Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
112~
BACKGROUND OF THE INVENTION
1. Field of the invention.
Thc invention relates to an improvement in alumin-
ous refractory compositions containing carbon and silicon,
the tcrm carboll including ~morphous carbon and graphite.
2. Description of the Prior Art.
The excellent ability of aluminous r~fractories
containinO carbon to withstand erosion by molten iron and
slag is well Icnown and such materials arc con~lonly used to
advantage in iron-ulakin~ oundry and blast furnace facilities,
particularly in tap hol.e and iron and slag spou.t ar~as.
The usual. carbon refractory materials exhibit tlle
disadvantage of rapid o~idation at temperatures above 900 F
limiting theLr working life. Patents 3,810,768; 3,8;~6,14i~;
3,842,760 and 3,923,531, in which applicant is one of the in-
ventors, disclose the combination of powdered silicon me~aLwith carbon along with aluminous refrac~ory material to in-
hibit G~idation and improve mechanical properti.es. Tbese
carbon refractories also exhibit slag resistance, but their
slag resistance is limited by the fact that increasing the
carbon content increases oxidation so that there is a prac-
tical limit to t'ne amount of carbon that may be used in the
composition, generally less than 50% and usually not sub-
stantially higher than 35% by weight.
High alumina-chromic oxide compositions are dis-
closed in Manigault U.S. Patents 3,888,687 and 3,948,670.
These compositions do not contain carbon in the form of
graphite or otherwise. There is no disclosure of the value
10 of chromic oxide in increasing slag resistance and it is
believed that such compositions without carbon are relatively
ineffective in improving resistance against contact with
basic slag compounds.
It is an object of my invention to obtain improved
slag resistance without excessige high carbon content in
aluminous-carbon refractory compositions.
SUMMAR~ OF THE INVENTION
I have found that the addition of chromic oxide to
an aluminous refractory composition containing carbon and
20 silicon is more advantageous in resisting molten iron and
slags, especially basic slags, than refractories based on
carbon or chrome additions not combined. The improvement is
essentially in having the chromic oxide and carbon present in
the aluminous composition in amount to give greater resistance
to slag over that of aluminous compositions in which the
--2--
chromic oxide and carbon are absent. The improvement is es-
pecially important in compositions containing up to about 35%
carbon.
The composition may contain as low as 10% of alumina
or aluminum silicate, but preferably an alumina or clay aggre-
gate is used containing a minimum of 40% alumina or aluminum
silicate. A~ounts of alumina or aluminum silicate up to 75%
and even higher may be used depending upon the amount of carbon,
chrome oxide, silicon metal and other ingredients present.
The chrome oxide may be present in 5-30% by weight,
the carbon in 5-35% and the silicon metal in 5-25% or in
amount sufficient to substantially inhibit oxidation of the
carbon.
Compositions containing more than 35% by weight of
carbon are of good slag resistance without the addition of
chromic oxide although some slight improvement exists by the
addition of chromic oxide at above 35% carbon such as, even
as high as 50-75% carbon. However, such high carbon composi-
tions do not have~ the strength of lower carbon compositions
20 so that this invention of using not more than 35% carbon, such
as 5-35% carbon with 5-30% chromic oxide, has the advantage of
high strength with the same or better slag resistance of the
high carbon compositions.
The compositions are therefore essentially comprised
of alumina or aluminum silicate, carbon, chromium oxide and
silicon metal.
~%~
The materials are mixed ~or use in the form of par-
ticles which may vary from fines to coarse particles. A mix-
ture of coarse particles or grains is referred to herein as an
aggregate, for example an alumina aggregate.
Binders such as a plastic clay, coal tar pitch,
phosphoric acid and the like are preferably present in the
mix or may be added later. Where the original mixture con~
tains aluminous material in the form of a plastic aluminum
silicate clay with or without calcined clay, this plastic clay
10 may serve both as the aluminous material and the binder.
