GB1117832A - An annular die for extrusion of tubular films - Google Patents

Abstract

1,117,832. Annular extrusion die for tubular films; extrusion nozzles. ETHYL CORP. 5 Jan., 1967, No. 763/67. Headings B5A and B5B. An annular die 10 comprises a body member 11 (Fig. 2) comprising a base 14 containing a centrally positioned inlet aperture 13 and having an annular wall 12 mounted thereon and defining a cylindrical recess bounded by the inner surface of the wall 12 and the upper surface 21 of the base 14, and a generally cylindrical mandrel 15 also of circular cross-section disposed within the cylindrical recess of body member 11 and supported on the base 14 by attachment means 20 so that the circular face 16 of mandrel 15 is in proximity to the aperture-containing circular face 21 of body member 11 thereby forming the uniform horizontally disposed radial flow channel 17 which lies essentially in a plane perpendicular to the longitudinal axis of the die 10. Flow channel 17 is essentially perpendicular to orifice 18. The circumferential surface 19 of mandrel 15 need not be flat and parallel to surface 12, but is preferably V- shaped. The die 10 may be made by casting in a single step or alternatively by fabrication from separate components. The direction of flow of the melt is shown by the lines 50-51 in Fig. 5. In a preferred embodiment, the mandrel is supported on the base by at least three and suitably four or six spaced apart attachment means 20 extending between the circular faces of the mandrel and the base and radially disposed at approximately equal intervals between them. Attachment means 20 have an elliptical cross-section whose longitudinal axis is generally parallel to the radii of the circular faces 16 and 21 of mandrel 15 and body member 11 respectively. As shown in Fig. 6 said means also have relatively sharp leading and trailing edges, and the outer surfaces have a generally symmetrical concave configuration as this contributes materially to the substantial elimination of weld lines in the extruded continuous seamless tubing. Alternatively, said means 20 may have outer curvilinear surfaces which are straight instead of concave. In a modification, the orifice is of elliptical instead of circular crosssection. If desired mandrel 15 may be provided with a conical deflector 40 centrally positioned within its circular face 16, as shown in Fig. 7. The deflector aids in radially distributing the flow into the uniform horizontal radial flow channel 17 as the flow impinges upon the conical surface of the deflector. In operation the flow is caused to make two consecutive 90- degree bends or turns as it proceeds from the inlet aperture 13 to the horizontal radial flow channel 17 and thence to annular orifice 18. The utilization of this type of flow arrangement materially reduces the overall height of the die, and the optical properties of films, especially polyethylene films, produced with the die are superior to the optical properties of films made on conventional dies. Such dies also show exceptional mechanical stability and can withstand operating pressures as high as 10,000 p.s.i. The die is suitable for the extrusion of polyethylene, polypropylene, or polyvinyl chloride.