Ring spinning produces yarn in a package form called cops.
Since cops from ringframes are not suitable for further processing, the winding process serves to achieve additional objectives made necessary by the requirements of the subsequent processing stages.
Following are the tasks of winding process
- Extraction of all disturbing yarn faults such as the short, long thick ,long thin, spinners doubles, etc
- Manufacture of cones having good drawing - off properties and with as long a length of yarn as possible
- paraffin waxing of the yarn during the winding process
- introduction into the yarn of a minimum number of knots
- achievement of a high machine efficiency i.e high produciton level
The winding process therefore has the basic function of obtaining a larger package from several small ring bobbins. This conversion process provides one with the possibility of cutting out unwanted and problematic objectionable faults. The process of removing such objectionable faults is called as yarn ‘ clearing’ .
Practical experience has proven that winding alters the yarn structure.This phenomenon does not affect yarn evenness, but affect the following yarn properties
- thick places
- thin places
- standard deviation of hairiness
If winding tension is selected properly, the following tensile properties are not affected
- work- to- break
But excessive tension in winding will deteriarate the above said tensile properties.
Changes in the yarn surface structure due to winding cannot be avoided. Since the yarn is accelerated from zero speed to 1200 or 1350 meters per min in a few milli seconds while being pulled off the bobbin, dragged across several deflection bars and eyelets, forced into a traverse motion at speed that make it invisible, and finally rolled up into a firm construction called package or cone.
The factors that affect the yarn structure during winding include the frictional properties of the yarn itself, the bobbin geometry and the bobbin unwinding behaviour, winding speed, winding geometry as well as the number and design of the yarn / machine contact points.
However, the bobbin unwinding behaviour is the major limiting factor for winding speed which also is the main reason for the above said changes in yarn structure. Most of the damage occurs at the moment when the end is detached and removed from the tight assembly of yarn layers on the bobbin and dragged along the tube at very high speeds.
High speed automatic winders have frequently been blamed for causing higher nep counts but this is not a correct statement. typical nep-type imperfections, i.e shor mass defects, can be identified as tight fibre entanglements, clumps of immature or dead cotton fibres, or seed coat fragments. Naturally, such defects are not produced by the winding machine. The increase in nep counts after winding is related to the formation of loose fiber accumulations. These fibre accumulations represent a true mass defect, yet their apperance in the yarn and in the final fabric is clearly different from that of typical fibre entanglements or seed coat fragments.
Some very fine and delicate yarns will result in marginal structural changes after winding. But this is not the result of mechancial stress like in winding but a natural reaction caused by the reversal of the yarn running direction. irectional influences are omnipresent, they become apparent in all subsequent processing stages.
In earlier days, knotters were used in winding machine to join two ends after cutting the fault and after chaning the ringframe bobbin . But now , splicing of the yarn ends has become quite popular and has gradually replaced knotting by way of its better appearance while at the same time retaining sufficient strength.
Waxing is the process which is almost exclusively used in all automatic and manual winding machines for yarns which are meant for knitting. This helps to reduce the coefficient of friction of yarns created during knitting process.
Extensive tests have shown that the coefficient of friction of waxed yarn is not constant, but depends on the amount of wax on the yarn. It is proved that both too little and too much wax cause increase in coefficient of friction and thus detrioration in running efficiency on the knitting machine.
The recommended wax pick up for different material are given below:
- cotton and its blends - wax take-up of 1.0 to 2.0 grams per kg of yarn
- synthetics - wax take-up of 0.5 to 1.5 gram per kg of yarn
- wool and its blends - wax takep-up of 2.0 to 3.0 grams per kg
From the technical point of view, it is interesting to note that very small amounts of wax are already sufficient to give an optimal reduction in friction coefficient. If for example, we take 1 kg of 50s metric yarn, there are 50000 meters of yarn. It is quite sufficient to apply 1 gm of wax on this length of yarn, to obtain optimum reduction in friction.
As the original coefficients of friction of non-waxed yarns are so varied, due to different raw materials and blends, dye-stuffs, additives, twist etc, so also are the values obtained with waxed yarns. The table shows several typical examples of coefficient of friction for unwaxed and waxed yarns.
Absolute comments about coefficients of friction are not possible. It depends on several factors, such as type of material, count, twist, dyeing process, yarn moisture content, atmospheric conditions etc.
|KIND OF YARN COUNT (METRIC)||friction coefficient of unwaxed yarn||friction coefficient of waxed yarn||percentage of friction coefficient decrease %|
|cotton , 50s combed||0.285||0.145||49|
|cotton, 40 bleachd cbd||0.30||0.14||53|
|wool, 36s natural||0.33||0.155||53|
|polyester 40s white||0.42||0.21||50|
Even with efficient waxing , the results in knitting can still be adversely affected, if the package of waxed yarn is subsequently handled. A typical example is conditioning of waxed packages. The conditioning causes an increase in friction coefficient, and thus a deterioration in running properties. Therefore one should not condition waxed packages. An increase in moisture content causes an increase in friction coefficient.
If too-damp bobbins are creeled at the winding machine, poor waxing results, because yarns with high moisture content take up hardly any wax. If bobbins have to be conditioned or steamed, the yarn should be allowed to stand for atleast 24 hours, so that it can return to its normal condition before winding.
A further problem can arise during steaming, or any other treatment involving the application of heat to a waxed package.
Low yarn tension will affect the wax pickup
Dimensions and form of wax rollers will affect the wax uniformity
As it is clear and is important that, if the waxed particles are to carry out their function, they must remain on the surface of the yarn. When the yarn is subjected to heat however, the wax melts and penetrates to the inside of the yarn body: it can then no longer work effectively.
When choosing the wax, it is essential to consider the type of yarn and fibre, the temperature in the production area, etc., and the characteristics indicated by the wax manufacturer
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