Yarn Appearance Research Articles

3D Structural Simulation of Tubular Braided Fabrics for Net-Shape Composites

A circular braiding machine can be used to produce complex shapes by overbraiding a contoured mandrel and adjusting the process parameters. To simplify the design process and advance this technology, a CAD model is developed to describe the geometry of a 3D circular braid both externally and internally. A quadrilateral mesh is used to generate the over-all yarn appearance from a wire-frame model with texturing and light reflection applied to the surface. Comparison with other simulated structures using different models and with real yams shows that the simulated fabric described in this paper is more accurate and yields an improved visual representation of real preforms. The model takes into account the structural characteristics of yams and the finite dimensions of fibers. The effects of yam crimp, weave pattern, and tubular shape on the yarn appearance in the preform are examined. Some applications of the model to net-shape composite designs are presented, such as a canoe paddle, a drive shaft, and a shaped preform.

Filament Pre-tension in Core Yarn Friction Spinning

Core yams are known to improve cotton yam properties. In this research, core yarns are spun by introducing filaments under tension into the yarn-forming zone of an ex perimental friction spinning apparatus. A 30-denier (3.3 tex) nylon monofilament and a black 75-denier (35f) nylon multifilament make up the core, and cotton fibers are used as the sheath. The effect of filament pre-tension on the structural parameters and mechanical properties of the core yarn is examined, and core yarn properties are com pared with those of equivalent 100% cotton yarns. The photographic and fiber tracing methods are used to consider the appearance of the yarns and the geometric position of the core in the core yarns. The results show that the appearance of the core yarn is similar to that of regular cotton yarns, with the exception of core yarns produced with 00 gf/fil pre-tension. Core yarn irregularity does not change with filament pre-tension, and it is less than that of cotton yam. Core yam strength significantly increases as filament pre-tension and filament percentage increase, and it is greater than that of cotton yarn. Core yarn elongation is less than that of cotton yarn at a low filament percentage and greater than that of cotton yarn at a high filament percentage.

World production and use of polypropylene fibres and thread. A review

The existence of sources of accessible and inexpensive raw material has caused the turbulent development of PP fibres and thread. At present, they occupy third place in the world in production volume, after polyamide and polyester fibres and yarns, and could be in first place by 2000 based on the production growth rates. The cause of this rapid development is the relatively simple and ecologically “clean” technology and low production costs. Industrial production of PP fibres and thread is still concentrated in Western Europe, the US, and Japan, where 70% of all PP is produced. In the 1990s, the proportion began to decrease due to production in developing countries in South America, Asia, and Africa. Since the mid-1980s, PP fibre and yarn production capacity has increased, while the development of production capacities for film fibres and monofilaments has virtually stabilized. The areas of application of PP fibres and yarns are determined by their properties. Carpet manufacture is the largest and most developed area of their use. In the future, PP fibres and thread could move to first place in production of carpets, outstripping polyamide fibres; this could be due to the appearance of BSF PP yarns from DuPont (USA) on the world market. The increase in the market for PP floor coverings is related to their use in the automobile industry. Nonwovens from PP fibres are used in both the home and in industry (construction, agriculture, automobile, furniture, and shoe industries, etc.). Development of sanitary and hygienic nonwovens made of PP fibres has increased.

The Simulation of the Geometry of Two-component Yarns. Part I: The Mechanics of Strand Compression: Simulating Yarn Cross-section Shape

The geometry of two-components yarns is investigated, and a new approach is presented which addresses some of the limitations of other models The model takes account of the compressional deformation of the individual strands caused by transverse forces generated during the twisting process. The change in the cross-section takes account of the mechanical properties of the strands and the observed changes in cross-section shape caused by lateral compression. The outcome is a methodology and predictive equations for modelling the compressed shape of strands in two-component yarns; the model has been successfully used in CAD systems to simulate yarn appearance.

Modelling of Two-component Yarns Part II: Creation of the Visual Images of Yarns

This is the second part of a two-part series. It introduces a method for simulating a two-component yarn based on the compression model described in Part I. A quadrilateral mesh is employed to generate the over-all yarn appearance from a wire-frame model with texturing and light reflection applied to the surface. Comparison with other simulated yarns using different models and with real yarns show that the simulated yarns using the method described in this paper are more accurate and yield an improved visual representation of real yarns.

