DEVELOPING A TECHNOLOGY FOR PRODUCTION
OF BOTTOM BLOCKS WITH A LOW MODULUS OF ELASTICITY
I. V. Rybyanets,
L. N. Ruzhevskaya,
N. P. Nonishneva,
and S. A. Podkopaev
Translated from Novye Ogneupory, No. 11, pp. 16 – 17, November, 2004.
Original article submitted June 22, 2004.
The need for substantiated formulation of quality requirements for cathode blocks is emphasized. The ratio
of the bending strength to elasticity modulus is proposed as a criterion for evaluating the strength properties
of blocks. Techniques for improving this ratio in the production of carbon graphite materials are discussed.
The operational reliability of cathode blocks is deter-
mined by their physicomechanical properties which, in turn,
are specified by the corresponding technical documentation.
Over the past 5 years, requirements placed on cathodes
blocks have time and again been revised, which finally re-
sulted in a poorly substantiated and somewhat relaxed mar-
gin of performance. As shown by practice, formal confor-
mance with the specifications placed on cathode blocks is
not necessarily a guarantee of their reliable performance. The
strength properties of cathode blocks have been and continue
to be one of the most debatable and controversial issues.
In deciding on which of the strength characteristics is
most informative, the reasoning is usually based on the con
cept of the weakest link.
The strength characteristics of carbon graphite materials
are typically arranged in ascending order tension – bending –
compression, that is, the weakest link is tensile strength.
However, according to reported data , viewed technologi
cally, tensile strength is a less sensitive feature than bending
strength in the preparation of carbon graphite materials (for
example, in regard to the amount of pitch added). The low
sensitivity of tensile strength to central technological para
meters (such as porosity or specific electric resistance) may
be due to imperfectness of the method (diametral compres
sion) used for determining this strength characteristic. Thus,
the bending strength has been recognized to be the best infor
mative index for evaluating strength properties of cathode
blocks. A similar opinion was also voiced in  on the
grounds that this parameter gives a measure of the resistance
to buckling and shear stress.
A still fuller evaluation of the strength properties of
blocks is the ratio of the strength to the elasticity modulus
considering that this ratio characterizes the maximum per-
missible strain to failure of the material. Based on the previ-
ously reported data , it has been decided on taking the ra-
tio of the bending strength to the dynamic modulus of elas-
ticity as the best informative evaluation of maximum permis-
sible strain of graphite materials. The higher the ratio, the
higher the ability of a material to sustain loading conditions;
the ratio can be made higher either by increasing the bending
Refractories and Industrial Ceramics Vol. 46, No. 1, 2005
1083-4877/05/4601-0040 © 2005 Springer Science+Business Media, Inc.
Chelyabinsk Electrode Plant Joint-Stock Co., Chelyabinsk, Russia.
TABLE 1. Characteristics of Bottom Blocks Commercially
Available from the Chelyabinsk Electrode Plant JSC
Property PB40M PB38M
apparent 1.54 1.55
Total porosity, % 19
compressive 50.0 45.0
bending 14.0 12.5
Heat conductivity, W/(m × K)
Specific resistance, mW × m
TLEC (20 – 520°C), 10
Elastic modulus (on blocks), GPa 11 8
Ash content, % < 3.0
Elongation, % 0.5