Title of Invention

SYSTEM FOR ONLINE ELONGATION MEASUREMENT AND OFF-GAUGE DETECTION FOR QUALITY APPRAISAL OF STEEL STRIP DURING SKIN PASS ROLLING

Abstract

A system for on-line measurement of elongation imparted to and off-gauge occurring in a strip subjected to rolling in a skin pass mill having an input side with an uncoiler means and an output side with a coiler means, a main stand between input side and output side to effect skin pass or temper rolling. The system when used for measuring elongation comprises measurement means on input side and output side for sensing the physical parameters of the strip and generating pulses representative of such parameters, means for processing such pulses and for calculating, indicating and recording elongation factor for quality appraisal. The system when used for determining off-gauge in a strip comprises means for measuring the gauge of the strip and for generating signals representative of measured thickness, means for processing such signals and for detecting and indicating off-gauge conditions of the strip.

Full Text

FIELD OF INVENTION The present invention relates to a system for elongation factor measurement and off-gauge detection of steel strip during skin pass rolling in a skin pass mill. BACKGROUND OF INVENTION Elongation Factor (EF) measurement in skin pass mill is very critical for applications where specific elongation is desired during skin passing process. An on-line system for precise measurement of elongation factors enables continuous monitoring over elongation imparted to strip, thereby ensuring consistency in quality as per customer requirement. The variation in gauge of strip is another important parameter which needs to be kept within a specified tolerance as per requirement of various customers. An on-line off-gauge detection and characterization system enables control of quality and reduction in customer complaints due to off-gauge. In the existing systems for measuring EF in the mill, two measurement rolls on either side of the main stand were connected to shaft-encoders. Pulses from these shaft-encoders were connected to a dedicated electronic card for computation of elongation factor and then feeding the same for correction in the elongation control panel to get the desired elongation. A dedicated software stored in the EPROM of the cards was used to carry out all the functions. This system does not have much flexibility for modifying the measurement accuracy and resolution and therefore cannot be used effectively under 2 stringent and varying rolling conditions and strip conditions where some flexibility in EF control was required. The system did not have any facility for display of the elongation factor being measured. Neither did the system have any facility for recording elongation factor and other related data for analysis by operation personnel and hence it does not aid the operation personnel in the analysis of data and take subsequent corrective actions to improve the quality. While the thickness (gauge) of the strip is being measured by a Gamma-ray based system, but there is no facility for detecting the off-gauge occurring in the strip, i.e. detecting when the gauge is deviating from the required gauge with respect to tolerance range. No system or mechanism is known for the on-line measurement of elongation factor and for on-line off-gauge detection having features like displays, alarms, recording, classification as per off-gauge lengths, elongation factor, etc. built into a single system and therefore there has been a long felt need for such a system. OBJECTS OF THE INVENTION It is therefore the principal object of the present invention to provide a system for on-line measurement of elongation imparted to strip and to detect off-gauge occurring in the strip with built in additional features which is not available presently in any existing system for dedicated measurement of elongation factor or Off-gauge detection. It is a further object of the invention to provide a system for on-line measurement of elongation factor or Off-gauge detection which is cost efficient and easy to operate. 3 SUMMARY OF THE INVENTION The present invention relates to a system for on-line measurement of elongation imparted to a strip subjected to rolling in a skin pass mill having an input side and an output side, an uncoiler means on the input side and a coiler means on the output side, a main stand between the coiler and uncoiler means for effecting skin pass or temper rolling, the system comprising measurement means, provided on either side of the main stand, said measurement means being provided with means for sensing the physical parameters of the strip and generating pulses representative of such parameters, means for processing such pulses and for measuring and indicating elongation factor for quality appraisal. The present invention also relates to a system for on-line detection of off-gauge occurring in a strip subjected to rolling in a skin pass mill having an input side and an output side, an uncoiler means on the input side and a coiler