A new era in spinning technology.
In spite of significant developments and refinements of the system, following the commercial acceptance of the Open-end spinning, many new spinning systems were developed, some of which have gained popularity.
Open-end spinning machine, specifically manufactured for short staple fibers, was considered a good rival because of much higher production and better evenness of the yarn. However, further development of this system showed that the best performance of the OE system is limited to the coarse categories of yarn.
On the other hand, Ring Spinning Systems have been refined during the last 30 years, the ultimate objectives of spinning dialectologists are focussed on higher production speed, combined with adequate quality. The quest for higher yarn quality has become in line with the much more exacting requirements and the performance criteria of the knitter, weaver etc.
Structure of a Model of Yarn Formation
Qualitative assessment of model yarn can be deduced by the mechanical behaviour of fibers when bundled into yarn. A textile fiber is mechanical body of extreme length and flexibility; even the cellulosic fibers with a breaking elongation lower than 10%.
The formation of yarn should fulfill following conditions:
* The fibers must overlap in staggered way so that they join as assembly.
* The fibers must stick together so that tensional force is transmitted from fiber to fiber and this way distributed within the bundle.
* The number of individual fibers in the section must be sufficient so that discontinuity in force distribution due tot he fiber ends does not significantly weaken the yarn.
The figure shows self-locking arrangements of the fibers within a yarn, as the tension is imposed on the yarn and the sticking force of fibers at the periphery increases.
The self locking effect depends upon the surface properties of fibers, providing the sticking and path of the fibers within the body of yarn, to facilitate compressing force at least part of the fibers must wrap around the yarn.
A simple way to achieve this to introduce an even twist with constant pitch throughout the yarn (as in Ring frame). The same effect can be produced by a core sheath arrangement with the large section with low twist in the center, compressed by wrapper fibers to the periphery (in case of open-end yarn). It is also possible to produce this with a mixture of fibers that are twisted in opposite direction This is called false twist spinning process i.e. Air jet Spinning.
Consider the Process of Yarn Formation
Ring spinning is a three-step process of drafting, twisting and winding. As the roving strand passes through the draft zone of the spinning frame, from the back rolls to the front roll, the roving strand is drafted into fibre stand that has the linear density of the yarn. The yarn emerging from the front roller nip is in the shape of a flat ribbon, that is twisted, forms a triangle generally expressed as 'spinning triangle'. The traveller, ring and spindle are responsible for twisting and formation of yarn.
Yarn structure which was examined microscopically revealed that all the fibers do not contribute in the formation of yarn (i.e. not bounded fully in the yarn structure) particularly longer fibers, causing hairiness, also the short fibers which are not part of the body contribute to the 'fly lint' waste.
Limitations in Present Systems of Spinning
The limitations during formation of yarn in order to get appropriate quality product at desired speed of production lead the technologist and researcher to develop the new spinning techniques and modify the present systems of spinning.
When we look at ring spinning the major limitation is metal to metal rubbing contact between ring and traveller, which restricts the spindle speed. Secondly, the necessity of bobbin rotation for twist insertion restricts the output rate. Another important limitation of the ring spinning frame is the formation of spinning triangle by the ribbon of drafted fibres emerging from the nip of the front drafting rollers as shown in the above figure. Also it is further reported that fibers, being twisted into the yarn due to formation of spinning triangle, are under unequal initial tension that may cause a break in yarn either individually or in small groups and not simultaneously.
The open-end rotor spinning system overcomes the limitations of the ring spinning system in respect of output rate. However, the open-end rotor spinning systems also subject to limitations e.g. the disorientation of the fibers, deposited in the rotor groove, the twist loss due to rotation of the free end results in development of low spinning tension which require the minimum number of fibers at the yarn formation point. This drawback limits the spinning limit in open-end rotor spinning to coarser yarn counts as compared to that in ring spinning.
New Spinning Systems
In 70's many spinning system were introduced which lead to latest technique in the formation of yarn. As a matter of fact the productive capacity of system was about 10/ 11 times higher than that of conventional machines, the quality of the product has also improved and a wide range for further developments exist.
Arrangement of fibers in the cross-section of an Open-end yarn structure shows an irregular picture irrespective that there are not much loose fibers, also wrapper fibers are twisted in wrap direction. However, these odd arrangements of fibers do not show an adverse impact on the eventless of yarn.
In the Air Vortex Spinning the fiber arrangements are much improved defining more close spinning and real twisted yarn Murata Vortex Spinner is an improved shape of Murata Air-jet spinning machine and is claimed that it is capable of spinning 100% carded cotton at high speeds. MVS frame imparts real twist in the fibers. as opposed to the 'false twist' principle, used by Murata's jet spinning. Instead of using a pair of opposing air blasts from air nozzles to impart structural integrity to the yarn mass against as previously used by MJS, a unique guide called a spindle, a needle holder and a single air nozzle is used. The MVS utilizes a four-line roller/apron drafting system similar to that used in MJS technology.
One more intriguing feature of the MVS machine is that relatively high percentage of short fibers less than 12.5mm in length is removed in the spinning zone thus a small scale of combing is achieved at this stage converting the resultant yarn into a more valuable-added product.
Compact Spinning is the modified version of ring spinning in which the process of twisting is improved by minimizing or eliminating the spinning triangle. After the draft zone the ribbon is condensed into a strand before twist insertion. Airflow is used to condense the fibre ribbon. The compacted fibre strand is twisted into yarn with little or no spinning triangle, resulting in essentially ideal yarn formation conditions.
Summary Ring Spinning System, compared to rotor and air-jet spinning, is capable of giving much stronger yarn and a fabric of much better hand but rotor and air-jet spinning because of faster way of spinning have gained increasing importance. Still rigorous research and efforts are being made and spinders are hoping to produce new systems that deliver improved quality at higher speeds.
Recently textile manufacture has developed new technologies for the spinning of short-staple yarns of higher quality at higher speeds.
Besides, to make higher-quality products at lower cost textile technologist are putting more emphasis on value-added products and product differentiation.
Two major spinning technologies have been introduced in the recent years: Murata vortex spinning and Compact Spinning. The characteristics of the yarns spun on these two systems are much improved but still area could be broadened towards yarn compatibility to value added fabric formation.
Newly evolved systems i.e. compact yarn spinning system unlike open-end spinning is not diverted form of ring spinning system. These systems are based on ring spinning machine; improvement is made by introducing condensing zone, fitted immediately after the delivery nip of the conventional drafting unit, eliminate the spinning triangle and its adverse effects on yarn characteristics.