Title of Invention

A VIBRATION BASED NON-CONTACT SLAG DETECTION METHOD AND SYSTEM

Abstract

A vibration based non-contact slag detection system comprising: - a velocity transducer (1) for sensing a vibration signal from an oscillating ladle shroud (8); - a laser distance meter (2) for determining the extent of opening/closure of slide gates of said ladle shroud; and - a processor (5) located away from said ladle shroud (8) for receiving signals from said laser velocity transducer (1) and said laser distance meter (2) and performing tundish level calculation for detecting the arrival of slag by a display unit (7) provided as man/machine interface located in the caster control room.

Full Text

FIELD OF THE INVENTION The present invention relates to a vibration based non-contact slag detection method and system. The vibration-based system indicates the arrival of slag from the ladle to the tun dish. BACKGROUND OF THE INVENTION Liquid steel/slag enters the tundish via a refractory tube attached to the bottom of the ladle, called shroud. The passage of liquid steel through the shroud causes it to vibrate in a pattern which changes considerably as the slag starts to flow through it. At present the detection system is based on electromagnetic sensor, which detects the arrival of slag by determining the change in magnetic flux as the fluid through the nozzle changes from steel to slag. Such a system requires electromagnetic sensor to be fitted in each of the ladle and is thus highly susceptible to thermal and physical damages. The ladle must be specifically adapted to accept the coil and as each ladle arrives at the teeming position, a cable connection must be performed which could be hazardous in view of possible ladle reactions. Steel penetration in the nozzle block can damage the coil or impede its operation. The ladle is removed from the operation cycle to replace the damaged or malfunctioning coil. SUMMARY OF THE INVENTION The main object of the present invention therefore is to provide a low cost and low maintenance effort vibration based non-contact slag detection system. This object is achieved by locating the sensing device away from the harmful conditions of the ladle shroud and manipulator arm. The non-contact slag detection system comprises of a sensing arrangement, which is located away from the harmful conditions of the ladle shroud and its manipulator arm. A laser sensor is positioned on the shroud, which measures the velocity of the vibration using the Doppler effect. That is, it measures the wavelength of the laser beam as it is reflected from the vibrating receiver. The laser is capable of remote measurement of the velocity of vibration between the range of 10 to 1000mm/sec situated at a distance of 200 meters. The system reads the vibration signature and analyses the change that occurs at the onset of slag arrivaLThe system is thus able to discriminate between steel flow and slag flow through the ladle shroud. This is a complete application with versatile as well as user friendly graphical user interface. Here, user can interact with the main application by giving different constant parameters (e.g. initial threshold value, initial' mean value, variance and change of mean value). Thus the present invention provides a vibration based non-contact slag detection system comprising a velocity transducer 1 for sensing a vibration signal from an oscillating ladle shroud 8 and a processor 5 located away from said ladle shroud 8 for receiving signals from said laser velocity transducer 1 and said laser distance meter 2 and performing tun dish level calculation for detecting the arrival of slag. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will now be described with reference to the accompanying drawings where : Figure 1 shows in schematic form the non-contact slag detection system of the present invention; Figure 2 shows the flow diagram of the method of slag detection of the present invention. The arrangement of the non-contact slag detection system of the present invention is schematically represented in Fig. 1. A ladle 9, after receiving liquid steel tapped into it from the basic oxygen furnace, is brought onto the continuous casting floor. The molten liquid steel from the ladle 9 is poured into a refractory lined container called tun dish (not shown). The role of the tundish is to maintain a continuous supply of liquid steel to the mould even when the ladle 9 is changed. The ladle rests on a device called turret, which comprises two arms and has the rotation feature (about the vertical axis). One of the turret arms brings the filled steel ladle 9 over the tundish while the other arm of the turret, holding the empty tun dish, swings out the ladle from over the tundish to facilitate its removal and replacement by another filled ladle. In order to ensure a good quality of continuously cast product - it is important that the molten steel surface, during its transfer from ladle into the tundish, is completely insujted from coming into contact with the