The Blowing Moulding Machine plastic process is a proce […]
The Blowing Moulding Machine plastic process is a process of biaxial stretching (longitudinal and transverse). During this process, the PET chains are bidirectionally extended, oriented and aligned, thereby increasing the mechanical properties of the bottle wall and increasing the tensile, tensile, and impact strength. , And have 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 process, this temperature is determined by the length of the cooling process in the injection molding process, so the relationship between the injection and the blowing of the two stations should be bridged.
During the blowing moulding machine process, there are: stretching - blowing once - blowing twice. The time for the 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 blowing molding machine 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.
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