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Yarn Manufacturing Process : Drawframe

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Detail Study of Draw frame process.

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Yarn Manufacturing Process : Drawframe

  1. 1. Subject Code : BTTEX05002 Semester : Vth Textile Technology Department CTF, MPSTME, SVKMs, NMIMS, Shirpur By: Prof. P. P. Kolte
  2. 2. Objectives:  To study necessity of draw frame  To study objectives of draw frame  To study construction and working of draw frame
  3. 3. Drawing is the operation by which slivers are blended, doubled and leveled. In short staple spinning the term is only applied to the process at a draw frame. In drawing slivers are elongated when passing through a group of pair rollers, each pair is moving faster than previous one. This permits drawing and elongating of several slivers to make them strong and uniform.
  4. 4. Objectives:  To straighten the fibres and to make them parallel to the central axis of the sliver.  To improve the evenness of the sliver by drafting and doubling.  To produce a proper weight of sliver required for the following process.  To reduce weight per length unit of sliver.  To blend raw material of same hank perfectly.  To remove dust from slivers. Necessity:  To parallelization of fiber and blending the carded sliver. To parallel trailing hooks and leading hooks.
  5. 5. C, card; GI, drawframe GIl, drawframe II H, roving frame R, ring spinning machine
  6. 6. Main sections of Drawframe: (1) Creel Section (2) Drafting Section (3) Sliver Condensing Section (4) Coiler Section Fig. Passage of material on Drawframe m/c
  7. 7. (1) Creel Section (2) Drafting Section (3) Sliver Condensing Section (4) Coiler Section
  8. 8. Creel Section Coiler Section Drafting Section Sliver Condensing Section
  9. 9. Questions:  What is necessity of draw frame.  What are made in objectives of draw frame.  Tell me the working of draw frame.
  10. 10. Objectives:  To study creel of draw frame  To study drafting requirement of arrangement  To study influence of draft  To study elements of drafting arrangement
  11. 11.  Creel  The drafting arrangement  Suction system for the drafting arrangement  Coiling
  12. 12.  The creel must be designed so that; - False drafts are avoided - The machine stops upon occurrence of a sliver break - Sliver breaks can be dealt with easily, comfortably and safety.  Creel arrangement are of two types: - Nested type - In-line arrangement  Sliver may be fed in from up to 8 cans per drawing head.  Can may have diameter up to 1000mm [40 inches]  Slivers lie closely adjacent to each other not on top of one other.
  13. 13. The drafting arrangement: - Requirements - Influences on the draft - Factors dependent upon the fiber material - Factors dependent upon the drafting arrangement - Elements of drafting arrangement - Bottom roller - Top roller - Top roller pressure - Forms of drafting Arrangement
  14. 14. Requirements of drafting arrangement:  The drafting arrangement is the heart of the draw frame.  Drafting arrangement exerts most decisive influences on sliver quality.  The requirements placed on the drafting arrangements are mentioned below:- 1. Simple, uncomplicated construction. 2. Stable design with smooth running roller. It means rollers should be centric and smooth running. 3. A mode of operation giving a high quality product at even high running speeds. 4. High Degree of flexibility, suitability for all raw materials. 5. Optimal control over the movement of the fibers during the drafting operation. 6. High precision in both of operation and adjustment. 7. Rapid and simple adjustability of roller spacing and draft levels. 8. Ease of maintenance of cleanings. 9. Optimal ergonomic design.
  15. 15. Influences on the draft - Factors dependent upon the fiber material: - Mass of the fibers in the strand cross section. - Degree of order of the fiber. - Shape of cross section of the fiber strand. - Compactness of the fiber strand. - Length of fiber. - Adhesion between the fiber depends upon:- - Surface structure - Crimp - Lubrication - Compression of the strand. - Evenness of distribution of fiber length. - Twists present in the fiber strands. Cont…
  16. 16. - Factors dependent upon the drafting arrangement  Diameter of the rollers.  Hardness of the top rollers.  Pressure exerted by the top rollers.  Surface characteristics of the top rollers.  Fluting the bottom rollers.  Type and form of fiber guiding devices, such as pressure rods, pin bars, aprons, condenser etc.  Clamping distance.  Level of the draft.
