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Basics of Kniting by Vasant Kothari

Basics of Knitting - Introduction
2. Basic Terminologies
3. Knitting Machine Needles
4. Basic Elements of Knitting
5. Knit, Tuck & Miss Stitch
6. Weft Knitting
7. Knitting Loop Structure & Notations
8. Single Jersey & Rib Fabric
9. Purl & Interlock Fabric
10. Straight Bar Knitting Machine
11. Flat Knitting Machine
12. Circular Knitting Machine
13. Warp Knitting
14. Warp Knitted Fabrics
15. Warp Knitting Machine
16. Tricot Machine
17. Raschel Machine
18. Compound Needle Machine
19. Yarn Requirements for Knitting
20. Knitting Fabric Quality Parameters
21. Defects in knitted fabrics
22. Testing of Knitted Fabrics
23. Production Calculations
24. Costing Of Knitted Fabrics
25. Processing of Knitted Fabric
26. Relaxation of Knitted Fabric
27. Development Process of Knitted Fabric
28. Sourcing of Knitted Fabric
29. Garment Manufacturing of Knitted Fabrics
30. Seamless Knitting

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Basics of Kniting by Vasant Kothari

  1. 1.       www.vasantkothari.com     A Series of Articles On Basics of Knitting By Vasant Kothari
  2. 2.       www.vasantkothari.com INDEX 1. Basics of Knitting - Introduction 2. Basic Terminologies 3. Knitting Machine Needles 4. Basic Elements of Knitting 5. Knit, Tuck & Miss Stitch 6. Weft Knitting 7. Knitting Loop Structure & Notations 8. Single Jersey & Rib Fabric 9. Purl & Interlock Fabric 10. Straight Bar Knitting Machine 11. Flat Knitting Machine 12. Circular Knitting Machine 13. Warp Knitting 14. Warp Knitted Fabrics 15. Warp Knitting Machine 16. Tricot Machine 17. Raschel Machine 18. Compound Needle Machine 19. Yarn Requirements for Knitting 20. Knitting Fabric Quality Parameters 21. Defects in knitted fabrics 22. Testing of Knitted Fabrics 23. Production Calculations 24. Costing Of Knitted Fabrics 25. Processing of Knitted Fabric 26. Relaxation of Knitted Fabric 27. Development Process of Knitted Fabric 28. Sourcing of Knitted Fabric 29. Garment Manufacturing of Knitted Fabrics 30. Seamless Knitting
  3. 3. 20/KNITTING VIEWS/JANUARY-FEBRUARY 2010 Knitting is the second most frequently used method of fabric construction. The term “Knitting” describes the technique of constructing textile structures by forming a continuous length of yarn into columns of vertically intermeshed loops. Knitted fabrics have been gaining popularity during the past two decades, thanks to the increased versatility of techniques and adaptability of the many new manmade fibres. Knitted fabrics are now widely used in the applications where woven fabrics formerly predominated. Today, the usage of knitted fabrics ranges from hosiery, underwear, sweaters, slacks, to rugs and other home furnishings. Why knits are popular? Knitted fabrics are popular today because: • It is usually soft and drapes well • It molds and moves easily with body movement • It has good stretch ability • It resists wrinkles • Most importantly, knits relate well to contemporary life-styles History From the beginning the art of knitting was an occupation for women. Traditional hand knitting, using knitting needles or pins, has been practiced for thousands of years. The earliest example of true knitting is a pair of knitting socks found in Egypt, dating back to 1100 A.D -just over 9 centuries ago! Socks and stockings were knitted because they had to be shaped to the foot or leg. By the 16th century knitting had advanced into a craft, the first real evidence of a production knitting machine was the stocking frame, invented by the Reverend William Lee in 1589. The invention laid the foundation for the development of knitting technology. Lee’s invention enabled the knitting of loops at 10 times the speed of traditional hand pin knitting. Basics ofBasics ofBasics ofBasics ofBasics of KNITTINGKNITTINGKNITTINGKNITTINGKNITTING - An introduction- An introduction- An introduction- An introduction- An introduction VASANT R KOTHARI - has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his first input from the series of articles that will be published in upcoming issues of knitting Views)
  4. 4. KNITTING VIEWS/JANUARY-FEBRUARY 2010/21 Weaving Knitting Convertingyarnintofabricby Convertingyarnintofabricby interlacementofwarpandweft interlopingusingknittingelements Thecapitalinvestmentishigh Capitalinvestmentisusuallylower Noteasyascomparedwithknitting Settingupamachineiseasyandfaster Lessproductivity Highproductivity Designmodificationisdifficult Stylesanddesignscanbechanged easilyandfaster Wovenfabric Knittedfabric Lessextensibility Highextensibility Highelasticrecovery Incompleteelasticrecovery Lesscreaseresistance Highcreaseresistance Generallyfabricisthin Fabricisthicker (Forthesameyarncount) (Forthesameyarncount) Easytotear Difficulttotear Requiresironing Ironingnotrequired Highpleatsharpness Lesspleatsharpness Lesspermeabilitytoair Morepermeabilitytoair Strongerfabrics Lessstrongerfabrics Morerigidascompared Feelofthefabricissofter Nosuchproblems Anysmalldefectoccurringinthefabric can leadtofurtherdamageinthecloth becauseitcannotbemendedeasily Testedbyloadingorextending Testedbymulti-directionalfabric fabricsinwarp/weft burstingstrengthtest Difference between knitting and weaving The major difference between knitted and woven structures lies in the way the yarns are interconnected geometrically. In weaving, two sets of parallel yarns are interconnected by interlacing them at right angles. Different woven structures are produced by varying this basic principle. In knitting, the yarns are initially formed into loops, and then these loops are interconnected in a variety of ways in order to produce a textile structure. Based on this principle, a textile fabric is produced by using only one set of yarns. As a result of this interlooping of yarns, the structure of a weft or a warp knitted fabric is more open when compared to the structure of a woven fabric. Because of this interloping of yarns, a knitted fabric could be stretched more than a woven fabric, even when only a small force is applied. Once this force is eased the fabric slowly returns to its original dimensions. In fact, weft and warp knitted fabrics have higher elongation values than woven fabrics due to their structure, and their elastic behaviour generally exceeds the elastic properties of the yarns used to knit the fabric.
  5. 5. 22/KNITTING VIEWS/JANUARY-FEBRUARY 2010 Comparedwithwarpknitting,weftknittingisamoreversatilemethod of fabric production in terms of both the range of fabric structures that can be produced and the yarn types that can be utilised. Weft knitting is the simplest method of converting a yarn into a fabric. Inwarpknitting,eachwarpthreadisfedmoreorlessinlinewiththe direction in which the fabric is produced, and each needle in the knitting width must be fed with at least one thread at each course. Compared to weaving and weft knitting it is the fastest method of converting yarn into fabric, though modern developments in weft knitting machines mean that there is now very little difference in terms of production between the two forms of knitting Weft knitting Warp knitting Course-wiseyarnfeeding Walewiseyarnfeeding Yarnpathhorizontal Yarnpatheitherverticalordiagonal Theloopsareformedacross Theloopsareformedvertically thewidth offabric downthelengthoffabric Needlesknitsequentially Needlesknitconcurrently Possibletoknitwithoneyarn Needwarpyarnsheet Coneorcheeseyarnsupply Onelongbeamoranumberofsmall warpbeamsyarnsupply Usuallystaplefibreyarns Onlyfilamentyarnscanbe canbeworked successfullyworked Normallylatchneedlesareused Latch,beardorcompoundneedlesareused Lessversatility Moreversatility Changingdesignaffectthespeed Changingdesigndoesnotaffectthespeed Relativelynotconsistentand Consistentanduniformqualityproduct uniformqualityproduct Loopsarenotuniform Loopsareuniform Stretchinbothdirection Stretchinwidthwisedirection Dimensionallylessstable Dimensionallymorestable Weftknittingmachinesare Warpknittingmachinesaremoreexpensive lessexpensive Runningcostsisless Runningcostsishigh Softeryarnisrequired(lesstwist) Strongeryarnisrequired(moretwist) Shortproductionruns Formassscaleproduction Smallfloorspacerequirements Needmorespace E.g.CircularKnittingmachine E.g.TricotandRaschelmachine Due to the structure and good elastic behaviour of knitted fabrics, knitted garments are comfortable to wear. The air trapped in the loops of a knitted garment insulates the human body against cold. At the same time the relatively loose and open structure aids in the perspiration process of the human body, especially when the knitted fabric is made of yarns spun from natural fibres. Due to the interlooping of yarns, the knitted fabrics also have better crease recoveringpropertiescomparedtofabricswovenfromsimilaryarns. Classification of knitted fabrics The knitting industry is divided into two distinct sectors, weft knitting and warp knitting. Weft knitting In weft knitting, the loops are formed across the width of the fabric, and each weft thread is fed more or less at a right angle to the direction in which the fabric is produced. It is possible to knit with only one thread or cone of yarn, though production demands have resulted in circular weft knitting machines being manufactured with up to 192 threads. Warp knitting Warp Knitting is a method of producing a fabric by using needles similar to those used in weft knitting, but with the knitted loops made from each warp thread being formed down the length of the fabric; the loops are formed vertically down the length of the fabric from one thread as opposed to across the width of the fabric, as in case of weft knitting.
