Warp Knitting

Warp knitting represents the fastest method of producing fabric from yarns. Warp knitting differs from weft knitting in that each needle loops its own thread. The needles produce parallel rows of loops simultaneously that are interlocked in a zigzag pattern. Fabric is produced in sheet or flat form using one or more sets of warp yarns. The yarns are fed from warp beams to a row of needles extending across the width of the machine (Figure 9b). Two common types of warp knitting machines are the Tricot and Raschel machines. Raschel machines are useful because they can process all yarn types in all forms (filament, staple, combed, carded, etc.). Warp knitting can also be used to make pile fabrics often used for upholstery.

Warp knitting is the sequential formation and interlinking of loops in an axial direction on a lateral array of needles with at least one separate thread being supplied to each needle. The loops are joined together in a widthwise direction by moving the threads back and forth between adjacent needles.

Warp knit structureWarp 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.

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 travelling 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.

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.

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.

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.

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.

1  Guide bars

2  Needle bar 

3  Closure bar

4  Compound sinker bar

The Copcentra range includes tricot machines from 2 to 4 guide bars. All types are equipped with the LIBA compound needle system. The proportion between needle shaft length and thickness ensures resistance to lateral drift. The edges of the guides are rounded resulting in a smooth yarn path. Thus the processing of microfibres is  possible at high operating speeds. All knitting elements are fitted on special light and strong  hollow profile bars

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

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.

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

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.

1.1 Lapping diagram

1.2 Actual guide movement

Numerical notation related to chain link heightThe numerical notation is best understood in relation to the mechanical system that is used to generate the lateral displacements (shogs) of the guide bars (refer to the module Warp knitting machine technology for a description of the shogging mechanism).

1.3 Guide bar movement due to chain link heightIf 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. 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.

Chain link arrangementThe 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: 01

In the opposite direction: 10

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

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.

Open and closed stitches

1.4 Open stitch

1.5 Closed stitchThe 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

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

Yarn threading plan

1.6 Yarn guide movement around a needleIn 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.

The actual guide bar motion consists of an underlap, swing-through, overlap and swing-back movement, and this motion is known as lapping.

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.

Single bar structuresA 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.

Pillar lap

1.7 Lapping diagram for pillar stitch constructionA 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 neighbouring wales, the stitches are only interconnected in the direction of the wales. 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.

Open or closed pillar stitches can be produced depending on the guide bar movement.

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.

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.

1.8 1 and 1 lap (tricot lap)Guide bar motions:

First course:

Under 1 needle to the right ↓(UL)swing through 1over 1 needle to the right ↓(OL)swing back 0Second course:

under 1 needle to the left ↓swing through 1over 1 needle to the left ↓swing through 2Result:

Therefore, the chain link arrangement is:

10

  1  2 closed 1 and 1 stitchAs a result of the underlaps, the diagonal sinker loops are formed. These pull the stitch heads of each alternate row into the same direction.

2 and 1 lap

1.9 2 and 1 lapswing through → 1swing back → 0 swing through →2swing back → 3 swing through → 1swing back → 03 and 1 lap

1.10 3 and 1 lapswing through → 1swing back → 0

swing through → 3swing back → 4

swing through → 0swing back → 1

swing through → 4swing back → 34 and 1 lap

1.11 4 and 1 lapswing through → 1swing back → 0

swing through → 4swing back → 5Atlas lap

1.12 Atlas lapThe 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/

Double bar structuresRules for plotting lapping diagrams

The lapping movement of each guide bar must be represented separately The lapping diagrams of all guide bars must be plotted from the same course in

order to illustrate the relative lateral position of the guides

Guide for creating lapping diagrams

Dotted papers are used to create lapping diagrams.

1. Plot the lapping movement of the first guide bar2. Plot the lapping movement of the second guide bar starting from the same course

3. Number the spaces between the needles from right to left if the patterning mechanism is on the right hand side of the machine. Number the spaces separately for each guide bar

4. Consider only the overlap in order to generate the chain-link arrangements of the guide bars

Threading arrangement of guide barsThe threading arrangement describes how individual yarn guides should be threaded i.e. which should be threaded and which should be left empty.

