In modern life, plastics are used in a wide range of industries and can be found almost everywhere around us, and these different types of plastic products are produced in many different processes, of which blow moulding and calendering are two. Both processes are the main production methods for polyolefin films, with blow moulding being the older method, but due to its limitations and the insurmountable defects of particular materials, the cast method emerged and, thanks to the use of multi-layer co-extrusion, soon became popular. Later, as technology continued to advance, the two became more and more interchangeable. So, about these two production processes, how should we as and choose? Next, let us take a look at them.
1, the thickness of the film, because the flow delay method uses a flat die head, and there are special retention grooves inside the die head, which allows the material to flow evenly in the production process, and there is an automatic adjustment device on the die head, with a very high control accuracy, can ensure that the production of the film error in less than 3%. The blow moulding method uses an annular die head and a multi-layer core, which requires high machining and assembly precision, so it is more difficult to control the error, although there are already technologies that can control the error below 3%, but the overall error is still around 5%. Therefore, in this respect, the flow-delay method performs better.
2, production efficiency, cast method compared to the blow moulding method has a higher efficiency, and in the production process generated less waste, high material utilisation, production is very large, suitable for high-volume orders. The blow moulding method has greater advantages in cost control and scheduling of small orders and some custom orders. advantage.
3. The mechanical properties of the film are such that, when using the cast method, the film is stretched as much as possible in the longitudinal direction during the production process, while there is almost no stretching in the transverse direction. When using the blow moulding method, the film is stretched to varying degrees in both the longitudinal and transverse directions, so it has a certain resistance to tearing in both directions. Therefore, for those packaging films that require certain mechanical properties in both vertical and horizontal directions, films produced by the blow moulding method have more advantages.
Although the main resistance to high temperatures comes from the resin used in the production of the film, the cast and blow moulding methods still have some influence on this performance. The blow moulding process causes the film to be stretched in different directions, which may cause the molecular chains to retract and distort the film during the post-forming sterilisation phase. In contrast, the molecular arrangement of the film produced by the calendering method is orderly and has a better resistance to high temperatures.
In short, both the cast and blow moulding methods are good plastic production processes, each with its own advantages in different situations.
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