Blow molding uses air pressure to inflate soft plastic into the cavity of a mold. It produces one-piece plastic parts that are hollow with thin walls, like bottles and other containers. These blow mold plastics typically are produced in very large quantities because many are utilized for mass-market consumer beverages.
Blow Molding Technology – Where It Originated
Blow molding technology originated with the glass industry, which competes with the plastics industry in the recyclable and disposable bottle market.
The Steps of Blow Molding Production
Blow molding has two steps.
1. The first step is fabricating a molten plastic tube, known as a parison. This is done either through injection molding or extrusion.
Injection molding uses an injection unit and a clamping unit and can form three-dimensional shapes. Extrusion pushes the material through a two-dimensional opening and through a series of sizes or shapes until it reaches the desired form. It produces linear shapes.
2. The second step in blow molding is inflating the tube until it reaches the desired shape.
Blow molding only is used for thermoplastics.
Materials Used for Blow Mold Plastics
The most commonly used polymer is polyethylene, especially high molecular weight polyethylene (HMWPE) and high density polyethylene (HDPE).
These more expensive materials are more economical than low-density polyethylene, since the stiff container walls can be thinner. Blow moldings also can be made from polyethylene terephthalate, polyvinyl chloride and polypropylene.
Most products from blow molding production are used for disposable containers for liquid consumer goods. Other products include 55-gallon shipping drums for powders and liquids, 2000-gallon storage tanks, automobile gasoline tanks, toys and small boat and sailboard hulls.