Ring Spinning Machine

3.1 Introduction toRing Spinning Frame

Introduction The ring spinning machine was invented in the year 1828 by the American Thorp. In 1830, another American, Jenk, contributed the traveller rotating on the ring. In more than 150 years that have passed since that time, the machine has experienced considerable modification in detail, but the basic concept has remained unchanged. Fig. 1 shows a typical ring frame. Fig.1 : Typical view of a Ring Frame The long central section of the machine, on which production is actually carried out, consists primarily of longitudinal members in the form of spindle rails and drafting rollers extending over the complete machine length. These longitudinal members are secured to intermediate sections arranged at short intervals along the machine length. The sections also serve as supports for the creel . The ring spinning machine has been the most widely used form of spinning and it will continue for some more time, because it has unique advantage over new spinning technologies: It is universally applicable, most of the textile fibres can be spun to required fineness. The yarn spun from this machine demonstrate excellent quality features like uniform structure and good strength. It is easy to operate as compared to other spinning machines. The “know-how” for operation of the machine is well established. It is flexible as regard to quantities in terms of blend and lot sizes. For these reasons, new spinning processes (with the exception of rotor spinning) have difficulty in gaining wide spread acceptance. Disadvantages associated with ring spinning are: More process stages. Roving stage exists as an extra process compared to the other systems. Yarn breakages are more frequent as a result of ring traveller friction and yarn to air drag forces. Interruptions, broken ends and piecing up problems exist because of the yarn breakages. The high speed of the traveller damages the fibers. The capacity of the cops is limited. Energy cost is very high. Low production rate. In long term, the ring frame can survive in longer term only if further success is achieved in automation of the ring spinning process. Also, spinning costs must be markedly reduced since this machine carries significant cost factor in spinning mill. Operation of the Ring frame Task of the ring spinning Attenuate the roving until the required fineness is achieved To impart strength to fiber strand by twisting it To wind up the resulting yarn in a form suitable for storage, transportation and further processing Principles of operation Fig. 2 shows the operating parts of the ring frame and the principle of operation is explained below: Fig.2 : Operating Parts of Ring Frame The roving bobbins (1) are creeled (A) in appropriate holders (3). Guide rails (4) lead the rovings (2) into the drafting arrangement (5) which attenuates them to the final required count. The drafting arrangement (B) is inclined at an angle of about 45 – 600. It is one of the most important assemblies on the machine since it has considerable influence on irregularities present in the yarn. After the drafting arrangement, the machine have twisting and winding zone (C). Upon leaving the front rollers, the emerging fine fiber strand (6) receives the twist needed to give it strength. This twist is generated by the spindle, which rotates at high speed. Each revolution of the spindle imparts one turn of twist to the fiber strand. Spinning of the yarn is thus complete. In order to wind up the twisted yarn to bobbin mounted on Spindle( 8) , a traveller (9) is required to cooperate with the spindle. The traveller moves on guide provided on the ring (10) encircling the spindle. The traveller has no direct drive; instead, it is carried along by the yarn it is threaded with. The speed of the traveller is lower than that of the spindle owing to significant friction generated between the traveller and ring. This difference in speed enables winding of the yarn to bobbin. Winding of the yarn on to the bobbin is done by raising and lowering the ring rail. The traverse stroke of the ring rail is less than that of the bobbin height. The ring rail must therefore be raised by small amount after each layer of coils. Cross-section of the machine Fig. 3 shows the cross-section of a typical ring spinning machine. The ring frames are two sided machines with the spinning positions located on both sides of the machine. Each spindle is a spinning position. The spindle rail houses the spindles. The creel housing the feed roving bobbins are arranged in two rows on each side of the machine. The drafting arrangement is carried on the roller beams. Each intermediate section stands on two feet adjustable in height by means of screws, thereby permitting easy leveling