1. CRM Complex
6 High Reversible Cold Rolling Mill
Training Manual
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2. LINE VIEW
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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
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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.
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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
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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
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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)
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8. PAY OFF REEL
SNUBBER ROLL
MENDREL
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9. THREE ROLL FEEDER ASSY.
ROLLS
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10. ENTRY TENSION REEL
SNUBBER
MENDREL
OUT BOARD
BEARING
SUPPORT
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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
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12. DELIVERY TENSION REEL
BELT WRAPPER OILER ROLL OUT BOARD BEARING
GUARD SUPPORT
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13. ROLL CHANGING CAR (RCC)
FRONT VIEW REAR VIEW
This Assy. is used to change rolls of 6 High rolling mill USED ROLLS
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14. SIDE VIEW OF 6 HIGH REVERSIBLE MILL
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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.
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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.
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17. VARIOUS LOAD CONDITION
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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.
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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 result
in large shape errors. These changes are immeasurable by current thickness
measurement devices, but the changes in strip length may be either directly
measured off-line or by means of tension distribution on-line. According to our
definition of shape, a device is required that will enable the length differences
across the sheet, (or web), width.
If the sheet were not subject to tension forces, it would be possible to
measure any buckles optically. When cold rolling, sufficient tension forces are
applied to make the sheet appear to be optically flat. Tension distribution is usually
used as a means of obtaining a measurement of strip shape.
The tension distribution is measured using some form of sensing roll, over
which the strip wraps. This roll is either an existing deflector, or pass line, roll or an
extra roll. A popular sensor is the Plenicim Roll.
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20. TYPES OF SHEET SHAPE
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21. TYPICAL PLENICIM ROLL DISPLAY
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22. CR DEFECTS
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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.
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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.
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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.
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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.
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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.
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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.
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29. EDGE WAVY
DEFINITION:
UNDULATIONS AT THE EDGES IN THE
FORM OF WAVES.
CAUSE OF FORMATION:
EXCESS LOAD AT THE EDGES DURING
ROLLING OPERATION.
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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
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31. COIL SET
DEFINITION:
LONGITUDINAL CAMBER OF THE
STRIP IN THE ROLLING DIRECTION.
CAUSE OF FORMATION:
DEFLECTION AROUND SMALL GUIDE
ROLL DIAMETER
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32. PINCH MARKS
DEFINITION:
LINEAR MARKINGS ON THE STRIP OF
SINGLE OR PERIODIC OCCURRENCE.
CAUSE OF FORMATION:
LACK OF STRIP FLATNESS
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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.
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34. IMULSION MARKS
DEFINITION:
CRACKED EMULSION RESIDUES ON THE
STRIP SURFACE.
CAUSE OF FORMATION
INADEQUATE WIPING OR BLOWING TO
REMOVE EXCESS EMULSION.
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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.
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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.
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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.
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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.
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39. Thank you
Compiled by :
Rajiv Arora