Defects in garments

      Defects in garments

For every industry or business, to get increased sales and better name amongst consumers and fellow companies it is important to maintain a level of quality. In the garment industry quality control is practiced right from the initial stage of sourcing raw materials to the stage of final finished garment. For textile and apparel industry product quality is calculated in terms of quality and standard of fibres, yarns, fabric construction, colour fastness, surface designs and the final finished garment products. However quality expectations for export are related to the type of customer segments and the retail outlets. There are a number of factors on which quality fitness of garment industry is based such as performance, reliability, durability, visual and perceived quality of the garment. Quality needs to be defined in terms of a particular framework of cost.

The national regulatory quality certification and international quality Programmes like ISO 9000 series lay down the broad quality parameters based on which companies maintain the export quality in the garment and apparel industry. Here some of main fabric properties that are taken into consideration for garment manufacturing for export basis:

• Overall look of the garment.
• Right formation of the garment.
• Feel and fall of the garment.
• Physical properties.
• Colour fastness of the garment.
• Finishing properties
• Presentation of the final produced garment.

There are certain quality related problems in garment manufacturing that should not be over looked:

• Sewing defects - Like open seams, wrong stitching techniques used, same colour garment, but usage of different colour threads on the garment, miss out of stitches in between, creasing of the garment, erroneous thread tension and raw edges are some sewing defects that could occur so should be taken care of.
• Colour effects - Colour defects that could occur are difference of the colour of final produced garment to the sample shown, accessories used are of wrong colour combination and mismatching of dye amongst the pieces.
• Sizing defects - Wrong gradation of sizes, difference in measurement of a garment part from other, for example- sleeves of XL size but body of L size. Such defects do not occur has to be seen too.
• Garment defects - During manufacturing process defects could occur like faulty zippers, irregular hemming, loose buttons, raw edges, improper button holes, uneven parts, inappropriate trimming, and difference in fabric colours.

Various defects in garments:

v      Broken buttons

v      Broken snaps

v      Broken stitching

v      Defective snaps

v      Different shades within the same garment

v      Dropped stitches

v      Exposed notches

v      Exposed raw edges

v      Fabric defects

v      Holes

v      Inoperative zipper

v      Loose / hanging sewing threads

v      Misaligned buttons and holes

v      Missing buttons

v      Needle cuts / chews

v      Open seams

v      Pulled / loose yarn

v      Stain

v      Unfinished buttonhole

v      Zipper too short

Garment defects, classified according to the various manufacturing stages are:

Pattern defects in garment:

Some parts of pattern are missing, probably because the marker did not include the correct number of parts. Mixed parts, probably because the marker is not correctly labeled, resulting in a marriage of wrong sized parts. Patterns not facing in correct direction on napped fabrics. Not all patterns facing in same direction (either way) on a one-way fabric. Patterns not aligned with respect to the fabric grain. Poor line definition (e.g. too thick chalk; indistinctly printed line, perforated lay not powdered) leading to inaccurate cutting. Skimpy marking, caused by either the marker did not use the outside edge of the pattern; or the pattern was moved or swung after partial marking to squeeze the pattern into a smaller space for economizing the fabric. Marking back from miniature markers also can cause trouble unless the miniature marker making is in the hands of experienced operators. Alternatively the full size pattern may be having worn out edges.

Generous marking, especially in combination with skimpy marking results in components being sewn together with puckering and pleating. When the marker is too wide, the garment parts at the edges of the lay get cut with bits missing. Not enough knife clearance freedom. Wrong check matching, i.e. lines across the seam are not matching.

Wrong check boxing, i.e. checks are not showing a full or partial box across the seam.
Notches and drill marks omitted, indistinct or misplaced.

Spreading defects in garment:

Not enough plies to cover quantity of garments required. Plies misaligned, resulting in garment parts getting cut with bits missing in some plies at the edge of the spread. Narrow fabric, causes garment parts at the edge of the lay getting cut with bits missing. Incorrect tension of plies, i.e. fabric spread too tight or too loose. This will result in parts not fitting in sewing, and finished garments not meeting size tolerances. Not all plies facing in correct direction (whether 'one way' as with nap, or 'one way either way' as with some check designs). This happens when fabric is not spread face down, face up, or face to face as required. Unacceptable damages in the garment parts. Parts not fully included owing to splicing errors. Spread distorted by the attraction or repulsion of plies caused by excessive static electricity. Plies are not spread accurately one above another for cutting. This results in mismatching checks.