  6. 6. 22/KNITTING VIEWS/MARCH-APRIL 2010 Machine knitting Knitted structures are progressively built-up from row after row of intermeshed loops. The newly-fed yarn is converted into a new loop in each needle hook. VASANT R KOTHARI - has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his second input from the series of articles in knitting Views) The needle then draws the new loop head first through the old (fabric) loop, which it has retained from the previous knitting cycle. Theneedles,atthesametime,release,(cast-offorknock- over) the old loops so that they hang suspended by their heads from the feet of the new loops whose heads are still held in the hooks of the needles. Basic terminologies for fabric knitting
  7. 7. KNITTING VIEWS/MARCH-APRIL 2010/23 A cohesive knitted loop structure is thus produced by a combination of the intermeshed needle loops and yarn that passes from needle loop to needle loop. The knitted loop structure may not always be noticeable because of the effect of structural fineness, fabric distortion, additional pattern threads or the masking effect of finishing processes. Knitted loops are arranged in rows, roughly equivalent to the weft and warp of woven structures. These are termed ‘courses’ and ‘wales’ respectively. Wales Wales are columns of loops across the length of the fabrics; they are measured in units of (Wales/cm). Wales generally produced by the same needle knitting at successive (not necessarily all) knitting cycles. A wale commences as soon as an empty needle starts to knit. The numbers of wales determine the width of fabric. Loop length Looplength,measuredinmillimetres,isthe length of yarn in one knitted loop. It is one of the most important factors controlling the properties of knitted fabrics. Generally, the larger the loop length, the more open and lighter the fabric. Courses Courses are rows of loops across the width of fabrics; they are measured in units of (Courses/cm). Courses are produced by adjacent needles during the same knitting cycle. The number of courses determines the length of fabric. Stitch density Stitch density refers to the total number of loops in a measured area of fabric. It is measured in units per square per centimetre/inch. The figure is obtained by counting the number of courses or pattern rows in one inch (or centimetres) and the number of wales in one inch (or centimetres), then multiplying the number of courses by the number of wales. Stitch density gives a more accurate measurement than does a linear measurementofonlycoursesoronlywales. Tension acting in one direction might produce a low reading for the courses and a high reading for the wales; when they are multiplied together this effect is cancelled out. Stitch density is directly related to the “loop length,” which is the length of yarn contained in one complete knitted loop. Loop length will affect the following parametres: • Stitch density/fabric density • Tightness factor • Fabric weight • Fabric cost • Dimensional stability • Physical performance; pilling, burst strength As loop length decreases, stitch density, tightness factor, fabric weight, fabric cost, dimensional stability increases and vice versa. There is a definite correlation between the yarn count and loop length of a fabric and this can be defined as the “cover factor.” The cover factor hence determines the handle, drape and performance of the fabric. Just as the yarn type dictates the optimum loop length, this in turn dictates the gauge or knitting machine required to knit the yarn. Gauge In knitting, the word gauge, technical abbreviation GG, refers to "Knitting machines" fineness and is the number of needles in a measured space on the knitting machine. Higher-gauge fabrics (those with more stitches) are made with finer needles; lower -gauge fabrics are made with coarser or larger needles. "Gauge,” is also termed as “cut” and “tension.” This “unit of measure” is equal to the number of needles contained in the
  8. 8. 24/KNITTING VIEWS/MARCH-APRIL 2010 “gauge” (size) and it is simply countable on the bed of needles of each knitting machines, flat or circular. To describe the stitch density of a single or double knit fabric, the fabric may be designated as an 18-, 20-, 22-, or 24-cut fabric. Higher the cut, closer the stitches; lower the cut, coarser the fabric. Varying types of knitting machines measure gauge over different distances on the machine. For example, circular knit hosiery measures the number of needles in 1.0 inch, full-fashioned knitting in 1.5 inches, and Rachel knits in 2.0 inches. Because of these differences, it is best to keep in mind the generalised principle that the higher the gauge, the closer the stitches. The size of the needle and the spacing of the needles on knitting machines determine the number and size of the knit stitches and their closeness. Each wale is formed on one needle. The number of needles is equal to the number of wales. The closeness of the stitches determines whether a knit fabric will be lightweight and open, or heavier and denser. The term gauge is also used to describe the closeness of knit stitches. If we move clockwise from Ato D in the pictures above, we find that the knitted structures are progressively decreasing in gauge and in fineness. Gauge is very important as everyone knits a little differently; some people knit loosely, while some knit very tight. When the same yarn and the same sized needles are given to two different knitters, there is a good chance that they will come up with a different gauge. The gauge of a knitted fabric depends on the pattern of stitches in fabric, kind of yarn, size of knitting needles, and tension of the individual knitter. • The coarser the yarn, coarser will be the gauge and the fewer stitches per inch • The finer the yarn, finer will be the gauge and the more stitches per inch • The larger (thicker) the needle, coarser will be the gauge and the bigger the stitches • The smaller (thinner) the needle, finer will be the gauge and the smaller the stitches • The bigger the stitches, coarser will be the gauge and the fewer stitches per inch • The smaller the stitches, finer will be the gauge and the more stitches per inch In the next session, we would be discussing about various kinds of knitting needles 4GG 5GG 6GG
  9. 9. 38/KNITTING VIEWS/MAY-JUNE 2010 VASANT R KOTHARI - has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his third input from the series of articles in knitting Views) The fundamental elements in construction of knitted fabrics are the knitting needles as they are the main elements for intermeshing of loops. The quality of the knitted fabric is largely dependent on the effectiveness and accuracy of the loop, which in turn largely depends on the needle. Small variations in the needle manufacture can lead to irregular fabric. The surface of needles should be highly polished allowing the yarn and the loop to slide free. The needle must have high strength and toughness to give durability. A typical needle must performseveralmillionknittingactionswithoutfault. Types of knitting needles: There are three types of needles. These are:- 1. Bearded needle 2. Latch needle 3. Compound needle Heart of KnittingHeart of KnittingHeart of KnittingHeart of KnittingHeart of KnittingHeart of KnittingHeart of KnittingHeart of KnittingHeart of KnittingHeart of Knitting Knitting Needles MachinesKnitting Needles Machines
  10. 10. KNITTING VIEWS/MAY-JUNE 2010/39 The Latch needle is primarily used in weft knitting, and the other two are used for warp knitting. A coarse (large and thick) needle usually knits with a coarse yarn (large hook), whereas a fine (small and thin) needle usually knits with fine yarn (small hook). Bearded needle The bearded needle was used by William Lee in his stocking frame to enable a single needle to undertake the tasks achieved by hand knitters with two needles. This needle is the simplest and cheapest to produce, but it does require an additional element to close the beard during knitting. In the case of warp knitting it is a presser bar. The majority of modern high speed warp knitting machines now use compound needles rather than bearded needle. The needle consists of five main parts. 1.Shaft or stem – used with the jack sinkers to form new loops 2.Head – the point at which the stem is bent to form the beard, it helps to draw the new loop through the old loop 3.Beard – the needle continues from the head to be turned back on itself to form the beard. The beard is used to trap new loops while old loops are pushed over the top 4.Grooveoreye–asmallgrooveisworked into the stem of the needle to allow the beard to fit flush with the stem and ensure the old course is pushed over the beard 5.Shank – bent for individual location in the machine or cast with others in a metal ‘lead’. The shank is used to attach the needle to the frame Bearded needle characteristics 1. The knitting section occupies a considerable amount of space, thus limiting productivity 2. The needles can set vertically or horizontally 3. The needle has the disadvantage of requiring a pressing edge to close the bearded hook 4. The presser may be in the form of a bar, blade, verge or wheel 5. Finer in Cross Section, therefore, more needles in unit space. Hence Finer Gauge (60 needles/per inch) can be achieved 6. High wear and tear and can break easily 7. Strain on the yarn is less 8. No possibility of fluff or lint accumulation on the needle 9. Most of the warp knitting machines use beard needles Fig 3.1 Bearded needle in the open and closed positions Fig 3.2 Latch needle Head Beard Eye Stem Shank Hook Latch-Blade Latch Spoor Stem Butt Tail
  11. 11. 40/KNITTING VIEWS/MAY-JUNE 2010 Latch needle Matthew Townsend, a Leicester hosier, patented the latch needle in 1849, and compared to the bearded needle, which evolved some 260 years earlier, it has the advantage of being self acting, though it is slightly more expensive to produce. The needle consists of seven main parts: 1.Stem – Used to hold the course of old loops 2.Hook – The hook is used to catch a thread and form loops 3.Rivet – The rivet, which may be plain or threaded, holds the latch in place and allows it to pivot 4.Latch – The latch combines the task performed by the presser bar and the beard of the bearded needle 5.Latch spoon – The latch spoon is an extension of the blade, and bridges the gap between the hook and the stem covering the hook when closed 6.Butt – The butt enables the movement of the needle to be controlled by a cam mechanism. A track raises and lowers the needle 7.Tail – Used to provide support to the needle Latch needle characteristics: 1. Most widely used in weft knitting 2. More expensive than the bearded needle, because of the assembly of the needle and latch 3. It is self-acting or loop-controlled, and is sometimes termed the ‘automatic’ needle 4. It can work at any angle 5. Needle Depth determines the loop length 6. Variation of the height of reciprocating action produces knit, tuck or miss stitch 7. It is ideally suited for use with computer-controlled electronic selection devices 8. It makes a longer stroke in the cycle of knitting 9. The Latch needle takes a longer time to knit a loop and hence the knitting machine is generally found slower 10. Latch needles are thick and rigid 11. Needle deflection is difficult 12. It imposes a certain strain on the yarn 13. There is also a possibility of fluff or lint accumulation on the latch due to rubbing action of the yarn on the needle Compound needle Compound needles were designed in the mid of 19th Century. It consists of two separately controlled parts; these are-the open hook and the sliding closing element (tongue, latch, piston, and plunger). The two parts rise and fall as a single unit but at the top of the rise, the hook moves faster to open the hooks and at the start of the fall the hook descends faster to close the hook. It is easier to drive the hooks and tongues collectively to form two separate bars as in warp knitting; than to move each hook and tongue individually as in weft knitting. Two types of compound needle have been employed in warp knitting machines: 1. The open stem “Pusher type” or slide needle has a closing wire or tongue that slides externally along a groove on the edge of the flat hook member 2. The tubular pipe needle has its tongue sliding inside the tube of the open hook Compound needle characteristics: 1. The compound needle is expensive 2. It offers a much shorter, smoother and simpler knitting action in comparison to other needles 3. Both members of Compound Needle have a straight moment, thus the knitting speed can be increased 4. There is no strain on the yarn Fig 3.3 Hook Fig 3.4 Latch spoon Fig 3.5 Latch movement Fig. 3.6 Compound needle (Pusher type) Fig. 3.7 Compound needle (Tubular pipe)
