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Warp and Weft K nitting Principles. Dr. MIRELA BLAGA Faculty of Textiles and Leather Engineering, Iaşi, Romania.

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dr mirela blaga faculty of textiles and leather engineering ia i romania

Warp and Weft Knitting Principles

Dr. MIRELA BLAGA

Faculty of Textiles and Leather Engineering,

Iaşi, Romania

slide2

A warp knitted structure is produced on a warp knitting machine like Tricot or a Raschel. The structure is produced from a large number of yarns which run vertically (warp direction) in the fabric. The zig-zag movement is usually required to join the vertical wales. In most cases, the yarns are fed from warp beams [1].

A weft knitted structure is produced with a small number of yarns which runs horizontally (weft direction) in the fabric. The yarns are fed from bobbins positioned on a stand or a creel making the process efficient and simple.

Warp knitted loop structureWeft knitted loop structure

slide3

Weft Knitted Fundamentals [1]

A weft knitted structure is produced with a small number of yarns which runs horizontally (weft direction) in the fabric. The yarns are fed from bobbins positioned on a stand or a creel making the process efficient and simple.

“Reverse” side“Face” side

weft knitted structures
Weft Knitted Structures

Plain Knit 

  • Plain (single knit) is a knit structure family which is produced by the needles of only one needle bed, front or rear.
  • Since all the needles, participating in the production of plain knit are placed side by side in the same needle bed, they are all producing identical loops.
  • General characteristics:

- each side of the fabric is made of a single type of loop, ie either face or reverse;

- the fabric is stretchable although not always elastic. Usually, the fabric can be stretched much more in the width then in the length.

weft knitted structures7
Weft Knitted Structures

Double Knit

  • When the fabric is viewed from one side, it exhibits one wale made of face loops, one wale made on reverse loops and so on. The fabric is very elastic in the width direction. The reason for this behavior is the tendency of the yarns forming the individual loops to relax, straighten and regain their previous arrangement.
  • General characteristics:

- on each side of the fabric there are face and reverse wales. The arrangement is alternate in 1x1 rib and different in various other rib structures;

- the fabric usually being symmetrical on both sides, is not subjected to unbalanced stresses and does not curl which simplifies further handling;

- the tendency of the fabric to contract brings together the face wales of each side, hiding between them the reverse wales; this behavior makes the fabric look as if it made only of face loops on both sides (Rechts/Rechts – German, meaning Face/Face);

- rib structures are stretchable rather then elastic in the length direction;

- rib structures are bulkier and heavier then plain knit structures made of similar yarn thickness on machines of a similar gauge.

weft knitted structures8
Weft Knitted Structures

Purl Knit Constructions

  • In a basic 1x1 purl fabric, one course is made of face loops while the next course is made of reverse loops. The wale is thus made of alternative loops.
  • General characteristics:
  • - basic purl knit structures as 1x1 or 2x2 contract in the length direction, hide the face loops and show on both sides the needle and connection arches typical of reverse loops (Links/Links – German, meaning Reverse/Reverse);
  • - fabrics made of the purl structures have, due to contraction, a horizontal cord or rib effect which makes them elastic in the length direction; this is a great advantage, compared with the very limited lengthwise extensibility of plain or rib structures;
  • - the fabric is stretchable in the width
  • - purl knits are usually bulkier then plain knits.
warp knitted fundamentals 1
Warp Knitted Fundamentals [1]

Technical face

Technical back

warp knitting tricot machine construction
Warp Knitting (Tricot) Machine Construction

Yarns Supply:The large number of yarns required for the processes are fed from warp beams.

Knitting zone: The knitting elements process the yarns and convert their straight from into loops.

Take-Down zone: while the fabric is constructed, the take-up pulls it from the knitting elements and transports it to the fabric collection unit or the batching mechanisms.

The collection system rolls the fabric to facilitate finishing processes and to enable safe transportation.

knitting elements
Knitting elements

Yarn guides– there are thin plates of steel with a hole, each accommodating a yarn. A set of guides is rigidly connected to a guide bar and move together as one unit. All the yarns threaded in one guide bar come from a single beam.

