Basics of KNITTING - An introduction K nitting is the second most frequently used method of fabric construction. The term “Knitting” describes the technique of constructing textile structures by forming a continuous length of yarn into columns of vertically intermeshed loops. VASANT R KOTHARI - has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his first input from the series of articles that will be published in upcoming issues of knitting Views) 20/KNITTING VIEWS/JANUARY-FEBRUARY 2010 Knitted fabrics have been gaining popularity during the past two decades, thanks to the increased versatility of techniques and adaptability of the many new manmade fibres. Knitted fabrics are now widely used in the applications where woven fabrics formerly predominated. Today, the usage of knitted fabrics ranges from hosiery, underwear, sweaters, slacks, to rugs and other home furnishings. Why knits are popular? Knitted fabrics are popular today because: • It is usually soft and drapes well • It molds and moves easily with body movement • It has good stretch ability • It resists wrinkles • Most importantly, knits relate well to contemporary life-styles History From the beginning the art of knitting was an occupation for women. Traditional hand knitting, using knitting needles or pins, has been practiced for thousands of years. The earliest example of true knitting is a pair of knitting socks found in Egypt, dating back to 1100 A.D -just over 9 centuries ago! Socks and stockings were knitted because they had to be shaped to the foot or leg. By the 16th century knitting had advanced into a craft, the first real evidence of a production knitting machine was the stocking frame, invented by the Reverend William Lee in 1589. The invention laid the foundation for the development of knitting technology. Lee’s invention enabled the knitting of loops at 10 times the speed of traditional hand pin knitting. Difference between knitting and weaving The major difference between knitted and woven structures lies in the way the yarns are interconnected geometrically. In weaving, two sets of parallel yarns are interconnected by interlacing them at right angles. Different woven structures are produced by varying this basic principle. In knitting, the yarns are initially formed into loops, and then these loops are interconnected in a variety of ways in order to produce a textile structure. Based on this principle, a textile fabric is produced by using only one set of yarns. Woven fabric Knitted fabric Less extensibility High extensibility High elastic recovery Incomplete elastic recovery Less crease resistance High crease resistance Generally fabric is thin (For the same yarn count) Fabric is thicker (For the same yarn count) Easy to tear Difficult to tear Requires ironing Ironing not required High pleat sharpness Less pleat sharpness Less permeability to air More permeability to air Stronger fabrics Less stronger fabrics Feel of the fabric is softer Weaving Knitting More rigid as compared Converting yarn into fabric by interlacement of warp and weft Converting yarn into fabric by interloping using knitting elements No such problems The capital investment is high Capital investment is usually lower Any small defect occurring in the fabric can lead to further damage in the cloth because it cannot be mended easily Not easy as compared with knitting Setting up a machine is easy and faster Tested by loading or extending fabrics in warp/weft Tested by multi-directional fabric bursting strength test Less productivity High productivity Design modification is difficult Styles and designs can be changed easily and faster As a result of this interlooping of yarns, the structure of a weft or a warp knitted fabric is more open when compared to the structure of a woven fabric. Because of this interloping of yarns, a knitted fabric could be stretched more than a woven fabric, even when only a small force is applied. Once this force is eased the fabric slowly returns to its original dimensions. In fact, weft and warp knitted fabrics have higher elongation values than woven fabrics due to their structure, and their elastic behaviour generally exceeds the elastic properties of the yarns used to knit the fabric. 21 KNITTING VIEWS/JANUARY-FEBRUARY 2010/ Due to the structure and good elastic behaviour of knitted fabrics, knitted garments are comfortable to wear. The air trapped in the loops of a knitted garment insulates the human body against cold. At the same time the relatively loose and open structure aids in the perspiration process of the human body, especially when the knitted fabric is made of yarns spun from natural fibres. Due to the interlooping of yarns, the knitted fabrics also have better crease recovering properties compared to fabrics woven from similar yarns. Classification of knitted fabrics The knitting industry is divided into two distinct sectors, weft knitting and warp knitting. Weft knitting In weft knitting, the loops are formed across the width of the fabric, and each weft thread is fed more or less at a right angle to the direction in which the fabric is produced. It is possible to knit with only one thread or cone of yarn, though production demands have resulted in circular weft knitting machines being manufactured with up to 192 threads. Warp knitting Warp Knitting is a method of producing a fabric by using needles similar to those used in weft knitting, but with the knitted loops made from each warp thread being formed down the length of the fabric; the loops are formed vertically down the length of the fabric from one thread as opposed to across the width of the fabric, as in case of weft knitting. 22/KNITTING VIEWS/JANUARY-FEBRUARY 2010 Weft knitting Warp knitting Course-wise yarn feeding Wale wise yarn feeding Yarn path horizontal Yarn path either vertical or diagonal The loops are formed across of fabric The loops are formed vertically the width down the length of fabric Needles knit sequentially Needles knit concurrently Possible to knit with one yarn Need warp yarn sheet Cone or cheese yarn supply One long beam or a number of small warp beams yarn supply Usually staple fibre yarns can be worked Only filament yarns can be successfully worked Normally latch needles are used Latch, beard or compound needles are used Less versatility More versatility Changing design affect the speed Changing design does not affect the speed Relatively not consistent and uniform quality product Consistent and uniform quality product Loops are not uniform Loops are uniform Stretch in both direction Stretch in widthwise direction Dimensionally less stable Dimensionally more stable Weft knitting machines are less expensive Warp knitting machines are more expensive Running costs is less Running costs is high Softer yarn is required (less twist) Stronger yarn is required (more twist) Short production runs For mass scale production Small floor space requirements Need more space E.g. Circular Knitting machine E.g. Tricot and Raschel machine Compared with warp knitting, weft knitting is a more versatile method of fabric production in terms of both the range of fabric structures that can be produced and the yarn types that can be utilised. Weft knitting is the simplest method of converting a yarn into a fabric. In warp knitting, each warp thread is fed more or less in line with the direction in which the fabric is produced, and each needle in the knitting width must be fed with at least one thread at each course. Compared to weaving and weft knitting it is the fastest method of converting yarn into fabric, though modern developments in weft knitting machines mean that there is now very little difference in terms of production between the two forms of knitting