Textile Handbook The Hong Kong Cotton Spinners Association (2001) (2)-569-648

Chapter 4
KNITTING
AND
KNITTED
FABRICS
4-2
Knitting and Knitted Fabrics
CHAPTER 4.........
.........KNITTING AND KNITTED FABRICS
SECTION 1
KNITTING
1.1 Knitting Process
Knitting is a fabric manufacturing process in which yarn loops are
intermeshed to form a fabric. The conversion of yarn into loops can
be done either in a horizontal direction or in a vertical direction.
Therefore, two types of knitting trades have been developed,. The fabric
built up in horizontal direction is called weft-knitting, while the fabric
built up in vertical direction is called warp-knitting.
Knitting
Weft-Knitting
V-bed Machine,
Circular Machine
(Latch needle)
Warp-Knitting
Straight Bar
Machine,
Loop Wheel
Machine
(Beard needle)
Tricot Machine
(Beard/Compound
needle), Raschel
Machine (Latch/
Compound needle)
1.2 Weft-Knitting
This is a flat or circular knitting process that places one yarn at a time
to form loops running across the fabric. In a weft-knitted structure,
the intermeshed loops touch each other only in a few places, and the
fabric can be stretched along the width or the length under a low
stress.
Textile Handbook 4-3
Figure 1.2
Plain Knit Structure
1.3 Weft Knitting Machines
1.3.1 Two Types of Knitting Machines Using Beard
Needles
a) The straight bar type, in which the beard needles are arranged
in a straight line. An example of this type of machine is
the fully-fashioned straight bar machine. A fully-fashioned
straight bar machine is usually programmed to knit the
parts of a knitted garment in the shape required, that is
the front panel, back panel, sleeve, etc.
Figure 1.3.1 a Fully-Fashioned Straight Bar Machine (Monk Cotton
International Ltd)
Knitting and Knitted Fabrics
Machines for plain knitting can be generally divided into two groups
based on types of needles being used: the beard needle group of machines
and the latch needle group of machines.
4-4
Knitting and Knitted Fabrics
b) The circular bar type, in which the beard needles are arranged
in a circle on a cylinder. A typical example of this type of
machine is a loop wheel machine. On this machine, the
fabric is drawn vertically above the cylinder so that the
last course of loops is held in tension at the needle heads.
The loop wheel machine can be used for producing plain,
fleecy and terry fabrics. However, this machine is now
rarely used.
1.3.2 Two Types of Knitting Machines Using Latch
Needles
a) The flat bed type, in which the latch needles are arranged
in a straight line. A V-bed flat machine is a typical example
of this type. As its name implies, the V-bed machine has
two needle beds arranged in an inverted v-shape. This
machine can be hand-operated or controlled by computer.
The flat bed machine is widely used in the sweater industry.
Figure 1.3.2 a
Hand Flat Knitting Machine
b) The circular type, in which one set of latch needles is
arranged on the circumference of a vertical cylinder, and
another set of needles may be arranged perpendicular to
the first set and mounted on a horizontal dial. Typical
examples of this type of machine are the open top sinker
machine, and the cylinder and dial machine. Most of the
circular knitting machine are used for the piece-goods trade.
Textile Handbook 4-5
Figure 1.3.2b
Circular Knitting Machine (Mayer & Cie)
1.4.1 Knitting Needles
Knitting needles have been the heart of the weft-knitting process. There
are three main types of needles in industrial knitting; latch, spring
beard and compound.
Beard Needle: the beard needle is the oldest type. To open and close
the hook during loop production, the beard needle needs an auxiliary
attachment, a presser. The attachment restricts the production speed
and limits the use of this needle type in modern knitting machine.
Latch Needle: this is the most popular needle used in knitting. The
latch of the needle is pivoted and can swivel to open and close the
hook.
Compound Needle: this is commonly used in warp knitting and is
seldom found in weft-knitting. The hook of the compound needle is
opened and closed by a closing element sliding within a grove in the
main part of the needle.
Knitting and Knitted Fabrics
1.4 Key Components for Weft Knitted Fabric
Formation
4-6
Knitting and Knitted Fabrics
Figure 1.4.1 Knitting Needles
1.4.2 Needle Bed
The needle bed of a flat knitting machine is a metal plate in which
precisely measured slot (tricks) are milled. Needles are inserted in
these tricks and are forced to slide backwards and forwards to form
the knitting sequence. For a plain circular knitting machine, the needles
are housed vertically in the tricks of a cylinder. For a double jersey
knitting machine, there is another set of needles mounted on a dial,
which is perpendicular to the cylinder needles.
Figure 1.4.2 Needle Bed
Textile Handbook 4-7
1.4.3 Cam Box
To facilitate the knitting action of a flat bed machine, a carriage assembly
is moved back and forth along the needle bed. During the traverse of
the carriage, the needle butts are guided by the cam track to slide up
and down in the tricks. This carriage is connected to a cam system
which consists of several individual cams which form together the
cam track.
Figure 1.4.3
Cam Box of a V-bed Knitting Machine
On the flat bed machine, yarn coming off from cone(s) and through
the tensioning device is then threaded through a yarn carrier. The carrier
is set on a profiled rail, along which it can slide the length of the
needle bed to provide the descending knitting needles with yarn. On
a modern circular knitting machine, the yarn supply equipment consists
of a cone carrier device, a yarn guiding and monitoring device, a yarn
tensioner and a yarn metering and storage device.
Figure 1.4.4 (1)
Yarn Feeding of a V-bed Machine
Knitting and Knitted Fabrics
1.4.4 Yarn Feeding
4-8
Knitting and Knitted Fabrics
Figure 1.4.4 (2)
Yarn Feeding of a Circular Machine
2
1
1. Yarn package
2. Stop motion
3. Positive feed
4. Yarn break detector
5. Yarn feeder
3
4
5
1.4.5 Sinker
In the production of plain knitted fabric on a circular type singlejersey knitting machine or straight-bar type flat knitting machine, sinkers
are used to hold the fabric in position while the needle rises. This
means that the fabric is tighter and the appearance and knitting speed
can be improved. For Circular machine, the sinker is made of metal,
housed in the radial grooves of a sinker ring placed on the top part of
the needle cylinder. The movement of the sinkers is controlled by the
sinker cam segment which is fixed to a stationary sinker cam ring.
Figure 1.4.5 Sinker
(1) Throat, (2) Nib, (3) Platform
Textile Handbook 4-9
1.4.6 Key Terms of Knitted Fabric
a) Wales and Courses: Vertical columns of stitches in a knitted
fabric are called wales. Wales run lengthwise through the
entire fabric, and in that sense are similar to the warp in a
woven fabric.
Horizontal rows of stitches are called courses. Courses
run widthwise from side to side of the cloth, and in that
sense are similar to the weft in a woven fabric.
Figure 1.4.6a
Courses and Wales
1 inch
1 inch
Course
Wale
b) Cut and Gauge : These are the expressions of fineness
and coarseness of stitches in knitted materials. A five-cut
fabric has five wales per inch. In a weft knitting machine,
the number of slots per inch is called the cut of the machine.
The term “cut” is used in weft knits only.
Gauge is a term used in both weft and warp knitted fabrics.
In fully-fashioned straight-bar type knits, gauge refers to
the number of needles in 1.5 inches of the knitting machine.
In a circular knitting machine, this refers to the number of
needles in 1 inch. In warp knitted tricot, the term also
refers to 1 inch, but in warp-knitted raschel, the gauge is
the number of needles in 2 inches.
Knitting and Knitted Fabrics
The number of wales-per-unit width of fabric depends on
the closeness of the needles and their thickness. The number
of courses-per-unit length of fabric depends upon the distance
the needle pulls the yarn when the loop is made, or the
amount of yarn fed and wrapped around the needle.
4-10
Knitting and Knitted Fabrics
One should be careful of the fact that the terms “cut” and
“gauge” refer to measurements. The number of wales per
inch in a fabric may not exactly correspond to the cut or
gauge designation.
1.5 Stitch (loop) Formation Sequence on a Latch
Needle
One working cycle of a latch needle produces a single knitted loop.
The sequence of loop formation is illustrated in Figure 1.5.
Figure 1.5
Stitch Formation by Latch Needle
Yarn feeder
Previous loops
New yarn
Needle bed
1
2
3
4
5
Stitch formation sequence:
1,2 and 3
The needle rises and, as it does, the previous loop opens
the latch and slides down onto the needle shank.
4
As the needle begins to descend, a new yarn is fed
onto the needle hook. As the needle continues to descent,
the previous loop slides onto it and causes the latch to
close.
5
The needle continues downward and the old loop slides
off the needle compleltly (called the knock-over action).
In doing so, it becomes interlooped with a new loop
which has just been formed in the needle hook, thus
creating the knitted fabric structure.
Textile Handbook 4-11
1.6 Types of Knitting Stitches
There are three fundamental stitches utilised in knit fabrics. They are
plain stitch, miss-stitch and tuck stitch. These three stitches form the
basis of all knitted fabrics.
1.6.1 Plain Stitch
The plain stitch is the basic knitting stitch. It has two different faces
according to the relative positioning of the producing needle and the
fabric. When the fabric is viewed from the side where the loop exhibits
the arms of the curved formation, this is called a plain stitch. If the
loop, viewed on the same side of the fabric, exhibits the arc of the top
and the root of the structure, this loop is called a purl stitch.
A miss stitch is created when one or more knitting needles are deactivated
and do not move into position to accept a yarn. The yarn merely
passes by and no stitch is formed. The idled needle has retained its
loop longer than the rest of the needle. The miss stitch is used to
create colour and figure designs in knitted fabric.
1.6.3 Tuck Stitch
A tuck stitch is formed when a knitting needle holds its old loop and
then receives a new yarn, two loops will then be collected in the needle
hook. The action may be repeated several more times, but the yarns
eventually are cast off the needle and knitted. The different appearance
of the tuck stitch can be used for patterning, increasing fabric weight,
thickness and fabric width, etc.
Knitting and Knitted Fabrics
1.6.2 Miss Stitch (Welt or float)
4-12
Knitting and Knitted Fabrics
Figure 1.6
Formation of the three basic knitting stitches
Figure 1.6 shows the height of movement of needles to form the various
stitches. Needles 6 to 10 represents the completion of a cycle to form
a plain stitch. To produce a miss stitch, needles 11 to 14 should not
ascend the slope of the raising cam and should instead be unaffected
throughout the sequence. In order not to activate the needle, the raising
cam should be withdrawn from contact with the needle butt. For tuck
stitch, needles 1 to 5 should ascend the slope of the raising cam into
a tucking height but not all the way to the clearing position. To achieve
this, the raising cam is divided into two individually controlled parts,
of which the upper raising cam should be inactive.
1.7 Recent Developments in Weft Knitting
The focus of development is placed on expansion of processing methods
for new products, the effectiveness and flexibility related to quick
machine conversion for pattern and material changes.
In the area of expansion of processing methods for new products,
knitting machine makers are endeavouring to improve the processing
of spandex yarns on flat and circular machines. In additional, efforts
have been made to produce complete three-dimensional products directly
on knitting machine which opens up new possibility of “seamless”
fashioning applicable for elegant women’s clothing and technical textiles.
In terms of flexibility, some flat knitting machines are using multi-
Textile Handbook 4-13
gauge techniques to provide a wide spectrum for fashion design, while
the manufacturers of circular machine provides easy cam changeover
system and quick change of cylinder size or cylinder gauge without
the need to change cams.