of the machine. Fig.3 : Cross-section through the machine In modern machines, an auto-doffer is also provided. Including the auto-doffer, the width of the machine varies from 800 to 1000 mm (up to 1400 mm when the doffer arm is swung out). Today, the machine length can reach 50 m. Spindle gauges usually lie between 70 and 90 mm. Sources : W. Klein, “Technology of Short Staple Spinning”, The Textile Institute, Manual of Textile Technology, All volumes. Carl A. Lawrence , “ Fundamentals of Spun Yarn Technology”, CRC Publications, 2003. P.R. Lord, Hand Book of Yarn Production : Science, Technology and Economics, Tailor and Francis, 2003. Eric Oxtoby, “Spun Yarn Technology”, Butterworths, 1987. NCUTE publications on Yarn Manufacturing, Indian Institute of Technology, Delhi. 3.2 Ring frame machine parts-I The creel In design terms, the creel is a simple device. It can nevertheless, influence the performance of the machine as well as the yarn quality by introducing number of faults. In particular, if the roving bobbin does not unwind perfectly, then false draft can arise, or in worst case it may lead to end breakage Fig.1 : Bobbin suspension Holder To avoid this problem, the bobbin suspension holders are provided in the machine which is shown in Fig.1. This is provided for each spindle. Each holder has in its lower portion the actual retainer device for the bobbin tube. When the ring is pushed up as far as it will go by the upper end of a tube inserted into the holder, the bobbin retainer swings out; when the ring is pushed up for second time, the retainer is retracted and the bobbin can be withdrawn, for example when it is empty. The holders are suspended on ball bearings. A light brake arm presses gently against the bobbin to prevent it rotating quickly. Modern creels take up a lot of space in breadth since very large bobbins are used now. The drafting arrangement Influence on quality and economics If the quality is taken as the sole criterion, then the drafting arrangement is the most important part of the machine. It influences mainly evenness and strength. The following aspects are therefore of great significance: The type of drafting arrangement like the roller configuration Design of the drafting elements Precision of roller settings Selection of correct individual elements Choice of appropriate draft Service and maintenance However, the drafting arrangement also exerts an influence on the economics of the machine – directly through the end breakage rate, and indirectly through the draft level. If higher drafts can be set in the drafting setup, then coarser roving can be used as feed stock. This implies a higher production rate at the roving frame and thus a saving in roving spindles, i.e. a reduction in the total no. of machines, space, personnel, and so on. On the other hand, increase in draft usually adversely affect the yarn quality. Draft limits in ring frame S. No Material Draft level 1 Carded Cotton Up to 35 2 Carded Blend (Combed cotton and blended yarns) Up to 40 3 Medium fineness Up to 40 4 Fine yarns Up to 45 5 Synthetic fibers Up to 45 (~50) The break draft must be adapted to the total draft in each case since the main draft should not exceed 25 to 30. Accordingly, normal break drafts are: Total draft up to 40 : 1.1 – 1.4 (often 1.14 – 1.25) Strongly twisted roving : 1.3 – 1.5 Where the total draft exceeds 40 : 1.4 – 2.0 Design concepts in the structure of the drafting arrangement The ring spinning machines are fitted with 3 line double apron drafting arrangements. They comprise of three lower fluted steel rollers to which the drive is applied. Top rollers carried in a pivoted weighting arm, are arranged above the fluted rollers and are pressed against them. The strand contains only few fibers when it reaches the main drafting field; accordingly, this is provided with a guide device consisting of an upper and a lower revolving apron. Fig.2 : Position of top rollers in drafting arrangement Normally, the top rollers are arranged as shown in Fig.2(a). The front top roller is set slightly forward by a distance relative to the front bottom roller. While the middle top roller is arranged a short distance behind the middle bottom roller. In each case the distance is about 2 – 4 mm. This position gives smooth running of the top rollers; furthermore, the overhang of the front roller shortens the spinning triangle. This has a favorable influence on the end breakage rate. An alternative roller arrangement is offered by the INA Company in the so-called V-draft drafting arrangement as shown inFig 2(b). Here, the back pair of rollers are shifted upwards and the back top roller is shifted rearward relative to the bottom roller. The large encircling curve produces an additional fiber guidance zone. The Top