  12. 12. KNITTING VIEWS/MAY-JUNE 2010/41 Fig 3.9 Fig 3.8 Commonpoints The three needles considered above, while differing in design, have the following points in common. 1.Hook – to take & hold newly fed yarn 2.Closing mechanism – to allow the held loop to leave the needle 3.Stem 4.Control Butt – for individual or collective movement Loop formation process During yarn feeding, the hook is opened to release the retained old loop and to receive the new loop which is then enclosed in the hook (As shown in Fig. 3.8). The new loop is then drawn by the hook through the old loop which slides on the outside of the bridge of the enclosed hook (As shown in Fig. 3.9). All needles must therefore have some method of closing the knitting needle hook to retain the new loop and exclude the old loop (As shown in Fig. 3.10). Fig 3.10 Fig 3.11 Needles at 90º on cylinder (Vertical) and dial (Horizontal) Fig 3.12 Needles at rectangular or flat bed Needle orientation Needlesintheknittingmachineareusually orientedeithervertically,horizontally,orat 45º. Needles are held in the position by needle beds - pieces of metal into which slots or grooves have been cut. The beds can be rectangular or circular. Fig 3.13 Needles at 45º on V Bed Knitting Machine In the next session, we would be discussing about the elements of knitting. Comparisonofneedles Bearded needle Latch needle Required another element to close the hook Self acting needle Less expensive More expensive Beard needles are thin and flexible Latch needles are thick and rigid Usually mounted on finer gauge Usually mounted on coarser gauge It wears and breaks easily Strong in nature No strain on yarn Imposes certain strain on yarn It makes a shorter stroke in the knitting cycle It makes a longer stroke in the knitting cycle Stitches are tight and minimum loop robbing Stitches are loose No fly and fluff generation Due to rubbing, fly and fluff generation is high Time required to knit the loop is less Takes longer time to knit the loop The speed of the machine is high The speed of the machine is less Latchneedle Compoundneedle Self acting needle Consist of two separately-controlled parts Less expensive Very expensive Preferred for Weft Knitting Preferred for Warp Knitting Vibration is more Short, smooth, simple harmonic movement, so there is less vibration Yarns are under stress No stress on yarn The vertical clearing height is very good The vertical clearing height is not so good Latch needles produces the long & The needle can knit tight, uniform stitches that narrow loops tend to be rounder Latch needles are relatively thick Because of its slim construction and short hook fine warp knitted are possible Speed is relatively less Can work at high speed
  13. 13. 24/KNITTING VIEWS/JULY-AUGUST 2010 VASANT R KOTHARI - has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his fourth input from the series of articles in knitting Views) Basic elements of knitting The basic elements of knitting machines are knitting needles, sinkers, jack, cams and yarn feeding. Knitting needles are the main elements of any knitting machines which have already been discussed in the previous article. The sinker The sinker is the second primary knitting element. It is a thin metal plate with an individual or a collective action operating approximately at right angles from the hook side of the needle bed, between adjacent needles. 24/KNITTING VIEWS/JULY-AUGUST 2010
  14. 14. KNITTING VIEWS/JULY-AUGUST 2010/25 The main parts of sinkers are as follows: 1 – Butt 2 – Butt breadth 3 – Height of shank 4 – Buldge 5 – Neb 6 – Length of neb 7 – Throat angle 8 – Sinker platform height 9 – Breadth of lower shank 10 – Clearance 11 – Throat Fig 4.1 Position of sinker and needle Fig 4.2 Main components of sinker Sinkers may perform one or more of the following functions; dependent upon the machine’s knitting action and consequent sinker shape and movement: • Loop formation • Holding-down • Knocking-over The main function of the sinker is to assist the needles in the loop formation by sinking or knitting newly laid yarns into loop as its forward edge or catch (C) advances between the two adjacent needles. This is only for bearded needle, whereas on latch needle weftknittingmachinesandwarpknittingmachines,loopformation is not a function of the sinkers. The second and more common function of sinkers on modern machines is to hold down the old loops at a lower level on the needle stems than the new loops that are being formed, and to prevent the old loops from being lifted as the needles rise to clear them from their hooks. The protruding nib or nose of sinker (N) is positioned over the sinker loop of the old loop (O), preventing it from rising with the needle. The third function of the sinker – as a knock-over surface – is illustrated in Fig.4.4 where its upper surface or belly (B) supports the old loop (O) as the new loop (NL) is drawn through it. Fig 4.3 Action of the loop- forming sinker The jack The jack is a secondary weft knitting element, which may be used to provide versatility of latch needle selection and movement. It is placed below and in the same trick as the needle and has its own operating butt and cam system. The cam Knitting cams are solid steel plates and with the assembly of different cam plates a track for a butt can be arranged. Each needle movement can be obtained by means of cams acting on the needle butt. The fig 4.5 shows the simplest cam design. Fig 4.4 Action of the knock- over sinker Cams are devices, which convert the rotary machine drive into a suitable reciprocating action for the needles and other elements. The upward movement of the needle is obtained by the rising cam or clearing cam. The rising cam places the needle at a certain level as it approaches the yarn area. Cams controlling the downward movement of the needles are called stitch cam. The stitch cam draws the needle down below the knitting level, thereby drawing a loop formed by the fed yarn through the loop already on the needle. The lowest point to which the needle is Fig 4.5 Knitting cam design
  15. 15. 26/KNITTING VIEWS/JULY-AUGUST 2010 drawn by the stitch cam is called the “cast-off” position. They are screwed to the cylindrical cam ring and are adjustable in vertical direction. If the stitch cam is raised, then shorter loop is drawn below the sinker level and a tighter fabric will result. With lowering the cam, a reverse result is obtained. Guard cam keeps the needle butts in their raceway. Running cam or up-through cam keep the needle butts at a low level until they meet the next rising cam. The needle cam race consists of 1 Clearing cam 2 Stitch cam 3 Up-throw cam, which are vertically adjustable together for alteration of stitch length 4 and 6 Guard cam 5 Return cam The three sections of the sinker cam race are 7 Race cam 8 Sinker withdrawing cam 9 Sinker-return cam, which is adjustable in accordance with the stitch length Cam systems generate both the needle and the sinker displacements for sinker machines and cylinder and dial displacements for double jersey machines. Fig 4.7 shows both the sinker cam track above and the needle cam track below. The needle track shows the typical three stage needle displacement of (1/4) the raising or clearing cam, (2/3) the lowering or stitch cam and (5/6) the guard cam that returns the needle to its entry position for the next cam system. The sinker track shows the engaged position (section 7) when the needle is clearing. The sinker disengages in sections 8 and 9 so that knock-over can take place and re-engages into section 7. The displacement diagrams of the needles and sinkers are also shown. Fig 4.6 Cams and Latch needle moment Fig 4.7 Needle and Sinker cam system Yarn feeding Basically two types of yarn feeding are there • Moving the needles past the stationary yarn feed • Most circular weft knitting machines have revolving needle cylinders and stationary cams, feeders and yarn packages. In this case, the fabric tube must revolve with the needles, as must the fabric rollers and take-up mechanism • Moving the yarn past the stationary needle bed • As when the yarn moves past the needles, the fabric will be stationary because the loops hang from the needles. This arrangement exists on all warp knitting machines, and on weft knitting machines with straight beds and circular machines with stationary cylinders and dial Fig 4.8 Modern four track cylinder cam block (Inthenextissue,wewouldbediscussingabout the Knitted loop structure and notations.)
  16. 16. 22/KNITTING VIEWS/SEPTEMBER-OCTOBER 2010 There are three principle stitches utilised in knit fabrics: Knit, tuck and miss stitch. These three stitches, or combinations of them appearing in the same fabric, form the basis of all knitted fabrics. Formation of loop structures The weft knitted structures described so far have been totally composed of knitted loops, which are produced whenever the needle clears the old loop, receives the new yarn and knock over the old loop from the previous knitting cycle. Fig. 6.1 shows the three possible positions of the needle at the time of feeding the yarn. They are referred to as knit, tuck and miss positions. These different stitches are produced by controlling the height of the needles and the individual selection of needles enable knit, tuck or miss stitches to be formed. For different stitch requirements, swing cams or auxiliary cams are placed between the rising cams and the stitch cams to change the path of the needle butts to form a raceway and the needle butts travel in this restricted path accordingly to form knit, tuck and miss stitch. VASANT R KOTHARI - has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his fifth input from the series of articles in Knitting Views) 22/KNITTING VIEWS/SEPTEMBER-OCTOBER 2010
  17. 17. KNITTING VIEWS/SEPTEMBER-OCTOBER 2010/23 Knit stitch The knit stitch is the basic stitch. It is also called the plain stitch. Knit stitch is formed when the needle carries out a complete stroke, reaching the maximum height on the looping plane. The tuck loop will always lie at the back of the held loop. The numbers of consecutive tucks on any one needle is limited by the amount of yarn that the needle hook can hold, with the maximum usually being between four to five loops. Fig 6.5 shows the technical face of the tuck stitch along with the knitting notations. Fig 6.1 Three needle positions for the production of three stitch types. Fig 6.2 Cam setting for different stitches Tuck stitch A tuck stitch is formed when a knitting needle holds its old loop and then receives a new yarn. Two loops then collect in the needle hook. The previously formed knitted loop is called the held loop and the loop which joins it is a tuck loop. Fig 6.3 Face and back of knit stitch Fig 6.4 Tuck stitch produced on a latch needle machine Fig 6.5 Technical face of tuck stitch fabric with stitch notations
  18. 18. 24/KNITTING VIEWS/SEPTEMBER-OCTOBER 2010 The resultant stitch is elongated. Tuck stitches appear on the back of a fabric and may be recognised as an invertedV, sometime elongated for two or more courses, depending on how many times the stitched was tucked. Fig 6.6 shows a single tuck viewed from technical face and back of the fabric. Fig 6.7 shows a single tuck viewed from the technical back and, in addition, how this structure is represented using conventional stitch notations. Tuck stitches tends to reduce the length of the fabric and increase its width (Wales are pushed apart), resulting in the fabric being thicker (yarn from the tuck stitch lies on top of the preceding stitch) with less extension in the width. The tuck stitch is used in knitted fabric to create design effects in colour, raised surface texture, or a hole or eyelet effect. Miss stitch A miss stitch is created when one or more knitting needles are deactivated and do not move into position to accept the yarn. The yarn merely passes by and no stitch is formed. The float will lie freely on the reverse side of the held loop, which is the technical back, and in the case of rib and interlock structures it will be inside the fabric. Fig 6.10 illustrates that the float will extend from the base of one knitted or tucked loop to the next. Fig 6.6 Tuck stitch Fig 6.7 Tucking over four adjacent plain needles Fig 6.8 Tuck stitch (Face and Back) Fig 6.9 Float stitch produced on a latch needle machine Fig 6.10 Technical face of float stitch Miss stitch is also known as float stitch or welt stitch. Fig 6.11 shows the face and the back of the miss stitch. Fig 6.12 shows a four needle float viewed from the technical back, together with the conventional stitch notation used to represent this structure. The introduction of miss stitches results in the fabric becoming narrower in width, since the wales are pulled closer together and theheldloop‘robs’yarnfromadjacentloops.Thistendstoimprove fabric stability. The miss stitch also has a tendency to increase
  19. 19. KNITTING VIEWS/SEPTEMBER-OCTOBER 2010/25 fabric weight, and reduce both stretch, and width. Amiss stitch is used to create colour and figure designs in knitted fabric since it permits the selective positioning of yarns in a fabric. Fig 6.11 Miss stitch 6.12 Floating across four adjacent plain needles Fig 6.14 Successive tucks and floats (In the next edition, we would be discussing about Weft Knitting.) Fig 6.13 Miss stitch (Front and back) Knit, tuck and miss stitches can be used in any of the four fabric types – single jersey, rib, purl or interlock – to produce a wide range of structural effects. Fig 6.14 shows the combination of all three stitches.