1.7.1. Examples of Recent Developments in Flat Knitting
Machines
a) The Shima Seiki SWG-X Whole Garment Knitting
Machine
b) The Stoll CMS 330 TC4 Knit and Wear
This is another flat knitting machine to produce complete
garments. It can apply the Stoll-multi-gauge feature. This
feature allows a wide variety of gauge combinations to be
produced without gauge conversion or needle exchange.
The knitting system is controlled by step motor, so that
cam functions and stitch tensions are collectively controlled.
Flexible stitch can be freely programmable. Stitches of
differing tensions can be knitted in one and the same course
Figure 1.7.1.b
Step Motor for Knitting System Control (Stoll)
Knitting and Knitted Fabrics
The SWG-X is capable of producing shaped, fine gauge,
whole garment products. By using their slide needle and
pull down device which adjust take down tension
independently for front and back bodies, three-dimensional
shaping can be performed. Slide needle is a compound
needle with a divided slider for stitch transfer. Stitch transfer
operations necessary for fashioning is carried out with the
slide needle, transfer jack and holding down sinker holders.
The SWG-X is configured with 4 needle beds and an
additional loop presser bed.
4-14
Knitting and Knitted Fabrics
c) Shima Seiki SES 122 RT Rib Transfer Flat Knitting
Machine
This is a four needle bed knitting machine consists of two
additional beds to the conventional V-bed design. This
arrangement combines conventional transfer between the
lower front and back beds, and together with transfer with
and between the additional upper beds. This multiple transfer
capability enhances shaping and integral knitting through
the use of inside narrowing of rib stitches, tubular stitches,
Milano and Cardigan stitches.
Figure 1.7.1.c
Four Needle Bed Transfer System (Shima Seiki)
1.7.2 Examples of Recent Developments in Circular
Knitting machines
a) Piezo Individual Needle Selector
In this individual needle selection system, it consists of a
piezoceramic bending transducer module composed of two
ceramic plate stacked together. When one of the plates is
bent by the effect of current and voltage it makes the levers
in the selector move up or down to execute needle selection.
Textile Handbook 4-15
b) Quick Cam Change System
The introduction of the drop cam system by Terrot allows
the cams of either cylinder or dial to be changed from the
outside of the cam box which eliminates the time spent in
taking out the cam box block for changeover. There is
another system developed by Fukuhara called Rotary Drop
Cam system having similar objective. The Rotary Drop
Cam System required no yarn re-threading when changing
fabric construction. All cam changes are done externally
without the need to remove needles or cam section. It
allows more than one technician to work on the machine
simultaneously. These quick cam change systems bring
about simpler operation and more flexible in design changes.
The MCTmatic is a monitoring system for setting and
altering the yarn infeed and tensioning. It is able to set
motors for feed wheel, central stitch adjustment and fabric
takedown. All the above settings can be set by one
command.
Figure 1.7.2.c(1)
Setting of Motors for Feed Wheel (Mayer & Cie)
Knitting and Knitted Fabrics
c) Mayer & Cie MCTmatic Quality Monitoring System
4-16
Knitting and Knitted Fabrics
MCTmatic also makes a substantial contribution to quality
assurance. In the event of non-conformance within a userselected tolerance, the machine will be stopped and the
fault indicated in the display of the system.
Figure 1.7.2.c(2)
MCTmatic Display Panel
Textile Handbook 4-17
SECTION 2
TYPICAL WEFT-KNIT STRUCTURE
All common weft-knitted fabric structures are classified into three basic
groups according to the arrangement of loops in their courses and
wales. These basic structures are the plain (jersey), the rib and the
purl.
2.1 Methods Used to Represent Weft-Knitted
Structures
a) Loop Diagram: the actual loop of the fabric is drawn.
One can see the fabric structure clearly. This is suitable
for simple structure.
Figure 2.1.1a
Loop Diagram
b) Notation: special symbols are used to represent a particular
stitch. A cross is used to represent a plain stitch and a
circle represents a reverse plain stitch (back side of a plain
stitch). A blank space is used to represent a miss stitch
and a dot represents a tuck stitch. It is quite difficult to
use this methods to indicate an interlock fabric which is
knitted with two sets of needles lying directly opposite
each other.
Knitting and Knitted Fabrics
2.1.1 Three kinds of methods used to represent Weft
Knitted Structure
4-18
Knitting and Knitted Fabrics
Figure 2.1.1b
Notation
Plain stitch
Purl stitch
Tuck stitch
Float stitch
(Blank)
c) Yarn-path diagram: this is the best way to represent any
weft knitted structure. A straight line perpendicular to the
yarn path is used to represent a needle. For a single jersey,
one set of straight lines is used to represent one set of
needles. For double jersey structure, two sets of straight
lines are used to represent two sets of needles. A stitch is
represented by a loop drawn around the needle. A tuck
stitch is represented by the yarn touching the tip of the
needle and the miss stitch is represented by the yarn drawn
across the needle without touching it.
Figure 2.1.1c
Yarn Path Diagram
Knit stitch
Tuck stitch
Miss stitch
2.2 Single Knit Structures
2.2.1 Plain Knit.
Plain knit is also known as single knit or “Jersey” in the trade. This
is the simplest and most basic structure. Fabrics of this type have all
loops drawn to one side of the fabric (all plain stitches) and are easily
recognized by the fact that the smooth side is the face, while the back
has a textured and mottled appearance.
Plain knitted fabric is stretchable, and usually it can be stretched more
along the curling width than along the length. The fabric is unbalanced,
and has a tendency to curl at the edges because the loops are being
pulled in one direction. This condition can be corrected in fabric
finishing.
Textile Handbook 4-19
One disadvantage of jersey fabric is that if one yarn breaks, it causes
an unravelling of adjoining stitches, called a “run”.
A wide variety of knitted fabrics are made with jersey knit, ranging
from lightweight hosiery to thick, bulky sweaters.
Figure 2.2.1 Plain Knit Structure
This is a four courses repeat single knit structure, while knitting the
four courses, tuck stitches are included in every alternate course and
on alternate needles. It has a honeycomb appearance, will not ladder
easily. This structure is generally knitted on a fine gauge machine for
summer T-shirts.
Figure 2.2.2 Lacoste
Knitting and Knitted Fabrics
2.2.2 Lacoste
4-20
Knitting and Knitted Fabrics
2.3 Double Knit Structures
2.3.1 Rib
This structure is produced by the needles of both beds with alternate
wales of plain stitches and purl stitches on both sides of the fabric.
When all the needles in the machine participate in the knitting procedure,
a 1x1 rib is formed.
If two wales of plain stitches and two wales of purl stitches appear
alternately on both sides of the fabric, this is called a 2x2 rib. A 3x1
rib has three wales of plain stitches and one wale of purl stitches on
one side.
Rib-knit fabric, usually being symmetrical on both sides, is not subjected
to unbalanced stresses. It does not curl at the edges. Also, rib knits
have greater elasticity in their width than their length. Rib structures
are bulkier and heavier than plain structure provided the yarn used
and machine gauge are similar.
Rib structure cannot be unravelled from the edge knitted first, that is
from the bottom. Similar to plain structure, a dropped stitch can start
a chain reaction and produce a “ladder” in the structure.
Figure 2.3.1 Ribs
1x1 Rib
2x2 Rib
2.3.2 Half Milano
This is a rib based, two courses repeat structure. The first course is
1x1 rib, the second course knit on the front needle and welt (miss) on
the back needle. The fabric is harsher and tighter than ordinary rib,
and this method is mainly used for sweater production.
Textile Handbook 4-21
Figure 2.3.2 Half Milano
Face
Back
2.3.3 Full Milano
Figure 2.3.3 Full Milano
2.3.4 Full Cardigan
This is a rib based two courses repeat structure, the first course knit
knit on the front needle and tuck on rear needle. the second course is
the reverse of the first course. It has same appearance on both side,
but it is shorter and wider than ordinary rib structure. Because of the
large number of tuck stitches, full cardigan are very bulky. They are
used for heavy outerwear when knitted in coarse gauge. It also can
be used as T-shirt collar.
Knitting and Knitted Fabrics
This is a rib based, three courses repeat structure. The first course is
simply 1x1 rib. The second course is knitted on the back needle but
missed on the front needle. The third course is knitted on the front
needle but missed on the back needle. Full milano has the same
appearance on both faces of the fabric. As the structure contains miss
stitches, the widthwise stretchability of the fabric is tighter than 1x1
rib fabric.
4-22
Knitting and Knitted Fabrics
Figure 2.3.4 Full Cardigan
2.3.5 Half Cardigan
This structure is a special effect produced when one half of the cardigan
repeat is substituted for a regular 1x1 rib structure. One side of the
fabric looks like a “Cardigan” structure, while the loops of the other
side acquires a very rounded and attractive shape which is usually
used as the face side.
Figure 2.3.5 Half Cardigan
2.3.6 Purl Structure
Purl knits require the participation of both needle beds for the production
of the loops. In purl-knit fabrics, each wale contains both plain stitches
and purl stitches. Simple purl fabric looks the same on both sides of
the fabric, and they both appear somewhat like the back of jersey. A
purl-knit fabric, where one course has all plain stitches and the next
course has all purl stitches, and the cycle repeats on the third course,
is known as a 1x1 purl.
Textile Handbook 4-23
Originally, purl-knit production required special equipment using double
ended latch needles. The needle beds of this machine are set on the
same plane instead of being in an inverted “V” formation. It is called
a links/links machine, thus, the fabric produced is sometimes called
links/links fabric. Nowadays, purl structure can be produced on a
sophisticated “V” bed flat knitting machine with loop transfer mechanism.
Purl-knit fabrics tend to lie flat and do not curl as jersey knits do.
Basic purl knit structures, such as 1x1 or 2x1, contract in the length
direction. They have greater elasticity in the length direction. It is
probably this property that makes purl knits so widely used in infant’s
and children’s wear. Also purl knits are thicker and thus better insulators
than jersey knits of the same yarns and densities.
Sinker
Needle bed
Figure 2.3.6(2)
Purl Knitted Structure
1x1 Purl
Fancy Purl
Knitting and Knitted Fabrics
Figure 2.3.6(1) Knitting Procedure of a Links/Links Machine
4-24
Knitting and Knitted Fabrics
2.3.7 Interlock Fabrics
This is a variation of rib knits made on the interlock gating circular
machine. On interlock knits, columns of wales are directly behind
each other, thus the back of any given plain stitch on the interlock
fabric will reveal another plain stitch directly behind it.
Interlock knits, when compared to similar 1x1 rib knits, are smoother,
more stable and better insulators. Their dimensional stability plus the
fact that they do not tend to easily stretch out of shape contributes to
their popular usage for outerwear and underwear.
Figure 2.3.7 Interlock
2.4 Structures and Techniques Commonly Applied to
Sweaters
2.4.1 Intarsia
This is a weft-knitted plain or purl fabric containing designs in two or
more colours. Each area of colour is knitted from a separate yarn,
which is contained entirely within that area.
Figure 2.4.1 Intarsia
Textile Handbook 4-25
2.4.2 Designs Through Loop Transfer
These include open-work design such as pointelle, cable design and
fully-fashioned knits.
a) Pointelle: this is an open-work design, where the aperture
is created by transferring loops from needles to their adjacent
needles. The empty needles can later resume the knitting
operation and produce the desired apertures.
