Patent GB-707931-A (GB)
Title: Improvements in or relating to a method of and apparatus for extruding metal
Inventor: BRIDGE ARCHIBALD CLAUDE
IPC: B21C23/21
Filed: 1951-12-28
Abstract: 707,931. Extruding. CRITTALL-LUXFER, Ltd., and FIELDING & PLATT, Ltd. June 3, 1952 [Dec. 28, 1951], No. 30321/51. Class 83 (4) A machine for cold impact extrusion comprises hydraulic apparatus including a ram and a cylinder, a die so mounted that the operative face therof is clear of obstruction, means for maintaining the billet to be extruded in operative position with respect to the ram and die, the said means during the extrusion period containing the operative face of the die so as to provide an effective seal around said die face, a pressure fluid accumulator for storing fluid under a predetermined pressure, means for controlling the speed of impact of the ram as it strikes the billet and means for supplying said pressure fluid to the cylinder to act upon the ram in such a manner that the full pressure required to effect extrusion of the billet is rendered effective substantially instantaneously. Billet chambers 10, 11, Fig. 1, each with a mandrel 12, 13, are mounted with a shear knife 14 on a slide 8 on the face of the ram 2 operated by a differential piston 5. The slide is reciprocable across the face of the ram by a pneumatic piston Y, to position either billet chamber opposite the die 15. Billets are fed to either side of the die by gravity down chutes 18 and pushed to the loading positions 20 by pneumatic devices 21. In operation, on the operative stroke of the ram a billet is extruded from one billet chamber, while the mandrel of the other billet chamber enters another billet. The ram then returns and slide 8 is moved to cause the discard to be sheared from the die by the knife 14, and the other billet to be positioned above the die for extrusion on the next operative stroke. To ensure accurate positioning of the billet chambers with respect to the die, a photo-electric device' in the control circuit prevents operation unless apertures in shutters on the ram and press frame are in line, Figs. 11, 12 (not shown). A further safety device incorporates switches with pins interlocking with grooves on the slide 8 such that the control circuit is completed only when a billet chamber is aligned with the die. The hydraulic circuit for the main ram 2, Fig. 8, includes a gas loaded hydraulic accumulator 36 connected to the main cylinder 4 through a needle valve 37a, and to the underside of the differential piston 5 to hold the ram in the retracted position through a two way valve 35 having a connection to exhaust. Control of the speed of impact of the ram with the billet is effected by adjustment of the needle valve 37a. In a modification, Fig. 7, the ram is held retracted by auxiliary rams 31, 32, the cylinders of which are connected to the accumulator 36. In a further modification Fig. 13, the apparatus comprises one billet chamber 44, the slide 8 carrying mandrels 12, 13 and shear knife 14. The billet chamber is mounted on guide pillars 45, Fig. 18, so as to be reciprocable towards or away from the ram under the action of pistons 60, 61, Fig. 20, connected to the hydraulic accumulator through a valve 59 In operation, billets are picked up alternately by the mandrels 12, 13, as the slide 8 reciprocates in front of the face of the ram, as in the embodiments described above. When the parts are in the position shown in Fig. 13, the slide 8 moves until the billet 22 on mandrel 13 occupies the position shown by the mandrel 12, the ram 2 being held retracted due to the differential pressure on the piston 5. Control valve 59 is then operated to raise the billet chamber to the position shown dotted in Fig. 20, and as the ram descends the chamber is forced downwardly to embrace the die to prevent " flashout" and the billet is extruded through the die. At the same time the mandrel 12 engages a billet in the loading position 20. Liquid in the cylinders 56, 57 of the pistons 60, 61 is forced back to the accumulator during the extrusion stroke and the valve 59 is opened to exhaust at the end of the stroke of the main ram. On the return stroke of the ram, the chamber remains in the lower position, and the slide is then moved back across the face of the ram to sever the discard and bring the mandrel 12 with a billet thereon into register with the die. Photo-electric safety devices and interlock switches are provided to prevent operation until all moving parts are in true alignment for correct operation. Expanding and stretching; cooling work; strippers.-The extruded section while still ductile due to the heat developed by extrusion is tensioned to straighten it by an air operated grab 66, Figs. 25, 26, which seizes the end of the section and is mounted on a bracket 74 slidable on a slide 77. The bracket 74 is connected by toggles 72, 73 to a lug 75 and the toggles are operated by a piston 71, so that straightening of the toggles will apply a stretching force to the section, the operation being timed so that the stretching force is applied while the section is still held by the discard. Pressure air supplied through a pipe 80 is forced through and around the section and assists in its removal from the guide 79 after severance from the discard, and also cools it.