GB1413163A - Method and apparatus for the extrusion of plastics net and net- like structures - Google Patents

Abstract

1413163 Plastics nets by extrusion CONWED CORP 10 Oct 1972 46559/72 Heading B5A In the formation of a plastics tubular net structure, e.g. of polypropylene, and of circular, square, or rectangular section, longitudinally extending net strands are continuously delivered from one set of extrusion die passages, and strand formations extending transversely thereto, are intermittently delivered on one or both sides thereof to become welded to the longitudinal strands, from between die forming surfaces which are intermittently moved between a closed abutting, and a spaced apart position to extrude the transverse strands. The transverse strands are brought into welding contact with the longitudinal strands by the force of their extrusion, and by the force of the squeezing action of the forming surfaces moving into contact. The longitudinal and transverse strands may comprise plastics from different extrusion sources or, as described, from the same source. In the Fig. 2 embodiment, the longitudinal strands 16 are vertically extruded from circumferentially spaced passages 14 of a die member 12, and the transverse strands 22 from between forming surfaces 19, 20 defined on die member 12 and a die member 11, either or both of which effect vertical reciprocation between a spaced apart, and an abutting position to extrude the transverse strands 22. In this embodiment the surfaces 19, 20 are inclined towards the direction of extrusion of the strands 16, but in the Fig. 1 embodiment (not shown) are at 90 degrees thereto. The surfaces 19, 20 alternatively be located exteriorly of the passages 14. Leakage of polymer along the reciprocating die parts is minimized by drain holes 26. The Fig. 3 embodiment (not shown) is similar to the Fig. 2 embodiment, but a flange on the die part (11) extends above the passages (14) and is provided with semi-spherical projections (28) which aligned with the passages (14), and act to decrease the extrusion therethrough during extrusion of the transverse strands, to provide a thinner joint at the junction between the strands. In the Fig. 6 embodiment, the forming surfaces 19, 20 are located exteriorly of the passages 14, and extend to the pitch circle of the passages 14 between the passages 14, but are cut away at 31 around the outlets 30 of passages 14, to produce the net section of Fig. 7. In this embodiment, thinning at the strand junction is obtained due to upward movement of orifices 14 during separation of surface 20 from surface 19. Welding between the strands may be enhanced by extrusion around a mandrel effecting stretching.