6 High Reversible Cold Rolling Mill

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6 High Reversible Cold Rolling Mill

  1. 1. CRM Complex6 High Reversible Cold Rolling Mill Training Manual0
  2. 2. LINE VIEW 1
  3. 3. SCHEMATIC DIAGRAM OF 6 HIGH ROLLING MILLS Hydraulic jack Back Up roll Back up rolls Intermediate Pinch rolls Pinch Rolls rolls Pinch rolls Shear Shear Work rolls Uncoiler Uncoiler Recoiler Bottom foundation 2
  4. 4. INTRODUCTION When sheet is entered between a pair of rolls and any kind of force applied to that sheet, like that generated when making a reduction, the rolls, since they are supported at the roll ends, will bend around the sheet. This will tend to make the sheet relatively thick in the middle and thin on the edges. On thin sheet, this will be seen as wavy edges. The phenomenon of “rolls bending around the sheet” is often called Roll deflection. 3
  5. 5. LINE SPECIFICATIONS CRM - I Min thickness rolled : 0.15 mm Max. rolling speed : 1200 MPM Max. reduction / pass : 38 % Max. No. of passes : 5 Capacity : 0.2 MTPA Load for reduction Thickness tolerances : 0.8 X width of sheet In rolled sheet : + 0.03 mm Max. front tension : 12.2 MT Max. back tension : 8.5 Mt Max. width rolled : 1270 mm Min. width rolled : 700 mm 4
  6. 6. Technical information about the six high mill Roughness Freq. Of roll Diameter (mm) Ra (micron) change Work roll 425 (max) 380 (min) 0.5 – 0.6 500 tonnes Intermediate rolls 490 (max) 440 (min) 0.6 – 0.7 1000 tonnes Back up rolls 1250 (max) 1050 (min) 0.6 – 0.8 10000 tonnes 5
  7. 7. EQUIPMENT DETAILS CRM-1 CONSISTS FOLLOWING EQUIPMENTS : 1. COIL STORAGE SADDLE 2. COIL CAR 1, 2 & 3 3. PAY OFF REEL 4. THREE ROLL FEEDER ASSY. 5. ENTRY TENSION REEL 6. 6 HIGH REVERSIBLE MILL 7. DELIVERY TENSION REEL 8. BELT WRAPPER 9. ROLL CHANGING CAR (RCC) 6
  8. 8. PAY OFF REEL SNUBBER ROLL MENDREL 7
  9. 9. THREE ROLL FEEDER ASSY. ROLLS 8
  10. 10. ENTRY TENSION REEL SNUBBER MENDREL OUT BOARD BEARING SUPPORT 9
  11. 11. 6 HIGH REVERSIBLE MILL TOP BACK UP ROLL TOP INTERMEDIATE ROLL TOP WORK ROLL BOTTOM WORK ROLL BOTTOM INTERMEDIATE ROLL BOTTOM BACK UP ROLL 10
  12. 12. DELIVERY TENSION REEL BELT WRAPPER OILER ROLL OUT BOARD BEARING GUARD SUPPORT 11
  13. 13. ROLL CHANGING CAR (RCC) FRONT VIEW REAR VIEWThis Assy. is used to change rolls of 6 High rolling mill USED ROLLS 12
  14. 14. SIDE VIEW OF 6 HIGH REVERSIBLE MILL 13
  15. 15. OPERATIONAL INSTRUCTIONS  A rolling mill should operate at its maximum power or maximum speed. It becomes obvious that poor shape prevents productivity, by reducing speed.  A double hit is taken on thin gauges as poor shape can cause strip breaks with often associated mechanical damage and consequential downtime.  The use of tension, particularly the application of rewind tension as a means of producing “flat sheet” on a rolling mill is not good practice.  Although this visibly appears to work, the shape defects are still there and some other effects are present as well.  These can range from high forward slip values causing poor roll life and a tendency for the mill to chatter, to residual stress problems that manifest themselves as coil set, transverse bow, poor formability etc. 14
