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ALUMINIUM SMELTING INDUSTRY
Advanced technology from Brochot –
A proven solution for anode slot cutting
P. Dunabin, Brochot
The French-based company Brochot is a
well-established supplier of production
process equipment to the non-ferrous
metals industry. The company is represented
on a worldwide basis with offices
in Canada, China, Russia and the Middle-East
and with three workshops in
Quebec, France and China. The company’s
portfolio is extensive and increasing,
in particular with the addition of recent
equipment supply to the copper and
zinc industries by the Brochot Hydromet
division. However, Brochot’s principal
activity remains the design, development,
manufacturing and supply of equipment
for the primary aluminium sector. In this
sector the company is well known for the
supply of individual machines as well as
for complete turnkey projects for anode
rodding shops and anode handling installations.
A recent successful installation is an anode
slot cutting machine at the Nalco plant in Angul,
India. This machine is part of Brochot’s
on-going development of anode slot cutting
concept which seeks to improve and adapt
the design to the varying criteria of individual
smelter sites. Brochot continues to invest in
development of new and revised designs for
its slot cutting machine, and future orders will
incorporate a number of improvements to improve
cycle times and to adapt to client slotting
requirements.
Advantages of slotted anodes
The use of slotted anodes is now well established
in aluminium smelter potlines. The slotting
of anodes is known to give improvements
in pot efficiency by reducing the formation of
bubble films (which create higher electrical
resistance), by reducing anode cracking and
by allowing increased pot currents. The cost
of aluminium production depends critically on
the cost of energy used in the reduction process,
and so efficiency gains from slotted anodes
have a direct cost benefit.
Studies have shown that the gases (mostly
carbon dioxide and carbon monoxide) generated
by the reduction process form mainly on
the underside of the anode block, where they
build up of a layer of gas which increases the
Brochot anode slot cutting machine during workshop testing
cell resistance. The distance and time for a gas
bubble to escape from the underside of the
anode are determining factors of the thickness
of the bubble layer: basically, the shorter the
escape distance the lower will be the extra
resistance created by the gas layer. As anode
sizes grow, so the problem of the gas layer increases.
Thus the slots in the anode, for as long
as they exist, stimulate the shorter escape path
for gas bubbles formed on the underside of a
smaller anode.
Slot configurations
Anode slotting arrangements have existed
in two configurations – lengthwise slots and
transverse slots. These slots can be formed
in two ways: either by moulding during the
formation of green anodes, or by machining
the slots in baked anodes. It is accepted that
the longitudinal slot configuration delivers the
greatest benefit, and the Brochot slot cutting
machine produces slots in this direction.
The use of moulded slots has a number of
disadvantages compared to machined slots.
Slot forming plates introduced in green anode
moulds can affect the paste distribution and
compaction around the slots. The slots are
wider than machined slots, and they can become
clogged with packing coke at the anode
baking stage. The wider slots also reduce the
overall mass of carbon, consequently reducing
the life of an anode. Slots make the green
anodes more fragile and so increase rejection
rates during the green anode forming, cooling
and transportation stages. These problems are
exacerbated with increases in the slot depth,
although deeper slots would be potentially
useful to maintain their function through a
greater part of the anode life.
Machine installation and construction
The Brochot slot cutting machine is intended
to be used as an integral part of the anode handling
system. The machine is integrated into
the anode conveying lines, receiving anodes
from the baked anode storage areas, and cutting
the slots in them before they proceed to
the anode rodding shop. At Nalco the Brochot
machine was integrated as a retrofit into the
existing conveyor line just before feeding the
anode rodding station. The machine installation
was adapted to the existing slope of the
conveyor, and the design also allows the possibility
of configuring it for a ‘pass through’
process without slotting. Space restrictions in
this plant do not allow the use of a separate
by-pass conveyor.
The basic elements of the machine are: a
© Brochot
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