The needles– are also made of stainless steel and have a hook which is used to form the loops. All the needles are connected to the needle bar and move simultaneously.

The sinkers - are place between the needles and combine with them in loop formation.

the knitting cycle
The Knitting Cycle

I. Clearing position

The needles are at the “clearing” position. At this height, the top of the needles’ hooks are leveled with the center of the guides’ holes. The closing elements are kept down so that the hooks are open. The fabric is held by the throats of the sinkers.

II. Overlap sequences

The needles are kept at the clearing position. The guides swing between the needles to the hook side as the first step of the “overlap” sequence.

The guides are moved laterally by one needle space and then swing out to complete the overlap. With this movement, each yarn is placed directly into the hook of a needle.

slide13
III. Underlap sequence

The needles start their descent. The closing elements are kept at the same height so that the hooks are closed. The overlapped yarns are within the hooks’s enclosure. The sinkers are moved back pushing the fabric up. The guide bar start their “underlap” lateral movement in which they are positioned in front of the needles to be overlapped in the next cycle.

IV. Knockover position

The needles and closing elements descend together into “knockover” position while maintaining closed hooks. New loops are pulled into the loops of the previous cycle.

V. Ascending to clearing position

One knitting cycle is completed and one course of loops has been formed across the width of the knitting machine. The sinkers move forward to hold the fabric in their throats. The needles ascend to “clearing” position. The closing elements ascend as well but their movement is shorter so that the hooks are opened.

basic designing principles
Basic Designing Principles
  • Structural representation
  • Lapping movement
  • Simplified representation of lapping movement

Simplified description of the lapping movement

the correspondence between the chain links and lapping movement
The correspondence between the chain links and lapping movement

The swinging movements, produced by the guide bar driving mechanism are represented by the dotted lines, while the shogging movements produced by the patterning mechanism, are represented by a fully-drawn line.

To traverse the guide bar, the patterning mechanism uses patterning links of different heights.

The link marked as 0 is the lowest one. The second pattern link available is marked with 1 and is higher than link 0 by one needle space.

