowering process takes place 7.5 as a function of t:hE~ ingot length i.e. as a function of the vertical casting table position, and based on the difference between the,actual and nominal value of the metal level. The control of the metal supply after the start time is takes place by the ingot; length-dependent difference between the actual and nominal value of the metal level. As the lowering process normally proceeds at constant rate, the ingot length increases linearly ~rith time sv that the metal supply even during the lowering process is controlled according to the time-dependent difference between the actual and nominal values of the metal ;level.
Preferably time to of the start of level control is determined by measurement of the metal level, in particular by level measurement. by means of a laser optical process.
The triggering of level measurement using the second measurement system, i.e. the time of change of measurement systems, can take p~l.ace either by a control unit on the basis of the metal level measured, or according to a preferred embodiment, in particular when using a second measurement system with an inductive measurement process, be triggered directly by the melt level in that the measurement system change takes place at a time at which the melt enters, for example, a cavity formed by an inductively working measurement coil.
The process according to the invention is suitable fvr casting installations with just one ingot mould; in particular however it is suitable for vertical continuous casting installations with several ingot moulds.
According to the invention the sensors of the two measuring systems of a casting unit assume a fixed position in relation to the ingot mould, constant throughout the entire continuous casting process, i.e. measurement is carried out without any mechanical guidance device in the farm of a height adjustment of the sensors, for example. Preferably, level measurement takes place during the first fill phase contactless in relai:ion to the molten metal.
The measurement systems comprise continuous and discontinuous action level detection systems. Consequently, the process according to the invention can be performed by a continuous and/or discontinuous level measurement. In level measurement Wlth thE: second measurement system, a cor~tinuous metal level measurE~ment is preferred. Equally preferably, measurement takes place with the first measurement system at discrete times, in particular with 3 to 10 measurement values, whereas the level measurement with the second measurement system i.s performed continuously.
In casting installations with several ingot moulds, lowering of the casting table with the bases suitably begins as soon as the start level is reached in one ingot mould.
Preferably, the metal level in the transfer trough system from the start of 'the filling phase of the bases and the ingot moulds up to and including the stationary casting phase (lowering phase) is kept at a constant level.
Further advantageous embodiments of the process according to the ~.nventivn are described in the sub-claims.
The continuous casting installation according to the invention and the process according to the invention are suitable for casting all continuously castable metals, but preferably for continuous casting of aluminium, magnesium and copper alloys_ The continuous casting installation according to the invention and the process according to the invention are however suitable in particular for continuous casting of aluminium alloys.
Further advantages, features and details of the invention arise from the examples shown in Figures 1 and 2 and the description of figures.
Figure 1 shows dia<~rammatically a simplified Cross-section through part of an ingot mould with the base retracted.
Figure 2 shows diagrammatically a nominal set-point curve of the temporal development of the metal level in another :ingot mould.
The vertical continuous casting system shown in Figure 1 contains an ingot mould i0 with a base 14 arranged on a lowerable casting taible 16, a lift/lower device 11 for the casting table which is driven by a motor 12, where the motor is controlled by way of a control unit 34, a metal level measurement device consisting of two measurement systems 22, 26, a transfer trough system 20 fvr conveying molten metal 18 from a furnace (not shown) to the ingot mould 10, where a flow control device 30 controlled by the control unit 34 determines the quantity of molten metal introduced into the ingot mould. The control unit 34 determines amongst others the starting point t~~ of ingot mould filling, the start time is of the lowering process, the filling of the ingot mould or the quantity of the metal 18 to be introduced per time unit into the ingot mould 10 during the fill phase and during the lowering process, and the lowering rate of the casting table 16, where the control unit 34 works as a function of the metal Level measurement N(t) and a predetermined nomin<31 set-point curve Nsoll(t)~
The flow control device 30 shown as an example in Figure 1 substantially consists of an inlet opening 33 in the transfer trough s;Ystem 20 which can be closed by a vertically moving stopper 32. The stopper 32 can be brought into the closed position by lowering into the inlet opening 33, or by lifting this the opening cross-section arid hence the supply of molten metal 18 into the ingot mould 10, can be enlarged accordingly. Ttie stopper 32 has a stopper rod which is guided by a~ holder device and driven by a motor 31, where the motor is c:antrolled by the control unit 34.
Before the start of casting, during a testing phase all settings in the c:astinq system are checked. When all starting conditions are fulfilled, by tipping the furnace containing the liquid metal, the transfer trough system 20 is filled to a preset metal level. As soon as a sensor - for example an inductive measurement value emitter - indicates a preset fall level in the Lransfer trough system 20, the inlet opening 33 of the transfer trough system 20 is cleared by raising the stopper 32 of the flow control device 30 and the filling of the base 14 and the ingot mould 10 with liquid metal 18 begins. The metal level N(t) in the base 14 or the ingot mould 10 is determined, e.g. PID-controlled, by way of a measurement device containing two measurement systems 22, 26.
