Title of Invention

A METHOD FOR REDUCTION IN OPERATIONAL TIME IN A REVERSING COLD ROLLING MILL

Abstract

The invention relates to a method for reduction in operational time in a reversing cold rolling mill producing metal strips, comprising maintaining the starting thread speed in registration with that of the first pass wherein, the end thread speed is gradually increased towards the end of the pass such that a differential thread speed is achieved in which the final end thread speed is nearly double the starting thread speed.

Full Text

-1A- Field of Invention The present invention relates to a method for reduction in operational time in a reversing cold rolling mill producing metal strips. Background of the invention In the reversing cold rolling mills, the rolls rotate under high pressure and hot rolled strip passes through the rolls, get pressed and elongated. The speed with which the strip comes out from the mill (exit side) and is wrapped on the coiler is called the speed of the mill. In a cold rolling technology, the speed of the mill is represented by twin terminology namely thread speed and run speed. When the mill is started, initially its speed is slow and then it gradually attends the full maximum speed. This slow speed is called the thread speed and may vary from 25 MPM to 130 MPM. The thread speed is very important because when the mill is running at thread speed, all the other parameters like GCS, Bending, Tension are tuned and starts functioning in a synchronous way. Unless the whole system is synchronised, strip breakage or pinching may take place. After all the parameters are tuned, the mill is then accelerated to full maximum speed known as the run speed in auto or manual mode. When the coil is towards the end, the mill speed is not brought down to zero directly from the run speed but the run speed comes down gradually to the starting thread speed once again and then it stops. At present in all reversing cold rolling mills, the thread speed in the starting of any pass is the same as the thread speed at the end of that pass. The main drawback of the present system is that due to slow end thread speed, the rolling time at the end portion of the coil is more and also the guage correction is poor. -2- It has been established that at a relatively higher mill speed good quality of surface, good gauge and higher rate of production is achieved. But, there is a limitation for the start thread speed. It cannot be increased randomly because during starting thread speed there are lot of parameters that are to be tuned in. Thus, the start thread speed is to be kept at a predetermined value. In cold rolling mills, thinner gauge sheets are rolled and in case the start thread speed crosses it limitation, the gauge will become cyclic at the start of pass and pinching tendency will be more. However, towards the end pass the end thread speed can be increased as the requirement to the product and mill parameters are comparatively less than that in the starting. Moreover, the chance of gauge becoming cyclic (common problem in rolling mill) is not there at the pass end. Thus, unlike the starting thread speed the end thread speed can be easily increased. The difference in the starting thread speed and end thread speed is called Differential thread speed. It is an object of the present invention to provide a method for reduction in operational time in a reversing cold rolling mill producing metal strips, the operational time being the summation of individual time consumed by plurality of passes requiring phase transformation of the inputted raw materials, the reversing cold mill comprising plurality of roll stands arranged in multiple tires, each roll stand comprising a selected number of rolls constituting of back-up rolls, work rolls, and intermediate rolls, the reversing sequence being carried-out in a roll-stand disposed at the upper-most tier, the method-comprising the steps of: (i) feeding the processed raw-material generally in the form of pickled coils into the mill and imparting roll force to achieve partial reduction in thickness of the coil in a first pass, the run speed of the mill being maintained during the pass so as to synchronize the starting thread speed and the end thread speed; -3- (ii) applying roll force by back-up rolls into the pre-processed coils such that rolling in the second pass taking place in a direction reverse to that of the first pass, the starting thread speed being maintained in registration with that of the first pass wherein the end thread speed is gradually increased with the pass approaching an end such that a differential thread speed is achieved in which the final end thread speed is nearly double the starting thread speed; repeating Steps at (i) and (ii) in the subsequent passes till such time the desired reduction in thickness of the coils is achieved, thereby extensively reducing the total operational time. It is another object of the invention to provide a method wherein the numeric value of the end thread speed is maintained at a higher value than the numeric value of the start thread speed in all the passes except the first pass. The first pass is not included as there is the auto tail out process to stop the mill i.e. when the tail end of the coil leaves the pay-off reel, mill has to stop in auto mode. Also if the thread speed is kept high at the end, coil has the tendency to shift after it leaves the mandrel due to its mass. It is further object of the present invention to provide a method for increasing production without any investment in same reversing cold rolling mill (CRM). It is a still further object of the present invention to provide a method wherein power consumption is less and improvement in gauge conformity is obtained. -4- Summary of Invention According to the invention there is provided a method for reduction in operational time in a reversing cold rolling mill producing metal strips, the operational time being the summation of individual time consumed by plurality of passes requiring phase transformation of the inputted raw materials, the reversing cold mill comprising plurality of roll stands arranged in multiple tires, each roll stand comprising a selected number of rolls constituting of back-up rolls, work rolls and intermediate rolls, the reversing sequence being carried-out in a roll-stand disposed at the upper-most tier, the method comprising the steps of: (i) feeding the processed raw-material generally in the form of pickled coils into the mill and imparting roll force to achieve partial reduction in thickness of the coil in a first pass, the run speed of the mill being maintained during the pass so as to synchronize the starting thread speed and the end thread speed; (ii) applying roll force by back-up rolls into the pre-processed coils such that rolling in the second pass taking place in a direction reverse to that of the first pass, the starting thread speed being maintained in registration with that of the first pass wherein the end thread speed is gradually increased with the pass approaching an end such that a differential thread speed is achieved in which the final end thread speed is nearly double the starting thread speed; repeating Steps at (i) and (ii) in the subsequent passes till such time the desired reduction in thickness of the coils is achieved, thereby extensively reducing the total operational time. -5- Brief Description of the accompanying drawings Fig, 1- Block diagram of a 6H1 Reversible Rolling mill. Fig, 2- Equal thread speed and time graph. Fig. 3- Differential thread speed and time graph. Detailed description of the invention with reference to the accompanying drawings. The invention is described with the operation of 6-HI reversible cold rolling mill. In this type of mill, there are 6 nos. of rolls arranged in two tire. The bottom most roll is backup roll, second one is intermediate followed by work roll and the reversing sequence is followed in the upper tire. This arrangement provides the facility to roll out the steel strip in between the work roll where the roll force required for rolling is provided by the backup roll with the help of Hydraulic Gap Control. In this arrangement only the work roll is power driven and the rest of the roll is friction driven i.e. it receives the inertia from the work roll by friction. In reversible cold rolling mill, the raw material used is hot rolled pickled coil as the coils strips after pickling become oxide / rust free. First the pickled coils are fed in the un-coiler / pay-off reel and the front end of the coil is gripped in the reversing reel through the gap in between the work rolls. Now the gap between the work rolls is closed and the required roll force is provided with the help of Hydraulic Gap Control. The tension in the steel strip is provided in between the reversing reel-2 and the pay off reel. -6- The rolling process is completed in several passes depending upon the input and output thickness of strip, percentage reduction in the pass etc. So the first pass is completed with the operation of pay-off reel and reversing reel-2. After completion of this pass almost 30 to 35 % thickness is being reduced. Now the job of pay-off reel is over and the last end is now fed in the reversing reel-1. Now again the roll force is imparted by back-up roll and the tension is provided now in between the reversing reel-1 and the reversing reel-2, after that the second pass rolling is completed in the reverse direction with regard to the first pass. In the same way all the six passes is completed and the desired thickness of the strip is achieved with a thickness reduction of almost 87 to 90%. As this is the cold rolling process so during rolling due to friction in between roll and strip, a high heat generation takes place. To take care of this heat generation, emulsion (type of coolant and also act as lubricant) spray is used in between the strip and the work roll. This emulsion consist of 95% to De- mineralized water and 5% of rolling oil. When the second pass rolling starts, it starts at the thread speed. After few seconds, mill is accelerated to the run speed. Again when the pass approaches to the end, the slow down process starts and the mill again comes to end thread speed and then stops. An illustration is given below to explain the invention based on the following assumptions but not intending to limit the scope of the invention. 6-H1 Reversible cold Rolling Mill Start Thread Speed =100 mpm End Thread Speed = 200 mpm Length of 1 coil = 32 metres of stip -7- Then, time taken to roll 32 metres of strip at the start thread speed = length / mpm = 32/100 = 0.32 min/pass. Time taken to roll 32 metres of strip at the end thread speed = 32/200 = 0.16 min/pass. Time saving in 5 passes = 5x0.16= 0.80 minute If 850 coils are rolled in a month. Time saved in a month = 850x0.80 = 680 min = 11 hrs and 33 min Time saving per annum = 12x 680 min = 8160 min = 136 hours. If the mill output is 21.5 tonnes/hr Gam in production = 21.5x 136 = 2924 MT If the value addition after cold rolling is Rs 1900 per MT. Then, total gain = 1900x2924 = Rs 55, 55,600 per annum. -8-We claim 1. A method for reduction in operational time in a reversing cold rolling mill producing metal strips, the operational time being the summation of individual time consumed by plurality of passes requiring phase transformation of the inputted raw materials, the reversing cold mill comprising plurality of roll stands arranged in multiple tires, each roll stand comprising a selected number of rolls constituting of back-up rolls, work rolls and the intermediate rolls, the reversing sequence being carried-out in a roll-stand disposed at the upper-most tier, the method comprising the steps of: (i) feeding the processed raw-material generally in the form of pickled coils into , the mill and imparting roll force to achieve partial reduction in thickness of the coil in a first pass, the run speed of the mill being maintained during the pass so as to synchronize the starting thread speed and the end thread speed; (ii) applying roll force by back-up rolls into the pre-processed coils such that rolling in the second pass taking place in a direction reverse to that of the first pass, the starting thread speed being maintained in registration with that of the first pass Wherein the end thread speed is gradually increased with the pass approaching an end such that a differential thread speed is achieved in which the final end thread speed is nearly double the starting thread speed; repeating Steps at (i) and (ii) in the subsequent passes till such time the desired reduction in thickness of the coils is achieved, thereby extensively reducing the total operational time. -9- 2. A method as claimed in claim 1, wherein a positive differential thread speed is maintained by keeping the numeric value of the end thread speed higher than the numeric value of the starting thread speed. 3. A method as claimed in claim 1, wherein the starting thread speed is more than zero but less than the run speed of the mill. 4. A method as claimed in claim 1, wherein the end thread speed is more than the start thread speed but less than the run speed of the mill. 5. A method as claimed in claim 1, wherein the numeric value of the end thread speed which is more than the start thread speed can be varied according to the thickness of inputted coils and the required thickness of the outputted strips. 6. A method for reduction in operational time in a reversing cold rolling mill as substantially herein described and illustrated with reference to the accompanying drawings. The invention relates to a method for reduction in operational time in a reversing cold rolling mill producing metal strips, comprising maintaining the starting thread speed in registration with that of the first pass wherein, the end thread speed is gradually increased towards the end of the pass such that a differential thread speed is achieved in which the final end thread speed is nearly double the starting thread speed.

Documents:

00338-kol-2003-abstract.pdf

00338-kol-2003-claims.pdf

00338-kol-2003-correspondence.pdf

00338-kol-2003-description (complete).pdf

00338-kol-2003-drawings.pdf

00338-kol-2003-form-1.pdf

00338-kol-2003-form-13.pdf

00338-kol-2003-form-19.pdf

00338-kol-2003-form-2.pdf

00338-kol-2003-form-26.pdf

00338-kol-2003-form-3.pdf

338-kol-2003-granted-abstract.pdf

338-kol-2003-granted-assignment.pdf

338-kol-2003-granted-claims.pdf

338-kol-2003-granted-correspondence.pdf

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

338-kol-2003-granted-drawings.pdf

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

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

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

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

338-kol-2003-granted-form 26.pdf

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

338-kol-2003-granted-letter patent.pdf

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

338-kol-2003-granted-specification.pdf