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A METHOD FOR MAKING BEVERAGE CAN SHEET
Background of the Invention
The present invention relates to a process for making
aluminum alloy beverage containers, and more particularly, to a
process for making such can ends and tabs for such containers
allowing them to be produced more economically and efficiently.
PKior Art
It is now conventional to manufacture beverage
containers from aluminum alloys. An aluminum alloy sheet stock
is first blanked into a circular configuration and then cupped.
The side wall are ironed by passing the cup through a series of
dies having diminishing bores. The dies thus produce an iron-
ing effect which lengthens the sidewall to produce a can body
thinner in dimension than its bottom.
Thus, formability is a key characteristic of aluminum
alloy to be used in manufacturing cans. Such cans are most
frequently produced from aluminum alloys of the 3000 series.
Such aluminum alloys contain alloy elements of both magnesium
and manganese. In general, the amount of manganese and magne-
sium used in can body stock is generally present at levels less
than about 1% by weight.
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In the manufacture of such beverage containers, it
has been the practice in the industry to separately form both a
top lid of such cans and tabs for easy opening of such lids
separately and using different alloys. Such lids and tabs are
then shipped to the filler of the beverage can and applied once
the containers has been filled by a filler. The requirements
for can ends and tabs are generally quite different than those
for can bodies. In general, greater strength is required for
can ends and tabs, and that requirement for greater strength
has dictated that such can ends and tabs be fabricated from an
aluminum alloy. One such alloy commonly used is alloy AA5182,
an aluminum alloy containing relatively high amounts of magne-
sium to provide the added strength necessary for can ends and
tabs. AA5182 typically contains magnesium in an amount ranging
from 4.4% by weight, thus adding to the cost of the alloy for
can ends and tabs.
It has been proposed to employ, as the aluminum alloy
used in the fabrication of can ends and tabs, alloy from the
3000 series, such as AA3104. Because such alloys generally
have diminished strength as compared to AA5187, it has been
necessary to employ can ends fabricated from AA3104 which have
a greater thickness and thus are more expensive.
It is accordingly an object of the present invention
to provide can end and tab stocks and can ends and tabs made
therefrom which overcome the foregoing disadvantages.
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It is more specifically an object of the present
invention to provide can ends and tabs and a method for fabri-
cating same in which use is made of aluminum alloys containing
less alloying elements without sacrificing strength.
It is a more specific object of the present invention
to provide can ends and tabs therefor and a method for fabri-
cating them which can be employed with aluminum alloys contain-
ing less than 2% magnesium without sacrificing the necessary
strength of the can ends and tabs.
These and other objects and advantages of the inven-
tion appear more fully hereiinafter from a detailed description
of the invention.
Summary of the Invention
The concepts of the present invention reside in the
discovery that aluminum alloys containing lesser amounts of
alloying elements can, nonetheless, be used in fabricating can
ends and tabs without sacrificing strength by utilizing a
fabrication process in which the aluminum alloy, preferably
containing less than 2% by weight of magnesium as an alloying
element, is formed into sheet stock for making can ends and
tabs. In accordance with the practice of the invention, the
aluminum alloy is strip cast between a pair of continuous
moving metal belts to form a hot strip cast feedstock, and then
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the feedstock is rapidly quenched to prevent substantial pre-
cipitation of aluminum alloying elements as intermetallic
compounds.
It has been unexpectedly found that such a fabrica-
tion process provides an aluminum alloy feedstock having equal
or better metallurgical characteristics as compared to aluminum
alloys conventionally used in forming can ends and tabs.
It has been found in accordance with the preferred
embodiment of the present invention that the fabrication pro-
cess can be applied to alloys of the 3000 series such as AA3104
without the need to increase the thickness of the can ends and
tabs to achieve comparable strips. Without limiting the pres-
ent invention as to theory, it is believed that the techniques
of strip casting followed by rapid quenching provide an alloy
sheet stock having improved strength by reason of its eutectic
constituents which provide increased strengths. In addition,
it is believed, once again, without limiting the present inven-
tion as to theory, that formability of the sheet stock of this
invention used in forming can ends and tabs is improved over
aluminum alloys containing greater qualities of alloying ele-
ments because it is unnecessary, in the practice of the inven-
tion, to use an annealing step typically used by the prior art.
Thus, the present invention allows can ends and tabs to be produced from less
expensive aluminum alloys without sacrific-
___
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ing the metallurgical properties of those more expensive alloys.
In one preferred embodiment of the invention, the
sequence of steps of strip casting, quenching and rolling is
preferably greater within a continuous, in-line sequence. That
has a further advantage of eliminating process and material
handling steps typically employed in the prior art. The strip
casting can be used to produce a cast strip having a thickness
less than 1.0 inches, and preferably within the range of 0.01
to 0.2 inches. In addition, in accordance with the most pre-
ferred embodiment of the invention, the widths of the strip is
narrow contrary to conventional wisdom. That facilitates ease
of in-line threading and processing and allows production lines
for the manufacture of can ends and tabs to be physically
located with or as part of a can making facility. A filler
location that has the further advantage of eliminating addi-
tional handling and shipping costs, thus promoting the overall
economics of a can making operation.
In accordance with another embodiment of the inven-
tion, the aluminum alloy is strip cast between a pair of con-
tinuous moving metal belts to form a hot strip cast feedstock,
and then the feedstock is rapidly quenched to prevent substan-
tial precipitation of aluminum alloying elements as
intermetallic compounds. Thereafter, with or without addi-
tional rolling, the quenched feedstock is annealed and rapidly
quenched, also to prevent substantial precipitation of alloying
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elements. It has been found that the intermediate annealing
and quenching steps substantially improve the formability of
the feedstock while maintaining exceptionally high metallurgi-
cal =
properties including ultimate tensile strength and yield
strength.
It has been unexpectedly found that such a fabrica-
tion process provides an aluminum alloy feedstock having equal
or better metallurgical and formability characteristics as
compared to aluminum alloys conventionally used in forming can
ends and tabs.
It has been found in accordance with a preferred
embodiment of the present invention that the fabrication pro-
cess can be applied to alloys of the 3000 series such as AA3104
without the need to increase the thickness of the can ends and
tabs to achieve comparable strips. Without limiting the pres-
ent invention as to theory, it is believed that the techniques
of strip casting followed by rapid quenching provide an alloy
sheet stock having improved strength by reason of its solid
solution and age hardening. In addition, it is believed, once
again, without limiting the present invention as to theory,
that form-ability of the sheet stock of this invention used in
forming can ends and tabs is equal to or better than these DC-
cast aluminum alloys containing greater quantities of alloying =
elements. Thus, the present invention allows can ends and tabs
to be produced from less expensive aluminum alloys without
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sacrificing the metallurgical properties of those more expen-
sive alloys. It has also been found that the intermediate
anneal and quench steps promote the formability of the can end
and tab stock without adversely effecting its strength.
In accordance with yet another embodiment of the
invention, the aluminum alloy is strip cast, preferably between
a pair of continuous moving metal belts, to form a hot strip
cast feedstock, and then the feedstock is rapidly, with or
without additional rolling, annealed and rapidly quenched to
prevent substantial precipitation of alloying elements.
It has been found that the intermediate annealing
and quenching steps substantially improve the formability of
the feedstock while maintaining exceptionally high metallurgi-
cal properties including ultimate tensile strength and yield
strength. The omission of the first quenching step represents
more efficient utilization of energy since it is not necessary
to reheat the feed stock to the desired annealing temperature
after it has been cooled by initial quenching. It has also
been found that the omission of such a first quench step as
described also makes it more possible to efficiently utilize
the concepts of the present invention in a continuous in-line
sequence of steps. That, in turn, provides substantial eco-
nomic benefits in carrying out the method of the present inven-
tion.
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It has been unexpectedly found that such a fabrica-
tion process provides an aluminum alloy feedstock having equal
or better metallurgical and formability characteristics as
compared to aluminum alloys conventionally used in forming can
ends and tabs.
It has been found in accordance with a preferred
embodiment of the present invention that the fabrication pro-
cess can be applied to alloys of the 3000 series such as AA3104
without the need to increase the thickness of the can ends and
tabs to achieve comparable strengths. Without limiting the
present invention as to theory, it is believed that the tech-
niques of strip casting followed by rapid annealing and quench-
ing provide an alloy sheet stock having improved strength by
reason of solid solution and age hardening. Strip casting
followed by a rapid anneal and quench step, either with or
without hot rolling before annealing, facilitates the rapid
processing of the feed stock so that precipitation of alloying
elements of intermetallic compounds is substantially minimized.
