Warp Knitting Basicslibvolume8.xyz/textile/btech/semester5/knitting... · 2016-05-09 · Warp Knit...

64
4/13/2016 1 Warp Knitting Basics March 26,2010

Transcript of Warp Knitting Basicslibvolume8.xyz/textile/btech/semester5/knitting... · 2016-05-09 · Warp Knit...

4/13/2016 1

Warp Knitting

Basics

March 26,2010

4/13/2016 2

Weft Warp

4/13/2016 3

Warp Knits--the possibilities

4/13/2016 4

4/13/2016 5

4/13/2016 6

Needle Technology

• Until relatively recently warp knitting machines used four types of needle:

– The bearded needle

– The latch needle

– The compound needle

– The carbine needle

• Bearded and compound needles were used on tricot machines, the latch needle on raschel and crochet machines and the carbine needle on crochet machines.

4/13/2016 7

4/13/2016 8

4/13/2016 9

4/13/2016 10

Knitting Technology

• Recently the bearded needle has been

dropped and development has focused on the

compound needle due to its greater rigidity

and ability to withstand higher yarn lapping

forces (see Loop formation) than the bearded

or latch needle.

4/13/2016 11

Knitting Technology

• Furthermore at the highest speeds (above

2,500 cycles/minute) the issue of latch impact

on the hook starts to become a problem with

latch needles.

• In contrast the compound needle can be

closed gently in a controlled manner even at

the highest knitting speeds.

4/13/2016 12

Warp Knitting Technology

• Warp knitting machines--needles are mounted

collectively and rigidly in a horizontal metal

bar (the needle bar that runs the full knitting

width of the machine).

• Equally the yarn guides are also set rigidly into

a horizontal metal bar (the guide bar that runs

the full width of the machine).

4/13/2016 13

Knitting Element Displacements

• The diagram

summarizes the

somewhat confusing

displacements made by

the guide bar. The front

of the machine lies to

the right of the

diagram.

4/13/2016 14

Knitting Element Displacements

• The diagram shows the individual yarn guides set in a solid bar. The front-to-back movements are called swings. The first swing from front to back is followed by a lateral shog: the overlap, which wraps the yarn in the needle hook.

4/13/2016 15

Knitting Element Displacements

• The next movement is a

swing from back to

front followed by the

underlap that may be

from 0 to 8 needle

spaces depending on

the fabric structure

being knitted.

4/13/2016 16

Tricot Knitting

• In diagram (1.3 a & b)

the guide bar swings

from the front of the

machine (on the right

hand side of the

diagram) to the back of

the machine taking the

yarn through the gap

between two adjacent

needles.

4/13/2016 17

Tricot Knitting

• Diagram (1.4 c) shows the guide bar moving laterally towards the observer. This is known as a shog movement, specifically the overlap that wraps the yarn around the beard of the needle.

• Diagram (1.4 d) shows the second swing in the cycle taking the yarn between adjacent needles back to the front of the machine. At this time the needle bar moves upwards to place the overlap below the open beard on the shank of the needle.

4/13/2016 18

Tricot Knitting

• Diagram (1.5 e) shows the presser bar moving forward to close all the needles and in (1.5 f) the closed needle passes down through the old loop and the sinkers move backwards to release the old loops so that knock-over can take place.

4/13/2016 19

Tricot Knitting

• In figure (1.6 g) the sinker

bar moves forward to

secure the fabric prior to

the needle rising in the

next cycle and at this

stage the guide bar makes

a second shog, this time

an overlap which may be

of 0 to 8 needle spaces

depending on the

structure being knitted.

4/13/2016 20

Tricot Knitting

• The machine type in this series of diagrams is a tricot machine and on this type of machine there is no continuous knock-over surface.

• The belly' of the sinker provides support to the fabric by preventing the underlaps from moving downwards.

• For this reason it is not a good idea to knit fabrics with few underlaps such as net or lace on a tricot machine.

