Peter R. Lord

The Structure of Open-End Spun Yarn

If open-end spun yarns are to find wide use, it is necessary to understand more fully the structure of the yarns. The differences in structure arise because of the manner in which the yarn is made. Bridging fibers are converted into hooks in the spinning process and this reduces the effective fiber length in the yarn. Fibers migrate in a different way and the fiber-helix wavelengths vary according to radius; also, fiber tensions are lower. All these factors tend to make the yarn weaker, more bulky, and more extensible. Because of these differences, the yarns behave in a different way in subsequent processing, and also the fabrics take on a different character from those normally encountered.

Comparison of Physical Properties of Fabrics Woven from Open-End and Ring Spun Yarns

It is well established that open-end yarns are different from ring yarns; in particular OE yarns are weaker and more bulky in spite of the higher twist levels used. The introduction of these yarns into woven fabric affects the structure and the characteristics of the fabrics. The fabric structure traps non-load bearing fibers and thus gives increases in fabric strength and decreases in fabric extensibility. Crimp levels are altered which affect the initial modulus and the breaking extension of the fabric. This and the different yarn characteristics lead to considerable difference in tear strength. In the cases, of both ring and OE fabrics, the looser the structure, the worse the pilling performance and the better the tear performance. Compromises have to be made according to end-use. The changes in structure alter the topography of the fabric which affects the wear behavior. The changes in structure also affect the crease resistance and flexural rigidity characteristics of the fabrics. Thus the differences in the yarn structure play a distinct part in determining the final nature of the fabric.

The Performance of Open-End, Twistless, and Ring Yarns in Weft Knitted Fabrics:

Open-end, twistless, and ring yarns made from cotton and spun to different twists were knitted into single-jersey fabrics to assess their performance. Further tests at a given twist level for a range of polyester/cotton yarns were also included. A variety of yarn and fabric relaxations were used, and it was evident that unrelieved torque is a prime cause of loop distortion, spirality, and fabric shrinkage. It became apparent that autoclaving the yarns was the best way of reducing twist liveliness and the associated difficulties in manufacturing the fabric; it also improves the properties of the fabric. Properly relaxed, open-end yarn makes a fabric with good appeal, reasonable shrinkage, and acceptable strength and abrasion resistance. Twistless yarns gave good fabric hand, high luster, zero spirality, and little shrinkage, but there was some loss in strength for the fabric tested.

A Comparison of the Performance of Open-End and Ring Spun Yarns in Terry Toweling

The relative moisture uptake characteristics of ring and open-end yarns are investigated by a variety of methods. Wicking height and volume of moisture elevated differ as the yarn structure is altered. Open-end yarn wicks better and more evenly but only elevates about the same volume of water for a given yarn count as ring yarn. Water can enter a fabric from the edge (by wicking) or by contact with the surface, and this affects the performance marginally. The yarn and fabric structures both play a part in determining performance. It is concluded that there is little difference in the ultimate capacity of ring and open-end yarns of a similar twist and count when made up into a similar fabric. The rate of dye exhaustion is initially, more rapid for open-end yarns and this is of benefit in dyeing.

The Twist Structure of Open-End Yarns:

A single measurement of twist is insufficient to typify open-end yarns because the twist (tpi) of the fibers comprising the yarn core is different from those comprising the outer sheath, and both are usually lower than the machine value. The differences may be expressed in terms of a twist gradient which is a function of machine design, operating conditions, and fiber characteristics. In these experiments the differences were particularly marked with high polyester blends.

A Comparison of Various Woven Fabrics Containing Friction, Rotor, and Ring Spun Cotton Yarn Fillings:

Fabrics made from friction spun fillings (friction fabrics) had a hand that was judged to be equivalent to fabrics made from ring spun fillings of the same count (ring fabrics). Fabrics with rotor spun fillings (rotor fabrics) had a hand that was harsher than either of the others. The friction spun fillings only had a tenacity of about 57% of ring yarns. Plain weave friction fabrics had a tenacity in the filling direction of about 70% of ring fabrics and 66% for twill weave fabrics. The tear strength was 63% of the ring fabric. Warps were common in each set, but the substitution of one filling by another type altered the fabric performance in the warp direction even though the filling yarn count was unchanged. The topography of the fabric surface was changed by the substitution. Harmonic analysis of surface roughness data showed the effects to be considerable. Fabric bending stiffnesses changed by altering the fabric and yarn structures, but the two methods of measurement did not give identical assessments of these differences. Fabric shear and hysteresis losses suggest that friction fabric might tend to “bag.”

A Comparison of the Hairiness and Diameter of Ring and Open-End Yarns

This paper presents a comparison between the hairiness and diameter of open-end and ring yams spun from various polyester/cotton blends. The yarn hairiness and diameter were measured using an optical technique. The study covered the effects of blend ratio, yarn count, and twist on the hairiness and diameter of open-end and ring yams. The results show that the yams spun on the BD 200 machine had a diameter roughly 10% larger than correspond ing ring yams. The open-end yarns were also found to be less hairy than ring yams, but the hairiness was found to have a higher coefficient of variation.

Twistless Yarns and Woven Fabrics1

Traditional fabrics utilize twisted yarns and the purpose of the twist is often misunderstood. The twist is introduced partly because of its effect on the fabric, but mostly its real function is to permit the manipulation of the yarns during processes leading to the final fabric. The current series of tests show that fabrics made of twistless yarns are remarkably strong and have many favorable characteristics. For example, both knitted and woven fabrics suffer much less shrinkage in the fabric forming process. Good cover can be obtained because the yarns flatten within the fabric structure. The changed disposition of the fibers tends to give a softer hand. The system is not without problems; for example, if the fibers are scoured before manufacture, it is difficult to remove the size. The frictional characteristics of the fibers are affected and this seems adversely to affect the tearing strength. Work is being carried out to eliminate the need to scour the fibers, and attempts are being made to draft the fibers when thoroughly wetted by a low-viscosity size recipe. The wetting, drafting, drying, and winding are carried out in a single continuous operation. Wet drafting is found to produce substantial advantages, particularly with cotton fibers.

The Behavior of Twistless and Low-Twist Staple Yarns in a Plain-Weave Fabric

Bonded untwisted staple yam has been used experimentally in the production of fabrics. The present study, an extension of previous work, has shown that the tensile strength of fabric made from twistless filling was low. The addition of twist to the filling increases the strength of both the yarn and fabric. Waxed yarns provided the strongest fabrics and caused the tear strength in the warp direction to be markedly improved. Fabric made from bonded yams were less permeable than those made from ring filing.

Plain-Weave Fabrics Made from Twistless and Low-Twist Staple Yarns

Although considerable data exists for plain-weave fabrics with twistless and low- twist fillings in combination with ring-spun warps, little data have been published about twisted fillings in combination with a twistless warp. The twist level, yarn spacing, and location of the yarn in either the warp or filling have major effects on the yarn crimp levels in the fabric. These in turn affect the properties of the fabric. In this work, twistless warps were used and the effects of changing the filling were studied. The filling twist levels were varied from zero to the value normally used in ring yarns; the fiber lengths and pick spacings were also varied over a wide range. The critical com binations of these parameters, beyond which failure by fiber slippage occurs, were identified and other forms of fabric failure studied. In particular, the effects of the unusual yarn geometry within the fabric produced considerable differenoes in the resistance of the fabric to tearing. The whole work underlines the importance of the in-situ yarn crimp in determining fabric properties.