Title of Invention

A CONTROL SYSTEM FOR CONTINUOUS MEASUREMENT OF LIQUID STEEL LEVEL IN A MOVABLE TUNDISH

Abstract

A control system for continuous measurement of liquid steel level in a movable tundish for feeding liquid metal in a continuous casting mould comprising: a level measurement laser sensor (6) for sensing the free metal level in the tundish (3) and sending the generated signal to be processed in a processor (16); a distance meter sensor (8) focused on the upper surface of the shell of the tundish (3) to locate the instantaneous position of the vertically movable tundish (3) connected to the caster through a submerged entry nozzle (4) and sending the generated signal to a processor (16); a converter (14) for converting the current signals received from said level measurement sensor (6) and distance meter sensor (8) into voltage signals; and a processor (16) with a display unit (18) coupled to the converter for receiving the voltage signals wherein the level of the liquid steel in the tundish is measured on prior knowledge of inclination of both the sensors from vertical and maximum vertical movement (h) of the tundish obtained by carrying out calibration of the two sensors (6 and 8) through mathematical relationships.

Full Text

The present invention relates to a continuous measurement of liquid steel level in a movable tundish for feeding liquid metal in a continuous casting mould. Liquid steel, after tapping from BOF is carried in ladles to the secondary metallurgical units like basic oxygen furnace (BOF), Online purging (OLP), ladle furnace (LF) and Rheinstahl-Heraeus (RH) for refinement. Thereafter the ladle is transferred to casters. Liquid steel from the ladle is teemed through a refractory shroud into an intermediate refractory lined container, known as tundish, which in turn feeds the liquid steel into the continuous casting moulds through submerged entry nozzles. The metal level in the tundish is required to be operated, at a healthy position so that suction of tundish slag into the mould can be minimized. Maintaining the liquid steel level in the tundish will also maximize inclusion floatation. Furthermore, the tundish is moved in a vertical plane in order to safeguard the submerged entry nozzles against the preferential wearing at the interface. For measuring the level of liquid steel in the tundish, usually load cells are used which determine the weight of metal in the tundish. Such load cell based weighing system gives an indirect estimate of the level of liquid steel in the tundish. The load cell based system of indicating the level of liquid steel in tundish, however requires regular calibration. Such calibration procedures are time consuming and requires great deal of attention.The system also needs regular maintenance. The main object of the present invention therefore, is to provide a continuous level control system for measuring with greater accuracy the liquid level in the tundish without the need for frequent calibration. Another object of the present invention is to provide a continuous level control system that is robust in construction and needs very little maintenance. These and other objects are achieved by using a distance meter sensor and a level measurement sensor for measuring the free metal level in the tundish. The distance meter sensor can be a laser distance meter manufacured by Leica,Switzerland. For the level measurement sensor a high temperature ievel measurement sensor manufactured by Riegl laser measurement system can be used. The optical unit in the high temperature level measurement laser sensor device senses the free metal level in the tundish and sends the signal to the level sensor electronic circuitry of the device. The laser distance meter is focussed on the upper surface of the tundish shell for locating the instantaneous position of the tundish in the vertical plane. The above mentioned two sensors generate current signals in milli-amperes which can be converted to voltage signals with the help of a signal converter. The two signals from the two sensors in conjunction dynamically provide the instantaneous metal level in the tundish. For this, the voltage signals from the level measurement and distance meter sensors are processed in a processor with a built in analog to digital converter. The liquid metal level in the tundish can then be displayed in a display unit connected to the signal processor. The invention thus provides a continuous level control system for measuring the liquid steel level in a tundish, comprising a ladle with a ladle nozzle shroud, an intermediate container or tundish for receiving liquid steel from the ladle, said tundish being