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TECHNOLOGY
Fig. 3: A hollow copper inductor dissipates
more heat, and so requires water for cooling
tek stirrer generates only low I 2 R losses which
an air flow at a certain speed and mass flow
can easily remove. Our stirrers have been designed
to optimise this cooling air flow.
For the water cooled inductor the heat
generated is so much higher that air-cooling
cannot remove it. This is why it needs water
with all of the associated complexities of supply
systems, piping, quality sealing and glands
to avoid leaks, as well as emergency back-up
water systems etc.
The Altek air-cooling system is designed to
ensure that the heat generated by the inductor
coil is easily dissipated by the cooling air flow.
The variables that affect this are:
• Inlet air temperature
• Size of current being applied to the
copper coil
• Radiated heat from the furnace
• Local ambient air temperature.
This design allows the air to be applied in a
special way within the inductor so as to remove
the lesser heat generated by the current
applied to the inductor coil. A secondary
benefit of this type of coil construction is that
promotes a very long life of the inductor by
reducing the risk of overheating of the coil,
which can easily cause serious damage to a
hollow copper tube type inductor coil.
As an example, the oldest solid inductor
installed in 1994 is still in operation today.
Energy consumption: There has long been
a myth that you need to use huge amounts
of electrical energy with EM stirring technology
to obtain a good mixing effect within the
furnace. This may be the case with alternative
designs, but the Siber Force technology has
significantly reduced the input energy needed
to achieve efficient stirring.
Thus one of the big differentiating factors
of the Altek stirring technology is its lower
electrical energy operating costs (due to the
special inductor design and control system).
This unique design and operation of the Altek
technology allows very low energy operation
such that some customers use less than 100
Fig. 4: Altek air-cooled side-mounted stirrer fitted
to the side of an 80-tonne dry-hearth furnace
kWh in total for a whole four-hour melting
cycle on a 50-tonne scrap melting furnace.
Clearly the amount of energy used very much
depends on the type of furnace, the type of
operation (scrap melting or holding / casting
furnace) etc.
The key focus of this stirring system is to
deliver the Lorenz Force within the aluminium
bath in the proximity
of the stirrer.
This impetus in the
liquid aluminium generates
a very effective
mass flow of aluminium
throughout
© Altek
the whole bath. Some
of the smaller models
of Siber Force stirrers
are being utilised on
furnace capacities of >
60 tonnes. The size of
stirring model chosen
is based upon the following
factors:
1. Size of furnace
2. Type of operation
(melter, holder, liquid,
dry hearth)
3. Refractory thickness
– to obtain correct
penetration of the
magnetic flux into the
bath
4. Available space.
A specially designed
and patented technique
for driving the inductor
coil, a technology
utilised in the induction
heating industry, allows us to use a relatively
low input current to the control system
from the clients facility (the input kVA range
is between 80 and 150 depending upon the
stirrer model size). Coupled with the special
stirring controls utilised in the cycle, we are
able to adapt and modify the stirring patterns,
depending upon the particular requirement at
that stage of the furnace cycle.
Furnace installations: There are many stationary
furnaces around the world that do not
have basements and therefore have no space
for bottom-mounted stirrers. Fig. 4 shows the
side stirrer fitted on a 80-tonne dry-hearth
scrap melting furnace with a relatively small
footprint.
Multiple furnace operation
Fig. 5 shows an increasingly common solution
for customers who are looking to share a
common inductor between several furnaces.
This fully integrated system can serve two
melting furnaces; it moves automatically between
the furnaces and is controlled by the
furnace master control system. A similar system
has been working very well in a large aluminium
company for the past 12 months.
When you consider continual movement of
Fig. 5: Altek stirrer in stirrer basement under two reverb furnaces, and
designed to serve multiple furnaces
Fig. 6: Altek type 500 stirrer for multiple furnaces undergoing FAT testing in
the Altek factory
50 ALUMINIUM · 3/2013