  17. 17. Elements of drafting arrangement: Bottom roller: Bottom rollers are made of steel and are mounted in roller strands or in frames by means of needle or ball bearings. They are positively driven from main gear transmission. On order to improve their ability to carry the fibers along, they are formed with flutes of one of the following types. - Axial flutes - Spiral flutes - Knurled flutes The diameter of the bottom roller lie between 20-90mm, but normally lies between 25-50mm. The distance between drafting roller is adjustable and depends on fiber length. As shown in fig.
  18. 18. Top roller: The top rollers are not positively driven; they are mounted by the means of ball bearings. These top rollers are made of steel and they are covered with thick coating of synthetic rubber. An important matter avoid this coating is its hardness. Soft rubbers coating can grip the fiber strand more perfectly than that of hard one, but soft coating of rubber wear out more quickly. Hardness of rubber coating on top rollers in specified in terms of degree shore. Soft coating -> 60-70° shore Medium coating -> 70-90° shore Hard coating-> Above 90° shore
  19. 19. Top roller pressure: To clamp the fibers, the top rollers must be forced at high pressure towards the bottom roller. This pressure can be generated by: - Load by means of dead weight - Spring weighing (the most usual form) - Hydraulic systems (Hardly used) - Pneumatic weighing (The Rieter company) - Magnetic weighing (The Saco Lowell company)
  20. 20. Questions:  What is the influence of draft in drafting.  What are requirement of drafting arrangement .  Tell me the elements of drafting arrangement.
  21. 21. Objectives:  To study various forms of drafting arrangement To study draft and attenuation To study drafting operation To study drafting force
  22. 22. Forms of drafting Arrangement: - 3 over 4 drafting system - 3 over 3 drafting system - 4 over 3 drafting system - 5 over 3 drafting system In extreme case the break draft and total draft lies between 1.05 – 2.5 and 3.5 – 12 respectively, but usually they are 1.25 – 1.8 and 4-8 respectively.
  23. 23. The degree of reduction in the linear density of the fibre material is called as the draft. Attenuation defined as: Attenuation = Draft x [100/100-p] Where, p: elimination or loss of fiber into waste Draft can be expressed in two forms: (1) Actual or Technical Draft Actual Draft = Linear Density of Input / Linear Density of output (2) Mechanical Draft Mechanical Draft = Linear Speed of Output / Linear Speed of Input If the percentage waste removal during the carding machine is (W) then the actual and mechanical draft are related to each other as: Mechanical Draft = Actual Draft (1 – W/100)
  24. 24. The drawing operations are primarily concerned with converting card slivers into drawn slivers in which fibers have been straightened and aligned with a high degree of parallelism. It is essential that the short-, medium-, and long-term irregularities of drawn slivers are as low as possible, with no periodic variation present. If the roller are rotated that their peripheral speed in the through flow direction increases from roller pair to roller pair, then the drawing apart of the fiber, i.e. draft. This is defined as the ratio of the delivery length [LD] to feed length [LF], or the ratio of the peripheral speeds: V= LD / LF = VD / VF ……………….V= peripheral speed of cylinder C
  25. 25. The drafting arrangement has three drafting zone: Break draft zone [S1] : DB = V2 / V1 Middle draft zone [S2] : DMiddle = V3 / V2 Main draft zone [S3] : DM = V4 / V3 The total draft is always product of the individual drafts and not sum: Dtotal = DB x DMiddle x DM = V4 / V1 Fig. Drafting Arrangement
  26. 26. What is drafting force? Drawing apart of the fibres is effected by fibres being carried along with the roller surfaces. For this to occur, the fibres must take on the peripheral speed of the rollers. This transfer of the roller speed to the fibres represents one of the problems of drafting operations. The transfer can be effected only by friction, but the fibre strand is fairly thick and only its outer layers have contact with the rollers, and furthermore various, non-constant forces act on the fibres. Drafting takes place in three operating stages: - Straightening of the fibres (decrimping) - Elongation of the fibres - Sliding of the fibres out of the surrounding fibre strand.
  27. 27. Drafting force is heavily dependent upon: - Fibres in the cross section - The arrangement of the fibres in the strand (parallel or crossed) - Cohesion between fibres (surface structure, crimp, finish etc.) - Fibre length; - Nip spacing. Drafting force(DF) influenced by different parameters during drafting: - DF directly proportional numbers of fibers in cross section. - DF inversely proportional draft used. - DF ↑, roller setting ↓. - Nature of material (degree of entanglement & fiber orientation) - Relative humidity - Temperature - Nip contact - Roller slip - Type of drafting system
  28. 28. Fig. Draft through a roller drafting . Fig. Forces acting on a fibre (f) during drafting Fig. Drafting Force Diagram Where, F - Magnitude of drafting force D - Magnitude of draft m to n – Highest impact of draft w.r.t. drafting force
  29. 29. Questions:  What is draft and attenuation.  What are the different forms of drafting.  Tell me the drafting operation.  What is drafting force.
