Tension in the yarn and its oscillations during the over-end unwinding of the yarn from stationary packages depend on the unwinding speed, the shape and the winding type of the package, the air drag ...coefficient, and also the coefficient of friction between the yarn and the package. The yarn does not leave the surface package immediately at the unwinding point. Instead, it first slides on the surface and then lifts off to form the balloon. The problem of simulating the unwinding process can be split into two smaller subproblems: the first task is to describe the motion of the yarn in the balloon; the second one is to solve the sliding motion. In spite of the seemingly complex form of the equations, they can be partially analytically solved as we show in the paper.
The methods for loop length measurement have mostly been developed for knitted fabrics made from conventional yarns. When measuring the loop lengths of knitted structures made from highly extensible ...staple yarns, problems arise because of an uncontrolled yarn extension at the low stresses. The present study proposes a test method for knitted loop length determination in which variable preloads are applied. In the study, the loop lengths measured on an INSTRON dynamometer using variable preloads and a HATRA Course Length Tester using a fixed preload were compared. The results demonstrated that knitted structures made from elasticised yarns exhibit only small changes in loop length after relaxation. The addition of elastane does not significantly influence loop lengths for fabrics knitted using the same machine, the same cam setting and relaxed by the same process. The loop lengths measured on an INSTRON dynamometer exceed the loop lengths measured on a HATRA Course Length Tester.
The development of knitted fabrics with incorporated elastane has increased in recent decades. Knitting with these elasticized yarns usually results in a very compact structure. Loop length is ...considered to be the primary parameter for knitted structures. Consequently, knowledge of all factors influencing loop length is vital for planning yarn consumption, comfort fit, quality, performance and aesthetic properties of knitted fabrics made from elasticized yarns. The objective of this research was to study the impact of material, knitted structure and relaxation process parameters on loop length. In addition, the objective was to examine the differences in loop length of single weft knitted fabrics, produced from different types of elasticized and non-elasticized yarns. For both groups of knitted fabrics, elasticized and non-elasticized, knitted fabric density and relaxation process influence the loop length most of all. Loop length decreases during the process of consolidation, but this decrease is not substantial. Addition of elastane does not significantly influence the loop length.
For decades, scientists have been trying to define relationships among yarn parameters, knitted fabric parameters, and knitting parameters with loop models. Recently, the geometrical loop models have ...returned to focus as they assist finding the effective parameters which cause dimensional changes during relaxation. Furthermore, they help designing knitted structures for technical applications and obtaining computer simulations of knitted structures. In the past, geometrical loop models considered more or less porous structures and the yarns used were mostly conventional, without elastane. The behavior and characteristics of compact knitted fabrics made from elasticized yarns have been investigated only recently. In general, mostly the structures with plated elastane threads have been analyzed. The aim of the research was to study the geometrical parameters (yarn thickness, loop width, loop height, fabric thickness, loop length) of plain single weft knitted structures made from various elasticized yarns, in comparison to equivalent structures made from conventional yarns. In the study, the most frequently applied loop models for the loop length calculations were evaluated with the emphasis on their adequacy for elasticized knitted structures. A new loop model for an elasticized weft knitted structure based on the multiple linear regressions was defined.
The importance of protection against ultraviolet radiation (UV) is increasing daily. The dependence of the UV protection level on different clothes is determined by the shape and design of fabrics, ...and especially by their construction parameters. The fabric structure represents an important factor which is in most cases the only condition for good protection. Other possibilities to ensure good or even excellent protection, mainly by finishing treatments, can be efficient only if the fabric structure is closed enough. To determine the key parameters which contribute to the closeness of the structure and offer suitable UV protection, an analysis of monofilament woven fabric structure was made. Monofilament fabric samples used in the production of high-module screen-printing meshes, which are characterized by the excellent dimension stability of the structure, the properties of which change with varying diameters of the monofilaments and the fabric density, were chosen for this research. A broad spectrum of similar but structurally different fabrics assures referential samples are available for the evaluation of UV protection properties. In all the samples tested, the parameters of transmission and reflection were measured. Moreover, the values of absorption and the ultraviolet protection factor (UPF) were calculated. The values calculated on the basis of a determined mathematical model matched well with the measured values and they can together represent the basis for successful planning of fabrics with suitable UV protection properties.