Rollers Classification Spinning mills operates with two types of top rollers (weighted rollers): Those supported at both ends (in the draw frame and comber); and Double-boss roller in the roving frame and ring spinning machine. The second ones are supported in their centre sections by the weighting arm. They can swing slightly relative to the axis of the bottom rollers. They are available in two versions: fixed rollers, with the two pressure bodies (Fig. 3) at left and right forming a rigid unit which can only be rotated together and loose rollers, with the two pressure bodies separately mounted and able to rotate independently of each other. A distinction is also made according to whether the roller bodies can be removed from the shaft (removable shell), or are permanently attached to the shaft (non-removable shell). The roller bodies are mounted on single-row or double-row ball bearings. Fig.3 : Top roller assembly Coverings on the top rollers are made of synthetic rubber. The covering is drawn on to the boss in the form of a short tube under tension, and is glued in place. This operation should be carried out with the utmost care. Covering hardness can be classified into Soft, Medium and Hard roller covers with the following shore hardness values: Soft 60o to 70o shore Medium 70o to 90o shore Hard above 90o shore Covering with hardness less than 60o shore are normally unsuitable because they cannot recover from the deformation caused by squeezing out on each revolution of the roller. Soft coverings have a great area of contact, enclose the fiber strand more completely and therefore provide better guidance for the fibers. However, they also wear out significantly faster and tend to form more laps. Where possible, therefore, harder coverings are used, for example at the entrance to the drafting arrangement. At that point, a compact, self-sufficient strand, with a slight twist, is fed in and does not require any additional guidance. At the delivery, on the other hand, only few fibers remain in the strand and these exhibits tendencies to slide apart. Additional fiber guidance is therefore advantageous. Accordingly, coverings with hardness levels of the order 80o to 85oshore are mostly used at the back roller, and 63o to 65o at the front roller. In the case of coarse and synthetic fibers, roller covers with high degree of shore hardness are normally used to avoid of increased wear of roller cover and lapping tendency. Since the covering wear out, they must be buffed from time to time (after about 3000 to 4500 operating hours). This operation is carried out by special grinding machines. The amount to be removed from the diameter lies in the region of 0.2 mm, but the total covering thickness should never be reduced below 3.5 mm. Guidelines in selecting the cots For processing combed cotton, soft cots (60 to 65 degree shorehardness) will result in lower U%, thin and thick places There are different types of cores (inner fixing part of a rubber cot)available from different manaufacturers. Aluminimum core,PVC core,etc. It is always better to use softer cots with aluminium core. When softer cots are used, buffing frequency should be reduced to 45 to 90 days depending upon the quality of the rubber cots, if the mill is aiming at very high consistent quality in cotton counts. If the lapping tendency is very high when processing synthetic fibres for non critical end uses, It is better to use 90 degree shore harness cots, to avoid cots damages. This will improve the working and the yarn quality compared to working with 83 degree shore hardness. If rubber cots damages are more due to lapping, frequent buffings as high as once in 30 days will be of great help to improve the working and quality. Of course,one should try to work the ringframe without lapping. Top roller Weighting Methods of applying pressure Three kinds of top roller weighting are presently in use: Spring weighting (most manufacturers) Pneumatic Weighting Magnetic Weighting (available from Saco Lowel) Load – applying support arms are needed to carry the top rollers in the first two groups. These support arms are mounted on shafts or tubes extending over the length of the machine behind the rollers. They can be swung away from the bottom rollers to release pressure, and towards the bottom rollers to apply it. This pendulum action is carried out with levers. Pendulum arms with spring Weighting The double-boss rollers are seated in respective guide arms (14/13, 17/13, 19/13), which are continuously adjustable to each other. For each top roller there is respective spring – for the front roller sometimes two – which presses the top roller against the bottom roller. In the SKF arm (Fig.4), weighting pressure can be simply adjusted in three steps with aid of a key. Color