Fully threaded: all the guides are threaded with yarns 2-in 2-out: first two guides to be threaded with yarns while the next two to be left

empty - this sequence should be continued right across the guide bar

Important

If the guide bars are to be partly threaded, or threaded with different coloured yarns, then the lapping diagram of the guide bars must be supplemented with the threading arrangement of the guide bars. The two sets of information must always correspond so that they both represent the swing-through position of the guide bars in the first knitting course.

It is also customary to draw a threading diagram when the sequence is long.

Rules for drawing threading diagrams

A short vertical line represents a guide with a yarn A dot represents an empty guide A row consisting of above symbols to represent a guide bar

Double tricot structure

1.14 Double tricot structureLapping movement

Front & back guide bars 1 and 1 lap in opposite directions

Threading arrangement

Front & back guide bars fully threaded

Fabric characteristics

Light weight fabric; splits very easily if a yarn breaks or a stitch drops

Locknit structuresLapping movement

Front guide bars 2 and 1 lap

Back guide bar 1 and 1 lap in opposite directions

Threading arrangement

Front & back guide bars fully threaded

Fabric characteristics

Good elasticity Due to free-floating underlaps the fabric has a smooth back, which is very

pleasant to touch. Light weight Non-splitting Edge curling towards the technical back The structure contracts in the lateral direction after leaving the needles by about

67% (the structure was traditionally knitted on E28 machines but today knitting on E32 - E40 is becoming popular)

Generally used to produce ladies lingerie

Satin structures

1.15 Satin structureLapping movement

Front guide bars 3(4) and 1 lap

Back guide bar 1 and 1 lap in opposite directions

Threading arrangement

Front & back guide bars fully threaded

Fabric characteristics

The fabric shrinks after leaving the needles. This is due to the long underlaps Good elastic properties Very comfortable to wear Edge curling towards the technical back

As the length of the underlaps increases, the structure exhibits a smooth and shiny technical back, but at the same time the structure becomes heavier

Reverse locknit structuresLapping movement

Front guide bars & bsp 1 and 1 lap

Back guide bar 2 and 1 lap in opposite directions

Threading arrangement

Front & back guide bars fully threaded

Fabric characteristics

Not so stable as locknit

Shark skin structureLapping movement

Front guide bars 1 and 1 lap

Back guide bar 3(4) and 1 lap in opposite directions

Threading arrangement

Front & back guide bars fully threaded

Fabric characteristics

The trapped longer underlaps restrict the fabric shrinkage Rigid and very stable structure (more stable than other structures) Rough technical back; the reason for the name

Queen s cord

1.16 Queen s cord structureLapping movement

Front guide bars pillar lap

Back guide bar 3(4) and 1 lap in opposite directions

Threading arrangement

Front & back guide bars fully threaded

Fabric characteristics

High degree of stability Minimum lateral shrinkage after leaving the needles; i.e. final width of the fabric is

closer to that of the knitted width

Net structuresNet structures can be classified into the following groups:

1. Net structures in which the distance between the wales is determined by the gap between the needles used to knit the structure. Generally the yarns of a second set of yarns are used to bridge the gap between the wales. The shape of the opening is determined by the lapping movement and by the tension in the yarns. If the yarn tension is high it would cause the wales to distort, but generally the pillars are vertical or almost vertical.

2. Net structures that are formed by interconnecting pillars. The side connections are achieved by inclining and distorting neighbouring wales. The typical openings of these nets are diamond shaped. It is also possible to produce nets with other openings.

Net structures with vertical pillars

1.17 Marquisette net structure

1.18 Structure with vertical pillarsThese net structures are produced using fully threaded yarn guide bars. The net appearance is achieved by using yarns that are too fine for the needles of the machine. Due to the longer underlaps of the laid-in yarns connecting a large number wales the net structure is relatively dense and has a very high width-wise stability. The fabric will not split if one of the chain stitches break.

The marquisette net structure is produced by not laying the yarns in every consecutive course. The front guide bar produces a pillar lap while the back guide bars lay yarns in opposite directions. The fabric is stable and is usually finished to the same width in which it was knitted.

