DREF Spinning

Introduction:

Friction (DREF) spinning system is an Open-end and or Core sheath type of spinning system. Along with the frictional forces in the spinning zone the yarn formation takes place. The DREF spinning system is used to produce yarns with high delivery rate(about 300mpm). Still it has to gain its importance with the growth along with technical textiles in India. Amongst the spinning systems, DREF provides a good platform for production of core spun yarns due its spinning principle.It offers less spinning tension to the core and core will be positioned exactly at the centre of the yarn.
Development of DREF core-spun yarns unveils a path for new products including high performance textiles, sewing threads and in the apparels due to its exceptional strength, outstanding abrasion resistance, consistence performance in sewing operation, adequate elasticity for the stretch requirements, excellent resistance to perspiration, ideal wash  and wear performance and permanent press.

Principle of Friction (DREF) spinning Systems:

The friction spinning system consists of opening & individualization of fibres from slivers, reassembling of individualized fibres, twisting and winding of yarn. The figure 1 describes the DREF spinning principle where the opened fibres made roll with an aid of a mechanical roller for reassembling and twisting. Due to separate yarn winding and method of twist insertion, it has capability to go for high production rate.

• DREF 1:

DREF-1 friction spinning system was developed in 1973 by Dr.Fehrer.A.G. of Austria.The schematic diagram of DREF 1 spinner is shown in the figure 2.The fibres were opened with an opening roller and allowed to fall on a single perforated cylindrical drum slot ,which has negative pressure for fibre collection.The rotation of the drum impart twist to fibre assembly .

The ratio of perforated drum to yarn surface is very large, hence the drum speed can be kept relatively low, even if one takes the unavoidable slippage into account. Due to the absence of positive control over the fibres assembly, slippage occurred between the fibre assembly and perforated roller, which reduced twist efficiency. Hence this development could not be commercialized.

• DREF-2:

This is the development with earlier machine. DREF-2 was exhibited in the year 1975 at ITMA exhibition. The feasibility of using two perforated rotating cylinders, (as fibre collecting means), while at the same time the spinning-in of fibres into yarn occurred. It operates on the basis of mechanical/aerodynamic spinning system with an internal suction and same direction of drums rotation. The schematic diagram of the DREF-2 friction spinner is shown in the figure3. Drafted slivers are opened into individual fibres by a rotating carding drum covered with saw tooth type wire clothing. The individualized fibres are stripped off from the carding drum by centrifugal force supported by an air stream from the blower and transported into the nip of two perforated friction drums where they are held by suction. The fibres are sub-sequentially twisted by mechanical friction on the surface of the drums. Suction through the perforations of the drums assists this process besides helping in the removal of dust and dirt, thereby contributing to production of cleaner yarn. The low yarn strength and the requirement of more number of fibres in yarn cross-section(minimum 80-100 fibres) were restricted the DREF-2 spinning with
coarser counts (0.3-6s Ne).

• DREF-3:

The DREF-3 machine is the next version of DREF 2 for improving the yarn quality came to the market in the year 1981.Yarns up to 18s Ne. can be spun thro this system.

This is a core-sheath type spinning arrangement. The sheath fibres are attached to the core fibres by the false twist generated by the rotating action of drums. Two drafting units are used in this system, one for the core fibres and other for the sheath fibres. This system produces a variety of core-sheath type structures and multi-component yarns, through selective combination and placement of different materials in core and sheath. Delivery rate is about 300 m/min. DREF 3 schematic diagram is shown in the figure 4.

• DREF-5:

It was developed by Schalafhorst, Suessen and Fehrer Inc. The range of count to be spun from this system is from 16’s to 40’s Ne.Production speed is up to 200m/min.The schematic diagram of the DREF 5 is shown in the figure 5. The individualized fibres from a single sliver are fed through a fibre duct into the spinning nip at an angle to the yarn axis, so that they are stretched as far as possible, when fed into the nip[7]. This spinning system was not commercialized due to some reasons.

• DREF-2000:

It is the latest development in friction spinning demonstrated in ITMA 99. DREF-2000 employs a rotating carding drum for opening the slivers into single fibres and a specially designed system being used for sliver retention. The fibres stripped off from front the carding drum by centrifugal force and carried into the nip of the two perforated spinning drums. The fibres are subsequently twisted by mechanical friction on the surface of the drums, which rotates in the same direction. The process assisted by air suction through the drum perforations. Insertion of twist in ‘S’ and ‘Z’ direction is possible without mechanical alterations to the machine. Yarns upto 14.5s Ne can be produced at speeds of 250 m/min.

