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Knitted Fabric Quality & Controls

Fabric quality

Stitch density

Stitch length

How to find loop length?

Course length

Fabric cover

Fabric weight per unit area

Fabric width

Fabric Shrinkage

Knitted faults

Yarn Faults

Stains

Pilling

Knitted fabric standards

Four-Point System

Knitted Garment Quality

Yarn quality assessment
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Fabric quality assessment

In-process quality control

Quality control during spreading

Quality control during cutting

Quality control during sewing

Final Inspection

Dimensional & design Considerations

Weight

Design Factors

Fabric quality

Before we understand fabric quality let us first know what are

the properties of knitted fabrics. The commonly used

terminology connected with the properties of the knitted

fabric is as follows. (These expressions are mostly used for

circular knitted fabrics)

1. Stitch density, or loop density

2. Stitch length, or loop length

3. Course length

4. Fabric cover

5. Fabric weight per unit square

6. Fabric width

7. Fabric shrinkage

Stitch density

The most important property of knitted fabric is its stitch

density or loop density, i.e., the number of loops (stitches)

per square inch or centimeter of the fabric (loops per square

inch or loops per square centimeter etc).

The loop density is directly related to;
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Fabric appearance,

Fabric weight per unit area,

Fabric thickness,

Fabric drape and many other factors.

Loop density in turn would depend upon the length of yarn,which makes one loop (stitch).

1.1.2 Stitch length

The length of the yarn in one loop is known as stitch length.

In the fabric shown in the figure above, there are 17 stitches

wale wise (width wise) and 14 stitches course wise (length

wise). Therefore, the loop density of the fabric is 17 x14 = 238

stitches per square inch.

In general terms, for any knitted fabric, as the stitch length

increases the loop density decreases, and higher stitch

lengths will make the fabric porous. So we can say that the

loop density is directly related to the loop length. For simple

fabrics the relationship between loop density and loop length

can be expressed as an equation given below:

S = K/L 2

Where S is the loop density, L is the loop length in

centimeters and K is a constant for the particular

construction. After a large amount of data and research

definite values of K have been proposed. These values range

19 to 21.6 depending upon the dry or relaxed state of the

fabric.

Stitch density is also expressed as follows;

Stitch density = wpi x cpi

Where, wpi stands for wales per inch and cpi stands for

courses per inch.

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The above formula is true only for plain knitted fabrics. For

complex structures the formula is not true.

How to find loop length?

From a given plain knitted fabrics, the loop length can be

found out by unraveling yarn from known number of loops of

the fabric and measuring its length in centimeters using a

crimp tester (or straightening the yarn by hanging a small

weight).

Length of the yarn unraveled divided by number of loops

unraveled will give the loop length.

To arrive at accurate loop length the mean of several lengths

unraveled is divided by the number of loops in the course

unraveled. It is usual to use 100 loops in this measurement.

The second precaution is that the yarn unraveled must be

straightened properly to remove the crimps in the yarn. Also

the yarn should not be over stretched while straightening.

Preferably a crimp tester should be used, if available.

Course length

A circular knitted fabric is composed of a number of courses

that spiral around the fabric. Yarns fed by number of feeders

positioned around the machine form these courses. Each

feeder can be regarded as a separate knitting entity

responsible for making a course in one circular rotation of the

machine. The yarn length fed by one feeder that has been

knitted in one complete rotation of the course is the course

length and the number of loops, which this yarn has created,

in one rotation are equal to the number of needles per

centimeters of the knitting machine.

If the feeding tension on each feeder differs, each feeder will

produce a different course length. In feeders having more

tension, tight course will be produced and where the feed

tension is less a loose course will be produced. It is the aim of

fabric quality control to make each course length as near as

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possible to the specified value (to be determined depending

upon the quality of the fabric to be knitted). When some

courses are wildly out of specification and differ from one

another, the fabric has horizontal bars that degrade its

appearance and lower its perceived quality.

Most modern circular machines producing simple fabrics are

fitted with positive feed units that ensure much closer

tolerances between feeders in respect of course length. For

machines that do not possess positive feed or for fabrics that

cannot be knitted under positive feed conditions it is difficult

to produce good quality fabric.

The tension of feeders is leveled using a combination of yarn

speed meters and tension meters. During these quality

control procedures it is essential that at lease one

measurement be made on each feeder. Modern knitting

machines can have in excess of 100 feeders, so the work can

be extensive.