In addition, it is believed, once again, without limiting the
present invention as to theory, that formability of the sheet
stock of this invention used in forming can ends and tabs is
equal to or better than these DC-cast aluminum alloys contain-
ing greater quantities of alloying elements. Thus, the present
invention allows can ends and tabs to be produced from less
expensive aluminum alloys without sacrificing the metallurgical
properties of those more expensive alloys. It has also been
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found that the anneal and quench steps promote the formability
of the can end and tab stock without adversely effecting its
strength.
Brief Description of the Drawinas
Fig. 1 is a schematic illustration of the continuous
in-line sequence of steps employed in the practice of the first
embodiment of the invention.
Fig. 2 is a schematic illustration of the continuous
in-line sequence of steps employed in the practice of the
second embodiment of the invention.
Fig. 3 is a schematic illustration of the continuous
in-line sequence of steps employed in the practice of the third
embodiment of the invention.
Fig. 4 is a schematic illustration of preferred
strip casting apparatus used in the practice of the invention.
Fig. 5 is a generalized time-temperature transforma-
tion diagram for aluminum alloys illustrating how rapid heating
and quenching serves to eliminate or at least substantially
minimize precipitation of alloying elements in the form of
intermetallic compounds.
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Fig. 6 is a schematic illustration showing a process
utilizing a continuous in-line sequence of steps for producing
aluminum alloy sheet stock.
Fig. 7 is a drawing of a blank produced with a
convoluted die to control earing in accordance with the inven-
tion.
Fig. 8 is a schematic illustration of two continuous
sequences of steps employed in accordance with another embodi-
ment of the invention.
Detailed Description of the Drawinas
The sequence of steps employed in the embodiment of
the invention are illustrated in Fig. 1. One of the advances
of the present invention is that the processing steps for pro-
ducing sheet stock can be arranged in two continuous in-line
sequences whereby the various process steps are carried out in
sequence. The practice of the invention in a narrow width (for
example, 12 inches) make it practical for the present process
to be conveniently and economically located in or adjacent to
sheet stock customer facilities. In that way, the process of
the invention can be operated in accordance with the particular
technical and throughput needs for sheet stock users.
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In the preferred embodiment, molten metal is delivered
from a furnace not shown in the drawing to a metal degassing and
filtering device to reduce dissolved gases and particulate
matter from the molten metal, also not shown. The molten metal
is immediately converted to a cast feedstock or strip 4 in
casting apparatus 3.
The feedstock employed in the practice of the present
invention can be prepared by any of a number of casting
techniques well known to those skilled in the art, including
twin belt casters like those described in U.S. Patent No.
3,937,270 and the patents referred to therein. In some appli-
cations, it may be preferable to employ as the technique for
casting the aluminum strip the method and apparatus described in
U.S. Patent No. 5,564,491.
The strip casting technique described in the forego-
ing U.S. Patent No. 5,564,491 which can advantageously be em-
ployed in the practice of this invention is illustrated in Fig.
2 of the drawing. As there shown, the apparatus includes a
pair of endless belts 10 and 12 carried by a pair of upper
pulleys 14 and 16 and a pair of corresponding lower pulleys 18
and 20. Each pulley is mounted for rotation, and is a suitable
heat resistant pulley. Either or both of the upper pulleys 14
and 16 are driven by suitable motor means or like driving means
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not illustrated in the drawing for purposes of simplicity. The
same is true for the lower pulleys 18 and 20. Each of the
belts 10 and 12 is an endless belt and is preferably formed of
a metal which has low reactivity with the aluminum being cast.
Low-carbon steel or copper are frequently preferred materials
for use in the endless belts.
The pulleys are positioned, as illustrated in Fig.
2, one above the other with a molding gap therebetween corre-
sponding to the desired thickness of the aluminum strip being
cast.
Molten metal to be cast is supplied to the molding
gap through suitable metal supply means such as a tundish 28.
The inside of the tundish 28 corresponds substantially in
width to the width of the belts 10 and 12 and includes a metal
supply delivery casting nozzle 30 to deliver molten metal to
the molding gap between the belts 10 and 12.
The casting apparatus also includes a pair of
cooling means 32 and 34 positioned opposite that position of
the endless belt in contact with the metal being cast in the
molding gap between the belts. The cooling means 32 and 34
thus serve to cool belts 10 and 12, respectively, before they
come into contact with the molten metal. In the preferred
embodiment illustrated in Fig. 2, coolers 32 and 34 are posi-
tioned as shown on the return run of belts 10 and 12, respec-
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tively. In that embodiment, the cooling means 32 and 34 can be
conventional cooling devices such as fluid nozzles positioned
to spray a cooling fluid directly on the inside and/or outside
of belts 10 and 12 to cool the belts through their
thicknesses. Further details respecting the strip casting
apparatus may be found in U.S. Patent No. 5,564,491.
Returning to Fig. 1, the feedstock 4 from the strip
caster 3 is moved through optional shear and trim station 5
into optional one or more hot rolling stands 6 where its
thickness is decreased. Immediately after the hot rolling
operation has been performed in the hot rolling stands 6, the
feedstock is passed to a quenching station 7 wherein the
feedstock, still at an elevated temperature from the casting
operation, is contacted with a cooling fluid. Any of a variety
of quenching devices may be used in the practice of the
invention. Typically, the quenching station is one in which a
cooling fluid, either in liquid or gaseous form, is sprayed
onto the hot feedstock to rapidly reduce its temperature.
Suitable cooling fluids include water, air,.liquefied gases
such as carbon dioxide or nitrogen, and the like. It is;
important that the quench be carried out quickly to reduce the
temperature of the hot feedstock rapidly to prevent
substantial precipitation of alloying elements from solid
solution.
It will be appreciated by those skilled in the art
that there can be expected some insignificant precipitation of
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intermetallic compounds that do not affect the final proper-
ties. Such minor precipitation has no affect on those final
properties either be reason of the fact that the intermetallic =
compounds are small and redissolved during the rapid annealing
step in any case, or their volume and type have a negligible
effect on the final properties. As used herein, the term
"substantial" refers to precipitation which affects the final
sheet properties.
In general, the temperature is reduced from a
temperature ranging from about 600 to about 950 F to a tempera-
ture below 550 F, and preferably below 450 F. The importance
of rapid cooling following hot rolling is illustrated by Fig. 3
of the drawings, a generalized graphical representation of the
formation of precipitates of alloying elements as a function of
time and temperature. Such curves, which are generally known
in the art as time-temperature transformation or "C" curves,
show the formation of coarse and fine particles formed by the
precipitation of alloying elements as intermetallic compounds
as an aluminum alloy is heated or cooled. Thus, the cooling
afforded by the quench operation immediately following hot
rolling is effected at a rate such that the temperature-time
line followed by the aluminum alloy during the quench remains
between the ordinate and the curves. That ensures that cooling
is effected sufficiently rapidly so as to substantially avoid
the precipitation of such alloying elements as intermetallic
compounds.
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In a preferred embodiment of the invention, the
feedstock is passed from the quenching step to one or more cold
rolling stands 19 in which the feedstock is worked to harden
the alloy and reduce its thickness to finish gauge. In the
preferred practice of the invention, it is sometimes desirable,
after cold rolling to age the cold roll strip at an elevated
temperature, preferably at temperatures within the range of
300-375 F for about 1 to about 10 hours. Because the strip has
been quenched immediately following low rolling so as to
substantially minimize precipitation of alloying elements as
intermetallic compounds, the cast strip has an unusually high
level of solute supersaturation. Thus, the aging step causes
the ultimate tensile strength and yield strength to increase
along with formability.
Thereafter, the cast strip which has been aged can
either be coiled until needed or it can be immediately formed
into can ends and/or tabs using conventional techniques.
As will be appreciated by those skilled in the art,
it is possible to realize the benefits of the present invention
without carrying out the cold rolling step in the cold mill 19
as part of the in-line process. Thus, the use of the cold
rolling step is an optional process step of the present inven-
tion, and can be omitted entirely or it can be carried out in
an off-line fashion, depending on the end use of the alloy
being processed. As a general rule, carrying out the cold
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rolling step off-line decreases the economic benefits of the
preferred embodiment of the invention in which all of the
process steps are carried out in-line.
It has become the practice in the aluminum industry
to employ wider cast strip or slab for reasons of economy. In
the preferred embodiment of this invention, it has been found
that, in contrast to this conventional approach, the economics
are best served when the width of the cast feedstock 4 is
maintained as a narrow strip to facilitate ease of processing
and enable use of small decentralized strip rolling plants.
