Faults in the Knitted Fabrics:

Faults in the Knitted Fabrics:


Faults in the Knitted Fabrics:
A defect of the knitted fabric is an abnormality which spoils the aesthetics i.e. the clean & uniform appearance of the fabric & effects the performance parameters, like; dimensional stability etc.
There are various types of defects which occur in the Knitted fabrics of all types caused by a variety of reasons. The same type of defects may occur in the fabric due to a variety of different causes e.g. Drop Stitches, Spirality etc.







Category of Defects:
Yarn Related Defects:
Almost all the defects appearing in the horizontal direction in the knitted fabric are yarn related. These defects are mainly;

Knitting Elements Related Defects:
Almost all the defects appearing in the vertical direction in the knitted fabrics are as a cause of bad Knitting Elements.These defects are mainly;

1. Needle & Sinker Lines
2. Drop Stitches etc.

Machine Settings Related Defects:
These defects appear randomly in the knitted fabrics due to the wrong  knitting machine settings &that of the machine parts. The defects are mainly;

1. Drop Stitches
2. Yarn Streaks
3. Barriness
4. Fabric press off
5. Broken Ends
6. Spirality

Dyeing Related Defects:
The Dyeing related defects are as follows;

1. Dyeing patches
2. Softener Marks
3. Shade variation
4. Tonal variation
5. Color fading (Poor  Color Fastness)
6. Dull shade
7. Crease or rope Marks

Finishing Related Defects:
Defects caused mainly due to the wrong process parameters are;

1. High Shrinkage
2. Skewing
3. Spirality
4. Surface Hairiness & Pilling
5. Tonal variation
6. Snagging (Sharp points in the dyeing machine or trolley etc)
7. Fold Marks
8. Wet Squeezer Marks
9.  GSM variation
10. Fabric Width variation
11. Curling of S.J. Fabrics

Drop Stitches (Holes)
Definition:
Drop Stitches are randomly appearing small or big holes of the same or different size which appear as defects in the Knitted fabrics.







Major Causes:

• High Yarn Tension
• Yarn Overfeed or Underfeed
• High Fabric Take Down Tension
• Defects like Slubs, neps, Knots etc.
• Incorrect gap between the Dial & Cylinder rings.

Remedies:

1. Ensure uniform yarn tension on all the feeders with a Tension Meter.
2. Rate of yarn feed should be strictly regulated as per the required Stitch Length.
3. The fabric tube should be just like a fully inflated balloon, not too tight or too slack.
4. The yarn being used should have no imperfections like; Slubs, Neps & big knots etc
5. The gap between the Cylinder & the Dial should be correctly adjusted as per the knitted loop size.

Barriness
Definition:
Barriness defect appears in the Knitted fabric in the form of horizontal stripes of uniform or variable width.

Causes:

• High Yarn Tension
• Count Variation
• Mixing of the yarn lots
• Package hardness variation

Remedies:

• Ensure uniform Yarn Tension on all the feeders.
• The average Count variation in the lot should not be more than + 0.3
• Ensure that the yarn being used for Knitting is of the same Lot .
• Ensure that the hardness  of all the yarn packages is uniform using a hardness tester.

Streakiness
Definition:
Streaks in the Knitted fabrics appear as; irregularly spaced & sized, thin horizontal lines.

Causes:

• Faulty winding of the yarn packages.
• Yarn running out of the belt on the Pulley

Remedies:

• Winding of the yarn package should be proper.
• The yarn should be running between the belt and around the pulley.

Imperfections
Definition:
Imperfections appear on the fabric surface in the form of unevenly placed or randomly appearing Knots, Slubs & Neps, Thick & Thin places in the yarn.

Causes:

• Big Knots, Slubs & Neps in the yarn, Thick & Thin yarn.

Remedies:

• Specify the quality parameters of the yarns to be used for production to the yarn supplier.

Snarls
Definition:
Snarls appear on the fabric surface in the form of big loops of yarn getting twisted due to the high twist in the yarn.

