Abstract
Twisting is an important process to form a continuous yarn from short fibres and to determine the structure and properties of the resultant yarn. This paper proposes a new theoretical model of yarn dynamics in a generalized twisting system, which deals with two important phenomena simultaneously, that is, twist generation and twist propagation. Equations of yarn motion are established and the boundary value problems are numerically solved by Newton-Raphson method. The simulation results are validated by experiments and a good agreement has been demonstrated for the system with a moving rigid cylinder as the twisting element. For the first time, influences of several parameters on the twisting process have been revealed in terms of twist efficiency of the moving rigid cylinder, propagation coefficients of twist trapping and congestion. It was found that the wrap angle and yarn tension have large influence on the twisting process, and the yarn torsional rigidity varies with the twisting parameters.
Highlights
Twisting is a key process of making a continuous yarn[1] from short discontinuous fibers, such as carbon nanotubes, cotton or wool etc
A novel twisting system has been developed by introducing a moving rigid cylinder[35], which is incorporated in a ring spinning machine as a false-twisting element, and at the same time blocks the twist propagation generated by the spindle and by the false-twisting element
The difference between simulated values and experimental observations is smaller than 10%, which implies that the simulated figures match well with the measurement values and the theoretical model can predict a relatively accurate value of the problem
Summary
Twisting is a key process of making a continuous yarn[1] from short discontinuous fibers, such as carbon nanotubes, cotton or wool etc It strongly influences the structure, mechanical strength, rigidity, thermal and electric conductivity as well as surface characteristics of the resultant yarn. During the formation of continuous composite fibers with one-dimensional fillers like nanotubes and liquid crystals, twisting may introduce a desired orientation and distribution of the fillers in the fibers[2] In all these yarns, the majority of the surface fibres follow a helical path with a helix angle β with respect to the yarn direction, as shown in the SEM micrograph of Fig. 1, β = tan−1(2πR0T ). A novel twisting system has been developed by introducing a moving rigid cylinder[35], which is incorporated in a ring spinning machine as a false-twisting element, and at the same time blocks the twist propagation generated by the spindle and by the false-twisting element. Influences of various system parameters on the twist efficiency of the moving rigid cylinder, the propagation coefficients of twist trapping and congestion are identified
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