A bottle blowing machine is a machine that can blow the finished preforms into bottles through certain technological means. At present, most of the blow molding machines adopt the two-step blowing method, that is, preheating - blow molding.
1. Preheating
The preform is irradiated through a high temperature lamp to heat and soften the body of the preform. In order to maintain the shape of the bottle mouth, the preform mouth does not need to be heated, so a certain cooling device is required to cool it.
2. Blow molding
This stage is to place the preheated preform into the prepared mold, inflate it with high pressure, and blow the preform into the desired bottle.
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 having a very high performance. 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.
Blowing is carried out between the glass transition temperature and the crystallization temperature, generally controlled between 90 and 120 degrees. In this range, PET exhibits a high elastic state, and it becomes a transparent bottle after rapid blow molding, cooling and setting. 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—two blows. The three actions take a very short time, 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, the overall temperature distribution of the preform can be controlled. The temperature gradient of the outer wall. 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.