Specialized metallurgical processes – compositions for use therei – Compositions – Solid treating composition for liquid metal or charge
Patent
1997-07-23
1999-09-14
Wyszomierski, George
Specialized metallurgical processes, compositions for use therei
Compositions
Solid treating composition for liquid metal or charge
148513, 266202, 428403, 428469, 75332, C22B 910
Patent
active
059517387
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the production of solid metallic granules from molten metal and, in particular, to the production of granules of a reactive metal such as magnesium or a magnesium alloy.
BACKGROUND ART
There is a need in industry for reactive metal granules and, in particular, for granules of Mg or Mg alloy for the treatment of steel, aluminum or other metals and for other purposes such as thixotropic injection moulding. These applications require granules of at least 1 mm in size and the granules should be substantially free of surface oxides. For some uses, granules coated with a layer protecting them from oxidation may be advantageously used and various salts, for example, have provided this advantage.
There are few commercial processes which directly produce reactive metal granules. For many applications, such granules are produced by cutting or shearing material from larger pieces of metal.
U.S. Pat. No. 4,457,775 issued on Jul. 3, 1984 Legge et al. discloses a method for producing Mg granules by mixing Mg into a salt bath of specific composition with agitation, then partially separating the product from the bath to obtain a salt/granule mixture. Because of the production method, the composition is somewhat variable.
Metal granules or shot from less reactive metals (iron, steel, copper, etc.) have been produced by injection from a nozzle into liquid baths or into counter-current gas streams. The former process is a difficult operation for a reactive metal and the latter process requires a spray tower of substantial height, and is limited in practice to granules of small diameter because of cooling considerations.
Furthermore, in order to be adapted to reactive metals, substantial quantities of inert gas would be required.
PCT publication WO-A-86 06013 (and equivalent U.S. Pat. No. 4,915,729) disclose a process in which a molten metal is contacted with a bed of moving beads. The molten metal breaks up into fine particles which are rapidly cooled in contact with the beads. However, the mechanical agitation produces particles of metal in the form of angular flakes rather than spherical granules. The method is not well suited to the formation of particles of reactive metals, since the large surface area tends to encourage oxide formation and reaction.
There is accordingly a need for an improved method of producing granules of reactive metals.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a method for producing acceptably uniform metal granules, preferably of a reactive metal, with substantially no surface contamination.
Another object of the invention is to provide a method for producing acceptably uniform metal granules, preferably of a reactive metal, of a size range suitable for alloying with metals, for example steel or aluminum.
Another object of the invention is to provide a method for producing metal granules, preferably of a reactive metal, which avoids the use of molten salt baths, liquid coolants and excessive quantities of gas.
Yet another object of the invention is to provide a method for producing reactive metal granules, preferably magnesium or magnesium alloy granules, that can be coated or doped in a controlled manner to reduce oxidation of the granules or to provide other chemical additives (such as fluoride or chloride salts) to the granule product.
Still another object of the invention is to provide a novel magnesium granule product for use in metal alloying applications.
According to one aspect of this invention, there is provided a process of producing granules of a metal, comprising providing a source of molten metal having a solidus temperature; forming discrete droplets of said molten metal from said source; fluidizing a bed of particles by means of a gas, and maintaining said bed at a temperature substantially below the solidus temperature of the metal, said particles being of a size substantially smaller than granules produced by freezing said droplets; immersing said droplets while still substantially molten in said
REFERENCES:
patent: 1637377 (1927-08-01), Heicke
patent: 4385929 (1983-05-01), Ichidate et al.
patent: 4457775 (1984-07-01), Legge et al.
patent: 5149514 (1992-09-01), Sanjurjo
patent: 5549732 (1996-08-01), Dube et al.
Dube Ghyslain
Dupuis Claude
Langlais Joseph
Lavoie Serge
Rompre Stephane
Alcan International Limited
Wyszomierski George
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