GB313044A - Improvements in and relating to electric induction furnaces - Google Patents

Abstract

313,044. Northrup, E. F. June 5, 1928, [Convention date]. Induction furnaces.-Leakage of molten metal due to fracture of the refractory wall of the crucible or container causes operation of a protective or warning device inserted in the circuit of a exploring winding disposed on or around the walls of the crucible. The exploring winding comprises conductors 25, 26 non-inductively wound on a cylinder 19 surrounding the refractory container 20. The air-cooled induction coil 20 is separated from the exploring winding by a protective cylinder 18 sufficiently strong and heat resistant to temporarily cheek the flow of molten metal if a fracture occurs in the container. In a modification the winding is embedded in the refractory 20. In a further modification the winding is arranged as a Gramme winding on the cylinder 19 which encloses a crucible, and the induction coil 13 is water-cooled. The conductors 25, 26, Fig. 3, are connected together at one end by a lamp 29 giving a white light and at the other end to current supply leads 27, a lamp 28 giving a red light being fitted as shown. Normally both lamps burn dimly. If a short 30 occurs the lamp 29 is extinguished. If either conductor fuses, both lamps are extinguished. In Fig. 4 the conductor 25 is reversed so that the total resistance of the part of the conductors in circuit when a short occurs is substantially constant wherever the fault may be. The lamps 29, 28 are replaced by a coil 34 and a resistance 32, a second coil 33 being fitted as shown. The coils 34, 33 comprise opposing coils of a differentially wound electromagnet which will cause operation of a visual or audible signal or interruption of the main supply when a fault occurs. In Fig. 6 the winding forms a part 39 of one arm of a Weatstone bridge, the other part of the arm being the coil 40 of an electromagnetic switch 45 controlling a relay switch 51 in the furnace circuit. The red lamp 28 is fitted as shown. The coil 40 may be replaced by the white lamp.