Why does PET bottle blowing need high pressure compressed air ?

Plastic food and beverage bottles come is a variety of forms and contents. These bottles are often made of PET. PET is short for Polyethylene terephthalate.

They are produced using blow molding techniques. The blow molding technique is the most common bottle making method today.

The principle is as follows. The thermoplastic material is extruded or injection molded [1]. While the material is hot, the mold is closed [2,3]. High pressure compressed air is injected into the mold [3]. This is to blow the material into shape [4,5]. The mold is opened and the product (bottle) is released [6,7]

The higher the number of bottles that is blown, relates the capacity of the compressed air system. The blowing process of PET bottle blowing requires compressed air of 35 to 42 Bar(g). It need such high pressure to instantly and flawlessly produce a bottle. During its blowing the material cools off, that is why this process of blowing needs to be done quickly.

If the PET bottle is used for filling food, medicine and beverages, the quality of the compressed air must meet the ISO 8573.1 “Class 0” standard for oil content. Generally that means 0% of oil, thus 100% oil free air.