Band 8, Heft 4

In the textile industry a tool is needed that can predict fibre and yarn movement in turbulent air streams. The Institut für Textiltechnik of RWTH Aachen University (ITA) has developed a yarn model that can be used to study the movement of single fibres and yarns in turbulent air flows. The kinematic model is described in this article. Special attention is paid to the aerodynamic forces that determine the flight path of fibres and yarns. The coefficient of drag tangential to the fibre axis ct was studied thoroughly using computational fluid dynamics (CFD). It is shown that the diameter has a strong influence on the wall shear stress. Neglecting this effect for thin fibres can lead to errors in the coefficient of drag of a factor of 500. The turbulence intensity also has an important influence on the boundary layer development, which also determines the coefficient of drag. The assumptions made for the yarn model were tested in an experiment in which yarn flight paths were detected with a high-speed video camera. The comparison to the simulation results confirms the usability of the yarn model.

Ring, Rotor and Air vortex spinning systems provide yarn with different structures and properties. Each system has its limitations and advantages in terms of technical feasibility and economic viability. 30's Ne, 100%cotton yarns were produced from the above systems and knitted in single jersey machine .The Rotor Spun yarns found with frequent breakage during knitting. Comparatively good knitting performances have shown by the Ring and Air vortex yarns. Tensile, evenness and hairiness of the yarns and bursting strength, abrasion resistance, pilling, drapability and color matching of the knitted fabrics were studied. The Ring spun yarns have high strength, low imperfection, and good bursting strength. It has high 'S3' value. Abrasion resistance of Rotor and Vortex yarns made fabrics were found higher than the ring spun yarns. Ring yarn knitted fabric has high bursting strength, Air-vortex yarn knitted fabric has poor drape due to stiffer yarn structure and the MVS yarn fabric has poor pilling resistance. Rotor, MVS yarns made fabrics have good abrasion resistance. Drapability of Vortex yarn knitted fabrics was poor than ring and Rotor yarn knitted fabrics. Good and equal depth of dye shade was found with Ring and Air vortex yarn made knitted fabrics. Ring yarn knitted fabric has shown smooth feeling than the other two fabrics.

Friction (DREF II) spinning system is one of the promising spinning methods to produce yarns for technical textile applications. The core positioned exactly center and the spinning tension will be very less compare to ring and rotor spinning systems. In an experimental study to produce 6's Ne core spun yarns in DREF II spinning machine, the polyester /viscose (70/30%) sliver was used as sheath component and drawn polyester filaments (150 denier/36) were used as core component. Yarns were produced with the different core/sheath components (0/100%, 16/84%, 30/70%, 50/50% and 70/30% respectively).Friction ratio was kept at 3.33 and the feed rate was changed to produce above 6's Ne core spun yarns. Core spun yarns found that more even and high modulus than the parent friction spun yarn. The filament-core in the yarn appeared to have twisted configuration. The direction and level of twist was difficult to ascertain in these yarns. High core component yarns were found less hairy. S3 values of the yarn found minimum with increment in the core proportion in the yarn. Sheath strength contribution was analyzed with respect to the core filaments and found that the less core proportion yarns have high contribution to the tenacity.

The ease of accomplishing a tight knot in a rope depends mainly on the bending resistance of that rope, hence the bending behaviour of ropes becomes a matter of considerable importance. Reducing the bending resistance of ropes, while retaining their other physical and mechanical properties unchanged is a demand of rope consumers. Unfortunately there is no standardised method to measure the bending resistance of ropes. The bending resistance as a mechanical property depends on many factors, such as the type of material used, the processing methods, and the technical specification of the rope. In the present work, four factors were subjected to study, these being: filament denier twist in the primary strand, twist in the final strand, and percentage distribution of filament between core and sheath. A simple method, similar in principle to that used in the Shirley Fabric Stiffness Tester, was used to measure the bending length of polyethylene ropes. A simple model was derived to calculate the bending resistance of ropes. Multiple regression analysis was used to determine multiple correlation factors, degree of contribution of each factor to the measured properties, and its significant levels. Surface plots are used to demonstrate the shape of the effect of the factors that have significant effects.