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Fig. 2: A modern furnace door system with an opening of 9.2 x
1.95 m on a 120 t melting and casting furnace
• a proper bath temperature measuring
device.
These items are all important standard
features of modern furnace installations.
It is also possible to retrofit
them to existing furnaces enabling improvements
in quality to be achieved
in stages with correspondingly smaller
investments being needed. Fig. 1
shows an example of an existing furnace
that was modernised to include
the following main items:
• a new sealed-type furnace door
system
• a new burner system (changing
from a cold air system to a
regenerative one)
• a furnace pressure control system.
The revamp resulted in a modernised
furnace equipped with state-of-the-art
technology that fulfilled environmental
and energy-consumption requirements
and led to higher productivity.
Modern furnace door installation
A modern furnace door installation
should have:
• a hydraulically operated up/down
movement by means of one or
two door-lifting cylinders
• a door that travels on a rail-type
system that is pressed against or
moved away from the furnace
door frame when the door is being
closed or opened
• a door blade made from two or
three elements that are connected
by cardan joints in a common
door frame; this compensates
for possible thermal distortion
and keeps the furnace chamber
sealed, prevents flames escaping,
which would lead to a deteriora-
tion, and prevents the ingress of
false air, which would create dross
ALUMINIUM · 6/2007
• a burner system and flue gas pres-
sure control system linked to the
movements of the furnace door.
Depending on the type of furnace, the
frame of the furnace door should be
equipped with a water cooling system
to reduce thermal distortion and to
keep the front blades of the furnace
door straight (recommended for larger
furnace doors).
An example of such a modern furnace
door system can be seen in Fig. 2,
which shows the door of a 120 t melting/casting
furnace with a door opening
of 9.2 x 1.95 m, equipped with two
lifting and two clamping cylinders, and
a water cooled frame. This system was
installed in 1999 and is still operating
to the end-user’s satisfaction.
Fig. 3 shows a combined melting/
casting furnace, which can be charged
with solid metal (via charging machines)
as well as with molten metal.
The furnace has a melting rate of 22 t/
h and a low energy consumption; the
bath surface area is approx. 64 m 2 and
is fitted with three pairs of regenerative
burners with a capacity of 5 MW
per pair (total capacity: 15 MW).
TECHNOLOGY
Fig. 3: A revamped melting and casting furnace which has a
melting rate of 22 t/h and a bath surface area of approx. 64 m 2
Furnace pressure control
and regulation system
To maintain proper heat transfer from
the hot burner gases to the charged
metal, it is important to keep such hot
gases inside the furnace chamber for
as long as possible before they escape
through the flue gas outlet. A slight
overpressure should therefore be
maintained inside the furnace chamber.
This necessitates the installation
of:
• a door system that seals properly
• good covers on all furnace open-
ings that are not in constant use
• a cover on the furnace pouring
spout.
A pressure regulation valve (gate or
butterfly type) should be installed in
the flue gas outlet of the furnace. This
valve, which can be actuated electrically
or pneumatically, regulates the
flow of the flue gases exiting the furnace
chamber. The valve should be
installed downstream of the first bend
in the flue gas pipe coming from the
furnace roof (see Fig. 4). The pressure
regulation unit shown here is control-
Fig. 4: A pressure regulation valve should be installed in the flue gas outlet of the furnace
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