means on the output side, a main stand between the coiler and uncoiler means for effecting skin pass or temper rolling, the system comprising means for measuring the gauge of the strip and for generating signal representative of the measured thickness, means for processing such signal and for detecting and indicating off-gauge conditions of the strip. According to a preferred aspect of the invention the measurement means comprises at least two measuring rolls provided on either side of the main stand are provided. The said measurement rolls are in direct contact with the strip being rolled. The means for sensing elongation are sensors which are in contact with the measurement rolls. The sensors provided in the system are shaft-encoders. Means for thickness measurement is thickness gauge and tolerance range through thumb-wheel switches. The means for processing comprises electronic cards in programmable logic controller for computation of the elongated factor and for feeding the same for correction in the elongation control panel to get the desired elongation. 4 Likewise processing means are provided for detection and computation of the off-gauge. The system is equipped with processing means for determining elongation factor or for detecting off-gauge or both. The means for processing the pulses is a high speed counters in the programmable logic controller adapted to count the pulses. The pulses are measured and elongation factor evaluated by an application software which generates analog signal representative of the elongation factor which is then displayed in a digital display means. The analog signal representatives of the measurement of the thickness are measured and computed with respect to the desired thickness to indicate the off-gauge. DETAILED DESCRIPTION The electronic cards along with application software is adapted to compute the elongation factor are based on the following equation Where L1 & L2 are the strip lengths measured for the same length of time at the entry side and the exit side after rolling. The system for checking elongation factor measurement and off-gauge quality detection of steel strip during skin pass rolling is implemented in a flat rolling mill in which annealed cold rolled coils are fed into the rolling mill where the coil is subjected to rolling. The percentage elongation factor of the strip is output from the programmable logic Controller (PLC) in the form of analog signal from an analog out put card of the PLC and if desired displayed in display means. The actual elongation factor and the desired elongation factor is then generated by the PLC. The analog signal 5 representing the desired elongation factor is fed to an automatic elongation system for effecting necessary alterations in the rolling process. The elongation factor measurement and off-gauge detection system is illustrated below in greater details with reference to accompanying drawings in which Fig. 1 shows a block schematic diagram of the system according to the invention. Fig. 2 is a flow chart showing the main routine for sequencing of operations in the Programmable Logic Controller. Fig. 3 is a flow chart showing methodology for Elongation Factor measurement and display. Fig. 4 is a flow chart showing methodology for off-gauge detection and alarm. Fig. 5 is a schematic diagram of system implemented in a skin pass mill. The system incorporates a programmable logic controller, shaft-encoders, display devices, operator interfaces etc. A special schematic was designed for getting the desired objectives of the system and interfacing the same with the existing mill schematics. An unique application software was developed for controlling the hardware & measurement and display of various parameters. A host of useful outputs has been provided like display of EF values at operator station, alarm in case of off-gauge, coilwise MIS reports etc. DESCRIPTION OF THE MILL: The system can be implemented in any flat rolling mill where strip is imparted an interstand elongation. This system has been tested in the Skin 6 Pass Mill p 2(SPM2) of Bokaro Steel Plant (BSL). SMP2 of BSL is a single stand four high temper or skin pass mill. The input to the mill is in the form of annealed cold rolled coils from annealing line. The output of the skin pass mill goes to the shearing or slitting line for cutting into sheets or slit coils respectively or directly to be shipped as coils. The mill consists of mainly an uncoiler, a main stand and a coiler. Apart from this it also consists of two free running measurement rolls on either side of main stand. The various mill signals are connected into the regulation panels in the motor room and control panels in the PLC control room. All the controls of the mill are through Simatic S3 and S5 cards. A Gamma-ray based gauge monitor, installed after the main stand, is used to measure the thickness of the strip. The thickness value is displayed near the mill. COMPONENTS OF THE MEASUREMENT SYSTEM: The broad schematic for measurement of elongation factor, off-gauge detection and display is shown