Rotor spinning

task of rotor spinning, concept of open end spinning, operational sequence on rotor machine, twist in yarn, wrapping fibres, fibre integration, rotor

1. ROTOR SPINNING

2. Tasks of the Rotor Spinning Machine:  The basic tasks of the rotor spinning machine are Opening (& attenuating) almost to individual fibers (fiber separation).  Cleaning.  Homogenizing through back doubling.  Combining i.e. forming a coherent linear strand from individual fibers.  Ordering (the fibers in the strand must have an orientation as far as possible in the longitudinal direction).  Improving evenness through back-doubling.  Imparting strength by twisting  Winding.

3. Historical perspectives of rotor spinning 1937-The first idea and basic rotor patented by Berthelsen (Denmark). 1951-Meimberg (Germany) developed the invention further and built the first spinning models. 1965-Rohlena and his group (Czechoslovakia) found the correct combination of spinning elements and showed the first commercially functional units in Brunn.KS200 rotor spinning machine was introduced at 30000 rotor rpm. 1967 -The Czech firm ELITEX exhibited its rotor spinning machine (BD200) near the international textile machinery exhibition (ITMA) in Basel, Switzerland. The machine had a rotor diameter of 75 mm, a rotating speed of 25,000 rpm, and a high twist multiplier (TM=6, or a twist factor of about 5740 tpm . 1967 Improved BD200 Rieter were presented with first mill of OE coming under Production. Many textile machinery companies, such as Platt of UK, Rieter of Switzerland, Zinser,Ingolstadt, Suessen, Schlafhorst of Germany, Woogay of Belgium, Barber- colman of the USA, and so on, started to develop the new rotor spinning machines with "air-exhausting Rotor unit.

4. 1970 Rieter, Schubert&Salzer and Platt formed a consortium to develop the rotor spinning Process and this resulted in the appearance at the 1971 ITMA of a number of prototypes at various stages of development. invention of the twin disk rotor drives allowing higher rotor speed (Suessen). With smaller rotors (60 mm), the rotor speed increased to 35,000 rpm. 1971–1975 There was a considerable increase in machine manufacturer and newer and improved version of machines was launched with increased speed of 100000 rpm. 1975 -Witnessed Schlafhorst with Autocoro machines, which made a mark in open-end market. 1978-Introduction of 40-50 mm diameter rotors, improved spinbox geometries, lower yarn twist possible, first automatic yarn piecer and package doffer fitted on the rotor spinner. 1989-Smaller rotors with speeds of 100,000 rpm. 1992-Quality yarns as fine as 13-15 Tex produced commercially at rotor speeds up to 120,000 rpm.

5. 1999-Rotor speeds up to 150,000 rpm possible. 2005 - Rotor speeds of up to 170 000 rpm are technically possible without any difficulty. Many models appeared one after another. They are, Rieter : BD-200M,BD-200R, BD-200RC(RCE,RN),BD-200S(SCE,SN) and BD-SD, BDA10 (N), D-D1, BD-D2, BDA20,BD-D30. New models R20,R40, R60, R65,and R75. Cangnan Jinchan Cotton Co.,LTD, has produced rotor spinning machines:RU11,14,RU03, 04, M1/1, 2/1 and R1  

6. Schlafhorst Autocoro 192, 216,240, 288, 312, 360 and 400. Schlafhorst and Rieter have occupied the largest share of world market.Besides , other rotor spinning machines such as, SAVIO FRS of Italy, Zinser 342 and SKF of Germany, Platt T883 and 887M of the UK and SACM-3000 of France. China F1603, F1604, F1605 of Jingwei Textile Machinery Co. FA1603 and FA608 of Chuanjiang Machinery Co. in Sichuan province. 

7. Concept of O.E. Spinning Continuous supply of fibrous feed material Opening fibrous strand to individual fiber state Restoring continuity by depositing individualized fibers to the rotating yarn

8. Open End Spinning/ Break Spinning/ Free Fiber Spinning: 1. Fibrous material is highly drafted to separate out individual fibers. They are then carried forward as free fibers (allowing them to relax under considerable reduced drafting force before twisting) by an air stream for spinning: Free fiber spinning. 2. Individual fibers are subsequently collected on to the open end of the already been formed (seed) yarn. This is rotated to twist the fibers into the yarn structure to form a continuous strand of yarn.: Open end Spinning 3. The fiber supply is interrupted during twisting action : Break Spinning.

9. In conventional spinning ,the fibre supply is reduced to the required mass per unit length by drafting & then consolidated into a yarn by the application of twist . The fibre supply is reduced, to individual fibres, which are then carried forward on an air-stream as free fibres. This permits internal stresses to be relaxed & gives rise to the term “free fibre spinning”. These fibres are then progressively attached to the tail or “open end” of already formed rotating yarn. This enables twist to be imparted by rotation of the yarn end. Thus the continuously formed yarn has only to be withdrawn & taken up on a cross-wound package. Open End  Spinning

10. Three major Commercialized Open end Spinning methods: Rotor Spinning Friction Spinning and Vortex Spinning (not commercialized)

11. Object: Overcome Limitations of Ring Spinning Poor Economy Low production rate Low spindle speed Low Efficiency Smaller cop size Reduced yarn content Increased doffing frequency More number of heads Longer production route Low drafting capacity Higher Pre spinning & Post spinning Operations Smaller size delivery package Due to common twisting & Winding media Increased doffing & creeling Mandatory Post spinning Operation Use of Heavy weight spindle Higher power consumption, storage, maintenance etc.

12. FEEDING OPENING CONDENSING TWISTING WINDING

13. Tangential fiber feed into the rotor and fiber transport to the fiber collecting groove of the rotor

14. Feed stock : Card sliver or drawn sliver (first or second passage). Condenser/ feed trumpet : Opening of the condenser can be set to suit the hank of sliver and avoid processing of double sliver. Feed roller: Grips the sliver & pushes it over the spring loaded feed plate into the region of the opening roller. In the event of an end-break, the feed unit is stopped either by stopping the feed roller rotation or by pivoting in feed trumpet, in each case sliver feed stops automatically. The signal pulse causing this effect is generated by a yarn-sensing arm.  1. Sliver Feeding: Feed roll: Steel roller with helical flutes

15. 2. Fiber Separation & Transportation Roller drafting is replaced by Roller opening . It opens fiber tufts to individual fibers. Opening roller is clothed with needles or saw teeth , combs through the fiber beard projecting from the nip between the feed roller & the feed plate. Trash is separated by cleaning system and opened fibers are transported further for spinning.

16. Opening Roller: Saw tooth clothing Roller Base

17. Fiber transport from opening roller to rotor : The suction stream in the feed tube (transport channel) lifts the fibers off the surface of the opening roller & leads them to the rotor. In the course of transport movement, both the air & the fibers are accelerated because of the convergent form of the feed tubes. This gives a second draft following the feed nip trough/ opening roller & giving further separation of the fibers. Moreover partial straightening of the fibers is achieved in this air flow. Individualized Fiber Transport Air flow is generated by central fan that draws air by suction through leads from each rotor box which is airtight sealed.

18. A negative pressure created within the rotor either by external vacuum or by air exhausted through pumping holes situated in the centre of the rotor; induces the air flow through feed and delivery tubes. pumping holes

19. The detached fibers from the opening roller pass into the rotor groove at much higher speed to attain fiber alignment by avoiding fiber crumpling, disorientation or clumping together. Adequate air stream is used to carry forward individualized fibers in straight and to prevent twist from running back to drafting system. Unit fiber flux require the draft value at combing roller equals to number of fiber in the cross section of sliver; nearly equals to ten thousand. In practical term fiber flux is always more than unity but should not be too high. 4. Fiber collection / allignment Fiber collection in the rotor groove : The centrifugal forces in the rapidly rotating rotor cause the fibers to move from the conical rotor wall toward the rotor groove and be collected there to form a fiber ring.

20. A third draft arises upon arrival of the fibers on the wall of the rotor because the peripheral speed of the rotor is several times as the speed of the fiber in transport tube. The last straightening of the fibers occurs as the fiber slides down the rotor wall into the groove under the influence of the enormous centrifugal forces work within the rotor. This draft contributes significantly to good orientation of the fibers. 4. Fiber collection / allignment

21. Fibers entering rotor groove from transport duct are having 80% speed of this rotating body, gives fourth draft normally of the order of 1.25 and 1.4 . Sufficient to lay fibers in straight configuration in the rotor groove. This can integrate fiber with yarn structure in straight configuration results in maximum utilization of fiber strength. Fibers entering the rotor are deposited on the internal sliding wall) and move on this surface to rotor groove in parallel and straight fashion to form fiber ring. The sliding wall is the part of the transit system; surfaces must be well designed and should be kept clean. The sliding movement of the fibers gives cleaning of this surface

22. Real twist is applied to the yarn by the motion of the rotor acting on the yarn arm that passes from the rotor groove to the yarn withdrawal point inside the rotor. One rotation of rotor inserts one turn of twist into the yarn length (in inches) withdrawn from working region in that time interval.   Fibers are not firmly gripped at the peeling off point in rotor by any discrete nip. Thereby twist usually runs back to rotor groove and some fibers are laid onto an already twisted core of fibers. This affects yarn structure 5. Yarn formation / Twist insertion

23. Yarn arm speed = Rotor speed; until take up is not started. Parallel rotation generates turns of twist Distributed between navel & take up roller; also slip past to yarn arm in absence of firm grip at navel; helps in piecing. Yarn arm speed = Rotor speed + take up speed; Difference causes peeling of fiber ring.

24. Gives pathway for yarn withdrawal from the rotor. It deflects seed yarn path by 90 o . Separator plate is introduced sometime to prevent premature capture of the incoming fibers by the outgoing yarn. The yarn emerging the navel rolls on the inside surface. This rolling action inserts a false twist in the section of the yarn inside the rotor. This false twist is in addition to real twist created by rotation of the rotor. Navel

25. A = Centrifugal force acting on yarn B = Yarn withdrawal force. Due to these two opposing forces acting on seed yarn it is pressed against the rim of the navel. Rotor rotates in clockwise direction. Yarn arm rotates in clockwise direction just like epicycle gearing. Yarn arm speed is always higher than rotor as it is an outcome of rotor speed & yarn pull. The yarn arm is rotated around the inner wall of navel through the rotation of the rotor, the frictional force ( R) is exerted on the yarn. Frictional force (R ) creates a torque in the yarn pressing it against the navel and thereby creates false twist.

