Patent EA-001998-B1 (EA)
Title: Plasticizing screw
Inventor: LEVEQIE ALAIN YVES
IPC: B29C48/625
Filed: 1999-05-06
Abstract: 1. A screw (27) comprising a screw shaft (39) having a thread (41) spirally positioned about the screw shaft (39) so as to form a plurality of flights, said screw (27) having a feeding zone (29), a compression zone (31) and a metering zone (33), wherein the depth, width and pitch of the flights (43) in the feeding zone (29) are designed based upon the bulk density of the material to be used in the screw (27) and the depth, width and pitch of the flights (47) in the metering zone (33) are designed based upon the melt density of the material to be used in the screw (27) so as to provide an actual volumetric flow of material and theoretical volumetric drag flow of material in the feeding zone (29) and an actual volumetric flow of material and theoretical volumetric drag flow of material in the metering zone (33) such that the difference in the ratio of the actual volumetric flow of material to the theoretical volumetric drag flow of material in the feeding zone (29) and the ratio of the actual volumetric flow of material to the theoretical volumetric drag flow of material in the metering zone (33) is less than 0.2. 2. The screw (27) of claim 1, wherein the difference in the ratio of the actual volumetric flow to the theoretical volumetric drag flow of material in the feeding zone (29) and the ratio of the actual volumetric flow to the theoretical volumetric drag flow of material in the metering zone (33) is less than 0.1. 3. The screw (27) of claim 1, wherein the difference in the ratio of the actual volumetric flow to the theoretical volumetric drag flow of material in the feeding zone (29) and the ratio of the actual volumetric flow to the theoretical volumetric drag flow of material in the metering zone (33) is less than 0.05. 4. The screw (27) of claim 1, wherein the ratio of the actual volumetric flow of material to the theoretical volumetric drag flow of material in the feeding zone (29) is between 0.8 and 1.0. 5. The screw (27) of claim 1, wherein the ratio of the actual volumetric flow of material to the theoretical volumetric drag flow of material in the metering zone (33) is between 0.8 and 1.0. 6. The screw (27) of claim 1, wherein the pitch of at least a portion of the flights (47) in the metering zone (33) is greater than the pitch of at least a portion of the flights (43) in the feeding zone (29), the pitch of at least a portion of the flights (43) in the feeding zone (29) is less than fhe outside diameter of the screw (27), the pitch of at least a portion of the flights (47) in the metering zone (33) is greater than the outside diameter of the screw (27), the pitch of at least a portion of the flights (45) increases through the compression zone (31), and the depth of at least a portion of the flights (45) decreases through the compression zone (31) moving from nearer the feeding zone (29) to nearer the metering zone (33). 7. The screw (27) of claim 6, wherein the pitch of the flights (47) in the metering zone (33) is greater man the pitch of the flights (43) in the feeding zone (29). 8. The screw (27) of claim 6, wherein the pitch of the flights (47) in the metering zone (33) is approximately equal. 9. The screw of (27) claim 6, wherein the pitch of the flights (43) in the feeding zone (29) is less than the outside diameter of the. screw (27). 10. The screw (27) of claim 6, wherein the pitch of the flights (43) in the feeding zone (29) is approximately equal. 11. The screw (27) of claim 6, the pitch of the flights (47) in the metering zone (33) is greater than the outside diameter of the screw (27). 12. The screw (27) of claim 6, wherein the depth of the flights (47) in the metering zone (33) is approximately equal. 13. The screw (27) of claim 6, wherein the depth of the flights (45) decreases through the compression zone (31) moving from nearer the feeding zone (29) to nearer the metering zone (33). 14. The screw (27) of claim 6, wherein the depth of the flights (43) in the feeding zone (29) is approximately equal. 15. In a screw (27) comprising a screw shaft (39) having a thread (41) spirally positioned about the screw shaft (39) so as to form a plurality of flights, said screw (27) having a feeding zone (29), a compression zone (31) and a metering zone (33), wherein the pitch of at least a portion of the flights (47) in the metering zone (33) is greater than me pitch of at least a portion of the flights (43) in the feeding zone (29), the pitch of at least a portion of the flights (43) in me feeding zone (29) is less than the outside diameter of the screw (27), the pitch of at least a portion of the flights (47) in the metering zone (33) is greater than the outside diameter of me screw (27), the pitch of at least a portion of the flights (45) increases through the compression zone (31), and the depth of at least a portion of the flights (45) decreases through the compression zone (31) moving from nearer me feeding zone (29) to nearer the metering zone (33),  characterized in that the depth, width and pitch of the flights (43) in the feeding zone (29) are based upon the bulk density of the material to be used in the screw (27) and the depth, width and pitch of the flights (47) in the metering zone (33) are based upon the melt density of the material to be used in me screw (27) so as to provide an actual volumetric flow of material and theoretical volumetric drag flow of material in me feeding zone (29) and an actual volumetric flow of material and theoretical volumetric drag flow of material in the metering zone (33) such that me difference in the ratio of the actual volumetric flow of material to the theoretical volumetric drag flow of material in the feeding zone (29) and the ratio of the actual volumetric flow of material to the theoretical volumetric drag flow of material in the metering zone (33) is less than 0.2. 16. A method of designing a screw (27) for use in injection molding or extrusion which screw comprises a screw shaft (39) having a thread (41) spirally positioned about me screw shaft (39) so as to form a plurality of flights, and said screw (27) having a feeding zone (29), a compression zone (31) and a metering zone (33), comprising the steps of: selecting the material to be used in the screw (27), selecting a mass flow rate of material, calculating a volumetric flow rate of material in the feeding zone (29), calculating a volumetric flow rate of material in me metering zone (33), selecting the depth, width and pitch of the flights (43) in the feeding zone (29) and the depth, width and pitch of the flights (47) in fee metering zone (33) so as to provide an actual volumetric flow of material and theoretical volumetric drag flow of material in the feeding zone (29) and an actual volumetric flow of material and theoretical volumetric drag flow of material in the metering zone (33) such that the difference in the ratio of the actual volumetric flow of material to the theoretical volumetric drag flow of material in the feeding zone (29) and the ratio of the actual volumetric flow of material to the theoretical volumetric drag flow of material in the metering zone (33) is less than 0.2.