in Fig. 1. SCHEME FOR ELONGATION FACTOR MEASUREMENT AND ITS DISPLAY Elongation Factor is defined as the increase in length per unit length during skin passing or temper rolling. If L1 & L2 are the strip lengths measured for the same length of time at the entry side and the exit side after rolling, elongation factor E is given as : For a single stand mill, two free running measurement rolls also known as dummy rolls of diameters D1 & D2 are used, one on input side and the other on output side, i.e. one measurement roll between Uncoiler and the main stand and the other between the main stand and the Coiler. During rolling, the strip is in contact with these rolls. The rolls have been installed in such a manner that the wrap angle of the strip is substantially adequate. 7 Identical shaft encoders are coupled with each measurement roll, the pulses of which are counted in two counters of a programmable logic controller (PLC). The counter readings are proportional to the strip lengths before and after rolling. Using these readings, the elongation is calculated through the application software developed for the PLC. The % elongation factor of the strip is output from the PLC in form of 4-20 mA analog signal from an analog output card of PLC. This analog signal is connected to a 4 digit digital display installed near the operator's post. The average elongation factor for the whole coil as well as instantaneous values are calculated and stored for reporting purposes also. A provision of setting the desired Elongation factor for a coil is given on the operator post via a 4 digits BCD thumb wheel switch. Accordingly, the PLC can generate an analog signal corresponding to the actual measured EF and the desired EF and this signal can be fed as an input to an automatic elongation control system if desired. PRINCIPLE OF MEASUREMENT OF LENGTHS L1 & L2: Let: Dl & D2 : Diameters of measuring rolls on Uncoiler and Coiler side Zo : Pulses per revolution of shaft encoder Zl & Z2 : Counter readings corresponding to S.E. 1 and S.E.2 Nl & N2 : Number of revolution of measuring rolls. Length on entry side L1= p D1*N1= ? Dl*(Z1/Z0) Length on exit side L2 = p D2 * N2 = p D2 * (Z2/Z0) 8 Elongation Factor E' = (L2 - L1)/L1 = [? D2 (Z2/Z0) - p Dl (Zl/Zo)] / p Dl (Zl/Z0) or E' = [D2 Z2 - D1Z1] / D1Z1 Expressed in percentage E = E'* 100 MEASUREMENT & RECORDING STRATEGY: The algorithm for EF measurement, display and recording is given as a Flow Chart in Figure 3. The sequence of measurement is broadly as follows: • Set counter Z1 to a present count • Initialize counter Z2 • Up-count Z2 while down-counting Zl • Read counter Z2 when Zl becomes zero. Reading of Zl corresponds to initial length of a section of strip and reading of Z2 corresponds to length L2 after rolling. • Measurement roll diameters are stored as fixed values in the PLC memory. • Calculate Elongation Factor through equation mentioned above. • Monitor speed of mill and since slippage is maximum when speed variation is non-uniform, reject the erroneous EF readings corresponding to intermediate haphazard speed variations. • Calculation performed at 20 ms interval, with automatic setting of counter Zl to a preset count at the start of the calculation process. • Output every 1 sec, updated average value of elongation factor reading in 4-20mA to Digital Panel meter. • Output average and instantaneous values for report. 9 SCHEME FOR DETECTION OF OFF-GAUGE OCCURRING IN THE STRIP AND GENERATION OF ALARM. Off-gauge is defined as the amount by which the actual gauge deviates from the specified gauge or thickness along the length of strip. For acceptable quality, it is important that the thickness of the strip remains within a specified tolerance value as desired by a specific customer and therefore it is imperative to have continuous monitoring of the same to reduce rejection due to off-gauge. The signal from a thickness measurement device is connected to an analog input card of the PLC. Thickness desired or the tolerance value for various key customers and the set or the rated thickness of the coil can be input through 4 digits BCD thumb wheel switch. The gauge encountered is continuously compared with the desired gauge and in case of any deviation, an alarm is generated at the operator post. Both positive off-gauges, i.e. deviation more than set thickness and negative, i.e. deviation less than set thickness are monitored. Percentage off-gauge length in a coil is also calculated for reporting purpose. For calculation of lengths, once again the pulses from the shaft encoder on exit side is used. MEASUREMENT & RECORDING STRATEGY: The algorithm for Off-gauge detection & alarm and off-gauge length calculation & recording is given as a Flow Chart in Figure 4. The sequence of measurement is broadly as follows: • Input coil no. and Customer ID and specified thickness of the coil. • Select tolerance range for the specific customers from look up table in the PLC memory. 