KNITTING

Knitted fabrics may be described as structures produced by the interlooping of yarns.

In actual fabric construction, loops are formed and then new loops are drawn through those previously formed.

The continuing addition of new loops creates the knitted fabric. A knitted loop is usually referred to as stitch when it is pulled

through another loop. Stitches are produced with knitting needles.

Movement, mobility & elasticity:

knitted fabrics tend to mold & fit easily to body shapes & to move easily with body movement.

Woven fabrics are usually rigid; do not mould to body shape & tend to resist body movement.

Recovery from wrinkling: knitted fabrics recover from wrinkling

more readily than woven fabrics and takes less crease than wovens.

Insulation & warmth: bulky knit fabrics provide excellent insulation in still air but because of the open structure of knitted fabric they provide poor insulation in wind.

Tightly woven fabrics provide high degree of wind resistance. Thus sweaters are good clothing insulators indoors, but when worn outdoors in wind conditions they need to be covered by a tightly woven wind resistant jacket.

Knit fabrics tend to stretch out of shape and/or snag on sharp articles more than woven fabrics.

Vertical columns of stitches in knitted fabric are called wales. Number of wales per unit width of fabric depends on density of

needles or needles per inch. Horizontal rows of stitches are called Courses. Number of courses per unit length of fabric is dependent on the

height of the stitch loop. Wales & Course per inch contribute to the fabric weight, hand,

insulation, shape retention, drapability & cost.

Two main categories: Circular knit & Flat knit Circular Knitting machines – knitting needles are in circular

configuration and the fabric produced is tubular in form. The diameter of the machine varies from 2.5”– over 30” depending on what product the machine was designed to produce.

Circular knits can be cut open along entire length and become in effect flat fabrics.

Flat knitting Machines – knitting needles in straight configuration thus producing open width fabric

Range from 12” – over 200” depending on end use. It produces fabric slowly than circular knitting but produces fabric

that circular machine cannot.

Examples include shaped articles such as complex patterns, shaped articles etc

Three main types of needles used in industrial knitting – latch needles, spring beard needles and compound needles.

Weft knitting – latch needle mostly

Warp knitting – other two

Compound needle enables higher rate

of production. Needles are usually oriented horizontal,

vertical or at 45º in the machine.

Needles are held in position by needle beds pieces of metal into which slots or grooves have been cut.

The number of slots is called the cut of the machine.

The term cut is used regarding weft knits only.

It is used as an expression of fineness & coarseness of stitches in knitted materials.

6 cut fabric – heavy fabric; 28 cut fabric – T shirt.

Used in both weft & warp knitted fabrics.

It refers to the needles per measured length in the knitting machine.

Gauge reflects the fineness & coarseness of knitted cloth.

Higher the gauge number finer the fabric.

1-3: needle rises & as it does the previous

loop opens the latch & slides down onto the

needle shank.

4- As the needle descends a new yarn is fed

onto the needle hook. As the needle continues

to descend, the previous loop slides onto it &

causes the latch to close.

5 – needle continues downward & the old loop

slides off needle completely. It becomes

interlooped with new loop which has been

formed in the needle hook, thus creating the

knitted fabric structure.

Stitches in weft & warp knits

Four principal stitches utilized in knit fabrics – knit, purl, miss & tuck.

These 4 stitches or combinations of them appearing in the same fabric form the basis of all knitting fabrics.

Knit stitch Purl Stitch Miss stitch Tuck stitch

Basic knitting stitch Also called plain stitch. This stitch is also the basis of the fabric called jersey. Purl stitch is the reverse of the knit stitch & in fact is sometimes

called the reverse knit stitch.

Also called float stitch

Created when 1 or more knitting needles are deactivated & do not move into position to accept a yarn.

Yarn merely passes by & no stitch is formed.

Can be recognized by the floating unknit yarn

on the back of the fabric.

Reduce fabric weight, stretch & width.

Formed when knitting needle holds its old loop & then receives a new yarn.

Two loops then collect in the needle hook.

Action may be repeated several more

times but the yarns eventually have to be

cast off the needle & knitted.

Resultant stitch is elongated. Tuck stitches appear on the back of a fabric & may be recognized as an

inverted V, sometimes elongated for 2 or more courses depending on how many times the stitch was tucked.

Tuck stitch is used in knitted fabrics to create design effects in color, raised surface texture, or hole or eyelet effect.

Increase fabric weight, width & thickness.

Two main classifications of knitted fabrics – weft knits & warp knits

Weft knits – yarn traverses from side to side, interacting with needles to form new fabric stitches.

