GB689726A - Semi-continuous furnace for melting and casting metals or alloys - Google Patents

Abstract

689,726. Vacuum casting-machines; metal-pouring; moulds. NATIONAL RESEARCH CORPORATION. Aug. 25, 1951, No. 20090/51. Class 83 (i). [Also in Group XI] A semi - continuous furnace for melting and casting in vacuo comprises a series of three vacuum - tight chambers, the first two having means to evacuate them, vacuum-tight closures between the chambers, for admitting metal to be melted to the first and for permitting removal of the mould, means for transferring the metal from the first chamber to a crucible in the second chamber, electric means for heating the metal in the crucible and means for discharging molten metal from this into the mould. The closure 24, Fig. 4, of the first chamber 12 is opened and the metal to be melted, in scrap or other form, is fed to a bucket 20 which is supported by rails 106, 130. The closure 24 is then closed, and a closure 26, Fig. 2, being also closed, the chamber 12 is evacuated to about the same pressure as the previously evacuated second chamber 10. The closure 26 is then opened and the bucket 20 moved to the left by a rack and pinion 112, 114 operated by an external handle 115 until a pin 108 connected to the bucket engages a detent connected to turning-means 110 which operates to discharge the metal into the crucible 38, the lid 80 having been first removed into the position shown in Fig. 3 by means 88, 90. The bucket is then returned and the closure 26 closed and, if the crucible is not full enough, these operations are repeated. Heating by electricity.-The lid 80 is replaced and a high-frequency water-cooled copper coil 46 is energized to melt the charge. The lid is then removed and the crucible tilted about its lip 66, by externally-operated means 68, 70, 72, 76, to discharge the molten metal by means of trough 22, lined with magnesia or alumina and provided with a radiant electric heater 151, into a water-cooled mould 154, the closure 144 and heat shield 150 having been previously withdrawn to the left. These are then returned and argon or other inert gas may be admitted to improve the casting. Finally, the joint 30 is disconnected, the mould removed and replaced by an empty mould. If a casting other than an ingot is required a precision or other mould is placed within the part 154 which becomes merely a vacuum chamber. The handle 147 for operating the closure 144 has cams 148 so that, after moving said closure into line with the passage 142, the handle can be turned to press the closure tightly over the hole. A similar construction may be used for the closure 26. The crucible is made of pure refractory, e.g. graphite or magnesia, and is packed into the coil 46 with a magnesia mix preferably precoated with phenolic resin and glass tape to prevent arcing. The ends of the coil 46 are connected to sockets 54, Fig. 6, embedded in an insulating block 48 and when the crucible is upright the sockets are engaged by contacts 52 connected to concentric tubes 60, 62 cooled by circulating water and supplied with the H.F. current. The tube 62 is earthed. A water-cooled stirring rod 36 and observation windows 34, 160 may be provided.