  16. 16. FUNDAMENTALS OF SHEET SHAPE Very often, the only practical way to achieve anything that resembles flat shape is to hand the problem over to some form of an automatic shape sensing device and control system. There are two reasons for this:  The first is that the operator is incapable of detecting “bad shape” and the  Second is that he/she cannot adjust the sprays quickly enough to achieve the required level of control. High reductions contribute more to the “ROLLS BENDING AROUND THE SHEET EFFECT”. To counteract this, it is necessary to develop more heat in the rolls to generate more thermal roll growth or crown. Now, this mechanism leads to a situation where the rolls are much hotter in the centre of the sheet than out near the sheet edges, in fact, there will probably be quite a temperature gradient in the interface zone between reduction and no reduction taking place on the rolls. What this means is that this temperature gradient will be transferred into the sheet. This is bad. 15
  17. 17. VARIOUS LOAD CONDITION 16
  18. 18. FUNDAMENTALS OF SHEET SHAPE A solution to this problem is presented by the six high mill. In this case, a set of intermediate rolls is inserted between the work rolls and the backup rolls. These rolls are placed asymmetrically in the mill so that the edge of the intermediate roll is close to the strip edge. By adjusting the side shift on these rolls, the fulcrum points for roll bending and roll deflection are changed and it is reported that buckles may not only be changed but eliminated. The adjusting the intermediate rolls on a six high mill is an adjustment of mechanical crown. A simple roll coolant system is then used to satisfy the lubrication and cooling requirements. Recently, the concept has been further developed with intermediate rolls taking on “coke” bottle shapes. Originally, these mills were designed to be without shape control, as it was thought that the mechanical crown adjustments would suffice, however, modern quality and productivity requirements have meant that successfully operated mills do possess sophisticated shape control systems. 17
  19. 19. SHAPE DEFINITION Strip shape is defined as the length distribution across the strip width.Length is chosen because very small non-uniform changes in thickness may resultin large shape errors. These changes are immeasurable by current thicknessmeasurement devices, but the changes in strip length may be either directlymeasured off-line or by means of tension distribution on-line. According to ourdefinition of shape, a device is required that will enable the length differencesacross the sheet, (or web), width. If the sheet were not subject to tension forces, it would be possible tomeasure any buckles optically. When cold rolling, sufficient tension forces areapplied to make the sheet appear to be optically flat. Tension distribution is usuallyused as a means of obtaining a measurement of strip shape. The tension distribution is measured using some form of sensing roll, overwhich the strip wraps. This roll is either an existing deflector, or pass line, roll or anextra roll. A popular sensor is the Plenicim Roll. 18
  20. 20. TYPES OF SHEET SHAPE 19
  21. 21. TYPICAL PLENICIM ROLL DISPLAY 20
  22. 22. CR DEFECTS21