The aggregate aluminous grains can be selected for
a wide choice of materials including calcined clays, calcined
bauxites, fused or tabular aluminas, i.e., aluminum silicates
to pure aluminum oxides. The aggregate component can be of
1/2 inch siæe maximum graded to finer sizes. Preferably max-
imum grain sizing is 3/8 inch by downs with 75% of the aggre-
gate coarser than 20 mesh and at ].east 90% over 100 mesh.
The coarsest grain size can be as fine as 1/16 inch, but thi.s
will not be as protective of the carbon component as aggre-
20 gate in the 1/4 to 3/8 inch range.
The carbon content may be in the form of amorphous
carbon or natural or synthetic graphite. Grain sizing may
start as coarse as 1/~ inch by downs or coarser, but the bulk
of it is preferably -30 mesh.
~ he chromic oxide is preferably present as the ses-
quioxide (Cr203)-and -is preferably of the pigment grade for
4~3~
maximum effectiveness, that is, essentially sub-micron. How-
ever, even coarser sizing has effectiveness, as for example,
100 mesh and coarser.
Silicon metal powder is added as an oxidation in-
hibitor for the graphite and suitably may be -20 mesh, pref-
erably finer.
Also, there may be included in the composition clays
useful for workability, green binders for prefired strength,
coal tar pitch for reduced penetrability and increased carbon
10 content. High alumina fines produce the most advantageous
matrix, having at least 60% alumina content and grain sizing
or -200 mesh, preferably -325 mesh. Further additions such as
for extending shelf life of chemical bonded formulations or
wetting agents are not precluded by suggested compositional
ranges.
The refractory products made according to this des-
cription may be in the form of ramming plastics, pressed
shapes, drier granular ramming mixes, castables, gunning
mixes, hand patching plastics, and vibration placement mixes.
The method of application determines grain sizing,
water content, and type and amount of clay addition.
Our preferred range of formulation can be summar-
ized as follows (dry basis):
% by weight
Alumina or aluminum silicate aggregate 20-52
High alumina fines, -200 mesh 0-12
Carbon or graphite 5-35
Silicon metal powder 5-25
Chromic oxide 5-30
Fine plastic clays 0-15
Coal tar pitch 0-10
Green binders (lignosulfonates or aluminum sulfate) 0-7
High alumina cement 0-25
10 Phosphoric acid or aluminum phosphate 0-8
Water would be added in most cases, varying from
about 12% for patching mixes, 10% for plastics, 5% for gra~u-
lar ramming mixes, 3% for prewetted gun mixes to dry for cast-
ables.
DET~ILED DESCRIPTION AND PREFERRED EMBODIMENTS
The following examples are provided to show a range
of products intended by this invention.
EXAMPLE 1
A ramming plastic formulation was prepared as follows:
% by wei~ht
Calcined bauxite (1/4" by downs) 47
-325 mesh calcined alumina 9
-30 mesh Mexican graphite 12
Pelletized coal tar pitch 5
Plastic ball clay 2
Western bentonite 6
Silicon metal powder 8
Chromi-~m oxide 8
Aluminum sulfate 3
1~2~9~1
Water was added to give a final moisture content of 10%.
This product has been manufactured by extrusion and slicing,
placed into cartons, and has performed remarkably well against
foundry slags over a wide variety of basicities.
EXAMPLE 2
A granular ramming mix was prepared as follows:
% by weight
Calcined bauxite (1/4" by downs)51
-325 mesh calcined alumina 8
Mexican graphite (1/4" by downs)11
Plastic ball clay 8-1/2
Silicon metal powder 6-1/2
Chromium oxide 8-1/2
Phosphoric acid (75%) 6-1/2
Water was added to give a final moisture level of 6%. An ad-
dition of approximately 0.25% of citric acid can provide ex-
tended working life, particularly in warm environments.
EXAMPLE 3
A gunning mix was formulated as follows:
% by wei~ht
Calcined bauxite (1/4" by downs)54
Chromium oxide 8-1/2
Silicon metal powder 6
Calcium aluminate cement (~70% A1203) 8-1/2
Mexican graphite ~1/4" by downs)12-1/2
Western bentonite 2
- - -100 mesh kyanite 8-1/2
--7--
~4~1
This material is bagged dry, but can be prewetted with 3%
water addition just prior to gunning.