coded makings indicate the setting. Fig.4 : Top roller loading Pendulum arms with pneumatic weighting Fig.5 shows pneumatic weighting used in ring frame. The load applying top arm is stamped from sheet steel and is mounted on a hexagonal tube extending over the length of the machine behind the rollers. The tube contains a pressure hose connected to a central compressor installation. There are three top roller holders in the top arm itself, mounted on two bearing slides. Three holes are provided at to receive a pin acting as a fulcrum. Depending upon the hole selected, the total weighting pressure, originating at the pressure air hose and acting through a cam on the whole weighting arm, is applied more strongly to the back roller or to the two front rollers. A second hole –and – pin system acting on the bearing slide for the two front rollers enables distribution of the pressure applied to these two rollers also. Variation in the total pressure applied to all top rollers is obtained through by simple adjustment of the pressure in the hose using a pressure reducing valve at the end of the machine. Fig.5 : Pneumatic loading The main advantages of pneumatic loading are: Simple and very rapid central pressure variation; Simple and rapid pressure reduction to minimum when the machine is stopped, so that the roller coverings are not deformed during long interruptions in operation. Additional expense in relation to the compressed air system represents a disadvantage in comparison with spring weighting. Fiber Guiding Devices Double apron drafting arrangements with longer lower aprons In double-apron drafting arrangements, two revolving aprons driven by the middle rollers form a fiber guiding assembly. In order to be able to guide the fibers, the upper apron must be pressed with controlled force against the lower apron. For this purpose, a controlled spacing (exit opening), precisely adapted to the fiber volume, is needed between the two aprons at the delivery. Upper aprons, often made up of synthetic material, are always short; lower aprons may be of the same length as the upper aprons or may be significantly longer. They are then guided correspondingly around rolls. Long bottom aprons have the advantage in comparison with short ones, that they can be easily replaced in the event of damage. Also, there is less danger of them choking with fly. Sources : W. Klein, “Technology of Short Staple Spinning”, The Textile Institute, Manual of Textile Technology, All volumes. Carl A. Lawrence , “ Fundamentals of Spun Yarn Technology”, CRC Publications, 2003. P.R. Lord, Hand Book of Yarn Production : Science, Technology and Economics, Tailor and Francis, 2003. Eric Oxtoby, “Spun Yarn Technology”, Butterworths, 1987. NCUTE publications on Yarn Manufacturing, Indian Institute of Technology, Delhi.                                                                                                                              3.3 Ring frame machine parts-II The Thread Path The yarn produced by twisting at the delivery of the drafting arrangements is guided with the aid of a thread guide to a position directly over the spindle. Before passing to winding up on the spindle, the yarn turns through a second guide position, the balloon control ring. Winding on the spindle itself arises from interplay between the speed of the traveller rotating on the ring and the rotational speed of the spindle. The later is therefore the third most important machine element, following the drafting arrangement and the ring/traveller combination. Mechanically, the spindle is capable of speeds up to 28,000 rpm, but this maximum speed cannot be exploited commercially because the traveller speed is limited. Influence of the spindle on spinning Spindles, and their drive, have a great influence on power consumption and noise level in the machine. The running characteristics of a spindle, especially imbalance and eccentricity relative to the ring, also affect yarn quality and of course the number of end breakages. Almost all yarn parameters are disadvantageously affected by poorly running spindles. Hence, the mill must ensure at all times that centering of the spindles relative to the rings is as accurate as possible. Since the ring and spindle form independent units and are able to shift relative to each other in the operation, these two parts must be re-centered from time to time. Previously, this was done by shifting the spindle relative to the ring, but it is now usually carried out by adjusting the ring. Mechanical or electronic devices are used for centering. Fig 1 : Components of the Spindle Fig. 2 : Spindle Supports and bearings The Spindle A ring frame spindle consists of two separate parts, spindle center shaft and enclosed bearing housing as shown in