Roving Frame


Roving machine is complicated, liable to faults, causes defects, adds to production costs and delivers a product that is sensitive in both winding and unwinding. This machine is forced to use by the spinner for the following two reasons.

  1. Sliver is thick, untwisted strand that tends to be hairy and to create fly. The draft needed to convert this is around 300 to 500. Drafting arrangements of ring frames are not capable of processing
    this strand in a single drafting operation to create a yarn that meets all the normal demands on such yarns.
  2. Drawframe cans represent the worst conceivable mode of transport and presentation of feed material to the ring spinning frame.

· TASKS OF ROVING FRAME:

  1. Attenuation- drafting the sliver into roving
  2. twisting the drafted strand
  3. winding the twisted roving on a bobbin

· Fibre to fibre cohesion is less for combed slivers. Rollers in the creel can easily create false drafts.Care must be taken to ensure that the slivers are passed to the drafting arrangement without disturbance.
Therefore, a perfect drive to the creel rollers is very important.

· The drafting arrangement drafts the material with a draft between 5 and 15.The delivered strand is too thin to hold itself together at the exit of the front bottom roller.

· Bobbin and flyer are driven separately, so that winding of the twisted strand is carried out by running the bobbin at a higher peripheral speed than the flyer.

· The bobbin rail is moving up and down continuously, so that the coils must be wound closely and parallel to one another to ensure that as much as material is wound on the bobbin.

· Since the diameter of the packages increases with each layer, the length of the roving per coil also will increase. Therefore the speed of movement of bobbin rail must be reduced by a small amount after
each completed layer

· Length delivered by the front roller is always constant. Owing to the increase in the diameter of the package for every up and down movement, the peripheral speed of package should keep on changing , to maintain the same difference in peripheral speeds between package and flyer.

· There are two types of drafting systems.

  1. 3/3 drafting system
  2. 4/4 drafting system

In general 3/3 drafting system is used, but for higher draft applications 4/4 drafting system is used.

· The draft often has limits not only at the upper limit (15 to 20), but also at lower limit. It is around 5 for cotton and 6 for synthetic fibers. If drafts below these lower limits are attempted, then the fibre masses to be moved are too large, the drafting resistance becomes too high and the drafting operation is difficult to control.

It is advisable to keep the break draft (predarft) as low as possible, because lower break draft always improves roving evenness.

· In general two condensers are used in the drafting arrangement. The purpose of these condensers is to bring the fibre strands together. It is difficult to control, Spread fibre masses in the drafting zone and they cause unevenness. In addion, a widely spread strand leaving the drafting arrangement leads to high fly levels and to high hairiness in the roving. The size of condensers should be selected according to the volume of the fibre sliver.

· Flyer inserts twist. Each flyer rotation creates one turn in the roving. Twist per unit length of roving depends upon the delivery rate.
Turns per metre = (flyer rpm)/(delivery speed (m/min))
Higher levels of roving twist, therefore, always represent production losses in Roving frame and possible draft problems in the ring spinning machine. But very low twist levels will cause false drafts and roving breaks in the roving frame.

· Centrifugal tension is created at the bobbin surface as the layers are being wound and is created by the rotation of the package. Each coil of roving can be considered as a high-speed rotating hool of roving on which centrifugal tension increases with increasing diameter of the package. centrifugal tension in the roving is proportional to the square of the winding surface velocity.In this context, centrifugal force acts in such a manner as to lift the top roving strand from the surface of the package so that the radial forces within the strand that hold the fibres together are reduced and the roving can be stressed to the point of rupture. Breaks of this type may occur at the winding-on Point of the presser or in strands that have just been wound on the top surface of the package. This phenomenon is known as “bobbin-bursting”. This phenomenon will be prominent if the twist per inch is less or the spindle speed is extremely high when the bobbin is big.

· Apart from inserting twist, the flyer has to lead the very sensitive strand from the flyer top to the package without introducing false drafts. Latest flyers have a very smooth guide tube set into one flyer leg
and the other flyer leg serves to balance the flyer. The strand is completely protected against air flows and the roving is no longer pressed with considerable force against the metal of the leg, as it is in
the previous designs. Frictional resistance is considerably reduced, so that the strand can be pulled through with much less force.

· False twisters are used on the flyers to add false twist when the roving is being twisted between the front roller and the flyer.Because of this additional twist, the roving is strongly twisted and this reduces the breakage rate. Spinning triangle is also reduced which will reduce the fibre fly and lap formation on
the front bottom roller.

· Because of the false twister, the roving becomes compact which helps to increase the length wound on the bobbin. This compactness helps to increase the flyer speed also.

· Roving strength is a major factor in determining winding limitations. It must be high enough for the fibres to hold together in a cohesive strand and low enough for satisfactory drafting at the spinning machine. The factors affecting roving strength are as follows:

  • the length, fineness, and parallelisation of fibres
  • the amount of twist and compactness of the roving
  • the uniformity of twist and linear density.

· BUILDER MOTION: This device has to perform the following tasks

  1. to shift the belt according to the bobbin diameter increase
  2. to reverse the bobbin rail direction at top and bottom
  3. to shorten the lift after each layer to form tapered ends

· Shifting of the belt is under the control of the ratchet wheel. The ratchet wheel is permitted to rotate by a half tooth. The bobbin diameter increases more or less rapidly depending upon roving hank. The belt must be shifted through corresponding steps. The amount of shifting, which depends upon the thickness of the roving, is modified by replacement of the ratchet wheel or by other gears.If a ratchet wheel with fewer teeth is inserted, then the belt is shifted through larger steps, i.e. it moves more rapidly, and vice versa.

