Dynamic analysis of over-end unwinding of yarn

The over-end unwinding of yarn from a stationary helically wound package is investigated. The thesis work presents dynamics analysis of yarn unwinding from midsection of package, and across end regions of package as well.; An integrated model of three-region analysis for unwinding from conical package, which covers the balloon region, the sliding region on the package, and the stationary region on the package, has been developed. An iterative method to calculate the value of λ = ωc/ V is introduced. The results show that for non-zero wind angle, λ is always greater than 1 for front-to-back unwinding, and is less than 1 for the reverse direction. Tension at the guide eye is highly sensitive to the value of λ; tension increases significantly with the increase of λ value. Tension in sliding region on package may increase from the lift-off point to the unwind point substantially for front-to-back unwinding.; A parametric study has been carried out and the influences of key variables on unwinding have been studied for front-to-back (λ > 1) and back-to-front (λ < 1) unwinding. The yarn tension increases significantly with an increase in wind angle, conicity of package, and the unwind point height from the guide eye for front-to-back direction. In the other direction, it decreases with an increase in wind angle and conicity of package. Residual tension in package, however, does not affect tension distribution in balloon and sliding region.; Unwinding yarn across end regions of package, where wind angle and residual tension varies due to winding process is studied. It shows that yarn tension, as well as λ value subjects to decrease sharply when unwinding across the region. It is observed that for larger conicity package and yarn wind angle, tension variation becomes wider across the far end region. When unwinding across near end region, the study is confined to a closed region as that regular perturbation scheme could be applied for half loop balloons. Analysis of balloon and sliding regions are investigated separately. Discontinuity of tension and tangential vector at the end of package must be allowed in order to satisfy the boundary conditions. Forces exerted on yarn at the end of package are studied to splice these two regions together. An iterative method is introduced to calculate the tension at the end of balloon region and at the beginning of the sliding region. Results shows that an abrupt decrease of yarn tension may occur at this point. Continuity of tangential vector at the point is broken as well. Tension in the sliding region is small and the third region may be eliminated.