Blow molding is a process for shaping thermoplastic into a hollow product. A hot thermoplastic tube is stretched with air pressure and cooled against a mold surface.
Mold material requirements
Blow molding is a low pressure method where strength and wear demands are very moderate. Some parts of the mold, like shot off areas and/or neck ring, may require higher strength material. PVC is a common material for bottles and may cause corrosion problems. Blow molding is a very high productivity method where cycle times are of great importance. The most common material to use in blow molds is aluminium alloys with inserts of higher hardness materials. Steel is also used, and in some cases, even in the soft annealed condition.
Mold material properties
Important properties are: