Friction Spinning (DREF): Principle, Structure & Uses

What Is DREF Friction Spinning?

Friction spinning, exemplified by the DREF system, is an open-end spinning technology that can also be configured to produce core-sheath yarn structures. Yarn formation occurs in the spinning zone under the action of frictional forces generated by rotating perforated drums. The DREF system can produce yarns at high delivery speeds, typically up to about 300 m/min. Although friction spinning remains a specialised technology in conventional apparel yarn manufacturing, it has gained importance with the growth of technical textiles. Among spinning systems, DREF provides a particularly suitable platform for producing core-spun yarns because its spinning principle imposes relatively low tension on the core and helps maintain the core close to the yarn centre. The development of DREF core-spun yarns has created opportunities for new products, including high-performance technical textiles, sewing threads, and selected apparel applications, owing to their potential for improved strength, abrasion resistance, consistent sewing performance, adequate elasticity for stretch requirements, resistance to perspiration, and good wash-and-wear and durable-press performance.

Principle of Friction (DREF-3) Spinning System

A friction spinning system opens and individualises fibres from slivers, reassembles them into a yarn structure, inserts twist, and winds the yarn. The DREF-3 spinning principle is illustrated in Figure 1. In this system, opened fibres are collected, condensed, and twisted by frictional contact with rotating perforated drums. Because yarn winding is mechanically separated from twist insertion, the production rate can be high. DREF-3, introduced in 1981 as a successor to DREF-2, was developed to improve yarn quality. The system typically spins coarser yarns, generally up to about 18 Ne, depending on raw material and machine settings. The DREF-3000 spinning system (Figure 2) produces bundled yarns according to the friction-spinning principle. Essentially, it extends the DREF-2000 process by incorporating a drafting arrangement (2) before the spinning drums (4). A draw-frame sliver (1) with a linear density of 2.5-3.5 ktex is fed into a three-line double-apron drafting arrangement (2). The drafted strand (3), containing about 100-150 fibres, passes from the delivery of the drafting unit to the convergent region between the two perforated drums (4). A pair of take-off rollers (7) draws this strand through the convergent region of the drums and out of the spinning zone.

The coherent fibre strand is held between the drafting arrangement (2) and the take-off rollers (7) and is rotated between these points by the pair of perforated drums (4). It is therefore false-twisted between the two nips: twist is present between the drafting delivery and the drum region, but little or no real twist remains between the drum region and the take-off rollers. If this action continued alone, the strand would untwist and disintegrate. Before this occurs, staple fibres are fed in free flight from above (5) into the convergent region between the drums. Owing to the rotation of the perforated drums, these incoming fibres wrap around the horizontally moving strand, and a bundled yarn is formed. The fibre cloud (5) is supplied by a second feed unit with two opening rollers, which is fed with four to six draw-frame slivers of 2.5-3.5 ktex. This is a core-sheath spinning arrangement. The sheath fibres are bound to the core fibres by the false twist generated by the rotating drums. Two drafting units are therefore used in this system: one for the core fibres and the other for the sheath fibres. The system can produce a variety of core-sheath structures and multi-component yarns through the selective combination and placement of different materials in the core and sheath. The delivery rate is about 300 m/min.

Fibre Integration

Through the feed tube, fibres are conveyed into the shear field between two rotating spinning drums, where they assemble on the yarn core or yarn tail positioned between the drums. The shear field causes the sheath fibres to wrap around the yarn core. Fibre orientation depends strongly on how the decelerating fibres arrive at the assembly point through the turbulent air flow. In the friction drum zone, the incoming fibres may be integrated into the sheath in two probable ways. In one case, the fibres are first deposited completely on the perforated drum and are then transferred to the rotating yarn sheath. In the other, the fibres are laid directly onto the rotating sheath.

Twist Insertion

The twist insertion mechanism in friction spinning has been studied extensively. In friction spinning, fibres receive twist more or less individually, without the cyclic tension differentials typical of many conventional twisting zones. As a result, fibre migration in friction-spun yarns is limited. The mechanisms of twist insertion differ in core-type friction spinning and open-end friction spinning. These two mechanisms are described separately.

Twist Insertion in Core-Type Friction Spinning

In core-type friction spinning, the core, which may be a filament or a drafted bundle of staple fibres, is false-twisted by the spinning drums. The sheath fibres are deposited on the false-twisted core surface and wrap helically around the core with varying helix angles. It is generally assumed that most of the false twist in the core disappears once the yarn emerges from the spinning drums; consequently, the core may be virtually twistless in the final yarn. However, some temporary twist may remain locked in because the sheath fibres can trap it during yarn formation in the spinning zone.