• They are much better knitted on a Raschel machine with a continuous knock-over trick plate.

4/13/2016 21

Tricot Knitting

• The diagrams you are about to see illustrate a tricot machine with compound needles.

• The sequence of events is almost exactly the same as for the bearded needle with the exception that the overlap lays the yarn into the open hook and not onto the beard, and the compound needle is closed by relative displacement between the needle and the closing element.

4/13/2016 22

Tricot Knitting

4/13/2016 23

Tricot Knitting

4/13/2016 24

Tricot Knitting

4/13/2016 25

Guide Bar Shog, Overlap and Underlap

• The displacements shown for the needle,

sliding latch, guide bar swing and sinker bar

are the same irrespective of the type of fabric

being produced by the machine.

4/13/2016 26

Guide Bar Shog, Overlap and Underlap

• The shog movements determine the type of fabric produced and they need to be changed each time the fabric structure is modified.

• Crucially the shog movements must place the guides at the centre of the gap between adjacent needles with 100% accuracy every knitting cycle for the entire lifetime of the machine.

• If there was a failure in the shog displacement and the needle bar moved by less than a full needle pitch then in all likelihood the yarn guides would collide with the needles during the swing movement causing serious damage to the machine.

4/13/2016 27

Graphical Representation of

Warp Knitting Structures

4/13/2016 28

Warp Knit Structure

• Warp knitting is defined as a stitch forming process in which the yarns are supplied to the knitting zone parallel to the selvedge of the fabric, i.e. in the direction of the wales.

• In warp knitting, every knitting needle is supplied with at least one separate yarn.

• In order to connect the stitches to form a fabric, the yarns are deflected laterally between the needles.

• In this manner a knitting needle often draws the new yarn loop through the knitted loop formed by another end of yarn in the previous knitting cycle.

4/13/2016 29

Warp Knit Structure

• A warp knitted structure is made up of two parts. The first is the stitch itself, which is formed by wrapping the yarn around the needle and drawing it through the previously knitted loop.

• This wrapping of the yarn is called an overlap. The diagram shows the path taken by the eyelet of one yarn guide traveling through the needle line, making a lateral overlap (shog) and making a return swing. This movement wraps the yarn around the needle ready for the knock-over displacement.

4/13/2016 30

Warp Knit Structure

• The second part of stitch formation is the

length of yarn linking together the stitches

and this is termed the underlap, which is

formed by the lateral movement of the yarns

across the needles.

4/13/2016 31

Warp Knit Structure • The length of the underlap is defined in terms

of needle spaces.

• The longer the underlap, the more it lies at

right angles to the fabric length axis.

• The longer the underlap for a given warp the

greater the increase in lateral fabric stability,

• conversely a shorter underlap reduces the

width-wise stability and strength and

increases the lengthways stability of the

fabric.

4/13/2016 32

Warp Knit Structure

• The length of the underlap also influences the fabric weight.

• When knitting with a longer underlap, more yarn has to be supplied to the knitting needles.

• The underlap crosses and covers more wales on its way, with the result that the fabric becomes heavier, thicker and denser.

• Since the underlap is connected to the root of the stitch, it causes a lateral displacement in the root of the stitch due to the warp tension.

• The reciprocating movements of the yarn, therefore, cause the stitch of each knitted course to incline in the same direction, alternately to the left and to the right.

4/13/2016 33

Warp Knit Structure

• In order to control both the lateral and longitudinal properties, as well as to produce an improved fabric appearance with erect loops, a second set of yarns is usually employed. The second set is usually moved in the opposite direction to the first in order to help balance the lateral forces on the needles. The length of the underlap need not necessarily be the same for both sets of yarns. – Run-in: the yarn consumption during 480 knitted courses

– Rack: a working cycle of 480 knitted courses

• The run-in

………….is the yarn consumption for one rack.

