supercalender performance improvement for coating machine
DESCRIPTION
How to improve supercalendar performance, and get better cotton roll lifeTRANSCRIPT
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Supercalender Performance Improvementby Process Optimization
By:D K Singhal M S Gaur
Chandpur Enterprises Ltd.,Sargam Theatre, Chandpur-246725Dist. Bijnor, (U.P.), [email protected]
TechaidsD-121-122,Industrial Area Phase VII,Mohali, [email protected]
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Conventional Supercalender
Type: Typical 12 roll Supercalender Make: ECK Haubold Unwind: Single flat disc water cooled 11 intermediate paper rolls Dyno-drive center winder
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Upgrades During Installation
All chilled rolls were hard chrome plated and superfinished.
Hard chrome plating: No specific benefit in terms of roll hardness Chemical properties of surface greatly altered No development of a thin layer of corrosion products on
roll surface No corrosion during a shut for a couple of days Better surface finish possible after hard chrome plating.
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Upgrades During Installation
Installation of hydraulic accumulator.
Hydraulic Accumulator: Basically a pressurized variable volume
storage device Stores hydraulic oil at desired pressure Reduced electricity consumption Low hydraulic oil temperature Better hydraulic cylinder life
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Chilled Roll Superfinishing
Done by Modinagar Rolls Ltd., by their specially developed method (Mod-Finish) for hard chrome rolls.
Surface smoothness achieved: approx. 0.25Ra.
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Initial Problems
Low speed: 60-70mpm Low production capacity Frequent joints Unstable gloss Time consuming reel change Time consuming tail feeding
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Installation of Proximity Sensor
A proximity sensor was mounted on to the shaft of a paper roll near key
The reset button of the counter was deactivated.
The difference between shift readings indicated roll revolutions
More difference ≈ More paper length
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Installation of Proximity Sensor
A healthy competition started between operators
Within a few of weeks, production increased by 2.5 times
* This technique works well if the operators are too cautious to speedup the machine.
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On-machine Gloss Indication
Variation in gloss in machine direction. Inconsistent nip loading. Analog pressure gauges difficult to read
accurately Due to manual control of loading. It takes time to draw a sample and check for
gloss.
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Lighting System Improvement
Tubelights were fitted Operators can see the reflection Visual information about the
gloss.
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Unwind
Original: Disk brake, water cooled. Larger brake area, low air pressure for
braking, poor control. Poor response at low speeds, particularly at
startup.
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Unwind Modification
Disk brake was replaced with a locally fabricated drum brake.
Optimized diameter pneumatic cylinder for better breaking control.
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Winder
Original Winder- Center winder Dyno-drive based tension control Paper slippage between layers Poor winding Frequent breaks
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Winder Modification
Modified Winder- Surface winder Gear coupled DC Motor DC motor was replaced by AC motor later on. Gear box was replaced by V-Belt drive Main calender drive and pope reel drive
synchronized.
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Winder Modification
Results: Excellent winding No joints at winder Uniform tension profile Reduced side trimings
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Removal of Paper Rolls
Normal Operation Schematic Paper rolls used for web cooling Soft rolls life improvement
Problems Faced: Time consuming reel change Time consuming tail feeding Increased tail feeding losses
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Removal of Paper Rolls
Advantages: Reduced reel changing time Reduced tail feeding time Reduced tail feeding losses Improved runnability
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Soft Roll Performance
Problems: Frequent failures immediately after a startup. Roll slicing ►Roll became unusable Often a deep cut desirable. Roll life was very low. Uneven nip profile.
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Improving in Soft Roll Performance
Warming up before startup Installation of in-house grinder Uni-run operation Frequent sponge humidification Climatic improvements
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Roll Material
Feature Paper Rolls Glosvax (Cotton) Rolls
Effect
Composition Cotton / Wool / Linen Cotton + Wool
Process Die Cutting / Pressing Carding / Caking Better interlocking and hence low possibility of slicing.
Assembly Fast Pressing Slow Pressing Better interlocking and hence low possibility of slicing.
Finishing Turning / Grinding Turning / Polishing Better surface of roll and hence better gloss.
Hardness 80-92 Shore D 72-82 Shore D Increased nip width resulting in better results even at high speed operation.
Flexibility Low High Better resistance to score marks
Mark Resistance Moderate / Low Excellent / Moderate
Frequent grinding is avoided.
Cut Depth Low Depth Deep Cut Grinding time is reduced significantly.
Grinding Frequency
Very High Moderate / Low Lesser downtime for fewer roll changes.
Costing Moderate Economical
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Installation of In-house Grinder
Roll grinding done at a local workshop.
Grinding cost- not a big issue.
Transit in tractor trolley, prone to roll damage.
A new grinder (double chuck type) was purchased & installed.
Quality of grinding was also improved significantly.
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Slicing
Cotton rolls rotation in clockwise or anticlockwise possible.
In case roll position change, sometimes direction of rotation reverses.
Reverse rotation ►Slicing.
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Uni-run Operation
To avoid slicing, rolls were marked for Uni-run operation.
Slicing problem eliminated.
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Roll Cotton Behaviour
Cotton: Absorbs moisture in high humidity environment and vice
versa. Around roll area, temperature is higher, and so relative
humidity is lower. So, cotton rolls tend to release moisture during operation. Deterioration of cotton rolls speeds up if the moisture is
lower than a critical level. This results in roll failure (burn out).
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Frequent Sponge Humidification
Frequent wetting the roll surface, particularly in the dry weather (RH< 50%) helps a lot by- Maintaining desired moisture in the roll cotton. Lowering down the temperature of roll. Improving the flexibility of roll, thus better nip. Reduced CD caliper variation. Increase roll life between grindings.
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Frequent Sponge Humidification
Initial trials of sponge humidification used water along with detergents e.g. Nirma, Wheel, Ezee and shampoos like sunsilk etc.
Use of Techzyme was found very useful.
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Frequent Sponge Humidification
Advantages: Grinding to grinding span improved. CD caliper variation reduced significantly. Much better reel winding. Improvement in roll life.
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Localized Roll Burn Out
More roll failures during dry weather rather than during summer.
Often, such failures required deep cuts.
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Climatic Improvements
Sponge humidification is good technique, but, it needs loss of production for 4-5 minutes after say every reel.
Sometimes, operators may tend to skip it a couple of times.
So, we needed to have a better solution.
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Climatic Improvements
Use of air cooler was planned. Three coolers were installed at one side of
supercalendar. Objects were-
To increase the humidity. To reduce the climatic temperature. To reduce the dependency on sponge
humidification.
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Climatic Improvements
Definite advantages were observed. Over a period of 4 months, there were at
least 6 incidences when no roll had been changed during 7 consecutive days.
Reel winding improved further. Physical work (sponge humidification) by
operators was reduced.
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Overall Results
Better runnability Better reel winding Reduced trim losses Reduced joints Reduced gloss variation Reduced caliper variation Reduced grindings per ton of paper Improved roll life
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Overall Results
And of course-
Happier Customers…..!Happier Operators……!!Happier Mill………….!!!
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Thank You.