  20. 20. 20/KNITTING VIEWS/NOVEMBER-DECEMBER 2010 VASANT R KOTHARI - has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is one of the inputs from the series of his articles) Knitted fabrics provide comfortable wear to almost any style of garment. Most knits contour to the body's silhouette without restricting movement because of its open structure. This makes knit fabrics ideal for innerwear, bodywear and sportswear garments. While many variations of knit fabrics exist such that used for hosiery, there are two basic types of knit fabrics—weft knits and warp knits—and it’s the direction in which the yarns making up the fabric are looped that determines which type of knit the fabric is. From these two types of knit fabrics come various subtypes that consumers encounter in fabric stores and read within garment descriptions. Weft knitting is the simplest method of converting a yarn into fabrics. Weft knitting is a method of forming a fabric in which the loops are made in horizontal way from a single yarn and intermeshing of loops take place in a circular or flat form on a crosswise basis. In this method each weft thread is fed, more or less, at right angles to direction in which fabric is formed. Each course in a weft knit builds upon the previous knitted course. Most of the weft knitting is of tubular form. It is possible to knit with only one thread or cone of yarn, though production demands have resulted in circular weft knitting machines being manufactured with upto 192 threads (feeders). Common weft knits In woven fabric structures, three weaves, are called basic weaves, viz., plain, twill andsatin.Inasimilarway,inaweftknitting structure, the following four structures are considered as basic weft knit structure. • Plain jersey fabric • Rib fabric • Purl fabric • Interlock fabric Plain jersey fabrics, also known as single jersey, have an identifiable right/face and wrong /back side. Other types are known Basics of knitting - Weft knitting as double jersey, just as the name implies, uses two sets of yarns on opposed needles resulting in a heavier fabric that looks the sameoneitherside.Doubleknitfabricshave little stretch; retain their shape and works best for tailored garments. Each of these fabric types is unique in appearance and function. Plain jersey fabric Plain jersey fabric is the simplest weft knitted structure that is possible to produce with one set of needle. It is very economical to produce. It is having definite face and back and is most easily recognised. Face is having all knit stitches with smooth texture, while back is having purl stitches with textured and mottled appearance. These fabrics are produced on flat as well as circular machines. Characteristics of jersey knits • Stretch crosswise and lengthwise • Stretches more in the crosswise
  21. 21. KNITTING VIEWS/NOVEMBER-DECEMBER 2010/21 • Tend to run or ladder if stitch breaks • Fabric less stable and curls when cut • Special finishes counteract curling and improve stability • Highest machine productivity End-uses of jersey knits • Sheets • Sweaters • Terry robes • T-shirts • Men’s underwear • Dresses • Hosiery and pantyhose • Fully fashion garments Jersey knit variations • Fleece • Intarsia • Jacquard knits • Knitted terry • Knitted velour • Lisle • Plaited knits • Silver-pile knits End-uses of rib knits • Collars and cuffs • Necklines • Bottom edges of sweaters • Double knits jackets •Knit hats • Men’s hosiery End uses for purl knits • Infant and children’s wear • Sweaters • Scarves • Fancy garment parts Interlock fabric Interlock structure consists of two 1 x 1 rib fabrics knitted one after the other by means of two separate yarns, which knits alternately on the face and back of the fabric and are interlocked together. Interlock is a reversible fabric, which has similar smooth appearance on each side. Interlock is produce on a cylinder and dial circular weft knitting machine, with alternate long and short needles opposite to each other on cylinder and dial. Characteristics of interlock knits • Reversible • It does not curl • Firmer fabric • Less extensible as compared to other jersey fabrics • Heavier and thicker as compare to rib • It unroves from the course knitted the last • Costlier fabric • Better insulator Fig: Rib fabric Fig: Plain jersey fabric Rib fabric Rib fabric is a double jersey knitted fabric with vertical rows (wales) of loops meshed in the opposite direction to each other. Simplest rib fabric is 1 x 1 rib having alternate wales knitted to the front and back. The ribs tend to close up to create a double faced fabric, which has the same appearance on both sides. Rib knits fabrics are produced with the knitting machines having two sets of needle, normally positioned at rights angle to each other. Characteristics of rib knits • Also called as double jerseys fabric • Its reversible fabric • More elastic than jersey knits • More thicker than jersey knits • More stretch crosswise than lengthwise • Edges do not curl • Very stable • Running and laddering still a problem • More expensive to produce • Next highest machine productivity Purl fabric Purl fabric has loop knitted to the front and back on alternate courses, in contrast to a rib fabric, which is knitted to the front and back on alternate wales.Asimple purl fabric looks like somewhat like the back of jersey knit on the both side of the fabric. The simples purl fabric is known as 1 x 1 fabrics. Purl fabrics are made on knitting machinescalledpurlknitmachinesorlinks- or-links machines. Characteristics of purl knits • Slowest of the knitting machines • Both side similar appearance • More expensive • Good stretch in all direction • Stretches out of shape easily • Crosswise stretch less than a jersey knit • Thicker than jersey knits • Does not curl • Can be unroved from either end Fig: Purl fabric Fig: Interlock fabric End-uses for interlock knits • Outwear fabric • Dress wear • Skirt • Blouses • T-shirts Variables in weft knitted fabric A great deal of variety may be created by manipulating the following: • Fibre content • Yarn type and twist • Fabric count • Colouration • Finishes and • Variations of tuck, knit and miss stitches (In the next issue, we would be discussing about Plain jersey and rib fabrics.) www.vasantkothari.com
  22. 22. 22/KNITTING VIEWS/JANUARY-FEBRUARY 2011 VASANT R KOTHARI has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his seventh input from the series of articles in Knitting Views) The needle loop The upper part of the loop produced by the needle drawing the yarn is called the needle loop. It is the basic unit of a knitted structure. Each stitch or knitted loop consists of a top arc (head), two legs and two bottom half-arcs (feet). At the base of each leg is a foot, which meshes through the head of the loop formed at the previous knitting cycle, usually by that needle. The yarn passes from the foot of one loop into the foot and leg of the next loop formed by it. The sinker loop The lower part of the knitted loop is technically referred as sinker loop. It is the piece of yarn that joins one weft-knitted needle loop to the next. On bearded needle weft knitting machines, loop-forming sinkers form the sinker loops in succession between the needles – hence the origin of the term sinker loop. On latch needle weft knitting machines, however, the sinker loops are automatically formed as the needles, in succession, draw their new loops. Fig 5.1: Components of needle loop
  23. 23. KNITTING VIEWS/JANUARY-FEBRUARY 2011/23 Fig 5.2: Intermeshing points of a needle loop Fig 5.3: Needle loop and sinker loop Face loop During loop formation, when the new loop emerges through the old loop from back to the face (or front) side, it is called as face loop or weft knit loop. Back loop If the new loop passes from the face side to the back side of old loop, it is called as back loop or weft purl loop. The knitted stitch The knitted stitch is the basic unit of intermeshing which usually consists of three or more intermeshed needle loops. The centre loop has been drawn through Fig 5.4: Face loop and back loop the head of the lower previously-formed loop and is, in turn, intermeshed through its head by the loop above it. The repeat unit of a stitch is the minimum repeat of intermeshed loops that can be placed adjoining other repeat units in order to build up an unbroken sequence in width and depth For a stitch, depending on the position of the legs at the binding points, a technical back and a technical front side is defined. Fig 5.5: The knitted stitch Fig 5.6 Technical face The side of knitted fabric that consists all of face or knit loops, is called as technical faceofthefabric.Itisthefrontsideoffabric. Technical back Thesideofknittedfabrichavingfullofback or purl loops, is called as the technical back of the fabric. It is the back side of the fabric. Fig 5.7: Face side of plain knitted fabric Fig 5.8: Back side of plain knitted fabric Face Back Knitting notations A knitting notation is a simple, easily- understood, symbolic representation of Fig 5.9: Technical face and back of single jersey fabric Needle Loop Sinker Loop Face Loop Back Loop The technical back of a stitch The technical front of a stitch
  24. 24. 24/KNITTING VIEWS/JANUARY-FEBRUARY 2011 a knitting repeat sequence and its resultant fabric structure that eliminates the need for time-consuming and possibly confusing sketches and written descriptions. Graph paper This method is developed by the Leicester School of Textiles for weft knitting only. In this method each square represents a needle or stitch. An ‘X’ symbol is placed in a square where a face stitch occurs and an ‘O’ where there is a reverse stitch Basically two methods are recognised for knitting notations: 1. Point paper 2. Graph paper Point paper Eachpointrepresentsaneedleinplainview from above and, after the thread path has beendrawn,italsorepresentsitsstitch.Each horizontal row of points thus represents adjacent needles during the same knitting cycleandthecourseproducedbythem.The lowest row of points represents the starting course in knitting. Fig 5.10 Fig 5.11 Fig 5.12: Point paper notations of various knitting designs Fig 5.12: Graph paper notations of various knitting designs New Loop Face loop stitch and notation Old loop Old loop New Loop Reverse loop stitch and notation www.vasantkothari.com
  25. 25. 22/KNITTING VIEWS/MARCH-APRIL 2011 VASANT R KOTHARI has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his eighth input from the series of articles in Knitting Views). Single jersey fabric If a weft knitted fabric has one side consisting only of face stitches, and the opposite side consisting of back stitches, then it is described as a plain knitted fabric. It is also frequently referred to as a single jersey fabric (single fabric). Technical face of single jersey fabric is smooth, with the side limbs of the needle loops having the appearance of columns of V’s in the wales. These are useful as basic units of design when knitting with different coloured yarns. On the technical back, the heads of the needle loops and the bases of the sinker loops form columns of interlocking semi-circles, whose appearance is sometimes emphasised by knitting alternate courses in different coloured yarns. Plain is the simplest and most economical weft knitted structure to produce and has the maximum covering power. It normally has a potential recovery of 40 per cent in width after stretching. Fig 8.1: The technical face of plain jersey Fig 8.2: The technical back of plain jersey Fig 8.3: Face & back side of plain jersey fabric Back side of the fabric.. Fig 8.4: Face side of the fabric Cross section
