Defects in the Knitted Fabrics

Defects in the Knitted Fabrics

Introduction:

A defect in 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. Prime causes of the fabric defects are, as follows;

·        Yarns

·        Knitting Elements

·        Knitting Machine Settings

·        Dyeing

·        Finishing

v Types of Defects:

·        Drop Stitches or Holes

·        Barriness

·        Streakiness

·        Imperfections

·        Snarling

·        Contaminations

·        Spirality

·        Needle Lines

·        Broken Needles

·        Sinker Lines

·        Oil Lines or Stains

·        Broken or Missing Ends

·        Fabric Press Off

·        Surface Hairiness & Piling

·        Snagging

·        Bowing

·        Dyeing Patches

·        Softener Marks

·        Stains

·        Color Fading

·        Shade Variation

·        Tonal Variation

·        Wet Squeezer Marks

·        Fold Marks

·        Crease or Rope Marks

·        Skewing or Diagonal Grain Lines

·        Shrinkage

·        GSM Variation

·        Width Variation

·        Curling of Edges

·        Measurements

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;

·        Barriness

·        Thick & Thin lines

• Dark or Light horizontal lines (due to the difference in dye pick up)
• Imperfections
• Contaminations
• Snarling
• Spirality

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;

·        Needle & Sinker Lines

• 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;

·        Drop Stitches

·        Yarn Streaks

·        Barriness

·        Fabric press off

·        Broken Ends

·        Spirality

Dyeing related defects

The Dyeing related defects are, as follows;

·        Dyeing patches, Softener Marks

·        Shade variation

·        Tonal variation

·        Color fading (Poor Color Fastness)

·        Dull shade

·        Crease or rope Marks

Finishing related defects

Defects caused, mainly due to the wrong process parameters are;

·        High Shrinkage

·        Skewing

·        Spirality

·        Surface Hairiness & Pilling

·        Tonal variation

·        Snagging (Sharp points in the dyeing machine or trolley etc)

·        Fold Marks

·        Wet Squeezer Marks

·        GSM variation

·        Fabric Width variation

• 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

• Obstructions in the yarn passage, due to the clogging of eyelets, yarn guides & tension discs, with wax & fluff etc.

• Defects like; Slubs, Neps, Knots etc.

• Incorrect gap between the Dial & Cylinder rings.

Remedies:

     

• Ensure uniform yarn tension on all the feeders, with a Tension Meter.

• Rate of yarn feed should be strictly regulated, as per the required Stitch Length.

• The fabric tube should be just like a fully inflated balloon, not too tight or too slack.

• Eyelets & the Yarn Guides, should not have, any fibers, fluff & wax etc. stuck in them.   

• The yarn being used, should have no imperfections, like; Slubs, Neps & big knots etc

• 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 / Merge no.

• Ensure that the hardness of, all the yarn packages, is uniform, using a hardness tester.

Streakiness

Definition:

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

     

Causes:

• Yarn slippage on the IRO Pulley, due to the yarn slipping in & out from underneath the IRO Belt, due to a tilted IRO Pulley.

• Worn out IRO belts, yarn guides & eyelets etc

• Faulty winding of the yarn packages

• Yarn running out of the belt, on the IRO Pulley

Remedies:

• Ensure very smooth, clean & obstruction free passage of the yarn, through the eyelets, yarn & tension discs etc.

• No cuts or rough surfaces, in the Porcelain Eyelets, Yarn Guides & the Yarn Feeder holes etc. 

• Flawless winding of the, Yarn Package (The yarn coils should unwind smoothly, without any obstruction)       

• The yarn should be running under the IRO belt, between the belt & around the IRO 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 (Uneven USTER) 

Remedies:

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

• Specify the number of acceptable Imperfections / Km. of the yarn & the USTER evenness %, while ordering the yarn.

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 (Unbalanced twist yarn).

Causes:    

• High, twist in the, yarn.

• Hosiery yarns are soft twisted. High, twist in the yarn, is the cause of snarling.

• (Snarls cause, fabric defects & needle breakages)

Remedies:

• Ensure using Hosiery Yarns, of the recommended T.P.M. only.

• (Hold a few inches of the yarn in both the hands, in the form of a ‘U’.

• The yarn has a balanced twist, if it doesn’t tend to rotate or turn, in the form of a snarl.

• (Such yarn can be used for Hosiery applications.)

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 fibers etc.      

• Dead Fibers appear in the fabric, as a result of the, presence of excessive immature Cotton fibers, in the Cotton fiber crop.

• Dead fibers do not pick up color during Dyeing.

• Presence of the foreign materials, in the, staple fiber mixing

• (Kitty, Husk, Broken Seeds, dyed fibers & fibers like Poly Propylene, Polyester, Viscose 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.M. of the Hosiery Yarn

              

• (Spirality is caused, by the Twisting Torque as a result, of the high yarn T.P.M.)

• (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.

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 Calander, 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

• Tight Needles in the grooves

• 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.

• Replace all the defective needles having, bent latches, hooks or stems.

• Remove the fibers accumulated in, the Needle tricks (grooves).

• Replace any bent Needles, running tight in the tricks.

• Check the Needle filling sequence in the Cylinder / Dial grooves (tricks).

Broken Needles

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.

Causes:

       

• High Yarn Tension

• Bad Setting of the Yarn Feeders

• Old & Worn out Needle set

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.

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 (Grooves)

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.

• Oil lines appear in the fabric, in the lengthwise direction, even after dyeing.

• 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 surfaces.

• (Rectify, if found rough)

• 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:

• (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 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:

• (Washing, Crocking, Chlorine, Light, Perspiration)

• 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

• (Tonal variation in the fabric is caused, due to the variations, in the fabric processing parameters i.e. Temperature, Time & Speed etc. of the Shrink 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.

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 (Pique, S.J. etc.)

• 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 marks)

• Spread the fabric in loose & open form & not in the rope form, in the Hydro Extractor.

Skewing or Diagonal Grain Lines (Wales)

Definition:

Fabric Wales appear in the diagonal direction, to the edges of the fabric, instead of being parallel.

Causes:

• Improper feeding of the fabric, while Calandering & 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 Calander, or the Compactor machines.

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 processes)

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 & Widthwise stretching of the dyed fabric, on the Stenter, Calander & 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 MAKE 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.  

Problems faced in Knits on the Cutting Table

(Curling of the Single Jersey Fabrics)

Definition:

Single Jersey fabrics, when layered on the cutting table tend to, curl at the edges.

Causes:

• Dimensional instability of the Single Jersey knitted fabrics

• The face side of the fabric has loops, whereas the back side has only yarn floats. So, there is an imbalance, between the face & the back side of the fabric.

Remedies:

• Gumming on both the edges of the S.J. fabrics, while Stentering, can control the curling.

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.