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Root Causes Analysis of knitted Fabric Faults & Their Remedies

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Content Introduction Causes of Fabric faults due to yarn Causes of Fabric faults due to knitting Causes of Fabric faults due to Dyeing &

Finishing Conclusion

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Introduction Due to increasing the demand for quality knitted

fabrics, high quality requirements are today greater since customer has become more aware of “Non-quality" problems, in order to avoid fabric rejection, knitting mills have to produce fabrics of high quality, constantly. Detection of faults during production of knitted fabric with circular knitting machine is crucial for improved quality and productivity. Any variation to the knitting process need to be investigated and corrected. The high quality standard can be guaran teed incorporating appropriate quality assurance. Industrial analysis indicate that quality can be improved, and defect cost minimized, by monitoring of the circular knitting process.

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Our aim of this project is to study on root causes analysis of knitted fabric faults. To do so we have collected various type of faults from many industries and classify them in a systematic manner

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Causes of Fabric faults due to Yarn

Almost all the defects appearing in the horizontal direction, in the knitted fabric are, yarn related.

These defects are mainly:I) BarrinessII) SpiralityIII) ShrinkageIV) Thick & thin place

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I). BARRINESS

Definition: Barriness defect

appears in the Knitted fabric, in the form of horizontal stripes of uniform or variable width.

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Fig: Barriness

Causes Of Barriness:

factors which may cause or contribute to barre are listed as follows:

Raw material/fiberYarn formation /supplyKnitting machine

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Raw Material/Fiber:

Failure to control fiber diameter (micronaire or denier) from lay down to lay down.

Too high a C.V. of micronaire in the lay down for a given mill's opening line blending efficiency.

Failure to control the fiber color in the mix (grayness Rd, yellowness +b).

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Yarn Formation/Supply:Poor blending of fiber in opening through

finisher drawing. Mixing yarns of different counts.Mixing yarns from different spinning systems.Mixing yarns with different twist level/twist

direction.Mixing yarns with different degrees of hairiness.Mixing yarns with different amounts of wax.Excessive back winding or abrasion during this

process.

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Knitting Machine:

Improper stitch length at a feed.Improper tension at a feed.Variation in fabric take-up from loose to

tight.Excessive lint build-up.Variation in oil content.Worn needles, which generally produce

length direction streaks. Uneven cylinder height needles (wavy barre). Double feed end.

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RemediesRemedies::

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.

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II).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.

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Fig: Spiraility

Influencing Factors:

A) Influence of yarn properties Count Twist Blend

B) Influence of fabric properties: Fabric Stitch length: Fabric Structure Fabric Tightness

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(III). SHRINKAGE

A dimensional change resulting in a decrease in the length or width of a specimen subjected to specified conditions is known shrinkage. Shrinkage is mainly due to yarn swelling and the resulting crimp increase during washing in case of cotton fabrics

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Causes of Shrinkage:

Twisst factor: twist factor increases so that shrinkage will be increases,

Stitch length: stitch length increases so that shrinkage will be increases,

GSM: GSM increases so that shrinkage will be increases

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Remedies of Shrinkage

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 Calendaring machines.

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(IV) Thick & Thin Places

It causes due to yarn problem. If thick & thin places remain in yam & fabric is knitted with that yarn, then, this problem found in fabric.

Fig: Thick Thin Place

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Causes of Fabric faults due to Knitting

Almost all the defects appearing in the vertical direction, in the knitted fabrics, are as a cause of bad Knitting Elements. And some defects appear randomly in the knitted fabrics, due to the wrong knitting machine settings & that of the machine parts

About Different type of faults are discuses

bellow

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Cracks Or HolesLocal holes obtained when yarn breaks during loop formation.

CausesPresence of knot in

yarn. Weak places in yarn.Yarn tension too high.Yarn too dry.Yarn - guide not

properly set,Poorly lubricated

yarn.

Fig: Hole

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Remedies:

Use of flat knots. Yarn regularity control.Yarn consumption & coulier re-adjustment.Precise yarn - guide resetting. Air humidification.guide blowing.Use of protective filter creel.

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Pin HoleCauses:Improper tension.Same drive for both knit &

tuck stitch. Curved needle latch.

Remedies:Different drive have to

maintained Needle has to change.

Needle has no change. Fig: Pin Hole

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Fly ContaminationsCauses:Presence of dead fibers & other foreign materials,

such as; dyed fibers, husk & synthetic fibers etc. Dead fibers do not pick up color during Dyeing.

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Fig: Fly contamination

RemediesUse 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

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Needle BrokenCauses:High Yarn TensionBad Setting of the Yarn

FeedersOld & 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.

Fig: Needle Broken

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Sinker MarkCauses:Sinker not cleans.Defected /broken sinker.When darts deposited in

sinker, it is raised & causes this fault.

Remedies:Sinker has to be clean.It should be checked

that the sinker having correct thickness and depth.

Replacement of defected sinkers.

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Fig: sinker mark

Stains or Oil Lines

Causes:Grease & Oil stains from

the unguarded moving machine parts

Fabric touching the floors & other soiled places, during transportation, in the trolleys.

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

Fig: Stain or oil line

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

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Fabric Press OffFabric 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.

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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. Fig: Press off

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.

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Lycra outCauses:Fail to catch the Lycra yarn by

needle.Low tension of Lycra yarn.Lycra yarn breakage.Faulty auto stop motion

Remedies:Ensure the feed of lycra yarn to

every needle.The tension of lycra yarn should be

uniform.Auto stop motion should work

properly

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Fig: Lycra out

Lycra DropCauses:Low tension of Lycra yarnFail to catch the Lycra yarn by

needle

Remedies:Ensure the feed of lycra yarn

to every needle.The tension of lycra yarn

should be uniform.

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Slub

Causes:Usually caused by a thick

or heavy place in yarn or by ling getting onto yarn feeds.

Remedy:By using Good quality

yarn

Fig: Slub

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Causes of Fabric faults Due To Dyeing & Finishing

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The Dyeing and finishing related defects are, as follows

Shade variation/Uneven shade

 Pin-hole damage Crease mark

Dye spots  Dead cotton on dyed

cotton

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Wrong slitting

Lycra burn

 Band line

 Dust

Shade Variation/Uneven Shade

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.

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Fig: Shade Variation/Uneven Shade

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.

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Pin Hole Damage:Causes:Oxidation of the knitting oil/lubricant on

the fabric stored for a long duration.Presence of sharp metallic part in some

parts of machinePresence of heavy metal ions in peroxide

bath. Remedies:Check presence of any sharp object in

machineProvide magnetic filters in water/ steam

line

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Fig: Pin Hole Damage

Crease Mark: In knit dyeing crease mark is a common dyeing

fault.

Causes: More cycle time. Faulty plaiting device. Slack on tight selvedge causes creases at an angle to

each selvedge. Incorrectly set bowed-expander. Variation of heating and cooling rate. Improper fabric movement.  

Remedy: Anti- creasing agents are used to avoid crease mark

problem.

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Fig: Crease Mark

Dye SpotsCauses:These are most often caused by

operators not correctly mixing and thoroughly dissolving the dyestuff, in the right amount of water.

Dye bath hardness. Not agitation of dyestuff.

 

Remedies:Use adequate amount sequestrate to

lower bath hardness.Proper agitation.

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Fig: Dye Spots

Dead Cotton On Dyed Cotton:

Causes:Poor quality cottonMore abrasion during process

Remedies:Try to minimize the abrasion

during processUse acid Cellulosic softener

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Fig: Dead Cotton On Dyed Cotton

Wrong Slitting:Causes: It causes due to operator

carelessness. Sometimes workers do not slit fabric through slitting mark.

Remedies:Operators have to slit fabric

through slitting mark or fed fabric in slitting m/c in proper way so that m/c can slit fabric through slitting mark

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Fig: Wrong Slitting

Lycra Burn:Cause:Overflow heat on the fabric during

heat setting. Incorrect speed of stenter m/c

during heat setting.

Remedies:Provide correct temperature in

stenter m/c.To keep correct speed of stenter

m/c.

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Fig: Lycra Burn

Band Line:Causes: If the fabric is wet condition in long time.During drying the fabric if any part of the fabric is

wet then it can occur.Un proper fixing during dyeing

Remedies:To use short time for wet conditioning of the fabric.Equal drying of the fabric.Proper fixing during dyeing.

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Dust:Causes:Due to dirty finishing floor.Unclean the trolley of finishing floor.Due to unclean the m/c surface.Unclean the compactor m/c after using the

varies color of fabrics.Drop the footstep in white fabric. Remedies:To keep clean the finishing floor.Clean the trolley of finishing floor.To clean the m/c surface.Clean the compactor m/c after using varies

color of fabrics.

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Fig: Dust

CONCLUSION:CONCLUSION:Detection of faults during production of knitted fabric is crucial

for improved quality and productivity.

This presentation will present and discuss the detection of faults and malfunctions during the production remedies of knitted fabric.

We believe that our work will help the knitters to identify the source of de tected faults & proposes specific solutions for theses faults causes. So Knitters can take necessary remedial steps to overcome the faults.

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