Theoretical Study of Wrapping Twist in Single Jet False Twist Spinning

We investigate the differences in the structure of polyester and cotton wrappers, thus gaining some idea of their wrapper-fiber-forming tendencies. We observe and photograph forty randomly selected locations along a yarn length with a scanning electron microscope to determine the numbers of polyester and cotton wrappers, the numbers of loose polyester and cotton wrappers, and the wrapping angle for each wrapping fiber. We also study the effects of polyester length, denier, cotton fiber type, and yam delivery speed on these parameters. We investigate the possibility of nep formation in air jet spinning by studying the structure of neps with the scanning electron microscope. The results show that though polyester fibers contribute more to the total number of wrappers, cotton seems to have better wrapperforming tendencies when the numbers of polyester and cotton wrappers are expressed as percents of the respective numbers of fibers in the yarn cross sections. Cotton forms more loose wrappers than polyester, and the wrapping angle for cotton is greater. The structural study of neps collected from air-jet spun yarns shows that some of them have probably formed during spinning.All important yam properties are known to depend on yam structure. Differences in the properties of yams . spun with different technologies can be attributed to the differences in their structures, and yarn structure has therefore been a subject of wide interest among researchers. A number of studies on the structure of air jet spun yarn have put more emphasis on investigating and classifying various structures observed along the yarn length. Thus, Grosberg et al. divided the air-jet spun yarn structure into four classes [ 4 ] , while Chasmawala et al. [ 3 ] and Lawrence and Baqui [ 7 ] divided it into three classes. The effects of various factors on yarn structure and the consequent changes in yam characteristics have also been explained [ 1,3,4,[7][8][9].Though polyester/cotton blends can be successfully spun on an air-jet system, it is known to produce poor quality cotton yams. This leads us to hypothesize that polyester fibers yield a greater number and better quality of wrappers, which in the polyester/cotton blends mainly consist of polyester. Earlier, cotton fibers were believed to be unable to form good quality wrappers due to their short lengths and high bending and torsional rigidities [ 1, 101. but no experimental study involving comparisons of polyester and cotton wrappers has been reported so far. We therefore began this yam structural study to investigate the differences in the ... numbers of polyester and cotton wrappers and their structures in polyester/cotton blended air-jet spun yams. Our aim was to determine whether cotton fibers form fewer wrappers than polyester, whether cotton fibers form greater numbers of loose wrappers than polyester, and whether the wrapping angles are different for polyester and cotton. We also investigated nep formation in air-jet spinning, possibly due to obstructions to the movement of the separated ...

Section: Resultscontrasting

confidence: 61%

Section: Methodscontrasting

confidence: 61%

The Structure of Polyester/Cotton Blended Air-Jet Spun Yarn

Bhortakke

Nishimura

Matsuo

1999

“…Of particular concern is the analysis of the initial wrapping formation in the nozzle. The initial wrapping is so important that Krause and Soliman [9] We adopted high-speed photography to capture images of a fiber passing through the nozzle of an air-jet spinning machine. The nozzle used for experiments was enlarged, since the geometry of the actual nozzle is too small on the photographs.…”

Section: Numerical Simulationmentioning

confidence: 99%

“…The principle of yam formation and the investigation of the yarn structure indicate that the formation of wrapper fibers in the first nozzle plays a dominant role in this technology. Krause and Soliman theoretically analyzed the wrapping twist in a single-jet air system [8]. In this work, we use the numerical method to simulate fiber motion in the nozzle of an air-jet spinning machine, showing the process that causes an edge fiber (free fiber) to wrap while it is being delivered by the air flow in the nozzle.…”

mentioning

confidence: 99%

Numerical Simulation of Fiber Motion in the Nozzle of an Air-Jet Spinning Machine

Zeng

2004

A two-phase flow model is developed to simulate the fiber motion in the nozzle of an air-jet spinning machine. The computational results coincide with the images captured by high-speed photography. Three parameters, the first nozzle pressure, the jet orifice angle, and fiber flexural rigidity, are discussed in terms of their influences on wrapper formation and, consequently, on yarn structure and yarn quality. The predictions of yarn tensile properties tally with the experimental results reported by several researchers.Air-jet spinning is becoming an important system in short staple spinning because it is advantageous for processing speeds, costs, and ability to spin fine counts. Researchers have been paying much attention to this spinning method since the first single air-jet system was developed by Du Pont in 1963. Studies have focused on three subjects: the principle of yam formation, the structure of the yarn, and the effects of various parameters on yarn quality. Regarding the principle of yarn formation, there have been two points of view [1, 7, 18], and we maintain the following viewpoint: The edge fibers wrap the false twisted core in the opposite direction while passing through the first nozzle, and the second nozzle inserts the false twist into the fiber strand coming out of the front roller. Untwisting downstream of the second nozzle produces considerably more twist in these wrapper fibers, thus giving the yarn its strength. Investigations of yarn structure have been reported, and several classification systems have been developed [4, 7, 10]. The effects of the parameters of process conditions, nozzle design, and fiber properties on yarn quality have been studied using experimental techniques [ 1,4,7,10,[13][14][15]19]. The principle of yam formation and the investigation of the yarn structure indicate that the formation of wrapper fibers in the first nozzle plays a dominant role in this technology. Krause and Soliman theoretically analyzed the wrapping twist in a single-jet air system [8]. In this work, we use the numerical method to simulate fiber motion in the nozzle of an air-jet spinning machine, showing the process that causes an edge fiber (free fiber) to wrap while it is being delivered by the air flow in the nozzle. Fiber Motion Model.

“…A theoretical approach has been presented to calculate and predict the strength of a false-twist yarn spun by a single air orifice. It is based on an idealized yarn structure model [2]. Numerical simulation of the air twist-nozzle with a double air orifice was studied as reference.…”

Section: A Design Study Of An Air-twist Nozzle By Analysis Of Fluid Flowmentioning

confidence: 99%

A Design Study of an Air-twist Nozzle by Analysis of Fluid Flow

Juraeva

Song

Chun

2010

The efficiency of the air-twist nozzle has a direct effect on the uniform tension of spandex yarn during the winding and unwinding process. The different geometries of the air-twist nozzle were studied as a reference. Compressed air coming out of the air orifice flows through the wall of the yarn channel in a twisting motion. The purpose of this research is to develop an air-twist nozzle geometry which has well-twisted motion, with reasonable vorticity strength and velocity. The paper presents investigations of the effects of the inlet pressure and the yarn channel shape of the air-twist nozzle. The Ansys CFX was used to perform steady simulations of jet flow inside the air-twist nozzles. Results of computational simulations for the two most promising cases were confirmed by experimental tests. The twist and flow patterns, specifically vorticity and velocity inside the air twist nozzles, are discussed in this paper. As a result of this research, an air-twist nozzle of improved design is now being produced for commercial use.