The ingot mould 10 shown in Figure 1 is shown in closed stage i.e.. the base :lies against the ingot mould 10, where the lowering process has not yet begun. The filling phase is however almost concluded as the ingot mould 10 is already filled to close to the second sensor 28 with liquid metal 18, The first sensor 29. is at a greater distance from the base 14 than the second sensor 28. This ensures that the first sensor 24, based on a laser optical process, cannot come into contact with the melt 18. The second sensor 28, based on an inductive measurement process, however requires at least partial direct: contact with the melt 18.
Sensors 24 and 28 are connected at a fixed distance with the respective remainders of the measurement systems 22 and 26.
The two measurement systems 22 and 26 are also firmly connected together mechanically i.e. normally the two measurement systems together form one mechanical unit.
The distance of the sensors 24, 28 from the ingot mould is constant throughout the entire continuous casting process, i.e. the distance of the sensors 24, 28 from the metal surface changes constantly, in particular during the ingot mould filling phase. Consequently, the distance of sensors 24, 28 from the molten metal surfac, or the base 14, is greatest at the start of the filling phase, whereas this distance diminishes continuously or discontinuously during the filling phase and remains substantially constant after reaching the start level Ns i.e. at the start of and during the lowering process.
The embodiment shown in the drawing relates to continuous casting with a conventional ingot mould. The vertical continuous casting installation according to the invention however also includs~s other casting processes, for example casting in an electromagnetic alternating field (EMC) i.e.
using an electromagnetic ingot mould.
Figure 2 shows as an example a nominal set-point curve Nsoll(t) for the process according to the invention. As soon as the metal in a ingot mould 10 has reached a predetermined starting level tva at starting time ta, the metal level control begins on the basis of the set-point curve Nsoll~t~
and the measured m,atal level N( t ) until the metal level has reached the starting level Ns at start time is in the ingot mould 10 closed by the base 14, whereupon lowering of the casting cable to generate the metal continuous casting begins.
The nominal set-point cuxve Nsoll(t) shown in Figure 2 is polygonal and suitable for example for discontinuous control of the metal level. In an area close to the starting level lp Na, the nominal set-point curve Nsoll(t) has a gradient greater than the mean gradient (Ns - Na) / (ts - ta). In contrast the nominal set-point curve Nsoll(t) in an area lying close to the starting area Ns has a gradient less than the mean gradient.
At time tw nominal 'value Nsoll(tw) has height Nw. At time tw a switch occurs from the first measurement system 22 to the second measurement system 26. In the second measurement system 26, based on an inductive measurement process, and shown in Figure 1, tame tw is determined by the entry of the melt into a cavity formed by an inductively working measurement coil. The metal height N(t) above the base 14 during the first fill phase, i.e. until the fill height as reached the value Nw, is determined with the first measurement system a2 which has a large measurement range.
After time tw the ms~t:al height is determined with the second measurement system 26, the measurement range of which is less than that of the first measurement system 22 but which has a high measurement accuracy. The high measurement accuracy is essential in particular after time tw as thereafter the nominal set-point curve Nsoll(t) runs preferably flatter than the mean gradient and hence the metal supply to the individual casting units in a continuous casting system with several ingot moulds 10 can be controlled optimally until the actual casting start is which is initiated by lowering of the casting table 16.
_ 18 _ The start level Ns. i.e. the heiqht of the surface of the liquid metal 18 above the base 14 at start time ts, typically lies between 100 and 200 mm, and in particular between 120 and 3.90 mm. The start level Ns - starting from an initial time to -- is typically reached in a time of 20 to 90 s or preferably within 2b to 45 s.
To improve the measurement accuracy of the level measurement of a molten metal during the initial phase of ingot mould filling, ,1P--A-08019844 describes a measurement device with two sensors fitted above the ingot mould. During the start phase of casting the molten metal into the ingot moulds, to measure the molten metal level a laser beam or ultrasound sensor is us~ad where the corresponding measurement signal is used to monitor the metal melt level and determine the time for the addition of powder. As soon as the metal melt level reaches the measurement range of the second sensor, the metal level is monitored and the time for starting the lowering process of the ingot mould base determined on the basis of the molten metal level established using a sensor based on an eddy process.
For precise fil:1 level determination inductive or capacitati.ve sensors are suitable. The necessary precision can however only be achieved with inductive sensors within a measurement range ofd approximately 30 - 50 mm. Vertical continuous casting :installations known from the state of the art therefore normally use devices in which such sensors are guided by means of precision mechanics zn co-operation with a servo or stepped motor so that the measurement range permitted for the required measurement accuracy is not exceeded. Capacitat:ive sensors can be used for large measurement ranges .of for example up to 300 mm; however, they are greatly dependent on external measurement conditions sa frequent recalibration is required.