  26. 26. KNITTING VIEWS/MARCH-APRIL 2011/23 Production of single-jersey fabric Single jersey fabrics are produced on flat as well as circular machines, having one set of needles in one needle bed and are called jersey machines, plain-knit machines, or single knit machines. Most of the single-jersey fabrics are produced on circular machines whose latch needle cylinder and sinker ring revolve through the stationary knitting cam systems that, together with their yarn feeders, are situated at regular intervals around the circumference of the cylinder. The yarn is supplied from cones, placed either on an integral overhead bobbin stand or on a free-standing creel, through tensioners, stops motions and guide eyes down to the yarn feeder guides. The fabric, in tubular form, is drawn downwards from inside the needle cylinder by tension rollers and is wound onto the fabric-batching roller of the winding-down frame. The knitting action Figure 8.6 – 8.10 shows the knitting action of a latch needle and holding- down sinker during the production of a course of plain fabric. Tucking in the hook orrest position: The sinker is in forward position, holding down the old loop (fabric) whilst the needle rises from the rest position. Fig 8.5: Knitting notation of single jersey fabric Clearing: The sinker is still forward as the needle has been raised to its highest positionclearingtheoldloopfromitslatch. Fig 8.6: Tucking in the hook or rest position Yarn feeding: The sinker is partially move back allowing the feeder to present its yarn to the descending needle hook and also freeing the old loop so that it can slide up the needle stem and under the open latch spoon. Fig 8.7 Clearing Knock-over: Thesinkerisfullywithdrawn whilst the old loop has closed the latch to trap the new yarn; needle descends to knock over its old loop on the sinker belly. Fig 8.8: Yarn feeding Holding-down: Thesinkermovesforward to hold down the new loop in its throat whilst the needle rises under the influence of the up throw came to the rest position where the head of the open hook just protrudes above the sinker belly. All needles in one bed can pull loops in only one direction as shown in fig 8.11. As a consequence, jersey-knit materials Fig 8.9: Knock over are unbalanced and have a tendency to curl at the edges. This condition can frequently be corrected in fabric finishing. If not corrected, this problem can be quite troublesome in cutting and sewing operations. Jersey-knit fabrics stretch more in the width directions. Fig 8.10: Holding down A wide variety of knitted fabrics are made with the jersey-knit construction, ranging from sheer, lightweight hosiery to thick, bulky sweaters. Most full-fashioned sweaters are fundamentally jersey-knit fabric types. Additional fabrics that use jersey-knit construction are men's underwear, T-shirts, pantyhose, knit terry, knit velour, and many more. One shortcoming of jersey-knit fabrics is that if one yarn breaks, it causes an unravelling of adjoining stitches in the wale, called a run. Lightweight filament-yarn jerseys are especially susceptible to runs due partially totheverysmoothsurfaceoffilament yarn. Rib fabric Rib has a vertical cord appearance because the face loop wales tend to move over and in front of the reverse loop wales. One vertical row of wale is meshed in the Fig 8.11: Single jersey circular knit fabric on machine
  27. 27. 24/KNITTING VIEWS/MARCH-APRIL 2011 opposite direction to the other vertical row of wales. Face row or loops tends to close up in one plane and so also the back row of loops in the other plain. Thus stitches of rib fabrics lie in two planes and hence the rib structure is also known as double jersey structure. 1 x 1 rib has the appearance of the technical face of plain fabric on both sides until stretched to reveal the reverse loop wales in between. Relaxed 1 x 1 rib is theoretically twice the thickness and half the width of an equivalent plain fabric, but it has twice as much width-wise recoverable stretch. In practice, 1 x 1 rib normally relaxes by approximately 30 per cent compared with its knitting width. Fig 8.12: Technical face and back of rib fabric Production of rib fabric Rib-knit fabrics are produced with knitting machines that are somewhat different from those used for jersey knits. Because rib knits have stitches drawn to both sides of the fabric, the machines used to make them, called rib-knit machines, require two sets of needles usually positioned at right angles to each other; each set of needles Fig 8.13: Rib fabric structure Fig 8.15: Knitting notation of rib fabric Fig 8.14: Top view of rib fabric Fig 8.14: Front view of rib fabric Fig 8.14: Cross section view of rib fabric Fig 8.14: Back view of rib fabric is capable of producing stitches. The fabric is formed between the two needle-holding beds. The machinery required to produce rib-knitfabricissubstantiallymorecomplex and operates at slower speeds than knitting machines used for jersey fabrics. Rib knits are produced on flat (V-Bed) as well as circular machines. The knitting action of the circular rib machine Theknittingactionofacircularribmachine is shown in Fig. 8.18 – 8.21: Clearing: In clearing position, the cylinder and dial needles move out to clear the plain and rib loops formed in the previous cycle Fig 8.16: Two sets of needle on rib knitting machine Fig 8.17: Graphic representation of two sets of needle on rib knitting machine Yarnfeeding:Theneedlesstarttheirreturn moment and are withdrawn into their tricks so that the old loops are covered by the open latches and the new yarn is fed into the open hooks. Fig 8.18: Clearing Fig 8.19: Yarn feeding
  28. 28. KNITTING VIEWS/MARCH-APRIL 2011/25 Knocking-over: The needles are withdrawn into their tricks so that the old loops are knocked over and the new loops are drawn through them. If cylinder needle is knocking over before dial needle, then it is known as delayed timing, which is very popular in production of rib fabric as it produces tighter fabric due to robbing back (this is where some yarn is taken from the previously knitted stitch to make the current stitch). If both, cylinder and dial needle knock over together, to produce loops of equal size, it is known as synchronised timing. Fig 8.20: Knocking over Fig 8.21: Knock over 1 x 1 rib is balanced by alternate wales of face loops on each side; it therefore lies flat without curl when cut. It is a more expensive fabric to produce than plain and is a heavier structure; the rib machine also requires finer yarn than a similar gauge plainmachine.Likeallweft-knittedfabrics, it can be unroved from the end-knitted last by drawing the free loop heads through to the back of each stitch. It can be distinguished from plain by the fact that Fig 8.22: Delayed timing Fig 8.23: Synchronised timing the loops of certain wales are withdrawn in one direction and the others in the opposite direction, whereas the loops of plain are always withdrawn in the same direction, from the technical face to the technical back. Rib cannot be unroved from the end knitted first because the sinker loops are securely anchored by the cross-meshing between face and reverse loop wales. This characteristic, together with its elasticity, makes rib particularly suitable for the extremities of articles such as undergarments, tops of socks, cuffs of sleeves, knit hats, rib borders of garments, and stolling and strapping for cardigans. Rib structures are elastic, form- fitting, and etain warmth better than plain structures (In the next article, we would be discussing about purl and interlock fabrics.) (The Author can be contacted at www.vasantkothari.com)
  29. 29. 22/KNITTING VIEWS/MAY-JUNE 2011 VASANT R KOTHARI has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his ninth input from the series of articles in Knitting Views). Purl fabric The Purl fabrics are also known as link- linkfabrics.Purlwasoriginallyspelt‘pearl’ and was so named because of its similar appearance to pearl droplets. In purl, the loops of one course are intermeshed in one direction and the loops of the next course intermeshed in opposite direction, i.e. the alternate courses having face and back loops. It means each wale contains both knit stitches and purl stitches. This differs from the rib fabric, in which the wales contain either knit or purl stitches. A simple purl fabric looks somewhat like the back of a jersey knit on both sides of the fabric. The simplest purl fabric is Fig 9.1: The technical face of purl fabric Fig 9.2: 1 x 1 purl fabric Fig 9.3: Face and back side of plain jersey fabric known as 1 x 1 purl, in which one course has all knit stitches and the next course has all purl stitches. The cycle repeats on the third course.A2 x 2 purl knit fabric is made with two courses of knit stitches followed by two courses of purl stitches. Fig 9.5: Knitting notation of purl fabric Fig 9.4: Face side of the fabric Cross section Back side of the fabric
  30. 30. KNITTING VIEWS/MAY-JUNE 2011/23 Fig 9.9: Interlock fabric structure Fig 9.6: Circular and flatbed purl knitting machine Fig 9.8: Purl needle transfer action Production of purl fabric Purl-knit fabrics are made on knitting machinescalledpurl-knitmachinesorlinks- and-links machines. The purl knitting machines are basically of flat and circular types as shown in fig 9.6. The flat is having two horizontal beds for needle movement and central gap for fabric formation. The circular type has two cylinders, one above the other and thus referred as super imposed cylinder machine. As stitches are sometimes drawn to the front and sometimes to the back, two sets of needles arerequiredtoproducethesefabrics.Inpurl machines,however,ratherthantwodistinct, separate sets of needles, one set of double- headed latch needles is used as shown in fig9.7.Thetwoneedlebedsareinalignment with each other. The double headed needles movefromoneneedlebedtotheother,from side to side of the knitted fabric as it is produced,alternatelymakingstitchesonone fabric side and then the other. The purl-knit machines used to produce purl knit fabrics are the most versatile industrial knitting machines. These machines can produce plain and rib as well as purl fabrics. By selective programming of needle motion, fabrics of all three types, sometimes with unique design effects are possible. Purl-knit machines are widely used in the sweater industry. Although extremely versatile, the purl knit machines have the lowest rate of production of all knitting machines. The knitting action Fig 9.8 shows the knitting action of a flatbed purl machine which has tricks in each of the needle beds. They are in line with one another to enable the transfer of purl needle from the control of a slider in one bed into the control of a slider in the opposite bed. Position 1 shows engagement of the head of the receiving slider with the needle hook that was originally knitting from the opposing bed. In position 2, the needle has been moved to the centre, with both sliders engaging the needle hook. The sliders then start to move back, but the slider in the back bed is pressed down by a cam, so that front bed slider is freed from the needle hook and the needle is transferred to the back bed. In position 3, the slider in the back bed has control of the needle and it can be seen that the yarn is fed to the opposite end of the needle, when compared to that of position 1.Thenthesliderinthebackbedhasmoved the needle to knock over position to complete the formation of the purl stitch. It should be noted that a purl stitch is made when a loop is formed by one hook and then at the next course by the other hook of the same needle, so that one course is formed on the front bed and the next course is formed on the back bed to create a 1 x 1 purl structure. Fabric characteristics To identify a purl-knit fabric, fabric need to stretch in its length direction. The appearance of alternating rows of knit stitches and purl stitches in the course direction is evidence of a purl knit. Generally purl-knit fabrics tend to lie flat and do not curl as do jersey knits. Purl fabric has same appearance in face and back. It can unroved from either end. Lengthwise extension is more as compare to width wise and hence purl fabric contract towards the centre in a course wise direction. Thickness of fabric is two to three times more as compare to single jersey fabric. The fabric is commonly used for children’s wear and sweaters. Interlock fabric Interlock-knit fabrics are a variation of rib knits made on the interlock machine. Interlock is an interlocking of two 1 x 1 rib structures in such a way that the face wale of fabric “1” is directly in front of the ‘reverse wale’ of the rib fabric “2”. Interlock has the technical face of plain fabric on both sides, but its smooth surface cannot be stretched out to reveal the reverse meshed loop wales because the wales on each side are exactly opposite to each other and are locked together as shown in Fig. 9.9. Each interlock pattern row (often termed an ‘interlock course’) requires two feeder courses, each with a separate yarn that knits on separate alternate needles, producing two half- Fig 9.7: Double headed latch needle Therefore, the cost per pound of fabric produced is highest for purl knit fabrics. Knitting machines for jersey knits have the highest productivity but the lowest versatility. Productivity for rib-knit machines falls between those for jersey and purl machines.
