Stability of a Blown Film Extrusion Process

Abstract

The stability of a blown film extrusion process has been investigated using a simple isothermal Newtonian model. Although the Newtonian model may be an oversimplification for polymer melts, it serves as a reasonable first approximation for linear polymers (e.g., linear low density polyethylene) in extensional flow situations. The results obtained by the method of linear stability analysis indicate that the blown film process becomes unstable if the blow-up ratio (BUR) or the film thickness reduction is larger than a certain critical value. In addition, existence of an optimum freeze-line-height is predicted at which the region of stable operation is largest in terms of the BUR and the film thickness reduction. These predicted trends are in qualitative agreement with experimental observations for linear polymers such as LLDPE.

Transient solutions of the dynamics in film blowing processes

“…This transformation has essentially converted the free-end-point problem into a computationally amenable fixed-end-point one. Second, instead of the so-called cylindrical approximation in calculating the amount of the air pressure inside the bubble as used by others [4][5][6]9], the actual shape of the bubble is traced in calculating the real bubble volume. This is an important point because it allows the exact temporal shape of the propagating bubble disturbances to be captured in the simulation during the oscillating instability.…”

“…Over the past four decades many theoretical and experimental studies have been conducted on this important process. Among the major research results [1][2][3][4][5][6], the most comprehensive stability analysis was first carried out by Cain and Denn [4] and then followed by Yoon and Park [5,6]. Along with many interesting stability findings, the draw resonance instability, a self-sustained limit cycle-type supercritical Hopf bifurcation, has been well documented in these studies.…”

Investigation of Polymer Stretching Instabilities: Application to Film Blowing

“…A few authors tried to model film blowing instabilities in the tangent (and hence moving) frame first with a Newtonian isothermal hypothesis (Yeow, 1976;Cain and Denn;Yoon and Park, 1999;Andrianarahinjaka and Micheau, 1996). Hyun et al (2004) and Lee et al (2001) investigated the stability of viscoelastic non isothermal film blowing in the axisymmetric case.…”

Existence of optimal cooling conditions in the film blowing process

“…1), i.e., Petrie and Pearson [1,2] establishing the first modeling standards for the process, and Cain and Denn [3] reporting the first comprehensive stability and multiplicity analysis of the process, there have been many research efforts throughout the world enhancing both the theoretical understanding of and the concurrent experimental improvements on the process [4][5][6][7][8][9][10][11][12][13][14][15][16]. Lately the transient solutions of the film blowing dynamics have been obtained by Hyun et al [13] for the first time in 30 years, employing new mathematical and numerical schemes like an orthogonal collocation on finite element and a coordinate transformation for solving the governing equations of the non-isothermal process of viscoelastic fluids.…”