Metallurgical apparatus – Process
Reexamination Certificate
1999-10-05
2001-05-22
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Process
C266S205000, C266S228000
Reexamination Certificate
active
06235234
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the recycling of dross formed in galvanizing processes, and particularly to a method and apparatus for removing dross from a vessel of molten zinc in a manner such that the zinc concentration remaining in the dross is minimized.
BACKGROUND OF THE INVENTION
In the galvanizing art, practitioners have long combated the formation of dross on the tops of the vessels of molten zinc. Dross is a skim which forms on the top of a bath of molten metal and, in the case of zinc, consists of a mush-like mixture of iron, aluminum and zinc intermetallic particles, oxide skims and liquid zinc alloy. The dross consists of about
96
% zinc and
2
% each of aluminum and iron. The dross is frequently removed for processing to prevent fouling the surface of the galvanizing strip product and to recover the zinc retained in the dross.
Even most contemporary procedures for removing dross in galvanizing and other molten metal processes are relatively crude, generally labor-intensive and dangerous for the operators of the removal apparatus. The removal process generally consists of having an operator use a long-handled paddle or rake to skim the surface of the molten bath. The dross is then scooped into a nearby mold.
Some of the apparatus and processes proposed in the past have numerous moving parts which are prone to breakdowns in the hostile environment of the galvanizing plant. Examples of apparatus having numerous parts are the mechanical skimmers disclosed in U.S. Pat. No. 3,941,360 to Blank, U.S. Pat. No. 4,165,866 to Hetra, et al., and U.S. Pat. No. 4,007,119 to Antonevich. Mechanical skimmers are still not used in many facilities because of various shortcomings in their design and because the process does not lend itself well to automation.
Various prior art workers have observed that, while galvanizing dross typically contains considerable amounts of zinc, the zinc tends to drain back into the vessel if the dross is contained in a temporary enclosure. Typically the temporary enclosure has perforations or other holes in it to permit the zinc to drain back into the main body of molten metal. An illustration of such an enclosure similar to that sometimes used in the galvanizing art is the one shown by Reding in U.S. Pat. No. 3,843,355, said to be specifically for the magnesium purifying art. See also the temporary enclosure or “flotation box” of Tyler, et al. shown in U.S. Patent No. 4,386,958.
In U.S. Patent No. 4,003,559, Kuwano, et al. note that a common practice in the art has been to agitate the dross manually to hasten the coalescing of the zinc droplets or particles, to drain zinc from the dross. We have found that since the manual agitation of the dross is difficult and dangerous to perform, it is seldom performed efficiently, resulting in a high concentration of useable zinc remaining in the dross for recovery in a remote location rather than directly into the molten bath. Kuwano, et al. go on to suggest the use of a plurality of “scrape plates” for mechanical, rather than manual, agitation of the dross. The scrape plates are disposed within a container which is separate from the main metal bath. The container has perforations or holes for draining coalesced metal.
SUMMARY OF THE INVENTION
Our invention is an apparatus for assisting the operator of a dross removal process. It results in a dross having less usable zinc therein, less likelihood of injury on the job, and a saving of labor.
The invention eliminates the most dangerous and difficult part of the dross removal operation the lifting of the dross-laden basket from the bath. This is accomplished by providing an apparatus which mechanically lifts the dross-laden basket out of the bath, rotates the basket away from the molten bath, and deposits the dross into a recycle box. Recycled dross is then sold as scrap. The lifting of the dross basket out of the molten bath and the rotating of the basket away from the molten bath is accomplished, in the preferred embodiment, by the use of an air or hydraulic cylinder, while the rotating of the basket to an inverted position to dump the dross into the recycle bin is accomplished by an air or hydraulic rotary actuator.
It is desirable to remove as much of the useable zinc from the dross as possible before depositing the dross in the recycle box. This can be accomplished to a large degree by compressing or “chopping” the dross, thereby separating the useable molten zinc from the undesirable waste products in the dross. The useable zinc is then returned to the molten bath for immediate use.
Our invention provides (a) a perforated basket for accumulating dross while permitting draining of molten zinc therefrom, (b) means for lifting the basket, containing dross, from the surface of a molten metal bath, (c) means for agitating the dross in the basket to enhance the draining of zinc from the dross in the basket, and (d) means for delivering the dross, containing minimal residual zinc metal, to a container external of the molten metal vessel.
REFERENCES:
patent: 3198505 (1965-08-01), Amdur et al.
patent: 3770132 (1973-11-01), Quast et al.
patent: 3843355 (1974-10-01), Reding
patent: 3941360 (1976-03-01), Blank
patent: 4003559 (1977-01-01), Kuwano et al.
patent: 4007119 (1977-02-01), Antonevich
patent: 4057232 (1977-11-01), Rosa et al.
patent: 4165866 (1979-08-01), Hetra, Jr. et al.
patent: 4269398 (1981-05-01), Hogan et al.
patent: 4386958 (1983-06-01), Tyler et al.
patent: 4460166 (1984-07-01), Ritchie et al.
patent: 4540163 (1985-09-01), van Linden et al.
patent: 5051180 (1991-09-01), Williams
patent: 28 42 742 (1980-04-01), None
patent: 2 128 520 (1984-05-01), None
patent: 5 211 6722A (1977-09-01), None
patent: 5-302157 (1993-11-01), None
patent: 10 317120 (1998-12-01), None
Hennessy Ann J.
Lemper Herbert
Buchanan Ingersoll
International Zinc Co.
Kastler Scott
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