  31. 31. 24/KNITTING VIEWS/MAY-JUNE 2011 Production of interlock fabric Interlock is produced mainly on special cylinder and dial circular machines and on some double-system V-bed flat machines. In interlock machine • Interlock gating, the needles in two beds being exactly opposite each other so that only one of the two can knit at any feeder • Both, the cylinder and dial beds should have two types of needles viz., long and short needles • Alternate placement of long and short needles in both the beds is required • The long needle of one bed should face the short needle of the other bed and vice versa • Two separate cam systems in each bed, each controlling half the needles in an alternate sequence, one cam system controlling knitting at one feeder, and the other at the next feeder • Needles set out alternately, one controlledfromonecamsystem,thenext from the other; diagonal and not opposite needles in each bed knit together • Minimum of two yarns are required to knit one interlock course and hence a minimum of two feeders supply • The knitting style is in such a manner that only long needles of dial and cylinder will knit with the first feeder and only short needles of dial and cylinder will knit with second feeder Fabric characteristics To determine whether a fabric is an interlock or a rib, spread the fabric width wise, and view the fabric wales carefully at the top edge of the cloth. If the knit stitches are one behind the other, the fabric is interlock. If the wales of knit stitch alternate, the fabric is rib. Interlock fabric is a reversible balanced, smooth, stable structure that lies flat withoutcurl.Like1x1rib,itwillnotunrove from the end knitted first, but it is thicker, heavier and narrower than rib of equivalent gauge, and requires a finer, better, more expensive yarn. It unroves from the course knitted the last. The fabric becomes costlier due to thickness and less production. Interlock is used for outwear fabrics, often using wool, acrylic and polyester yarns, while cotton and polyester/cotton blends are used for the production of underwear fabrics. Interlock fabrics are also popular for blouses, dresses, and dressy T-shirts. Their dimensional stability and the fact that they do not tend to easily stretch out of shape contribute to these popular uses. Interlock fabrics offer a smooth surface for printing by both screen and heat- transfer methods In the next article, we would be discussing about straight bar knitting machine. (The Author can be contacted at www.vasantkothari.com) Fig 9.17: Interlock cam system gauge 1 x 1 rib courses whose sinker loops cross over each other. Thus, odd feeders will produce alternate wales of loops on each side and even feeders will produce the other wales. Fig 9.16: Graphic representation of two sets of needle on interlock knitting machine Fig 9.15: Knitting notation of interlock fabric Fig 9.10: Interlock fabric structure Fig 9.11: Interlock fabric structure Fig 9.12: Front view of interlock fabric Fig 9.13: Back view of interlock fabric Fig 9.14: Cross section view of interlock fabric
  32. 32. 22/KNITTING VIEWS/JULY-AUGUST 2011 VASANT R KOTHARI has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his tenth input from the series of articles in Knitting Views) Aknitting machine is a device used to createknittedfabricsinasemiorfully automated fashion. There are numerous types of knitting machines, ranging from the simple, non-mechanical, to the highly complex and electronic. All, however, producesinglejerseyfabricstocomplicated jacquard knitted fabrics, usually either flat or tubular, and of varying degrees of complexity. Pattern stitches can be selected by hand manipulation of the needles, or with push-buttons and dials, mechanical punch cards, or electronic pattern reading devices and computers. These knitting machines also ranges from high production to limited production capacity. The three main groups of weft knitting machinery may broadly be classified as either straight bar frames, flats, or circulars, according to their frame design and needle bed arrangement. From table it can be seen that the simplest weft knitting machinery has one set of needles, arranged either in a straight line (flat bar/straight bar) or around cylinder (circular). These machines are capable of producing single jersey fabrics, but not double jersey fabrics, and can use a combination of three types of stitch: knit, miss or tuck.With two needle beds, double jersey fabrics such as rib and interlock can be produced on both flat bar machines and circular machines. Straight bar frame machines Straight bar frames is a specific type of machine having a vertical bar of bearded needles whose movement is controlled by circular engineering cams attached to a revolving cam-shaft in the base of the machine? The length of the machine is divided into a number of knitting heads (‘sections’ or ‘divisions’) and each head is capable of knitting a separate but identically-dimensioned fashion-shaped garment panel.
  33. 33. KNITTING VIEWS/JULY-AUGUST 2011/23 Classification of various groups of weft knitting machine Knitting action of straight bar machine Below figure shows the movement of the knitting elements to produce one course of loops in straight bar machine. In thread laying process, the carrier moves across the knitting head for laying the yarn on the noses of the sinkers and dividers and on the beard side of the needles to form the new course in the fabric. The next step is Sinking, in which the slurcockcontacts the jacks; it is shaped so that each jack in turn pushes thesinker forwards to kink a loop around every two adjacent needles. The needle bar starts moving away from the pressing-edge and the sinkers and dividers withdraw so that the newly- formed course of loops drops off their noses onto the knocking-over bits. At the time of completion of knock-over, the needle bar descends to its lowest position. As the heads descend below the belly of the knocking-over bits, the old course of loops is collectively knocked-over. The sinkers and dividers move collectively forward to hold down the fabric, the needle bar rises to the thread-laying position. The catch bar is slightly raised to release the sinkers for individual movement at the start of the next course. In dividing step, the catch bar moves the dividers forwards, collectively, whilst the needle bar tips slightly outwards to allow the double loops to be divided into equal- sized needle loops around every needle. The needle bar start descending, placing the new loops inside the hooks of the beards. The catch bar is now lowered so that the sinkers, as well as the dividers, are collectively controlled by it for the rest of the knitting cycle. They now start to withdraw. The needle bar moves towards the sinker verge, causing the beards to be pressed. A further downward movement of the needle bar ‘lands’ the previous course of loops, resting on the knock-over bits, onto the closed beards. Straight bar frames are long and expensive machines that are highly productive in a very narrow sphere of garment manufacture. The knitting width is small and fashion tends not to encourage full exploitation of the fashion shaping and stitch-transfer patterning potential of the machines. Straight bar machines are known for their production of high-quality garments as a result of the gentle knitting action, low fabric tension and fashion shaping, which reduces the waste of expensive yarn during cutting and is emphasised on the garments by carefully-positioned fashion marks. The straight bar frame is the only bearded needle weft knitting machine that is still commercially viable, although it now faces serious competition from electronically- controlled flat machines Source: Knitting Technology by David J Spencer (Third Ed) (In the next session, we would be discussing about flat knitting machine.) Fig 10.7: Knocking over the loops Fig 10.1: Knitting head of straight bar machine Fig 10.4: Dividing the loop Fig 10.5: Pressing Fig 10.2: Laying the thread Fig 10.3: Sinking the loops Fig 10.6: Landing the loops
  34. 34. 24/KNITTING VIEWS/SEPTEMBER-OCTOBER 2011 Flat knitting machines, also referred to as “Flatbeds” or “V-beds,” have two rib gated, diagonally-approaching needle beds, set at between 90 and 104 degrees to each other and are positioned so that the upper ends form an inverted “V”. The interactions between the yarn and the knitting elements that create the fabric occur at the apex of the V and the fabric moves away downward between the two beds, drawn down by the take- down system. This knitting machine stitch potential includes needle selection on one or both beds, racked stitches, needle-out designs, striping, tubular knitting, changes of knitting width, and loop transfer. Further, a wide range of yarn counts may be knitted for each machine gauge, including a number of ends of yarn at each knitting system; the stitch length range is also wide; and there is the possibility of changing the machine gauge. The modern V-bed knitting machine is a highly engineered, fully automated, electronically controlled, precision knitting system. The operation and supervision of the machines of the simpler type are also less arduous than for other weft knitting machines. The number of garments or panels knitted across the machine depends upon the knitting width, yarn carrier arrangement, yarn path and yarn package accommodation. (The machine shown in fig. 11.2 is a member of the Stoll CMS family of machines. The knitting needles, beds and other active elements are enclosed within sliding covers to reduce noise and fibre contamination and to enhance safety.) V-bed knitting machine A solidly built machine frame supports the two rigid needle beds. Needles slide up and down the beds in slots known as “tricks,” cut into rigid needle beds, which maintain the orientation and spacing of the needles and support them when they impact with the CAM system. The tricks in the opposing beds are arranged so that the needles can pass between each other VASANT R KOTHARI has done Master’s in Textiles TechnologyfromDKTE’sTextileandEngineeringInstitute, Ichalkaranji(ShivajiUniversity,Kolhapur),Maharashtra.He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management fromNIFT,Bangalore.Presently,he’sworkingasanAssistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his eleventh input from the series of articles in Knitting Views) Fig 11.1: Needles in V-bed Fig 11.2: V-bed machine The flat knit machines are the most versatile of the weft knitting machines.
