Development of Low-Earing Can Body Stock
Using the 4-stand Hot Finishing Mill at the Fukui Worksby Katsumi Koyama *, Sachio Urayoshi *, Toyonobu Tanaka *,Ryo Shoji *, Yoshikazu Tsuzuki *2 and Hiroshi Matsuda *3

In the effort to reduce the weight of aluminum beverage cans, progress is being

ABSTRACT made in reducing lid diameter and there is a need for materials with lower anisotropy (earing). To obtain such low-earing materials, it is necessary to arrange for the texture to be
dominated by crystals of the cube orientation prior to cold rolling. Accordingly a study was made ofthe effect of hot rolling conditions on the formation and growth of cube oriented grains during recrystallization.
To obtain a structure with cube orientation (a strong cube texture) during recrystallization, it was
found necessary that, during hot rolling, a strong rolling texture first be formed. To this end thenumber of finishing stands in the tandem hot-rolling mill at Furukawa Electric's Fukui Works wasincreased to four. This made it possible to improve manufacturing productivity and increase the sizeof coils manufactured, as well as to manufacture low-earing can body material to facilitate the ongoing program of diameter reduction.

Aluminum cans account for a large percentage of packaging containers, and it is estimated that in 1997 over 15.7
billion cans were consumed in Japan alone1).
Aluminum's light weight and good thermal conductivity
make it particularly attractive for use in beer cans, and it
has attracted further attention in recent years from thestandpoint of recycling. Despite these excellent properties, this material is in fierce competition with steel cansand PET (polyethylene tetraphthalate) bottles, necessitating cost reductions. One way to do this is to reduceweight, and this approach has long been actively pursued2).
A particularly effective way to decrease weight is to reduce lid diameter, and Figure 1 shows the progress madeover the years in the United States3). The percentage ofreduction in lid weight effected by diameter reduction alone,even as roughly estimated by the surface ratio, has reached
37% and should go even further. More than the forming of
the lid per se, the main technological problems in reducing lid diameter involve the necking of the can body inresponse to smaller lid diameter and the development ofmaterials that can accommodate these smaller neck diameters4). This paper discusses technological problems
involving the materials for can bodies resulting from the* Material Research Sec., Fukui Lab., R&D Div.
* 2 Materials Research Center, Yokohama Lab., R&D Div.
* 3 Products Engineering Sec. (Currently with Production
Engineering Sec.), Fukui Works

Thickwall (mm)INTRODUCTION

Thickwall (in)

1.

Year

Figure 1

Historical perspective in the reduction in averageneck diameter for 12-oz aluminum can bodies in the
U.S.A. (outer diameter notation: 206, equals 2-6/16 in)Blanking
Cupping

Cupping press

Redrawing#1 Ironing#2 Ironing

Coatingandbaking#3 Ironing

Forming of can body Trimming(re-drawing and ironing)
Body maker

Figure 2

Necking

Flanging

Manufacturing process for aluminum D&I canbodies97

recent movement to reduce lid diameter, as well as themeasures taken by Furukawa Electric to solve them.

Necked can height variation (mm)Earing of Starting Stock

Reduction by necking (%)

Figure 3

Can height variation in the necked can vs. reduction
by necking

Shear

CoilerFinisher

Figure 598

mass %
JIS
designation

Si

Fe

Cu

A3004

0.3
max.

0.7
max.

0.25
max.

PROBLEMS ARISING FROM DIAMETER
REDUCTION

Figure 2 is a schematic showing the manufacturing process for aluminum D&I can bodies. Cans are stamped
from coiled sheet, and after being deep drawn into theshape of a cup on the cupping press, are drawn and ironed(D&I) on a bodymaker to obtain the desired can height.
They are then trimmed to a uniform height and washed,
and the inner and outer surfaces are coated with lacquer
and baked. This is followed by the necking of the can bodyto the outer diameter of the lid. Finally, the can end is attached to the body with the formation of a flange.
As a result of the texture of the material, earing--unevenness in can height--may occur during the drawing
process. In the past the problem of earing that occurs during deep drawing and redrawing has received attention
due because heavy earing of the cans after the cuppingand D&I processes both interferes with their smooth transport and can result in pinholes or cracking during ironingof the can body. Further, a high level of earing creates the
problem of wastage because a larger amount of aluminum must be trimmed to avoid valleys in the edge of thetrimmed can.
Figure 3 shows the relationship between reduction bynecking and earing. Earing is also produced in the sidewallof the can by the necking process that follows D&I4). Further the trend in earing during the necking process is thesame as that occurring during deep drawing and redraw-

Chemical composition of A3004 alloy for can body
stock
Mn

Mg

1.0~1.5 0.8~1.3

Zn

Al

0.25
max.

remainder

Earing (%)

2.