Causes:

• High twist in the yarn.

Remedies:

• Twist in the yarn should be in required TPM.

Contaminations
Definition:
Contaminations appear in the form of foreign matter such as; dyed fibers, husk, dead fibers etc. in the staple spun yarn or embedded in the knitted fabric structure.

Causes:

• Presence of dead fibers & other foreign materials, such as; dyed fibers, husk & synthetic fibres etc.
• Dyed & other types of fibers flying from the adjacent Knitting machines cling to the yarn being used for knitting & get embedded in the Grey Fabric.

Remedies:

• Use rich fiber mixing for the yarns to be used for Knitting in order to have less dead fibers appearing in the fabric.
• Rigid control measures in the Blow Room to prevent the mixing of foreign matters in the Cotton mixing.
• Segregate the Spinning & Knitting Machines, with Plastic Curtains or Mosquito Nets, to prevent the fibers flying from the neighboring machines, from getting embedded in the yarn / fabric.

Spirality
Definition:
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.I. of the Hosiery Yarn
• Uneven Fabric tension on the Knitting machine.
• Unequal rate of Fabric feed on the Stenter, Calender & Compactor machines.

Remedies:

• Use the Hosiery yarns of the recommended TPM level for Knitting.
• Ensure uniform rate of feed of the dyed fabric on both the edges while feeding the fabric to the Calender, Compactor or Stenter machines.

Needle Lines
Definition:
Needle lines are prominent vertical lines along the length of the fabric which are easily visible in the grey as well as finished fabric.

Causes:

• Bent Latches, Needle Hooks & Needle stems
• Wrong Needle selection (Wrong sequence of needles, put in the Cylinder or Dial)

Remedies:

• Inspect the grey fabric on the knitting machine for any Needle lines.
• Check the Needle filling sequence in the Cylinder / Dial grooves (tricks).

Horizontal lines
Causes:

• Fault in bobbin
• Irregular tension on cams.

Remedies:

• Replace that bobbin.
• Check cams positioning 

Horizontal line in fabric

Broken Needles/ Laddering
Definition:
Defects caused by the broken needles show prominently as vertical lines parallel to the Wales. There are no loops formed in the Wale which has a broken needle.

Laddering effects

Causes:

• High Yarn Tension
• Bad Setting of the Yarn Feeders
• Old & Worn out Needle set
• Cylinder Grooves are too tight restricting needle movement
• Breakage of hook or butt in needle.

Remedies:

• Ensure uniform & the right Yarn tension on all the feeders.
• Keep the recommended gap between the Yarn Feeders & the Needles.
• Periodically change the complete set of needles.
• Remove fly or blockage from groove.
• Replace defective needle.

Sinker Lines
Definitions:
Sinker lines are prominent or feeble vertical lines appearing parallel to the Wales along the length of the knitted fabric tube.

Causes:

• Bent or Worn out Sinkers
• Sinkers being tight in the Sinker Ring grooves

Remedies:

• Replace all the worn out or bent sinkers causing  sinker  lines in the fabric.
• Sinker lines are very fine & feeble vertical lines appearing in the fabric.
• Remove the fibers clogging the Sinker tricks (Groove

Oil Lines
Definitions:
Oil lines are prominent vertical lines which appear along the length of the knitted fabric tube. The lines become permanent if the needle oil used is not washable & gets baked due to the heat during the finishing of the fabric.

Causes:

• Fibers & fluff accumulated in the needle tricks which remain soaked with oil.
• Excessive oiling of the needle beds.

Remedies:

• Fibers accumulated in the needle tricks cause the oil to seep into the Fabric.
• Some lubricating oils are not washable & can not be removed during Scouring.
• Remove all the Needles & the Sinkers of the machine periodically.
• Clean the grooves of the Cylinder & Dial of the machine thoroughly with petrol.
• Blow the grooves of the Cylinder Dial & Sinker ring with dry air after cleaning.

