Title of Invention	A METHOD FOR CONTROLLING TENSION ROLLING IN CONTINUOUS CASTING
Abstract	A control system for minimum tension in continuous casting comprising means for extrapolation of the current comparison techniques for dynamic in-stock control, means comprising recipe based control for seven quantisation levels, means for an integrated cobble detection and means for on-line impact drop, recovering time etc. for preventive maintenance of equipments. It is possible by way of the above system to automatically control speeds of the multiple stands continuous billets with dynamic rolling conditions and without operators intervention. The control provides for elimination of mill catastrophic conditions viz. looping/skidding due to excessive compression/tension respectively. Moreover, the system assists in achieving around 40%-50% improvement in length variations and provide for simple and effective operation of rolling mills.

Title of Invention

A METHOD FOR CONTROLLING TENSION ROLLING IN CONTINUOUS CASTING

Abstract

A control system for minimum tension in continuous casting comprising means for extrapolation of the current comparison techniques for dynamic in-stock control, means comprising recipe based control for seven quantisation levels, means for an integrated cobble detection and means for on-line impact drop, recovering time etc. for preventive maintenance of equipments. It is possible by way of the above system to automatically control speeds of the multiple stands continuous billets with dynamic rolling conditions and without operators intervention. The control provides for elimination of mill catastrophic conditions viz. looping/skidding due to excessive compression/tension respectively. Moreover, the system assists in achieving around 40%-50% improvement in length variations and provide for simple and effective operation of rolling mills.

