Meaning
Plastic forming process that combines biaxial stretching with pneumatic inflation produces high-strength, thin-walled hollow containers. In stretch blow moulding, a pre-moulded preform is reheated and then mechanically stretched by a rod while high-pressure air inflates it against a mould cavity.
Biaxial Orientation
Molecular alignment occurs during the stretching phase, greatly improving the mechanical and barrier properties of the plastic. In stretch blow moulding, this orientation is induced both axially by the stretch rod and hoop-wise by the compressed air. This dual-axis alignment allows for thin-walled bottles with high top-load strength and low carbon dioxide permeability.
The resulting stiffness allows the bottle to withstand carbonation pressure without deforming, which is critical for carbonated beverage packaging.
Process Variable
Consistent bottle quality requires precise control of the preform heating profile. If the preform is too cold during stretch blow moulding, the polymer will not stretch uniformly, causing thin spots and haziness in the finished bottle. Alternatively, excess heat can cause the polymer to crystallize prematurely, making it brittle and difficult to blow.
Tooling Wear
Mould maintenance is essential to prevent cosmetic defects and maintain production efficiency. Since stretch blow moulding involves high-speed ejection of cooled bottles, the aluminum or steel moulds must be regularly inspected for wear. Venting channels must also be kept clear to prevent trapped air from causing incomplete bottle inflation.
