The present invention provides
blowing agent introduction systems and methods for introducing
blowing agent into polymeric foam
processing systems. The methods may involve introducing one or more doses of
blowing agent into polymeric material in an extruder during a plastication period of a molding cycle. Prior to introduction, a
dose is confined in an accumulator which, for example, has a volume defined between an
inlet valve and an outlet valve. A
control system may receive inputs related to
system parameters (e.g., pressure of polymeric material in extruder, axial position of screw in
barrel, whether screw is rotating, and the like) and based on the inputs coordinates operation of the valves to confine and introduce the blowing agent
dose(s). The introduction systems may be used in discontinuous plasticating processes, such as injection molding and
blow molding, and can be particularly useful in processes that use precise quantities of blowing agent.