MAKING DENSE FINE-GRAINED LARGE GRAPHITE BLOCKS
N. A. Lobastov
and A. N. Chernyavets
Translated from Novye Ogneupory, No. 3, pp. 140 – 142, March, 2008.
Original article submitted May 25, 2007.
Ways are considered of making large blocks of fine-grained graphite on the basis of fired coke. One method is
to press the hot mass immediately after mixing instead of making from this mass a press powder and
subsequently pressing it. Pressing the hot mass also reduces the pressing pressure. This eliminates laborious
and polluting operations: cooling the mass after mixing with subsequent crushing. Also, pressing the hot mass
immediately after mixing appreciably raises the yield of acceptable blanks after heat treatment (firing and
Strong graphites with perfect macrostructure are widely
used, and the demand for them increases every year,
particularly for blocks with large sizes. For example, there is
sometimes a need for fine-grained graphite for blocks of
diameter and height about 1000 mm with strength in
compression not less than 45 MPa, but at present the industry
is equipped for producing blocks of diameter not more than
320 mm. There are various reasons why it is difficult to
increase the sizes of the blocks, the main one being the lack
of research on the production of coke-pitch composites for
Fine-grained graphite blocks are usually made by
pressing powders under room conditions with elevated
contents of pitch as bonding agent, and at higher pressures
than are used in pressing hot masses of medium-grained
coke-pitch composites. This difference is determined by the
need to provide good consolidation on pressing and to obtain
a final graphite with a good level of physicomechanical and
working properties. However, there is a rise in the inverse
elastic aftereffect in the blocks as the residual stresses are
relaxed, and the stability of these blocks against damage is
reduced on pressing and heat treatment.
A radical way of obtaining dense fine-grained graphites
for large blocks is the shaping of fine-grained coke-pitch
compositions immediately after mixing, i.e., at elevated tem-
peratures. This does not require high pressures and there is
no need for the laborious and polluting operations such as
cooling the mass after mixing with subsequent crushing,
reduction to fine powder, and pressing.
We examined a coke-pitch composite based on fired coke
with an initial particle size less than 0.15 mm. The bonding
agent was medium-temperature hard-coal pitch. The content
of it varied widely: from 18 to 26 wt.%. Blocks of diameter
70 mm were pressed at 20 MPa. Table 1 gives the results.
Refractories and Industrial Ceramics Vol. 49, No. 2, 2008
1083-4877/08/4902-0126 © 2008 Springer Science+Business Media, Inc.
NIIgraphite Company, Russia.
TABLE 1. Effects of Binder Content on the Physicomechanical Properties of Coke-Pitch Composites
Composites with binder contents in wt.%
18 20 22 23 24 25 26 30*
after pressing 1540 1610 1670 1670 1700 1700 1710
after graphitization 1680 1700 1720 1700 1700 1700 1710
Compressive strength, MPa 46.0 52.0 52.5 49.7 52.0 46.0 50.0
Volume shrinkage, % 12.2 11.5 10.6 9.9 9.8 9.5 10.2
Mass loss in % on heat treatment 4.40 5.90 8.00 8.40 8.60 9.70 9.75
* Press powder composite. The first entry is for pressing at the pressure adopted under industrial conditions, and the second is under a pressure
analogous to the pressure in obtaining hot-pressed fine-grained materials.