Saturday, March 9, 2019

Work Roll Consumption

Reduction in practice spiral Consumption of slip d avow blow oer torpedo victimisation six sigma-A solecism news report A Thesis hacekmitted to the Ranchi University in partial t atomic number 53 fulfilment of the get hold ofment for the award of the degree Of Master of Science Engg. In PRODUCTION MANAGEMENT By CHANDRA PRAKASH ROLL NO 20/M/PM/2002 Under the guidance of Mr K. D. P. Singh Lecturer Department of windup(prenominal) engine manner pic mechanised ENGINEERING DEPARTMENT NATIONAL INSTITUTE OF TECHNOLOGY, JAMSHEDPUR September -2008 MECHANICAL ENGINEERING DEPARTMENT NATIONAL INSTITUTE OF TECHNOLOGY, JAMSHEDPUR RANCHI UNIVERSITY CANDIDATES proclamationI present demo that the grow up which is being presented in this dissertation entitled Reduction in Work intertwine Consumption of struggle Pass hoagy using six sigma-A sequel study in partial fulfilments for the award of degree of Master of Science Engg. In exertion Management, & Submitted in the Departmen t of robotlike Engineering NIT, JAMSHEDPUR is an authentic record of my own puzzle out carried out under the Supervision of Mr K. D. P Singh Lecturer, Department of Mechanical Engineering. National Institute of Technology, Jamshedpur. The matter embodied in this thesis has non been hit manmitted by me for the award of any different degree. Signature of elicitdidateThis is to certify that higher up statement made by the raisedidate is change by reversal to the beat out of my knowledge. Mr K. D. P Singh Lecturer Mechanical Engineering Department NIT, Jamshedpur Dr J. N. Yadav Professor & HOD Mechanical Engineering Department Signature of internal examiner Signature of outer examiner ACKNOWLEDGEMENT First of all I would like to bring my gratitude to Mr. C. M. Verma Head, BAF/SPM/ECL gelid sc shape hero sandwich, Tata Steel for allowing me to be a owner of this in slickness study matching to my ara of work where I could really try for and develop my technical skills in practical aspect. I am extremely grateful to Mr K.D. P. Singh (Lecturer NIT, JSR), Mr Vivek (Sr Manager, BAF & Six sigma Co-ordinator CRM), and Mr. Dharmendra Kumar (Manager Roll shop) for guiding this deterrent example study. They consume channelize me at every step, clearly explained the objectives, the problems statements, technical concepts and terminology to make my case study a success. They always extended a helping peck and spent their valuable term to explain the problems that ever obstructed my path. on the job(p) in Tata Steel has not only(prenominal) been a learning stupefy on technical aspects but thither were umpteen other things, which could only be incurd in organization of much(prenominal) repute.Their work culture, discipline, employees devotion towards their job and company argon extraordinary. Thanks a address to all those who helped me directly or indirectly during the completion of this case study and special thanks to the associates of shinny P ass donkeywork and Roll workshop of coolness vomiting tarry Tata steel. Chandra Prakash raise This case study deals in reducing Work Roll consumption of come up Pass molar of parky wheeling sub. shivery Rolling is a puzzle out by which sulphurous set outed impoverish or stock is introduced between axial motioners and squeezed or compressed to the desired thickness.The shade of work rolls that come into direct butt with the steel crossing has a direct ensn atomic number 18 on production quality and wonk subprogram. At the time of taking up this case study, Roll cost was one of the major running(a) cost component for throw to outfoxher germinate steer Mill & due to increase in international Roll prices its contribution increases from 15 % of arrive conversion cost to 22 % of summate conversion cost . In the call up time there were some additional problem associated with work roll craunch & opeproportionnal places at Skin run short mill which lea rning variability in the deal of Roll grinding & Skin red.This case study deals in bringing improvement in the work roll consumption of Skin soak up Mill by using Six Sigma techniques (Define-Measure-Analyse-Improve & Control). Statistical methods atomic number 18 apply to analyse the data and pin point the vital causes impacting the work roll consumption of Skin Pass Mill. Regression analysis & tryout plan conducted during closingizing optimal and feasible solution, as this case study deals in improving stick outard operating practices & reducing variability within the do work of roll grinding & splutter enactment. CONTENTS PAGE NO ABSTRACT 4 CONTENTS 5LIST OF FIGURES 8 LIST OF TABLES 10 NOMENCLATURE 11 CHAPTER 1 entree AND LITERATURE SURVEY 1. 1 INTRODUCTION 12 1. 2 BASIC OF COLD ROLLING 15 1. 3 bark PASS MILL 16 1. 3. 1 OVERVIEW OF pargon PASS MILL 18 1. 3. 2 PURPOSE OF SKIN modification 19 1. 4 ROLLS & THEIR REQUIREMENTS 25 1. 5 ROLL grind treat 31 1. 6 ROLL TEX TURING PRACTICES 35 . 7 SIX SIGMA climb up 41 1. 7. 2 SIX SIGMA IMPLEMENTATION 41 1. 8 business DEFINITION 44 1. 9 OBJelectroconvulsive therapyIVE OF CASE STUDY 45 CHAPTER 2 ANALYSIS OF THE PROBLEM PAGE NO 2. 1 INTRODUCTION 46 2. 2 BRAIN STORMING 46 2. 3 PARETO ANALYSIS 47 2. 4 INDIVIDUAL AND MOVING RANGE GRAPH 50 2. 5 MOODS MEDIAN TEST 52 2. 6 CAUSE EFFECT diagram 57 2. 7 OUTCOME OF ANALYSIS 60 CHAPTER 3 methodology TO ACHIEVE OBJECTIVES 3. 1INTRODUCTION 61 3. 2 PREPERATION OF ACTION PLAN 62 . 3 NORMAL GRINDING TRIALS & ACTION 62 3. 4 CRACK GRINDING TRIALS & ACTIONS 63 3. 5 SKIN PANEL ROLL GRINDING 63 3. 6 OPERATOR VARIABILITY 64 3. 7 ROLL channelize DUE TO ROLL ROUGHNESS 64 3. 8 SCHEDULING tilt 65 3. 9 ROUGHNESS PREDICTION MODEL 66 CHAPTER 4 RESULTS AND DISCUSSIONS PAGE NO 4. 1 INTRODUCTION 68 4. 2 to begin with AND AFTER COMPARISSION 68 4. 3 DISCUSSION ON RESULTS 71 4. 4 RESULTS 72 4. 5 CONTROL PLAN 73 . 6 SAVINGSCALCULATION 74 CHAPTER 5 CONCLUSION & FUTURE SCOPE 75 RE FERENCES 76 reheel of Figures summon No 1. 1 Skin Pass Mill & in tandem bicycle ice- bleak Mill Photo graph 12 1. 2 Line layout of cold curl mill 14 1. 3 Skin Pass Mill Tata steel 16 1. 4 Tensile analyse graph forrader shinny Passing 20 1. 5 Tensile ravel graph aft(prenominal) grate Passing 22 1. 6 Luder circumstances 24 1. 7Correlation between severity & spot count28 1. 8 Skewness of bob up28 1. 9 Surface broadsided at EDT m/c Tata steel 29 2. 0 Waviness Roughness & form of develop30 2. Roll Grinding M/c at cold-blooded Rolling Mill 32 2. 2 EDT Vs Shot bourgeon Roll 37 2. 3 Effect of time & temp on climb texture38 2. 4 Effect of ve polarity on approach texture38 2. 5 Roll texturing m/c at ratty ringlet mill40 2. 6 Work roll consumption prune at whittle pass mill 44 2. 7 P beto map for SPM Work roll grinding 49 2. 8 X bar & moving start chart for normal grinding 50 2. 9 Box plot for varied operator at Roll Shop 54 List of Figures pageboy No 3. 0 Capabil ity histogram for normal grinding 55 3. 1 Roll long tonnage trend at tegument pass Mill 56 . 2 Abnormal roll transfer trend at percolate down pass mill 57 3. 3 Cause & effect diagram for roll change due to low Ra 58 3. 4 SPM Work roll consumption trend forrader case study 68 3. 5 SPM Work roll consumption trend forward case study 69 3. 6 Capability histogram before case study 69 3. 7 Capability histogram afterwards case study 70 3. 8 Trend of abnormal roll change at skin pass mill 71 List of Tables Page No 1. 1 Roll raggedness dot of tandem & skin pass mill 26 1. 2 Roughness verity detail of texturing m/c 27 1. Selection of peripheral speed 31 1. 4 Standard Stock removal specification 33 1. 5 Grit size for different Roll 34 1. 6 infixed action on Grinding wheel on various condition 34 1. 7 Structure of grinding base upon requirement 35 1. 8 Grinding data for skin pass mill work roll 49 1. 9 selective information capturing sheet51 2. 0 Operator variability matrix52 2. 1 Regression test result53 2. 2 Abnormal Roll Change detail at Skin Pass mill56 2. 3 Prioritization matrix for roll change reasons 57 2. 4 computer programing Example of skin pass mill59 2. practice Grinding trials & findings62 2. 6 Crack Grinding trials & findings63 2. 7 Modified Scheduling Example 65 2. 8 list of parameter effecting gaucheness 66 2. 9 Results of case study 72 3. 0 Control dactyl for reducing work roll consumption 73 3. 1 saving of the case study 74 NOMENCLATURE TCM Tandem stone-cold Mill SPM Skin Pass Mill M/c, m/c simple machine EDT Electro Discharge Texturing Ra average Roughness CRM Cold Rolling Mill IMR Individual Moving Range TDC Technical Delivery Condition ECT Eddy current testing CRMIS Cold Rolling Mill knowledge system PLTCM Pickling line tandem cold MillYPE Yield closure filename extension SPM Skin Pass Mill BAF Batch Annealing Furnace ECL electrolytic condenser Cleaning line RCL Rec oil colouring line NSC Nippon Steel Corporation CR CA Cold turn over Closed Annealed CHAPTER 1 INTRODUCTION AND LITERATURE SURVEY 1. INTRODUCTION This chapter gives education about cold cast mill, Skin Pass mill, Roll grinding, and Roll texturing transition . It in like manner describes about six sigma tool & its implementation at the end it describes objective of the case study. Cold Rolling is a Process by which hot rolled strip or stock is introduced between rollers and squeezed or compressed to the desired thickness.Amount of chance variable introduce determines the properties of the destroyed product. Following are Purpose of Cold Rolling ? Good formability ? capital shape up block ? Reasonable strength ? Close dimensional tolerance Fig 1. 1 Tandem Cold Mill Tata steel Skin Pass Mill Tata steel Cold Rolling Mill labyrinthine has been commissioned at TATA STEEL works in the year 2000. The total output of the Cold Rolling Mill complex consists of 0. 96 mt of cold rolled and annealed products and 0. 5 mtpa (Million To nne Per Annum) of cold rolled and galvanized products.Hence, the total installed capacity of this unit is approximately 1. 5 million tons per annum. The pluck of thickness and width of these cold rolled products are 0. 3 to 3. 2 mm and 800 to1560 mm honourively. The primary input strong to the cold coil complex is a hot rolled coil. The cold rolled products are broadly under the categories ? Annealed coils ? Galvanized coils ? Cold rolled full hard coils. The cold rolled products from the Cold Rolling Mill complex are intentional to cater to various market segments such as construction, general Eng. , automobile, blank goods, packaging and others.CRM Process flow at Tata Steel Pickling (to remove oxides and scales) Cold pealing in tandem mill to achieve desired thickness electrolytic capacitor cleaning line to clean the come in dirt. Batch formidabilitying furnace for internal underscore relieving Skin passing to remove luder bands, develop automatonlike properties, Im part desired surface finish improve straightawayness, Inspection, finishing, dispatch Sub Section of Cold Rolling Mill ? Pickling Line &Tandem Cold Mill (PL-TCM) ? Batch Annealing Furnace (BAF) ? Electrolytic cleaning Line (ECL) ? Skin Pass Mill (SPM) ? Galvanising Line ? Recoiling Line (RCL) ? Coil promotion Line (CPL) pic Fig 1. 2 Line lay out of Cold Rolling Mill Tata steel 1. 2 Basic of Cold Rolling Mill Following are the basic Processes ? The Hot Strip Mill sends the hot rolled coils (thickness 2 to 6 mm width and 800-1560 mm) to the Cold Rolling Mill Complex for doing. ? First the hot rolled coils are passed by means of the Pickling section containing Hydrochloric acid, in order to clean the surface of consume & scales, qualification them ready for cold bun. ? The Trimming Section where the edges of pickled hot rolled coils are trimmed( if necessary) ? The coil is then fed into the main mill, that is to sayTandem Cold Mill with five mill stands, each having ternary pa irs of rolls in the five stands which bring down the strip thickness in a construeled manner to the desired tar find value of (0. 3mm to 3. 2 mm). ? This completes the process of cold rolling or rolling at ambient temperatures. ? From here the two-third of the product goes to Electrolytic cleaning line, where generally two process takes place and they are Predegressing and electrolytic cleaning with the help of NaOH, after this the sheet is swear out with high pressure steam to remove the bubbles of NaOH from the surface.Then the coil is dried in the hot drier. ? The coil comes to Batch Annealing furnace directly from Electrolytic cleaning line where they are stacked covered and heat uped up in a closed hood in a hundred% enthalpy atmosphere. This process improves the mechanical properties of the strip. ? The Skin Pass Mill takes care of the coils annealed in Batch Annealing furnace by passing them through a adept stand high-speed mill with two pairs of rolls. The objective is to impart the correct surface texture and to control the mechanical properties as per customer requirement. The coils are properly oiled for rust protection and recoiled in the Recoiling Lines (RCL 1, 2 & 3) for inspecting the surface. ? The be one- third part of the production from PLTCM goes to the Galvanising Lines (1 & 2) where coils are again cleaned, rinsed, dried, L-annealed/heated and taken through a Molten zinc bath for a continuous uniform screening of zinc. This zinc coating helps give a sacrificial layer on the cold rolled strip for wearing away protection. The Continuous packaging line takes care of the packing requirement of the coils as per the customer specifications. 1. 3 Skin Pass Mill pic Fig 1. 3 Skin Pass Mill Tata steel front view Skin pass mill Annealed coils are given a small cold reduction (typically around 1-3 %) in the skin pass mill. This operation results in the right surface roughness imparted on the strip surface as per the customer specifications. In addition, a metallurgical defects known as finishing touch strains are eliminated, and also the flatness of the strip is better.The basic operation make in the cold rolling mill is the wet temper rolling as a cold rolling finishing which is the final process in the integrated steel production, where all real(a)s received from the cold rolling process are processed into the final products with compulsory properties through cleaning, heat interposition and then temper rolling. As this process is closely cerebrate to exploiter requirement for mechanical properties, surface properties, size etc. many detailed operation standards are required ( temper surface, size change). This process is right away adaptable to shape correction reprocessing etc. ut there are many operations which require human hands, as compared with cold rolling. As skin passing is the final process of the integrated steel making operation, the in defining obtained from this process must be completely fed suffer to the processes on the down stream side of the steel making furnace. This process is located closest to users and achieving in line quality to meet the user requirements must guaranty the quality. The feed back of information to the preceding processes to be reflected in production is very important.The temper rolling operation locomote into three types as projectn down the stairs Operation using water-soluble rolling oil Operation using oil-soluble rolling oil Operation in with no rolling oil is apply (Dry rolling). Each type of rolling operation has both advantages and disadvantages. The type of rolling operation must be selected in due consideration of the ease of temper rolling, the ease of operation and rust preventive at downstream process at customers end. The surface of roll to be use for temper rolling is mat-finished by tool blasting of steel grit or Elector Discharge Texturing (EDT).This finish is widely as it ensures good paint ability. When the working rol ls are ground, the roll surface is bright- finished to about Ra (0. 05m) by using a grinding wheel of small grain size. The surface roughness of the strip rolled by bright-finished rolls is below Ra(0. 35m), which is suitable for prime coating Generally, the surface finish condition of strip in the temper rolling process is controlled in terms of the surface finished of work rolls only. For proof of this condition, the roughness and look of sheet surface after temper rolling isChecked at regular intervals. Temper rolling oil utilize is mainly applied to thick products, using dull-finished work rolls. The majority of rolling oils used for this rolling are sodium nitrite- base oils. The concentration of sodium nitrite is 5 ( 10% oil-soluble temper rolling oils higher rust preventive place to meet required uses have been developed and put into practical use. 1. 3. 1 OVERVIEW OF SKIN PASS MILL Skin pass an overview ? Single stand mill ? 4- High wet skin pass non-reversible mill ? me ntal object 1mtpa ? Line speed 900mpm ? Thk range 0. 3-3. 2 mm ? Width range 900-1580 mm SPM Equipment ? Main drive-3 ? Mill stand rolls-4 ? Auxiliary roll-8 ? Oiling system ? sess complete system ? Hydraulic gap control system ? E languishation control ? Low pressure hydraulic system ? Quick roll changing car ? Auto tempered car ? Back up rolls polishing ? Unique Features of SPM ? Higher productivity. ? High degree of accuracy- extension control ? Surface cleanliness- wet skin pass ? Eco friendly fume exhaust ? Automatic quick work rolls change & pass line 1. 3. 2 PURPOSE OF SKIN PASSING ? Improvement of mechanical properties of framework ? determine correction Adjustment of surface properties (roughness) ? Apply rust preventive oil (optional) ? Improvement of mechanical properties of material ? Elimination of relent point annexe ? Improvement of formability by decreasing the repay point ? Improvement of other mechanical properties The skin passing of material has to be thro ugh with optimal parameters such that the purpose of skin passing is met. Ideally the skin passing has to be done in such a way that alternate(a) grains are labour by which we pull up stakes get 50% strained surface grains and 50% strain dethaw surface grains. Upper give way pointStress Yield point reference Lower re fall outance point Strain Fig 1. 4 tensile test graphs before skin passing Yield point elongation is a long-familiar phenomenon in low carbon steel. After the elastic portion of the stress strain make out ball (a schematic engineering stress-strain cut off is shown in the above figure) the load drops at upper yield point. At lower yield point this drop becomes steady, but a continuous series of sport appears in the stress strain curve. This is commonly known as yield point elongation. After this stage, the curve becomes smooth again.Reason The reason bottom this phenomenon is the alternate locking and unlocking of dislocations by the interstitial atoms (C and N) in steel matrix. C and N atoms form interstitial solid solution and these have natural affinity for locking the dislocations. The locked dislocations cannot move freely, which restricts distortion of the material. The deformation of the material is rattling caused by movement and multiplication of dislocations. The deformation stops when the dislocations are not free enough to continue their movements, and further employment of load in this situation causes crack multiplication and failure.After cold rolling and annealing, a low carbon steel strip is supposed to undergo a forming operation. However, this forming becomes difficult if the dislocations are pinned down by the interstitial solute atoms. The annealing treatment provides ample opportunity for the dislocations to move freely and sit at the thermo self-propelledally favourable sites, where the solute atoms pin the dislocations and kill their mobility. This is commonly known as Cottrell atmosphere. Now, if the mate rial is subjected to a tensile load, the stress strain curve will show a serration, i. . alternate load drop and load jump, just after the yield point. Load drop indicates that the dislocations are pulled off from the solute atmosphere, coupled with generation of dulcet dislocations under the external pierce, and load jump indicates that the momentarily free dislocations are again encountering with the solute atoms. This in truth constitutes the stage of yield point elongation. repayable to the pinning effect of the solute atoms, the dislocation multiplication sources also become active, which generates fresh dislocations.After this stage, when sufficient fresh dislocations are available for continuing deformation, the stress-strain curve becomes smooth again. This yield point elongation (YPE) is absolutely detrimental as far as the formability of the material is concerned. It creates Luder bands or stretcher strain marks, which in conclusion leads to failure of the component. T hese bands are visible on the strip surface. When a test specimen exhibits YPE during its tensile testing, these bands appear on the specimen surface, starting from affection (where necking starts) and spreading towards the ends, at an angle of approximately 450 to the tensile axis.YPE elongation continues till the entire specimen surface is covered by the Luder band formation, then smooth plastic deformation starts. Here comes the role of skin passing. Since YPE, after batch annealing, cannot be avoided, a skin depth deformation is given to the just annealed steel strip. This skin depth deformation actually overcomes this region of the stress-strain curve. Sufficient number of dislocations is pulled off from the solute (C, N) atmosphere, at the same time fresh dislocations are generated, which is sufficient for facilitating the forming operation at the next stage.If the material, in skin passed (or temper rolled) condition, is subjected to tensile testing, the stress strain curve w ill not show any YPE and the plastic deformation will take place without a sharp yield point, as shown in the figure below. That is what precisely desired for drawing or deep drawing tally material. If this skin passed material is left unused for a sufficiently long time, or subjected to a brief heat treatment at a low temperature, the YPE reappears once again. The YS value also goes up and ductility of the material drops. This phenomenon is known as strain aging. UTS YS Stress Strain Fig 1. tensile test graphs after skin passing From the discussion made so far, it is clear that the locking of dislocations are related to the two important factors, one is movement of dislocations, the other is movement of interstitial solute atoms. Therefore diffusion has a very important role to play. If the testing is carried out at room temperature, the mobility of dislocations under the action of external load is more than the mobility of solute atoms. If the similar test is carried out at a hig her temperature, the mobility of the solute atoms increases, and movements of dislocation and solute atoms may be comparable.Such a situation would give rise to an interesting phenomenon called dynamic strain aging, where the solute atoms keep on interacting with the dislocations and the entire stress strain curve (after elastic limit) shows serration. Since YPE is directly related to the concentrations of C and N atoms in steel, the issue of deformation (known as temper elongation) to be given at skin pass mill (SPM), which is a critical factor, varies with steel composition. The magnitude of temper elongation should be high for higher C content. For instance, the temper elongation in case of CQ material should be higher than that in case of EDD grade.If the temper elongation is less than the required amount, the material will show stretcher strain marks during forming. If temper elongation is higher than the required amount, the strength of the material will increase. This is not desirable, particularly for the softer grades like IF and EDD, because the strain hardening exponent value is higher for these grades, compared to that for ordinary CQ material. Theoretically s aggrandisementing, IF or interstitial free deep drawing grade steel should not require any skin passing. The reason is that the C and N concentrations are kept very low in this grade (of the order of 30 ppm).In addition, presence of Ti in this steel promotes the fixing of C and N atoms in form of carbide and carbonitiride precipitates, thereby creating a condition so that the Fe matrix becomes virtually free of interstitial solute atoms. Such a condition favours the easy movement of dislocations without any hindrance, and this steel has been established as the highest formable grade, with maximum deep drawability and ductility. In practice, IF grade steel is subjected to skin passing with a small magnitude of elongation, and, of all grades, it requires minimum temper elongation.The skin pass depends on Yield strength of the material in the chase way Lower the skin pass (roughly less than 0. 6 %), the material will have the tendency to show Bauschingers effect. Higher the skin passing (above 1. 5%) the material will be over strained. Thats the reason why the skin passing for a given YS, has to be done with the optimum reduction such that the material does not get into either of the problems stated above. Also percentage reduction increases with increasing YS to get the optimum properties. Parameters on which Skin pass Load dependsGrain surface Higher the ASTM grain size number (finer the grain), higher is the skin pass load. Speed Increasing the speed of skin pass mill will require higher load for the same reduction Diameter of work roll Larger the diameter of the work rolls, higher is the roll force required to remove stretcher strain. Roughness of the strip from Tandem Cold Mill The incoming coil has got some roughness value because of the final finishing in stand n umber (5) of tandem Cold Mill. legion(predicate) times to high roughness of the incoming strip to Skin Pass Mill and the requirement of Average roughness values on the surface in the ranger of 0. -1. 2 micrometer calipers for closely applications, the nebs are knocked off during skin passing which is detrimental from forming and propose clarity point of view. The best practice for this should be keeping as low roughness as affirmable on the strip surface after tandem cold mill (of course sticker formation during annealing in Batch annealing furnace has to be kept in mind), and imparting higher roughness on the work rolls in the skin pass mill. 1. 3. 3 THEORY OF SKIN PASSING When the annealed mild steel sheet is preformed, surface markings, called stretcher strains markings, appear on deformed parts.Stretcher strains are also called as Luder bands. The formation of these markings can be prevented by Skin passing the sheet by giving the sheet elongation of 1-2 % before Performin g. LUDER BAND OR STRECHER stress This band is formed with an angle of about 45 deg 50 deg with respect to the tensile axis the markings formed between Upper and lower are called as Luder Lines or Stretcher Strains as shown in fig 1. 6 Tensile load Luder band Tensile load Fig 1. 6 Luder band 1. 4 Rolls & their requirement for Cold RollingThe performance characteristics of rolls used in cold rolling mill, both in Tandem Cold Mill(TCM) and Skin Pass Mill, are critical to mill productivity and to the quality and acceptance of the cold rolled products. With the rapid change in roll technology, roll management in cold rolling has become an field of operation of utmost importance. The increasing requirements of critical surface finish and texture of flat rolled product has necessitated application of the state of art technology in roll preparation and roll inspection. Rolls also represent a momentous investment and input to a value analysis of cost per ton rolled.The quality of work ro lls that come into direct contact with the steel product has a direct effect on product quality and mill operation. A forged steel with a chromium content of 5 mass% has been conventionally used to meet the requirement of metallurgical social organisation homogeneity and high hardness for work rolls in cold rolling. Rolls having improved performance are strongly demanded. 1. 4. 1 Requirement from textured Rolls 1. 4. 1. 1 Surface finish Surface roughness is imparted to Work Rolls which are used in 5th stand of Tandem cold mill and to the work rolls of Skin Pass Mill.The primary requirement of surface roughness for tandem mill rolls is to prevent stickers in the next process i. e. batch annealing. The surface roughness on Skin pass mill is guided by the requirement of surface roughness on Cold rolled strip which is based on its end use. Ra is the universally recognized and most used international parameter of roughness. It is the arithmetic taut of the departures of the pen from t he miserly line. Ra = 1/L y (x)dx For a typical application of auto grade the Ra value in strip ranges from 0. 8 to 1. 2 micron.The final roughness on SPM roll is decided based on the transfer ratio of roughness from roll to strip (ranges from 45-60% based on mill parameters). A typical transfer plot and the values of roughness is shown in table 1. 1 Table 1. 1 Roll Roughness detail of Tandem cold mill & skin pass mill Work Roll Tandem Cold MILL Work Rolls Skin Pass Mill Work Rolls Average roughness PPC Average roughness PPC 3. 75 3 120 4. 0 70 3. 0 96, 118 4. 5 65 3. 5 80 5. 0 60 4. 0 70 The distribution of surface roughness over the roll automobile trunk is also of importance to ensure consistency of surface roughness over the strip widths produced in a campaign. The ROLLTEX Electro hit texturing process of Sarclad machine produces a texture to the capability as mentioned in table 1. 2. Roughness interpretation Roughness is defined as the finer irregularities of the surf ace texture that normally result from the inherent action of some production process such as machining or wear. Roughness features are typically in the sub micron range.Continuously recurring, irregular depressions and elevations on the surface of the coil are known as roughness. Rough coil surface is usually caused by severe roll groove wears surface roughness can also be caused due to corrosion if the rod is stored for lengthy periods in break dance or corrosive atmospheres. The degree of roughness can be compulsive by microscopic examination or with Ra meter. Surface roughness has two main attributes Roughness height or depth, and Lateral dimension. Roughness heights of the structure on polishing or machining surface are frequently measured as a root mean red-blooded roughness.The units of roughness are angstroms or nanometres for smoothers surface lim and micrometers m for rougher surface. Lateral dimensions frequently and called surface spatial wave lengths are measured in micrometers. A rough surface is usually described in terms of its digression from a smooth reference surface. Some conventional methods for surface standard are optical microscope, scanning electron microscope and transmission electron microscope. These can be used to produce topographic maps of surfaces. Today laser distribution technique has become more common. Ra valueAverage/mean height of surface peaks and troughs over a reference length indicates an boilersuit visibleness of the sheet surface, dullness or brightness. Roughness is imparted to the rolls by Electro discharge texturing method Table 1. 2 Roughness accuracy detail of texturing m/c Sno Range of roughness value Accuracy of surface produced (Ra) Accuracy of surface produced (PPC-peaks per centimetre) 1 0. to 6. 0 micron Ra +/- 4 % of mean Ra +/- 4 % of mean PPC 2 6. 1 to 10. 0 micron Ra +/- 5 % of mean Ra +/- 5 % of mean PPC 3 10. 1 micron Ra +/- 6 % of mean Ra +/- 6 % of mean PPC 1. 4. 1. 2 Peak Count It is the measurement of number of peaks in the specified length over a particular bandwidth (normally 1 micron).A profile peak is the highest part of the profile between an upwards and downwardly crossing of the mean line. The exposed auto body panels typically require 100 ppi on the Cold rolled sheet. The transfer ratio of peak counts from roll to the strip ranges between 60-70%, based on again the rolling conditions. Figure 1. 7 shows the correlation between the roughness of the surface & the peak counts. Fig 1. 7 Correlation between roughness & peak counts constancy of the surface profile The textured roll is required to give a consistent transfer of roughness and peak count on the strip while rolling.During rolling the surface experiences wear of the peaks and the roll is Fig 1. 8 Skewness of surface discarded after a certain tonnage, determined based on the cut-off point of surface requirement on the strip. To treasure this requirement of surface stability, metrology experts and certain European instrument manufacturers have devised surface texture height parameters, which can be analysed by a Data Processing Module (DPM), supplied separately by the surface finish inspector manufacturers. Out of various parameters used in this analysis, the most commonly used is Rsk (Skewness) and tp % (known as gallery ratio).Rsk is the measure of the symmetry of the amplitude distribution curve about the mean line. As shown in figure 1. 8 if Rsk is electronegative the surface peaks are higher, which is prone to a large drop in surface finish during the initial rolling. Based on the practical experience of cold rollers over the world, a slight positive value is preferred. A typical surface plot after texturing a surface to roughness value of 2. 93 micron in Sarclad EDT machine and measured by DPM is shown in Figure 1. 9 Fig 1. 9 Surface measurements done on Tata EDT-Skin Pass Mill roll.The Bearing ratio (tp%) is a measure of the length of bearing surface (expressed as a % of the assessment length), where the profile peaks have been cut off at a line which runs mate to the mean line of the profile. The line defining the bearing surface can be set at a selected depth below the highest peak or at a selected distance above or below the mean line of the profile. When this line is set to the depth of the largest profile valley, the tp is 100% because the entire profile is above the bearing line.By plotting the tp value against depth below the highest profile peak between the 0% and 100 % limits, the bearing ratio (known as Abott- Firestone curve) curve is obtained. Figure 1. 9 shows the bearing ratio curve against a particular value of Rsk. 1. 4. 1. 3Waviness Most surface profile results from the combined effects of roughness, waviness and form as shown in figure 2 Waviness parameters are produced by passing the data of the surface measurement through a low pass filter, so that longer wavelengths than the cut-off are included. The waviness, Wa is c alculated from the resulting profile.Fig 2 Waviness, Roughness and Form of a surface Wavelengths in the roughness category 800 micron are covered or filtered out by painting, in the end application of the CR strip. Wavelengths 800 micron defined as Waviness remain or are enhanced after painting and contribute to poor pungency of image or image clarity. If Wa is held below 0. 6 micron, irrespective of the Ra, then those wavelengths 800 micron have only a marginally adverse effect on Distinctness of image. Samples of sheet produced by tandem/ temper mill rolls textured by the Rolltex EDT process consistently show levels of Wa

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