Aluminium beverage cans

1 Aluminium food packaging

Aluminum is widely used in various cans for food packaging (Figure 1.1).

The main methods for manufacturing food and drink aluminum cans, round and rectangular, are shown in Figure 1.2.

Figure 1-1 – Variety of aluminum food cans [1]

Figure 1-2 – Methods for manufacturing food and drink cans from aluminum sheet [1]

2 Aluminium beverage can

Unlike aluminum food containers, aluminum beverage cans (drink cans):

Required in vast quantities mainly in only several standard sizes (Fig. 1-3).
These sizes have the several standard body diameter (and hence use the same lid) and are merely of different lengths.
A limited number of types and sizes of beverage cans makes it possible to produce them in huge quantities on high-speed equipment.

The beverage (drink) can has to withstand an internal pressure of 6,7 atmosphere. It has a relatively thick inwardly domed base but a very thin wall as adequate rigidity is provided by the high pressure within the can (Figure 2-1).

Lightweighting of the body has been achieved by

attention to detailed design
fine-tuning the alloy metallurgy
process route to achieve maximum strength yet retain adequate formability.
necking-in the top of the can body to accept a smaller diameter (hence stronger) lid.

Figure 1-3 – Far from complete diversity of types and sizes of aluminum drink cans [8]

The thoughtful design

The aluminum drink can is an example of the careful and thoughtful design of an aluminum product. Each component of the can performs its function [2]:

BODY. Body is made thicker at the bottom for added integrity. It withstands an internal pressure of 6 atmospheres and can support 100 kilograms.
BASE. The bottom of the can assumes a dome shape in order to resist the internal pressure.
NECK. The body of the can is narrowed here to accommodate the smaller lid.
LID (END). The lid may make up 25 percent of the can total weight. It consists of an alloy that contain less manganese but more magnesium than the body does. This make the lid stronger. The diameter of the lid is made smaller that that of the body. This saves the mass.
FLANGE. After the top of the can is trimmed, it is bend and seamed to secure the lid after filling.
SCORED OPENING. The lid is scored so that the metal piece pushes in easily without detaching.
TAB. This separate piece of metal is held in place by the integral rivet.
RIVET. Used to secure the tab to the can. This integral piece of the lid is made by sretching the center of the lid upward slightly. It is then drawn to form a rivet.

Figure 2-1 – General view of a typical beverage can and
the functions of its various elements [2]

Body

Figure 2-2 shows a typical can body [1]:

It is produced from 0.30 mm thick strip
This dimension is substantially preserved in the can base
The base is profiled not only to withstand the high internal pressure but also to ensure the base is stackable on the appropriate lid.
The wall is ironed down to 0,110 mm thickness over most of body length.
The top of the can is not ironed to the same extent and finishes at around 0,16 mm thickness. This facilitates necking.
The thicker flange assists the subsequent lid seaming operation.

Figure 2-2 – Typical thickness of walls of aluminium beverage can [1].

Flange

Beverage can lids are fitted to the can body after filling by a double lock seam (Figure 2-3) [1]:

First, the rim of the lid is curled under the body flange which is then bent down
Second, the seam is closed tight.

Figure 2-3 – Steps in the Formation of a Double Lock Seam [1]

3 Easy-Open Lids (Ends)

The success of the aluminium beverage had begun by the introduction in 1960s of the easy-open lid (рисунок 2-4).
All easy-open can lids are produced from pretreated and lacquered coil.
Wide coils are used on 24-out shell presses, which can run at up to 300 strokes/min.

Рисунок 3-1 – “Stay-on Tab” Version of Beverage Can Easy-Open Lids [1]

Рисунок 3-2 – The lid is made of a stronger aluminium alloy then the alloy used for the body.
The opening is scored for easy removed by the consumer. Even with one hand [6]

Figure 3-3 – A new solution for cans that bridges the gap
between traditional drinking cans and the demands of the “generation on the go”.
The solution is tailored to meet the requirements of increasingly mobile lifestyles [8]

Integral rivet and tab

Steps in the formation of the Easy-Opening are shown in Figure 3-4 [1]:

The first stage is to form a bubble.
The bubble is then redrawn to form the button (i.e. the rivet).
The base of the lid around the button is thinned (coined) to extend more metal into the button.
When the tab has been placed over the button, the rivet is thinned to extend the metal in the finished rivet head.