atmospheric air. This objective is achieved by providing a refractory tube called a shroud 8 at the bottom of the ladle 9. The other end of the shroud is dipped into the molten steel in the tundish to ensure complete insulation of falling stream from atmospheric contact. The ladle nozzle opening and closing is achieved by means of a slide gate mechanism of a hydraulic cylinder, a refractory moving plate and a fixed plate. The fixed and the movable plate both having an opening (bore) cut on them. The closed state of the ladle is achieved by moving the bore of the movable plate away from the fixed plate" bore while the open state of the ladle is achieved by aligning both the bores. The movement of the movable plate is done with the help of slide gate cylinder. The system architecture includes a laser velocity transducer I like an OMETRON VS-100 transducer for sensing the vibration signal. This is an industrially engineered interferometer, which functions as a non-contacting velocity transducer capable of remote measurement of the velocity of a continuously moving solid surface. The primary instrument output is an analog voltage proportional to surface velocity, which can be fed to external signal analysis equipment. A laser distance meter 2 is provided focused on a target plate mounted on the slide gate cylinder piston. This is needed to know the extent of slide gate opening/closure. A voltage to current converter 3 like the one from M/s Analog Devices, USA is needed for converting the signals generated by the laser velocity transducer before it is fed to current to voltage converter. This enables the proper transmission of velocity transducer signal to a long distance. A milli ampere to voltage converter 4 like the one from M/s Analog Devices, USA is used for converting the current signals obtained from the voltage to current converter to voltage signals before it is fed to a processor. A processor 5 receives voltage signals from both the level measurement velocity transducer 1 and the distance meter 2. The tundish level calculation is performed (as given below) which can then be displaced in a man/machine interface display unit 7 located in the caster control room. The processor 5 can be a Motorola 68000 processor from Pep Modular Computer, Germany with an inbuilt analog to digital converter. A 422/232 converter 6 like ADAM 4520 can be used for transmitting the output of the laser distance meter 2 obtained in the serial data form to a long distance before it is fed into the processor 5. The method of detecting the arrival of slag in the present invention has been illustrated comprehensively in Fig. 2. The steps include generating a vibration signal from an oscillating shroud 8 using a laser velocity transducer I. A signal is then generated using a laser distance meter 2 indicating the extent of opening/closure of slide gates of said ladle shroud 8. The signals from both the laser velocity transducer I and the laser distance meter 2 are then transmitted long distance before feeding to a processor 5 for performing tun dish level calculations and detect the arrival of slag in the ladle shroud 8. For transmitting the signals to long distance a voltage to current and a current to voltage converter are used in the case of the laser velocity transducer 1. A 422/232 converter 6 is used in the case of the signal from said laser distance meter 2. The vibration signal of the oscillating shroud 8 is obtained with the help of laser velocity transducer 1. During casting operation a number of noise signals get superimposed on the basic shroud vibration. These noise signals are captured (e.g. slide gate movement, turret movement, tundish movement etc) as digital input signals in to the system and are handled appropriately. The detection module is based on a fault detection and diagnosis one based on the statistical framework. When the signals are corrupted with noise that is random in nature its values are assumed in a particular probability density function. The basic approach of the calculation is to obtain "CUSUM" (cumulative sum) by calculating "log-likelihood ratio" from the vibration signals. The calculated CUSUM is compared with its threshold value. Whenever the CUSUM value exceeds the prefixed threshold value, alarm is generated that the fault (slag) has arrived. The calculation for detection is given below : Cumulative Sum (CUSUM) of log likelihood ratio statistics, Sk is defined as, where Yk is the random sequence with probability density P? (y) and ? is the scalar parameter, where, ? = ?1 and i represents a notation of a particular value of vibration signal displayed in serial data form, fed into the processor. The aim is to detect and estimate this change in the parameter 9. The algorithm is based on single statistics, the log-likelihood ratio. Let and denote expectation of the random variables under two distributions P?0 and P?0 respectively. A change in 0 is reflected as change in sign of the mean value of the log likelihood ratio. WE CLAIM 1. A vibration based