  30. 30. Objectives:  To study behavior of fibre in drafting zone  To study fibre friction field  To study role of fibre-fibre friction in drafting
  31. 31. Fibres arriving for processing exhibit very considerable length variations. In a drafting field, they are therefore found in two conditions: - Guided (a, b, c) - Floating (d) In guidance of floating fibres is favorably influenced by: - a sufficient number of longer fibres as carrier fibre, for the shorter ones - guiding devices such as rollers needles, aprons, etc - the friction held Fig. Guided and floating fibres in drafting field
  32. 32. The top rollers must be pressed against the bottom rollers with considerable pressure to ensure that the fibres are transported. This pressure is not only effective in the vertical direction, but spreads through the fibre stock also in the horizontal direction. The compression of the fibres, and thus the inter-fibre friction, is transmitted into the drafting field. The intensity declines, however with increasing distance from the nip line and finally reduces to zero. The friction field is an extremely important medium of fibre guidance. It keeps the disturbing effect of drafting within tolerable bounds. Fig. The friction field created in the fibre by applied pressure
  33. 33. Friction field affects by: - Pressure of the top rollers - Hardness of the top roller covering - Roller diameter - Mass of the fibre strand - Density of the strand - Cross-section of the strand - Breadth of the strand - Twist in the strand
  34. 34. A large number of fibres called as 'back beard fibres' are held by the back rollers moving slowly towards front rollers at a velocity VR Relatively small number of fibres called as 'front beard fibres' held by front rollers are moving faster at a velocity VF . At a given instant, the back roller releases some of the back beard fibres. Since, FF - Tensile force FR - Friction force FD - Drafting force For the fibre to be just accelerated, FF ≥ FR Fig. Frictional Force during Drafting
  35. 35. This force FF is the drafting force for a single fibre. The total drafting force is, FD = FF Once the fibre is accelerated to the front roller velocity, the nature of friction between its leading portion and neighboring front beard fibres will be static one. While their friction between trailing end and back beard fibres is a dynamic one, slowly reducing due to reduced area of contact, as the fibres progress forward. This dynamic friction force at trailing end is less than FR. Before the fibre is accelerated, fibre straightening followed by elongation takes place. This is illustrated in neighboring Fig. Fig. Stick-slip phenomenon Where, n is the number of fibres being accelerated to the front roller velocity at given point of time.
  36. 36. Questions:  What is fibre friction field.  Tell me the role of fibre-fibre friction in drafting  How fibre behaves in drafting zone
  37. 37. Objectives: To study nature of fibre friction in drafting To study distribution of draft To study additional effect of draft To study Perfect and real drafting
  38. 38. Figure shows the general frictional behavior of liquid-lubricated textile yarns relating the frictional coefficient with yarn speed, lubricant viscosity, and pressure between yarn and guide. The dashed line represent the contribution of the boundary and hydrodynamic components respectively. The frictional behavior seen in practice is the solid line, which is the result of the boundary and hydrodynamic contribution to the friction. The semi-boundary region represents the transition between boundary and hydrodynamic frictions. It is the region of minimum friction for the system. Fig. General frictional behavior of yarn
  39. 39. This occurs between draft range of 1 to 2. This drafting range is called "Critical drafting range," For cotton sliver, the critical drafting region lies somewhere between 1.15 and 1.4, and for cotton roving (on the ring spinning machine) between 1.3 and 1.7. For synthetic fibres, for which the stick-slip effect is usually more stro -ngly marked, the range lies somewhat higher, depending upon delustring, spin finish, etc. Operating in the critical drafting region can be risky. Fig. Drafting force diagram for Stick-slip zone
  40. 40. The drafting arrangement has two drafting zone: Break draft zone [S1] : DB = V2 / V1 Main draft zone [S2] : DM = V3 / V2 The total draft is always product of the individual drafts and not sum: Dtotal = DB x DM = V3 / V1 Fig. Drafting Arrangement
  41. 41. The task of the break draft in the first draft field is to straightened and extended the fibres to such degree that the main draft can immediately cause fibre movements. The main draft must be adapted to the drafting conditions, mainly the fibre mass in the drafting field and the arrangement of the fibres in the strand. The draft can be increased with increasing fineness of the intermediate product and also with increasing parallelisation of the fibres.