· To form a package, the layer must be laid next to its neighbours. For that the lay-on point must continually be moved. The shift of the winding point is effected by moving the bobbin rail. This raising and lowering is done by rails.Since the package diameter is steadily increasing, the lift speed must be reduced by a small amount after each completed layer.

· During winding of a package, the ratchet is rotated at every change-over.Reversal of the bobbin layer occurs little earlier for every reversal.This gives a continuous reduction in the lift of the rail . Thus bobbins are built with taper.

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RING FRAME


Ring spinning machine (year of constr. 1988) i...
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The ring spinning will continue to be the most widely used form of spinning machine in the near future,because it exhibits significant advantages in comparison with the new spinning processes.

· Following are the advantages of ring spinning frame

  • It is universally applicable, i.e.any material can be spun to any required count
  • It delivers a material with optimum characteristics, especially with regard to structure and strength.
  • it is simple and easy to master
  • the know-how is well established and accessible for everyone

· Functions of  ring frame

  • to draft the roving until the required fineness is achieved
  • to impart strength to the fibre, by inserting twist
  • to wind up the twisted strand (yarn) in a form suitable for storage, transportation and further processing.

DRAFTING

· Drafting arrangement is the most important part of the machine. It influences mainly evenness and strength The following points are therefore very important

  • drafting type
  • design of drafting system
  • drafting settings
  • selection of drafting elements like cots, apron, traveller etc
  • choice of appropriate draft
  • service and maintenance

· Drafting arrangement influence the economics of the machine – directly by affecting the end break rate and indirectly by the maximum draft possible.

· If higher drafts can be used with a drafting arrangement, then coarser roving can be used as a feeding material. This results in higher production rate at the roving frame and thus reducing the number roving machines required, space, personnel and so on.

· In fact increase in draft affects the yarn quality beyond certain limit. Within the limit some studies show that increase in draft improves yarn quality. The following draft limits have been established for
practical operation:

  • carded cotton- upto 35
  • carded blends – upto 40
  • combed cotton and blends(medium counts) – upto 40
  • combed cotton and blends(fine counts) – upto 45
  • synthetic fibres – upto 50

· The break draft must be adapted to the total draft in each case since the main draft should not exceed 25 to 30. It should be noted that higher the break draft, more critical is the break draft setting

· The front top roller is set slightly forward by a distance of 2 to 4mm relative to the front bottom roller, while the middle top roller is arranged a short distance of 2mm behind the middle bottom roller.

· Overhang of the front top roller gives smooth running of the top rollers and shortens the spinning triangle. This has a correspondingly favourable influence on the end break rate.

· Rubber cots with hardness less than 60 degrees shore are normally unsuitable because they can not recover from the deformation caused by the pressure on the top roller while running.

· Soft rubbercots for top rollers have a greater area of contact, enclose the fibre strand more completely and therefore provide better guidance for the fibres.However softer cots wear out significantly faster
and tend to form more laps.

· Normally harder rubbercots are used for back top rollers, because the roving which enters the back roller is compact , little twisted and it does not require any additional guidance for better fibre control.

· In the front top roller, only few fibres remain in the strand and these exhibit a tendency to slide apart. Additional fibre guidance is therefore necessary.Therefore rubbercots with hardness levels of the order 80 degrees to 85 degrees shore are mostly used at the back roller and 63 degrees and 65 degrees at the front roller.

· If coarse yarns and synthetic yarns are being spun, harder rubbercots are used at the front roller because of increased wear and in the case of synthetic yarns to reduce lapups.

· Three kinds of top roller weighting(loading) are presently in use

  • spring loading
  • pneumatic loading
  • magnetic weighting

· With pneumatic loading system, the total pressure applied to all top rollers is obtained by simple adjustment
of the pressure in the hose using pressure reducing valve. Moreover the rubbercots will not get deformed if
the machine is stopped for a longer duration, because the pressure on top rollers can be released to the
minimum level.

· The fibre strand in the main drafting field consists of only a few remaining fibres. There is hardly any friction field and fibre guidance provided by the rollers alone is inadequate. Special fibre guiding devices are therefore needed to carry out a satisfactory drafting operation. Double apron drafting arrangements with longer bottom aprons is the most widely used guiding system in all the modern ringframes.

· In doube apron drafting system two revolving aprons driven by the middle rollers form a fibre guiding  assembly. In order to be able to guide the fibres, 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 fibre volume is needed between the two aprons at the delivery. This spacing is set by “spacer” or “distance clips”. Long bottom aprons have the advantage in comparison wiht short ones, that they can be easily replaced in the event of damage and there is less danger of choking with fluff.

· 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 flange, also affect yarn quality and of course the number of end breakage. Almost all yarn parameters are affected by poorly running spindles. Hence it should be ensured that the 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 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 now it is usually carried out by adjusting the ring.

· In comparison with Tangential belt drive, the 4-spindle drive has the advantages of lower noise level and energy consumption, and tapes are easier to replace.

· Lappet guide performs the same sequence of movements as the ringrail, but with a shorter stroke, this movement of the guide ensures that differences in the balloon height caused by changes in the ring rail
positions do not become too large. This helps to control the yarn tension variation with in control, so that ends down rate and yarn charactersitics are under control.