Full Text	The present invention relates to a method for controlling minimum tension rolling at continuous mills. A continuous mill is a mill in which the stock is simultaneously rolled in more than one stands i.e. the distance between the stands is quite less as compared to the length of the whole stock. In such a mill, it is necessary to regulate the volume throughput through each stand as per the desired operating norms, thereby controlling interstand tension. For tension free rolling (Equal volume throughput from each stand): where A1 = Area of cross section of 1th stand (roll gap); V1 = Linear Velocity of the billet at the stand; A1+1 and V1+1 are same for the next stand. As evident, equation (I) can be realised either by controlling A1 & A1+1 (Roll Gap Control) or by controlling V1 & V1+1 , in other words V1 & V1+1 (Speed Control). However, the former control can be exercised only when there is a deviation from the set roll gap. Else, it shall affect the breakdown sequence. Moreover, for different shape rolling sections the effective diameters are different. Therefore, the latter approach is more popular for tension control. Thus tension control connotes a tandemness of material flow amongst all stands and the key to tension control is to sustain this tandemness despite parametric variations. The latter implies all tangible variants such as temperature, grade of the stock, roll gap, input profile, mechanical variants such as roll eccentricity etc. These can be measured up by suitable integro-differential equations. However, parametric variations also encompass certain imprecisions which are difficult to quantify such as subcatenous blow-holes, both instock and interstock variation in lateral temperature profile due to nonunique soaking regimes etc. 2 A more perceptible delineation for understanding of interstand tension/ compression situations is through push-pull concepts. If the succeeding stand is pulling the stock more that what the preceeding stand is able to cater, then we have a situation of tension in that interstand. It implies that there is a deficit of material in It, since the volume taken out by the succeeding stand is more that what supplied by the preceeding stand. Such greater deficits have a possibility of twisting of the stock and underfilling the passes leading to mill jamming and dimensional aberrations respectively. Whreas, If the preceeding .stand is pushing the stock more that what the succeeding stand is able to cater, then we have a situation of compression in that interstand. It implies that there is a surplus of material in it since the volume taken out by the preceeding stand is more that what supplied by the succeeding stand. Such greater surpluses have a possibility of looping of the stock and overfilling of passes leading to mill jamming and dimensional aberrations (fins) respectively. Presently there exists different methods for measurement of tension, whether directly or indirectly, with each method having Its own merit and demerit. For example, the Forward Slip Technique (FST) though highly accurate is expensive and also necessitates accurate assessment of modulus of rigidity at the stock temperature. The Ratio Control Technique (RCT) which is in vogue these days requires mounting of pressure cells in the stands for rolling force measurement; whereas the rolling torque is calculated by the main armature current. Since the latter is the most fundamental parameter of the Current Comparison Technique (CCT), it becomes well obvious the significance of main armature current in tension estimation at continuous mills Techniques of Tension Estimation : (i) CCT: The CCT which has been picked up here offers, a low cost solution for indirect tension measurement. It assumes that the main armature current is a true reflection of the torque requirement and by measuring this current at close intervals periodically and by instantiating them with some biting instances we can have a by and large accurate estimation of the tension. 3 There is no changes in mill structure i.e. no additional mountings (as with FST and RCT). The close monitoring and control of speed and current shifts CCT Into the domain of automation and control to a great extent. In other techniques too, once the tension is measured / estimated state-space control models come into picture with high-level control strategies and process models. The so called limitation of this technique is that it is limited to only head end control i.e. it is not able to handle the turbulences occurring after the head end stabilisation. However; a novel approach has been developed in this work so as to extrapolate CCT over the entire rolling of stock. However, this technique necessitates that there should not be any pseudo current generated due to mechanical obstructions, eccentricity etc. Another advantage of CCT is that it is quite generic, i.e. it can be applied to any type of section without changing the hardware/software or any fresh mounting. (ii) FST: FST is an indirect method based on volume and speed ratios in the roll gap. In simple words, In this method the tension is estimated by measurement of the forward slip in the interstand. After some standard assumptions and approximations it can be shown the following : Where, S (t) = tension in the interstand at any instant T EB = Modulus of elasticity Lo = Strip length between stands v(t) = Linear velocity at entry / exit The stock speed is measured and stored until the strip enters the subsequent stands. For FTC. the control adjusts the speed of the previous stand in such a fashion so as to restore the longitudinal force-free value. These change in velocities are extremely small. Therefore, for error free tension estimation, the velocity measuring equipment should be a highly accurate one. 4 This necessitates use of Doppler velocitimeters each at entry and exit of every stand. For several stands the cost is too high and moreover these remain vulnerable to milt repairs and cobbles. One more difficulty with this technique is that at temperatures above 800°C, it is somewhat difficult to predict EB (iii) RCT: RCT involves measurement of a) rolling force (roll separating force) by pressure cells I pressductors I load cells etc. b) rolling torque by main armature current and /or field current & speed and c) lever arm. The basic principle of RCT is that the ratio of rolling force to deformation torque provides an accurate index of interstand tension. In actual rolling the effect of the deformation torque is much more pronounced on interstand tension than that of the rolling force which itself changes very little. Same modalities of cascaded control is done here too i.e. This ratio is stored in the memory and after the biting of the next stand the previous stand speed is so adjusted so as to restore the ratio value to the previous one. This method is more accurate than CCT, but involves additional mounting of pressure cells etc. This technique is in vogue as evinced in the literature survey. (iv) CMFT: With the advent of mass flow gauges, the tension controlled is achieved through speed adjustments so as to have equal mass throughput from each stand. However, these are very expensive and calls for a lot of improvisation with sections of different shapes. It is also disclosed in "Speed Control of Rolling Mills", Raymond G Brister, Control Techniques Asia Pacific (CTAP) -Singapore, Asia Steel 1996, pp 219 that Control Techniques Asia Pacific (CTAP) Ltd, Singapore, a global exponent of Automation and Control has used current comparison technique for both tension estimation and speed control in rolling mills. Since this work is quite recent (1996), it only evinces that the CCT has its own merits over its sophisticated counterparts viz. FST and RCT. A newly developed 32 bit processor card MD29 enables to transfer 5 many tasks from PLC to drive for faster speed control. It also discusses initial speed setting calculations based upon constant volume throughput. For all these calculations the basic reference is the linear speed of the stock head after the last stand. "Dynamic process modelling for tension control in a merchant bar rolling mill", D.C. McFariane and P.M. Stone, BHP research and new technology, Dimensional Control of rolling mills. London, 11-13 Sep. 1990 emphasises the necessity of a process model for dynamic tension estimator. It blends FST and RCT and along with a Kalman estimator predicts the motor power change as a result of tension changes. It acknowledges CCT, but suggests that its scope is limited to head end control only. The starting point is the ubiquitous dynamic discretised state space model. The whole modeling comprises six modules viz. Speed Control Module, Bar Speed Module, Bar Tension Module, Bar Temperature Module, Roll Separation Force Module and Motor Power Module. The hardware platform is DEC3100 and the software platform is MATLAB. Loopless tension controlled rolling of austentic and ferrite stainless grades in hot strip finishing mill", Drexler et all., V DE, Krupp Stahl, AEG, 4th International Rolling Conference, Deauville, France, 1-3 June 1987 underiines the virtues of loopless / loopertess rolling. Though CCT, FST and RCT have been dealt at length, it is the RCT which has been applied. It opines that one of the disadvantages of CCT is that temperature fluctuations are difficult to compensate for. In the first stage Minimum Tension Rolling (MTC) was first experimented and tried out for the F1 - F2 interstand. Only after its successful stabilisation, it was installed in the mill. "Research and Development of control technology for bar and wire rod rolling, Noguchi et al, Nippon Steel, Nippon Steel Technical Report (53), 45-55 Apr. 1992 discloses multivariable control system for interstand tension taking speed and roll gap as control Inputs. A continuous rolling model and an optimal regulator theory has been used for in-stock dimension control. Also an inter-stock dimensional control system based on profilemeter signal processing and tension-free setup. 6 Thus volume throughout control is effected both through speed and roll gap control. There is a novel presence of hybrid control (both through advanced conventional adaptive controls as well as fuzzy logic based speed control). "Looper-less tension control of a hot strip mill finisher", Akamatsa et al, Nippon Steel and Toshiba, pp 410-417, Proceedings, Internationa! conference on steel rolling, Sep. 29- Oct.4, 1980, Tokyo, Japan describes the looper-less tension control of a hot strip mill finisher. The interstand tension control has been done through looper for conventional hot strip mill finisher. The 6 stand hot strip mill at Muroran works, Nippon Steel was added M stand just before the crop shear, and this became the 7th stand finisher. Looper-less tension control by using FTC (Free Tension Rolling) was adopted to control the tension between M and F1 stand. Here, similar to a mixture of RCT & CCT, a cascaded Torque comparison technique (TCT) has been propounded alongwith measuring roll force. "New tension control system in finishing stands of a hot strip mill", Oishi et at, Nippon steel and mitsubishi, pp 418-427, Proceedings, International conference on steel rolling. Sep. 29-Oct.4, 1980, Tokyo, Japan provides in finishing stands of a hot strip mill, a new tension control system has been theoretically and practically developed to detect indirectly and to control the interstand tension without using looper measurements. This system was tested through the practical rolling in the No. 1 -No. 4 stands of the finishing train of the No.2 hot strip mill at yawata works, Nippon steel corporation. From the results of actual rolling tests, it has become clear that this system presents various improved control characteristics on the viewpoints of dynamic response. It opines that TCT and RCT are more efficacious for the thicker cross sections. It innovates these methodologies by extrapolating it to finishing stands. "A new tension control system for hot strip finishing mill", Hayashi et al, Nippon kokan k.k., pp 101-106, IFAC 1dh Triennial world congress, Munich, FRG, 1987 discloses that by suitably blending FST and RCT, NKK has developed a new 7 tension control method for the hot strip mill and applied it to kelhin works. The behaviour of the interstand tension through looper control was evaluated by simulation and it was concluded that the mass moment of looper inertia should be reduced drastically. To achieve this a full stand looperless rolling technique using statistical technique was developed for the large sectioned material use. For optimal control of the multivariable system least square method along with kalmal filter was used. "Simulation of rolling with tension effects to improve thickness control in hot strip mill". Bertrand et al., SOLMER, INRIA and ISRID. pp 287-295, Proceedings international conference on steel rolling, Sep. 29-Oct.4, 1980. Tokyo, Japan discloses ISRID, France with cooperation of INRIA and SOLMER had developed a mathematical model of the finishing mill of a hot strip mill which has been used in this work. Both head end control and the dynamic mid section control has been dealt here. Strip temperature is considered an important parameter her. "Minimum tension control in finishing train of hot strip mills", Gordon v. Bass and Rudolf Harlmann, Siemens Energy and Automation Inc., Rosewell Ga., Eriangen, West Germany., I & S Engg., Nov. 1987 discloses replacement of loopers by MTC. Superimposed on the main electrical drive control system, it generates the correct cascaded speed control setpoints to control interstand material flow based on tension dependent changes on rolling torque. Each MTC performs sequence control, torque arm determination, tension torque value calculation, PI controller, correction and cascade value output etc. The load torque is determined through the observer model. The rolling torque is calculated by measuring drive speed, armature current and field current. RCT ITCT has been used here. "A computer program for the calculation of roll force and torque with strip tension in cold rolling", T.A. El-Bitar, Central Metallurgical Research and Development Institute (CMDRI). Cairo. Egypt, I & SM, May 1993 focuses on the amount of force and torque applied to the rolls for bringing about the desired thickness of the strip. A theoretical rolling intensive work thus develops a computer program based on certain algorithms. 8 "The automatic tension and gauge control at tandem cold mill", Takaharu et al., Kawasaki steel and research laboratory, hitachi, pp 439-450, Proceedings, International conference on steel rolling, Sep. 29-Oct 4, 1980, Tokyo, Japan discloses mass flow detector used for controlling the mass throughput. It also serves as a basic sensor for tension estimation. For controlling tension speed control selected instead of roll gap control, since the latter was found to be sluggish in Mizushima's tandem rolling mill. "Characteristics of rolling in a continuous Billet mill with drive free vertical rolls", Shikano, Kusaba and Hayashi, R&D, Sumitomo Metal Industries Ltd., ISIJ int., 1991 discloses a unique and quite interesting logistics of a 5 stand H-V-H billet mill, where the, drive free vertical rolls are used as prime movers for some power generation elsewhere. This setup necessitates fluctuating TIC throughout the rolling. Each entry and exit to a stand completely changes the TIC patterns giving rise to the deliberate buckling (due to compression) and skidding (due to tension). The paper describes how to adjust speed in order to control the rolling torque and rolling load dynamically with a buckling estimation by tejamur's formula. However, methodology of speed control has not been described. "Reliable roll force prediction in cold mill using multiple neural networks"; S.Cho. member, IEEE et. al., IEEE transactions on neural networks, vol. 8, no.4, 1997 discloses prediction of roll force using artificial neural network. While several known art of controlling tension of continuous rolling mill stands is in use such known systems suffer in that comparison technique is not for the entire stock. Due to this, the speed adjustments are done only after biting with an assumption that biting conditions hold on till the tail end leaves the stands. Generally, due to operational variances this assumption does not hold on. Thus optimised speed control can not be implemented. It is thus the basic object of the present invention to provide a system for controlling tension in continuous rolling which would be based on the entire stock 9 and provide for both feed back and feed forward control thereby effecting control in tension both in terms of post-facto control after sensing the turbulence due to the parametric variations and also after sensing of the parameters of rolling and net result turbulence to the interstand tension even before the stock Is charged. Another object of the present Invention is to provide a system for controlling tension in continuous rolling which would be adapted to track longitudinally the whole stock to thereby effect the controlling based upon the net turbulence at all times and at all linear positions of the stock. The system would thus provide for control of tension for the entire stock right from head-end to tall-end. Yet further object of the present Invention is to provide a system for controlling tension in continuous rolling which would provide both in-stock control implying control of the present rolled stock with input values of the same stock and inter-stock control implying that the parametric values of the present stock will be utilised in anticipation of the next stock. Yet further object is directed to provide a system for minimum tension controlled continuous rolling which would provide for improvement in length and cross-section of rolled stock and substantially avoid the problems of rejection of finished stock in continuous rolling. Yet further object is directed to provide a system for minimum tension controlled continuous rolling which would avoid problems of operational delay due to looping/twisting of metals during rolling. Yet further object is directed to provide a system for minimum tension controlled continued rolling which would avoid problems of damage of mill equipments injury to persons and ensure safe, smooth rolling and favouring the production process. Thus according to the present invention there is provided a method for controlling minimum tension rolling in continuous casting comprising: 10 identifying zones for tension control by means of analysis of samples of main armature current and stand speed wherein each inter-stand is logically divided into four inter-stand time zones (ITZs) comprising an impact recovery zone signifying the biting turbulence, processing and calculating zones, impact compensation by means for real-time speed connection and gearing up for impact compensation; measuring main armature current to compress the torque requirement; measuring main armature current at close intervals periodically; estimating tension by means of instantiating the said armature values with some biting instances; generating output based on set parameter values by means for effecting head end control and/or dynamic control. In the above-disclosed method of controlling tension both feedback and feed forward control is achieved. The approach to tension control is two fold i.e. feedback or feedforward. The former does not need to know the root cause or the genesis of the parametric variations. Whatsoever may be the cause, the tension will be controlled post-facto after sensing the turbulence due to the parametric variation. The other fold is feedforward control which is anticipative in nature. The rolling parameters are sensed early and their net resultant turbulence to the interstand tension is predicted even before the stock is charged. Since the whole stock is longitudinally tracked, so the controller knows the amount of net turbulence at all times and at all linear positions of the stock. Accordingly, it manipulates the control output (speed or gap) keeping in mind the Total Throughput Time (TTT). TTT is the combined time between the actuating an output signal given by the controller and the realisation of the output in the field equipment. The art of tension control is to shift maximum controls to the feedforward realm so that the turbulences can be nipped in the bud and smooth rolling can take place. However, this necessitates veritable sensing of rolling parameters and accurate tracking of the stock which is certainly challenging. 11 Moreover, it assumes unflinching adherence to standard rolling practices. Majority of the tension control systems are composite i.e. with mixed controls of feedforward and feedback. It is thus possible by way of the method of the invention to successfully extrapolated the control for the entire stock control which means right from head-end to tail-end. In-stock implies controls of the present roiled stock with input values of the same stock; whereas by inter-stock control it is meant that the parametric values of the present rolled stock shall be utilised in anticipation for the next stock. There is to be separate strategies for both in-stock and inter-stock controls. Real-time considerations come for the former in which the control regime is divided into water-tight compartments of certain actions at specific times. Whereas for the latter the turbulences through the entire stock are studied and the speeds are so adjusted (after the exit of the present stock) so as to give a synergetic tuning for the next stock. Zones of Tension Control : Zones are identified by analysis of samples of the main armature current and stand speed in the PLC adapting application software. Based upon type of controls and their specific time windows, each interstand is logically divided into four interstand Time Zones (ITZs) as shown in fig. 2 ITZ 1 is called the impact recovery zone. It signifies the biting turbulence. It starts with the biting instance and ends at that sampling instance, where the software declares that steady state values are achieved by initial condition calculation. This is the zone meant for elimination i.e. the parametric values of this zone are to be discarded for speed control calculations. However, the biting speed drop and impact recovery time for the trial billet are calculated in tills zone. ITZ 2 starts with steady state conditions reached and finishes at that instance where the software declares sufficiency of: steady state values for speed control calculations. ITZ 3 starts with the end of ITZ 2 and finishes at that instance where the software sets up the reference calculated for the drive. ITZ 4 is for Impact Compensation (IC) I speed lead adjustment To increase the life of rolls and to reduce biting turbulence I compression, a preemptive increase (equal to the biting drop) in the drive speed is made just before the biting and that extra bit is withdrawn matching with the recovery characteristics. As stated earlier tine drop and the recovery characteristics are found out from the trial billet. 