Table 1

Cold rolling reduction ratio (%)

Figure 4

Earing vs. reduction ratio of cold rolled sheets

ing described above so both are considered to be phenomena caused by the texture of the material. Earing during the necking process is manifested as variation in flange
width and results in a poor fit to the lid. With the further
progress in lid diameter reduction now taking place, theappearance of earing during the necking process has cometo constitute a major problem.

3.

EARING AND TEXTURE

The material most commonly used for aluminum can bodies is fully work-hardened (H19) sheets of JIS-A3004 (seeTable 1), which has high strength and high drawability. Figure 4 shows the relationship between the cold rolling reduction ratio and earing ratio. Rolling imparts deformation
to the material in only one direction, resulting in a rolling
texture with grains aligned in a specific direction. It is known
that the alloy used here has a rolled texture composed
primarily of S orientation {123} <634>, Bs orientation {110}<112> and Cu orientation {112} <111>5). Together with thedevelopment of this rolled texture, earing occurs at 45°
with respect to the direction of rolling.
Recrystallization textures known to be obtained by annealing, on the other hand, are of the cube orientation{100} <101> and the Goss orientation {110} <001>5). In

Shear Slab Spray

Edger

Soaking
furnaceRougher

Layout of the hot rolling line at Furukawa Electric's Fukui Works

Furukawa Review, No. 18. 1999

the cube orientation, high earing occurs in the 0/90° direction, while in Goss orientation it occurs in the 0/180° direction. It is possible to obtain a material having a low
earing ratio by a suitable combination of crystals with anorientation that results in 45° earing and those that produce 0/90° earing6). Thus it is apparent that to obtain material of the requisite strength by cold rolling, it is necessary that a recrystallization texture be formed prior to coldrolling -- that is after hot rolling or during the subsequentannealing process -- in which crystals with a cube-orientation such that 0/90° earing occurs have a clear dominance6).

4.

FORMING CUBE-ORIENTATION DURING
HOT ROLLING

Cube orientation density f(g)Figure 5 shows the layout of the hot rolling line at Furukawa
Electric's Fukui Works. Most industrial-scale hot rolling lines
combine a reversing mill, called a rougher with a multistand tandem mill, called a finisher. In the rougher, theingot is repeatedly rolled back and forth to achieve a thickness that can be accepted by the finisher. The tandem
finisher consists of 4 stands arranged in series that rollthe sheet successively. The sheet is then wound into coils
by the coiler.Then, after the hot-rolled coil has completely
recrystallized using the residual heat from hot rolling, theproduct is brought to its final thickness by cold rolling.
Photo 1 shows the crystal grain structure of the material
immediately after hot finishing. When the final temperature is low, the result is a partially recrystallized microstructure in which granular crystals that are completely
recrystallized are intermixed with worked material with afibrous appearance in which recrystallization has not occurred. When the final rolling temperature is high, on theother hand, a recrystallized structure with equiaxed grains
is obtained.
Both hot-rolled bands take on a completely crystallized
structure after annealing (at, for example, 360°C for 2
hours). As already noted, obtaining a material with low
earing requires an increase in the volume fraction of cube
texture at the point at which complete recrystallization
occurs. It is known that the recrystallized texture is strongly

influenced by the amount of solute in solid solution in thematerial, the distribution of the dispersoids, and the hotrolling conditions7). It is thought that these factors are related to the nucleation of the cube orientation, grain growth
and the formation of other recrystallization textures (R orientation or random orientation), and determines the volume fraction of cube orientation7).
Figure 6 shows the relationship between the total rolling reduction and cube orientation density in a hot tandem finishing mill. As the total rolling reduction in the hot
finisher increases, a recrystallization texture with dominant cube orientation is obtained. This demonstrates thatthe nucleation and growth of the cube texture is related tothe degree of development of the rolling texture.
However, no relationship was found between the cube
orientation density after annealing and the total reduction
during reversible hot rolling, which is the step that precedes hot finishing. This is thought to be due to the waiting time (several seconds to several minutes) between
each pass during reversible hot rough rolling, during which
partial recrystallization occurs8). The formation of the rolling texture is thus interrupted between every pass. Up until
now the dominant theory holds that the cube orientation
has its origin in cube oriented bands seen in the hot-rolledsheet6). Cube oriented bands are residual of the grains
recrystallized during hot rough rolling that have been elongated during the hot finish rolling step. It has been confirmed that subgrains within the cube oriented bands act
as the nuclei of discontinuously recrystallized grains, andthese grow faster than recrystallized grains of other orientations6). The above results, however, demonstrate thatwhen the rolled texture becomes extremely well developed
the formation and growth of recrystallized grains of cube
orientation from elsewhere than the cube orientation bandis dominant.
Figure 7 plots the effect of total rolling reduction during
hot finishing on the ODF of two materials having different
volume fractions of the cube orientation.
The cube orientation fraction in these completely recrystallized specimens differed, but there was no difference inthe other specified orientation densities. That is to say, thecrystal grains having other than cube orientation had an
unaligned, random orientation. In rolled material (Photo 2)