Lapping movements

Front guide bar 1-0//

2nd guide bar 2-2/0-0/1-1/0-0/2-2/1-1//

3rd guide bar 0-0/3-3/2-2/3-3/0-0/1-1//

Net structures with interconnected wales

1.19 Net structure with interconnected wales

The basic structure of such a net is produced by the guide bars that are threaded 1-in and 1-out. Principally each guide bar produces a pillar lap. After knitting a predefined number of courses the guide bars carry out an underlap of one needle spacing in opposite directions. In this course the needles form knitted loops through those previously formed by neighbouring yarns.

Laying-in structuresA guide bar is used to insert yarn ends into the fabric structure. The laid-in yarn end is not knitted into the structure, but it is held in the structure between the stitches (in the technical front) and the underlaps (formed by other yarns in the technical back).

Basic principal of laying-in

1. Laying-in is achieved using a back guide bar. Generally, at least one fully threaded guide bar in front of the laying-in guide bar(s) produces the ground structure.

2. A laying-in guide bar can be fully or partially threaded. Fully threaded laying-in guide bars increase the fabric stability. Partially threaded laying-in guide bars are utilised for patterning purposes.

3. The laying-in guide bars carry out only the underlaps.

Advantages of laying-in

Laying-in technique allows one to knit yarns that are otherwise difficult to knit Any yarn which is capable of passing freely through the guide eye and between

the needles can be inserted into the fabric Laid-in yarns contribute very little towards the fabric weight because of the lack of

loops Saves on patterning yarn, which is usually more expensive, i.e. a commercial

advantage

Designers can use this technique to enlarge the range of designs by laying-in yarns with coarser counts (up to thousands of dtex) and yarns of different texture. Laying-in technique is used in creating lace and curtain fabrics

Warp knitting machine technologyMachine architecture / constructionWarp knitting machines produce the widest range of fabric types and qualities of any fabric forming technology. There is a vast range of machine sizes, types and configurations, ranging from 10cm-wide crochet machine to a five metre-wide geotextiles machine. Consequently it is difficult to encapsulate such a range within a simple description. The diagram and summary show a typical knitting machine producing fabric for apparel.

1.1 Basic structure of a single bar knitting machineThe main machine frame is constructed from sturdy cast steel or welded vertical side frames held together and stabilised by a large welded steel box section transverse girder. The needle bar and the yarn guides are mounted transversely above the box section girder in the middle of the machine and run virtually the full width of the machine. Machine widths range from 1 metre to 5 or 6 metres depending on the type and end use of the fabric.

The yarn supply may be carried on warp beams situated above the knitting elements on beam control systems mounted on the side frames. Alternatively the beams may be mounted on A-frames behind the machine to permit greater beam capacities, or the machine may be supplied from individual yarn packages mounted in creels behind the machine.

The fabric is taken away downwards and to the front of the machine to a take-up roller, or it may travel under a walkway for the operator, to be taken-up on a bulk fabric roller that is remote from the machine.

Warp knitting machines are divided into two classifications: tricot and raschel, each of which uses a different configuration of knitting elements and is suitable for producing different types of fabric structure.

Modern warp knitting machines are engineered to operate at high knitting speeds (up to 3,000 cycles/minute) and these machines may produce in excess of 5 square metres/minute.

Needle technologyUntil 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.

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.

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.

On warp knitting machines the 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).

Subsequent diagrams (1.2 - 1.6) show a bearded needle knitting on a tricot machine.

Knitting element displacementsThe diagram summarises the somewhat confusing displacements made by the guide bar. The front of the machine lies to the right of the diagram.

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.

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.

1.2 Guide bar movementTricot knitting: 1 of 2In 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.

1.3 Bearded needle knittingDiagram (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.

1.4 Bearded needle knittingDiagram (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.

1.5 Bearded needle knittingIn 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 (see the module Warp knit fabric structures).

1.6 Bearded needle knittingThe 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'

Tricot knitting: 2 of 2The diagrams (1.7 to 1.9) 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.

1.7 Compound needle knitting

1.8 Compound needle knitting

1.9 Compound needle knittingRaschel knittingAgain the basic sequence of events is the same with diagram (1.10 a) showing the needle bar starting to move upwards from knock-over and the holding down sinkers moving forward over the fabric to prevent it rising with the needles. At the same time the underlap is taking place.

In (1.10 b) the needle moves upward through clearing and the latch wire prevents the latch from flicking closed as the old loop drops off.

In (1.10 c) the front to back swing of the guide bar is followed by the overlap that wraps the yarn into the open hook of the needle.

1.10 Single needle bar knittingIn (1.11 d) below, the guide bar swings from the back to front of the machine. In (1.11  e) the needle bar drops the needles towards knock-over and the sinkers have retracted to allow the old loops to pass over the hooks and in (1.11 f) the needles continue their descent to pull the new loop.

Note that the fabric is supported by the top of the trick plate, which runs continuously across the front of the machine.

1.11 Single needle bar knittingYarn feeding technologyYarn is fed to the needle typically from a warp beam that will contain yarns spaced at the same pitch as the machine gauge. Modern warp beams may contain 30,000 to 50,000 metres of warp.

On earlier raschel machines and even today on raschel machines with more than six guide bars and warp systems, the yarn tension developed in the warp by the pull of the needles was used to turn the warps against a warp tension controlled warp brake system or let-off.

The diagram (1.12) illustrates such a let-off system. The warp sheet (shown in grey) pushes on the rocking bar and as the tension builds the brake is released to feed the warp towards the needles. This type of let-off is relatively cheap and is the only option when the machine has a large number of guide bars.

The problem is that as the warp is used up and the warp diameter reduces the same warp tension exerts a lower torque on the warp beam and the amount fed forward tends to reduce. This changes the quality of the fabric unless adjustments are made periodically to the brake band.

1.12 Warp let off systemThe solution to this problem is to replace the brake release with a DC or servo motor drive that will rotate the warp beams to release a precise length of yarn to each cycle of the knitting elements. This is positive feeding and it produces a consistent loop length in the fabric from the beginning to the end of the warp. It is the only system suitable for high speed, high production modern machines.

Knitting element displacement technology

The diagram is a displacement/time diagram showing the displacements against degrees of rotation of the main shaft of the machine for each of the knitting elements of a modern high speed compound needle tricot machine.

On earlier warp knitting machines the displacements were derived from cylindrical cams but they become noisy and unreliable at speed in excess of 400 revolutions/minute. Modern machines are driven by displacements derived from crankshafts. These eccentric drives generate simple harmonic motion (SHM) displacements similar to the blue displacement shown for the guide bar swing.

In order to generate the modified SHM necessary for the other elements the SHM displacement is linked to a multi-bar chain that alters the movement, producing the necessary dwells, for example in the sliding latch, shown by the purple trace, when it lags behind the upward movement of the needle hook, thus causing the needle to open.

1.13 Time displacement diagramsCrankshaft drives are robust and are capable of speeds in excess of 3,000 revolutions/minute and have a long working life at those speeds.

uide bar shog, overlap and underlap: 1 of 2The 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.

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. On earlier machines the shog displacements were generated by links in a pattern chain.

The diagram shows a chain link pattern mechanism. The chain links pass around the drum B in the diagram and the cam follower attached to the pivoting segment A runs along the profile cut in the different size links of the chain.

As a result the up and down movements of the cam follower translate into later movements of the guide bar in such a way that a chain link size 0 places the right hand yarn guide before the right hand needle. A chain link size 1 places the same guide in the first gap. A chain link size 2 places the guide in the second gap and so on.

This method is reliable and safe but it is a slow process to put together long pattern repeats and the system is noisy and will not run at speeds higher than 600 cycles/minute.

1.14 Chain link mechanismGuide bar shog, overlap and underlap: 2 of 2At speeds higher than this there are two alternatives to the chain link system. Firstly the displacements can be cut into the diameter of a disk cam, which may hold 16 cycles of shogs. The second is to use an electrically programmed bank of eccentric drives to generate the required displacements.

The diagram shows the way in which this system works. The eccentrics are engaged to the rotating shafts by electromagnets. When they are engaged they push a roller between two sliding segments of the vertical column thus creating an upward displacement. This can be seen in the diagram where the topmost eccentric has engaged and rotated pushing the small roller between the two topmost segments producing a shog of 16 needle positions in this case.

