GB1492590A - Extruder screws - Google Patents

Abstract

1492590 Extruder screw FRANCIS SHAW & CO (MANCHESTER) Ltd 17 Feb 1976 [25 Nov 1974] 51029/74 Heading B5A [Also in Division B1] An extruder screw for rubber or plastics material comprises at least one, and preferably a pair of flights BF1, BF2, which extend continuously through intake, IS, mixing, MS, and discharge regions, DS, and a further flight, or preferably a pair of flights IF1, IF2, in the mixing section, the flights BF1, BF2 being of a greater clearance from the extruder barrel in the mixing region MS, than in the other regions and than the flights IF1, IF2, so that the material is sheared and homogenized in being transferred across the greater clearance of flights BF1, BF2, between adjacent screw channels which are respectively of progressively decreasing and increasing depth. In the Fig. 1 embodiment, showing the regions in planar development, the flights 1FP1 and 1FP2 extend parallel to the flights BF1, BF2, and dams IFD1, IFD2 may be provided, respectively at the upstream and downstream ends of adjacent channels and which may have a greater clearance from the barrel, as shown, so that the material passes partially over the dams, or may not have a greater clearance so that all of the material passes over the flights BF1, BF2. In the Fig. 2 embodiment (not shown), the flights IF1, IF2 are of smaller pitch than and extend between adjacent flights BF1, BF2. To provide for a transfer across the flights equivalent to the material capacity of the remainder of the screw, the mixing section extends for substantially three diameters along the screw, and the transfer clearance across the flights is 10 to 18%, and preferably 14% of the channel depths. The mixing section is preferably between ¢ and 2/3 of the length of the screw from the intake, and a number of mixing sections may be provided along the screw.