Textile Research Journal current issue

Occurrence of a Singular Point in a Bundle Flow System and the Sensitivity of the Bundle Thickness to Perturbations in a Steady State Draft Process

Huh, Y., Kim, J. S. — 2008-09-23

Roll drafting is an important unit operation that transforms fiber bundles into attenuated ones, improving their properties with more efficient material usage. Fibers are thus thrown into a flow field having constraints at both ends incurring layer-to-layer flow shearing, which governs the individual fiber movement. The parameters of the flow characteristics are disturbed or changed during processing and the output of the roll drafting operation can have either more or less fluctuating properties. In this research, we perturbed the model parameters related to the roll drafting process to identify their effects on the process dynamics and consequently the quality of the processed product. Based on the random phase spectral method, stochastic signals having an exponentially decaying auto-correlation function were generated and applied to the mathematical model that described the dynamic behavior of the flowing bundle. Thus, the profiles of the linear density and velocity of the bundle flow field in steady state were simulated. In extreme perturbations the bundle can break, which was simulated and confirmed by experiments. This research showed that a singular point in the draft zone existed which implied a bundle breakage. The singular point in the draft zone could be attributed to the inadequate set-up of the process conditions, specifically, to two parameters in the model: one was related to the bundle properties and the other to the process conditions. Considering the bundle property related parameter as a stochastic process, the range of the parameter variation to ensure a continuous drafting operation was limited. The influence of the perturbations on the draft process also became more sensitive as the process speed and the draft ratio increased.

Objective Evaluation of Fabric Handle by Simple Measurement Methods

Sular, V., Okur, A. — 2008-09-23

In this study, objective and subjective evaluations of fabrics were made to predict fabric handle in a simple way. The aim of this research was to select a suitable form of regression model and predict total handle value with a minimum number of parameters to make a practical approach by using simple laboratory measurements. For this purpose, a wide database of 71 worsted men's suitings was prepared by making subjective and objective evaluations. Subjective tests of primary handle attributes (softness-stiffness, thickness-thinness, and roughness-smoothness) and total handle were evaluated by an expert jury consisting of 18 members, and a subjective total handle value was also calculated using these data. Objective measurements consisted of fabric tensile, bending, shear, compression and surface properties, and pulling through a nozzle tests. A new surface roughness tester was used for measuring surface properties, and it was found that these roughness results might be useful for fabric handle prediction. Linear and log linear regression equations were tested by using 43 parameters. Consequently, some simple regression equations that were practical solutions were obtained to predict fabric handle. A very good result was obtained with a value of the adjusted R² = 0.88 with eight parameters (LOGP1, LOGB, T42, Rq1, Rp2, Rq1, Rp_mean, P1) from four different property blocks (pulling through a nozzle, bending, tensile, and surface), and in particular, the regression equations reaching an adjusted R² value over 0.80 are recommended.

Techniques for Torque Modification of Singles Ring Spun Yarns

Bin Gang Xu, , Xiao Ming Tao, — 2008-09-23

This article reports on a systematic study of various spinning techniques to produce torque-free singles ring spun yarns on a modified ring frame. The modification units, including optional fiber separation devices and a false twist device, were incorporated into the conventional ring spinning frame so that the balanced or reduced yarn residual torque could be achieved in one step. Three modification systems were proposed and two of them were investigated on a ring frame to produce pure cotton singles yarns. The spirality of the resultant single jersey knit fabrics was greatly reduced. Properties and performance characteristics of control and modified yarns, as well as their resultant fabrics, were evaluated, including yarn tensile properties, hairiness, evenness, snarling, burst strength, air permeability, handle, and pill resistances.

Revision on the Titration Method for Accurately Measuring the Amounts of Residual Monomers in Polyacrylic Sizes

Zhifeng Zhu, , Jie Yu, , Kun Qian, , Cuiyun Yu, — 2008-09-23

An attempt has been made to develop a revised titration method for accurately measuring the content of residual monomers in polyacrylic sizes. It was found that the conventional titration method widely used nowadays for the content measurement cannot determine the content accurately if a certain number of hydrophobic structural units are contained in the size macromolecules. Since most mills and size companies do not possess a chromatograph, a revised titration method is studied and proposed. By choosing three to four sample weights in the range of 0.1— 0.6 g to achieve three to four corresponding values of the monomer content, a straight regression line can be easily obtained in a coordinate. The ordinate value of intersection of the line with ordinate is just the measured value. A gas chromatograph demonstrates that the revised method is suitable for the determination of the content when the polymeric molecules of the sizing agents incorporate hydrophobic constitutional units. The effectiveness and accuracy of the revised method are examined by mixing a known amount of monomer into the sizes. The results demonstrate that the regression and chromatograph values are correlated well and the differences are relatively small. The accuracy of the revised method is much higher than that of the original one.