Cutting defects in garment:

Failure to follow the marker lines resulting in distorted garment parts. Top and bottom plies can be a different size if the straight knife is allowed to lean, or if a round knife is used on too high a spread. Notches, which are misplaced, too deep, too shallow, angled, omitted, or wrong type to suit fabric .Drill marks, which are misplaced, wrong drill to suit fabric, omitted, not perpendicular through the spread. Frayed edges, scorched or fused edges, caused by a faulty knife, not sharp enough, or rotating at too high a speed. Knife cut. Garment part damaged by careless use of knife, perhaps overrunning cutting previous piece. Marker incorrectly positioned on top of spread. Garment parts have bits missing at edge of lay. If too tight or too loose then garment parts are distorted. Slits opened inaccurately or omitted.

Garment Twist

A rotation, usually lateral, between different panels of a garment resulting from the release of latent stresses during laundering of the woven or knitted fabric forming the garment. Twist may also be referred to as Torque or Spirality.

Identification of knitted fabric defects:

It is very natural that in the course of knitting fabrics, imperfections occur. The imperfections may be the result of faulty yarn, knitting machine malfunction or improper finishing. The defects in knitting construction are considered in terms of appearance and nature.

Various Types of Defects in Knitted Fabrics

.

Bands and Streaks

There are different kinds of bands and streaks that may occur in knitting. Some of the popular defects are as follows:

v    Barrie Effect: A Barrie effect has the appearance of a stripe with shaded edges. It is horizontal in weft knits and vertical in warp knits. The barrie effect is caused by various factors like:

       »  Lack of uniformity in yarn size, color or luster.

       »  Mush tension on the yarns during knitting one section of the fabric.

       »  Uneven shrinkage or other finishing defects.

v    Bowing: A line or a design may curve across the fabric. This bowing is the distortion caused by faulty take-up mechanism on the knitting machine.

v    Streak or Stop Mark: A straight horizontal streak or stop mark in the knitted fabric is due to the difference in tension in the yarns caused by the machine being stopped and then restarted.

v    Skewing: Skewing effect is seen as a line or design running at a slight angle across the cloth.

v    Needle Lines: Needle lines or vertical lines are due to a wale that is either tighter or looser than the adjacent ones. This is caused by needle movement due to a tight fit in its slot or a defective sinker.

Stitch Defects

There are various kinds of stitch defects like:

v    Boardy: The knitted fabric becomes boardy (a stiff or harsh hand) when the stitches have been knit very tightly.

v    Cockled or puckered: If the knitted fabric is cockled or puckered, it is due to uneven stitches or uneven yarn size.

v    Dropped Stitch: This is an un knitted stitch caused either by the yarn carrier not having been set properly or the stitch having been knitted too loosely.

v    Run or ladder: A run or ladder indicates a row of dropped stitches in the wale.

v    Hole: A large hole or a press off is the result of a broken yarn at a specific needle feed so that knitting cannot occur.

v    Tucking: This is the result of an unintentional tucking in the knitted fabric. This is also called the bird's eye defect.

v    Float: This is caused by a miss stitch which is the result of failure of one or more needles to have been raised to catch the yarn.

Common Denim Seam Quality Defects

Broken Stitches - Needle Cutting:

Where the thread is being broken where one seam crosses another seam (ex: bar tacks on top of waistband stitching, seat seam on top of riser seam) resulting in stitch failure.

 

 Minimizing broken stitches due to Needle Cutting

v    Use a higher performance Perma Core or D-Core thread.

v    Use a larger diameter thread on operations where the thread is being cut.

v    Make sure the proper stitch balance is being used. On a chain stitch seam on denim, you normally would like to maintain a 60%/40% relationship of Needle thread to looper thread in the Seam.

v    Use needles with the correct needle point.

v    Change the needles at regular intervals on operations where the Needle Cuts are occurring frequently.