12 In accordance with a preferred aspect in the method provides for impact compensation/speed lead adjustment comprising: identifying fall in speed of stand with every stock biting and time for recovery by means of monitor; comparing of the drop characteristic with trial billets adapting sensor; generating matching signal reference for actuating the drive for necessary speed adjustments. In accordance with another preferred aspect In the aforesaid the method system is provided with means for feed forward temperature compensation comprising means for spatially and temporally synchronised the temperature profile with the biting. In particular, form such feed forward temperature compensation the system is provided with means to Identify the longitudinal temperature profile of the stock and also means for identifying at identifying the time when such temperature are subjected to different stands ; and means for selecting speed references in anticipation based on the above temperature profile in the respective stands. According to yet further preferred aspect of the present invention the method comprises cobble detection and activation of corrective measures based on mill logistics by means of current detector. According to yet further aspect the method provides control system adapting means for sensor smoothening comprising each net stand sensors having independent current sensors. The details of the invention, its object and advantages are explained hereunder in greater detailed in relation to the non-limiting exemplary embodiments of the control system discussed in relation to the accompanying figures wherein Fig. 1 is a schematic illustration of the hardware and network architecture of the control system in accordance with the present invention. 13 Fig. 2 is an illustration of the four differed interstand zones used in the system of the invention. Fig. 3A to 3C are flow charts of the basic tension control algorithm. Fig. 4 is a flow chart illustrates the speed correction system. Fig. 5 to 8 illustrate typical speed controlling in typical rolling patterns. Fig. 9 is an illustration of the effect of speed change on the various interstands. In the present method of the invention the control system is a realisation of the principle of CCT and its extrapolation to the dynamic overall control. The settled steady state value after the biting turbulence with no succeeding stand loaded is taken as the sacrosanct setpoint. In case if a preceding stand(s) is(are) loaded then the set point shall be logged only after the previous interstand(s) is(are) tension-free after speed readjustments. The final set point is arrived after certain statistical adjustments of the current samples of steady state zone. The no. of samples differ from rolling scheme to rolling scheme. As for the head end control, the head end steady state values after the next stand biting (again after statistical processing) are compared with the original set point are desired speed adjustments are done. Whereas for the dynamic control, the set point remains the same whereas the dynamic current values are processed in short packets and dynamically compared to the set values for TIC estimation in all interstands (Since now all preceding stands are loaded). Now these interstand TICs are multiple setpoints around which the present system is built up. Obviously, the embedded knowledge base of the system bring down these interstand TICs to lowest levels in a 'synergetic manner' by adjustments of the stand speeds. Preferably seven levels of quantisation are provided comprising High Tension (HT), Medium Tension (MT), Low Tension (LT), No Tension (NT), Low Compression (LC), Medium Compression (MC) and High Compression (HC). The analog values attached to these levels have been done after detailed logistics study. The validation of this dynamic tension estimation was by and large done when the improper soaked tail ends exhibited compression. Also, it was found that looping phenomena was concomitant with very high compression. Thus, the CCT was adroitly extrapolated for dynamic control. 14 Features of the system guidance recipe: As shown in fig. 3A, at the start of the operation initiation of 5D current logging is done. In the next step 20 samples or on an average 50 samples are filtered after which this average result is stored as X. After this 6D biting is initiated with respect to 5D and subsequent correction is made. In figure 3B during basic tension control next 50 samples of 1 to 5D are tested and the result is stored as Y. Then the difference is calculated as X-Y. In figure 3C again the next 50 samples of 1 to 5D are tested and the result is stored as Z. After that the difference X-Z. Then the billet end Is crossed to check 9D/7D. if the result is Yes then the program terminates and if No then it is looped back to check for the next 50 samples of 1 to 5D. The first target was to locate No Tension Zones (NTZ), if any. If yes, then the complexity reduces. For example, If there are 1 to n stands {1 to (n-1 ) interstands} and let the pth interstand {p-(p+1 )} with n After this, the system identifies the win-win zones in which the adjacent interstands have opposite polarity. Exact opposite polarities are most desired e.g. HT -HC, MT -MC or L T -LC. One quantum difference is the next desired e.g. HT -MC, MT -LC, MT -HC, L T -MC, HC- MT. MC-L T, MC-HT and LC-MC. Simllarly, the next desired is difference of two quantum e.g. HT -LC, HC-L I, LC-HT and L T -HC. For the first category it is easier to convert both into NTZ by manipulating a single stand. For the second and third the speed adjustment is done in such a way so as to create at least one NTZ in the next PLC scan. For example If the zones are HT -LC, then the mid stand speed shall be decreased assuming a L T -LC pattern that the pattern next PLC scan changes to MT -NT or L T -NT. The reason for this is that as no. of NT zone increases the degree of complexity decreases. Moreover, the system target Is to have all interstands as NTZ. The PLC continues to do this until there is no opposite polarity zone. Now, the balance is what the system identifying is for i.e. zones with same polarity. For example HT -MT, HT -L T, MT -HT. MT -L T, L T -MT, L T -HT, HC-MC. HC-LC, MC-HC. MC-LC, LC-MC or LC-HC. Here only two stands have been shown. These patterns could be for more than two interstands. But essentially, these pattern shall have NTZs in between. These Isolated same polarity compartments are lose-lose zones in which the speed of the first and last stand are decreased and increased or increased and decreased simultaneously as the case may be. Again an HT -L T zone is adjusted as L T -L T, which changes the 15 pattern to MT -NT or L T -NT. This is repeated till all are NTZs. Some typical speed control algorithm implementations have been shown in figs. 5 to 8. While deciding the magnitude of all these speed adjustments, the system has in mind the percolating effect of the stand speeds. For example a speed change made in the first stand has say 100% impact on the 1st interstand, a 30% effect on the 2nd interstand and a 8% effect on the third interstand and so on. This has been dileanated in fig. 8. By way of illustration a ten step control with 25ms scan time shall require a fourth of a second (quite real-time!). All depends a lot upon the shortest time of stand to stand entry, it shall be easier to analyse, if N stand continuous mill control is divided in the following three Time Zones (TZs): Time Zone I: Where the material has entered in less than N stand. Time Zone II: Where all the N stands are loaded with material. Time Zone III: Where the material has left less than N stand. In time zone I there is both head end and dynamic control and shortest stand to stand time determines the criteria for head end control. Since the sacrosanct set point can only be arrived at if the preceding interstands are tension-free. Whereas for any dynamic control, irrespective of any zone the only real-time criteria is the drive response alone. However, this criteria is not as stringent as the earlier one provided the basic process has convergence. By convergence is meant that while normal rolling there should not be any abrupt change of two or more quanta, for example form MT it should either go to HT or L T. but not say MC. Generally, this convergence is there in process. Moreover, the quantisation levels should be such defined so that their frequency change in the worst mill conditions should match the drive response. This means for slower drives, the levels should be sparsely spaced so that their switching frequency (based on rolling conditions) is less and therefore the references generated are slow enough for the drives. 16 Time zones II and III have no head end control but only dynamic control. If NTZs are maintained In zone II then there shall be no turbulence while the tall end starts leaving one by one stand. In other words, there shall be no change in the linear velocity of the metal. This is where the dynamic control scores over head end control. Since in mills where a periodic cutlength is made of the rolled stock, the length of the last pieces go haywire, if there is uneven TIC patterns. This is because the linear velocity of the stock changes each time the tail end leaves each stand. The TZs exhibit temporal compartmentalisation, while the spatial compartmentalisation of one interstand into four different ITZs has been shown in fig. 2 These ITZs exist only for real-time cascaded control. As an exemplary illustration the hardware configuration and networking in the system of the invention is shown in Fig. 1. As shown in Fig. 1 the system configuration is as discussed hereunder: Hardware used: The hardware comprises a PLC 5/80C Allen-Bradley make processor with Dl, DO, All AO modules; a 14" coloured operator station for the pulpit operators and a pentium PC as the programming terminal and MMI station. This PLC was hooked to the old cobble detection PLC. The drivers for control net and DH+ are 1784- KTC(X) and 1784- KT respectively which are on the PC. Software used: The logic is developed in RsLoglx software, while the network is configured in RsNetworX, the driver software is RsLinx, whereas the MMI is RsView32. The operator station development software is Panelbuikier. Provision is made for the inter-operatibility amongst them. The RsLogix software is a family of ladder logic programming helping to maximize performance, save project development and improve productivity. RsLogix supports the Allerv Bradley PLC S/80C. RxLogix offers reliable communications, powerful functionality and superior diagnostics. This eases the maintenance across hardware platforms. The network of the RsLogix is configured through RsNetworx allowing maximum productivity with controlnet and/or device net installations. The device can be simply configured through RsLinx, which is a software interface, supporting multiple software applications simultaneously, communicating to a variety of devices on many different networks. Rsview 32 is an integrated, component based MMI for monitoring and controlling automation machine and processes. Operator Interface: Panelview 1400e,a 14" terminal is the operator station. Following are its functions: 1. On-line monitoring of the TIC pattems ( Operators are tuned to the 7 different colours of diff. Quant. Levels), in turn monitoring the speed control system. Also having digital information of on-line quantities viz. stand current, speed, group reference voltage, billet temperature, biting drop, recovery time, speed 17 corrections, speed variations, shift production etc. Even the metal position in the roughing mill also can be monitored from here. Monitoring is done through suitable process visualisation screen developed in RsView 32. 2. Initial Condition calculations: The system from the historic record automatically downloads the last billet speeds once the rolling scheme is selected by the operator. Moreover, the operator enters the changes in Roll Dia, reduction factor (roll gap), gear ratio etc. so that the system automatically calculates the desired mill stand speeds. 3. All futuristic controls replacing all existing control of the pulpit viz. shear, tilter, speed fine / coarse regulator, slow/fast/emergency stops, electrical switches and push buttons for stands and roll table etc. have been incorporated for futuristic use which is readily implementable by suitable i/o interfacing. As discussed above in accordance with a preferred aspect the system in the method is further provided under means for impact compensation or speed lead adjustment: Whenever the stock enters a stand there is an impact. A distinct sound with mechanical vibration in the whole stand assembly is observed. Hot Metal Detectors (HMDs), Pyrometers etc. if mounted with the stand assembly undergoes a shock with every stock charged. To lessen this impact and to increase the roll life, IC is applied. Its electrical spin offs are also prolific. With stock biting the speed of that stand falls down and takes certain time for recovery (fig. 2). If this drop is more and the recovery rate is slow then it causes an undesired biting compression in the previous interstand. It also vitiates the realtime considerations at head-end control. ITZ 1 eats away ITZ 2 (fig. 2). For this the drop characteristics the trial billet is noted and a matching signal reference is enerated by the controller and sent to the drive just before the TTT of biting instance. Successive error approximation with the next billet and subsequent updates are made. TCSs eliminate looping in ITZ 2,3 & 4; whereas IC eliminates looping in ITZ 1. These characteristics vary for different chemistries and temperatures of the stock. Therefore a built in look up table should be provided in the system. 18 According to another preferred aspect the system comprises means for feedforward temperature compensation : As mentioned hereinbefore that it is always better to have more anticipative feedforward controls so that the TCSs face least turbulence. Temperature Is one of the most influential factors in any speed setting agenda. The temperature profile should be spatially and temporally synchronised with the biting, i.e. the controller must have the following two information : i) Longitudinal temperature profile of the stock, ii) At what time these are subjected to different stands. Accordingly the speed references will be provided In anticipation. The process experts provide the desired speeds for different temperatures of the stock. This compensation is both for interstock and instock. In the sense that base speeds are set for the average stock temperature, and additionally differential references are provided for in-stock temperature variations. It Is judicious to sense the temperature just after drafting since the stock is scale free at that time. The system further comprises means for cobble detection and suitable action. Since for any TCS, head-end tracking is an inbuilt necessary component. Once the head-end is tracked, it is easy to detect the front end (no entry) cobbles. This is done through analog output card of the PLC giving an output of -5 to +5 volts, depending upon raw count value of -2048 to +2048, which in turn means speed changes between -250 and +250 RPM (revolution per minute). Knowing the value of the speed to be decreased or increased, the raw count value may be fed. Suitable action depending upon the mill logistics can be taken instantaneously, for example cutting or stopping the preceeding stands. This reduces the mill delays due to front-end cobbles. The system is also provided with means for sensor smoothening. Since the control logic is highly instantiative (scan position dependent), therefore it is imperative that these instances are truthful. It means that all biting instances should be reflected as well as no false biting instance should arrive. For this it was necessary to make the current sensors fool-proof. Generally, the actual biting were echoed, it was only the pseudo bitings which exacerbated the logic. A novel logic interwoven amongst the sensor was developed. Each net stand sensor has three independent current sensors. Two are of the hardware type and the third is software tunable. The special mentionable feature of the third is that two separate reference levels are configurable (unlike the other two). For example, if the peak 19 current of the toughest chemistry (SAILMA I M500) of 50 is 1400 A, and for the mildest (Rimming) is 800 A, then 750 is a suitable reference for latching on the 3rd 50 sensor ( 1st reference value); whereas some 25-30 A may serve as the 2nd reference (for turning off)since notwithstanding any grade, since the current crosses this value as soon as the metal leaves 50. Never shall the current droop down to 25-30 A for any mid section value. Moreover, the fait accompli of the metal to pass and leave all stands once charged (unless emergency stop) was utilised in interlocking sensors. Once this was implemented, sensor misbehaviour and pseudo bitings disappeared. It is thus possible by way of the present control system of the invention to achieve benefits of minimum tension controlled rolling It effectively addresses to the growing market demand of closer dimensional tolerances. It improves both the length and the cross-section of the rolled stocks and substantially avoids rejections for finished products and problem in the internal quality chain. Also majority of the operation delays due to looping/twisting of the metal and also avoided and thereby chances of damaging the mill equipment and cause injury to the mill personnel is also reduced to ensure safe smooth rolling and favour the production process. The method of tension control of the invention is a requirement of all continuous mills irrespective of the nature of the rolled stock. Thus it is equally applicable for both flat and long products. Whether be it billet, rod, bar, section or hot / cold strip, for all tension controlled rolling is desirable. Also the system would provide for dimensional accuracies in continuous rolling. 20 WE CLAIM: 1. A method for controlling minimum tension rolling in continuous casting comprising: Identification of zones for tension control main armature current and stand speed wherein each inter-stand is logically divided into four inter-stand time zones (ITZs) comprising an impact recovery zone signifying the biting turbulence, processing and calculation of zones, impact compensation (IC)/speed lead adjustment by means for real-time speed connection and gearing up for impact compensation (IC); measurement of main armature current to compress the torque requirement; measurement of main armature current at close intervals periodically; estimation of tension by means of instantiating the said armature values with some biting instances; generation of output based on set parameter values by means for effecting head end control and/or dynamic control. 2. A method as claimed in claim 1 wherein identification of four Inter-stand Time Zones (ITZs) comprises first time zone (ITZ1) starting at the biting instance and ending at the sampling instance when steady state values are achieved; second time zone (ITZ2) of the said four inter-stand time zone (ITZs) comprises starting of the steady state conditions reached and finishing instance when the sufficiency of steady state is attained ; third time zone (ITZS) of the said four inter-stand time zones (ITZs) comprises ending of second time zone and finishing instance when references calculated for the drive are set up; and fourth time zone (ITZ4) of the said four inter-stand time zones (ITZs) comprising impact compensation (IC)/speed lead adjustments. 3. A method as claimed in claim 1 wherein impact compensation (IC)/speed lead adjustment is carried out by pre-emptive increase in drive speed before biting and withdrawing the extra bit matching with the recovery characteristics based on trial billets by means for real time speed comprising current sensors. 21 4. A method as claimed in claim 3 wherein impact compensation (IC) /speed lead adjustment comprising: Identification of fall in speed of stand with every stock biting and time for recovery by means of monitor; comparison of the drop characteristic with trial billets adapting sensor; generation of matching signal reference for actuating the drive for necessary speed adjustments. 5. A method as claimed in claim 1 wherein generation of output comprising the head end steady state values after the next stand biting (after statistical process) are compared with the original set point and desired speed adjustments are made by means of analog output card. 6. A method as claimed in claim 1 wherein the dynamic control for the set point is maintained the same whereas the dynamic current values are processed in short packets and dynamically compared to the set values for TIC estimation in all Inter-stands. 7. A method as claimed in claim 6 wherein the said inter-stand TICs are multiple set points around which the system is operated. 8. A method as claimed in claim 1 wherein identification of zones comprising: a) Locating No Tension Zones (NTZ), if any by means of controller, if any b) locating adjacent inter-stands which have opposite polarity (win-win zones) and categorising as herein described adapting PLC; c) effecting conversion into NTZ by manipulating single stand; d) effecting speed adjustments to create at least one NTZ in the next PLC scan; e) identifying zone of same polarity and effecting corresponding speed adjustments. 9. A method as claimed in anyone of claim 1 comprising providing the continuous mill control divided into three time zones comprising time zone I where material entered is less than N stand, time zone II where all the N stands are loaded with material and time zone III where material has left less than N stands said time zone I providing for both head end and dynamic control and said time zones II and III only provide for dynamic control. 10. A method as claimed in claim 1 wherein the processing and calculation comprise of initial condition calculation wherein automatic calculation of the desired mill stand speed based on historic record of last billet speeds and selected rolling scheme. 11. A method as claimed in claim 1 comprising cobble detection and activation of corrective measures based on mill logistics by means of current detector. 12. A method as claimed in claim 1 comprising providing for sensor smoothening adapted for identification of false biting by means of interwoven sensor. 13. A method as claimed in claim 12 wherein neutralisation of sensor misbehaviour and pseudo biting is achieved by means of three independent current sensors. 14. A method for controlling minimum tension in continuous casting substantially as herein described and illustrated with reference to the accompanying figures. A control system for minimum tension in continuous casting comprising means for extrapolation of the current comparison techniques for dynamic in-stock control, means comprising recipe based control for seven quantisation levels, means for an integrated cobble detection and means for on-line impact drop, recovering time etc. for preventive maintenance of equipments. It is possible by way of the above system to automatically control speeds of the multiple stands continuous billets with dynamic rolling conditions and without operators intervention. The control provides for elimination of mill catastrophic conditions viz. looping/skidding due to excessive compression/tension respectively. Moreover, the system assists in achieving around 40%-50% improvement in length variations and provide for simple and effective operation of rolling mills.

