RESISTANCE OF REFRACTORY LINING MATERIALS
OF HIGH-POWER ALUMINUM ELECTROLYTIC FURNACES
V. Yu. Bazhin
Translated from Novye Ogneupory,No.2,pp.3–4,February, 2010.
Original article submitted September 23, 2010.
The problem of the service life of cathodic devices used in high-power aluminum electrolytic furnaces (more
than 300 kA), a problem that is closely related to the quality and resistance of refractory materials, is dis
cussed. Factors responsible for the destruction of the graphite hearth and refractory heat-insulating layers are
Keywords: aluminum electrolytic furnace, graphite blocks, hearth welds, sodium expansions, overhauling.
The demand for nonferrous metals has dropped sharply
in connection with the unfavorable financial and economic
situation, and this has led to a reduction in the volumes of
production and resulted in a more than two-fold drop in the
price for aluminum. In order to solve economic problems,
many aluminum firms have begun to reduce production on
unprofitable equipment in order to significantly reduce pro-
duction costs. Thus, questions have arisen related to increas-
ing the operating life of electrolytic furnaces.
The service life of a cathodic device, the basic compo-
nent of an aluminum electrolytic furnace, is determined by
the capacity of the graphic hearth and side lining, as well as
the refractory base to maximally preserve its properties in the
coruse of a particular period of time. A service life of up to
2000 days has been established for high-power aluminum
electrolytic furnaces (strength of current over 300 kA).
As a result of abrasive and chemical actions, wear of the
graphite hearth amounts to 1.5 – 2.2 cm per year. Abrasive
wear in the course of the entire service life is related to clear
ing of the hearth from cryolite-alumina deposits during the
anode change operation, while chemical wear occurs due to
the action of reverse reactions related to the interaction of
aluminum and carbon.
The graphic hearth of an electrolytic furnace is saturated
with sodium throughout its entire operational life. Adsorp
tion of sodium promotes infiltration of sodium into the car
bon lining, inducing disordering of the carbon. The strength
and elastic properties of the hearth blocks, which have indi
cators of volumetric expansion caused by sodium infiltration
0.35 – 0.65%, vary markedly depending on the rate at which
carbon is added to the refractory. The degree of expansion
depends on the quality of the hearth blocks and the content of
graphite in the blocks. Graphite possesses the lowest suscep-
tibility to sodium. In stable operation of the carbon hearth of
a serial electrolytic furnace, sodium expansion amounts to
0.8 – 1.2% following 24 months of operation, and 0.18 – 0.29%
for a cathodic device with graphitized hearth blocks .
In order to realize a lengthy service life for a cathodic de-
vice, it is necessary to create a reliable lining that must be
able to resist seepage, erosion into melts, and infiltration. By
the quality of the graphite hearth blocks is usually under
stood high mechanical characteristics and resistance to the
action of sodium-containing compounds.
The factors responsible for the destruction of lining may
include horizontal delamination, cracks in the walls of the
side blocks, and deformation of the jacket, all of which are
related to thermal expansion of the blocks. Due to the signifi
cant tensile stresses in the course of operation, the dimen
sions of the graphite blocks, particularly their length (7 – 8 mm),
vary while the transverse seams exhibit shrinkage of up to 12
mm . Expansion of the cathodic lining may be reduced
through application of a high degree of graphitization and
application of a coating of TiB
, though this leads to a direct
increase in the cost of overhauling.
A large quantity of micro-cracks is formed on the surface
of the blocks and in peripheral and inter-block seams at the
stage of roasting and start-up of an electrolytic furnace. In
the transverse seams between the hearth blocks, shrinkage of
the hearth mass in the horizontal plane is completely com
Refractories and Industrial Ceramics Vol. 51, No. 1, 2010
1083-4877/10/5101-0004 © 2010 Springer Science+Business Media, Inc.
RUSAL VAMI, St. Petersburg, Russia.