Warp knits – set of yarns traverses lengthwise, interacting with the needles to form new fabric stitches.

Weft knits account for at least 75% of knitted fabrics.

Basic types of fabrics in weft knitting are

Jersey knit Rib knit Purl knit

All loops drawn to one side of the fabric ie all knit stitches

Most easily recognized by the fact that the face is smooth & back has a textured & mottled appearance.

Have one set of needles in one needle bed.

Fabric is unbalanced & have the tendency

to curl at the edges.

Stretch approximately equally in both the length & width.

Fabrics are produced on flat as well as circular machines.

Shortcoming – one yarn breaks, it causes unraveling of adjoining stitches in the wale called RUN.

Lightweight filament yarn jersey are especially susceptible to runs due partially to the very smooth surface of filament yarn.

Made with alternate wales of knit stitches & purl stitches on both sides of the fabric.

Each wale in a rib knit contains either

all knit stitches or all purl stitches.

Requires 2 sets of needles usually positioned

at right angles to each other. Slow production than jersey knitting machines. Rib knits are produced on flat as well as circular machines.

Contd…

Have a very distinct lengthwise rib effect on both sides of the fabric.

2X2 rib – 2 wales of knit stitches & 2 wales of purl stitches.

Lie flat & do not curl at the edges.

Have greater elasticity in their width than length.

Used for sweater waistbands, knit cuffs, hats etc.

Made with alternate courses of knit stitches & purl stitches on both sides of the fabric.

Each wale contains both knit stitches

& purl stitches.

Purl fabric looks somewhat like the back

of jersey knit on both sides of the fabric.

To identify it is necessary to stretch the

fabric in its length direction.

Produced on flat or circular machines.

Rather than 2 set of needles one set of double headed latch needles is used.

Double headed needles move from one needle bed to other, from side to side of fabric.

Tend to lie flat & do not curl

Thicker & thus better insulators than jersey of same WPI & CPI

Widely used in sweater industry. Purl knitting machine is versatile Lowest rate of production of all knitting machine. Cost of fabric is highest for purl knit fabrics.

Jersey fabrics Rib fabrics Purl fabrics

Knit stitches on face; purl stitches on back.

Wales predominate on face & back

Courses predominate on face & back

Definite face & back May be reversible May be reversible

Stretches approximately equally in both length & width

Greater stretch in width

Greater stretch in length

Highest machine productivity

Next highest productivity

Lowest machine productivity

Uses- hosiery, T shirts, sweaters, knit terry robes, knit velour jogging suits, full fashion garments

Uses-collars, cuffs, socks, double knit jackets, interlock

dresses

Uses-infants wear, fancy sweaters, fancy

garment parts.

Effect of WPI & CPI on knitted fabric propertie Fabric with more WPI is more stable in width direction.

Fabric with more CPI is more stable in length direction.

More WPI & CPI better ability to recover from stretching.

Lesser WPI & CPI molds to body shapes easily.

More WPI & CPI tends to shrink less in width & length direction.

SPECIALISED KNIT FABRICS

Variation of rib knit fabrics columns of wales are directly each other.

Back of any knit stitch on the interlock

fabric reveals another knit stitch directly

behind it.

Fabric is more smooth, more stable,

better insulative & more expensive.

Interlock fabrics are popular for blouses, dresses & T-shirts because of their dimensional stability & their tendency not to easily stretch out of shape.

Also known as sliver knits.

Type of jersey knit fabric made by unique procedure that involves feeding staple fiber in the form of sliver into the knit material while the yarns being knitted.

The fibers are caught in the knit structure &

is thus held within & between the plain stitches.

Can be given variety of finishing treatments to

produce animal fur imitations.

Knitted terry fabrics are jersey knit materials that are knitted with 2 yarns feeding simultaneously into same knitting needles – Plating.

One of the yarn is called loop yarn & other ground fabric yarn. Loop yarns are pulled out by special devices & become the loop

pile of the knitted terry fabric. Terry fabrics are softer, more flexible, more absorbent than woven

terry fabrics. But do not hold shape & not durable. Used in bath robes, beach wear & similar applications.

Fabric manufacture are same as knitted terry. After the fabric is knitted, the loop pile is cut by process called

shearing & then it is brushed. Fabrics are soft, suede like texture resembling velveteen. But more soft & more flexible. Used for dresses, jogging suits etc.

Full fashioning is method of shaping a knitted fabric during knitting process.

Minimises fabric wastage. Generally done on flat bed full fashioned knitting machines

capable of producing the shaped garment by increasing or decreasing the number of wales at the shaped area.

Fabric is widened by increasing the number of needles in action & vice versa.