Full Text

The present invention relates to a method for controlling minimum tension rolling at continuous mills.
A continuous mill is a mill in which the stock is simultaneously rolled in more than one stands i.e. the distance between the stands is quite less as compared to the length of the whole stock. In such a mill, it is necessary to regulate the volume throughput through each stand as per the desired operating norms, thereby controlling interstand tension.
For tension free rolling (Equal volume throughput from each stand):

where A1 = Area of cross section of 1th stand (roll gap); V1 = Linear Velocity of the billet at the stand; A1+1 and V1+1 are same for the next stand.
As evident, equation (I) can be realised either by controlling A1 & A1+1 (Roll Gap Control) or by controlling V1 & V1+1 , in other words V1 & V1+1 (Speed Control). However, the former control can be exercised only when there is a deviation from the set roll gap. Else, it shall affect the breakdown sequence. Moreover, for different shape rolling sections the effective diameters are different. Therefore, the latter approach is more popular for tension control.
Thus tension control connotes a tandemness of material flow amongst all stands and the key to tension control is to sustain this tandemness despite parametric variations. The latter implies all tangible variants such as temperature, grade of the stock, roll gap, input profile, mechanical variants such as roll eccentricity etc. These can be measured up by suitable integro-differential equations. However, parametric variations also encompass certain imprecisions which are difficult to quantify such as subcatenous blow-holes, both instock and interstock variation in lateral temperature profile due to nonunique soaking regimes etc.

