Abstract: An annular exhaust gas passage 2 and an airtight retention member 3 for keeping the inside of a crucible induction furnace 1 airtight are installed on the top of the furnace 1, and an exhaust system under atmospheric pressure is connected to a valve 4 via an air duct that penetrates the airtight retention member 3. In addition, a sealing cover 7 that has a valve 8, which can be opened and closed, is used to keep the inside of the furnace airtight, while a system under reduced pressure is connected to the valve 8. These two systems constitute the entire exhaust system.

Abstract: In a fast-melting induction furnace, an elevationally movable pressing cover 4 suppresses the swell of molten metal 3 inside a crucible 2 on which a coil 1 is wound. The pressing cover 4 has a lower surface which is made concave. An upper half part of the motion of the molten metal 3 caused by electromagnetic force is made in conformity with the concave shape of the lower surface 5, so that the dangerous blowout of molten metal through a gap 8 is effectively prevented. Accordingly, the fast melting by the supply of high electric power can be performed. The lower surface 5 may be shaped as a cylindrical surface, a paraboloidal surface of revolution, a partial spherical surface, or the like, or may be shaped like a runner bucket of a Pelton turbine which has a slightly projecting center portion.

Abstract: A crucible induction furnace is disclosed which is provided with a preventive measure against low melting point metals and having a crucible refractory within an induction coil in a barrel container, in which the crucible induction furnace comprises a coil protection member located between the crucible refractory and the induction coil and which includes at least one air-permeating portion. An air supply pipe is in communication with the air-permeating portion for supplying pressurized air to the crucible refractory. The air permeating portion is disposed to distribute pressurized air having a higher pressure adjacent to the bottom portion of the crucible refractory than to the upper portion of the crucible refractory.

Abstract: An induction furnace in which a graphite crucible is encompassed by a spaced thermal insulating sheath. The annular space therebetween is sealed and a coil is circumferentially mounted about the sheath. The crucible thus constructed is placed on a furnace bed which is provided with a conduit for discharging the molten metal therein.