Good results have been obtained where the cast feedstock is
less than 24 inches wide, and preferably is within the range of
2 to 20 inches wide. By employing such narrow cast strip, the
investment can be greatly reduced through the use of small,
two-high rolling mills and all other in-line equipment. Such
small and economic micromills of the present invention can be
located near the points of need, as, for example, can-making
facilities. That in turn has the further advantage of minimiz-
ing costs associated with packaging, shipping of products and
customer scrap. Additionally, the volume and metallurgical
needs of a can plant can be exactly matched to the output of an
adjacent micromill.
In the practice of the invention, the hot rolling
exit temperature is generally maintained within the range of
300 to 1000 F. Hot rolling is typically carried out in temper-
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atures within the range of 300 F to the solidus temperature of
the feedstock.
As will be appreciated by those skilled in the art,
the extent of the reductions in thickness effected by the hot
rolling and cold rolling operations of the present invention
are subject to a wide variation, depending upon the types of
alloys employed, their chemistry and the manner in which they
are produced. For that reason, the percentage reduction in
thickness of each of the hot rolling and cold rolling opera-
tions of the invention is not critical to the practice of the
invention. However, for a specific product, practices for
reductions and temperatures must be used. In general, good
results are obtained whenthe hot rolling operation effects
reduction in thickness within the range of 15 to 99% and the
cold rolling effects a reduction within the range from 10 to
85%. As will be appreciated by those skilled in the art, strip
casting carried out in accordance with the most preferred
embodiment of the invention provides a feedstock which does not
necessarily require a hot rolling step as outlined above.
As indicated, the concept of the present invention
make it possible to utilize, as sheets stock for fabricating
can ends and tabs, aluminum alloys containing smaller quanti-
ties of alloying elements as compared to the prior art. As a
general proposition, the concepts of the present invention may
be applied to aluminum alloys containing less than 2% magne-
_
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sium. Representative of suitable aluminum alloys include the
3000 series of aluminum alloys such as AA3004 and AA3104.
Because of the unique combination of processing steps employed
in the practice of the invention, it is possible to obtain
strength levels with such low in aluminum content aluminum
alloys that are equal to or better than the more expensive
aluminum alloy heretofore used. In general, such alloys con-
tain 0 to about 0.6% by weight silicon, from 0 to about 0.8% by
weight iron, 0 to about 0.6% by wight copper, about 0.2 to 1.5%
by weight manganese, about 0.2 to 2% by weight magnesium and
about 0 to about .25% by weight zinc, with the balance being
aluminum with its usual impurities.
In general, such aluminum alloys treated in accor-
dance with the practice of the present invention have ultimate
tensile strengths and yield strengths greater than 50,000psi.
Having described the basic concepts of this embodi-
ment of the present invention, reference is now made to the
following examples which are provided by way of illustration
and not by way of limitation to the invention.
Bxam l~ e 1
An aluminum alloy with the following composition is
strip cast to a thickness of 0.080 inches:
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~ ..................
~ .~
r ,::: . ,:. ;, .<: := .
':..:r..'.i3:: ..Se~.t~ . ~k, it= ..::..:%~:=r .
, . . ::.. ..=
i.. '
. ~f5:,: . ~'~~... v".....: . .;.
y ......:. . .?=.=::
t ik
~ yc,.~3i:, = =v J.:.: =
::f~:.=, r... . ~2:.. = ~~CR;;".ri4:;4k;=c=..:
Si 0.3
Fe 0.45
Cu 0.2
Mn 0.90
Mg 0.80
Aluminum and Balance
impurities
The hot cast strip was hot rolled to a thickness of 0.037
inches and then quenched with water. Thereafter, it was cold
rolled to a finished gauge of 0.116 inches. The cast strip was
then cooled and aged for several hours at 320 F. The ultimate
tensile strength (UTS), yield strength (YS) and percent elonga-
tion (%Elg) for the cast strip was determined and is set forth
in Table 1.
Example 2
In this example, use was made of aluminum alloy
having the following composition:
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. ..~;, ;:=,::~:: k= ~ .s:<:.,;;,u::. =a . =
'>:' ~'=;~:~ .~''~~.:::=''~'.=''=.~'Y' ;t{:~.~in'~' ..:.sF =...:=.....:..~} .
~;~~:'
~'iit:iv:=~i '$:: +'ST:%}>:~:{' 4't2)tt~~.:v n~'rx<~}rf+i.iY..
v'{'.; ~ti.. -hq=.w'==' >' ~'.v..~v.ti'.i}t.=.;=....{,4~}:=i}5::.:A.v::..,.~~
}\~ih:1i.4,+y4 =
= ' .~. .
~ . : . = ... , .. r = : .. .. . .y,. v.:
.> : = ' ~'i"'r=K '.~1~~1 y; q\~ . = ... . ~~~ .hT=~t'+i:*
~S~'Z''~4\~~~::{'~~'r"'~'wviK:,.~.'v~ ~i::
= ..3~= . ~<W:::~.vi:i:::9,v =
Si 0.3
Fe 0.45
Cu 0.2
Mn 0.94
Mg 0.92
Aluminum and Balance
Impurities
In this example, the foregoing aluminum alloy was strip cast to
a thickness of 0.080 inches and then subjected to fast air cool
quenching. Thereafter, it was hot rolled to a finished gauge
of 0.110 inches and stabilized at 320-340 F. Its properties
are likewise set forth in Table 1.
Example 3
Using the same alloy as described in Example 2, the
aluminum alloy strip cast to a thickness of 0.080 inches and
subjected to water quenching. Thereafter, it was cold rolled
to a finished gauge of 0.0110 inches and aged at 320-340 F for
several hours. Its properties are likewise set forth in Table
1.
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TABLE 1
,. ..v ... .::: . ::.~:..:....v .. .
- . .::,;:~k. ;: =- ~:~~:~x<;~ n- ;~.: .}:, . , .}
;:A : . . . . . S.R.>.:il, ,' i~,'k,:: , k" ,~'' : =~..~ ;. k ; :. t '
~=;;~-,~,<,Y:~4;~,, ,'4~
. . . , .:: ;k~õ~''~'~~r:~:;v~ ;;::'=:7~ '~;,: ".~ .3.:~ss~:skf:.~~.'',~... -
~s: " k <:=~r~ .:k.".".'~,.
~ ~.}}4'= , 4:'Y= = $kti=' f..,:Ki'.n 4' : { ff
'. .} :.} . i~y O.. nvt'. .cZ.=:,.k>'~ . ' :="{y ~~( f~~'." ~'
-:~\.}:N..:;k:tfn'.}: }ik:KWiO'~~= ..k~+m' .=,.k:5:'J~i-w? v=,'"~ui
}.4T:~:i:}j~ry-=y'~'ff'.p, ~~;$~ ,~= ,~=,y': . '~g ?.
i eii~-=i?i>i~:.:~.,v'y~,+,~.~,=~'.==-,,.,~,===,~:h#: .;;i=
Example 1 51.6 47.8 7.2
Example 2 55.8 52.8 6.5
Example 3 58.2 55.0 4.6
For purposes of comparison, there is set forth below
Examples A & B using, in the case of comparative Example A,
conventionally prepared aluminum alloy AA5182 having a finished
gauge of 0.0112 inches and, in the case of Example B another,
standard can lid aluminum. The compositions and the physical
properties associated with them are set forth in the following
table. The data shows that it is possible to employ in the
practice of the invention, as the aluminum alloy for fabrica-
tion of can lids and tabs, low-aluminum content aluminum alloy
without any sacrifice in metallurgic properties.
T'ABLE 2
f . f:5~'' ,= ~ '; ~i':,',f=~~':=:k: '.~:.o :2 ' '~f'f~ti '' =}~''';:=
;?,:fi.x,,. = t : ,'.,:: ,';ii{;Y,;;;:. ~. . -: =.'+},.,t:.}'x.::.. . ' a$F:=
. õ , = y =~
:=: = v . a :.. ..
,=.i . . .~,ya :=}+:.'õ ;''w' ,i? .: ii:r,~}.'=?::?'r.:=<a'a.::, f t'k=+ :i:}.
.'S4+:'.,G: ~i:
u _ ~ .:.,r.=.S.}. ""~yr:>~ ~.. ,
,y.,:.:r: h= : = ,;: }. .}i .. ,~r.õ :}..
'iii71: :' f <=. ~::8:;,=
-:. =.
- .. . ~:
::~:} I i'i0~
d: .== =V.
~;it4,:=' {f. .;. :ih'='}=k'...::':f.'=;'' i:;.~ ~ :r: .
.:= := = . . . "...= . .
-.,~.~,~,~~.:.''.~,/.:=> iY,;fo,l,. ,..:}5<,3~::. .,,:,=r . r<. ,.. .T ..}y.:r
r:,..,..r.::::=...~=. i:
.::=.. .. .... ::. ...:. :. .::.:,c:v.....,c:f .:. tt=.. ':~a.=.:.:
:!i?::}:w::.,,.}.n :,::: = ,.,:,:::~,?.:;=:, '",i..,k;:.::5<:;k#.'=,-
~:4'':.,''= :r:ic.S.ck=:.-'.=:.N}..! , ~~:i<3.~,.
..:. . .:: ...... . f '.;f .'~.:::'.-.'="::::}:...:.. . . . :. .. +r: -:
i~i.:T ..:::. .:.. .... . :': :':: i{:;.::=.
A 0.1 0.2 0.05 0.3 4.4- 53-56 46-49 6-9
4.6
B 0.15 0.40 0.17- 0.90- 1.07- 44-47 40-44 5-6
0.25 1.12 1.30
The second embodiment of the invention utilizing an
intermediate anneal step is illustrated in Fig. 2. The strip
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casting operation in strip caster 3, the optional hot rolling 6
and quench 7 are the same as shown in Fig. 1.
After quenching, the feedstock may be rolled and
stored until needed. Alternatively, it may be continuously
passed to an optional cold rolling stand 15 and then to a flash
annealing furnace 17 in which the feedstock, in either coil or
strip form, is rapidly heated. That rapid annealing step
provides an improved combination of metallic properties such as
grain size, strength and formability. Because the feedstock is
rapidly heated, substantial precipitation of alloying elements
is likewise avoided. Thus the heating operations should be
carried out to the desired annealing and recrystallization
temperature such that the temperature-time line followed by the
aluminum alloy does not cross the C-curves illustrated in Fig.
in such a way as to cause substantial precipitation.
Immediately following the heater 17 is a quench
station 18 in which the strip is rapidly cooled or quenched by
means of a conventional cooling fluid to a temperature suitable
for cold rolling. Because the feedstock is rapidly cooled in
the quench step 18, there is insufficient time to cause any
substantial precipitation of alloying elements from solid
solution.
In a preferred embodiment of the invention, the
feedstock is passed from the quenching step to one or more cold
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rolling stands 19 in which the feedstock is worked to harden
the alloy and reduce its thiclcness to finish gauge. In the
preferred practice of the invention, it is sometimes desirable,
after cold rolling to age the cold-rolled strip at an elevated
temperature, preferably at temperatures within the range of
220-400 F for about 1 to about 10 hours. Because the strip has
been quenched immediately following hot rolling so as to sub-
stantially mini-mize precipitation of alloying elements as
intermetallic com-pounds, the cast strip has an unusually high
level of solute supersaturation. Thus, the aging step causes
the ultimate tensile strength and yield strength to increase
along with formability.
Thereafter, the strip which has been aged can either
be coiled until needed or it can be immediately formed into can
ends and/or tabs using conventional techniques.
As will be appreciated by those skilled in the art,
it is possible to realize the benefits of the present invention
without carrying out the cold rolling step in the cold mill 19
as part of the in-line process. Thus, the use of the cold
rolling step is an optional process step of the present inven-
tion, and can be omitted entirely or it can be carried out in
an off-line fashion, depending on the end use of the alloy
being processed. As a general rule, carrying out the cold
rolling step off-line decreases the economic benefits of the
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preferred embodiment of the invention in which all of the
process steps are carried out in-line.
In the practice of the invention, the hot rolling
exit temperature is generally maintained within the range of
300 to 1000 F. Hot rolling is typically carried out in temper-
atures within the range of 300 F to the solidus temperature of
the feedstock.
The annealing step in which the feedstock is sub-
jected to solution heat treatment to cause recrystallization is
effected at a temperature within the range of 600 to 1200 F for
less than 120 seconds, and preferably 0.1 to 10 seconds.
Immediately following heat treatment, the feedstock in the form
of strip 4 is water quenched to temperatures necessary to
continue to retain alloying elements in solid solution, typi-
cally at temperatures less than 400 F.
As will be appreciated by those skilled in the art,
the extent of the reductions in thickness effected by the hot
rolling and cold rolling operations of the present invention
are subject to a wide variation, depending upon the types of
alloys employed, their chemistry and the manner in which they
are produced. For that reason, the percentage reduction in
thickness of each of the hot rolling and cold rolling opera-
tions of the invention is not critical to the practice of the
invention. In general, good results are obtained when the hot
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rolling operation effects reduction in thickness within the
range of 15 to 99% and the cold rolling effects a reduction
within the range from 10 to 85%. As will be appreciated by
those skilled in the art, strip casting carried out in accor-
dance with the most preferred embodiment of the invention
provides a feedstock which does not necessarily require a hot
rolling step as outlined above.
As indicated, this embodiment of the present inven-
tion make it possible to utilize, as sheets stock for fabricat-
ing can ends and tabs, aluminum alloys containing smaller
quantities of alloying elements as compared to the prior art.
As a general proposition, the concepts of the present invention
may be applied to aluminum alloys containing less than 2%
magnesium. Represen-tative of suitable aluminum alloys include
the 3000 series of aluminum alloys such as AA3004 and AA3104.
Because of the unique combination of processing steps employed
in the practice of the invention, it is possible to obtain
strength and formability levels with such low alloy content
aluminum alloys that are equal to or better than the more
expensive aluminum alloy heretofore used. In general, such
alloys contain 0 to about 0.6% by weight silicon, from 0 to
about 0.8% by weight iron, 0 to about 0.6% by weight copper,
about 0.2 to 1.5% by weight manganese, about 0.2 to 2% by
weight magnesium and about 0 to about .25% by weight zinc, with
the balance being aluminum with its usual impurities.
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Having described the basic concepts of this embodi-
ment of the present invention, reference is now made to the
following examples which are provided by way of illustration
and not by way of limitation to the invention.
Exam~le 4
An aluminum alloy with the following composition was
strip cast to a thickness of 0.090 inches:
... -,,.,= _
:. ..::~ ~ ,}<. ., . = = . :. A.=. ? = = :::,~::;;~, : -,.~, . <.:;.
;~. ... =. .
.=:,}=. .... v......; ...
.:rnL= :. .. ; .v'f'..::n.C ' ={::{n A }:;,
: :~ }K: =:=..,= :. =}. =4{=.'+ :~ } ~~+ .:.'õ ..,v.}'. v:
Yv1.:::'.:
...,
:.= .; . }=.
. .:.::.}r
, . ::::.. .
. : >:.. .'4,= ;==.~'y:,.~ 4i'{:.}~,J}= ='
, '= = '
=~' > '~!:.:2~.. :.~~:.' '~ ~~>=:
~' :.~~~~ :s~~ ::f'~'; ~'=.,' " ;;
'..;
;~ == ,:=.. ., . ..;
i:.. =: : . . = . ;;..}..~~ , :. =. ....:.: : :
~, ~..:,.. , ~.=~~5=' , =} .;~:; :.:::Y >.{
. ...i}:~:4:=:i=:tv:..iw:T:. .. . K=.:'i'~.+}Jh:}J4;~.K=:
Si 0.3
Fe 0.45
Cu 0.2
Mn 0.90
Mg 0.80
Aluminum and Balance
Impurities
The hot cast strip was then immediately rolled to a
thickness of 0.045 inches and heated for five seconds at a
temperature of 1000 F and immediately thereafter quenched in
water. The feedstock was then rolled to a thickness of 0.0116
inches and stabilized at 320 F for two hours at finish gauge.
It had an ultimate tensile strength of 56,000 psi, a yield
strength of 50,600 psi and 7.2% elongation.
The third embodiment of the invention is shown in
Fig. 3 of the drawings and utilizes an annealing step prior to
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quenching. As before, the strip casting operation 3 and the
optional hot rolling 6 operations are the same as described in
relation to Figs. 1 and 2.
Immediately after the optional hot rolling operation
has been performed in the hot rolling stands 6, the feedstock
is passed to a annealing furnace 27 wherein the feedstock,
still at an elevated temperature from the casting operation,
is rapidly heated, as by flash annealing. That rapid annealing
provides an improved combination of metallurgical properties
such as grain size, strength and formability. Because the feed
stock is rapidly heated, substantial precipitation of alloying
elements is avoided.
Immediately following the annealing furnace 27 is a
quench station 8 in which the feedstock is rapidly cooled or
quenched by means of a conventional cooling fluid to a
temperature suitable for cold rolling. Because the feedstock
is rapidly cooled in the quench station 8, there is likewise
insufficient time to cause any substantial precipitation of
alloying elements from solid solution. It is important as
before that the quench be carried out quickly to reduce the
temperature of the hot feedstock rapidly to prevent
substantial precipitation of alloying elements from solid
solution.
