Study on design and experiments of extrusion die for polypropylene single-lumen micro tubes

Abstract

The extrusion die is one of the most important parts in extrusion processing. It is difficult to design and manufacture to the land length of the die for polypropylene single-lumen micro tubes. In the paper, the land length was designed by rheological properties of polypropylene. For single-lumen micro tubes, the land length with a small air hole was so small that it was easily to be broken, especially in the processing. Therefore, the land length was manufactured by micro-EDM. Then, the experimental results showed that the designed and manufactured die was reasonable and could meet the using requirements. According to the further extrusion experiments, the relationships between tube sizes and extrusion processing parameters were explored. The results indicated that the die temperature had little effect on the tube sizes. That was because the increasing temperature reduced the viscosity and the pressure drop in the die simultaneously. With the given temperature and the constant screw speed, the macromolecules of the polymers with the increasing pulling speeds were straightened to the limit and slipped among the macromolecules, which caused the diameters and wall thicknesses of the micro tubes to decrease in the nonlinear curves. Meanwhile, in the given temperature and the constant pulling speed, the higher the screw speeds got, because of the shear thinning, the smaller the shear viscosity was. However, the increasing amplitudes of the pressure in the die were getting small. So the volume flow rates were also reduced accordingly. Thus the change rates of the diameters and wall thicknesses were also getting small. In the other word, the relations between the micro tube sizes and the screw speeds were not linear, but nonlinear. These results were very valuable for the extrusion die designs of multi-lumen micro tubes and the extrusion processing.