Tx 203 lecture 7 monday 02 12-2013


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Tx 203 lecture 7 monday 02 12-2013

  1. 1. CHAPTER 3 Yarn Production
  2. 2. Definitions  A textile yarn is an assembly of a substantial length and relatively small cross – section of fibres and/or filaments with or without twist.  Yarns can be can be classified as; Spun staple fibre yarns – Yarns in which staple fibres are assembled and bound together by various means e.g. Twist insertion and use of adhesive Continuous filament yarns – Yarns produced from continuous filament fibres 02/12/2013 88
  3. 3. Staple FibreYarns  A staple spun fibre yarn is a linear assembly of fibres held together by the insertion of twist to form a continuous strand, small in cross-section but of any specified length.  Staple spun fibre yarns are used in processes such as knitting, weaving and sewing  Staple fibre yarns can also be classified according to; Fibre length: Short staple yarns: made of fibres of length less than 60mm Long staple Fibres : made of fibres of fibre of length greater 60mm 02/12/2013 89
  4. 4. Staple FibreYarns Yarn Construction i.e.They way a yarn is made Single yarn: One yarn made up of twisted fibres Plied or folded yarns : Made of two or more single yarns twisted together Cabled yarns: Made of two or more plied yarn twisted together FancyYarns:Yarns having deliberately produced irregularities Spinning System Used Ring SpunYarns:These are produced on the ring spinning machine Rotor spun yarn: Made on rotor spinning machine 02/12/2013 90
  5. 5. Staple FibreYarns Friction Spun Yarns: Made on friction spinning machine Wrap spun Yarns: made of a parallel bundle of staple fibres bound in a compact structure by a continuous filament yarn. Staple fibre yarns can also be used. Core Spun Yarns: Yarns having a central core wrapped with fibres e.g. Filament core wrapped with fibres Fasciated yarns: Yarns made up of parallel bundles of fibres bound into a compact structure by surface wrappings at regular intervals 02/12/2013 91
  6. 6. Staple FibreYarns Twistless Yarns: Yarns produced without twist where coherence is provided by adhesives 02/12/2013 92
  7. 7. Yarns Fancy Yarn
  8. 8. Yarn Dimensions  As with fibres, It is not easy to measure the diameter of a yarn.  Yarns have different dimensions/thickness depending on the end uses and how the yarn is made.  It is thus accepted to express the yarn thickness using the yarn counting systems i.e. in terms of its linear density  There are two main Systems used to indicate the yarn linear density namely direct system and indirect system 02/12/2013 93
  9. 9. Direct System  In this system, the fineness (linear density) of a yarn is expressed as the mass of a yarn per unit length. Linear density = mass of a yarn/length of a yarn  In this system, the lower the linear density, the finer the yarn  The direct system is called the Tex system. Units used in this system and their conversion are given below. 1Tex = 10 Decitex (dTex), 1 kilotex (kTex) =1000Tex 1 dTex = 0.9 Denier 1Tex = 9 Denier 1Tex = 1000Millitex  This system is used internationally i.e. it is a universal system 02/12/2013 94
  10. 10. Indirect System  In this system the yarn thickness is expressed as the length of a yarn in a unit mass. Linear Density = Length of a yarn/mass of a yarn  In this system, the yarn can be measured in; Metric count (Nm): Number of 1000 lengths in a kilogram. i.e. The number of kilometres in one kilogram of a yarn. Cotton Count (Ne): Number of 840 yard Hanks of a yarn in one pound. 02/12/2013 95
  11. 11. Indirect System Conversion factors: Cotton count (Ne) = 590.5/Tex Metric Count (Nm) = 1000/Tex Note: For a given yarn linear density, the number of fibres in the cross-section of a yarn can be calculated if the fibre linear density is also known. Example:The linear density of a yarn is 20Tex and the yarn is made of fibres of a linear density of 0.5dTex. Find the number of fibres in a yarn cross – section. Formula: Number of Fibres = linear density of yarn/linear density of fibres 02/12/2013 96
  12. 12. Yarn Production Methods  There are two main systems of yarn production namely ring spinning and open end spinning systems.  Ring spinning is done on ring spinning frame (machine)  Open end spinning system including systems such as rotor spinning, friction spinning, vortex spinning, wrap spinning  Several systems of open end spinning exist but only rotor and friction spinning systems have been commercially successful, with rotor spinning dominating the market. 02/12/2013 97
  13. 13. Ring Spinning Frame  The ring spinning frame consists of the drafting system, the spindle, the yarn guide and the ring rail.  The rings are built in the ring rail.  The yarn guide, the ring and the spindle share the same vertical axis.  The yarn from the roving passes through the drafting system, where it is reduced to a lower linear density.  The roving is gradually reduced as it progresses from the back to the front roller.  The back roller draft is normally set at 1.25 which is much lower compared to the front roller draft 02/12/2013 98
