Once the hot, molten aluminium has been extracted from the
reduction cells, it is transported to holding furnaces before being
cast into products - a process that takes place at temperatures
above 700°C. While in the furnaces, the pure aluminium is alloyed
by combining it with magnesium, silicon, manganese or other
elements for additional strength, corrosion resistance and other
properties (as specified by the end-users).
The aluminium is then cast into ingots, large blocks (called
sows), T-bars or long cylindrical logs (called billets) of specific
dimensions. Generally, special ingot casting machines are used to
automatically cast, stack, strap and weigh the ingots ready for
transport. Billets are cast according to customer specifications
using a vertical drill chill casting technique; then bundled and
securely strapped for transport. T-bars are produced using
horizontal casting machines.
During furnace charging and preparation, aluminium dross (a
thick liquid or solid phase) forms at the surface of molten
aluminium. It is a mixture of aluminium oxides that are treated so
as to recover the aluminium that would otherwise be lost.
Casting of aluminium at DUBAL
DUBAL's casting operations have a total production capacity of
1,265,000 metric tonnes per year - the largest in the global
aluminium industry. The facility is equipped to receive and process
the entire primary aluminium production from our potlines. The hot,
molten aluminium tapped from the cells is transferred by crucible
to the casthouses, based on a tapping schedule.
Hot, molten aluminium received from the reduction cells is
weighed and sent to specific furnaces depending upon product
specifications. Metal, solid scrap and/or alloying additions are
added and mixed in the furnaces, which are kept hot using natural
gas as fuel. Metallurgical analysis verifies quality conformance to
customer specifications before distributing the hot, molten,
alloyed (or pure, unalloyed) aluminium to the relevant casting
centre using a system of launders. The metal is cast into the
moulds and transported using conveyors that operate at
predetermined rates for various product types (different alloys
require different casting and finishing parameters).
More than 330 different products are manufactured in three main
categories:
- Extrusion billets - Used for construction, industrial and
transportation purposes, as well as for forging purposes in
automotive industries, log-shaped billets are produced in various
different diameters and lengths.
- Foundry alloy - Used for automotive applications, re-melt
foundry products are cast in four types: standard ingots, small
ingots, T-ingots, and properzi ingots.
- High purity aluminium - Used for the electronics and aerospace
industries, high purity aluminium products are cast in three types:
standard ingots, low profile sow, and high profile sow ingots.
The aluminium dross formed during furnace charging and
preparation is processed to recover metal back from it.
