Read the blow molding process of pet bottles in an article

The production of PET blow bottle can be divided into injection stretch blow (injection stretch blow) and extrusion stretch blow (extrusion stretch blow) according to the different preform. Among the two forming methods, the injection drawing blowing process is easy to control, high production efficiency and less waste and defective products.

PET blow molding bottles can be divided into two categories, one is pressure bottles, such as bottles filled with carbonated drinks; the other is non pressure bottles, such as bottles filled with water, tea, oil, etc. Tea beverage bottle is a modified PET bottle mixed with polyethylene naphthalate (pen) or a composite bottle of PET and thermoplastic poly (aryl ester). It is classified as a hot bottle with heat resistance of more than 80 ℃; water bottle is a cold kind with no requirement for heat resistance. In molding process, the hot bottle is similar to the cold bottle.

The following mainly discusses the forming process of the pressure beverage bottle in the cold bottle.

Equipment is the core of PET bottle blowing technology. With the continuous progress of science and technology and the scale of production, PET bottle blowing machine is becoming more and more automatic and efficient. The production capacity of the equipment is constantly improving, from thousands of bottles per hour to tens of thousands of bottles per hour. The operation is also developed from the past manual button type to the present full computer control, which greatly reduces the difficulty of process operation as well as increases the stability of the process.

According to the orientation conditions, at this time, the lamp can be moved out of 2-3 tubes as shown to open above the injection point, and the injection point is fully heated to provide enough heat to promote its rapid orientation. Because of the time temperature difference effect, the two forming processes are similar. Compared with the normal performance, the required heat is much less and the pre blowing pressure can be reduced properly.

Auxiliary machine and mold: auxiliary machine mainly refer to the equipment to maintain mold constant temperature. Mold constant temperature plays an important role in maintaining product stability. Generally, the body temperature is high, and the bottom temperature is low. For the cold bottle, the cooling effect at the bottom determines the degree of molecular orientation, so it is better to control the temperature at 5-8 ℃, while the temperature at the bottom of the hot bottle is much higher. The mold is an important factor affecting the blow molding process of PET bottle. The shape of the mold will reduce or increase the difficulty of process adjustment, such as the stiffener, the radian of the transition area and the heat dissipation at the bottom.

Environment is also significant. The quality of production environment also has a great influence on process adjustment. Constant conditions can maintain the stability of process and product. PET bottle blow molding is generally better at room temperature and low humidity.

As for the other requirements, the pressure bottle shall meet the requirements of stress test and pressure test at the same time. Stress test is an internal quality control to prevent the cracking and leakage caused by the degradation of molecular chain in the process of contact between the bottle bottom and lubricant (alkaline) during the filling of PET bottle; pressure test is a quality control to prevent the bottle from bursting after being filled with certain pressure 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 withstand voltage is poor; the center point is thick, the withstand voltage test is good, and the stress test is poor. Of course, the results of stress test also have a great relationship with the accumulation of materials in the transition area around the center point, which should be adjusted according to practical experience.

To conclude, the adjustment of PET bottle blow molding process is based on the corresponding materials. If the materials are not good, the process requirements are very strict, and even it is difficult to blow molding qualified bottles.