Warp Knitting, Production of warp knitted fabric

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Knitted fabrics are divided into two general types: (1) those produced by weft knitting, where one continuous yarn forms courses across the fabric; (2) those produced by warp knitting, where a series of yarns forms wale’s in the lengthwise direction of the fabric. 

Warp Knitting 

This form of knitting is very different from standard hand knitting; the earliest warp knitting machine was Crane’s tricot machine (England), built about 1775. In warp knitting, a yarn is fed to each needle from the lengthwise direction. A bar guiding the yarns to the needles can move from side to side, or to the front or back of the needle, so that the loops can be interlocked in a zigzag pattern. Very wide (over 400 cm, nearly 170 in.), flat fabric can be produced by warp knitting, at speeds in the order of 1,000 courses per minute, giving almost 3 m2/min (3.6 sq. yds./min). The two main machine (fabric) types are tricot and raschel. 

Diagram of simple warp knit fabric. 

Tricot warp knitted fabric: Tricot is a machine with one needle bar (spring beard type) and one to three guide bars, +0 3++most are two-bar or three-bar. The spring beard needle, accepting mainly filament yarns, has limited the depth of texture that can be achieved in tricot fabrics; some fine spun tricot, produced on machines with hybrid needles, was introduced many years ago, but does not seem to have taken hold in the market place. Tricot does not ravel, can curl somewhat, and has almost no stretch or “give” lengthwise but a little crosswise. 

Raschel warp knitted fabric: Raschel is the other main warp-knitting machine. Fabric from these machines may be of any weight or thickness from lace to carpet; the one feature they share is a pillar-and-inlay effect; Wales like hand crochet chains forming the “pillar” with other yarns laid in to form patterns or the main body of the fabric, usually making up the right side. Raschel machines have one or two needle bars (usually latch, but may be spring beard), set horizontally on wide or narrow machines with 1 to over 30 guide bars. The multi guide bar types are used mostly for laces; most of our moderate-priced laces are knit on this type of machine. They do not have the depth of texture that the twisted Leavers laces or the embroidered Schiffli laces have. Powernet, knit on the raschel machine, incorporates elastomeric yarn to give one- or two-way power stretch for contour fashion Variations on raschel-type machines include crochet, ketten raschel, and Cidega machines. The latter, similar to raschel, can knit various fabrics side by side, and so is used for many narrow trims called “braids,” such as gimp and ball fringe. 

Minor Warp Knits: Simplex is a machine with two horizontal needle bars and two guide bars, producing a double tricot type of warp knit in a fine gauge, with two threads to each loop. The needles in one bar are directly behind those in the other, in much the same way that needles in the weft knit interlock are aligned; like interlock, simplex looks like plain-stitch jersey on both sides. The fabric is very firm and stable, used for its greater firmness in lounge wear, uniforms, and gloves.

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Weft Knitting, Produce weft knitted fabric

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Weft Knitting 

There are three fundamental stitches in weft knitting: (1) plain knit stitch, (2) purl stitch, (3) rib stitch. Novelty stitches are variations of these three stitches. The hand method of knitting is weft knitting. On a knitting machine, the individual yarn is fed to one or more needles at a time 

1. Plain-knit Stitch: The plain knit is the basic form of knitting. It can be produced in flat-knit or in tubular (or circular) form. The flat knit is also called jersey stitch because the construction is like that of the turtleneck sweaters originally worn by English sailors from the Isle of Jersey; it is sometimes called balbriggan stitch after the hosiery and underwear fabrics made in Balbriggan, Ireland. Plain flat knits may be shaped or full-fashioned. The knitting is done with a row of latch or beard needles arranged in a linear position on a needle plate or in a circular position on a cylinder. All the needles are evenly spaced side by side and are moved by cams, which act on the needle butts. The spacing of the needles is referred to as the gauge, gage, or cut. As applied to many flat knits and some circular ones, gauge refers to the number of needles in 11/2 inches; for example, a 60-gauge machine would have 40 needles per inch. 

2. Purl Stitch: This construction is also referred to as the link-sand links stitch after the German word “links,” or on the left). It is made on flat-bed and circular machines by needles using hooks on both ends to alternately draw loops to the front of the fabric in one course and to the back in the next course. It is a slower and more costly technique. The fabric looks the same on both sides and resembles the back of the plain knit. Like the plain knit, the purl knit will run up and down if a loop is broken. But a purl knit fabric will not curl at the edges. 

