Warp Knitting Warp Knitting Technology •Warp knitting machines--needles are mounted...

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Transcript of Warp Knitting Warp Knitting Technology •Warp knitting machines--needles are mounted...

  • 4/13/2016 1

    Warp Knitting

    Basics

    March 26,2010

  • 4/13/2016 2

    Weft Warp

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    Warp Knits--the possibilities

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    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.

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    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.

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    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.

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    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).

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    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.

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    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.

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    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.

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    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.

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    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.

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    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.

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    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.

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    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.

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    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.

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    Tricot Knitting

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    Tricot Knitting

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    Tricot Knitting

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    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.

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    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.

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    Graphical Representation of

    Warp Knitting Structures

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    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.

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    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.

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    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.

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    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.

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    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.

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    Warp Knit Structure

    • In order to control both the lateral and longitudinal properties, as well as to pro