• DREF-3000:

In the ITMA 2003, the first public appearance of the DREF 3000 was made. The yarn can be spun form 0.3Ne to 14.5Ne.The features of DREF 3000 includes a drafting unit and opening head with infinitely variable drive control, spinning units with two infinitely variable suction spinning drums, take-off and winding units with infinitely variable speeds and filament guide with monitoring device. The drafting unit can handle all types of synthetic fibres, special fibres such as aramid, FR and pre-oxidized fibres, polyimides, phenol resin fibres (e.g. Kynol), melamine fibres (e.g. Basofil), melt fibres (e.g. PA, PES, PP), natural fibres (wool, cotton, jute, linen, flax, etc.), as well as glass fibres in blends with other materials. The DREF 3000 processes these fibres in the form of slivers composed of one type of fibre, or using slivers with differing fibre qualities at one and the same time. Slivers with a homogenous fibre mixture can also be employed. DREF 3000 core yarns offer high output, breakage-free spinning and weaving mill operation and thus up to 95% efficiency can be achieved.

Yarn formation in Friction spinning system:

The mechanism of yarn formation is quite complex. It consists of three distinct operations, namely: Feeding of fibres, Fibres integration and Twist insertion.

Feeding:

The individualized fibres are transported by air currents and deposited in the spinning zone. The mode of fibre feed has a definite effect on fibre extent and fibre configuration in yarn and on its properties. There are two methods of fibre feed 1) Direct feed and 2)Indirect feed.

In case of direct feed, fibres are fed directly onto the rotating fibre mass that outer part of the yarn tail. In indirect feed, fibres are first accumulated on the in-going roll and then transferred to the yarn tail. Figure 7 (a) and (b) are showing the above methods of fibre feed.

Fibres Integration:

The fibres through feed tube assembles onto a yarn core/tail within the shear field, is provided by two rotating spinning drums and the yarn core is in between them. The shear causes sheath fibres to wrap around the yarn core. The fibre orientation is highly dependent on the decelerating fibres arriving at the assembly point through the turbulent flow. The fibres in the friction drum have two probable methods for integration of incoming fibres to the sheath. One method, the fibre assembles completely on to perforated drum before their transfer to the rotating sheath. In the other method, fibres are laid directly on to rotating sheath.

Twist insertion:

There has been lot of deal with research on the twisting process in friction spinning. In friction spinning, the fibres are applied twist with more or less one at a time without cyclic differentials in tension in the twisting zone. Therefore, fibre migration may not take place in friction spun yarns. The mechanism of twist insertion for core type friction spinning and open end friction spinning are different,which are described below.

Twist insertion in core-type friction spinning:
In core type friction spinning, core is made of a filament or a bundle of staple fibres is false twisted by the spinning drum. The sheath fibres are deposited on the false twisted core surface and are wrapped helically over the core with varying helix angles. It is believed that the false twist in the core gets removed once the yarn is emerged from the spinning drums, so that this yarn has virtually twist less core. However, it is quite possible for some amount of false twist to remain in the fact that the sheath entraps it during yarn formation in the spinning zone.

Twist insertion in Open end type friction spinning:
In open end type friction spinning the fibres in the yarn are integrated as stacked cone. The fibres in the surface of the yarn found more compact and good packing density than the axial fibres in the yarn. The Figure 8 shown the arrangement of fibres in the DREF-3 yarn as stacked cone shape .

Structure of the yarn tail:

The yarn tail can be considered as a loosely constructed conical mass of fibres, formed at the nip of the spinning drums. It is of very porous and lofty structure.The fibres rotating at very high speed. Lord and Rust have been studied a number of short-duration photographs of the yarn tail during the yarn formation. In these photographs, they located an appendage protruding from the open-end of the yarn tail and called it as the tip of the tail. Observing through the perforated drums, they found this tip to be very unstable, flickering about like a candle flame a draught. With the help of the photographs, they have concluded that the yarn tail is enlarged and torpedo-shaped being squashed by the nip of the perforated drums and the fibres on its surface are loosely wrapped. Moving away from the tip, these wrappings have been shown to
become tighter. They have further added that the surface structure of the tail consists of outstanding fibres, which stand out almost radically.

