Chapter 4 KNITTING AND KNITTED FABRICS 4-2 Knitting and Knitted Fabrics CHAPTER 4......... .........KNITTING AND KNITTED FABRICS SECTION 1 KNITTING 1.1 Knitting Process Knitting is a fabric manufacturing process in which yarn loops are intermeshed to form a fabric. The conversion of yarn into loops can be done either in a horizontal direction or in a vertical direction. Therefore, two types of knitting trades have been developed,. The fabric built up in horizontal direction is called weft-knitting, while the fabric built up in vertical direction is called warp-knitting. Knitting Weft-Knitting V-bed Machine, Circular Machine (Latch needle) Warp-Knitting Straight Bar Machine, Loop Wheel Machine (Beard needle) Tricot Machine (Beard/Compound needle), Raschel Machine (Latch/ Compound needle) 1.2 Weft-Knitting This is a flat or circular knitting process that places one yarn at a time to form loops running across the fabric. In a weft-knitted structure, the intermeshed loops touch each other only in a few places, and the fabric can be stretched along the width or the length under a low stress. Textile Handbook 4-3 Figure 1.2 Plain Knit Structure 1.3 Weft Knitting Machines 1.3.1 Two Types of Knitting Machines Using Beard Needles a) The straight bar type, in which the beard needles are arranged in a straight line. An example of this type of machine is the fully-fashioned straight bar machine. A fully-fashioned straight bar machine is usually programmed to knit the parts of a knitted garment in the shape required, that is the front panel, back panel, sleeve, etc. Figure 1.3.1 a Fully-Fashioned Straight Bar Machine (Monk Cotton International Ltd) Knitting and Knitted Fabrics Machines for plain knitting can be generally divided into two groups based on types of needles being used: the beard needle group of machines and the latch needle group of machines. 4-4 Knitting and Knitted Fabrics b) The circular bar type, in which the beard needles are arranged in a circle on a cylinder. A typical example of this type of machine is a loop wheel machine. On this machine, the fabric is drawn vertically above the cylinder so that the last course of loops is held in tension at the needle heads. The loop wheel machine can be used for producing plain, fleecy and terry fabrics. However, this machine is now rarely used. 1.3.2 Two Types of Knitting Machines Using Latch Needles a) The flat bed type, in which the latch needles are arranged in a straight line. A V-bed flat machine is a typical example of this type. As its name implies, the V-bed machine has two needle beds arranged in an inverted v-shape. This machine can be hand-operated or controlled by computer. The flat bed machine is widely used in the sweater industry. Figure 1.3.2 a Hand Flat Knitting Machine b) The circular type, in which one set of latch needles is arranged on the circumference of a vertical cylinder, and another set of needles may be arranged perpendicular to the first set and mounted on a horizontal dial. Typical examples of this type of machine are the open top sinker machine, and the cylinder and dial machine. Most of the circular knitting machine are used for the piece-goods trade. Textile Handbook 4-5 Figure 1.3.2b Circular Knitting Machine (Mayer & Cie) 1.4.1 Knitting Needles Knitting needles have been the heart of the weft-knitting process. There are three main types of needles in industrial knitting; latch, spring beard and compound. Beard Needle: the beard needle is the oldest type. To open and close the hook during loop production, the beard needle needs an auxiliary attachment, a presser. The attachment restricts the production speed and limits the use of this needle type in modern knitting machine. Latch Needle: this is the most popular needle used in knitting. The latch of the needle is pivoted and can swivel to open and close the hook. Compound Needle: this is commonly used in warp knitting and is seldom found in weft-knitting. The hook of the compound needle is opened and closed by a closing element sliding within a grove in the main part of the needle. Knitting and Knitted Fabrics 1.4 Key Components for Weft Knitted Fabric Formation 4-6 Knitting and Knitted Fabrics Figure 1.4.1 Knitting Needles 1.4.2 Needle Bed The needle bed of a flat knitting machine is a metal plate in which precisely measured slot (tricks) are milled. Needles are inserted in these tricks and are forced to slide backwards and forwards to form the knitting sequence. For a plain circular knitting machine, the needles are housed vertically in the tricks of a cylinder. For a double jersey knitting machine, there is another set of needles mounted on a dial, which is perpendicular to the cylinder needles. Figure 1.4.2 Needle Bed Textile Handbook 4-7 1.4.3 Cam Box To facilitate the knitting action of a flat bed machine, a carriage assembly is moved back and forth along the needle bed. During the traverse of the carriage, the needle butts are guided by the cam track to slide up and down in the tricks. This carriage is connected to a cam system which consists of several individual cams which form together the cam track. Figure 1.4.3 Cam Box of a V-bed Knitting Machine On the flat bed machine, yarn coming off from cone(s) and through the tensioning device is then threaded through a yarn carrier. The carrier is set on a profiled rail, along which it can slide the length of the needle bed to provide the descending knitting needles with yarn. On a modern circular knitting machine, the yarn supply equipment consists of a cone carrier device, a yarn guiding and monitoring device, a yarn tensioner and a yarn metering and storage device. Figure 1.4.4 (1) Yarn Feeding of a V-bed Machine Knitting and Knitted Fabrics 1.4.4 Yarn Feeding 4-8 Knitting and Knitted Fabrics Figure 1.4.4 (2) Yarn Feeding of a Circular Machine 2 1 1. Yarn package 2. Stop motion 3. Positive feed 4. Yarn break detector 5. Yarn feeder 3 4 5 1.4.5 Sinker In the production of plain knitted fabric on a circular type singlejersey knitting machine or straight-bar type flat knitting machine, sinkers are used to hold the fabric in position while the needle rises. This means that the fabric is tighter and the appearance and knitting speed can be improved. For Circular machine, the sinker is made of metal, housed in the radial grooves of a sinker ring placed on the top part of the needle cylinder. The movement of the sinkers is controlled by the sinker cam segment which is fixed to a stationary sinker cam ring. Figure 1.4.5 Sinker (1) Throat, (2) Nib, (3) Platform Textile Handbook 4-9 1.4.6 Key Terms of Knitted Fabric a) Wales and Courses: Vertical columns of stitches in a knitted fabric are called wales. Wales run lengthwise through the entire fabric, and in that sense are similar to the warp in a woven fabric. Horizontal rows of stitches are called courses. Courses run widthwise from side to side of the cloth, and in that sense are similar to the weft in a woven fabric. Figure 1.4.6a Courses and Wales 1 inch 1 inch Course Wale b) Cut and Gauge : These are the expressions of fineness and coarseness of stitches in knitted materials. A five-cut fabric has five wales per inch. In a weft knitting machine, the number of slots per inch is called the cut of the machine. The term “cut” is used in weft knits only. Gauge is a term used in both weft and warp knitted fabrics. In fully-fashioned straight-bar type knits, gauge refers to the number of needles in 1.5 inches of the knitting machine. In a circular knitting machine, this refers to the number of needles in 1 inch. In warp knitted tricot, the term also refers to 1 inch, but in warp-knitted raschel, the gauge is the number of needles in 2 inches. Knitting and Knitted Fabrics The number of wales-per-unit width of fabric depends on the closeness of the needles and their thickness. The number of courses-per-unit length of fabric depends upon the distance the needle pulls the yarn when the loop is made, or the amount of yarn fed and wrapped around the needle. 4-10 Knitting and Knitted Fabrics One should be careful of the fact that the terms “cut” and “gauge” refer to measurements. The number of wales per inch in a fabric may not exactly correspond to the cut or gauge designation. 1.5 Stitch (loop) Formation Sequence on a Latch Needle One working cycle of a latch needle produces a single knitted loop. The sequence of loop formation is illustrated in Figure 1.5. Figure 1.5 Stitch Formation by Latch Needle Yarn feeder Previous loops New yarn Needle bed 1 2 3 4 5 Stitch formation sequence: 1,2 and 3 The needle rises and, as it does, the previous loop opens the latch and slides down onto the needle shank. 4 As the needle begins to descend, a new yarn is fed onto the needle hook. As the needle continues to descent, the previous loop slides onto it and causes the latch to close. 5 The needle continues downward and the old loop slides off the needle compleltly (called the knock-over action). In doing so, it becomes interlooped with a new loop which has just been formed in the needle hook, thus creating the knitted fabric structure. Textile Handbook 4-11 1.6 Types of Knitting Stitches There are three fundamental stitches utilised in knit fabrics. They are plain stitch, miss-stitch and tuck stitch. These three stitches form the basis of all knitted fabrics. 1.6.1 Plain Stitch The plain stitch is the basic knitting stitch. It has two different faces according to the relative positioning of the producing needle and the fabric. When the fabric is viewed from the side where the loop exhibits the arms of the curved formation, this is called a plain stitch. If the loop, viewed on the same side of the fabric, exhibits the arc of the top and the root of the structure, this loop is called a purl stitch. A miss stitch is created when one or more knitting needles are deactivated and do not move into position to accept a yarn. The yarn merely passes by and no stitch is formed. The idled needle has retained its loop longer than the rest of the needle. The miss stitch is used to create colour and figure designs in knitted fabric. 1.6.3 Tuck Stitch A tuck stitch is formed when a knitting needle holds its old loop and then receives a new yarn, two loops will then be collected in the needle hook. The action may be repeated several more times, but the yarns eventually are cast off the needle and knitted. The different appearance of the tuck stitch can be used for patterning, increasing fabric weight, thickness and fabric width, etc. Knitting and Knitted Fabrics 1.6.2 Miss Stitch (Welt or float) 4-12 Knitting and Knitted Fabrics Figure 1.6 Formation of the three basic knitting stitches Figure 1.6 shows the height of movement of needles to form the various stitches. Needles 6 to 10 represents the completion of a cycle to form a plain stitch. To produce a miss stitch, needles 11 to 14 should not ascend the slope of the raising cam and should instead be unaffected throughout the sequence. In order not to activate the needle, the raising cam should be withdrawn from contact with the needle butt. For tuck stitch, needles 1 to 5 should ascend the slope of the raising cam into a tucking height but not all the way to the clearing position. To achieve this, the raising cam is divided into two individually controlled parts, of which the upper raising cam should be inactive. 