26. Yarn is withdrawn through doff tube towards take up shaft. Angle of withdrawal ∞ Spinning Tension between doff tube and take up roll. Angle of withdrawal: 30, 60 & 90. Winding: Traversing + Grooved drum + Waxing device. Product: Cone or Cheese. Take up tension = 10 to 20% of spinning tension. Yarn formation : When a spun yarn end emerges from the draw-off nozzle into the rotor groove, it receives twist from the rotation of the rotor outside the nozzle, which then continues in the yarn into the interior of the rotor. The yarn end rotates around its axis and continuously twists-in the fibers deposited in the rotor groove, assisted by the nozzle, which acts as a twist retaining element.

27. 6.

28. Yarn take-off , winding: The yarn formed in the rotor is continuously taken off by the delivery shaft and the pressure roller through the nozzle and the draw-off tube and wound onto a cross-wound package. Between takeoff and package, several sensors control yarn movement as well as the quality of the yarn and initiate yarn clearing if any pre- selected values are exceeded.

29. Principle of Rotor Spinning: Input : Drawn sliver is drawn through condenser and fed to the drafting system by a feed roller operating in connection with feed pedal. Drafting & Fiber Transport: A sliver with 20,000 or more fibers in its cross-section use for the production of a yarn with 100 fibers per cross-section; will require a minimum total draft of 200. This amount of draft is substantially higher than that of ring spinning. This is accomplished by using a comber roll (pin/ saw tooth) which opens the input sliver to almost individual state and also releases trash entrapped. Separated trash is collected in central chamber from where it is periodically removed. Transport tube sucks fibers from the opening roller and transfers on to the inner grooved periphery of rotor by an accelerating air stream (gives air draft). These two operations produce an amount of draft that is high enough to reduce the 20,000 fibers entering the comber roll down to few fibers (5-10 fibers).

30. Advantages offered by Rotor Spinning: Lower power consumption per unit quantity of yarn produced. Higher speed of twist insertion resulting in very high yarn delivery speed A significant increase in productivity Larger delivery package size Elimination of pre spinning processes like speed frame and post spinning like winding More uniform quality of yarn due to higher doubling.

31. Twist in Yarn Twist / metre =rpm of Rotor/ withdrawl speed {l}. The spun yarn is withdrawn through a passage in the navel “ T” which rolls continually on naval. The partial rolling of the yarn gives rise to false twist between the twisting-in point {G} for the fibres & the navel {T}. Twist level between “G to B” is 20-40% higher than those at navel.  Yarn tension is generated by the withdrawl rolls during withdrawl in opposition to the centrifugal force in the rotor. Tension is highest at the withdrawl rolls themselves & declines towards rotor wall. The yarn tension & twist level are inversely proportional .

32. Formation OF The Yarn The yarn end is pressed against the rotor wall by the high centrifugal force, & the separation point therefore rotates within the rotor .  Each revolution of the yarn at this point inserts one turn of twist. The yarn twist penetrates into the fibre ring in the collecting groove, where the fibres are to be bound together to form a yarn. The length of this binding in zone is of some significance for the spinning conditions & the the yarn characteristics. Too short length - high ends-down rate too long length - twisting-in will be very tight , & there will be many wrapping fibres

33. Wrapping Fibres Normally , incoming fibres that have not yet been twisted in, but, in the binding -in zone , they strike an already-twisted yarn section rotating around its own axis. Fibres arriving here can not be bound into the strand: They wrap themselves around the yarn core in the form of of a band , called wrapping fibres . The number of wrapping fibres is dependent upon :- The position at which the fibres land on the rotor wall. The length of binding-in zone. The ratio of the fibre length to the rotor circumference. The false twist  level. The rotor rpm   Fibre fineness.

34. Fibers have some freedom of movement during twist insertion, the outer fibers tends to slip more than the core fibers. O.E. Yarn structure is thereby made up of three parts: Densely packed core consisting of about 80% of fibers substantially aligned with the yarn axis. Loosely packed fibers twisted around the core at an angle to the axis; and Wrapper fibers on the outside

35. Structure of Rotor Spun Yarn Wrapper fibers Loosely packed fibers Densely packed core The core contains densely-packed fibers similar to ring-spun yarns. Sheath fibers are loosely packed round the yarn core at a low angle to the yarn axis. The wrapper or belt fibers are wrapped around the outside of the yarn at a very large inclination to the yarn axis. Fiber migration in rotor yarn is relatively local: fibers in each layer are only tied to the fibers of adjacent layers.