When narrowing occurs, FASHION MARK results from stitches being transferred to adjacent needles (distorted).

Popular in sweater where the shape & contour of the shoulder actually can be knitted to body contour shape.

Sleeves can be sewn later in separate operation to complete the sweater.

Mock fashioned marks are knit into conventional cut & sew garments.

made with tuck stitches. Can be distinguished with pick glass as the number of wales

varies in a full fashioned garment at the fashion mark. Generally full fashion garments are considered to be superior.

Warp Knitted Fabrics

Yarns run vertically in the length of the fabric.

Source of yarn is warp beam containing a very large number of parallel yarns.

Yarns form vertical loop in one course & then move diagonally to make a loop in the following course.

Yarns zigzag from side to side along the length of the fabric.

Each loop in a course is made by different yarn. Each warp yarn is knitted by one needle. Each yarn is threaded through a yarn guide. Movement of guide bar moves all the yarns. The movement & patterning of the guide bar are computer

controlled through CAD systems.

Identifying warp knits

By using pick glass.

Face of the fabric has clearly defined knit stitches generally running vertically( in the lengthwise direction), but slightly angled from side to side.

Back of the fabric has slightly angled horizontal floats called Underlaps formed from sideways movement of the warp yarns as the fabric is made.

Tricot fabrics

Represent the largest portion of yardage produced in warp knit category.

Flat machine made in various widths, some producing fabrics over 200 inches wide.

They are categorised as fine gauge machines ranging from 14 – 36 gauge (needles per inch).

Most popular 28 gauge for intimate apparel;22-23 for outerwear.

Commonly equipped with 2-4 guide bars.

Raschel Fabric

Same principle of knitting. Raschel machine uses latch or compound needles Range 4 – 50 yarn guide bars hence greater variation in the fabric. Produce fabrics ranging from fine lace like material to heavy

blankets, even carpets. Fabrics with interesting surface effects can be produced.

Distinguishing Tricot & Raschel fabrics Raschel – fabrics having heavy yarns, intricate designs,

complex “open spacing” & surface effect patterns

Tricot – fabrics with fine yarns, without designs or simple geometric designs.

Laid in yarn fabrics

Done in both warp & weft knit fabrics.

Some extra yarns are added to knit fabrics during the knitting process called laid in yarns.

They are not knitted but merely caught by stitches.

May be used to introduce novelty yarns or thicker yarns to increase cover, stability & warmth or

Knit elastic fabrics – stretch yarns may be added as extra laid in yarns.

Inlay yarns & Weft Insertion knits

When the extra yarns run lengthwise in a warp knit fabric & come from a separate warp beam they are called inlay yarns.

Fabrics made by inserting yarn crosswise into warp knit fabric – weft insertion knits.

Property Weft Knits Warp Knits

Stretch In length & width Limited Stretch

Run/Ravel May run / ravel Do not run or ravel easily

Machine changeover Rapid to new designs Slower & more costly to new designs

Production May be flat or circular Flat only. Produces yardage only.

Knitted fabric defects

Barre – Streaks or bands in the fabric caused by differences in yarn size, tension on yarns or fabric or color, luster, shrinkage from one section to adjacent area. The bands are horizontal & are found only in weft knitted fabrics.

Birdseye – Unintentional tucking caused by bent latch on the latch needle or by needle not being raised to the proper height for the old loop then to be cast off.

Boardy – Very harsh or stiff hand, caused by stitches being too tight or yarn being too large

Contd

Bowing – Design or line effect that curves across the fabric, a distortion caused by the take up mechanism of the knitting machine or through malfunctions in a machine.

Broken filaments – Filament yarn fabrics in which some filaments of the yarn have broken or split. The resultant fabric may have mottled or fuzzy appearance, depending on the amount of filament breakage.

Cockled fabric – Fabric does not lie flat caused by uneven stitches or uneven yarn size.

Contd

Drop Stitch – unknitted stitch caused by a stitch being loose or improper setting of yarn carrier.

Float – Unwanted miss stitch caused by needle not raised.

Needle line – Lengthwise marks or lines in the fabric resulting from wale that is tighter or looser than the other. May be needle being tight in the machine slot.

Press Off – Large hole in the fabric, caused by yarn breaking at particular feed so knitting cannot occur

Contd

Run or ladder – Series of dropped stitches in a wale.

Skewing – Design or line effect that is straight across in the fabric, but not perpendicular to the fabric edges.

Sleazy – flimsy or underconctructed knit fabric.

Stop mark – horizontal fabric streak resulting when the knitting machine is stopped. It is caused by tension difference in the yarns.