What is reciprocating screw blow molding?

Reciprocating screw blow molding machinery is characterized by the following sequence of operations in the making of a bottle:

  1. Plastic resin is melted by an extruder with temperatures ranging from 350F to 375F. As the screw rotates to melt the plastic, it also retracts, allowing molten resin to form a “shot” of resin in the front of the barrel. 
  2. When enough plastic is melted, hydraulic pressure is activated to push the screw forward, forcing the shot of resin through flow heads and dies to form parisons.
  3. When the parison is fully extruded, which can happen in 1.8 seconds, the mold halves are closed under hydraulic pressure.
  4. Air enters the hollow parison, forcing it outward against the chilled mold halves. Air pressure is maintained until the plastic has cooled sufficiently to eject the part from the mold.
  5. Air pressure is relieved before opening the mold halves. 
  6. The parts are removed from the mold. Parts may be released by gravity (with the aid of a part stripper) or removed using a part extractor. The parts are then ready for external trimming of "flash", or scrap plastic.
  7. Cycle time for a round gallon handle jug is 13.5 seconds.


Here is additional context for Altium's project:

  • A reciprocating screw platform is used to manufacture monolayer parts, as intermittent processes are not well suited for coextrusion.
  • Altium currently provides barrier solutions, using multi-layer constructions on continuous extrusion shuttle and wheel platforms in select locations.
  • Having a monolayer barrier solution that runs on a reciprocating screw platform would provide a competitive edge to Altium due to the large number of these machines currently in operation throughout our North American network.