36. Wrapper fibers : Improves yarn abrasion resistance but Reduces wicking properties of yarn.

37. Figure shows the surface structure of typical rotor yarn. The core contains densely-packed fibers similar to ring-spun yarns. Sheath fibres are loosely packed round the yarn core at a low angle to the yarn axis. The wrapper or belt fibres are wrapped around the outside of the yarn at a very large inclination to the yarn axis. It has been reported that fibre migration in rotor yarn is relatively local: fibers in each layer are only tied to the fibers of adjacent layers. Rotor spinning generates lots of hooks and looped fibers even if a well parallelized sliver or roving is fed into the rotor. The typical distribution of fibers shapes in rotor-spun yarn the yarn is: 39% folded or buckled fibres in the core, 31% straight fibres in the core, 15% leading hooks and 15% trailing hooks in the outer layers. Given its structure, fibers in rotor yarn are less packed than ring yarn. Rotor yarns are known to be 5-10% bulkier than ring yarn. Across the cross-section, the packing is not uniform. The packing is maximum at a point approximately one third to one quarter of yarn radius from the central axis. This has been attributed to greater buckling if fibres in the core. As a result, packing of rotor yarn is concentrated nearer the yarn axis and less towards the outer surface of the yarn in comparison to ring yarn.

38. Rotor spun yarn is less strong than comparable ring spun yarn. This is because of the straight, parallel arrangements of fibers and denser packing of fibers in ring spun yarn which contrast with the higher numbers of disoriented folded fibers in rotor spun yarn, lower levels of fibre migration, less packing and the presence of non-load bearing wrappers and belt fibres . Rotor spun yarns are generally more extensible than ring spun yarns. The higher breaking extension of rotor yarn is due to presence of a lot of hooked, looped and disoriented fibers in the structure. However, the dense, more tangled structure of fibres in the core offers very little freedom of movement of fibres in rotor yarns. Rotor yarns are therefore less flexible than ring yarns which have a more uniform helical arrangement of fibres . Due to its unique structure, rotor yarn shows higher abrasion resistance than ring spun yarn. The loosely-wrapped sheath fibers can easily yield to an abrasive surface, and, given its greater bulk, the yarn can flatten, giving further abrasion resistance. Rotor yarns also have fewer irregularities and imperfections compared to carded ring-spun yarns. This has been attributed to the mechanism of yarn formation, i.e. back doubling in the rotor groove before twist insertion which irons out irregularities.

39. Fiber Integration During Rotor Spinning

40. Various Types OF Binding Fibres Class 1 fibre :- The yarn tail picks up the trailing end of a fibre which lies wholly on the surface of the rotor. The fibre is integrated into the yarn & tends to take a helical form, which will be distorted by migration. The original fibre direction is reversed. This fibre is called as class1 fibre. Class 2 fibre :- The fibre is just emerging from the transparent tube as the yarn tail sweeps past. The leading end of the fibre is picked up & moves towards the centre ; the trailing end is flung onto the surface of the rotor ;The fibre becomes a “bridging fibres”. I.E., Fibres that bridge the gap that should theoretically occur behind the pick-up point, p. The fibre is integrated in the yarn & tends to take a helical form as in class 1, but there is no change in fibre direction. This fibre is called as class 2 fibre. Class 3 fibre : A fibre that has partly emerged when the yarn tail arrives : the leading part is on the surface of the rotor ; the trailing part is tube. The fibre is picked up at some point along its length. The leading end is integrated in the reverse direction . the trailing end is integrated in the forward direction. A leading hook is created. This fibre  is called as class 3 fibre.

41. Fibre configuration

42. Class I fiber Yarn arm picks up the trailing end of the fiber that is straight & lies fully on the surface of the rotor before the yarn arm sweep past Attain helical configuration on twisting. Goes to the core under nominal tension Original fiber direction gets reversed

43. Class II fiber Yarn arm picks up the leading end of the fiber that is just emerged out of the transport tube as the yarn arm sweep past Attain helical configuration on twisting. Original fiber direction does not get reversed. Fiber acts as bridging fiber Since fiber tension is not build up initially twisted loosely on surface and then on gradual development of tension makes it to be get shifted to core.

44. Class III fiber Yarn arm picks up the fiber that is partially emerged out of the transport tube as the yarn arm sweep past Front end behaves like class I attain helical configuration on twisting and original fiber direction gets reversed. Part next to pick up point acts as bridging fiber; class II Creates leading hook

45. The probability (P) of fiber’s falling into class III depends on Fiber length/ fiber extent (E) & Circumference of the rotor (∏D). As P (%) = (100E) / (∏D) Shorter fibers are less likely to fall in class III. & Fewer class III fibers are to be expected with large diameter (D) rotor.

46. If ∏D < E; yarn arm would pass through the fiber entry zone at least twice during the period that the fiber was being peeled off; this will surely brings ends down. Higher production rate demands working with smaller Rotor diameter (D); Restricts processability of long fine fibers. Or else results in higher number of wrapper fibers with higher number of wrappings. – Poor yarn quality With condition ∏D > E; spins short fibers efficiently; thereby spinning of finer yarn count not becomes possible. – Limited for Coarser & Medium count Spinning

47. Rotor Yarn structure depends on the mode of integration of Class I-III fibers. Class I fibers : firmly embedded with rotor groove at the point of pick up & integrated into yarn under due tension; goes to core.