This array of eccentrics enables any displacement from 1 needle position produced by the bottom eccentric, through 2,3,4,5,6 and up to 16 and then step by step up to 32.

This allows the patterning to be controlled by electronic means rather than a cumbersome mechanical system.

1.15 Electronic pattern mechanismsTake-down technologyThe take-down system on warp knitting machine is relatively simple as compared with weft knitting machine. The fabric is drawn down through the nip of a two or three roller system driven by a gear train or by chains and gears directly from the main shaft of the machine.

In the diagram roller 1 is the main driven roller pulling the fabric from the sinker via yarn tension a1. Roller 2 is a pressure roller pressed against roll 1 by spring 3 to prevent the fabric slipping. The fabric passes through the nip between roller 1 and 2. The other group of three rolls show the fabric being wound-up on the fabric roller.

1.16 Fabric take-up systemsMachine controlThe machine control systems are relatively simple compared to a v-bed weft knitting machine. They comprise: a motor controller, which drives the main motor; typically 2 to 6 DC or synchronous motor controllers to control the warp let-off systems; a microprocessor to control the electronic shogging system if fitted and finally, a production statistics system, which logs and records the total number of revolutions and stoppages etc.

Tricot machines Characteristics

• Compound sinker bar (2-point knockover).• Warp beams are placed mainly at the back of the machine or perhaps above the machine.• Needles can be changed from the front side of the machine.

• Up to 5 guide bars are used at the moment.• Use of compound needles.• Starting-up without fabric take-up possible.• Only pillar loops cannot be knitted (only by support through inlay motion),(lateral 2-point knock-over)• Angle between incoming yarn sheet and fabric take-up is 90° (considerable needle stress).• Simple machine construction.• Short run-in of the threads because of the beam positions.• High number of courses possible up to total stop of the beams (for pleats) because working without fabric take up is possible.• High yarn run-in is possible (overfeed).• Handling of the knitting elements from the knitter's side possible.• Piles for terry effects are possible.• Simple construction of pile fingers for plush.• Soft fabric touch.

Disadvantages of Tricot machines

• Problems with small number of stitches and reduced yarn run-in (fabric take-up 90°) (high tension for the needle, loose selvedges lead to yarn twisting and fault).• Processing of elastomeric yarn mainly possible only as loop.• Net constructions are difficult to be made since the knock-over of the wales connection is not possible(lateral 2-point knock-over).• Processing of filler yarns is very difficult (see fabric take-up,90°).• Common machine gauges from E 24 to E 40.

Raschel machines Characteristics

• Separate knock-over bar (trick plate) 3-1point knock-over and stitch comb bar.• Warp beams are placed on the top of the machine.• Needles have to be changed from the back side of the machine (due to the knock-over comb bar).• Nowadays up to 78 guide bars are possible.• Usage of compound needles and sometimes of latch needles.• Loop formation without fabric take-up is not possible;main knockover at the front edge (take-up).• Angle between incoming yarn sheet and fabric take-up is 170°(low needle stress).• High take-up tension allows the production of open fabric structures and the manufacture of elastomeric inlays (powernet) as well as the production of elastic pleated fabrics.• Vertical laying-in (filler threads) can be processed (170°fabric take-up).• The high yarn tension does not affect the needles directly. Hence, low stitch densities and short yarn run-in possible at high fabric stability and low needle stress.• Various materials can be used: film tapes, glass,aramide, carbon, metal wires.• Wide range of gauges.

Disadvantages of Raschel machines

• Starting-up only with fabric take-up possible.• Loose yarn run-in (overfeed) and high stitch densities(velvet, pleats) are not possible fabric touch less soft.• Longer yarn path due to beam positions.• Changing of needles only from the back side.

he kind of knitting elements depends of the respective warp knitting machine type.Here with the knitting elements

on tricot warp knitting machine and raschel warp knitting machine.The knitting elements mounted on its bar.

1. Knitting elements on tricot warp knitting machine

2. Knitting elements on raschel warp knitting machine

  

3.Knitting elements on double needle raschel warp knitting machine.

On Karl Mayer double needle bar raschel machines there used latch needle for working needle instead of

compound needle. 

4. Knitting elements on stitch bonding warp knitting machine,Malimo type