EXAMPLE 4
A product formulated for placement by vibration in a
form, which can then be stripped for heating the lining so
that it can soon be placed in service, is the following:
% by wei~ht
Calcined bauxite (1/4" by downs)38.8
-325 mesh calcined alumina 7.8
Graphite (1/4" by 30 mesh) 9.7
Graphite (-30 mesh) 9.7
-35 mesh kyanite 7.8
Powdered silicon metal 9.7
Pelleti~ed coal tar pitch 5.8
Chromic oxide 7.8
Lignosulfonate water suspension 2.9
This material can be used at total water levels of 4-1/2 - 6%,
providing a trade-off on ease of vibration vs. tendency to
slump on removal of forms.
EXAMPLE 5
Effective economical formulations are based on useage
of calcined refractory clay aggregates, such as are available
commercially from sources in Missouri and Georgia with alumina
contents ranging from 40-70%. A formulation of a ramming mix
using calcined clay aggregate of 40-47% alumina is as follows:
~.Z94~l
V/o by wei~ht
Calcined clay aggregate (1/4" by downs) 50.5
-325 mesh calcined alumina 6.Q
-30 mesh natural graphite 12.0
Pelletized coal tar pitch 4.5
Plastic ball clay 4.5
Western bentonite 3.0
Silicon metal powder 7.5
Chromium oxide 9.0
Aluminum sulfate 3.0
Water is added to give a moisture in the 6-7% range. This
material can be boxed as a granular product.
EXAMPLE 6
Increased resistance to slag pepetration is achieved by
increasing carbon and chrome oxide contents, as well as in-
creased silicon metal content to protect the carbon, as in the
following formulation:
% by wei~ht
Calcined clay aggregate (1/8" by downs) 20
-30 mesh natural graphite 17
Pelletized coal tar pitch 5
Fine plastic clays 12
Silicon metal powder 23
Chromium oxide 23
Water is added to give a moisture in the 6-7% range for a ram-
ming mix, about 9% for an extrudable refractory plastic.
Higher moisture will provide hand patching or troweling con-
sistencies.
_g_
41
Highly oxidation resistant versions are made using cal-
cined bauxi.tic clay aggregates of 60-70% aluminum oxide, such
as Mulcoa~ 60 and Mulcoa~ 70 sold by C-E Minerals Corporation:
% ~y wei~ht
Calcined clay aggregate (Mulcoa
60 or 70) -4x20 mesh 50
-200 mesh Mulcoa 70 10
-30 mesh natural graphite 11
Fine plas tlC clays 8
Silicon metal powder 8
Chromium oxide 8
Lignosulfonate liquor, 50%
aqueous suspensi.on 5
Water is added to make a granular ramming mix in the 4-5~O
moisture range ~or maximum density and effectiveness.
EXAMPLE. 8
Higher purity systems are ormulated ~tlL tabular
alumina and low ash carbon fines.
/O b~_weigl
-6 mesh tabular alumina 44
Fine plastic clays 9
Silicon metal powder 8
Chromium oxide 28
-30 mesh coke fines 11
Water is add2d to produce a ramming mix or plastic consis-
tency.
- 10-
.,
~;29~
EXAMPLE 9
_
Phosphate bonding is an effective means of obtaining
high strength by preliminary heating to cure prior to use in
service, providing initial impact resistance to molten metal
flow after installation.
% bY weight
-6 mesh tabular alumina 45
-30 mesh natural graphite 6
Western bentonite, -200 mesh 8
Silicon metal powder 8
Chromium oxide 27
75% concentrated phosphoric acid 6
Water is added as in previous example to achieve a ramming
mix or plastic consistency.
In the specification and claims the term "high
alumina" refers to an alumina-containing composition contain-
ing at least 40% by weight alumina, preferably at least 60%
A1203 .
All percentages are in weight percent.
