Knitted fabric faults and their remedies

ON Root Causes Analysis of knitted Fabric Faults & Their Remedies...  Introduction  Causes of Fabric faults due to yarn  Causes of Fabric faults due to knitting  Causes of Fabric

Total Textile Process at a Glance

ON

Root Causes Analysis of knitted

Fabric Faults & Their Remedies

 Introduction

 Causes of Fabric faults due to yarn

 Causes of Fabric faults due to knitting

 Causes of Fabric faults due to Dyeing & Finishing

 Conclusion

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

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

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) Barriness II) Spirality III) Shrinkage IV) Thick & thin place

I) BARRINESS

Definition:

Barriness defect appears in

the Knitted fabric, in the

form of horizontal stripes

of uniform or variable

width.

Fig: Barriness

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).

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.

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.

 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

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.

Fig: Spiraility

B) Influence of fabric properties:

 Fabric Stitch length:

 Fabric Structure

 Fabric Tightness

(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

Causes of Shrinkage:

 Twi st factor: twist factor increases so that s

shrinkage will be increases,

 Stitch length: stitch length increases so that

shrinkage will be increases,

 GSM: GSM increases so that shrinkage will be increases

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

(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

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

Cracks Or Holes

Local holes obtained when yarn breaks during

loop formation.

Causes

 Presence of knot in yarn.

 Weak places in yarn.

 Yarn tension too high.

 Yarn too dry.

 Yarn - guide not properly

set,

 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.

Pin Hole

Causes:

 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

 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

Needle Broken

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. Fig: Needle Broken

Sinker Mark

Causes:

 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 .

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.

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

 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

 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.

 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.

Lycra out

Causes:

 Fail to catch the Lycra yarn by needle.

 Low tension of Lycra yarn.

 Lycra yarn breakage.

 Faulty auto stop motion

 Auto stop motion should work

properly Fig: Lycra out

Lycra Drop

Causes:

 Low tension of Lycra yarn

 Fail to catch the Lycra yarn by needle

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

Causes of Fabric faults Due

To Dyeing & Finishing

The Dyeing and finishing related defects are, as follows

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 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

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

Provide magnetic filters in water/ steam

Fig: Pin Hole Damage

Crease Mark:

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. Fig: Crease Mark

Dye Spots

Causes:

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.

Fig: Dye Spots

Dead Cotton On Dyed Cotton:

Causes:

 Poor quality cotton

 More abrasion during process

Remedies:

 Try to minimize the abrasion

during process

 Use acid Cellulosic softener

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

Fig: Wrong Slitting

Lycra Burn:

Cause:

Overflow heat on the fabric during

heat setting

Incorrect speed of stenter m/c

during heat setting.

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.

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.

Fig: Dust

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.