Rieter

The idea of producing yarn using the rotor spinning process is far from new:

• Patent applications for this method were filed allready in 1937 (basic rotor patent by Berthelsen).
• However, the first usable design was not proposed until 1951 by J. Meimberg at the Spinnbau company in Bremen, but further development of the machine was discontinued because performance proved unsatisfactory.
• The idea was taken up again in Czechoslovakia during the 1960s, and the first machine really suitable for industrial application was shown in 1965 at the Brno fair. This was followed in 1967 by the presentation of the BD 200 machine at an exhibition parallel to the ITMA of that year. This was also when the rotor spinning process came into industrial use in spinning mills.
• In the early 1970s Rieter, Schubert&Salzer and Platt formed a consortium to develop the rotor spinning process, and this resulted in the appearance at the 1971 ITMA of a number of prototypes at various stages of development.

The years that followed were characterized by intensive development effort aimed at exploiting both the technological and the economic potential of the rotor spinning system.
Systematic work was pursued on:

• substantially expanding the count range of rotor-spun yarn, paying particular attention to yarn quality;
• optimizing the wearing properties of rotor-spun yarns, for example by improving their hand in end products;
• improving the yarns‘ physical textile properties in order to take account of the often rapid increases in perfor-mance of subsequent process stages.

Continuing research and further development have resulted in improvements in spinning elements and conditions, so that it is now hardly possible to distinguish rotor-spun yarn from  ring-spun yarn.
The rotor spinning machine itself is no longer just a spinning machine in the traditional sense, but a highly productive, computerized and complex system for converting sliver into yarn.

The improvement in economics has been even more remarkable than the technological advances. For example, since the introduction of rotor spinning in the 1960s rotor speeds have increased from the original level of around 30 000 rpm to that of 160 000 rpm in practical use today (Fig. 1). Nowadays (in 2005) rotor speeds of up to 170 000 rpm are technically possible without any difficulty. A rotor spinning unit produces five to ten times as much as a ring spinning spindle. In countries with high wage levels, rotor spinning is more economical than ring spinning for yarn counts up to Ne 60.

With more than 8 million rotor spinning positions installed worldwide (Fig. 2), some 20% of staple fiber yarns have already been spun consistently for some years. In some countries (e.g. USA, Germany) the proportion of rotor-spun yarns is already around 50% of total yarn volume. Developments in fashion and textile applications, as well as developments in spinning machinery manufacturing, continue to expand and also reposition the range of applications of rotor-spun yarns. Air-jet spun yarns have been able to secure a certain market share to date mainly in the USA. Despite intensive development effort, certain limitations in the processing of pure cotton remain a barrier to their wider use. In recent years the share of automated rotor spinning machines world-wide is about 35%. This figure is influenced by the huge number of not automared machines installed in China. In other parts of the world the share is much higher. Fig. 3 is showing as an example the situation in Turkey, a big investor in rotor spinning during the last decade. Shortly after introduction of automated rotor spinning, in Turkey within a few years the share increased over 80%. Nowadays systems are also available for automatic can transport between the drawframe and the rotor spinning machine as well as systems for package transport from the rotor spinning machine to the material store or directly to downstream processing. This fact has contributed substantially to the improvement in the economics of rotor spinning.

The rotor spinning process enables fibers up to 60 mm (2.25˝) long to be processed and thus covers the classical short staple cotton range. The machines developed by various manufacturers (Schubert & Salzer, Duesberg Busson) for processing longer fibers with larger rotors were, however, unable to establish themselves on the market. Fig. 4 shows the distribution of yarn counts of rotor-spun yarns in the short staple range. The main emphasis of rotor-spun yarns is in the count range between Ne 6 and Ne 40, but covers the overall range from Ne 3 to Ne 60, albeit with a small proportion of yarn volume.

Cotton is the predominant fiber for spinning on rotor spinning machines, with approx. 55% of total yarn volume, but almost all short staple spinning materials can be spun pure or in blends. Besides cotton, the processing of polyester fibers (PES) has developed into a major field of application for rotor-spun yarns. The growth in world-wide fiber consumption of about 3% p.a. will increasingly be met mainly by polyester fibers.  

Viscose, Modal, polyacrylic and their blends with each other and with cotton also represent a fixed proportion of yarn volume. However, the processing of these and a whole series of other natural and man-made fibers is usually much more subject to the dictates of fashion, so that their shares fluctuate widely, both regionally and seasonally. A further economic aspect of interest in some applications arises from the possibility of spinning mill-waste fibers (secondary materials) on the rotor spinning machine. It was not previously possible to use these materials.

Since this spinning system was introduced, rotor-spun yarns have established themselves firmly in fields of application for woven and knitted fabrics. In many cases the processing of rotor-spun yarns into the end product actually resulted in advantages compared with ring-spun yarns, which led to a higher-quality end product. First of all, rotor-spun yarns could be used successfully where the specific properties of the rotor-spun yarns corresponded especially closely to the requirements of the end products. Fig. 5 shows the main end products in which rotor-spun yarns are used, subdivided according to yarn count. This chart shows that mainly denim weaves, trouser fabrics, sportswear and leisurewear, shirts/blouses and underwear are produced in the clothing sector, while terry products and upholstery fabrics are the main applications for rotor-spun yarns in the home textiles sector. Also worth mentioning as end products using rotorspun yarns are socks and sweaters in the clothing sector, sheets and upholstery fabrics in the home textile sector, as well as technical textiles, for example as textile backing for emery cloth or for awnings and roller sunblinds.