IMPROVING LIFE OF
SUPERCALENDAR COTTON ROLLS
deveshksinghal@gmail.com
Cotton Rolls
Cotton rolls are very important in a supercalendar
because of the following reasons-
1. After electricity, th...
This Presentation
Unfortunately, much information is not available on
handling and care of supercalendar rolls.
Some exper...
Why Rolls Fail
Let us first discuss different reasons for why the
cotton rolls fail during operation.
SlicingSlicing
Overh...
Slicing
"Improving Life of Supercalendar Cotton Rolls", May 2014
Slicing
You may notice different slices in a cotton roll after
some time of operation.
In fact, the manufacturer make some...
Slicing
During run, shear forces may result in minor
relocation of these slices, particularly if there had
been insufficie...
Slicing
That is why most suppliers want the rolls should be
rotated in one direction only.
They are right.
To ensure your ...
Overheat
Cotton rolls get overheat during operation, and as
cotton itself is a bad conductor of heat, the locally
elevated...
Startup Overheat
"Improving Life of Supercalendar Cotton Rolls", May 2014
Startup Overheat
In such case, the roll top surface looks almost
perfect, except a small black scar on it showing that
‘so...
Startup Overheat
Starting a cold supercalendar and increasing the
load much before the rolls have come to an
equilibrium i...
Startup Overheat
Starting the supercalendar at reduce operating nip
load for a couple of hours with gradually increasing
l...
Operational Overheat
The next greatest problem is operational
overheating of the roll.
In fact, while many operators and s...
Operational Overheat
In an study conducted in a small plant, it was
observed that such problems were more in cold
weather....
Operational Overheat
So, ambient temperature was not affecting the
performance of the roll.
Then what was it?
"Improving L...
Relative humidity
In hot and humid summer the problems were much
less than in dry cold winters.
This information gave an i...
Cotton
Cotton Fiber is made of cellulose.
"Improving Life of Supercalendar Cotton Rolls", May 2014
Cellulose
Cellulose is made up of glucose molecules joined
together in a chain like structure.
"Improving Life of Supercal...
Cellulose
These molecules are joined together with hydrogen
bonds.
Cotton absorbs moisture from the ambient under
humid co...
Hydrogen Bonding
The hydrogen bonds between water and cellulose
molecules are weak and break down even by small
energy.
"I...
Moisture Absorption
Cotton moisture absorption is a function of
environment humidity.
"Improving Life of Supercalendar Cot...
Back to Cotton Rolls
Now, if there is adequate moisture in cotton, due to
the heat generated during supercalendaring
proce...
Temperature Increase
Furthermore, when the temperature is increased,
two different phenomena may occur.
"Improving Life of...
Slow Heating
At relatively higher temperatures (ca. 150-200˚C),
cellulose bonds start breaking.
This results in darkening ...
Rapid Heating
But, the first reaction is slightly exothermic, thus
producing more heat, and the resultant reaction
produce...
Instant Rapid Heating
In some cases, the heating
process is so fast that we do not
observe the darkening of the
roll surfa...
Simplification to Operator
In other words, we may say that we
need to check the first phase of
temperature increase.
There...
Effect of Moisture
In last slide, we have
seen that increase in
temperature leads to tar
generation or
spontaneous combust...
Increasing Roll Moisture
There are several methods of increasing moisture
content in a cotton roll.
Rub the roll with a we...
Monitoring Roll Condition
Continuous monitoring of roll condition plays an
important role in getting good life of cotton r...
Monitoring Roll Condition
Regularly monitoring roll surface color is a good
tool in such cases.
If there is a lack of mois...
Monitoring Roll Condition
Roll in better condition
Lighter color
Roll in poor condition
Darker shade
"Improving Life of Su...
Observing Grinder
Often, the dust generated at grinder gives good
information about the roll condition.
Uniform, white, gr...
Observing Grinder
On the other hand, very fine, dark colored dust
indicates that the roll cotton had started degrading.
"I...
Observing Supercalendar
So, if cotton rolls remain in brighter, lighter color,
one can expect of getting better life compa...
Future Scope
As we can see the concept of applying moisture is
to provide additional low energy hydrogen bonds,
which can ...
Glycerol
Glycerol can also be added with water and this
mixture can be uniformly applied on the cotton roll.
In case of an...
Caution with Glycerol Application
I MUST indicate that I have never used glycerol for
such application. I just ‘FEEL’ that...
