Problem VIII Design of a Film Blowing Process for Garbage Bags

DESIGN PROBLEM VIII DESIGN OF A FILM BLOWING PROCESS FOR GARBAGE BAGS 

The LDPE exiting the die is assumed to exhibit die swell (see Fig. 3.1 in Chapter 3), which can be calculated from Eq. 3.89 (i.e., assume that capillary die swell is equal to diameter and thickness swell from an annular die). Melt fracture (Section 7.2.2) for LDPE appears when the maximum wall shear stress exceeds 1.13 x 10 Pa. To secure uninterrupted production a safety factor of 3 is applied with regard to the maximum wall shear stress. The power-law relationship for LDPE at 170 °C and for y 0.1 s is 

We then consider the analysis of the film blowing process, which should be based on the maximum die swell dimensions as the initial dimensions and isothermal conditions are assumed. Calculate the pressure of the blowing air, the drawing force, and the velocity at the nip rolls if the dimensionless frost line height is confined to 5 and the distance of the nip-roll system from the position where the maximum die swell level occurs is 1.5 m. 

Polymer Processing Principles and Design, Second Edition. Donald G. Baird and Dimitris I. ColUas. 2014 John Wiley Sons, Inc. Published 2014 by John Wiley Sons, Inc. 

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