Weft Knitted Fabrics PDF

Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Plain Single Jersey Fabrics If a weft knitted fabric has one side consisting only of face stitches, and the opposite side consisting of back stitches, then it is described as a plai...

Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Plain Single Jersey Fabrics If a weft knitted fabric has one side consisting only of face stitches, and the opposite side consisting of back stitches, then it is described as a plain knitted fabric. It is also frequently referred to as a single jersey fabric (single fabric). Plain jersey fabric is the simplest weft knitted structure that is possible to produce with one set of needle. Plain is the base structure of hosiery, fully- fashioned knitwear. It is having definite face and back and is most easily recognized. Face is having all knit stitches with smooth texture, while back is having purl stitches with textured and mottled appearance. Technical face of single jersey fabric is smooth, with the side limbs of the needle loops having the appearance of columns of V’s in the wales. On the technical back, the heads of the needle loops and the bases of the sinker loops form columns of interlocking semi-circles, whose appearance is sometimes emphasized by knitting alternate courses in different coloured yarns. Face side Cross section Back side Characteristics of Plain Single Jersey Fabrics Plain fabrics are economical to produce and has the maximum covering power. It normally has a potential recovery of 40 % in width after stretching. The production rate is very high because of stitch simplicity and its cost is low because of machine simplicity. These fabrics are produced on flat as well as on circular machines. Stretch is both crosswise and lengthwise and stretchZ is more crosswise. The fabric can be unroved from either end or if a stitch is broken, the wale will disintegrate causing the stitches in that line to undo or ladder or run. Fabric is less stable and curls when cut. Prepared By: Engr. Shakeel Ahmad Paracha Page 1 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Special finishes counteract curling and improve stability. The stitch length can be varied with cam setting giving more courses per unit length with short stitch length and vice versa. The properties such as rigidity, air permeability, weight per unit area, bursting strength changes with the stitch length. The fabric may appear thick or flimsy if the stitch length is reduced or increased. When the fabric is used for the manufacturing of garments by cutting pattern pieces then sewing, some difficulty can be experienced during making-up because the fabric tends to curl at the ends and at the sides unless it has been heat set during the finishing. All needles in one bed can pull loops in only one direction. As a result, jersey-knit materials are unbalanced and have a tendency to curl at the edges. This condition can frequently be corrected in V fabric finishing. If not corrected, this problem can be quite troublesome in cutting and sewing operations. Jersey-knit fabrics stretch more in the width directions. Production of Plain Single Jersey Fabrics Single jersey fabrics are produced on flat as well as circular machines, having one set of needles in one needle bed and are called jersey machines, plain-knit machines, or single knit machines. Most of the single-jersey fabrics are produced on circular machines whose latch needle cylinder and sinker ring revolve through the stationary knitting cam systems that, together with their yarn feeders, are situated at regular intervals around the circumference of the cylinder. The yarn is supplied from cones, placed either on an integral overhead bobbin stand or on a free-standing creel, through tensioners, stops motions and guide eyes down to the yarn feeder guides. The fabric, in tubular form, is drawn downwards from inside the needle cylinder by tension rollers and is wound onto the fabric-batching roller of the winding-down frame. The Knitting Action of Plain Single Jersey Fabrics Following steps are performed during the knitting action of a latch needle and holding down sinker during the production of a course of plain fabric. 1. Tucking in the hook or rest position: The sinker is in forward position, holding down the old loop (fabric) whilst the needle rises from the rest position. 2. Clearing: The sinker is still forward as the needle has been raised to its highest position clearing the old loop from its latch. 3. Yarn feeding: The sinker is partially move back allowing the feeder to present its yarn to the descending needle hook and also freeing the old loop so that it can slide up the needle stem and under the open latch spoon. 