Carbonaceous refractory composition for pressing brick shapes

A more pressable composition for making graphitic refractory brick from oxide aggregate with a carbon bond is obtained when the refractory oxide aggregate is substantially all coarser than 0.15 mm (+100 mesh), preferably coarser than 0.2 mm (+65 mesh), and most preferably coarser than 0.4 mm (+35 mesh), and the matrix is entirely carbonaceous material, such as graphite, particularly flake graphite, resin, particularly a phenol formaldehyde resin, together with such other carbonaceous materials as carbon black, calcined coke, anthracite, and the like.

BACKGROUND OF THE INVENTION 
This invention pertains to carbonaceous refractory compositions, 
particularly such compositions suited for pressing into brick shape. 
It is known to form a refractory brick by pressing a composition of 
refractory aggregate (for example, refractory periclase grain) combined 
with a pitch bond which may also contain other carbonaceous materials, 
such as carbon black, graphite, and the like. In order to form a pressed 
brick which has adequate strength to be handled and shipped without 
slumping or breaking, it is customary to use a bonding pitch with a high 
(for example, 110.degree. C.) softening point. This means that the brick 
must be formed (pressed) with a hot aggregate/pitch mixture which, when it 
cools, hardens to form a strong, coherent brick. 
In recent years, for various reasons, for example, to avoid working with 
hot pitch mixtures, it has become the practice to use a synthetic resin, 
for example a phenol formaldehyde resin, as bond. These resins can be used 
in liquid form at room temperature to form the brick and are then set by 
heating at temperatures of, for example, 110.degree. to 300.degree. C. to 
form strong, hard, refractory shapes. 
These products are placed in service without firing at elevated 
temperatures, although they may be tempered at temperatures up to 
500.degree. C. and, in rare instances, coked at temperatures up to 
1000.degree. C. When placed in service in a furnace which is raised to an 
elevated temperature, the carbonaceous materials in the brick coke, 
forming a carbon bond. 
When a synthetic resin bond was substituted for the tar or pitch bond in 
refractories containing graphite, it was found that the substitution led 
to low density, high porosity, and lowered strength in the brick. In other 
words, the bonding of the grains by the matrix was generally poorer when 
the resin was substituted directly for the pitch in prior compositions. 
The present invention is directed to the solution of this problem. In other 
words, the present invention permits the forming of resin-bonded, 
graphite-containing refractory compositions into brick which have as high 
density and strength, and as low porosity, as the former tar or 
pitch-bonded refractories containing graphite. In addition, the invention 
has further application in that it also improves the properties of 
graphitic refractory brick bonded with a natural resin, such as coal tar 
pitch. 
SUMMARY OF THE INVENTION 
The foregoing problem is solved by using a carbonaceous refractory 
composition for pressing brick shapes consisting essentially of (1) from 
60 to 90% refractory oxide aggregate, substantially all of which is 
coarser than 0.15 mm (+100 mesh), and (2) a carbonaceous matrix of from 2% 
to 30% graphite, substantially all finer than 0.4 mm (-35 mesh), 2% to 8% 
resin and from 0% to 6% other carbon material, said matrix being 
substantially free of oxide refractory material, all percentages being by 
weight and based on the total weight of the composition. 
DETAILED DESCRIPTION 
The refractory aggregate used in practicing the invention may be any such 
known material, for example, tabular alumina, calcined flint clay, and the 
like. However, the invention is most useful with periclase refractory 
aggregate. A particularly preferred aggregate is periclase containing at 
least 95% MgO. 
In general, the aggregate will be sized according to wellknown principles 
to obtain maximum packing and density. However, in the practice of the 
invention, the sizing of the aggregate is different from that of 
conventional oxide refractories. In conventional refractories, the sizing 
of the aggregate ranges from a top size of, for example, 4.7 or 6.7 mm (-4 
or -3 mesh) down to material finer than 44 microns (-325 mesh), the 
so-called sub-sieve size material or ball mill fines. This material finer 
than 44 microns can be as much as 15 or 20% of the total weight of the 
refractory aggregates in conventional compositions. 
In the present invention, on the other hand, the oxide refractory aggregate 
is all coarser than 0.15 mm (100 mesh), and preferably is coarser than 0.2 
mm (65 mesh), and most preferably contains no material smaller than 0.4 mm 
(35 mesh). It is the discovery of this invention that when the oxide 
refractory aggregate is confined to these coarser sizes, and the matrix 
material consists entirely of carbonaceous material, that the problems 
originally encountered in substituting the synthetic resin bond for the 
pitch bond, the decreased density and strength, are overcome. 