Broken Stitches:

Where thread on the stitch line is broken during stone-washing, sand blasting, hand sanding, etc. Broken stitches must be repaired by re stitching over the top of the stitch-line.

Minimizing broken Stitches due to abrasion

v    Use a higher performance Perma Core or D-Core thread;

v    Use a larger diameter thread on operations where excessive abrasion is occurring

v    Make sure stitches are balance properly,

v    Use a Magic air entangled thread in the Looper due to its lower seam profile making it less susceptible to abrasion

v    Monitor the Finishing Cycle for compliance to specs.

Broken Stitches by Chemical Degradation

Where thread is being compromised by the chemicals used during laundering resulting in loss or change of color and seam failure.

Minimizing broken stitches due to Chemical Degradation:

v    Use a higher performance Perma Core NWT that has greater resistance to chemical degradation.

v    It is recommended to go to larger thread sizes when the Denim Garments will be subject to Harsh Chemical washes.

v    To achieve the best laundering results make sure that the water temperatures and PH Levels are correct and that the proper amounts and sequence of chemical dispersion are within guidelines

v    Make sure the garments are being rinsed properly to neutralize the chemicals in the fabric.

v    Monitor the drying process, cycle times, and temperatures to make sure they are correct so that the best possible garment quality can be achieved.

Unraveling Seams:

Generally occurs on 401 chain stitch seams where either the stitch has been broken or a skipped stitch has occurred. This will cause seam failure unless the seam is Re stitched.

Minimizing unraveled Stitches:

v    Use a high performance Perma Core or D-Core thread that will minimize broken stitches and skipped stitches;

v    Insure proper machine maintenance and sewing machine adjustments;

v    Observe sewing operators for correct material handling techniques.

Restitched Seams

Where there is a "splice" on the stitch line. If this occurs on Topstitching, then the seam does not appear to be 1st quality merchandise. Caused by:

1. Thread breaks or thread run-out during sewing; or
2. Cut or broken stitches during a subsequent treatment of the finished product (I.e., stone washing

Minimizing Restitched Seams:

v    Use a better quality sewing thread. This may include going to a higher performance thread designed to minimize sewing interruptions.

v    Insure proper machine maintenance and sewing machine adjustments;

v    Make sure sewing machines are properly maintained and adjusted for the fabric and sewing operation

v    Observe sewing operators for correct material handling techniques.

Sagging or Rolling Pockets:

Where the pocket does not lay flat and rolls over after laundering.

 

Minimizing Sagging or rolling front & back Pockets:

v    Make sure the sewing operators are not holding back excessively when setting the front pocket.

v    Make sure the hem is formed properly and that excessive fabric is not being being put into the folder that will cause the hem to roll over.

v    Check to make sure pocket is cut properly and that pocket curve is not too deep.

v    Use a reinforcement tape on the inside of the pocket that may help prevent the front panel from stretching along the bias where the front pocket is set.

v    The type and weight of denim, along with the fabric construction, may contribute to this problem.

Skipped Stitches:

Where the stitch forming device misses the needle loop or the needle misses the looper loop. Skips are usually found where one seam crosses another seam and most of the time occurs right before or right after the heavy thickness.

Minimizing Skipped Stitches:

v      Use core spun thread.

v      Use minimum thread tension to get a balanced stitch.

v      Use the ideal foot, feed and plate that help to minimize flagging.

v      Training sewing operators NOT to stop on the thickness.

v      Make sure the machine is feeding properly without stalling.

v      Make sure the machine is not back feeding.

Ragged / Inconsistent Edge

Where the edge of the seam is either extremely "ragged" or "rolls" inside the stitch.

Solutions to Ragged / Inconsistent Edge:

v    Make sure the sewing machine knives are sharpened and changed often;

v    The knives should be adjusted properly in relationship to the "stitch tongue" on the needle plate to obtain the proper seam width or width bite.

Wavy Seams on Stretch Denim:

Where the seam does not lay flay and is wavy due to the fabric stretching as it was sewn or during subsequent laundering and handling operations.