For fill, level and distance measurements, in principle laser optical, ultrasound and microwave processes are known, Laser optical processes can only be used within limits for fill level measurement oI highly reflective measurement products. Such procsases are therefore suitable mainly for level measurement of metal alloys, for example aluminium alloys, during the filling phase of the ingot moulds and at the start of the lowering phase. During the lowering phase, a few minutes after the start of the lowering phase, a highly reflective oxide layer forms - at least in aluminium alloys - which severely hinders or renders impossible the use of laser optical processes for level measurement, Ultrasound and microwave processes according to the radar principle have a large measurement range and allow contactless level measurement but do not however have the necessary measurement accuracy, at least not for the lowering phase of the continuous casting process. Ultrasound fill level measurement processes are also highly temperature-dependent: and microwave fill level measurement processes are influenced by the measurement environment.
The invention is therefore based on the task of providing a vertical continuous casting installation of the type described initially with a precise, reliable and low cost fill Ievel measurement and a process of the type specified initially in which metal level measurement can be performed in a simple manner with high precision.
_ According to the invention, the task on which the vertical continuous casting installation is based is solved in that the measurement de~~:ice consists of two measurement systems working physically differently, each with one sensor, where 5 the first measurement system is used to measure the time--dependent molten metal level N(t) during a first filling phase from an initial time to determined by the control unit until reaching a -time tw determined by the control unit, and the second measurennent system is used to measure the time-dependent molten metal level N(t) during the subsequent filling and lowering phase, the sensors of each measurement device are fixed at a predetermined and set distance from the ingot mould, the first. measurement system has a measurement accuracy of at least + 2 mm in a measurement range of at least 200 mm, and the second measurement system has a measurement accuracy of at least + 0.1 mm in a measurement range of at least 20 mm.
The solution according to the invention is based on the idea that at the start of the continuous casting process, i.e.
during the first filling phase of the ingot mould initially closed by the base" during the remaining filling phase and during the lowerin<t process of the casting table, various level measurement devices can be used which take optimum account of the specific requirements during the various principal phases.
The invention is a:Lso based on the knowledge that a large measurement range of approximately 200 mm is required only during the first filling phase of the ingot mould initially closed by the base, and in the subsequent filling and lowering phase of the casting table a smaller measurement range of for example 15 - 20 mm is sufficient. Also during the starting phase a lower measurement accuracy is required than in the subsequent filling and lowering phase as the fill level changes very quickly in the first filling phase.
During the subsequent: filling and lowering phase in contrast a very high measurement accuracy is required.
' , CA 02348613 2001-04-18 - 5a -The term measurement range means a measurement value range in which the value: can lie in the entire range between a maximum and a minimum measurement value, where the difference between the maximum and minimum value corresponds in amount to they measurement range. For example the measurement values in a measurement z~ange of 200 mm lie in a value range between 0 and 200 mm.
A measurement device is preferred in Which the first measurement system is based on an optical, capac:itative, ultrasound or microwave process, and the second measurement system on an inductive, capacitative or optical process.
- g Particular preference is given to a measurement device in which the first measurement system is based on an optical or ultrasound or microwave process and the second measurement system on an i.nduct.i.ve or capacitative process.
The first filling phase of the ingot mould closed by the base is usually performed at the maximum possible speed so that the metal level. rises very quickly at the start of the ingot mould filling. As a result a turbulent flow is formed in the ingot mould .at the start of the filling phase sv that at the start of the filling process there is no flat melt surface so the reflection properties of the melt surface are substantially less than those of a flat surface of the same metal. For this reason, and because of the oxide skin not yet formed in this process phase, the first filling phase allows measurement: by means of laser optical processes. For the subsequent casting phase i.e, during the remaining filling phase and during the lowering process of the casting table, use of a laser optical level measurement process is not suitable for all alloys because of the'high reflection of the substantially flat molten metal surface.
According to the irwention the first measuring system can concern measuring recorders or sensors Which are based on one of the fill level measurement process described below:
a) ultrasound process b) optical process c) microwave process on the radar principle d) capacitative process.
A fill level measurement with ultrasound is based either on measurement of the run time of a sound pulse or on measurement of sound .absorption. Measurement of the run time of an ultrasound pula3e is preferred i.e. the distance of the melt surface is calculated from the run time between the signal being sent and received. The run time process normally works on t:he echo principle i.e. an electric pulse is converted into aui ultrasound pulse for example by a piezoelectric oscillator arranged on the base or the lower area of the ingot mould, where this pulse is emitted into the melt and partly reflected by the melt-air boundary layer, where the rE~flected ultrasound pulse (echo) meets a similar piezoelectric oscillator in which the echo is converted back into an electric pulse. The fill level is calculated from the run time of the sound pulse and the speed of sound. The fill level can be measured using the same echo principle: if the ultrasound emitter and receiver l0 are arranged in the air chamber above the melt surface. For ultrasound fill level measurement the temperature of the measurement media must be taken into account as the speed of sound is temperatur~a-dependent.