Fig. 1 and2 . Usually, the center shaft is made of an aluminum alloy and has slight taper, say 1:64. To ensure that the tube is firmly seated on the shaft, it has a tube coupling at the top. For large spindles there is one more at the bottom. The bottom end of the shaft is in the form of a cap wharve. It is hollow and can therefore be fitted over the spindle collar accommodated in the bearing housing. The tensile forces generated by the drive belt therefore act directly on the bearing, which favorably influences the smooth running of the spindle. However, the size of the wharve is important as well as its shape. If its diameter can be kept small, equally high spindle speeds can be achieved at lower drive speeds (cylinder/belts). This results in lower energy consumption. However, in order to ensure that the drive belt rotates the spindle slip-free, the diameter of the wharve must also not be too small. Wharve diameters of 19 to 22 mm are common at present. Bearing section is bolted firmly to ring rail by nut. The spindle bearing consists of 2 parts, a spindle collar bearing and a spindle step bearing. Both parts are connected via housing. The spindle collar comprises a precision roller bearing. The spindle step, designed as a friction bearing (conical bearing), is responsible for the elastic centering and cushioning of the spindle center shaft. Two centering and cushioning elements control the bearing shaft. An oil-filled spiral mounted symmetrically with the spindle step ensures optimum cushioning. Spindle step also absorbs all vertical forces acting on the spindle. The spindle collar can be a friction bearing or a roller bearing. The noise level can be reduced considerably by using friction bearings, but energy consumption is somewhat higher. Most spindles are therefore equipped with roller bearings. The spindle collar is rigidly friction-set in the bearing housing in standard spindles. Bearing vibration is therefore transmitted to the spindle frame without damping. This results in high noise levels at higher speeds. For speeds over 18 000 rpm, spindles are therefore mostly used in which not only the spindle step, but also the spindle collar is attached flexibly to the bearing housing. These spindles are more expensive, but permit higher speeds and reduce noise levels in ring spinning machines by some 10 dB compared with standard spindles. Spindle step is always a friction bearing and flexible, i.e. it can tilt sideways to a small extent. The spindle is therefore able to center itself, which enables it to operate in hypercritical ranges. This results in a significant reduction in bearing forces. High-performance spindles are inconceivable without damping devices. Various systems are used, such as damping spirals, damping tubes or damping oil around a steel tube. If damping spirals are used, spiral spring (a) is compressed at one side when the spindle is deflected to side (b) (Fig. 2). The oil therefore flows from this side to the other side, where the gaps become wider (c). The resistance the oil has to overcome in the process damps the vibration in the spindle step and ultimately in the shaft. The cavity between the spindle blade and the bearing housing is largely filled with lubricating oil. Since the oil is used up, it has to be replenished from time to time. This is necessary after about 10 000 - 25 000 operating hours. Spindle Drive Classification Basically, three groups of spindle drives can be distinguished, Tape drives Tangential belt drives Direct drives Tape drives can be further considered under the headings single spindle drives, and group drives, and direct drives under the headings individual mechanical, and individual motor drives. Short-staple spinning mills use practically only group drives, in the form of the 4-spindle tape drive, and tangential belt drives. The latter type is coming into use to an increasing extent. In comparison with tangential belts, the 4-spindle drive has the advantages of lower noise level and energy consumption, and tapes are easier to replace. The advantages of the tangential belt drives are, Elimination of drive components under the machines Less disturbance to the air-current under the machine Possibly, a slightly reduced maintenance requirement. 