Incoming fabric to the cutting room store would be

examined for bars due to course length variations,

and measure for loop density. Weight per square

meter would also be taken, to alert Quality Control to

possible aberrations.

With circular machines the relationship of a particular feeder

to the course it produces in the fabric is simple and

consecutive.

With flat machines the situation can be more complex. With

knitting taking place from left to right and then right to left, a

different set of cams on the machine produce the knitting left

to right, than produce it right to left. On simple flat machines

with one cam box, alternate course will be knitted in right or

left direction. In this case if feed tension differs in each

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direction the course length variations is expected to alternate.

On more complex knitting machines with two or more knitting

systems (cams) traversing, the situation is more complex. On

a two system V-bed flat machine there are four different

groups of cams producing knitted courses A, B, C, D. if thecam carriage is moving from right to left, the two trailing

systems B, D are knitting, with B knitting the first course

followed by D. When the carriage is moving from left to right

A and C are knitting, with C knitting before A.

It is essential to know this aspect of knitting in order to set up

the machine or locating a faulty course length distortion.

Fabric cover

Fabric cover is a simple ratio of the area of knitted fabric

covered by yarn to the area covered by the gaps in between

loops. Obviously, the cover of the fabric would depend upon

two things;

1. Loop density2. Yarn diameter (or count)

A fabric knitted with higher loop density will have higher

cover; similarly, a yarn with higher diameter will knit a fabric

with higher cover. A fabric with higher cover is usually tightly

knit and that with a lower cover is loosely knit. A normal fabric

is one that is neither too tight nor too loose or floppy.

So, the cover factor of a knitted fabric is related with yarn

diameter (or count) and loop density or stitch length. There is

simple formula that can be used to express cover factor or

tightness factor.

_________

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Cover factor (cf) = Count in tex/L

Where L is the loop length in centimeters.

Usually in knitted fabrics, for fabrics of a similar construction,

in order to maintain same cover, a higher loop length would

require higher size of yarn (coarser count).

Fabric weight per unit area

Weight per unit area of fabric is an important property that is

again related to another properties of the fabric, i.e., loop

density and yarn size. Thus the weight of the fabric isdetermined by two factors that interact: the loop size and the

yarn size. The effect of the loop size is simple to express: if

the size of the yarn remains constant, then increase a loop

size produces a fabric with lower loop density and produces a

decrease of weight per unit area.

So by doubling the loop size, the yarn per square area of the

fabric becomes half, and so the weight per unit area will also

become half.

The calculations for weight/m2 is as under

Specifications for knitted fabrics usually include quantities for

loop density, width of the fabric and weight per m. The

weight of the knitted fabrics is referred to as grams per

square meters (GSM). Construction details of some of the

important circular knitted fabrics are given below.

S.

No

Type of

Fabric

M/C

Gauge

M/C

Dia

No of

Needles

Count

(Ne)

GSM

Min :

GSM

Max:

1 Single Jersey 24 30" 2256 20s/1 135 170

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2 Single Jersey 28 30" 2640 30s/1 110 145

3 Single Jersey 28 30" 2640 40s/1 85 110

4 Inter Lock 24 30" 4512 30s/1 215 270

5 Inter Lock 24 30" 4512 32s/1 195 210

6 Inter Lock 24 30" 4512 36s/1 180 195

7 Inter Lock 24 30" 4512 40s/1 155 190

8 Rib (1x 1) 18 30" 3360 30s/1 155 165

9 Rib (1x 1) 18 30" 3360 40s/1 110 125

10 Rib (2 x 2) 18 30" 2240 30s/1 155 165

11 Rib (2 x 2) 18 30" 2240 40s/1 115 130

Fabric width

Fabric width of knitted fabrics is an important property. In

order to avoid fabric wastage, the garment patterns should fit

in the fabric width in such a way so that very little wastage is

produced while cutting pieces. But if the fabric width is

different than specified, it may produce high wastage.

The fabric width of tubular fabrics or flat knitted fabrics may

become different (usually lesser) than on the machine.

Knitted fabric may change dimensions with time, handling

and with subsequent wet treatments including steaming, and

such changes can even occur after the garment has been

produced and sold to the public. This phenomenon occurs

due to relaxation of the fabric from the knitting tensions.