1.7 Recent Developments in Weft Knitting The focus of development is placed on expansion of processing methods for new products, the effectiveness and flexibility related to quick machine conversion for pattern and material changes. In the area of expansion of processing methods for new products, knitting machine makers are endeavouring to improve the processing of spandex yarns on flat and circular machines. In additional, efforts have been made to produce complete three-dimensional products directly on knitting machine which opens up new possibility of “seamless” fashioning applicable for elegant women’s clothing and technical textiles. In terms of flexibility, some flat knitting machines are using multi- Textile Handbook 4-13 gauge techniques to provide a wide spectrum for fashion design, while the manufacturers of circular machine provides easy cam changeover system and quick change of cylinder size or cylinder gauge without the need to change cams. 1.7.1. Examples of Recent Developments in Flat Knitting Machines a) The Shima Seiki SWG-X Whole Garment Knitting Machine b) The Stoll CMS 330 TC4 Knit and Wear This is another flat knitting machine to produce complete garments. It can apply the Stoll-multi-gauge feature. This feature allows a wide variety of gauge combinations to be produced without gauge conversion or needle exchange. The knitting system is controlled by step motor, so that cam functions and stitch tensions are collectively controlled. Flexible stitch can be freely programmable. Stitches of differing tensions can be knitted in one and the same course Figure 1.7.1.b Step Motor for Knitting System Control (Stoll) Knitting and Knitted Fabrics The SWG-X is capable of producing shaped, fine gauge, whole garment products. By using their slide needle and pull down device which adjust take down tension independently for front and back bodies, three-dimensional shaping can be performed. Slide needle is a compound needle with a divided slider for stitch transfer. Stitch transfer operations necessary for fashioning is carried out with the slide needle, transfer jack and holding down sinker holders. The SWG-X is configured with 4 needle beds and an additional loop presser bed. 4-14 Knitting and Knitted Fabrics c) Shima Seiki SES 122 RT Rib Transfer Flat Knitting Machine This is a four needle bed knitting machine consists of two additional beds to the conventional V-bed design. This arrangement combines conventional transfer between the lower front and back beds, and together with transfer with and between the additional upper beds. This multiple transfer capability enhances shaping and integral knitting through the use of inside narrowing of rib stitches, tubular stitches, Milano and Cardigan stitches. Figure 1.7.1.c Four Needle Bed Transfer System (Shima Seiki) 1.7.2 Examples of Recent Developments in Circular Knitting machines a) Piezo Individual Needle Selector In this individual needle selection system, it consists of a piezoceramic bending transducer module composed of two ceramic plate stacked together. When one of the plates is bent by the effect of current and voltage it makes the levers in the selector move up or down to execute needle selection. Textile Handbook 4-15 b) Quick Cam Change System The introduction of the drop cam system by Terrot allows the cams of either cylinder or dial to be changed from the outside of the cam box which eliminates the time spent in taking out the cam box block for changeover. There is another system developed by Fukuhara called Rotary Drop Cam system having similar objective. The Rotary Drop Cam System required no yarn re-threading when changing fabric construction. All cam changes are done externally without the need to remove needles or cam section. It allows more than one technician to work on the machine simultaneously. These quick cam change systems bring about simpler operation and more flexible in design changes. The MCTmatic is a monitoring system for setting and altering the yarn infeed and tensioning. It is able to set motors for feed wheel, central stitch adjustment and fabric takedown. All the above settings can be set by one command. Figure 1.7.2.c(1) Setting of Motors for Feed Wheel (Mayer & Cie) Knitting and Knitted Fabrics c) Mayer & Cie MCTmatic Quality Monitoring System 4-16 Knitting and Knitted Fabrics MCTmatic also makes a substantial contribution to quality assurance. In the event of non-conformance within a userselected tolerance, the machine will be stopped and the fault indicated in the display of the system. Figure 1.7.2.c(2) MCTmatic Display Panel Textile Handbook 4-17 SECTION 2 TYPICAL WEFT-KNIT STRUCTURE All common weft-knitted fabric structures are classified into three basic groups according to the arrangement of loops in their courses and wales. These basic structures are the plain (jersey), the rib and the purl. 2.1 Methods Used to Represent Weft-Knitted Structures a) Loop Diagram: the actual loop of the fabric is drawn. One can see the fabric structure clearly. This is suitable for simple structure. Figure 2.1.1a Loop Diagram b) Notation: special symbols are used to represent a particular stitch. A cross is used to represent a plain stitch and a circle represents a reverse plain stitch (back side of a plain stitch). A blank space is used to represent a miss stitch and a dot represents a tuck stitch. It is quite difficult to use this methods to indicate an interlock fabric which is knitted with two sets of needles lying directly opposite each other. Knitting and Knitted Fabrics 2.1.1 Three kinds of methods used to represent Weft Knitted Structure 4-18 Knitting and Knitted Fabrics Figure 2.1.1b Notation Plain stitch Purl stitch Tuck stitch Float stitch (Blank) c) Yarn-path diagram: this is the best way to represent any weft knitted structure. A straight line perpendicular to the yarn path is used to represent a needle. For a single jersey, one set of straight lines is used to represent one set of needles. For double jersey structure, two sets of straight lines are used to represent two sets of needles. A stitch is represented by a loop drawn around the needle. A tuck stitch is represented by the yarn touching the tip of the needle and the miss stitch is represented by the yarn drawn across the needle without touching it. Figure 2.1.1c Yarn Path Diagram Knit stitch Tuck stitch Miss stitch 2.2 Single Knit Structures 2.2.1 Plain Knit. Plain knit is also known as single knit or “Jersey” in the trade. This is the simplest and most basic structure. Fabrics of this type have all loops drawn to one side of the fabric (all plain stitches) and are easily recognized by the fact that the smooth side is the face, while the back has a textured and mottled appearance. Plain knitted fabric is stretchable, and usually it can be stretched more along the curling width than along the length. The fabric is unbalanced, and has a tendency to curl at the edges because the loops are being pulled in one direction. This condition can be corrected in fabric finishing. Textile Handbook 4-19 One disadvantage of jersey fabric is that if one yarn breaks, it causes an unravelling of adjoining stitches, called a “run”. A wide variety of knitted fabrics are made with jersey knit, ranging from lightweight hosiery to thick, bulky sweaters. Figure 2.2.1 Plain Knit Structure This is a four courses repeat single knit structure, while knitting the four courses, tuck stitches are included in every alternate course and on alternate needles. It has a honeycomb appearance, will not ladder easily. This structure is generally knitted on a fine gauge machine for summer T-shirts. Figure 2.2.2 Lacoste Knitting and Knitted Fabrics 2.2.2 Lacoste 4-20 Knitting and Knitted Fabrics 2.3 Double Knit Structures 2.3.1 Rib This structure is produced by the needles of both beds with alternate wales of plain stitches and purl stitches on both sides of the fabric. When all the needles in the machine participate in the knitting procedure, a 1x1 rib is formed. If two wales of plain stitches and two wales of purl stitches appear alternately on both sides of the fabric, this is called a 2x2 rib. A 3x1 rib has three wales of plain stitches and one wale of purl stitches on one side. Rib-knit fabric, usually being symmetrical on both sides, is not subjected to unbalanced stresses. It does not curl at the edges. Also, rib knits have greater elasticity in their width than their length. Rib structures are bulkier and heavier than plain structure provided the yarn used and machine gauge are similar. Rib structure cannot be unravelled from the edge knitted first, that is from the bottom. Similar to plain structure, a dropped stitch can start a chain reaction and produce a “ladder” in the structure. Figure 2.3.1 Ribs 1x1 Rib 2x2 Rib 2.3.2 Half Milano This is a rib based, two courses repeat structure. The first course is 1x1 rib, the second course knit on the front needle and welt (miss) on the back needle. The fabric is harsher and tighter than ordinary rib, and this method is mainly used for sweater production. Textile Handbook 4-21 Figure 2.3.2 Half Milano Face Back 2.3.3 Full Milano Figure 2.3.3 Full Milano 2.3.4 Full Cardigan This is a rib based two courses repeat structure, the first course knit knit on the front needle and tuck on rear needle. the second course is the reverse of the first course. It has same appearance on both side, but it is shorter and wider than ordinary rib structure. Because of the large number of tuck stitches, full cardigan are very bulky. They are used for heavy outerwear when knitted in coarse gauge. It also can be used as T-shirt collar. Knitting and Knitted Fabrics This is a rib based, three courses repeat structure. The first course is simply 1x1 rib. The second course is knitted on the back needle but missed on the front needle. The third course is knitted on the front needle but missed on the back needle. Full milano has the same appearance on both faces of the fabric. As the structure contains miss stitches, the widthwise stretchability of the fabric is tighter than 1x1 rib fabric. 4-22 Knitting and Knitted Fabrics Figure 2.3.4 Full Cardigan 2.3.5 Half Cardigan This structure is a special effect produced when one half of the cardigan repeat is substituted for a regular 1x1 rib structure. One side of the fabric looks like a “Cardigan” structure, while the loops of the other side acquires a very rounded and attractive shape which is usually used as the face side. Figure 2.3.5 Half Cardigan 2.3.6 Purl Structure Purl knits require the participation of both needle beds for the production of the loops. In purl-knit fabrics, each wale contains both plain stitches and purl stitches. Simple purl fabric looks the same on both sides of the fabric, and they both appear somewhat like the back of jersey. A purl-knit fabric, where one course has all plain stitches and the next course has all purl stitches, and the cycle repeats on the third course, is known as a 1x1 purl. Textile Handbook 4-23 Originally, purl-knit production required special equipment using double ended latch needles. The needle beds of this machine are set on the same plane instead of being in an inverted “V” formation. It is called a links/links machine, thus, the fabric produced is sometimes called links/links fabric. Nowadays, purl structure can be produced on a sophisticated “V” bed flat knitting machine with loop transfer mechanism. Purl-knit fabrics tend to lie flat and do not curl as jersey knits do. Basic purl knit structures, such as 1x1 or 2x1, contract in the length direction. They have greater elasticity in the length direction. It is probably this property that makes purl knits so widely used in infant’s and children’s wear. Also purl knits are thicker and thus better insulators than jersey knits of the same yarns and densities. Sinker Needle bed Figure 2.3.6(2) Purl Knitted Structure 1x1 Purl Fancy Purl Knitting and Knitted Fabrics Figure 2.3.6(1) Knitting Procedure of a Links/Links Machine 4-24 Knitting and Knitted Fabrics 2.3.7 Interlock Fabrics This is a variation of rib knits made on the interlock gating circular machine. On interlock knits, columns of wales are directly behind each other, thus the back of any given plain stitch on the interlock fabric will reveal another plain stitch directly behind it. Interlock knits, when compared to similar 1x1 rib knits, are smoother, more stable and better insulators. Their dimensional stability plus the fact that they do not tend to easily stretch out of shape contributes to their popular usage for outerwear and underwear. Figure 2.3.7 Interlock 2.4 Structures and Techniques Commonly Applied to Sweaters 2.4.1 Intarsia This is a weft-knitted plain or purl fabric containing designs in two or more colours. Each area of colour is knitted from a separate yarn, which is contained entirely within that area. Figure 2.4.1 Intarsia Textile Handbook 4-25 2.4.2 Designs Through Loop Transfer These include open-work design such as pointelle, cable design and fully-fashioned knits. a) Pointelle: this is an open-work design, where the aperture is created by transferring loops from needles to their adjacent needles. The empty needles can later resume the knitting operation and produce the desired apertures. Figure 2.4.2a Pointelle Figure 2.4.2b Cable c) Fully-fashioned knits: fashioning is a method of shaping (narrowing and widening) a knitted fabric during the knitting process. It is popular in sweater manufacture where the shape and contour of the shoulder and bust can actually be knitted to body contour shape. Full fashioning is done on flat bed full-fashioned knitting machines. The knitting machine adds or drops stitches at the end of the fabric to Knitting and Knitted Fabrics b) Cable design: when two groups of needles transfer their loops from one to another and then continue to knit through them, their wales cross at the transfer points and produce the cable design. 