Aluminium recycling

Aluminium alloys for food and beverage cans

Aluminum cans make up a significant portion of old aluminium scrap. What alloys are they made from? Can they be used for remelting aluminium scrap, for example, for extrusion ingots?

Old aluminium scrap

The main sources for the processing of aluminium scrap from structures and products, that have completed their service life, are (Figure 1):

  • construction;
  • transport;
  • mechanical engineering;
  • electrical industry;
  • food packaging.

Figure 1 – The most important sources of old aluminium scrap [3]

Aluminium food packing

The use of aluminium in food packaging falls into two subcategories:

  • rigid containers (jars) and
  • foil.

The figure 2 different methods of manufacturing aluminium containers are shown, cans and jars for food and beverage packaging, including beer.

Figure 2 – Methods of Making Cans from Sheet [2]

3-piece cans

In the old days, all cans were made of three parts: cases, bottom and lid. The body of a round can was rolled up from a sheet blank, and then connected with a longitudinal weld. At the ends of this cylinder, a separate bottom and lid were rolled up (see Figure 1 on left). This method was used in the manufacture of steel (tin) fruit cans., greens and meat, as well as beer and drinks. Three-piece aluminium cans were bonded and welded. To do this, a long welded pipe was cut into cylinders for can bodies. These methods for aluminium cans were abandoned after the invention of the two-piece can..

2-piece cans

Currently, all aluminium cans are made using the two-piece method with a combined wall and bottom. A separate lid is installed after filling the jar (Fig. 1, right).

Aluminium cans are made by two different methods.. Food cans, which, after filling and processing, have a low internal pressure, have a bottom and a wall of the same thickness. These cans are made by stamping and shallow drawing from lacquered sheet.. The equipment is quite simple with a wide range of customization options for different sizes and shapes.

On the other hand, beer and beverage cans must withstand fairly significant internal pressure. Therefore they are thick, domed bottom, but may have a very thin wall. In this case, the necessary rigidity is provided by high pressure inside the can. These aluminium cans are made by drawing a cup from plain aluminum sheet and thinning, or ironing, the walls to about one third of the base thickness.

The equipment requires a high degree of precision. This equipment is designed to produce only one size of cans. However, it is justified, as the market demands billions of cans a year.

Recycling

Aluminium ingot from scrap aluminum only requires 5 % energy, from that, which is needed for the production of primary aluminum from bauxite. Usually aluminium from used cans is recycled, to produce new cans or new similar products [2].

Can body

Food cans

Everyone is familiar with rectangular or oval fish tins, as well as small round jars for various food products (figure 3). They are prepared with a one-time drawing from a varnished tape or sheet..

Basic aluminum alloys and states, which are used for the manufacture of food aluminium cans are shown in the table in the figure 4.

  • Low bodies of food cans are usually made of alloy 3005 in H46 condition (lacquered, 3/4 hardening).
  • Deeper drawing requires higher formability, than an alloy 3005, but with the same strength. In this case, an alloy with magnesium is used. 5052 in H44 condition (lacquered, 1/2 hardening).

Lids require a high degree of formability, including when seaming when closing the can. They also make them alloy 5052 in condition 1/2 nagartovki. For lids without an easy opener, an alloy is used 3207 in H48 condition (lacquered, full work hardening) [2].

Figure 3 – Varieties of Aluminium Food Cans [2]

Figure 4 – Principle Food Can Alloys

Aluminium beverage cans

The figure 5 showing a typical soda and beer can body. Usually they are made from a strip of thickness 0,30 mm and this thickness remains for its bottom. This thickness and the special dome shape of the bottom of the can withstand the high internal pressure and weight of the stack of full cans.. The wall is rolled out to 0,110 mm almost the entire length of the jar, except top neck. Here the thickness is 0,16 mm. Thick flange helps securely seal a filled jar.

Figure 5 – The typical body of the aluminium beverage can [2]

The body of cans for carbonated drinks are made of alloy 3004 or its modification alloy 3104 in state H19 (table in the figure 6).

Figure 6 – Aluminum Alloys for Carbonated Drink Can Body [2]

Easy-open lids (ends)

It is the invention in 1964 the year of the built-in device for easy opening of an aluminium can was the reason for its resounding success (figure 7). Then such a built-in “the bottle opener was introduced into other types of aluminium packaging, including, in jars for canned fish (figure 8).

Figure 7 – Lids for beverage and beer cans with built-in openers [2]

Figure 8 – Lids of various aluminium cans [2]

  • For the manufacture of lids for drinks and beer cans, lacquered aluminium tape with a thickness of 0,26 mm alloy 5182 able to H48.
  • Lids for food jars are made from lacquered tape with a thickness of 0,25 mm or 0,28 mm alloy 5052 in H44 condition.
  • Openers (“tabs”) cans for drinks and beer are made from a tape thick 0,45 mm alloy 5042 in H18 condition.
  • Openers (“tabs”) food cans are also made from alloy tape 5042, but in the state of H48 (varnished) due to the peculiarities of the technology for the production of canned food.

Figure 9 – Aluminium alloys for caps and openers (“tabs”) various aluminium cans [2]

Sources:

1. Mark E. Schlesinger, Aluminum Recycling, 2011

2. TALAT Lecture 3710 – Case Study on Can Making

3. Association of the Aluminum Industry e.V. – www.aluinfo.de