Meaning
Expansion processes use pressurized air to shape a heated plastic component against a mould wall. During preform inflation, a thick walled tube of plastic is stretched and blown into its final shape, such as a bottle. The process requires precise control of air pressure and timing to ensure the wall thickness is uniform.
It is the final stage of the stretch blow moulding cycle.
Material Distribution
Stretching the plastic before blowing aligns the polymer chains for increased strength. The speed of preform inflation determines how the material moves from the center to the edges. If the air is applied too quickly, the walls may become too thin in certain areas.
Heat Management
Temperature of the preform must be just above the glass transition point for successful expansion. If the plastic is too cold, it will tear during inflation. If it is too hot, the material will flow too easily and fail to hold its shape.
Final Geometry
Air pressure holds the plastic against the cool mould surface until it solidifies. This contact transfers the details of the mould, such as threads or logos, to the part. High pressure is necessary to ensure the plastic reaches all the corners of the cavity.
The cooling phase begins as soon as the preform inflation is complete.
