The bottle blowing process of the bottle blowing machine is divided into two parts.

preheat

The preform (embryo) is irradiated by an infrared high-temperature lamp to heat and soften the body of the preform. In order to maintain the shape of the bottle mouth, the mouth of the preform does not need to be heated, so a certain cooling device is required to cool it. .

Blow molding

This stage is to place the preheated bottle preform into the already prepared blow mold and inflate it under high pressure. The preform (embryo) is blown into the required bottle. The fully automatic bottle blowing machine combines the two operations of bottle blowing through the operation of the robot, eliminating the manual process of placing the preheated bottle preform into the blow mold. Greatly speed up the production speed.

The process flow of the blowing machine

The blow molding process is a bidirectional stretching process, in which the PET chain is bidirectional extension, orientation and arrangement, thereby increasing the mechanical properties of the bottle wall, improving the tensile, tensile and impact strength, and has good air tightness. Although stretching helps to improve strength, it can not be stretched too much, and it is necessary to control the ratio of stretching and blowing: radial should not exceed 3.5 ~ 4.2 times, axial should not exceed 2.8 ~ 3.1 times. The wall thickness of the embryo should not exceed 4.3mm.

The blowing is carried out between the glass transition temperature and the crystallization temperature, which is generally controlled between 90 and 110 degrees. In this section, PET shows a high elastic state, and becomes a transparent bottle after rapid blow molding and cooling.

In the blow molding process, there are: stretching – one blow – two blows, the time of the three actions is very short, but it must be matched well, especially the first two steps determine the overall distribution of the material and the quality of the blow bottle. Therefore, it is necessary to set the parameters: stretching start time, stretching speed, pre-blowing start and end time, pre-blowing pressure, pre-blowing flow rate, etc., if possible, it is best to control the overall temperature distribution of the bottle embryo and the temperature gradient of the inner and outer walls of the bottle embryo.

During the rapid blowing and cooling process, induced stress is generated in the bottle wall. For inflatable beverage bottles, it can resist internal pressure and has advantages, but for hot filling bottles, it is necessary to ensure that it is fully released above the glass transition temperature.

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

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.

Bottle blank

When preparing for blow molding bottle, first PET slice injection molding into the bottle, it requires that the proportion of secondary recovery material can not be too high (less than 5%), the number of recycling can not be more than two times, and the molecular weight and viscosity can not be too low (molecular weight 31000-50000, characteristic viscosity 0.78-0.85cm3 / g). According to the national food Safety Law, secondary recycled materials may not be used for food and pharmaceutical packaging. The injection molded billet should be stored for more than 24 hours before it can be used. The unused billets after heating must be stored for more than 48h before they can be reheated. The storage time of the preform shall not exceed six months.

The pros and cons of the bottle billet largely depend on the pros and cons of the PET material, should choose easy to blow, easy to shape the material, and develop a reasonable bottle billet forming process. The experiment shows that the same viscosity of PET material forming bottles, imported raw materials than domestic material is easy to blow molding; The same batch of billets, the production date is different, the blow molding process may also be greatly different. The quality of the billet determines the difficulty of the blow molding process, and the requirements of the billet are pure, transparent, no impurities, no color, the length of the injection point and the surrounding halo spot.

Heat

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.

Preblow

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.

Auxiliary machinery and molds

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

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.

Other requirements ‍
The pressure bottle should meet the requirements of stress test and pressure test at the same time. Stress testing is an internal quality control to prevent cracking, leakage, etc., caused by the degradation of molecular chains in the process of contact between the bottom of PET bottle and lubricant (alkaline) when filling beverages; Pressure test is a quality control to prevent the bottle from bursting after filling a certain pressure of gas. In order to meet these two needs, the thickness of the center point should be controlled within a certain range. Generally, the center point is thin, the stress test is good, and the pressure resistance is poor. The center point is thick, the pressure test is good, the stress test is poor. Of course, the results of the stress test also have a lot to do with the accumulation of materials in the transition area around the center point, which should be adjusted according to actual experience.

Peroration
The adjustment of the blow molding process of PET bottles is carried out for the corresponding material, if the material is not good, the requirements for the process are very harsh, and it is even difficult to blow out qualified bottles.