The importance of rapid heating and quenchinq is
illustrated by Fig. 3 of the drawings, a generalized graphical
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-
representation of the formation of precipitates of alloying
elements as a function of time and temperature. Thus, the
heating effected in the annealing step and the cooling effected
by the quench operation immediately following annealing is
effected at a rate such that the temperature-time line followed
by the aluminum alloy during the heating and quenching remains
between the ordinate and the curves. That ensures that heating
and cooling is effected sufficiently rapidly so as to avoid
substantial precipitation of such alloying elements as
intermetallic compounds.
In this embodiment of the invention, the feedstock
is passed from the quenching step to one or more cold rolling
stands 19 in which the feedstock is worked to harden the alloy
and reduce its thickness to finish gauge. In the preferred
practice, it is sometimes desirable, after cold rolling to age
the cold-rolled strip at an elevated temperature, preferably at
temperatures within the range of 220-400 F for about 1 to about
hours. Because the strip has been quenched immediately
following annealing so as to substantially minimize precipita-
tion of alloying elements as intermetallic compounds, the cast
strip has an unusually high level of solute supersaturation.
Thus, the aging step causes the ultimate tensile strength and
yield strength to increase along with formability.
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Thereafter, the strip which has been aged can either
be coiled until needed or it can be immediately formed into can
ends and/or tabs using conventional techniques.
As will be appreciated by those skilled in the art,
it is possible to realize the benefits of this embodiment of
the present invention without carrying out the cold rolling
step in the cold mill 19 as part of the in-line process. Thus,
the use of the cold rolling step is an optional process step of
the present invention, and can be omitted entirely or it can be
carried out in an off-line fashion, depending on the end use of
the alloy being processed. As a general rule, carrying out the
cold rolling step off-line decreases the economic benefits of
the preferred embodiment of the invention in which all of the
process steps are carried out in-line.
In the practice of this embodiment, the hot rolling
exit temperature is generally maintained within the range of
300 to 1000 F. Hot rolling is typically carried out in temper-
atures within the range of 300 F to the solidus temperature of
the feedstock.
The annealing step in which the feedstock is sub-
jected to solution heat treatment to cause recrystallization is
effected at a temperature within the range of 600 to 1200 F for
less than 120 seconds, and preferably 0.1 to 10 seconds.
Immediately following heat treatment, the feedstock in the form
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of strip 4 is quenched to temperatures necessary to continue to
retain alloying elements in solid solution, typically at tem-
peratures less than 550 F.
As will be appreciated by those skilled in the art,
the extent of the reductions in thickness effected by the hot
rolling and cold rolling operations of this embodiment of the
invention are subject to a wide variation, depending upon the
types of alloys employed, their chemistry and the manner in
which they are produced. For that reason, the percentage
reduction in thickness of each of the hot rolling and cold
rolling operations of the invention is not critical to the
practice of the invention. In general, good results are ob-
tained when the hot rolling operation effects reduction in
thickness within the range of 15 to 99% and the cold rolling
effects a reduction within the range from 10 to 85%. As will
be appreciated by those skilled in the art, strip casting
carried out in accordance with the most preferred embodiment of
the invention provides a feedstock which does not necessarily
require a hot rolling step as outlined above.
As indicated, the concept of the present invention
make it possible to utilize, as sheets stock for fabricating
can ends and tabs, aluminum alloys containing smaller quanti-
ties of alloying elements as compared to the prior art. As a
general proposition, the concepts of the present invention may
be applied to aluminum alloys containing less than 2% magne-
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sium. Representative of suitable aluminum alloys include the
3000 series of aluminum alloys such as AA3004 and AA3104.
Because of the unique combination of processing steps employed
in the practice of the invention, it is possible to obtain
strength and formability levels with such low alloy content
aluminum alloys that are equal to or better than the more
expensive aluminum alloy heretofore used. In general, such
alloys contain 0 to about 0.6% by weight silicon, from 0 to
about 0.8% by weight iron, 0 to about 0.6% by weight copper,
about 0.2 to 1.5% by weight manganese, about 0.2 to 2% by
weight magnesium and about 0 to about .25% by weight zinc, with
the balance being aluminum with its usual impurities.
Having described the basic concept of this
embodiment, reference is now made to the following examples
which are provided by way of illustration and not by way of
limitation to the invention.
Examr)le 5
An aluminum alloy with the following composition was
strip cast to a thickness of 0.090 inches:
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.. =. .:.. .
..;
~ = r. .,:N:;::: :.:' '; ' ~ ' ~.
.. . .'::
.:.
...: ~~ . ~~~. ...:..:
. :=.=.. ;:~ '
,. ..
~ .:, .:. =.<:
. . .. :..... ' '~:.::.
... . . Y ' = õ3',.v,.. .f . .:...... =n .:. :....=.:: . .
:.:.:.:~....n:::=:... ::.C,.... .
si 0.3
Fe 0.45
Cu 0.2
Mn 0.90
Mg 0.80
Aluminum and Balance
Impurities
The hot cast strip was then immediately rolled to a
thickness of 0.045 inches and heated for five seconds at a
temperature of 1000 F and immediately thereafter quenched in
water. The feedstock was then rolled to a thickness of 0.0116
inches and stabilized at 320 F for two hours at finish gauge.
It had an ultimate tensile strength of 56,000 psi, a yield
strength of 50,600 psi and 7.2% elongation.
The concepts as described above all relate to the
manufacture of can ends and tabs for aluminum alloy beverage
containers which present different problems as compared to the
manufacture of aluminum alloy can stock employed in the making
of the side walls and bottoms of aluminum alloy beverage con-
tainers. As is also described above, it is often times advan-
tageous to employ continuous in-line sequences of the foregoing
steps in the processing of aluminum alloy in the manufacture of
aluminum alloy can stock.
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In U.S. Patent No. 5,496,423 there is disclosed a
new concept in the processing of aluminum alloys in the
manufacture of aluminum can stock. It has been discovered that
it is possible to combine casting, hot rolling, annealing,
solution heat treating, quenching and cold rolling into one
continuous, in-line operation in the production of aluminum
alloy can body stock. One of the advantages afforded by the
process of the foregoing application is that it is possible to
operate the continuous, in-line sequence of steps at very high
speeds, of the order of several hundred feet per minute. One
of the disadvantages that has been discovered in connection
with the process of the foregoing application is that the
intermediate annealing step, which provides re-solution of
soluble elements and earing control through recrystallization
of the sheet, may be a limiting factor on the speed at which
the process can be operated. Thus, as production speed
increases, the continuous annealing furnace preferably used in
the practice of the process disclosed in the foregoing
application must be made longer and be run at higher energy
levels, representing an increase in the cost of capital
equipment and the cost in operating the process. It would,
therefore, be desirable that the continuous annealing step be
avoided.
It is possible to produce aluminum alloy sheet
stock, and preferably aluminum alloy can body stock having
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desirable metallurgical properties by using, in one continuous
sequence of steps, the steps of providing a hot aluminum alloy
feedstock which is subjected to a series of rolling steps to
rapidly and continuously cool the feedstock to the thickness
and metallurgical properties without the need to employ an
annealing step conventionally used in the prior art. In simi-
lar prior art processes, such as that described in U.S. Patent
No. 4,282,044, it has been suggested that aluminum alloy can
body stock can be produced by strip casting, followed by roll-
ing and coiling whereby the rolled feedstock in the form of
coils is allowed to slowly cool. Thereafter, the coil is later
annealed to improve the metallurgical properties of the sheet
stock.
It has been found, in accordance with the present
invention, that when the feedstock is rapidly cooled following
casting, it is unnecessary to employ annealing steps to attain
the desired metallurgical properties resulting from solution of
soluble elements. Without limiting the present invention as to
theory, it is believed that the rapid cooling effected by the
continuous, in-line rolling operations is carried out in a
sufficiently short period of time to prevent precipitation of
alloying elements contained in the aluminum feedstock as inter-
metallic compounds. That precipitation reaction is a
diffusion-controlled reaction, requiring the passage of time.
Where the feedstock is rapidly cooled during rolling, there is
insufficient time to permit the diffusion-controlled precipita-
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tion from occurring. That, in turn, not only facilitates in-
line processing of the aluminum alloy to minimize the number of
materials handling steps, so too does the rapid cooling prevent
substantial precipitation of alloying elements, making it un-
necessary to utilize a high temperature annealing step to
attain the desired strength in the final can product.
The feedstock produced by the method of the present
invention is characterized as being produced in a highly
economical fashion without the need to employ a costly anneal-
ing step. As will be understood by those skilled in the art,
annealing has been used in the prior art to minimize earing.