2.5 Special Knit Fabrics Produced by Circular Knitting ... 4-26 2.5.1 2.5.2 2.5.3 2.5.4 2.5.5 2.5.6 2.5.7 High-Pile Knits ............................................................ 4-26 Knitted Terry ............................................................... 4-27 Knitted Velour ............................................................. 4-28 Fleecy Fabric ............................................................... 4-28 Coloured Stripe Fabrics ............................................... 4-29 Jacquard Fabric ........................................................... 4-30 Polar Fleece ................................................................. 4-31 Section 3 - Yarn Count and Machine Gauge ........... 4-32 3.1 Yarn Count and Machine Gauge for Circular Knit ...... 4-32 3.2 Yarn Count and Machine Gauge for Wool Knitwear .... 4-34 Section 4 - Quality and Production of Circular Knitting .................................................... 4-36 4.1 Pre-requisites of a Circular Knitting Machine ............... 4-36 4.2 Production Conditions for Knitting ................................ 4-37 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.3 Production Calculations ................................................... 4-38 4.3.1 4.4 Selection of Proper Yarn Count ................................... 4-37 Setting of the Knitting Machine. ................................. 4-37 Yarn Storage ................................................................ 4-38 Air Conditioning of the Knitting Plant ........................ 4-38 Cleaning of Knitting Machines ................................... 4-38 Introduction ................................................................. 4-38 Quality Characteristics of Ring-spun 100% Combed Cotton Yarn for Circular Weft Knitting ......................... 4-40 Section 5 - Fabrics analysis ........................................ 4-45 5.1 The Geometry of Plain Weft-knitted Fabric .................. 4-45 5.2 ßStitch Density (Fabric count) ......................................... 4-46 5.3 Cover Factor ...................................................................... 4-46 5.4 Prediction of Knitted Performance by Mathematical Model ................................................................................. 4-47 5.4.1 5.4.2 5.4.3 5.4.4 5.5 Engineering the Fabric ................................................ 4-47 Checking the Specification ......................................... 4-47 Calculations Based on K values .................................. 4-48 Limitations of K values ............................................... 4-50 STARFISH - Engineered Knitted Program for Cotton Circular Knits ................................................................... 4-51 4-26 Knitting and Knitted Fabrics widen or narrow the cloth desired. Fully-fashioned articles can be recognized by fashioning marks which appear as distorted stitches in the area of the shaped portion. Figure 2.4.2c Shaping of a Knitted Panel 2.5 Special Knit Fabrics Produced by Circular Knitting Many unique and versatile fabrics can be created in weft-knitting. Fabrics which look like terry cloth towelling, a smooth velour, or even a simulated fur are examples of this group of specialized knit fabrics. 2.5.1 High-Pile Knits Imitation furs are usually made from a special type of jersey knit which involves feeding staple fibre in the form of sliver into the knit material while the yarns are passing through the knitting needles as the fabric is being made. Acrylic is the most popular fibre used for the pile portion. After knitting, a variety of finishing treatments are given to produce the desired fur-like effect. In addition to their popular use in imitated fur coats, high-pile knits are widely used as coat lining, car and airline blankets, lining for footwear and hat. Textile Handbook 4-27 Figure 2.5.1(1) High-pile Circular Knitting Machine SK-18 II (Mayer Industries Inc.) Figure 2.5.1(2) High-pile Knitted Falnic Back 2.5.2 Knitted Terry These fabrics are jersey-knit materials which are knitted with two yarns feeding simultaneously into the same knitting needles. When completed, one yarn appears on the face, the other on the back. One of the yarns is called a loop yarn, the other a ground yarn. The loop yarns are pulled out by special devices and become the loop pile of the knitted terry fabric. Figure 2.5.2(1) Terry Structure Ground yarn Loop yarn Knitting and Knitted Fabrics Face 4-28 Knitting and Knitted Fabrics Figure 2.5.2(2) Special Sinker for Pile Loop Formation Figure 2.5.2(3) Knitted Terry Fabric Technical Back Technical Face 2.5.3 Knitted Velour These fabrics are made in the same way as knitted terry. The loop pile is cut by a process called shearing, and then brushed. Knitted velours have a soft, downy, suede-like texture, resembling velveteen. They are softer and more flexible than velveteen. Figure 2.5.3 Knitted Velour 2.5.4 Fleecy Fabric Two-thread fleecy and three-thread fleecy fabrics are mainly produced on plain circular knitting machines. On the technical back side (the side that V-shaped loops cannot be seen) of these fabrics yarn floats along the rows and is inlay tucked at intervals into the fabric base. Such yarns are called backing or fleecy yarns. Textile Handbook 4-29 The most common form of the interlacing points for inlay tucking are at each second needle (1:1 fleecy) or at each fourth needle (3:1 fleecy) of a row. Fig 2.5.4 shows the technical back of a staggered 3:1 fleecy. In row 8, the fleecy yarn 7 is inlay tucked at the wales 3, 7, 11, etc., and in row 10 the fleecy yarn 9 is inlay tucked at the wales 1, 5, 9,. etc. It is common that the technical back of the fleecy fabric will be raised to produce a soft hairy surface. In the three-thread fleecy fabric structure, the fleecy yarn is invisible on the technical front even when using yarns with differing thickness. The structure is composed of fleecy yarn, binding yarn and face yarn. It is produced on a special plain circular knitting machine. The specially constructed holding-down/knocking-over sinker has two throats. Simple Staggered Fleecy 3:1 Structure 1,2,3,4,5 = wales 6,7,8,10,12 = ground yarn 7,9,11 = fleecy yarn Figure 2.5.4(2) Fleecy Fabric Back Face 2.5.5 Coloured Stripe Fabrics Horizontal colour stripes in weft-knit fabrics is the simplest designer technique by colour arrangement of yarns. In circular knitting, it requires only the proper arrangement of colour yarn cones in sequence on the yarn creel. No mechanical adjustments or alteration of stitch types is necessary. Using this method, a wide variety of colour combinations is possible. However, the size of the repeat pattern of the horizontal colour stripe produced by colour yarn cones arrangement is limited. If uneven colour stripe width and larger pattern repeats are required, it is neceesary to apply the yarn changer device-stripers. The striping Knitting and Knitted Fabrics Figure 2.5.4(1) 4-30 Knitting and Knitted Fabrics pattern is achieved by selecting the colour finger on each feeder. The number of fingers on each feerder is ranged from 4 to 6. The selection of the colour finger is either controlled by a series of pin on a mechanical chain (engineering stripe) or controlled by a microprocessor where the pattern data is stored (computerised auto stripe). Figure 2.5.5 Yarn Change Device (Terrot) 2.5.6 Jacquard Fabric In jacquard knits, each needle can be individually controlled for each course and therefore patterns can be created. Jacquard structure can be produced on either single or double jersey fabrics. Single jersey colour jacquard is usually composed of two or more yarns of differing colour to give a construction that consists essentially of knit and float loops. If the float is too long, tuck loop is incorporated. The surface pattern is derived from the chosen arrangement of the colour yarns and of the knit and float loops. For rib colour jacquard produced on a circular machine, the pattern-based needle selection is undertaken on the cylinder needles, while the reverse side of the jacquard fabric is produced on the dial needle. In order to control the fabric weight and the course density on the back side of the jacquard fabric, different knitting patterns (backing) can be used for the dial needles. Figure 2.5.6 Jacquard Fabric Textile Handbook 4-31 2.5.7 Polar Fleece Figure 2.5.7 Polar Fleece Fabric Face Back Knitting and Knitted Fabrics This is a knitted fabric either with very high specific volume or very bulky. The bulkiness of polar fleece is obtained by brushing both sides of the knitted fabric. Regular polar fleece fabric weighs 240 g/ m2, 280 g/m2 and 320 g/m2 and has a width of 60 to 62 inches. Singlesided loop pile knitted fabric, commonly known as French Terry, is used as the ground fabric structure. After dyeing, the fabric is brushed. Brushing is the process to convert the plush fabric into polar fleece. The whole process consists of several stages of brushing. To give a finishing touch to the face side of the polar fleece, a raising process is carried out by passing the fabric over a flexible card wire machine. The raising process has the effect of paralleling the fibres on the fabric surface and also increasing the bulk. Shearing takes place right after raising to give an even surface. The transformation of a plush fabric into a polar fleece fabric can be considered as completed. However, most polar fleece fabrics are subjected to a further process called antipilling for improving the pilling resistance. The entire process is carried out using a tumble dryer. Mechanical agitation and heat causes the fibres on the fabric surface to tend to bunch up and form regular beads on the surface. Bunched up fibres reduce the freedom of fibre movement and the pilling resistance can be improved. Finally, the fabric goes through a stenter to heat set the dimension and adjust the required fabric weight. 