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Fig. 8 shows the actual stirrer in position under a
dome-type melting furnace in Hulett Aluminium,
South Africa
melt rate (20% increase, Fig. 9) and energy
economy (14% reduction, Fig. 10), with electrical
energy operating costs of between 2 and
4 kWh/t. The total energy reduction for the
whole melt cycle (inductor, controls and air
cooling fan) is 155 kWh.
Alloying benefits: One customer who
makes AlSi alloys (9% and 11% Si) found
that using the EM stirrer improved his Si yield
significantly towards 99%. Also, by changing
his alloying practices was able to reduce his
dross generation as is shown in Fig 11.
A second benefit was that the titanium
purchase costs could be significantly reduced
due to different alloy purchasing. Many plants
use Ti waffle as it is easier to get into solution
without stirring. However, the EM stirrer
(whether bought for production or for energy
saving reasons) may also allow savings from
purchasing less soluble forms of alloying elements
that may now be
easy to get into solution
using a stirrer. Fig.
12 shows the different
costs of Ti additions.
Clearly each aluminium
casthouse will
utilise different levels
of Ti additions depending
upon their particular
circumstances and
what level of support
they are looking for to
help grain refining or
reduce cracking, but
if we assume a typical
smelter casthouse using
200 tonnes of TiAl
10% waffle per year:
200 t of TiAl 10% W =
20 t of Ti units. Based
on the numbers above,
this works out at a total cost of USD379,500.
If the plant instead uses Ti80%zf tablets for
example, thanks to having a stirrer to aid the
dissolution of the Ti into the melt, then the table
above gives a Ti cost of USD168,000. This
leads to yearly savings of USD211,500.
Furnace modelling
Excellent and powerful circulation is being
Fig. 11: Reduced dross generation/cycle and increased Si yield
Fig.: 9
Fig. 12: Table showing different Ti alloy costs by alloy type
Fig.: 10
Fig. 13: Furnace circulation modelling with a bottom mounted stirrer (120-
tonne furnace)
52 ALUMINIUM · 3/2013