It has been found, in accordance with the practice of this
invention, that, the conditions (time and temperature) of hot
rolling, the thickness of the alloy as strip cast and the speed
at which it is cast can be used to control earing. For exam-
ple, casting the aluminum alloy at reduced thickness is be-
lieved to reduce earing; similarly, casting at higher speeds
can likewise reduce earing. Nonetheless, where use is made of
processing conditions which tend to yield an aluminum alloy
strip having a tendency toward higher earing, that phenomenon
can be controlled by means of an alternative embodiment.
In accordance with that alternative embodiment of
the invention, the high earing that can occur on the feedstock
can be compensated for by cutting the processed feedstock into
non-circular blanks prior to cupping, using what has become
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known in the art as convoluted die. The use of a convoluted
die compensates for any earing tendencies of the sheet stock,
by removing metal from those peripheral portions of the blank
which would be converted to ears on cup-drawing. Thus, the
convoluted die offsets any earing that would otherwise be
caused by the omission of high temperature annealing.
In accordance with a preferred embodiment of the
invention, the strip is fabricated by strip casting to produce
a cast thickness less than 1.0 inches, and preferably within
the range of 0.01 to 0.2 inches.
In another preferred embodiment, the width of the
strip, slab or plate is narrow, contrary to conventional wis-
dom; this facilitates ease of in-line threading and processing,
minimizes investment in equipment and mini.mizes cost in the
conversion of molten metal to can body stock.
The preferred process of the present invention
involves a new method for the manufacture of aluminum alloy
cups and can bodies utilizing the following process steps in
one, continuous in-line sequence:
(a) In the first step, a hot aluminum feedstock is
provided, preferably by strip casting; and
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(b) The feedstock is, in the preferred embodiment,
subjected to rolling to rapidly and continu-
ously cool the sheet stock to the desired
thickness and attain the desired strength prop-
erties.
The cooled feedstock can then be either formed into a coil for
later use or can be further processed to form non-circular
blanks by means of a convoluted die to effect earing control,
in accordance with conventional procedures.
It is an important concept of this embodiment of the
invention that the rolling of the freshly cast strip be ef-
fected rapidly, before there is sufficient time for the
diffusion-controlled reaction by which alloying elements are
precipitated from solid solution as intermetallic compounds.
In that way, the process of the present invention makes it
possible to omit high temperature annealing as is required in
the prior art to effect solution of soluble alloying elements.
In general, the cast feedstock must be cooled to cold rolling
temperatures in less than 30 second, and preferably in less
than 10 seconds.
In a preferred embodiment, the overall process of
the present invention embodies characteristics which differ
from the prior art processes: ~
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(a) The width of the can body stock product is
narrow;
(b) The can body stock is produced by utilizing
small, in-line, simple machinery;
(c) The tendency of the non-annealed aluminum alloy
to exhibit high earing is offset through the
use of a convoluted die while achieving desir-
able strength properties; and
(d) The said small can stock plants are located in
or adjacent to the can making plants, and
therefore packaging and shipping operations are
eliminated.
The in-line arrangement of the processing steps in a
narrow width (for example, 12 inches) makes it possible for the
process to be conveniently and economically located in or adja-
cent to can production facilities. In that way, the process of
the invention can be operated in accordance with the particular
technical and throughput needs for can stock of can making
facilities.
In the preferred embodiment of the invention as
illustrated in Fig. 6, the sequence of steps employed in the
practice of the present invention is illustrated. One of the
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advances of the present invention is that the processing steps
for producing can body sheet can be arranged in one continuous
line whereby the various process steps are carried out in
sequence. Thus, numerous handling operations are entirely
eliminated.
In the preferred embodiment, molten metal is
delivered from a furnace 1 to a metal degassing and filtering
device 2 to reduce dissolved gases and particulate matter from
the molten metal, as shown in Fig. 1 The molten metal is
immediately converted to a cast feedstock 4 in casting appara-
tus 3. As used herein, the term "feedstock" refers to any of a
variety of aluminum alloys in the form of ingots, plates, slabs
and strips delivered to the hot rolling step at the required
temperatures. Herein, an aluminum "ingot" typically has a
thickness ranging from about 6 inches to about 30 inches, and
is usually produced by direct chill casting or electromagnetic
casting. An aluminum "plate", on the other hand, herein refers
to an aluminum alloy having a thickness from about 0.5 inches
to about 6 inches, and is typically produced by direct chill
casting or electromagnetic casting alone or in combination with
hot rolling of an aluminum alloy. The term "slab" is used
herein to refer to an aluminum alloy having a thickness ranging
from 0.375 inches to about 3 inches, and thus overlaps with an
aluminum plate. The term "strip" is herein used to refer to an
aluminum alloy, typically having a thickness less than 0.375
inches. In the usual case, both slabs and strips are produced
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by continuous casting techniques well known to those skilled
in the art.
The feedstock employed in the practice of this
embodiment of the present invention can be prepared by any of
a number of casting techniques well known to those skilled in
the art, including twin belt casters like those described in
U.S. Patent No. 3,937,270 and the patents referred to therein.
In some applications, it is preferable to employ as the
technique for casting the aluminum strip the method and
apparatus described in U.S. Patent Nos. 6,102,102, 5,515,908,
and 5,564,491. The strip casting technique described in the
foregoing U.S. patents which can advantageously be employed in
the practice of this invention is illustrated in Fig. 4 of the
drawing as described above.
The feedstock 4 is moved through optional pinch
rolls 5 into one or more hot rolling stands 6 where its thick-
ness is decreased. In addition, the rolling stands serve to
rapidly cool the feedstock to prevent or inhibit precipitation
of the strengthening alloying components such as manganese,
copper, magnesium and silicon present in the aluminum alloy.
As will be appreciated by those skilled in the art,
use can be made of one or more rolling steps which serve to
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reduce thickness of the strip 4 while simultaneously rapidly
cooling the strip to avoid precipitation of alloying elements.
The exit temperature from the strip caster 3 varies within the
range of about 700 F to the solidus temperature of the alloy.
The rolling operations rapidly cool the temperature of the cast
strip 4 to temperatures suitable for cold rolling, generally
below 350 F in less than 30 seconds, and preferably in less
than 10 seconds, to ensure that the cooling is effected suffi-
ciently rapidly to avoid or substantially minimize precipita-
tion of alloying elements from solid solution. The effect of
the rapidly cooling may be illustrated by reference to Fig. 5
of the drawing, showing the formation of intermetallic precipi-
tates in aluminum as a function of temperature and time. It is
importance in the practice of the present invention to rapidly
cool the feedstock during the rolling operations so that the
strip 4 is cooled along a temperature time line that does not
intersect the curves shown on Fig. 5 of the drawing. The prior
art practice of allowing a slow cool of, for example, a coil,
results in a temperature time line which intersects those
curves, maintaining that the slow cooling causes precipitation
of alloying elements as intermetallic compounds.
The effect of the reductions in thickness likewise
effected by the rolling operations are subject to wide varia-
tion, depending upon the types of feedstock employed, their
chemistry and the manner in which they are produced. For that
reason, the percent reduction in thickness of the rolling
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-
operations is not critical to the practice of the invention.
In general, good results are obtained when the rolling opera-
tion effects a reduction in thickness within the range of 40 to
99 percent of the original thickness of the cast strip.
Alternatively, it is preferred to immediately cut
blanks using a convoluted die and produce cups for the manufac-
ture of cans instead of coiling the strip or slab 4. Convo-
luted dies useful in the practice of the present invention are
known to the art, and are described in U.S. Patent Nos.
4,711,611 and 5,095,733. Such dies are now conventional and
well known to those skilled in the art. The convoluted dies
used in the practice of this invention may be used to form a
non-circular blank having the configuration shown in Fig. 7
which in turn can be used to form a cup having the configura-
tion shown in the same Figure. Thus, the convoluted die can be
used, where necessary, to minimize earing tendencies of the
sheet stock.
As will be appreciated by those skilled in the art,
it is also possible, before treating the sheet stock with a
convoluted die, to coil the sheet stock.
The concepts of this embodiment of the present
invention are applicable to a wide range of aluminum alloys for
use as can body stock. In general, alloys suitable for use in
the practice of the present invention are those aluminum alloys
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containing from about 0 to about 0.6% by weight silicon, from 0
to about 0.8% by weight iron, from about 0 to about 0.6% by
weight copper, from about 0.2 to about 1.5% by weight manga-
nese, from about 0.2 to about 4% by weight magnesium, from
about 0 to about 0.25% by weight zinc, with the balance being
aluminum with its usual impurities. Representative of suitable
alloys include aluminum alloys from the 3000 and 5000 series,
such as AA 3004, AA 3104 and AA 5017.