4/13/2016 34

Warp Knit Structure

• For a given machine with a given warp:

– A longer run-in produces bigger stitches and a

generally slacker, looser fabric

– A shorter run-in produces smaller and tighter

stitches

– With more than one guide bar the ratio of the

amount of yarn fed from each warp is termed the

run-in ratio

4/13/2016 35

Lapping Diagrams

• With the exception of the

very simplest structures,

it is too time consuming

to represent warp knitted

fabric using stitch or loop

diagrams. For this reason

two methods of fabric

representation are

commonly used.

– Lapping diagrams

– Numerical representation

4/13/2016 36

Looping Diagrams

Actual Guide Movement

• This is the symbolic image

of the technological process

of lapping. This diagram can

also be derived from a stitch

chart by not drawing in the

stitch legs but only the head

and feet of the stitches.

4/13/2016 37

Looping Diagrams

• The needle heads are represented on paper as dots. The path of the guide bars is drawn in front of and behind the needles

• The yarns will not lie as straight in the fabric as they do when they are conducted through the guide bars and around the needles on the machine. The yarn path in the lapping diagram is rounded off to represent this

4/13/2016 38

Looping Diagrams

• Each dot represents one needle and each horizontal row of dots a single stitch forming process, i.e. one course. Several rows of dots from bottom to top represent the succession of several stitch-forming processes or courses recording a complete repeat of the fabric structure.

4/13/2016 39

Numerical Notation Related to Chain Link

Height

• The numerical notation

is best understood in

relation to the

mechanical system that

is used to generate the

lateral displacements

(shogs) of the guide

bars.

4/13/2016 40

Numerical Notation Related to Chain Link

Height

• If the pattern drive is on the right hand side of the machine, then the movement of the guide bar from the smallest chain link height (0) is only possible towards the left. With a chain link (1), the guide bar is moved to the left by one needle space (division), with a chain link (2) by two needle spaces, etc.

4/13/2016 41

Numerical Notation Related to Chain Link

Height

• On dotted paper, therefore, the numbers read from right to left and are entered between each needle space. The numbering is done from left to right when the pattern drive is on the left-hand side of the machine. The lateral movement of the guides is initiated by chain links of various heights marked with 0, 1, 2, 3, 4, etc. This guide bar movement is an especially important part of the pattern development.

4/13/2016 42

Chain Link Arrangement

• The guide bar is positioned with the follower roller on chain link 0'; it swings through, then moves to the left as the roller moves to chain link 1'. It swings back and returns to its starting position (chain link 0').

– The chain should read: 0

1

– In the opposite direction: 1

0

• The smallest repeating unit (repeat) extends over one course: height repeat = 1 stitch, width repeat = 1 stitch.

4/13/2016 43

Chain Link Arrangement

• Application

– Pillar stitch construction can be employed in the

production of outerwear and for ribbed velour

fabrics (corduroy). Even in these fabrics, the open

pillar stitch is more popular as it provides the

necessary longitudinal stability and runs freely. It

is used in conjunction with the binding element

in-lay' in laces and curtains, though always with a

second guide bar.

4/13/2016 44

Open and Closed Stitches

• The stitch formed has an open or

closed character according to the

direction of the underlap and overlap

motions. The underlaps can be of

differing magnitudes and directions:

– If the underlap and overlap are in

opposite directions then the stitch

formed would have a closed character

– If the underlap and overlap are in the

same direction, then the stitch formed

will have an open character

4/13/2016 45

Open and Closed Stitches

• The stitch is open when the feet do not cross and closed when the feet cross. The structure of a warp knitted fabric depends on the lapping motion of the guide bars, and therefore the structure could be represented by:

– Drawing a stitch or stitch chart diagram, which takes time and is difficult

– Lapping diagram

4/13/2016 46

Yarn Threading Plan

• In warp knitting a yarn guide wraps the yarn around the needle hook, thus forming a loop. However, to form a fabric, the yarn guide must wrap the yarn around a different needle during the next course. The yarn guides, therefore, must be displaced laterally during knitting. Different warp knitted structures are produced by varying the magnitude of their lateral displacement. Therefore warp knitted structures can be described by noting the guide bar displacement.

