A reciprocating blow molding unit includes an extruder screw foundation and an extrusion unit coupled to the extruder screw foundation. The extruder screw foundation includes a screw housing formed to include an interior cavity configured to receive polymeric material. The extrusion unit includes an extruder screw arranged to lie at least partially within the interior cavity and is configured to rotate about a longitudinal rotation axis to advance the polymeric material through the interior cavity.

Provided are methods for automatically positioning ramps in a station for the heating of preforms. The method includes acquiring an image of a preform traveling along a slot delimited by a pair of ramps, where at least one of the ramps is transversely mobile to vary the width of the slot (56) and where a motorized device transversely moves the at least one mobile ramp and is controlled automatically by an electronic control unit. The method further includes automatically determining the diameter below the neck of the preform by computer processing the image and automatically adjusting the width of the slot by moving the at least one mobile ramp according to the determined diameter below the neck.