Systems and methods for continuous production of gas atomized metal powders

Abstract

Raw material feed into an electric arc furnace (“EAF”) is melted into heated liquid metal at a controlled temperature with impurities and inclusions removed as a separate liquid slag layer. The heated liquid metal is removed from the EAF into a passively heatable ladle wherein it is moved into a refining station where they are placed into a inductively heated refining holding vessel and wherein vacuum oxygen decarburization is applied to remove carbon, hydrogen, oxygen, nitrogen and other undesirable impurities from the liquid metal. The ladle and liquid metal is then transferred to a refining station/gas atomizer having a controlled vacuum and inert atmosphere wherein the liquid metal is poured from an inductively heated atomizing holder vessel into a heated tundish at a controlled rate wherein high pressure inert gas is applied through a nozzle to create a spray of metal droplets forming spherical shapes as the droplets cool.

What is claimed is: 
     
         1 . A method for continuous production of atomized metal powders, comprising the steps of:
 a) forming molten metal;   b) transferring the molten metal to a passively heatable ladle;   c) moving the passively heatable ladle into a holding vessel,   d) heating the holding vessel to maintain a desired temperature of the metal within the passively heatable ladle to remove impurities from the metal within the passively heatable ladle;   e) removing the passively heatable ladle from the holding vessel, through open air, to a gas atomizer;   g) transferring the metal from the passively heatable ladle to a tundish within the gas atomizer, wherein the tundish is located within a controlled vacuum and inert atmosphere chamber confined within the gas atomizer; and   h) flowing the metal from the tundish to form spherical shaped metal powder.   
     
     
         2 . The method of  claim 1 , wherein the molten metal is poured into the passively heatable ladle. 
     
     
         3 . The method of  claim 1 , wherein transferring the metal from the passively heatable ladle to a tundish within the gas atomizer comprises pouring molten metal from the passively heatable ladle into the tundish. 
     
     
         4 . The method of  claim 1 , wherein heating the holding vessel comprises generating an electromagnetic field and inductively producing heat inside the holding vessel and further heating the molten metal inside the passively heatable ladle to thereby maintain the molten metal in a liquid state. 
     
     
         5 . A method for continuous production of atomized metal powders, comprising the steps of:
 (a) feeding raw materials comprising metal into a furnace;   (b) melting the raw materials into molten metal at a temperature sufficient to remove impurities as a separate liquid slag layer forming on top of the molten metal within the furnace;   (c) removing the molten metal from the furnace into a first passively heatable ladle by tilting the furnace and pouring the liquid metal through at least one of a spout or tap hole formed in the furnace;   (d) moving the first passively heatable ladle full of molten metal into a first inductively heated refining holding vessel, wherein the first inductively heated refining holding vessel is configured to generate an electromagnetic field and inductively produce heat inside the first inductively heated refining holding vessel and further heat the molten metal inside the first passively heatable ladle to thereby maintain the molten metal in a liquid state;   (e) moving the first inductively heated refining holding vessel that is housing the first passively heatable ladle through a refining station and removing undesirable impurities, inclusions or gasses from the liquid metal, while controlling the molten metal temperature with the first electromagnetic field by inductively heating the molten metal held inside the first passively heatable ladle;   (f) repeating steps (a) through (e) for preparing a second passively heatable ladle containing molten metal;   (g) moving the first and second inductively heated refining holding vessels containing their passively heatable ladles from the refining station to an atomizer station having a controlled vacuum and inert atmosphere chamber and a heated tundish disposed therein, the controlled vacuum and inert atmosphere chamber within the atomizer station comprising a first receiving area accessible via a first door and a second receiving area accessible via a second door;   (h) locating the first inductively heated atomizing holding and the first passively heatable ladle containing molten metal into the first receiving area of the atomizer station by moving the first inductively heated atomizing holding and the first passively heatable ladle through the first door of the atomizer station and locating the second inductively heated atomizing holding and the second passively heatable ladle containing molten metal into the second receiving area of the atomizer station by moving the second inductively heated atomizing holding and the second passively heatable ladle therein through the second door of the atomizer station;   (i) tilting the first inductively heated atomizing holding vessel located in the first receiving area to pour the molten metal from the first passively heatable ladle into the heated tundish at a controlled rate to maintain a minimum level of metal in the heated tundish while continuing to control the molten metal temperature in the first passively heatable ladle by applying an electromagnetic field capable of inductively heating the molten metal inside the first passively heatable ladle from the first inductively heated atomizing holding vessel;   (j) tilting the second inductively heated atomizing holding vessel located in the second receiving area to pour the molten metal from the second passively heatable ladle into the heated tundish at a controlled rate to maintain a minimum level of metal in the heated tundish while continuing to control the molten metal temperature in the second passively heatable ladle by applying an electromagnetic field capable of inductively heating the molten metal inside the second passively heatable ladle, wherein tilting the heated second inductively heated atomizing holding vessel occurs after the first inductively heated atomizing holding vessel completes its pouring of molten metal into the heated tundish; and   (k) applying high pressure inert gas through a nozzle coupled to the heated tundish to produce a spray of droplets in the atomizing chamber and forming spherical shapes as the droplets cool and fall to a cone shaped bottom formed in the atomizing chamber;   wherein the first and second inductively heatable ladles are largely transparent to electromagnetic radiation wavelengths so that the molten metal can be heated while in the respective first and second passively heatable ladles by an electromagnetic field from each of the respective first and second inductively heated atomizing holding vessels without overheating the first and second passively heatable ladles.   
     
     
         6 . The method of  claim 5 , further comprising the step of removing the spherical powder from the atomizing chamber for classification by particle size. 
     
     
         7 . The method of  claim 5 , further comprising the step of removing the spherical powder from the atomizing chamber and processing through screens and blenders to classify the spherical powder by particle size. 
     
     
         8 . The method of  claim 5 , wherein functions of the first and second inductively heated atomizing holding vessels are alternated for subsequent passively heated ladles undergoing processing by the atomizer station. 
     
     
         9 . The method of  claim 5 , wherein prior to the step of tilting the first inductively heated atomizing holding vessel to enable molten metal to pour from the first passively heatable ladle into the heated tundish, the molten metal held by the first passively heatable ladle previously completed steps of being transferred from a first inductively heated refining holding vessel at the refining station into a cavity of the first inductively heated atomizing holding vessel located near the first receiving area of the atomizer station, the first inductively heated atomizing holding vessel configured to generate an electromagnetic field and thereby inductively produce heat inside the cavity of the first inductively heated atomizing holding vessel via the first passively heatable ladle to thereby maintain the molten metal in a liquid state, and moving the first inductively heated atomizing holding vessel by a first mechanical means through first atmosphere controlling doors into the atomizer station and next to the controlled vacuum and inert atmosphere chamber, while controlling the molten metal temperature by continually applying an electromagnetic field from the first inductively heated atomizing holding vessel for inductively heating the molten metal held by the first passively heatable ladle. 
     
     
         10 . The method of  claim 5 , wherein prior to the step of tilting the second inductively heated atomizing holding vessel to enable molten metal to pour from the second passively heatable ladle into the heated tundish, the molten metal held by the second passively heatable ladle previously completed steps of being transferred from a second inductively heated refining holding vessel at the refining station into a cavity of the second inductively heated atomizing holding vessel located near the second receiving area of the atomizer station, the second inductively heated atomizing holding vessel configured to generate an electromagnetic field and thereby inductively produce heat inside the cavity of the second inductively heated atomizing holding vessel via the second passively heatable ladle to thereby control the temperature of the molten metal, and moving the second inductively heated atomizing holding vessel by a second mechanical means through second atmosphere controlling doors into the atomizer station and next to the controlled vacuum and inert atmosphere chamber, while controlling the molten metal temperature by continually applying an electromagnetic field from the second inductively heated atomizing holding vessel for inductively heating the molten metal held by the second passively heatable ladle. 
     
     
         11 . The method of  claim 10 , wherein prior to the first passively heatable ladle previously completing steps of being transferred from a first inductively heated refining holding vessel at the refining station into a cavity of the first holding vessel located near the first receiving area of the atomizer station, the heated liquid metal contained by the first passively heatable ladle is removed from an electric arc furnace into the first passively heatable ladle by tilting the electric arc furnace and pouring the liquid metal through at least one of a spout or tap hole formed in the electric arc furnace, while the first passively heatable ladle and the molten metal contained therein is then moved to the refining station where processes of vacuum oxygen decarburization are conducted prior to movement of the first passively heatable ladle and the molten metal to the atomizer station. 
     
     
         12 . The method of  claim 11 , wherein prior to the second passively heatable ladle previously completing steps of being transferred from a second inductively heated refining holding vessel at the refining station into a cavity of the second holding vessel located near the first receiving area of the atomizer station, the heated liquid metal contained by the second passively heatable ladle is removed from an electric arc furnace into the second passively heatable ladle by tilting the electric arc furnace and pouring the liquid metal through at least one of a spout or tap hole formed in the electric arc furnace, while the second passively heatable ladle and the molten metal contained therein is then moved to the refining station where processes of vacuum oxygen decarburization are conducted prior to movement of the second passively heatable ladle and the molten metal to the atomizer station. 
     
     
         13 . A system for producing atomized metal powders, comprising:
 a) a furnace for forming molten metal;   b) at least one passively heatable ladle for containing the molten metal;   c) a holding vessel for housing the passively heatable ladle; wherein the inductively holding vessel comprises one or more electric coils to generate an electromagnetic field within the holding vessel to passively heat the molten metal within the passively heatable ladle;   e) an atomizer station having a controlled vacuum and inert atmosphere chamber;   g) a tundish located within the gas atomizer;   h) a nozzle for forming spherical shaped metal powder, and   i) a discharge hopper for collecting the spherical shaped metal powder from the nozzle,   wherein the passively heatable ladle containing the molten metal is configured to move between the holding vessel and the atomizer station.   
     
     
         14 . The system of  claim 13 , wherein the passively heatable ladle is largely transparent to electromagnetic radiation wavelengths so that liquid metal contained within the passively heatable ladle can be heated by an electromagnetic field without overheating the passively heatable ladle itself. 
     
     
         15 . The system of  claim 13 , wherein the passively heatable ladle containing the molten metal is configured to pour the molten metal into the tundish within the controlled vacuum and inert atmosphere chamber within the atomizer station. 
     
     
         16 . The system of  claim 13 , further comprising a series of screens and blenders to classify the spherical powder as a product by particle size. 
     
     
         17 . The system of  claim 13 , further comprising:
 a refining station including a VOD and an inductively heated refining holding vessel wherein the passively heatable ladle is placed during refining wherein a process of vacuum oxygen decarburization is carried out to remove undesirable impurities including at least one of carbon, hydrogen, oxygen, nitrogen, and other, inclusions or gasses from the liquid metal,;   wherein the at least one passively heatable ladle moves between the furnace and the refining station, and then moves between the refining station and the atomizer station; and   wherein molten metal is carried in the at least one passively heatable ladle after processing by the furnace and during processing by the refining station prior to being processed by the atomizer station.   
     
     
         18 . The system of  claim 13 , wherein the atomizer station comprises at least two different receiving areas, each comprising an access door for receiving one of the inductively heated atomizing holding vessels. 
     
     
         19 . The system of  claim 13 , wherein the atomizer station has two receiving doors and contains two inductively heated atomizing holding vessels simultaneously.