Warp knitting

Manufacturing process

Warp knitting is defined as a loop forming process in which the yarn is fed into the knitting zone, parallel to the fabric selvage. It forms vertical loops in one course and then moves diagonally to knit the next course. Thus the yarns zigzag from side to side along the length of the fabric. Each stitch in a course is made by many different yarns. Each stitch in one wale is made by several different yarns.

Credit for the invention is usually given to a mechanic called Josiah Crane in 1775. He likely sold his invention to Richard March who patented (No. 1186) a warp frame in 1778. In the intervening three years March likely had discussed the device with Morris who submitted a similar patent (No.1282) for a twisting machine for making Brussels point lace. These early machines were modifications of the stocking frame with an additional warp beam. In 1795, the machine was successfully used to make lacy fabrics. Warp frames could be used with any thread, and the warps provided a fixed anchor for the transverse threads. In 1786, Flint invented the point bar which kept the threads at a fixed distance. In 1796, Dawson introduced cams to move the bars, and regulate the twist. Brown and Copstake succeeded in imitating Mechlen net. Lindley invented the bobbin in 1799, and Irving and Skelton the regulator spring. In 1802, Robert Brown of New Radford patented the first twist frame, a knitter that could produce wide net. Whittaker's frame of 1804 had half its thread mounted on a warp beam and half wound on bobbins mounted on a carriage. Heathcote's 1808 improvement of Whittaker's frame was essentially a warp knitting frame. The bobbin carrying beam was reduced to the same size as the machine he called it a bobbinet. Heathcote's second patent, in 1809, was for a bobbinet that could produce wide fabrics; this was the Old Loughborough.

In general, warp knitting machine is to distinguish between tricot and raschel by the type of sinkers with which the machine is equipped and the role they play in loop formation. The sinkers used for tricot knitting machines control the fabric throughout the knitting cycle. The fabric is held in the throats of the sinkers while the needles rise to clear and the new loops are knocked over in between them. In Raschel knitting, however, the fabric is controlled by a high take up tension and the sinkers are only used to ensure that the fabric stays down when the needles rise.

Tricot is very common in lingerie and underwear. The right side of the fabric has fine lengthwise ribs while the reverse has crosswise ribs. The properties of these fabrics include having a soft and 'drapey' texture with some lengthwise stretch and almost no crosswise stretch.

Milanese is stronger, more stable, smoother and more expensive than tricot and, hence, is used in better lingerie. These knit fabrics are made from two sets of yarn knitted diagonally, which results in the face fabric having a fine vertical rib and the reverse having a diagonal structure, and results in these fabrics being lightweight, smooth, and run resistant. The Jacquard apparatus was adapted to it in the 1870s. The Raschel machine could work at higher speeds than the Leavers machine and proved the most adaptable to the new synthetic fibres, such as nylon and polyester, in the 1950s. Most contemporary machine made lace is made on Raschel machines. Raschel knits do not stretch significantly and are often bulky; consequently, they are often used as an unlined material for coats, jackets, straight skirts and dresses. These fabrics can be made out of conventional or novelty yarns which allows for interesting textures and designs to be created. and is commonly used for the production of composite materials and technical textiles. Stitch bonding machines are used for the sewing processing of nonwoven fabric, to increase its fastness and toughness. The stitch bonding warp knitting machine or Non woven warp knitting machine is for producing technical textiles such as shoe interlining, shopping bag, geotextile dewatering bags, reinforced composite glass fiber textile and other fabrics. As a method of production, stitch bonding is efficient, and is one of the most modern ways to create reinforced textiles and composite materials for industrial use. The advantages of the stitch bonding process include its high productivity rate and the scope it offers for functional design of textiles, such as fiber reinforced plastics. This is created through a warp knitting thread system, which is fixed on the reverse side of the fabric with a sinker loop, and a weft thread layer.

Needle shift technique is when both outer warp layers are secured in one procedure by incorporating a shift of the needle bar during stitching, creating endless possibilities for the arrangement and patterns in stitch bonding. that for the building of only one loop at one cycle there are 18 geometric configurations of the yarn ends – 3 different directions from which the guide is coming, multiplied by 2 loop types open or closed, multiplied by 3 different directions in which the yarn/guide is after that going left, up, or right). For two guide bars the configurations are combinations and the modern machines have 4 and more guide bars. Kyosev and Renkens created various versions of CAD software for 3D design of warp knitted fabrics and contributed with it in a book with the fundamentals of the patterning, where about 100 samples can be downloaded and viewed as 3D structure.

Warp knitted fabrics have several industrial uses, including producing mosquito netting, tulle fabrics, sports wear, shoe fabric, fabrics for printing and advertising, coating substrates and laminating backgrounds. Research is also being conducted into the use of warp knitted fabrics for industrial applications (for example, to reinforce concrete), and for the production of biotextiles.

The warp knitting process is also being used to create biotextiles. For example, a warp knitted polyester cardiac support device has been created to attempt to limit the growth of diseased hearts by being installed tightly around the diseased heart. Current research on animals "have confirmed that the implantation of the device reverses the disease state, which makes this an alternative innovative therapy for patients who have side effects from traditional drug remedies".