The blow molding machine blow molding process is a two- […]
The blow molding machine blow molding process is a two-way stretching process in which 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 a good air tightness. Although the stretching helps to increase the strength, it cannot be excessively stretched. The tensile inflation ratio should be controlled: the radial direction should not exceed 3.5 to 4.2, and the axial direction should not exceed 2.8 to 3.1. The wall thickness of the preform should not exceed 4.5 mm.
The blowing is carried out between the glass transition temperature and the crystallization temperature, and is generally controlled between 90 and 120 degrees. In this interval, PET is in a highly elastic state, which is quickly blow molded, cooled and shaped to become a transparent bottle. In the one-step method, this temperature is determined by the length of cooling in the injection molding process (such as the Aoki blow molding machine), so it is necessary to connect the two injections.
In the blow molding process: stretching - one blowing - two blowing, the three movements are very short, but must be well coordinated, especially the first two steps determine the overall distribution of the material, the quality of the blowing. Therefore, it should be adjusted: stretching start timing, stretching speed, pre-blowing start and end timing, pre-blowing pressure, pre-blowing flow, etc., if possible, it is best to control the overall temperature distribution of the preform, bottle The temperature gradient of the inner and outer walls of the blank.
In the process of rapid blow molding and cooling, induced stress is generated in the bottle wall. For a carbonated beverage bottle, it is resistant to internal pressure and is beneficial, but for hot-filled bottles it is necessary to ensure that it is fully released above the glass transition temperature.
Common problems and solutions
1. Upper and lower thickness: delay the pre-blowing time, or reduce the pre-blowing pressure to reduce the air flow.
2. Thick and thin: contrary to the above.
3. There are wrinkles under the bottleneck: pre-blowing too late or pre-blowing pressure is too low, or the billet cooling is not good here.
4. The bottom is white: the preform is too cold; excessive stretching; pre-blowing too early or pre-blowing too high.
5. There is a magnifying glass at the bottom of the bottle: too much material at the bottom of the bottle; pre-blowing is too late, and the pre-blowing pressure is too low.
6. There are wrinkles in the bottom of the bottle: the bottom temperature is too high (the gate is not well cooled); the pre-blowing is too late, the pre-blowing pressure is too low, and the flow rate is too small.
7. The entire bottle is turbid (opaque): insufficient cooling.
8. Partial whitishness: Excessive stretching, where the temperature is too low, or pre-blowing too early, or hitting the stretching rod.
9. Eccentricity of the bottom of the bottle: It may be related to preform temperature, stretching, pre-blowing, high-pressure blowing, etc. Reduce the preform temperature; speed up the drawing; check the gap between the rod head and the bottom mold; delay the pre-blowing to reduce the pre-blowing pressure; delay the high-pressure blowing; check whether the preform is eccentric.