PET blow molding machine technical problem solution


The blow molding process of the blow molding machine is […]

The blow molding process of the blow molding machine is a two-way stretching process. In this process, the PET chain is bidirectionally extended, oriented and aligned, thereby increasing the mechanical properties of the bottle wall and improving the tensile, tensile and impact strength. And has good air tightness. Although stretching helps increase strength, it should not be stretched too much. Control the stretch inflation ratio not to exceed 3.5 to 4.2 in the radial direction and not to exceed 2.8 to 3.1 in the axial direction. The wall thickness of the preform should not exceed 4.5mm.

Bottle blowing is performed between the glass transition temperature and the crystallization temperature, and is generally controlled between 90 and 120 degrees. In this interval, PET shows a high elasticity state, and it becomes a transparent bottle after rapid blow molding and cooling and setting. In the one-step method, this temperature is determined by the cooling time during the injection molding process (such as the Aoki blow molding machine), so the relationship between the injection and blowing stations must be well connected.

In the blow molding process, there are: stretching—one blow—second blow. The three actions are short in time, but they must be well coordinated, especially the first two steps determine the overall distribution of the material and the quality of the blow bottle. Therefore, it is necessary to adjust: the start timing of the stretching, the stretching speed, the timing of the start and end of the pre-blowing, the pre-blowing pressure, the pre-blowing flow, etc. If possible, it is best to control the overall temperature distribution of the preform Temperature gradient of the inner and outer walls of the billet.

In the process of rapid blow molding and cooling, induced stress is generated in the bottle wall. For inflatable beverage bottles, it can resist internal pressure, which is good, but for hot-filled bottles, it must be guaranteed to fully release above the glass transition temperature.

Common problems and solutions

1. Upper thickness and lower thickness: delay the pre-blowing time, or reduce the pre-blowing pressure and reduce the air flow.

2. Lower thickness and upper thin: opposite to the above.

3. There are wrinkles under the bottleneck: the pre-blowing is too late or the pre-blowing pressure is too low, or the billet does not cool well here.

4. Whitening at the bottom: preform is too cold; stretch too much; pre-blowing too early or pre-blowing pressure is too high.

5. There is a magnifying glass at the bottom of the bottle: there is too much material at the bottom of the bottle; the pre-blowing is too late and the pre-blowing pressure is too low.

6. There is a wrinkle in the bottom of the bottle: the bottom temperature is too high (the gate is not cooled well); the pre-blowing is too late, the pre-blowing pressure is too low, and the flow is too small.

7. The entire bottle is cloudy (opaque): insufficient cooling.

8. Partial whitening: Excessive stretching, where the temperature is too low, or the pre-blowing is too early, or the stretching rod is touched.

9. Eccentric bottom of the bottle: It may be related to the preform temperature, stretching, pre-blowing, high-pressure blowing, etc. Reduce the temperature of the preform; increase the stretching speed; check the gap between the rod head and the bottom mold; postponed pre-blowing to reduce the pre-blowing pressure; postponed high-pressure blow;