PET bottle blowing machine principle and technical process

At present, most of the PET bottle blowing machine are still two-step blow molding machines, that is, the plastic raw materials must be made into preforms first, then blown. Nowadays, environmentally friendly plastics made of PET are generally used.

The principle of PET bottle blowing machine

The blowing process of PET bottle blowing machine is divided into two parts
1. Preheat
The preform is irradiated by an infrared high-temperature lamp to heat and soften. To maintain the shape of the bottle neck, the water chiller is needed.

2. Blow to shape
In this stage, the preheated preform is placed into the blow mold and inflated with high pressure. Blow and stretch the preform into the required bottle shape.
The automatic PET bottle blowing machine combines the two parts by robot hand. Greatly accelerated the rate of production.

Schematic diagram of PET bottle blowing machine

Process flow of bottle blowing machine

The blow molding process is a two-way stretching process. During this process, the PET chains are bidirectionally extended, oriented and arranged, thereby increasing the mechanical properties of the bottle wall and improving the tensile and impact strength, also has good airtightness. Although stretching helps to improve the strength, it should not be stretched too much. The stretch-to-expansion ratio should be controlled: the radial direction should not exceed 3.5-4.2, and the axial direction should not exceed 2.8-3.1. The wall thickness of the preform should not exceed 4.5mm.
Bottle 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 becomes a transparent bottle after rapid blow molding, cooling and setting. In one-step method, this temperature is determined by the length of cooling time in the injection molding process (such as Aoki blow molding machine), so the relationship between the injection and blowing stations must be well connected.

The blow molding process includes: stretching-first blowing-second blowing. 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 blown bottle. Therefore, it is necessary to adjust: stretching start timing, stretching speed, pre-blowing start and end timing, pre-blowing air pressure, pre-blowing air flow, 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.

During the rapid blow molding and cooling process, there is induced stress in the bottle wall. For inflatable beverage bottles, it can resist internal pressure, which is beneficial, but for hot-fill bottles, it must be guaranteed to be fully released above the glass transition temperature.