4-spindle tape drive In this system, a tape drives two spindles on one side of the machine and a further two spindles on the opposite side as shown inFig.3. In running from the one machine side to the other, the tape passes around a drive pulley. One or two tension pulleys ensure even and firm tension of the drive tape. Fig. 3 : Four Spindle Tape Drive Tangential belt drive Fig. 4 and 5 depict the different types of tangential belt drives for ring spinning. In this drive, a belt extends from the suspended motor past the inner side of each spindle. A plurality of pressure rolls ensures even pressure of the belt on all spindles. Three basic forms must be distinguished: single belt, double belt, and grouped drives. Fig. 4 : Tangential Drive for the Spindles (a) Double belt (b) Single belt In the first case, one endless belt drives the spindles on both machine sides. In the second case, two belts are provided, a first belt to drive the spindles on one side and a second belt to drive the spindles of the other side. The double belt system gives better evenness of spindle revolutions. Where the single belt principle is used, differences can arise owing to the considerable variation in tension along the belt. This effect is especially marked in long machines. In grouped drives, groups of spindles are driven by a single belt. Fig. 5 : Tangential Drive for the Spindles – Grouped drive Yarn Guiding Devices Lappets Fig.6 : Lappets Mounted directly above each spindle is a lappet designed to lead the yarn centrally over the spindle axis as shown in Fig 6. The lappet consists of a thread guide made of bent wire ‘o’, and a pivotable support arm ‘k’. The guide is adjustably mounted on the support arm to enable centering using the centering tool ‘S’, while the arm itself is secured to a lappet rail ‘r’which extends over the length of the machine. This rail, along with the lappets can be raised and lowered. During winding of a cop, the lappet rail performs the same sequence of movements as the ring rail, but with a shorter stroke, that is: Continual up and down movement during winding of the layers, Continual upward shift through a small distance in accordance with builder motion. As shown in figure, this movement guides ensures that differences in the balloon height caused by changes in the ring rail positions do not become too large. Otherwise, excessive tension variation in the yarn would produce corresponding negative effects on the ends down rates and the yarn characteristics. Thread guide must be centered from time to time using a setting device which is mounted temporarily on the spindle. Since the yarn path does not run through the middle of the guide, but on its inner edge, the point of the setting device must be directed towards the inner edge of the guide. The balloon control ring (BCR) Spindles used today are relatively long. The spacing between the ring and thread guide is correspondingly long, thus giving a high balloon. Fig.7 : Balloon Control Ring (BCR) This has two problems, A high balloon is associated with a large balloon diameter, causing space problems. The large balloon dimensions lead to relatively high air drag on the yarn in the balloon. This in turn caused increased deformation of the balloon curve out of the plane intersecting the spindle axis. This deformation can lead to balloon instability; there is increased danger of collapse. These above two problems could be nullified by an increase in yarn tension corresponding with a heavier traveller. However, it may cause more end breakage rate. In order to avoid these problems, balloon control rings are used, each dividing its balloon into two smaller sub-balloons as shown inFig.7. In spite of its large overall height, the double balloon created in this way is thoroughly stable even at relatively low yarn tensions. BCRs are also having lifting movements of the ring rail but with a shorter stroke length. Separators Most ends down arise from breaks in the spinning triangle, because there very high forces are exerted on a strand consisting of fibers which have not yet been fully bound together. If a break occurs in the triangle, then the newly created free yarn end must be drawn to the cop and wound onto it. Fig.8 : Separators in Ring Frame During this process, the broken end thread end lashes around the spindle. In the absence of protective devices, this broken end would be hurled into the neighboring yarn balloon and would cause an end down on that spindle also. This procedure would be repeated continuously so that a wave of ends down would travel along the row of spindles. In order to prevent this happening, separator plates of aluminium or plastics material are arranged between the individual spindles as shown in Fig. 8. Sources : W. Klein, “Technology of Short Staple Spinning”, The Textile Institute, Manual of Textile Technology, All volumes. Carl A. Lawrence , “ Fundamentals of Spun Yarn Technology”, CRC Publications, 2003. P.R. Lord, Hand Book of Yarn Production : Science, Technology and Economics, Tailor and Francis, 2003. Eric Oxtoby, “Spun Yarn Technology”, Butterworths, 1987. NCUTE publications on Yarn Manufacturing, Indian Institute of Technology, Delhi. Copyright IIT Delhi © 2009-2011. All rights reserved. Copyright IIT Delhi © 2009-2011. All rights reserved.