48. Class II fibers: Starts to be integrated while still lies mainly inside the transport tube or before coming under the influence of rotor or its centrifugal force. Tension within the fiber is low & thereby starts as loosely wound surface fiber. Its trailing end is withdrawn progressively from the tube, it makes increasing contact with rotor surface, and the tension in the fiber builds up, such that the tail end of the fibers tends to work its way into the core of the yarn.

49. Class III fibers: Picked up at some point along its length, leading part being pressed onto the rotor surface by centrifugal force & trailing part is still in the tube. Forms leading hook Original leading end being under tension enters the core of the yarn. Original trailing end starts on the surface but works its way into the core as in the case of class II fiber.

50. Open end spun yarns are basically of a three part construction due to presence of class I –III fibers and their difference in behaviour at the point of integration. Core: It is made up of substantially twisted straight fibers Sheath: Loosely wound fibers with low twist angle Tightly wound belts. Fibers can fall into more than one category.

51. Machine & Process Variables of Rotor Spinning

52. Machine Variables Feed Unit Opening Roller Transport Duct Rotor Navel

53. a = opening roller, b = feed plate, c = feed roll, d = Fixed beard support, e = Trash ejection, f =adjustable bypass Additional grip from Fixed beard support (d) used at High speed Rotor unit. Controls variations in thickness of sliver. 1. Feed Unit : Feed Plate (b) + Feed Roller (c)

54. Feed Roller   A fluted feed roller –Diagonal flutes To increase the clamping effect The distance must be decreased for finer feed sliver or smoother fibres or both. The opening roller rotates between 5000 & 10000 rpm, usually between 6500 & 8000rpm. Higher speed –Coarser Yarn , Slower speed – finer yarn Drafts of up to 2000. Diameter - 60 & 80mm

55. Performance of opening roller is decided by a) Type of teeth. b) Teeth specifications ( Rack angle, Pitch/density, Height). c) Surface speed of opening roller. d) Condition of teeth. 2. Opening Roller

56. A) Types of teeth : a) Pin type and b) Saw tooth type. Pin type Saw tooth higher wear resistance, longer life higher wear resistance, longer life It results in fewer fibre breakages especially at high opening roll speed It results in higher fibre breakages Fibre removal from opening roller to transport tube is difficult. Ease of fiber transfer irrespective of opening roller speed. More difficult to manufacture Easy to manufacture Does not offer the wide range in tooth specifications. Wide range of tooth specification

57. B) Tooth Height (h) ∞ Intensity of combing action ∞ B etter individualisation and trash removal Higher “h” should be preferred for coarse trashy cottons. Lower height should be used gentler action but fibre individualisation will be inferior. h d

58. Rake angle (a) Rake angle is the angle made by front edge of teeth with horizontal. Action of opening roller will increase as rake angle reduces and at the same time fibre breakages will increase. Clothing rake angle 66 to 80° for cotton and 90° and above for synthetics. Coarse cottons with higher trash, opening roller with lower rake angle is preferred. Finer cottons higher rake angle Man-made fibres, 90° or negative rake should be used. a b h d

59. Tooth Pitch/ Point Density (b) Higher pitch, reduces density and drops intensity of combing action. Lower pitch increases PPSI and ensures better individualisation as well as trash removal. It should be preferred for coarse trashy cottons and higher opening roll speed. Lower pitch should be used for higher opening roller speed to reduce opening roller load without affecting fibre individualisation.

60. Decoding of tooth 1. Application Field B – Preferred field of application for cotton S - Preferred field of application for Cotton & Man made fibers 2. Tooth shape The number after the letter is representing tooth shape code number 3. Material DN – Diamond coated & Nickel plated D – Diamond coated No symbol used – Nickel plated

61. Standard tooth type used for opening roller.

62. Opening roller used mainly for cotton

63. Universal Opening roller Wide application range but primarily used for manmade fibers and their blends with cotton

64. Higher opening roller speed results in; Better sliver opening. Better trash extraction. Fewer imperfections like thick and thin places in the yarn. Higher Production rate But also More dust formation. More fiber damage. Reduce the yarn strength. C) Opening roller Speed

65. The opening roller speed should be increased when there is inadequate trash extraction. The opening roller speed should be decreased when too many good fibers are removed with high proportion of short fibers. The speed of the opening roller depends on the fiber material and opening roller type. The service life of the opening roller can be improved by the shape of tooth and tooth coating.

66. Excessively high opening roller speeds result in: More or less severe damage to – i.e. Shortening of – fibers, and thus Losses in yarn tenacity and the strength of the fabrics produced from them, An increase in fiber fly on the spinning machine and in downstream processing, melting points when processing man-made fibers.

67. Opening roll Speed Optimum speed depends upon fibre and its properties. Optimum roller speed is around 8000 to 9000 rpm for coarse and trashy cottons, 7000 to 8500 for long staple cottons and 6000 - 7000 for man-made fibres.

68. Trash-removal devices The high peripheral speed of the opening roller causes the coarser trash particles to be hurled outwards at this position [a] while the fibres continue with the roller & pass into the feed tube [b]. · The trash removal depends upon : The design of the assembly. The air-flow conditions. The degree of opening of the feedstock. The speed of rotation of the opening roller.