The influence of conventional acid and alkaline high temperature dyeing procedures on fabric construction is investigated. The effects of weave construction, orange, red, and blue disperse dyes, ...double layers of fabrics, and UV absorber on the ultraviolet protection factors (UPF) of polyester fabrics are the topics of this research. A spectrophotometer with an integrating sphere is used to measure the uv transmittance of polyester fabrics according to an AATCC test. Small differences in the weight of fabrics after blind dyeing procedures already influence the uv transmittance of fabrics. Pale orange and blue dyed fabrics show a high enough UPF, while a pale red dyed fabric does not reach such values. Deep dyed and double layered fabrics and fabrics aftertreated with a UV absorber reach high UPF values.
Yarn motion during unwinding from packages Praček, Stanislav; Možina, Klemen; Sluga, Franci
Mathematical and computer modelling of dynamical systems,
12/2012, Volume:
18, Issue:
6
Journal Article
Peer reviewed
Open access
We study the motion of yarn modelled as a one-dimensional inelastic string. In textile production, the yarn is being withdrawn from cross-wound packages in warping and weft insertion. During ...unwinding, there appear forces in the yarn that are approximately proportional to the square of the unwinding velocity. The yarn tension is not constant, but it oscillates within some interval. This is especially noticeable in over-end unwinding from a static cross-wound package. Even when the yarn is not strongly stressed, so that the tension never exceeds a few percent of the breaking strength, the yarn can still break sometimes. The production process requires as large warping and weaving speeds as possible; therefore, it is necessary to improve our understanding of the cross-wound package unwinding and to find the necessary modifications of the yarn unwinding process. In addition to empirical tests, it has proved useful to study yarn unwinding by mathematical modelling and computer simulations. We state the equations of motion that describe the yarn unwinding and develop a mathematical model that permits to simulate the process of unwinding.
We derive a system of coupled nonlinear differential equations that govern the motion of yarn in general. The equations are written in a (non-uniformly) rotating observation frame and are thus ...appropriate for description of over-end unwinding of yarn from stationary packages. We comment on physical significance of virtual forces that appear in a non-inertial frame and we devote particular attention to a lesser known force, that only appears in non-uniformly rotating frames. We show that this force should be taken into account when the unwinding point is near the edges of the package, and the quasi-stationary approximation is not valid because the angular velocity is changing with time. The additional force has an influence on the yarn dynamics in this transient regime where the movement of yarn becomes complex and can lead to yarn slipping and even breaking.
Yarn unwinding from a package is important in many textile processes. The stability of the unwinding process has a direct influence on the efficiency of the process and on the quality of the end ...product. During the unwinding, the tension is oscillating. This is especially noticeable in over-end unwinding from a static package, where the yarn is being withdrawn with a high velocity in the direction of the package axis. The optimal form of the package allows an optimal shape of the yarn balloon and low and steady tension even at very high unwinding velocities.The purpose of this work is to write down the equations that describe the motion of yarn during unwinding and to construct a mathematical model whichwould permit to simulate the process of unwinding.
Many studies have been devoted to the problem of harmful effects of UV radiation on human skin. The incidence rate for all forms of skin cancer is rising quickly. Considering this fact, there is ...currently a need for diligent preventive work, not only from dermatologists but also from other doctors and scientists. Textiles represent simple and effective protection against UV radiation. Good protective clothing can reduce UV radiation on the surface of skin by at least 95%. Even though numerous studies present the effects of various textile parameters on UV protection, not many have been conducted for determining the degree of agreement between in vivo and in vitro measurements of UPF.
This study presents the effect of various constructional parameters on UPF values (determined using spectrophotometry). The phenomenon of minimal erythema doses on the skin of test subjects was tested based on in vitro calculated UPF values.
Despite some differences in values, the study nevertheless showed a good correlation between both methods and confirms the congruity of in vivo and in vitro UPF values.
It is clear that both methods are needed for a more precise look at the UV protection offered by textiles.
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