PET bottle blow molding should pay attention to technical details

The PET bottle blowing process is a biaxial stretching process in which the PET chain is bi-directionally extended, oriented and aligned, thereby increasing the mechanical properties of the bottle wall and increasing the tensile, tensile, and impact strength, and Has a good air tightness. Although stretching helps to increase the strength, it must not be excessively stretched, and the stretch blow ratio must be controlled so that it does not exceed 3.5 to 4.2 in the radial direction and 2.8 to 3.1 in the axial direction. The wall thickness of the preform should not exceed 4.5 mm.
Blowing is carried out between the glass transition temperature and the crystallization temperature and is generally controlled between 90 and 120 degrees. In this range, PET exhibits a high elasticity, and is quickly blow molded and cooled to become a transparent bottle. In the one-step method, this temperature is determined by the length of the cooling time in the injection molding process, so the relationship between the injection and blowing two stations should be connected.
In the process of blow molding: stretching → blowing once → blowing twice, the time for three actions is very short, but it must be well coordinated, especially the first two steps determine the overall distribution of the material and the quality of the blowing bottle. Therefore, it is necessary to adjust well: starting time of stretching, stretching speed, starting and ending timing of pre-blowing, pre-blowing pressure, pre-blowing flow, etc. If possible, it is better to control the overall temperature distribution of the preform, bottle The temperature gradient inside and outside the billet.
In the rapid blow molding and cooling process, induced stress occurs in the bottle wall. For carbonated beverage bottles, it is good for internal pressure resistance, but for hot-fill bottles, it must be ensured that it is fully released above the glass transition temperature.