Yarn Structure

The yarn tail may be regarded as a loosely constructed conical mass of fibres formed at the nip of the spinning drums. It is a highly porous and lofty structure. The fibres rotate at very high speed in an appendage protruding from the open end of the yarn tail, referred to as the tail tip. When viewed through the perforated drums, this tip appears highly unstable, flickering much like a candle flame. The yarn tail is enlarged and torpedo-shaped, compressed by the nip of the perforated drums, and the fibres on its surface are loosely wrapped. Away from the tip, these wrappings become progressively tighter. In addition, the surface structure of the tail contains protruding fibres that stand out almost radially.

Advantages of Friction Spinning System

The yarn tail in the spinning zone rotates at very high speed, allowing very high twist insertion rates compared with many other spinning systems. Twist insertion rates of about 300,000 turns/min can be achieved. Yarn tension is relatively independent of spinning speed; consequently, very high production rates, up to about 300 m/min, are attainable. Friction-spun yarns are generally bulkier than rotor-spun yarns. DREF-2 yarns are used in many applications. DREF fancy yarns are used for interior furnishings, wall coverings, draperies, and filling yarns. Core-spun yarns produced by friction spinning are used in footwear components, ropes, and industrial cable manufacture. Filter cartridges for liquid filtration can also be produced effectively from these yarns. Secondary backing for tufted carpets can be manufactured from waste fibres in this spinning system. Upholstery, tablecloths, wall coverings, curtains, handmade carpets, bed coverings, and other decorative fabrics can be produced economically by the DREF spinning system. Heavy flame-retardant fabrics, conveyor belts, clutches and brake linings, friction linings for the automotive industry, packings, and gaskets are further examples in which DREF yarns can be used effectively. DREF-3 yarns have been used in fabrics for applications such as backing fabrics for printing, belt inserts, electrical insulation, hoses, filter fabrics, and felts based on monofilament cores. Fabrics made from these yarns are also used in hot-air filtration and wet filtration in the food and sugar industries, as well as in clutch and brake linings in the automotive sector. The multi-component yarns manufactured using DREF-3000 technology are mainly employed in high-performance technical textiles. Depending on fibre selection, they can provide heat and wear protection, good dimensional stability, good dyeing and coating performance, wearer comfort, and long service life, together with a range of technical and economic advantages. These advantages may include cost savings through the use of less expensive sheath materials and the incorporation of special fibres, filaments, or wires as yarn cores. In addition to their strength, DREF-3000 yarns are notable for good abrasion resistance, acceptable uniformity, and improved Uster evenness values compared with earlier systems.

Limitations of Friction Spinning System

Low yarn strength and poor fibre orientation make friction-spun yarns comparatively weak. Fibre disorientation and buckling become more pronounced with longer and finer fibres. Friction-spun yarns may also show a relatively high snarling tendency in some constructions. The high air requirement of the system results in high power consumption. Twist variation from the surface to the core is considerable, which further reduces yarn strength. Maintaining steady spinning conditions can be difficult. In addition, the spinnable count range is constrained by drafting limitations and fibre characteristics.

Conclusion

Friction spinning, particularly the DREF system, is best understood as a specialised process rather than a universal alternative to ring or rotor spinning. Its strengths lie in high delivery speed, low core tension, and the ability to produce core-sheath and multi-component yarns efficiently. These qualities make it well suited for technical and industrial textiles. However, poor fibre orientation, uneven twist distribution, and limited count range remain real constraints. For textile engineering students, the key takeaway is straightforward: DREF spinning should be evaluated by its functional suitability for a given end use, not by conventional yarn quality standards alone.

References

[1] Lawrence, C.A. (2003). Fundamentals of Spun Yarn Technology. CRC Press.

[2] Klein, W. (1993). New Spinning Systems: Short-Staple Spinning Series. The Textile Institute, Manchester.

[3] Lord, P.R. (2003). Handbook of Yarn Production: Technology, Science and Economics. Woodhead Publishing.

[4] Oxtoby, E. (1987). Spun Yarn Technology. Butterworths.

[5] McCreight, D.J., Feil, R.W., Booterbaugh, J.H., and Backe, E.E. (1997). Short Staple Yarn Manufacturing. Carolina Academic Press.

[6] Lawrence, C.A. (Ed.) (2010). Advances in Yarn Spinning Technology. Woodhead Publishing.

[7] Kumar, L. A., & Vigneswaran, C. (2015b). Electronics in Textiles and Clothing: Design, products and applications.

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