Method for producing low oxide metal powders

Abstract

A method is disclosed for producing high purity metal powders having an irregular and angular shape and a very low oxygen content (less than 0.25% oxygen in iron and steel powders). The invention utilizes a high pressure liquid atomization procedure for converting the molten metal to angular particulate form, and provides for the very rapid subsequent cooling of the hot particles under conditions of high pressure sprays and violent turbulence of the powder particles in the liquid that minimize the formation of oxide impurities on the particle surface. High pressure atomization to produce angular and irregular particles tends to create an oxidizing environment because of the mixture of hot particles and liquid. By rapidly quenching the particles immediately after formation, in a quenching environment that creates a violently turbulent condition at the surface of the metal, the formation of vapor or steam films is minimized and more rapid heat transfer from the particles to the cooling medium is realized.

I claim:  .[.1. A method of atomizing molten metal to a powder having irregular, angular particles predominantly of 40 to 325 mesh, and in which while normally oxidizable under water atomizing conditions, said formed metal powder contains less than 0.25 percent oxygen by weight, comprising: 
     
        .Iaddend..Iadd. 6.  A method of atomizing molten metal to a powder having irregular, angular particles predominantly of 40 to 325 mesh, and in which while normally oxidizable under water atomizing conditions, said formed metal powder containing a low oxygen content, comprising: (a) directing a stream of the molten metal into an enclosed non-vented atomizing chamber having an open lower end of smaller cross section than said atomizing chamber,   (b) in an atomizing zone of said chamber, impinging on said stream of metal, in a first stage, a first pair of opposed, flat, solid high pressure streams of water directed downwardly at an angle to the metal stream,   (c) said first pair of streams being under sufficient pressure to atomize said metal stream into said irregular particles,   (d) quenching immediately thereafter, said particles, by violent turbulent contact with at least one additional pair of opposed high pressure jets of cooling water,   (e) the action of the high pressure jets of cooling water within said enclosed chamber effecting a partial evacuation of said chamber under normal operating conditions,   (f) discharging the quenched particles, along with the atomizing and cooling water, from the bottom of said chamber into a body of water below the surface thereof, and   (g) introducing a non-oxidizing gas into the upper portion of said chamber to control and limit the rise of water into said upper portion of said chamber resulting from said partial evacuation. .Iaddend. .Iadd. 7. A method of atomizing molten metal which comprises   (a) introducing a stream of molten metal into the upper end of an effectively enclosed non-vented atomizing chamber having an open lower end forming a discharge opening of smaller cross section than said atomizing chamber,   (b) in an atomizing zone of said chamber, impinging on said metal stream with two or more pairs of opposed high pressure streams of water,   (c) discharging the water and atomized metal particles from the lower end of the atomizing chamber,   (d) maintaining a body of collecting water at a level above the discharge opening of the atomizing chamber,   (e) the action of said water jets in said chamber effecting a partial evacuation therein which raises the water level in said atomizing chamber, and   (f) controlling and minimizing said pressure reduction, and thereby controlling and limiting the raising of the water level in said atomizing chamber, by the introduction into an upper portion of said atomizing chamber of a gas having non-oxidizing characteristics with respect to the metal. .Iaddend. .Iadd. 8. The method of claim 6 wherein the water and the formed metal particles are discharged from an opening in the lower end of said chamber, said opening having a cross sectional flow area less than that in the atomizing zone of said non-vented atomizing chamber. .Iaddend..Iadd. 9. The method of claim 7 wherein at least the first pair of water jets are discharged at a pressure of at least 500 psi. .Iaddend..Iadd. 10. The method of claim 9 wherein said first pair of water jets are flat and solid. .Iaddend. .Iadd. 11. A method of atomizing molten metal to a powder having irregular, angular particles predominantly of 40 to 325 mesh, and in which while normally oxidizable under water atomizing conditions, said formed metal powder contains less than 0.25 percent oxygen by weight, comprising:   (a) directing downwardly a stream of molten metal into an enclosed atomizing chamber to preclude the entry of air thereinto;   (b) impinging upon said stream of metal in a first stage, a pair of opposed, thin, flat solid streams of water directed downwardly at an angle of 15-30 degrees from the vertical and under a pressure of at least 500 p.s.i. to atomize said metal stream into said irregular particles;   (c) quenching immediately thereafter said formed particles by violently turbulent contact with water, including at least impinging upon said formed particles in a second stage immediately below said first stage opposed high pressure jets of water, to rapidly quench by said violently turbulent contact with water said formed particles to a temperature below which oxidation of said formed particles readily occurs, to minimize the formation of surface films of steam and the exposure of said particles to said films, and   (d) collecting said quenched metal particles in a body of water for further   
     
     
        cooling. .Iaddend. .Iadd. 12.  The method of claim 11 wherein the water from said opposed streams and opposed jets is discharged with said quenched metal particles from said atomizing chamber into an open body of water. .Iaddend..Iadd. 13. The method of claim 11 wherein said water and said metal particles are horizontally discharged beneath the surface of said body of water with sufficient velocity to maintain substantial turbulence therein. .Iaddend..Iadd. 14. The method of claim 11 further characterized by: (a) separating from the water and cooled metal particles, particles of lower density than said metal particles;   (b) separating thereafter the metal particles from the water, and   (c) drying under non-oxidizing conditions said metal particles which have an oxygen content less than 0.25% by weight. .Iaddend.