provided with a submerged entry nozzle and movable in a vertical plane through a distance characterized in that said system is provided with a level measurement sensor for sensing the free metal level in the tundish and generating a signal, a distance meter sensor for focussing on the upper surface of the tundish to locate the instantaneous position of the tundish in the vertical plane, a converter for converting the current signals received from said level measurement sensor and distance meter sensor into voltage signals and a processor coupled to said converter for receiving said voltage signals and calculating therefrom the level of liquid steel in said tundish. The invention will now be described in detail with the help of the accompanying drawings, where : Figure 1 shows the weight of steel in a tundish as a function of metal fill height of the tundish, Figure 2 shows schematically the layout of a continuous casting facility, Figure 3 shows in block diagram form the layout of the system of present invention, Figure 4 shows schematically the calibration layout of the present invention. As shown in Figure 2, in a typical casting facility, liquid steel from the steel ladle 1 is teemed through a refracting ladle nozzle shroud 2 into an intermediate container 3. This intermediate container 3 is refractory lined and is known as tundish. This tundish 3 in turn feeds the liquid steel through a submerged entry nozzle 4 into the continuous casting moulds S. The tundish is moved in a vertical plane through distance H for safeguarding the submerged entry nozzles 4 against wear at the interface, The level control system comprises a level measurement laser sensor 6, as shown in Figure 3. This level measurement laser sensor 6 is provided with high temperature level sensor electronics and an optical unit. The electronics may be LD90-3100 HT-GF and the optical unit MK 56 in a Riegl Laser Measurement Systems, GmbH make laser sensor and their details are not shown in Figure 3. The optical unit of the level measurement laser sensor 6 senses the free metal level in the tundish 3 and sends a signal to the high temperature level sensor electronics. A distance meter sensor 8 is focussed on the upper surface of the shell of the tundish 3, to locate the instantaneous position of the tundish 3 in the vertical plane. The distance meter sensor 8. can be a Leica Switzerland make laser distance meter. The two signals generated by the level management laser sensor 6 and laser distance meter S are current signals of 4 to 20 milli amperes. These are converted to voltage signals with the helpof a converter 14 before being fed to a processor 16. The processor 16 is provided with a built-in analog to digital (A/D) converter (not shown) for receiving the signals from the level measurement sensor 6 and distance meter sensor 8, now converted into voltage signals. The processor 16 for calculating and displaying in a visual display unit 18 the metal level of tundish 3 can be a Motorola 68000 processor. The tundish level calculations require prior knowledge of inclinations (from vertical) of both the sensors, which is obtained by carrying out calibration of the two sensors. The calibration layout is schematically shown in Figure 4. The maximum vertical movement (h) of the tundish is known. The two sensors inclinations can be estimated by using the following formulae: Where, 8 = Level measurement laser sensor's inclination from the R vertical B = Laser distance-meter sensor's inclination from the L vertical RT - Level measurement laser sensor's reading of the bottom of B the tundish when it is at its lower most position in the vertical plane. RT = Level measurement laser sensor's reading of the bottom of T the tundish when it is at its upper most position in the vertical plane LT = Laser distance measurement reading of the upper surface of B the tundish when it is at its lower most position in the vertical plane LT = Laser distance measurment reading of the upper surface of T the tundish when it is at its upper most position in the vertical plane. In order to obtain the height of steel filled in the tundish fallowing formula is used : RTT x cose +(cosθL x(Dist.Meas Reading- LTT)-(LevelDistRead,xcosθR) From the three dimensional structural drawing of the tundish volume of steel at different selected fill heights of metal can be obtained. Knowing the density of liquid steel volume is converted to weight unit. A piecewise non-linear regression is then carried out between the height of metal and the corresponding calculated tundish weight. Table 1 shows the result of the regression for a tundish used for slab casting. WE CLAIM 1. A control system for continuous