Figure 2.4.2a Pointelle
Figure 2.4.2b
Cable
c) Fully-fashioned knits: fashioning is a method of shaping
(narrowing and widening) a knitted fabric during the knitting
process. It is popular in sweater manufacture where the
shape and contour of the shoulder and bust can actually
be knitted to body contour shape. Full fashioning is done
on flat bed full-fashioned knitting machines. The knitting
machine adds or drops stitches at the end of the fabric to
Knitting and Knitted Fabrics
b) Cable design: when two groups of needles transfer their
loops from one to another and then continue to knit through
them, their wales cross at the transfer points and produce
the cable design.
2.5
Special Knit Fabrics Produced by Circular Knitting ... 4-26
2.5.1
2.5.2
2.5.3
2.5.4
2.5.5
2.5.6
2.5.7
High-Pile Knits ............................................................ 4-26
Knitted Terry ............................................................... 4-27
Knitted Velour ............................................................. 4-28
Fleecy Fabric ............................................................... 4-28
Coloured Stripe Fabrics ............................................... 4-29
Jacquard Fabric ........................................................... 4-30
Polar Fleece ................................................................. 4-31
Section 3 - Yarn Count and Machine Gauge ........... 4-32
3.1
Yarn Count and Machine Gauge for Circular Knit ...... 4-32
3.2
Yarn Count and Machine Gauge for Wool Knitwear .... 4-34
Section 4 - Quality and Production of Circular
Knitting .................................................... 4-36
4.1
Pre-requisites of a Circular Knitting Machine ............... 4-36
4.2
Production Conditions for Knitting ................................ 4-37
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
4.3
Production Calculations ................................................... 4-38
4.3.1
4.4
Selection of Proper Yarn Count ................................... 4-37
Setting of the Knitting Machine. ................................. 4-37
Yarn Storage ................................................................ 4-38
Air Conditioning of the Knitting Plant ........................ 4-38
Cleaning of Knitting Machines ................................... 4-38
Introduction ................................................................. 4-38
Quality Characteristics of Ring-spun 100% Combed
Cotton Yarn for Circular Weft Knitting ......................... 4-40
Section 5 - Fabrics analysis ........................................ 4-45
5.1
The Geometry of Plain Weft-knitted Fabric .................. 4-45
5.2
ßStitch Density (Fabric count) ......................................... 4-46
5.3
Cover Factor ...................................................................... 4-46
5.4
Prediction of Knitted Performance by Mathematical
Model ................................................................................. 4-47
5.4.1
5.4.2
5.4.3
5.4.4
5.5
Engineering the Fabric ................................................ 4-47
Checking the Specification ......................................... 4-47
Calculations Based on K values .................................. 4-48
Limitations of K values ............................................... 4-50
STARFISH - Engineered Knitted Program for Cotton
Circular Knits ................................................................... 4-51
4-26
Knitting and Knitted Fabrics
widen or narrow the cloth desired. Fully-fashioned articles
can be recognized by fashioning marks which appear as
distorted stitches in the area of the shaped portion.
Figure 2.4.2c
Shaping of a Knitted Panel
2.5 Special Knit Fabrics Produced by Circular
Knitting
Many unique and versatile fabrics can be created in weft-knitting.
Fabrics which look like terry cloth towelling, a smooth velour, or
even a simulated fur are examples of this group of specialized knit
fabrics.
2.5.1 High-Pile Knits
Imitation furs are usually made from a special type of jersey knit
which involves feeding staple fibre in the form of sliver into the knit
material while the yarns are passing through the knitting needles as
the fabric is being made. Acrylic is the most popular fibre used for
the pile portion. After knitting, a variety of finishing treatments are
given to produce the desired fur-like effect.
In addition to their popular use in imitated fur coats, high-pile knits
are widely used as coat lining, car and airline blankets, lining for
footwear and hat.
Textile Handbook 4-27
Figure 2.5.1(1)
High-pile Circular Knitting Machine
SK-18 II
(Mayer Industries Inc.)
Figure 2.5.1(2)
High-pile Knitted Falnic
Back
2.5.2 Knitted Terry
These fabrics are jersey-knit materials which are knitted with two yarns
feeding simultaneously into the same knitting needles. When completed,
one yarn appears on the face, the other on the back. One of the yarns
is called a loop yarn, the other a ground yarn. The loop yarns are
pulled out by special devices and become the loop pile of the knitted
terry fabric.
Figure 2.5.2(1)
Terry Structure
Ground yarn
Loop yarn
Knitting and Knitted Fabrics
Face
4-28
Knitting and Knitted Fabrics
Figure 2.5.2(2) Special Sinker for Pile Loop Formation
Figure 2.5.2(3)
Knitted Terry Fabric
Technical Back
Technical Face
2.5.3 Knitted Velour
These fabrics are made in the same way as knitted terry. The loop
pile is cut by a process called shearing, and then brushed. Knitted
velours have a soft, downy, suede-like texture, resembling velveteen.
They are softer and more flexible than velveteen.
Figure 2.5.3 Knitted Velour
2.5.4 Fleecy Fabric
Two-thread fleecy and three-thread fleecy fabrics are mainly produced
on plain circular knitting machines. On the technical back side (the
side that V-shaped loops cannot be seen) of these fabrics yarn floats
along the rows and is inlay tucked at intervals into the fabric base.
Such yarns are called backing or fleecy yarns.
Textile Handbook 4-29
The most common form of the interlacing points for inlay tucking are
at each second needle (1:1 fleecy) or at each fourth needle (3:1 fleecy)
of a row. Fig 2.5.4 shows the technical back of a staggered 3:1 fleecy.
In row 8, the fleecy yarn 7 is inlay tucked at the wales 3, 7, 11, etc.,
and in row 10 the fleecy yarn 9 is inlay tucked at the wales 1, 5, 9,.
etc. It is common that the technical back of the fleecy fabric will be
raised to produce a soft hairy surface.
In the three-thread fleecy fabric structure, the fleecy yarn is invisible
on the technical front even when using yarns with differing thickness.
The structure is composed of fleecy yarn, binding yarn and face yarn.
It is produced on a special plain circular knitting machine. The specially
constructed holding-down/knocking-over sinker has two throats.
Simple Staggered Fleecy 3:1 Structure
1,2,3,4,5
= wales
6,7,8,10,12 = ground yarn
7,9,11
= fleecy yarn
Figure 2.5.4(2)
Fleecy Fabric
Back
Face
2.5.5 Coloured Stripe Fabrics
Horizontal colour stripes in weft-knit fabrics is the simplest designer
technique by colour arrangement of yarns. In circular knitting, it requires
only the proper arrangement of colour yarn cones in sequence on the
yarn creel. No mechanical adjustments or alteration of stitch types is
necessary. Using this method, a wide variety of colour combinations
is possible. However, the size of the repeat pattern of the horizontal
colour stripe produced by colour yarn cones arrangement is limited.
If uneven colour stripe width and larger pattern repeats are required,
it is neceesary to apply the yarn changer device-stripers. The striping
Knitting and Knitted Fabrics
Figure 2.5.4(1)
4-30
Knitting and Knitted Fabrics
pattern is achieved by selecting the colour finger on each feeder. The
number of fingers on each feerder is ranged from 4 to 6. The selection
of the colour finger is either controlled by a series of pin on a mechanical
chain (engineering stripe) or controlled by a microprocessor where
the pattern data is stored (computerised auto stripe).
Figure 2.5.5
Yarn Change Device (Terrot)
2.5.6 Jacquard Fabric
In jacquard knits, each needle can be individually controlled for each
course and therefore patterns can be created. Jacquard structure can
be produced on either single or double jersey fabrics. Single jersey
colour jacquard is usually composed of two or more yarns of differing
colour to give a construction that consists essentially of knit and float
loops. If the float is too long, tuck loop is incorporated. The surface
pattern is derived from the chosen arrangement of the colour yarns
and of the knit and float loops. For rib colour jacquard produced on
a circular machine, the pattern-based needle selection is undertaken
on the cylinder needles, while the reverse side of the jacquard fabric
is produced on the dial needle. In order to control the fabric weight
and the course density on the back side of the jacquard fabric, different
knitting patterns (backing) can be used for the dial needles.
Figure 2.5.6
Jacquard Fabric
Textile Handbook 4-31
2.5.7 Polar Fleece
Figure 2.5.7 Polar Fleece Fabric
Face
Back
Knitting and Knitted Fabrics
This is a knitted fabric either with very high specific volume or very
bulky. The bulkiness of polar fleece is obtained by brushing both
sides of the knitted fabric. Regular polar fleece fabric weighs 240 g/
m2, 280 g/m2 and 320 g/m2 and has a width of 60 to 62 inches. Singlesided loop pile knitted fabric, commonly known as French Terry, is
used as the ground fabric structure. After dyeing, the fabric is brushed.
Brushing is the process to convert the plush fabric into polar fleece.
The whole process consists of several stages of brushing. To give a
finishing touch to the face side of the polar fleece, a raising process is
carried out by passing the fabric over a flexible card wire machine.
The raising process has the effect of paralleling the fibres on the fabric
surface and also increasing the bulk. Shearing takes place right after
raising to give an even surface. The transformation of a plush fabric
into a polar fleece fabric can be considered as completed. However,
most polar fleece fabrics are subjected to a further process called antipilling for improving the pilling resistance. The entire process is carried
out using a tumble dryer. Mechanical agitation and heat causes the
fibres on the fabric surface to tend to bunch up and form regular beads
on the surface. Bunched up fibres reduce the freedom of fibre movement
and the pilling resistance can be improved. Finally, the fabric goes
through a stenter to heat set the dimension and adjust the required
fabric weight.
4-32
Knitting and Knitted Fabrics
SECTION 3
YARN COUNT AND MACHINE
GAUGE
3.1 Yarn Count and Machine Gauge for Circular Knit
The following tables contain practical values of the average count of
yarn to be used depending on the machine gauge and several fabric
types. The values in Ne refer to staple fibre yarns and those in dtex
are related to filament yarns. Filament yarns are always finer as compared
to staple fibre yarns due to the differences in the running behavious.