Having described the basic concepts of this
embodiment of the invention, reference is now made to the
following examples which are provided by way of illustration of
the practice of the invention.
Examnle 6
A sheet of finish gauge can stock which was not
annealed was formed into a cup using a conventional round die.
The earing was measured as 6.6%.
An adjacent sheet from the same processing (still
without an anneal) was formed into a cup with a convolute cut
edge on the blanking die. The earing was measured as 3.1%.
Example 7
A thin strip of metal 0.09 inch thick was cast at
300 feet per minute and immediately rolled in three passes at
high speed from 0.090 inch thick to 0.0114 inch thick while
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decreasing in temperature during rolling from 900 F to 300 F.
The earing of the sheet so produced was 3.8%. The ultimate
tensile strength of the sheet was 43,400 psi and the elongation
4.4%.
A variation of the continuous in-line operation for
aluminum alloy can stock disclosed and claimed in United States
Patent No. 5,356,495 in which use is made of two sequences of
continuous, in-line operations. In the first sequence, the
aluminum alloy feedstock is first subjected to hot rolling,
coiling and coil self annealing and the second sequence in-
cludes the continuous, in-line sequence of uncoiling, quenching
without intermediate cooling, cold rolling and coiling. The
process as described in the latter patent has the advantage of
eliminating the capital costs of an annealing furnace while
nonetheless providing aluminum sheet and can stock having
strength associated with aluminum alloys which have been heat
treated.
It has now been discovered that aluminum alloys and
can stock can be produced by utilizing two different sequences
of in-line continuous operation in which the first sequence
includes a quenching step and the second sequence includes a
rapid annealing step to provide aluminum alloy sheet stock and
can stock having highly desirable metallurgical properties. It
has been found that the rapid quenching in the first sequence
of steps and the rapid heating followed by quenching in the
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second sequence of steps do not permit substantial precipita-
tion of alloying elements present in the alloy and, thus,
affords an aluminum alloy sheet and can stock having highly
desirable metallurgical properties.
It is possible to combine casting, hot rolling and
rapid quenching in a first continuous sequence of steps whereby
the rapid quenching does not permit substantial precipitation
of alloying elements from solid solution, thereby ensuring that
the alloying elements remain in solid solution. Thereafter, in
a second sequence of continuous, in-line steps, the aluminum
alloy sheet can be flash annealed and rapidly quenched to
ensure that alloying elements are in solid solution. The
annealing followed by quenching in the second sequence of steps
maximizes alloying elements in solid solution to strengthen the
final product.
As used herein, the term "anneal" or "flash anneal"
refers to a heating process to effect recrystallization of the
grains of aluminum alloy to produce uniform formability and to
control earing. Flash annealing, as referred to herein, refers
to a rapid annealing process which serves to recrystallize the
aluminum grains without causing substantial precipitation of
intermetallic compounds. Slow heating and cooling of the
aluminum alloy are known to cause substantial precipitation of
intermetallic compounds. Therefore, it is an important concept
of the invention that the heating, flash annealing and quench-
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ing be carried out rapidly. The continuous operation in place
of batch processing facilitates precise control of process
conditions and therefore metallurgical properties. Moreover,
carrying out the process steps continuously and in-line elimi-
nates costly materials handling steps, in-process inventory and
losses associated with starting and stopping the processes.
The process of the present invention thus involves a
new method for the manufacture of aluminum alloy sheet and can
body stock utilizing the following process steps in two con-
tinuous, in-line sequences. In the first sequence, the follow-
ing steps are carried out continuously and in-line:
(a) A hot aluminum feedstock is hot rolled to re-
duce its thickness;
(b) The hot reduced feedstock is thereafter rapidly
quenched without substantial precipitation of
alloying elements such as manganese to a
temperature suitable for cold rolling;
(c) The quenched feedstock is, in the preferred em--
bodiment of the invention, subjected to cold
rolling to produce intermediate gauge sheet ;
and
(d) The feedstock is coiled for further processing.
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Thereafter, in a second sequence, the following
steps may be carried out continuously and in-line:
(a) The feedstock is uncoiled and, optionally, can
be subjected to cold rolling if desired to
further reduce the thickness of the stock;
(b) The feedstock is subjected to a flash anneal to
effect recrystallization of the aluminum grains
at a sufficiently rapid rate to avoid substan-
tial precipitation of alloying elements as
intermetallic compounds and, thereafter, the
feedstock is subjected to a rapid quench, also
effectedrapidly so as to substantially avoid
precipitation of alloying elements as
intermetallic compounds; and
(c) The quenched feedstock is thereafter subjected
to further cold rolling and coiling to finish
gauge.
It is an important concept of the invention that the
flash anneal and the quench operation be carried out rapidly to
ensure that alloying elements, and particularly manganese, as
well as compounds of copper, silicon, magnesium and aluminum,
remain in solid solution. As is well known to those skilled in
the art, the precipitation hardening of aluminum is a diffusion
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controlled phenomena which is time dependent. It is therefore
important that the flash annealing and quenching operations of
the second sequence of steps be carried out sufficiently rap-
idly that there is insufficient time to result in substantial
precipitation of intermetallic compounds of copper, silicon,
magnesium, iron, aluminum and manganese. At the same time, the
annealing and quenching operations of the second step likewise
minimize earing. That is particularly important when the
aluminum alloy is a can stock alloy since earing is a phenome-
non frequently found in the formation of cans from can body
stock in which the plastic deformation to which the aluminum
alloy is subjected is non-uniform. Thus, minimizing precipita-
tion of intermetallic compounds raises the strength, allows
recrystallization to be done at a lighter gauge, minimizes
finish cold work and thereby reduces earing.
In accordance with a preferred embodiment of the
invention, the strip is fabricated by strip casting to produce
a cast thickness less than 1.0 inches, and preferably within
the range of 0.06 to 0.2 inches. In another preferred embodi-
ment, the width of the strip, slab or plate is narrow, contrary
to conventional wisdom. This facilitates ease of in-line
threading and processing, minimizes investment in equipment and
minimizes cost in the conversion of molten metal to the sheet
stock.
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The sequence of steps employed in this embodiment of
the invention are illustrated in Fig. 8. One of the advances
of the present invention is that the processing steps for pro-
ducing sheet stock can be arranged in two continuous in-line
sequences whereby the various process steps are carried out in
sequence. The practice of the invention in a narrow width (for
example, 12 inches) make it practical for the present process
to be conveniently and economically located in or adjacent to
sheet stock customer facilities. In that way, the process of
the invention can be operated in accordance with the particular
technical and throughput needs for sheet stock users.
In the preferred embodiment, molten metal is
delivered from a furnace not shown in the drawing to a metal
degassing and filtering device to reduce dissolved gases and
particulate matter from the molten metal, also not shown. The
molten metal is immediately converted to a cast feedstock 4 in
casting apparatus 3.
The strip casting technique described in the forego-
ing co-pending applications which can advantageously be em-
ployed in the practice of this invention is illustrated in Fig.
4 of the drawing as described above. The feedstock 4 from the
strip caster 3 is moved through optional shear and trim station
into one or more hot rolling stands 6 where its thickness is
decreased. Immediately after the hot rolling operation has
been performed in the hot rolling stands 6, the feedstock is
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passed to a quenching station 7 wherein the feedstock, still at
an elevated temperature from the casting operation, is con-
tacted with a cooling fluid. Any of a variety of quenching
devices may be used in the practice of the invention. Typi-
cally, the quenching station is one in which a cooling fluid,
either in liquid or gaseous form, is sprayed onto the hot
feedstock to rapidly reduce its temperature. Suitable cooling
fluids include water, liquified gases such as carbon dioxide or
nitrogen, and the like. It is important that the quench be
carried out quickly to reduce the temperature of the hot
feedstock rapidly to prevent substantial precipitation of
alloying elements from solid solution.
It will be appreciated by those skilled in the art
that there can be expected some insignificant precipitation of
intermetallic compounds that do not affect the final proper-
ties. Such minor precipitation has no affect on those final
properties either by reason of the fact that the intermetallic
compounds are small and redissolve during the rapid annealing
step in any case, or their volume and type have a negligible
effect on the final properties. As used herein, the term
"substantial" refers to precipitation which affects the final
sheet properties.
In general, the temperature is reduced from a
temperature ranging from about 600 to about 950 F to a tempera-
ture below 550 F, and preferably below 450 F. Thereafter, the
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feedstock can be coiled usirig conventional coiling apparatus in
a coiler 8. Alternatively, before coiling, the feedstock 4 can
be subjected to cold rolling as an optional step prior to
cooling.
