In the process of blowing the film blowing machine, the plastic is extruded from the extrusion machine's head mouth die to blow into a film, experiencing a series of changes such as viscosity, phase change, and these changes are closely related to the temperature of the material in the extrusion process, whether the speed of the screw is stable, the pressure of the head and the structure of the mouth die, the cooling of the air ring and the cooling of the indoor air and the pressure of the blown air. The cooperation and coordination of the membrane tube tensile effect directly affect the performance of the film and the production efficiency.
The temperature control of each stage of the extruder is the most important factor in the extrusion of the tube billet. Usually, along the barrel to the direction of the head die, the temperature of the plastic is gradually increased, and a stable control must be achieved. In this experiment, LDPE blow molding, the principle of the barrel temperature is 140℃, 160℃, 180℃ increasing, the head of the die slightly lower. The increase of melt temperature, the decrease of viscosity, the decrease of head pressure and the increase of extrusion flow are conducive to the increase of yield. However, if the temperature of the film blowing machine is too high and the screw speed is too fast, the shear effect is too large, it is easy to decompose the plastic, and the film tube is poorly cooled, so that the diameter of the film tube is difficult to stabilize, and the phenomenon of unstable film bubble "long neck" will be formed, and the diameter and wall thickness of the bubble (film) tube are uneven, and even affect the smooth operation. Therefore, the extrusion temperature and speed of the film blowing machine are usually controlled slightly lower.