Machine gauge
Needles/inch
14
15
16
18
20
22
24
26
28
30
32
Table 3.1(1)
Machine gauge
Needles/inch
12
14
15
16
18
20
22
24
26
28
30
32
Yarn count
Ne
8.5/1 - 14.0/1
10.5/1 - 16.5/1
12.0/1 - 19.0/1
14.0/1 - 23.5/1
18.0/1 - 26.0/1
21.5/1 - 29.5/1
23.5/1 - 35.5/1
426.01 - 41.5/1
29.5/1 - 47.5/1
35.5/1 - 59.0/1
41.5/1 - 71.0/1
dtex
200 x 2 - 235 x 1
150 x 2 - 200 x 1
250 x 1 - 167 x 1
200 x 1 - 150 x 1
167 x 1 - 122 x 1
150 x 1 - 110 x 1
140 x 1 - 100 x 1
122 x 1 - 84 x 1
110 x 1 - 76 x 1
100 x 1 - 67 x 1
84 x 1 - 55 x 1
Yarn Count and Machine Gauge for Single Jersey Fabric
Yarn count
Ne
2.5/1 - 9.5/1
3.5/1 - 12.0/1
4.7/1 - 14.0/1
6.0/1 - 16.5/1
7.0/1 - 18.0/1
8.5/1 - 20.0/1
10.5/1 - 23.5/1
14.0/1 - 26.0/1
16.5/1 - 29.5/1
19.0/1 - 35.5/1
21.5/1 - 41.5/1
23.5/1 - 47.5/1
dtex
720 x 2 - 622 x 1
620 x 2 - 500 x 1
500 x 2 - 420 x 1
833 x 1 - 360 x 1
660 z 1 - 300 x 1
500 x 1 - 280 x 1
360 x 1 - 200 x 1
300 x 1 - 167 x 1
250 x 1 - 150 x 1
200 x 1 - 122 x 1
150 x 1 - 110 x 1
122 x 1 - 84 x 1
Textile Handbook 4-33
Table 3.1(2) Yarn Count and Machine Gauge for Fleecy Fabric
Machine gauge
Needles/inch
14
15
16
18
20
22
24
Yarn count
Ne
16.5/1 - 23.5/1
20.0/1 - 29.5/1
23.5/1 - 35.5/1
29.5/1 - 47.5/1
41.5/1 - 53.0/1
47.5/1 - 59.0/1
53.0/1 - 71.0/1
dtex
235 x 1 - 150 x 1
200 x 1 - 122 x 1
167 x 1 - 100 x 1
150 x 1 - 90 x 1
122 x 1 - 76 x 1
100 x 1 - 67 x 1
84 x 1 - 55 x 1
Table 3.1(4) Yarn Count and Machine Gauge for Interlock Fabric
Table 3.1(5)
Yarn count
Ne
12.0/1 - 16.5/1
14.0/1 - 19.2/1
16.5/1 - 21.5/1
21.5/1 - 23.5/1
23.5/1 - 29.5/1
28.5/1 - 35.5/1
33.0/1 - 41.5/1
35.5/1 - 47.5/1
41.5/1 - 53.0/1
47.5/1 - 59.0/1
53.0/1 - 71.0/1
dtex
235 x 1 - 167 x 1
220 x 1 - 150 x 1
200 x 1 - 133 x 1
167 x 1 - 110 x 1
150 x 1 - 100 x 1
133 x 1 - 100 x 1
122 x 1 - 90 x 1
110 x 1 - 84 x 1
10 x 1 - 76 x 1
90 x 1 - 67 x 1
76 x 1 - 50 x 1
Yarn Count and MachineGauge for Jacquard Fabric
Machine gauge
Needles/inch
14
15
16
18
20
22
24
26
28
30
Yarn count
Ne
13.0/1 - 18.0/1
14.0/1 - 19.0/1
16.5/1 - 21.5/1
18.0/1 - 23.5/1
21.5/1 - 26.0/1
23.5/1 - 28.5/1
26.0/1 - 33.0/1
dtex
235 x 1 - 200 x 1
220 x 1 - 167 x 1
200 x 1 - 150 x 1
167 x 1 - 122 x 1
150 x 1 - 110 x 1
122 x 1 - 100 x 1
100 x 1 - 84 x 1
84 x 1 - 78 x 1
78 x 1 - 67 x 1
67 x 1 - 50 x 1
Knitting and Knitted Fabrics
Machine gauge
Needles/inch
14
15
16
18
20
22
24
26
28
30
32
4-34
Knitting and Knitted Fabrics
Table 3.1(3) Yarn Count and Machine Gauge for Fine Rib Fabric
Fibre
Wool
Cotton
Polyester
filament
Polyamide
filament
Acylic yarn
Machine gauge (needles/inch)
10 12 14
640 500 420
300
280 235 190
15
300
280
140
16
30
235
140
18
250
220
140
20
250
194
122
22-24 28-32 40-42
200
150 125 63
95
50
400 350 250 150 150
125
125
100
300 235 200 200 200
167
150
76
33
Table 3.1(6) Mean Yarn Counts (in dtex) for some Fibre Materials in relation
to the Machine Gauge
3.2 Yarn Count and Machine Gauge for Wool
Knitwear
Table 3.2 on yarn count conversion and machine gauge has been compiled
for guidance only. It should be stress that this information is only
intended as a rough guide and knitting trials should always be carried
Textile Handbook 4-35
out when introducing a new yarn to a machine.
Machine Type
Machine Gauge
Metric Count
Tex
Needles per
Table 3.2 Relationship
between Machine Gauge and Yarn for Wool Knitwear
Straight Bar
Fully Fashioned
Double Jersey
Single Jersey
8/2 - 11/2
11/2 - 18/2
13/2 - 20/2
20/2 - 28/2
22/2 - 32/2
28/2 - 36/2
32/2 - 40/2
250/22 - 176/2
176/2 - 110/2
147/2 - 98/2
98/2 - 74/2
88/2 - 64/2
74/2 - 55/2
64/2 - 50/2
Needles per
Inch
2 1/2
3 1/2
5
7
8
10
12
14
2/2 - 4/2
3/2 - 7/2
7/2 - 16/2
13/2 - 18/2
16/2 - 25/2
25/2 - 36/2
30/2 - 47/2
36/2 - 60/2
885/2 - 442/2
590/2 - 295/2
295/2 - 126/2
147/2 - 110/2
126/2 - 80/2
80/2 - 55/2
68/2 - 42/2
55/2 - 34/2
Needles per
Inch
12
14
16
18
22
18/1 - 26/1
22/1 - 32/1
28/1 - 36/1
32/1 - 40/1
36/1 - 45/1
55/1- 40/1
44/1 - 32/1
37/1 - 28/1
32/1 - 25/1
28/1 - 22/1
Needles per
Inch
5
7&8
10
12
14
16
18
20
22
24
26
28
11/2 - 27/2
18/2 - 32/2
22/2 - 36/2
27/2 - 40/2
32/2 - 45/2
36/2 - 50/2
40/2 - 30/1
45/2 - 32/1
28/1 - 34/1
32/1 - 39/1
36/1 - 45/1
40/1 - 50/1
176/2 - 74/2
110/2 - 63/2
88/2 - 552
74/2 - 50/2
63/2 - 44/2
55/2 - 40/2
50/2 - 34/1
44/2 - 32/1
37/1 - 30/1
32/1 - 26/1
28/1 - 22/1
25/1 - 20/1
Knitting and Knitted Fabrics
Flat ‘V’ Bed
and Circular
1.5 inches
9
12
15
18
21
24
27
4-36
Knitting and Knitted Fabrics
SECTION 4
QUALITY AND PRODUCTION OF
CIRCULAR KNITTING
4.1 Pre-requisites of a Circular Knitting Machine
• The machines must be installed on a horizontal floor and, as far as
possible without vibration.
• The bobbin carriers must be mounted in such a way that the yarn
does not rub against the sides of the package when it is withdrawn.
• Yarn should be guided from the package up to the knitting area
without unnecessary deviations in order to avoid additional increases
in tension.
• If basic knitted structures are used to a large extent, the machines
should be equipped with yarn feeding units which generate a constant
and low yarn tension (running-in tension) and deliver a uniform yarn
length.
• Yarn guide devices must be flawless; eyelets made of porcelain or
sintered ceramic must have a smooth surface without any furrows.
• The needles must also be flawless. If synthetic yarns are processed
to a large extent in a 3-shift operation, they might have to be renewed
after just 6 months.
• The shape of the needle, and especially of the needle hooks, must be
adapted to the machine gauge and the yarn count.
• The needle beds must be exactly centered towards one another.
• Needle beds are subject to a high strain while producing tight fabrics
from synthetic yarns. If wear and tear occurs here, it can cause
problems in subsequent processing (roughening, cracks)
• The fabric take-down and wind-on tensions must be capable of being
set individually and in such a way that tension peaks, reverting back
to the knitting zone, do not arise.
Textile Handbook 4-37
4.2 Production Conditions for Knitting
4.2.1 Selection of Proper Yarn Count
The selection of yarn count is primarily determined by the gauge of
the knitting machine. For example, for a worsted type 100% wool
yarn:
Machine pitch x 2 = correct yarn count (Ne or Nm), except for plain
and purl machines
Machine pitch x (1.0 to 1.5) = correct yarn count (Ne or Nm) for
plain and purl machines.
• different machine types and difference in basic construction of the
same type of machine;
• knitted structure related to number of feeders involved; and
• types of yarn such as processing a blended yarn when in practice a
finer yarn should be used;
Figure 4.2.1 Relation Between Knitted Structures and Processing Problems
The degree of difficulty in processing varies with the different knitted structures.
Degree of Difficulty in Processing
Structures
Low
Interlock, 2-colour jacquard, 3-colour jacquard,
2:2 cross tubular, Ponti di Roma
Medium
Double pique, 4-colour jacquard
High
Rib, Half milano, Relief and combined patterns
of muticolour jacquard
4.2.2 Setting of the Knitting Machine.
Optimum setting is difficult because several factors must be balanced
against one another in a proper relationship. This balanced relationship
should be found between :
• yarn tension before and after the yarn feeder (minimum yarn tension
prior to the yarn feeder)
Knitting and Knitted Fabrics
Deviations from this formula may be due to factors including
4-38
Knitting and Knitted Fabrics
• drawing-in of yarn at the cylinder and the dial (it is easier to obtain
a loose fabric by having a larger distance between dial and cylinder
than by having a longer drawing-in range for the needles)
• height of dial (with the tightest setting a minimum distance between
dial and cylinder is necessary)
• fabric take-up tension (it should be as low as possible)
4.2.3 Yarn Storage
Dried yarn has limited extension, so it should be stored in rooms with
at least 65% relative humidity (at 200C). Storage under extreme
temperatures must be avoided because in high temperatures there might
be a danger of wax migration, while at low temperatures water
condensations build up.
4.2.4 Air Conditioning of the Knitting Plant
It is recommended a relative humidity of 55% ± 10% at a temperature
of 25oC ± 3oC.
4.2.5 Cleaning of Knitting Machines
Fluff removal should take place at least at the end of each shift, fly
accumulated in the cam area should be removed as it becomes visible,
and residual wax on tension discs and yarn guide elements should be
removed occasionally
4.3 Production Calculations
4.3.1 Introduction
The performance of the circular knitting machine is affected by the
elements such as frame, drive, yarn feeder, cam set-up, fabric takeup, yarn delivery device and monitoring and servicing devices. To
calculate the production it is necessary to have several characteristic
values of the corresponding knitting machine and the product being
produced.
