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EliTwist - A compact yarn for superior demands

Dr Norbert Brunk

The elimination of the spinning triangle by incorporating a condensing zone after the drafting system has opened up new interesting prospects to ring spinning. While the first attempts of the new compacting methods were restricted in practice to fine weaving yarns of combed cotton, there is now hardly any important yarn sector which has not been infiltrated by compact yarns. The EliTe process with its unsurpassed flexibility has played an essential role in this development.

The purpose of this article is to present another variant developed for this process, which allows the very efficient production of two-ply compact yarn for superior demands directly on the ring spinning frame. EliTwist even improves the utilization of fibre substance further. This fact and the attractive structure of such yarns simultaneously offer new aspects for the production of core yarns and special-purpose yarns.

Production of two-ply yarn on the ring spinning frame

In order to spin two-ply yarn directly on the ring spinning frame, two fibre strands drafted parallel at a relatively large distance must be combined in a twisting point after passing the front roller pair of the drafting system. The speciality of such yarns is that the direction of twist in both legs is the same as in the resulting two-ply yarn. Well-known processes are SiroSPUN and DUOSPUN. From the twisting point, the twist spreads out in both yarn legs, each of which forms a long spinning triangle at the front roller pair of the drafting system due to the high yarn tension on the one hand and to the low twist on the other hand.
The dimension of the twisting triangle depends on the distance of the twisting point Z from the nip point of the front roller pair and the distance A of the two emerging fibre strands. Point Z is the closer to the nip point, the lower is the spinning tension and the closer is the distance A of the two fibre strands. It is obvious that only a very small twisting triangle allows a high spinning stability.

The number of turns per metre produced in the two yarn legs up to the nip point is about 20% lower than the twist of the yarn after the twisting point. In other words, the twist coefficient of the two yarn legs is only about half as high as in the final two-ply yarn. In this respect, detailed theoretical and experimental investigation has been made.

Fibre loss at the drafting system exit is very high due to the very low twist in the two yarn legs. There is also a risk that if one strand breaks, only one component runs onto the bobbin. Even with yarn detectors at the twisting triangle, conventional methods of producing two-fold like yarn are therefore not able to achieve the high spindle speeds in short-staple spinning usual today.

Principle of the EliTwist method

The patented EliTwist process allows to reduce the twisting triangle to a degree that the restrictions mentioned above are eliminated. This is realized by the two fibre strands first passing a condensing zone. During condensing, both components get closer and reach a minimum distance by means of two suction slots in the condensing zone in a V-shaped arrangement.

Owing to condensing, the two components -after leaving the condensing zone - do not form spinning triangles. Consequently, no fibres are sticking out, spreading up to the other yarn component or not being embedded in the yarn. The twist, running into the two yarn legs from the twisting point, need not overcome any resistance and easily reaches the clamping line. As a result, the two fibre strands can be led very closely and the twisting point has a very small distance from the clamping line of the front roller pair. In short-staple spinning, this distance is only between 4 and 5 mm, depending on the spinning tension. Both Siro and EliTwist yarns have the same count and analogous yarn and spinning parameters. The substantial fibre fly of the conventional Siro yarn can clearly be seen, whereas in EliTwist all fibres are safely embedded. This difference is also visible, when fibre loss at the suction tubes is measured.

In reality, fibre loss in conventional spin-twisting is even much higher, if we take into account the fibre dust in the ambient air. The EliTwist process produces yarn with a novel structure combining all advantages of condensing and doubling. Yarn surface and appearance of EliTwist are comparable to a single compact yarn. If possible at all, its surface is even more clearly structured and closed. However, as the twist in the two yarn legs is identical, EliTwist has more snarling tendency.

For industrial practice an essential advantage of EliTwist over all conventional spin-twisting methods is that no detection devices are required for the twisting triangle. In case of a short term material interruption at one of the two components, the broken component will piece up automatically due to the prevailing geometrical conditions.