10 • Input analog signal corresponding to measured thickness from thickness gauge into the PLC. • Compare the measured thickness with set value. • Set alarm in case of off-gauge. A separate alarm is generated for positive and negative off-gauge. • Calculate percentage length of strip having off-gauge. • Output off-gauge status and calculated off-gauge lengths for MIS report. CONTROL SYSTEM FOR SEQUENCING THE OPERATIONS AND OBTAINING THE DESIRED RESULTS. The control system for sequencing the operations and achieving the above measurement functions is realized through a programmable logic controller. An Industrial computer is interfaced with the PLC via compatible communication hardware and is used as a programming terminal for the PLC and as MM1. The sequence of operations inside the PLC is broadly given as a flowchart in fig.2. The process is repeated cyclically. In case an emergency stop button is pushed, the process will be stopped at that point. The various parameters are calculated in the PLC (instantaneous, average etc.) for generating coil-wise data on shift and day basis with 30 days data in history. The period for retaining data can be modified as per requirement. Important parameters like coil number, customer ID no. for gauge tolerance, average elongation imparted to strip, average load imparted, set thickness, average thickness, +ve or -ve off gauge encountered, % off-gauge length in the coil, etc. are computed in the PLC for the purpose. Instantaneous values are calculated by the PLC to produce trends of the various parameters. In addition, dynamic mimic displays on the terminal utilizing mill and other hardware information output from the PLC enable effective operational as well as electrical supervision. 11 The system also consists a provision for on-line calibration of display meters, thumb wheel switches and other operator interfaces. Calibration is possible from a central place itself. Easy fault diagnosis of the system as well as many other vital mill parameters. HARDWARE CONFIGURATION: System design and the hardware configuration is based on the objective of achieving an accuracy of + 0.1% over a range of 0 - 5% for E.F. measurement and an accuracy of 1.0% for off-gauge length calculation. Accordingly, the measurement system consists of the following hardware: • Free running measurement rolls D1 & D2 also known as dummy rolls. • Incremental Shaft encoders SE1 & SE2. • Programmable logic controller consisting of the following modules: High speed single slot processor designed for sequential & regulatory control application and supporting multiple programming language and built in communication control, digital input module, digital output module, differential analog input module, analog output module, counter card with programmable count range & ASCII Communication card • 4 digit BCD thumb wheel switches, alarm lamps. • Analog output from thickness gauge. • Digital Panel meters for display of elongation factor and thickness. • PC serving as programming terminal for PLC. Following field signals of the mill are connected to PLC to inform the PLC about operating condition of the mill. • Mill speed reference and feedback signals • Mill control contacts for tension, mill operation, Uncoiler and Coiler operations etc. 12 Following field signals are output from the PLC : • 4-20 mA signal corresponding to E.F. range of 0 - 5.0%. • Analog signal corresponding to calculated E.F. for interfacing with E.F. control mechanism if desired. • Alarms for positive off gauge and negative off gauge. • Shaft encoder healthy • Thumb wheel switch interrogation signals SOFTWARE CONFIGURATION: • Application software was developed for measurement and display of elongation factor and off-gauge as per measurement algorithm discussed in scheme for elongation factor measurement and scheme for detection of off-gauge occuring in the strip as discussed above and illustrated in figs. 2, 3 and 4 and the same was integrated with the hardware. A standard PLC programming software package compatible with the PLC was used in the system. Apart from measurement of the above parameters, the software also incorporates routines for system health monitoring and diagnostics. Interrogating signal is generated through the application program which is output through the digital output card for reading the thumb wheel switch values. Pulses from the shaft encoders are read into the counter card of the PLC. All these readings are read cyclically and are utilized for computing the various parameters like lengths of strip at entry and exit side, thickness of strip etc. These computed values are converted to suitable engineering units and then converted to analog signals compatible with the displays provided. The data required for MIS purpose is read from the PLC into the personal computer using PLC communication card and compatible data acquisition software. Application program has been written for acquiring various mill data and hardware status and display of different values on the various dynamic screens developed on the personal computer. 