4-32 Knitting and Knitted Fabrics SECTION 3 YARN COUNT AND MACHINE GAUGE 3.1 Yarn Count and Machine Gauge for Circular Knit The following tables contain practical values of the average count of yarn to be used depending on the machine gauge and several fabric types. The values in Ne refer to staple fibre yarns and those in dtex are related to filament yarns. Filament yarns are always finer as compared to staple fibre yarns due to the differences in the running behavious. Machine gauge Needles/inch 14 15 16 18 20 22 24 26 28 30 32 Table 3.1(1) Machine gauge Needles/inch 12 14 15 16 18 20 22 24 26 28 30 32 Yarn count Ne 8.5/1 - 14.0/1 10.5/1 - 16.5/1 12.0/1 - 19.0/1 14.0/1 - 23.5/1 18.0/1 - 26.0/1 21.5/1 - 29.5/1 23.5/1 - 35.5/1 426.01 - 41.5/1 29.5/1 - 47.5/1 35.5/1 - 59.0/1 41.5/1 - 71.0/1 dtex 200 x 2 - 235 x 1 150 x 2 - 200 x 1 250 x 1 - 167 x 1 200 x 1 - 150 x 1 167 x 1 - 122 x 1 150 x 1 - 110 x 1 140 x 1 - 100 x 1 122 x 1 - 84 x 1 110 x 1 - 76 x 1 100 x 1 - 67 x 1 84 x 1 - 55 x 1 Yarn Count and Machine Gauge for Single Jersey Fabric Yarn count Ne 2.5/1 - 9.5/1 3.5/1 - 12.0/1 4.7/1 - 14.0/1 6.0/1 - 16.5/1 7.0/1 - 18.0/1 8.5/1 - 20.0/1 10.5/1 - 23.5/1 14.0/1 - 26.0/1 16.5/1 - 29.5/1 19.0/1 - 35.5/1 21.5/1 - 41.5/1 23.5/1 - 47.5/1 dtex 720 x 2 - 622 x 1 620 x 2 - 500 x 1 500 x 2 - 420 x 1 833 x 1 - 360 x 1 660 z 1 - 300 x 1 500 x 1 - 280 x 1 360 x 1 - 200 x 1 300 x 1 - 167 x 1 250 x 1 - 150 x 1 200 x 1 - 122 x 1 150 x 1 - 110 x 1 122 x 1 - 84 x 1 Textile Handbook 4-33 Table 3.1(2) Yarn Count and Machine Gauge for Fleecy Fabric Machine gauge Needles/inch 14 15 16 18 20 22 24 Yarn count Ne 16.5/1 - 23.5/1 20.0/1 - 29.5/1 23.5/1 - 35.5/1 29.5/1 - 47.5/1 41.5/1 - 53.0/1 47.5/1 - 59.0/1 53.0/1 - 71.0/1 dtex 235 x 1 - 150 x 1 200 x 1 - 122 x 1 167 x 1 - 100 x 1 150 x 1 - 90 x 1 122 x 1 - 76 x 1 100 x 1 - 67 x 1 84 x 1 - 55 x 1 Table 3.1(4) Yarn Count and Machine Gauge for Interlock Fabric Table 3.1(5) Yarn count Ne 12.0/1 - 16.5/1 14.0/1 - 19.2/1 16.5/1 - 21.5/1 21.5/1 - 23.5/1 23.5/1 - 29.5/1 28.5/1 - 35.5/1 33.0/1 - 41.5/1 35.5/1 - 47.5/1 41.5/1 - 53.0/1 47.5/1 - 59.0/1 53.0/1 - 71.0/1 dtex 235 x 1 - 167 x 1 220 x 1 - 150 x 1 200 x 1 - 133 x 1 167 x 1 - 110 x 1 150 x 1 - 100 x 1 133 x 1 - 100 x 1 122 x 1 - 90 x 1 110 x 1 - 84 x 1 10 x 1 - 76 x 1 90 x 1 - 67 x 1 76 x 1 - 50 x 1 Yarn Count and MachineGauge for Jacquard Fabric Machine gauge Needles/inch 14 15 16 18 20 22 24 26 28 30 Yarn count Ne 13.0/1 - 18.0/1 14.0/1 - 19.0/1 16.5/1 - 21.5/1 18.0/1 - 23.5/1 21.5/1 - 26.0/1 23.5/1 - 28.5/1 26.0/1 - 33.0/1 dtex 235 x 1 - 200 x 1 220 x 1 - 167 x 1 200 x 1 - 150 x 1 167 x 1 - 122 x 1 150 x 1 - 110 x 1 122 x 1 - 100 x 1 100 x 1 - 84 x 1 84 x 1 - 78 x 1 78 x 1 - 67 x 1 67 x 1 - 50 x 1 Knitting and Knitted Fabrics Machine gauge Needles/inch 14 15 16 18 20 22 24 26 28 30 32 4-34 Knitting and Knitted Fabrics Table 3.1(3) Yarn Count and Machine Gauge for Fine Rib Fabric Fibre Wool Cotton Polyester filament Polyamide filament Acylic yarn Machine gauge (needles/inch) 10 12 14 640 500 420 300 280 235 190 15 300 280 140 16 30 235 140 18 250 220 140 20 250 194 122 22-24 28-32 40-42 200 150 125 63 95 50 400 350 250 150 150 125 125 100 300 235 200 200 200 167 150 76 33 Table 3.1(6) Mean Yarn Counts (in dtex) for some Fibre Materials in relation to the Machine Gauge 3.2 Yarn Count and Machine Gauge for Wool Knitwear Table 3.2 on yarn count conversion and machine gauge has been compiled for guidance only. It should be stress that this information is only intended as a rough guide and knitting trials should always be carried Textile Handbook 4-35 out when introducing a new yarn to a machine. Machine Type Machine Gauge Metric Count Tex Needles per Table 3.2 Relationship between Machine Gauge and Yarn for Wool Knitwear Straight Bar Fully Fashioned Double Jersey Single Jersey 8/2 - 11/2 11/2 - 18/2 13/2 - 20/2 20/2 - 28/2 22/2 - 32/2 28/2 - 36/2 32/2 - 40/2 250/22 - 176/2 176/2 - 110/2 147/2 - 98/2 98/2 - 74/2 88/2 - 64/2 74/2 - 55/2 64/2 - 50/2 Needles per Inch 2 1/2 3 1/2 5 7 8 10 12 14 2/2 - 4/2 3/2 - 7/2 7/2 - 16/2 13/2 - 18/2 16/2 - 25/2 25/2 - 36/2 30/2 - 47/2 36/2 - 60/2 885/2 - 442/2 590/2 - 295/2 295/2 - 126/2 147/2 - 110/2 126/2 - 80/2 80/2 - 55/2 68/2 - 42/2 55/2 - 34/2 Needles per Inch 12 14 16 18 22 18/1 - 26/1 22/1 - 32/1 28/1 - 36/1 32/1 - 40/1 36/1 - 45/1 55/1- 40/1 44/1 - 32/1 37/1 - 28/1 32/1 - 25/1 28/1 - 22/1 Needles per Inch 5 7&8 10 12 14 16 18 20 22 24 26 28 11/2 - 27/2 18/2 - 32/2 22/2 - 36/2 27/2 - 40/2 32/2 - 45/2 36/2 - 50/2 40/2 - 30/1 45/2 - 32/1 28/1 - 34/1 32/1 - 39/1 36/1 - 45/1 40/1 - 50/1 176/2 - 74/2 110/2 - 63/2 88/2 - 552 74/2 - 50/2 63/2 - 44/2 55/2 - 40/2 50/2 - 34/1 44/2 - 32/1 37/1 - 30/1 32/1 - 26/1 28/1 - 22/1 25/1 - 20/1 Knitting and Knitted Fabrics Flat ‘V’ Bed and Circular 1.5 inches 9 12 15 18 21 24 27 4-36 Knitting and Knitted Fabrics SECTION 4 QUALITY AND PRODUCTION OF CIRCULAR KNITTING 4.1 Pre-requisites of a Circular Knitting Machine • The machines must be installed on a horizontal floor and, as far as possible without vibration. • The bobbin carriers must be mounted in such a way that the yarn does not rub against the sides of the package when it is withdrawn. • Yarn should be guided from the package up to the knitting area without unnecessary deviations in order to avoid additional increases in tension. • If basic knitted structures are used to a large extent, the machines should be equipped with yarn feeding units which generate a constant and low yarn tension (running-in tension) and deliver a uniform yarn length. • Yarn guide devices must be flawless; eyelets made of porcelain or sintered ceramic must have a smooth surface without any furrows. • The needles must also be flawless. If synthetic yarns are processed to a large extent in a 3-shift operation, they might have to be renewed after just 6 months. • The shape of the needle, and especially of the needle hooks, must be adapted to the machine gauge and the yarn count. • The needle beds must be exactly centered towards one another. • Needle beds are subject to a high strain while producing tight fabrics from synthetic yarns. If wear and tear occurs here, it can cause problems in subsequent processing (roughening, cracks) • The fabric take-down and wind-on tensions must be capable of being set individually and in such a way that tension peaks, reverting back to the knitting zone, do not arise. Textile Handbook 4-37 4.2 Production Conditions for Knitting 4.2.1 Selection of Proper Yarn Count The selection of yarn count is primarily determined by the gauge of the knitting machine. For example, for a worsted type 100% wool yarn: Machine pitch x 2 = correct yarn count (Ne or Nm), except for plain and purl machines Machine pitch x (1.0 to 1.5) = correct yarn count (Ne or Nm) for plain and purl machines. • different machine types and difference in basic construction of the same type of machine; • knitted structure related to number of feeders involved; and • types of yarn such as processing a blended yarn when in practice a finer yarn should be used; Figure 4.2.1 Relation Between Knitted Structures and Processing Problems The degree of difficulty in processing varies with the different knitted structures. Degree of Difficulty in Processing Structures Low Interlock, 2-colour jacquard, 3-colour jacquard, 2:2 cross tubular, Ponti di Roma Medium Double pique, 4-colour jacquard High Rib, Half milano, Relief and combined patterns of muticolour jacquard 4.2.2 Setting of the Knitting Machine. Optimum setting is difficult because several factors must be balanced against one another in a proper relationship. This balanced relationship should be found between : • yarn tension before and after the yarn feeder (minimum yarn tension prior to the yarn feeder) Knitting and Knitted Fabrics Deviations from this formula may be due to factors including 4-38 Knitting and Knitted Fabrics • drawing-in of yarn at the cylinder and the dial (it is easier to obtain a loose fabric by having a larger distance between dial and cylinder than by having a longer drawing-in range for the needles) • height of dial (with the tightest setting a minimum distance between dial and cylinder is necessary) • fabric take-up tension (it should be as low as possible) 4.2.3 Yarn Storage Dried yarn has limited extension, so it should be stored in rooms with at least 65% relative humidity (at 200C). Storage under extreme temperatures must be avoided because in high temperatures there might be a danger of wax migration, while at low temperatures water condensations build up. 4.2.4 Air Conditioning of the Knitting Plant It is recommended a relative humidity of 55% ± 10% at a temperature of 25oC ± 3oC. 4.2.5 Cleaning of Knitting Machines Fluff removal should take place at least at the end of each shift, fly accumulated in the cam area should be removed as it becomes visible, and residual wax on tension discs and yarn guide elements should be removed occasionally 4.3 Production Calculations 4.3.1 Introduction The performance of the circular knitting machine is affected by the elements such as frame, drive, yarn feeder, cam set-up, fabric takeup, yarn delivery device and monitoring and servicing devices. To calculate the production it is necessary to have several characteristic values of the corresponding knitting machine and the product being produced. Textile Handbook 4-39 a) Elements Knitting Machine Parameters - machine diameter “D” (inch) - gauge “E” - no. of feeders “S” - no. of machine revolutions/min “n” - efficiency “ η“ Product Parameters - structure - type and count of yarn - course density “MR./cm” - wale density “MS/cm” - fabric weight “FG” (g/m 2) The efficiency (“η ”) is the ratio of the practically obtained performance to the theoretical performance and is always smaller than 1. b) Formulae : Machine performance “L” in metre per hour (m/h): S x n x 60 xη feeders / course x MR / cm x 100 Fabric width “B” in metres: B (m) = D x 3.14 x E MS / cm x 100 Machine performance “G” in kg per hour (kg/h) G (kg / h) = L x B x FG 1000 c) Example : - Machine diameter 30 inch - gauge E 28 - no. of feeders 96 - machine speed 35 rpm - efficiency η 0.85 - structure : plain (single jersey) - yarn : cotton Ne29.6/1 - course density 18 MR/cm - wale density 13 MS/cm - fabric weight 125 g/m2 Machine performance L (m/h) 96 x 35 x 60 x 0.85 =95.2m / h L= 1 x 18 x 100 Fabric width B (m) 30 x 3.14 x 28 =2.03m B= 13 x 1000 Machine performance G (kg/h) G= 95.2 x 2.03 x 125 =24.2kg / h 1000 Knitting and Knitted Fabrics L (m / h) = 4-40 Knitting and Knitted Fabrics 4.4 Quality Characteristics of Ring-spun 100% Combed Cotton Yarn for Circular Weft Knitting (Source: Zellweger Uster) A knitting yarn (100% combed cotton) for high-production circular weft knitting and good quality knitwear should exhibit the following quality characteristics Table 4.4 (1) Quality Requirement of a Cotton Yarn for Knitwear Count variation CVt, cut length 100 m** Count variation CVt, cut length 10m** Breaking tenacity* [Fmax/tex] Variation of breaking force [CVF max] Elongation at breaking force [Efmax] Variation of elongation at break Yarn twist ( ∝ m value) Paraffin waxing/surface friction value Yarn irregularity ** Thin places/Thick places/Neps Hairiness H*** Between-bobbin hairiness variation H**** CVb Seldom-occurring thin and thick places faults (CLASSIMAT values) Remaining yarn faults (CLASSIMAT values) <1.8% <2.5% <10 cN/tex <10% <5.0% <10% Ring-spun yarn 94-110 ideal around 0.15µ <25% value of the USTER® STATISTICS <25% value of the USTER® STATISTICS [e.g.