measurement of liquid steel level in a movable tundish for feeding liquid metal in a continuous casting mould comprising: - a level measurement laser sensor (6) for sensing the free metal level in the tundish (3) and sending the generated signal to be processed in a processor (16); - a distance meter sensor (8) focused on the upper surface of the shell of the tundish (3) to locate the instantaneous position of the vertically movable tundish (3) connected to the caster through a submerged entry nozzle (4) and sending the generated signal to a processor (16); - a converter (14) for converting the current signals received from said level measurement sensor (6) and distance meter sensor (8) into voltage signals; and a processor (16) with a display unit (18) coupled to the converter for receiving the voltage signals wherein the level of the liquid steel in the tundish is measured on prior knowledge of inclination of both the sensors from vertical and maximum vertical movement (h) of the tundish obtained by carrying out calibration of the two sensors (6 and 8) through the equations Where, θR = Level measurement laser sensor's inclination from the vertical θL = Laser distance-meter sensor's inclination from the vertical RTB = Level measurement laser sensor's reading of the bottom of the tundish when it is at its lower most position in the vertical plane. RTT = Level measurement laser sensor's reading of the bottom of the tundish when it is at its upper most position in the vertical plane. LTB Laser distance measurement reading of the upper surface of the tundish when it is at its lower most position in the vertical plane. LTT Laser distance measurement reading of the upper surface of the tundish when it is at its upper most position in the vertical plane. 2. The system as claimed in claim 1, wherein said processor 16 is connected to a visual display unit 18 for displaying a calculated level of liquid steel in the tundish. 3. The system as claimed in the preceding claims wherein said high temperature level laser sensor comprises high temperature level sensor electronics LD90-3100 HT-GF for sending a signal generated by said laser sensor 6. 4. A control system as claimed in claim 1 wherein the height of steel filled in the tundish being measured by the equation RTTx COSΘR + (cosθLx (Dist.Meas Reading - LTT) - (LevelDistRead xcosθR) 5. A control system as claimed in claim 1 wherein the weight of tundish is measured from the obtained metal level in the tundish from the three dimensional structural drawing of the tundish at different selected fill heights of metal and the obtained volume of the liquid metal is converted to weight unit from the density of liquid steel and on carrying out a piecewise non-linear regression between the height of metal and corresponding calculated tundish weight to generate a regression equation h = 7 x 10-6 h2 + 0.004 h - 0.0086 where h is height of liquid steel from the bottom of the tundish. Dated this 30th day August 2002 A control system for continuous measurement of liquid steel level in a movable tundish for feeding liquid metal in a continuous casting mould comprising: a level measurement laser sensor (6) for sensing the free metal level in the tundish (3) and sending the generated signal to be processed in a processor (16); a distance meter sensor (8) focused on the upper surface of the shell of the tundish (3) to locate the instantaneous position of the vertically movable tundish (3) connected to the caster through a submerged entry nozzle (4) and sending the generated signal to a processor (16); a converter (14) for converting the current signals received from said level measurement sensor (6) and distance meter sensor (8) into voltage signals; and a processor (16) with a display unit (18) coupled to the converter for receiving the voltage signals wherein the level of the liquid steel in the tundish is measured on prior knowledge of inclination of both the sensors from vertical and maximum vertical movement (h) of the tundish obtained by carrying out calibration of the two sensors (6 and 8) through mathematical relationships.

Documents:

510-cal-2002-granted-abstract.pdf

510-cal-2002-granted-claims.pdf

510-cal-2002-granted-correspondence.pdf

510-cal-2002-granted-description (complete).pdf

510-cal-2002-granted-drawings.pdf

510-cal-2002-granted-examination report.pdf

510-cal-2002-granted-form 1.pdf

510-cal-2002-granted-form 13.pdf

510-cal-2002-granted-form 18.pdf

510-cal-2002-granted-form 2.pdf

510-cal-2002-granted-form 3.pdf

510-cal-2002-granted-gpa.pdf

510-cal-2002-granted-pa.pdf

510-cal-2002-granted-reply to examination report.pdf

510-cal-2002-granted-specification.pdf