4. Knock-over: The sinker is fully withdrawn while the old loop has closed the latch to trap the new yarn; needle descends to knock over its old loop on the sinker belly. Prepared By: Engr. Shakeel Ahmad Paracha Page 2 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) 5. Holding-down: The sinker moves forward to hold down the new loop in its throat whilst the needle rises under the influence of the up throw came to the rest position where the head of the open hook just protrudes above the sinker belly. Knitting Cams Fig. shows the arrangement and relationship between the needle and sinker cams as the elements pass through in a left to right direction with the letters indicating the positions of the elements at the various points in the knitting cycle. The needle cam race consists of the following: o The clearing cam (1) and its guard cam (4), the stitch cam (2) and upthrow cam (3) which are vertically adjustable together for alteration of stitch length, and the return cam (5) and its guard cam (6). The three sections of the sinker cam race are: o The race cam (7), the sinker with drawing cam (8) and the sinker-return cam (9) which is adjustable in accordance with the stitch length. Variations of Plain Single Jersey Knits Fleece Intarsia Jacquard knits Knitted terry Knitted velour Lisle Plaited knits Silver-pile knits End-Uses of Plain Single Jersey Knits A wide variety of knitted fabrics are made with the jersey-knit construction, ranging from sheer fabrics, and lightweight hosiery to thick, bulky sweaters. Most full-fashioned sweaters are fundamentally jersey-knit fabric types. Additional fabrics that use jersey-knit construction are hosiery, T-shirts, knit terry, knit velour, and many more. Lightweight filament yarn jerseys are especially susceptible to runs due partially to the very smooth surface of filament yarn. Prepared By: Engr. Shakeel Ahmad Paracha Page 3 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Rib Fabrics The term rib is used to describe a double jersey knitted fabric with vertical rows (wales) of loops meshed in the opposite direction to each other. Rib has a vertical cord appearance because the face loop wales tend to move over and in front of the reverse loop wales. Face row or loops tends to close up in one plane and so also the back row of loops in the other plane. Thus stitches of rib fabrics lie in two planes and hence, the rib structure is also known as double jersey structure. Simplest rib fabric is 1 x 1 rib having alternate wales knitted to the front and back. The ribs tend to close up to create a double faced fabric, which has the same appearance on both sides. Rib knits fabrics are produced with the knitting machines having two sets of needle, normally positioned at rights angle to each other. 1 x 1 rib has the appearance of the technical face of plain fabric on both sides until stretched to reveal the reverse loop wales in between. Relaxed 1 x 1 rib is theoretically twice the thickness and half the width of an equivalent plain fabric, but it has twice as much width-wise recoverable stretch. In practice, 1 x 1 rib normally relaxes by approximately 30% compared with its knitting width. Characteristics of Rib Fabrics Rib fabrics are generally produced on V-bed or circular machines. In both the cases, loop formation is effectively same, with V-bed machines having a front bed and a back bed, while circular machines have a cylinder and dial. It is a reversible structure, i.e. face and back side has the same appearance in 1 x 1, 2 x 2, 3 x 3, ribs. It is heavier and thicker structure than the plain knit structure with similar gauge used. The rib machine also requires finer yarn than a similar gauge plain machine. It is a more expensive fabric to produce than plain. Prepared By: Engr. Shakeel Ahmad Paracha Page 4 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) The fabric does not curl at the edges due to its balanced nature. This property of rib structure is particularly useful in cutting and sewing operation. Like all weft-knitted fabrics, it can be unravelled from the end knitted last by drawing the free loop heads through to the back of each stitch. Rib cannot be unravelled from the end knitted first because the sinker loops are securely anchored by the cross-meshing between face and reverse loop wales. This characteristic, together with its elasticity, makes rib particularly suitable for the extremities of articles such as undergarments, tops of socks, cuffs of sleeves, knit hats, rib borders of garments, and stolling and strapping for cardigans. Running and laddering is still a problem. Rib structures are elastic, formfitting, and retain warmth better than plain structures. Rib fabrics are extensively used in the production of outwear garments. The width occupied by 1 x 1 rib fabric is about half the width of a plain produced on the same number of needles, but it does have nearly twice as much elasticity in the width. It can be distinguished from plain by the fact that the loops of certain wales are withdrawn in one direction and the others in the opposite direction, whereas the loops of plain are always withdrawn in the same direction, from the technical face to the technical back. Rib fabrics