>50% value of the USTER® STATISTICS] <7% A3/B3C2/D2 OR D1 or more sensitive (clearing limit) A3 + B3 + C2 + D2 = <5/100,000m * A low breaking force value must be compensated by a higher elongation at breaking force value ** Highest requirements with single jersey *** Higher, but constant hairiness as a result of the cloth appearance and handle. The minimum hairiness value must be set based on agreements between the partners **** Variation between packages. Higher values can lead to rings with singlecoloured fabrics. Textile Handbook 4-41 From Table 4.4 (1), it can be seen that it is not one single peak value which determines the quality of the end product, but a compromise between the various quality characteristics. In contrast to weaving yarns, the yarn strength of knitwear yarns, for example, is secondary, as the loading placed on the yarn during knitting is lower than that with a high-production weaving machine. The yarn must, however, exhibit enough elongation and elasticity. There must be no weak places or thick places which can result in stops, holes in the knitted material or even broken needles. Particularly important is the ability of the yarn to be guided easily through the various elements of the machine (low friction value). The moisture content of the yarn should be evenly distributed. Conditioned yarns provide better running properties and better appearance of the finished fabric. Particularly important is the yarn evenness and count variation. Both the short and medium-term, as well as the long-term count variations lead to cloudy or stripy fabrics as soon as a certain mass variation level is over stepped. Also neps and vegetable matter, as well as a high dust content, refer to the types of foreign matter which are particularly disturbing. These lead to wear of the needles, holes in the knitted material and even to dyeing problems. All these yarn characteristics can be responsible for downgrading the knitted fabric, and can have some influence on the ‘knitability’, ‘spirality’, ‘dyeability’ or ‘contamination’ problems associated with circular weftknit fabrics. A large European Knitwear manufacturer has set out the yarn specifications for certain types of knitted structure. Table 4.4.(2) shows the yarn quality specifications corresponding to the yarn count and recommended raw material. Knitting and Knitted Fabrics In most cases, an even and high hairiness value with a low twist is required in order to achieve a soft material handle. This hairiness value must, however, remain constant and be without periodic variations. 4-42 Knitting and Knitted Fabrics Table 4.4 (2) Yarn specifications demanded by a European knitwear manufacturer Evenness Thin Neps Knitwear Thick (cvm%) places places per km type * per km per km * (-50%) Nm (Tex) Cotton Combed Twist factor /(inch) Break tenacity (cN/ tex) CV (Fmax %) 34 (29.5) Am 3.3 12.5 9.0 13.0 4 50 60 Single jersey 40 (25) Am 3.3 13.0 9.0 13.0 6 50 70 Single jersey 50 (20) Maco 3.3 3.3 9.0 14.0 8 35 80 Double rib 50 (20) Peru 3.5 12.0 9.0 14.5 10 70 80 Double rib 50 (20) Am 3.5 13.0 9.0 14.5 10 70 90 Fine rib 55 (18.2) Am 3.5 13.5 9.0 15.0 12 90 110 60 (16.6) Maco 60 (16.6) Am 3.4 16.0 9.0 14.5 12 50 90 Fine rib + Single jersey Double jersey 3.5 13.5 9.0 15.0 15 100 150 Double jersey 70 (14.4) Am 3.6 13.5 10.0 15.5 20 100 120 Tricot + Fine rib 70 (14.4) Maco 3.3 16.0 9.0 14.5 15 50 90 Fine rib 85 (11.8) Maco 3.5 16.0 9.0 15.0 20 60 100 2/85 Tricot 2:2 100 (10) Maco 3.5 16.0 10.0 15.5 25 70 100 Fine rib 120 (8.4) Maco 3.6 16.5 11.0 16.5 40 90 120 Fine rib • Settings of sensitivity at the USTER® TESTER 3 Textile Handbook 4-43 There is another set of yarn specifications for knitted fabric recommended by a well-known European retailer of knitted goods. It refers to five yarn counts of 100% combed cotton yarns used for various structures in weft circular knitted fabrics. Table 4.4 (3) Yarn specifications demanded by a European retailer of knitted goods Ne 24 25 tex Ne 30 20 tex Ne 34 17.5 tex Ne 38 15.5 tex Evenness CVm% max.* max.* A% CVt100% Twist/m ±* ≤* 568±38 ±* ≤* 675±85 max. 12.3 ±1.5 ≤1.8 755±38 max. 13.0 ±1.5 ≤1.8 826±38 max. 13.5 ±1.5 ≤1.8 910±38 THIN/km (-50%)** THICK/km ** NEPS/km ** Tenacity Fmax/tex CVFmax% max.* max.* max.5 max.5 max.8 max.* max.* max.20 max.25 max.35 max.* max.* max.40 max.60 max.80 min.13CN min.13CN min.13CN min.13CN min.13CN ≤10.0 ≤10.0 ≤10.0 ≤10.0 ≤10.0 Elongation at Break Efmax% min.6.2 min.6.0 min.5.8 min.5.6 min.5.5 A1/B1/ C1/D1*** /100km (remain) A3/B3/ C2/D2*** /100km (remain) mean 75 max.150 mean 85 max.170 mean 100 max.200 mean 125 max.250 mean 150 max.300 mean 3 max.5 mean 3 max.5 mean 3 max.5 mean 4 max.7 mean 5 max.8 E/100km*** (remain) max.1 max.1 max.1 max.1 max.1 H2/I2 100km*** (remain) max.3.5 max. 3.5 max. 3.5 max. 3.5 max. 3.5 * ** *** According to agreements with the yarn processor Settings of sensitivity at the USTER®TESTER 3 Sensitivity levels of the USTER®CLASSIMAT Knitting and Knitted Fabrics Ne 18 27 tex 4-44 Knitting and Knitted Fabrics If it is to be expected that the setting out of yarn specifications as the basis for agreements between the yarn manufacturer and the yarn processor will become a standard procedure in the same way that a yarn can be “engineered”, based on the fibre properties, a knitted fabric can also be “engineered” based on the yarn quality characteristics. This will necessitate a closer collaboration between the spinner and the knitter, and the need for the knitter to become better acquainted with the yarn quality characteristics and the values which can be expected. Textile Handbook 4-45 SECTION 5 FABRIC ANALYSIS 5.1 The Geometry of Plain Weft-knitted Fabric The dimension and construction properties of fabrics are important for the control of quality as well as for end-use determination. The theory of fabric geometry for a plain weft knitted fabric can be defined as follows: S = the number of stitches per square unit c = the number of courses per unit length l = the stitch or loop length. Wales/cm = w Courses/cm = c Stitch length = AB = l mm Stitches/cm2 = S Figure 5.1 A Plain Weft Knitted Structure Apart from the dominant factor, that is, the length of yarn in the knitted loop (stitch length), there are three dimensionally stable (relaxed) states possible for a knitted structure must be considered when applying the theory of the fabric geometry. Knitting and Knitted Fabrics w = the number of wales per unit width; and 4-46 Knitting and Knitted Fabrics The three relaxed states of a knitted fabric are: • Dry-relaxed state: the fabric has been taken off the knitting machine and in course of time attains a dimensionally stable condition called the dry-relaxed state. • Wet-relaxed state: if the fabric is soaked in water and allowed to dry flat, the wet-relaxed state is attained, again a dimensionally stable condition. • Finished relaxed state: in order to reach this stable condition, the fabric is subjected to agitation in water or steam, and a denser fabric results. 5.2 Stitch Density (Fabric count) The stitch density of a weft-knitted fabric can be expressed as the number of wales per unit length times the number of courses per unit length. 5.3 Cover Factor Covering power refers to the ability of an item to occupy space or to cover an area. A fabric with better cover will be warmer, look and feel more substantial, and be more durable. Cover Factor can be defined as a number that indicates the extent to which the area of a knitted fabric is covered by the yarn. It is also an indication of the relative looseness or tightness of the knitting. The Cover Factor (C.F.) can be determined by the following formula: CF= tex stitch length (mm) or CF= 1 stitch length (inch) x worsted count Textile Handbook 4-47 5.4 Prediction of Knitted Performance by Mathematical Model 5.4.1 Engineering the Fabric Fabric engineering in the modern sense implies that equations have to be available which can be used to calculate the fabric properties of interest, starting from the known manufacturing and processing conditions. The known manufacturing and processing conditions comprise: • The yarn (or selection of yarns) available for knitting. • The knitting specification (essentially, the length of yarn fed for each revolution of the machine). • The wet processing and finishing machinery characteristics. 5.4.2 Checking the Specification Normally the dyer and finisher does not participate in the fabric design and specification exercise. He has to accept whatever fabric is supplied, and he will usually be required to deliver the dyed and finished fabric at a certain weight and width and with certain maximum levels of shrinkage. If the fabric has not been appropriately engineered, then there is no way that the dyer and finisher will be able to meet all of these requirements. Therefore, it is absolutely essential that the dyer and finisher should be able to check whether the fabric is correctly engineered before he puts it into work. If the dyer and finisher has access to the equations which are used for fabric engineering, then he is able to make such checks. Knitting and Knitted Fabrics • The knitting machinery characteristics (essentially, the number of needles). 4-48 Knitting and Knitted Fabrics 5.4.3 Calculations Based on K values The K values were derived from observations made by research workers more than two decades ago that there is a strong relationship between the number of courses and wales per cm in a relaxed cotton knitted fabric and the reciprocal of the loop length used in knitting (see Figure 5.4.3). “Relaxed” means after the fabric has been subject to an appropriate wetting and drying procedure (e.g. a shrinkage test). Loop length is the average length of yarn in each knitted loop. It is given by the length of yarn fed to the knitting machine per revolution (or per pattern repeat) divided by the number of needles which are knitting. The two basic equations are: Course per cm = Kc/loop length in cm Wales per cm = Kw/loop length in cm Kc and Kw are constants for a given fabric construction and fibre type, and these K values can be used to calculate the course and wale densities in any fabric, provided only that the knitted loop length is known. Once the course and wale densities have been found for the relaxed fabric, then these can be used together with yarn count, the knitted loop length, and the number of needles in the knitting machine to calculate the relaxed fabric weight and width. Wt = tex x loop length x course x wales x F1 Width = number of needles/wales x F2 Where F1 and F2 are scaling factors, depending on the units of measurement. Courses and wales, weight and width in the unrelaxed fabric (i.e. as delivered to the customer) can then be derived by proportional scaling, according to the appropriate level of shrinkage. Length Shrinkage = (Cr - Cd) / Cr Width Shrinkage = (Wr - Wd) / Wr Where Cr and Wr and the relaxed courses and wales, Cd and Wd are the as-delivered values. Textile Handbook 4-49 If the calculated as-delivered weight and width values do not coincide with what the customer has specified, then the fabric has not been correctly engineered, and this is a matter for serious discussion between the dyer and finisher and the customer. If the calculated weight and width do coincide with the customer’s requirements, then the calculated values for as-delivered courses and wales provide the dyer and finisher with his primary finishing targets. If he can hit these values in the delivered fabric, then the calculated weight and width, and the shrinkage values used in the calculation are guaranteed. Since the yarn count and loop length should be known from the knitting specification, it would seem to be a simple task for the dyer and finisher to check that a given grey fabric has been correctly engineered so that the weight, width and shrinkages required by the customer can actually be delivered. Kc and Kw values can easily be picked up from the literature, or can be determined on the grey fabric already to hand. Figure 5.4.3 Effect of Loop Length on Grey Courses and Wales per cm Knitting and Knitted Fabrics The finishing targets can be used as the basis for setting and operating control systems on stenter and compactors, which will aid the finisher in achieving his targets, and thus the required fabric performance. In practice the width will be used in preference to the number of wales per cm for control purposes, but there is no satisfactory substitute for courses per cm as the primary length control parameter. 