Metal deforming – By use of roller or roller-like tool-element – With cutting of work or product
Reexamination Certificate
2000-06-07
2002-09-24
Tolan, Ed (Department: 3725)
Metal deforming
By use of roller or roller-like tool-element
With cutting of work or product
C072S199000, C072S229000, C072S365200
Reexamination Certificate
active
06453712
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the rolling of metal ingots and, more particularly, to methods and apparatus for increasing ingot rolling yields and rolling mill efficiency by minimizing end crop losses in the rolling of flat slabs, for example. This favorable increase in material yield and rolling efficiency is achieved by a novel slab ingot end geometry and formed in one or both ends of the ingot, preferably during ingot casting. The invention is most advantageously applied to the manufacture of aluminum mill products.
2. Description of the Prior Art
A widely used method of manufacturing aluminum plate, sheet and foil products initially involves the vertical semicontinuous casting of slab-shaped ingots which includes a bottommost leading end, referred to in the art as the “butt” of the ingot. The butt is formed as the liquid metal solidifies on the movable bottom block or starter block which is in the open bottom of the mold. After solidification, the butt assumes the shaped geometry of the bottom block. The bottom block continuously moves downwardly and away from the mold as the solidified metal ingot exits at the open end of the mold at the location previously occupied by the bottom block. The cross-section of the vertically cast ingot of metal assumes the horizontal cross-sectional geometry of the mold. The sidewalls of the mold and the sidewalls of the solidified ingot exiting the mold are sprayed with water to increase the solidification rate. This casting technique is referred to as direct chill or “DC” casting, all of which are well-known in the art. After the cast ingot has reached a desired length, the molten metal flow to the mold is terminated and the solidified ingot is removed from the casting pit for further processing. It is common practice in commercial DC casting to pour a plurality of ingots in a casting run from a plurality of side-by-side molds. Of course, it will be readily understood by those skilled in the art that the present invention is suitable for use in conjunction with other semicontinuous casting systems such as, for example, electromagnetic casting (EMC casting).
The DC or EMC cast ingots may then be scalped to remove as-cast surface imperfections and homogenized by heating in a furnace to provide a uniform chemistry across the ingot cross-section prior to rolling. In order to process the thus treated ingots to useful end products, such as sheet, plate, foil or the like, the ingots are heated to a desired rolling temperature and subjected to a plurality of hot rolling roughing passes in a slabbing mill. Such rolling mills conventionally use one or more reversing roughing mill stands.
The free surfaces existing on an ingot or slab of finite width, thickness and length allow nonuniform rolling deformation to occur in the length and width dimensions during hot rolling. This nonuniform deformation causes an elongation of the slab in the center region thereof which forms a convex, longitudinally extending “tongue” condition at the ends thereof, particularly in aluminum slabs which are roughed down in reversing mills, usually without the use of side or edge rolls. Formation of a tongue condition is, however, not uncommon in the rolling of aluminum even in mills equipped with edge rolls. The aforesaid nonuniform deformation phenomenon is more severe in the length direction of the slab leading to another condition referred to in the art as “fold over”, “overlap” or “alligatoring”. These objectionable conditions at the ends of the slab grow worse as rolling continues and must eventually be removed by a crop shear to permit further rolling to continue. Some mills have a limitation on the crop length, due to crop shear equipment limitations, and must take two or more crops to crop off the necessary length dictated by the overlap and tongue deformations. In some cases, it has been observed that severe slab end elongation may occur during the early rolling passes which would ideally call for removal by intermediate end cropping but may not be possible if the slab thickness is too great for the crop shear. In such cases, the end deformation then worsens, causing additional end crop losses as rolling continues. It is known that less cropping length provides obvious metal recovery benefits and/or operational benefits if cropping can be postponed to later rolling operations. In addition, it is known that the overlap or alligatoring phenomenon may sometimes, in severe cases, cause the upper and lower surfaces of the slab to flair upwardly and downwardly beyond the ends of the slab at the horizontal centerline. This overlap must be sheared to allow rolling to lower thicknesses for safe entry into continuous mill equipment. In addition, the flared ends of the “alligator” move or otherwise damage table roll surfaces and work rolls which disrupts production. It is also well-known that the overlap causes an internal lamination crevice in the metal which grows during rolling and will result in unsound plate and sheet products unless it is removed by crop shearing.
Previous experimental work has been undertaken by Applicants' colleagues in an effort to reduce slab rolling cropping losses by tapering the ends of slab ingots by machining away the upper and lower transverse edges of the ingot so as to form a somewhat truncated, arrow-shaped end profile when the ingot is viewed in a longitudinal side view. In-house tests were run on ingots having 30°, 38° and 45° tapered ends. The optimum shape was noted to be between a 30° and 34° taper to reduce the “foldover”, “overlap”, “alligatoring” problem. This 30°-34° deep taper achieved by machining represents an added cost to the manufacturing process and also causes some material loss. In addition, while the “alligatoring” problem was reduced somewhat by the machined tapered ends, the “tongue” elongation problem, i.e., a convexly shaped protruding end (in plan view) was still present.
A process for preventing the growth of “fish mouth” overlap is proposed in U.S. Pat. No. 4,344,309 to Matsuzaki dealing with the rolling of steel slabs. Recesses are formed at the ends of the steel slab by partially rolling the ends of the slab in several short reverse rolling bites which are said to minimize the formation of overlaps in steel slabs. Recesses are also formed in the widthwise direction at opposite side edges of the ends of the slab by vertically extending side rolls in the same manner in an attempt to prevent the formation of fishtails. Rolling then progresses to reduce the steel slab, with additional side edge rolling, with the formation of intermediate recesses required. This elaborate rolling schedule which is said to minimize the formation of overlaps and fishtails in steel slabbing requires additional rolling time and, thus, adds cost to the end product. In addition, many slab roughing mills, particularly in the aluminum industry, are not equipped with the vertical side rolls required in U.S. Pat. No. 4,344,309. The literature also suggests the shaping of steel ingot ends by forming a truncated pyramid shape at the bottom end of an ingot to minimize cropping losses while employing edge rolling of steel slabs. Once again, these proposals are not applicable to aluminum roughing mills which do not employ side or edge rolling using vertically oriented rolls.
The present invention overcomes the shortcomings of the prior art by providing a method, apparatus and shaped slab ingot for reducing hot mill end crop on at least the butt end of a slab which greatly improves mill productivity and metal yield, particularly in the hot rolling of aluminum mill products.
The present invention contemplates a method, a product and apparatus which provide an ingot having a special configuration formed on at least the butt end of an ingot, preferably formed during casting thereof. The specially configured slab ingot provided by the present invention minimizes the occurrence of overlapping/alligatoring as well as tonguing during slab rolling, thus reducing the cropping losses to
Crowley Mark D.
Klosterman Lawrence E.
Maslanka Andrzej
Richter Ray T.
Alcoa Inc.
Baldauf Kent E.
Buckwalter Charles Q.
Smith Matthew W.
Tolan Ed
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