Solutions for wavy seams on stretch Garments

v    Use minimum presser foot pressure

v    Instruct sewing operators to use proper handling techniques and not stretch the fabric as they are making the seam.

v    Where, available, use differential feed to compensate for the stretch of the fabric.

Ropy Hem:

Where hem is not laying flat and is skewed in appearance.

Solutions for Ropy Hems

v    Usually caused by poor operator handling.

v    Instruct the sewing operator to make sure they get the hem started correctly in the folder before they start sewing. Also, make sure they don't hold back excessively as the seam is being sewn.

v    Use minimum roller or presser foot pressure.

Twisted Legs:

Is where the side seam twists around to the front of the pant and distorts the appearance of the jeans.

Solutions for Twisted Legs:

v    Usually caused by poor operator handling. Instruct the sewing operator to match the front and back properly so they come out the same length. Sometimes notches are used to insure proper alignment. They should NOT trim off the front or back with scissors to make them come out the same length

v    Make sure the cut parts are of equal length coming to the assembly operation.

v    Check fabric quality and cutting for proper skew

v    Make sure the sewing machine is adjusted properly for uniform feeding of the top and bottom plies.

Disappearing Stitches in Stretch Denim:

Is where the thread looks much smaller on seams sewn in the warp direction than in the weft direction of the fabric.

Solutions to minimizing disappearing stitches on stretch Denim:

v    Use a heavier thread size on topstitching.

v    Go to a longer stitch length (from 8 to 6 spi).

v    Make sure the thread tensions are as loose as possible so the thread sits on top of the fabric rather than burying in the fabric on seams sewn in the warp.

Thread discoloration after Laundry

It is the thread picks up the indigo dyes from the fabric giving the thread a 'dirty' appearance. A common discoloration would be the pick-up of a greenish or turquoise tint.

Solutions to Thread Discoloration

v    Use thread with proper color fastness characteristics.

v    Correct PH level (too low) and Water Temperature (too low) during laundry.

v    Use the proper chemicals & laundry cycles.

v    Use Denimcol PCC in wash or similar additive

v    Do not overload washers with too many garments at one time.

Poor Colorfastness after Laundry is where the thread does not wash down consistently in the garment or changes to a different color altogether.

Solutions to poor Colorfastness after Laundry:

v    Use thread with proper color fastness characteristics.

v    Use threads from the same thread supplier and do not mix threads in a garment.

v    Always do preproduction testing on denim garments using new colors to assure that they will meet your requirements.

v    Make sure sewing operators select thread by type and color number and do not just pick a thread off the shelf because it looks close in color.

Conclusion

Quality is ultimately a question of customer satisfaction. Good Quality increases the value of a product or service, establishes brand name, and builds up good reputation for the garment exporter, which in turn results into consumer satisfaction, high sales and foreign exchange for the country. The perceived quality of a garment is the result of a number of aspects, which together help achieve the desired level of satisfaction for the customer. Therefore quality control in terms of garment, pre-sales service, posts sales service, delivery, pricing, etc are essentials for any garment exporter.

About the Authors:

D. Gopalakrishnan is the faculty in South India Institute of Fashion Technology & Arpita Nayak is the student of UG Technology Programme (Apparel Manufacturing & Information Tech.)

Cotton Contamination - Its Sources & Remedial Measures
By: Ms. Madhuri V. Kakde & Prof. H. R. Shah





















ABSTRACT

According to recent survey by ITMF, Indian cottons are amongst the most contaminated cottons in the world due to the lack of availability of systematic instruments to judge the level of contamination. Contaminations present in the fabric not only deteriorate the quality and appearance of fabric, but also affect on the profits of the organization. Here, we have tried to highlight the sources and remedial measures for contamination, practiced in the cotton cultivation to yarn manufacturing industry.

INTRODUCTION

As prevention is better than cure, it is always more desirable not to generate contamination at all than to have to clean it at different stages of processing. To achieve this, all concerned industries have to work together. According to recent survey by ITMF, Indian cottons are amongst the most contaminated cottons in the world so; producing yarns of world class quality from Indian cottons is a greater challenge. This challenge can be met with selection of suitable cottons, appropriate work practices and proper use of modern machines and technologies. Contamination represents a significant threat and element of cost to spinning mills and this led them to implement a range of costly methods to remove the contamination. On analysis it was found that amongst all the areas of textile sectors, "Fiber cultivation to Yarn spinning stage" remains major source of contamination. Therefore, we have highlighted certain facts and few recent developmental steps, which are being taken to reduce or minimize the contamination level in this area.