Some fabrics come in the pre-shrunk condition, if a bettertechnology for finishing the fabrics has been used; however,

there will still be some shrinkage due to relaxation.

The concept of the relaxed state for knitted fabrics is well

recognized and determined. Quality control must ensure that

before knitted garments are cut, the fabric is in a relaxed or

near relaxed condition, i.e., that there will be little shrinkage

of fabric/garment when it is in the consumers possession.

Relaxation tests can be carried out on fabric as a routine

procedure, or as spot checks. Most test procedures involve

agitation of a square cut piece of fabric in water solution

followed spinning and tumble-drying. The change in the

dimensions before and after wash treatment will tell us about

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the extent of shrinkage which the garment may suffer under

actual wash condition during usage. This test will also tell us

the changes in the length and width the fabric will undergo

while washing. This much allowance in the dimensions of the

garment should be kept in mind while cutting the pieces.

Fabric Shrinkage

There are two types of shrinkages present in knitted fabrics;

(1) Relaxation shrinkage

(2) Washing shrinkage

We have talked about these shrinkages above under the headof fabric width. Relaxation shrinkage occurs with the passage

of time. The fabric becomes relaxed free from knitting

tensions and so shrinks.

Washing shrinkage occurs due to two factors, 1) due to

release of any residual tension in the yarns with which the

fabric is made of and the fabric itself, 2) due to inherent nature

of the fibres of the fabric.

Wool knitted fabrics with shrink-resist treatment pose little

problem of shrinkage and deformation. Steaming of knitted

garments blanks or garments on an open steam bed release

the majority of stress in wool fabrics.

Acrylic fabrics made from bulked yarns present few problems

in dimensional stability. Steaming of knitted garments blanks

or garments on an open steam bed release the majority of

stress in wool fabrics.

But, cotton knitted fabrics presents the greatest problems in

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fabric shrinkage or deformation on account of both of the

factors mentioned above. These fabrics may shrink up to 20%

or more. Therefore, cotton knitted fabrics should be

preshrunk and compacted before cutting and garment

making. In view of this the technology for finishing cotton

knitted fabrics is more elaborate, sophisticated and costly.

The finishing technology of cotton fabrics include following

steps and machinery;

1. Dyeing and bleaching in soft-flow dyeing machines: These

machines generate less of the tension on the fabrics.

2. Hydro-extraction: This is done on a continuous hydro-extracting

machine, which also spreads the width of the fabric while water is

being extracted from the fabric.

3. Relax dryer: These machines dry the fabrics in a fully relaxed

state, so the fabric assume its relaxed width.

4. Compacting calendar: This machine compact the fabric

mechanically and calendars (press) to impart a good finish to the

cotton fabrics.

Fabrics treated with this technology has very less shrinkage,

but still at least 2% to 5% potential shrinkage is still left, which

is difficult to remove.

A knitwear designer should know all terms and phenomenon

of knitted fabrics so that a proper fabric may be designed for

making garments. It is not the duty of the knitwear designer to

set the machines or to select the treatment, which the knitting

masters should do, however, it is essential that the designers

should guide the knitting masters as to what sort of fabric is

required by them.

Knitted faults

Some faults appear in the knitted fabrics and garments. These

faults may be due to knitting itself or due to the yarns used.

These faults have been tabulated below.

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KNITTING FAULTS

Spun-in Coloured Fibres

Foreign Matters

Long Thick Places

YARN

FAULTS

Hole Spun-in

Coloured

FibresStains/Contamination Foreign

Matters

Fly Short Thick

places

Missed Stitch Long Thick

Places

Tear off Thin Ring

Double stitch Long Thin

Places

Needle break Thick ring

Transfer Stitch Short thin

places

Rings (mixed yarns) Knot/Splice

Dropped Stitch UnevennessLoop distortions Periodic

Variations

These faults, if appear in the garments will downgrade the

garment value.

The knitted fabric or garment portions at the start of garment

making process may exhibit the following observable faults;

1. Variable loop length/course construction, showing horizontal

barring;

2. Horizontal barring from a number of yarn characteristics;

3. Vertical faults that are machine determined;

4. Stains due to oiling or lint contaminating fabric

Other than above a knitted fabric may have wrong

specifications of the fabric.

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The wrong construction, with loop length, width and

weight per square meter variations from the

specifications;

All these observable faults are the subject of inspection

procedures at the start of the garment construction process.