· Spindles used today are relatively long. The spacing between the ring and the thread guide is correspondigly long, thus giving a high balloon. This has two negative influence

  • A high balloon results in large bobbin diameter leading to space problems
  • Larger the balloon diameter , higher the air drag on the yarn.This inturn causes increased deformation of the balloon curve out of hte plane intersecting the spindle axis.This deformation can lead to balloon stability, there is increase danger of collapse.

Both these disadvantages result in higher yarn tension, thereby higher endbreaks.In order to avoid this, balloon control rings are used. It divides the balloon into two smaller sub-balloons. Inspite of its large overall
height, the double-balloon created in this way is thoroughly stable even at relatively low yarn tension.

· Balloon control rings therefore help to run the mahcine with long spindles(longer lift) and at high spindle speed, but with lower yarn tension. Since the yarn rubs against the control ring, it may cause roughening
of the yarn.

· Most ends down arise from breaks in the spinning triangle, because very high forces are exerted on a strand consisting of fibres which have not yet been fully bound together in the spinning triangle.

RING and TRAVELLER COMBINATION:

· The following factors should be considered

  • materials of the ring traveller
  • surface charecteristics
  • the forms of both elements
  • wear resistance
  • smoothness of running
  • running-in conditions
  • fibre lubrication

· For the rings two dimensions are of primariy importance. 1.internal diameter 2. flange width.

· Antiwedge rings exhibit an enlarged flange inner side and is markedly flattened on it upper surface. This type of profile permitted to use travellers with a lower centre of gravity and precisely adapted bow(elliptical travellers), which in turn helped to run the machine with higher spindle speeds. Antiwedge rings and elliptical travellers belong together and can be used in combination.

· Low crown profle has the following advantage. Low crown ring has a flattened surface top and this gives space for the passage of the yarn so that the curvature of the traveller can also be reduced  and the centre of gravity is lowered.In comparison with antiwedge ring, the low crown ring has the advantage that the space provided for passage of the yarn is somewhat larger and that all current traveller shapes can be applied, with the exception of the elliptical traveller. The low crown ring is the most widely
used ring form now.

· The ring should be tough and hard on its exterior. The running surface must have high and even hardeness in the range 800-850 vikcers. The traveller hardness should be lower (650-700 vickers), so that wear occurs
mainly on the traveller, which is cheaper and easier to replace. Surface smoothness should be high, but not too high, because lubricating film can not build up if it too smooth.

· A good ring in operation should have the following features:

  • best quality raw material
  • good, but not too high, surface smoothness
  • an even surface
  • exact roundness
  • good, even surface hardness, higher than that of the traveller
  • should have been run in as per ring manufacturers requirement
  • long operating life
  • correct relationship between ring and bobbin tube diameters
  • perfectly horizontal position
  • it should be exactly centered relative to the spindle

· In reality, the traveller moves on a lubricating film which builds up itself and which consists primarily of cellulose and wax. This material arises from material abraded from the fibres.If fibre particles are caught
between the ring and traveller, then at high traveller speeds and with correspondingly high centrifugal forces, the particles are partially ground to a paste of small, colourless, transparent and extremely thin platelets. The platelets are continually being replaced during working. The traveller smoothes these out to form a continuous running surface.The position, form and structure of lubricating film depends on

  • yarn fineness
  • yarn structure
  • fibre raw material
  • traveller mass
  • traveller speed
  • height  of traveller bow

Modern ring and traveller combination with good fibre lubrication enable traveller speeds upto 40m/sec.

· Traveller imparts twist to the yarn. Traveller and spindle together help to wind the yarn on the bobbin. Length wound up on the bobbin corresponds to the difference in peripheral speeds of the spindle and traveller. The difference in speed should correspond to length delivered at the front rollers. Since traveller does not have a drive on its own but is dragged along behing by the spindle.

· High contact pressure (upto 35 N/square mm)is generated between the ring and the traveller during winding, mainly due to centrifugal force. This pressure leads to generation of heat. Low mass of  the traveller does not permit dissipation of the generated heat in the short time available. As a result the operating speed of the traveller is limited.

· When the spindle speed is increased, the friction work between ring and traveller (hence the build up) increases as the 3rd power of the spindle rpm. Consequently if the spindle speed is too high, the traveller sustains thermal damage and fails. This speed restriction is felt particularly when spinning cotton yarns of relatively high strength.

· If the traveller speed is raised beyond normal levels , the thermal stress limit of the traveller is exceeded, a drastic change in the wear behaviour of the ring and traveller ensues. Owing to the strongly increased adhesion forces between ring and traveller, welding takes place between the two. These seizures inflict  massive damage not only to the traveller but to the ring as well.Due to this unstable behaviour of the ring and traveller system the wear is at least an order of magnitude higher than during the stable phase. The traveller temperature reaches 400 to 500 degrees celsius and the danger of the traveller annealing and failing is very great.

· The spinning tension is proportional

  • to the friction coefficient between ring and traveller
  • to the traveller mass
  • to the square of the traveler speed

and inversely proportional

  • to the ring diameter
  • and the angle between the connecting line from the traveller-spindle axis to the piece of yarn between the traveller and cop.

