Metallurgical apparatus – Means for melting or vaporizing metal or treating liquefied... – With means to cool treating means
Reexamination Certificate
1997-12-01
2001-04-10
King, Roy (Department: 1742)
Metallurgical apparatus
Means for melting or vaporizing metal or treating liquefied...
With means to cool treating means
C266S242000, C373S155000, C373S156000
Reexamination Certificate
active
06214286
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to induction skull melting of metal and alloys.
BACKGROUND OF THE INVENTION
Induction melting processes and apparatus using a water cooled segmented, copper crucible were developed by the US Bureau of Mines, for example, as described in U.S. Pat. Nos. 3,775,091 and 4,058,668. These patents illustrate use of a CaF
2
skull in the crucible and refractory packing material/spacers between the segments. The CaF
2
skull prevents contact between the molten metal and the crucible segments. Typically, the CaF
2
is melted and solidified on the cooled crucible segments to form an insulating lining or skull between the melt and the crucible segments.
U.S. Pat. No. 4,738,713 illustrates an induction melting process wherein a reactive metal is melted in a water cooled segmented, copper crucible in the absence of a CaF
2
lining or skull. In this patent, a refractory packing material is required between the tubular segments of the crucible to avoid molten metal penetration therebetween and subsequent skull locking.
The Diehm et al. U.S. Pat. No. 4,923,508 discloses a ceramicless induction skull crucible having a plurality of upstanding, water cooled metallic fingers that collectively form an upper metallic sleeve of the melting crucible and a water cooled metallic bottom. The crucible fingers are spaced by gaps small enough to avoid penetration of molten metal between the fingers that could produce skull locking.
There is a need in the art for an induction skull melting apparatus and method that avoids water cooled crucible sleeve segments or fingers as well as use of CaF
2
and other refractory skulls and refractory packing materials between segments that can contaminate the melt and also provide improved service in use in melting metal or alloy charges in a production environment.
An object of the invention is to provide induction skull melting apparatus and method that satisfy this need.
SUMMARY OF THE INVENTION
The present invention provides induction skull melting apparatus and method wherein a charge of metal or alloy is induction melted in a crucible comprising a reusable monolithic refractory tubular sleeve disposed on a reusable water cooled metallic base by an induction coil means disposed about the sleeve.
In one embodiment of the invention, a charge of metal or alloy, such as a reactive superalloy or titanium alloy, is induction melted in a crucible comprising a monolithic refractory cylindrical sleeve disposed on a water cooled metallic disc-shaped base by an induction coil means disposed about the ceramic sleeve. The monolithic sleeve can comprise alumina, zirconia, and other suitable ceramic material compatible with the metal or alloy to be melted. Alternately, the cylindrical sleeve can comprise graphite. The water cooled base can comprise single or multiple copper members that define water cooling channels therebetween.
The induction coil is energized to inductively heat the solid charge to a molten state including forming a solidified skull of the metal or alloy on inner surfaces of the sleeve and the base to confine the molten charge. Thereafter, the molten charge can be removed, for example, by pouring from the melting chamber, leaving the solidified skull in place on the inner surfaces of the sleeve and base.
The invention is advantageous in that water cooled crucible sleeve segments or fingers are eliminated. In addition, the need for CaF
2
and other refractory skulls is eliminated. Morever, the need for refractory packing materials between segments that can contaminate the melt is eliminated. The induction melting apparatus of the invention provides improved service in use in melting metal or alloy charges in a production environment in that damage to or spreading of previously used metal crucible segments or fingers is eliminated as a source of crucible downtime. Moreover, practice of the invention can provide a 25% to 50% reduction in electrical power requirements for melting as compared to power requirements using a segmented melting crucible, and greater levitation of the melt in the crucible and thus less reaction with the crucible before a skull forms thereon.
The above objects and advantages of the invention will become more readily apparent to those skilled in the art from the following detailed description taken with the following drawings.
REFERENCES:
patent: 2958913 (1960-11-01), Schaefer
patent: 3013315 (1961-12-01), Smith
patent: 3593775 (1971-07-01), Privett
patent: 3775091 (1973-11-01), Clites et al.
patent: 4058668 (1977-11-01), Clites
patent: 4675879 (1987-06-01), Meredith
patent: 4738713 (1988-04-01), Stickle et al.
patent: 4856576 (1989-08-01), Peterson
patent: 5149488 (1992-09-01), Dickson
patent: 5257281 (1993-10-01), Cignetti et al.
patent: 5425048 (1995-06-01), Heine et al.
patent: 5741349 (1998-04-01), Hubble et al.
Merriam-Webster's Collegiate Dictionary, 10th edition. 1997 p. 1008.
Bierstine Donald L.
Biondi Richard A.
Larsen Robert L.
Larsen, Jr. Donald E.
Stabile Christine M.
Howmet Research Corporation
King Roy
McGuthry-Banks Tina
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