Note: Descriptions are shown in the official language in which they were submitted.
~ Case 649~
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CARBONACEOUS ~EFRACTORY COMPOSITION FOR PRESSING
BRI~K SHAPES
Back~round of the Invention
Fhis invention pertains to carbonaceous refractory
compositions, particularly such compositions suited for press-
ing 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 2S carbon black,
graphite, and the like. In order to for~ a pressed brick
which has adequate ~tren8th to be handled and shipped without
10 slumping or breaking, it is customary to use a bonding pitch
with a high (for example, 110C) 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
20 then set by heating at temperatures of, for example, 110 to
300C to form strong, hard, refractory shapes.
These products are placed in service without fir-
ing at elevated temperatures, although they may be tempered
at temperatures up to 500C and, in rare instances, coked at
25 temperatures up to 1000C. 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 synthe~ic resin bond was substitu~ed for
30 the tar or pitch bond in refractories con~aining graphite,
it was found that the substitution led to low density, high
porosity, and lowered streng~h in the brick. In other
words, the bonding of the gr~ins by the matrix was generally
~2
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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, ~he present invention
permits the forming of resin-bond~od, graphite-containing
refractory compositions into brick which have as high
density and strength, and as low porosity, as the former
tar or pitch-bonded refractorie 5 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.
Swmmary of the Invention
The foregoing problem is solved by using a carbon
aceous refractory composition for pressing brick shapes
consisting essentially o (1) from 60 to 90% refractory
oxide aggregate, substantially all of which is coarser than
O. 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 materi~l, all percen~ages 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 alwmina, calcined 1int clay, and the like. However,
the invention is most useful with periclase refractory ag
gregate. A particularly preferred aggregate is periclase
containing at least 95% MgO.
In general~ the aggrega~e will be sized according
to wellknown principles to o`btain m~;ml1m packing and dens-
ity. However, in the practîce of ~he invention, ~he sizing
of the aggregate is different from ~hat of conventional
oxide re~ractories. In conven~ional refractories, the siz-
ing 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 si~e
material or ball mill fines. This material finer than 44
microns can be as much as 15 or 20% of the total weight OL
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
10 (35 mesh). It is the discovery of this invention that when
the oxide refrac~ory aggregate is confined to these coarser
æizes, and the matrix material consists entirely o carbon-
aceous material, that the problems originally encountered
in substituting the synthetic resin bond for the pitch bond,
15 the decreased density and strength, are overcome.
The resin may be any such material, but is prefer-
ably 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
20 of limi~ed heat, for example, temperatures up to 110 to
300C. A particularly preferred form o 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 Technolo~y.
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 ~ar pitch,
and the term "resin," as used in the specification and
claims, is intended to include such materials.
The graphite use~ may be any such material, pre-
ferably of high purity9 i.e., less than 10% ash, and most
preferably is of the type known as "flake graphite".
The matrix of ~he brick of this invention can con-
tain other carbonaceous material, ~or example, carbon black,
35 such as thermal black or furnace black, ground an~hraci~e,
gro~md coke, and ~he like.
Refractory shapes are made from the composition of
the present invention by mixing ~he various ingredients, for
example in an Eirich or Muller mixer, pressing the compo-
5 sition into brick shape, for exam~le on a mechanical press,at a pressure o up to 1400 kg/cm (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 180C, to
hasten the set~ing o~ the resin bond. The brick are then
10 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 mechan-
ical or toggle press, on which it has proven very difficult
to press graphi~e-containing brick.
Examples
Tab~e I sets forth various compositions, some of
which are within ~he scope of this invention. Specifically,
Composi~ions 3, 4, 6, 7, 8, and 9 ~re within the scope of
the invention, the other compositions being comparison compo-
20 sitions.
The aggregate used in the examples is a periclasehaving the following typical chemical compositiono 2.3% CaO,
0.8% SiO2, 0 2% Al2O39 0.2% Fe2O3, 0-03% B2O3~ and, by
difference, 96.5% MgO. In Table I, the percentage amounts
25 for the different grain sizes are based on the total weight
of grain whereas the amounts of ~he other ingredients are
based on parts by weight.