13 PRINCIPAL FEATURES OF THE CONTROL SYSTEM Salient features of the system are as follows : • Computation of elongation factor with an accuracy of 0.1%. • Novel provision to take care of specific gauge tolerances specified by various key customers. • Detection of +ve as well as -ve off gauges and computation of off-gauge lengths in a coil enabling classification of coils. • Host of useful information provided for operation and electrical supervision and instantaneous analysis which is not normally available in a dedicated measuring system. • Calibration and trouble shooting of system as well as other vital mill parameters possible on-line. A specific method for the working of the invention is demonstrated below : The system has been implemented in Skin Pass Mill p 2 of cold rolling mill of SAIL/Bokaro Steel Plant. The schematic diagram of the implementation with various inputs and outputs is given in Fig.5. The specific hardware and software used to achieve the desired results is as follows : i) 2 Nos. measurement rolls of diameter 500 mm each. ii) 2 Nos. Incremental shaft encoders 2500 pulses per revolution with compatible couplings. iii) Digital display meter having 4-20mA input, 4 digit seven segment display with programmable decimal point. 14 iv) Voltage Isolator Dual channel Input 0-10V, output 0-10V. v) 3 Nos. BCD thumb wheel switches and a diode interface board specifically fabricated for low cost multiplexing of the thumb wheel signals. vi) Programmable Logic Controller type A-B 5/30 with 32 point 24V de Digital Input Module, 16 point 24V de Digital Output Module, 4 point high speed Pulse Input Module with programmable count range of (0-999999), 4 point 0-10V Analog Input Module and 4 point 4-20mA Analog Output Module. vii) Programming software consisting of 6200 Series PLC 5 s/w for A-B 5/30 PLC and RS View works with Linx for MIS. viii) Industrial grade PC and printer. ix) Communication link between PLC and PC consisting of ASCII communication card, connector and DH+ Interface cable. x) 0-10V analog signal from existing Gamma Ray thickness gauge from mill. xi) Existing Digital contacts from mill like Forward Thread (FT), Forward Run (FR), Coiler Tension (CT) ON, Uncoiler Tension (UCT) ON, Coiler Mandrel Collapse (CM), Uncoiler Mandrel Collapse (UM), Coiler retractable guide (CR) ON. xii) 0-10V analog signal from existing mill speed tacho corresponding to mill speed. The utility of the system according to the invention is as under : 15 The developed system can be utilized in any flat rolling mill where an inter-stand elongation is imparted to strip like skin pass mill, double cold reduction mills, temper roll stands of pickling lines. The system delivers immense benefit specially in skin pass mills and DCR mills where, elongation imparted is a measure of the quality of strip and where the output is directly dispatched to customers giving stress on control of off-gauge. The benefits obtained on implementation of the system are as follows: • Special high quality orders from customers requiring specific elongation can be processed. • System helps in categorizing coils with respect to its gauge enabling reduction in customer complaints due to off-gauge. • Effective operational analysis, and easy trouble shooting & maintenance of electrical mill equipment. • Cost effective solution compared with the volume of utilities available because of effective utilization of existing field sensors. • User friendly system for operation as well as maintenance personnel. ADVANTAGES OF THE SYSTEM: • Measurement of elongation factor with an accuracy of +/- 0.1%. • Detection of off-gauge with respect to specific tolerance requirements of customers. • Providing MIS for electrical and operational supervision. 16 We claim : 1. A system for on-line measurement of elongation imparted to a strip subjected to rolling in a skin pass mill having an input side and an output side, an uncoiler means on the input side and a coiler means on the output side, a main stand between the coiler and uncoiler means for effect skin pass or temper rolling, the system comprising measurement means, provided on either side of the main stand, said measurement means being provided with means for sensing the physical parameters of the strip and generating pulses representative of such parameters, means for processing such pulses and for measuring and indicating elongation factor for quality appraisal. 2. A system as claimed in claim 1, wherein the measurement means comprises at least two measurement rolls on either side of the main stand in direct contact with the strips. 3. A system as claimed in claim 1, wherein the sensors are shaft encoders. 4. A system as claimed in claim 1, wherein the means for processing comprises electronic cards, thumb wheel switch and application program for computation of the elongated factor and for feeding the same for correction in the elongation control panel to get the desired elongation, said hardware being adapted to (a) compute the elongation factor based on the following equation L2 - L1 E(Elongation factor) = L1 where L1 & L2 are the strip lengths measured for the same length of time at the entry side and the exit side after rolling. 