Blowing agent introduction into hopper of polymer foam processing

Abstract

Methods and systems that include introducing blowing agent into a hopper of a polymeric foam system.

What is claimed: 
     
         1 . A system comprising:
 an extruder including a screw configured to rotate in a barrel to convey a mixture of polymeric material and blowing agent in a downstream direction in a polymer processing space defined between the screw and the barrel;   a mold connected to an outlet of the extruder, the screw being configured to periodically move in a downstream direction in the barrel to inject a shot of the mixture of polymeric material and blowing agent into the mold;   a hopper configured to hold polymeric material pellets and blowing agent in a chamber volume, the hopper including at least one inlet connectable to a source of the blowing agent, the hopper including an outlet connectable to the polymer processing space in the extruder;   a pressure regulator constructed and arranged to control the pressure of blowing agent supplied to the hopper;   at least one processor; and   at least one storage medium having encoded thereon executable instructions that, when executed by the at least one processor, cause the at least one processor to carry out a method comprising:   controlling a pressure of the blowing agent supplied to the hopper to a desired pressure using the pressure regulator based, at least in part, on the desired weight percentage of blowing agent in the shot of the mixture of polymeric material and blowing agent.   
     
     
         2 . The system of  claim 1 , wherein controlling a pressure of the blowing agent supplied to the hopper to a desired pressure comprises:
 determining the volume of blowing agent in the hopper.   
     
     
         3 . The system of  claim 1 , wherein the source of blowing agent comprises nitrogen. 
     
     
         4 . The system of  claim 1 , wherein the mold comprises an injection mold. 
     
     
         5 . The system of  claim 1 , wherein the hopper includes multiple chambers. 
     
     
         6 . A method comprising:
 providing a hopper configured to hold polymeric material pellets;   supplying blowing agent to the hopper at a desired blowing agent pressure based, at least in part, on a desired weight percentage of blowing agent in the shot;   supplying blowing agent and the polymeric material pellets to an inlet of an extruder including a screw configured to rotate in a barrel;   conveying a mixture of polymeric material and the blowing agent in a downstream direction in the extruder;   accumulating a shot of the mixture of polymeric material and blowing agent; and   injecting the shot into a mold to form a molded polymeric foam article.   
     
     
         7 . The method of  claim 6 , wherein a pressure regulator is configured to provide the desired blowing agent pressure. 
     
     
         8 . The method of  claim 6 , further comprising determining the desired blowing agent pressure, in part, from the volume of blowing agent in the hopper. 
     
     
         9 . The method of  claim 6 , wherein the source of blowing agent comprises nitrogen. 
     
     
         10 . The method of  claim 6 , wherein the mold comprises an injection mold. 
     
     
         11 . The method of  claim 6 , wherein the hopper includes multiple chambers. 
     
     
         12 . A system comprising:
 an extruder including a screw configured to rotate in a barrel to convey a mixture of polymeric material and blowing agent in a downstream direction in a polymer processing space defined between the screw and the barrel;   a mold connected to an outlet of the extruder, the screw being configured to periodically move in a downstream direction in the barrel to inject a shot of the mixture of polymeric material and blowing agent into the mold;   a blowing agent introduction system including a source of blowing agent and a pressure regulator; and   a hopper including a chamber volume having a port fluidly connected to the source of blowing agent, wherein the hopper is configured to hold polymeric material pellets and blowing agent in a chamber volume, the hopper including a first outlet configured to supply polymeric material pellets and blowing agent to the polymer processing space in the extruder; and   wherein the system is configured to recycle blowing agent in the chamber volume to a location in the blowing agent introduction system upstream of the pressure regulator.   
     
     
         13 . The system of  claim 12 , wherein the system is configured to recycle residual blowing agent in the chamber volume after the polymeric material pellets have been supplied to the polymer processing space. 
     
     
         14 . The system of  claim 12 , wherein the source of blowing agent comprises nitrogen. 
     
     
         15 . The system of  claim 12 , wherein the mold comprises an injection mold. 
     
     
         16 . The system of  claim 12 , wherein the hopper includes multiple chambers. 
     
     
         17 . (canceled) 
     
     
         18 . The system of  claim 1 , wherein the system is configured to selectively supply the blowing agent and polymeric material from either the first chamber volume or the second chamber volume to the polymer processing space in the extruder. 
     
     
         19 . The system of  claim 18 , wherein the hopper further comprises a third chamber volume configured to connect to an outlet of the first chamber volume and an outlet of the second chamber volume, the third chamber volume including an outlet connected to the polymer processing space in the extruder. 
     
     
         20 . The system of  claim 18 , wherein the mold comprises an injection mold.