The graphites used were flake graphites manufac-
tured by Asbury Graphite Mills, Inc., the various numbers
30 indicated in Table I being grade designa~ions applied by the
manufacturer. Typically, the graphi~e has an ash content of
8%, the rem~inder being carbon. The carbon blacks are
thermal blacks, the NS grade being manuactured by Cabot
Corp. and ~he MT being manufactured by R. T. Vanderbilt.
35 Typically, these are aggregates of roughly spherical part
icles with earbon eQntentS greater than 97%, produced by
the thermal decomposition of oil or natural g~5.
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--5--
As to the bonding material~ the pitch used was a
116C softening point (cube-in-air equlvalent) coal tar
pltch, and the res~n wa~ a phenol formaldehyde liquld bond~
ing resin sold by t~e Borden ~hemical Company under the
name "Durite". It ha~ a viscosity ~t 77~F (25C~ o from
250 to 350 Cp8, and a gel time at 121C o from 32 to 40
minute~. The sulfur added ln the case of the pitch bond
was flower~ of sulfur, a very finely divlded fonm of ~ulfur.
In Table I, bulk density i~ giYen ln pounds per
10 cubic foot3 measured a~ the brick came off the press; cold
modu~ U5 of rupture (CMOR~ is given in pounds per square
inch and measured after c~r~ng; apparent porosity is in
volume percent, measured ater coklng; sonic veloclty is in
feet per second~ measured along the length (L~ width ~W~
15 and thickness (T) o the cured brick~
Compositio~ 1 is a comparison composition which
is typical of prior art tar bondzd periclase reractory
brick. As can be seen, ~t conta~ns a substantial amount
(17%3 of material finer than 44 microns ~-325 mesh).
20 Composition 2 i9 another comparison example~ and shows ~ha~
the direct subst~tution of a synthetic resin bond for the
pitch bond lesds to grPatly reduced densities and strengths~
even thou~h the amount of material under 44 micron~ ~s
considerably le~s tha~ in Composition lo
The foregoing compositions are to be com~ared with
Compo~itions 3 and 49 made a~cording to the presen~
invention. A~ can he seen from Table I~ all the periclase
aggregate finer than 0~4 mm ha~ been ell~n~ed from these
compositionsO This change resulted i~ brlck of increased
30 density compared to Compositio~ 29 a densl~y ~ui~e s~m~l~r
to that o brick made from Compositio~ 1. The difference
be~ween Compositlon~ 3 and 4 is in the max~m~m size of the
periclase aggregateg Composi~i.on 3 contalning ~ggregat~ all
of which wa~ sm~ller than 4.~ mm, and Compositioa 4 con
35 taining aggregate as large aq 10 mm~
~ "r;'~
* Trade Mark
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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 veloci~y 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 3 are also wi~hin 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
~ 970C for 3 hours to coke them, and then, after cooling,
- weighing the coked brick. The specimen is then ignited to
20 burn off all the carbon and again weighed, the difference
in the two weights indicating the amount of residual carbon
in the coked brickA
-~ The brick whose properties are shown in Table I
were made by m;~;rlg the indicated ingredients for 7 or 8
25 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/cm2), depending on composition.
From the foregoing examples, it can be seen that
30 e~clusion 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 composi~ion co~taining ox~de refractory
material in the finer, or ma~rix~ portionO
In addi~ion ~o the improvement in quanti~atively
~ 6
-7-
measurable properties, petrographic examination of the
compositions of the presen~ invention shows them to have
better bond continuity and particle compaction ~han compo-
si~ions 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
10 parts are by weight unless otherwise indica~ed, except that
porosities are expressed in volurne 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
15 Hill Book Company, at page 963. For example, a 100 mesh
screen opening corresponds to 147 microns, and 325 mesh to
44 microns. Ar~alyses of mineral components are reported in
the usual manner, expressed as simple oxides, e.g. MgO and
SiO2, although the components may actually be present in
20 various combinations, e.g. as a magnesium silicate.