NATURE OF CONTAMINATION

Before finding any measures for elimination of contamination first of all let us understand the possible sources of contamination and necessity for contamination removal. Once these sources are sorted out, elimination process becomes effective and easier. Contamination is "the presence of extraneous and undesirable substance in yarn which leads to impure the quality of final textile product". Contaminations at yarn stage are mainly categorized in three types:
1. Removal contaminations like dust, rust, mud and washable finish stains.
2. Partially removable contaminations like loose fly spun, oil stain and grease stain.
3. Irremovable contaminations like bleached fiber, fibers having optical brightening agent and dyed fiber contaminations which get spun with the yarn.
According to International Textile Manufacturers Federation (ITMF), the major contaminant found in cotton bales were pieces of cloth from either woven or knitted clothing in various colors made from either cotton or polyester or blends.
For India the need for the removal of contamination is felt much more since currently India is a topmost exporter of the cotton yarn. Contamination is one of the most serious problems affecting the cotton fibers. The whole product is rejected due to contamination, even though the basic material has been from the best of cottons and the product was made using the latest machines, which causes the serious problem in cotton spinning industry worldwide. Contamination is one of the critical issues for spinners to maintain first grade yarn quality because it causes the breakages in the warping, sizing, and weaving results in tile defective packages as well as faults in the fabric thus lowering the efficiency means increased cost of production.

                                                        Table 1: Types of contaminant

White contaminants    Alien fibers    Colored objects         Oily substances        Dense objects
White plastic fabric                Hair                    Colored cotton fabric   Sticks/twigs                Metal pieces
White plastic strings             Feather               Colored cotton yarn     Leaves                        Paper

White/transparent                 Colored cotton     Jute fabric                   Oily/Rusty/Black         Sand, stones
 Plastic film                             fibers                                                       cotton clumps 
                                                 Coir fibers            Jute yarn                     Stamp colored/            Leather bits          
                                                                                                                Yellow cotton lumps 
                                                 Colored plastic      Coir yarn                    Tar/Grease-affected     Wooden pieces   
                                                 fibres                                                        cotton clumps
                                                                          Colored plastic fabric   Colored plastic string, film    


SOURCES OF CONTAMINATION


Contaminations are not being grown with cotton balls in the tree. These are mostly "added" in fresh cotton during picking. Contaminations to raw cotton take place at every step i.e. from the farm picking to the ginning stage. Since cotton is picked manually by ruler woman so human hair, contamination caused by cloth pieces and fabric sheets are the biggest source of contamination.
International Textile Manufactures Federation (ITMF), Zurich, which conducts a survey on cotton contamination every two years, has identified five major sources of contamination:

1. Strings made of jute.
2. Strings made of hessian.
3. Fabric made of jute.
4. Fabric made of hessian.
5. Organic matter such as leaves, feather, paper, leather etc.
Contamination within raw material

There are the two possibilities of contamination. As the natural fiber cultivation, ginning, and packing process are mostly manual, chances of oil/grease/rust stain on fiber after the stoppages, or the maintenance activities of spinning machines exist.

Handling of packing material during raw material opening

Due to poor wrapper quality, wrapper stripe is passing with fiber mixing and converting in small fiber/strip during carding and finally, gets spun with fiber and creates contamination in yarn.

Cleaning of mixing and conditioning bin

To create difference between product and lot, different chemicals like antistatic, lubricant, optical brightening agent and tint apply on the fiber gets stick on wall and floor and apply on next chemical free mixing will results in contamination if the cleaning is not followed properly.

Frequent product change and loose fly spun

Running gray and dyed material in the same department causes fibers floating from dyed material, getting contaminated with gray material and vice versa. The starting of dyed material after run out of gray material on the same machine produce contaminated yarn. When two or more different products are running in same department, then contamination is mainly caused due to lose fly.

