Refractory cement

A dry ramming refractory cement composed principally of coarse dense alumina grains, silicon metal powder, calcined alumina and sodium hexametaphosphate, and optionally one or more materials from the group including silicon carbide, fused white alumina, chromia, periclase, kyanite, graphite and cryolite.

FIELD OF THE INVENTION 
This invention relates to a dry ramming cement, especially suitable for 
forming linings in troughs, runners and the like for conveying molten iron 
and slag, and for forming walls in metal melting furnaces. More 
particularly a refractory cement formulation is shown that has particular 
properties that adapt it well for use in induction furnace walls and 
troughs and runners from blast furnaces for processing molten iron having 
high lime-silica slags. 
PRIOR ART STATEMENT 
The following United States Letters Patents are representative of the most 
relevant prior art known to the Applicant at the time of the filing of the 
application: 
U.S. Pat. No. 1,277,227 to Linbarger, 8/27/18; U.S. Pat. No. 1,289,578 to 
Tone, 12/31/18; U.S. Pat. No. 2,845,360 to King et al, 7/29/58; U.S. Pat. 
No. 2,852,401 to Hansen et al, 9/16/58; U.S. Pat. No. 3,617,319 to Sadran 
et al, 11/2/71; U.S. Pat. No. 3,846,144 to Parsons et al, 11/5/74; U.S. 
Pat. No. 3,854,966 to Kanbara et al, 12/17/74; U.S. Pat. No. 4,060,424 to 
Hofmann, 11/29/77; U.S. Pat. No. 4,204,878 to Nudelman et al, 5/27/80 and 
U.S. Pat. No. 4,222,782 to Alliegro et al, 9/16/80. 
Linbarger U.S. Pat. No. 1,277,227 and Tone U.S. Pat. No. 1,289,578 show 
refractory formulations adapted for mixing with water and designed to be 
cast into a shape for subsequent firing before being put into use as a 
crucible or the like. 
A number of the above noted references show refractory cements that are 
designed to be mixed with water and cast or otherwise formed into a 
desired shape such as disclosed in King et al U.S. Pat. No. 2,845,360, 
Hansen et al U.S. Pat. No. 2,852,401, Sadran et al U.S. Pat. No. 
3,617,319, Parsons et al U.S. Pat. No. 3,846,144, Kanbara et al U.S. Pat. 
No. 3,854,966, and Nudelman et al U.S. Pat. No. 4,204,878. 
The Hofmann U.S. Pat. No. 4,060,424 and the Alliegro et al U.S. Pat. No. 
4,222,782 each describes a refractory cement that may be placed in a dry 
condition by vibratory or a ramming procedure. The Hoffmann product may be 
used either as a dry ramming cement or it may be mixed with water to be 
placed with a gunning action. Both of these last two mentioned patents 
disclose refractory layers that are fired in place to sinter the 
constituent grains in the cement and promote reactions within the mass of 
the mix after it is in place to produce a protective refractory surface 
for containing molten metal. 
The Hofmann and Alliegro et al patents both include discussions of other 
cements known in the prior art, which discussions are incorporated herein 
by reference. 
DISCLOSURE OF THIS INVENTION 
The present formulation builds on the known art and provides an improved 
refractory ramming cement that is easy to install in its dry state to form 
a wall in induction furnaces and in troughs and runners to receive molten 
metal flowing from a blast furnace. The furnace's troughs and runners can 
be put into use immediately after the cement has been put in place. This 
cement provides a combination of refractory grain in selected sizes that 
may be sintered in situ to form a liner especially adapted to receive 
molten ferrous metal and slag, including lime silica slags. The cement is 
conditioned by the molten metal flow to form a permanent liner in a 
furnace and in a trough and its runners or the like, which liner provides 
improved resistance to corrosion that is caused by the flow of molten iron 
and particularly the slag flowing from a blast furnace or contained in an 
induction furnace used to melt iron. 
The cement includes a preponderance of from 45 to 80% by weight of dense 
alumina in grain sizes varying from 6 to 20 mesh size and finer, together 
with smaller proportions of from 5 to 10% by weight of a fine calcined 
alumina, from 0.25 to 5% by weight of silicon metal particles and from 0.5 
to 3% by weight of (NaPO.sub.3).sub.6. (All mesh sizes are based on U.S. 
Standard Sieve Series.) 
