Title of Invention

AN IMPROVED METHOD FOR MEASUREMENT AND CONTROL OF ENTRY SIDE GUIDE GAP IN STEEL ROLLING PROCESS.

Abstract

In a rolling the entry side guide gap measurement and control system comprises of Incremental Encoder. CAM Switch, Programmable Controller System, Buffer amplifier, Display Unit and PC based Man Machine Interface. The new system has replaced the earlier selsyn system based guide gap measurement system which was less accurate and of obsolete technology. The new system measures the entry side guide gap with an accuracy of + 1 mm.

Full Text

FIELD OF INVENTION The present invention relates to a rolling mill having an improved entry side guide gap measurement and controlling system. More particularly, the invention relates to measurement and control of entry side guide in a hot strip mill during rolling of hot slab into strip, which would enable measurement and control of the entry side guide gap, by incremental encoder and Programmable controller based system and would thus be simple and accurate. BACKGROUND In a Hot Strip Mill, strips of different thickness and width are rolled from slab. The Hot Strip Mill of Rourkela Steel Plant, where the innovation has been developed consists of 3 Roughing stands and 6 Finishing stands. The first roughing stand (R0/V0) is a combination horizontal stand and a vertical stand. The other two roughing stands (R1 and R2) are 4 high horizontal stands. There is a delay table after R2 stand, one coil box and a crop shear at the end of the delay table. There are six numbers of 4 high finishing stands (F1 to F6) and two hydraulic down coilers. There are entry side guides before coil box, crop shear and finishing stands F1 to F6. A 10 kW AC motor through a gear (ratio 6.3 : 1) and rack & pinion arrangement adjusts the entry guide gap. Each finishing stand and the crop shear is having entry side guide to hold the material during rolling. The entry side guides gap should be 10-20 mm more than the width of the strip being rolled. The mill rolls strips whose width varies in the range of 700 to 1400 mm and thus the entry guide gap is to be adjusted as per the width of the strip. Thus precise measurement of the gap is important for rolling of strip. In a conventional rolling mill the entry guide gap was measured by synchro transmitter receiver based angle measurement system where resolution was poor and inconsistent. Such conventional manually operated system for entry guide gap measurement and control suffers from drawbacks / disadvantages which are discussed hereunder: A. Resolution is in the order of 20 mm. B. No provision for storing the gap information. C. Automatic setting of gap based on strip width information was not possible. D. Operator used to adjust the entry guide with more tolerances than norm as the correct measurement was not available. Less gap creates cobble and more gap creates wobbling of the coil back end and coil shape becomes bad. E. Jamming of mechanism could not be known, as there was no indication. F. There was no system to indicate guide extreme position and stopping the motor to prevent over travelling. OBJECTS OF THE INVENTION It is thus basic object of the present innovation to provide a precise measurement of entry side guide gap and control of the motor to prevent over travelling of the guides in a rolling mill. Yet another object of the present invention is to provide a solution in an existing rolling mill to have a record of entry side guide gap. This helps in analysis and cause of cobble. SUMMARY OF THE INVENTION Thus according to the present invention there is provided a rolling mill having an improved entry side guide gap measurement and controlling system, said rolling mill comprising: an entry side guide having a variable gap; a gap guide motor having a motor shaft; a gear box having multiple stages of reduction and connected to the motor shaft;, an encoder for sensing motor shaft rotation and generating signals ; a CAM switch connected with the motor shaft, each CAM switch adapted to sense the maximum and minimum travel of the motor and having multiple independent contacts adapted to be disposed in ON or OFF positions by adjusting the CAM with respect to a predefined relation between CAM switch angular displacement and linear displacement of guide ; a programmable controller system for calculating the entry guide gap and generating an analog output for rotating the entry guide motor in a forward and reverse direction; a signal isolation unit having a signal isolation amplifier for isolating the signal represented by the analog output generated by the programmable controller system; one or more display units for displaying the entry guide gap ; and control units for altering the entry side gap. A schematic diagram of entry guide gap measurement system is shown in Fig 1 DETAILED DESCRIPTION The system consists of the following components (i) Encoder (ii) CAM switch (iii) Gear box (iv) Programmable controller (v) Buffer amplifier (vi) Digital display (vii) Human machine Interface (viii) Open / Close contact (ix) Output contactor Encoder Encoder used