Knitting Process PDF

Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) What is Knitting? Knitting is a cloth manufacturing process in which a knitted fabric is produced by transforming yarn (s) into a loop then intermeshing the loop with the adjacent loops o...

Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) What is Knitting? Knitting is a cloth manufacturing process in which a knitted fabric is produced by transforming yarn (s) into a loop then intermeshing the loop with the adjacent loops on both sides and above and below. Knitted fabric is produced by the process of knitting. The yarn used in knitting has to be soft because it has to be transformed into a loop and is called as knitting or hosiery yarn. For this purpose, such yarns are spun with a twist multiplier (TM) of about 2. In comparison, the yarn used for weaving has a TM of 3 to 6. The process of interlooping involves the formation of a loop of yarn which is interconnected or intermeshed with the previously created loop. Loops of yarn are created and intermeshed together using needles. The interlooping can be carried out manually using knitting needles. However, in commercial knitting machines specially designed needles driven by cams are used to create a knitted fabric at very high speeds. Hand Knitting Interlooping of a yarn Knitted fabric Knitted V/S Woven Fabrics The knitting process follows a shorter route of fabric formation. Does not involve lengthy preparation. Therefore, the production rate of knitting is much faster than weaving. Prepared By: Shakeel Ahmad Paracha Page 1 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) In addition to various other applications, knitted fabrics are preferred in applications where stretch is required. Woven fabric Knitted fabric Knitted Structure – Needle Loop One loop is the basic repeating unit of knitted fabric just as one point of interlacement is the basic repeating unit of a woven fabric. A needle loop consists of a head (H) and two side limbs or legs (L). At the base of each leg is a foot (F), which meshes through the head of the loop formed at the previous knitting cycle. The yarn passes from the foot of one loop into the foot and leg of the next loop formed by it. Knitted Structure ─ The Stitch The stitch is the smallest dimensionally stable unit of all knitted fabrics. It consists of a yarn loop, which is held together by being intermeshed with another stitch or other loops. By changing the type of stitches, various knitted fabric structures can be formed. The type of stitch is also dependent upon the type of knitting needle used. Prepared By: Shakeel Ahmad Paracha Page 2 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Knitted Structure ─ Loop & Stitch Knitted Structure ─ Needle & Sinker Loop A needle loop is one which has been drawn through a previous loop. The upper part of the loop produced by the needle drawing the yarn. A sinker loop is one which connects adjacent needle loops. The lower part of the knitted loop is technically referred to as sinker loop, the connection of two legs belonging to the neighbouring stitches lying laterally. Needle loop Sinker loop Knitted Structure ─ Types of Loops Face loop o During loop formation, when the new loop emerges through the old loop from back to the face (or front) side. Back loop o If the new loop passes from the face side to the back side of the old loop, it is called as back loop or weft purl loop. Open loop o Loop forming yarns does not cross at the bottom of the loop. Closed loop o The legs of the loop cross so that the loop closing takes place. Prepared By: Shakeel Ahmad Paracha Page 3 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Knitted Structure ─ Wales & Courses When the knitted fabric is produced by intermeshing number of loops of yarn together, vertical and horizontal lines appear on the surface of the fabric. Technically, a series of adjacent loops forming a horizontal row across the width of the fabric is called as a course. Whereas series of adjacent loops forming a vertical column across the length of the fabric is called as wale. Sometimes when the yarn used for knitting is very fine, or the loops are very closely held together, in such cases courses and wales may not be clearly visible. The number of wales and courses per inch determines the quality of knitted fabric just as ends and picks per inch determine the quality of a woven fabric. The courses per inch are denoted by CPI while the wales per inch are denoted by WPI. Greater the number of CPI and WPI, denser will be the fabric, and its weight and cover will be more. The wales per inch depend upon the machine gauge, i.e. how close or far the knitting needles are placed. Whereas the courses per inch would depend upon the stitch length. Representation of Courses Representation of Wales Knitted Structure ─ Stitch Length (l) The Stitch length (l) is the length of the yarn taken up by one loop in the knitted fabric as shown by the length AB in the following figure: Prepared By: Shakeel Ahmad Paracha Page 4 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Knitted Structure ─ Stitch Density (S) The total number of loops present in a unit area is expressed as stitch density (S). Stitch density can be calculated by multiplying the total number of courses and wales per unit length. Therefore, stitch density (S) per square inch would be: Stitch density( S ) = CPI x WPI Knitted Fabrics Specifications Courses per inch Wales per inch Stitch length Stitch density (Stitches per unit area) Thread count Weight per unit area [grams per square metre (GSM)] Knit design Types of Knitting Knitted fabrics can be produced by two methods: o Weft knitting o Warp knitting Prepared By: Shakeel Ahmad Paracha Page 5 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Weft Knitting In weft knitting, the loops are formed across the width of the fabric (course wise), and each thread is fed at a right angle to the direction in which the fabric is produced. The weft knitting is a more versatile method of production as compared to warp knitting in terms of the variety of structures that can be produced and in its ease and simplicity of operation. Weft knitting has two further classes: o Flat weft knitting o Circular weft knitting Flat Weft Knitting In flat weft knitting, an open width knitted fabric is produced. Sweaters and other clothing made by ladies in homes using knitting needles is a classic example of flat weft knitting. In flat weft knitting, the needles are placed in horizontal form and a lot of production time is lost while travelling from one end to the other while creating a fabric. Therefore, the production of flat weft knitting machines is low. A computerized flat weft knitting machine Circular Weft Knitting In circular weft knitting, needles are arranged in a circle and are held vertically producing a tubular cloth. Knitting is carried out by moving the needles in a circle and keeping the threads stationary. The tubular cloth is used to produce seamless garments such as vests, t-shirts, socks, sacks, etc. Tubular cloth produced by circular knitting can also be cut into an open width flat form to produce garments by stitching. Usually, the diameter of the tubular cloth ranges from 8" to 20". However, in modern circular weft knitting machines diameters up to 60" are also available. Since needles or threads move in a circle, so no time is wasted in moving from side to the other as in case of flat weft knitting. Circular weft knitting is much faster than flat weft knitting. Moreover, they occupy very less space. Prepared By: Shakeel Ahmad Paracha Page 6 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Circular weft knitting is widely used in the industry because of their high production and also because variety of designs can be produced on them. Circular weft knitting machine Warp Knitting In warp knitting, many threads are collected on a beam in a process similar to that employed in weaving. The beam is then taken to the knitting machine, where knitted fabric is produced. In warp knitting, loops are made from each warp thread vertically down the length of the fabric with each warp thread being fed in line with the direction in which the fabric is produced. Warp knitting machines occupy much space as compared to weft knitting machines. Even though warp beam preparation takes much time, but the production on the machine is very fast. Although warp knitting is the fastest method of fabric formation as compared to both weaving and weft knitting, but limited designs can be produced by this method. Warp knitting - Loop formation mechanism Prepared By: Shakeel Ahmad Paracha Page 7 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Warp knitting machine Weft V/S Warp Knitted Fabric Weft knitted fabric Warp knitted fabric Knitting Motions The mechanical motions carried out on a knitting machine to create a loop of yarn and then to intermesh it with the previously made loop are called as knitting motions. To form a new stitch, specific knitting steps must be carried out in the correct sequence. This correct sequence of knitting operations or steps is called as the knitting cycle. Knitting Elements ─ Knitting Needles Knitting needles are the most important element of a knitting machine because it is directly responsible for interlooping of yarns. It is also considered as the primary knitting element as it directly comes in contact with the yarn supplied. Prepared By: Shakeel Ahmad Paracha Page 8 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The knitting needle is made of metal and has a hook at one end. The quality of the knitted fabric is largely dependent on the effectiveness and accuracy of the loop, which in turn largely depends on the needle. Small variations in needle manufacturing may lead to irregular fabric. The surface of needles should be highly polished allowing the yarn and the loop to slide free. The needle must have high strength and toughness to give durability. A typical needle must perform several million knitting actions without fault. Knitting Elements ─ Sinkers Sinker is the second most important element of knitting after the knitting needles. Sinker is a thin metal plate made up of pressed steel. Sinkers are placed between the knitting needles approximately at right angles. Apart from other functions, the main function of the sinker is to convert a newly laid yarn into a loop. Knitting Elements – Needle Bed The function of a needle bed: o Is to hold together the knitting needles and sinkers at exact defined distance and position. o To guide the needles and sinkers during the stitch formation process. Needle beds could be classified into various types depending upon the type of knitting process. Prepared By: Shakeel Ahmad Paracha Page 9 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Classification of Needle Beds Single-needle bed Double-needle beds Knitting Elements – Knitting Cam Prepared By: Shakeel Ahmad Paracha Page 10 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The Knitting Cycle The stages of the knitting cycle may vary for different types of needles. However, there are four significant stages of the knitting cycle: o Yarn laying/Yarn feeding o Loop formation o Bridge formation/Knock over o Linking-up/Casting-off Yarn laying, i.e. feeding of yarn to the knitting needle. Prepared By: Shakeel Ahmad Paracha Page 11 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Loop formation, i.e. the yarn is made to form into a loop. Bridge formation, i.e. the yarn is clamped by the knitting needle by closing the needle hook. Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Prepared By: Shakeel Ahmad Paracha Page 12 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Prepared By: Shakeel Ahmad Paracha Page 13 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Prepared By: Shakeel Ahmad Paracha Page 14 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Linking-up, i.e. the newly formed yarn loop is drawn through the last formed loop (intermeshing) creating a new stitch. Types of Knitting Needles There are three main classes of knitted needles: o Bearded needles o Latch needles o Compound needles The stages of the knitting cycle slightly vary for all these types of needles. All needles must have some method of closing and opening its hook in order to catch and retain the yarn loop and to perform intermeshing. Bearded Needles These needles were the first ever type used in a knitting machine. William Lee invented bearded needles in 1589. Bearded needles are the cheapest and simplest in operation and are easy to manufacture. Prepared By: Shakeel Ahmad Paracha Page 15 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Bearded needles have five main parts as shown in the figure. Bearded Needles ─ Knitting Cycle First of all, the yarn feeding takes place (Yarn laying). Then the yarn is made to form a loop (Loop formation). Prepared By: Shakeel Ahmad Paracha Page 16 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The needle moves down (Landing). The presser closes the hook, and the yarn is clamped (Knock over or Bridge formation). Intermeshing takes place by stitching (Linking-up). Prepared By: Shakeel Ahmad Paracha Page 17 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Intermeshing takes place by stitching (Linking-up). Intermeshing takes place by stitching (Linking-up). Intermeshing takes place by stitching (Linking-up). Prepared By: Shakeel Ahmad Paracha Page 18 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Intermeshing takes place by stitching (Linking-up). Intermeshing takes place by stitching (Linking-up). Intermeshing takes place by stitching (Linking-up). Prepared By: Shakeel Ahmad Paracha Page 19 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Latch Needles Latch needles are more expensive to manufacture as compared to bearded needles. It has the advantage of being self-acting and therefore is also as automatic needles. Bearded needles are more prone to produce needle marks. Precisely manufactured latch needles are widely used to produce high-quality fabrics. Latch Needles ─ Knitting Cycle First of all, the yarn feeding takes place (Yarn laying). Then the yarn is made to form a loop (Loop formation). Prepared By: Shakeel Ahmad Paracha Page 20 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Bridge formation and linking-up take place in one motion. Bridge formation and linking-up take place in one motion. Bridge formation and linking-up take place in one motion. Prepared By: Shakeel Ahmad Paracha Page 21 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Bridge formation and linking-up take place in one motion. Bridge formation and linking-up take place in one motion. Bridge formation and linking-up take place in one motion. Prepared By: Shakeel Ahmad Paracha Page 22 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The needle moves up to let go the last loop (clearing). Compound Needles The compound needles, unlike the bearded or latch needles, work with two independent working parts, i.e. the hook and the tongue. The motion of the tongue helps to close the hook and catch the yarn. The yarn is fed to the hook using a guide bar. Compound needles are difficult to manufacture, but they give high-quality fabrics at high speeds. These needles overcome the problems of knitting marks as faced with bearded or latch needles. Compound Needles ─ Knitting Cycle First of all, the guide bars feed the yarn to the hook (Yarn laying). Prepared By: Shakeel Ahmad Paracha Page 23 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The tongue closes the hook to catch the yarn (Bridge formation). The tongue closes the hook to catch the yarn (Bridge formation). The needle action then completes interlooping (Link-up). Prepared By: Shakeel Ahmad Paracha Page 24 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The needle action then completes interlooping (Link-up). The needle action then completes interlooping (Link-up). The needle action then completes interlooping (Link-up) Pitch & Machine Gauge The distance between the two consecutive needles is called as the pitch which determines machine gauge. The machine gauge is defined as the number of knitting needles present in a reference length. Prepared By: Shakeel Ahmad Paracha Page 25 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) The pitch also shows the space available for the yarn. For a particular pitch of the machine, only a specific range of yarn counts can be knitted. The gauge of the machine also controls the number of wales per unit length. With finer gauge machines, a greater number of wales can be accommodated in a unit length and vice versa. The gauge of the machine influences the choice of the yarns and counts and affects the knitted fabric properties such as appearance and weight per unit area. Fabric made on the coarse gauge Fabric made on the fine gauge Basic Knitted Structures Using only the main binding element, i.e. the stitch, four basic knitted structures are possible to knit: o Plain knitted structure o Rib knitted structure o Purl knitted structure o Interlock knitted structure These structures are usually associated with weft knitted fabrics but can also be incorporated warp knits. Prepared By: Shakeel Ahmad Paracha Page 26 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Plain Knitted Structure Rib Knitted Structure Purl Knitted Structure Prepared By: Shakeel Ahmad Paracha Page 27 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Interlock Knitted Structure Patterning Elements In order to create further designs in a knitted fabric other than the four basic knitted structures, following patterning techniques can be used: o Using different types of stitches o Using Tuck loops/Stitches o Using Floats loops/Stitches o Using an Inlaid yarn Different stitches Tuck loops/Stitches Floats loops/Stitches Prepared By: Shakeel Ahmad Paracha Page 28 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Inlaid yarn Knitted Jacquard Characteristics of Knitted Fabrics Elastic and stretchable in both lengthwise & width wise. Limited design capabilities as compared to woven fabrics. Produced at a much faster rate as compared to weaving. Handling & Processing is difficult. Dyeing is possible, but printing is difficult and limited. Uses of Knitted Fabrics Sweaters & Jerseys T-Shirts & Sweatshirts Socks Shawls & Scarves Hats & Mufflers Blankets Prepared By: Shakeel Ahmad Paracha Page 29 of 30  Textile Institute of Pakistan, Karachi. TEXT202 (Fabric Technology) Decorative rugs & mats Curtains & Sofa cloth Dress fabrics Prepared By: Shakeel Ahmad Paracha Page 30 of 30