Structure of Ring Frame Yarn Packages

Structure of Ring Frame Yarn Packages                                                                   Build of cops

The cop as shown in Figure.1 comprises of three visually distinct parts – the barrel like base A, the cylindrical middle part W, and the conically convergent tip K. It is built up from bottom to top from many conical layers as shown in Figure.2, but constant conicity is achieved only after the formation of the base.

Figure 1 : The cop as a yarn package

Figure 2 : Building up the cop in layers

In the base portion itself, winding begins with an almost cylindrical layer on the cylindrical tube. The initial layers are conical in shape, thicker at the base and thinner at the tip. With the deposition of one layer on another of these conical layers, the conicity gradually increases.

Each layer comprises a main layer, also called as winding layer and a cross-layer, also called as binding layer which are shown in Figure 3. The main layer is formed during slow raising of the ring rail, individual coils being laid close to each other or on each other.

Figure 3 : Main layers and cross layers

Figure 4 : The winding mechanism

The main layers are the effective cop filling layers. The cross layers are made up of widely separated steeply downward-inclined coils of yarn and are formed during rapid lowering of the ring rail.

They form the separating layers between the main layers and prevent pulling down of several layers simultaneously, known as slough off when yarn is drawn off at high speed in back winding machines. In the absence of such separating layers, individual yarn layers would inevitably be pressed into each other and layer-wise draw-off of yarn would be impossible.

Raising and lowering of the ring rail is caused by the heart shaped cam and is transmitted by chains, belts, rollers, etc. to the ring rail. The long flat part of the cam surface forces the ring rail upward, slowly but with increasing speed. The short steep portion causes downward movement that is rapid but with decreasing speed.

The formation of the base

The heart-shaped cam and the delivery roller are coupled together by the drive gearing. Thus, the length of yarn delivered for each revolution of the cam is always the same. But, due to the presence of the cam N (Figure-4) between the tape and the pulley during the initial stages of cop building, the lift or the height of the layer is shorter to start with. The position and design of the cam N is selected such that the height of the layer increases gradually, till it is moved totally away from getting in contact with the tape. This is attained by winding of the tape on the Drum T for each double layer formation. Once this stage is reached, the heights of the further layers do not change till the end.

Figure 5 : The formation of the curvature at the cop base

Therefore, the volumes of the individual double layers need to be equal. Deposition of double layers on the tube begins with a small average layer diameter d1. The average diameter increases gradually with each newly deposited layer.

With constant layer volume and increasing height of the layers in the beginning, this can have only one result, namely a continual reduction of the layer width from b1 to b2 to b3, and so on till the height reaches fixed level.

Since the ring rail is also raised by a constant amount ‘h’ after each deposited layer, it follows that curve, rather than straight line, arises automatically in the base portion.

The formation of the conical layers

It has already been mentioned that the ring rail is not moved uniformly. Its speed increases during upward movement and falls during downward movement. At the tip of each layer it is higher than at the base of the layer that is the ring rail does not dwell as long at the tip as it does at the base – less material is wound, the layer is thinner at the tip.

If it is assumed by way of example that the ring rail is moving twice as fast at the top of its strokes as at the bottom of the stroke, the first layer would be half as thick at the top as at the bottom, i.e. b1/2instead b1.

Figure 6 : The formation of the conical layers

The first layer would correspond to a trapezium with the side b1 at the bottom and the side b1/2 at the top. This is followed by the deposition of the second layer. Owing to the lifting of the ring rail, the upper portion of the new layer would again be deposited on the bare tube.

The average diameter at the top would be the same as that of the first layer, and the volume, and hence the thickness, would also be the same, that is b1/2.

Each newly deposited layer will have this thickness of b1/2 at the top. At the bottom, however, the diameter is increasing continually, the layer thicknesses decline from b1 to b2 to b3 to b4… Accordingly, continually narrowing trapezia are produced.

At some stage, the trapezium will become a parallelogram, i.e. the lower side will be the same size as the upper side: both will be b1/2. Since all other winding conditions now remain the same, no further variation can now arise in the layering.

One conical layer will be laid upon the other until the cop if full, that is when the cylindrical portion of the cop is formed.

The gearing change wheel has little influence on this sequence of events. If too many teeth are inserted, the final condition of constant conical layers will be reached too soon and the cop will be too thin. It will be too thick if the ring rail is lifted too slowly.

The winding Process

The winding Principle

As in the case of the roving frame, two components with different speeds must be used in order to enable winding to occur. One assembly is the spindle, the other is the traveller representing the remnant of the flyer.

Also, the speed difference must be equal over time to the delivery length at the front cylinder. In the roving frame, each assembly has its own regulated drive. In the ring spinning frame this is true only for the spindle. The traveller is dragged by the spindle acting through the yarn.

The speed of the traveller required to give a predetermined speed difference arises through more or less strong braking of the traveller on the running surface of the ring. Influence can be exerted on this process by way of the mass of the traveller.

Variation in the speed of the traveller

In ring frame winding, diameter of winding changes continually with raising and lowering of the ring rail, since the winding layers are formed conically. The traveller must have different speeds at the base and the tip.

Assuming for example a spindle speed of 18,000 rpm, the layer diameters of 46mm at the base and 25mm at the tip, and a delivery of 25 m/min, the traveller speed at the base will be,

Variation in the Yarn Twist

The equation is generally used to calculate the number of turns in the yarn. As just established, this is not wholly accurate since the turns arise from the traveller and not from the spindle.

In the given example, 173 turns per minute are missing at the base of the winding on the cop (larger diameter), and 318 turns per minute at the tip (smaller diameter). However, these missing turns are a theoretical rather than a practical problem, for two reasons.

Firstly, the inaccuracy of measurement in estimation of yarn twist in instruments is greater than this twist variation. Secondly, the yarn finally receives its full twist in any case. This happens as soon as the yarn is drawn off the cop over the end, since each rotation of the yarn about the tube leads to insertion of an additional turn in the yarn. The compensation of the missing turns can then be explained easily.

If 318 turns per minute are missing at the top, and 25 m of the yarn to be wound up in this period, the result is

Drm = 318 /25 = 12.73 turns / m

During unwinding, each yarn wrap on the cop (one circumference) produces one additional turn. At the tip (cop diameter 25 mm):

Dra = 1000 mm/min / 25 mm = 12.73 turns /m.

That is, exactly the number of turns previously missing. Care must however be taken that cops are always unwound over end, even during twist tests.

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.