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Fault of knitted fabrics

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Detection of faults during production of knitted fabric is crucial for improved quality and productivity. The yarn input tension is an important parameter that can he used for this purpose. We can Problems faced in the Knitted Fabrics, due to the Dyeing & Finishing processes

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Fault of knitted fabrics

  1. 1. Fault of Knitted Fabric Azmir Latif
  2. 2. Problems faced in the Knitted Fabrics, due to the Dyeing & Finishing processes
  3. 3. Stains (See Picture) Stains appear as spots or patches of Color, Grease, Oil, & dust on a neat & clean, finished fabric surface. Causes: Dyeing Machine not cleaned thoroughly, after dyeing a fabric lot. Grease & Oil stains from the unguarded moving machine parts, like; Gears, Shafts, Pulleys & Trolley wheels etc. Fabric touching the floor & other soiled places, during transportation, in the Trolleys. Handling of the fabric, with soiled hands & stepping onto the stored fabric, with dirty feet or shoes put on.
  4. 4. Remedies: Wash & clean the dyeing machine thoroughly, after dyeing every dye lot. Follow the dyeing cycle of Light- Medium- Dark shades & then reverse the cycle, while dyeing the fabric. All the lubricated moving machine parts, should be protected with safety guards. Make sure that the fabric is neatly packed in or covered with Polythene sheets, while transporting or in storage. Handle the fabric carefully, with clean hands & do not let anyone step onto the stored fabric.
  5. 5. Dyeing Patches (See Picture) Dyeing patches appear, as random irregular patches on the surface of the dyed fabrics. Causes: (Scouring, Dyeing Recipe, Dyeing Machine stoppage & Softener). Inadequate Scouring of the grey fabric is one of the primary causes of the dyeing patches. Improper leveling agent is also one of the causes of the patches. pH value not maintained. Dyeing machine stoppage, due to power failure, or the fabric entanglement, in the dyeing machine are, a major cause of the dyeing patches.
  6. 6. Remedies Scour the grey fabric thoroughly, to remove all the impurities from the fabric, before dyeing. Use appropriate leveling agents, to prevent patchy dyeing. Maintain the correct pH value, during the course of dyeing. Use a power back up (Inverter), for the dyeing operation to be completed uninterrupted. Use Nylon separation thread, for knitting the Collars & Cuffs, to prevent the breaking off of the thread & the subsequent entanglement of the Collars & Cuffs in the dyeing machine.
  7. 7. Crease Marks or Rope Marks Crease marks, also called “Rope Marks”, appear in the knitted fabric, as dark haphazard, broken or continuous lines. Causes: Damp fabric moving at high speed in twisted form, in the Soft Flow machine & the Hydro Extractor (Centrifuge). Remedies: Use anti Crease chemicals, during the Scouring & the Dyeing process. (The use of anti Crease, swells the Cellulose & prevents the formation of crease marks.) Spread the fabric in loose & open form & not in the rope form, in the Hydro Extractor. Don’t let the damp fabric rope lie in the trolley for long, if the next process requires a long wait. Keep the fabric in the open sheet form.
  8. 8. Crease mark hydroextractor
  9. 9. Softener Marks Definition: Softener marks appear as distinct irregular patches in the dried fabric, after the application of softener. Causes: Softener not being uniformly dissolved in water. Correct pH not maintained. Remedies: Ensure that the softener is uniformly dissolved in the water & doesn’t remain un- dissolved, as lumps or suspension. Use the right softener & the correct procedure for the application, i.e. Exhaust or Padding method. Maintain the correct pH value of the softener, before it’s application.
  10. 10. Wet Squeezer Marks (See Picture) The fabric on the edges of the fabric tube gets, permanent pressure marks, due to the hard pressing of the squeezer rolls. These marks appear as distinct lines, along the length of the fabric & can’t be corrected. Causes: Excessive pressure, of the squeezer rolls of the Wet Squeezer, on the wet fabric, while rinsing. Remedies: Adjust the gap between the squeezer rolls, to prevent too high a pressure on the fabric being squeezed. Use a hydro extractor (Centrifuge) for the extraction, to avoid the squeezer roll marks. Soon after hydro extraction, open the fabric manually, to prevent crease marks, appearing in the damp fabric.
