Faults/Defects in the Knitted Fabrics

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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;
  1. Barriness
  2. Thick & Thin lines
  3. Dark or Light horizontal lines (due to the difference in dye pick up)
  4. Imperfections
  5. Contaminations
  6. Snarling
  7. 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;
  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.
Hole in fabric
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 fibers 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 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 & 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.
Author of This Article:
Shubham Yadav
B.Sc. in Textile Engineering
Government Central Textile Institute,
Kanpur, Uttar Pradesh




2 comments:

Moon Rain said...

Very good information about knitted fabric fault. I am also a student of textile. I have many textile books in my collection. I also like to create a blog like yours... But i already created a blog side with some famous poetry. I you have some time in your hand you can visit my blog. Thank you.

Mazharul Islam Kiron said...

@Moon Rain You can publish article in this blog which is published with your reference. thanks

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