· The yarn strength is affected only little by the spinning tension. On the other hand the elongation diminishes with increasing tension, for every tensile load of the fibres lessens the residual elongation in the fibres and hence in the yarn. Increasing tension leads also to poorer Uster regularity and IPI values.

· If the spinning tension is more, the spinning triangle becomes smaller . As the spinning triangle gets smaller, there is less hairiness.

SHAPE OF THE TRAVELLER:

· The traveller must be shaped to match exactly with the ring in the contact zone, so that a single contact surface, with the maximum surface area is created between ring and traveller. The bow of the traveller should be as flat as possible, in order to keep the centre of gravity low and thereby improve smoothness of running. However the flat bow must still leave adequate space for passage of the yarn. If the yarn clearance opening is too small, rubbing of the yarn on the ring leads to roughening of the yarn, a high level of fibre loss as fly, deterioration of yarn quality and formation of melt spots in spinning
of synthetic fibre yarns.

WIRE PROFILE OF THE TRAVELLER:

· Wire profile influences both the behaviour of the traveller and certain yarn characteristics, they are

  • contact surface of the ring
  • smooth running
  • thermal transfer
  • yarn clearance opening
  • roughening effect
  • hairiness

MATERIAL OF THE TRAVELLER

· The traveller should

  • generate as little heat as possible
  • quickly distribute the generated heat from the area where it develops over the whole volume of the traveller
  • transfer this heat rapidly to the ring and the air
  • be elastic, so that the traveller will not break as it is pushed on to the ring
  • exhibit high wear resistance
  • be less hard than the ring, because the traveller must wear out in use in preference to the ring

· In view of the above said requirements, traveller manufacturers have made efforts to improve the running properties by surface treatment. “Braecker” has developed a new process in which certain finishing components diffuse into the traveller surface and are fixed in place there. The resulting layer reduces temperature rise and increases wear resistance.

· Traveller mass determines the magnitude of frictional forces between the traveller and the ring, and these in turn determine the winding and balloon tension. Mass of the traveller depends upon

  • yarn count
  • yarn strength
  • spindle speed
  • material being spun

If traveller weight is too low, the bobbin becomes too soft and the cop content will be low. If it is unduly high, yarn tension will go up and will result in end breaks. If a choice is available between two traveller weights, then the heavier is normally selected, since it will give greater cop weight, smoother running of the traveller and better transfer of heat out of traveller.

· When the yarn runs through the traveller, some fibres are liberated. Most of these fibres float away as dust in to the atmosphere, but some remain caught on the traveller and they can accumulate and form a tuft. This will increase the mass of traveller and will result in end break because of higher yarn tension. To avoid this accumulation , traveller clearers are fixed close to the ring, so that the
accumulation is prevented. They should be set as close as possible to the traveller, but without affecting its movement. Exact setting is very important.

· Specific shape of the cop is achieved by placing the layers of yarn in a conical arrangement. In the ending of a layer, the ring rail is moved slowly but with increasing speed in the upward direction and quickly but with decreasing speed downwards. This gives a ratio between the length of yarn in the main up) and cross(down) windings about 2:1.

· The total length of a complete layer (main and cross windings together) should not be greater han 5m (preferably 4 m) to facilitate unwinding. The traverse stroke of the ring rail is ideal when it
is about 15 to 18% greater than the ring diameter.

· End break suction system has a variety of functions.

  • It removes fibres delivered by the drafting arrangement after an end break and thus prevents multiple  end breaks on neighbouring spindles.
  • It enables better environmental control, since a large part of the return air-flow of the air-conditioned system is led past the drafting system, especially the region of the spinning triangle.
  • In modern installations, approx. 40 to 50 % of the return air-flow passes back into the duct system of the air-conditioning plant via the suction tubes of pneumafil suction system.
  • A relatively high vacuum must be generated to ensure suction of waste fibres
    • for cotton – around 800 pascals
    • for synthetic – around 1200 pascals
  • A significant pressure difference arises between the fan and the last spindle. This pressure difference ill be greater , the longer the machine and greater the volume of air to be transported. The air flow rate is normally between 5 and 10 cubic meter/ hour.
  • Remember that the power needed to generate an air-flow of 10 cubic meter/ hour , is about 4.5 times he power needed for an air-flow of 6 cubic meter/ hour, because of the significantly higher vacuum
    level developed at the fan.

SPINNING GEOMETRY:

· From Roving bobbin to cop, the fibre strand passes through drafting arrangement, thread guide, balloon control rings and traveller. These parts are arranged at various angles and distances relative to each other.
The distances and angles together are referred to as the spinning geometry,has a significant influence n the spinning operation and the resulting yarn. They are

  • yarn tension
  • number of end breaks
  • yarn irregularity
  • binding-in of the fibres
  • yarn hairiness
  • generation of fly etc.

· Spinning Triangle:
Twist in a yarn is generated at the traveller and travel against the direction of yarn movement to the ront roller. Twist must run back as close as possible to the nip of the rollers, but it never penetrates completely to the nip because, after leaving the rollers, the fibres first have to be diverted inwards and wrapped around each other. There is always a triangular bundle of fibres without twist at the exit of the rollers, this is called as SPINNING TRIANGLE. Most of the end breaks originate at this point. The length of the spinning triangle depends upon the spinning geometry and upon the twist level in the yarn.

· The top roller is always shifted 3 to 6 mm forward compared to bottom roller. This is called top rolleroverhang.This gives smoother running and smaller spinning triangle. The overhang must not be made too large,
as the distance from the opening of the aprons to the roller nip line becomes too long resulting in poorer fibre control and increased yarn irregularity.