  11. 11. Surface Hairiness & Piling (See Picture) Surface hairiness or fibrillation, appears in the form of excess superfluous fibers, on the surface of the knitted fabrics, which have either been reprocessed, tumble dried, or due to the ruptured fibers of regenerated filament yarns, like; Viscose & Tencel. Pilling appears as, small fiber balls formed on the fabric surface, due to the entanglement of loose surface fibers. Fiber staple length, low T.P.M. & long yarn floats etc. also contribute to pilling. Causes: Abrasion due to the contact with rough surfaces Excessive surface hairiness due to the abrasive tumbling action (Fabric friction in the Tumble Dryer) Rough Dyeing process & abrasive machine surfaces (Soft Flow machine tubes, Tumble Dryer drums etc.) Reprocessing of the fabric is, also a major cause of piling.
  12. 12. Remedies: Avoid using the Tumble Dryer, as far as possible. Control shrinkage by maximum fabric relaxation & over feed in the processing. Regularly inspect the fabric contact points on all the machines, for any rough surfaces & rectify, if found rough. Avoid repeated reprocessing of the fabrics. Use anti pilling chemical treatments (FORNEX- W from CIBA GEIGY) for the fabrics, prone to piling.
  13. 13. Snagging (See Picture) Definition: Snagging appears on the knitted fabric surface, as a pulled up yarn float, showing up in the form of a large loop. Causes: Caused by the pulling or the plucking of yarn from the fabric surface by sharp objects, like; nails or damaged contact points of the machines. Remedies: Inspect & rectify, the sharp, fabric contact points on all the machines, like; (Winch, Soft Flow Dyeing, Tumble Dryer drum, Centrifuge drum & Trolleys etc.), on which snagging is taking place.
  14. 14. Tonal Variation (See Picture 62.) Roll to roll or within the same roll difference in the color perception i.e. Greenish, Bluish, Reddish or Yellowish etc., is attributed as tonal variation in the shade. Causes: Dyeing recipe. Individual components of different colors in a shade, try to dominate each other, causing tonal variation. Level dyeing not being done, due to the use of inappropriate leveling agents. Improper fabric Scouring (Impurities like, Oil & Wax etc. not being completely removed in Scouring).
  15. 15. Uneven application of heat in the drying chambers, during the fabric drying process, due to the variation in the process parameters, e.g. Temperature, Time & Speed etc. (Tonal variation in the fabric is caused, due to the variations, in the fabric processing parameters i.e. Temperature, Time, & Speed etc. of the Relax Dryer & Stenter, especially if, the machine is repeatedly stopped). Remedies Use appropriate leveling agents, to ensure uniform & level dyeing. Scour the grey fabric thoroughly, to ensure the removal of all the impurities. Ensure that the whole lot of the dyed fabric is processed, under uniform process parameters. The processing of the fabric roll in hand, should be completed at the time of shift change, by the same set of workers.
  16. 16. Color Fading (Poor Color Fastness) The color of the garment or the fabric appears, lighter & pale, in comparison to the original color of the product, after a few uses. Causes: (Washing, Crocking, Chlorine, Light & Perspiration) Dyeing recipe i.e. the poor fixing of the dyes on the fabric is a major cause of color fading.Using the wrong combination of colors in a Secondary or Tertiary shade. Use of strong detergents & the quality of water are also the common causes of color fading.Prolonged exposure to strong light will, also cause the colors to fade. High level of acidity or alkalinity in the perspiration of individuals, will also cause the garments, to fade.
  17. 17. Remedies Use the correct dyeing recipe i.e. the appropriate leveling, fixing agents & the correct dyes. Follow the wash care instructions rigidly. Use mild detergents & soft water for washing the garments. Don’t soak the garments for more than 10- 15 minutes, in the detergent, prior to washing. Turn the wet garments, inside out, while drying. Dry in shade & not in direct sunlight. Protect the garments against prolonged direct exposure to strong lights, especially in show rooms.
  18. 18. Uneven Yarn Dyeing Bariness or “Patta”, is the main defect in the fabric, caused due to the uneven dyeing of the yarn. Causes: Uneven yarn dyeing, can be as a result of the mixing of the yarns of two different lots, causing variation in the dye pick up. Uneven dyeing is also caused, by the variation in the process parameters i.e. Recipe, Time, Temperature & pH etc. from one yarn lot to the other. Power failure, causing the dye liquor circulation in the machine, to stop. Remedies: The grey yarn used for the dyeing of one shade, should be from the same lot. Ensure that the same process parameters (Recipe, Time, Temperature & pH etc.) are used, for the dyeing of each dye lot. Use a power back up (Inverter), for the uninterrupted running of the dyeing machine.