Textile Handbook 4-39
a) Elements
Knitting Machine Parameters
- machine diameter “D” (inch)
- gauge “E”
- no. of feeders “S”
- no. of machine revolutions/min “n”
- efficiency “ η“
Product Parameters
- structure
- type and count of yarn
- course density “MR./cm”
- wale density “MS/cm”
- fabric weight “FG” (g/m 2)
The efficiency (“η ”) is the ratio of the practically obtained performance
to the theoretical performance and is always smaller than 1.
b) Formulae :
Machine performance “L” in metre per hour (m/h):
S x n x 60 xη
feeders / course x MR / cm x 100
Fabric width “B” in metres:
B (m) =
D x 3.14 x E
MS / cm x 100
Machine performance “G” in kg per hour (kg/h)
G (kg / h) =
L x B x FG
1000
c) Example :
- Machine diameter 30 inch
- gauge E 28
- no. of feeders 96
- machine speed 35 rpm
- efficiency η 0.85
- structure : plain (single jersey)
- yarn : cotton Ne29.6/1
- course density 18 MR/cm
- wale density 13 MS/cm
- fabric weight 125 g/m2
Machine performance L (m/h)
96 x 35 x 60 x 0.85 =95.2m / h
L=
1 x 18 x 100
Fabric width B (m)
30 x 3.14 x 28 =2.03m
B=
13 x 1000
Machine performance G (kg/h)
G=
95.2 x 2.03 x 125 =24.2kg / h
1000
Knitting and Knitted Fabrics
L (m / h) =
4-40
Knitting and Knitted Fabrics
4.4 Quality Characteristics of Ring-spun 100%
Combed Cotton Yarn for Circular Weft Knitting
(Source: Zellweger Uster)
A knitting yarn (100% combed cotton) for high-production circular
weft knitting and good quality knitwear should exhibit the following
quality characteristics
Table 4.4 (1)
Quality Requirement of a Cotton Yarn for Knitwear
Count variation CVt, cut length 100 m**
Count variation CVt, cut length 10m**
Breaking tenacity*
[Fmax/tex]
Variation of breaking force [CVF max]
Elongation at breaking force [Efmax]
Variation of elongation at break
Yarn twist ( ∝ m value)
Paraffin waxing/surface friction value
Yarn irregularity **
Thin places/Thick places/Neps
Hairiness H***
Between-bobbin hairiness variation H****
CVb
Seldom-occurring thin and thick places
faults (CLASSIMAT values)
Remaining yarn faults (CLASSIMAT values)
<1.8%
<2.5%
<10 cN/tex
<10%
<5.0%
<10%
Ring-spun yarn 94-110
ideal around 0.15µ
<25% value of the USTER®
STATISTICS
<25% value of the USTER®
STATISTICS
[e.g.>50% value of the USTER®
STATISTICS]
<7%
A3/B3C2/D2 OR D1 or more
sensitive (clearing limit)
A3 + B3 + C2 + D2 = <5/100,000m
*
A low breaking force value must be compensated by a higher elongation at
breaking force value
**
Highest requirements with single jersey
*** Higher, but constant hairiness as a result of the cloth appearance and handle.
The minimum hairiness value must be set based on agreements between the partners
**** Variation between packages. Higher values can lead to rings with singlecoloured fabrics.
Textile Handbook 4-41
From Table 4.4 (1), it can be seen that it is not one single peak value
which determines the quality of the end product, but a compromise
between the various quality characteristics.
In contrast to weaving yarns, the yarn strength of knitwear yarns, for
example, is secondary, as the loading placed on the yarn during knitting
is lower than that with a high-production weaving machine. The yarn
must, however, exhibit enough elongation and elasticity. There must
be no weak places or thick places which can result in stops, holes in
the knitted material or even broken needles. Particularly important is
the ability of the yarn to be guided easily through the various elements
of the machine (low friction value). The moisture content of the yarn
should be evenly distributed. Conditioned yarns provide better running
properties and better appearance of the finished fabric.
Particularly important is the yarn evenness and count variation. Both
the short and medium-term, as well as the long-term count variations
lead to cloudy or stripy fabrics as soon as a certain mass variation
level is over stepped. Also neps and vegetable matter, as well as a
high dust content, refer to the types of foreign matter which are
particularly disturbing. These lead to wear of the needles, holes in
the knitted material and even to dyeing problems.
All these yarn characteristics can be responsible for downgrading the
knitted fabric, and can have some influence on the ‘knitability’, ‘spirality’,
‘dyeability’ or ‘contamination’ problems associated with circular weftknit fabrics.
A large European Knitwear manufacturer has set out the yarn
specifications for certain types of knitted structure. Table 4.4.(2) shows
the yarn quality specifications corresponding to the yarn count and
recommended raw material.
Knitting and Knitted Fabrics
In most cases, an even and high hairiness value with a low twist is
required in order to achieve a soft material handle. This hairiness
value must, however, remain constant and be without periodic variations.
4-42
Knitting and Knitted Fabrics
Table 4.4 (2) Yarn specifications demanded by a European knitwear
manufacturer
Evenness Thin
Neps Knitwear
Thick
(cvm%) places places per km
type
*
per km per km
*
(-50%)
Nm
(Tex)
Cotton
Combed
Twist
factor
/(inch)
Break
tenacity
(cN/
tex)
CV
(Fmax
%)
34
(29.5)
Am
3.3
12.5
9.0
13.0
4
50
60
Single
jersey
40
(25)
Am
3.3
13.0
9.0
13.0
6
50
70
Single
jersey
50
(20)
Maco
3.3
3.3
9.0
14.0
8
35
80
Double rib
50
(20)
Peru
3.5
12.0
9.0
14.5
10
70
80
Double rib
50
(20)
Am
3.5
13.0
9.0
14.5
10
70
90
Fine rib
55
(18.2)
Am
3.5
13.5
9.0
15.0
12
90
110
60
(16.6)
Maco
60
(16.6)
Am
3.4
16.0
9.0
14.5
12
50
90
Fine rib +
Single
jersey
Double
jersey
3.5
13.5
9.0
15.0
15
100
150
Double
jersey
70
(14.4)
Am
3.6
13.5
10.0
15.5
20
100
120
Tricot +
Fine rib
70
(14.4)
Maco
3.3
16.0
9.0
14.5
15
50
90
Fine rib
85
(11.8)
Maco
3.5
16.0
9.0
15.0
20
60
100
2/85
Tricot
2:2
100
(10)
Maco
3.5
16.0
10.0
15.5
25
70
100
Fine rib
120
(8.4)
Maco
3.6
16.5
11.0
16.5
40
90
120
Fine rib
• Settings of sensitivity at the USTER® TESTER 3
Textile Handbook 4-43
There is another set of yarn specifications for knitted fabric recommended
by a well-known European retailer of knitted goods. It refers to five
yarn counts of 100% combed cotton yarns used for various structures
in weft circular knitted fabrics.
Table 4.4 (3) Yarn specifications demanded by a European retailer of knitted
goods
Ne 24
25 tex
Ne 30
20 tex
Ne 34
17.5 tex
Ne 38
15.5 tex
Evenness
CVm%
max.*
max.*
A%
CVt100%
Twist/m
±*
≤*
568±38
±*
≤*
675±85
max.
12.3
±1.5
≤1.8
755±38
max.
13.0
±1.5
≤1.8
826±38
max.
13.5
±1.5
≤1.8
910±38
THIN/km
(-50%)**
THICK/km
**
NEPS/km
**
Tenacity
Fmax/tex
CVFmax%
max.*
max.*
max.5
max.5
max.8
max.*
max.*
max.20
max.25
max.35
max.*
max.*
max.40
max.60
max.80
min.13CN
min.13CN
min.13CN
min.13CN
min.13CN
≤10.0
≤10.0
≤10.0
≤10.0
≤10.0
Elongation at
Break
Efmax%
min.6.2
min.6.0
min.5.8
min.5.6
min.5.5
A1/B1/
C1/D1***
/100km
(remain)
A3/B3/
C2/D2***
/100km
(remain)
mean 75
max.150
mean 85
max.170
mean 100
max.200
mean 125
max.250
mean 150
max.300
mean 3
max.5
mean 3
max.5
mean 3
max.5
mean 4
max.7
mean 5
max.8
E/100km***
(remain)
max.1
max.1
max.1
max.1
max.1
H2/I2
100km***
(remain)
max.3.5
max. 3.5
max. 3.5
max. 3.5
max. 3.5
*
**
***
According to agreements with the yarn processor
Settings of sensitivity at the USTER®TESTER 3
Sensitivity levels of the USTER®CLASSIMAT
Knitting and Knitted Fabrics
Ne 18
27 tex
4-44
Knitting and Knitted Fabrics
If it is to be expected that the setting out of yarn specifications as the
basis for agreements between the yarn manufacturer and the yarn
processor will become a standard procedure in the same way that a
yarn can be “engineered”, based on the fibre properties, a knitted fabric
can also be “engineered” based on the yarn quality characteristics.
This will necessitate a closer collaboration between the spinner and
the knitter, and the need for the knitter to become better acquainted
with the yarn quality characteristics and the values which can be expected.
Textile Handbook 4-45
SECTION 5
FABRIC ANALYSIS
5.1 The Geometry of Plain Weft-knitted Fabric
The dimension and construction properties of fabrics are important
for the control of quality as well as for end-use determination.
The theory of fabric geometry for a plain weft knitted fabric can be
defined as follows:
S = the number of stitches per square unit
c = the number of courses per unit length
l = the stitch or loop length.
Wales/cm = w
Courses/cm = c
Stitch length = AB = l mm
Stitches/cm2 = S
Figure 5.1 A
Plain Weft Knitted Structure
Apart from the dominant factor, that is, the length of yarn in the knitted
loop (stitch length), there are three dimensionally stable (relaxed) states
possible for a knitted structure must be considered when applying the
theory of the fabric geometry.
Knitting and Knitted Fabrics
w = the number of wales per unit width; and
4-46
Knitting and Knitted Fabrics
The three relaxed states of a knitted fabric are:
• Dry-relaxed state: the fabric has been taken off the knitting machine
and in course of time attains a dimensionally stable condition called
the dry-relaxed state.
• Wet-relaxed state: if the fabric is soaked in water and allowed to dry
flat, the wet-relaxed state is attained, again a dimensionally stable
condition.
• Finished relaxed state: in order to reach this stable condition, the
fabric is subjected to agitation in water or steam, and a denser fabric
results.
5.2 Stitch Density (Fabric count)
The stitch density of a weft-knitted fabric can be expressed as the
number of wales per unit length times the number of courses per unit
length.
5.3 Cover Factor
Covering power refers to the ability of an item to occupy space or to
cover an area. A fabric with better cover will be warmer, look and
feel more substantial, and be more durable.
Cover Factor can be defined as a number that indicates the extent to
which the area of a knitted fabric is covered by the yarn. It is also an
indication of the relative looseness or tightness of the knitting. The
Cover Factor (C.F.) can be determined by the following formula:
CF=
tex
stitch length (mm)
or
CF=
1
stitch length (inch) x worsted count
Textile Handbook 4-47
5.4 Prediction of Knitted Performance by
Mathematical Model
5.4.1 Engineering the Fabric
Fabric engineering in the modern sense implies that equations have to
be available which can be used to calculate the fabric properties of
interest, starting from the known manufacturing and processing
conditions. The known manufacturing and processing conditions
comprise:
• The yarn (or selection of yarns) available for knitting.
• The knitting specification (essentially, the length of yarn fed for
each revolution of the machine).
• The wet processing and finishing machinery characteristics.
5.4.2 Checking the Specification
Normally the dyer and finisher does not participate in the fabric design
and specification exercise. He has to accept whatever fabric is supplied,
and he will usually be required to deliver the dyed and finished fabric
at a certain weight and width and with certain maximum levels of
shrinkage.
If the fabric has not been appropriately engineered, then there is no
way that the dyer and finisher will be able to meet all of these
requirements. Therefore, it is absolutely essential that the dyer and
finisher should be able to check whether the fabric is correctly engineered
before he puts it into work. If the dyer and finisher has access to the
equations which are used for fabric engineering, then he is able to
make such checks.
Knitting and Knitted Fabrics
• The knitting machinery characteristics (essentially, the number of
needles).
4-48
Knitting and Knitted Fabrics
5.4.3 Calculations Based on K values
The K values were derived from observations made by research workers
more than two decades ago that there is a strong relationship between
the number of courses and wales per cm in a relaxed cotton knitted
fabric and the reciprocal of the loop length used in knitting (see Figure 5.4.3).
“Relaxed” means after the fabric has been subject to an appropriate
wetting and drying procedure (e.g. a shrinkage test). Loop length is
the average length of yarn in each knitted loop. It is given by the
length of yarn fed to the knitting machine per revolution (or per pattern
repeat) divided by the number of needles which are knitting.
