Patent GB-778529-A (GB)
Title: Improvements in or relating to extrusion presses
IPC: B21C25/06
Filed: 1956-01-20
Abstract: 778,529. Extruding; working at specified temperatures. WESTERN ELECTRIC CO., Inc. Jan. 20, 1956 [Jan. 26, 1955; Jan. 26, 1955], No. 1981/56. Class 83 (4). An extrusion press for forming metal tubes, particularly for sheathing cable cores 17 with aluminium 18, comprises a pair of opposed plungers 10, 11 axially slidable within a billet container 12, a mandrel 15 and a hollow die 16 defining a circular extrusion orifice 14 located substantially on the centre line of the container, the extrusion orifice, Fig. 4, being located between inner and outer coaxial conical surfaces 43, 44 on the mandrel and die respectively and the outer conical surface 44 terminating in a sharp edge at the tip of the die past which the billet metal is forced by the plungers into the extrusion orifice. The container 12 has end-plates 30, 31 freely slidable on four tie rods 32, 34, each of which has one end screwed into a pressure plate 24, 25 and its opposite end formed with a head 36 adapted to engage the adjacent container end-plate 30, 31 for limiting the movement apart of the two pressure plates 24, 25. The plungers 10, 11 are mounted for transverse sliding movement on the pressure plates whereby when the latter have been withdrawn the plungers may be moved transversely away from the container to facilitate recharging of the latter. Guide bushes 23 are provided for the plunger and electric heating elements 19, 21 surroind the plungers and billet container respectively. The mandrel 15 is lined with heat-resistant material 22 such as polytetrafluoroethylene, for preventing scorching of the paper-wrapped core 17. During extrusion pressure is applied to the pressure plates 24, 25 whilst the container is freely supported on the rods 32, 34 whereby the latter is supported vertically only by the force applied through the two plungers and hence a uniform rate of extrusion is maintained from both sides of the extrusion orifice. The inclination of the mandrel surface 43, Fig. 4, is between 20 and 45 degrees, preferably 35 degrees; the angle B of the surface 44 is between 5 and 20 degrees larger than the angle A whereby the two surfaces 43, 44 converge in the direction of extrusion; angle B is preferably 45 degrees. The outer conical surface 45 of the die has an angle C between 30 and 60 degrees, preferably 45 degrees. For extruding aluminium at temperatures of 250 to 450‹ C., the length of the surface 44 is between 5 and 50 mm., preferably 20 mm. The surfaces 43, 44 are provided with a heatpolymerized and partially carbonized coat of oil prior to use to provide lubrication during extrusion. This coating is produced by dipping the end portions of the die and mandrel in a mineral oil and then heating them in air to 350‹ C. by radiant heat. The aluminium billets used are formed by casting aluminium in a long cylindrical bar and cutting the latter into suitable lengths. To prevent air being trapped within the containers during re-charging, a number of longitudinal V-shape grooves are cut along the billets for the escape of air. Additionally or alternatively, the new billets to be charged into the press are heated to a temperature below that of the billets already in the press. The heat flow from the residual charge to the new billet causes a temperature gradient within the latter which causes them to have greater plasticity at their inner end whereby as pressure is applied the billets fill up the clearance space between themselves and the container wall by spreading progressively outwards towards the plungers and thus expelling air. Examples are given for the extrusion of aluminium having different degrees of purity with different temperatures and pressures. A comparison is made between the extrusion speed of aluminium using the die of this invention and that using a conventional die having a rounded dip.