Process of hot continuous rolling

In a process of hot continuous rolling of an aluminium alloy blank formed by a continuous casting grooved wheel wherein the blank from the wheel is fed at the normal temperature for hot rolling between the cylinders of a train of two-cylinder stands, at least at the first stand the thickness H of the blank is reduced by a value .DELTA.H satisfying the relationship (h/a ).ltoreq. C, where h = H - (.DELTA.H/2), a = .sqroot.R.DELTA. H, R is the radius of the rolling cylinders and C is a constant depending on the alloy.

The present invention relates to improvements in the continuous hot rolling 
of an aluminium alloy blank produced by continuous casting in a grooved 
wheel. 
Particularly in the manufacture of wire, a continuous production process 
including the continuous casting of a blank in a grooved wheel is often 
used. The groove in the wheel is partially closed by a metal strip and the 
metal cast inside the closed portion of the groove solidifies 
progressively to emerge as a solid blank when the metal strip exposes the 
groove. The blank is then immediately caught in a rolling train comprising 
successive grooved two-cylinder stands acting successively in different 
directions to reduce all the transverse dimensions of the blank. 
The production of the blank by cooling of the metal in the groove 
inevitably leads to defects in the internal homogeneity of the blank, due, 
for example, to contraction cavities formed in the course of 
solidification, and expressed by porosity in the solid metal leaving the 
grooved wheel. To permit the production of fine wires of high mechanical 
quality, by first rolling the blank down to relatively small sections and 
then by wire-drawing, it is necessary to cause these internal defects to 
disappear. Such a lack of internal homogeneity would, in fact, lead to 
breakage of the wire in the final phases of wire-drawing, or would create 
regions of reduced mechanical strength in the finished wire which could 
lead to breakages in use. 
The rolling of the blank, through the welding effect which it constitutes, 
is liable to cause such porosity to disappear by rewelding the walls under 
the effect of the stresses developed in the heart of the metal by the 
combined action of the temperature and of the local pressure. 
Hitherto, however, it has not been possible, in the case of the grooved 
rolling of a long product, to define the rolling conditions to be adhered 
to in order that these stresses at the heart of the metal may be 
sufficiently high compression stresses to reclose and reweld completely 
the defects present in continuously cast blanks. It has even been observed 
that, on numerous existing rolling-mills, the reverse results are 
obtained, that is to say, after the first rolling pass, the porosity and 
internal defects in the blank are amplified. This is because the theory of 
rolling long products, such as bars, wires and sections, in grooves or 
between rollers is still in the field of research. No precise information 
has yet been published for the calculation of the internal stresses in 
this case. In contrast to what it has been possible to do in the rolling 
of sheet and of strip, it has not yet been possible, for rolling in 
grooves or between rollers, to define the geometrical conditions of a 
rolling pass which lead reliably to the closure of the internal defects in 
the blank. 
The invention provides a solution to the above problem by defining a new 
parameter from the geometrical conditions of a rolling pass on a grooved 
rolling-mill and by specifying the limits of this parameter enabling the 
porosity, cracks, contraction cavities and other internal defects to be 
reclosed and rewelded completely. 
According to the invention, there is provided a process of hot continuous 
rolling of an aluminium alloy blank from a continuous casting grooved 
wheel comprising feeding the blank at the normal temperature for hot 
rolling of the alloy between the cylinders of a plurality of pairs of 
cylinders, wherein at least at the first pair of cylinders the thickness H 
of the blank is reduced by passage between the cylinders by a value 
.DELTA.H satisfying the relation (h/a) .ltoreq. C, where h = H - 
.DELTA.H/2 and a = .sqroot.R.DELTA.H, R being the radius of the rolling 
cylinders and C being a constant depending on the nature of the alloy. 
The invention will be better understood from the following description of 
embodiments thereof, given by way of example only with reference to the 
accompanying drawing.