For fill level measurement with microwave using the radar principle, the microwave transmitter and receiver and an antenna are fitted .above the ingot mould. The surface of the molten metal partly reflects the usually frequency-modulated electromagnetic waves or pulses emitted by the microwave transmitter. The distance between antenna and melt surface is measured on t:he radar principle. In a preferred embodiment of this process, a microwave signal of constant amplitude is emitted and after reflection received again and mixed with part of the transmission signal: the frequency of the mixer output. signal is proportional to the run time and hence a measure of the distance between the transmitter and melt surface.
Optical fill level measurement processes can be interferametric distance measurement, a laser run time process or a triangulation process.
For interferometric distance measurement, the distance of the reflective melt surface from a sensox is measured. As a measurement signal either the phase angle difference between the reflected and x~on-reflected modulated laser beam is analysed or the displacement of the reflector surface (melt surface) is measured with a counter laser interferometer. In interferometric distance measurement suitably monochromatic laser beam is split on a semi-transmissive mirror into a measurement and a reference beam. The two beams are each reflected by a reflector, one fixed and one moving_ The reflecaed beams are overlaid on the semi-transmissive mirror causing interference stripes which lie transverse to the receiver and are analysed by this. A
distance change of the melt surface of ~,/4 (~, = wavelength of laser beam) causESS a maximum change in light intensity so that the change in melt level arises from the number of registered maxima ox' minima and the wavelength.
In laser run time processes, the fill level measurement can be carried out by a direct run time measurement of a light pulse or' by phase measurement_ In phase measurement the transmission signal is suitably modulated onto a carrier signal, for example in the MHz range, where measurement of the phase shift takes place after demodulation in the receiver. Direct run time measurement takes place on the radar principle where the smallest time difference is measured in the nano- to pico-second range.
In the triangulation process the fill Level measurement is traced back to an angle measurement. A tightly focussed light beam of a laser hits the melt surface at an acute angle and is reflected from this. Depending on the fill level the reflected light beam hits a certain point on the receiver i.e. for e~s;ample a position detector. The position detector can for example consist of a CCD line (charge-coupled device) which consists of a high number of light-sensitive elements (pixels) arranged in a line. with a CCD
line, this position can be detected and converted into the fill level by the angle or path difference. The place of breakdown of the reflected laser beam on the position detector moves as a function of the distance of the melt surface from the sensor.
- g _ in capacitativa fill level measurement, the capacitance is measured as a function of the melt level. The capacitance changes, for example due to the degree of cover or the distance between two given surfaces. The capacitance however also changes on a change in dielectric constant (e.g. of air) due to the introduction of molten metal. A change in capacitance is shown, for example, by the change in a capacitative resistor.
According to the invention the second measurement system concerns measurement recorders or sensors which are based on one of the fill level measurement processes described below:
e) capacitative f) inductive g) optical.
Inductive sensors are preferably based on measurement of the change in inductive resistance XL with:
XI. _ ~L, where L = N2 . p . A
S
and N = number of windings S = path length of magnetic flux lines A = area crossed by magnetic flux lines ~ = permeability of material.
According to the invention the sensors are arranged at a predetermined and fixed distance from the ingot mould, i.e.
the two measurement systems have no device for height adjustment of the sensors.
Preferably also, measurement systems are used Which have no mechanically moving parts, and in particular no mechanical precision parts. Measurement systecus which work contactless in relation to the triolten metal are also preferred.
A measurement device for each casting unit (ingot mould) is preferred in which the first measurement system is based on an optical process, in particular a triangulation process, and the second measurement system on an inductive process.
Particularly preferred is a first measurement system with a measurement range of up to 200 mm, where an accuracy of _+ i mm is achieved over the entire measurement range, The measurement accuracy of the first measurement system is typically between ~ 0.1 mm and + 2 mm, preferably between +
0.1 mm and + 1 mm.
The measurement range of the second measurement system is typically 20 to 50 mm where the measurement accuracy is typically between + 0.01 ncn~ and + 0.1 mm, preferably between + 0.01 mm and + 0.013 mm.
The combination of an optical sensor with an inductive sensor allows the provision of a compact and efficient measurement device which firstly has no expensive, sensitive and complex mechanic: al sensor guidance devices and secondly, because of the sensor properties adapted fn measurement range and precision to the individual casting phases, allows an efficient level measurement of the molten metal with sufficiently high precision. The continuous casting installation according to the invention is particularly suitable for a control algorithm for introduction of metal into the individual .ingot moulds in which non-linear nominal set-point curves are: used to control the molten metal level.
By avoiding mechanical sensor guidance devices, for level measurement conside:viably less space is required with regard to the vertical dimensions, so the casting system can be constructed more compactly.
To solve the task according to the invention with regard to the process, the measurement of the time-dependent metal level N(t) is performed by a measurement device consisting of two measurement systems working physically differerntly, ' CA 02348613 2001-04-18 where starting from an initial time to determined by the control unit until reaching a time tw determined by the control unit, a first measurement system with a first sensor is used which has an accuracy of at least _+ 2 mm in a measurement range of at least 200 mm, and for further measurement of the time-dependent metal level N(t) during the subsequent filling and lowering phase a second measurement system with a second sensor (28) is used which has an accuracy o~ at least + 0.1 mm in a measurement range of at least 20 mm, and the sensors of the two measurement systems assume a fixed position in relation to the ingot mould which is constant throughout the entire continuous casting process.