Optional ingredients may also be included in the cement mixture that may be 
selected from the compositions consisting of an amount of from 0 to 20% by 
weight of black silicon carbide of 150 mesh and finer, 0 to 20% by weight 
of fused white alumina 16 mesh and finer, 0 to 20% by weight of fused 
white alumina grain that is 70 mesh and finer, chromium oxide pigment in 
an amount of from 0 to 10% by weight that is one micron and finer, 0 to 5% 
of periclase (magnesia) that is 140 mesh and finer, kyanite (Al.sub.2 
O.sub.3 SiO.sub.3) in an amount of from 0 to 8% by weight that is 200 mesh 
and finer, graphite powder in an amount of from 0 to 5% by weight that is 
200 mesh and finer, and cryolite (Na.sub.3 AlF.sub.6) in an amount of from 
0 to 3% by weight and in a mesh size of 200 mesh and finer. 
While fused alumina is the peferred aggregate or grain, because of its high 
density and stability at high temperature, either tabular alumina or 
calcined refractory bauxite can be substituted in whole or in part for the 
fused alumina. These substitutions may result in a somewhat shorter life 
in use, but they result in a lower cost cement. 
The (NaPO.sub.3).sub.6 which may be in the form of readily available 
Calgon, is used as a bonding agent in the cement, which bond is active 
over a wide range of temperatures. The silicon metal powder is provided in 
the cement mix to combine with any oxygen that may be present in or that 
would otherwise penetrate into the cement, to form SiO.sub.2 that fills 
the pores within the mass of the cement layer in order to produce a 
non-porous liner that resists the penetration of molten slag and iron into 
the body of the material lining the troughs or runners. 
With respect to the optionally selected ingredients, the kyanite and fine 
alumina particles present in the cement when it is placed in a furnace 
wall or conduit, react when heated by the molten metal, to form mullite 
that fills pores and channels within the mass of the cement. This reaction 
begins during the initial sintering of the cement when the heat from the 
molten metal begins to flow into the cement, and the presence of the 
mullite reduces the tendency of the cement liner to shrink. 
The graphite component may be added optionally to reduce the wetting of the 
cement by the molten iron and slag and is also useful when a fine silicon 
carbide additive is used in the cement mix, the graphite serving as a 
scavenger to inhibit oxidation of the silicon carbide. The black silicon 
carbide component may also be used as an optional ingredient in the mix to 
reduce the wetting of the cement by the molten slag and the black silicon 
carbide, which contains some free carbon, is preferred for this purpose. 
The cryolite component may be used if needed as a flux to strengthen the 
cement at a temperature below the melting point of iron when deemed 
desireable. 
Chromia and periclase may be added to form a spinel in situ within the body 
of the cement, to further close pores, which results in the most preferred 
cement. 
A cement mixture made with the essential ingredients described above, or 
one that in addition includes any of the optional ingredients described, 
may be placed in a furnace or in trough and runner structures by tamping 
or vibration, as a dry composition, to form a liner adapted to receive 
molten iron and is especially recommended for use when such metal is 
refined in a process that results in the production of a slag that has a 
high lime-silica content. When the molten metal flows over the cement 
packed over the surface of the trough and its runners, the liner is 
sintered in situ and either the basic cement or a cement composition that 
includes various of the optional ingredients suggested above reacts as 
described, to fill the pores in the liner and bond it more permanently in 
place. As the molten flow continues, the sintering reaction progresses 
throughout the mass of the body of the liner layer which becomes stronger 
and more resistant to the corrosive action resulting from the iron and 
slag flowing through the trough and its associated runners. The cement 
layer becomes quickly bonded in place and as it is heated by the flow of 
molten metal the cement continues to mature until a strong, substantially 
impervious, non-porous, corrosion resistant liner for the conduit and 
runners is formed in situ to more efficiently contain a molten ferrous 
metal and any slag, including especially a high lime-silica containing 
slag flowing from a blast furnace. 
When the present cements are utilized as the wall lining in, for example, 
an induction furnace used to melt iron in a foundry, the major erosion of 
the lining is due to the lime-silica slag which is present during the 
fusion.

EXAMPLES OF THE PREFERRED EMBODIMENTS 
Mixtures of the ingredients described above, may be made in any 
conventionally known blending equipment to form a dry mixture that may be 
packed by vibration or any other known dry placement procedure to form a 
liner for equipment for containing molten iron and slag. 
