Precautions In The PET Bottle Blow Molding Process

Precautions in the PET bottle blow molding process.

The blow molding process is a two-way stretching process, in which the PET chains are extended, oriented and aligned in both directions, thereby increasing the mechanical properties of the bottle wall, improving the tensile, tensile and impact strength, and have a high Good air tightness.Although stretching helps to improve the strength, it should not be stretched too much. The stretch-blow ratio should be well controlled: the radial direction should not exceed 3.5 to 4.2, and the axial direction should not exceed 2.8 to 3.1. The wall thickness of the preform should not exceed 4.5mm.

In the stretch 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: the starting timing of stretching, the stretching speed, the starting and ending timing of pre-blowing, the pre-blowing pressure, the pre-blowing flow rate, etc. If possible, it is best to control the overall temperature distribution of the preform, the bottle The temperature gradient of the inner and outer walls of the billet.

In the process of rapid blow molding and cooling, induced stress is generated in the bottle wall. For carbonated beverage bottles, it can resist internal pressure, which is good, but for hot-fill bottles, it is necessary to ensure that it is fully released above the glass transition temperature.