4-50 Knitting and Knitted Fabrics 5.4.4 Limitations of K values Unfortunately, it is now know that Kc and Kw are actually not constants. They are affected quite significantly by several factors including especially certain aspects of the yarn specification, and any wet processing which may have been carried out on the fabric. For example, K values for plain jersey fabrics, which have appeared in the literature over the last two decades, range from 5.1 to 5.8 for Kc and 4.1 to 4.95 for Kw. This range of variation is not some kind of experimental error. It is a reflection of real differences in K values, due to differences in the experimental conditions used by the various workers. It also represents approximately the range of K values which are found in experimental work. Some of these effects are illustrated by Figure 5.4.4 (1) and Figure 5. 4.4 (2) which show the influence of knitted Tightness Factor and wet processing on the values of Kc and Kw for a wide range of plain jersey fabrics, knitted from seven different yarns. Tightness Factor is given by the square root of the yarn count in tex divided by the Loop Length in cm. There are relatively large differences between the K values for grey fabric and those for the two sets of finished fabrics, and the wide scatter in the data, within a given wet process, is a reflection of the influence of the yarn properties upon the K values. In this context, it should be noted that a difference of only a unit in Kc represents difference in length shrinkage of about two percentage points; a similar difference in Kw represents two and a half percentage points of width shrinkage. Figure 5.4.4(1) Effect of Tightness Factor on Kc Textile Handbook 4-51 Figure 5.4.4(2) Effect of Tightness Factor on Kw 5.5 STARFISH - Engineered Knitted Program for Cotton Circular Knits (Source: Cotton Technology International) STARFISH is short for “START as you mean to FINISH. The STARFISH computer program is a simulator. It models the key elements of production and processing of cotton circular knitted fabrics and it calculates their expected performance. The STARFISH computer program is founded on a database which comprises test data on more than 5,000 separate fabric qualities, and is still growing year by year. Almost all of the data come from fabrics which have been manufactured and processed at full scale. These data are mainly of two types. Firstly, there are the systematic series of fabric qualities to perform the basic mathematical analysis to develop the underlying equations. Secondly, there are the results from sets of serial samplings of individual qualities, taken over a period of weeks or months in dyeing and finishing plants. These serve to validate the Knitting and Knitted Fabrics Therefore, a dyer and finisher who wants to make use of simple K values to check for correct fabric design, or to develop finishing targets, should take care to use the appropriate values. Because the K values are affected by the wet process, he would be well advised to carry out determinations of courses and wales on his own finished fabrics. It is definitely not the case that he can determine K values on the grey fabrics and use these for making calculations. Indeed, the only value for the dyer and finisher in making measurements on grey fabrics is to ensure that the yarn count and loop length are exactly as specified. 4-52 Knitting and Knitted Fabrics predictions of the current program and also to establish the normal variation which can be seen in commercial production. Using these data, it is possible to model (amongst others) the average influence of different types of yarns and different wet processing regimes, so that these average effects are already built into the model. Thus, using the STARFISH computer program, the average values for courses and wales, and the weight and width of an extremely wide range of dyed and finished fabrics can be estimated very rapidly and pretty accurately without the need for any physical knitting or finishing trials. The program will also calculate finishing targets for any desired level of shrinkage or any requested weight and width. It will also show whether a given set of customer demands can actually be met in principle, using the yarns, knitting machines, and wet processing machinery which are actually available. It should be emphasised that the equations used by STARFISH are not dependent in any way on K values. They include additional terms which allow for the yarn type, the yarn count, the wet process, and the depth of shade. To get started with a basic simulation model, the user can select from a list of four standand yarn types, ten standard processes and eight depths of shade. Up to nine different yarn count values can be specified, as well as nine different knitting machines (to simulate a body-width range). Section 6 - Typical Fabric Imperfections on Circular Knitting .................................... 4-53 6.1 Fabric Skew ........................................................................ 4-53 6.1.1 6.1.2 6.1.3 6.1.4 6.2 Definition .................................................................... 4-53 Causes ......................................................................... 4-53 Evaluation of the Effect of Yarn, Knitting and ............ Finishing Parameters on Skew .................................... 4-54 Summary ..................................................................... 4-58 Barre .................................................................................. 4-58 6.2.1 6.2.2 Definition of Barre ...................................................... 4-58 Causes of Barre ........................................................... 4-58 Section 7 - Warp Knitting and Warp Knitted Fabrics ..................................................... 4-61 7.1 Warp Knitting ................................................................... 4-61 7.2 Warp Knitting Machine Classification ........................... 4-61 7.2.1 7.2.2 7.3 Knitting Elements of Warp Knitting Machine ............... 4-63 7.3.1 7.3.2 7.3.3 7.3.4 7.4 Tricot Machines ........................................................... 4-62 Raschel Machines ........................................................ 4-62 Needle ......................................................................... 4-63 The Sinker ................................................................... 4-64 Guides and Guide Bars ................................................ 4-64 Driving Mechanisms of Knitting Elements ................. 4-65 Key Terms of Warp Knits ................................................ 4-66 7.4.1 7.4.2 7.4.3 7.4.4 7.4.5 7.4.6 7.4.7 Course and Wales ........................................................ 4-66 Stitch Density .............................................................. 4-66 Loop Parts ................................................................... 4-66 Open and Closed Laps ................................................ 4-67 Technical Back ............................................................ 4-67 Technical Face ............................................................. 4-67 Run-in .......................................................................... 4-68 7.5 Common Warp Knit Fabric Structures and their Characteristics .................................................................. 4-68 7.5.1 7.5.2 Tricot Fabrics .............................................................. 4-68 Raschel Fabrics ........................................................... 4-72 Textile Handbook 4-53 SECTION 6 TYPICAL FABRIC IMPERFECTIONS ON CIRCULAR KNITTING 6.1 Fabric Skew (Source: Cotton Incorpocated) 6.1.1 Definition Figure 6.1.1 Examples of Skew 6.1.2 Causes When discussing tubular knit goods, the skew deviation is usually composed of distortion caused by the yarn, the number of feeders on the machine, and the manner in which the yarn is knitted. Skew caused by the yarn is realized as a spiraling of the wales at a steep angle around the knitted tube. This type of skew causes the tube to torque. If a single wale is followed up the length of this tube, it can easily be seen that the wale will spiral around the tube. The courses will generally not be deflected from the horizontal. Distortion of the wale loops is usually seen in goods that are processed in tubular form in a preparation or dyeing process. In fact wale skew is readily seen when the fabrics are unloaded from the preparation or dyeing vessel Knitting and Knitted Fabrics Skew can be defined as a fabric condition resulting when the knitted wales and courses are angularly displaced from the ideal perpendicular angle. Other terms such as torque, spirality, bias and shear distortion are often used to refer to the same phenomena. Regardless of the term used, this displacement of the courses and wales can be expressed as a percentage or as an angle measurement in degrees. Examples of skew can be seen in Figure 6.11. 4-54 Knitting and Knitted Fabrics prior to de-twisting and extraction. If the fabric is then finished in a tubular manner and the wales are not straightened, then the distortion of the wales will be obvious. The level of course skew will include both yarn and machine influence. Also, it is important to realize that if the fabrics are slit in the grey on the same wale line and are undergo from wet processing to dry processing, then the wales will be straight and the courses may be skewed. Machines with a large number of feeders will make a fabric that has substantial ‘course skew’ as the fabric comes off the knitting elements. However, the course skew will be eliminated when the fabric is slit into open-width form. Yarn parameters that affect skew include twist level (twist multiple or turns per inch of twist), twist direction (S or Z), twist liveliness, and the spinning system. It is important to realize that skew from the yarn and the skew from the number of feeders on the machine can combine together to create more skew, or they may partially offset each other and result in less skew. This addition or subtraction of skew depends primarily on the yarn twist direction and the direction of rotation of the cylinder on the knitting machine. 6.1.3 Evaluation of the Effect of Yarn, Knitting and Finishing Parameters on Skew a) Test Method: the sample fabrics are measured for skew using a proposed test method being developed by AATCC. The samples are marked with a square before washing and tumble drying. If the fabric skews after five washes and dry cycles, the square can be measured for percent skew. The method uses a mathematical formula for shear distortion (skew) and is shown below: 2(AC-BD) x 100 % Skew = AC + BD Textile Handbook 4-55 Figure 6.1.3.a Proposed Test Method for Shear Distortion (Skew) of Knitted Fabric Where AC and BD are the diagonals of the square, <DAB = 90o, A’B’CD = Location of square after relaxation, b) Effect of Twist Multiple, Twist Direction and Yarn Spinning System on Skew The sample fabrics are knitted into 18 gauge single jersey with 18/1 Ne carded 100% cotton yarn. The Twist Multiples (TM) used for the Ring and O-E spinning systems are 3, 3.5 and 4. However, only one TM is used for the Air Jet spinning system. Table 6.1.3.b Effect of Twist Multiple, Twist Direction and Yarn Spinning System on Skew Grey Goods Ring Spun Z twist 3.0 3.5 4.0 Ring Spun S twist 3.0 3.5 4.0 Open-End Z twist 3.0 3.5 4.0 Murata Air Jet Z S % Skew (5 HLTD’s)* Skew Direction 10.5 12.6 18.5 Right Right Right 15.8 17.6 20.3 Left Left Left 3.5 5.2 8.7 Right Right Right 12.3 17.6 Right Left Note: * 5 washes and dry cycles Knitting and Knitted Fabrics DA’B’ > 90o 4-56 Knitting and Knitted Fabrics c) Effect of Twist Multiple, Twist Direction and On Machine Cylinder Rotation Direction on Skew Sample fabrics were made on two 28 gauge single jersey machine. 