The fill phase beq.ins on introduction of the liquid metal onto the base and ends at the start of lowering of the base i.e. when the start level Ns is reached at time ts. The metal level control normally only begins when a certain metal level Na is reached at time to in the ingot mould initially closed by the base. The first fill phase indicates the period from thE: start of introduction of liquid metal into the ingot mould until time tw at which the system switches to the second measurement system for determining the metal level, where tw indicates the time at which the metal level in the :ingot mould initially closed by the base reaches a predeterm:W ed height Nw. The time between tw and is describes the second or further fill phase, or the first subsequent fill phase. The lowering phase begins on reaching the start level Ns at time is and lasts until the end or interruption of the continuous casting process.
The flow control device is controlled as a function of the difference of the measured metal level N(t) from the nominal set-point curve Nsoil(t) using a control unit where the flow control device determines the quantity of molten metal flowing into the izxg~ot mould. The control unit, for example, determines the initial time to of ingot mould filling, time tw for the change of measurement system, start time is of - ila -the lowering proce:as, the filling of the ingot mould or the quantity of the metal to be introduced into the ingot mould per time unit during the filling phase and during the lowering process, t:he lowering rate of the casting table and the control of the measurement system responsible for level measurement N(t). The control unit is also however sometimes used for monitoring and control of further process parameters e.g. coolant water supply, COx supply, supply of grain refining agents, EMC power supply, and for example automatically initiates the lowering process of the casting table.
In a preferred embodiment of the process according to the invention, the metal supply in the individual ingot moulds is controlled only until start time is directly by the time-dependent difference between the actual and nominal values of the metal level.. Thereafter, direct control of the metal supply after the start. of the lowering process takes place 7.5 as a function of t:hE~ ingot length i.e. as a function of the vertical casting table position, and based on the difference between the,actual and nominal value of the metal level. The control of the metal supply after the start time is takes place by the ingot; length-dependent difference between the actual and nominal value of the metal level. As the lowering process normally proceeds at constant rate, the ingot length increases linearly ~rith time sv that the metal supply even during the lowering process is controlled according to the time-dependent difference between the actual and nominal values of the metal ;level.
Preferably time to of the start of level control is determined by measurement of the metal level, in particular by level measurement. by means of a laser optical process.
The triggering of level measurement using the second measurement system, i.e. the time of change of measurement systems, can take p~l.ace either by a control unit on the basis of the metal level measured, or according to a preferred embodiment, in particular when using a second measurement system with an inductive measurement process, be triggered directly by the melt level in that the measurement system change takes place at a time at which the melt enters, for example, a cavity formed by an inductively working measurement coil.
The process according to the invention is suitable fvr casting installations with just one ingot mould; in particular however it is suitable for vertical continuous casting installations with several ingot moulds.
According to the invention the sensors of the two measuring systems of a casting unit assume a fixed position in relation to the ingot mould, constant throughout the entire continuous casting process, i.e. measurement is carried out without any mechanical guidance device in the farm of a height adjustment of the sensors, for example. Preferably, level measurement takes place during the first fill phase contactless in relai:ion to the molten metal.
The measurement systems comprise continuous and discontinuous action level detection systems. Consequently, the process according to the invention can be performed by a continuous and/or discontinuous level measurement. In level measurement Wlth thE: second measurement system, a cor~tinuous metal level measurE~ment is preferred. Equally preferably, measurement takes place with the first measurement system at discrete times, in particular with 3 to 10 measurement values, whereas the level measurement with the second measurement system i.s performed continuously.
In casting installations with several ingot moulds, lowering of the casting table with the bases suitably begins as soon as the start level is reached in one ingot mould.
Preferably, the metal level in the transfer trough system from the start of 'the filling phase of the bases and the ingot moulds up to and including the stationary casting phase (lowering phase) is kept at a constant level.
Further advantageous embodiments of the process according to the ~.nventivn are described in the sub-claims.
The continuous casting installation according to the invention and the process according to the invention are suitable for casting all continuously castable metals, but preferably for continuous casting of aluminium, magnesium and copper alloys_ The continuous casting installation according to the invention and the process according to the invention are however suitable in particular for continuous casting of aluminium alloys.
Further advantages, features and details of the invention arise from the examples shown in Figures 1 and 2 and the description of figures.
Figure 1 shows dia<~rammatically a simplified Cross-section through part of an ingot mould with the base retracted.
Figure 2 shows diagrammatically a nominal set-point curve of the temporal development of the metal level in another :ingot mould.
