Patent GB-879933-A (GB)
Title: Improvements in or relating to refining the grain of metals
IPC: C22F3/00
Filed: 1959-12-15
Abstract: 879,933. Altering molecular structure. DU PONT DE NEMOURS & CO., E. I. Dec. 15, 1959 [Dec. 18, 1958], No. 42631/59. Class 83 (4). A process for refining the grain of metals, e.g. iron, steel, copper, aluminium, magnesium cobalt, beryllium, chromium, vanadium, nickel, zinc, titanium, tungsten, manganese, tantalum, niobium, zirconium and their alloys comprises initiating a layer of detonating explosive placed substantially parallel to, and conforming substantially in configuration with, a surface of the metal and thereafter heating to a temperature at which recrystallization occurs and maintaining such a temperature until the grain is refined while stored energy is dissipated. The metal may be in the form of rods, plates, discs or any configuration formed by casting, extrusion or forging and the process is suitable for treating weldings. When treating metals liable to fracture a moderating material, e.g. lead, steel, copper, water, glycol, wax, rubber or air is placed in contact with the metal surface or spaced a slight distance away. The metal may be exposed to a single or a series of shock waves followed by a single heat treatment. A metal cylinder 1 to be treated is surrounded by a layer of explosive 2 and the explosive is confined in lead sheeting 3. To one end of the cylinder is attached a solid cone 4 of an inert material e.g. clay and around the cone is disposed a layer 5 of explosive. An initiator 6 is placed on the apex of the cone. A flat metal plate 1 is treated either as shown in Fig. 2A or as shown in Fig. 3 wherein spall blocks 9 are placed around the plate 1 which is positioned on an anvil plate 8. A driver plate 10 is supported above the plate and spall blocks on elements 11 the driver plate acting as a moderating agent which transmits the explosively generated shock wave to the workpiece. The explosive layer 2 is positioned on top of the driver plate and on the explosive layer is placed a planewave generator 12 and its initiator 6. The generator 12 comprises a pair of wooden supports 13 carrying a pair of glass plates 14 and 15 between which is interposed an explosive layer 16 and a line-wave generator 17 actuated by an initiator 6. For treating brittle metals the workpiece is surrounded by spall blocks 9 and is supported on the upper of two base plates 18 each consisting of 2 or 4 adjoining segments. On top of the workpiece is placed a cover plate 20 which is separated from the driver plate 10 by support blocks 11. An explosive layer 2 and a plane wave generator 12 is positioned on the driver plate 10. The assembly is inserted into a loosely fitting water-tight bag 22 and placed on a frangible supporting stand 19 in a cardboard container 23 resting on a pipe inserted in the earth. Water is introduced into the pipe and container to a level just above the cover plate 20. In operation, the plane wave generator is actuated and sets up a plane detonation front in the explosive layer 2 which propels the driver plate straight downwardly. The cover plate 20 acts as a moderating shock wave-transmitting medium and the base plates 18 serve to prevent rarefaction wave effects. The base plates are thrown outwardly by the explosion and allow the workpiece to pass through the frangible support and into the water-filled pipe which decelerates the workpiece and prevents its breakage upon hitting the ground. In another example the driver plate is eliminated and the workpiece is inserted in a cavity in a block 26 (Fig. 8) which is suspended within a water-filled tube 27 on the surface of the ground. A cover plate 28 having a central protuberance 29 for contacting the workpiece is placed on top of the block and an explosive layer 2 with attached initiator 6 rests on the cover plate. The sheet explosive comprises 70 to 92.5% by weight of P.E.T.N. and 7.3 to 30% by weight of a binding agent consisting of 75 to 25% by weight of an elastomer and 25 to 75% by weight of a thermoplastic terpenehydrocarbon resin. Several examples of treating different metals are given in the Specification. Specifications 637,332, 851,259, 863,194, 876,951 and 878,196 are referred to.