30/1 Ne Combed cotton ring spun yarns were knit at a tight stitch. The difference between the machines was the direction of cylinder rotation. Knitting evaluations included three yarn feeder setups. Comparisons included fabrics made with all feeds of S twist, all feeds of Z twist and alternating feeds of S and Z twist. Grey goods were tested for skew using the proposed AATCC method for shear distortion (skew)-the results are shown in Table 6.1.3c Table 6.1.3.c Effect of Twist Multiple, Twist Direction and on Machine Cylinder Rotation Direction on Skew Grey Goods % Skew (5 HLTD’s) Clockwise Rotation Z 15.3 S&Z 1.4 S 11.0 Counterclockwise Rotation Z 5.7 S&Z 2.6 S 7.5 Skew Direction Right Right Left Right Right Left d) Effect of Tightness of Stitch on Skew Sample fabrics were knitted with four different stitch tightness on a 28 gauge single jersey machine. The yarn used is a 30/1 ring spun 100% cotton and both grey goods and dyed goods were compared for skew. Table 6.1.3.d Effect of Stitch Tightness on Skew Course Length (ins) 245 260 270 280 Skew (5 HLTD’s) * Grey 8.6 12.3 15.1 16.8 Note: * All samples had right hand skew. Dyed Corrected for Skew 8.1 9.5 15.2 17.2 Textile Handbook 4-57 e) Effect of Skew Using Plied and Parallel Yarn The used of balanced, plied yarns has been practiced for years to give torque free fabrics. Table 6.1.3.e shows the skew test data for “S” and “Z” yarns spun side-by-side on a Air-jet spinning system and wound parallel onto the same package, and two strand of “Z” twist wound onto the same package and then plied on an uptwister at different twist. Table 6.1.3.e Effect of Parallel and Plied Yarns on Skew Using the Murata Air Jet Spinning System S & Z - 0 TPI 1.2 Z & Z - 0 TPI 21.0 Z & Z - 2.5 TPI Z & Z - 6.5 TPI Z & Z - 12.5 TPI Z & Z -14.5 TPI % Skew 5 HLTD’s Direction Right Right 17.0 11.3 0.0 3.5 Right Right None Left Note : * Each individual strand was a 40/1 Ne Air Jet Yarn. f) Effect of Finishing Techniques on Skew Sample fabrics, knitted on a 28 gauge single jersey machine with a 30/1 Ne combed ring spun yarn, were pre-treated and dyed on a jet machine, dried and finished by either compaction or resin treatment. One group of the finished fabrics has included skew correction. The skew test result are shown in table 6.13f Table 6.1.3.f Effect of Finishing Techniques of Skew Sample Grey Dyed & Compacted Dyed & Resin Finished % Skew, 5 HLTD’s With Correction — 8.1 6.0 Without Correction 8.6 3.5 2.0 Knitting and Knitted Fabrics 18 Cut, 100% Cotton* 4-58 Knitting and Knitted Fabrics 6.1.4 Summary Skew on 100% cotton single jersey is related to the level of yarn twist, the spinning system used, the strand configuration, the tightness of the knitted stitch, the number of feeders on the knitting machine, the rotational direction of the knitting cylinder and the finishing technique used. Any process that could be developed to reduce the twist liveliness of yarns could help reduce the total level of skew. Also, development of finishing techniques that could relax the yarns without inducing torque would be of interest. Today, the best answer for skew reduction is either the use of plied yarns or alternating feeds of opposite twist. If single yarns must be used, then resin finishing offers reasonable control of skew. 6.2 Barre 6.2.1 Definition of Barre The noun “BARRE” is defined by ASTM as an unintentional, repetitive visual pattern of continuous bars and stripes usually parallel to the courses of circular knit fabric. In a warp knit, barre normally runs in the length direction, following the direction of yarn flow. 6.2.2 Causes of Barre a) Factors which may cause or contribute to barre are listed as follows: (i) Raw Material - Fibre • Failure to control fibre diameter (micronaire or denier) from laydown to laydown. • Too high a C.V. of micronaire in the laydown for a given mill’s opening line blending efficiency. • Failure to control the fibre colour in the mix (greyness Rd, yellowness +b). Most, if not all, fibre barre can be controlled by the above three items; however, under certain unusual circumstances it may be beneficial to select mixes using ultraviolet reflectance information for each bale of cotton. Textile Handbook 4-59 (ii) Yarn Formation/Supply • Variations in carding; i.e., different amounts of nonlint content removal from card to card. • Poor blending of fibre in opening through finisher drawing. • Running different types of spindle tapes on ring spinning frame. • All cots running on a given set of ring frames producing yarn for the same end use should be exactly the same. • Mixing yarns of different counts. • Mixing yarns with different blend levels. • Mixing yarns from different suppliers. • Mixing yarns with different twist level/twist direction. • Mixing yarns with different degrees of hairiness. • Mixing yarns with different amounts of wax. • Mercerization differences. • Excessive backwinding or abrasion during this process. • If yarns are conditioned, then each lot must be uniformly conditioned. (iii) Fabric Formation • Improper stitch length at a feed. • Improper tension at a feed. • Variation in fabric take-up from loose to tight. • Excessive lint build-up. • Variation in oil content. • Worn needles, which generally produce length direction streaks. • Uneven cylinder height needles (wavy barre). • Double feed end. Knitting and Knitted Fabrics • Mixing yarns of different spinning systems. 4-60 Knitting and Knitted Fabrics b) Prevention of Barre Barre is caused by inconsistencies in materials, equipment, or processing. To prevent barre from occurring, consistency must be maintained through all phases of textile production. Stock yarns should be properly and carefully labelled to avoid mixups. Fugitive tints can be useful for accurate yarn segregation. Inventory should be controlled on a First In/First Out basis. All equipment should be properly maintained and periodically checked. Before beginning full scale production, sample dyeings can be done to check for barre. Salvaging a fabric lot with a barre problem may be possible through careful dye selection. Colour differences can be masked by using shades with very low light reflectance (navy blue, black), or high light reflectance (light yellow, orange, or finished white). Dye suppliers should be able to offer assistance in this area. Also, if the cause of the barre is an uneven distribution of oil or wax, a more thorough preparation of the fabric prior to dyeing may result in more uniform dye coverage. With close cooperation between production and quality control personnel, barre problems can be successfully analyzed and solved. Textile Handbook 4-61 SECTION 7 WARP KNITTING AND WARP KNITTED FABRICS 7.1 Warp Knitting Warp knitting is defined as a loop-forming process in which the yarn is fed into the knitting zone, parallel to the fabric selvedge. The source of yarn on a warp knitting machine is a warp beam similar to a warp beam on a loom. The yarns form a vertical loop in one course and then move diagonally (shogging) to another wale to make a loop in the following course. The yarns zigzag from side to side along the length and connect the loops into a fabric. Figure 7.1 Warp Knitting Mechanism Warp Knitting Mechanism 7.2 Warp Knitting Machine Classification There are two types of warp knitting machines: Tricot and Raschel. The distinction between Tricot and Raschel machines can be made by the type of sinkers with which the machine is equipped, and the role they play in loop formation. Knitting and Knitted Fabrics Warp knitting machines are usually flat machines, and each warp yarn is knitted by one needle. All the needles of the machine are mounted on a long needle bar equal to the width of the machine. When the needle bar is activated, all the needles act in unison. Each yarn is threaded through a yarn guide, and all the yarn guides are mounted on a yarn guide bar. Movement of the guide bar moves all the yarns mounted on it. The yarn guide bar moves laterally from left to right for several wales, and then back again. It guides the yarn to a new needle and wraps the yarn around it for its next stitch. 4-62 Knitting and Knitted Fabrics Figure 7.2 Tricot Machine (Karl Mayer) 7.2.1 Tricot Machines The sinkers used for tricot 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. Modern tricot machines are constructed with compound needles, while in the past tricot machines were equipped with beard needles. Tricot machines are commonly equipped with from two to four yarn guide bars and require the same number of warps to be used. 7.2.2 Raschel Machines In Raschel knitting, the sinkers are only used to ensure that the fabric stays down when the needles rise. The fabric is controlled by a high take-up tension, for this reason, the fabric produced on a raschel machine is pulled tightly downwards from the knitting zone, at an angle of about 160o to the backs of the needles. In the past, a raschel machine could be distinguished from a tricot machine by its use of latch needles; however modern raschel machines use compound needles. Raschel machines are usually equipped with a larger number of guide bars than the tricot machines. The number ranges from 4 to 70 allow the greater patterning capability of these machines. Two types of guide bars are used in Raschel knitting. The first type is fully threaded and used for the construction of the ground fabric. In most cases 1 to 3 such guide bars are used. The second type of guide bars are use to apply the pattern onto the fabric. These bars usually require only 1 thread for each patterning repeat, so that only a few yarns are threaded across the whole width of such a bar. Textile Handbook 4-63 7.3 Knitting Elements of Warp Knitting Machine 7.3.1 Needle Beard and latch needles are cast in units of 1 inch long. Compound needles are set in tricks cut in the needle bed of the machine, while the closing elements, being cast in units half an inch long, are set in a separate bar. Figure 7.3.1(1) Beard Needle Unit Figure 7.3.1(2) Latch Needle Unit Knitting and Knitted Fabrics Figure 7.3.1(3) Compound Needle and Closing Element 4-64 Knitting and Knitted Fabrics 7.3.2 The Sinker The sinker is a thin plate of metal which is placed between each needle. The sinkers are usually cast in units 1 inch long, which in turn are screwed into the sinker bar. The neb of the sinker and throat are used to hold down the fabric, while the belly of the sinker is used as a knocking-over platform. Figure 7.3.2 A Sinker Unit (Tricot Machine) 7.3.3 Guides and Guide Bars The individual guides of a tricot machine are usually cast in 1 inch units which in turn are fitted on the guide bars. The guides swing between and around the needles in order to wrap the yarn around them to form a new loop. They also shog sideways to join the wales into a fabric. In a raschel machine, the bars are designed to be narrow and light-weight strips of metal with individual guide fingers attached so that a greater number of bars can be assembled. The guide bars can be set in groups in the same displacement line called “nesting”. Each nest can be considered as one guide bar for the swing movement. Tube guide fingers can be used for bulky and fancy yarns. Figure 7.3.3 (1) Jacquard Displacement Bar (Raschel Machine) Textile Handbook 4-65 Figure 7.3.3 (2) A Guide Unit 7.3.4 Driving Mechanisms of Knitting Elements The guide bar needs a combination of a swing movement and a shogging lateral movement to wrap the yarn around the needle and to displace the yarn guides from one needle to another. The swing movement is generated by a mechanism very similar to that which produces the vertical movement of the needle. It is transmitted by the push rod and converted by the lever into the swing movement of the guide bars. The lateral movement of the guide bars is generated by the patterning mechanism which consists of a pattern drum and pattern chain (see Figure 7.3.4 (2)). A chain made of links of different heights is placed on the pattern drum. While rotating, the different chain links move the roller and slide so that the push rod moves the guide bar and displaces it laterally. Since raschel machines are equipped with more pattern guide bars, a pattern mechanism which operates the guide bars through shogging levers are used. In addition, an electronically controlled patterning mechanism is used to replace the traditional chain link mechanism. Figure 7.3.4 (1) Main Shaft with Cranked Drive for Knitting Elements (Tricot Machine) Knitting and Knitted Fabrics The needle bar and the sinkers are driven up and down or horizontally by means of cams or eccentrics. In order to achieve a movement containing the dwelling of the needle bar at the clearing position, the eccentrics are connected to the needle bar by a crank assembly (see Figure 7.3.4 (1)). 