  35. 35. KNITTING VIEWS/SEPTEMBER-OCTOBER 2011/25 Fig 11.7: CAM plate and knitting carriage The yarn supply is situated above the machine and the yarn is fed to the needles via yarn feeders that culminates in a tube or bore to precisely position the yarn. The feeder is fixed to a feeder block that slides along a feeder rail located above the needle bed. Modern machines typically have four feeder rails with 4/6 knitting feeders/rail. The feeder precedes the needle movement across the bed in such a way that the yarn is placed across the open latch of the needle during the clearing displacement so that when the needle retracts and the latch closes the yarn is trapped in the hook. On the most basic V-bed machines a roller traction system pulls the fabric down between the needle beds to provide the take-down tension necessary to maintain the position of the old loop against the verge of the needle bed during the clearing displacement. The modern flat knit machine also has its own on-board control and programming computer and the LCD monitor display built into the sliding machine covers. Normally, in a production environment these machines can be networked and knitting programmes can be downloaded from the CAD/programming stations directly to the machine's computer. Equally, production statistics can be collected centrally. Knitting action of flat knitting machine Fig 11.3: Line diagram of V-bed knitting machine Fig 11.6: Carriage movement and its influence on knitting needle Fig 11.4: Rib gaiting Fig 11.5: Needles in tricks The front edge of the needle bed also acts as a knock-over support by helping to maintain the position of the fabric during knock-over. The needle then tracks through the CAM system as shown by the blue line in the following diagram 1 The rest position: The tops of the heads of the needles are level with the edge of the knock-over bits. 2 Clearing: The needle butts are lifted as to raise the needles to ‘tucking in the hook’ height. 3 Yarn feeding: The yarn is fed as the needles descend under the control of guard cam. The required loop length is drawn by each needle as it descends the stitch CAM. 4 Knocking-over:Toproducesynchronised knocking-over of both needle beds simultaneously, the stitch CAM in the front system is set lower than the auxiliary stitch CAM, so that the latter is rendered ineffective. 5 Delayed timing: If, however, delayed timing of the knock-over is employed, knock-over in the front bed will occur after knock-over in the back bed. Delayed timing is only normally used ongauges finer than 8 NPI and cannot be used for broad ribs during loop formation. This arrangement of the beds is called rib gaiting. The two CAM systems are contained within the carriage. The carriage or “CAM box” traverses across the needle beds and selects needles to be knitted as it reciprocates side to side. The carriage effectively raises and lowers the needles on both beds simultaneously as it passes over them, depending on the desired pattern. Needle bed lengths can vary from 1.0 m to 2.2 m width and each is designed for a specific task or purpose. Fig 11.8: Knitting action of flat knitting machines (In the next session, we would be discussing about circular knitting machines.) Bow Yarnfeeder Yarntake-back spring Yarn guides Yarn Carriage Needlebed Fabric take-down roller Control unit Lowering cam (Stitch cam) Guiding cam High butt needle Lowbutt needle The raising CAM is in half position Brushes Yarn carrier
  36. 36. 24/KNITTING VIEWS/NOVEMBER-DECEMBER 2011 The term ‘circular’ covers all those weft knitting machines whose needle beds are arranged in circular cylinders and/or dials, including latch, bearded, or (very occasionally) compound needle machinery, knitting a wide range of fabric structures, garments, hosiery and other articles in a variety of diametres. Circular knitting machines are either of body size or larger, having a single cylinder or double cylinder, cylinder and dial arrangement, as is also the case with small diametre machines for hosiery. The modern circular knitting machine is a highly engineered, electronically controlled, precision knitting system capable of producing high quality fabric at very high speeds. The main features of a circular knitting machine are: 1. The frame or body is circular according to needle bed shape supports the majority of the mechanisms of the machine VASANTRKOTHARI hasdoneMaster’s inTextilesTechnology from DKTE’s Textile and Engineering Institute, Ichalkaranji (ShivajiUniversity,Kolhapur),Maharashtra.Hehasalsodone Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his twelfth input from the series of articles inKnitting Views) 2. The yarn supply system or the creel for holding the yarn packages 3. Yarn tensioning devices 4. Yarn feed control 5. Yarn stop motion 6. Yarn feed carriers or guides 7. The knitting system, which includes the housing and driving of knitting elements and needle selection device 8. The fabric take down mechanism 9. Start, stop and inching buttons 10. The automatic lubrication system In circular knitting machine, the yarn from the package is unwounded and comes downward through guides, tensioners, stop motion, for being supplied to the needles. The knitted fabric is taken down inside the cylinder and ultimately rolled on the cloth roller. Since the needles are arranged in a circle on a circular knitting Fig 12.1: Circular knitting machine Fig 12.2: Closet view of tubular fabric
  37. 37. KNITTING VIEWS/NOVEMBER-DECEMBER 2011/25 machine, the fabric is a tubular. It is usually slit open when used. Normally, circular knitting also adopts the same knitting principles as the flat bed machines. The circular machine starts to knit when the CAM systems on the needle beds (cylinder and dial) move along the surface quite similar to that of the carriage on a flat bed machine. The only difference is that the operation is continuous as CAM system of the circular machine does not need to stop during knitting because there is no beginning or end of a course. CAM technology Circular knitting CAM systems only allow for unidirectional knitting. CAM systems generate both the needle and the sinker moment for single jersey machines and cylinder and dial moment for double jersey machines. The given diagram shows both the sinker CAM track above and the needle CAM track. The needle track shows the typical three stage needle displacement of (1&4) the raising or clearing CAM, (2&3) the lowering or stitch CAM and (5&6) the guard CAM that returns the needle to its entry position for the next CAM system. The sinker track shows the engaged position (section 7) when the needle is clearing. The sinker disengages in sections 8 and 9 so that knock-over can take place and re- engages into section 7. The moment diagrams of the needles and sinkers are also shown in between CAMs. Multi system circular machine Similar to a flatbed machine, multi-system circular knitting is also possible. Fig 12.4 is a schematic diagram of a circular knitting machine having eight systems. As shown in figure, it is clear that every CAM system is knitting at the same time and each of CAM system is having its own supply of yarn for its own course. So, when the machine runs, all eight systems move together and hence eight courses of fabric are in knitting at the same time. In other words, at the end of one revolution of the CAM system, eight courses of fabric are completed. Similarly, if there is more CAM systems around the machine, there will be more fabric courses being produced in a single revolution of the machine, for example, say if there are 30 CAM systems, 30 courses of fabric will be completed in one revolution of the CAM system. As compared to a flatbed machine with a circular machine, the CAM systems of a circular machine always operate at their maximum speed. Also, circular machines always have much more CAM systems than flat bed machines. A double system machine with 100-inch needle bed produces about 45 courses per minute and a 30-inch, 90-feed circular machine produces about 2,700 courses per minute. Further,incircularknittingmachine,needle action is a result of the relative motion between the CAM plates and the needle butt. The same needle action will be achieved whether the CAM plate is moving across the needle butt or the needle butt is moving across the CAM plate. So basically, there are two types of circular machines distinguished by the rotation of the machine. I. CAM box revolving machine II. Cylinder revolving machine If the CAM plates are moving across the needle butts, the needle bed or the cylinder will be stationary keeping the needle butts in place while the CAM box carries the CAM plates, yarn feeders with their yarn packages are all rotating around the machine. This type of machine is called CAM box revolving machine. On the other hand, if the needle butts are moving across the CAM plates, the CAMFig 12.3: CAM system It may be noted that the number of systems around the machine is limited by the circumference of the needle cylinder. Usually all the space on the circumference is issued up for placing CAM systems. The actual number of CAM systems depends on the cylinder diametre and the dimensions (width) of the CAM boxes. For example, a 30-inch diametre machine may have 72 to 90 CAM systems. Since each CAM system must have its own yarn supply and hence a yarn feeder, such machine can be referred as 30-inch, 90-Feed machine. From above figure, further, it can be seen that whether there are eight systems or 80 systems, the space taken up by the machine will not be changed. Fig 12.4: Multi system circular machine Package for cam system 1 Cam Box 1 Cylinder
  38. 38. 26/KNITTING VIEWS/NOVEMBER-DECEMBER 2011 boxes will be stationary keeping the camplates in place. The needle bed will then have to move across the CAM boxes with the needle butts in the needle tricks. For a circular machine, the needle bed is cylinder and then it rotates and that will be the only moving part with the CAM boxes, yarn feeders and yarn packages all stationary. This type of machine is called cylinder revolving machine. It would be clear that cylinder revolving machine is simpler in construction and consumes less power than CAM box revolving machine since there are less moving components. As a matter of fact, most of the circular machines are cylinder revolving type. Only those machines such as the garment length machines are CAM box revolving because of their complexity. Those are machines with 6-18 feeds producing complex knitting structures which cannot be accomplished if the machine is cylinder revolving. Circular knitting machine is naturally the choice for the volume production. Since it is ideal for volume production, there are purposely built circular machines. For example, plain knit fabric is always in Reference: Weft knitting – Introduction by Dr TY Lo, Institute of Textiles & Clothing, Hong Kong demand and large quantities. Circular with justone set of needles in the cylinder is available for plain knit only.All other knit structures requiring the second set of needles will be impossible but just producing plain fabric will be able to keep it occupied all the time (In the next session, we would be discussing about warp knitting.)
