Discontinuous blowing agent delivery system and method

A polymeric foam processing system operable to, in a repetitive cycle, plasticate polymeric material and eject an accumulated mixture of polymeric material and blowing agent through an outlet, the system comprising:

• an extruder having a polymer processing screw constructed and arranged to rotate within a barrel, during a plastication period of the cycle, to convey polymeric material in a downstream direction at a flow rate within a polymer processing space defined between the screw and the barrel, the extruder including a blowing agent port formed in the barrel;
• a blowing agent delivery system having an outlet fluidly connected to the blowing agent port, the blowing agent delivery system including a chamber designed to confine a fixed mass of blowing agent in an enclosed volume and a piston mounted within the chamber, the piston defining, in part, the enclosed volume of the chamber, and moveable from a first position to a second position to force blowing agent through the outlet of the chamber and the blowing agent port and into the polymeric material, during the plastication period, to form a mixture of polymeric material and blowing agent in the polymer processing space, the blowing agent delivery system being equipped to measure temperature and pressure of the blowing agent confined in the chamber;
• and
• a controller in communication with the blowing agent delivery system, the controller designed to receive the inputs of the temperature and pressure of the blowing agent confined in the chamber from the blowing agent delivery system, and an input of a pre-determined mass of blowing agent, the controller being capable of calculating a pre-determined volume of blowing agent from the inputs, the controller designed to send a signal to the blowing agent delivery system to move the piston to the first position to set the enclosed volume of the chamber equal to the pre-determined volume and to move the piston to the second position at a rate coupled to the flow rate of polymeric material.