Effects of Geometry on the Flow Characteristics and Texturing Performance of Air-Jet Texturing Nozzles

Abstract

Air-jet texturing is a versatile process for producing a range of synthetic yarns with a spun-like appearance, which are widely used for apparel and furnishing fabrics and industrial textiles. There is no universal nozzle capable of processing any supply yam of any linear density. The role played by nozzle geometry is still not fully understood. The experimental study presented here seeks to compare air flow characteristics and texturing data for nine nozzles under realistic texturing conditions as a basis for an improved understanding of the effect of nozzle geometry. Compressed air consumption results show that the nozzle flow is choked at air inlets; thus the nozzles behave as converging-diverging passages. The exit flow distribution is approximately axisym metric in all cases. Nozzle exit flow characteristics are typical of underexpanded jets with a ratio of jet exit plane static pressure to ambient pressure smaller than or equal to approximately 2. Textured yams with varying visual appearance were produced by different nozzles under identical processing conditions. Nevertheless, the strength properties of the yams were broadly the same, as was their increase in linear density. Of all test variables, the tension in the stabilizing zone was the only quantity to show some promise as a correlating parameter with texturing quality. Neither the presence of shock waves in the exit region nor the magnitude of the exit zone velocity correlated with texturing effectiveness. The texturing results of these trials highlight the fact that the current descriptions of air-jet texturing are not fully capable of explaining the subtle effects due to nozzle geometry and can at best be described as incomplete.