· Continuous variation of the operating conditions arises during winding of a cop.The result is that the tensile force exerted on yarn must be much higher during winding on the bare tube than during winding on
the full cop, because of the difference in the angle of attack of the yarn on the traveller. When the ring rail is at the upper end of its stroke, in spinning onto the tube, the yarn tension is substantially higher
than when the ring rail is at its lowermost position. This can be observed easily in the balloon on any ring spinning machine.

· The tube and ring diameters must have a minimum ratio, between approx. 1:2 and 1:2.2, in order to ensure that the yarn tension oscillations do not become too great.

· Yarn tension in the balloon is the tension which finally penetrates almost to the spinning triangle and which is responsible for the greater part of the thread breaks. It is reduced to a very small degree by
the deviation of the yarn at the thread guide. An equilibrium of forces must be obtained between the yarn tension and balloon tension.

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RINGS & TRAVELLERS :


Ringspinnen
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In most cases, the limit to productivity of the ring spinning machine is defined by the traveller in interdependence with the ring, and yarn. It is very important for the technologist to understand  this and act on them to optimise the yarn production.

  • The following factors should be considered
    • materials of the ring traveller
    • surface characteristics
    • the forms of both elements( ring and traveller)
    • wear resistance
    • smoothness of running
    • running-in conditions
    • fibre lubrication

TRAVELLER:

Traveller imparts twist to the yarn. Traveller and spindle together help to wind the yarn on the bobbin. Length wound up on the bobbin corresponds to the difference in peripheral speeds of the spindle and traveller. The difference in speed should correspond to length delivered at the front rollers. Since traveller does not have a drive on its own but is dragged along behind by the spindle.

High contact pressure (upto 35 N/square mm)is generated between the ring and the traveller during winding, mainly due to centrifugal force. This pressure leads to generation of heat. Low mass of the traveller does not permit dissipation of the generated heat in the short time available. As a result the operating speed of the traveller is limited.

Heat produced when by the  ring traveller  is around 300 degree Celsius. This has to be dissipated in milliseconds by traveller into the air.

Parts of a traveller:

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Height of bow:  It should be as low as possible for stable running of traveller. It should also have sufficient yarn passage.

Yarn passage: According to count spun the traveller profile to be selected with required yarn passage.

Toe gap : This will vary according to traveller number and flange width of the ring

Wire section: It plays an important role for yarn quality, life of traveller.

Ring contact area: This area should be more, uniform, smooth and continuous for best performance.

Inner width: This varies according to traveller profile and ring flange.

SALIENT FEATURES OF A TRAVELLER:

  • Generate less heat
  • dissipate heat fastly
  • have sufficient elasticity for easy insertion and to retain its original shape after insertion
  • friction between ring and traveller should be minimal
  • it should have excellent wear resistance for longer life
  • hardness of the traveller should be less than the ring

When the spindle speed is increased, the friction work between ring and traveller (hence the build up) increases as the 3rd power of the spindle rpm. Consequently if the spindle speed is too high, the traveller sustains thermal damage and fails. This speed restriction is felt particularly when spinning cotton yarns of relatively high strength.

If the traveller speed is raised beyond normal levels , the thermal stress limit of the traveller is exceeded, a drastic change in the wear behaviour of the ring and traveller ensues. Owing to the strongly increased adhesion forces between ring and traveller, welding takes place between the two. These seizures inflict massive damage not only to the traveller but to the ring as well.Due to this unstable behaviour of the ring
and traveller system the wear is atleast an order of magnitude higher than during the stable phase. The traveller temperature reaches 400 to 500 degrees celcius and the danger of the traveller annealing and failing is very great.

The spinning tension is proportional

  • to the friction coefficient between ring and traveller
  • to the traveller mass
  • to the square of the traveller speed

and inversely proportional

  • to the ring diameter
  • and the angle between the connecting line from the traveller-spindle axis to the piece of yarn between the traveller and cop.
  • In order to maintain the same friction or spinning tension with different coefficients of friction, different traveller weights must be used. The coefficient of friction is determined by the fiber lubrication and is subject to fluctuation. Dry cotton means higher coefficient of friction. For manmade fibres depending upon the manufacturer, lower to medium coefficient of friction.

The coefficient of friction with fiber lubrication can vary from 0.03 and 0.15.

R = Coefficient of friction  x N

where

R – traveller friction in mN

N = Normal force >= (Fc x ML x V xV)/(R)

Fc – centrifugal force

ML – mass of the traveller in mg

V – traveller speed in m/s

R – radius of the ring (inside)

  • The yarn strength is affected only little by the spinning tension. On the other hand the elongation diminishes with increasing tension, for every tensile load of the fibres lessens the residual elongation in the fibres and hence in the yarn. Increasing tension leads also to poorer Uster regularity and IPI values.
  • If the spinning tension is more, the spinning triangle becomes smaller . As the spinning triangle gets smaller, there is less hairiness.

SHAPE OF THE TRAVELLER:

  • The traveller must be shaped to match exactly with the ring in the contact zone, so that a single contact surface, with the maximum surface area is created between ring and traveller. The bow of the traveller should be as flat as possible, in order to keep the centre of gravity low and thereby improve smoothness of running. However the flat bow must still leave adequate space for passage of the yarn. If the yarn clearance opening is too small, rubbing of the yarn on the ring leads to roughening of the yarn,
    a high level of fibre loss as fly, deterioration of yarn quality and formation of melt spots in spinning of synthetic fibre yarns.