Effect of Suction Air Pressure in Friction Spinning on Yarn Properties

We have studied the effects of suction air pressure on the structural parameters and mechanical properties of yarn. Changing the amount of suction air pressure improves the fiber extent in yam and yarn appearance. Therefore, photographic and fiber tracing methods are used to evaluate, respectively, yam appearance and fiber extent in the yam. To consider the effect of suction air pressure on yarn diameter, yam tension at the yarn-forming zone and yam diameter are measured simultaneously on a friction spinning machine using various levels of suction air pressure, and then the relationship between them is considered using the cross correlation method. The results show that at high suction air pressure, yarn di ameter, yarn unevenness, and yam irregularity decrease, while fiber extent in the yarn and twist efficiency increase. On the other hand, the value of the correlation coefficient demonstrates that there is a high correlation between variations in yam tension and yarn diameter. The results of yam mechanical property measurements show that at high suction air pressure, yam tenacity increases and yarn elongation decreases. Results are reported from experiments on 100% cotton yams.

The Role of False Twist in Wrap Spinning

Using a false twister for hollow spindle wrap yam spinning is supposed to facilitate operations. However, our investigation shows that a high level of false twist can sig nificantly influence yarn appearance and mechanical properties. Wrap yarn spun with a false twister has a tortuous structure, while wrap yarn spun without a false twister is smooth. Compared with equivalent zero false twist wrap yarns, false twist wrap yarns display a similar twist-strength relationship, but lower moduli and bending rig idities at increased wrap twist. Twist contraction of the yam core during initial wrapping is the primary cause for the tortuous structure of the false twist wrap yarns. When a false twister is used, the yarn core first contracts under false twist, and at the same time is wrapped with a low wrap twist because of the difference in rotational speed between the wrapper balloon and the yarn core. Then, as the false twist is removed from the core and further wrap twist is formed at the exit side of the false twister, the core recovers from twist contraction and buckles to form a helix under the tension of the wrapper.

Comparison of Properties of Cotton Yarns Produced by the DREF-3, Ring, and Open-End Spinning Methods

The DREF-3 spinning method produces a yarn by wrapping a fibrous core with a fibrous sheath at production speeds up to 200 meters per minute. The comparative merits of this high-production spinning method to spin all-cotton yarns are inves tigated and reported. Two sets of cotton differing mainly in fiber length, strength, and Micronaire reading are used in this experiment. Yarns produced by the DREF- 3 machine are compared with yams spun by conventional ring and open-end methods. The influence of fiber properties on yarns spun by the three methods are discussed in terms of yarn strength, elongation, uniformity, and appearance. The effect of exhaust air pressure on yarns spun by the DREF-3 is also discussed.

Properties of Blend Yarns

Two properties of blended yarns are of high importance from the wearer's point of view: aesthetic appearance and elastic recovery. To predict the appearance of yarn after it is dyed in finished goods, a method is proposed that con sists of dyeing yarn in the laboratory with a dye of different affinity to component fibers. Next, the lengths of segments of strands of every kind of fiber on the surface of the yarn in the direction of the yarn axis were measured, as well as the lengths of strands consisting of mixtures of fibers. The distribution of the lengths of strands are presented and discussed. Elastic recovery of yarns made of viscose, acetate, and polyamide fibers and of their blends were analyzed at various levels of strains. Basing upon results obtained, the mechanics of elastic recovery of blended yarn is discussed.

Effects of Oil Contamination on Cotton Quality: Methods of Analysis and Characterization of Contaminants

Oil contamination of cotton is a recurring problem that adversely affects cotton quality. Processing problems occur in carding through spinning, and both yarn strength and appearance are lowered. Problem severity increases as the level of contamination increases. A simple method is described for quantitative determination of contamination. Contaminants are characterized and differentiated from each other and from the natural constituents of cotton by use of infrared spectrophotometry and gas-liquid chromatography.