non-contact slag detection system comprising: - a velocity transducer (1) for sensing a vibration signal from an oscillating ladle shroud (8); - a laser distance meter (2) for determining the extent of opening / closure of slide gates of said ladle shroud (8); and - a processor (5) located away from said ladle shroud (8) for receiving signals from said laser velocity transducer (1) and said laser distance meter (2) and performing tundish level calculation for detecting the arrival of slag by a display unit (7) provided as man / machine interface located in the caster control room. 2. The slag detection system as claimed in claim 1, wherein said laser velocity transducer (1) is OMETRON VS 100 nan-contacting velocity transducer capable of remote measurement of velocity of a continuously moving surface. 3. The slag detection system as claimed in claims 1 and 2, wherein sard laser distance meter (2) is focused on a target plate mounted on a slide gate cylinder piston of said ladle shroud (8). 4. The slag detection system as claimed in the preceding claims, wherein a voltage to current converter (3) and a milli ampere to voltage converter (4) are provided to enable proper transmission of said velocity transducer signal to a long distance for feeding the signal to said processor (5) when voltage to current converter (3) is capable of converting voltage signals of -10 volts to +10 volts to current signals before feeding to said current to voltage converter (4). 5. The slag detection system as claimed in claim 4, wherein said voltage to current and current to voltage converters (3, 4) are of M/s. Analog Device, USA. 6. The slag detection system as claimed in claim 1, wherein said processor (5) is a Motorolla 68000 processor and is provided with an inbuilt analog to digital converter for receiving voltage signals. 7. The slag detection system as claimed in claim 1, wherein a 422/232 converter (6) like ADAM 4520 is provided for transmitting the output of said laser distance meter (2) obtained in serial data form to a long distance before feeding to said processor (5). 8. A vibration based non-contact slag detection method to carryout the system according to claim 1 comprising the steps of: - generating a vibration signal from an oscillating shroud (8) using a laser velocity transducer (1); - generating a signal indicating the extent of opening / closure of slide gates of said ladle shroud (8) using a ladle distance meter (2); and - processing and analyzing said signals generated by said velocity transduder (1) and said laser distance meter (2) for performing tundish level calculations on the basis of cumulative sum of log likelihood ratio statics using a processor (5) located away from said ladle shroud (8) for detecting the arrival of slag in said ladle shroud (8) through a display unit (7) provided as man / machine interface located in the caster control room. 9. The method as claimed in claim 8, wherein the signals generated by said velocity transducer (1) and said laser distance meter (2) are transmitted long distance before feeding to said processor (5). 10. The method as claimed in claim 9, wherein the signal from said velocity transducer (1) is transmitted via a voltage / current converter (3) and a current to voltage converter (4) before feeding to processor (5). 11. The method as claimed in claim 8, wherein said signal from said laser distance meter (2) is transmitted via a 422/232 converter (6) before feeding to said processor (5). 12. A vibration based non-contact slag detection method as claimed in claim 8 wherein the cumulative sum (CUSUM) of log likelihood ratio statics is defined as in which yk is the random sequence with probability density P? (y) and ? is the scalar parameter, where and i represents a notation of a specific value of vibration signal displayed in a serial data form, fed into the processor. A vibration based non-contact slag detection system comprising: - a velocity transducer (1) for sensing a vibration signal from an oscillating ladle shroud (8); - a laser distance meter (2) for determining the extent of opening/closure of slide gates of said ladle shroud; and - a processor (5) located away from said ladle shroud (8) for receiving signals from said laser velocity transducer (1) and said laser distance meter (2) and performing tundish level calculation for detecting the arrival of slag by a display unit (7) provided as man/machine interface located in the caster control room.

Documents:

603-kol-2003-granted-abstract.pdf

603-kol-2003-granted-claims.pdf

603-kol-2003-granted-correspondence.pdf

603-kol-2003-granted-description (complete).pdf

603-kol-2003-granted-drawings.pdf

603-kol-2003-granted-examination report.pdf

603-kol-2003-granted-form 1.pdf

603-kol-2003-granted-form 13.pdf

603-kol-2003-granted-form 18.pdf

603-kol-2003-granted-form 2.pdf

603-kol-2003-granted-form 3.pdf

603-kol-2003-granted-form 5.pdf

603-kol-2003-granted-gpa.pdf

603-kol-2003-granted-reply to examination report.pdf

603-kol-2003-granted-specification.pdf