Total rolling reduction (true strain: ln(to/t))
300˚C

Photo 1335˚CGrain structure of AA3004 hot band rolled at two
different temperature

Figure 6

Relationship between total rolling reduction ratio
and cube orientation density in tandem hot
finishing mill99

Orientation-distributed
density f(g)the lines indicating old grain boundaries can be seen to
curve around Al-Mn-Fe particles.
This is due to the fact that strain concentrations occurred
around the dispersoid, and the deformation was disordered.
Crystals having random orientation --that is to say no orientation with respect to the direction of rolling-- are thought
to originate from the regions surrounding eutectic constituent particles in which the amount of deformation was verylarge and the direction of deformation was disordered. This
corresponds to the description that by decreasing theamount of Fe in the material thereby decreasing the eutectic constituent, the volume fraction of cube texture iscomparatively increased9).
On the other hand, it is difficult to conceive that an increase in reduction during hot rolling would be accompanied by the suppressed formation of recrystallization nuclei near the dispersoids. It is therefore concluded that thedevelopment of a rolling texture promoted the formationand growth of cube orientation from the matrix.
Other hot rolling conditions such as hot rolling temperature, and rolling speed can be combined using a parameter such as the Zener-Hollomon parameter. These otherhot rolling conditions are also known to affect the formation of cube orientation10). The Zener-Hollomon parameter

Orientation-distributed
density f(g)/degOrientation-distributed
density f(g)Euler angle 2/deg
Total true strain: 1.9

Orientation-distributed
density f(g)/degEuler angle 2/deg
Total true strain: 2.6100

Effect of total rolling reduction ratio in tandem hot
finishing mill on the fiber texture of completely
recrystallized hot band

RESPONSES TO LID DIAMETER REDUCTION

In order to develop a low-earing material that can copewith the reductions in lid diameter that will continue as
productivity rises, Furukawa Electric has augmented thestands of its tandem hot finishing mill in accordance with
the information described above. This has led to a dramatic reduction in earing in D&I can bodies; it has been
confirmed that the range of deformation of can height(flange width) following necking has been reduced to about
half that of conventional materials. This level of earing iscompatible not only with current lid diameters but with the
reduced lid diameters expected in the future.

6.

Euler angle

Grain structure of material hot rolled at a low
deformation temperatureis related to the amount of mechanical energy that accumulate in the metal --energy which is required for recrystallization to proceed-- and is known to affect the formation of cube texture.
In addition, the Zener-Hollomon parameter is thought toinfluence the competition for growth between those recrystallization grains originating from the regions surrounding the eutectic constituents and those originating fromthe matrix.

5.

Euler angle

Figure 7

Photo 2

CONCLUSION

The manufacture of can body materials with low earing toaccommodate reduced lid diameters requires a recrystallization texture after hot rolling in which the cube orientation predominates. Accordingly this study investigated the
hot rolling conditions that are considered important to recrystallization behavior, and it was found that the formation and growth of cube oriented recrystallized grains is
promoted by the development of a rolling texture during
hot rolling. Based on this information, Furukawa Electric
has augmented the number of hot finishing stands, thereby
raising productivity and increasing coil diameter, and making possible the manufacture of a can body stock with low
earing suited to smaller lid diameters, which has foundfavor with can manufacturers around the world.

Furukawa Review, No. 18. 1999

REFERENCES(1) Aluminum Can Recycling Association; Beverage Japan
194(1998), 38. (in Japanese)(2) K. Oishi; Aluminum, 1(1994), 1-9. (in Japanese)(3) P. Smith; The Canmaker, 8(1995)m 161.
(4) D. Johnson; Aluminum alloys for packaging II, edited by J.G.
Morris et al., TMS, (1996), 161.
(5) N. Hansen and D. J. Jensen: Met. Trans. A, 17A(1986), 253.
(6) O. Daaland and E. Nes: Acta Mater., 44(1996), 1389.
(7) J. G. Morris, Z. Li, L. Chen and S. K. Das: Aluminium,
66(1990), 1069.
(8) T. Doko and S.Asami: Furukawa Review, 9(1991), 41.
(9) A. Karlsson, A. Oscarsson, B. Lehtinen and W.B.Hutchinson;
Homogenization and Annealing of Aluminum and Copper Alloys, edited by H.D. Merchant et.al., The Metallurgical Society, (1988), 99.
(10) B.Ren; Aluminum alloys for packaging III, edited by S. K.
Das, TMS,(1998), 49.
Manuscript received on July 14, 1998.

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