담당자 : Tracy Wu
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August 5, 2020
The blow molding process is a two-way stretching process in which the PET chain is bidirectionally extended, oriented and aligned, thereby increasing the mechanical properties of the bottle wall, improving the tensile, tensile, and impact strengths. Good air tightness. Although stretching helps to increase the strength, it cannot be excessively stretched. The tensile inflation ratio should be 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 4.5 mm.
The blowing is carried out between the glass transition temperature and the crystallization temperature, and is generally controlled between 90 and 120 degrees. In this interval, PET is in a highly elastic state, which is quickly blow molded, cooled and shaped to become a transparent bottle. In the one-step method, this temperature is determined by the length of cooling in the injection molding process (such as the Aoki blow molding machine), so it is necessary to connect the two injections.
In the blow molding process: stretching - one blowing - two blowing, the three movements are very short, but must be well coordinated, especially the first two steps determine the overall distribution of the material, the quality of the blowing. Therefore, it should be adjusted: 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, bottle The temperature gradient of the inner and outer walls of the blank.
In the process of rapid blow molding and cooling, induced stress is generated in the bottle wall. For a carbonated beverage bottle, it is resistant to internal pressure and is beneficial, but for hot-filled bottles it is necessary to ensure that it is fully released above the glass transition temperature.