The alloy used in the tests described below is an 
aluminium-magnesium-copper alloy designated AU4G under the French standard 
AFNOR A 02 001, or 2017 under the ASTM standards of the United States. 
The tests were carried out on a conventional installation comprising a 
continuous casting grooved wheel immediately followed by a continuous 
rolling train for the blank, consisting of eight stands each with two 
grooved cylinders and of which the first stand is shown in FIG. 1. The 
rolling took place at the usual temperature for hot rolling of this type 
of alloy, namely 400.degree. to 480.degree. C. The cylinders 1 of the 
first stand each comprise a groove 2 with a diameter of 250 mm at the 
bottom of the groove. The blank 3 of height H leaving the casting wheel is 
converted into a blank 4 of height H.sub.1 after passage between the 
cylinders. 
Two simple parameters which were taken into consideration in the course of 
these tests were the mean value h = (H + H.sub.1 /2) of the thickness of 
the product before and after rolling, and the length a of the arc of 
contact of each cylinder with the blank. These parameters are connected in 
a simple manner both to the geometrical characteristics of the 
rolling-mill (radius R of the cylinder), and to the geometrical 
characteristics of the blank (initial thickness H and reduction in 
thickness .DELTA.H). 
In fact it is possible to write h = H - .DELTA.H/2 and a = 
.sqroot.R.DELTA.H. It has been found possible to establish a limit C of 
the ratio h/a such that by maintaining rolling conditions such that h/a 
.ltoreq. C, a total closing and rewelding of the internal defects of the 
cast blank are ensured. The following are the conditions of four tests: 
__________________________________________________________________________ 
Test 
##STR1## 
Exit thick- ness H.sub.1 
.DELTA.H 
##STR2## 
R 
##STR3## 
##STR4## 
__________________________________________________________________________ 
1 28.5mm 
25mm 
3.5mm 
26.75mm 
125mm 
20.9mm 
1.3 
2 28.5 23 5.5 27.75 125 26.2 1 
3 28.5 21 7.5 24.75 125 30.6 0.8 
4 28.5 19 9.5 23.75 125 34.5 0.7 
__________________________________________________________________________ 
The above table gives the rolling conditions and the corresponding ratio 
h/a for each series of tests. 
Checking by sweating of the internal quality of the blanks after the first 
stand revealed the presence of defects for the first three series of tests 
whereas the blanks obtained in the fourth series, with a ratio h/a 
.ltoreq. 0.7 were sound. 
The tests enabled the value C to be determined for each usual alloy of 
aluminium. It has also been found that this limit C is, in fact, 
substantially the same for each of the alloys which can be included in the 
same class of the two classes of aluminium alloy already known, that is to 
say: 
the slighly alloyed alloys or "soft" alloys, for which the limiting 
constant C can be taken as 0.9. 
the heavily charged alloys or "hard" alloys, for which the limiting 
constant C may be taken as 0.7. 
In every case it remains necessary to adhere, at the entrance to the stand, 
to a temperature situated within the usual range for hot rolling of the 
alloy in question. 
It will be recalled that the class of soft aluminium alloys or those 
slightly alloyed includes the aluminiums of commercial purity by various 
names, and the alloys comprising various additions of magnesium or 
manganese not exceeding 2.5% by weight, or additions of silicon of less 
than 7%. Included for example in this class are the following alloys 
designated first by their reference according to the French standard AFNOR 
A 02 001 and, in brackets, by their equivalent reference, where it exists, 
according to the ASTM standards of the United States: AG2 -- AM1 (3003) -- 
AS5 (4043) -- A5 (1060) -- AGS (6063). 
The class of hard or heavily charged alloys, on the other hand, includes 
the aluminium alloys comprising additions of one or more of the following 
elements: magnesium, copper, zinc, at least one of the additions being in 
the range of 2.5 to 5% for magnesium, 2 to 5% for copper, 5 to 8% for 
zinc; such alloys may also comprise other elements such as manganese, 
silicon, lead, bismuth, in small quantities. Included for example in this 
class are the following alloys designated as above: AG2.5 (5052) -- AG4 
(5086) -- AG5 (5056) -- AU4G (2017) -- AU5PbBi (2011) -- AZ5GU (7075). 
The above described rolling conditions not only apply to the rolling in the 
first stand of the continuous train following the casting wheel but may 
also apply to the second stand and to the following stands. Adhering to 
the condition h/a .ltoreq. C in the second stand further improves the 
elimination of the casting defects and renders it possible to obtain a 
perfectly compact metal after this second stand, on condition, of course, 
that the temperature is still within the appropriate range. 
For the following stands, maintenance of the same limit of the ratio h/a is 
recommended without it being so imperative. Actually, it is possible to 
accept ratios of h/a slightly greater than C if the defects have been 
eliminated by the first two passes. If this had not been the case it would 
be more difficult to achieve this because there would be a risk of the 
temperature being too low. 
Finally while the invention has been described in relation to rolling in 
two-high stands with grooved cylinders, it applies equally well to smooth 
cylinders, the radius R being taken externally for the smooth cylinders 
and at the bottom of the groove for grooved cylinders.