  42. 42. In addition to the reduction in diameter, draft causes: - Stretching out of the fibres - Straightening of fibre hooks - Paralleling of the fibres - Scraping away of dust particles all of which represent important operations for spinning
  43. 43. Perfect / Ideal Drafting Real / Actual Drafting - All fibers in sliver are straight and having equal length. - Not straight & equal length. - Perfect orientation of fiber along the sliver axis. - Not perfectly orientated. - Distance between consecutive fiber ends is uniform throughout the sliver. -Not constant. - All fiber in sliver are parallel to the sliver axis. - Not parallel - Speed of the fiber = speed of the back roller until gripped by front roller. - Not - Arrangement of the fiber, variation, front end fiber density of the sliver is uniform w.r.t. draft through out the sliver. - Not
  44. 44. Questions:  What is Perfect and real drafting.  Tell me additional effect of draft in drafting  How draft distributed in drafting zone
  45. 45. Objectives:  To study nature of drafting irregularities  To study suction system for drafting  To study coiling
  46. 46. Drafting irregularities are generated in the roller drafting due to the lack of complete control on the fiber movement in the drafting zone. Some of these irregularities are in form of periodic thickness variations, which are recognised by their amplitude and wave-length. Classification of drafting irregularity variation: Sliver Variation Wavelength Band Some possible causes Ultra short term 10 cm Fibre distribution, Mechanical vibration. Short term 10cm to 10m Drafting waves, Piecing waves. Medium term 10m to 100m Card, Broken sliver, Chute feed, Scutcher Long term 100m to infinity Blending, Opening, feeding, Chutes, etc.
  47. 47. Factors Influencing Drafting Irregularity: The factors determining zone drafting irregularity are; - The size of draft - The count of the input material - Multiple inputs or doubling - Roller or drafting zone setting - The degree of parallelism, length, and fineness of fibers in the input material. The uniformity in the drafted strand is determined by: - draft ratio - Roller setting - Material characteristics - Pressure exerted by the top roller - Fluting of bottom rollers - Distribution of draft between various drafting stages
  48. 48. One of the tasks of the draw frame is dust removal. Each roller of the arrangement has an associated cleaning device so that fly and fibers tending to adhere to the rollers can also be carried away. The air draw away is passed via tube directly into the exhaust ducts of the air-conditioning system, or to filters within the machine. The accumulation of the fibrous mass on the surface of the rollers causes unevenness in drafting and sometimes also causes sliver breakages causing the machine to stop. Fig. Suction clearer for drafting arrangement
  49. 49. Coiling zone of the draw frame includes following components: - Delivery - Condensing - Sliver coiling - Can Changer
  50. 50. To avoid disintegration of the web, it must be collected together in a converging tube (1), immediately after the delivery roller and guided to the sliver trumpet. The bore of this sliver trumpet (2) must be adapted precisely to the sliver volume ( = sliver hank). The sliver trumpet is therefore replaceable. The bore ( in mm) should be determined approximately by the relation. d = k x √(ktex) Where, k varies between 1.6 (for' finer slivers). to 1.9 (coarser slivers). Fig. Delivery Assembly 1 2
  51. 51. The fibre web leaving the front pair of drafting rollers is passed through a converging tube and is guided to a specially designed condensing funnel called as the trumpet guide as shown below: The degree of condensing at the trumpet guide is essential for providing a good fibre to fibre cohesion to hold them better in a sliver. However if too much condensing is done then the drawn sliver develops thick places. After condensing of fibres at the trumpet guide back into a sliver form, the sliver is passed through a pair of calendar rollers which does a further compressing of the fibre mass and ultimately deposits the drawn sliver into a sliver can. Fig. Delivery Assembly 1 2
  52. 52. The drawn sliver coming out of the calendar rollers is passed through a coiler tube fixed on a coiler plate. The coiler gears fixed on the coiler plate help to rotate the coiler tube so that sliver can be laid in the can in form of special coils. The can rests on the rotating plate, with the rotation of the plate the can also rotates. The rate of rotation of the can is kept slower than the rate of rotation of the coiler tube which helps in proper deposition of drawn sliver in a spiral arrangement. Fig. Sliver Coiler
  53. 53. It is necessary to keep the sliver deposition rate slightly higher than the sliver delivery so that blockage of the sliver in the tube may be avoided. However this difference should not be too large where false draft may arise in the sliver. Fig. Sliver Coiler
  54. 54. Modern high-performance draw frames are usually fitted with automatic can changers. These reduce the burden on the personnel, enabling more machines to be allocated to one person reduce the necessity for attendance of the operative at the machine, and also increase efficiency. They can be classified into: - single-step changers (flying change) - 8 multiple-step changers (interrupted change) Single-step changers give higher machine efficiency because full cans are replaced by empty ones at full speed i.e. without stopping the machine. Multiple step changers give lower machine efficiency because machine must be brought to stop during the change.
