1. 2 – roll
2. 3 – roll
3. 4 – roll
4. L shaped 4 – roll
5. Inverted L shaped 4 – roll
6. Z roll
The calendar is a heavy – duty machine consisting of three or more chrome plated
steel rolls that revolve in opposite directions.
The roller temperature is controlled via steam and water.
The bottom roll is maintained in fixed position in the calendar frame and is driven
from the output shaft of a gear reducer.
The top roll is moveable for gage adjustment and for cleaning purposes. It is
driven from the fixed roll by a set of connecting gears.
The rolls are drilled for maximum heat transfer.
The roll gap or the space between the rollers is a very important parameter. It is adjusted
either by two motor driven screw down devices or two hydraulic cylinders on the top
roll.
During calendering, enormous forces are generated by the
compound while passing through the nip.These forces are
capable of lifting such heavy rolls thereby causing variation in
the gauges.
In a Calender, due to force generated the rolls will distort and the
gauge in the center will be higher that at the edges.
Roll Crowning
To compensate this, the rolls were ground with varying
diameter from center to the sides. The diameter being more in
the center and less in the sides. This process is called
“CROWING “
During calendering, the force generated by the compound
bends the roll, more in the center than in the sides.
With the crowing in place, the net result will be a sheet of
uniform gauge
Axis Crossing
Roll crossing is accomplished by tilting the plane of axis of
one of two adjoining rolls in relation to the common plane axis
of the two.
The journal boxes of the crossing roll slide either toward or
away from their mates on the adjoining roll
Mechanical screws, hydraulic systems and sliding wedges are
being used.
The rolls on either side of the film forming nips are crossed –
for eg., Rolls 1 and 4 of a 4 roll Calender
Axis Crossing –Advantages
Considerable greater range in gauge
Almost no increased stresses are imposed on Calender
frames, bearings and adjusting screws
Axis Crossing –Disadvantages
Setting for the desired increase is more involved – Initial tilting
causes little changes in gauge , later a small increase in cross
axis results in considerable gauge change
Automatic gauge control is more complicated
Only increase in gauge is possible
Roll wear is somewhat faster
Response time is slower because motor inertia must be
overcome and back slash in drives taken up
Roll Bending
2 additional bearings are provided in the rolls in addition to the
regular taper bearings. A Hydraulic cylinder is connected to
these bearings.Hydraulic force is applied to the bearings and
the rolls are deflected forcibly.
This deflection will be opposite in direction to the deflection
caused by the compound and hence they compensate the
outward deflection produced at the centre.
Roll Bending -- Advantages
The bending response is fast and instantaneous.
Actions and reactions are linear
Adjustment required is very small.
Less Roll Wearing
Better gauge control
The hydraulics maintains Zero clearance on Bearings
Roll Bending -- Disadvantages
Load on bearing increases
Wear on adjusting screws and nuts is greater
Greater the correction greater the deviation especially at the
edges as compared with center.
2. 3 – roll
3. 4 – roll
4. L shaped 4 – roll
5. Inverted L shaped 4 – roll
6. Z roll
The calendar is a heavy – duty machine consisting of three or more chrome plated
steel rolls that revolve in opposite directions.
The roller temperature is controlled via steam and water.
The bottom roll is maintained in fixed position in the calendar frame and is driven
from the output shaft of a gear reducer.
The top roll is moveable for gage adjustment and for cleaning purposes. It is
driven from the fixed roll by a set of connecting gears.
The rolls are drilled for maximum heat transfer.
The roll gap or the space between the rollers is a very important parameter. It is adjusted
either by two motor driven screw down devices or two hydraulic cylinders on the top
roll.
During calendering, enormous forces are generated by the
compound while passing through the nip.These forces are
capable of lifting such heavy rolls thereby causing variation in
the gauges.
In a Calender, due to force generated the rolls will distort and the
gauge in the center will be higher that at the edges.
Roll Crowning
To compensate this, the rolls were ground with varying
diameter from center to the sides. The diameter being more in
the center and less in the sides. This process is called
“CROWING “
During calendering, the force generated by the compound
bends the roll, more in the center than in the sides.
With the crowing in place, the net result will be a sheet of
uniform gauge
Axis Crossing
Roll crossing is accomplished by tilting the plane of axis of
one of two adjoining rolls in relation to the common plane axis
of the two.
The journal boxes of the crossing roll slide either toward or
away from their mates on the adjoining roll
Mechanical screws, hydraulic systems and sliding wedges are
being used.
The rolls on either side of the film forming nips are crossed –
for eg., Rolls 1 and 4 of a 4 roll Calender
Axis Crossing –Advantages
Considerable greater range in gauge
Almost no increased stresses are imposed on Calender
frames, bearings and adjusting screws
Axis Crossing –Disadvantages
Setting for the desired increase is more involved – Initial tilting
causes little changes in gauge , later a small increase in cross
axis results in considerable gauge change
Automatic gauge control is more complicated
Only increase in gauge is possible
Roll wear is somewhat faster
Response time is slower because motor inertia must be
overcome and back slash in drives taken up
Roll Bending
2 additional bearings are provided in the rolls in addition to the
regular taper bearings. A Hydraulic cylinder is connected to
these bearings.Hydraulic force is applied to the bearings and
the rolls are deflected forcibly.
