Implementation of a virtual wall

1,068,337. Extrusion machines. MONSANTO CHEMICAL CO. Nov. 7, 1963 [Nov. 13, 1962], No. 43957/63. Heading B5A. [Also in Division F2] In an extrusion machine variations in the cross-section of tubular extrusions are produced by the variation of the configuration of an extrusion outlet and of the pressure and rate of supply of plastic material to the outlet. Plastic material from a hopper 1 is fed continuously through a heated plasticizing unit 2 at a substantially constant pressure by a screw 5 into a passage 8, into which a plunger 10 may be reciprocated by a piston and cylinder assembly 15, 16 to increase or decrease the pressure and rate of supply of material to an extrusion outlet 27. A mandrel 24 mounted in a passage 23, in an extrusion head 22, leading to the extrusion outlet 27, is mounted for reciprocation by a piston and cylinder 32, 33 to vary the distance between the tip 25 of the mandrel 24 and the surface of a ring member 26 which contains the outlet 27. The reciprocable plunger 10 and mandrel 24 are actuated by the supply of fluid to the cylinders 16 and 33, respectively, controlled by a mechanical, electrical, pneumatic or hydraulic control mechanism, incorporating a timing mechanism. In operation it is suggested that by use of suitable timing of the movement of the plunger 10 and mandrel 24 tubular forms of the desired internal and external dimensions which vary along the axial length of the tube as illustrated in Figs. 9 and 11 (not shown) may be produced. In a further embodiment, Fig. 2 (not shown), the reciprocation of the plunger and mandrel is produced by timer controlled cam and follower mechanisms. A mandrel (54), Fig. 12 (not shown), is provided with a tip (56) of varying configuration which is mounted in an extrusion orifice (49), in order that by movement of the mandrel the appropriate portion of the tip may be brought into register with the orifice to produce a desired circular or oval bore, Fig. 15 (not shown), where required in the extruded tube. A knife (B), Fig. 12, may be provided to reciprocate across the mouth of the extrusion orifice to sever desired lengths of the continuously extruding tube. It is suggested that the capacity of the passage 8 may be varied by its walls being selectively expansible or contractible and that relative movement between the mandrel tip and the ring member containing the extrusion orifice may be achieved by moving the ring member or by joint mandrel and ring movement.