4-66 Knitting and Knitted Fabrics Figure 7.3.4(2) Pattern Drum and Pattern Chain 7.4 Key Terms of Warp Knits 7.4.1 Course and Wales Similar to weft knit, a horizontal row of loops is called a course while a vertical column of loops form by a single needle is called a wale. Figure 7.4.1 Two-guide Bar Loop Structure 7.4.2 Stitch Density The stitch density in the fabric is defined as the total number of loops in an unit area. The stitch density is the number of wales times the number of courses in that area. 7.4.3 Loop Parts The warp knitted loop structure is made of two parts. The first one is the loop which is formed by the yarn being wrapped around the needle and drawn through the previous loop. This part of the structure is called an overlap. The second part is the length of yarn connecting the loops, which is called an underlap. It is formed by the shogging movements of the ends across the needles. The length of the underlap is defined by needle spaces according to the shogging movement. The longer the underlap, the more stable in widthwise direction, but a shorter underlap will increase lengthwise stability. Textile Handbook 4-67 In order to control the dimensional stability and the appearance of the fabric, a second set of ends are knitted in an opposite shogging movement to the first. 7.4.4 Open and Closed Laps Two different lap forms are used in warp knitting, depending on the way the yarns are wrapped around the needles to produce an overlap. When the overlap and the next underlap are made in the same direction, an open lap is formed. If the overlap and the following underlap are in opposition to one another, a closed lap is formed. Figure 7.4.4 Open and Closed Lap Configurations Knitting and Knitted Fabrics a = Open loop; b = Closed loop 7.4.5 Technical Back The structure can be recognized by the underlaps floating on the surface and is called the “technical back”. This side is facing the knitter while working on the machine. 7.4.6 Technical Face The loop structure shows on the “technical face” of the fabric. When the fabric is formed by more than one set of yarn ends, all the yarns which overlap the needle will appear in the loop. 4-68 Knitting and Knitted Fabrics 7.4.7 Run-in All yarn ends threaded through the guides of one guide bar knit the same construction and are fed equally. The yarn consumption of each guide bar is called “run-in” and is measured as the length of each yarn knitted into the fabric during 480 knitting cycles. A cycle of 480 knitted courses is called a “rack”. By feeding different amounts of yarn into the knitting zone, the size of the loops is changed. A longer run-in produces a looser fabric while a shorter run-in produces small and tight loops. When a new fabric is produced, the run-in should always be recorded. This information will be very useful to reproduce the fabric again at a later stage. When knitting with more than one guide bar, the relative amount of yarn fed from each warp is very important; this relation is called the “run-in ratio”. 7.5 Common Warp Knit Fabric Structures and their Characteristics 7.5.1 Tricot Fabrics Tricot fabrics are used for a wide variety of fabric weights and designs. Typical uses for tricot fabrics are lingerie, sleepwear, blouses, shirts, dresses, slacks, uniform for nurses, bonded fabric material, outerwear, and automobile upholstery. Most lingerie tricot is two-bar fabric. Dress wear tricot and men’s wear tricot are often three-bar or four-bar fabrics. a) Plain tricot or tricot jersey: this is the basic fabric using two-bar constructions. The most widely produced warp knitted fabric is probably locknit. Locknit structure is produced when the back guide bar shogs a 1- and -1 lapping movement, and the front guide bar shogs two needle spaces. The lapping movement of the two guide bars is illustrated in Figure 7.5.1 a. Locknit gives a pleasant touch and a considerable elasticity make the fabric most suitable for ladies’ lingerie. Locknit construction tends to contract on leaving the knitting zone. The final width may only be two-thirds of the needle bar width. Locknit fabric is normally produced on 28, 32 and 40 gauge machines. Textile Handbook 4-69 Figure 7.5.1 a Locknit Loop Structure FGB BGB FGB= Front Guide Bar BGB= Back Guide Bar Figure 7.5.1 b Three-needle Satin Loop Structure FGB BGB c) Sharkskin : the sharkskin fabric is constructed as a reverse version of satin. The structure shows the longer underlaps of the back guide bar locked under the short underlaps of the front guide bar. These trapped underlaps restrict the shrinking potential of the fabric which is therefore more rigid and more stable than locknit and satin tricot. Knitting and Knitted Fabrics b) Satin tricot : is a variation of the locknit structure with an increased lapping movement up to 6 wales on the front bar. While the technical face is similar in appearance to locknit, the technical back is smoother and shiner. It should be noticed that the longer the underlap floating on the surface of the technical back, the heavier the fabric and the greater the risk of snagging. 4-70 Knitting and Knitted Fabrics Figure 7.5.1 c Sharkskin Loop Structure FGB BGB d) Queen’s Cord : the fabric is formed when the front guide bar moves in the shortest lapping so that the yarn is knitted continuously on the same needle while the back guide bar has a reciprocating 3- and-1 or 4- and -1 movement. The dimensions of queen’s cord fabric change only very slightly in width on leaving the knitting zone, and the final width is very similar to the knitted width. If the front guide bar is threaded with coloured yarns, a pin-stripe effect is produced. This makes queen’s cord very popular for the production of shirting fabric. Figure 7.5.1 d Queen’s Cord Loop Structure FGB BGB Textile Handbook 4-71 e) Brushed Tricot (Pile Fabric) : Two-bar fabrics can be produced or finished as pile fabric in order to improve their appearance or their thermal properties. In brushed fabric, the lapping movements of both bars are carried out in the same direction. The fibres raised out of the long underlaps of the front guide bar can be easily pulled out during the finishing process. Brushed fabric is widely used for robes and sleepwear. Using of heavier yarns, fabrics for upholstery (automotive and furniture) can be made. Figure 7.5.1 e Brushed Tricot Knitting and Knitted Fabrics f ) Mesh-Effect and Fancy Open-Effect Tricot Fabrics : By omitting some knitting needles and yarns at intermittent places, mesh or open effect can be produced. These fabrics are used for producing novelty lingerie or curtains. Figure 7.5.1 f Net Loop Structure (Tricot) FGB BGB 4-72 Knitting and Knitted Fabrics 7.5.2 Raschel Fabrics The large number of guide bars in a raschel knitting machine provides the potential for wide diversification and great variation in raschel fabric from fine laces to heavy blankets and even carpets. For example, a widely used type of thermal underwear with a distinct waffle surface effect is a raschel knit structure. Power net fabrics used in foundation garments and swimwear are also raschel fabrics. a) Net Fabrics: Net fabrics can be considered as one of the major products manufactured by the raschel machine. Net structures can be classified into the following two types: (i) Structures with Vertical Pillars: The net in which the distance between the vertical pillars (wales) is determined by the distance between the knitting needles. Usually, the horizontal mesh bars are produced by another set of yarns which bridge the gap between each two wales. The shape of the opening is determined by the lapping movement and by the tension applied to the yarns. In most cases the pillars (vertical chain of loops) can keep straight. To produce this type of net structure, the guide bars are usually fully threaded and the net appearance is obtained by using fine yarns. A simple construction of this structures is illustrated in Figure 7.5.2.a.(1) Figure 7.5.2 a (1) A Pillar and Inlay Loop Structure FGB BGB Textile Handbook 4-73 Figure 7.5.2 a (2) Marquisette Loop Structure FGB BGB Knitting and Knitted Fabrics Sometimes, the horizontal mesh bars may not necessarily be produced during each knitted course. The Marquisette net structure is formed in this way. The loop structure of three-guide-bar Marquisette net is shown in Figure 7.5.2 a (2). The front guide bar is constantly chaining to produce the vertical pillars whilst the horizontal connections are produced by the inlay yarns which are threaded in the back guide bars. These two bars work in opposite direction during the tracing of the vertical pillars and during the horizontal crossings. It is usual to shog one of the back guide bars by one needle space and the other one by two needle spaces. In this way the fabric is sufficiently stable and is usually finished to the same width in which it has been knitted. Marquisette structures are very popular in the production of net curtains. 4-74 Knitting and Knitted Fabrics (ii) Structure with Interlacing Pillars: The side connections are formed by the inclination and distortion of the wale, no special yarns are necessary to connect the pillars. The typical openings of these nets are diamond shaped although other openings can be produced. The basic structure of this type of net is shown in Figure 7.5.2 a (3). To produce this structure, the guide bars are threaded in a sequence of 1 in, 1 out. Both guide bars are constantly chaining with each yarn to produce only one pillar on the same needle. After a number of courses, the guide bars are shogged in opposition to one needle space. During this course, each of the guide bars draws its new loops through the loops previously made by the adjacent yarns. When the connection is made, each guide bar is shogged to its original position and resumes the chaining lapping movement. The next connection is carried out in the opposite direction to the first and diamond shaped openings are formed. A typical product of this type of structure is fishing net. Figure 7.5.2 a (3) The Loop Structure of a Net with Diamond Shaped Openings FGB BGB Textile Handbook 4-75 b) Dress laces : Lace fabrics are produced by multi-guidebar raschel machine with 32, 42, 56 or 78 guide bars and usually with an electronically controlled patterning mechanism. The ground structures of dress laces can be classified into two major groups. One group is the tulle ground structure (interlacing pillars) as shown in Figure 7.5.2. b (1) & (2) and the other is made of a chaining bar with the pillars being pulled together and connected by the patterning yarns as shown in Figure 7.5.2 b (3) & (4). Figure 7.5.2 b (1) A Tulle Net Loop Structure Figure 7.5.2 b (2) BGB A Lace Fabric with Tulle Ground Structure Knitting and Knitted Fabrics FGB 4-76 Knitting and Knitted Fabrics Figure 7.5.2 b (3) A Lace Fabric with Ground Chains Connected by Patterning Yarn