are thicker than single jersey knits. More stretch crosswise than lengthwise. Rib fabrics very stable. Next highest machine productivity. Production of Rib Fabrics Rib-knit fabrics are produced with knitting machines that are somewhat different from those used for jersey knits. Because rib knits have stitches drawn to both sides of the fabric, the machines used to make them, called rib-knit machines. Rib-knit fabrics require two sets of needles usually positioned at right angles to each other; each set of needles is capable of producing stitches. The fabric is formed between the two needle-holding beds. The machinery required to produce rib-knit fabric is substantially more complex and operates at slower speeds than knitting machines used for jersey fabrics. Prepared By: Engr. Shakeel Ahmad Paracha Page 5 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) The Knitting Action of Rib Fabrics Following steps are performed during knitting action of the rib fabrics on the circular rib machine. 1. Clearing (a): In clearing position, the cylinder and dial needles move out to clear the plain and rib loops formed in the previous cycle. 2. Yarn feeding (b): The needles start their return moment and are withdrawn into their tricks so that the old loops are covered by the open latches and the new yarn is fed into the open hooks. 3. Knocking-over (c & d): The dial needle has retracted before the cylinder needle and is in the process of knocking-over the old loop. The needles are withdrawn into their tricks so that the old loops are knocked over and the new loops are drawn through them. Needle Timing Needle timing is the relationship between the loop forming positions of the dial and cylinder needles measured as the distance in needles between the two stitch cams knock-over points. Collective timing adjustment is achieved by moving the dial cam- plate clockwise or anti-clockwise relative to the cylinder; individual adjustment at particular feeders (as required) is obtained by moving or changing the stitch cam profile. Synchronized Timing If both the cylinder and dial needles knock over together, to produce loops of equal size, it is known as synchronised timing. Delayed Timing If cylinder needle is knocking over before dial needle, then it is known as delayed timing, which is very popular in production of rib fabric as it produces tighter fabric due to robbing back (this is where some yarn is taken from the previously knitted stitch to make the current stitch). With delayed timing, the dial knock over occurs after about four cylinder needles have drawn loops and are rising slightly to relieve the strain. Prepared By: Engr. Shakeel Ahmad Paracha Page 6 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) The dial loops are thus larger than the cylinder loops and the fabric is tighter and has better rigidity; it is also heavier and wider, and less strain is produced on the yarn. Variations of Rib Knits Mock Rib Broad Rib Swiss Rib English Rib Cable Full / half Cardigan Ottoman Pointelle Rack Shaker End-Uses of Rib Knits Collars and cuffs Necklines Bottom edges of sweaters Double knits jackets Knit hats Men’s hosiery Prepared By: Engr. Shakeel Ahmad Paracha Page 7 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Purl Fabrics The Purl fabrics are also known as link-link fabrics. Purl was originally spelt ‘pearl’ and was so named because of its similar appearance to pearl droplets. In purl, the loops of one course are intermeshed in one direction and the loops of the next course intermeshed in opposite direction, i.e., the alternate courses having face and back loops. It means each wale contains both knit stitches and purl stitches. This differs from the rib fabric, in which the wales contain either knit or purl stitches. A simple purl fabric looks somewhat like the back of a jersey knit on both sides of the fabric. The simplest purl fabric is known as 1 x 1 purl, in which one course has all knit stitches and the next course has all purl stitches. The cycle repeats on the third course. A 2 x 2 purl knit fabric is made with two courses of knit stitches followed by two courses of purl stitches. There are two types of purl needle bed machines - flat bed purls, which have two horizontally opposed needle beds and circular purls (double cylinder machines), which have two superimposed cylinders one above the other. Both types of machine generally produce garment lengths. Characteristics of Purl Fabrics Slowest of the knitting machines. Both side similar appearance. More expensive. Good stretch in all direction. Stretches out of shape easily. Crosswise stretch less than a jersey knit. Thicker than jersey knits. Does not curl. Can be unroved from either end. Thickness of fabric is two to three times more as compare to single jersey fabric. Prepared By: Engr. Shakeel Ahmad Paracha Page 8 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Production of Purl Fabrics Purl-knit fabrics are made on knitting machines