Metal founding – Process – Shaping liquid metal against a forming surface
Reexamination Certificate
2000-06-29
2002-07-16
Dunn, Tom (Department: 1725)
Metal founding
Process
Shaping liquid metal against a forming surface
C164S436000, C164S435000
Reexamination Certificate
active
06419005
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to materials processing and more particularly to an apparatus and method for producing high quality, thin cast slabs.
Typically, metals such as steel are formed into slabs or strands suitable for transportation and subsequent use in industrial applications. It has been found, in this connection, that the manner in which the metals are formed determines substantially the quality of the product.
During continuous casting, molten steel, for instance, is initially poured into a mold cassette. The cassette is formed by a pair of vertically disposed, opposed broad walls and a pair of vertical opposed narrow walls, the narrow walls usually being adjustable for changing the width of the slab or strand during casting. Each wall is lined by a face plate covering substantially the inner face of the wall, e.g., a thin copper plate or face plate 25 mm thick or less, mounted such as by bolting to a steel back-up plate, e.g., 75 mm thick, and inserted into a frame of the mold.
After the molten steel contacts the face plates, a solidified skin forms, defining a semi-solidified steel slab. As the slab moves down through the cassette, the solidified skin gradually increases in thickness. Upon exiting the cassette, the slab encounters a series of opposing, wide and narrow face rollers. These rollers carry the slab vertically down through the casting system, gradually placing it in a horizontal orientation for exiting the system.
Casting systems of this general configuration are shown, for example, in U.S. Pat. No. 5,297,612, issued Mar. 29, 1993, and in U.S. Pat. No. 5,490,555, issued on Feb. 13, 1996, the disclosures of which are hereby incorporated by reference in their entireties.
Conventional casting systems typically cast slabs to a thickness generally within the range of 6 to 10 inches (or about 15 cm to about 25 cm). To produce these slabs, the appropriate cassette wall configuration has essentially been a rectangle. Hence, the broad walls of such systems have been equally spaced from one another at any level within the cassette. Characteristically, these systems have also be used to cast relatively thin slabs, reducing slab thickness to about 2 inches, i.e., about 5 cm, or less to bypass roughing stands in a hot-strip mill. Thinner slabs are considered advantageous because less reheating is required, and in some cases no reheating, prior to charging to a hot strip mill. This eliminates the need for reheat furnaces, roughing strands, and intermediate conditioning operations. Not only are capital and production costs lowered, but also production yield is increased.
Another feature of traditional systems is their use of thin casting molds with a funnel-like upper portion for receiving liquid metal. Although useful, their walls are not fully adjustable during casting operations, limiting the range of slab widths that may be cast. Other molds for thin casting utilize straight-sided narrow walls that are adjustable to different slab widths and broad walls that are funnel-shaped in their upper central portion. Although helpful, this configuration limits the spacing to which the narrow walls may be adjusted to the length of a straight side portion at the broad wall outer ends, rather than that of the funnel-shaped central portion. As a result, an assortment of different sized molds (e.g., a large size and a small size) must be maintained in order to produce castings over the broad spectrum of widths required by customers.
In addition, the funnel-shaped design fundamentally causes multidimensional deformation of the slab during solidification. Multidimensional deformation, in turn, leads to surface defects (known as “folds” or “laps”) in the final coil product. A defect free or “Exposed Automotive” surface is the industry standard for automotive applications, e.g., side panels, doors and hoods. Unfortunately, “folds” may not be rolled out by further processing, such as by running the slab through a hot strip mill. Hence, where folds are present, it is considered generally impossible to produce a defect free surface.
In addition, operation of funnel molds often requires expendable copper plates. Their complex design requires copper plates generally greater than five (5) inches thick, and several man days of machining to form a funnel area on one side of the plate (a.k.a. the “hot face”). An extensive array of water channels machined into the opposite side of the copper plate (a.k.a. the “cold face”) for extracting heat from the copper plate during casting, also require detailed machining to form and maintain. Accordingly, while conventional funnel designs are efficient, their maintenance costs are often extraordinarily high.
Accordingly, a mold cassette is desired that not only improves the quality of relatively thin strands being cast, but is also convenient and economical to operate and maintain.
SUMMARY OF THE INVENTION
According to one aspect of the present invention is a continuous casting mold cassette, which comprises:
a trough including a pair of vertically disposed, opposed broad walls and a pair of opposed narrow walls, the trough having an entry end for receiving molten material and an exit end for dispensing the material, the narrow walls being generally wider at the entry end than the exit end and being adapted for sealing engagement with the broad walls so as to prevent leakage of the material therebetween;
at least one of the narrow walls being oriented at a selected tilt and adjustable at the tilt for changing the width of the slab during casting, back edges of at least one of the adjustable narrow walls being relieved in a region corresponding generally to the transition zone of the trough to allow positioning of the narrow wall in a generally less than vertical plane during casting while maintaining the narrow and broad walls in sealing engagement with one another;
at least one of the narrow walls further comprising a face plate with horizontally disposed, concave portions continuously from about the wider end to the narrower end of the plate, to accommodate deformation of solidified portions of the material without undue stress and cracking; and
a multi-directional drive assembly for adjusting the spacing between the narrow walls and for maintaining the tilt of at least one of the narrow walls while retaining the broad and narrow walls in sealing engagement with one another.
In accordance with another aspect of the present invention is a cassette for a continuous casting mold, the cassette comprising:
a trough including a pair of vertically disposed, opposed broad walls and a pair of opposed narrow walls, the trough having an entry end for receiving molten material and an exit end for dispensing the material, the narrow walls being generally wider at the entry end than the exit end and being adapted for sealing engagement with the broad walls so as to prevent leakage of the material therebetween;
at least one of the narrow walls being oriented at a selected tilt and adjustable at the tilt for changing the width of the slab during casting, back edges of at least one of the adjustable narrow walls being relieved in a region corresponding generally to the transition zone of the trough to allow positioning of the narrow wall in a generally less than vertical plane during casting while maintaining the narrow and broad walls in sealing engagement with one another;
at least one of the narrow walls comprising a face plate and a back-up plate, the face plate having cooling slots therein, the slots being deeper in the lower section of the narrow face plate than in the upper section;
at least one of the narrow walls further comprising a face plate with horizontally disposed, concave portions continuously from about the wider end to the narrow end of the plate, to accommodate deformation of solidified portions of the material without undue stress and cracking; and
a multi-directional drive assembly for adjusting the spacing between the narrow walls and for maintaining the tilt of at least one of the narrow walls while reta
Dunn Tom
Pollack Grant E.
Steinberg & Raskin, P.C.
Tran Len
Vöest-Alpine Services and Technologies Corporation
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