Some faults are not necessarily observable at the start. Such

faults relate to fabric shrinkage after being made into

garments. The potential for shrinkage can only be detected by

testing.

Some of these faults are discussed below.

Yarn Faults

Two types of faults are seen in the knitted fabrics.

Horizontal faults

Vertical faults

Most faults that result in horizontal bars (thick sections

distinguishable from the body of the fabric) are mainly due to

yarn used. These faults occur due to;

Difference in the counts of the yarn used: Supposing in a cone

few meter of the yarn is thicker or thinner than the remaining yarn.

The thick or thin portion when knitted along with normal yarn

sections will show as a horizontal bar.

Different dyeing shades in yarns used: Supposing in a cone few

meter of the dyed yarn has different yarn shade than the

remaining yarn. The dark or lighter portion of yarns when knitted

along with normal shade of the yarn sections will show as a

horizontal bar.

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Different spinning batch/source of yarns: A fabric produced from

cones having yarns of different batches produced in the spinning

mills, when dyed may show horizontal bars. Since different

batches of yarn may differ in cotton type and mixing and pick-up

different dye content during dyeing process.

Different bulking heat treatment given to acrylic yarns: The

bulking treatment (steam heating in a chamber) given to high bulk

acrylic yarns (2/32s acrylic yarn types) may pick-up different heat

due non-uniform steam spread in the chamber. The yarns with

lesser bulking may pick-up different dye contents and when

knitted may show-up as bars.

All these faults characterize themselves as bars across the

fabric, of density, colour or luster, and must be detected in the

fabric before is cut into the garment, otherwise these faults

will spoil the appearance of the garments.

Vertical faults usually result from knitting process but can

occur with finishing. A common vertical fault is needle line.

Faulty needles result in vertical lines of occasional or

frequent tuck stitches. Such faults in garment blanks or fully-

fashioned panels render them unusable.

Stains

The knitting industry uses oils to lubricate machinery in the

immediate vicinity of where the fabric is being produced, i.e.,

on the needles themselves. Such oils mixed with

atmospheric dust and metallic powder can, in certain

circumstances, cause stains on the fabric or garments being

knitted. Two procedures are used to minimize this:

1. Control of oil itself, by applying in minimum quantities and

delivering it quickly, so that it is present in fabric but does not

show up in any build up of soiled material that would result from

spasmodic application;

2. Using oils that are readily mixed with water, so called scour able

or clean oils.

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The majority of knitted piece goods are wet finished before

cutting and there is little likelihood that oil staining will remain

in finished fabric. On stitched shaped garments it can present

major problems if tight control is not exercised in the knitting

room. As these garments are not generally wet finished,

stains are usually dealt with during examination by solventbased spotting guns. The problem is negligible in fully-

fashioned industry where oil is not used on the needles and

where wet finishing is usual.

Stains due to oil on knitted fabrics show as dirty areas, or

horizontal markings, associated with a course or group of

courses, or vertical lines following one or more wales and

fading away with distance.

Other stain characteristics of knitted fabrics occur when

accumulated lint (fibre dust0 falls into knitting zones and gets

incorporated into the fabric. Some circular machines are

equipped with vacuum or blower devices to clear the

immediate vicinity of the knitting zones. Such devices are not

usual on flat machines and good housekeeping during theknitting process is essential.

Cleaning down is particularly important where the knitting of

light coloured fabric and garments occurs after the knitting of

darker coloured fabrics. Similar problems occur if coloured

fabrics/garments pieces are knitted in the same location as

white or pastel coloured ones.

Some faults in knitted fabric and garments are only detected

when the garment is in use. One such fault, common to all

textiles, is fading of colour. The other problem that occurs

infrequently is pilling.

Pilling

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Pilling is the formation on the surface of knitted fabrics of

small balls of abraded fibre. It is connected with several

factors:

1. The type and size of fibre mixture used in the component yarn;

2. The construction of yarn in terms of twist factor;

3. The type and tightness of knitted construction;

4. The nature of the surface against which the knitted fabric has

abraded.

Wool pills are considered weak and indeed sometimes drop

off spontaneously. Pills produced in fabric containing

polyamide or polyester fibres are considered strong and

persist, making garments on which they occur unsightly un-

wearable, even though not worn out.