called purl-knit machines or links-and-links machines. The purl knitting machines are basically of flat and circular types as shown in Fig. 1 The flat is having two horizontal beds for needle movement and central gap for fabric formation. The circular type has two cylinders, one above the other and thus referred as super imposed cylinder machine. As stitches are sometimes drawn to the front and sometimes to the back, two sets of needles are required to produce these fabrics. In purl machines, however, rather than two distinct, separate sets of needles, one set of double headed latch needles is used as shown in Fig 2. The two needle beds are in alignment with each other. The double headed needles move from one needle bed to the other, from side to side of the knitted fabric as it is produced, alternately making stitches on one fabric side and then the other. The purl-knit machines used to produce purl knit fabrics are the most versatile industrial knitting machines. These machines can produce plain and rib as well as purl fabrics. By selective programming of needle motion, fabrics of all three types, sometimes with unique design effects are possible. Purl-knit machines are widely used in the sweater industry. Although extremely versatile, the purl knit machines have the lowest rate of production of all knitting machines. Therefore, the cost per pound of fabric produced is highest for purl knit fabrics. Knitting machines for jersey knits have the highest productivity but the lowest versatility. Productivity for rib-knit machines falls between those for jersey and purl machines. The Knitting Action of Purl Fabrics Fig. 3 shows the knitting action of a flatbed purl machine which has tricks in each of the needle beds. They are in line with one another to enable the transfer of purl needle from the control of a slider in one bed into the control of a slider in the opposite bed. Position 1 shows engagement of the head of the receiving slider with the needle hook that was originally knitting from the opposing bed. Prepared By: Engr. Shakeel Ahmad Paracha Page 9 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) In position 2, the needle has been moved to the centre, with both sliders engaging the needle hook. The sliders then start to move back, but the slider in the back bed is pressed down by a cam, so that front bed slider is freed from the needle hook and the needle is transferred to the back bed. In position 3, the slider in the back bed has control of the needle and it can be seen that the yarn is fed to the opposite end of the needle, when compared to that of position 1. Then the slider in the back bed has moved the needle to knock over position to complete the formation of the purl stitch. It should be noted that a purl stitch is made when a loop is formed by one hook and then at the next course by the other hook of the same needle, so that one course is formed on the front bed and the next course is formed on the back bed to create a 1 x 1 purl structure. Variations of Purl Knits Alpaca Moss Basket End Uses of Purl Knits Infant and children’s wear Sweaters Scarves Fancy garment parts Prepared By: Engr. Shakeel Ahmad Paracha Page 10 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Interlock Fabrics Interlock is a popular double jersey structure produced on a cylinder and dial circular weft knitting machine. Interlock-knit fabrics are a variation of rib knits made on the interlock machine. Interlock is an interlocking of two 1 x 1 rib structures in such a way that the face wale of fabric “1” is directly in front of the ‘reverse wale’ of the rib fabric “2”. Interlock structure consists of two 1 x 1 rib fabrics knitted one after the other by means of two separate yarns, which knits alternately on the face and back of the fabric and are interlocked together. Interlock is a reversible fabric, which has similar smooth appearance on each side. Interlock is produce on a cylinder and dial circular weft knitting machine, with alternate long and short needles opposite to each other on cylinder and dial. Interlock has the technical face of plain fabric on both sides, but its smooth surface cannot be stretched out to reveal the reverse meshed loop wales because the wales on each side are exactly opposite to each other and are locked together as shown in Fig. 1. Each interlock pattern row (often termed an ‘interlock course’) requires two feeder courses, each with a separate yarn that knits on separate alternate needles, producing two half-gauge 1 x 1 rib courses whose sinker loops cross-over each other. Thus, odd feeders will produce alternate wales of loops on each side and even feeders will produce the other wales. Characteristics of Interlock Fabrics To determine whether a fabric is an interlock or a rib, spread the fabric width wise, and view the fabric wales carefully at the top edge of the cloth. If the knit stitches are one behind the other, the fabric is interlock. If the wales of knit stitch