K. Greenwood

8—THE SCOPE FOR FABRIC ENGINEERING BY MEANS OF THE WEAVE

The concept of fabric engineering—the design of fabrics with predetermined physical properties—is used in relation to the structure of woven fabrics, and it is shown from theoretical considerations, with the aid of computer analysis, that a large discrepancy exists between the number of weaves of comparatively small size that can be woven and the number that are actually produced. Experimental results obtained on fabrics woven in accordance with a particular plan indicate that the weave has a very marked effect on both tearing strength and stiffness. The results further suggest that weave modification can provide a means of obtaining very accurate control of the two properties investigated and of their possible combinations, and the same may well be true of other physical properties of fabrics.

Constant-bulk False-twist Texturing. Part I: Principle and Method

Current false-twist texturing processes are all carried out under constant-temperature conditions. White the product is good and commercially acceptable, changes in bulk and hence in dyeability do occur, due, for example, to alterations in yarn properties caused by changes in package build from inside to outside. New work described in this paper shows that, by texturing at constant bulk, substantially improved yarn and fabrics can be obtained. The new process developed at UMIST uses very small heaters (4–8 inches in length) under feedback control. The bulk and dyeability of the textured yarn are monitored on-line. A closed-loop system is used, and texturing conditions are automatically changed to keep the bulk and dyeability of the textured yarn constant. In this new process, the texturing temperature is changed in such a way as to keep the bulk constant. The process is therefore non-isothermal, in contrast to the isothermal, constant-temperature approach of all current false-twist texturing equipment. Th...

The Computerised Weaving of Preforms for Composites Part I: The Flattening of 3-dimensional Preforms

This is the initial paper of a series which examines the computerised weaving on conventional looms of fabric structures which already have most of the geometrical properties of the desired fabric preform; the design can be easily transformed into an actual preform by use of a simple opening up or unfolding procedure. A further aim of the work is to transfer to a computer the complete process of generating the necessary weaving instructions once the ultimate product geometry has been chosen. In this way, the costly manual process of conversion is avoided. Part I describes the methodology of flattening and examines how it is used to develop the software program needed to allow the flattened design to be woven on a conventional loom. A substantial range of useful preforms can be woven on the basis of the approach outlined in this first paper.

The Computerised Weaving of Preforms for Composites Part II: Feature Analysis of the Flattened Structures

In Part 1 of this series of papers, it was shown how the three-dimensional design of the target preform is transformed into a substantially two-dimensional one which can then be woven on a conventional weaving machine. The present paper explains how the features of the flattened structure are analysed for the purpose of generating the weaving instructions. In the weaving of preforms, the traditional shuttle loom offers many advantages over the shuttleless one and therefore, with regard to contents and terminology, this paper is orientated primarily but not exclusively towards shuttle weaving. Where shuttleless weaving is appropriate, the term “shuttle” can be taken to refer to any weft insertion element such as a projectile, rapier or air-jet.

The Computerised Weaving of Preforms for Composites. Part III: The Generation of a 3D Net-shaped Preform Weave Pattern and Weaving Instructions

The algorithms required for generating the weaving instructions (jacquard designs) for weaving truly 3D preforms in flattened form on conventional 2D looms are described. The basic approach is to divide the flattened structures into areas, each area into levels, and each level into fabric layers. Together with the chosen basic weave (plain, twill, satin, etc.) and the required number of shuttle paths, the number and size of these structural elements determine the size, in terms of numbers of ends and picks, of the over-all weave repeat of the whole structure. In principle, several repeats of the same structure can be woven side by side, but the structures chosen for analysis were too large for this purpose. In the warp direction, however, any desired number of repeats could be woven.

Constant Bulk False Twist Texturing

The false twist threadline length has been substantially reduced by the use of very small high intensity heaters using hot fluids as the heat transfer medium. The use of rapid response heaters permits a feed back loop to be introduced. Various methods of on-line bulk measurement are discussed and it is shown theoretically that if a tension barrier is deliberately introduced in the second zone of the false twist threadline that measurement of velocity correlates with yarn bulk. Experimental work has verified this approach and a high speed machine, of low cost that can be used in flexible shift patterns of working is described. Substantial yarn quality improvements flow from the use of feed back control to keep the heat flux to the twisted yarn constant, while permitting the temperature of the heating medium to change.

18—THE DEVELOPMENT OF TWIST IN A FALSE-TWIST TEXTURING MACHINE WITH A FRICTION TWISTER

In a false-twist texturing machine, the yarn can be rotated by means of either a pin or a friction twister. Irrespective of the type of twister used, the yarn twist can only be stable when it is numerically equal to the ‘speed ratio’ (the ratio of rotational to linear speed). When the machine is started up, the yarn has no twist, and a certain length of yarn has to be processed before the twist attains its stable value. The nature of this initial development of twist depends on the type of twister used. With a pin twister, the speed ratio is a machine setting and is independent of the yarn twist. When the machine is started up, the speed ratio attains its stable value almost instantaneously, and the yarn twist approaches this value exponentially. With a friction twister, the speed ratio is not a machine setting and is inversely related to the yarn twist except under certain theoretical limiting conditions, which hardly ever occur in practice. Since the yarn twist equals zero when the machine is started up...

Problems and Perspectives of Continuous Yarn Testing

The main features of continuous yarn testers designed to operate at speeds in excess of 600 m/min and with substantially greater versatility than conventional testers are discussed. Six possible functions of such testers are described and examples are given of the type of test results that may be obtained. Details are given of the experimental tester that was built in the course of this work. In view of the very large number of possible combinations of design parameter, it was decided to study these combinations by means of a computer simulation. The algorithms used in the simulation are explained and results obtained from the simulation are discussed. In so far as the simulation dealt with conditions that were also explored experimentally or where results were known from the literature or industrial practice, the agreement between simulation and practical results was good. This suggests that the simulation can be used with confidence to predict results to be expected from hitherto unexplored design parameter combinations.

16—THE WEFT-INSERTION RATE OF MULTI-SECTION LOOMS WITH FLYING SHUTTLES

An analysis of the factors determining the weft-insertion rate of weaving machines shows that these factors are essentially the same on all looms in which shuttles or weft carriers are used, such as conventional shuttle looms, gripper-shuttle looms, and multi-phase looms. The phase number of a loom is defined as the average number of shuttles or weft carriers inserting weft simultaneously. It is shown that existing multi-phase looms must have high phase numbers to compensate for their low shuttle velocity. The analysis suggests that looms with high-velocity flying shuttles would achieve equally high weft-insertion rates with moderate increases in the phase number. Such moderate increases in the phase number can be obtained by dividing the shedding and beat-up motions into a comparatively small number of sections. The suggested alternative would avoid many of the textile and engineering problems arising in existing multi-phase looms.