G. R. Wray

32—AN ANALYSIS OF THE AIR-JET YARN-TEXTURING PROCESS PART VII: THE EFFECTS OF PROCESSING PARAMETERS ON YARN PROPERTIES

The properties of the supply yarn and the processing parameters together determine the final properties of air-jet-textured yarns. An investigation is reported on how variations in overfeed, air-pressure, and texturing speed, wet or dry processing, and the use of an impact element each affect the properties of the yarn textured. The test plan and the test methods are described, prior to a report of the test results. It is concluded that the test results agree with the predictions made from the postulated mechanism of loop formation.

4—AN ANALYSIS OF THE AIR-JET YARN-TEXTURING PROCESS PART II: EXPERIMENTAL INVESTIGATION OF THE AIR-FLOW

An account is given of an experimental investigation of the characteristics of the air-flow in a scaled-up model of a currently used nozzle for the air-jet texturing of yarns. The flow was found to be supersonic, turbulent, and of a non-uniform profile. Flow visualizations of the undisturbed and disturbed flows made by using the actual-size nozzle provided evidence that challenges previously postulated mechanisms of loop formation based on shock waves.

18—AN ANALYSIS OF THE AIR-JET YARN-TEXTURING PROCESS PART IV: FLUID FORCES ACTING ON THE FILAMENTS AND THE EFFECTS OF FILAMENT CROSS-SECTIONAL AREA AND SHAPE

Fluid (drag) forces acting on filaments in an air-flow are theoretically analysed, and equations to calculate them are derived. Drag forces acting on filaments are shown to vary with the filament cross-section, the position of the filaments across the nozzle, and the local air velocity. Since finer filaments have a smaller inertial resistance to fluid forces and have lower stiffness, yarns with finer filaments are shown to be more suitable for air-jet texturing. Theoretical modelling of a filament as it emerges from the nozzle shows that, for filaments with identical linear densities, those with cross-sections having reduced bending and torsional stiffness, such as elliptic cross-sections, may be more suitable for air-jet texturing.

9—THE PROPERTIES OF AIR-TEXTURED CONTINUOUS FILAMENT YARNS

A processing programme is outlined in which yarn pre-twist, applied air-pressure, and supply-yarn overfeed are systematically varied in the air-jet bulking process to investigate their effects on air-textured nylon 6.6 continuous-filament yarns. Optical magnification of the air-textured yarns enables the average loop sizes and frequencies to be measured. The experimental results are shown to be in general agreement with a suggested mechanism of the process, which argues that the initial filament twist in the parent yarn redistributes itself as snarled loops and that the overfed yarn contributes to the size of such loops; the deflexion of filaments by air-drag forces is also shown to make a contribution to a looping effect, which can be estimated theoretically. Increasing the yam overfeed increases both the loop size and the loop frequency. Increasing the yam pre-twist decreases the loop size and increases the loop frequency. Increasing the air-pressure also decreases the loop size and increases the loop f...

Air-Jet Textured Yarns: The Effects of Process and Supply Yarn Parameters on the Properties of Textured Yarns:

Characteristics of air-jet textured yarns are determined by the instability, linear density, and strength, together with structural properties such as loop size, loop frequency, and degree of entanglement. Such characteristics are affected by various process parameters and supply yarn properties. The effects of these parameters on the final yarn properties have been investigated using instability, linear density, and strength tests, together with SEM photographs for visual assessment of the yarn structure. Optimizing any given yarn property almost always affects other yarn characteristics, and therefore this must be remembered when selecting suitable process parameters and supply yarns for specific end uses. For a given texturing nozzle and conditions, there is an optimum filament fineness and number of filaments that can be textured effectively.

30—AN ANALYSIS OF THE AIR-JET YARN-TEXTURING PROCESS PART V: THE EFFECT OF WETTING THE YARNS

It is shown that the quantity of water mixing into the air-flow is an insignificant proportion of the total amount of water used in the air-jet texturing process and that this has a negligible effect on the air-flow in the texturing nozzle. It is suggested that only a fraction of this water is needed to impart the desired effects of wetting. Experimental investigations show that water acts as a lubricant to reduce the filament–filament and filament–solid-surface friction and hence aids the longitudinal displacements of the filaments relative to each other. A realignment of the yarn path minimizes the friction between the filaments and solid surfaces.

17—AN ANALYSIS OF THE AIR-JET YARN-TEXTURING PROCESS PART III: FILAMENT BEHAVIOUR DURING TEXTURING

Experiments performed with a current industrial-texturing nozzle on a specially designed singlehead texturing machine are described. These involve the use of high-speed still and cine photography, together with measurements of yarn speed on emergence from the nozzle and yarn-tension measurements at various stages of the process. The results of these experiments provide a better understanding of the filament behaviour during the texturing process. They also provide useful information regarding the effects of texturing speed, overfeed ratio, and texturing with and without water on the mechanisms of the process.

15—TRANSDUCERS FOR THE PRECISION MEASUREMENT OF WEFT-KNITTING FORCES. PART I: A CAM-FORCE TRANSDUCER

A description is given of a transducer, with its associated instrumentation, that has been developed to measure the dynamic forces between a latch needle and the stitch and guard cams during the formation of a knitted loop. Such forces are referred to as ‘cam forces’.

31—AN ANALYSIS OF THE AIR-JET YARN-TEXTURING PROCESS PART VI: THE MECHANISM OF LOOP FORMATION

After a brief summary of the findings and conclusions of the previously reported investigations on the air-jet texturing process, a mechanism of loop formation is postulated. The factors affecting loop formation are analysed in the light of the mechanism described. This mechanism of loop formation is claimed to be valid for all types of texturing nozzle because the underlying requirement to create a supersonic, turbulent, and non-uniform flow is common to all satisfactory air-jet texturing nozzles.

Air flow in yarn texturing nozzles

The air-jet texturing process, a purely mechanical means of texturing continuous filament yarns, is described. Industrial texturing nozzles are reviewed and categorized in two groups, either as converging-diverging or cylindrical type nozzles. A mathematical model is developed for the complex airflow in cylindrical type texturing nozzles, and experimental data obtained from various nozzles verify the flow predicted by this model. The mathematical model is also shown to be in good agreement with the data obtained from a modified experimental nozzle, which has a trumpet shaped diverging exit. Further experimental work with a scaled-up model of a typical industrial texturing nozzle is also reported.