Non-isothermal film casting : determination of draw resonance

The important industrial process of casting polymeric films suffers from the "draw resonance" instability that appears as sudden oscillations in the product dimensions. This instability influences the quality of the end-product and negatively limits productivity and efficiency of the process. The draw resonance originates when a material is being processed beyond the limits of its intrinsic properties. Research is conducted with the intention to find those process and material properties that allow to optimize the production process while keeping it stable. This paper concentrates on a non-isothermal analysis of the stability of the film casting. The mathematical model of the process is given by a quasi-linear system of first order PDEs with two point boundary conditions. The constitutive polymer behavior is approximated by the modified Giesekus model. Linear stability analysis combined with the Laplace transformation of the resulting linear system is applied to find parameters that determine mathematical and thus process instability. It all comes down to determining the spectrum of a compact operator; corresponding eigenfunctions can be regarded as the characteristic modes of the system. For implementation, the modification of Galerkin approach is used. The major advantage of the mathematical and numerical method is that the full spectrum is calculated in a matter of seconds. Our results agree perfectly with the ones from literature for isothermal case, and with the experimental data for the non-isothermal case. The results also indicate that non-isothermality is highly important and cannot be excluded from modeling

Traveling waves along viscous filaments

In this article, deflections of a viscous filament in a classical fiber spinning set-up are analyzed. The deflections are considered in a direction perpendicular to the vertical equilibrium state of the spin line. The result is a traveling wave equation with non-uniform coefficients representing the non-uniform filament velocity and non-uniform tension in the spin line. Under neglect of air drag, the system is conservative with respect to an energy functional, so that its eigenmodes have purely imaginary characteristic values. A numerical analysis of the eigenmodes of the system reveals that deflections propagate from take-up wheel to spinneret, with frequencies being multiples of a basic frequency and amplitudes sinus shaped with the maximum being shifted toward the spinneret. From the numerical results, a formula is derived, which approximates the basic frequency and traveling wave velocity directly in terms of the spinning process parameters. Keywords: Deflection – Eigenmode – Fiber spinning – Frequency – Traveling wave – Viscous filament – Viscous string mode

Non-isothermal film casting : determination of draw resonance

The important industrial process of casting polymeric films suffers from the draw resonance instability that appears as sudden oscillations in the product dimensions. This instability influences the quality of the end-product and negatively limits productivity and efficiency of the process. The draw resonance originates when a material is being processed beyond the limits of its intrinsic properties. Research is conducted with the intention to find those process and material properties that allow to optimize the production process while keeping it stable. This paper concentrates on a non-isothermal analysis of the stability of the film casting. The mathematical model of the process is given by a quasi-linear system of first order PDEs with two point boundary conditions. The constitutive polymer behavior is approximated by the modified Giesekus model. Linear stability analysis combined with the Laplace transformation of the resulting linear system is applied to find parameters that determine mathematical and thus process instability. It all comes down to determining the spectrum of a compact operator; corresponding eigenfunctions can be regarded as the characteristic modes of the system. For implementation, the modification of Galerkin approach is used. The major advantage of the mathematical and numerical method is that the full spectrum is calculated in a matter of seconds. Our results agree perfectly with the ones from literature for isothermal case, and with the experimental data for the non-isothermal case. The results also indicate that non-isothermality is highly important and cannot be excluded from modeling

Traveling waves along viscous filaments Traveling waves along viscous filaments

Abstract In this article, deflections of a viscous filament in a classical fiber spinning set-up are analyzed. The deflections are considered in a direction perpendicular to the vertical equilibrium state of the spin line. The result is a traveling wave equation with non-uniform coefficients representing the non-uniform filament velocity and non-uniform tension in the spin line. Under neglect of air drag, the system is conservative with respect to an energy functional, so that its eigenmodes have purely imaginary characteristic values. A numerical analysis of the eigenmodes of the system reveals that deflections propagate from take-up wheel to spinneret, with frequencies being multiples of a basic frequency and amplitudes sinus shaped with the maximum being shifted toward the spinneret. From the numerical results, a formula is derived, which approximates the basic frequency and traveling wave velocity directly in terms of the spinning process parameters

Constitutive model parameters estimation from rheotens steady state and resonance characteristics

This paper presents a method to determine the parameters in a polymer constitutive model using data obtained from a Rheotens experiment. The novelty of the suggested approach is the simultaneous fitting of model parameters to different types of data given by Rheotens, i. e., force-velocity curve, onset of draw resonance and frequency of oscillations. To determine the onset and frequency of oscillations, a stability analysis is exploited and the spectrum of a quasi-hyperbolic differential operator is calculated. The proposed approach is efficient and accurate. To demonstrate its applicability and consistency, a modified Giesekus constitutive model is chosen and model parameters are fitted to the Rheotens data for three different types of polymer (LLDPE, PP, PS)

Traveling waves along viscous filaments

In this article, deflections of a viscous filament in a classical fiber spinning set-up are analyzed. The deflections are considered in a direction perpendicular to the vertical equilibrium state of the spin line. The result is a traveling wave equation with non-uniform coefficients representing the non-uniform filament velocity and non-uniform tension in the spin line. Under neglect of air drag, the system is conservative with respect to an energy functional, so that its eigenmodes have purely imaginary characteristic values. A numerical analysis of the eigenmodes of the system reveals that deflections propagate from take-up wheel to spinneret, with frequencies being multiples of a basic frequency and amplitudes sinus shaped with the maximum being shifted toward the spinneret. From the numerical results, a formula is derived, which approximates the basic frequency and traveling wave velocity directly in terms of the spinning process parameters. Keywords: Deflection – Eigenmode – Fiber spinning – Frequency – Traveling wave – Viscous filament – Viscous string mode