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Blow molding


1. INTRODUCTION

Blow molding, also known as blow forming, is a manufacturing process by which hollow plastic parts are formed. It is a process used to produce hollow objects from thermoplastic.
In general, there are three main types of blow molding: extrusion blow molding, injection blow molding, and stretch blow molding.
The blow molding process begins with melting down the plastic and forming it into a parison or preform. The parison is a tube-like piece of plastic with a hole in one end in which compressed air can pass through.
The basic process has two fundamental phases. First, a preform (or parison) of hot plastic resin in a somewhat tubular shape is created. Second, a pressurized gas, usually air, is used to expand the hot preform and press it against a mold cavity. The pressure is held until the plastic cools. Better dimensional control at final product can be achieved . Once the plastic has cooled and hardened the mold opens up and the part is ejected.