Several examples of prefered mixtures of such a cement that may be placed 
dry in furnace walls and in troughs and runners that form conduits for 
molten iron and slag, are the following: 
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Weight Percent 
Possible 
Material Mix A Mix B Mix C Mix D Range 
______________________________________ 
Fused Dark 18 20 24 9 8-20 
Aluminum 
Oxide 
6-10 mesh 
Fused Dark 20 20 25 24 15-25 
Aluminum 
Oxide 
12-16 mesh 
Fused Dark 20 25 35 24 20-35 
Aluminum 
Oxide 
20 mesh 
and finer 
Black Silicon 
-- 15 -- -- 0-20 
Carbide 
150 mesh 
and finer 
Fused White 15 -- -- 15 0-20 
Alumina 
16 mesh 
and finer 
Fused White 10 -- -- 10 0-20 
Alumina 
70 mesh 
and finer 
Calcined 7 10 10 8 5-10 
Aluminum Oxide 
200 mesh 
and finer 
Chromium Oxide 
5 -- -- -- 0-10 
Pigment 
less than 
1 micron 
Periclase MgO 
3.5 -- -- 7 0-5 
140 mesh 
and finer 
Kyanite -- 4 -- -- 0-8 
Al.sub.2 O.sub.3 SiO.sub.2 
200 mesh 
and finer 
Graphite Powder 
-- 3 -- 3 0-5 
200 mesh 
and finer 
Silicon metal 
0.5 1 3 -- .25-3 
powder 
90 mesh 
and finer 
Calgon (NaPO.sub.3).sub.6 
1 1 3 -- .5-3 
200 mesh 
and finer 
Powdered Cryolite 
-- 1 -- 0.5 0-3 
Na.sub.3 AlF.sub.6 
200 mesh 
and finer 
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(All mesh sizes are U.S. Standard Sieve sizes except for the chromia for 
which the longest average dimension of the individual particles in a batch 
of particles, as estimated from a microscopic analysis, is given.) 
Typically Mix B had a packing density of 170 lbs/ft.sup.3 while mixes A, C 
and D had packing densities of about 180 lbs/ft.sup.3. 
Of the foregoing example mixes of the preferred embodiments, the most 
preferred is that exemplified by Mix A. When chromia and magnesia 
(periclase) are incorporated as a bonding medium in addition to the sodium 
hexameta-phosphate, the resulting cement is even more resistant to the 
corrosive and erosive effects of calcia-silica slag and the metal, than 
are the embodiments of mixes B, C, and D of the present invention, and 
dramatically more resistant than a current state of the art commercial 
cement composition which had the following weight percent formulation: 
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Fused Dark Aluminum Oxide 
6-10 mesh 23 
Fused Dark Aluminum Oxide 
12-16 mesh 23 
Fused Dark Aluminum Oxide 
20 mesh and finer 
10 
Silicon Carbide 10 mesh and finer 
8 
Silicon Carbide 90 mesh and finer 
10 
Graphite 200 mesh and finer 
10 
Ball Clay 8 
Bentonite 2 
Silicon Nitride 220 mesh 5 
Goulac 1 
______________________________________ 
The resistance of refractory linings to erosion by both molten cast iron 
and CaO/SiO.sub.2 slag was measured using Mixes A, B, and D of the present 
invention, and the foregoing commercial cement composition as linings in 
an induction furnace. The test was carried out in the following manner: 
A small induction furnace measuring 17.78 cm (7 inches) in inside diameter 
and 30.48 cm (12 inches) deep was lined with refractory made of 
compositions corresponding to Mixes A, B, D and the prior art cement 
formulation set out above. About 12.7 cm (5 inches) of the depth of the 
furnace was filled with cast iron and the iron heated to 1600.degree. C. 
To the molten iron was added 0.23 kg (0.5 pound of a lime-silica slag 
having a CaO/SiO.sub.2 ratio of about 1. The furnace run was continued for 
5 hours with the old slag being removed and replaced by an equal amount of 
fresh slag every 0.5 hour of the five hours. After the 5 hour run the 
furnace was completely emptied and allowed to cool. The refractory lining 
of the furnace was removed and the wear or erosion of the thickness of the 
refractory wall was measured both where the iron and the slag had 
contacted the wall during the heating run. The total erosion of the wall 
thickness for the 5 hours in the case of each refractory composition was 
as follows: 
______________________________________ 
Erosion Caused By: 
Refractory Slag Iron 
______________________________________ 
A 3.0 mm <0.05 mm 
B 6.0 mm 2.5 mm 
D 6.0 mm 1.0 mm 
Prior Art 28.0 mm 20.2 mm 
______________________________________ 
Mix C was not tested because it was basically a composition between those 
of mixes B and D. 
As can be readily seen from the tabulated erosion data, all compositions of 
the present invention were far superior to the prior art refractory 
lining. Among the invention compositions, Mix A was clearly superior to 
both Mix B and Mix D. That superiority of Mix A was the result of the in 
situ formed chromia-magnesia spinel formed when the chromium oxide and 
periclase containing mix was heated during the initial phase of the iron 
melt; the chromium oxide and periclase combination was present only in Mix 
A. 
The above description of the invention is based upon the best data known to 
the inventor at the present time and is not to be considered as limiting. 
The invention is set forth in the following claims: