Combing:
For getting high quality of yarn, one extra process is introduced in cotton spinning which is called combing process. Generally, combing operation is used when high-quality fine cotton yarns (finer than approximately 15 tex) are required, improving the fiber straightening and alignment and removing short fibers, fiber hooks and any remaining neps and trash particles, thereby enabling finer, stronger, smoother and more uniform yarn to be produced. The combing process is carried out in order to improve the quality of the sliver coming out of the card. The process eliminates short fibers, it achieves better parallelization of fibers, it straightens curls, and it removes neps and residue impurities. So it play very important role for increasing the yarn strength. Usually one, (sometimes two) drawframe passages are used prior to combing so as to straighten and orientate the fiber hooks, thereby enabling optimum combing performance.
The purpose of combing is removing the short fibers (fibers having length lesser than a specified minimum) in the sliver and improving the mean length, removing the neps and sticky trash along with the short fibers and converting the combed cotton into a sliver form, coiling and delivering it in cans for next process.
Short fibers which are removed in combing are called comber noil or comber waste. The comber noil can be recycled in the production of carded yarn. Yarn which is get from comber sliver is called comber yarn. Carded sliver are combine into comber lap in a single continuous process stage.
Main Problems / Defects in Combing Process:
- Problems due to lap preparation
- Lap licking on combers
- Uneven laps
- Inadequate removal of short fibers and neps
- Short term unevenness
- Hank variations
- Effect of humidity
- Higher sliver breaks at coiler
- Frequent coiler tube choke-ups
- Web breakages at draw box
- Breakages on comber heads
- Breakages at sliver table
- Laps with damaged edges
- Bulged laps
- Breakages on comber heads
- Detaching roller lapping
- Low neps removal efficiency
- Excessive lap licking and splitting
Causes and way of remedies of above combing problems / defects / faults:
1. Problems due to lap preparation:
a. Lap licking on combers:
Normal reasons for lap licking are high total draft in combing preparation, excessive rack pressure during wind up, excessive tension draft between the lap rollers, more than 5 lakhs (500,000) fibers in batt cross section, higher delivery speed and insufficient pressure on calendar rollers.
b. Uneven laps:
Uneven laps are mainly due to folding of slivers while feeding, improper functioning of stop motions, very low draft during lap preparation, inadequate pressure on drafting rollers, and worn-out bearings.
2. Inadequate removal of short fibers and neps:
Check head to head and comber to comber noil percent variations, and check the individual heads for web defects, such as uncombed portions due to slippage under feed roller, slippage of fibers under detaching rollers, plucking of fibers by half lap from nipper grip, web disturbance due to air currents due to defects in brush or/in aspirator. Check the machines thoroughly for bent and hooked needles on half lap and top comb, broken needles, nipper grip, feed roller grip, condition of detaching roller cots, condition of the gears driving bottom detaching rollers and damaged air seals in the aspirator box.
3. Short term unevenness:
Prominent piecing waves, drafting waves, uneven fiber control due to worn out top roller cots in draw box, eccentric rollers in drafting / detaching field, play in draw box drive, high or low tension draft, and improper settings are the main reasons for short term variations in a combed sliver. Check U% and make use of spectrogram diagram to identify the source of the problem.
4. Hank variations:
Single, double or uneven working of sliver on table due to improper selection of tension draft, rough surface of the sliver table, variation in the feeding lap, lap licking while unwinding, etc., are main reasons for variation in hank. If between comber variations are high, check the combers for variations in lap roller feed per nip, draft wheels on draw box, tension drafts at tables, draw box and coiler, and noil level variations.
5. Effect of humidity:
Combers are very sensitive to changes in temperature and humidity, and hence it is essential to maintain the required temperature and humidity. In many cases the bad working is attributed to fluctuations in temperature and humidity.
6. Higher sliver breaks at coiler:
Sliver guides with rough surfaces, coiler calendar rollers having eccentricity or jerky motion, high tension draft, improper balancing of sliver stop motion working on gravity principle, worn out gears, excess parallelization of fibers in the sliver, improper condensation are the main reasons for sliver breaks. Check whether tension draft between draw box calendar roller and coiler calendar roller is too high causing stretching of sliver, or too low causing slackening of sliver. Check balancing of sliver break stop-motion and ensure that it presses against the sliver very lightly.
7. Frequent coiler tube choke-ups:
If the coiler tubes are loaded with wax and trash, the sliver gets chocked. Clean the coiler tube with a rough rope. If cans are over filled, or the can spring is forcing the sliver to coiler plate, the choke up shall take place.
8. Web breakages at draw box:
Burrs or accumulation of wax/trash particles at trumpet, too much spreading of web, defects in gear wheels, improper tension drafts are the main reasons for breakages in the draw box zone. In cases where the top rollers are buffed badly, the cottons shall stick to top rollers and lap.
9. Breakages on comber heads:
The main reasons for breaks at comber heads are a tight or slack web, improper positioning of web trays, unclean web trays, burrs in calendar trumpets, improper calendar trumpet (heavy or light), improper functioning of clearer rollers in detaching section, piecing waves, and the trumpets set too away from the nip of calendar rollers.
10. Breakages at sliver table:
Waxy and rough surfaces of the table, improper tension drafts and piecing waves are the main reasons for breakages on the sliver table.
11. Laps with damaged edges:
Laps with damaged edges are normally due to flanges holding the lap tight while lap is built.
12. Bulged laps:
Bulged laps are normally due to inadequate pressure on calendar rollers and on the rack heads. Increasing the pressure on calendar roller shall be more helpful as it can reduce lap licking also.
13. Breakages on comber heads:
A tight or slack web, improper positioning of web trays, unclean web trays, burrs in calendar trumpets, improper calendar trumpet (heavy or light), improper functioning of clearer rollers in detaching section, piecing waves, and the trumpets set too away from the nip of calendar rollers are the main reasons for breaks at comber heads.
14. Detaching roller lapping:
Rough or waxy surfaces on top roller cots, improper functioning of clearer rollers, too wide a setting of web guides are some of the reasons for lapping on detaching rollers. As the detaching top rollers tend to bend at the center because of loading at both the ends, taper buffing is recommended.
15. Low neps removal efficiency:
The normal reasons for low neps removal efficiency in combers are insufficient penetration of top comb, too wide gap between unicomb and nipper, excessive lap weight, insufficient total draft in lap preparation, uncleaned unicomb or half lap, unicomb not moving backwards to the required extent, poor condition of brushes and improper setting of brushes.
16. Excessive lap licking and splitting:
Improper tension drafts and roller setting, excessive draft in the lap former, uneven lap and tight winding while lap preparation are the main reasons for lap licking and splitting.
Combers are very sensitive to changes in temperature and humidity, and hence it is essential to maintain the required temperature and humidity. In the majority of cases the bad working is attributed to fluctuations in temperature and humidity.
References:
- Training and development of technical staff in textile industry by B. Purushothama
- Handbook on Cotton Spinning Industry by B. Purushothama
- Cotton: Science and Technology Edited by S. Gordon and Y-L. Hsieh
- Reference book for spinning by Ezio Carissoni, Stefanno Dotti, Franco Fleiss, Luigi Petaccia, Lucia Pieri
- http://www.scribd.com/doc/62931880/Spinning
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