  39. 39. 28/KNITTING VIEWS/JANUARY-FEBRUARY 2012 VASANT R KOTHARI has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his thirteenth input from the series of articles in Knitting Views) 28/KNITTING VIEWS/JANUARY-FEBRUARY 2012
  40. 40. KNITTING VIEWS/JANUARY-FEBRUARY 2012/29 Another interesting segment of the knitting industry is the warp knitting. Warp knitting is defined as a loop forming process in which the yarn is fed into knitting zone, parallel to the fabric selvedge. Warp knitted fabrics are a product of a technology process carried out on warp knitting machines. The history of warp knitting is closely associated with two names, William Lee and Karl Mayer. In 1589 William Lee applied for patent of his first machine for making knitted articles, in that way he laid the foundations for mechanical manufacturing and making the technical base to develop warp knitting technology. In 1947, the insightful entrepreneur and mechanic, Karl Mayer showed off first warp knitting loom. The machine was compiled two guide bars, and with bearded needles, attained a speed of 200 rpm. It marked the starting of technical era in pioneering leaps in the field of warp knitting. fromweft-knitandtheirmachinery.Inwarp knitting, each needle loops have its own thread, means there is one warp for one wale, and it also differs in the way in which the yarn is fed to the needles. Further, the source of yarn on a warp-knitting machine is a warp beam containing a very large number of parallel yarns, similar to a warp beamonaloom.Sometimes,morethanone warp is needed, depending upon the fabric design. stitches on the face of the fabric appear vertically, but at a slight angle; and the stitches on the back appear horizontally as floats at a slight angle. These floats called laps, or under laps, is a distinguishing identification of warp knits. Warp knitting may be flat or tubular and can be produced in many varieties of patterns. It can yield cloth with a dimensional stability almost equal to that of woven fabric. Yet, a modern 28-gauge machine can produce a cloth 168 inches wide at a rate of 1,000 courses per minute that is 4,700,000 stitches per minute. Warp and weft knitting are similar fabric manufacturing processes as both utilise needles to form and intermesh loops. As the name implies, the loop formation is warp wise, i.e., vertically upward. Unlike, weft knitting, most of the warp knitting machine is open width/flat knitting. Generally, warp knitting is done by machine, whereas weft knitting is done by both hand and machine. Formation of warp knit fabrics Warp-knit fabrics and the machinery used to produce them are substantially different In weft knitting, a single yarn end may be fed to all the needles and knitting progresses around, or across the machine to produce the weft knitted fabrics for any number of courses and wales. In warp knitting, however, each needle is supplied with a yarn (or yarns) and all the needles knit at the same time producing a complete course at once so the total number of individual yarns is equal to the total stitches in a row.The needles produce parallel rows of loops simultaneously that are interlocked in a zigzag pattern, as shown in fig 13.5. In this way, the warp knittedfabricisformedbyknittingthewarp yarns on the adjacent needles course by course and intermesh the loops with the neighbouring yarns to form fabric. The Advantages of warp knit fabric Dimensional stability • In general, warp knitted fabric are more stable than weft knitted fabric. By modifying its structure (by weft insertion), the warp knitted can be as good as woven fabric Fabric tightness • The warp knitted fabrics are thinner than double knitted fabrics and the loops are smaller than double knitted fabric Fabricappearance • Most regular warp knitted fabrics give a nice, clean and balanced loop on surface. Normally the technical face and back for warp knitted are different 13.4: Warp knit fabric (face) 13.2: Basic weft knit (a) and warp knit (b) loop The subsequent loops formed from one thread are placed in the same course The subsequent loops formed from one thread are placed in the subsequent courses 13.3: Weft and warp knitted structure Fig 13.1: Warp knitted fabric 13.5: Warp knit fabric (back)
  41. 41. 26/KNITTING VIEWS/MARCH-APRIL 2012 VASANT R KOTHARI has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his fourteenth input from the series of articles in Knitting Views) Warp knitting is defined as a stitch forming process in which the yarns are supplied to the knitting zone parallel to the selvedge of the fabric, i.e. in the direction of the wales. In warp knitting, every knitting needle is supplied with at least one separate yarn. In order to connect the stitches to form a fabric, the yarns are deflected laterally between the needles. In this manner a knitting needle often draws the new yarn loop through the knitted loop formed by another end of yarn in the previous knitting cycle. A simple warp knitted loop structure is shown in fig 14.1 – 14.3. As compared to weft knitting in warp knitting also, the vertical line of loops (i.e. wales) and the horizontal line of loops (i.e. course), the loop portion (i.e. overlap) and the diagonal floats of yarns (i.e. underlap) are seen in fig 14.3. The warp knitted fabric structure has dissimilar appearance on the technical face and technical back side as shown in figure 14.1 and 14.2. Practically all warp-knitted fabrics can be identified and distinguished from weft-knitted materials by careful examination of the face and back of the fabric, usually with the aid of a pick glass. The face of the fabric has rather clearly defined knit stitches generally running vertically (in the lengthwise direction), but slightly angled from side to side. At the back side of the fabric, the diagonal line of yarns (i.e. underlaps) run right and left throughout in a zigzag manner. These Fig 14.3: Overlap and underlap in warp knitted fabric Fig 14.2: Warp knit fabric structure (Back)Fig 14.1: Warp knit fabric structure (Face) Fig 14.4: Formation of warp knitted fabric underlaps play an important role in influencing the pattern effects. The length or extent of these underlap floats and their direction of running cause a variety of design possibilities in warp knitting. The recognition of laps in a knitted fabric is the most important distinguishing feature identifying warp knits.
  42. 42. KNITTING VIEWS/MARCH-APRIL 2012/27 Warp knitted laps Loops are termed ‘laps’ in warp knitting because the warp guides lap their yarn around the needles in order to form the loop structure. A warp knitted structure is made up of two parts. The first is the stitch itself, which is formed by wrapping the yarn around the needle and drawing it through the previously knitted loop. This wrapping of the yarn is called an overlap. The diagram shows the path taken by the eyelet of one yarn guide travelling through the needle line, making a lateral overlap (shog) and making a return swing. This movement wraps the yarn around the needle ready for the knock-over displacement. The second part of stitch formation is the length of yarn linking together the stitches and this is termed the underlap, which is formed by the lateral movement of the yarns across the needles. 1)Overlaponly In overlap, the guide bar only feed yarn to the same needle all the time. The result is that each needle knits a chain of stitches. Example: 1-0/01, known as pillar stitch.A pillar stitch is not a fabric, but is commonly used with other lapping movements to form a fabric. 2)Underlaponly Underlapalonecannotformintoafabricand is commonly used with other lapping movements. If a guide bar only made underlaps in a multi-guide structure, this guidebariscalledinlaybarandthewarpare calledinlayyarn,whichneverformintoloops but only “tie-in” at the back of the fabric. 3)Overlapwithunderlap When overlap and underlap are worked together, two types of fabrics can be formed. The first one, as shown in fig 14.8- 14.10, when overlap and underlap are moving in the same direction, an open lap fabric will be formed. The second one, as shown in fig 14.11 – 14.13, when overlap and underlap are moving in opposite direction, closed lap will be produced. Fig 14.5 a: Subsequent courses Fig 14.5 b: Same needle, wale Fig 14.5 c: Subsequent courses and subsequent wales Fig 14.6: Guide bar movement Fig 14.7: Overlapping and underlapping Fig 14.8: Open lap Fig 14.9: Open lap Fig 14.10: Open lap Fig 14.11: Closed lap Point paper diagram: Each point shows a needle in a course; each row shows a different course Basic combination of overlap and underlaps All warp knit fabric structures are composed of both overlap and underlap: 4)Neitheroverlapnorunderlap This seems to be warp float in the fabric. The guide bars give no lateral movements for a few courses in the repeat, laying the warps straight in the fabric. For a multi guide bar fabric, it is used to hide colour warps at the back for a colour pattern. Fig 14.12: Closed lap Fig 14.13: Closed lap Characteristics of warp knitted fabrics • Extremely versatile in pattern effects with yarn • Rigid to elastic • Cannot be raveled • Good air and water permeability • Good crease resistance • Good drapability • Good dimensional stability • Good strength (In the next session, we would be discussing about warp knitting machines)
  43. 43. 32/KNITTING VIEWS/MAY-JUNE 2012 The history of warp knitting machine is closely associated with two names – William Lee and Karl Mayer. Unlike weft knitting machines, most of the warp knitting machines is open width/ flat type. As the name implies, loop formation is warp wise i.e. parallel to fabric selvedge. In warp knitting, fabric is madebyformingloopsfromyarnscomingfromwarpbeam,which run in the direction of fabric formation. Every needle is fed by separate yarn for loop formation. In order to connect the loops into a fabric, the yarns are shifted (shogged) between the needles. In this manner the needle draws the new loop through the loop formed by another yarn in the previous knitting cycle. This unique feature of the loop continuity in upward direction makes the warp knitting fabrics more special with respect to their characteristics, production and applications. Warp knitting machines produce the widest range of fabric types and qualities of any fabric forming technology. Though the machine initiation has started very long back, in the middle of 20th century only the major developments in the manufacture of warp knitting machines has taken place. The warp knitting machines have gained their importance due to advent of manmade fibres such as nylon, polypropylene, polyester, acrylic, etc. Today, there is a vast range of machine sizes, types and configurations, ranging from 10 cm-wide crochet machine to a 5 mtr-wide geotextiles machine are available in the market. Modern warp knitting machines are engineered to operate at high knitting speeds (upto 3,000 cycles/min) and these machines may produce in excess of 5 sq mtr/min. Consequently, it is difficult to encapsulate such a range within a simple description. The given figure shows a typical knitting machine producing fabric for apparel. The main machine frame is constructed from sturdy cast steel or welded vertical side frames held together and stabilised by a large welded steel box section transverse girder. The needle bar and yarn guides are mounted transversely above box section girder in middle of the machine and run virtually full width of machine.Machinewidthsrangefrom1mtrto5or6mtrdepending on type and end-use of fabric. The yarn supply may be carried on warp beams situated above the knitting elements on beam control systems mounted on the side frames. Alternatively the beams may be mounted on A- frames behind the machine to permit greater beam capacities, or machine may be supplied from individual yarn packages mounted in creels behind machine. The fabric is taken away downwards and to the front of the machine to a take-up roller, or it may travel under a walkway for the operator, to be taken-up on a bulk fabric roller that is remote from the machine. Basics of knitting Warp Knitting Machines VASANT R KOTHARI has done Master’s in Textiles Technology from DKTE’s Textile and Engineering Institute, Ichalkaranji (Shivaji University, Kolhapur), Maharashtra. He has also done Diploma in Export Management (Apparel Export) from the Indian Institute of Export Management, and Garment Export and Merchandising Management from NIFT, Bangalore. Presently, he’s working as an Assistant Professor in Department of Fashion Technology, NIFT, Bangalore. (This is his fifteenth input from the series of articles in Knitting Views)
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Basics of Knitting - Introduction 2. Basic Terminologies 3. Knitting Machine Needles 4. Basic Elements of Knitting 5. Knit, Tuck & Miss Stitch 6. Weft Knitting 7. Knitting Loop Structure & Notations 8. Single Jersey & Rib Fabric 9. Purl & Interlock Fabric 10. Straight Bar Knitting Machine 11. Flat Knitting Machine 12. Circular Knitting Machine 13. Warp Knitting 14. Warp Knitted Fabrics 15. Warp Knitting Machine 16. Tricot Machine 17. Raschel Machine 18. Compound Needle Machine 19. Yarn Requirements for Knitting 20. Knitting Fabric Quality Parameters 21. Defects in knitted fabrics 22. Testing of Knitted Fabrics 23. Production Calculations 24. Costing Of Knitted Fabrics 25. Processing of Knitted Fabric 26. Relaxation of Knitted Fabric 27. Development Process of Knitted Fabric 28. Sourcing of Knitted Fabric 29. Garment Manufacturing of Knitted Fabrics 30. Seamless Knitting

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