Oil and grease stain after machine maintenance

In case of some machine parts getting oil or grease stains during its maintenance and are not properly cleaned then it results in contamination.
                       Table 2: Various sources of contamination, their effect and remedial stages

Source of contamination                   Effect                                                 Remedies

Strings/fabrics of                  Increased end breakage rate at ring/rotor.                    Avoid use of hessian for jute/hessian                          Poor yarn appearance           differential dye pick-up.                                                   transport use cotton cloth  

Strings/fabrics of cotton        Poor quality yarn/cloth                                                Manual picking, automatic 

                                                                                                                                             transportation, training

Strings/fabrics of woven      Differential dye pick-up Very Poor quality yarn/       Avoid use of plastic,      

plastics/plastic film               cloth. Damaged to machinery                                        better hose keeping 

Organic matter - Leaves,     Increased waste, machinery damage                           Use of pre-cleaner at ginning, use .

feather, paper, leather etc                                                                                             of gravity trap, better housekeeping

Inorganic matter                              ,,                                                                              Use of pre-cleaner at ginning,metal 

1 . sand dust                                                                                                                    detector, better house keeping                                                                        

2. metal/wire

Oily matter                          Mars yarn/fabric appearance                                     Avoid use of stamp color, hosue keeping   
1. Stamp color
2. Grease/oil

Hair- human                       Increased end breaks at ring rotor                                 Use of caps, automatic transportation          
                                          Poor yarn/fabric appearance                                             continuous training

Stones                                Damaged to machinery                                                   Better housekeeping and practices

Seed coats                         Increased waste at spinning Poor                                 Use pre-cleaner and post cleaner at ginning    

                                         yarn/fabric appearance

Pouches - Gutkha             Damaged to machinery part                                             Bet ter practices, education/ training

CONTAMINATION DETECTION SYSTEM

Manual process

Contaminants like jute, chindies, HDPE, gutkha packs, etc. can be removed by the workers. It is difficult to detect the contamination -due to their unpredictable size, shape, material and position as some of the contaminants get inside the cotton fiber layer and become invisible. This system is costly, time consuming and chances of human error are more. The accuracy of this system is also very poor.
Gravimetric method
In this system the contaminated material is removed because of gravity only. In this method of detection of cotton contaminants, a mechanical model is used. For the vision system and the sorting system, synchronized with the movement of cotton on the conveyor, an encoder is installed at the shift of the conveyor and driven by the belt. In this system only heavy contamination can be removed. Efficiency of this system is less due to lot of mechanical parts.
Electro-optical method
Electro-optical method used for cotton contaminant is based on the High Volume Instrument (HVI). This system is suitable for the extensive quality control of all the bale proceeds in a spinning mill. In this system Digital Image Process Technique is used, and this is the one of most efficient method of removal of contaminations.

WORKING PRINCIPLE

Contamination detection by optical means
All systems detect contamination by optical means. Yarn clearers and the" sorter of Loptex use photo sensors and detect the contamination as being darker than the cotton. Optical sensor can only see what visible means is, it cannot detect the contamination which is hidden within the cotton tufts. This permit detection of colorless contamination namely, packing material in polypropylene.
Contamination ejection by ultrasonic means
The degree of reflectance of acoustic waves depends on the surface structure of the object in their path. The sensor consists of a number of emitters of ultrasonic therefore not hearable waves. The receiver will receive waves which are reflected by the contamination contained in the lose cotton. If no contamination is present, the ultrasonic wave will be absorbed in the absorber box located on the other side of the system.
Contamination ejection by pneumatic valves
In case of the detection of a contamination by the optical or the acoustic system, the electronic control will activate pneumatic valves which are variable. It depends on the  size of contamination. It takes into account the transportation speed of the raw material and releases the air blow after the necessary delay. The air blow will be targeted since only the valves are activated, which are located in front of the passing contamination.

CONTAMINATION REMOVAL AT VARIOUS STAGES OF SPINNING

Contamination can be detected at any stage of the processing, from bale to yarn. From the point of view of contamination removal, however each stage has its own advantage and disadvantage in terms efficiency, reliability and impact.

