Effects of geometry on the flow characteristics and texturing performance of air-jet texturing nozzles

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

Effect of geometry on the performance of intermingling nozzles

This study investigates the effect of nozzle geometry on the intermingling process. The dimensions of intermingling nozzles with single air inlets extended across the width of a rectangular yam channel are systematically varied. Nozzles with this cross-sectional shape prove to be easy to manufacture and efficient at intermingling. The performance is evaluated by visually inspecting the intermingled yarns and by measuring the nip fre quency. We have found that the performance of nozzles with large inlet widths is weakly dependent on yam channel geometry. The performance of nozzles with the smallest air inlet widths, on the other hand, is sensitive to yarn channel geometry. The smallest and largest yam channels we have considered give poor intermingling results. Control of the yam path is beneficial for the success and consistency of the intermingling process. Using yam guides to create a diagonal yarn path across the nozzle has the additional advantage of decreasing noise production. Our extended air inlet slot ensures continuous exposure of the yarn to the supply air stream across the entire width of the yarn channel in this arrangement. We also compare our designs with four industrial nozzles under identical process conditions. This study reveals similar trends for nip frequency and power consumption. The results agree with the broad trend established in the geometry study that the shape of the yam channel is not critical, provided the air inlet is large enough

Effect of nozzle geometry on air-jet texturing performance

This paper systematically investigates the effect of a number of geometric parameters on the texturing performance of air-jet texturing nozzles. In order to facilitate the research, an air-jet texturing nozzle with a rectangular cross section has been developed. The texturing performance of the nozzles is assessed by means of process observations and on-line measurement of stabilizing zone tension, and also by measuring the in creased linear density of the yams on textured yarn samples. Furthermore, instability, elongation at break, and tenacity are measured, and texturing quality is judged by visual inspections and examination of scanning electron microscopy images of the textured yarns. Tension in the stabilizing zone, increase in linear density, and to a somewhat lesser extent instability are reliable measures of texturing quality. The best texturing comes from nozzles with a slightly diverging main channel and a single air inlet hole located far from the nozzle exit. A curved diverging exit profile is essential for successful texturing. The results of the tests to determine the effect of air inlet angk are inconclusive and require further investigation

The mechanism of the air-jet texturing: the role of wetting, spin finish and friction in forming and fixing loops

A comprehensive review of the roles played by the airflow, wetting and spin finish on the air-jet texturing process is given. An experimental investigation of the air-jet texturing process using residual spin finish, yarn-to-yarn static and kinetic friction, filament strength, filament diameter, and on-line tension measurements and high-speed cine-photography is reported. Filament yarn motion in different regions of the texturing nozzle during dry and wet texturing is analysed. It is found that water acts as lubricant to reduce friction between the filaments in the wet texturing process as the filament yarn travels through the nozzle enabling easier relative motion of the filaments resulting in enhanced entanglement. Wet texturing also reduces spin finish on the yarn surface, which in turn, causes an increase in static friction between the filaments of the textured yarn resulting in better fixing of the loops and consequently superior yarns

Texturing and intermingling processes by using air-jets

The air-jet texturing (AJT) and intermingling (INT) processes are two applications of air jets used to modify the structure of synthetic multifilament yarns. The modification is performed by high-speed jets, which are created by purpose designed nozzles. The present work experimentally investigates the interrelation between properties of the yarn produced and air flow and the nozzle geometry in order to gain an improved understanding of the AJT process. Firstly, a number of industrial AJT nozzles were selected for detailed analysis. undisturbed flows created by these nozzles are investigated by means of total pressure measurements and shadowgraphy. The effect of nozzle geometry on the AJT process is investigated by using a series of systematically designed nozzles. A number of geometrical parameters of cylindrical type AJT nozzles are specified for successful texturing, after assessing performance of the nozzles by stabilising zone tension and the properties of yarns produced. It is found that large exit length and slightly diverging main duct are beneficial for texturing. Also the trumpet shaped exit profile is found to be necessary for adequate texturing. Low tilt angle of air inlet hole is recommended. Effect of wetting on AJT is investigated with special reference to yarn-to-yarn and yarn-to-metal friction. It is found that when the supply yarn is treated with water interfilament friction prior to the nozzle is reduced, but increased slightly in the texturing area. The former may make relative movement of filaments easier. The latter is considered to be one of the ways through which wetting improves the process, since it assists anchoring the loops in the yarn. Subsequently high-speed cine-photograpy is deployed to visualise the AJT process inside and around exit area of the nozzle. The nozzle used has rectangular cross-section and one glass wall, which allows to see inside the main channel. It is found that for successful texturing loop formation and fixing the loops are both necessary. The INT process is investigated by using again several systematically designed nozzles with reference to correlation between nip frequency and nozzle geometry. Rectangular nozzles are found to be performing adequately, depending on their dimensions. The nozzles with area ratio smaller than unity perform adequate intermingling. It is also found that small aspect ratio is benefical in terms of nip frequency. A better understanding of the INT is achieved by means of SEM, high speed video and cine-photography and yarn tension measurements. The yarn is found to be necessary to run constantly against the incoming flow to reduce missing nips