Broken Ends
Definition:
Broken ends appear as equidistant prominent horizontal lines along the width of the fabric tube when a yarn breaks or is exhausted.

Causes:

• High Yarn Tension
• Yarn exhausted on the Cones.

Remedies:

• Ensure correct yarn tension on all the feeders.
• Ensure that the Yarn detectors on all the feeders are working properly.
• Depute a skilled & alert machine operator on the knitting machine.

Fabric Press Off
Definition:
Fabric press off appears as a big or small hole in the fabric caused due to the interruption of the loop forming process as a result of the yarn breakage or closed needle hooks.

Press off takes place, when the yarn feeding to both the short butt & long butt needles suddenly stops due to the yarn breakage.

At times complete fabric tube can fall off the needles if the needle detectors are not functioning or are not properly set.

Causes:

• End breakage on feeders with all needles knitting.
• Yarn feeder remaining in lifted up position due to which the yarn doesn’t get fed in the hooks of the needles.

Remedies:

• Needle detectors, should be set precisely to detect the closed needles & prevent the fabric tube from completely pressing off.
• Proper yarn tension should be maintained on all the feeders.

Surface Hairiness & Piling
Definition:
Surface hairiness appears in the form of excess superfluous fibers, on the surface of the knitted fabrics, which have either been reprocessed, or tumble dried.

Pilling appears as, small fiber balls formed on the fabric surface, due to the entanglement of loose surface fibers.

Factors such as, the fiber staple length, low T.P.M. & fabric construction (with long yarn floats) etc. also contribute to pilling.

Causes:

• Abrasion due to the contact with rough surfaces
• Excessive surface hairiness caused, due to the abrasive tumbling action
• Fabric friction in the Tumble Dryer
• Rough Dyeing process & abrasive machine surfaces (Soft Flow Machine tubes, Tumble Dryer drum etc.)
• Reprocessing of the fabric is, also a major cause of piling.

Remedies:

• Avoid using the Tumble Dryer.
• Control shrinkage by maximum fabric relaxation & over feed in the processing.
• Regularly inspect the fabric contact points on all the machines, for any rough & sharp surface.
• Avoid repeated reprocessing of the fabrics.
• Use anti pilling chemical treatments for the fabrics prone to pilling.

Snagging
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.

Remedies:

• Inspect & rectify the fabric contact points on all the machines (Soft Flow Dyeing, Tumble Dryer & Centrifuge etc), on which snagging is taking place.

Bowing
Definition:
Bowing appears as rows 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 (MAHLO) is also available for correcting the bowing in the knitted fabrics.

Dyeing Patches
Definition:
Dyeing patches appear, as random irregular patches on the surface of dyed fabrics.

Causes:

• 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 dyeing patches.
• Correct 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.

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.

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

Remedies:

• Scour the grey fabric thoroughly to remove all the impurities from the fabric before dyeing.
• 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.
• Maintain the correct pH value of the softener before application.

Stains
Definition:
Stains appear as spots or patches of grease oil or dyes of different color, in a neat & clean finished fabric surface.

Causes:

•   Dyeing machine not cleaned thoroughly after dyeing a lot.
• Grease & Oil stains from the unguarded moving machine parts like; Gears Shafts Driving Pulleys & Trolley wheels etc.
• Fabric touching the floors & 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 on.

Remedies:

• Wash & clean the dyeing machine thoroughly after dyeing every dye lot.
• Follow the dyeing cycle of Light- Medium- Dark shades & then the 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.

Color Fading (Poor Color Fastness)
Definition:
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:

• Dyeing recipe i.e. the poor fixing of the dyes 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 for 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 also causes color fading.

Remedies:

• Use the correct dyeing recipe i.e. the appropriate leveling, fixing agents & the correct combination of 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 (show rooms or exhibitions etc.).

Shade Variation
(Roll to roll & within the same roll)

Definition:
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 fabric.