  55. 55. Questions:  What is components in coiling zone.  Tell me nature of drafting irregularities  How suction system works in drafting zone
  56. 56. All diagrams covered in Unit-I & Unit-II have to draw in the assignment book.
  57. 57. Objectives:  To study Draft ratio  To study Roller Setting  To study Fibre Crimp
  58. 58. Faisal EI-Sharkawy et al have provided a simplified treatment to obtain the relationship between the drafting Force and the parameters like fibre length, number of fibre ,in the cross section, roller setting and draft. Assumptions made in the development of the equations are: 1] The drafting force is dependent on the degree of contact between the beards under the front and back roller grips. 2] Fibres in the sliver are straight are parallel to the sliver axis and have the same length. 3] Fibre to fibre contact is constant. 4] Sliver are perfectly regular, with same number of fibre in cross section
  59. 59. Consider a sliver with N fibres in its cross section on that is being subjected to draft D between two pairs of rollers,so that the number fibres in the drafted sliver will be N/D. Under steady-state condition, the (back beard)beard will be gripped by the back roller and another beard will be gripped by the front draft roller. The taper of the front and back beards in the drafting zone will be given by the following equation Y = (ND) (x- eL)/L …..(1)…….(from x = eL to x = L) and Y' = N(1-x/L) …..(2)…….(from x = 0 to x = L) Where, Y= number of fibres in the cross-section of the front beard. Y' = number of fibres in the cross-section of the back beard. D = draft. x = any position in front of the back roller. L = fibre length. Cont….
  60. 60. e = a dimensionless quantity that can take any value between zero and one; it can be considered as a measure of the degree of disconnection between the front and back beards. The drafting force will be proportional to the number of contact points between the two fibre beards. i.e., proportional to the sum of the areas of the smaller triangle A1 and A2 in fig. F α A1 + A2 It is easy to show from the above that: A1 = NLD (1- e)² / 2 (D + 1)² and A2 = NL (1 - e)² / 2 (D + 1)² Hence, F α NL (1- e)² / (D + 1) ………(3) Fig. Taper of back and front beard in d/f system
  61. 61. According to Equation (3), when the draft D increases, the drafting force decreases. However, for very low drafts, the drafting force increases first to a peak as the draft increases and then decreases as shown in fig. D0 is the draft corresponding to the maximum force. Up to this draft, there is no fibre slippage but simple straightening out of fibres, which results in the extension D0 -1 for the sliver. This region is characterised by increasing contraction of the sliver cross-section. This is due to the removal of fibre crimp and alignment of the fibres. Fig. Relation between D/F force (F) and Draft (D)
  62. 62. As the fibre crimp is removed, the effective stiffness of each fibre increases sharply, and the sliver resistance to further deformation increases with it. Meanwhile the Poisson contraction effect increases both the number of fibre to fibre contacts and the pressure at these contact points, thus increasing the sliver resistance to fibre slippage. In order, allow for this extension, Equation 3 must be corrected so that it now becomes: F α NL (D0 - e)² / (D - D0 +1) ……………………….(4) When the sliver cross-section remains unaltered with the change of draft, drafting force is inversely proportional to the draft.
