PET plastic bottle blowing process introduction.

1. Equipment

At present, PET automatic blowing machine manufacturers are mainly imported from France SIDEL Company, Germany KRONES Company, domestic Fujian Quanguan Company and so on. Although the manufacturers are different, the equipment principle is similar, and generally includes five major parts: the billet system, the heating system, the blowing system, the control system and the auxiliary machine.

2. Blow molding process ‍

PET bottle blow molding process.

The important factors affecting the PET bottle blow molding process are the bottle billet, heating, pre-blowing, mold and production environment.

2.1 Bottle blank

When preparing blow molded bottles, PET slices are first injected into bottles, which requires that the proportion of secondary recovery material cannot be too high (less than 5%), the number of recovery times cannot exceed two times, and the molecular weight and viscosity cannot be too low (molecular weight 31000-50000, characteristic viscosity 0.78-0.85cm3 / g).

2.2 Heating

The heating of the billet is completed by the heating oven, whose temperature is manually set and automatically adjusted. In the oven, the far infrared light tube emits far infrared radiation to heat the billet, and the heat circulation is carried out by the fan at the bottom of the oven to make the temperature in the oven uniform. The billet rotates while moving forward in the oven, so that the wall of the billet is heated evenly.
The arrangement of the lamp tube in the oven is generally in a "zone" shape, with more ends and less in the middle. The heat of the oven is controlled by the number of lamps opened, the overall temperature setting, the power of the oven and the heating ratio of each section. The opening of the lamp tube should be adjusted in combination with the pre-blown bottle.
In order to make the oven play a better role, the adjustment of its height, cooling plate, etc., is very important, if the adjustment is improper, it is easy to appear when blowing the bottle (bottle mouth becomes larger), hard neck (neck material can not be opened) and other defects.

2.3 Pre-blowing
Preblowing is a very important step in the two-step blowing method, which refers to the process of blowing in the drawbar down at the same time to start preblowing, so that the bottle shape. In this process, the pre-blowing position, the pre-blowing pressure and the blowing flow rate are three important process factors.

The shape of the pre-blown bottle determines the difficulty of the blow molding process and the performance of the bottle. The normal shape of the pre-blown bottle is spindle shape, and the abnormal one is sub-bell shape and handle shape. The reasons for the abnormal shape are improper local heating, insufficient pre-blowing pressure or blowing flow rate, and the size of the pre-blowing bottle depends on the pre-blowing pressure and the pre-blowing position. In production, the size and shape of all pre-blown bottles of the entire equipment should be maintained. If there are differences, the specific reasons should be found. The heating or pre-blown process can be adjusted according to the pre-blown bottle situation.

The size of the pre-blowing pressure varies with the bottle specifications and equipment capabilities, and the general capacity is large and the pre-blowing pressure is small. High production capacity and high pre-blowing pressure.

2.4 Auxiliary machinery and mold

Auxiliary machinery mainly refers to the equipment that maintains the constant temperature of the mold. The mold constant temperature plays an important role in maintaining the stability of the product. Generally, the bottle body temperature is high, and the bottom temperature is low. For cold bottles, because the cooling effect at the bottom determines the degree of molecular orientation, it is better to control the temperature at 5-8℃; The bottom of the hot bottle is much hotter.

2.5 Environment

The quality of the production environment also has a greater impact on the process adjustment, and the constant temperature conditions can maintain the stability of the process and the stability of the product. PET bottle blow molding is generally better at room temperature and low humidity.

3. Other requirements ‍

The pressure bottle should meet the requirements of stress test and pressure test at the same time.

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