  23. 23. RUST DEFINITION: CORROSION PRODUCTS OF IRON, APPEARS IN THE FORM OF REDDISH YELLOW TO BLACK PATCHES ON THE STRIP. CAUSE OF FORMATION: PRESENCE OF AQUEOUS LIQUIDS ON THE METAL SURFACE, PROMOTED BY TEMPERATURE FLUCTUATIONS, HIGH AIR HUMIDITY AND LONG STORAGE TIMES. 22
  24. 24. COOLANT PATCH DEFINITION: THESE ARE PERMANENT STAINS THAT APPEAR ON THE STRIP AFTER COLD ROLLING CAUSE OF FORMATION: COOLANTS USED DURING ROLLING ARE NOT REMOVED COMPLETELY. 23
  25. 25. SLIVER DEFINITION: LINE TYPE SURFACE DEFECTS OFTEN WITH TWO PARALLEL LINES DISTRIBUTED SPARSLY ACROSS THE STRIP WIDTH AND THROUGHOUT THE COIL LENGTH. CAUSE OF FORMATION: DEFECT CONTAINS FINE OXIDES AND OTHER METALLIC OXIDES FORMED DUE TO OXIDES BEING TRAPPED AND SUBJECTED TO HIGH TEMPERATURES. 24
  26. 26. ROLLED IN SCALE DEFINITION: SCALES WHICH ARE NOT REMOVED DURING PICKLING AND IS ROLLED INTO THE SURFACE DURING COLD ROLLING OPERATIONS CAUSE OF FORMATION: INADEQUATE PRELIMINARY DE- SCALING OR PICKLING OF HOT STRIP. 25
  27. 27. ROLL MARKS DEFINITION: THEY ARE INDENTATIONS OR DEPRESSIONS ON THE STRIP OF REGULAR FORM WHICH OCCUR PERIODICALLY. CAUSE OF FORMATION: FOREIGN BODIES ON THE WORK ROLLS CAUSE THEM. 26
  28. 28. CENTER BUCKLING DEFINITION: UNDULATIONS AT THE CENTRE OF THE STRIP RUNNING PARALLEL TO THE DIRECTION OF ROLLING. CAUSE OF FORMATION: EXCESS LOAD AT THE CENTRE DURING ROLLING OPERATION. 27
  29. 29. EDGE WAVY DEFINITION: UNDULATIONS AT THE EDGES IN THE FORM OF WAVES. CAUSE OF FORMATION: EXCESS LOAD AT THE EDGES DURING ROLLING OPERATION. 28
  30. 30. CROSS BOW DEFINITION: CROWN OR CAMBER RUNNING TRANSVERSE TO THE DIRECTION OF ROLLING. CAUSE OF FORMATION: DIFFERENTIAL FRICTION BETWEEN THE STRIP AND THE UPPER AND LOWER WORK ROLLS 29
  31. 31. COIL SET DEFINITION: LONGITUDINAL CAMBER OF THE STRIP IN THE ROLLING DIRECTION. CAUSE OF FORMATION: DEFLECTION AROUND SMALL GUIDE ROLL DIAMETER 30
  32. 32. PINCH MARKS DEFINITION: LINEAR MARKINGS ON THE STRIP OF SINGLE OR PERIODIC OCCURRENCE. CAUSE OF FORMATION: LACK OF STRIP FLATNESS 31
  33. 33. SCRATCH LINE DEFINITION: GROOVES, GOUGES AND DEEP SCRATCHES WHICH OCCUR DURING OR AFTER COLD ROLLING. CAUSE OF FORMATION: PRIMARILY CAUSED BY FRICTION BETWEEN THE STOCK AND PARTS OF THE EQUIPMENT DUE TO RELATIVE MOVEMENTS. 32
  34. 34. IMULSION MARKS DEFINITION: CRACKED EMULSION RESIDUES ON THE STRIP SURFACE. CAUSE OF FORMATION INADEQUATE WIPING OR BLOWING TO REMOVE EXCESS EMULSION. 33
  35. 35. HOLES DEFINITION: DISCONTINUITIES IN THE MATERIAL WHICH EXTEND THROUGH RIGHT FROM TOP TO THE BOTTOM SURFACE CAUSE OF FORMATION: LOCAL WEAKNESS SUCH AS BLOW HOLES, COARSE INCLUSIONS, ROLLED IN SCALE OR SEVERE MECHANICAL DAMAGE. 34
  36. 36. SAW EDGES DEFINITION: HACKSAW LIKE PROFILE OF THE EDGES OF THE STRIP OFTEN RUNNING THROUGHOUT THE LENGTH OF THE COIL. CAUSE OF FORMATION: IMPROPER TRIMMING AT THE EDGES PRIOR TO ROLLING. 35
  37. 37. EDGE CUT DEFINITION: BLACKISH BANDS ON THE SURFACE OF THE STRIP RUNNING PARALLEL TO THE ROLLING DIRECTION. CAUSE OF FORMATION: IMPROPER COOLING OF THE STRIP DUE TO WIPING NOZZLE CHOKING. 36
  38. 38. HEAT BAND DEFINITION: BLACKISH BANDS ON THE SURFACE OF THE STRIP RUNNING PARALLEL TO THE ROLLING DIRECTION. CAUSE OF FORMATION: IMPROPER COOLING OF THE STRIP DUE TO WIPING NOZZLE CHOKING. 37
  39. 39. Thank you Compiled by : Rajiv Arora

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