Patent GB-1359672-A (GB)
Title: Extruder screw
IPC: B29C48/62
Filed: 1971-05-27
Abstract: 1359672 Extrusion screw PLAST-UND ELASTVERARBEITUNGSMASCHINENKOMBINAT KARL-MARX-STADT 27 May 1971 17654/71 Heading B5A [Also in Division B1] The volume of an extruder screw channel 3, Fig. 1, in a melting zone downstream of the extruder inlet port 2 is progressively decreased by a channel portion 5 of increased diameter into which the melt separates, and which commences on the downstream and/or upstream side of the screw web 4 and is respectively of greater or lesser pitch than the screw web 4 to effect the increasing compression. The screw provides communication with the molten material, of the pressure developed by the unmelted material upstream thereof. The screw core may be cylindrical or slightly conically tapering, and the step 9 between the channel portion 5 of larger, and the portion 7 of smaller diameter, may at right angles or oblique to the screw core. The configuration of the Fig. 1, screw may be effected in a two start thread. An increased diameter portion 5 adjacent the downstream thread side, as in Fig. 1, is preferable for polyethylene or polyamide materials which adhere to the screw, and an increased diameter portion on the upstream thread side is preferable for non-adhering material such as rigid P.V.C. The screw of the Fig. 1 embodiment may be provided with an axial passage extending upstream from the melting zone and serving to remove volatiles via radial bores connecting to the melting zone channel portion 7 of smaller diameter. The extruder may employ a pair of contra-rotating and non-intermeshing screws of the Fig. 1 configuration. In a modification of the Fig. 1 screw, Fig. 3 (not shown), a further similar channel portion of greater diameter than the portion 5 is provided adjacent the downstream side of the screw thread 4 and commencing and terminating downstream of the commencement and termination of the portion 5, and the three channel portions of differing depth provide for materials having a viscoelastic state, intermediate solid, and a molten state. In a further modification of the Fig. 1 embodiment, the portion 5 may terminate at a tapering section of the channel base into a metering channel of increased depth. In the Fig. 5 embodiment, channel portions 5 of increased diameter are provided on both the upstream and downstream side of the thread 4, and both terminate in a channel of the same depth which thereafter is of progressively decreasing compression effected by grooves 13 and 14 respectively adjacent the downstream and upstream side of the thread 4 and which are respectively of greater and lesser pitch than web 4. A mixing screw, e.g. for mixing of soluble or insoluble dyestuffs and pigment, is shown in Figs. 9 and 11, in which both a channel portion 5 of increased diameter and a portion 10 of further increased diameter are provided on the downstream thread side. Semi-circular grooves 18, 19, are provided respectively between the portions 5, 10 and between the portion 5 and the thread 4, and the portions 5, 10 are provided with recesses 17 which, on the portion 10, may be provided to the tip of the screw. A flow pattern along the recess 17 is provided superimposed on the flow tangentially to the portions 5, 10 caused by rotation of the screw, and the mixing effect of these flows is enhanced by the mixing thereof in the grooves 18, 19.