Modern rotor spinning system from raw material to yarn.

Interest in bast fibers such as flax or hemp has recently increased as environmental movements have gained great popularity. Bast fibers are very versatile and valuable for textile and non-textile applications. Rieter offers tailor-made, economical solutions for processing bast fibers in short staple fiber spinning.

Bast fiber is a type of plant fiber that can be collected from the inner bark of plants such as flax, hemp or ramie. Linen (made of flax) is one of the oldest textiles developed, dating back nearly 10 000 years.

With today’s increasing environmental awareness, textiles made of bast fibers are being rediscovered for everyday use as well as for luxury fabrics. Bast fibers are very sustainable. For the cultivation of flax, for example, very few pesticides are used and the water requirement is low (Fig. 1).

Fig. 1: Flowering flax field

Flax – a fiber with a difference
Especially in summer, the advantages of linen clothing are obvious. The fabric absorbs moisture from the air and exchanges it with the ambient air. Thus, the fabric has a cooling effect and is still dry. An additional benefit of this water absorption is the antistatic effect.
The linen fiber is very tear-resistant, so the fabric is hard-wearing and extremely durable. As a result, a linen garment can last for many years without damage.

Cottonization of bast fibers

Flax is used as an example to explain the spinning process for bast fibers. Flax is unique in the fact that different types of fibers can be extracted from the same raw material. Some of these fibers are processed via the traditional wet spinning process which,
however, is very cost intensive. Other extracted fibers are well suited to be shortened which is a precondition for manufacturing yarns economically using cotton spinning technologies. The process of reducing the flax fibers to short staple fibers and giving them the same characteristics as cotton is called “cottonization”. This works in a very similar way with other bast fibers, like for example hemp.

From flax tow to short fibers
To prepare the flax tow for short-staple fiber spinning, Rieter is cooperating with the German company Temafa. They are a global expert on blending and opening, recycling, air engineering and natural-fiber extraction. The so called Rieter-Temafa-concept prepares the flax tow in such a way that high-quality yarns can be produced from it using the rotor spinning process. The flax tow is progressively relieved of shives and dust – without a cutting process (Fig. 2). The raw material is refined in different opening and cleaning stages using machines from Temafa and Rieter. The cottonized material then passes into a baling press.

Fig. 2: Preparing the flax tow for the spinning mill

In this process, the fine cleaner UNIflex B 60 is responsible for giving the
fiber material the same length, fineness, purity and spinning characteristics as cotton

Fig. 3: The fine cleaner UNIflex B 60 gives the flax fiber material the
same length, purity and spinning characteristics as cotton

(Fig. 3). The desired fiber length is set by adjusting the nipping point. This also reduces the short-fiber content and thick, non-fibrillated fibers are removed. The variable opening intensity opens the fiber bundles into individual fibers. Intensive cleaning is performed at the same time by precisely setting the cleaning intensity. The quantity of waste is controlled via the VARIOset function. Using VARIOset and the integrated dedusting unit reduces trash accumulation at the card.

 

The card is adapted to suit the flax fibers using appropriate carding elements. The focus is on the fiber’s refinement, length and purity. The one-roller licker-in module is used to open the fibers gently. The mote knife on the licker-in module ensures that any remaining shives, unopened flax bundles and dust are removed efficiently. The efficient removal of these components and the short fibers is continued by the carding elements in the pre- and post-carding zones. The main carding zone facilitates the separation and removal of short fibers, contamination and fiber neps. The cottonized web sliver passes into a baling press. The bales are then ready for spinning preparation.

Optimum fiber and spinning preparation

The specific structure of the bast fibers calls for suitable preparation technology. The automatic bale opener UNIfloc A 12 copes well with the heterogeneous flax fibers. It opens material uniformly from the bale and prepares the optimum tuft size for the subsequent machines.

When it comes to mixing, the UNImix B 72 with its three-point mixing principle is the ideal machine. The large storage capacity provides for an appropriate dwell time for the material and thus ensures a trouble-free production flow. Depending on the yarn counts to be spun, an integrated autoleveler draw frame module after the card is sufficient for 100% flax.

For blends with cotton or man-made fibers the spinning preparation process is different and involves the blender UNIblend A 81. Depending on the quality requirements, carding is followed by one or two draw frame passages.

Decisive advantages with rotor spinning of bast fibers

Fig. 4: Yarns of 100% flax or blends can be produced
economically on a rotor spinning machine

Rotor spinning machines offer advantages for the spinning of bast fibers. The incoming draw frame sliver is opened into single fibers in the spinning box, whereby the fiber material undergoes further cleaning and particles can be removed. In the case of blended yarns, the blend is improved by the re-doubling in the rotor grove. With the spinning nozzles in rotor spinning the yarn characteristic can be additionally influenced.

Yarns made of flax blends or of 100% flax are manufactured efficiently on the Rieter rotor spinning machines R 70 fully.

Depending on raw-material quality, yarn counts of Ne 4 to Ne 10 can be spun from 100% flax. The finer the yarn count the higher the amount of fine fibers required. With blends yarn counts up to Ne 20 are possible.

Flax yarns produced on rotor spinning machines offer advantages in the end product compared to traditional ring spinning. The yarns have higher elongation, lower hairiness, a lower shive and dust content and significantly better downstream processing behavior. In addition, the conversion and equipment costs are low. Blended yarns are suitable for producing easy-care garments. The blends offer a wide scope for designing fashion items and thus enable a considerable expansion of the product range. The woven fabrics and end products offer good abrasion resistance and higher dye retention.