| 摘要 |
Thermoplastic granules mixed with a blowing agent are processed in a barrel unit which encloses a rotating screw which mixes, works and plasticizes the mixture so that at the leading end of the barrel it is in a molten condition suitable for extrusion or injection molding. The screw has two compression stages with an intermediate decompression stage therebetween. At a location corresponding to the decompression stage of the screw the barrel has a vent therein which permits the escape of moisture vapors and other unwanted volatiles in the mixture. At the vent zone the forward faces of the screw flights are undercut to minimize the discharge of mixture through the vent. |
