Memis Acar

Improvement of the efficiency of energy transfer in the hydro-entanglement process

Hydro-entanglement is a versatile process for bonding non-woven fabrics by the use of fine, closely-spaced, high-velocity jets of water to rearrange and entangle loose arrays of fibres. The cost of the process mainly depends on the amount of energy consumed. Therefore, the economy of the process is highly affected by optimisation of the energy required. In this paper a parameter called critical pressure is introduced which is indicative of the energy level requirement. The results of extensive experimental work are reported and analysed to give a clear understanding of the effect of the web and fibre properties on the critical pressure in the hydro-entanglement process. Furthermore, different energy-transfer distribution schemes are tested on various fabrics. The optimum scheme which involves the lowest energy consumption and the best fabric properties is identified.

Effect of nozzle geometry on the flow characteristics of hydroentangling jets

Cone-capillary nozzles with varying cone angles from 10° to 120° and a capillary diameter of 120μ are experimentally investigated for their application in the hydroen tanglement process. Cone-up and cone-down configurations in a range of water pressures of 30-120 bar are tested. The effects of the cone angle on flow parameters such as discharge and velocity coefficients and intact length are studied. Flow visualization techniques are used to recognize the flow regimes and characteristics and to inspect and compare the intact length and appearance of the jets. Cone-down nozzles with more consistent flow properties, lower discharges, and higher velocity coefficients are more suitable for the hydroentanglement process. Single-cone nozzles without capillaries and with varying cone angles are also tested. The flow properties of the jets from the single-cone nozzles are compared with the cone-capillary nozzles of the same cone angle to study the effect of the capillary section. The effect of the interaction of adjacent nozzles on the flow from multi-hole nozzles is studied, and the characteristics of the jets from the multi-hole nozzles are compared with the single-hole nozzles.

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.

Computer vision for textured yarn interlace (Nip) measurements at high speeds

This paper deals specifically with interlace measurements of intermingled, false-twist textured yarns. A system has been built which is capable of analysing yarns at slow-speed/high-resolution, and also at high-speed/low-resolution. An outline description of the system is given here, along with descriptions of techniques used in the hardware and software which improve the system performance. To monitor interlace, a signal processing algorithm is developed and explained which enables reliable interlace detection, and is effective against diametric noise. Several tests are carried out, which prove the ability of the system to match the results from careful manual inspection of the yarn. The final test is to run the yarn at a high speed, and to compare the results with the slow-speed analysis. The results show that at high speeds, the system is reliable.

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.

Signal Modelling and Hidden Markov Models for Driving Manoeuvre Recognition and Driver Fault Diagnosis in an urban road scenario

Hidden Markov models (HMM) are used to identify a vehicles manoeuvre sequence and its appropriateness for a given urban road driving situation. One of the novel aspects of this work has been the development of an efficient signal modelling approach to form a context-aware, flexible system which proved to respond well in urban road scenarios, especially in situations where the driver is likely to have an accident due to impaired performance. Another contribution has been to clarify how HMMs can be used not just to recognize vehicle manoeuvres but also to distinguish an impaired driver from a normal one in complex driving contexts. The system has worked well on simulator data and is about to be implemented in the real conditions of an urban trajectory.

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. The results of 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 are reported. Filament yarn motion in different regions of the texturing nozzle during dry and wet texturing was analyzed. During the study it was found that water acted as lubricant to reduce friction between the filaments in the wet texturing process as the filament yarn traveled through the nozzle enabling easier relative motion of the filaments resulting in enhanced entanglement. Wet texturing also reduced spin finish on the yarn surface, which in turn, caused an increase in static friction between the filaments of the textured yarn resulting in better fixing of the loops and consequently superior yarns.

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.