The vertical continuous casting system shown in Figure 1 contains an ingot mould i0 with a base 14 arranged on a lowerable casting taible 16, a lift/lower device 11 for the casting table which is driven by a motor 12, where the motor is controlled by way of a control unit 34, a metal level measurement device consisting of two measurement systems 22, 26, a transfer trough system 20 fvr conveying molten metal 18 from a furnace (not shown) to the ingot mould 10, where a flow control device 30 controlled by the control unit 34 determines the quantity of molten metal introduced into the ingot mould. The control unit 34 determines amongst others the starting point t~~ of ingot mould filling, the start time is of the lowering process, the filling of the ingot mould or the quantity of the metal 18 to be introduced per time unit into the ingot mould 10 during the fill phase and during the lowering process, and the lowering rate of the casting table 16, where the control unit 34 works as a function of the metal Level measurement N(t) and a predetermined nomin<31 set-point curve Nsoll(t)~
The flow control device 30 shown as an example in Figure 1 substantially consists of an inlet opening 33 in the transfer trough s;Ystem 20 which can be closed by a vertically moving stopper 32. The stopper 32 can be brought into the closed position by lowering into the inlet opening 33, or by lifting this the opening cross-section arid hence the supply of molten metal 18 into the ingot mould 10, can be enlarged accordingly. Ttie stopper 32 has a stopper rod which is guided by a~ holder device and driven by a motor 31, where the motor is c:antrolled by the control unit 34.
Before the start of casting, during a testing phase all settings in the c:astinq system are checked. When all starting conditions are fulfilled, by tipping the furnace containing the liquid metal, the transfer trough system 20 is filled to a preset metal level. As soon as a sensor - for example an inductive measurement value emitter - indicates a preset fall level in the Lransfer trough system 20, the inlet opening 33 of the transfer trough system 20 is cleared by raising the stopper 32 of the flow control device 30 and the filling of the base 14 and the ingot mould 10 with liquid metal 18 begins. The metal level N(t) in the base 14 or the ingot mould 10 is determined, e.g. PID-controlled, by way of a measurement device containing two measurement systems 22, 26.
The ingot mould 10 shown in Figure 1 is shown in closed stage i.e.. the base :lies against the ingot mould 10, where the lowering process has not yet begun. The filling phase is however almost concluded as the ingot mould 10 is already filled to close to the second sensor 28 with liquid metal 18, The first sensor 29. is at a greater distance from the base 14 than the second sensor 28. This ensures that the first sensor 24, based on a laser optical process, cannot come into contact with the melt 18. The second sensor 28, based on an inductive measurement process, however requires at least partial direct: contact with the melt 18.
Sensors 24 and 28 are connected at a fixed distance with the respective remainders of the measurement systems 22 and 26.
The two measurement systems 22 and 26 are also firmly connected together mechanically i.e. normally the two measurement systems together form one mechanical unit.
The distance of the sensors 24, 28 from the ingot mould is constant throughout the entire continuous casting process, i.e. the distance of the sensors 24, 28 from the metal surface changes constantly, in particular during the ingot mould filling phase. Consequently, the distance of sensors 24, 28 from the molten metal surfac, or the base 14, is greatest at the start of the filling phase, whereas this distance diminishes continuously or discontinuously during the filling phase and remains substantially constant after reaching the start level Ns i.e. at the start of and during the lowering process.
The embodiment shown in the drawing relates to continuous casting with a conventional ingot mould. The vertical continuous casting installation according to the invention however also includs~s other casting processes, for example casting in an electromagnetic alternating field (EMC) i.e.
using an electromagnetic ingot mould.
Figure 2 shows as an example a nominal set-point curve Nsoll(t) for the process according to the invention. As soon as the metal in a ingot mould 10 has reached a predetermined starting level tva at starting time ta, the metal level control begins on the basis of the set-point curve Nsoll~t~
and the measured m,atal level N( t ) until the metal level has reached the starting level Ns at start time is in the ingot mould 10 closed by the base 14, whereupon lowering of the casting cable to generate the metal continuous casting begins.
The nominal set-point cuxve Nsoll(t) shown in Figure 2 is polygonal and suitable for example for discontinuous control of the metal level. In an area close to the starting level lp Na, the nominal set-point curve Nsoll(t) has a gradient greater than the mean gradient (Ns - Na) / (ts - ta). In contrast the nominal set-point curve Nsoll(t) in an area lying close to the starting area Ns has a gradient less than the mean gradient.
At time tw nominal 'value Nsoll(tw) has height Nw. At time tw a switch occurs from the first measurement system 22 to the second measurement system 26. In the second measurement system 26, based on an inductive measurement process, and shown in Figure 1, tame tw is determined by the entry of the melt into a cavity formed by an inductively working measurement coil. The metal height N(t) above the base 14 during the first fill phase, i.e. until the fill height as reached the value Nw, is determined with the first measurement system a2 which has a large measurement range.
After time tw the ms~t:al height is determined with the second measurement system 26, the measurement range of which is less than that of the first measurement system 22 but which has a high measurement accuracy. The high measurement accuracy is essential in particular after time tw as thereafter the nominal set-point curve Nsoll(t) runs preferably flatter than the mean gradient and hence the metal supply to the individual casting units in a continuous casting system with several ingot moulds 10 can be controlled optimally until the actual casting start is which is initiated by lowering of the casting table 16.
