The blow molding process of the PET bottle blowing mach […]
The blow molding process of the PET bottle blowing machine is a bidirectional stretching process. In this process, the PET chains are bidirectionally extended, oriented and arranged, thereby increasing the mechanical properties of the bottle wall and improving the stretching, tensile and impact resistance. strength, and has excellent air tightness. Although stretching helps to increase strength, it should not be overstretched, and the stretch-to-blow ratio should be controlled.
Blowing is carried out between the glass transition temperature and the crystallization temperature, usually controlled between 90 and 120 degrees. In this range, PET exhibits a high elastic state, and it becomes a transparent bottle after being rapidly blown, cooled and shaped. In the one-step method, this temperature is determined by the cooling time in the injection molding process (such as the Aoki blow molding machine), so the relationship between the injection and blowing stations should be well connected.
In the blow molding process, there are: stretching—one blow—second blow. The time of the three actions is very short, but they must be well coordinated, especially the first two steps determine the overall distribution of the material and the quality of the blowing. Therefore, it is necessary to adjust: stretching start timing, stretching speed, pre-blowing start and end timing, pre-blowing pressure, pre-blowing flow, etc. If possible, it is best to control the overall temperature distribution of the preform, and the internal The temperature gradient of the outer wall. In the process of rapid blow molding and cooling, induced stress occurs in the bottle wall. For inflatable beverage bottles, it can resist internal pressure and has advantages, but for PET bottle blowing machines, it is necessary to ensure that it is fully released above the glass transition temperature.