In extrusion blow molding the parison is formed by forcing molten plastic through an annular orifice in a die that is part of the die head assembly. The orifice is formed by the space between the mandrel and the die. Extrusion may be directly from an extruder, or for large parts for which more material is needed than the extruder can continuously provide an accululator is used.

The parison is extruded and drops to between the mold halves and when the mold closes the parison is sealed. Air injected into the parison inflates it to the shape of the mold cavity. After cooling and solidification the mold is opened and the part removed.

• Extrusion Blow Molding General Processing Guidelines

Raw Materials
This process usually use commodity materials such as:

• Polypropylene PP
• Polyethylene PE
• Polyethylene – Terephthalate PET
• Polyvinyl chloride PVC

Important factors one should consider for extrusion blow molding include the following:

• Polymer viscosity at high & low shear rates
• Melt strength (important for uniform wall thickness, no holes)
• Strain recovery (MW & Distribution)
• Crystallization rate (slow rate desired)
• Thermal properties (thermal diffusitivity, thermal conductivity, specific heat, etc.)

Advantages of Extrusion Blow Molding:

• Low initial mold tooling costs.
• Flexibility of tooling. Molds can accommodate interchangeable neck finishes and body sections.
• Flexibility in production: Neck inner diameters (I.D.) can be easily controlled to varying requirements. Bottle weights are adjustable.
• Container sizes can range from less than 1 oz. to 55 gallons and up. (Custom Bottle’s equipment is most efficient producing containers up to 1 liter in capacity.)
• Container shape is not restricted by blow-up ratios. Bottles can be long and flat or have handles.
• Wide selection of machine sizes: Molds can be geared to volume requirements.

Applications

• Bottles and containers
• Automotive fuel tanks
• Venting ducts
• Watering cans
• Boat fenders etc