Investigation of the Water Repellence of Different Experimental and Commercial Coatings for Synthetic Mountaineering Ropes

Spierings, A.B., Ritter, A., Henkel, O., Holzdoerfer, U. — 2008-09-23

All manufacturers of synthetic mountaineering ropes provide chemically coated ropes in order to reduce their water uptake in a wet environment. As common static test methods for the investigation of the water repellent behavior of ropes do not move or bend the ropes, the measured water uptakes are usually below about 10%. In this study we have investigated the water uptake of coated ropes under conditions that are closer to practice conditions than all other methods. Our results show that commercially coated ropes provide a sufficient water repellent behavior as long as the ropes are not in practical use with, for example, carabiners. As soon as the ropes sustain a practical use, the water is worked through the sheath into the core of the ropes so that the water uptake is comparable to the values of uncoated ropes. As a result, the safety performance is decreased both in terms of the number of drops sustained and the impact load. Furthermore, we have investigated experimental coatings and found one chemical (a wax-based coating) and one physical (plastic tape between the sheath and the core of the rope) coating, which were both able to reduce the water uptake even in dynamic conditions.

Application of Stretch-breaking Force Analysis on Optimum Drafting Conditions in Tow-to-yarn Direct Spinning

Su, C.-I., Huang, L.-Y., Cheng, S.-P. — 2008-09-23

This study discusses the evaluation of stretch-breaking force and its CV% in the tow-to-yarn direct spinning with 12k oxidized filament tow. We aimed to describe a new method for determining suitable draft conditions in the direct spinning to obtain the best oxidized yarn quality. To correlate the stretch-breaking force and the yarn quality, oxidized direct spun yarns were spun on a modified laboratory spinning frame for one-step conversion of a tow-to-yarn system. Base on the correlation of stretch-breaking force CV and direct oxidized yarn quality, the drafting ratio and roller gauge corresponding to the lower unevenness (CV%) of the direct oxidized yarn could be chosen as the suitable draft condition in direct yarn spinning to obtain the best oxidized yarn quality. Obviously, the results revealed that the technique of stretch-breaking force could be applied on the optimum draft condition of tow-to-yarn direct spinning.

Simulating Liquid Flow through Virtual Glass Fiber Mats

Jaganathan, S., Maze, B., Vahedi Tafreshi, H., Pourdeyhimi, B. — 2008-09-23

The focus of this paper is on simulating the in-plane and through-plane penetration of liquid water in virtual non-wovens. We consider a series of unsteady state two-phase (air—water) simulations performed in two-dimensional geometries obtained from a simulated three-dimensional glass fiber mat. The simulation planes are the cross-sectional planes in the horizontal and vertical directions. Simulations revealed that liquid penetration and spread depend strongly on the fiber orientation distribution as well as on the hydrophilic properties of the fibers. Our results are in good qualitative agreement with the available experimental data.

Comparing and Modeling the Dynamic Drape of Four Natural-fiber Fabrics

Lin, J.-Y., Wang, P.-N., Shyr, T.-W. — 2008-09-23

This study primarily analyzed the dynamic drape coefficient of four natural-fiber fabrics at speeds of 0—450 rpm. A tangent partition method was used to divide the drape coefficient curve into four regions, characterized as drape coefficient increment initial growth, fast growth, slow growth and dynamic stable regions. The ANOVA test was used for validation. The dynamic drape coefficients of these four natural-fiber fabrics were then compared. The order of the drape coefficient of these fabrics changed three times in the fast growth region and then remained unchanged throughout the slow growth and dynamic stable regions. The order of the static drape coefficient of fabrics could not represent the drape coefficient of fabrics in dynamic performance. Therefore, a linear model, a growth model and a nonlinear logistic model were used to analyze the dynamic drape coefficient curve fit, and the F-test was used for validation. The results showed that the nonlinear logistic function could be used to fit the drape coefficient curves throughout the static state and the dynamic stable region.

Analysis of Geometrical Parameters using a CAD System for a 3-D Braided Preform

Tea Jin Kang, , Kim, S., Jung, K. — 2008-09-23

To estimate the precise mechanical properties of the three-dimensional (3-D) braided composite, a geometric study of a 3-D braided preform was performed. Describing yarn paths using third-order spline curves, which are close to the real pathway of the 3-D braided structure, the unit cells and the representative volume elements were determined. Finally, the CAD system for the 3-D circular braided preform was developed following these modeling sequences and applied to the parametric study of the preforms. A parametric study was conducted on the important geometric factors such as yarn retraction factor, yarn orientation angle, and yarn volume fraction and the theoretical maximum yarn volume fraction was determined. Using the developed CAD system, the relationships between processing variables and geometric parameters have been established.

Sen'i Gakkaishi, Vol. 64, No.10

2008-09-23

Future Events

2008-09-23