4/13/2016 47

Yarn Threading Plan

• The actual guide bar

motion consists of an

underlap, swing-

through, overlap and

swing-back movement,

and this motion is

known as lapping.

4/13/2016 48

Yarn Threading Plan

• The yarn is wrapped around the needle hook due to the swing-through, overlap and swing-back movement of the yarn guide, and this forms a stitch. A warp knitted fabric is, therefore, made from stitches (overlap) and connecting underlaps.

4/13/2016 49

Single Bar Structures

• A plain warp knitted structure is produced on a single needle bar. The resulting structures are known as single face fabrics. Rib and interlock warp knitted structures are produced on double needle bars, and these structures are known as double face fabrics.

• In single face structures (plain), stitches are visible on one side, known as the technical face, and on the other side (known as the technical back) only underlaps are visible.

4/13/2016 50

Pillar Lap

• A pillar stitch (or chain

stitch) is a stitch

construction where lapping

of a yarn guide takes place

over the same needle.

• As there are no lateral

connections between the

neighboring wales, the

stitches are only

interconnected in the

direction of the wales.

4/13/2016 51

Pillar Lap

• Due to the absence of underlaps, a fabric is not created, only chains of disconnected wales.

• Single bar pillar lap is technically possible only on Raschel machines where the trick plate acts a knock-over bed.

• On a tricot machine the sinkers are unable to control the position of the old loop when there is no underlap (pillar stitch) and so the knitting of pillar stitch on its own is impossible.

4/13/2016 52

Pillar Lap

• Open or closed pillar

stitches can be

produced depending on

the guide bar

movement.

4/13/2016 53

1 and 1 Lap (Tricot Lap)

• The laps are executed in alternate overlap and underlap motions on two defined needles.

• This stitch creates a textile fabric as the underlaps connect both the courses and the wales.

• The simplest of this group of structures is made between two adjacent needles.

4/13/2016 54

1 and 1 Lap (Tricot Lap)

• The laps are executed in alternate overlap and underlap motions on two defined needles.

• This stitch creates a textile fabric as the underlaps connect both the courses and the wales.

• The simplest of this group of structures is made between two adjacent

needles.

4/13/2016 55

1 and 1 Lap (Tricot Lap)

• Guide bar motions:

• First course:

Under 1 needle to the right ↓(UL)

swing through 1

over 1 needle to the right ↓(OL)

Swing Back 0

4/13/2016 56

1 and 1 Lap (Tricot Lap)

• Second course:

Under 1 needle to the left ↓

swing through 1

over 1 needle to the left ↓

Swing Through 2

4/13/2016 57

1 and 1 Lap (Tricot Lap)

• Result:

• Therefore, the chain link arrangement is:

1

0

1

2 closed 1 and 1 stitch

• As a result of the underlaps, the diagonal sinker loops are formed. These pull the stitch heads of each alternate row into the same direction.

4/13/2016 58

2 and 1 Lap

• Swing through → 1

• swing back → 0

• swing through →2

• swing back → 3

• swing through → 1

• swing back → 0

4/13/2016 59

3 and 1 Lap

• Swing through → 1

• swing back → 0

• swing through → 3

• swing back → 4

• swing through → 0

• swing back → 1

• swing through → 4

• swing back → 3

4/13/2016 60

4 and 1 Lap

• Swing through → 1

• swing back → 0

• swing through → 4

• swing back → 5

4/13/2016 61

Atlas Lap

• The atlas construction

differs in that the laps

are continued over two

or more courses in one

direction and then

return in the other

direction to the point

where they started.

• Lapping movement • 0-1/2-1/3-2/4-3/5-4/3-4/2-3/1-2/

4/13/2016 62

• video

4/13/2016 63

4/13/2016 64

Stitch Diagram and Notation?