Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1989-01-19
1990-02-13
Rutledge, L. Dewayne
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
B22F 100
Patent
active
049003550
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method of making metal powder, and more particularly to a method of making high-purity fine metal powder through a dry process by forming fine molten droplets of the metal with centrifugal force and quenching the fine molten droplets by their collision with a rotary cooling board.
BACKGROUND ART
Heretofore, several methods have been known for making metal powder directly from a melt of the metal by using rotation; such as a method in which a melt of metal in a fixed crucible is dropped through a nozzle bored at its lower portion toward the central portion of a rotary disk so that the molten metal is centrifugally dispersed and formed into powder particles, a method that uses a specimen rod of metal as an electrode so as to melt a part of it with a plasma arc or the like while rotating it so as to disperse the molten metal for producing the metal powder particles, and a method of forming metal powder particles by jetting melt of the metal into a rotating liquid coolant for causing collision of the jetted melt with the coolant.
In the first two methods using the rotary disk and the rotating electrodes, respectively, an annular belt of the melt is centrifugally formed on the rotary disk or the outer surface of the revolving metal rod, and metallic droplets are dispersed from the annular belt of the melt. Thus, a very high revolving speed is required in order to produce minute droplets. Accordingly, the conventional methods have shortcomings in that minute powder particles are difficult to produce because the revolving speed of the rotary disk and the revolving rod is limited from the standpoint of the safety of rotating device, and that, when the coolant is an inert gas, its cooling speed is not so high and a long flying distance is required for the droplets to solidify, and the apparatus for making the metal powder tends to become large and deposition of the powder metal on the apparatus wall tends to increase. A method, in which melt of metal in a fixed crucible is jetted in an atomized fashion by gas pressure into a rotary drum containing water, has excellent property in producing fine powder particles but has a shortcoming in that the surface of powder particles tends to be contaminated by the liquid coolant and a large amount of powder particle deposit on the outer wall.
There is a method in which a melting vessel and a liquid coolant tank are rotated simultaneously while allowing variation of the revolving speed ratio thereof and changing of the revolving directions, and the melt in the melting vessel is jetted centrifugally into the liquid coolant in the cooling tank so as to produce metal powder particles. Such a method also has excellent property in producing fine powder particles but has shortcomings in that contamination of the powder particles cannot be avoided and that it is not suitable for metals with a high melting point.
DISCLOSURE OF THE INVENTION
An object of the invention is to solve the above-mentioned shortcomings of the conventional methods by providing a method for producing high-purity fine spherical metal powder by causing collision of centrifugally atomized droplets of molten metal with rotary cooling board for quenching into solid powder particles.
A method according to the present invention comprises steps of melting metal by high-frequency induction, lowering the melting vessel to a jetting position where a rotary cooling board is disposed along outer periphery of the melting vessel, centrifugally jetting the molten metal from the melting vessel by rotating the melting vessel in a direction while rotating the rotary cooling board in an opposite direction, and simultaneously quenching and splitting the centrifugally jetted molten metal droplets by causing the molten metal droplets to collide with the rotary cooling board, said steps from the melting of metal to the simultaneous quenching and splitting being effected in vacuo or in an inert gas atmosphere.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate an
Tanno Koichi
Yagi Masaaki
Miyagi National College of Technology
Rutledge L. Dewayne
Schumaker David W.
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