69. BY pass open (maximum trash removal) BY pass half open (medium trash removal) BY pass closed (minimum trash removal) Setting for Trash Removal

70. Combing out will be more intensive & even if: The thinner the fibre strand {sliver fineness}, The more parallel the fibres arrangement The more highly straightened the fibres, The smoother the fibres [lustrous or delustred] , The shorter the clamping distance The optimum rotational speed of the roller high roller speed will damage the fibres while lower roller speed would deteriorates yarn quality

71. Transport tube: After opening the fibers must be supplied to the rotor. Transport tube; a closed fiber channel in the shape of a flow passage serves as a means of guidance. Centrifugal forces of the opening roller and a vacuum in the rotor housing cause the fibers to disengage from the opening roller. Transport of the disengaged fibers through the fiber channel to the rotor is effected by an air current generated by suction of air from the hermetically sealed rotor housing. 3. Transport Tube

72. Velocity profile of air in the opening roller to transport tube junction Velocity of the air in the opening roller near transport tube increases in the radial direction from the opening roller towards wall of transport tube and as a result, pressure reduction occurs in the radial direction away from opening roller teeth. This helps in removing the fibres from the teeth to the high velocity air stream rushing into transport tube as fibre reaches the junction of the two.

73. In order to achieve satisfactory doffing and transportation, velocity of air must be 1.5 - 2 times circumferential velocity of opening roller . too high or too low ratio of circumferential velocity of opening roller to airflow velocity is not conducive to good quality of yarn due to recirculation of air at outer cover side or opening roller side.

74. SPEEDpass : This is an additional opening in the fiber guide channel through which a certain proportion of the fiber transport air is extracted in order to increase the air volume and thus the rate of flow in the fiber guide channel. Promotes the disengagement of fibers from the opening roller clothing and suitable for processing man-made fibers and blends containing more than 50% man-made fibers. Higher volume of air proves beneficial in the manufacture of coarse count yarns or for high material throughput. Cotton dust (finishing abrasion in the case of man-made fibers) is also extracted through this opening. Fine dust therefore does not accumulate in the rotor groove, and yarn characteristics and yarn values remain stable.

75. Fiber guide channel (a) with SPEEDpass (b)

76. There is one with SPEEDpass available for spinning man-made fibers and coarse cotton yarns. The SPEEDpass permits more air to be pulled through the fi ber channel. This enhances the fiber separation at the opening rollers and the stretched transport of the fibers into the rotor. Residue is removed from the material flow over the SPEEDpass . As a result, the rotor grooves, which impact the yarn quality decisively, remain clean. Highest performance for productivity and yarn quality

77. Important terms: Spinning Stability: Spinning desired yarn quality without causing end break or by imparting due control on interference factors (trash particles, foreign fibers, fiber accumulation etc.) which can result in a yarn break. If more disruptive effects are endured with yarn breakages than spinning stability is said to be poor. Minimum Spinning twist ( α min ) : It represents minimum degree of yarn twist required after piecing at a given constant delivery speed to continue with spinning without deteriorating yarn quality and causing end break or other way round the level of twist up to which spinning is possible or stable. False twist: Temporary twist which is generated during the course of spinning and counter balance by equivalent opposite direction twist on leaving the spinning zone.

78. Thus material and surface characteristics of rotor are prime important for defining false twist insertion and thereby rotor yarn quality.

79. Phenomenon of False twist at Rotor: At take-off the yarn continuously rolls off on the surface of the draw-off nozzle due to the rotation of the rotor. This rolling-off temporarily inserts additional twist into the yarn (contrary to the direction of twist of the yarn), thus creating the false-twist effect required for spinning stability, which can be up to 60% of the set yarn twist. The greater the false-twist effect, the higher the spinning tension. While rolling off on the surface of the nozzle, the yarn is repeatedly raised briefly in rapid succession, depending on the surface structure. This high-frequency vibration – together with the false-twist effect – promotes twist propagation into the rotor groove. The more pronounced the structure of the nozzle surface, the more vigorously the yarn vibrates, thus supporting twist propagation and the false twist effect extending into the rotor all the more.

80. Yarn twist in rotor spinning is normally produced outside the rotor between draw off nozzle (A) and subsequent yarn deflection or Nip point (U). But it continues from there against the yarn take up direction into the yarn arm within the rotor up to yarn peel off point (P) and beyond that another few millimeters into the mini sliver (fiber ring) in the rotor groove. This twisted length present in the rotor groove is defined as Length of Twist-in Zone L E . It is also known as Peripheral Twist Extent (PTE).  

81. Twist-in zone length l E Yarn twist should be diffused up to peel off point and a few millimeters beyond into the rotor groove (PTE zone) for reliable and continuous spinning. Higher the twist penetrates into the rotor groove, the more reliably the fibers deposited get spun in without small interruptions being able to cause end break. The PTE length is approx. 2 – 12 mm.

82. 4. Rotor

83. The rotor is the main spinning element of the rotor spinning machine. Yarn qualities, operating performance, productivity, etc., all depend chiefly on the rotor. The most important parameters of the rotor that exert influence are the inclination of the rotor wall (a); the coefficient of friction between the fibers and the surface conditions of the rotor wall (b); the design and the positioning of the rotor groove (c); rotor groove diameter (d) and rotor speed.