alternate, the fabric is rib. Interlock fabric is a reversible balanced, smooth, stable structure that lies flat without curl. Like 1 x 1 rib, it will not unrove from the end knitted first. It unroves from the course knitted the last. Fabric is thicker, stronger, and less elastic and hence, is nearer to the woven structure so that cutting and sewing operations are easier. Prepared By: Engr. Shakeel Ahmad Paracha Page 11 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Interlock fabric is heavier and narrower than rib of equivalent gauge, and requires a finer, better, more expensive yarn. Consequently, finer yarns are usually used to reduce the areal density of the fabric. The fabric becomes costlier due to thickness and less production. Interlock fabrics are dimensionally stable and the fact that they do not tend to easily stretch out of shape. Interlock fabrics offer a smooth surface for printing by both screen and heat transfer methods. Production of Interlock Fabrics Interlock is produced mainly on special cylinder and dial circular machines and on some double- system V-bed flat machines. Figure shows the needle set out on the machine, with long and short needles alternating on the cylinder. An interlock machine must have the following: o Interlock gating, the needles in two beds being exactly opposite each other so that only one of the two can knit at any feeder. o Both, the cylinder and dial beds should have two types of needles viz., long and short needles. o Alternate placement of long and short needles in both the beds is required. o The long needle of one bed should face the short needle of the other bed and vice versa. o Two separate cam systems in each bed, each controlling half the needles in an alternate sequence, one cam system controlling knitting at one feeder, and the other at the next feeder. o Needles set out alternately, one controlled from one cam system, the next from the other; diagonal and not opposite needles in each bed knit together. o Long needle cams were arranged for knitting at the first feeder and short needle cams at the second feeder. o Minimum of two yarns are required to knit one interlock course and hence, a minimum of two feeders supply. o The knitting style is in such a manner that only long needles of dial and cylinder will knit with the first feeder and only short needles of dial and cylinder will knit with second feeder. Fig. 1 shows the cylinder and dial needle camming to produce one course of ordinary interlock fabric, which is actually the work of two knitting feeders. The dial has a swing tuck cam that will produce tucking if swung out of the cam-track and knitting if in action. The cylinder cam system consists of: o A: Clearing cam which lifts the needle to clear the old loop. Prepared By: Engr. Shakeel Ahmad Paracha Page 12 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) o B, C: Stitch and guard cams respectively, both vertically adjustable for varying stitch length. o D: Upthrow cam, to raise the cylinder needle whilst dial needle knocks-over. o E, F: Guard cams, to complete the track. o G, H: Guide cams that provide the track for the idling needles. The dial cam system consists of: o 1: Raising cam to tuck position only. o 2, 3: Dial knock-over cams (adjustable). o 4: Guard cam to complete the track. o 5: Auxiliary knock-over cam to prevent the dial needle re-entering the old loop. o 6, 7: Guide cams that provide the track for the idling needles. o 8: Swing type clearing cam, which may occupy the knitting position as shown at feeder 1 or the tuck position as shown at feeder 2. The Knitting Action of Interlock Fabrics The knitting cycle of an interlock machine can be divided in to eight steps. These eight steps are as follows: o Position 1 (rest position): The head of these needles are in the range of the knock over edges of cylinder & dial respectively. o Position 2 (tucking position of dial needle): The dial needles are brought into the tucking position. o Position 3 (tucking position): The cylinder needles are brought in the tucking position. o Position 4 (clearing position of dial needle): The dial needles are come into the clearing position. o Position 5 (clearing position): The cylinder needle are come into the clearing position. o Position 6 (yarn presenting position): Both cylinder & dial are moved to the yarn presenting position. o Position 7 (cast-on position): Both cylinder & dial are moved to their cast on position. o Position 8 (knock-over position): Both cylinder & dial are reached the knock over position. Prepared By: Engr. Shakeel Ahmad Paracha Page 13 of 14  Textile Institute of Pakistan, Karachi. TEXT302 (Knitting Technology) Variations of Interlock Knits Eighthlock Cortina Fleecy interlock Cross tuck interlock End-uses of Interlock Knits Outwear fabrics Innerwear fabrics Dress wear Skirts Blouses T-shirts Comparison between Weft Knits (Plain, Rib, Purl, Interlock) Prepared By: Engr. Shakeel Ahmad Paracha Page 14 of 14