Warp knitting
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- dress
- floor covering
- yarn
- fibre
- cloth
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- Verviers - Facts
The two types of warp knitting are raschel, made with latch needles, and tricot, using bearded needles.
Raschel
Coarser yarns are generally used for raschel knitting, and there has recently been interest in knitting staple yarns on these machines. In the Raschel machine, the needles move in a ground steel plate, called the trick plate. The top of this plate, the verge, defines the level of the completed loops on the needle shank. The loops are prevented from moving upward when the needle rises by the downward pull of the fabric and the sinkers between the needles. Guide bars feed the yarn to the needles. In a knitting cycle, the needles start at the lowest point, when the preceding loop has just been cast off, and the new loop joins the needle hook to the fabric. The needles rise, while the new loop opens the latches and ends up on the shank below the latch. The guide bars then swing through the needles, and the front bar moves one needle space sideways. When the guide bar swings back to the front of the machine, the front bar has laid the thread on the hooks. The needles fall, the earlier loops close the latch to trap the new loops, and the old loops are cast off. Raschels, made in a variety of forms, are usually more open in construction and coarser in texture than are other warp knits.
Tricot
Tricot, a warp knit made with two sets of threads, is characterized by fine ribs running vertically on the fabric face and horizontally on its back. The tricot knitting machine makes light fabrics, weighing less than four ounces per square yard. Its development was stimulated by the invention of the so-called FNF compound needle, a sturdy device that later fell into disuse but that made possible improved production speeds. Although approximately half of the tricot machines in current use make plain fabrics on two guide bars, there is increasing interest in pattern knitting. In this type of knitting, the warp-knitting cycle requires close control on the lateral bar motion, achieved by control chains made of chunky metal links.
Special effects in warp knits
The scope of warp knitting has been extended by the development of procedures for laying in nonknitted threads for colour, density, and texture effects (or inlaying), although such threads may also be an essential part of the structure. For example, in the form called “zigzagging across several pillars,” the ground of most raschel fabrics, the front bar makes crochet chains, or “pillars,” which are connected by zigzag inlays.
An extension of conventional warp knitting is the Co-We-Nit warp-knitting machine, producing fabrics with the properties of both woven and knitted fabrics. The machines need have only two warp-forming warps and provision for up to eight interlooped warp threads between each chain of loops. These warp threads are interlaced with a quasiweft, forming a fabric resembling woven cloth on one side.
Other interlaced fabrics
Net and lace making
The popularity of handmade laces led to the invention of lace-making machines. The early models required intricate engineering mechanisms, and the development of the modern lace industry originated when a machine was designed to produce laces identical with Brussels lace. In the Heathcot, or bobbinet, machine, warp threads were arranged so that the threads moved downward as the beams unwound. Other threads were wound on thin, flat spools or bobbins held in narrow carriages that could move in a groove or comb in two rows. The carriages carrying the bobbins were placed on one side of the vertical warp threads and given a pendulum-like motion, causing them to pass between the warp threads. The warp threads were then moved sideways, so that on the return swing each bobbin thread passed around one of them. Then the warp threads moved sideways in the opposite direction, thus completing a wrapping movement. In addition, each row of bobbins was moved by a rack-and-pinion gearing, one row to the left and one to the right. As these movements continued, the threads were laid diagonally across the fabric as the warp was delivered. Improvements on the Heathcot machine followed through the 19th century: Nottingham-lace machines, used primarily for coarse-lace production, employ larger bobbins, and the pattern threads are wound independently on section spools; in another type, the Barmens machine, threads on king bobbins on carriers are plaited together, sometimes with warp threads.
Schiffli lace, a type of embroidery, is made by modern machines, evolved from a hand version, using needles with points at each end. Several hundred needles are placed horizontally, often in two rows, one above the other. The fabric to be embroidered is held vertically in a frame extending the full width of the machine, and the needles, supplied with yarn from individual spools, move backward and forward through the fabric. At each penetration a shuttle moves upward and interlaces yarn with the needle loop. Movement of both fabric and needles is controlled by Jacquard systems.
Many types of machine-made laces are made, frequently with geometrically shaped nets forming their backgrounds. Formerly made only of cotton, they are now frequently made from synthetic fibre yarns. Bobbinet lace, essentially a hexagonal net, is used as a base for appliqué work for durable non-run net hosiery, and, when heavily sized, for such materials as millinery and veilings. Barmens lace has a fairly heavy texture and an angular pattern; flowing lines, heavy outline cords, and fine net backgrounds are not usually made on Barmens machines.
The introduction of light-resistant polyester yarns led to a revival of Nottingham machine-made curtains. Leavers lace is available in an infinite variety of patterns, since the manufacturing technique allows use of almost any type of yarn. The high strength and comparatively low cost of synthetic fibre yarns has made sheer laces widely available.