Spinning Tension for DREF yarns:

Figure 9 explains that the Friction spun yarns have less spinning tension during the yarn formation. Due to less tension during the spinning the core component can be placed exactly at the centre of the yarn.

Friction Spun Yarns Properties:

Friction spun yarns (DREF) yarns have bulky appearance (100-140% bulkier than the ring spun yarns).The twist is not uniform and found with loopy yarn surface. Friction spun yarns with high %age of core have high stiffness. Friction spun yarns are usually weak as compared to other yarns. The yarns possess only 60% of the tenacity of ring-spun yarns and about 90% of rotor spun-yarns. The increased twist and wrapping of the sheath over the core improve the cohesion between the core and sheath and within the sheath.

The breaking elongation ring, rotor and friction spun yarns have been found to be equal. Better relative tenacity efficiency is achieved during processing of cotton on rotor and friction spinning as compared to ring spinning system.

Depending on the type of fibre, the differences in strength of these yarns differ in magnitude. It has been reported that 100% polyester yarns, this strength deficiency is 32% whereas for 100% viscose yarns, it ranges from 0-25%. On the other hand, in polyester-cotton blend, DREF yarns perform better than their ring-spun counterparts. A 70/30% blend yarn has been demonstrated to be superior in strength by 25%. The breaking strength of ring yarns to be maximum followed by the rotor yarn and then 50/50 core-sheath DREF-3 yarn.

DREF yarns have been seen to be inferior in terms of unevenness, imperfections, strength variability and hairiness. DREF yarns occupy an intermediate position between ring-spun and rotor spun yarns as far as short hairs and total hairiness s concerned. For hairs longer than 3mm, the friction spun yarns are more hairy than the ring spun yarns. Rotor spun yarns show the least value in both the values. DREF yarns are most irregular in terms of twist and linear density while ring spun yarns are most even.

Chattopadhyay and Banerjee have studied the frictional behaviour of ring, rotor, friction spun yarns of 59 and 98.4 Tex spun from cotton, polyester, viscose fibres, with varying levels of twist. The yarn to yarn and yarn to guide roller friction was measured at different sliding speeds and tension ratios. However for polyester fibres, the rotor spun yarn showed highest friction, followed by friction and ring spun yarns.

Advantages of Friction spinning system:

The forming yarn rotates at high speed compare to other rotating elements. It can spin yarn at very high twist insertion rates (ie.3,00,000 twist/min). The yarn tension is practically independent of speed and hence very high production rates (up to 300 m/min) can be attainable. The yarns are bulkier than rotor yarns.

The DREF II yarns are used in many applications. Blankets for the home application range, hotels and military uses etc. DREF fancy yarns used for the interior decoration, wall coverings, draperies and filler yarn. Core spun yarns thro this friction spinning are used in shoes, ropes and industrial cable manufacturing. Filler cartridge for liquid filtration also effectively made with these yarns. Secondary backing for tufted carpets can be produced with waste fibres in this spinning system .Upholstery, table cloths, wall coverings, curtains, hand-made carpets, bed coverings and other decorative fabrics can be produced economically by DREF Spinning system. Heavy flame-retardant fabrics, conveyor belts, clutches and brake linings, friction linings for automobile industry, packets and gaskets are some examples were the DREF yarns can be effectively used.

The DREF-3 yarns made fabrics used in many applications like backing fabrics for printing, belt inserts, electrical insulation, hoses, filter fabrics and felts made from mono-filaments core. Hot air filtration and wet filtration in food and sugar industries these yarns made fabrics are used. It also used in clutch lining and brake lining for automotive industries.he multi-component yarns manufactured using DREF 3000 technology are mainly employed for technical textiles of the highest quality. They provide heat and wear protection, excellent dimensional stability, outstanding suitability for dyeing and coating, wearer comfort, long service life , as well as a range of other qualitative and economic advantages. These include cost savings due to the use of less expensive materials, special fibres and wires as yarn cores. Apart from their strength, DREF 3000 yarns are also notable for their good abrasion-resistance,uniformity and excellent Uster values compare to previous systems.

Limitations of Friction spinning system:

Low yarn strength and extremely poor fibre orientation made the friction spun yarns very weak.The extent of disorientation and buckling of fibres are predominant with longer and finer fibres.Friction spun yarns have higher snarling tendency. High air consumption of this system leads to high power consumption.  The twist variation from surface to core is quite high; this is another reason for the low yarn strength. It is difficult to hold spinning conditions as constant.  The spinning system is limited by drafting and fibre transportation speeds.