84. Direct rotor bearing, with rotor shaft (a) encased in ball bearing housing (b) Support-disc bearing ( Twindisc bearing) with rotor fitted

85. Support-disc bearing ( Twindisc bearing) with pressure roller (b) for tangential belt (a) Axial rotor bearing with magnetic bearing – Positioning the magnetic bearing

86. Axial rotor bearing with EC bearing Sealed grease cup of the EC bearing Axial rotor bearing with AERO bearing Airflow with the AERO bearing; air pressure 6 bar

87. The rotor, consists of rotor shaft (a) with wear protection in some cases, Rotor cup (b) with rotor groove (C) and rotor wall (d). The wall inclination is necessary so that fibers emerging from the feed tube and passing to the wall can slide downward. Depending upon the material and area of use, the angle of the rotor wall to the vertical ranges between 12° and 50° This angle is dependent upon the make but will in all cases be smaller, the higher the rotation speed for which the rotor is designed. At the internal periphery in the lower region of the rotor cup, There is usually a groove that varies in width. This groove serves to collect fibers.

88. Rotors are made of steel and are in general surface-treated or coated to give them a longer useful life. The following means, which are customary and proven in mill practice, are available for protecting rotors against wear: diamond/nickel coating; The diamond coating usually consists of diamond dust embedded in a nickel layer and is the same as that used for protecting the opening rollers against wear. boron treatment; or a combination of both processes. Boronized rotors and boronized rotors with an additional layer of diamond coating have twice the lifetime of a diamond-coated rotor. However, the surface structure of the rotor wall changes depending on the type of treatment (boron or diamond coating), and thus also its influence – which should not be underestimated – on both yarn quality and spinning stability and the tendency for deposits to form in the rotor groove.

89. The best possible compromise between long service life of the rotor, good yarn values and stable spinning conditions is achieved with the combined boron/diamond coating. The rotor is a part subject to wear and must therefore be replaced periodically. Wear mainly affects the groove. The configuration of the rotor groove determines whether the yarn is bulky or compact, hairy or lean, and whether the yarn quality is excellent or only adequate and the spinning stability low or high. The groove also affects the extent to which dust and dirt tend to accumulate in the rotor. Depending upon the raw material used, the desired yarn characteristics and yarn values, different groove designs are used in practice.

90. Wide grooves produce a soft, bulky yarn with rather low Strength. used in the production of yarns for knitted fabrics, homespun-type fabrics and coarse articles. While narrow groove produce a compact, strong yarn with low hairiness. used for yarns required for the production of stronger fabrics with a smooth appearance. A fairly narrow groove is in most wide-spread use in classical short staple mills. The tendency to form more effects is also greater with the narrower groove, because fairly large dirt particles can jam in the groove. A speed range in which the rotors produce optimum results, in terms of technology, spinning stability and energy consumption.

91. Following parameters have effect on spinning:- Rotor diameter Rotor speed Rotor groove shape The quality of rotor spun yarn is influenced by the rotor specifications and speeds. When the rotor speed is too high, the tension during spinning increases and progress of twist in rotor groove is impaired. Soil particles easily gets embedded in rotor groove due to high centrifugal force, causing yarn breakage. Where as low rotor speed results in reduction in yarn tension, which adversely affect the false twist function on the delivery nozzle, further results in end breakage. Rotor

93. The probability (P) of fiber’s falling into class III (wrapper fiber formation) depends on Fiber length/ fiber extent (E) & Circumference of the rotor (∏D). As P (%) = (100E) / (∏D) Accordingly bigger rotor diameter reduces number of wrapper fibers ; but generation of higher centrifugal force and thereby higher false twist increases their number of wrappings.

94. Rotor diameter is dictated by the staple length of fiber. Normally rotor diameter should be at least 1.2 times that of fibre length. Optimum circumference of the rotor in relation to fiber length is about 3 to 5 times . Staple length (inches) Rotor Diameter (mm) Long staple (exceeding 64 mm) 60 - 100 Short fiber (38 to 64 mm) 50 -60 38 mm and shorter 40 -50

95.   Yarn Count (Ne) Rotor Diameter (mm) 4.5 to 14 40 and above 16 to 20 36 24 and above 33

96. Rotor diameter ∞ Rotor speed -1 . Technological problems at higher rotor speed The tension on the yarn should not be allowed to exceed 20% of the yarn breaking load Tension F 2 acting on yarn = ( n.D ) 2 ; Where n = rotor speed D = rotor diameter Rotor Diameter (mm) Rotor Speed (rpm) 50 and above 50,000 40 -50 65,000 to 70,000 36 Up to 90,000 33 1,20,000

97. Rotor diameter ∞ Rotor speed -1 . 2. Surface speed of rotor wall where the fibers are landing should have a certain optimum constant vlaue . Keeping n.D constant, ensures that the circumferential speed of the rotor remains constant 3. Force with which fibers are driven from slip surface (wall) to groove should be kept constant. 4. Centrifugal force acting on the fiber band in rotor groove should also remain constant. Keeping n.D constant does not ensure that centrifugal force acting on fiber band also remain constant.