The two basic equations are:
Course per cm = Kc/loop length in cm
Wales per cm = Kw/loop length in cm
Kc and Kw are constants for a given fabric construction and fibre
type, and these K values can be used to calculate the course and wale
densities in any fabric, provided only that the knitted loop length is
known.
Once the course and wale densities have been found for the relaxed
fabric, then these can be used together with yarn count, the knitted
loop length, and the number of needles in the knitting machine to
calculate the relaxed fabric weight and width.
Wt = tex x loop length x course x wales x F1
Width = number of needles/wales x F2
Where F1 and F2 are scaling factors, depending on the units
of measurement.
Courses and wales, weight and width in the unrelaxed fabric (i.e. as
delivered to the customer) can then be derived by proportional scaling,
according to the appropriate level of shrinkage.
Length Shrinkage = (Cr - Cd) / Cr
Width Shrinkage = (Wr - Wd) / Wr
Where
Cr and Wr and the relaxed courses and wales, Cd and Wd are
the as-delivered values.
Textile Handbook 4-49
If the calculated as-delivered weight and width values do not coincide
with what the customer has specified, then the fabric has not been
correctly engineered, and this is a matter for serious discussion between
the dyer and finisher and the customer.
If the calculated weight and width do coincide with the customer’s
requirements, then the calculated values for as-delivered courses and
wales provide the dyer and finisher with his primary finishing targets.
If he can hit these values in the delivered fabric, then the calculated
weight and width, and the shrinkage values used in the calculation are
guaranteed.
Since the yarn count and loop length should be known from the knitting
specification, it would seem to be a simple task for the dyer and finisher
to check that a given grey fabric has been correctly engineered so that
the weight, width and shrinkages required by the customer can actually
be delivered. Kc and Kw values can easily be picked up from the
literature, or can be determined on the grey fabric already to hand.
Figure 5.4.3
Effect of Loop Length on Grey Courses and Wales per cm
Knitting and Knitted Fabrics
The finishing targets can be used as the basis for setting and operating
control systems on stenter and compactors, which will aid the finisher
in achieving his targets, and thus the required fabric performance. In
practice the width will be used in preference to the number of wales
per cm for control purposes, but there is no satisfactory substitute for
courses per cm as the primary length control parameter.
4-50
Knitting and Knitted Fabrics
5.4.4 Limitations of K values
Unfortunately, it is now know that Kc and Kw are actually not constants.
They are affected quite significantly by several factors including
especially certain aspects of the yarn specification, and any wet processing
which may have been carried out on the fabric. For example, K values
for plain jersey fabrics, which have appeared in the literature over the
last two decades, range from 5.1 to 5.8 for Kc and 4.1 to 4.95 for Kw.
This range of variation is not some kind of experimental error. It is a
reflection of real differences in K values, due to differences in the
experimental conditions used by the various workers. It also represents
approximately the range of K values which are found in experimental
work.
Some of these effects are illustrated by Figure 5.4.4 (1) and Figure 5.
4.4 (2) which show the influence of knitted Tightness Factor and wet
processing on the values of Kc and Kw for a wide range of plain
jersey fabrics, knitted from seven different yarns. Tightness Factor is
given by the square root of the yarn count in tex divided by the Loop
Length in cm. There are relatively large differences between the K
values for grey fabric and those for the two sets of finished fabrics,
and the wide scatter in the data, within a given wet process, is a reflection
of the influence of the yarn properties upon the K values. In this
context, it should be noted that a difference of only a unit in Kc represents
difference in length shrinkage of about two percentage points; a similar
difference in Kw represents two and a half percentage points of width
shrinkage.
Figure 5.4.4(1)
Effect of Tightness Factor on Kc
Textile Handbook 4-51
Figure 5.4.4(2)
Effect of Tightness Factor on Kw
5.5 STARFISH - Engineered Knitted Program for
Cotton Circular Knits
(Source: Cotton Technology International)
STARFISH is short for “START as you mean to FINISH. The
STARFISH computer program is a simulator. It models the key elements
of production and processing of cotton circular knitted fabrics and it
calculates their expected performance.
The STARFISH computer program is founded on a database which
comprises test data on more than 5,000 separate fabric qualities, and
is still growing year by year. Almost all of the data come from fabrics
which have been manufactured and processed at full scale. These
data are mainly of two types. Firstly, there are the systematic series
of fabric qualities to perform the basic mathematical analysis to develop
the underlying equations. Secondly, there are the results from sets of
serial samplings of individual qualities, taken over a period of weeks
or months in dyeing and finishing plants. These serve to validate the
Knitting and Knitted Fabrics
Therefore, a dyer and finisher who wants to make use of simple K
values to check for correct fabric design, or to develop finishing targets,
should take care to use the appropriate values. Because the K values
are affected by the wet process, he would be well advised to carry out
determinations of courses and wales on his own finished fabrics. It is
definitely not the case that he can determine K values on the grey
fabrics and use these for making calculations. Indeed, the only value
for the dyer and finisher in making measurements on grey fabrics is
to ensure that the yarn count and loop length are exactly as specified.
4-52
Knitting and Knitted Fabrics
predictions of the current program and also to establish the normal
variation which can be seen in commercial production.
Using these data, it is possible to model (amongst others) the average
influence of different types of yarns and different wet processing regimes,
so that these average effects are already built into the model.
Thus, using the STARFISH computer program, the average values for
courses and wales, and the weight and width of an extremely wide
range of dyed and finished fabrics can be estimated very rapidly and
pretty accurately without the need for any physical knitting or finishing
trials. The program will also calculate finishing targets for any desired
level of shrinkage or any requested weight and width. It will also
show whether a given set of customer demands can actually be met in
principle, using the yarns, knitting machines, and wet processing
machinery which are actually available.
It should be emphasised that the equations used by STARFISH are
not dependent in any way on K values. They include additional terms
which allow for the yarn type, the yarn count, the wet process, and
the depth of shade.
To get started with a basic simulation model, the user can select from
a list of four standand yarn types, ten standard processes and eight
depths of shade. Up to nine different yarn count values can be specified,
as well as nine different knitting machines (to simulate a body-width
range).
Section 6 - Typical Fabric Imperfections on
Circular Knitting .................................... 4-53
6.1
Fabric Skew ........................................................................ 4-53
6.1.1
6.1.2
6.1.3
6.1.4
6.2
Definition .................................................................... 4-53
Causes ......................................................................... 4-53
Evaluation of the Effect of Yarn, Knitting and ............
Finishing Parameters on Skew .................................... 4-54
Summary ..................................................................... 4-58
Barre .................................................................................. 4-58
6.2.1
6.2.2
Definition of Barre ...................................................... 4-58
Causes of Barre ........................................................... 4-58
Section 7 - Warp Knitting and Warp Knitted
Fabrics ..................................................... 4-61
7.1
Warp Knitting ................................................................... 4-61
7.2
Warp Knitting Machine Classification ........................... 4-61
7.2.1
7.2.2
7.3
Knitting Elements of Warp Knitting Machine ............... 4-63
7.3.1
7.3.2
7.3.3
7.3.4
7.4
Tricot Machines ........................................................... 4-62
Raschel Machines ........................................................ 4-62
Needle ......................................................................... 4-63
The Sinker ................................................................... 4-64
Guides and Guide Bars ................................................ 4-64
Driving Mechanisms of Knitting Elements ................. 4-65
Key Terms of Warp Knits ................................................ 4-66
7.4.1
7.4.2
7.4.3
7.4.4
7.4.5
7.4.6
7.4.7
Course and Wales ........................................................ 4-66
Stitch Density .............................................................. 4-66
Loop Parts ................................................................... 4-66
Open and Closed Laps ................................................ 4-67
Technical Back ............................................................ 4-67
Technical Face ............................................................. 4-67
Run-in .......................................................................... 4-68
7.5
Common Warp Knit Fabric Structures and their
Characteristics .................................................................. 4-68
7.5.1
7.5.2
Tricot Fabrics .............................................................. 4-68
Raschel Fabrics ........................................................... 4-72
Textile Handbook 4-53
SECTION 6
TYPICAL FABRIC IMPERFECTIONS
ON CIRCULAR KNITTING
6.1 Fabric Skew (Source: Cotton Incorpocated)
6.1.1 Definition
Figure 6.1.1 Examples of Skew
6.1.2 Causes
When discussing tubular knit goods, the skew deviation is usually
composed of distortion caused by the yarn, the number of feeders on
the machine, and the manner in which the yarn is knitted. Skew
caused by the yarn is realized as a spiraling of the wales at a steep
angle around the knitted tube. This type of skew causes the tube to
torque. If a single wale is followed up the length of this tube, it can
easily be seen that the wale will spiral around the tube. The courses
will generally not be deflected from the horizontal. Distortion of the
wale loops is usually seen in goods that are processed in tubular form
in a preparation or dyeing process. In fact wale skew is readily seen
when the fabrics are unloaded from the preparation or dyeing vessel
Knitting and Knitted Fabrics
Skew can be defined as a fabric condition resulting when the knitted
wales and courses are angularly displaced from the ideal perpendicular
angle. Other terms such as torque, spirality, bias and shear distortion
are often used to refer to the same phenomena. Regardless of the
term used, this displacement of the courses and wales can be expressed
as a percentage or as an angle measurement in degrees. Examples of
skew can be seen in Figure 6.11.
4-54
Knitting and Knitted Fabrics
prior to de-twisting and extraction. If the fabric is then finished in a
tubular manner and the wales are not straightened, then the distortion
of the wales will be obvious.
The level of course skew will include both yarn and machine influence.
Also, it is important to realize that if the fabrics are slit in the grey on
the same wale line and are undergo from wet processing to dry
processing, then the wales will be straight and the courses may be
skewed.
Machines with a large number of feeders will make a fabric that has
substantial ‘course skew’ as the fabric comes off the knitting elements.
However, the course skew will be eliminated when the fabric is slit
into open-width form.
Yarn parameters that affect skew include twist level (twist multiple or
turns per inch of twist), twist direction (S or Z), twist liveliness, and
the spinning system. It is important to realize that skew from the yarn
and the skew from the number of feeders on the machine can combine
together to create more skew, or they may partially offset each other
and result in less skew. This addition or subtraction of skew depends
primarily on the yarn twist direction and the direction of rotation of
the cylinder on the knitting machine.
6.1.3 Evaluation of the Effect of Yarn, Knitting and
Finishing Parameters on Skew
a) Test Method: the sample fabrics are measured for skew
using a proposed test method being developed by AATCC.
The samples are marked with a square before washing
and tumble drying. If the fabric skews after five washes
and dry cycles, the square can be measured for percent
skew. The method uses a mathematical formula for shear
distortion (skew) and is shown below:
2(AC-BD)
x 100
% Skew =
AC + BD
Textile Handbook 4-55
Figure 6.1.3.a Proposed Test Method for Shear Distortion (Skew) of Knitted
Fabric
Where AC and BD are the diagonals of the square,
<DAB = 90o, A’B’CD = Location of square after relaxation,
b) Effect of Twist Multiple, Twist Direction and Yarn
Spinning System on Skew
The sample fabrics are knitted into 18 gauge single jersey
with 18/1 Ne carded 100% cotton yarn. The Twist Multiples
(TM) used for the Ring and O-E spinning systems are 3,
3.5 and 4. However, only one TM is used for the Air Jet
spinning system.