The importance of rapid cooling following hot
rolling is illustrated by Fig. 5 of the drawings, a generalized
graphical representation of the formation of precipitates of
alloying elements as a function of time and temperature. Such
curves, which are generally known in the art as
time/temperature-transformation or "C" curves, show the forma-
tion of coarse and fine particles formed by the precipitation
of alloying elements as intermetallic compounds as an aluminum
alloy is heated or cooled. Thus, the cooling afforded by the
quench operation immediately following hot rolling is effected
at a rate such that the temperature-time line followed by the
aluminum alloy during the quench remains between the ordinate
and the curves. That ensures that cooling is effected suffi-
ciently rapidly so as to avoid substantial precipitation of
such alloying elements as intermetallic compounds.
Once coiled, the cooled feedstock can be stored
until needed. The temperature of the feedstock has been previ-
ously rapidly reduced in the quenching station 7 to prevent
substantial precipitation of alloying elements and compounds
thereof; hence the coil can be stored indefinitely.
.r.=..
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In the second sequence of steps, when there is a need
to provide finished alloy, the stored coil can then be
subjected to the second continuous, in-line sequence of steps,
also as shown in Fig. 8. The coil previously formed is placed
in an uncoiler 13 from which it is passed to an optional cold
rolling station 25 and then to a flash annealing furnace 17 in
which the coil is rapidly heated. That rapid annealing step
provides an improved combination of metallurgical properties
such as grain size, strength and formability. Because the
feedstock is rapidly heated, substantial precipitation of
alloying elements likewise is avoided. Thus, the heating
operation should be carried out to the desired annealing or
recrystallization temperature such that the temperature-time
line followed by the aluminum alloy does not cross the C-curves
illustrated in Fig. 5 in such a way as to cause substaiztial
precipitation. Immediately following the annealing furnace 17
is a quench station 15 in which the strip is rapidly cooled by
means of a conventional cooling fluid to a temperature suitable
for cold rolling. Because the feedstock is rapidly cooled in
the quench step 15, there is insufficient time to cause any
substantial precipitation of alloying elements from solid
solution. That facilitates higher than conventional strength.
This reduces the amount of strengthening required by cold
working, and less cold working reduces earing.
In the preferred embodiment of the invention,, the
feedstock is passed from the quenching step to one or raore cold
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rolling stands 19 in which the feedstock is worked to harden
the alloy and reduce its thickness to finish gauge. After cold
rolling, the strip 4 is coiled to a coiler 21.
As will be appreciated by those skilled in the art,
it is possible to realize the benefits of this embodiment of
the present invention without carrying out the cold rolling
step in the cold mill 19 as part of the in-line process. Thus,
the use of the cold rolling step is an optional process step of
the present invention, and can be omitted entirely or it can be
carried out in an off-line fashion, depending on the end use of
the alloy being processed. As a general rule, carrying out the
cold rolling step off-line decreases the economic benefits of
the preferred embodiment of the invention in which all of the
process steps are carried out in-line.
It is possible, and sometimes desirable, to employ
appropriate automatic control apparatus; for example, it is
frequently desirable to employ a surface inspection device for
on-line monitoring of surface quality. In addition, a thick-
ness measurement device conventionally used in the aluminum
industry can be employed in a feedback loop for control of the
process.
In the practice of this embodiment, the hot rolling
exit temperature is generally maintained within the range of
300 to 1000 F. Hot rolling is typically carried out in temper-
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atures within the range of 300 F to the solidus temperature of
the feedstock. The annealing and solution heat treatment is
effected at a temperature within the range of 600 to 1200 F for
less than 120 seconds, and preferably 0.1 to 10 seconds.
Immediately following heat treatment at those temperatures, the
feedstock in the form of strip 4 is water quenched to tempera-
tures necessary to continue to retain alloying elements in
solid solution and to cold roll (typically less than 400 F).
As will be appreciated by those skilled in the art,
the extent of the reductions in thickness effected by the hot
rolling and cold rolling operations of the present invention
are subject to a wide variation, depending upon the types of
alloys employed, their chemistry and the manner in which they
are produced. For that reason, the percentage reduction in
thickness of each of the hot rolling and cold rolling opera-
tions of the invention is not critical to the practice of the
invention. However, for a specific product, practices for
reductions and temperatures must be used. In general, good
results are obtained when the hot rolling operation effects
reduction in thickness within the range of 15 to 99% and the
cold rolling effects a reduction within the range from 10 to
85%. As will be appreciated by those skilled in the art, strip
casting carried out in accordance with the most preferred
embodiment of the invention provides a feedstock which does not
necessarily require a hot rolling step as outlined above. In
those instances where the feedstock is produced by such strip
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casting techniques, the hot rolling step can be avoided alto-
gether and, thus, is optional in the practice of the invention.
The concepts of the present invention are applicable
to a wide range of aluminum alloys for use in a wide variety of
products. In general, alloys from the 1000, 2000, 3000, 4000,
5000, 6000, 7000 and 8000 series are suitable for use in the
practice of the present inveintion.
Having described the basic concepts of this
embodiment, reference is now made to the following example
which is provided by way of illustration of the practice of the
invention. The sample feedstock was as cast aluminum alloy
solidified rapidly enough to have secondary dendrite arm spac-
ings below 10 microns.
Example 8
In Tests 1 and 2, an aluminum alloy having the
composition set forth in Table 3 and a prior art example are
each carried out by casting aluminum alloys using a twin belt
strip caster in which the belts are cooled while they are not
in contact with either molten metal or the cast metal strip to
yield a cast metal strip having a thickness of 0.10 inches.
The cast stip is then processed as indicated in the Table for
each of the examples to yield the products whose characteris-
tics are set forth in Table 3. The prior art process illus-
trated is that in U.S. Patent No. 4,292,044, except that the
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strip casting in the prior art process is carried out using the
same technique as Tests 1 and 2. Table 3 also sets forth
typical data for aluminum alloys having the composition set
forth therein for AA3104 and AA5182 produced by the conven-
tional ingot process in which the ingots have thicknesses of 26
inches. Can buckle strengths are set forth for all alloys
except 5182, and have been corrected to 0.0112 inch gauge for
ease of comparison.
The Tests illustrate the unexpected results produced
by the present invention. Rapid quenching instead of slow
cooling in accordance with the concepts of this invention
results in significantly higher strength, either with or with-
out hot rolling. The strengths obtained in the practice of
this invention for low alloy content aluminum alloys approaches
that of AA5182, a high alloy content aluminum alloy typically
used for can lids and tabs, as the data shows. Not only does
the process of the invention provide superior strength, it
provides equivalent or lower earing as well.
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TABLE 3
Invention Examples Typical Ingot
Process
r ' gr:::. >=r =. x=..: } ~kk:}:r<.,
. :=.. .:
=~ .~
.fi
"=~'~= ;c .g ' = == 3 '::;5:: s. yyy~?'~ i,;r..= : : :.
. .. .: . = .~....=:.. .y .
.=:
>. .: . .;.M .:..i n ' = .v }, 'l.=>..n... = ~. ' ~=.:J,.=~ :>.
. =... . :
ti .. . = = ~}'4#== ., ~ :v.}:N .
= r}., =
... ..:
~~ .
"} = ::. . ?~;4n=:; =>S.
; . . :r= .. :f.. . l..: hh ~ f=.
:. . .
=:...5.1,?c... =.. . +bo.txc..r.J!~%>~.+=."~'r.a..~'~ .'=.. , :. . .F
Si 0.30 0.26 0.39 0.18 0.10
Fe 0.29 0.33 0.44 0.45 0.20
Cu 0.27 0.20 0.23 0.20 0.05
Mn 0.95 0.59 0.97 1.00 0.35
Mg 0.93 0.84 0.96 1.10 4.50
Cast Gauge, inch 0.10 0.09 0.10 26 26
Hot Rolling 0 53% 46% 99% 99%
Cooling Quench Quench slow slow slow
Anneal Type Rapid Rapid Rapid slow Slow
Anneal Gauge, inch 0.031 0.025 0.027 0.110 0.110
Anneal Temp, F 1075 1000 930 650 650
Finish Gauge, inch 0.0106 0.0109 0.0116 0.0112 0.0108
Ultimate Strength, ksi 51.5 46.2 39.8 44.0 58.0
Yield strength, ksi 46.6 41.7 37.5 41.0 50.0
Elongation 8.1% 5.3% 1.2% 6.0% 8.0%
Cup Earing N/A 2.1% 3.4% 2.2% N/A
Can Buckle strength, psi N/A 100.7 78.5 93.0 N/A
It will be understood that various changes and
modifications can be made in the details of procedure, formula-
tion and use without departing from the spirit of the inven-
tion, especially as defined in the following claims.