  63. 63. When the values of 1/D are sufficiently low, there is almost proportionality between the force and the reciprocal of the draft. For high values of l/D, i.e., as the draft approaches Do, there is a departure from linearity. Equation (4) also allows a quantitative study to be made on drafting force as a function of the roller setting. The reciprocal of the drafting force, 1/F, is plotted against the reciprocal of e (which is a quantity proportional to the roller setting) in Fig., where, as can be seen, there is a curvilinear relationship between these two quantities. Fig. The reciprocal of the draft Vs reciprocal of roller setting
  64. 64. Fibre crimp affects the geometrical arrangement of the fibre. The more highly crimped fibre (in terms of crimp frequency and crimp amplitude) exhibit a large drafting force because it has more opportunity to interlock spatially, entangle and mesh with neighboring fibres. Increased spatial interaction of crimped fibres also accounts for the larger lateral cohesion of the fibres in a crimped sliver compared to the ease of removing decrimped fibre from the surface of the sliver made of decrimped fibre. Increased fibre crimp is analogous to increased surface roughness with a result in improved fibre cohesiveness. With an increasing crimp, friction force increases in the static and low speed regions
  65. 65. Questions:  What is draft ratio.  Tell me about roller setting in drafting in drafting zone.  What is fibre crimp.
  66. 66. Objectives:  To study sliver density.  To study Roller lapping tendency  To study Selection of creel and web tension draft
  67. 67. The number of fibres in the sliver influences the level of the drafting force in two ways, First, in the additive sense, in that more fibre in a cross-section of sliver means more fibres moving relative to one another and more locations of resistance to this motion; hence, a large drafting force required. Second, as a result of bulk compressibility of the sliver, the effect of an increase of fibres obtained by vertically sandwiching input sliver is more than additive. Because the increased sliver thickness means a relatively larger nip constriction and this results in more resistance to drafting caused by more fibre to fibre contact points as well as more frictional restraint at each contact.
  68. 68. The packing density (more compactness) of the sliver entering the drafting zone greatly affects the drafting force, in direct proportion. Since relative fibre sliding is diminished in the compacted spot, this accordingly becomes a thick spot in the output sliver. Common source of fluctuating packing density: - Input sliver in can coiler - Twist inserted by can coiler The drafting force increases rapidly with increase in compactness of the sliver. The total drafting force is given by: FD = { nZ NZ / (nZ + NZ)} FZ
  69. 69. Where, z = a 1 cm section. NZ = the number of fiber in section z gripped by the front roller. nZ + NZ = the total number of fibre in section z. FZ = the force per unit length acting on a single fibre as it is withdrawn from the sliver of the density of section z. Sliver density ρ, is the ratio of volume of fibre to the total volume occupied by the sliver . If fibre to fibre friction is increased as a result of very high top roller pressure, the friction force per fibre increases giving a disproportionately high drafting force. When the roller setting is decreased, the sliver becomes more compact and drafting force increases accordingly.
  70. 70. Roller lapping tendency increases with: - high humidity for cotton, - low humidity for synthetics, - lower fibre crimp, - softer roller cot, - increased fibre length, - higher fibre flexibility, - lower fibre to fibre friction, - higher fibre to roller friction - roughness of top roller covering, Higher crimp level coupled with suitable spin finish formulation and percentage add-on will reduce the lapping tendency. This will result in abnormal increase in fibre to fibre friction, hindering the drafting performance.
  71. 71. For the synthetics and fibres with high crimp level, these draft should kept at lower levels compared to cotton. Synthetic fibres are crimped with the permanent set. Crimped fibre configuration improves the fibre cohesion Higher creel and web draft for the synthetics creates localised drafts at weaker places, partially decrimping the fibres, increasing the built up the internal stresses. With high creel draft for synthetic fibres may try to relieve the stress during drafting resulting in disturbances of neighboring fibres, in this high elastic recovery of the synthetic fibre takes place.
  72. 72. Questions:  What is roller lapping tendency in draw frame.  Tell me factors on which Selection of creel and web tension draft is depend.  What is the impact of sliver density in further processes after drafting.
  73. 73. Objectives:  To study Monitoring and Autolevelling.  To study integrated monitoring system.  To study blending at drawframe.
  74. 74.  Classification  Monitoring devices with self-compensation  Monitoring devices with autolevelling systems - Classification - Evener draw frames with open-loop control - Evener draw frames with closed-loop control - Combined evener draw frames  Correction length  Evening operation  The integrated monitoring system - Structure - Zellweger SLIVERDATA
  75. 75. Monitoring systems can be distinguished according to whether they monitor - The machine - Production or - Quality - Displays, - Self compensation - Autolevelling The first group, devices that detect faults but do not correct them, includes: - TEX-ALARM (Zellweger Uster) - SLIVERDATA (Zellweger Uster) - SLIVER CONTROLLER (Rieter)
  76. 76. It is offered at present only by the Zinser company as MECATROL. The so-called "toothed roller leveller" consists of a toothed roller pair (1) and a fluted/pressure roller pair (2) forming a small drafting device in front of the actual drafting arrangement. A fault in an individual sliver can be reduced to about 40-50%. Fig. MECATROL of Zinser
  77. 77. What is autoleveller? - It is a online monitering device in spinning process. - It has become an integral part of the spinning process for production of high quality yarn. - It helps in achieving consistent count cv%.
  78. 78. Need of autoleveller  To survive in this age of high competition, it has become necessary to produce an internationally accepted standard yarn quality.  Carded slivers fed to drawframe have high degree of uneveness that cannot be tolerated.  Comber contains infamous piecings.  Higher CV% affects the appearance of dyed fabrics by absorbing the dye unevenly.
  79. 79. Object of autoleveller To maintain consistent hank of sliver. Principle: Adjust the Draft continuosly, which will depend on thickness of material fed.
  80. 80. Types of autoleveller Open Loop Closed loop
  81. 81. Types of autoleveller   Open Loop Closed Loop This system is effective for short, medium and to some extent long term variations This system is effective for long term variations Lack of self monitering Self monitering More popularly used Rarely used
  82. 82. Various parts of autoleveller 1. Scanning roller 2. Signal convertor 3. Levelling processor 4. Servo drive 5. Quality monitor sensor 1 4 3 25
  83. 83. Important parameters for quality levelling  Levelling intensity  Levelling action point
  84. 84. Levelling Intensity  It indicates the amount of correction to be done.  It is to decide the amount of draft change required to correct feed variation.  The correlation between mass and volume for different fibres is not same.
  85. 85. Levelling action point  The calculated correction should be done on the corresponding defective place.  The time required for the defective material to reach the correction point should be known.  Levelling action point depends on break draft, main draft roller setting and delivery speed
  86. 86. The total volume of all slivers is measured at the infeed and adjustment is effected with the appropriate time delay in the main drafting field. Detection is usually carried out mechanically (rollers with grooves, bores or steps) or by capacitive sensors. Fig. Evener draw frames with open-loop control
  87. 87. In this system, the evenness of the delivered sliver is measured, not the infeed sliver as is the case with open loop control. Nevertheless, the adjustment is still made in the main drafting field. Mechanical or pneumatic sensing devices are generally used. Fig. Evener draw frames with close-loop control
  88. 88. To avoid the disadvantages of both open- and closed-loop control principles, open-loop and closed-loop devices are combined into an integrated autolevelling system. Capacitative sensing is generally used in the infeed, and mechanical or pneumatic sensing in the delivery. Fig. Evener draw frames with open-loop control
  89. 89. If there is a sudden deviation from the set volume as the material passes through, a corresponding signal is sent to a regulating device that is to correct the fault. Owing to the mass inertia of the system, compensation cannot be effected suddenly, but must be carried out by gradual adaptation. A certain time elapses before the delivered sliver has returned to the set volume. During this time, faulty sliver is still produced, although the deviation is being steadily reduced. The total length that departs from the set value is referred to as the correction length (I). Fig. Correction Length
  90. 90. In closed-loop systems, the correction length is additionally increased by the dead-time. In that case, it depends upon the dead time (II) and the correction time (III). The correction length depends upon the system and the speed of operation, and therefore varies considerably. Fig. Correction Length for close loop system
  91. 91. Evening is performed exclusively by adjustment of the draft. 'Theoretically, there are two possibilities for such adjustment, namely via the break draft and the main draft respectively. However, the main draft is always used because it is larger, and therefore finer adjustments are possible. Also, use of the break draft would run the risk of entering the stick/slip zone. Draft variation can also be carried out by adjusting the infeed or delivery speed. Adjustment of the infeed speed is generally used, since then lower masses have to be accelerated and decelerated at lower speeds. Additionally, the delivery speed, and hence the production rate remains constant.
  92. 92. It is nothing but the process control technique in the draw-frame. Structure : Integrated systems, comprehending the complete process, are finding steadily increasing application. The Zellweger MILL DATA - System is an example. The complete installation (see Fig.) comprises: - Decentralized process data systems for the individual departments - SLIVERDATA (spinning preparation); - RINGDATA; - CONEDATA; - ROTORDATA; - LABDATA; and - The central comprehensive MILL DATA system to which the decentralized process data systems are subordinated.