Net, an open fabric having geometrically shaped, open meshes, is produced with meshes ranging from fine to large. Formerly made by hand, the various types are now made on knitting machines. Popular types include bobbinet, made with hexagonal-shaped mesh and used for formal gowns, veils, and curtains, and tulle, a closely constructed fine net having similar uses. Fishnet, a coarse type with knots in four corners forming the mesh formerly made by fishermen, is now a popular machine-made curtain fabric.
Braiding or plaiting
Braid is made by interlacing three or more yarns or fabric strips, forming a flat or tubular narrow fabric. It is used as trimming and for belts and is also sewn together to make hats and braided rugs. Plaiting, usually used synonymously with braiding, may be used in a more limited sense, applying only to a braid made from such materials as rope and straw.
Noninterlaced fabrics
With the exception of felt, nonwoven materials are in the early stages of development. There is controversy about the precise meaning of the term nonwoven, but one authority defines nonwoven fabrics as textile fabrics made of a fibrous layer having randomly laid or oriented fibres or threads.
Felt
Felts are a class of fabrics or fibrous structures obtained through the interlocking of wool, fur, or some hair fibres under conditions of heat, moisture, and pressure. Other fibres will not felt alone but can be mixed with wool, which acts as a carrier. Three separate industries manufacture goods through the use of these properties. The goods produced are wool felt, in rolls and sheets; hats, both fur and wool; and woven felts, ranging from thin billiard tablecloths to heavy industrial fabrics used for dewatering in the manufacture of paper. Felts of the nonwoven class are considered to be the first textile goods produced, and many references may be found to felts and their uses in the histories of ancient civilizations. The nomadic tribes of north central Asia still produce felts for clothing and shelter, utilizing the primitive methods handed down from antiquity.
Bonding
Several methods for making nonwoven materials are now firmly established, and others are being developed.
In adhesive bonding, fabrics are made by forming a web of fibres, applying an adhesive, then drying and curing the adhesive. The web can be produced by a garnett machine or a conventional card, several layers being piled up to obtain the required thickness. Such webs are weak across the width, but this does not limit their use for certain end products. A more uniform product results from cross laying the web. Other machines, such as the Rando-Webber, lay down the fibres by an airstream.
The fibres in the web may be stuck together in various ways. The web may be sprayed with an emulsion of an adhesive—e.g., a latex based on synthetic rubber, acrylic derivatives, or natural rubber—or, alternatively, may be carried on a mesh screen through a bath of latex, the excess being squeezed out by a pair of rollers. Adhesives may also be applied as a foam or a fine powder. Thermoplastic fibres can be incorporated in the blend and on heating will bond together, giving strength to the mass of fibres.
Mechanically bonded nonwoven products (or fibre-bonded nonwovens) are webs strengthened by mechanical means. The web, sometimes reinforced by a thin cotton scrim in the middle or by texturized yarns distributed lengthwise through it, is punched by barbed needles mounted in a needle board. The fibres in the web are caught up by the needle barbs, and the resulting increased entanglement yields a compact product sufficiently strong for many purposes. Modern needle-felting or punching machines perform 900 punches per minute, and selection of appropriate needles is based on the fibre being processed and the desired product.
The Arachne machine, the best known unit for stitch bonding, operates much like a warp-knitting machine. Fibrous web is fed into the machine, and stitches are made by a series of needles placed about eight millimetres apart, giving the web longitudinal strength; lateral strength is provided by the fibre interactions. The products are attractive for many purposes and can be improved by treatment with polyester resins to increase their wear resistance and with thermosetting precondensates to reduce their tendency to pill (e.g., to form small tangles). A new device attached to the Arachne machine permits introduction of weft ends at every single course, making colour effects possible. Araloop machines yield loop-pile fabric suitable for towels and floor coverings.
Three sewing-knitting machines were invented in East Germany in 1958. In the Malimo machine process, warp yarns are placed on top of filling yarns and stitched together by a third yarn. The Maliwatt machine interlaces a web of fibres with a sewing thread, giving the effect of parallel seams. The Malipol machine produces a one-sided pile fabric by stitching loop pile through a backing fabric. A new British process makes double-sided terry fabric, called Terrytuft, by inserting pile yarn into a backing and knotting it into position.
Webs made of yarns having a core of one polymer and an outer sheath of another material having a lower softening point may be lightly pressed and then heated to an appropriate temperature. The core yarn will “spot weld” together at the junction points, binding the mass of fibres together. Products made in this way find uses as industrial fabrics, coatings, and interlinings.
Laminating
The joining of one fabric to another by an adhesive such as natural rubber has long been practiced in rainwear manufacture. Composite materials were later joined by bonding a layer of polyurethane or other foam to a conventional textile fabric. The two components were stuck together by flame bonding or by an adhesive in the form of a continuous coating, in spots, or as a powder. This laminating process has been extended to the joining of two layers of fabric. Each fabric layer can be quite thin, and the amount and type of adhesive are chosen to add only minimum stiffening. Such materials offer a variety of applications. A coating fabric, for example, may be joined to a lining; dimensionally stable composites can be made from cloth layers that are in themselves dimensionally unstable. Acetate knitted fabrics are frequently used as backing material in laminates.
