Post on 06-May-2015
Total Textile Process at a Glance
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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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