_ 18 _ The start level Ns. i.e. the heiqht of the surface of the liquid metal 18 above the base 14 at start time ts, typically lies between 100 and 200 mm, and in particular between 120 and 3.90 mm. The start level Ns - starting from an initial time to -- is typically reached in a time of 20 to 90 s or preferably within 2b to 45 s.
Claims (11)
1. Vertical continuous casting installation, in particular a vertical continuous casting installation for automatic continuous casting of aluminium alloys, comprising a control unit (34), several ingot moulds (10) with bases (14) arranged on a lowerable casting table (16), a transfer trough system (20) far conveying a molten metal from a furnace into the individual ingot moulds (10), a measurement device for each ingot mould (10) in order to determine the time-dependent level N(t) of the molten metal and a flow control device (30) to control the supply of metal to the individual ingot moulds (l0) as a function of the difference between a predetermined non-linear nominal set-point curve N soll(t) and the measured time-dependent level N(t) of the molten metal, characterised in that the measurement device consists of two measurement systems (22, 26) working physically differently, each with one sensor {24, 28), where the first measurement system (22) is used to measure the time-dependent molten metal level N(t) during a first filling phase from an initial time t a determined by the control unit (34) until reaching a time t w determined by the control unit (34), and the second measurement system (26) is used to measure the time-dependent molten metal level N(t) during the subsequent filling and lowering phase, the sensors (24, 28) of each measurement device are fixed at a predetermined and set distance from the ingot mould (10), the first measurement system (22) has a measurement accuracy of at least ~ 2 mm in a measurement range of at least 200 mm, and the second measurement system (26) has a measurement accuracy of at least ~ 0.1 non in a measurement range of at least 20 mm.
2. Vertical continuous casting installation according to claim 1, characterised in that the first measurement system (22) is based on an optical, capacitative, ultrasound or microwave process, and the second measurement system (26) is based on an inductive, capacitative or optical process.
3. Vertical continuous casting installation according to claim 1 or 2, characterised in that the first measurement system (22) is based on an optical or ultrasound or microwave process, and the second measurement system (26) on an inductive or capacitative process.
4. Vertical continuous casting installation according to any of claims 1 to 3, characterised in that the first measurement system (22) is based on an optical process, in particular a triangulation process, and a second measurement system (26) on an inductive process.
5. Vertical continuous casting installation according to any of claims 1 to 4, characterised in that the first measurement system (22) of each measurement device works contactless in relation to the molten metal (18).
6. Process for vertical continuous casting of metals, in particular aluminium alloys, in a casting installation comprising several ingot moulds (10), in which process the liquid metal is supplied from a furnace by way of a transfer trough system (20) to the individual ingot moulds (10) and by way of a flow control device (30) controlled by a control unit (34) into the ingot moulds (10) which are initially closed during a filling phase by bases (14) arranged tin a lowerable casting table (16), where starting from an initial level (N a) of the molten metal (18) at which a molten metal level control begins, up to a predetermined start level (N s) at which the lowering of the casting table (16) to create the metal continuous casting begins, and during the entire lowering phase, the time-dependent metal level N(t) in each ingot mould (10) is measured with a measurement device and compared with a time-dependent predetermined non-linear nominal value Nsoll(t), and the metal supply to the individual ingot moulds (10) is controlled by a flow control device (30) according to the time-dependent difference between the actual and the nominal metal level, characterised in that measurement of the time-dependent metal level N(t) is performed by a measurement device consisting of two measurement systems (22, 26) working physically differently, where starting from an initial time to determined by the control unit (34) until reaching a time t w determined by the control unit (34), a first measurement system with a first sensor is used which has an accuracy of at least ~ 2 mm in a measurement range of at least 200 mm, and for further measurement of the time-dependent metal level N(t) during the subsequent filling and lowering phase a second measurement system with a second sensor (28) is used which has an accuracy of at least ~ 0.1 mm in a measurement range of at least 20 mm, and the sensors (24, 28) of the two measurement systems (22, 26) assume a fixed position in relation to the ingot mould (10) which is constant throughout the entire continuous casting process.
7. Process according to claim 6, characterised in that the first measurement system (22) is based on an optical, capacitative, ultrasound or microwave process and the second measurement system (26) on an inductive, capacitative or optical process.
8. Process according to claim 6 or 7, characterised in that the first measurement system (22) is based on an -21a-optical process, in particular a triangulation process, and the second measurement system (26) on an inductive process.
9. Process according to any of claims 6 to 8, characterised in that the predetermined melt level (N w) at which the measurement system changes is determined by the vertical position of the lower opening of a cylindrical cavity formed by an inductively working measurement coil, where the longitudinal axis of the measurement coil lies substantially perpendicular to the surface of the molten metal.
10. Process according to any of claims 6 to 9, characterised in that the metal level N(t) is measured with the first measurement system (22) at discrete times and the metal level N(t) is measured with the second measurement system (26) continuously.
