Parison forming
Extrusion blow-molding of large hollow plastic bodies

Fed by the extruder(s), the extrusion head channels transform a cylindrical flow of material into an annular flow which, after passing through a die, forms an envelope called the parison, the blank of the blown body. The diameter and thickness of the parison are determined by the dimensions of the punch/die tooling (see § 4.4).

For large hollow bodies, there are two types of extrusion head.

1. Accumulation heads (figure 10 ): during the blowing cycle, material is progressively accumulated in a chamber (figure