  93. 93. Zellweger SLIVERDATA: This data system continually monitors: - the productivity of all spinning preparation machines connected into the system and - the quality at the drawframe (and possibly at, the comber and main cards). The results are available on call. Production monitoring covers: - the delivered quantity; - the frequency and length of interruptions, classified according to type; and - Efficiency. Quality monitoring relates to: - hank constancy; - coefficient of variation (over short lengths); and - possible periodicities of unevenness (Spectrogram). If settable tolerance levels are exceeded, alarm lamps light up and the corresponding machine is stopped.
  94. 94. What is blending and Doubling? Blending is the combining of different fibres together intimately to achieve a desired product characteristic. Doubling is the combination of several slivers that are then attenuated by a draft equal in number to the slivers combined, thereby resulting in one sliver of a similar count. Why for Blending ??? Raw materials used in the spinning mill are always inhomogeneous in their characteristics. In part, this is inevitable owing to the different cultivation conditions of natural fibers and the different production conditions for manmade fibers. Partly, it is deliberate in order to influence the end product and the process.
  95. 95. Blending is performed mainly in order to: - give the required characteristics to the end product (e.g. blending of man-made fibers with natural fibers produces the desired easy-care characteristics); - compensate for variations in the characteristics of the raw materials (even cotton of a single origin exhibits variability and must be blended); - hold down raw material costs (blending-in of raw material at low price level); - influence favorably the behavior of the material during processing (improve the running characteristics of short staple material by admixture of carrier fibers); and - achieve effects by varying color, fiber characteristics and so on.
  96. 96. Every doubling gives simultaneous blending -including the 6-8 doublings at the drawframe. This blending intensity is adequate for processing cotton. However, if cotton and synthetics are to be processed together, operation of the normal drawframe will no longer be optimal. This machine (see Fig.) has four preliminary drafting arrangements and one downstream drafting arrangement. Each preliminary drafting arrangement processes a separate set of six slivers. The webs produced in this way are brought together on a table and fed to the downstream drafting arrangement. The sliver issuing from this point is coiled in cans. Fig. 21 – Principle of the blending draw-frame
  97. 97. Three passages are almost always needed with normal draw frames. (blending draw frame and two subsequent draw frames), two passages suffice when a blending draw frame is used (one normal draw frame followed by one blending draw frame). In addition to this advantage, and the improved intermixing, a further favorable aspect should be mentioned, namely that-each raw material component can be processed in a drafting arrangement of its own. The disadvantages are: - five drafting arrangements being combined in one machine - complexity - cost when 100% cotton is to be processed (when blended yarns are not required). - difficult to attain random arrangement of fibres in the yarn cross section. - Additional drawing capacity needed. - Separate opening lines needed for each component.
  98. 98. Advantage - Easier to obtain uniform blend ratio. - During opening and carding, optimum settings for each blend component can be used for better quality of output with less damage of the fibres. - Easy working. Technical Data Delivery speeds, meters per minute: up to 800 Production per delivery, kg per hour: up to 300 Deliveries per machine: 1 or 2 Doublings : 4 to 8 Maximum feed weight kg : 55 Delivery hank, ktex: 3 to 7 Waste, in %: 0.5 to 1
  99. 99. 1. Discuss in detail the passage of material through draw-frame machine. 2. Explain in detail objective of draw frame. 3. Discuss in detail behavior of the fibers in the drafting zone. 4. Discuss in detail friction fields and fiber friction in drafting. 5. What is draft? Discuss in detail distribution of draft in drafting zone. 6. Explain in detail coiling delivery and condensing. 7. Discuss in detail perfect and real drafting. 8. Explain in detail nature of drafting irregularities.
  100. 100. 1. Discuss in detail drafting force in relation with draft ratio and roller setting. 2. Discuss in detail drafting force in relation with fiber crimp and sliver density. 3. Explain in detail coiling delivery and condensing. 4. Explain in detail roller lapping tendency, selection of creel and web tension draft. 5. Explain importance of blending in drawframe. 6. Discuss advantages and disadvantages of draw frame blending. 7. Discuss nature and role of fibre friction in drafting on draw frame m/c. 8. Elaborate on lapping tendency of : a) Top roller b) Bottom roller. 9. Discuss about the significance of autolevelling in draw frame m/c.