11. Process according to any of claims 6 to 10, characterised in that the metal is supplied to the ingot moulds (10) on the basis of the corresponding difference between the nominal set-point curve N soll(t) and the metal level measurement value N(t) under PID
control.
control.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP98811066.4 | 1998-10-23 | ||
| EP98811066A EP0995523A1 (en) | 1998-10-23 | 1998-10-23 | Vertical continuous casting plant with optimised molten metal level measuring |
| PCT/EP1999/007868 WO2000024535A1 (en) | 1998-10-23 | 1999-10-16 | Vertical continuous casting installation with optimized measurement of the metal level |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2348613A1 true CA2348613A1 (en) | 2000-05-04 |
Family
ID=8236404
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002348613A Abandoned CA2348613A1 (en) | 1998-10-23 | 1999-10-16 | Vertical continuous casting installation with optimized measurement of the metal level |
Country Status (7)
| Country | Link |
|---|---|
| EP (2) | EP0995523A1 (en) |
| AU (1) | AU749027B2 (en) |
| CA (1) | CA2348613A1 (en) |
| IS (1) | IS5920A (en) |
| NO (1) | NO20011978L (en) |
| WO (1) | WO2000024535A1 (en) |
| ZA (1) | ZA200102812B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20240001437A1 (en) * | 2021-01-26 | 2024-01-04 | Novelis Inc. | Cast aluminum alloys comprising calcium and related processes |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7296613B2 (en) * | 2003-06-13 | 2007-11-20 | Wagstaff, Inc. | Mold table sensing and automation system |
| WO2010078201A1 (en) * | 2008-12-31 | 2010-07-08 | Tenedora Nemak, S.A. De C.V. | Low-pressure sand casting of aluminum alloy cylinder engine parts |
| AT509736B1 (en) * | 2010-05-14 | 2012-03-15 | Inteco Special Melting Technologies Gmbh | METHOD AND DEVICE FOR CONTINUOUS RECORDING OF SLAG LEVEL IN ESU PLANTS WITH SHORT SLIDE COILS |
| DE102017111722A1 (en) | 2017-05-30 | 2018-12-06 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | METHOD AND DEVICE FOR CHARACTERIZING AN OBJECT, METHOD AND DEVICE FOR DETERMINING A COMPOSITION OF AN OBJECT, AND METHOD AND DEVICE FOR DETECTING AN ELECTRICALLY CONDUCTIVE AND / OR MAGNETIC PERMEABLE OBJECT |
| CN110508764B (en) * | 2019-09-20 | 2021-01-15 | 哈尔滨工业大学 | Semi-continuous casting equipment and semi-continuous casting method for traveling wave magnetic field/ultrasonic wave collaborative optimization of equal-outer-diameter thin-wall alloy casting |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4498521A (en) * | 1981-05-26 | 1985-02-12 | Kaiser Aluminum & Chemical Corporation | Molten metal level control in continuous casting |
| JPH0819844A (en) * | 1994-07-05 | 1996-01-23 | Sumitomo Metal Ind Ltd | Casting control method in continuous casting machine |
| US5918662A (en) * | 1995-02-28 | 1999-07-06 | Nkk Corporation | Method of controlling the operation of continuous casting and apparatus therefor |
| EP0855238A1 (en) * | 1997-01-24 | 1998-07-29 | Alusuisse Technology & Management AG | Process for vertical continuous casting of metals |
-
1998
- 1998-10-23 EP EP98811066A patent/EP0995523A1/en not_active Withdrawn
-
1999
- 1999-10-16 AU AU63407/99A patent/AU749027B2/en not_active Ceased
- 1999-10-16 EP EP99950752A patent/EP1133371A1/en not_active Withdrawn
- 1999-10-16 CA CA002348613A patent/CA2348613A1/en not_active Abandoned
- 1999-10-16 WO PCT/EP1999/007868 patent/WO2000024535A1/en not_active Ceased
-
2001
- 2001-04-05 ZA ZA200102812A patent/ZA200102812B/en unknown
- 2001-04-18 IS IS5920A patent/IS5920A/en unknown
- 2001-04-20 NO NO20011978A patent/NO20011978L/en not_active Application Discontinuation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20240001437A1 (en) * | 2021-01-26 | 2024-01-04 | Novelis Inc. | Cast aluminum alloys comprising calcium and related processes |
Also Published As
| Publication number | Publication date |
|---|---|
| AU749027B2 (en) | 2002-06-13 |
| ZA200102812B (en) | 2001-11-15 |
| IS5920A (en) | 2001-04-18 |
| AU6340799A (en) | 2000-05-15 |
| EP1133371A1 (en) | 2001-09-19 |
| EP0995523A1 (en) | 2000-04-26 |
| NO20011978D0 (en) | 2001-04-20 |
| WO2000024535A1 (en) | 2000-05-04 |
| NO20011978L (en) | 2001-06-08 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |