Palitha Bandara

Experimental study of dynamic air permeability for woven fabrics

Dynamic permeability is relevant to textile applications subjected to fluid/gas flow under high pressure, such as automotive airbags, wearable airbags and parachute fabrics. Dynamic permeability can be determined when a porous medium is tested under transient pressure conditions. This paper utilizes a reliable approach to measure and characterize dynamic permeability for woven fabrics. The experimental principle is based on the ideal gas law and the non-linear Forchheimer equation. Compared with static permeability measured under a constant low pressure, the dynamic permeability is an intrinsic property determined by change of fabric geometry and structure due to a high-pressure load. The pressure-induced deformation is identified, including effects on fiber and yarn arrangement, yarn porosity and fabric thickness. The level of deformation is a function of the number of fabric layers and initial pressure drop. The experimental results show that the dynamic permeability is higher than the static permeability for loose fabric, while it is lower for tight fabrics. For tight fabric, more fabric layers and a lower initial pressure can reduce the difference between the static and the dynamic permeability. Analytical models are used to explain and predict both static and dynamic permeability.

Instrumentation for the measurement of fabric air permeability at higher pressure levels

The construction and evaluation of a novel instrument for measuring air permeability characteristics of fabrics at differential pressure levels up to 3 bar is described. Fabrics requiring such testing have reduced porosity, leading to low air permeability, and as a result, the use of standard air permeability testers is impractical. A pressure-related measuring technique is therefore employed in the new instrument, which also enables air permeability characteristics to be measured over a range of pressure levels. The instrument is also equipped for the measurement of distension of the test specimens, so that any variation of fabric air permeability with pressure can be investigated. It was demonstrated that the technique can still be applied, in conjunction with a low pressure transducer, for the measurement of fabrics having normal levels of air permeability.

Woven fabric formation: principles and methods

This chapter describes woven fabric formation on shuttle weaving machines and shuttleless weaving machines. The peculiarities of the conditions of woven fabric formation by the different mechanisms employed are presented: the methods of moving the weft into the fell of the woven fabric, and methods of weft beat-up. A method of calculation of parameters of woven fabric formation for using in practice is given. The unique properties of the elastic system of fabric formation (ESFF) are discussed, and the chapter closes by covering the methods of reducing tension in the ESFF.

5 – Weft insertion

: This chapter describes the different methods of weft insertion used on weaving machines. These include shuttle, rapier, projectile, air-jet and water-jet methods. Weft insertion based on electromagnetic, pneumatic-rapier, microshuttle, and weft inertia methods are also discussed.

Weaving machine drives: mechanisms and types

This chapter reviews the different types of weaving machine drives and stopping mechanisms of both shuttle and shuttleless weaving machines.

Introduction: classification and mechanisms of weaving machines

This chapter provides general information on weaving machines. It introduces the reader to the different types of weaving machine, the basic mechanisms involved and the process of creating 2-D (two-dimensional, or flat) woven fabric. The next section discusses the calculation of quantities related to the elastic system of 2-D fabric manufacture, such as the tension and elastic deformation of threads in the let-off zone of the warp beam, the effect of friction on warp yarns and woven fabric on a stationary cylindrical surface, and the definition of the equivalent thread and fabric length.

Movement of raw materials and finished fabrics in weaving manufacture

This chapter describes the use of electrically driven vehicles for the transportation of raw materials and outputs between different units of production at the weaving factory.

Safety devices on weaving machines

This chapter describes the safety (protective) devices provided on weaving machines: warp stop motions, weft detectors and safety devices against the breakage of warp threads.

Control of woven fabric quality: defects and quality assurance of grey fabrics

This chapter describes the methods and special equipment used for the evaluation of the quality and the quantity of the woven fabric produced.

Warp shedding in weaving: parameters and devices

This chapter describes the geometry of the three parts of the warp shed, extending from the fell of the woven fabric to the back-rest. All types of shed, phases of their formation and warp thread elongation caused by the movement of healds are examined, and ways of reducing warp thread elongation are identified. The basic types of shedding device, and dobby and Jacquard machines are also described.