Method and device for atomizing molten metals

Abstract

In a method for atomizing metal melts, in which the liquid metal bath is sprayed from a tundish via an outlet opening by the aid of a gas into a cooling chamber, or onto a surface to be coated while compacting the comminuted particles by the aid of a propellant gas, the liquid metal melt via an annular gap is introduced into the outlet opening, into which a hot gas having a temperature of between 250° C. and 1300° C. and a supercritical pressure of between 2 and 30 bars is ejected through a Laval nozzle concentrically with said opening. The hot gas is contacted with the melt bath at a speed exceeding supersonic speed, with a radial outwardly directed component or with a twist. The device for carrying out the method includes a melt tundish ( 1 ) and an immersion tube ( 4 ) immersed in the melt ( 2 ) while forming an annular gap surrounding the outlet opening for the melt ( 2 ) and a lance ( 7 ) for the ejection of a propellant gas, wherein the height-adjustable lance ( 7 ) carries a Laval nozzle ( 9 ).

1 . A method for atomizing metal melts, in which the liquid metal bath is sprayed from a tundish via an outlet opening by the aid of a gas into a cooling chamber, or onto a surface to be coated while compacting the comminuted particles by the aid of a propellant, characterized in that the liquid metal melt via an annular gap is introduced into the outlet opening, into which a hot gas having a temperature of between 250° C. and 1300° C. and a supercritical pressure of between 2 and 30 bars is ejected through a Laval nozzle concentrically with said opening, and that the hot gas is contacted with the melt bath at a speed exceeding supersonic speed, with a radial outwardly directed component or with a twist.  
     
     
         2 . A method according to  claim 1 , characterized in that the hot gas is ejected via a deflector body.  
     
     
         3 . A method according to  claim 1  or  2 , characterized in that a lance comprising the Laval nozzle for the hot gas is conducted concentrically in a tube while forming an annular space, and that reactive gases such as, e.g., CO, H 2 , O 2  or H 2 O vapor, and/or inert gases such as, e.g., N 2  or Ar, and/or carbides such as, e.g., WC, TiC or VC, are sucked in via said annular space.  
     
     
         4 . A method according to  claim 3 , characterized in that reactive metal powders or additives such as, e.g., SiC, Al 2 O 3  or Y 2 O 3  are charged into the gas flow sucked in.  
     
     
         5 . A method according to any one of  claims 1  to  4 , characterized in that the hot gas is heated in a heat exchanger surrounding the melt particles ejected.  
     
     
         6 . A method according to any one of  claims 1  to  5 , characterized in that extremely fine particles of the solidifying melt, which ascend within the cooling chamber, are sucked off below the entry of the melt flow and discharged via a sluice.  
     
     
         7 . A method according to any one of  claims 1  to  6 , characterized in that a pressure of 1.5 to 25 bars is maintained within the tundish.  
     
     
         8 . A method according to any one of  claims 1  to  7 , characterized in that a pressure of 1.5 to 10 bars is maintained within the cooling chamber.  
     
     
         9 . A device for carrying out the method according to any one of  claims 1  to  8 , including a melt tundish ( 1 ) and an immersion tube ( 4 ) immersed in the melt ( 2 ) while forming an annular gap surrounding the outlet opening for the melt ( 2 ) and a lance ( 7 ) for the ejection of a propellant gas, characterized in that the height-adjustable lance ( 7 ) carries a Laval nozzle ( 9 ).  
     
     
         10 . A device according to  claim 9 , characterized in that a deflector body ( 10 ) is arranged in a height-adjustable manner in the widening opening region of the Laval nozzle ( 9 ) or following thereupon, viewed in the flow direction, the clear cross section between the nozzle ( 9 ) and the deflector body ( 10 ) being designed to increase in the axial direction towards the outlet end and to be larger than the narrowest cross section of the Laval nozzle ( 9 ).  
     
     
         11 . A device according to  claim 9  or  10 , characterized in that the lance ( 7 ) opens in the outlet opening of the tundish ( 1 ) below the lower edge of the immersion tube ( 4 ).  
     
     
         12 . A device according to any one of  claims 9  to  11 , characterized in that the outer diameter of the lance ( 7 ) is smaller than the clear diameter of the immersion tube ( 4 ) and the lance ( 7 ) is sealingly guided through a lid ( 6 ) of the immersion tube ( 4 ), and that a duct ( 24 ) for the supply of gases and/or reactive metal powders and/or additives opens into the space of the immersion tube ( 4 ) surrounding the lance ( 7 ).  
     
     
         13 . A device according to any one of  claims 9  to  10 , characterized in that the deflector body ( 10 ) is designed as a cone having deflector surfaces provided on its jacket.  
     
     
         14 . A device according to  claim 13 , characterized in that the deflector surfaces extend in an S-likely curved manner and, in the peripheral direction, terminate so as to be directed at the tangent of the base circle of the conical body each under the same angle.