here is incremental type encoder having 1024 number of pulses per revolution. The encoder is Heidhain (Germany) make. However the developed system can accept encoder of any make. The number of pulses decides the accuracy of the measurement system. The encoder generates Ua1, Ua2, Ua0 and complements of all the three pulses. In each 360° rotation of the encoder shaft, Ua1, Ua2 generates 1024 pulses, whereas Ua0 generates 1 pulse. Ua2 pulse leads Ua1 or lags Ua1, depending on the encoder shaft running forward or reverse direction. Gear box: The gear box is having four stages of reduction. The reduction in each stage is as given in Table-1. The gear box is connected with the motor shaft through love joy coupling. Speed reduction for the CAM switch is 480:1. Shaft for each gear is fabricated with EN 24 material. Material for gears is EN 9. Each shaft is mounted on bearing with bearing housing. The gear box body consist of two halves and manufactured from MS IS 2026 sheet. Gear box is foot mounted. CAM switch The CAM switch is connected with the motor shaft after a speed reduction of 480 as shown in Fig 2. Each CAM switch is having six independent contact. Each contact rated for 10 amps at 230 V AC. The switches can be made ON or OFF at any position by . adjusting the CAM. Relation between CAM switch angular displacement and^. linear displacement of guide is as derived below: Entry guide Motor speed 725 RPM Existing gear ratio 6.3:1 Therefore speed after reducer = 725 / 6.3 = 115 RPM Screw pitch = 10 mm 55.5 revolution of the screw shaft shifts each guide by 555 mm Therefore total gap = 555 * 2 = 1110 mm Minimum gap = 600 mm Maximum gap = 600 + 1110 = 1710 mm Gear ratio between motor shaft to CAM switch = 480:1 CAM switch rotation for 55.5 revolution of the screw shaft = 55.5 * 6.3 * 360 / 480 = 262 deg 262deg = 1110 mm 1 deg = 1110/262 = 4.24 mm Programmable Controller System The programmable controller system consists of CPU, Communication module, Counter module, Digital input module, Digital output module. The part number of the modules is listed in Table-2. The programmable controller system calculates the entry guide gap and generates an analog output (4-20 mA) through analog output card. This 4-20 mA corresponds to an entry guide gap of 0 to 1999 mm. Siemens make programmable controller have been used in this particular application. However programmable controller of any make having counter modules, digital input, digital output, analog output modules can be used in the measurement system. Signal isolation Unit The analog output module outputs 4-20 mA signal corresponds to entry guide gap of 0 to 1999 mm. This signal is isolated in a signal isolation amplifier. The specification of isolation amplifier is given in Table-3. Display unit The entry guide gap is displayed in the speed cabin through a seven segment type display device. Each display is having 3½ digit. Display unit accepts 4-20 mA and displays 0 to 1999 corresponds to input signal. Display unit is having span and offset adjustment facility. Display units are powered by 230 V AC. There are seven display units to show the entry guide gap for crop shear, F1 to F6 stand. OPEN / CLOSE contact The operator can increase or decrease the entry guide gap either from speed cabin or from the stand post. Two push buttons are there in speed cabin and two push buttons are in the stand post for each guide. These push buttons are designated for gap open and gap close contact. These inputs are brought to the digital inputs of the programmable controller. Output Contactor Entry guide motor can be rotated in forward or reverse direction by the programmable controller output. Two digital output lines are assigned for each entry guide motor to run in forward or reverse direction. Coil of each contactor is rated for 24 V DC and is having 4 NO + 4 NC contact. PC in the speed cabin Each entry guide gap is displayed in the speed cabin in a PC. WinCC package has been used to develop the MMI screen. DESCRIPTION OF PREFERRED EMBODIMENT Thus as detailed herein before the entry side guide gap measurement system of the invention basically utilizes (i) encoder, (ii) CAM switch, (iii) Gear box, (iv) Programmable controller, (v) buffer amplifier, (vi) Display unit and (vii) Human machine interface for operator"s guidance. The encoder system comprises (i) An incremental encoder having Ua1, Ua2, Ua0 and complements of all the three pulses output and having 1024 pulses per revolution The gear box with two output comprises (i) 1st output with a reduction of 16:1 to connect an encoder (ii) 2nd output with a reduction of 480:1 to connect a CAM switch The programmable controller comprising (i) Central Processing unit (ii) Counter module (iii) Digital input module (iv) Digital output module (v) Analog output module The buffer amplifier comprising (i) 4-20 mA input and 4-20 mA output The display unit comprises (i) 3½ digit seven segment type display (ii) Input 4-20 mA (iii) Display 0 to 1999 corresponds to 4-20 mA input signal. The measurement and control system thus provides (i) measurement of entry guide gap and display its value in engineering unit at the operator"s cabin (ii) control of entry guide motor through the inputs from CAM switch to prevent over travelling. The details of the invention, its objects and advantages are explained in great detail in relation to non limiting exemplary embodiments of the measurement system of the invention in relation to the accompanying figures wherein Fig 1 shows the schematic diagram of entry guide gap measurement system. Fig 2 is a flow chart for measuring and controlling mechanism. Reference is first invited to Fig 1 where general arrangement of the measurement system is shown. An incremental encoder (1) senses the Motor shaft rotation. The encoder signal will be processed in counter module (21) of the programmable controller (2). The gap (7) between guides (71) and (72) from the gear box (8) of gear ration 6.3:1 is calculated based on increase or decrease in count from a preset vale in the counter module. The motor output is reduced to 480:1 and a CAM switch (3) is connected on the reduced shaft. The CAM switch senses the maximum and minimum travel of the motor and passes on to Digital Input Module (23) of the programmable controller. The Digital Output Module (24) of programmable controller provides the motor forward and reverse contact output. The central processing unit (25) provides general information to the human machine interphase. Encoder signal is processed in a programmable controller. The programmable controller generates an analog output of 4-20 mA (via analogue output module (22)) corresponds to entry guide gap of 0 to 1999 mm. This signal is isolated via signal isolation unit (4) and fed to display unit at speed cabin (5). Fig 2 shows the flow chart of the measurement system. The encoder output is connected with the incremental encoder module in the PLC. Initially a preset value (PR) is loaded in the counter of the PLC. This corresponds to a gap of 1000 mm. As the encoder rotates, the counter reading (CR) changes. Number of pulse N = CR-PR Number of rotation NR =N/(1024*6.3) Gap=1000+ [NR* 10*2] It is thus possible by the way of the above-discussed system of the invention to measure the entry side guide gap. The system of the invention is thus a cost effective solution for entry side guide gap measurement and control of entry guide motor in a Hot Strip Mill. WE CLAIM 1. A rolling mill having an improved entry side guide gap measurement and controlling system, said rolling mill comprising an entry side guide having a variable gap; a gap guide motor having a motor shaft; a gear box having multiple stages of reduction and connected to the motor shaft; an encoder for sensing motor shaft rotation and generating signals ; a CAM switch adapted to be connected to the motor shaft after a predetermined speed is attained , each CAM switch adapted to sense the maximum and minimum travel of the motor and having multiple independent contacts adapted to be disposed in ON or OFF positions by adjusting the CAM with respect to a predefined relation between CAM switch angular displacement and linear displacement of guide ; a programmable controller system for calculating the entry guide gap and generating an analog output for rotating the entry guide motor in a forward and reverse direction; a signal isolation unit having a signal isolation amplifier for isolating the signal represented by the analog output generated by the programmable controller system; one or more display units for displaying the entry guide gap ; and control units for altering the enrty side gap. 2. A rolling mill having an improved entry side guide gap measurement system as claimed in claim 1, wherein the programmable controller has a counter module in which the encoder signal is processed and the gap is calculated based on increase or decrease in count from a preset value in the counter module. 3. A rolling mill having an improved entry side guide gap measurement system as claimed in claim 1, wherein the programmable controller comprises central processing unit, counter modules, digital input, digital output, analog output modules . A rolling mill having an improved entry side guide pap measurement and controlling system In a rolling the entry side guide gap measurement and control system comprises of Incremental Encoder, CAM Switch, Programmable Controller System, Buffer amplifier, Display Unit and PC based Man Machine Interface. The new system has replaced the earlier selsyn system based guide gap measurement system which was less accurate and of obsolete technology. The new system measures the entry side guide gap with an accuracy of ±1 mm.

Documents:

558-KOL-2004-FORM 27.pdf

558-kol-2004-granted-abstract.pdf

558-kol-2004-granted-claims.pdf

558-kol-2004-granted-correspondence.pdf

558-kol-2004-granted-description (complete).pdf

558-kol-2004-granted-drawings.pdf

558-kol-2004-granted-form 1.pdf

558-kol-2004-granted-form 2.pdf

558-kol-2004-granted-form 3.pdf

558-kol-2004-granted-letter patent.pdf

558-kol-2004-granted-pa.pdf

558-kol-2004-granted-reply to examination report.pdf

558-kol-2004-granted-specification.pdf