17 5. A system for on-line detection of off-gauge occurring in a strip subjected to rolling in a skin pass mill having an input side and an output side, an uncoiler means on the input side and a coiler means on the output side, a main stand between the coiler and uncoiler means for effect skin pass or temper rolling, the system comprising means for measuring the gauge of the strip and for generating signal representative of the measured thickness, means for processing such signal and for detecting and indicating off-gauge conditions of the strip. 6. A system as claimed in claim 5, wherein the means for measuring the thickness is a gamma ray based gauge monitor being provided in the exit 7. A system as monitor a of the rolled strip claimed in claim 6, wherein the said gamma ray based gauge dapted to generate analog signal representative of the thickness 8. A system as processing count the claimed in any preceding claims, wherein the means for the signals is a programmable logic controller adapted to pulses and process analog and digital signals. 9. A system as claimed in claim 1, wherein the application software for determined elongation factor is based on logic governed by the following equations : Length on entry side L1 = p D1*N1= ? D1*(Z1/Z0) Length on exit side L2= p D2*N2= p D2*(Z2/ZO) Elongation Factor E' = (L2 - L1)/L1 = [p D2 (Z2/Z0) - p Dl (Z1/Z0)] / p Dl (Z1/Z0) or E' = [D2 Z2 - D1Z1] / D1Z1 18 Expressed E = where D1 & D2 Z0 Zl & Z2 N1 &N2 in percentage E'* 100 Diameters of measuring rolls on Uncoiler and Coiler side Pulses per revolution of shaft encoder Counter readings corresponding to S.E.1 and S.E.2 Number of revolution of measuring rolls. 10. A system as claimed in anyone of the preceding claims, wherein the means for determining the elongation factor and off gauge comprises, application software which are adapted to generate analog signals representative of the elongation factor and off-gauge which are displayed in digital display means. 11. A system as claimed in claim 10, wherein the application software has structure adapted to measure the signals generated by the gamma ray based gauge monitor and to compute the same with respect to the desired thickness of the strip to indicate the off-gauge. 12. A system as claimed in claim 10, wherein the application software for the- measurement of elongation factor follows a sequence shown in the Flow Chart in Figure 3 of the accompanying drawing. 13. A system as claimed in claim 11, wherein the application software for detemining the off-gauge follows a sequence shown in the Flow Chart shown in Figure 4 of the accompanying drawings. 14. A system aS claimed in claim 10, wherein the application softwares having sequences as shown in flow chart in figures 2, 3 and 4 are integrated with the hardware. 19 15. A system as claimed in claim 8, wherein the programmable logic controller consists of the following modules : high speed single slot processor designed for sequential & regulatory control application and supporting multiple programming language and built in communication control, digital input module, digital output module, differential analog input module, analog output module, counter card with programmable count range & ASCII Communication card. 20 16. A system as claimed in any preceding claims, comprising display devices, operator interfaces and control panels. A system for on-line measurement of elongation imparted to and off-gauge occurring in a strip subjected to rolling in a skin pass mill having an input side with an uncoiler means and an output side with a coiler means, a main stand between input side and output side to effect skin pass or temper rolling. The system when used for measuring elongation comprises measurement means on input side and output side for sensing the physical parameters of the strip and generating pulses representative of such parameters, means for processing such pulses and for calculating, indicating and recording elongation factor for quality appraisal. The system when used for determining off-gauge in a strip comprises means for measuring the gauge of the strip and for generating signals representative of measured thickness, means for processing such signals and for detecting and indicating off-gauge conditions of the strip.

Documents:

00177-cal-2000 abstract.pdf

00177-cal-2000 claims.pdf

00177-cal-2000 correspondence.pdf

00177-cal-2000 description(complete).pdf

00177-cal-2000 drawings.pdf

00177-cal-2000 form-1.pdf

00177-cal-2000 form-19.pdf

00177-cal-2000 form-2.pdf

00177-cal-2000 form-3.pdf

00177-cal-2000 pa.pdf

177-cal-2000-granted-abstract.pdf

177-cal-2000-granted-claims.pdf

177-cal-2000-granted-correspondence.pdf

177-cal-2000-granted-description (complete).pdf

177-cal-2000-granted-drawings.pdf

177-cal-2000-granted-form 1.pdf

177-cal-2000-granted-form 18.pdf

177-cal-2000-granted-form 2.pdf

177-cal-2000-granted-form 3.pdf

177-cal-2000-granted-letter patent.pdf

177-cal-2000-granted-pa.pdf

177-cal-2000-granted-reply to examination report.pdf

177-cal-2000-granted-specification.pdf