Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1988-02-11
1989-04-04
Stallard, Wayland
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 05B, 264 13, 425 6, B22F 908
Patent
active
048182796
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION(S)
This United States application stems from PCT International Application No. PCT/FR87/00182 filed May 27, 1987.
The present invention relates to the field of granulation or in other words formation of spheroidal particles or solid granules from molten material and especially from a bath of molten metal, the granules being formed after solidification of said material.
The invention is more specifically concerned with a method for granulating metals or metal alloys from a mass of these materials in the molten state. In the present description, the notion of metal will also designate alloys of two or more metals as well as any mineral or organic compound containing a metal. However, it will be noted that the invention is also applicable to certain nonmetallic materials, the granulation of which gives rise to substantially the same problems as metals.
More specifically, the invention is directed to a method of granulation in which molten material is discharged in spray form and then solidified in the form of granules.
Various solutions have already been proposed for carrying out granulation of metals. Reference may be made to those described in German Pat. No. 1,268,792 and French Pat. No. 2,391,799 in which the molten metal is discharged in spray form by subjecting it to a movement of rotation which generates a centrifugal force. In these methods, rotation of the liquid metal is obtained under the influence of a rotating magnetic field produced by a stator surrounding a tube in which the liquid metal circulates. The stator has a bottom wall pierced by a calibrated orifice through which the metal is discharged in a conical spray sheet. Granules are accordingly formed by cooling in a suitable atmosphere.
It is clear that these devices and methods call for the use of costly equipment and that the process development involved is not always easy. These difficulties are more particularly related to the presence of rotating magnetic field generators which constitute potential sources of failure and represent additional costs if only in regard to power consumption costs. It is also necessary to determine the velocities of the rotating fields in order to obtain the best results but this preliminary adjustment is sometimes a difficult procedure.
Granulation of metals presents in addition a specific problem related to the presence of impurities, which often arises from a marked tendency towards oxidation. All the techniques applied to date, with or without rotating fields, have failed to solve this problem. Even if extreme purification of the metal is achieved immediately upstream of the spray atomization device, which complicates installations still further, randomly distributed particles of impurities are again found to be present in the droplets. These particles result in the formation of granules of variable size and composition, the shapes and surfaces of which are too irregular.
In order to achieve better granulation, the present invention proposes to carry out spray atomization by means of devices for subjecting the molten material to mechanical confinement in the form of helical streams as it flows towards the spray discharge orifice. Although devices of this type are already known per se for the purpose of spray delivery of water under pressure (usually 6 bar), it should be emphasized that they have never yet been considered as a solution to the problem stated earlier in relevant applications involving solidification of droplets from material which is liable to contain impurities.
Accordingly, the object of the invention is to provide a granulating device comprising means for feeding material into a container terminating in an orifice for spray discharge of material in the form of droplets at the inlet of a cooling enclosure in which the droplets solidify in the form of granules, characterized in that this container is provided on at least part of its internal wall with raised helical elements which cause the molten material to flow in the form of helical streams.
In a
REFERENCES:
patent: 1395442 (1921-11-01), McGregor
Chaleat Bernard
Vaxelaire Philippe
Extramet Industrie S.A.
Stallard Wayland
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