Testing procedure involves tumbling samples in pill drums or

pillboxes where they are abraded against both standard

surfaces and against selected fabrics.

Pilling, which is particularly deleterious phenomenon in

knitted garments, has also been discussed, with indications of

the factors involved in its formation but no magic, one-off

solution.

Knitted fabric standards

The standard for basic fabrics (including but not

limited to finished single knit, rib, terry, double knit

and interlock fabric) is determined as under.

1.7.1 Four-Point System

Penalty points are assessed to a piece of fabric

according to the length of 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 the fabric

only:

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LENGTH OF DEFECTS NUMBER OF PENALTY

POINTS

3 inches of less 1

Over 3 but not over 6 inches 2

Over 6 inches but not over 9 inches 3

Over 9 inches 4

a. Four penalty points per linear yard are the maximum

assessable for fabrics up to 60/62 inches in width.

b. For fabrics over 60/62 inches in width, maximum penalty

points are to be increased in proportion as the width

exceeds 60 inches.

c. Regardless of the length of the fabric, the quality shall be

expressed in the number of penalty points per 100-yard

length. (Example: a 20-yard piece with 3 penalty points is to

be rated as 15 points per 100 yards.)

This method of evaluating quality relates only to:

a. Knitting defects

b. Grease oil spots

c. Dye spots

d. Stains

e. Slubs except where they are an inherent part of the

yarn

f. Bars

Fabrics are to be examined for these defects on the face side.

Other than these a fabric may be rejected or downgraded if it

does not meet specifications of the user.

Basic fabrics shall be classified as first quality if the number

of penalty points does not exceed 40 points per 100 linear

yards. However the maximum number of defects may not

exceed 30 per 100 yards.

1.8 Knitted Garment Quality

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Defects in knitted fabrics were discussed in the previous

chapter. Faults incurred during the knitting and fabric-finishing

processes pass on to the knitted garment itself unless

detected and removed during fabric inspection. During the

progress of garment assembly of fully cut pieces or knitted

pieces additional faults can be accumulated. These faults may

occur during cutting, seaming or garment finishing. The

number of possible faults increases with the number of

processes that a garment passes through. It follows,

therefore, that fully cut garments have the greatest fault

potential and some fully-fashioned garments the least, with

stitched shaped cut falling in between.

For example a knitted sock cannot contain dimensional faults

arising from cutting, nor multiple seaming problems becauseit is neither cut nor much of the seamed. All the faults in a

sock can be classified as knitting or yarn faults or

dyeing/finishing faults. In contrast, a fully-fashioned garment

may have a dimensional abnormality, knitting defects due to

yarn faults, and fully cut garments may have dimensional

faults, seaming defects, yarn & knitted faults along with

finishing defects.

So a comprehensive quality control procedure is required to

check faults at all stages, to avoid cumulative faults.

Since fully cut garments pass through all the stages of

garment manufacturing, so quality control procedures

applicable to this process will cover most of the peculiarities

of knitted garments.

Yarn quality assessment

In a knitted fabric & garment integrated company fabrics for

fully cut garments are mostly produced within the company

itself and the company procures yarns from some spinning

unit. Therefore it essential to periodically check the quality of

the in coming yarns. Where deliveries of yarn are from

various spinners, more intensive sampling and testing is

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required.

Normally spinners send a quality check report with each

delivery of the lot, however, if not received it may be

demanded from the spinner. Many knitting and garment

manufacturing factories do have equipment to check qualityof the yarn and they rely on the quality reports of the

spinners.

A company consuming large amount of knitting yarn for

circular machines should possess some basic testing

equipment to check the quality of the yarns. Specification of

incoming raw materials is one of the most neglected areas of

knitting. The company should also have its standards of yarn

quality specifications. Testing of yarns implies that

specifications have been established against which to test.

Some basic but important factors to specify in knitting yarns

are;

Yarn Count;

Count variability

Yarn Evenness;

Single & doubling twist;

Twist variability

Yarn strength;

Other than above, some yarn characteristics associated with

the fibres types are important, such as fibre diameter in wool,

the extent of presence of trash and seed contamination in

cotton, the residual bulking in acrylic yarn, and crimp rigidity

in textured polyester and polyamide yarns.

Some or all of the tests may be carried out routinely, while

others may be only performed on suspect lots. The objective

of maintaining yarn standards is to produce fabric that meets

the specification laid down. As narrated in earlier chapter, all

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aberrations in yarn specifications produce measurable or

visible faults within the fabric.