2
A more perceptible delineation for understanding of interstand tension/ compression situations is through push-pull concepts. If the succeeding stand is pulling the stock more that what the preceeding stand is able to cater, then we have a situation of tension in that interstand. It implies that there is a deficit of material in It, since the volume taken out by the succeeding stand is more that what supplied by the preceeding stand. Such greater deficits have a possibility of twisting of the stock and underfilling the passes leading to mill jamming and dimensional aberrations respectively. Whreas, If the preceeding .stand is pushing the stock more that what the succeeding stand is able to cater, then we have a situation of compression in that interstand. It implies that there is a surplus of material in it since the volume taken out by the preceeding stand is more that what supplied by the succeeding stand. Such greater surpluses have a possibility of looping of the stock and overfilling of passes leading to mill jamming and dimensional aberrations (fins) respectively.
Presently there exists different methods for measurement of tension, whether directly or indirectly, with each method having Its own merit and demerit. For example, the Forward Slip Technique (FST) though highly accurate is expensive
and also necessitates accurate assessment of modulus of rigidity at the stock temperature. The Ratio Control Technique (RCT) which is in vogue these days requires mounting of pressure cells in the stands for rolling force measurement; whereas the rolling torque is calculated by the main armature current. Since the latter is the most fundamental parameter of the Current Comparison Technique (CCT), it becomes well obvious the significance of main armature current in tension estimation at continuous mills
Techniques of Tension Estimation :
(i) CCT:
The CCT which has been picked up here offers, a low cost solution for indirect tension measurement. It assumes that the main armature current is a true reflection of the torque requirement and by measuring this current at close intervals periodically and by instantiating them with some biting instances we can have a by and large accurate estimation of the tension.

3
There is no changes in mill structure i.e. no additional mountings (as with FST and RCT). The close monitoring and control of speed and current shifts CCT Into the domain of automation and control to a great extent. In other techniques too, once the tension is measured / estimated state-space control models come into picture with high-level control strategies and process models. The so called limitation of this technique is that it is limited to only head end control i.e. it is not able to handle the turbulences occurring after the head end stabilisation. However; a novel approach has been developed in this work so as to extrapolate CCT over the entire rolling of stock. However, this technique necessitates that there should not be any pseudo current generated due to mechanical obstructions, eccentricity etc. Another advantage of CCT is that it is quite generic, i.e. it can be applied to any type of section without changing the hardware/software or any fresh mounting.
(ii) FST:
FST is an indirect method based on volume and speed ratios in the roll gap. In simple words, In this method the tension is estimated by measurement of the forward slip in the interstand. After some standard assumptions and approximations it can be shown the following :

Where,
S (t) = tension in the interstand at any instant T
EB = Modulus of elasticity
Lo = Strip length between stands
v(t) = Linear velocity at entry / exit
The stock speed is measured and stored until the strip enters the subsequent stands. For FTC. the control adjusts the speed of the previous stand in such a fashion so as to restore the longitudinal force-free value. These change in velocities are extremely small. Therefore, for error free tension estimation, the velocity measuring equipment should be a highly accurate one.

4
This necessitates use of Doppler velocitimeters each at entry and exit of every stand. For several stands the cost is too high and moreover these remain vulnerable to milt repairs and cobbles. One more difficulty with this technique is that at temperatures above 800°C, it is somewhat difficult to predict EB (iii) RCT:
RCT involves measurement of a) rolling force (roll separating force) by pressure cells I pressductors I load cells etc. b) rolling torque by main armature current and /or field current & speed and c) lever arm. The basic principle of RCT is that the ratio of rolling force to deformation torque provides an accurate index of interstand tension. In actual rolling the effect of the deformation torque is much more pronounced on interstand tension than that of the rolling force which itself changes very little. Same modalities of cascaded control is done here too i.e. This ratio is stored in the memory and after the biting of the next stand the previous stand speed is so adjusted so as to restore the ratio value to the previous one. This method is more accurate than CCT, but involves additional mounting of pressure cells etc. This technique is in vogue as evinced in the literature survey.
(iv) CMFT:
With the advent of mass flow gauges, the tension controlled is achieved through speed adjustments so as to have equal mass throughput from each stand. However, these are very expensive and calls for a lot of improvisation with sections of different shapes.
It is also disclosed in "Speed Control of Rolling Mills", Raymond G Brister, Control Techniques Asia Pacific (CTAP) -Singapore, Asia Steel 1996, pp 219 that Control Techniques Asia Pacific (CTAP) Ltd, Singapore, a global exponent of Automation and Control has used current comparison technique for both tension estimation and speed control in rolling mills. Since this work is quite recent (1996), it only evinces that the CCT has its own merits over its sophisticated counterparts viz. FST and RCT. A newly developed 32 bit processor card MD29 enables to transfer

5
many tasks from PLC to drive for faster speed control. It also discusses initial speed setting calculations based upon constant volume throughput. For all these calculations the basic reference is the linear speed of the stock head after the last stand.
"Dynamic process modelling for tension control in a merchant bar rolling mill", D.C. McFariane and P.M. Stone, BHP research and new technology, Dimensional Control of rolling mills. London, 11-13 Sep. 1990 emphasises the necessity of a process model for dynamic tension estimator. It blends FST and RCT and along with a Kalman estimator predicts the motor power change as a result of tension changes. It acknowledges CCT, but suggests that its scope is limited to head end control only. The starting point is the ubiquitous dynamic discretised state space model. The whole modeling comprises six modules viz. Speed Control Module, Bar Speed Module, Bar Tension Module, Bar Temperature Module, Roll Separation Force Module and Motor Power Module. The hardware platform is DEC3100 and the software platform is MATLAB.
Loopless tension controlled rolling of austentic and ferrite stainless grades in hot strip finishing mill", Drexler et all., V DE, Krupp Stahl, AEG, 4th International Rolling Conference, Deauville, France, 1-3 June 1987 underiines the virtues of loopless / loopertess rolling. Though CCT, FST and RCT have been dealt at length, it is the RCT which has been applied. It opines that one of the disadvantages of CCT is that temperature fluctuations are difficult to compensate for. In the first stage Minimum Tension Rolling (MTC) was first experimented and tried out for the F1 - F2 interstand. Only after its successful stabilisation, it was installed in the mill.
"Research and Development of control technology for bar and wire rod rolling, Noguchi et al, Nippon Steel, Nippon Steel Technical Report (53), 45-55 Apr. 1992 discloses multivariable control system for interstand tension taking speed and roll gap as control Inputs. A continuous rolling model and an optimal regulator theory has been used for in-stock dimension control. Also an inter-stock dimensional control system based on profilemeter signal processing and tension-free setup.

6
Thus volume throughout control is effected both through speed and roll gap control.
There is a novel presence of hybrid control (both through advanced conventional adaptive controls as well as fuzzy logic based speed control).
"Looper-less tension control of a hot strip mill finisher", Akamatsa et al, Nippon Steel and Toshiba, pp 410-417, Proceedings, Internationa! conference on steel rolling, Sep. 29- Oct.4, 1980, Tokyo, Japan describes the looper-less tension control of a hot strip mill finisher. The interstand tension control has been done through looper for conventional hot strip mill finisher. The 6 stand hot strip mill at Muroran works, Nippon Steel was added M stand just before the crop shear, and this became the 7th stand finisher. Looper-less tension control by using FTC (Free Tension Rolling) was adopted to control the tension between M and F1 stand. Here, similar to a mixture of RCT & CCT, a cascaded Torque comparison technique (TCT) has been propounded alongwith measuring roll force.
"New tension control system in finishing stands of a hot strip mill", Oishi et at, Nippon steel and mitsubishi, pp 418-427, Proceedings, International conference on steel rolling. Sep. 29-Oct.4, 1980, Tokyo, Japan provides in finishing stands of a hot strip mill, a new tension control system has been theoretically and practically developed to detect indirectly and to control the interstand tension without using looper measurements. This system was tested through the practical rolling in the No. 1 -No. 4 stands of the finishing train of the No.2 hot strip mill at yawata works, Nippon steel corporation. From the results of actual rolling tests, it has become clear that this system presents various improved control characteristics on the viewpoints of dynamic response. It opines that TCT and RCT are more efficacious for the thicker cross sections. It innovates these methodologies by extrapolating it to finishing stands.
"A new tension control system for hot strip finishing mill", Hayashi et al, Nippon kokan k.k., pp 101-106, IFAC 1dh Triennial world congress, Munich, FRG, 1987 discloses that by suitably blending FST and RCT, NKK has developed a new

