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The invention provides a blowing agent delivery system for introducing a blowing agent into a polymeric foam processing system. The delivery system is designed to discontinuously introduce blowing agent from a continuous source into polymeric material within an extruder. The system, thus, may improv

The invention provides a blowing agent delivery system for introducing a blowing agent into a polymeric foam processing system. The delivery system is designed to discontinuously introduce blowing agent from a continuous source into polymeric material within an extruder. The system, thus, may improve control over blowing agent delivery in discontinuous polymer processing systems such as injection molding or blow molding. In some embodiments, the blowing agent delivery system selectively directs blowing agent flow from the source to the extruder barrel, or through a bypassing passageway. In this manner, blowing agent may be continuously supplied by the source but discontinuously injected into the extruder barrel. During use, the delivery system may cause blowing agent to flow through the bypassing passageway, for example, when the screw stops plasticating polymeric material.

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1. A system for injecting a blowing agent into polymeric material within a barrel of a polymer processing apparatus, wherein the polymer processing apparatus includes a screw mounted in the barrel and designed to reciprocate from an accumulation position, in which the screw plasticates polymeric mat

1. A system for injecting a blowing agent into polymeric material within a barrel of a polymer processing apparatus, wherein the polymer processing apparatus includes a screw mounted in the barrel and designed to reciprocate from an accumulation position, in which the screw plasticates polymeric material that accumulates downstream of the screw, and an injection position, in which the screw does not plasticate polymeric material and the accumulated polymeric material is injected through an outlet of the barrel, the system comprising:a conduit having an inlet connectable to a source of blowing agent and an outlet connectable to a port in the barrel to provide a pathway through which blowing agent flows from the source to the polymeric material within the barrel; and a flow controlling system including a bypassing passageway fluidly connected to the conduit at a position between the inlet and the outlet, the flow controlling system designed to selectively direct blowing agent flowing from the source to the polymeric material within the barrel through the bypassing passageway when the screw is in the injection position. 2. The system of claim 1, wherein the flow controlling system comprises a valve.3. The system of claim 2, wherein the valve is positioned at a junction of the conduit and the bypassing passageway and is switchable between a first position directing flow from the source to the barrel and a second position directing flow from the source to the bypassing passageway.4. The system of claim 2, wherein the flow controlling system further comprises a back-pressure regulator.5. The system of claim 3, wherein the flow controlling system further comprises a back-pressure regulator located in the bypassing passageway downstream of the valve.6. The system of claim 4, wherein the back-pressure regulator is designed to maintain a back pressure approximately equal to the pressure of the polymeric material proximate the blowing agent port when a screw rotates in the barrel to plasticate the polymeric material.7. The system of claim 5, wherein the back-pressure regulator is designed to maintain a back pressure approximately equal to the pressure of the polymeric material proximate the blowing agent port when a screw rotates in the barrel to plasticate the polymeric material.8. The system of claim 7, wherein the back-pressure regulator is designed to maintain a back pressure of between about 500 psi and 4000 psi.9. The system of claim 1, wherein an outlet of the bypassing passageway opens to atmosphere.10. The system of claim 1, wherein an outlet of the bypassing passageway is connected to a recovery container.11. The system of claim 1, wherein an outlet of the bypassing passageway is connectable to the source of blowing agent.12. The system of claim 1, wherein the flow controlling system comprises two valves, a first valve in the conduit downstream of a junction of the bypassing passageway and the conduit, and a second valve in the bypassing passageway downstream of the junction.13. The system of claim 12, including a controller that switches the first valve to an open position when the second valve is closed, and switches the second valve to an open position when the first valve is closed.14. The system of claim 12, further comprising a back-pressure regulator located in the bypassing passageway downstream of the second valve.15. The system of claim 13, further comprising a back-pressure regulator located in the bypassing passageway downstream of the second valve.16. The system of claim 1, wherein the flow controlling system comprises a valve in the conduit downstream of a junction of the conduit and the bypassing passageway, and a back-pressure regulator in the bypassing passageway downstream of the junction.17. The system of claim 1, wherein the flow controlling system comprises a shut-off valve, and a fluid pathway distance from the shut-off valve to the port in the barrel is no more than 3 inches.18. The system of claim 17, wherein the fluid pathway distance from the shut-off valve to the port in the barrel is no more than 1 inch.19. The system of claim 17, wherein the shut-off valve is located essentially adjacent to the port in the barrel.20. The system of claim 19, wherein the flow controlling system further comprises a second valve located in the bypassing passageway downstream of the junction.21. The system of claim 19, wherein the flow controlling system further comprises a second shut-off valve in the bypassing passageway downstream of the junction and a back-pressure regulator in the bypassing passageway downstream of the second valve.22. The system of claim 19, wherein the flow controlling system further comprises a back pressure regulator in the bypassing passageway downstream of the junction.23. The system of claim 19, further comprising a check valve between the shutoff valve and the port.24. The system of claim 23, wherein the flow controlling system further comprises a second valve located in the bypassing passageway downstream of the junction.25. The system of claim 23, wherein the flow controlling system further comprises a second shut-off valve in the bypassing passageway downstream of the junction and a back pressure regulator in the bypassing passageway downstream of the second valve.26. The system