A knitwear designer should understand these factors in

knitting yarns and its effect on fabrics quality. It is not the

duty of the designer to check the yarn or fabric quality, butthey can advise and suggest to the quality control department

to check certain yarn quality specifications.

Fabric quality assessment

Knitted fabric is usually examined at two stages:

After knitting and

After finishing.

But the quality control procedures start before and

during knitting;

Before knitting, the machine is correctly set

for stitch length and feed tension to

produce a particular quality, and

During knitting to check that quality is

being maintained and fabric damages are

not occurring due to needle or yarn

breakages.

Thus a knitting operator also acts as quality controller to

prevent the knitting machine producing faulty fabric. The

rough examination after knitting is to ensure that the fabric is

not being produced with visible faults that by feedback can be

rectified on a particular knitting machine. At this stage, some

rough mending may be carried out to rectify minor faults to

prepare the fabric for the dyeing and finishing process.

After finishing, the fabric is examined over an examination

table, faults are identified and their location marked so that

they can be dealt with during spreading or after cutting. In

order to locate defects at the spreading and cutting table, it is

usual practice to mark at the selvedge with coloured tag or

put a sticker.

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Fault counts can be maintained to assess improving or

deteriorating standards. Visual fault location cannot be 100%,

neither can an operative act other than subjectively, and

checks on the examiners also need to be carried out.

In-process quality control

Quality control during spreading

The operatives who prepare the fabric-lay are also

responsible for quality control of the operation, whether they

are spreading by hand or machine. During fabric spreading

care need to be taken to avoid stretching or distortion, in

particular that of knitted fabrics, which are more prone to

stretching. Faults marked in earlier examination must be

located and decision made about them as regards eliminatingthem from the lay.

Alignment of features and patterns of the fabrics must be

maintained where necessary. Also of great importance is

ensuring that the number of layers in the entire lay, and the

sub-numbers of particular colours or patterns, are correct.

Again, procedures must be established to check that this is

happening.

The accuracy of the marker and its positioning on the lay, or

the marking of the pattern pieces on the top layer, must be

the subject of close quality control. Dimensional problems

can be induced at this stage, as can misalignments of

garment portions or misalignment of patterns within or on the

fabric. Another common mistake at this stage is to forgetmarking one or more pieces of the garments, say pockets or

plackets, which can cause problem of mismatch if cut from

different lay.

It is also important to identify and label on the marker the

relevant sizes of the garment portions, so that after cutting

they are assembled in the correct bundles.

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Quality control during cutting

When cutting by hand with straight knives care should be

taken not to deform knitted fabric, particularly within the

depths of the lay. While the cutter is apparently following the

surface marker, the lower layers, which are not properly

aligned or deformed, are not necessarily being cut accurately.

Some fabrics are particularly difficult to cut, e.g. 1 x1 rib, and

the problem increases with depth of the lay. To cut these

fabrics lot of skill is required on the part of the cutter. Other

faults of bad cutting are the failure to accurately follow lines of

the marker, and the cutting off of corners.

Auto spreading and cutting pose less of a problem but it must

not be assumed that they are infallible. Constant checking by

sampling must be carried out to ensure good standards.

Measures must be taken to ensure that the bundles

assembled after cutting contains the correct number of pieces

and that faulty pieces have been identified and removed. In

one cut operations and bundle making all the pieces must befor the same size garment.

Quality control during sewing

Knitted garments, which are assembled by overlocking, pose

problem. The over locking machinery actually cuts off the

edge of the fabric to ensure a fixed dimension of bite.

Patterns for knitted garments often contain an allowance for

cutting by the overlock knife, which varies from 3mm to 6mm

bite. If care is not taken a careless overlocker can readily cut

20mm off a particular edge, altering the dimensions of the

garment considerably.

Other problems arise from the difficulties of controlling

alignment of two components (say, back & front panel) during

overlocking. Because knitted fabrics stretch it is easy for one

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of the components to stretch during seaming. Subsequent

attempts at correction within the length of the seam make

matters worse and the garment shows obvious distortions.

Even slight misalignments at cuff and waistband ribs can be

visually unacceptable.