This deflection will be opposite in direction to the deflection
caused by the compound and hence they compensate the
outward deflection produced at the centre.
Roll Bending -- Advantages
The bending response is fast and instantaneous.
Actions and reactions are linear
Adjustment required is very small.
Less Roll Wearing
Better gauge control
The hydraulics maintains Zero clearance on Bearings
Roll Bending -- Disadvantages
Load on bearing increases
Wear on adjusting screws and nuts is greater
Greater the correction greater the deviation especially at the
edges as compared with center.
Traditionally all the motors used were DC motors. Now with DTC, AC drives are
being used. The calendar rolls can be in individual motor configuration (i.e four motors)
or gear coupled configuration (i.e one motor).
The main calendar drives are 4Q DC drives. And if AC drives are used they are
standard drives with DBR (Dynamic Braking Resistor) for emergency condition
stopping.
In case of multi motor calendar configuration the main calendar drive’s speed
controller output goes to all the other calendar drives’ torque controller (to ensure load
sharing) i.e the three drives for the remaining three calendar rolls are in slave mode.
Window control may also be enabled.
The reference to all the drives contains maximum four quantities.
They are:
1. The line speed reference.
2. Accumulator level sensor feedbackto all the drives before it
i.e the pre tensioning rolls (entry side) and after it i.e the clamp rolls (exit side). The
function of the dancer is to maintain its normal position. The normal position of the
dancer is in the centre of the accumulator (as shown in the exit accumulator), when the
line gets slack, it moves up due to it getting more ”free”, and when the line becomes
more tense it moves down due to it being pulled down by the increasing tension. On the
dancer rod is a pot, which rotates as the dancer moves up or down thus supplying the
feedback mentioned above. If dancer moves up, the feedback will be positive so as to
increase the speed and vice- versa.
3. A trim (or stretch or draw): At any of the drives in the entire
system the operator can give a small offset in the reference of that individual drive. This
is called trim or stretch or draw. Consequently the drive speed changes at this location. If
this change is not passed on to other drives then the tension in the fabric may get upset.
This passed on reference is called progressive draw.
4. Load cell feedback to both the centering system drives. This also
gets passed down to drives before it (entry side) and after it (exit side). Not only that it
percolates down to other drives, which are before or after it respectively.
Eg. If the tension at the centering rolls is high, then load cell feedback will dictate it to
slow down and as it slows down it becomes imperatives for all the drives before it to
slow down if line tension is to be maintained.
The winder is in indirect torque control with diameter calculation. In indirect torque
control, the current limit is set and the speed set point is set above the line speed so
that the current controller is always in saturation. As the diameter of the winder
increases, torque demand increases and so the current limit is increased. Thus the
winder is always pulling. Also the clamp roll can be equipped with a load cell whose
feedback can be given to the winder.
being used. The calendar rolls can be in individual motor configuration (i.e four motors)
or gear coupled configuration (i.e one motor).
The main calendar drives are 4Q DC drives. And if AC drives are used they are
standard drives with DBR (Dynamic Braking Resistor) for emergency condition
stopping.
In case of multi motor calendar configuration the main calendar drive’s speed
controller output goes to all the other calendar drives’ torque controller (to ensure load
sharing) i.e the three drives for the remaining three calendar rolls are in slave mode.
Window control may also be enabled.
The reference to all the drives contains maximum four quantities.
They are:
1. The line speed reference.
2. Accumulator level sensor feedbackto all the drives before it
i.e the pre tensioning rolls (entry side) and after it i.e the clamp rolls (exit side). The
function of the dancer is to maintain its normal position. The normal position of the
dancer is in the centre of the accumulator (as shown in the exit accumulator), when the
line gets slack, it moves up due to it getting more ”free”, and when the line becomes
more tense it moves down due to it being pulled down by the increasing tension. On the
dancer rod is a pot, which rotates as the dancer moves up or down thus supplying the
feedback mentioned above. If dancer moves up, the feedback will be positive so as to
increase the speed and vice- versa.
3. A trim (or stretch or draw): At any of the drives in the entire
system the operator can give a small offset in the reference of that individual drive. This
is called trim or stretch or draw. Consequently the drive speed changes at this location. If
this change is not passed on to other drives then the tension in the fabric may get upset.
This passed on reference is called progressive draw.
4. Load cell feedback to both the centering system drives. This also
gets passed down to drives before it (entry side) and after it (exit side). Not only that it
percolates down to other drives, which are before or after it respectively.
Eg. If the tension at the centering rolls is high, then load cell feedback will dictate it to
slow down and as it slows down it becomes imperatives for all the drives before it to
slow down if line tension is to be maintained.
The winder is in indirect torque control with diameter calculation. In indirect torque
control, the current limit is set and the speed set point is set above the line speed so
that the current controller is always in saturation. As the diameter of the winder
increases, torque demand increases and so the current limit is increased. Thus the
winder is always pulling. Also the clamp roll can be equipped with a load cell whose
feedback can be given to the winder.
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