WIRE PROFILE OF THE TRAVELLER: 

  • Wire profile influences both the behaviour of the traveller and certain yarn characteristics, they are
    • contact surface of the ring
    • smooth running
    • thermal transfer
    • yarn clearance opening
    • roughening effect
    • hairiness

MATERIAL OF THE TRAVELLER

  • The traveller should
    • generate as little heat as possible
    • quickly distribute the generated heat from the area where it develops over the whole volume of the traveller
    • transfer this heat rapidly to the ring and the air
    • be elastic, so that the traveller will not break as it is pushed on to the ring
    • exhibit high wear resistance
    • be less hard than the ring, because the traveller must wear out in use in preference to the ring
  • In view of the above said requirements, traveller manufacturers have made efforts to improve the running properties by surface treatment. “Braecker” has developed a new process in which certain finishing components diffuse into the traveller surface and are fixed in place there. The resulting layer reduces temperature rise and increases wear resistance.
  • Traveller mass determines the magnitude of frictional forces between the traveller and the ring, and these in turn determine the winding and balloon tension. Mass of the traveller depends upon
    • yarn count
    • yarn strength
    • spindle speed
    • material being spun

If traveller weight is too low, the bobbin becomes too soft and the cop content will be low. If it is unduly high, yarn tension will go up and will result in end breaks. If a choice is available between two traveller weights, then the heavier is normally selected, since it will give greater cop weight, smoother running of the traveller and better transfer of heat out of traveller.

  • When the yarn runs through the traveller, some fibres are liberated. Most of these fibres float away as dust in to the atmosphere, but some remain caught on the traveller and they can accumulate and form a tuft. This will increase the mass of traveller and will result in end break because of higher yarn tension. To avoid this accumulation , traveller clearers are fixed close to the ring, so that the accumulation is prevented. They should be set as close as possible to the traveller, but without affecting its movement. Exact setting is very important.
  • For the rings two dimensions are of primarily importance. 1.internal diameter 2. flange width.
  • Antiwedge rings exhibit an enlarged flange inner side and is markedly flattened on it upper surface. This type of profile permitted to use travellers with a lower centre of gravity and precisely adapted bow(elliptical travellers), which in turn helped to run the machine with higher spindle speeds. Antiwedge rings and elliptical travellers belong together and can be used in combination.
  • Low crown profile has the following advantage. Low crown ring has a flattened surface top and this gives space for the passage of the yarn so that the curvature of the traveller can also be reduced and the centre of gravity is lowered.In comparison with antiwedge ring, the low crown ring has the advantage that the space provided for passage of the yarn is somewhat larger and that all current traveller shapes can be applied, with the exception of the elliptical traveller. The low crown ring is the most widely used ring form now.
  • The ring should be tough and hard on its exterior. The running surface must have high and even hardeness in the range 800-850 vikcers. The traveller hardness should be lower (650-700 vickers), so that wear occurs mainly on the traveller, which is cheaper and easier to replace. Surface smoothness should be high, but not too high, because lubricating film can not build up if it too smooth.
  • A good ring in operation should have the following features:
    • best quality raw material
    • good, but not too high, surface smoothness
    • an even surface
    • exact roundness
    • good, even surface hardness, higher than that of the traveller
    • should have been run in as per ring manufacturers requirement
    • long operating life
    • correct relationship between ring and bobbin tube diameters
    • perfectly horizontal position
    • it should be exactly centred relative to the spindle
  • In reality, the traveller moves on a lubricating film which builds up itself and which consists primarily of cellulose and wax. This material arises from material abraded from the fibres.If fibre particles are caught between the ring and traveller, then at high traveller speeds and with correspondingly high centrifugal forces, the particles are partially ground to a paste of small, colourless, transparent and extremely thin platelets.
    The platelets are continually being replaced during working. The traveller smoothed these out to form a continuous running surface.The position, form and structure of lubricating film depends on
  • yarn fineness
  • yarn structure
  • fibre raw material
  • traveller mass
  • traveller speed
  • high of traveller bow

Modern ring and traveller combination with good fibre lubrication enable traveller speeds upto 40m/sec.

TECHNOLOGICAL GUIDELINES:

  • When the ring diameter is less,  balloon diameter will be small. This leads to more yarn tension. Hence use lighter travellers.
  • When the ring diameter is bigger, balloon diameter will  be more. This  leads to less yarn tension and the balloon touches the separator. Hence use heavier travellers
  • When the tube length  is short, the yarn tension will be more. Hence use lighter travellers
  • When the tube length is long, the yarn tension will be less, hence use heavier travellers
  • When the yarn contact area and ring contact area in traveller is closer, fibre lubrication is better especially in cotton. For this use heavier travellers
  • When spindle speed is increased use lighter traveller with low bow height. At higher speeds, lighter travellers give lesser yarn tension. When low bow height travellers are used centre of gravity will be closest to the ring which aids in running of traveller.
  • Use lighter travellers on new rings. This is done to reduce end breakages by reducing the yarn tension.
  • Use heavier travellers on old rings. This is done to avoid bigger balloons
  • Heavier travellers reduce hairiness
  • When using lighter travellers, yarn stretch will be less. It helps for better yarn elongation
  • During running-in the end breakage rate  should be kept minimum, hence use lighter travellers.
  • The shorter the  balloon, the lighter the traveller to be used, the higher traveller speeds can be achieved.
  • The ring traveller, together with the  yarn as a pull element, is set into motion on the ring by the rotation of the spindle. If the direction of pull deviates too much from the running direction of the traveller (spinning angle less than 30 degrees) the tension load will be too high.