The resin may be any such material, but is preferably a synthetic resin 
which is initially liquid, and remains so during the forming process, but 
which subsequently sets up, either at ambient temperature or under the 
application of limited heat, for example, temperatures up to 110.degree. 
to 300.degree. C. A particularly preferred form of resin is one of the 
phenol formaldehyde resins. These are described in detail in the article 
on "Phenolic Resins" in Mark-Gaylord's Encyclopedia of Polymer Science and 
Technology. 
While the present invention is particularly useful with synthetic resins, 
such as the phenolic resins, it can also be used with "natural" resins, 
such as coal tar pitch, and the term "resin," as used in the specification 
and claims, is intended to include such materials. 
The graphite used may be any such material, preferably of high purity, 
i.e., less than 10% ash, and most preferably is of the type known as 
"flake graphite". 
The matrix of the brick of this invention can contain other carbonaceous 
material, for example, carbon black, such as thermal black or furnace 
black, ground anthracite, ground coke, and the like. 
Refractory shapes are made from the composition of the present invention by 
mixing the various ingredients, for example in an Eirich of Muller mixer, 
pressing the composition into brick shape, for example on a mechanical 
press, at a pressure of up to 1400 kg/cm.sup.2 (20,000 psi). The brick so 
formed are allowed to harden or they may be subjected to gentle heating, 
for example, to a temperature of 180.degree. C., to hasten the setting of 
the resin bond. The brick are then shipped to the user who places them in 
a furnace structure, for example a basic oxygen furnace. The use of this 
invention is particularly advantageous when using a mechanical or toggle 
press, on which it has proven very difficult to press graphite-containing 
brick.

EXAMPLES 
Table I sets forth various compositions, some of which are within the scope 
of this invention. Specifically, Compositions 3, 4, 6, 7, 8, and 9 are 
within the scope of the invention, the other compositions being comparison 
composition. 
The aggregate used in the examples is a periclase having the following 
typical chemical composition: 2.3% CaO, 0.8% SiO.sub.2, 0.2% Al.sub.2 
O.sub.3, 0.2% Fe.sub.2 O.sub.3, 0.03% B.sub.2 O.sub.3, and, by difference, 
96.5% MgO. In Table I, the percentage amounts for the different grain 
sizes are based on the total weight of grain whereas the amounts of the 
other ingredients are based on parts by weight. 
The graphites used were flake graphites manufactured by Asbury Graphite 
Mills, Inc., the various numbers indicated in Table I being grade 
designations applied by the manufacturer. Typically, the graphite has an 
ash content of 8%, the remainder being carbon. The carbon blacks are 
thermal blacks, the NS grade being manufactured by Cabot Corp. and the MT 
being manufactured by R. T. Vanderbilt. Typically, these are aggregates of 
roughly spherical particles with carbon contents greater than 97%, 
produced by the thermal decomposition of oil or natural gas. 
TABLE I 
__________________________________________________________________________ 
Composition 1 2 3 4 5 6 7 8 9 
__________________________________________________________________________ 
Aggregate 
amount 84.3 
84.5 
84.5 
84.5 
78.8 
78.8 
78.0 
78.0 
65.9 
% 0.4 mm 31.8 
21.1 
0 0 30.1 
0 4.0 
0 4.0 
% 0.2 mm 28.4 
18.3 
0 0 28.8 
0 0 0 0 
% 0.15 mm 26.7 
13.6 
0 0 26.9 
0 0 0 0 
% 44 17.0 
-- 0 0 17.2 
0 0 0 0 
Graphite 
type 3221 
3166A 
3166A 
3166A 
3166A 
3166A 
3166A 
3166A 
3166A 
amount 7.5 
9.6 
9.6 
9.6 
12.4 
12.4 
16.0 
16.0 
28.1 
Carbon Black 
type NS MT MT MT NS NS MT MT MT 
amount 2.4 
2.9 
2.9 
2.9 
2.7 
2.7 
2.9 
2.9 
2.9 
Bond 
type pitch 
phenol 
phenol 
phenol 
pitch 
pitch 
phenol 
phenol 
phenol 
amount 5.3 
3.0 
3.0 
3.0 
5.6 
5.6 
3.1 
3.1 
3.1 
Sulfur - amount 
0.5 
0 0 0 0.5 
0.5 
0 0 0 
Bulk Density 
184.4 
180.9 
183.2 
184.0 
176.1 
178.1 
176.9 
178.3 
162.4 
CMOR 1800 
812 1524 
1416 
1462 
1443 
1706 
1595 
942 
App. Porosity 
9.6 
12.6 
10.3 
11.0 
11.0 
10.3 
11.4 
10.9 
14.2 
Sonic Velocity 
L -- 11.6 
-- 14.1 
14.0 
14.8 
-- 13.3 
3.5 
W -- 8.1 
-- 13.3 
13.8 
14.8 
-- 12.7 
9.0 
T -- 9.0 
-- 10.8 
5.2 
9.0 
-- 7.6 
5.7 
Residual Carbon (wt %) 
12.5 
13.3 
13.4 
13.4 
18.4 
18.4 
19.1 
19.0 
31.3 
__________________________________________________________________________ 
As to the bonding materials, the pitch used was a 116.degree. C. softening 
point (cube-in-air equivalent) coal tar pitch, and the resin was a phenol 
formaldehyde liquid bonding resin sold by the Borden Chemical Company 
under the name "Durite". It has a viscosity at 77.degree. F. (25.degree. 
