Abstract: Parasite arcs which occur during the operation of plasma torches have an adverse economic effect and endanger important parts of the torch. Countermeasures of the prior art are only partly effective. Equipping the annular passage between the electrode and the surrounding nozzle which carries the plasma gas with an electrically insulating lining on the inside of the nozzle provides only partial protection. To insulate the segment of the inner wall part of a water-cooled nozzle adjacent to the end wall part by means of insulating parts penetrating the wall part in question from the outer segment is very expensive and complex, depending on the design and the choice of insulation materials. The invention proposes that secondary passages be distributed uniformly between the annular passage for the plasma gas and an annular passage between the nozzle endpiece and the torch casing, uniformly over the circumference.

Abstract: A power supply for a three-phase plasma heating unit includes a three-phase transformer having a primary winding group with taps which are switched under load. The transformer also has secondary winding groups which are offset by a 60.degree. phase angle, the secondary winding groups being connected to the three-phase plasma heating unit. Converter units are also connected to the secondary winding groups. Each converter unit includes a three-phase thyristor bridge and a choke connected to the bridge. Another embodiment employs two three-phase transformers. The first transformer has a secondary winding group with taps which are switched under load. The second transformer has a primary winding group which is connected to the secondary winding group of the first transformer. The second transformer also has secondary winding groups which are offset by a 60.degree. phase angle, the secondary winding groups being connected to the three-phase plasma heating unit.

Abstract: Apparatus for supplying thermal energy to a metal melt present in a receiving vessel after having been discharged from a melting furnace, the receiving vessel having a central axis, the apparatus includes at least two plasma torches disposed above the melt in the receiving vessel to direct a transferred electric arc at the melt, the torches being operated with alternating current and with a gas which is inert to the melt, while being cooled with water.Apparatus according to the invention includes a cover over the top of the vessel, the cover having a passage for the electrodes, and a component establishing a gas-tight seal between the cover and the electrodes.

Abstract: In a plasma torch having an output end, the torch including an electrode having a longitudinal axis, and a generally cylindrical nozzle body surrounding, and positioned concentrically with, the electrode and the nozzle body, the nozzle body includes: a radially symmetrical, generally cylindrical inner wall spaced radially from the electrode; a radially symmetrical, generally cylindrical outer wall surrounding, and arranged concentrically with respect to, the inner wall; a front end wall located in the vicinity of the torch output end and joining together the inner and outer walls; and an electrical insulating component forming part of at least one of the inner and front end walls and extending entirely across its associated wall for electrically insulating the inner and outer walls from one another at at least one location in the vicinity of the front end wall.

Abstract: A plasma burner for introducing an ionizable gas stream into an electric arc comprises a nozzle having an outlet opening for discharging the gas stream. The outlet opening is defined by an outlet part of the nozzle; the outlet part has an inner nozzle face conically tapering, at an acute first cone angle, in a direction of the outlet opening. The plasma burner further has an electrode surrounded by the outlet part and having an outer electrode face conically tapering, at an acute second cone angle, in the direction of the outlet opening. The inner nozzle face and the outer electrode face together define a conical annular channel.

Abstract: Plasma burner having a frontal face from which a plasma jet is to be projected, for producing a long initial firing arc, having first and second concentrically arranged electrodes extending perpendicularly to the frontal face, and a nozzle surrounding the electrodes, the first electrode being centrally arranged to constitute an auxiliary electrode and having a cylindrical main portion, an electrode tip at its front end and a conically tapered portion located between the main portion and the electrode tip and tapering toward the electrode tip, the second electrode being annular and surrounding the first electrode to constitute a nozzle electrode, and having a central channel composed, successively, in the direction toward the frontal face, of a first cylindrical section, a conically tapered section and a second cylindrical section smaller in diameter than the first cylindrical section, the central channel and the first electrode together forming an annular channel.

Abstract: Method for producing steel from sponge metal with the use of a gas plasma in a melting vessel containing a metal bath. The sponge metal is fed into the melting vessel and is melted directly by the plasma without the addition of base or acid means. The slag produced from the melting of the sponge metal is removed continuously from the metal bath.

Abstract: A method for melting sponge iron is provided in which pieces or pellets of sponge iron, which may be partly replaced by scrap, are placed on the surface of a molten metal bath. Oxygen is added to the metal bath at a position below the surface of the bath. Further substances required for the melting process are added to the metal bath under pressure at a position below the surface of the bath. The further substances that are added include solid carbonaceous dust and fine-grained sponge iron.

Abstract: The present invention relates to a) a method for refining metal in which, e.g., oxygen and fine lime are introduced through at least one nozzle disposed below a molten bath surface in the refining vessel and a gas is fed in through one or a plurality of further nozzles associated with each first nozzle and to b) an apparatus for practicing the method.