Preconditions for good operating results

The maximum ability of the ring/traveller system to withstand occurring stress situation during operation determines the performance limit of the ring spinning and twisting machine. Traveller wear does not only depend on traveller material; problems of heat dissipation are of crucial importance, too. The heat generated between ring and traveller must be reduced as quickly as possible to avoid local temperature in the traveller wear zones. The ability of the traveller to resist to stress is determined by several factors. Investigations regarding improvements of rings and travellers aimed at a further increase of performance should above all make sure that all other conditions with a certain influence on the spinning process are optimal.

Therefore make sure that:

¥ the rings are correctly centered with regard to the spindles

¥ the yarn guide eyelet is well centered with regard to the spindle

¥ the spindle bearing is in good condition, thus preventing spindle vibrations

¥ the ratio between bobbin diameter and ring diameter  is correct

¥ the concentricity of the ballon control ring  with regard to the

spindle is correct

¥ the fibre tufts which accumulate on flange travellers are removed by

means of suitable traveller cleaners

¥ the climatic conditions (temperature and relative air humidity) are favourable

for the spinning process

¥ the air in the mill is free from disturbing particles that influence efficient

performance of the traveller

It has to be stressed that a smooth and well run-in track is of most importance.

Concentricity of spindle, ring, yarn guide and balloon control ring

Especially at high spindle speeds concentric positioning of ring, spindle, yarn  eyelet and balloon control ring is required for keeping the ends down rate at low level. Spindles and rings must be aligned and centered absolutely parallel. Ring rails or ring holders should, therefore, be installed absolutely horizontally compared to the vertically fitted spindles. Ring and traveller form the main elements in ring spinning and twisting. They determine to a large extent performance and operating conditions of the machine.

The traveller accomplishes two main tasks while running on the ring at high speeds:

a) It gives the roving  supplied by the feed rollers the necessary twist.

b) It assists in winding the yarn onto the bobbin in the form of a cop with ã correct  tension.

During this operation the ring guides the traveller, which is essential for the perfect positioning of the yarn and the formation of the cop. The traveller is pressed against the ring track by centrifugal forces. The resulting frictional forces reduce traveller speed, which is dragged along by the passing-through yarn, and provide the yarn with the tensile forces necessary for assembling the individual fibres into the spun yarn as well as for limiting the yarn balloon.

Steel travellers are hardened to a certain degree and polished to a mirror finish. They can be adapted in shape, weight and surface finish to the ring, yarn type and yarn count. Nylon travellers of standard quality (for HZ and J rings) are made of highly wear-resistant polyamide. Extremely aggressive yarns are processed with glass-fibre-reinforced a Super Nylon  travellers. Twisting and winding carried out by the traveller must be performed with appropriate yarn tension. The ratio between spindle speed and the speed at which the yarn is supplied determines yarn twist. Any change of this ratio is easily compensated by the traveller without having an influence on twisting, winding and tensioning.

On flange rings, the gliding speed of travellers having a suitable shape can be as rapid as 130 ft/s (88 MPH) or 40 m/s (140 km/h); on DIA-DUR coated rings the speed can to some extent reach 147 ft/s (100 MPH) or 45 m/s (160 km/h) . Having an average life span of 200-300 operating hours the traveller covers a distance of more than 18.000 miles (30.000 km) – a tremendous task for a small part of wire weighing only a few milligrams. These standards can even be surpassed by nylon travellers used on HZ rings, if operating conditions are favourable.

These high traveller speeds involve pressures of up to 35 N/mm 2 . But even if high-quality materials with an optimum of hardness and resistance to wear are used, these standards can only be reached if

¥ in the case of flange rings, a film of lubricating fibres is produced continuously,

¥ in the case of HZ and J rings, a sufficient amount of lubricant is consistently

provided.

d 1 = spinning ring diameter

d 2 = fitting diameter

h 1 = ring height

h 2 = ring height above ring rail

b = flange width

flange 1 = 3.2 mm

flange 2 = 4.1 mm

Spindles operating without vibrations contribute a great deal to a smooth operation of the traveller. Non-concentric spindles and spindles not running smoothly cause constant changes in yarn tension , because the traveller cannot run around the ring without being shaken.

Vibration-free movements of ring rail and ring holder

The ring rail should move smoothly without jerking. Vibrations and hard jolts at the reversing points of the ring rail disturb the operation of the traveller. Repeated changes in yarn tension cause the traveller to flutter. This results in increasing yarn breaks and in accelerated wear of ring and traveller.

Correct ratio between bobbin diameter, bobbin length, ring diameter and spindle gauge

Ratio bobbin length (H) : Inside ring diameter (D)

Thread tension increases with growing bobbin length. In view of the limited thread tension, the total bobbin length should not exceed 5 times the ring diameter. Only when using balloon control rings or similar devices this value can be exceeded.