common lapping movements in warp knitting 2

Lapping

e-english

g-german

f-french

e - closed pillar

g - geschlossene Franse

stitch

f - chaînette fermee

Loop

structure

Lapping movement

Chain notation

1 – 0

1 – 0

Knitted fabric

e - open pillar

stitch

g - offene Franse

f - chaînette ouvert

1 - 0

0 - 1

Common Lapping Movements in Warp Knitting [2]
slide17

Lapping

e-english

g-german

f-french

e- closed 1x1 lap

g-geschlossener

Trikot

f- tricot fermée

Loop

structure

Lapping movement

Chain notation

  1 - 0

1 - 2

Knitted fabric

e - open 1x1 lap

g - offener Trikot

f - tricot ouvert

0 - 1

2 - 1

slide18

Lapping

e-english

g-german

f-french

e - closed 2x1 lap

g – geschlossenes

Tuch

f - drap fermée

Loop

structure

Lapping movement

Chain notation

1 - 0

2 - 3

Knitted fabric

e- open 2x1 lap

g- offenes Tuch

f- drap ouvert

0 - 1

3 - 2

slide19

Lapping

e-english

g-german

f-french

e - closed 3x1 lap

g - geschlossener Satin

f - satin fermée

Loop

structure

Lapping movement

Chain notation

3 - 4

1 - 0

Knitted fabric

e - open 3x1 lap

g - offener Satin

f - satin ouvert

4 - 3

0 - 1

slide20

Lapping

e-english

g-german

f-french

e - closed 4x1 lap

g - geschlossener Samt

f - velours fermée

Loop

structure

Lapping movement

Chain notation

4 - 5

1 - 0

Knitted fabric

e- open 4x1 lap

g- offener Samt

f- velours ouvert

5 - 4

0 - 1

slide21

Lapping

e-english

g-german

f-french

Loop

structure

Lapping movement

Chain notation

0 - 1

2 - 3

4 - 5

7 - 6

5 - 4

3 - 2

0 - 1

Knitted fabric

e - 3 rows open atlas

g - 3 reiniger offener Atlas

f - 3 rangée ouvert

1 - 0

3 - 2

5 - 4

6 - 7

4 - 5

2 - 3

1 - 0

e - 3 rows closed atlas

g - 3 reinige

geschlossener Atlas

f - 3 rangée fermée

slide22

Lapping

e-english

g-german

f-french

Loop

structure

Lapping movement

Chain notation

Knitted fabric

e - open Koper pillar

g - offene

Koperfranse

stitch

f - chaînette Koper ouvert

0 - 2

2 - 0

e - closed Koper pillar

g - geschlossener Koperfranse

f-chaînette Koper fermee

2 – 0

2 - 0

slide23

Lapping

e-english

g-german

f-french

Loop

structure

Lapping movement

Chain notation

2 - 0

1 - 3

Knitted fabric

0 - 2

3 - 1

e - open Koper 1x1 lap

g – offener

Kopertricot

f - tricot Koper ouver

e - closed Koper 1x1 lap

g – geschlossener

Kopertricot

f- tricot Koper fermée

two guide bars constructions 1

The knitting elements of a tricot knitting machine are:

  • - compound needles
  • closing elements
  • sinkers
  • guide bars.
  • The two guide bars are used to accommodate the yarns fed from two separate beams.
  • The two sets of yarns are independently driven to knit different movements which are combined in one fabric.
Two Guide Bars Constructions [1]

The properties of a fabric construction depends on three main factors:

1.      1. The parameters of the different movements;

2.      2. The direction of the movements in relation to each other;

3. The position of each movement within the fabric structure.

slide25

Flexible Fabrics [3]

E: Double tricot

G: Rechts/Links-

Trikot-Trikot

weifadensystemig

It is produced with two sets of yarns in two guide bars. The opposite movements of the two sets correct the natural tendency of the loops to incline thus greatly improve the appearance of the fabric. This construction is flexible due to the short underlaps of both bars. The fabric is light weight but not very popular since it tends to split if one of the loops is dropped.

E: Locknit

G: Rechts/Links-

Tuch-Trikot-

Zweifadensystemig

F: Charmeuse

The most popular tricot fabric is produced with a tricot lap (1 and 1) on the rear guide bar and a jersey lap (2 and 1) on the front guide bar. The longer underlaps produced by the front guide bar float on the technical back and make the fabric smooth and soft. If the back guide bar is threaded with elastic yarn, a classic type of swimwear is formed.

E: Satin

G: Rechts/Links-

Satin-Trikot- zweifadensystemig

An increased underlap on the front guide bar creates a fabric with longer floats on the technical back, as shown in the drawing opposite. This fabric is called “satin” due to its very smooth shiny surface. The fabric is heavier then Locknit and has a better cover factor. As all fabrics with long underlaps produced by the front guide bar and short underlaps produced by the back guide bar, it shrinks inthe width immediately after leaving the needles.

slide26

Semi-stable and stable fabrics

E: Reverse Locknit

G: Rechts/Links-

Trikot-Tuch zweifadensystemig

F: Renversé

A longer underlap produced by the back guide bar results in different fabric characteristics. In this case, the longer underlaps are locked under the shorter underlaps of the front guide bar and their movements is thus restricted. The fabric shrinks much less while coming off the machine and is much less flexible. The surface of the fabric is rough and fabric “hand” is more rigid. Since the underlaps of the rear guide bar are not very long, the fabric is considered “semi-stable”.

E: Sharkskin

G: Rechts/Links-

Trikot-Satin

zweifadensystemig

An even longer underlap produced by the back guide bar results in a heavier fabric. The longer underlaps are locked under the shorter underlaps of the front guide bar and their movements is thus restricted. This fabric shrinks only slightly while coming off the machine and is very rigid. The surface is rough which accounts for its name “Sharkskin”

E: Queen’s Cord

G: Rechts/Links-

Franse-Satin

zweifadensystemig

The most stable, two guide bar tricot fabric is achieved with the shortest movement on the front guide bar (ie. Pillar stitch) and a long movement on the back guide bar. The fabric hardly shrinks coming off the machine and thus has very little elasticity. With the pillar stitch on the front guide bar, the fabric may be patterned with “pin stripes” by threading the front bar with different color yarns.

[3]