Scorelines

The score line is in the form of a truncated ″vee″ (Figure 3-5) usually to a depth leaving about 0,085 mm residual metal in the vicinity of the rivet, but thickening
slightly to about 0,110 mm on the opposite side of the lid.
This is to satisfy the lid opening criteria of ″pop″ value around 3 kg and ″tear″ value around 7 kg.
These limits are fixed to ensure that the score-line is not so weak that it fractures prematurely.
A secondary score line is usually formed at the same time as the main score line.
This is a shallow score located just inside the main score line. It is to slow down the flow of metal from the main score and prevent score-line fracture during forming [1].

Рисунок 3-4 – Steps in Forming an Integral Rivet [1]

Figure 3-5 The section on Scoreline [1]

The Ingenious Design of the Aluminum Beverage Can

4 Materials for aluminum beverage cans

For the body of the can, a strip of aluminшum alloy 3004 or aluminшum alloy 3104 is used, both in H19 temper.
For lids, 5182 aluminum alloy strip in H48 temper is used.
For tabs, a strip of 5042 aluminum alloy in H18 temper is used.

Table 1 – Aluminum alloys for the manufacture of beverage aluminium cans

5 Beverage can manufacturing

Manufacturing cycle

Рисунок 5-1 – Typical aluminium beverage can manufacturing diagram [4]

Can body

Figure 5-2 – Scematic of Typical Draw and Wall-Iron Method of Can Manufacture (33 cl Can) [1]

Figure 5-3 – The same as in Figure 4.2 more clearly:
The initial draw transforms the blank into a small cup (1).
The cup is transferred to a second punch, which redraws the can;
the sleeve holds the can in place to prevent wrinkling (2).
The punch pushes the can past ironing rings, which thin the walls (3).
Finally, the bottom is shaped against a metal dome (4).

Figure 5-4 – Cupping Press.
The cupper is a coil-fed multi-die press
where circles are cut and drawn into the first stage cup [1].

Figure 5-5 – Redrawing & Wall-Ironing Stages in Bodymaker [1]

Lids (ends)

The usual method is to make easy-open lids in two steps [1]:

Blanking and forming the plain lid (the shell press) plus curling the edge and applying lining compound;
Transferring the shells to a multi-tool transfer press (the conversion press) for embossing panels, forming the rivet, scoring and finally attaching the ring-pull tab.

Easy-Open Tabs

The manufacturing of the eyelet – the key-opener – includes about 13 operations (Figure 11) before it can be installed on the lid.

Figure 5-6 – The Steps of Tabs Manufacturing [3]

6 Used aluminium beverage can (UBC) scrap

Form of scrap

UBC scrap is supplied [9]:

in bales having dimensions not exceeding (800 x 1000 x 1200) mm and a specific mass between 200 kg/m3 and 350 kg/m3
in briquettes having dimensions not exceeding (400 x 400 x 600) mm and a specific mass between 350 kg/m3 and 700 kg/m3.

Note: The density of the aluminum melt is 2350 kg/m3. Therefore, bales and briquettes, when loaded into the furnace as a whole, will inevitably float in the aluminum melt.

Chemical composition of remelted UBC scrap

UBC scrap after decoating and melting usually have the chemical composition as shown in Table 2.

Table 2 – UBC scrap chemical composition [9]

Aluminium “alloy” of such a chemical composition fits well into the ranges of the chemical composition of alloys 3004 and 3104 (see the table above), which are used to make the body of the can. Therefore, the vast majority of aluminum can scrap is melted down and returned to their producers (Figures 6-1, 6-2 and 6-3).