H : D = 5 : 1

Ratio bobbin diameter (d) : Inside ring diameter (D)

The bobbin diameter d is equivalent to the mean outer bobbin diameter d 1 + d 2

The following values are recommended:

for spinning: d : D = 0.48 – 0.5 (a = 29°-30°), (minimum value a = 26°)

for twisting d : D = 0.44 – 0.5 (a = 27°-30°), (minimum value a = 22°)

For light and heavy bobbins, the values for light bobbin types are decisive for calculating d : D. If the ratio d : D is reduced thread tension increases.

Correct surface smoothness, i.e. optimum peak-to-valley height and evenness of the ring track

The traveller contact surfaces must be smooth and even. Only then a smooth operation of the traveller will be possible. The contacted surfaces should be clean and preferably without traces of wear. In addition, they should be designed in such a way that they offer sufficient adherence for potential lubricants (e.g. fibres, oil, grease).

Once the sliding surfaces have lost their original quality, even the best ring traveller will not be able to run smoothly. For maintaining the surface of the running track in a good condition, it is very important – besides a certain degree of maintenance – to run the ring well in.

Balloon control rings and separators

The influence of balloon control rings is quite considerable, especially at long cops. A reduction of the yarn balloon is advantageous or may even be the prerequisite for optimum performance. If balloon control rings are mounted at correct distance (the yarn balloon should be restricted as long as possible during one lift of the ring rail) then a marked performance increase is possible. The balloon control rings are removed when sensitive materials are processed and sufficiently long separators are installed to avoid many yarn breaks and to prevent fibre fly from accumulating on the adjacent spindles.

Traveller cleaners

Traveller cleaners are an excellent method for removing all fibre fly that  accumulates on the outer part of C and El travellers. The traveller cleaner should have the right distance to the outside ring flange. A distance of about 0.5 mm between cleaner and traveller (in operating position) is recommended. When adjusting the distance between outside ring flange and cleaner, the size of the traveller should be taken into consideration.

Room climate

Constant temperature and air humidity have positive effects on the operation of the traveller. Changes of the room climate, such as raised air humidity will increase wear by friction. Besides the regular exchange of air, the purity of the air is of great importance for the traveller. Any dust (also dust from unsuitable floors) or other impurities may impair traveller operation and lead to more ring/traveller wear.

Flange width and ring height

Optimal operating results are reached when the ideal flange width is chosen for flange rings and the ideal ring height is obtained for self-lubricating HZ and J rings, dependent on yarn count range, yarn quality and traveller type.

Ring profile and traveller shape

Determining the most favourable ring and traveller shapes is a precondition for obtaining the optimal individual performance. If ring profile and traveller shape match well, the traveller will adopt a stable position in the ring. It should have sufficient tolerance of movement, so that any obstacles which may occur especially when the machine is started are avoided. A satisfactory large yarn clearance counteracts yarn breaks and yarn damage.

Running-in of rings

Normally the running-in procedure is decisive for the future positive/nega tive behaviour of the ring and the length of its service life. Every ring requires a certain degree of running-in time if it is to maintain high traveller speeds with as little ring and traveller wear as possible.  During running-in the use of steel travellers without surface treatment is recommended. After the termination of the running-in process, steel travellers with surface treatment or nylon as well as bronze travellers can be used.

The running-in process, beginning with the starting phase, consists of improving the initial running properties of the metallic running surface up to the  optimal values by smoothing and passivation(oxidation) as soon as possible. In this way, together with fibre lubrication, constant minimum mixed friction conditions and minimum thermal stressing can be attained for the ring traveller. A careful running-in process will improve the lifetime of the rings.

In order to keep the stress on the traveller as low as possible during the starting phase, it is advisable to always change the traveller in the upper third part of the cops. Further advantages are brought with the use of a traveller running-in program(reduction of the speed by about 10% for 10 to 20 minutes, only available on modern spinning machines).

Spindle speed should be reduced at least for the first 10 traveller changes. If final speed is higher than 32m/sec, reduce by atleast 20%.   If final speed is lower than 32m/sec, reduce by at least 10%.

New rings  should not be degreased, but only rubbed over with a dry cloth.

In general, the running in should be done with the same traveller type which is used for normal operation with the 10 to 20% less than normal speed. It is not advisable to do running with the same speed but with  1to 2 numbers lighter travellers than usual.

The first traveller change should be carried out after 15 min

The second traveller change should take place after 30 min

The third traveller change should be made after 1 to 1.5 hours.

The fourth traveller change should be made after the first doff.

Further traveller changes are to be made  according to the manufacturers recommendations

HAIRINESS: Following are the reasons for higher yarn hairiness due to  ring and travellers

  • Poorly cantered spindles, anti balloon rings and yarn guides lead to inconsistent yarn tension.
  • Rough surfaces roughen the yarn(due to damaged parts)
  • Open anti balloon ring
  • The clearance between ring and cop should not be too small. Traveller will cut the fibres protruding from the cop.
  • the fibres get electrostatically charged
  • poor twist propagation to the spinning triangle due to lighter travellers
  • Heavy friction of the balloon on the anti-balloon ring respectively impact on the balloon separator( due to lighter traveller)
  • Poor ring cantering
  • crooked  tubes
  • yarn getting roughened in narrow yarn passage in the traveller
  • scratched up yarn passages catch the yarn and roughen it (due to very high traveller running time)
  • friction of the yarn due to very high traveller weight
  • rough gliding surface of the ring ( due to worn out rings)
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