003.Knitting Defects s

7/30/2019 003.Knitting Defects s

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Defected and Defect-free Fabric..

What is a Fabric Defect?

A Fabric Defect is any abnormality in the Fabric that

hinders its acceptability by the consumer.

What is a Defect-Free Fabric?

1. A Fabric that exhibits a consistent performance within

the boundaries of human use & human view.

2. A Fabric that exhibits a consistent appearance within

the human sight boundaries.


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Measurement of Bias ..

Skew or Bias - Measure the skewin three places spaced as widely

as possible along the length of the

fabric or along a minimum of 1

linear yard. If possible,

make no measurement closer to

the ends of the roll or piece of

fabric than 1 yard. Draw a line

perpendicular to the selvage

across the fabric from a point C

where the marked yarn or course

meets one selvage, meeting the

other selvage at point B. Measure

the distance between points A and

B or D and B, and B and C, as

shown in Fig. 2. Record the threeor more skew or bias

measurements. Calculate the

maximum skew or bias as a

percentage of the fabric width

using the equation:

"% Skew = Distance AB or DB x 100 /

width BC"


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Machine-Related Factors:

Failure of spinning preparation to eliminate or minimize short

and long-term variation Failure of opening and cleaning machines to completely

eliminate contaminants and trash particles

Failure of the mixing machinery to provide a homogenous blend

Excessive machine stops particularly during spinning

Excessive ends piecing during spinning preparation

Poor maintenance and housekeeping

Knitting-related defects

Dyeing and Finishing-related defects

What are the factors that

could lead to fabric defects?


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Material-Related Factors:

Fiber contaminants

Excessive neps and seedcoat fragments Excessive short fiber content

Excessive trash content

High variability between and within-mix

Clusters ofunfavorable fiber characteristics

Weight variation

Twist variation

Excessive Hairiness

What are the factors that

could lead to fabric defects?


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Some other Fabric Defects..

Small bits of

contaminants spun

into the yarn

Whitespecs

Synthetic fibre

contaminant


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Pointers focussing on the Defected area..


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Another Fabric Defect..


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Another Fabric Defect..


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Knit-in Contaminants..

There can be certain defects

which arise during the knit-in

process thus are shown here.


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Modelling Fabric Defects-The

Problem Theory..


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DEFECTS SEVERITY Barre Usually major

Askewd or bias Could be major or minor

Birdseye Major

Bowing Major or minor

Broken colour pattern Major

Crease streak Major or Minor

Drop stitches Major

End Out Usually Major

Hole Major

Missing Yarn Major

Mixed Yarn Major

Needle Line Major or Minor

Pin Holes Major

Runner Major

Slub Major or Minor


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Industry Practise..

PURPOSE

To establish a uniform method for determining, quantifying and measuring

the quality of warp knit elastomeric fabrics; and a method for measuring

length, width, and other physical properties.

METHOD Four-Point System - Penalty points are attributed to a piece of fabric

according to the length of its defects measured in inches. The following

schedule of penalty points is based on fabrics 60/62 inches in width for

defects visible when inspected on face side of fabric only:

Length of Defects:3 inches or less

Over 3, but not over 6 inches

Over 6, but not over 9 inches

Over 9 inches


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Industry Practise..

Number of Penalty Points

1

2

3

4

Four penalty points per linear yard are the maximum assessable for fabrics

up to 60/62 inches in width.

For fabrics over 60/62 inches in width, maximum allowable penalty pointsare to be increased in proportion as the width exceeds 60 inches.

Regardless of the length of fabric, the quality shall be expressed in the

number of penalty points per 100 yard length. (Example: A 40-yard piece

width six penalty points is to be rated as 15 points per 100 yards.)


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Industry Practise..

Identification and Rating Defects:

Examples of defects in evaluating quality are these:

Knitting defects, including holes other than pinholes

Grease/oil spots

Dye spots

Stains

Slubs-except where they are an inherent part of the yarn

Picks

Bowing and Skewing (bias): bowing and skewing may not exceed 5% of overall

width. Examples: 60" width - 3" tolerance and 72" width - 3.5" tolerance

Any yard containing bowing or skewing in excess of these limits shall be penalized

four points.

Fabrics are to be examined for these defects only on the agreed upon selling face

(which may be the technical face, or technical back).


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Facts about Fabric Defects..

99% of Fabric-Defects can be diagnosed with minimum or no testing if

every involved personnel from the fiber to the fabric sector is willing to

honestly tell his/her side of the story. Fabric-defect diagnostic work has

become more of detective work because of missing facts.

Poor Cotton Mixing is a Sure Defect-Causing Factor & Good Mixing alone

does not always guarantee a Defect-Free Fabric. Machine-Related Factors

cannot be emphasized enough.

High cost yarn testing equipments available today reveal minimum or no

prediction of potential fabric defects. Indeed, there is a significant gap

between yarn quality as tested in the yarn raw form and corresponding

yarn quality as it exists in the fabric.

There is a great loss of fabric as well as money due to fabric defects so

care should be taken to minimize them as much as can be done.

Fabric faults or defects are responsible for nearly 85% of the defects foundin the garment industry.


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Current Usual method of Detection and

Optimal measure..

Present Scenario-

Inspection is done manually, ie., when a significant

amount of fabric is produced,the fabric roll isremoved from circular knitting machine and then

sent to an inspection frame.

Optimal Solution-

To automatically inspect fabric as it is being produced

and to encourage maintainence personnel to prevent

production of defects or to cahnge process

parameters automatically and consequently improvefabric ualit .


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Flowchart of Defect

Segmentation..


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On-line Fabric Defect Detection..

Circular Knitting Machine


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..THANK YOU..

003.Knitting Defects s

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