The Extrusion blow molding process begins with the conventional extrusion of a parison or tube, using a die similar to that used for making plastic pipe. To manufacture Plastic Bottles, industry uses a process known as Blow Molding. This process is used to manufacture hollow plastic bottles such as; milk jugs, shampoo bottles, bleach bottles, or any one of countless products you might see on store shelves. The plastic is fed in pellet form into the machines hopper, (this machine is known as a Blow Molder), and the plastic is conveyed forward by a screw inside a heated barrel being softened by both friction and heat. The softened plastic is then forced downwards through a circular die forming a hollow plastic tube called a “parison”.
The parison is then clamped inside a hollow mold and inflated from with-in. The air pressure forces the parison to inflate against the mold surface, the plastic cools in the shape of the interior of the mold cavity. The mold then opens and the plastic bottle is ejected. The bottle may they be conveyed on to trimming, printing and filling stations. Other processes for Blow Molding include Stretch Blow and Injection Blow. Extrusion blow molding can be used to process many different plastics, including HDPE, PP, PET and LDPE.