Revolving Ring

A relatively simple but an effective mechanical device has been designed and developed which is capable of rotating the ring at any desired speed in the direction of the traveller. The comparative spinning tests on the conventional and revolving rings on the same conventional ring spinning frame have proved that the revolving ring is highly effective in reducing the end-breakages at high production rates. Besides increased production rates, the basic concept of revolving the ring has several added advantages, such as better yarn appearance, regularity and twist-distribution and longer life of the traveller.

Inter-relações das características tecnológicas da fibra e outras propriedades do algodão com as características do fio e com a produção

As características tecnológicas da fibra - comprimento (UHM), uniformidade, resistência e índice micronaire - e mais a porcentagem de fibra, o pêso de 1 capulho e o pêso de 100 sementes foram estudados em relação à produção do algodão em caroço, resistência e aparência do fio. Foram calculadas várias equações, através de análises de regressão múltipla, para mostrar o grau de associação entre as três características consideradas respostas e as sete variáveis independentes mencionadas. Através da análise de regressão múltipla foi possível determinar a ordem de importância de cada variável em relação a uma resposta específica. O estudo foi realizado em 57 algodões diferentes, compreendendo variedades e linhagens, num total de 801 amostras, provenientes de nove localidades do Estado de São Paulo.

Unevenness in the Appearance of Spun Yarn

Object: This article experimentally reviews the assumptions on theory and the theoretical equations presented in the previous instalments. It seeks to confirm the theories previously deduced and grasp the characteristics of apparent unevenness. The samples used are 30s spun rayon yarns.Results: 1. The over-level ratio introduced in part 1 will do as a measure, or yardstick, by which to indicate the perception of apparent unevenness.2. Apparent unevenness is characterized not by a certain level or expression, but by the curve of the over-level ratio proper.3. The theoretical equations derived in part 1 are practical.4. The value of the length distribution in an ideal yarn and the value of the length distribution in service yarn have similar density functions.5. Level, the number of uneven areas, and the relation between these two factors and length have been experimentally obtained. The mean length of uneven areas has been deduced.6. An apparent uneven area is determined by the over-level ratio of the area proper. It is not influenced by the unevenness of environs or by the dimensions of the uneven area, i.e., not by any disturbances.7. The over-level ratio which distinguishes an uneven area from an even area exists in each level. The value of this discrimination threshold range has been obtained.8. The theoretical equation of the total length of uneven areas on a black board, given in part 2, fits practical cases.

7—THE PREPARATION OF CORE YARNS ON A CONVENTIONAL DOUBLER

A brief summary is given of the various types of core yarn and their method of manufacture, which often involves the use of specially designed machinery. An investigation is described in which true core yarns are prepared on a conventional doubler by making use of the principle of differential twist contraction. The yarns are composed of a continuous-filament Terylene or nylon core surrounded by cotton covering yarns. The effects of twist construaion and processing conditions on yarn appearance and tensile properties are examined.

Unevenness in the Appearance of Spun Yarns

Object The relation between the apparent unevenness of a spun yarn and the apparent unevenness on the black board is discussed theoretically. The apparent unevenness on the black board is expressed by the total length of its various widths. Results1. The probability of the presence of uneven areas exceeding m in number in a band made of infinitely long, parallel yarns to the number of M is given as: P(_??_m, M)=1-∑<m-1><i=0> (M i)(α/β)i/(1+α/β)M, where α is the input density and β the output density of an uneven area in a yarn.2. The total length T of apparent uneven areas shown on a black board which has widths to the number of N and which is L in length is obtained as follows: T=L(N-M+1)[P(_??_m, M)-∑<m-1><j=1>P(_??_m, M-j)-{P(_??_m', M+1)-∑<M><j=1>p(_??_m', M+1-j)}]where m is the discrimination threshold for an uneven area having widths to the number of M, and m' is the discrimination threshold for widths to the number of M+1.3. The total length T of apparent uneven areas in ideal yarns and the total length T of service yarns Nos. 1 and 3 are calculated by using the foregoing results.4. The length distribution of apparent uneven areas is the transition probability of a high order in Markov's chain.

