| The literature on tubular film blowing is contradictory, even on such basic matters as to whether increasing inflation pressure increases or decreases the bubble radius. To provide a solid experimental base for physical understanding and theoretical modelling, detailed on-line measurements of the tubular film blowing process were made using three polyethylenes (a low density, a linear low density and a high density material, all of melt index 1.0). The measurements included blow-up ratio as a function of inflation pressure and take-up ratio; the extrusion temperature and the air flow rate were also varied. On-line distributions of radius, thickness, velocity and temperature along the machine direction were made in some runs. For the most part these data showed an "intuitive" effect of inflation pressure on blow-up ratio; that is, increasing the pressure caused the final radius (the blow-up ratio) to increase. However, at high blow-up ratios (typically values of 3;The validity of the two existing theoretical models (the earlier model of Pearson and Petrie and the newly proposed model in the author's M.S. thesis) are examined by making qualitative comparisons with experimental data. It is found that the predictions of the new model agree with the basic trends of data but those of Pearson-Petrie do not. Furthermore, the newly proposed model, incorporating a deformation-thinning viscosity equation, explained all of the essential features of the data.;Comparisons with the model of Pearson and Petrie were also made. If one does the analysis as one would in solid mechanics--in which the shape of the bubble is known a priori--there are not substantial differences between the predictions of the Pearson-Petrie model and that of the present paper. The reasons for this difference are not clearly understood. |