Contamination removal at ginning stage

It is more beneficial to remove the contamination in earlier processing stage because of two reasons, first, the early removal enables to prevent the contamination from spreading to a large extent and second, it also helps to avoid more numerous interventions in later stage.
Figure shows, the manual picking of cotton contaminant before feeding to the blow room. In many ginning factories, electronic contamination control system like Vision shield of Reiter, have been installed in the transportation line between ginning and storing, before putting the cotton fiber into Bale press. Average efficiency of this contamination control system is around 40-45% at this stage. The sorting efficiency is 55-70% with a sorting load of 165 kgs/person/8 hr.

Contamination removal on Blow room

Blow room equipped with different kinds of contamination detection equipment available from different manufacturers like Premier Fibre Eye, Uster Optiscan, and Barco Vision cotton Sorter, Loptex Sorter, and Vision Shield detects and removes the contaminants that can be distinguished by color immediately following the initial stages of opening in the blow room. Any contaminants that are completely masked by the bulk fiber are not detected. The working principle is optical based from all manufacturers. Optimum illumination with combined incident and transmitted light enables both light and dark contaminants to be detected.

Contamination removal on carding and comber

Foreign fibers and cotton contaminants are detected by using intensity and hue properties, they give the Cotton Contamination Analyzer for Micro Cards which convert the raw cotton into thin uniform web without removing any impurities scanned by the CCD camera. Imaging system is used to classify particles in terms of size and number and detect the contamination from the cotton. In case of carding, contaminants are removed with flat and licker-in waste and most of the hair contamination is removed through noil in comber.

Contamination removal on draw frame and lappers

BMS Vision Sliver watch system is installed in the creel of the draw frame for the purpose that it stops the draw frame if the contaminated sliver is detected. Any foreign fibers as well as the fibers of colors other than the cotton are detected. Short and intensive contaminants can also be detected by filter settings.
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On lappers up to 24 sensors can be installed in the creel to monitor the sliver and the lapper is stopped if the contaminants are detected.

Contamination removal on ring frame

In the ring frame no direct contamination removal procedure is available but many times yarn breaks where contamination is present. These contaminants go into pnumafit waste, although it does not occur most of the time for very fine fiber shaped plastic contaminations that are longer than cotton fiber and is spun into the yarn.

Contamination removal on winding

Winding is the last process in the spinning mill where the maximum contaminations are removed from the yarn. The procedures are as described below:
By using Electronic contamination channel (foreign matter detection) channel:
Such kind of electronic contamination clearing channels are available from different manufactures like Uster, Loepfe, Keissoki, and Premiere. The working principle is almost same and optical based for all manufactures. During yarn winding this channel measures the color intensity of the yarn and compares the portion every 2mm continuously against the base white yarn. In case of variation in color intensity, it detects and actuates the cutter assembly to cut the contamination portion.
By using PP (polypropylene) contamination detection channel:
The device like Loepfe, Zen it, Uster, Keissoki detect white colored polypropylene contaminants by using UV light. Polypropylene and other synthetic contaminants cannot be detected with conventional optical foreign fiber clearers as contaminants are transparent or look like cotton. The detection is based on the Tribo-electric effect is an electrical phenomenon in which fibers exchange electrons with the sensor, the so called Tribo-electric effect, where certain materials become electrically charged after coming into contact with another different material.

Contamination detection during inspection and packing

Ultra violet lights are installed in the packing and inspection department to detect chemical/oily substances and foreign fibers and other synthetic manmade fibers.

CONCLUSION

Contamination is one of the critical issues for spinners to maintain first grade yarn quality. Contamination comes from raw material, handling of material, ancillary products and work practices. Different methods to reduce contamination are now practiced in cotton ginning to yarn manufacturing processes, which have been reviewed. More and more involvement will definitely improve the contamination removal
efficiency of the industry and as a result such a burning issue of contamination may be solved with ease.

This article was originally published in the textile Review magazine, March, 2013 issue, published by Saket Projects Limited, Ahmedabad.
About the Authors:
Ms. Madhuri V. Kakde and Prof. H.R. Shah are associated with the D.K.T.E. Society’s Textile and Engineering Institue, Ichalkaranji.