Blow moulding process is a common method of plastic packaging container moulding. Blow moulding is a method of processing semi-molten tube blanks (or billets) obtained by extrusion or injection moulding into the die, then closed the die, and extended and expanded by injecting compressed air into the tube blank, so that it is close to the cavity wall, and then cooled and demoulded to obtain a certain shape of hollow products.

According to the different forming methods, blow moulding process can be divided into many kinds.

1、Extrusion blow moulding

Extrusion blow moulding is one of the most widely used moulding methods for plastic packaging containers. The granules (or powders) of thermoplastic plastics are plasticized by extruder, and then hot melted tubular billets are prepared through a specific die head. When the billet reaches a predetermined length, it enters the die, closes the die, and then blows.
The characteristics of this forming method are: high production efficiency, uniform parison temperature, large allowable range of shape, size and wall thickness of hollow container, strong adaptability, high strength of blow moulded products, simple equipment and low investment. But the precision of the product is not high, the inner wall of the thread changes with the change of the outer wall thread, and there are splicing seams at the bottom of the container. Most HDPE bottles are extruded and blow moulded, such as shampoo bottles, shower bottles, etc.

2、Injection blow moulding

Injection blow moulding is to inject the parison into the mandrel by an injection moulding machine. After the parison is properly cooled (solidified on the surface of the parison, the shape of the parison is not destroyed or salivated when the mandrel is moved), the mandrel and the parison are sent into the blow moulding mould together, the blow moulding die is closed, compressed air is introduced through the mandrel, and the required products are formed by blowing the parison into the air, and the products are taken out after cooling and setting.

The characteristics of this forming method are as follows: the products have no splicing seams and need no post-dressing; the dimension accuracy of thread and bottle mouth is high, and the inner wall of neck is smooth cylindrical surface; the output can be great, and the auxiliary equipment is few; the bottom strength of the product is high, the material loss is low; the wall thickness is uniform and the production efficiency is high. However, the equipment investment is large, the processing and production cycle is long, and the requirements for operators are high, the shape can not be too complex, and the size of the container is limited (the height of the container can not be too high). Suitable for the production of small precision containers. Medical plastic bottles and wide-mouth bottles are often formed by this method.