7
tension control method for the hot strip mill and applied it to kelhin works. The behaviour of the interstand tension through looper control was evaluated by simulation and it was concluded that the mass moment of looper inertia should be reduced drastically. To achieve this a full stand looperless rolling technique using statistical technique was developed for the large sectioned material use. For optimal control of the multivariable system least square method along with kalmal filter was used.
"Simulation of rolling with tension effects to improve thickness control in hot strip mill". Bertrand et al., SOLMER, INRIA and ISRID. pp 287-295, Proceedings international conference on steel rolling, Sep. 29-Oct.4, 1980. Tokyo, Japan discloses ISRID, France with cooperation of INRIA and SOLMER had developed a mathematical model of the finishing mill of a hot strip mill which has been used in this work. Both head end control and the dynamic mid section control has been dealt here. Strip temperature is considered an important parameter her.
"Minimum tension control in finishing train of hot strip mills", Gordon v. Bass and Rudolf Harlmann, Siemens Energy and Automation Inc., Rosewell Ga., Eriangen, West Germany., I & S Engg., Nov. 1987 discloses replacement of loopers by MTC. Superimposed on the main electrical drive control system, it generates the correct cascaded speed control setpoints to control interstand material flow based on tension dependent changes on rolling torque. Each MTC performs sequence control, torque arm determination, tension torque value calculation, PI controller, correction and cascade value output etc. The load torque is determined through the observer model. The rolling torque is calculated by measuring drive speed, armature current and field current. RCT ITCT has been used here.
"A computer program for the calculation of roll force and torque with strip tension in cold rolling", T.A. El-Bitar, Central Metallurgical Research and Development Institute (CMDRI). Cairo. Egypt, I & SM, May 1993 focuses on the amount of force and torque applied to the rolls for bringing about the desired thickness of the strip. A theoretical rolling intensive work thus develops a computer program based on certain algorithms.

8
"The automatic tension and gauge control at tandem cold mill", Takaharu et al., Kawasaki steel and research laboratory, hitachi, pp 439-450, Proceedings, International conference on steel rolling, Sep. 29-Oct 4, 1980, Tokyo, Japan discloses mass flow detector used for controlling the mass throughput. It also serves as a basic sensor for tension estimation. For controlling tension speed control selected instead of roll gap control, since the latter was found to be sluggish in Mizushima's tandem rolling mill.
"Characteristics of rolling in a continuous Billet mill with drive free vertical rolls", Shikano, Kusaba and Hayashi, R&D, Sumitomo Metal Industries Ltd., ISIJ int., 1991 discloses a unique and quite interesting logistics of a 5 stand H-V-H billet mill, where the, drive free vertical rolls are used as prime movers for some power generation elsewhere. This setup necessitates fluctuating TIC throughout the rolling. Each entry and exit to a stand completely changes the TIC patterns giving rise to the deliberate buckling (due to compression) and skidding (due to tension). The paper describes how to adjust speed in order to control the rolling torque and rolling load dynamically with a buckling estimation by tejamur's formula. However, methodology of speed control has not been described.
"Reliable roll force prediction in cold mill using multiple neural networks"; S.Cho. member, IEEE et. al., IEEE transactions on neural networks, vol. 8, no.4, 1997 discloses prediction of roll force using artificial neural network.
While several known art of controlling tension of continuous rolling mill stands is in use such known systems suffer in that comparison technique is not for the entire stock. Due to this, the speed adjustments are done only after biting with an assumption that biting conditions hold on till the tail end leaves the stands. Generally, due to operational variances this assumption does not hold on. Thus optimised speed control can not be implemented.
It is thus the basic object of the present invention to provide a system for controlling tension in continuous rolling which would be based on the entire stock

9
and provide for both feed back and feed forward control thereby effecting control in tension both in terms of post-facto control after sensing the turbulence due to the parametric variations and also after sensing of the parameters of rolling and net result turbulence to the interstand tension even before the stock Is charged.
Another object of the present Invention is to provide a system for controlling tension in continuous rolling which would be adapted to track longitudinally the whole stock to thereby effect the controlling based upon the net turbulence at all times and at all linear positions of the stock. The system would thus provide for control of tension for the entire stock right from head-end to tall-end.
Yet further object of the present Invention is to provide a system for controlling tension in continuous rolling which would provide both in-stock control implying control of the present rolled stock with input values of the same stock and inter-stock control implying that the parametric values of the present stock will be utilised in anticipation of the next stock.
Yet further object is directed to provide a system for minimum tension controlled continuous rolling which would provide for improvement in length and cross-section of rolled stock and substantially avoid the problems of rejection of finished stock in continuous rolling.
Yet further object is directed to provide a system for minimum tension controlled continuous rolling which would avoid problems of operational delay due to looping/twisting of metals during rolling.
Yet further object is directed to provide a system for minimum tension controlled continued rolling which would avoid problems of damage of mill equipments injury to persons and ensure safe, smooth rolling and favouring the production process.
Thus according to the present invention there is provided a method for controlling minimum tension rolling in continuous casting comprising:

10
identifying zones for tension control by means of analysis of samples of main armature current and stand speed wherein each inter-stand is logically divided into four inter-stand time zones (ITZs) comprising an impact recovery zone signifying the biting turbulence, processing and calculating zones, impact compensation by means for real-time speed connection and gearing up for impact compensation;
measuring main armature current to compress the torque requirement;
measuring main armature current at close intervals periodically;
estimating tension by means of instantiating the said armature values with some
biting instances;
generating output based on set parameter values by means for effecting head end control and/or dynamic control.
In the above-disclosed method of controlling tension both feedback and feed forward control is achieved. The approach to tension control is two fold i.e. feedback or feedforward. The former does not need to know the root cause or the genesis of the parametric variations. Whatsoever may be the cause, the tension will be controlled post-facto after sensing the turbulence due to the parametric variation. The other fold is feedforward control which is anticipative in nature. The rolling parameters are sensed early and their net resultant turbulence to the interstand tension is predicted even before the stock is charged. Since the whole stock is longitudinally tracked, so the controller knows the amount of net turbulence at all times and at all linear positions of the stock. Accordingly, it manipulates the control output (speed or gap) keeping in mind the Total Throughput Time (TTT). TTT is the combined time between the actuating an output signal given by the controller and the realisation of the output in the field equipment. The art of tension control is to shift maximum controls to the feedforward realm so that the turbulences can be nipped in the bud and smooth rolling can take place. However, this necessitates veritable sensing of rolling parameters and accurate tracking of the stock which is certainly challenging.

11
Moreover, it assumes unflinching adherence to standard rolling practices. Majority of the tension control systems are composite i.e. with mixed controls of feedforward and feedback.
It is thus possible by way of the method of the invention to successfully extrapolated the control for the entire stock control which means right from head-end to tail-end. In-stock implies controls of the present roiled stock with input values of the same stock; whereas by inter-stock control it is meant that the parametric values of the present rolled stock shall be utilised in anticipation for the next stock. There is to be separate strategies for both in-stock and inter-stock controls. Real-time considerations come for the former in which the control regime is divided into water-tight compartments of certain actions at specific times. Whereas for the latter the turbulences through the entire stock are studied and the speeds are so adjusted (after the exit of the present stock) so as to give a synergetic tuning for the next stock.
Zones of Tension Control : Zones are identified by analysis of samples of the main armature current and stand speed in the PLC adapting application software. Based upon type of controls and their specific time windows, each interstand is logically divided into four interstand Time Zones (ITZs) as shown in fig. 2 ITZ 1 is called the impact recovery zone. It signifies the biting turbulence. It starts with the biting instance and ends at that sampling instance, where the software declares that steady state values are achieved by initial condition calculation. This is the zone meant for elimination i.e. the parametric values of this zone are to be discarded for speed control calculations. However, the biting speed drop and impact recovery time for the trial billet are calculated in tills zone. ITZ 2 starts with steady state conditions reached and finishes at that instance where the software declares sufficiency of: steady state values for speed control calculations. ITZ 3 starts with the end of ITZ 2 and finishes at that instance where the software sets up the reference calculated for the drive. ITZ 4 is for Impact Compensation (IC) I speed lead adjustment To increase the life of rolls and to reduce biting turbulence I compression, a preemptive increase (equal to the biting drop) in the drive speed is made just before the biting and that extra bit is withdrawn matching with the recovery characteristics. As stated earlier tine drop and the recovery characteristics are found out from the trial billet.

12
In accordance with a preferred aspect in the method provides for impact compensation/speed lead adjustment comprising:
identifying fall in speed of stand with every stock biting and time for recovery by
means of monitor;
comparing of the drop characteristic with trial billets adapting sensor;
generating matching signal reference for actuating the drive for necessary speed
adjustments.
In accordance with another preferred aspect In the aforesaid the method system is provided with means for feed forward temperature compensation comprising means for spatially and temporally synchronised the temperature profile with the biting. In particular, form such feed forward temperature compensation the system is provided with means to Identify the longitudinal temperature profile of the stock and also means for identifying at identifying the time when such temperature are subjected to different stands ; and
means for selecting speed references in anticipation based on the above temperature profile in the respective stands.
According to yet further preferred aspect of the present invention the method comprises cobble detection and activation of corrective measures based on mill logistics by means of current detector.
According to yet further aspect the method provides control system adapting means for sensor smoothening comprising each net stand sensors having independent current sensors.
The details of the invention, its object and advantages are explained hereunder in greater detailed in relation to the non-limiting exemplary embodiments of the control system discussed in relation to the accompanying figures wherein
Fig. 1 is a schematic illustration of the hardware and network architecture of the control system in accordance with the present invention.