Table 6.1.3.b
Effect of Twist Multiple, Twist Direction and Yarn Spinning
System on Skew
Grey Goods
Ring Spun Z twist
3.0
3.5
4.0
Ring Spun S twist
3.0
3.5
4.0
Open-End Z twist
3.0
3.5
4.0
Murata Air Jet
Z
S
% Skew
(5 HLTD’s)*
Skew Direction
10.5
12.6
18.5
Right
Right
Right
15.8
17.6
20.3
Left
Left
Left
3.5
5.2
8.7
Right
Right
Right
12.3
17.6
Right
Left
Note: * 5 washes and dry cycles
Knitting and Knitted Fabrics
DA’B’ > 90o
4-56
Knitting and Knitted Fabrics
c) Effect of Twist Multiple, Twist Direction and On Machine
Cylinder Rotation Direction on Skew
Sample fabrics were made on two 28 gauge single jersey
machine. 30/1 Ne Combed cotton ring spun yarns were
knit at a tight stitch. The difference between the machines
was the direction of cylinder rotation. Knitting evaluations
included three yarn feeder setups. Comparisons included
fabrics made with all feeds of S twist, all feeds of Z twist
and alternating feeds of S and Z twist.
Grey goods were tested for skew using the proposed AATCC
method for shear distortion (skew)-the results are shown
in Table 6.1.3c
Table 6.1.3.c Effect of Twist Multiple, Twist Direction and on Machine
Cylinder Rotation Direction on Skew
Grey Goods
% Skew
(5 HLTD’s)
Clockwise Rotation
Z
15.3
S&Z
1.4
S
11.0
Counterclockwise Rotation
Z
5.7
S&Z
2.6
S
7.5
Skew Direction
Right
Right
Left
Right
Right
Left
d) Effect of Tightness of Stitch on Skew
Sample fabrics were knitted with four different stitch
tightness on a 28 gauge single jersey machine. The yarn
used is a 30/1 ring spun 100% cotton and both grey goods
and dyed goods were compared for skew.
Table 6.1.3.d Effect of Stitch Tightness on Skew
Course Length (ins)
245
260
270
280
Skew (5 HLTD’s) *
Grey
8.6
12.3
15.1
16.8
Note: * All samples had right hand skew.
Dyed Corrected for Skew
8.1
9.5
15.2
17.2
Textile Handbook 4-57
e) Effect of Skew Using Plied and Parallel Yarn
The used of balanced, plied yarns has been practiced for
years to give torque free fabrics. Table 6.1.3.e shows the
skew test data for “S” and “Z” yarns spun side-by-side on
a Air-jet spinning system and wound parallel onto the same
package, and two strand of “Z” twist wound onto the same
package and then plied on an uptwister at different twist.
Table 6.1.3.e
Effect of Parallel and Plied Yarns on Skew Using the Murata
Air Jet Spinning System
S & Z - 0 TPI 1.2
Z & Z - 0 TPI 21.0
Z & Z - 2.5 TPI
Z & Z - 6.5 TPI
Z & Z - 12.5 TPI
Z & Z -14.5 TPI
% Skew
5 HLTD’s
Direction
Right
Right
17.0
11.3
0.0
3.5
Right
Right
None
Left
Note : * Each individual strand was a 40/1 Ne Air Jet Yarn.
f) Effect of Finishing Techniques on Skew
Sample fabrics, knitted on a 28 gauge single jersey machine
with a 30/1 Ne combed ring spun yarn, were pre-treated
and dyed on a jet machine, dried and finished by either
compaction or resin treatment. One group of the finished
fabrics has included skew correction. The skew test result
are shown in table 6.13f
Table 6.1.3.f Effect of Finishing Techniques of Skew
Sample
Grey
Dyed & Compacted
Dyed & Resin Finished
% Skew, 5 HLTD’s
With Correction
—
8.1
6.0
Without Correction
8.6
3.5
2.0
Knitting and Knitted Fabrics
18 Cut, 100% Cotton*
4-58
Knitting and Knitted Fabrics
6.1.4 Summary
Skew on 100% cotton single jersey is related to the level of yarn
twist, the spinning system used, the strand configuration, the tightness
of the knitted stitch, the number of feeders on the knitting machine,
the rotational direction of the knitting cylinder and the finishing technique
used. Any process that could be developed to reduce the twist liveliness
of yarns could help reduce the total level of skew. Also, development
of finishing techniques that could relax the yarns without inducing
torque would be of interest. Today, the best answer for skew reduction
is either the use of plied yarns or alternating feeds of opposite twist.
If single yarns must be used, then resin finishing offers reasonable
control of skew.
6.2 Barre
6.2.1 Definition of Barre
The noun “BARRE” is defined by ASTM as an unintentional, repetitive
visual pattern of continuous bars and stripes usually parallel to the
courses of circular knit fabric. In a warp knit, barre normally runs in
the length direction, following the direction of yarn flow.
6.2.2 Causes of Barre
a) Factors which may cause or contribute to barre are
listed as follows:
(i) Raw Material - Fibre
• Failure to control fibre diameter (micronaire or denier)
from laydown to laydown.
• Too high a C.V. of micronaire in the laydown for a
given mill’s opening line blending efficiency.
• Failure to control the fibre colour in the mix (greyness
Rd, yellowness +b).
Most, if not all, fibre barre can be controlled by the
above three items; however, under certain unusual
circumstances it may be beneficial to select mixes
using ultraviolet reflectance information for each bale
of cotton.
Textile Handbook 4-59
(ii) Yarn Formation/Supply
• Variations in carding; i.e., different amounts of nonlint content removal from card to card.
• Poor blending of fibre in opening through finisher
drawing.
• Running different types of spindle tapes on ring
spinning frame.
• All cots running on a given set of ring frames producing
yarn for the same end use should be exactly the same.
• Mixing yarns of different counts.
• Mixing yarns with different blend levels.
• Mixing yarns from different suppliers.
• Mixing yarns with different twist level/twist direction.
• Mixing yarns with different degrees of hairiness.
• Mixing yarns with different amounts of wax.
• Mercerization differences.
• Excessive backwinding or abrasion during this process.
• If yarns are conditioned, then each lot must be
uniformly conditioned.
(iii) Fabric Formation
• 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.
Knitting and Knitted Fabrics
• Mixing yarns of different spinning systems.
4-60
Knitting and Knitted Fabrics
b) Prevention of Barre
Barre is caused by inconsistencies in materials, equipment,
or processing. To prevent barre from occurring, consistency
must be maintained through all phases of textile production.
Stock yarns should be properly and carefully labelled to
avoid mixups. Fugitive tints can be useful for accurate
yarn segregation. Inventory should be controlled on a First
In/First Out basis. All equipment should be properly
maintained and periodically checked. Before beginning
full scale production, sample dyeings can be done to check
for barre.
Salvaging a fabric lot with a barre problem may be possible
through careful dye selection. Colour differences can be
masked by using shades with very low light reflectance
(navy blue, black), or high light reflectance (light yellow,
orange, or finished white). Dye suppliers should be able
to offer assistance in this area. Also, if the cause of the
barre is an uneven distribution of oil or wax, a more thorough
preparation of the fabric prior to dyeing may result in more
uniform dye coverage.
With close cooperation between production and quality
control personnel, barre problems can be successfully
analyzed and solved.
Textile Handbook 4-61
SECTION 7
WARP KNITTING AND WARP
KNITTED FABRICS
7.1 Warp Knitting
Warp knitting is defined as a loop-forming process in which the yarn
is fed into the knitting zone, parallel to the fabric selvedge. The source
of yarn on a warp knitting machine is a warp beam similar to a warp
beam on a loom. The yarns form a vertical loop in one course and
then move diagonally (shogging) to another wale to make a loop in
the following course. The yarns zigzag from side to side along the
length and connect the loops into a fabric.
Figure 7.1
Warp Knitting Mechanism
Warp Knitting Mechanism
7.2 Warp Knitting Machine Classification
There are two types of warp knitting machines: Tricot and Raschel.
The distinction between Tricot and Raschel machines can be made by
the type of sinkers with which the machine is equipped, and the role
they play in loop formation.
Knitting and Knitted Fabrics
Warp knitting machines are usually flat machines, and each warp yarn
is knitted by one needle. All the needles of the machine are mounted
on a long needle bar equal to the width of the machine. When the
needle bar is activated, all the needles act in unison. Each yarn is
threaded through a yarn guide, and all the yarn guides are mounted on
a yarn guide bar. Movement of the guide bar moves all the yarns
mounted on it. The yarn guide bar moves laterally from left to right
for several wales, and then back again. It guides the yarn to a new
needle and wraps the yarn around it for its next stitch.
4-62
Knitting and Knitted Fabrics
Figure 7.2
Tricot Machine (Karl Mayer)
7.2.1 Tricot Machines
The sinkers used for tricot machines control the fabric throughout the
knitting cycle. The fabric is held in the throats of the sinkers while
the needles rise to clear and the new loops are knocked over in between
them. Modern tricot machines are constructed with compound needles,
while in the past tricot machines were equipped with beard needles.
Tricot machines are commonly equipped with from two to four yarn
guide bars and require the same number of warps to be used.
7.2.2 Raschel Machines
In Raschel knitting, the sinkers are only used to ensure that the fabric
stays down when the needles rise. The fabric is controlled by a high
take-up tension, for this reason, the fabric produced on a raschel machine
is pulled tightly downwards from the knitting zone, at an angle of
about 160o to the backs of the needles. In the past, a raschel machine
could be distinguished from a tricot machine by its use of latch needles;
however modern raschel machines use compound needles. Raschel
machines are usually equipped with a larger number of guide bars
than the tricot machines. The number ranges from 4 to 70 allow the
greater patterning capability of these machines. Two types of guide
bars are used in Raschel knitting. The first type is fully threaded and
used for the construction of the ground fabric. In most cases 1 to 3
such guide bars are used. The second type of guide bars are use to
apply the pattern onto the fabric. These bars usually require only 1
thread for each patterning repeat, so that only a few yarns are threaded
across the whole width of such a bar.
Textile Handbook 4-63
7.3 Knitting Elements of Warp Knitting Machine
7.3.1 Needle
Beard and latch needles are cast in units of 1 inch long. Compound
needles are set in tricks cut in the needle bed of the machine, while
the closing elements, being cast in units half an inch long, are set in a
separate bar.
Figure 7.3.1(1)
Beard Needle Unit
Figure 7.3.1(2) Latch Needle Unit
Knitting and Knitted Fabrics
Figure 7.3.1(3)
Compound Needle and Closing Element
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Knitting and Knitted Fabrics
7.3.2 The Sinker
The sinker is a thin plate of metal which is placed between each needle.
The sinkers are usually cast in units 1 inch long, which in turn are
screwed into the sinker bar. The neb of the sinker and throat are used
to hold down the fabric, while the belly of the sinker is used as a
knocking-over platform.
Figure 7.3.2
A Sinker Unit (Tricot Machine)
7.3.3 Guides and Guide Bars
The individual guides of a tricot machine are usually cast in 1 inch
units which in turn are fitted on the guide bars. The guides swing
between and around the needles in order to wrap the yarn around
them to form a new loop. They also shog sideways to join the wales
into a fabric. In a raschel machine, the bars are designed to be narrow
and light-weight strips of metal with individual guide fingers attached
so that a greater number of bars can be assembled. The guide bars
can be set in groups in the same displacement line called “nesting”.
Each nest can be considered as one guide bar for the swing movement.
Tube guide fingers can be used for bulky and fancy yarns.
