In the process of producing plastic bottles, the process control of the preform is very strict. If the quality of the bottle is to be good, it is necessary to improve its heat resistance, mainly according to the injection cooling time control, selection of reasonable design, and strict Control injection and drawing, circulating air blowing technology, and the application of blowing mold temperature adjustment technology, etc. are carried out. In the article, the editor brings you the skills to improve the heat resistance of the preform, as well as the precautions during injection molding, I hope to help you!
Techniques to improve the heat resistance of preforms:
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 output can be increased, and the spherical crystallization can be induced due to the higher residual temperature.
2. Choose a reasonable preform and bottle design
The optimized shape design of the preform and the design of the bottle mold help to improve the wall thickness distribution of the bottle and avoid distortion or shrinkage in different areas of the bottle body.
3. Strictly control injection and drawing
Blowing process parameters and temperature distribution in each area, to avoid residual stress released at the glass transition temperature of PET and cause preform deformation.
4、Circular blowing technology
When using hot blow molding, how to control the deformation of the bottle after demolding is very important. Before opening the mold, air is blown into the blowing mold and the cycle is emptied to cool and shape the bottle body, thereby controlling the deformation after demolding. The air intake of the circulating cooling air passes through the same passage as the primary blowing and secondary blowing, but exhausts from the small hole in the head of the drawing rod through the drawing rod.
5. Application of temperature adjustment technology for blowing mold
The hot oil circulation method is usually used to heat the bottle blowing mold. There are three kinds of cycles for the temperature adjustment of the bottle blowing mold: the cooling water circulation at the bottom of the bottle. Keep the bottom of the bottle at a low temperature of 10℃-30℃ to avoid excessive crystallization and whitening of the unstretched bottom part.
Precautions when preform injection:
1. Before the preform is injected, the material needs to be dried for three or four hours to prevent the moisture in the preform from exceeding the limit and affecting the quality of the product.
2. The injection molding machine template and mold will need to be separated by a heat insulation board. There should be enough exhaust when injection molding to prevent cracking.
3. The melt temperature is controlled at 270-295°C. When injection molding, the air injection method can be used for measurement.
4. The preform should be injected quickly, and the time can be controlled within four seconds.
5. The back pressure is lower than about 100bar to prevent the preform from wearing out during injection.
6. The preform should not stay too long. Usually, if the downtime does not exceed 15 minutes, only the air injection treatment is required, and the viscosity PE can be used for cleaning.
In the production of preforms, the quality of the entire product can only be guaranteed after all aspects are taken into account and the potential effects of all aspects are considered!