Rolling ingot

An improved ingot shape which when rolled to sheet or plate does not form laminated edges which must be trimmed. The narrow faces of the generally rectangularly shaped ingot have recesses along the length of the upper and lower portions thereof. The land area between the two recesses on each narrow face extends outwardly beyond the top and bottom edges of the ingot.

BACKGROUND OF THE INVENTION 
This invention relates to an improved shape for large rolling ingot used in 
the manufacture of sheet and plate, particularly sheet and plate from 
light metals such as aluminum and aluminum alloys. 
In the conventional manufacture of sheet and plate, a large DC cast rolling 
ingot having a generally rectangularly shaped transverse cross section is 
heated to a hot rolling or other elevated temperature and passed several 
times through a breakdown mill to produce an elongated slab of about 1-2 
inches thick. The slab is then passed through a multistand mill while 
still at an elevated temperature to form a sheet or plate of desired 
thickness. 
When conventional DC cast thick ingots are rolled at elevated temperatures, 
quite frequently laminations form at the longitudinal edges of the rolled 
product and these laminations can cause edge cracks during subsequent 
rolling which must be trimmed. During the initial hot rolling reductions, 
the top and bottom sections of the ingot are worked extensively, while the 
center section remains relatively undeformed. During the initial 
deformation there is a slight lateral spreading and relatively large 
longitudinal extension of the metal in the top and bottom sections of the 
ingot. However, because essentially no direct thickness reductions occur 
to the center section of the ingot during these initial stages of rolling, 
there is no lateral spreading of the ingot in this section. Indeed, there 
is usually a slight reduction in the width of the center section of the 
ingot due to the elongation of the center section caused by the extensions 
of the top and bottom sections during the early stages of rolling. In the 
later stages of rolling, the rolling reductions penetrate into the 
undeformed center section of the ingot, and this section also begins to 
spread due to these reductions, so that for the remainder of the hot 
rolling operation the lateral spread of the top center and bottom sections 
of the ingot are essentially the same. However, because the upper and 
lower sections of the ingot experience more lateral spread than the center 
section of the ingot, the over-hanging edges of the top and bottom 
sections are rolled closer together to ultimately form the laminations 
previously discussed. The metal in the laminated edges of the rolled slab 
is heavily worked and under tension and during subsequent rolling is 
subjected to excessive stresses which cause the formation of cracks. For 
an excellent discussion of this phenomenon, see Mechanical Metallurgy, 2nd 
ed. by G. B. Dieter, (1976), pp. 623-628. See, also, article by D. S. 
Wright et al., in Metals Technology, May 1981, pp. 180-89. 
Prior procedures used to minimize edge cracking comprise rolling the edges 
to extend them and thereby relieve some of the stresses. While these 
procedures have been effective for the most part in reducing edge 
cracking, they generate considerable equipment and maintenance problems 
because one or more sets of vertically oriented rolls must be provided in 
the mill train. Moreover, edgerolling required on a conventional ingot 
also increases the amount of liquated structure appearing on the edges of 
the final rolled surface which must be trimmed. On the latter point it 
should be noted that usually only the broad faces of the rolling ingot are 
scalped prior to rolling which removes the liquated structure which forms 
during casting. The liquated surface on the narrow faces is not removed so 
if it is rolled onto the surface at the edges it usually must be trimmed. 
DESCRIPTION OF THE INVENTION 
This invention is directed to an improved shape for elongated rolling ingot 
which minimizes edge laminations and the edge cracking which frequently 
results without the need for rolling the edges with vertical rolls. 
Moreover, by avoiding edge rolling, the amount of liquated structure 
appearing on the final rolled surface can be significantly reduced. 
The generally rectangularly shaped ingot in accordance with the invention 
has opposed narrow and broad faces with the rolling occurring on the broad 
faces. Elongated recesses are provided along the lengths of the upper and 
lower portions of the narrow faces. The intermediate sections or land 
areas of the narrow faces, between the two elongated recesses, extend out 
beyond the longitudinal corners of the ingot which lie at the intersection 
of the narrow and broad faces. These land areas may be flat or curved. The 
curvature and overall shape of the upper and lower recessed sections in 
the narrow faces are empirically designed so that during the initial 
stages of rolling, when the top and bottom sections of the ingot spread 
laterally, the edges of these sections spread out uniformly to the edges 
of the essentially undeformed center section of the ingot. Thereafter, 
during the rolling process the intermediate section of the ingot is also 
deformed by the rolling and the entire thickness of the ingot is deformed 
more or less equally. In this manner the laminations which are formed are 
insignificant and the amount of edge cracks from such laminations is 
negligible. Moreover, there is little evidence of a liquated structure on 
the edge surface of the final product. 
The recesses in the narrow faces of the ingots preferably have curved 
surfaces but angularly shaped planar surfaces will also be suitable. A lip 
should be provided along the longitudinal intersections between the narrow 
faces and broad faces of the ingot which overhang a portion of the 
adjacent recesses. 
The ingots of the invention are preferably DC cast so care must be 
exercised in the design of the ingot to ensure that the intersections of 
ingot surfaces are well rounded, because sharp intersections tend to cause 
ingot cracking during casting.

FIG. 1 illustrates in perspective a portion of an ingot 10, shaped in 
accordance with the invention. The ingot 10 has opposing narrow faces 11 
and 12 and relatively flat opposing broad faces 13 and 14. The narrow 
faces 11 and 12 are provided with elongated recesses 15 and 16 and 17 and 
18 which extend along the upper and lower sections, respectively, of the 
ingot 10. The intermediate surfaces 19 and 20 which are disposed on the 
narrow faces 11 and 12 between the recesses 15-18 extend out beyond the 
lips 21-24 at the intersection between the narrow faces 11 and 12 and the 
broad faces 13 and 14. Surfaces 19 and 20 are shown as flat but they may 
be curved. 
FIG. 2 represents in a simplified manner a partial perspective view of a 
sheet or plate product having edge cracking which results from the 
laminated edge formed from conventionally shaped ingots. 
FIGS. 3a-d illustrate the thickness reductions of a conventional ingot 30 
(on the left) and an ingot 10 of the invention (on the right) during the 
rolling process. FIG. 3a shows the partial cross sections of original 
ingots, FIG. 3b shows the partial cross sections after rolling reductions 
of about 60%, FIG. 3c shows the partial cross sections after rolling 
reductions of about 80% and FIG. 3d shows the partial cross sections after 
rolling reductions of about 95%. As evident from FIG. 3b the upper and 
lower edges (Point A) of the ingots have extended outwardly a significant 
amount due to the spreading of the upper and lower sections during the 
initial rolling. On the other hand, the width of the ingot at the center 
section has decreased by a significant amount. In FIG. 3d the width of the 
center section of the ingots has increased due to the spreading caused by 
rolling reductions. Most notable, however, is the extensive lamination 
evident with the conventional ingot and the lack of such lamination with 
the ingot of the invention. 
In rolling ingots as shown in FIGS. 3a-d width measurements were taken on 
the top surface (points A) and midpoints of both ingots (points B) and at 
the edges of the land or center section 19 (point C) at the start and at 
various stages of rolling. The ingot widths which were measured before 
rolling and after rolling reductions of 60, 80 and 95% are given in the 
table below. 
______________________________________ 
Width of Width of Ingot 
Thickness Point Conventional 
of the Invention 
Figure 
(inches) Location Ingot(inches) 
(inches) 
______________________________________ 
3a 24 A 51.50 50.25 
B 54.50 54.75 
C 54.75 
3b 1O A 55.63 53.50 
B 53.63 53.75 
C 54.25 
3c 5 A 55.88 53.75 
B 53.88 53.50 
C 54.00 
3d 1.5 A 56.25 53.75 
B 55.13 53.88 
C 54.25 
______________________________________ 
With both ingots, the initial rolling reductions cause the top and bottom 
sections of the ingots to spread laterally, whereas, the center section 
contracts laterally due to the longitudinal extension of the center 
section by the elongation of the upper and lower sections of the ingot. 
The thickness of the center section is not directly reduced by rolling 
until most of the reduction has been effected. However, after a thickness 
reduction of about 60-90% (i.e., to a thickness of 10-5 inches) the center 
section begins to be deformed directly by the rolling process causing the 
center section to spread laterally along with the upper and lower 
sections. At this point, up to two inches or more width differential 
exists in the slab between the top and bottom sections and the center 
thereof. This is to be compared with the width differential of about 0.25 
inch with the ingot of the invention. Subsequent rolling ameliorates these 
differentials in the slabs from both ingots but it does not eliminate the 
lamination which is formed with the conventional ingot during the initial 
rolling stages. 
During the rolling of the ingot of the present invention, these large width 
differentials are not formed and as a result little or no edge laminations 
occur. Note that in the above table the final maximum differential between 
the initial and final widths for the ingot design of the present invention 
was a negative 0.5 inch whereas with the conventional ingot the final 
width differential was a positive 1.12 inch. Furthermore, point A on the 
conventional ingot has spread 1.25" more than the ingot of the invention, 
and this spread gives rise to extra liquated surface during edge rolling 
which must be trimmed off. 
It is obvious that various modifications and improvements can be made to 
the invention without departing from the spirit thereof and the scope of 
the appended claims.