A refined variant of this method offers the possibility of feeding a filament in the centre of the twisting triangle, i.e.directly at the twisting point. This allows a perfect covering of the yarn core. But it is also possible to feed additional threads parallel to one or both yarn legs.

Spinning results

The running properties are excellent. There is no difference or even restriction in comparison with EliTe Single Yarn as regards possible traveller speeds. Two test series were realized with long-staple cotton, comparing EliTwist with twisted yarns and with singles yarns.

Test Series A: Comparison of

• EliTwist Ne 60/2 and Ne 100/2 with 2-for-1 twisted ring yarn Ne 60/2 and Ne 100/2
• 2-for-1 twisted EliTe Yarn Ne 60/2 and Ne 100/2
• Siro Ne 60/2 and Ne 100/2
• EliTwist Ne 60/2 and ring yarn Ne 30 and EliTe Yarn Ne 30

The most important results are summarized here:

The twist coefficient of all yarn types was in the range ae = 4.6 to 3.3. The clear superiority of EliTwist in all important yarn parameters is confirmed. When comparing the twisted yarns, it soon became obvious that Siro-spun yarns cannot be produced any more with a twist coefficient —— lower than 3.95. The spinning of one yarn Ne 100/2 with —— = 4.3 even had to be discontinued. In this respect, EliTwist properties are similar to conventionally twisted ring spun or EliTe yarn. The extremely good utilization of fibre substance of the EliTwist process offers clear advantages in yarn strength all through the tested yarn twist range, and they are even clearer the finer the yarn count.

This advantage is reflected by all yarn strength parameters like work capacity, elongation, minimum breaking load and breaking load variation. When comparing hairiness, EliTwist generally has better values.

Since the appearance of EliTwist resembles to a single compact yarn, test series B compared EliTwist with some corresponding singles yarns. In this comparison, the EliTwist advantages in all yarn parameters are even more striking. In addition to improved yarn strength and hairiness parameters, the doubling effect has an additional positive effect. This is particularly visible in improved USTER irregularity and imperfection values, which should not be neglected.

Essential characteristics of EliTwist and economic considerations

The utilization of fibre substance achievable with EliTwist is unrivalled by any other spinning process presently offered.

Outstanding characteristics are:

• Very smooth structure, closed yarn surface, circular yarn cross-section
• High regularity
• Considerably reduced fibre loss at the drafting system front roller pair
• Extremely low hairiness, especially of long fibres (S3, > 3mm)
• High breaking load and elongation, maximum work capacity
• Very high yarn slippage and abrasion resistance
• Very low pilling tendency
• Low twist coefficients
• Unrestricted traveller speeds
• Manufacturing costs reduced up to about 50% compared with conventional twisted yarn
• Saving or even elimination of sizing agent in most applications
• No restrictions in splicing

Compared with the standard EliTe spinning process, expenditure for top roller cot buffing is half as much with EliTwist, because the yarn quantity per buffing cycle is doubled.

Due to its special properties, EliTwist is particularly suitable for being processed on highly productive air-jet weaving machines. As regards two-ply core yarn, production can also be considerably increased and the filament percentage be reduced. The filament fed in the centre of the twisting triangle is perfectly covered by the two yarn legs. Undesired “naked points” are avoided, and consequently higher spindle speeds are possible.

Summary and prospects

EliTwist has succeeded in further improving the excellent textile and physical characteristics of compact yarn already known. The very economic application of this spinning process on existing ring spinning frames with the EliTe Compact Set underlines once again the high flexibility of the EliTe process.

Furthermore, EliTwist offers the possibility of producing numerous other interesting yarn designs and special-purpose yarns for most different applications. By means of the special SUESSEN Core Yarn Device EliCore, filaments can be fed in the centre of the twisting triangle or parallel to one or both yarn legs to create interesting effects. The technological potential is immense.

Orders for EliTe CompactSet to produce short and long staple EliTwist can be sent to Suessen’s sales department as from October 2003.

(The author is technical director ring spinning, SUESSEN)