Causes:

• Shade variation can be as a result of mixing of the, 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 fabrics with 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 the yarn.
• Ensure that the same process parameters (Width, Overfeed, Temperature & Machine Speed etc.) are used for each roll of a dye lot.

Tonal Variation
Definition:
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:

• Wrong Dyeing recipe
• Wrong leveling agent selection or wrong dyes combinations.
• Improper fabric Scouring.
• Impurities like Oil & Wax etc. not being completely removed in Scouring
• Level dyeing not being done due to the inappropriate leveling agents.
• Variation in the process parameters, e.g. Temperature, Time & Speed etc .

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.

Wet Squeezer Marks
Definition:
The fabric on the edges of the fabric tube gets permanent pressure marks due to the hard pressing by the squeezer rolls. These marks appear as distinct lines along the length of the fabric & can’t be corrected.

Causes:

• These marks are caused due to the excessive pressure, of the squeezer rolls of the Padding Mangle, on the wet fabric, while rinsing.

Remedies:

• Use the Padding mangle only for the application of the softener.
• Use a hydro extractor (Centrifuge) for the extraction to avoid the squeezer roll marks.
• Soon after extraction open the fabric manually to prevent crease marks in the damp fabric.

Folding Marks
Definition:
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 Calander & 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 .
• Gap between the two Calander rolls should be just enough to let the rolls remove the wrinkles in the fabric but put no pressure on the fabric sheet especially in the case of Pique & structured fabrics.

Crease Marks
Definition:
Crease 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 Hydro extractor (Centrifuge)

Remedies:

• Use anti Crease, during the Scouring & the Dyeing process .
• The use of anti Crease, swells the Cellulose & prevents the formation of Crease mark.
• Spread the fabric in loose & open form & not in the rope form, in the Hydro Extractor.

High Shrinkage
Definition:
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 & the fabric not being allowed to relax properly, thereafter.
• High shrinkage is primarily due to the fabric being subject to high tension, during the Knitting, Dyeing & the finishing process .

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 & the Calandering machines.

GSM Variation
Definition:
The fabric will appear to have a visible variation in the density, from roll to roll or within the same roll of, the same dye lot.

Causes:

• Roll to roll variation in the, process parameters, of the fabric, like; Overfeed & Width wise stretching of the dyed fabric, on the Stenter, Calender & Compactor machines.
• Roll to roll variation in the fabric stitch length.

Remedies:

• Make sure that all the fabric rolls in a lot, are processed under the same process parameters.
• The Knitting Machine settings, like; the Quality Pulley diameter etc. should never be disturbed.

Fabric Width Variation
Definition:
Different rolls of the same fabric lot, having difference in the finished width of the fabric.

Causes:

• Grey fabric of the same lot, knitted on different makes of Knitting Machines, having varying number of Needles in the Cylinder.
• Roll to roll difference, in the Dyed Fabric stretched width, while feeding the fabric on the  stenter  Calander & Compactor.

Remedies:

• The whole lot of the grey fabric should be knitted on the same make of knitting machines.
• For the same gauge & diameter of the knitting machines, there can be a difference of as high as 40 needles, from one makes to the other make of the machine.
• This difference, in the number of needles, causes a difference of upto 2”-3” in the finished width of the fabric
• The stretched width of the grey fabric should remain constant, during finishing on the stenter.

Measurement Problems
Definition:
The measurements of the garments totally change after, a few hours of relaxation & after the first wash. The arm lengths or the front & back lengths of the garments may vary, due to the mix up of the parts.

Causes:

• Shrinkage caused due to the inadequate relaxation of the knitted fabrics, before cutting.
• Mixing of the garment parts cut from, different layers or different rolls of the knitted fabric.

Remedies:

• Use a trolley, for laying the fabric on the table, to facilitate a tension free, laying.
• Let the fabric relax for a few hours, before cutting, especially the Lycra fabrics.
• Ensure the numbering of the different layers of the fabric, to prevent the mix up of the components. 

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.)