Spinning Total draft limitation

DRAFTING:
The break draft should depend upon the following,

• fibre type
• fibre length
• roving T.M
• main draft

Some examples are given below,

Normally 1.13 to 1.18 break draft is used for

• 100%cotton , Poly/cotton blend, 100% synthetic
• roving T.M. upto 1.3 for cotton and .80 for Poly/cotton blend, 0.5 to0.7 for synthetic
• ring frame back zone setting of 60mm for fibres upto 44mm and 70mm for fibres upto 51mm
• total draft in ringframe upto 35

1.24 to 1.4 break draft is used for

• 100%cottton, poly/cotton blend, 100%synthetic fibre
• strongly twisted roving i.e higher than the above mentioned T.M.s
• total draft from 33 to 45
• back zone setting(R.F) around 52mm for fibres upto 44mm and 60mm for fibres upto 51mm-

If the total draft is more than 45 or the fibre length is more than 51 and the fibre is a fine
fibre(i.e more number of fibres in the cross section)with a very high interfibre friction, break draft
more than 1.4 is used.

Please note that for most of the application, lower break draft with wider setting is used. With higher break
drafts, roller setting becomes very critical. Higher the break draft, higher the chances for thin places
i.e. H1 classimat faults.

Higher draft with improper back zone setting will lead to thin places and hence more end breaks
even though more twist flows into the thin yarn.

MAIN DRAFT ZONE:

Mostly for cotton fibres, short cradles are used in the top arm. Front zone setting is around 42.5 mm to 44 mm depending upon the type of drafting system. The distance between the front top roller and top apron should be around 0.5to 0.7mm when correct size top roller is used. This is normally taken care of by the machinery manufcturer. If a technician changes this setting, this will surely result in more imperfections, especially with karded count the impact will be more. Therefore when processing cotton fibres, care should be taken that the front zone setting should be according to the machinery manufacturers recommendation.

For synthetic fibres upto 44 mm , it is better to use short cradles. Even with 42.5 mm bottom roller
setting, 44 mm fibre works well without any problem. Because, the clamping distance will be around 52 mm or 50 mm. The imperfections and U% achieved with short cradle is better than with medium cradle(52mm setting).

Instead of using medium cradle for processing 44mm synthetic fibre, it is always better to use
short cradle with 1 or 2mm wider setting than the recommended to avoid bottom apron damages.
If a mill has got a problem of bottom roller lapping, the apron damages are extremely high, it is better to use short cradle for 44 mm fibre and widen the setting by 1 or 2mm. This will minimise the complaints and improve the basic yarn quality also.

Please note that if the bottom apron breakages are high, then the mill is working with a lot of
bottom apron which is defective and with a lot of top roller which is defective. Both the defective
parts produces a defective yarn, which can not rejected by older version of yarn clearers, and improperly set new type of clearers. This yarn will very badly affect the fabric appearance.

Therefore it is always advisable to use a wider front zone setting upto 2mm , if the mill faces a problem of excessive bottom roller lappings. Please note that the defective bottom apron and top roll will not only affect the quality, but also the production, because the defective bottom apron and top roll make the  spindle a sick spindle which will be prone to end breaks. A wider front zone setting will increase the imperfection and uster, but there will not be major deviations of yarn quality.
Nose bar height setting is very important. Depending upon the design, it is 0.7mm or .9 mm. Variation in heigh setting will affect the yarn quality and the apron movement. The distance between nose bar  and middle bottom roller should be less than apron thick ness or more than 3 mm to avoid apron buckling if there is any diturbance in apron movement.

Spinning Geometry

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 on the spinning opeartion 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 front 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 roller

· 
overhang.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.  

Spinning Suction pipe

·  ·  End break suction system has a variety of functions.

• It removes fibres delivered by the drafting arrangement after an end break and thus prevents mulitple
  end breaks on neighbouring spindles.
• It enables better environmental control, since a large part of the return air-flow of the aircondition
  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
  airconditioning 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 will 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 the power needed for an air-flow of 6 cubic meter/ hour, because of the significantly higher vacuum level developed at the fan.

Spinning Rings & Traveller

·  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
• heigh 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 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.

·  ·  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 hte 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 hte 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 winding 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
than 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.

Spinning Spindles

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.