FACTORS OF LARGE GRAPHITE CRUCIBLE LIFE
A. N. Chernyavets
and N. Yu. Beilina
Translated from Novye Ogneupory, No. 8, pp. 28 – 33, August 2008.
Original article submitted March 18, 2008.
Production methods used to prepare graphite crucibles with high operating properties are considered: use as a
filler of good graphitizing acicular coke, vibration molding of the original coke mix, use of production cycles
for impregnation with medium temperature coal-tar pitch - firing, firing of compacted billets in metal contain
ers, graphitization of fired billets in graphite cylinders. The last two production methods make it possible to
reduce the temperature drop throughout the volume of a billet during heat treatment, and as a consequence to
reduce crack development to a minimum as a result of reducing thermal stresses. All of the production meth
ods recommended may be entirely accomplished in existing electrode plants and may be used to increase
markedly the quality crucible graphite. It is possible to achieve a quality for these materials at the best world level.
In various branches of industry there is extensive use of
large (with a diameter of more than 500 mm) graphite cruci-
bles making possible in a considerable volume to melt metals
(uranium, copper), their alloys (bronze, brass, cupronickel),
quartz, optical glass, single crystals and other materials, and
therefore an increase in the quality and operating life of these
crucibles is an important task whose solution will make it
possible to reduce the level of scarce graphite billets re-
In performing production tests it has been established
that the operating life of crucibles depends on the heat resis
tance of the original graphite, its permeability for a melt and
the reaction resistance with respect to molten material.
It has been shown in [1, 2] that the heat resistance of
graphite increases considerably with an increase in the de
gree of its graphitization. According to the ideas of Kingery
 it is possible to present material heat resistance analyti
cally by the expression
R = sl/Ea, (1)
where R is Kingery heat resistance criterion; s is material ul
timate strength (in bending or tension); l is thermal conduc
tivity coefficient; E is dynamic elasticity modulus, a is linear
thermal expansion coefficient.
An increase in the degree of graphitizing (the
graphitizing temperature at the center of a core should be not
less than 2800°C) promotes an increase in heat resistance
from many points of view. First, with an increase in the de-
gree of graphitizing there is an increase in graphite thermal
conductivity, and this promotes a reduction in the tempera-
ture gradient over the height and diameter of a crucible, and
correspondingly a reduction in thermal stresses that arise.
Second, an increase in the degree of graphitizing provides a
reduction in the linear thermal expansion coefficient and
elasticity modulus, that also reduce thermal stresses in a cru-
cible. These factors promote an increase in the Kingery heat
resistance criterion. Third, an increase in the degree of
graphitizing leads to better reaction resistance of the wall
material and the bottom of a crucible towards molten mate
rial, that in the majority of cases is chemically aggressive to
wards graphite. Fourth, an increase in the degree of
graphitizing provides creation of a more complete material
structure and a reduction in Van der Waals forces that operate
between planes in the graphite crystal lattice. This in turn fa
cilitates growth of microcracks with a liberation of elastic
energy in a crucible stored under conditions of temperature
gradients. Microcrack growth makes it possible in an acci
dent-free regime to resolve the problem of energy release,
since with absence of this process energy release occurs in a
catastrophic regime: a crucible cracks, often separating into
two halves, and this leads to considerable problems in avoid
ing the consequences of such a situation, particularly in melt
ing radioactive metals.
In this respect an industrial experiment was performed at
the end of the 1980s. How in time it is possible to save a con
siderable amount of electrical energy by excluding the
graphitizing stage from production technology for graphite
Refractories and Industrial Ceramics Vol. 49, No. 5, 2008
1083-4877/08/4905-0343 © 2008 Springer Science+Business Media, Inc.
FGUP NIIgrafit, Moscow, Russia.