3. Rib Stitch: Rib-knit fabrics have alternating lengthwise rows of plain and purl stitches constructed so that the face and back of the fabric appear alike. This may be produced either on a flat rib machine or a circular rib machine. In the flat rib machine, one set of needles is placed opposite the other set of needles is placed opposite the other set of needles in an inverted V position of 45 degrees to the horizontal; in the circular rib machine, one set of needles is placed vertically in a cylinder and the other set of needles is placed horizontally on a dial. In both machines, one set of needles pulls the loops to the front and the other set pulls the loops to the back of the fabric. Each set of needles alternately draws loops in its own direction, depending upon the width of the rib desired. 

For example, rib stitches can be 1 x 1, 2 x 2, 2 x 1, 3 x 1, and so on. A combination of 1 x 1 and 2 x 2 is called an accordion rib. Rib construction is costlier because of the greater amount of yarn needed and the slower rate of production Rib knits are made on a two-bed machine with one set of needles forming the loops for one wale and the other set of needles forming the alternating wale.Rib knits have greater elasticity in the width than in the length. They are stable and do not curl or stretch out of shape as do the jersey knits. For this reason, they are often used to make cuffs and necklines on weft knitted garments. Rib knits are reversible unless the number of stitches in the alternating wales is uneven, as in a 2 X 3 rib.

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Knit Fabric; Different types and classification of knitted fabric

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Single Jersey Knits Fabric  

Knitting Machines with one needle bed and one set of needles are called jersey machines or single-knit machines. With one set of needles used for knitting and one needle bed, all needles face the same direction; all stitches are pulled to the same side of the knitted fabric. As a result, single jersey fabrics have a smooth face with a vertical grain on the right side of the fabric and a width wise grain on the back side. The knittig loops formed by the jersey machine are formed in one direction only, which gives a different appearance to each side of the fabric. The basic knit fabric produced by this knitting machine is known alternately as a plain, single knit, or jersey. The terms are interchangeable.Jersey stretches slightly more in the crosswise than the lengthwise direction. If one stitch breaks, the fabric may ladder, or run. Jersey fabrics tend to curl at the edges and are less stable than are some other types of knits. This is the result of the pressures exerted during knitting. In addition jersey knits may twist or skew after laundering, as the twisting tensions imposed during the knitting process are relaxed. 

Special finishing techniques are used to overcome these tendencies and maintain fabric stability; the principal ones use starches, gum mixtures, polyvinyl acetate emulsions, and resins. 

A great many items of hosiery, sweaters, and other wearing apparel are made from plain jersey knits. Consumer Brief 16.1 highlights one of the common uses of jersey knit fabrics: Tshirts. Plain knit fabrics can also be made into designs of two or more colors by use of a patterning mechanism that controls the selection and feeding of yarns and types of stitches to create jacquard knits. 

Double Jersey Knit Fabrics 

The term double knit is generally applied by consumers to fabrics that are, technically, double jersey fabrics. Double jersey fabrics are also made on two-bed knitting machines, but the arrangement of the needles is different from that for knitting rib fabrics. The layers of loops alternate from one side to the other, locking the two layers together. Double knit fabrics have the same appearance on both sides of the fabric, that is, exhibiting the appearance of the face or outer side of a single knit on both sides. Twice as much yarn is incorporated into double knit fabrics as into comparable single knits 

Interlock Knit fabric

Interlock knits are produced on a special machine that has alternating long and short needles on both beds. Long and short needles are placed opposite each other. Long needles knit the first feeder yarn; short needles knit the second feeder yarn. The fabric created is an interlocking of two 1 X 1 rib structures. The resulting fabric, like double knit fabrics, is thicker than single knit fabric, and more stable in the width wise direction. Interlock fabrics have been traditionally used for underwear. They are produced more slowly than are other rib knits and are generally made in plain colors or simple patterns because the addition of pattern slows down the manufacture even further 

High Pile Fabrics 

High-pile fabrics, such as imitation furs and plushes, are usually knitted by a jersey machine. While the knitting is taking place, a sliver of staple fiber is fed into the machine. These fibers are caught in the tight knit and are held firmly in place. Although any staple fiber can be used for the pile, the greatest quantity of these fabrics are made with acrylic and modacrylic fibers in the pile. By using staple fibers of varying lengths, adding color through fiber dyeing or printing on the surface of the pile, and by shearing or brushing the pile, an enormous variety of effects can be achieved. The use of knitted pile fabric ranges from excellent imitations of furs, such as leopard, tiger, mink, or mouton, to colorful pile outerwear, coat linings, or pile carpet fabrics.

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