13
Fig. 2 is an illustration of the four differed interstand zones used in the system of
the invention.
Fig. 3A to 3C are flow charts of the basic tension control algorithm.
Fig. 4 is a flow chart illustrates the speed correction system.
Fig. 5 to 8 illustrate typical speed controlling in typical rolling patterns.
Fig. 9 is an illustration of the effect of speed change on the various interstands.
In the present method of the invention the control system is a realisation of the principle of CCT and its extrapolation to the dynamic overall control. The settled steady state value after the biting turbulence with no succeeding stand loaded is taken as the sacrosanct setpoint. In case if a preceding stand(s) is(are) loaded then the set point shall be logged only after the previous interstand(s) is(are) tension-free after speed readjustments. The final set point is arrived after certain statistical adjustments of the current samples of steady state zone. The no. of samples differ from rolling scheme to rolling scheme. As for the head end control, the head end steady state values after the next stand biting (again after statistical processing) are compared with the original set point are desired speed adjustments are done. Whereas for the dynamic control, the set point remains the same whereas the dynamic current values are processed in short packets and dynamically compared to the set values for TIC estimation in all interstands (Since now all preceding stands are loaded). Now these interstand TICs are multiple setpoints around which the present system is built up. Obviously, the embedded knowledge base of the system bring down these interstand TICs to lowest levels in a 'synergetic manner' by adjustments of the stand speeds. Preferably seven levels of quantisation are provided comprising High Tension (HT), Medium Tension (MT), Low Tension (LT), No Tension (NT), Low Compression (LC), Medium Compression (MC) and High Compression (HC). The analog values attached to these levels have been done after detailed logistics study. The validation of this dynamic tension estimation was by and large done when the improper soaked tail ends exhibited compression. Also, it was found that looping phenomena was concomitant with very high compression. Thus, the CCT was adroitly extrapolated for dynamic control.

14
Features of the system guidance recipe: As shown in fig. 3A, at the start of the operation initiation of 5D current logging is done. In the next step 20 samples or on an average 50 samples are filtered after which this average result is stored as X. After this 6D biting is initiated with respect to 5D and subsequent correction is made. In figure 3B during basic tension control next 50 samples of 1 to 5D are tested and the result is stored as Y. Then the difference is calculated as X-Y. In figure 3C again the next 50 samples of 1 to 5D are tested and the result is stored as Z. After that the difference X-Z. Then the billet end Is crossed to check 9D/7D. if the result is Yes then the program terminates and if No then it is looped back to check for the next 50 samples of 1 to 5D. The first target was to locate No Tension Zones (NTZ), if any. If yes, then the complexity reduces. For example, If there are 1 to n stands {1 to (n-1 ) interstands} and let the pth interstand {p-(p+1 )} with n

After this, the system identifies the win-win zones in which the adjacent interstands have opposite polarity. Exact opposite polarities are most desired e.g. HT -HC, MT -MC or L T -LC. One quantum difference is the next desired e.g. HT -MC, MT -LC, MT -HC, L T -MC, HC- MT. MC-L T, MC-HT and LC-MC. Simllarly, the next desired is difference of two quantum e.g. HT -LC, HC-L I, LC-HT and L T -HC. For the first category it is easier to convert both into NTZ by manipulating a single stand. For the second and third the speed adjustment is done in such a way so as to create at least one NTZ in the next PLC scan. For example If the zones are HT -LC, then the mid stand speed shall be decreased assuming a L T -LC pattern that the pattern next PLC scan changes to MT -NT or L T -NT. The reason for this is that as no. of NT zone increases the degree of complexity decreases. Moreover, the system target Is to have all interstands as NTZ. The PLC continues to do this until there is no opposite polarity zone.
Now, the balance is what the system identifying is for i.e. zones with same polarity. For example HT -MT, HT -L T, MT -HT. MT -L T, L T -MT, L T -HT, HC-MC. HC-LC, MC-HC. MC-LC, LC-MC or LC-HC. Here only two stands have been shown. These patterns could be for more than two interstands. But essentially, these pattern shall have NTZs in between. These Isolated same polarity compartments are lose-lose zones in which the speed of the first and last stand are decreased and increased or increased and decreased simultaneously as the case may be. Again an HT -L T zone is adjusted as L T -L T, which changes the

15
pattern to MT -NT or L T -NT. This is repeated till all are NTZs. Some typical speed control algorithm implementations have been shown in figs. 5 to 8.
While deciding the magnitude of all these speed adjustments, the system has in mind the percolating effect of the stand speeds. For example a speed change made in the first stand has say 100% impact on the 1st interstand, a 30% effect on the 2nd interstand and a 8% effect on the third interstand and so on. This has been dileanated in fig. 8.
By way of illustration a ten step control with 25ms scan time shall require a fourth of a second (quite real-time!). All depends a lot upon the shortest time of stand to stand entry, it shall be easier to analyse, if N stand continuous mill control is divided in the following three Time Zones (TZs):
Time Zone I: Where the material has entered in less than N stand.
Time Zone II: Where all the N stands are loaded with material.
Time Zone III: Where the material has left less than N stand.
In time zone I there is both head end and dynamic control and shortest stand to stand time determines the criteria for head end control. Since the sacrosanct set point can only be arrived at if the preceding interstands are tension-free. Whereas for any dynamic control, irrespective of any zone the only real-time criteria is the drive response alone. However, this criteria is not as stringent as the earlier one provided the basic process has convergence. By convergence is meant that while normal rolling there should not be any abrupt change of two or more quanta, for example form MT it should either go to HT or L T. but not say MC. Generally, this convergence is there in process. Moreover, the quantisation levels should be such defined so that their frequency change in the worst mill conditions should match the drive response. This means for slower drives, the levels should be sparsely spaced so that their switching frequency (based on rolling conditions) is less and therefore the references generated are slow enough for the drives.

16
Time zones II and III have no head end control but only dynamic control. If NTZs are maintained In zone II then there shall be no turbulence while the tall end starts leaving one by one stand. In other words, there shall be no change in the linear velocity of the metal. This is where the dynamic control scores over head end control. Since in mills where a periodic cutlength is made of the rolled stock, the length of the last pieces go haywire, if there is uneven TIC patterns. This is because the linear velocity of the stock changes each time the tail end leaves each stand. The TZs exhibit temporal compartmentalisation, while the spatial compartmentalisation of one interstand into four different ITZs has been shown in fig. 2 These ITZs exist only for real-time cascaded control.
As an exemplary illustration the hardware configuration and networking in the system of the invention is shown in Fig. 1. As shown in Fig. 1 the system configuration is as discussed hereunder:
Hardware used: The hardware comprises a PLC 5/80C Allen-Bradley make processor with Dl, DO, All AO modules; a 14" coloured operator station for the pulpit operators and a pentium PC as the programming terminal and MMI station. This PLC was hooked to the old cobble detection PLC. The drivers for control net and DH+ are 1784- KTC(X) and 1784- KT respectively which are on the PC.
Software used: The logic is developed in RsLoglx software, while the network is configured in RsNetworX, the driver software is RsLinx, whereas the MMI is RsView32. The operator station development software is Panelbuikier. Provision is made for the inter-operatibility amongst them. The RsLogix software is a family of ladder logic programming helping to maximize performance, save project development and improve productivity. RsLogix supports the Allerv Bradley PLC S/80C. RxLogix offers reliable communications, powerful functionality and superior diagnostics. This eases the maintenance across hardware platforms. The network of the RsLogix is configured through RsNetworx allowing maximum productivity with controlnet and/or device net installations. The device can be simply configured through RsLinx, which is a software interface, supporting multiple software applications simultaneously, communicating to a variety of devices on many different networks. Rsview 32 is an integrated, component based MMI for monitoring and controlling automation machine and processes. Operator Interface:
Panelview 1400e,a 14" terminal is the operator station. Following are its functions: 1. On-line monitoring of the TIC pattems ( Operators are tuned to the 7 different colours of diff. Quant. Levels), in turn monitoring the speed control system. Also having digital information of on-line quantities viz. stand current, speed, group reference voltage, billet temperature, biting drop, recovery time, speed

17
corrections, speed variations, shift production etc. Even the metal position in the roughing mill also can be monitored from here. Monitoring is done through suitable process visualisation screen developed in RsView 32.
2. Initial Condition calculations: The system from the historic record automatically downloads the last billet speeds once the rolling scheme is selected by the operator. Moreover, the operator enters the changes in Roll Dia, reduction factor (roll gap), gear ratio etc. so that the system automatically calculates the desired mill stand speeds.
3. All futuristic controls replacing all existing control of the pulpit viz. shear, tilter, speed fine / coarse regulator, slow/fast/emergency stops, electrical switches and push buttons for stands and roll table etc. have been incorporated for futuristic use which is readily implementable by suitable i/o interfacing.
As discussed above in accordance with a preferred aspect the system in the method is further provided under means for impact compensation or speed lead adjustment: Whenever the stock enters a stand there is an impact. A distinct sound with mechanical vibration in the whole stand assembly is observed. Hot Metal Detectors (HMDs), Pyrometers etc. if mounted with the stand assembly undergoes a shock with every stock charged. To lessen this impact and to increase the roll life, IC is applied. Its electrical spin offs are also prolific. With stock biting the speed of that stand falls down and takes certain time for recovery (fig. 2). If this drop is more and the recovery rate is slow then it causes an undesired biting compression in the previous interstand. It also vitiates the realtime considerations at head-end control. ITZ 1 eats away ITZ 2 (fig. 2). For this the drop characteristics the trial billet is noted and a matching signal reference is enerated by the controller and sent to the drive just before the TTT of biting instance. Successive error approximation with the next billet and subsequent updates are made. TCSs eliminate looping in ITZ 2,3 & 4; whereas IC eliminates looping in ITZ 1. These characteristics vary for different chemistries and temperatures of the stock. Therefore a built in look up table should be provided in the system.