98. Yarn Strength: Bigger Diameter leads to higher centrifugal force acting on yarn arm, which increases wrappings and makes yarn more compact. Thereby makes yarn Stronger Less hairy Small diameter Yarn Elongation: Drops markedly with increase in diameter. Due to compact structure. Increases end breaks at peel off point Effect of Rotor Diameter on yarn properties:

99. Yarn Regularity: U% and thick and thin places are not much affected, but neps increase markedly with increase in rotor diameter. Increase in irregularity due to higher centrifugal force gives higher wraps per unit length of wrapper fibres is well compensated by the improvement from back doublings with higher diameter and as a result U% is unaffected. Neps increase with rotor diameter because of higher wraps per unit length

100. Higher spinning speed due to a correspondingly higher rotor speed Lower energy consumption Higher yarn strength Less yarn hairiness Smaller yarn diameter Reduced spinning stability, more yarn breaks A reduction in rotor diameter results in:-

101. The rotor diameter is increased, steep increase in nep level will be observed. Bigger rotor diameter Higher centrifugal force Higher false twisting at rotor zone Higher Untwisting after navel makes wrapper fibers intensively wrapped earlier to strip back results in an increased linear density. Such portion of yarn is accounted as nep.

102. Energy consumption ∞ Spinning tension ∞ Rotor diameter. Spinning tension F ( cN ) = k 1  R 2  n 2  t Where; k 1  is a constant, t = Yarn linear density ( tex ) R = Rotor groove radius (m), n = Rotor speed (rpm) Higher tension leads to higher end break Smaller rotor diameters should be used at higher rotor speeds. Rotor Diameter (mm) Rotor Speed rpm 33 75000-130000 36 60000-120000 40 55000-100000 46 80000-95000 56 65000-75000

103. 2. Rotor speed: Influence on Productivity: Higher the rotor speed higher the input (feed) & output (delivery) speed. Production ∞ Rotor speed Influence on Process Proficiency: Increase in Rotor Speed increases False twist; Results in more often winding of wrapper fibers with reduced α min. and thereby higher spinning stability up to certain extent. Higher centrifugal forces on the fibers in the rotor groove increases spinning tension & results in end break. Lower rotor speed Low power consumption & production as well as Poor spinning stability.

104. Effect of rotor speed on yarn quality; Yarn strength & elongation: Higher the rotor speed, higher will be the centrifugal force by which fiber-ring is pressed in the rotor groove. This require higher peeling force and thereby yarn tension. Higher yarn tension improves fiber orientation & thereby increases yarn strength. Higher the centrifugal force, more will be the number of wrapper fibers as well as their wrappings, increases yarn compactness and thereby yarn strength. Higher fiber stress at higher yarn tension and increased number of wrappings sacrifices yarn extension.

105. B. Yarn Evenness, imperfections and appearance grade: Higher the rotor speed; Reduced Degree of combing: Rate of feeding increases but not the opening roller speed. Reduced draft between feed roller & Opening roller: This gives loss in combing roller efficiency in fiber individualization, trash removal efficiency, deteriorates in yarn evenness, imperfection and appearance grade. Steeper increase in nep level: Wrapper fibers and their wrapping intensity increases with rotor speed due to increased centrifugal force. At the point wrapper fibers occurs, the yarn has a higher linear density because of greater fiber mass wrapped round the yarn and such places are counted as neps in rotor yarn.

106. Requires: For each rotor diameter there is a speed range in which spinning, is possible. Too low a rotor speed results in poor spinning stability, since due to excessively low yarn tension, the yarn twist cannot adequately penetrate to the rotor groove. Too high rotor speed also results in poor spinning stability de to the effect of powerful centrifugal forces on the fibers in the rotor groove, but also due to increasing tension yarn breaks resulting from excessive spinning tension.

107. Increased spinning speed Decreasing elongation at break More imperfections Improved spinning stability With identical rotor diameter, an increase in rotor speed results in:-

108. 3. Rotor Groove: Important parameters: Groove radius Groove angle and Groove surface roughness. The configuration of rotor groove has a pronounced effect on: Spinning stability, Rotor groove dust loading & Yarn quality.

109. Rotor with more open and smooth groove offers better twist penetration resulting in good spinning stability and bulkier yarn. Coarser yarns produced usually from inferior cotton results in higher trash deposit in rotor. So larger groove diameter is more suitable.

110. Shapes of Rotor Groove S- shape: Sharp edge without groove. Suitable for dirty cottons and coarse counts. G- Shape: rotor with narrow groove. Suitable for fine counts with clean back stuff (cotton) as they are difficult to be cleaned. Recommended for knitting. U-shape: Rotor with wide groove. Suitable for coarse count. Gives higher strength than S-type but more susceptible to moire effect due to partial soiling with higher trash.

111. Material of Rotor Wall / Surface characteristics of rotor: The roughness of the rotor wall is determined by rotor coating. A rough surface rotor gives higher yarn quality but too much roughness with a small wall inclination angle adversely affects spinning stability. Material: Made up of steel and surface hardened. Different coatings are used for protecting against wear; Diamond coated gives better yarn quality but difficult to clean with shorter shelf life. Boronized rotors have higher wear protection and ease of cleaning.