Figure 7.3.3 (1) Jacquard Displacement Bar (Raschel Machine)
Textile Handbook 4-65
Figure 7.3.3 (2)
A Guide Unit
7.3.4 Driving Mechanisms of Knitting Elements
The guide bar needs a combination of a swing movement and a shogging
lateral movement to wrap the yarn around the needle and to displace
the yarn guides from one needle to another. The swing movement is
generated by a mechanism very similar to that which produces the
vertical movement of the needle. It is transmitted by the push rod and
converted by the lever into the swing movement of the guide bars.
The lateral movement of the guide bars is generated by the patterning
mechanism which consists of a pattern drum and pattern chain (see
Figure 7.3.4 (2)). A chain made of links of different heights is placed
on the pattern drum. While rotating, the different chain links move
the roller and slide so that the push rod moves the guide bar and
displaces it laterally.
Since raschel machines are equipped with more pattern guide bars, a
pattern mechanism which operates the guide bars through shogging
levers are used. In addition, an electronically controlled patterning
mechanism is used to replace the traditional chain link mechanism.
Figure 7.3.4 (1)
Main Shaft with Cranked Drive for Knitting Elements
(Tricot Machine)
Knitting and Knitted Fabrics
The needle bar and the sinkers are driven up and down or horizontally
by means of cams or eccentrics. In order to achieve a movement
containing the dwelling of the needle bar at the clearing position, the
eccentrics are connected to the needle bar by a crank assembly (see
Figure 7.3.4 (1)).
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Knitting and Knitted Fabrics
Figure 7.3.4(2)
Pattern Drum and Pattern Chain
7.4 Key Terms of Warp Knits
7.4.1 Course and Wales
Similar to weft knit, a horizontal row of loops is called a course while
a vertical column of loops form by a single needle is called a wale.
Figure 7.4.1
Two-guide Bar Loop Structure
7.4.2 Stitch Density
The stitch density in the fabric is defined as the total number of loops
in an unit area. The stitch density is the number of wales times the
number of courses in that area.
7.4.3 Loop Parts
The warp knitted loop structure is made of two parts. The first one is
the loop which is formed by the yarn being wrapped around the needle
and drawn through the previous loop. This part of the structure is
called an overlap. The second part is the length of yarn connecting
the loops, which is called an underlap. It is formed by the shogging
movements of the ends across the needles. The length of the underlap
is defined by needle spaces according to the shogging movement. The
longer the underlap, the more stable in widthwise direction, but a shorter
underlap will increase lengthwise stability.
Textile Handbook 4-67
In order to control the dimensional stability and the appearance of the
fabric, a second set of ends are knitted in an opposite shogging movement
to the first.
7.4.4 Open and Closed Laps
Two different lap forms are used in warp knitting, depending on the
way the yarns are wrapped around the needles to produce an overlap.
When the overlap and the next underlap are made in the same direction,
an open lap is formed. If the overlap and the following underlap are
in opposition to one another, a closed lap is formed.
Figure 7.4.4 Open and Closed Lap Configurations
Knitting and Knitted Fabrics
a = Open loop; b = Closed loop
7.4.5 Technical Back
The structure can be recognized by the underlaps floating on the surface
and is called the “technical back”. This side is facing the knitter
while working on the machine.
7.4.6 Technical Face
The loop structure shows on the “technical face” of the fabric. When
the fabric is formed by more than one set of yarn ends, all the yarns
which overlap the needle will appear in the loop.
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Knitting and Knitted Fabrics
7.4.7 Run-in
All yarn ends threaded through the guides of one guide bar knit the
same construction and are fed equally. The yarn consumption of each
guide bar is called “run-in” and is measured as the length of each
yarn knitted into the fabric during 480 knitting cycles. A cycle of 480
knitted courses is called a “rack”. By feeding different amounts of
yarn into the knitting zone, the size of the loops is changed. A longer
run-in produces a looser fabric while a shorter run-in produces small
and tight loops. When a new fabric is produced, the run-in should
always be recorded. This information will be very useful to reproduce
the fabric again at a later stage. When knitting with more than one
guide bar, the relative amount of yarn fed from each warp is very
important; this relation is called the “run-in ratio”.
7.5 Common Warp Knit Fabric Structures and their
Characteristics
7.5.1 Tricot Fabrics
Tricot fabrics are used for a wide variety of fabric weights and designs.
Typical uses for tricot fabrics are lingerie, sleepwear, blouses, shirts,
dresses, slacks, uniform for nurses, bonded fabric material, outerwear,
and automobile upholstery. Most lingerie tricot is two-bar fabric. Dress
wear tricot and men’s wear tricot are often three-bar or four-bar fabrics.
a) Plain tricot or tricot jersey: this is the basic fabric using
two-bar constructions. The most widely produced warp
knitted fabric is probably locknit. Locknit structure is
produced when the back guide bar shogs a 1- and -1 lapping
movement, and the front guide bar shogs two needle spaces.
The lapping movement of the two guide bars is illustrated
in Figure 7.5.1 a. Locknit gives a pleasant touch and a
considerable elasticity make the fabric most suitable for
ladies’ lingerie. Locknit construction tends to contract on
leaving the knitting zone. The final width may only be
two-thirds of the needle bar width. Locknit fabric is normally
produced on 28, 32 and 40 gauge machines.
Textile Handbook 4-69
Figure 7.5.1 a Locknit Loop Structure
FGB
BGB
FGB= Front Guide Bar
BGB= Back Guide Bar
Figure 7.5.1 b Three-needle Satin Loop Structure
FGB
BGB
c) Sharkskin : the sharkskin fabric is constructed as a reverse
version of satin. The structure shows the longer underlaps
of the back guide bar locked under the short underlaps of
the front guide bar. These trapped underlaps restrict the
shrinking potential of the fabric which is therefore more
rigid and more stable than locknit and satin tricot.
Knitting and Knitted Fabrics
b) Satin tricot : is a variation of the locknit structure with
an increased lapping movement up to 6 wales on the front
bar. While the technical face is similar in appearance to
locknit, the technical back is smoother and shiner. It should
be noticed that the longer the underlap floating on the
surface of the technical back, the heavier the fabric and
the greater the risk of snagging.
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Knitting and Knitted Fabrics
Figure 7.5.1 c
Sharkskin Loop Structure
FGB
BGB
d) Queen’s Cord : the fabric is formed when the front guide
bar moves in the shortest lapping so that the yarn is knitted
continuously on the same needle while the back guide bar
has a reciprocating 3- and-1 or 4- and -1 movement. The
dimensions of queen’s cord fabric change only very slightly
in width on leaving the knitting zone, and the final width
is very similar to the knitted width. If the front guide bar
is threaded with coloured yarns, a pin-stripe effect is
produced. This makes queen’s cord very popular for the
production of shirting fabric.
Figure 7.5.1 d
Queen’s Cord Loop Structure
FGB
BGB
Textile Handbook 4-71
e) Brushed Tricot (Pile Fabric) : Two-bar fabrics can be
produced or finished as pile fabric in order to improve
their appearance or their thermal properties. In brushed
fabric, the lapping movements of both bars are carried out
in the same direction. The fibres raised out of the long
underlaps of the front guide bar can be easily pulled out
during the finishing process. Brushed fabric is widely
used for robes and sleepwear. Using of heavier yarns,
fabrics for upholstery (automotive and furniture) can be
made.
Figure 7.5.1 e Brushed Tricot
Knitting and Knitted Fabrics
f ) Mesh-Effect and Fancy Open-Effect Tricot Fabrics :
By omitting some knitting needles and yarns at intermittent
places, mesh or open effect can be produced. These fabrics
are used for producing novelty lingerie or curtains.
Figure 7.5.1 f
Net Loop Structure (Tricot)
FGB
BGB
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Knitting and Knitted Fabrics
7.5.2 Raschel Fabrics
The large number of guide bars in a raschel knitting machine provides
the potential for wide diversification and great variation in raschel
fabric from fine laces to heavy blankets and even carpets. For example,
a widely used type of thermal underwear with a distinct waffle surface
effect is a raschel knit structure. Power net fabrics used in foundation
garments and swimwear are also raschel fabrics.
a) Net Fabrics: Net fabrics can be considered as one of the
major products manufactured by the raschel machine. Net
structures can be classified into the following two types:
(i) Structures with Vertical Pillars: The net in which the distance
between the vertical pillars (wales) is determined by the
distance between the knitting needles. Usually, the
horizontal mesh bars are produced by another set of yarns
which bridge the gap between each two wales. The shape
of the opening is determined by the lapping movement
and by the tension applied to the yarns. In most cases the
pillars (vertical chain of loops) can keep straight. To produce
this type of net structure, the guide bars are usually fully
threaded and the net appearance is obtained by using fine
yarns. A simple construction of this structures is illustrated
in Figure 7.5.2.a.(1)
Figure 7.5.2 a (1)
A Pillar and Inlay Loop Structure
FGB
BGB
Textile Handbook 4-73
Figure 7.5.2 a (2)
Marquisette Loop Structure
FGB
BGB
Knitting and Knitted Fabrics
Sometimes, the horizontal mesh bars may not necessarily
be produced during each knitted course. The Marquisette
net structure is formed in this way. The loop structure of
three-guide-bar Marquisette net is shown in Figure 7.5.2 a (2).
The front guide bar is constantly chaining to produce the
vertical pillars whilst the horizontal connections are produced
by the inlay yarns which are threaded in the back guide
bars. These two bars work in opposite direction during
the tracing of the vertical pillars and during the horizontal
crossings. It is usual to shog one of the back guide bars
by one needle space and the other one by two needle spaces.
In this way the fabric is sufficiently stable and is usually
finished to the same width in which it has been knitted.
Marquisette structures are very popular in the production
of net curtains.
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Knitting and Knitted Fabrics
(ii) Structure with Interlacing Pillars: The side connections
are formed by the inclination and distortion of the wale,
no special yarns are necessary to connect the pillars. The
typical openings of these nets are diamond shaped although
other openings can be produced. The basic structure of
this type of net is shown in Figure 7.5.2 a (3). To produce
this structure, the guide bars are threaded in a sequence of
1 in, 1 out. Both guide bars are constantly chaining with
each yarn to produce only one pillar on the same needle.
After a number of courses, the guide bars are shogged in
opposition to one needle space. During this course, each
of the guide bars draws its new loops through the loops
previously made by the adjacent yarns. When the connection
is made, each guide bar is shogged to its original position
and resumes the chaining lapping movement. The next
connection is carried out in the opposite direction to the
first and diamond shaped openings are formed. A typical
product of this type of structure is fishing net.
Figure 7.5.2 a (3) The Loop Structure of a Net with Diamond Shaped Openings
FGB
BGB
Textile Handbook 4-75
b) Dress laces : Lace fabrics are produced by multi-guidebar raschel machine with 32, 42, 56 or 78 guide bars and
usually with an electronically controlled patterning
mechanism. The ground structures of dress laces can be
classified into two major groups. One group is the tulle
ground structure (interlacing pillars) as shown in Figure
7.5.2. b (1) & (2) and the other is made of a chaining bar
with the pillars being pulled together and connected by
the patterning yarns as shown in Figure 7.5.2 b (3) & (4).
Figure 7.5.2 b (1)
A Tulle Net Loop Structure
Figure 7.5.2 b (2)
BGB
A Lace Fabric with Tulle Ground Structure
Knitting and Knitted Fabrics
FGB
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Knitting and Knitted Fabrics
Figure 7.5.2 b (3) A Lace Fabric with Ground Chains Connected by Patterning
Yarn