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How to improve the heat resistance of the preform?
Jul 01,2022
In the process of producing plastic bottles, the process control of the preform is very strict. If you want the quality of the bottle to be good, it is necessary to improve its heat resistance, mainly according to the injection cooling time control, selection of reasonable design, strict Controlling injection and drawing, circulating air blowing technology, and application of blowing mold temperature adjustment technology are carried out.
1. Preform injection cooling time control
Strictly control the cooling time of the preform injection, so that the preform can be demolded as soon as possible. In this way, the molding cycle can be shortened and the yield can be increased, and spherical crystallization can be induced due to the higher residual temperature.
2. Choose a reasonable preform and bottle design
The optimized preform shape design and bottle mold design help to improve the wall thickness distribution of the bottle and avoid distortion or shrinkage deformation in different areas of the bottle body.
3. Strictly control injection and drawing
The parameters of the blowing process and the temperature distribution in each area can avoid the deformation of the preform caused by the release of residual stress at the glass transition temperature of PET.
4. Cyclic blowing technology
When using a hot blow mold, how to control the deformation of the bottle after demolding is very important. Before the bottle blowing mold is opened, air is blown in and the cycle is evacuated, and the bottle body is cooled and shaped, so as to control the deformation amount after demolding. The intake of circulating cooling air passes through the same channel as the primary blowing and secondary blowing, but is exhausted from the small hole in the head of the drawing rod through the drawing rod.
5. Application of blowing mold temperature adjustment technology
Usually, the hot oil circulation method is used to heat the blowing mold. There are three cycles for the temperature adjustment of the blowing mold: the cooling water circulation at the bottom of the bottle. The bottom of the bottle should be kept at a low temperature of 10℃-30℃ to avoid excessive crystallization and whitening of the unstretched bottom part of the bottle.
