jamaponji 
       

Translation in Urdu

‘magic’ of the twisted/helical structure is such that as the external forces applied to the yarn increase, the inwards pressure each fiber exerts on the structure also increases and so the friction increases to resist the slippage.   Indeed normally in yarn failure, the fibers themselves actually break rather than any fiber slippage occurring. A twisted yarn is indeed a very clever structure.

Yarn Production

Tension is applied to the yarn. However the ‘desire’ of helical shape to decrease its diameter or thickness will cause the fiber to press inwards on the neighboring fibers, and just like pressing our hands together with the ruler, the pressure enables frictional forces to develop and hinder slippage of fibers relative to one another.   The

Spinning Yarns

The process of converting cotton fibres from ginned lint into a yarn involves a number of processes that aim to clean, remove short fibres, align fibres and ultimately spin the yarn and prepare it for delivery.  Depending on the setup and machinery present in a spinning mill and the desired quality of the yarn needed to be produced will determine which processes are undertaken

Opening, Blending and Cleaning

Opening, blending and cleaning of the fiber are the first processes in the spinning mill.   In the mill, bales are selected to satisfy the requirements of a particular end use and then laid down in a row (called a laydown) to be opened and blended through a range of machines (Figure 5.4). The opening and blending processes ensure a consistent and homogeneous blend of fibers.   Blended fiber is then passed through more machines to further open (loosen) the fiber tufts and to clean and remove plant-based contaminants such as leaf, sticks, boll parts, bark and seed fragments.   In high-end mills a machine is also used to identify and remove contaminants such as fabric, plastic, polypropylene and other non-plant material, which create serious quality issues if contained within the cotton to the final product.

Carding

Once the fiber has been opened, blended and cleaned it is fed to the carding machine, which is often referred to as the

‘Heart of the spinning mill’.  This is for good reason as the carding machine individualizes, aligns and further cleans the fibers, before condensing them into a single continuous strand of overlapping fibers called a ‘sliver’.  Importantly, a large proportion of short fibres and naps are also removed during carding. The quality of the sliver assembly from the card determines both the quality and processing efficiency of products further up the processing chain.

Carding

Once the fiber has been opened, blended and cleaned it is fed to the carding machine, which is often referred to as the

‘Heart of the spinning mill’.  This is for good reason as the carding machine individualizes, aligns and further cleans the fibers, before condensing them into a single continuous strand of overlapping fibers called a ‘sliver’.  Importantly, a large proportion of short fibres and naps are also removed during carding. The quality of the sliver assembly from the card determines both the quality and processing efficiency of products further up the processing chain.

Drawing

Drawing is the process where the fibers are blended, straightened and the number of fibers in the sliver reduced in order to achieve the desired linear density in the spinning process. The drawing process also improves the uniformity or evenness of the sliver. The number of drawing passages utilized depends on the spinning system used and the end products

Combing

Combing is the process that removes the final proportion of short fiber, naps and other impurities such as vegetable matter and seed- coat fragments in cotton that has already been carded. The waste material, which is predominantly made up of short fiber, is referred to as noil or comber waste and commonly makes up between 15 and 20% by weight of the fiber into the comber.   Combed yarns are superior in quality when compared to carded yarns as they are generally finer, stronger, smoother and more uniform due to the removal of short fibers and the alignment of fibers (Figure 5.6). Combed yarns are however more expensive than carded yarns (approximately 10%) as combing involves additional processing stages and produces more waste.

Roving

In preparation for ring spinning, the sliver needs to be condensed into a finer strand known as a roving before it can be spun into a yarn. The roving frame draws out the sliver to a thickness of a few millimetres and inserts a small amount of twist to keep the fibres together. The drafted twisted strand is wound onto a bobbin which is then transported to the ring frame and used as the feed package for spinning yarn.

Figure 5.6: Combed yarns are generally finer, stronger, smoother and more uniform, due to the removal of short fibres and the alignment of fibres. (Photos: CSIRO).

Winding

The winding process is a necessity in the case of ring spun yarn in order to transfer the yarn from small bobbins (Figure 5.8), which hold short lengths of yarn, to larger packages (Figure 5.9) that hold longer lengths of yarn suitable for subsequent processes such as warping, weaving, yarn dyeing, and knitting.  Yarn faults or defects such as slubs, thin, thick and weak places as well as contaminants can be removed during winding by special fault clearing devices. The yarn can also be lubricated for knitting during winding.

Figure 5.7: Roving bobbins on the creel of a ring spinning machine.

The formation of roving reduces the sliver into a finer strand with the addition of twist. (Photo:  CSIRO).

Spinning

There are three main spinning systems used commercially to produce cotton and other short staple yarns, i.e. yarns produced from fibers typically with lengths up to 50 mm. 1. Ring spinning 2. Rotor spinning (also known as open-end spinning) 3. Air-jet spinning (including Vortex spinning) Ring spinning (Figure 5.8) was perfected as a process by the end of the 19th century. There are currently 213 million ring spindles installed world-wide that account for about 60% of all short-staple yarn production. Its prominence reflects its versatility in terms of productivity, the range of yarn counts that can be spun on it and the fiber types that can be used. Ring spun yarns are also superior in terms of yarn strength and character in terms of fabric handle and comfort. The majority of Australian cotton is spun into yarn using this system. Rotor spinning was introduced as a new short-staple spinning system in the mid 1960’s and achieved its greatest uptake during the 1980s when production speed and versatility were improved. Today, there are over 9 million rotor positions installed world-wide which account for about 30% of all short-staple yarn production. Air-jet spinning was developed in the 1960s but was not successful commercially until the early 1980’s when it was introduced by the Murata Company of Japan. Initially suited to longer staple polyester rich fiber blends, air-jet spun yarn could be delivered at speeds significantly higher than that of ring spinning. Later versions of air-jet spinning were adapted to 100% cotton fibers, e.g. Vortex spinning, and with delivery speed increased by nearly a factor of two over the original air-jet machines. There are currently around 500,000 air-jet spinning positions installed world-wide. The advantages of rotor and air-jet spinning over ring spinning are chiefly based around their superior productivity in the delivery of medium to coarse count yarns. Furthermore, both systems use drawn sliver as their feed stock and both are able build (wind) a yarn package that can be used directly by fabric manufacturers. Hence both systems avoid two processes required in ring spinning, i.e. the roving and winding processes.