  14. 14. Ring Spinning Frame 02/12/2013 99 Roving Twisted Yarn Drafting system
  15. 15. Relative Costs of Machinery (Spinning & Weaving) Preparation for spinning (opening, carding, drawing, roving) 18% Ring spinning 24% Preparation for weaving 15% Weaving 43%
  16. 16. Relative Costs of Carded Ring Spun Yarn Blowroom (opening) 11% Carding 13% Drawing 4% Roving 12% Ring spinning 60%
  17. 17. Ring Spinning Frame 02/12/2013 99 Roving Twisted Yarn Drafting system
  18. 18. Feed DeliveryVf VdV2 3 over 3 Double Apron Roller Drafting Drafting Apron Aprons move at V2 control short fibre movement reduce drafting wav
  19. 19. Spindle speed = Bobbin speed Vd Rotation of traveller Inserts twist Yarn Balloon
  20. 20. Ring Spinning  The twist is inserted by the traveller as it rotates around the ring,  Twist insertion rate depends on the diameter of the bobbin – any variation of twist?  As the traveller rotates the twist is inserted in the balloon length and propagates to the yarn guide and to the nip of the front rollers – creating a spinning triangle!  The package on the tube is built by up and down movement of the rail along the bobbin  Increasing yarn tension results to excessive breakage 02/12/2013 101
  21. 21. Spinning Triangle Front Drafting Rollers To spindle
  22. 22. Spindle speed = Bobbin speed Vd Rotation of traveller Inserts twist Yarn Balloon
  23. 23. Db Nt Ns Bobbin Traveller (Ns - Nt) π Db = Vd Ring VdSpindle speed = Bobbin speed Twists/Meter t = Nt / Vd Rotation of traveller Inserts twist
  24. 24. Vd = (Ns - Nt) π Db Vd / (π Db) = (Ns - Nt) Vd / (π Db) + Nt = Ns Nt = Ns - Vd / (π Db) During production: Ns, Vd do not change Db increases Nt increases
  25. 25. Twists/Meter t = Nt / Vd Nt = Ns - Vd / (π Db) Yarn twist increases during production t = Nt / Vd = Ns / Vd – 1 / (π Db) T ≅ Ns / Vd Small value Usually ignored
  26. 26. Twists/Meter t = Ns / Vd Vd = Ns / t Faster spindle speed: faster production More twist: slower production
  27. 27. Production rate (kg/h): NE tex Vd ××××× 60 1000 1 1000 NE K tex Ns ×××××× 60 1000 11 1000 5.1 textK = t Ns Vd = tex K Ns = K texNs = tex K t =
  28. 28. NE K tex Ns ×××××× 60 1000 11 1000 5.1 Production rate (kg/h): Increases with Spindle speed Ns Yarn tex Machine efficiency E Number of spindles N Decreases with twist level K
  29. 29. Machine efficiency is affected by: End breakage rate Package size Yarn tex Spindle speed End breakage rate is affected by: Machine condition Yarn strength (evenness, fibre, twist, tex) Yarn tension (spindle speed, balloon size, ring & traveller)
  30. 30. Package needs to Have maximum yarn Be free from yarn entanglement Be stable Be even in density and yarn tension
  31. 31. Main layer (slow lifting of ring rail) Ring Package (Cop) Tube Cross layer (fast descending) Package building motion
  32. 32. Ring Spinning  The increase of yarn balloon between the traveller and the yarn guide is the result of yarn tension increase  This increases at increased traveller speeds and type  Proper selection of the traveller weight for a particular yarn linear density and yarn type is crucial!  For yarn counts in the range of 20Tex to 30Tex, traveller weights of 3mg/Tex are recommended, and 2.6mg/Tex for higher count  A new ISO standard specifies the appropriate traveller number for a given yarn linear density 02/12/2013 102
  33. 33. Traveller weights recommended by ISO standards Cotton Synthetic fibres 17 45 56 20 56 71 24 71 90 30 90 100 36 100 112 02/12/2013 103 Linear density Traveller Number
  34. 34. Drafting in Ring Spinning 02/12/2013 104 Roving
  35. 35. Draft values for cotton and synthetic fibres Material Draft Carded cotton Up to 35 Medium fineness combed cotton up to 40 Fine cotton Up to 45 Synthetic fibres Up to 45 02/12/2013 105 • Accurate and precise drafting arrangement (rollers) is required; • Otherwise it can cause uneven yarn and thus contributing to end breaks. • Higher drafts contribute to reduction in yarn quality.
  36. 36. Minimum Number of Fibres inYarn Cross Section Combed cotton 33 fibres Carded cotton 75 fibres Carded synthetic fibres 50 fibres 02/12/2013 106 • Many fibres are required in the cross section for cotton than in synthetics since most cotton fibres are short compared to synthetic fibres. • The minimum number of fibres therefore sets the spinning limit.
  37. 37. Roving Production Calculation Example Given: Spindle speed: 1000 rpm Roving linear density: 400 tex Drafting roller diameter: 25 mm Drafting roller speed: 250 rpm Bobbin tube diameter: 5 cm Full bobbin diameter: 10cm Calculate: Roving twist factor Initial bobbin speed (empty bobbin) Bobbin speed when bobbin is full
  38. 38. Ring Spinning Production Calculation Example Given: Spindle speed: 18,000 rpm Yarn linear density: 36 tex Twist factor: 36 turns⋅cm-1⋅tex1/2 Machine efficiency: 90% Production rate: 100 kg/h Calculate: The number of spindles required. The production rate of the machine for a 9 tex yarn, all other conditions remain the same.