of claim 23, wherein the flow controlling system further comprises a back pressure regulator in the bypassing passageway downstream of the junction.27. The system of claim 1, wherein the flow controller system comprises a shut-off valve, wherein an enclosed volume between the shut-off valve and the port in the barrel is less than 0.50 cubic inches.28. The system of claim 27, wherein the enclosed volume between the shut-off valve and the port in the barrel is less than 0.10 cubic inches.29. The system of claim 1, wherein the flow controlling system comprises a shut-off valve at least a portion of which is positioned within a bore in the barrel.30. The system of claim 1, wherein a fluid pathway distance from the bypass valve to the port in the barrel is no more than 5 feet.31. The system of claim 1, wherein a fluid pathway distance from the bypass valve to the port in the barrel is no more than 1 foot.32. The system of claim 1, wherein the source of blowing agent continuously supplies blowing agent to the inlet of the conduit.33. The system of claim 1, wherein the source of blowing agent supplies blowing agent to the inlet of the conduit at a flow rate of less than about 60 lbs/hour.34. The system of claim 1, further comprising a metering device associated with the conduit, positioned between the source of blowing agent and the barrel port, the metering device constructed and arranged to control the flow rate of blowing agent supplied to the conduit.35. The system of claim 34, wherein the metering device controls the mass flow rate of blowing agent supplied to the conduit.36. The system of claim 1, wherein the conduit inlet is connectable to a source of blowing agent that is a gas at ambient conditions.37. The system of claim 1, wherein the conduit inlet is connectable to a source of blowing agent that is a liquid as delivered to the port in the barrel.38. The system of claim 1, wherein the conduit inlet is connectable to a source of blowing agent that is a supercritical fluid at conditions in the extruder.39. The system of claim 1, wherein the blowing agent comprises carbon dioxide.40. The system of claim 1, wherein the blowing agent comprises nitrogen.41. The system of claim 1, wherein the polymer processing apparatus comprises a discontinuous plasticating system.42. The system of claim 41, wherein the polymer processing apparatus comprises an injection molding apparatus.43. The system of claim 41, wherein the polymer processing apparatus comprises a blow molding apparatus.44. A system for processing polymeric foam material comprising:an extruder including a barrel and a screw designed to rotate within the barrel to convey polymeric material in a downstream direction within a polymer processing space between the barrel and the screw, the extruder having a port in the barrel comprising a plurality of orifices and positioned to introduce a blowing agent into polymeric material in the polymer processing space to allow formation therein of a solution of polymer and blowing agent; and a blowing agent injection assembly including a shut-off valve positioned within a sleeve defining the port comprising the plurality of orifices, the a shut-off valve having an inlet fluidly connected to a blowing agent source and an outlet fluidly connected to the port, the shut-off valve designed to selectively permit or prevent the flow of blowing agent therethrough, wherein a fluid pathway distance from the shut-off valve to the port in the barrel is no more than 3 inches. 45. The system of claim 44, wherein the shut-off valve is a two-way valve.46. The system of claim 45, wherein the shut-off valve is switchable between a first position directing flow of blowing agent from the source to the port, and a second position directing flow of blowing agent from the source to a bypassing passageway.47. The system of claim 45, wherein a fluid pathway distance from the shut-off valve to the port in the barrel is no more than 1 cm.48. The system of claim 45, wherein the outlet of the shut-off valve is located essentially adjacent to the port in the barrel.49. The system of claim 45, wherein an enclosed volume between the shut-off valve and the port in the barrel is less than 0.50 cubic inches.50. The system of claim 45, wherein an enclosed volume between the shut-off valve and the port in the barrel is less than 0.10 cubic inches.51. The system of claim 45, wherein an enclosed volume between the shut-off valve and the port in the barrel is less than 0.05 cubic inches.52. The system of claim 45, wherein the blowing agent injection assembly is positioned within a bore in the barrel.53. The system of claim 44, wherein the shut-off valve comprises a valve stem actuatable relative to a valve seat to selectively permit or prevent the flow of blowing agent therethrough and, the blowing agent injection assembly further comprises a ball check valve positioned within the sleeve between the outlet of the shut-off valve and the port, the ball check valve moveable between an open configuration which permits the flow of blowing agent therethrough to the port and a closed configuration which prevents the flow of molten polymeric material from the polymer processing space therethrough.54. A blowing agent injection assembly operable with polymer processing apparatus, comprising an inlet and a multi-orifice outlet, the assembly having an internal passageway connecting the inlet to the multi-orifice outlet, the blowing agent injection assembly including a valve coupled to the passageway and positioned within a sleeve defining the multi-orifice outlet, the valve moveable between a first position which permits the flow of blowing agent from the inlet to the outlet through the passageway and a second position which prevents the flow of blowing agent from the inlet to the outlet through the passageway.55. The blowing agent injection assembly of claim 54, wherein the valve is a two-way valve, wherein the second position directs the flow of blowing agent from the inlet to a bypassing passageway.56. The blowing agent injection assembly of claim 54, wherein the multi-orifice outlet includes at least 10 orifices.57. The blowing agent injection assembly of claim 54, further comprising a back-flow restrictor moveable between an open configuration which permits the flow of blowing agent from the inlet to the outlet through the passageway and a closed configuration which prevents the flow of molten polymeric material from the outlet to the inlet through the passageway.58. The blowing agent injection assembly of claim 54, wherein the back-flow restrictor comprises a ball check valve.59. The system of claims 58, wherein the valve comprises a valve stem actuatable relative to a valve seat to selectively permit or prevent the flow of blowing agent and, the ball check valve is positioned within the sleeve between the valve and the multi-orifice outlet.