The most difficult task for overlockers, cup seamers and flat

seamers alike, is maintaining alignment of stripes or patterns

on side seams. It is usual to select the most skilled operatives

and to pay premium rates. Stripes and patterns are more

usual on cut stitch shaped knitwear and overlockers in the

knitwear industry gradually gain the skills necessary to deal

with them.

The other common problem with overlocker seams in

particular is distortion by general stretching during seaming.

This shows as bowing or seam rippling. However, some or all

of this is recoverable during finished steaming.

The above factors that affect quality, and need to be subject

to control, relate to the operative and his/her skills ofassembly. Such factors are best dealt with thorough training,

rather than through checking. The best quality control

processes are built into the production system. Make well

and there is little need to check.

Other seaming factors relate to machine settings. Some

customers specify stitches per centimeter or inch and this

must be measured. The machine builders graded marks

(stitches/unit) indicated on the machines are only

approximations, not very accurate quantities. Where

customers do not set the standard the manufacturer must set

the standards appropriate to his particular quality perception.

Seam balance is important in seams using more than one

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thread. For knitted garment seams this in particular means

overlock seams and multithread chain stitches. It is strongly

advocated that thread run in is used as an assessment of

balance, rather than mere visual appearance. The single and

double chain stitch in particular, incorporated in the collar

seams; bear the load when the seam is stretched. Optimum

values for thread run-in must be established and maintained

to avoid customer complaints of seam failure.

Final Inspection

All knitted garment manufacturers have final inspection

procedures to ensure that the quality they promise to

customers is maintained. Analysis of the records of final

inspections should also provide suggestions to the

production section for action to improve quality. Examination

results in garments being categorized into firsts, seconds andrejects.

Firsts pass, are sent straight away for packing. Seconds may

be mended or the fault repaired in some other way, such as

stain removal, loose threads tidying, stitch mending etc.

Having corrections done, they move after re-examination into

first category if corrections are satisfactory. Likewise a major

rejection fault may be overcome to move the garment into

second category.

Very few companies allow absolute rejects to occur in their

production process, and such events are usually associated

with an unrecognized problem with the raw material, such as

excessive pilling, dye fading, dye bleeding etc. Some faults,

although measurable, are actually assessed visually.Examples include colour matching, colour variation between

components, dimensional distortions and misalignments.

Other faults more obviously fall into the subjective category

and pose difficulties in definition of their severity. Holes of all

sizes usually result in rejection and may be subjected to

mending that brings them into a second category. More

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difficult to categorise are flaws due to thick and thin localized

irregularities in yarn that may occur in an unobvious place in

the garment. Tidiness of make up is also judged at this stage,

with loose sewing threads, fragments of threads and trailing

overlock chains all tending to lower the perceived quality of

the garment.

Such subjective judgments are not normally written into a

garment specification but are covered by the premise that if

the garment was passed and sold the customer would return

it. This leads to another concept, of different qualities for

different customers. Manufacturers of knitted garments gain a

feel for what a particular customer/market will tolerate, and

adjust accordingly.

Dimensional & design Considerations

Measuring the dimensions of knitted garments poses

particular problems. These have already been aired earlier in

this chapter. The act of measuring itself is difficult. Handling

and placing a knitted garment on a flat surface can induce

stretch of up to 5%.

The edges of knitted garments can be indeterminate and of a

rounded fold rather than a precise, crisp edge. Tolerances of

width measurement need to be generous and related to more

absolute quantities such as a total number of wales.

Widths of waistbands, cuffs, collars and facings of knitwear

are commonly expressed in terms of the number of ribs, but

only on the coarsest gauges can the ribs be counted easilyduring production.

Weight

Weight of a garment can be used as a quality control measure

to assess overall variability. It is particularly useful in the

fully-fashioned industry. Used in conjunction with control

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chart it enables a selection to be made of garments that fall

outside control limits, for further examination.

Weight control charts also highlight trends towards higher or

lower limits that occur in production processes.

Weight is also useful during production to assess the

variability of cutting process and of garments length or piece

knitting. In such usage the two interacting factors of yarn size

and loop length are being assessed as well as the state of

relaxation.

Design Factors

In any market dealing with clothing, visual design itself is

considered a quality. It must be recognized that hitting the

right design for the market often overrides considerations by

the ultimate customer of such factors as durability, fitness for

purpose, neatness of make up and other utilitarian factors.

Good design must be considered a very important tool in the

armoury of quality assurance.

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