C.) of from 250 to 350 cps, and a gel time at 121.degree. C. of from 32 to 
40 minutes. The sulfur added in the case of the pitch bond was flowers of 
sulfur, a very finely divided form of sulfur. 
In Table I, bulk density is given in pounds per cubic foot, measured as the 
brick came off the press; cold modulus of rupture (CMOR) is given in 
pounds per square inch and measured after curing; apparent porosity is in 
volume percent, measured after coking; sonic velocity is in feet per 
second, measured along the length (L), width (W) and thickness (T) of the 
cured brick. 
Composition 1 is a comparison composition which is typical of prior art tar 
bonded periclase refractory brick. As can be seen, it contains a 
substantial amount (17%) of material finer than 44 microns (-325 mesh). 
Composition 2 is another comparison example, and shows that the direct 
substitution of a synthetic resin bond for the pitch bond leads to greatly 
reduced densities and strengths, even though the amount of material under 
44 microns is considerably less than in Composition 1. 
The foregoing compositions are to be compared with Compositions 3 and 4, 
made according to the present invention. As can be seen from Table I, all 
the periclase aggregate finer than 0.4 mm has been eliminated from these 
compositions. This change resulted in brick of increased density compared 
to Composition 2, a density quite similar to that of brick made from 
Composition 1. The difference between Compositions 3 and 4 is in the 
maximum size of the periclase aggregate, Composition 3 containing 
aggregate all of which was smaller than 4.7 mm, and Composition 4 
containing aggregate as large as 10 mm. 
The sonic velocity shown in Table I for several of the compositions is an 
indication of the tightness or strength of bonding together of the 
aggregate particles, higher sonic velocity indicating better bonding. As 
can be seen, the sonic velocity in Composition 4 is significantly greater 
than that of Composition 2. 
Composition 6 is a pitch-bonded brick with the sizing of the present 
invention, and shows, by comparison with Composition 5, the resulting 
improvement in properties. 
Compositions 7, 8, and 9 are also within the scope of the present 
invention, Compositions 7 and 8 having sufficient carbonaceous material to 
result in a residual carbon content of about 19%, whereas that of 
Composition 9 is about 30%. 
The residual carbon content of all these brick is determined by taking the 
brick, packing them in carbon granules in a closed container, heating to a 
temperature of 970.degree. C. for 3 hours to coke them, and then, after 
cooling, weighing the coked brick. The specimen is then ignited to burn 
off all the carbon and again weighed, the difference in the two weights 
indicating the amount of residual carbon in the coked brick. 
The brick whose properties are shown in Table I were made by mixing the 
indicated ingredients for 7 or 8 minutes in a Muller or Eirich mixer, 
depending on whether the bond was resin or pitch, and pressing the 
resulting mixture in a Boyd X press at a pressure of 5000 to 20,000 psi 
(350 to 1400 kg/cm.sup.2), depending on composition. 
From the foregoing examples, it can be seen that exclusion of the 
refractory oxide aggregate finer than 0.2 mm, and preferably excluding 
that finer than 0.4 mm, results in higher density for a resin-bonded 
product, as compared to the same composition containing oxide refractory 
material in the finer, or matrix, portion. 
In addition to the improvement in quantitatively measurable properties, 
petrographic examination of the compositions of the present invention 
shows them to have better bond continuity and particle compaction than 
compositions with fine oxide particles. Also, in pressing, it was very 
difficult, if not impossible, to get crack-free brick with the 
compositions containing fine oxide material, whereas the compositions 
according to this invention pressed very well, without cracking. 
In the specification and claims, percentages and parts are by weight unless 
otherwise indicated, except that porosities are expressed in volume 
percent. Mesh sizes referred to herein are Tyler standard screen sizes 
which are defined in Chemical Engineers' Handbook, John H. Perry, 
Editor-in-Chief, Third Edition, 1950, published by McGraw Hill Book 
Company, at page 963. For example, a 100 mesh screen opening corresponds 
to 147 microns, and 325 mesh to 44 microns. Analyses of mineral components 
are reported in the usual manner, expressed as simple oxides, e.g. MgO and 
SiO.sub.2, although the components may actually be present in various 
combinations, e.g. as a magnesium silicate.