Blow moulding process

Blow moulding is used to create hollow enclosed components and there are two basic types of technology: extrusion blow moulding and injection blow moulding. In extrusion blow moulding a parison or tube is produced by extrusion. A mould is then closed around the parison and the product is blown into the shape of the mould with compressed air. In injection blow moulding two moulds are used. A mandrel or blowing stick is placed in the first mould, and the thermoplastics material is then injected into the mould flowing around the mandrel to create a tube. This is then transferred to the second mould where air is introduced to expand it to the shape of the mould. A variation on this method is stretch blow moulding whereby the material is biaxially oriented to produce stronger products. This method is particularly used for the manufacture of PET bottles.