Unevenness in the Appearance of Spun Yarn

To clarify the substance of the sensory test of unevenness with a black board, this article makes an analysis which includes some sensory factors. The present installment suggests and discusses theoretically two criteria by which to represent apparent unevenness, i.e., the over-level ratio and length distribution of an uneven area. It also introduces an ideal yarn which has a more definite physical meaning than the usual random slivers. Over-level ratio R and length distribution ψ(l) of the ideal yarn are obtained as follows: R=e-n∑<+∞><n=n0> (n)n/n! ψ(l)={ψ(Δl)}l/Δlwhere n : mean number of fibers in a yarn n0 : given level l : given length of an uneven area Δl : a small length of uneven area ψ(Δl)=∑<∞><nM=n0> [(e-n nnM/nM!/ ∑<∞><nM=n0> e-nnn/n!){∑<∞><kb=0> e-λΔl ×(λΔl)kb/kb!(∑<∞><kf=kb-(nM-n0) e-λΔl (λΔl)kf/kf!)}] λ : input density of the front end of a fiber.Examples of calculation are given, the relation between U% and the over-level ratio is shown, and the mean length of an uneven area and the ideal value of the Imperfection Index are calculated for practical application.

44—AN INVESTIGATION INTO THE FORMATION OF FLY WASTE DURING WORSTED CAP SPINNING

Fly waste at the spinning frame is a potential cause of slubs and poor yarn appearance and may account for up to 1% by weight of the tops being processed. This paper is an attempt (a) to assess the effect of factors contributing to the formation of fly waste, and (b) to investigate the nature of fly waste.

紡績糸の外観むらに関する研究

目的 前報までに解明した諸成果の1つの応用として, 糸の測定値から糸条板上の外観むらを推定する実用的方法を導く.合わせて実験的に長さ分布の理論値と実験値を比較する.またM―T曲線の性質を考察する.最後に第1～5報の主要な結論をまとめる. 成果 (1) 糸のIPI値とU%を測定することにより容易にM―T曲線を得る実用的な方法を見出した. (2) 長さ分布の理想糸の値と実際の糸の値とは, 類似の密度関数を持つ. (3) レベルとむらの個数および長さの関係を実験的に調べ, また太さむら部分の平均長を求めた. (4) M―T曲線の性質を考察し, M―T法が肉眼判定と異なる点を示し, また確率空間との関係, 実測値の考え方, 各種要因との関係などを明らかにした.

紡績糸の外観むらに関する研究

目的 糸むらと, 糸条板上の外観むらとの関係を理論的に考察する.外観むらは, 外観むらの幅別の合計長と, 幅別の長さ分布とにより表わす.成果 1. 無眼に長いM本の平行糸帯中に, m本以上の太さむら部分が存在する確率は, つぎの通りである.p (≥m、M) =1-Σm-1t-0 (Mi) (α/β) t/ {1+ (α/β)} Mここにα, β は, それぞれ1本の糸の入力密度および出力密度である。2. 幅N本, 1周の長さLの糸条板に生ずる外観むら長さTは, つぎの通りである.T=L (N-M+1) 〔p (≥m、M) -ΣM-1j=1p (≥m、M-j) - {p (≥m'、M+1)-ΣMj=1p(≥m'、M+1-j)}ここにmは外観むら幅Mのときの弁別閾, m'は外観むら幅M+1のときの弁別閾である.3. 上式を用いて, 理想糸と実際の1号糸と3号糸について, 外観むら長さTを求めた.4. 外観むらの長さ分布が, マルコフ連鎖の高次の推移確率であることを示し, 計算例により分布の形を見出した.

紡績糸の外観むらに関する研究

目的 糸条板上に現われる外観むらと, 糸のむらとの関係を求める.第1報においては関連諸研究の問題点を明らかにし, 本研究との関係を述べ, さらに理想糸について太さむら部分が糸中に占める比率を求める. 成果 7項の仮定にもとづく理想糸モデルを導入し, このモデルについて任意の繊維本数n0以上の部分が全糸中に占める比率 [レベル超過率0 (+n0)] を次式の通り求めた.0 (+n0) =e-n (∞ Σ n=n0) nn/n!≒1/√2π∫∞t1e-t2/2dtここにnは糸中の平均繊維本数, t1= (n0-n) /√nである.つぎに応用として, 理想糸のレベル超過率の計算例を示し, さらに実際の糸のU%とレベル超過率との関係を導いた.また従来のランダムスライバと本研究の理想糸との相異点を明らかにした.