  19. 19. Shade Variation (Roll to roll & within the same roll) Sometimes, there appears to be a difference in the depth of shade, between the roll to roll & from place to place, in the same roll. The defect will show up clearly, in the garments manufactured from such fabrics. Causes: Shade variation can be a result of the mixing, of the grey fabrics of two different lots. Shade variation is also caused, by the variation in the process parameters i.e. Time, Temperature & Speed etc. from one fabric roll to the other. Shade variation can appear to be, in the fabrics having GSM variation, caused due to the uneven stretching, unequal fabric overfeed % etc. Remedies: Ensure that the grey fabric used for one shade, is knitted from the same lot of yarn. Ensure that the same process parameters (Width, Overfeed, Temperature & Machine Speed etc.) are used, for each roll of a dye lot.
  20. 20. Folding Marks (See Picture) Fold marks appear as distinct pressure marks, along the length of the fabric. Causes: High pressure of the fabric Take Down rollers of the Knitting machine, on the grey fabric, is one of the main causes. Too much pressure of the feeding rolls of the Calendar & Compactor is, the primary cause of the folding marks, in the knitted fabric. Remedies: Adjust the gap between the two rolls, as per the thickness of the fabric sheet (Pique, Single Jersey etc.) Gap between the two Calendar rolls should be just enough, to let the rolls just touch the fabric & remove, the wrinkles in the fabric, but put no pressure on the fabric sheet, especially in the case of Pique & structured fabrics.
  21. 21. Bowing (See Picture) Bowing is a row of courses or yarn dyed stripes forming a bow shape, along the fabric width. Causes: Uneven distribution of tensions, across the fabric width while, dyeing or finishing the fabric. Remedies: Bowing can be corrected, by reprocessing the fabric, by feeding it from the opposite end. A special machine attachment (MAHLO device) is also available for, correcting the bowing in the knitted fabrics. It is a Banana shaped roller, with individually controllable sections, which adjust the bowing in the fabric, after getting the command from sensors.
  22. 22. Skewing or Diagonal Grain Lines (Wales)- (See Picture) Fabric Wales appear in the diagonal direction, to the edges of the fabric, instead of running parallel to the edges. Causes: Improper feeding of the fabric, while Calendaring & Compacting. Remedies: Keep a slit line on one side of the tubular fabric. Use the slit line, as a reference line, to keep the grain lines straight, while feeding the fabric slowly, on the Calendar, or the Compactor machines. In order to achieve the best results, the fabric feeding should be at a very slow speed (12- 13 M/Min.)
  23. 23. Spirality (See Picture) Spirality appears in the form of a twisted garment, after washing. The seams on both the sides of the garment displace, from their position & appear on the front & back of the garment. Causes: High T.P.M. of the Hosiery Yarn (Spirality is caused, by the twisting Torque, as a result of the, high yarn T.P.M. (Twist per Meter). (Hosiery yarns are soft twisted, whereas the Warp yarns are hard twisted. Uneven Fabric Take down tension, on the knitting machine. Unequal rate of Fabric feed on the Stenter, Calender & Compactor machines.
  24. 24. Remedies: Use the Hosiery yarns of the recommended TPM level for knitting. (Hosiery yarns are soft twisted, in comparison to the Warp yarns). Fabric pull or the Take Down tension, on both sides of the grey fabric tube, on the knitting machine, should be equal. Ensure uniform rate of feed of the dyed fabric, on both the edges, while feeding the fabric to the Calendar, Compactor or Stenter machines.
  25. 25. High Shrinkage The original intended measurements of the Garment, go haywire, during storage or after the very first wash. Causes: High Stresses & strains exerted on the fabric, during Knitting, Dyeing & Processing operations & the fabric not being allowed to relax properly, thereafter. Storage of the grey & dyed fabric in roll form.
  26. 26. Remedies Keep the Grey Fabric in loose plated form, immediately after the roll is cut. Store the Finished fabric also in the plated form & not in the roll form. Allow the fabric to relax properly, before it is cut. Give maximum overfeed to the fabric, during the processing, on the Stenter, Compactor & Calendaring machines. In the next picture, the fabric is being over fed by 30- 35% on the Stenter (See Picture) The fabric should be laid on the cutting table, using a mechanized trolley, instead of the manual layering, in order to exert uniform pulling tension on every fabric layer. In view of the very high stretch in the Lycra fabrics, it is advisable to let the fabric lie & relax on the cutting table, overnight or at least for a few hours, after layering.

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