18
According to another preferred aspect the system comprises means for feedforward temperature compensation : As mentioned hereinbefore that it is always better to have more anticipative feedforward controls so that the TCSs face least turbulence. Temperature Is one of the most influential factors in any speed setting agenda. The temperature profile should be spatially and temporally synchronised with the biting, i.e. the controller must have the following two information :
i) Longitudinal temperature profile of the stock, ii) At what time these are subjected to different stands. Accordingly the speed references will be provided In anticipation. The process experts provide the desired speeds for different temperatures of the stock. This compensation is both for interstock and instock. In the sense that base speeds are set for the average stock temperature, and additionally differential references are provided for in-stock temperature variations. It Is judicious to sense the temperature just after drafting since the stock is scale free at that time.
The system further comprises means for cobble detection and suitable action. Since for any TCS, head-end tracking is an inbuilt necessary component. Once the head-end is tracked, it is easy to detect the front end (no entry) cobbles. This is done through analog output card of the PLC giving an output of -5 to +5 volts, depending upon raw count value of -2048 to +2048, which in turn means speed changes between -250 and +250 RPM (revolution per minute). Knowing the value of the speed to be decreased or increased, the raw count value may be fed. Suitable action depending upon the mill logistics can be taken instantaneously, for example cutting or stopping the preceeding stands. This reduces the mill delays due to front-end cobbles.
The system is also provided with means for sensor smoothening. Since the control logic is highly instantiative (scan position dependent), therefore it is imperative that these instances are truthful. It means that all biting instances should be reflected as well as no false biting instance should arrive. For this it was necessary to make the current sensors fool-proof. Generally, the actual biting were echoed, it was only the pseudo bitings which exacerbated the logic. A novel logic interwoven amongst the sensor was developed. Each net stand sensor has three independent current sensors. Two are of the hardware type and the third is software tunable. The special mentionable feature of the third is that two separate reference levels are configurable (unlike the other two). For example, if the peak

19
current of the toughest chemistry (SAILMA I M500) of 50 is 1400 A, and for the mildest (Rimming) is 800 A, then 750 is a suitable reference for latching on the 3rd 50 sensor ( 1st reference value); whereas some 25-30 A may serve as the 2nd reference (for turning off)since notwithstanding any grade, since the current crosses this value as soon as the metal leaves 50. Never shall the current droop down to 25-30 A for any mid section value. Moreover, the fait accompli of the metal to pass and leave all stands once charged (unless emergency stop) was utilised in interlocking sensors. Once this was implemented, sensor misbehaviour and pseudo bitings disappeared.
It is thus possible by way of the present control system of the invention to achieve benefits of minimum tension controlled rolling It effectively addresses to the growing market demand of closer dimensional tolerances. It improves both the length and the cross-section of the rolled stocks and substantially avoids rejections for finished products and problem in the internal quality chain. Also majority of the operation delays due to looping/twisting of the metal and also avoided and thereby chances of damaging the mill equipment and cause injury to the mill personnel is also reduced to ensure safe smooth rolling and favour the production process.
The method of tension control of the invention is a requirement of all continuous mills irrespective of the nature of the rolled stock. Thus it is equally applicable for both flat and long products. Whether be it billet, rod, bar, section or hot / cold strip, for all tension controlled rolling is desirable. Also the system would provide for dimensional accuracies in continuous rolling.

20
WE CLAIM:
1. A method for controlling minimum tension rolling in continuous casting comprising:
Identification of zones for tension control main armature current and stand speed
wherein each inter-stand is logically divided into four inter-stand time zones (ITZs)
comprising an impact recovery zone signifying the biting turbulence, processing and
calculation of zones, impact compensation (IC)/speed lead adjustment by means for
real-time speed connection and gearing up for impact compensation (IC);
measurement of main armature current to compress the torque requirement;
measurement of main armature current at close intervals periodically;
estimation of tension by means of instantiating the said armature values with some biting
instances;
generation of output based on set parameter values by means for effecting head end
control and/or dynamic control.
2. A method as claimed in claim 1 wherein identification of four Inter-stand Time Zones
(ITZs) comprises first time zone (ITZ1) starting at the biting instance and ending at the
sampling instance when steady state values are achieved;
second time zone (ITZ2) of the said four inter-stand time zone (ITZs) comprises starting of the steady state conditions reached and finishing instance when the sufficiency of steady state is attained ;
third time zone (ITZS) of the said four inter-stand time zones (ITZs) comprises ending of
second time zone and finishing instance when references calculated for the drive are set
up;
and fourth time zone (ITZ4) of the said four inter-stand time zones (ITZs) comprising
impact compensation (IC)/speed lead adjustments.
3. A method as claimed in claim 1 wherein impact compensation (IC)/speed lead
adjustment is carried out by pre-emptive increase in drive speed before biting and
withdrawing the extra bit matching with the recovery characteristics based on trial billets
by means for real time speed comprising current sensors.

21
4. A method as claimed in claim 3 wherein impact compensation (IC) /speed lead
adjustment comprising:
Identification of fall in speed of stand with every stock biting and time for recovery by
means of monitor;
comparison of the drop characteristic with trial billets adapting sensor;
generation of matching signal reference for actuating the drive for necessary speed
adjustments.
5. A method as claimed in claim 1 wherein generation of output comprising the head end steady state values after the next stand biting (after statistical process) are compared with the original set point and desired speed adjustments are made by means of analog output card.
6. A method as claimed in claim 1 wherein the dynamic control for the set point is maintained the same whereas the dynamic current values are processed in short packets and dynamically compared to the set values for TIC estimation in all Inter-stands.
7. A method as claimed in claim 6 wherein the said inter-stand TICs are multiple set points around which the system is operated.
8. A method as claimed in claim 1 wherein identification of zones comprising:

a) Locating No Tension Zones (NTZ), if any by means of controller, if any
b) locating adjacent inter-stands which have opposite polarity (win-win zones) and categorising as herein described adapting PLC;
c) effecting conversion into NTZ by manipulating single stand;
d) effecting speed adjustments to create at least one NTZ in the next PLC scan;
e) identifying zone of same polarity and effecting corresponding speed adjustments.
9. A method as claimed in anyone of claim 1 comprising providing the continuous mill
control divided into three time zones comprising time zone I where material entered is
less than N stand, time zone II where all the N stands are loaded with material and time
zone III where material has left less than N stands said time zone I providing for both

head end and dynamic control and said time zones II and III only provide for dynamic control.
10. A method as claimed in claim 1 wherein the processing and calculation comprise of initial condition calculation wherein automatic calculation of the desired mill stand speed based on historic record of last billet speeds and selected rolling scheme.
11. A method as claimed in claim 1 comprising cobble detection and activation of corrective measures based on mill logistics by means of current detector.
12. A method as claimed in claim 1 comprising providing for sensor smoothening adapted for identification of false biting by means of interwoven sensor.
13. A method as claimed in claim 12 wherein neutralisation of sensor misbehaviour and pseudo biting is achieved by means of three independent current sensors.
14. A method for controlling minimum tension in continuous casting substantially as herein described and illustrated with reference to the accompanying figures.
A control system for minimum tension in continuous casting comprising means for extrapolation of the current comparison techniques for dynamic in-stock control, means comprising recipe based control for seven quantisation levels, means for an integrated cobble detection and means for on-line impact drop, recovering time etc. for preventive maintenance of equipments. It is possible by way of the above system to automatically control speeds of the multiple stands continuous billets with dynamic rolling conditions and without operators intervention. The control provides for elimination of mill catastrophic conditions viz. looping/skidding due to excessive compression/tension respectively. Moreover, the system assists in achieving around 40%-50% improvement in length variations and provide for simple and effective operation of rolling mills.

Documents:

00596-cal-2000 abstract.pdf

00596-cal-2000 claims.pdf

00596-cal-2000 correspondence.pdf

00596-cal-2000 description(complete).pdf

00596-cal-2000 drawings.pdf

00596-cal-2000 form-1.pdf

00596-cal-2000 form-18.pdf

00596-cal-2000 form-2.pdf

00596-cal-2000 form-3.pdf

00596-cal-2000 letters patent.pdf

00596-cal-2000 p.a.pdf

« Previous Patent

Next Patent »

Patent Number

207103

Indian Patent Application Number

596/CAL/2000

PG Journal Number

21/2007

Publication Date

25-May-2007

Grant Date

23-May-2007

Date of Filing

24-Oct-2000

Name of Patentee

STEEL AUTHORITY OF INDIA LIMITED

Applicant Address

RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL DORANDA

Inventors:

#	Inventor's Name	Inventor's Address
1	BHASKAR UJJWAL	OF RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL DORANDA RANCHI
2	KUMAR RISHI SUMEET	OF RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL DORANDA RANCHI
3	SABLOK SUSHIL KUMAR	OF RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL DORANDA RANCHI
4	MAHAJAN GOPAL JIVAN	OF RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL DORANDA RANCHI

PCT International Classification Number

B 21 B 37/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA