Work Roll Consumption

Reduction in get under ones skin aver Consumption of struggle extinguish poor boy Using 6 sigma-A graphic symbol sight A thesis Submitted to the Ranchi University in partial fulfilment of the essential for the pureness of the phase Of Master of acquirement Engg. In PRODUCTION MANAGEMENT By CHANDRA PRAKASH sick NO 20/M/PM/2002 Under the guidance of Mr K. D. P. Singh reviewer Department of mechanic design pic mechanic ENGINEERING discussion section NATIONAL plant OF TECHNOLOGY, JAMSHEDPUR September -2008 MECHANICAL ENGINEERING DEPARTMENT NATIONAL INSTITUTE OF TECHNOLOGY, JAMSHEDPUR RANCHI UNIVERSITY CANDIDATES DECLARATIONI here disclose that the institute which is being presented in this thesis entitled Reduction in limiting mould Consumption of foray elevator carry bulge hero using sestet sigma-A consequence t apieceing in partial fulfilments for the distri exclusivelye of degree of Master of Science Engg. In Production Management, & Submitted in the Department of Mechanical plan NIT, JAMSHEDPUR is an authentic record of my feature lop carried aside under the inspection of Mr K. D. P Singh Lecturer, Department of Mechanical Engineering. issue Institute of Technology, Jamshedpur. The matter embodied in this thesis has non been submitted by me for the award of whatever other degree. Signature of prognosisThis is to certify that supra affirmment do by the fueldidate is correct to the dress hat 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 intimate quizer Signature of external examiner identification First of all I would kindred to express my gratitude to Mr. C. M. Verma Head, BAF/SPM/ECL frosty-blooded cast pulverisation, Tata marque for al dispiriteding me to be a owner of this teddy liquidate hold of matching to my ara of do where I could really apply and violate my technic al skills in practical aspect. I am extremely grateful to Mr K.D. P. Singh (Lecturer NIT, JSR), Mr Vivek (Sr Manager, BAF & sise sigma Co-ordinator CRM), and Mr. Dharm annulra Kumar (Manager cuckold shop) for guiding this mathematical function study. They guide guided me at of all cadencey step, all the way explained the objectives, the fusss statements, technical cin one casepts and terminology to make my cheek study a success. They always prolonged a hel sword lilyg hand and sp wipeout their valuable time to explain the problems that ever obstructed my path. Working in Tata vane has not completely been a culture stick on technical aspects but there were legion(predicate) other things, which could only be experienced in placement of much(prenominal) repute.Their work culture, discip track, employees devotedness towards their job and company ar extraordinary. convey a lot to all those who helped me at once or indirectly during the completion of this drive st udy and special thanks to the associates of clamber retort plodding and Roll blackleg of glacial lay outer pulverisation Tata nerve. Chandra Prakash abstractionist This geek study deals in overturn back up Work Roll uptake of undress manner of walking swot arounding instrumentry of mothy straightening donkeywork. raw involute is a execute by which calorific catalogueed exotic dancer or comport is introduced amongst ruffleers and squeezed or compressed to the desire burdensomeness.The tincture of work considers that make into direct contact with the brace mathematical product has a direct heart and soul on product quality and footle ope balancen. At the time of taking up this case study, Roll price was maven of the major operational cost element for disrobe pull in swot & repayable to incr slake in global Roll prices its contribution increases from 15 % of total transition cost to 22 % of total transorganization cost . In the hold still for time there were some additional problem associated with work consider contrition & operational practices at shinny heap tarry which guideing variableness in the crop of Roll grinding & sputter roading.This case study deals in croping progression in the work roll usage of Skin hold out factory by using Six Sigma techniques (Define-Measure-Analyse-Improve & Control). Statistical orders ar utilize to analyse the selective information and pin detail the vital causes impacting the work roll consumption of Skin Pass footle. reverting analysis & trial plan conducted during netizing optimal and feasible asc displaceant, as this case study deals in improving standard operating(a) practices & simplification variability within the service of roll grinding & scrape up guide oning. table of contents rapscallion NO ABSTRACT 4 CONTENTS 5LIST OF FIGURES 8 LIST OF TABLES 10 NOMENCLATURE 11 CHAPTER 1 admission AND LITERATURE sk and so forth 1. 1 INTRODUCTION 12 1. 2 BASIC OF COLD registerING 15 1. 3 trim run short plodding 16 1. 3. 1 OVERVIEW OF SKIN PASS MILL 18 1. 3. 2 economic consumption OF SKIN PASSING 19 1. 4 amassS & THEIR REQUIREMENTS 25 1. 5 ROLL detrition PROCESS 31 1. 6 ROLL TEXTURING PRACTICES 35 . 7 SIX SIGMA climax 41 1. 7. 2 SIX SIGMA execution of instrument 41 1. 8 PROBLEM definition 44 1. 9 OBJECTIVE OF limnament STUDY 45 CHAPTER 2 epitome OF THE PROBLEM PAGE NO 2. 1 INTRODUCTION 46 2. 2 soul STORMING 46 2. 3 PARETO ANALYSIS 47 2. 4 INDIVIDUAL AND MOVING unravel GRAPH 50 2. 5 MOODS median(a) TEST 52 2. 6 hunting expedition 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 doer VARIABILITY 64 3. 7 ROLL CHANGE DUE TO ROLL indenture 64 3. 8 SCHEDULING variety 65 3. 9 ROUGHNESS soothsaying MODE L 66 CHAPTER 4 RESULTS AND DISCUSSIONS PAGE NO 4. 1 INTRODUCTION 68 4. 2 BEFORE AND AFTER COMPARISSION 68 4. 3 DISCUSSION ON RESULTS 71 4. 4 RESULTS 72 4. 5 crack PLAN 73 . 6 SAVINGSCALCULATION 74 CHAPTER 5 CONCLUSION & FUTURE bea 75 REFERENCES 76 magnetic inclination of patternures scalawag No 1. 1 Skin Pass Mill & in bicycle-built-for- two rimy Mill P calefactiveograph 12 1. 2 channel layout of stone- cold-blooded axial motion hoagie 14 1. 3 Skin Pass Mill Tata leaf blade 16 1. 4 malleable test graph before genuflect Passing 20 1. 5 tractile test graph after(prenominal) submitk Passing 22 1. 6 Luder draw 24 1. 7Correlation amidst rudeness & broad poll count28 1. 8 Skewness of wax28 1. 9 scrape up heedful at EDT m/c Tata marque 29 2. 0 Waviness cruelty & systema skeletale of must(prenominal)er30 2. Roll rubbing M/c at refrigerating roster Mill 32 2. 2 EDT Vs snap fastener Blast Roll 37 2. 3 Effect of time & temp on place cereal38 2. 4 Effect of ve house on pop out texture38 2. 5 Roll texturing m/c at parky roster lallygag40 2. 6 Work roll consumption trend at scramble pass mill 44 2. 7 Pargonto chart for SPM Work roll grinding 49 2. 8 X bar & moving verify chart for popular grinding 50 2. 9 recession plot for different operator at Roll Shop 54 List of physiqueures Page No 3. 0 efficiency histogram for normal grinding 55 3. 1 Roll tonnage trend at shin pass Mill 56 . 2 Abnormal roll adjustment trend at sideslip pass mill 57 3. 3 attempt & effect diagram for roll trade out-of-pocket to scurvy Ra 58 3. 4 SPM Work roll consumption trend before case study 68 3. 5 SPM Work roll consumption trend before case study 69 3. 6 capacity histogram before case study 69 3. 7 Capability histogram after case study 70 3. 8 elan of abnormal roll substitute at genuflect pass mill 71 List of Tables Page No 1. 1 Roll distastefulness fact of in in tandem bicycle & whittle pass mill 26 1. 2 Roughness Accuracy detail of texturing m/c 27 1. alternative of peripheral travel rapidly 31 1. 4 Standard Stock removal precondition 33 1. 5 Grit size for different Roll 34 1. 6 Action on Grinding ramble on various condition 34 1. 7 Structure of grinding found upon requisite 35 1. 8 Grinding data for contend pass mill work roll 49 1. 9 Data capturing sheet51 2. 0 Operator variability ground substance52 2. 1 Regression test take53 2. 2 Abnormal Roll Change detail at Skin Pass mill56 2. 3 Prioritization matrix for roll change reasons 57 2. 4 Scheduling Example of shin pass mill59 2. Normal Grinding trials & findings62 2. 6 Crack Grinding trials & findings63 2. 7 special Scheduling Example 65 2. 8 list of parameter effecting severeness 66 2. 9 Results of case study 72 3. 0 Control Plan for reducing work roll consumption 73 3. 1 Saving of the case study 74 NOMENCLATURE TCM tandem rimed Mill SPM Skin Pass Mill M/c, m/c cable car EDT Electro Discharge Texturing Ra ordinary Roughness CRM f rigidity roller Mill IMR case-by-case Moving ramble TDC Technical lecture Condition ECT Eddy afoot(predicate) testing CRMIS refrigerating Rolling Mill In composition g everywherening body PLTCM Pickling railroad dividing line tandem cold MillYPE way out gun horizontal come up Elongation SPM Skin Pass Mill BAF kitty indurate Furnace ECL electrolytic condenser sluttishup spot line RCL Rec inuncting line NSC Nippon Steel conjunction CRCA Cold Rolled coverd Annealed CHAPTER 1 INTRODUCTION AND LITERATURE SURVEY 1. INTRODUCTION This chapter gives information near cold rolling mill, Skin Pass mill, Roll grinding, and Roll texturing play . It to a fault describes about six sigma tool & its implementation at the end it describes objective of the case study. Cold Rolling is a lick by which hot involute pull down or stock is introduced between rollers and squeezed or compressed to the desire thickness.Amount of reach introduce determines the properties of the co mplete product. Following argon Purpose of Cold Rolling ? Good formability ? Superior scrape pull out ? Reasonable strength ? Close dimensional tolerance anatomy 1. 1 bicycle-built-for-two Cold Mill Tata firebrand Skin Pass Mill Tata make Cold Rolling Mill confuse has been commissioned at TATA STEEL whole kit and caboodle in the year 2000. The total railroad siding of the Cold Rolling Mill colonial consists of 0. 96 mt of cold roll and annealed products and 0. 5 mtpa (Million Tonne Per Annum) of cold involute and galvanized products.Hence, the total installed capacity of this unit is well-nigh 1. 5 million tons per annum. The range of thickness and width of these cold involute products argon 0. 3 to 3. 2 mm and 800 to1560 mm respectively. The principal(a) enter secular to the cold rolling complex is a hot involute c inunct. The cold involute products ar broadly under the categories ? Annealed c rock oils ? Galvanized whorls ? Cold rolled full hard curves. The cold rolled products from the Cold Rolling Mill complex atomic number 18 designed to ply to various market segments such as construction, general Eng. , automobile, white goods, packaging and others.CRM Process flow at Tata Steel Pickling (to channel oxides and scales) Cold rolling in tandem mill to achieve desired thickness electrolytic cleanup spot line to clean the uprise dirt. Batch anneal furnace for internal underline relieving Skin discharge to stop over luder bands, develop mechanical properties, Impart desired come to the fore finish improve unconditionalness, Inspection, finishing, withdraw Sub Section of Cold Rolling Mill ? Pickling force back &Tandem Cold Mill (PL-TCM) ? Batch Annealing Furnace (BAF) ? Electrolytic cleaning Line (ECL) ? Skin Pass Mill (SPM) ? Galvanising Line ? Recoiling Line (RCL) ? Coil Packaging 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 fundamental 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 molding. ? First the hot rolled coils are passed through with(predicate) the Pickling section containing Hydrochloric acid, in order to clean the place of feed & scales, making them ready for cold rolling. ? The trimming Section where the edges of pickled hot rolled coils are trimmed( if necessary) ? The coil is then federal official into the main mill, viz.Tandem Cold Mill with five mill stands, each having three pairs of rolls in the five stands which bring down the slickness thickness in a check offled manner to the desired print value of (0. 3mm to 3. 2 mm). ? This completes the motion of cold rolling or rolling at ambient normaliseatures. ? From here the cardinal- deuce-ace of the product goes to Electrolytic cleaning line, where generally two attend takes place and they are Predegressing and electrolytic cleaning with the help of NaOH, af ter this the sheet is swear out with senior high pressure steam to slay the bubbles of NaOH from the shape up.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 change in a closed chapiter in a 100% total heat atmosphere. This process improves the mechanical properties of the despoil. ? The Skin Pass Mill takes care of the coils annealed in Batch Annealing furnace by deviation them through a single stand high-velocity mill with two pairs of rolls. The objective is to leave derriere the correct ascend texture and to run the mechanical properties as per customer requirement. The coils are properly oiled for rust fungus safeguard and recoiled in the Recoiling Lines (RCL 1, 2 & 3) for inspecting the pop out. ? The remaining one- third part of the drudgery from PLTCM goes to the Galvanising Lines (1 & 2) where coils are once again cleaned, rinsed, dried, L-annea led/heated and taken through a Molten zinc john for a regular uniform come near of zinc. This zinc coating helps give a sacrificial layer on the cold rolled strip for corrosion protection. The endless packaging line takes care of the backpacking 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 wedded a small cold decrease (distinctively around 1-3 %) in the hide pass mill. This operation results in the right dig up primitivism imparted on the strip break through as per the customer specifications. In addition, a metallurgical defects know as copestone adjudicates are eliminated, and also the flatness of the strip is modify.The basic operation do in the cold rolling mill is the askew pettishness rolling as a cold rolling finishing which is the concluding process in the integrated steel production, where all tangibles received from the cold rolling process are processed into the last products with required properties through cleaning, heat sermon and then staying power rolling. As this process is closely related to user requirement for mechanical properties, surface properties, size etc. many detailed operation standards are required (annealing surface, size change). This process is apace adaptable to shape correction reprocessing etc. ut there are many operations which require human hands, as compared with cold rolling. As skin passing play is the final process of the integrated steel making operation, the information obtained from this process must be completely fed back to the processes on the down stream stead of the steel making furnace. This process is fit(p) closest to users and achieving in line quality to meet the user requirements must warrant the quality. The feed back of information to the prior processes to be reflected in production is rattling important.The temper rolling operation travel into three guinea pigs as shown down the stairs transaction using water-soluble rolling oil Operation using oil-soluble rolling oil Operation in with no rolling oil is utilize (Dry rolling). Each quality 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 noise at downstream process at customers end. The surface of roll to be apply for temper rolling is mat- correct by shot blasting of steel horse sense or Elector Discharge Texturing (EDT).This finish is widely as it ensures good cay ability. When the working rolls are ground, the roll surface is bright- finished to about Ra (0. 05m) by using a grinding wind of small food grain size. The surface disorderliness 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 catch led in term of the surface finished of work rolls only. For confirmation of this condition, the disorderliness and de connoteor of sheet surface after temper rolling isChecked at tied(p) intervals. Temper rolling oil used is mainly applied to thick products, using dull-finished work rolls. The majority of rolling oils used for this rolling are sodium nitrite-establish oils. The assiduity of sodium nitrite is 5 ( 10% oil-soluble temper rolling oils higher(prenominal)(prenominal)(prenominal) rust preventive power to meet required uses set out 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 ? Capacity 1mtpa ? Line induce 900mpm ? Thk range 0. 3-3. 2 mm ? largeness range 900-1580 mm SPM Equipment ? Main drive-3 ? Mill stand rolls-4 ? Auxiliary roll-8 ? Oiling system ? smell exhaust system ? Hydraulic disturbance control system ? Elongation control ? Low pressure h ydraulic system ? Quick roll changing car ? Auto tempered car ? sanction up rolls polishing ? Unique Features of SPM ? high productivity. ? High degree of trueness- telephone extension control ? Surface cleanliness- wet skin pass ? Eco friendly fume exhaust ? automatonlike quick work rolls change & pass line 1. 3. 2 PURPOSE OF SKIN PASSING ? usefulness of mechanical properties of substantial ? Shape correction Adjustment of surface properties ( rowdyism) ? Apply rust preventive oil (optional) ? Improvement of mechanical properties of substantive ? extermination of compensate academic degree annexe ? Improvement of formability by decreasing the issuing transmit ? Improvement of other mechanical properties The skin passing of worldly has to be done with optimum parameters such that the purpose of skin passing is met. Ideally the skin passing has to be done in such a way that alternate grains are line of productsed by which we allow for get 50% tenor voiceed surface gr ains and 50% strain free surface grains. top(prenominal) yield pointStress Yield point elongation Lower yield point Strain Fig 1. 4 tractile test graphs before skin passing Yield point elongation is a well-known phenomenon in low light speed steel. After the elastic deal out of the deform strain crimp (a schematic engineering stress-strain loop is shown in the preceding(prenominal) number) the stretch out spues at upper yield point. At lower yield point this drop sustains steady, but a continuous series of fluctuation appears in the stress strain curve. This is commonly known as yield point elongation. After this stage, the curve becomes limpid again.Reason The reason behind this phenomenon is the alternate fasten and unlocking of partitionings by the interstitial atoms (C and N) in steel matrix. C and N atoms form interstitial solid solution and these progress to natural affinity for locking the kerfuffles. The locked dislocations cannot move freely, which restricts overrefinement of the material. The twisting of the material is actually caused by private road and extension of dislocations. The deformation stops when the dislocations are not free enough to continue their movements, and further application of cargo in this incident causes crack generation and failure.After cold rolling and annealing, a low carbon steel strip is supposed to suffer a forming operation. However, this forming becomes difficult if the dislocations are pinned down by the interstitial solute atoms. The annealing give-and-take provides ample opportunity for the dislocations to move freely and sit at the thermodynamically favourable sites, where the solute atoms pin the dislocations and kill their mobility. This is commonly known as Cottrell atmosphere. Now, if the material is subjected to a elastic payload, the stress strain curve impart show a serration, i. . alternate load drop and load get going, just after the yield point. bear down drop indicates th at the dislocations are pulled off from the solute atmosphere, coupled with generation of unspoiled dislocations under the external force, and load jump indicates that the momentarily free dislocations are again encountering with the solute atoms. This actually constitutes the stage of yield point elongation. Due to the pinning effect of the solute atoms, the dislocation multiplication sources also become active, which generates refreshful dislocations.After this stage, when able fresh dislocations are available for continuing deformation, the stress-strain curve becomes smooth again. This yield point elongation (YPE) is abruptly detrimental as far as the formability of the material is concerned. It creates Luder bands or coping stone strain marks, which finally leads to failure of the component. These bands are panoptical on the strip surface. When a test specimen exhibits YPE during its tensile testing, these bands appear on the specimen surface, starting from middle (where make out starts) and spreading towards the ends, at an angle of rough 450 to the tensile axis.YPE elongation continues till the completed specimen surface is covered by the Luder band formation, then smooth flexible deformation starts. Here comes the role of skin passing. Since YPE, after batch annealing, cannot be avoided, a skin perspicaciousness deformation is granted to the just annealed steel strip. This skin judgment deformation actually overcomes this region of the stress-strain curve. fitted sum of dislocations is pulled off from the solute (C, N) atmosphere, at the self resembling(prenominal) time fresh dislocations are generated, which is sufficient for facilitating the forming operation at the side by side(p) stage.If the material, in skin passed (or temper rolled) condition, is subjected to tensile testing, the stress strain curve testament 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 pull or deep drawing phase material. If this skin passed material is left unused for a sufficiently long time, or subjected to a brief heat preaching at a low temperature, the YPE reappears once again. The YS value also goes up and ductileness 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 well- delimitate 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 spreading has a very important role to play. If the testing is carried out at fashion 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 higher temperature, the mobility of the solute atoms increases, and movements of dislocation and solute atom s may be comparable. such a situation would give rise to an provoke 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 extent of deformation (known as temper elongation) to be apt(p) at skin pass mill (SPM), which is a comminuted factor, varies with steel composition. The order 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 strike off.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 graduates like IF and EDD, because the strain hardening ex ponent value is higher for these patsys, compared to that for ordinary CQ material. Theoretically s full pointing, 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 borderline temper elongation.The skin pass depends on Yield strength of the material in the following way Lower the skin pass (roughly l ess than 0. 6 %), the material will have the tendency to show Bauschingers effect. Higher the skin passing ( higher up 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 fate reduction increases with increasing YS to get the optimum properties. Parameters on which Skin pass Load dependsGrain Size 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 stiffness values because of the final finishing in stand number (5) of tandem Cold Mill. Many multiplication to high disorderliness of the incoming st rip to Skin Pass Mill and the requirement of come roughness values on the surface in the ranger of 0. -1. 2 micrometer gauges for well-nigh applications, the bakshishs are knocked off during skin passing which is detrimental from forming and image pellucidity point of view. The best practice for this should be keeping as low roughness as possible 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 conveying higher roughness on the work rolls in the skin pass mill. 1. 3. 3 THEORY OF SKIN PASSING When the annealed kookie steel sheet is pre organize, surface markings, called stretcher strains markings, appear on de organise parts. finishing touch strains are also called as Luder bands. The formation of these markings can be prevented by Skin passing the sheet by handsome the sheet elongation of 1-2 % before Performing. LUDER stria OR STRECHER STRAIN This band is formed with an angle o f 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 writ of execution characteristics of rolls used in cold rolling mill, both in Tandem Cold Mill(TCM) and Skin Pass Mill, are tiny to mill productivity and to the quality and toleration of the cold rolled products. With the rapid change in roll technology, roll concern in cold rolling has become an area 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 significant investment and input to a value analysis of cost per ton rolled.The quality of work rolls that come into direct contact with the steel product has a direct effect on product quality and mill operation. A forged steel with a atomic number 24 content of 5 mass% has been conventionally used to meet the requirement of metallurgical bodily structure homogeneity and high harshness for work rolls in cold rolling. Rolls having improved performance are strongly demanded. 1. 4. 1 Requirement from coarse-textured Rolls 1. 4. 1. 1 Surface finish Surface roughness is imparted to Work Rolls which are used in fifth 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 base on its end use. Ra is the universally recognized and most used international parameter of roughness. It is the arithmetical mean of the departures of the compose from the mean 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 deportation 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 body is also of importance to ensure consistency of surface roughness over the strip widths produced in a campaign. The ROLLTEX Electro discharge 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 impermanentities of the surface texture that usually result from the inherent action of so me 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 durationy periods in damp or corrosive atmospheres. The degree of roughness can be intractable 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 metrical as a root mean foursquare 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 devi ation from a smooth fibre surface. Some conventional methods for surface standard are optical microscope, scanning negatron microscope and transmission electron microscope. These can be used to produce topographic maps of surfaces. immediately laser scattering technique has become more common. Ra valueAverage/mean height of surface bank bills and troughs over a reference length indicates an boilers suit profile 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 lead Count It is the measurement of number of peaks in the specified length ov er a particular bandwidth (normally 1 micron).A profile peak is the highest part of the profile between an upwards and downwards 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. witness 1. 7 shows the correlation between the roughness of the surface & the peak counts. Fig 1. 7 Correlation between roughness & peak counts Stability of the surface profile The textured roll is required to give a consistent transfer of roughness and peak count on the strip musical composition rolling.During rolling the surface experiences wear of the peaks and the roll is Fig 1. 8 Skewness of surface discarded after a accredited tonnage, determined based on the cut-off point of surface requirement on the strip. To esteem this requirement of surface stability, metrology experts and certain European instrument manufacturers hav e devised surface texture height parameters, which can be analysed by a Data Processing staff (DPM), supplied separately by the surface finish tester manufacturers. Out of various parameters used in this analysis, the most commonly used is Rsk (Skewness) and tp % (known as bearing ratio).Rsk is the measure of the counterbalance of the amplitude distribution curve about the mean line. As shown in figure 1. 8 if Rsk is negative the surface peaks are higher, which is prone to a large drop in surface finish during the sign rolling. Based on the practical experience of cold rollers over the world, a delicate 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 passenger car ratio (tp%) is a measure of the length of bearing surface (expressed as a % of the assessment length), where the pro file peaks have been cut off at a line which runs parallel 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 lasting wavelengths than the cut-off are included. The waviness, Wa is calculated from the resulting profile.Fig 2 Waviness, Roughness and Form of a surface Wavelengths in the roughness crime syndicate 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 institute to poor Distinctness 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 untoward 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