With Glossy Paper Wishes…
"Improving Life of Supercalendar Cotton Rolls", May 2014
Thank You.Thank You.
"Improving Life of Supercalendar Cotton Rolls", May 2014
About the Author
Born in 1968, D K Singhal is B.E., M.E. (Pulp & Paper, 1993) from Deptt. of Paper Technology,
University ...
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Improving life of supercalendar Cotton Rolls

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Supercalendar, Cotton Rolls, Paper, Coated Paper, Thermal Degradation, cellulose

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Improving life of supercalendar Cotton Rolls

  1. 1. IMPROVING LIFE OF SUPERCALENDAR COTTON ROLLS deveshksinghal@gmail.com
  2. 2. Cotton Rolls Cotton rolls are very important in a supercalendar because of the following reasons- 1. After electricity, these are the major second cost1. After electricity, these are the major second cost center. 2. Proper care ensures not only a good life of the roll, but also better smoothness and gloss in supercalendared paper. "Improving Life of Supercalendar Cotton Rolls", May 2014
  3. 3. This Presentation Unfortunately, much information is not available on handling and care of supercalendar rolls. Some experts and many operators have tried to improve the performance of cotton rolls overimprove the performance of cotton rolls over decades, but still a lot of information is passed on verbally. "Improving Life of Supercalendar Cotton Rolls", May 2014
  4. 4. Why Rolls Fail Let us first discuss different reasons for why the cotton rolls fail during operation. SlicingSlicing Overheat "Improving Life of Supercalendar Cotton Rolls", May 2014
  5. 5. Slicing "Improving Life of Supercalendar Cotton Rolls", May 2014
  6. 6. Slicing You may notice different slices in a cotton roll after some time of operation. In fact, the manufacturer make some slices of cotton (mixed with the proprietary fiber of their choice) in(mixed with the proprietary fiber of their choice) in circular shape with a hole punched in it. They then put a lot of such rings on the roll shaft, and compress the same at a very high pressure, so that all the slices are mechanically joined to each other thus forming a roll. "Improving Life of Supercalendar Cotton Rolls", May 2014
  7. 7. Slicing During run, shear forces may result in minor relocation of these slices, particularly if there had been insufficient pressure applied while making the roll. If the roll is operated in one direction, this generally creates no problem. But, if the roll is taken for grinding and mounted again in reverse direction, these slices loosen up and make the roll unsuitable for use. "Improving Life of Supercalendar Cotton Rolls", May 2014
  8. 8. Slicing That is why most suppliers want the rolls should be rotated in one direction only. They are right. To ensure your operators may not accidently mountTo ensure your operators may not accidently mount a roll in reversed direction, consider putting labels on both side of shafts. You may also add this point in startup checklist after any roll has been replaced- “Ensure that the roll has been mounted to run in specified direction only”. "Improving Life of Supercalendar Cotton Rolls", May 2014
  9. 9. Overheat Cotton rolls get overheat during operation, and as cotton itself is a bad conductor of heat, the locally elevated temperature may result in burning of the cotton, thus making the roll unsuitable. Typical overheat behaviors are shown in following slides- "Improving Life of Supercalendar Cotton Rolls", May 2014
  10. 10. Startup Overheat "Improving Life of Supercalendar Cotton Rolls", May 2014
  11. 11. Startup Overheat In such case, the roll top surface looks almost perfect, except a small black scar on it showing that ‘something is wrong’ inside. Such defects appear typically within a couple ofSuch defects appear typically within a couple of hours of operation if the supercalendar has been started after a shut of one or more days. "Improving Life of Supercalendar Cotton Rolls", May 2014
  12. 12. Startup Overheat Starting a cold supercalendar and increasing the load much before the rolls have come to an equilibrium is a major cause of such problem. On load, due to friction between fibers a lot ofOn load, due to friction between fibers a lot of heat is generated locally inside the roll. Unfortunately, we measure temperature at the roll surface only which looks cooler compared to our normal operating condition. "Improving Life of Supercalendar Cotton Rolls", May 2014
  13. 13. Startup Overheat Starting the supercalendar at reduce operating nip load for a couple of hours with gradually increasing load and speed is essential to avoid such problems. Paper should be passed through the nips only afterPaper should be passed through the nips only after sufficient time (say 90-120 minutes) after startup. In plants where startup roll problems are common, the above practice helps a lot. "Improving Life of Supercalendar Cotton Rolls", May 2014
  14. 14. Operational Overheat The next greatest problem is operational overheating of the roll. In fact, while many operators and suppliers recommend operation of supercalendar at reducedrecommend operation of supercalendar at reduced temperature, many a times, temperature reduction means reduction in load and speed, and hence production. Alternatively, you need to stop supercalendar and wait for the rolls to cool down, and accept the production loss. "Improving Life of Supercalendar Cotton Rolls", May 2014
  15. 15. Operational Overheat In an study conducted in a small plant, it was observed that such problems were more in cold weather. In winter, where the temperature (outside) wasIn winter, where the temperature (outside) was below 10-15˚C, problem was 3-4 times more than in summer where the outside temperature reached beyond 40-45˚C. "Improving Life of Supercalendar Cotton Rolls", May 2014
  16. 16. Operational Overheat So, ambient temperature was not affecting the performance of the roll. Then what was it? "Improving Life of Supercalendar Cotton Rolls", May 2014
  17. 17. Relative humidity In hot and humid summer the problems were much less than in dry cold winters. This information gave an idea that HUMIDITY has something to do with performance of the cottonsomething to do with performance of the cotton rolls. To understand it further, let us have a look on cotton properties. "Improving Life of Supercalendar Cotton Rolls", May 2014
  18. 18. Cotton Cotton Fiber is made of cellulose. "Improving Life of Supercalendar Cotton Rolls", May 2014
  19. 19. Cellulose Cellulose is made up of glucose molecules joined together in a chain like structure. "Improving Life of Supercalendar Cotton Rolls", May 2014
  20. 20. Cellulose These molecules are joined together with hydrogen bonds. Cotton absorbs moisture from the ambient under humid conditions and releases the part of it whenhumid conditions and releases the part of it when kept in dry area. The water molecules are attached to the surface of cotton (cellulose) by hydrogen bonding. "Improving Life of Supercalendar Cotton Rolls", May 2014
  21. 21. Hydrogen Bonding The hydrogen bonds between water and cellulose molecules are weak and break down even by small energy. "Improving Life of Supercalendar Cotton Rolls", May 2014
  22. 22. Moisture Absorption Cotton moisture absorption is a function of environment humidity. "Improving Life of Supercalendar Cotton Rolls", May 2014
  23. 23. Back to Cotton Rolls Now, if there is adequate moisture in cotton, due to the heat generated during supercalendaring process, some of the water molecules get detached and evaporate. This process consumes energy from the cotton rolls thus saving the cellulose chain as well as individual cellulose (glucose) molecules intact. If cellulose chain is intact, the roll will run more time. "Improving Life of Supercalendar Cotton Rolls", May 2014
  24. 24. Temperature Increase Furthermore, when the temperature is increased, two different phenomena may occur. "Improving Life of Supercalendar Cotton Rolls", May 2014
  25. 25. Slow Heating At relatively higher temperatures (ca. 150-200˚C), cellulose bonds start breaking. This results in darkening of roll surface slightly. "Improving Life of Supercalendar Cotton Rolls", May 2014
  26. 26. Rapid Heating But, the first reaction is slightly exothermic, thus producing more heat, and the resultant reaction produces ‘Levoglucosan’, which is more exothermic. The process becomes so fast that the roll startsThe process becomes so fast that the roll starts ‘burning’. At this stage, you may feel the smell of ‘tar’. "Improving Life of Supercalendar Cotton Rolls", May 2014
  27. 27. Instant Rapid Heating In some cases, the heating process is so fast that we do not observe the darkening of the roll surface, but the inside temperature shoots up rapidlytemperature shoots up rapidly and rapid tar generation starts inside the roll. Here, roll may seem perfect at top, but at inside the damage has already been done. "Improving Life of Supercalendar Cotton Rolls", May 2014
  28. 28. Simplification to Operator In other words, we may say that we need to check the first phase of temperature increase. There are operators saying that theThere are operators saying that the roll temperature does not increase beyond 80-90˚C, but that is the temperature at roll surface. Inside roll temperature may become high enough to produce levoglucosan. "Improving Life of Supercalendar Cotton Rolls", May 2014
  29. 29. Effect of Moisture In last slide, we have seen that increase in temperature leads to tar generation or spontaneous combustion.spontaneous combustion. By adding Moisture to roll, we can reduce rate of temperature increase, and thus problems like this- "Improving Life of Supercalendar Cotton Rolls", May 2014
  30. 30. Increasing Roll Moisture There are several methods of increasing moisture content in a cotton roll. Rub the roll with a wet sponge.Rub the roll with a wet sponge. Directly spray water on the roll during reel change. Pass impinging air on rolls through a wet scrubber. Install humidifiers on supercalendars. "Improving Life of Supercalendar Cotton Rolls", May 2014
  31. 31. Monitoring Roll Condition Continuous monitoring of roll condition plays an important role in getting good life of cotton rolls. But, the problem is that roll surface temperature varies with time, speed and operating load.varies with time, speed and operating load. Furthermore, as you apply water using sponge or by spraying, the roll surface temperature goes down, and start increasing slowly as the supercalendar is running. "Improving Life of Supercalendar Cotton Rolls", May 2014
  32. 32. Monitoring Roll Condition Regularly monitoring roll surface color is a good tool in such cases. If there is a lack of moisture, the generated heat cracks hydrogen bonds between cellulose chains,cracks hydrogen bonds between cellulose chains, rather than bonds between cellulose and water molecules. As a result, the color of roll becomes darker. "Improving Life of Supercalendar Cotton Rolls", May 2014
  33. 33. Monitoring Roll Condition Roll in better condition Lighter color Roll in poor condition Darker shade "Improving Life of Supercalendar Cotton Rolls", May 2014
  34. 34. Observing Grinder Often, the dust generated at grinder gives good information about the roll condition. Uniform, white, granular dust is an indication of good roll condition.good roll condition. "Improving Life of Supercalendar Cotton Rolls", May 2014
  35. 35. Observing Grinder On the other hand, very fine, dark colored dust indicates that the roll cotton had started degrading. "Improving Life of Supercalendar Cotton Rolls", May 2014
  36. 36. Observing Supercalendar So, if cotton rolls remain in brighter, lighter color, one can expect of getting better life compared to the case where the rolls get dark too early. "Improving Life of Supercalendar Cotton Rolls", May 2014
  37. 37. Future Scope As we can see the concept of applying moisture is to provide additional low energy hydrogen bonds, which can break at minor temperature increase and protect the cellulose chains, there comes another possibility to use something else with water whichpossibility to use something else with water which may dissipate relatively more energy. This should be (obviously) colorless and miscible in water. "Improving Life of Supercalendar Cotton Rolls", May 2014
  38. 38. Glycerol Glycerol can also be added with water and this mixture can be uniformly applied on the cotton roll. In case of any temperature increase, bound water will evaporate first, leaving glycerol as a ‘fuse’ towill evaporate first, leaving glycerol as a ‘fuse’ to protect cellulose. "Improving Life of Supercalendar Cotton Rolls", May 2014
  39. 39. Caution with Glycerol Application I MUST indicate that I have never used glycerol for such application. I just ‘FEEL’ that glycerol addition may help. However, I would really like to hear from someoneHowever, I would really like to hear from someone who is willing to take such trial to get better cotton roll performance. "Improving Life of Supercalendar Cotton Rolls", May 2014
  40. 40. With Glossy Paper Wishes… "Improving Life of Supercalendar Cotton Rolls", May 2014
  41. 41. Thank You.Thank You. "Improving Life of Supercalendar Cotton Rolls", May 2014
  42. 42. About the Author Born in 1968, D K Singhal is B.E., M.E. (Pulp & Paper, 1993) from Deptt. of Paper Technology, University of Roorkee (now IIT, Roorkee). He was certified as Certified Energy Auditor in 2004 with Bureau of Energy Efficiency. With nearly 7 dozen publications, he has emphasized on development of low cost technologies and management practices for quality and profitability improvement. With publications on energymanagertraining.com and paperonweb.com, he has been constantly contributing to IPPTA. He is also serving IPPTA as a member of Editorial Board. He has also been a member of IPPTAHe is also serving IPPTA as a member of Editorial Board. He has also been a member of IPPTA Executive Committee. An initiative by D K Singhal, a cyber campaign initiated against unjustified targeting of paper industry by “Idea” mobile, in their “Sirjee” advertisement campaign, after which this advertisement was taken off air. He has also moderated a Yahoo group, “PaperTechnology” with nearly 365 members from India and abroad to discuss problems related to pulp & paper making. He can be contacted at deveshksinghal@gmail.com "Improving Life of Supercalendar Cotton Rolls", May 2014

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