Patent GB-1072113-A (GB)
Title: Improvements in or relating to the manufacture of tubular plastic netting and tubular reticulated film
Inventor: MARTIN KEITH FRASER
IPC: B29C48/12
Filed: 1963-01-25
Abstract: 1,072,113. Making tubular reticulated films and netting. PLASTIC TEXTILE ACCESSORIES Ltd. Jan. 15, 1964 [Jan. 25, 1963; April 17, 1963], Nos. 3296/63 and 15155/63. Headings B5A and B5B. An apparatus for producing extruded tubular netting such as tubular reticulated films by melt extruding an organic thermoplastic polymeric material comprises an inner die-carrying member 1 and an outer die-carrying member 2 (Fig. 1, not shown). The inner member 1 carries at its lower end an inner die 3 and the outer member 2 is provided with a circular series of spaced die orifices 4 conveniently in the form of open sided grooves formed in an outer die 5, the die 3 and the die orifices 4 constituting the die orifice means for melt extruding the material in the form of a tube of spaced parallel longitudinal strands 12. The inner die 3 is provided with an annular mould groove 15 disposed in axial juxtaposition with the series of die orifices 4 in the outer member 2 for the purpose of moulding spaced parallel closed ring strands 16 integrally with and circumferentially of the longitudinal strands 12. The inner member 1 is provided at its upper end with a shaft 6 to the upper end of which is secured a cam follower 7 which is urged upwards into engagement with a rotary cam 9 by a compression spring 8. In the position of cam 9 as depicted in Fig. 1, the inner and outer dies 3 and 5 are held in horizontal alignment, the inner die 3 being in its uppermost position (Fig. 2, not shown). Under these conditions the die orifices for the extrusion of the strands 12 are defined partly by the die orifices 4 in the outer die 5 and partly by portions of the inner die 3 adjacent the die orifices 4. The cam 9 is rotated continuously by the drive chain 13 and each time one of the protruding portions 14 of the cam 9 engages the cam follower 7, the shaft 6 and the inner die member 1 are momentarily thrust downwards axially of the series of die orifices 4, against the pressure of the spring 8, until the inner die 3 is in the position shown in Fig. 3 (not shown). The rate of downward movement of the inner die 3 is substantially that of the rate of extrusion of the strands 12 from the die orifices 4. In this position the annular groove 15, formed in the peripheral surface of the inner die 3 is located externally of the die orifices 4 and the plastic material in the groove 15 which is in the form of an above-mentioned closed ring strand 16 premoulded and integral with the longitudinal strands 12, is carried downwards with the longitudinal strands 12 and stripped from the groove 15 to form the circumferential closed ring strands of the tubular reticular film formed by the extrusion operation. Upon further rotation of the cam 9, the inner die 3 is returned to the position depicted in Fig. 2, and the groove 15 is refilled with plastic material from the die orifices 4 in readiness for the delivery of a succeeding pre-moulded closed ring strand. The extruded tubular reticular film is drawn off over a mandrel 17 which is of greater diameter than the ring of extrusion orifices 4 to facilitate the stripping of the ring strands 16 from the groove 15. The extruded tubular reticular film is cooled by passing it through a water bath, the level of which is indicated at 17a (Fig. 1). The melt to be extruded is introduced into the apparatus under pressure through an inlet 10 into a supply cavity 11 communicating with the extrusion orifices 4. In a described and illustrated preferred form of the apparatus the annular mould groove 15 is provided with its own feed ducts to ensure an adequate feed of melt to the groove. In order that the closed ring strands 16 may, like the longitudinal strands 12, be subjected in the apparatus to melt flow orientation, so that the tubular reticular film may be stretched circumferentially as well as longitudinally it is preferred to use a modified apparatus. In this described and illustrated form provision is made for bodily rotating the feed ducts to the annular groove 15 continuously during the reciprocation of the inner die 3.