Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
ALUMINO-SILICATE REFRACTORY BRICK
sackground of the Invention
-
~ atural alumino-silicates which include, among
others, clays, diaspore, kyanites, and bauxites, are the
major ingredients for a large number of refractory brick
currently manufactured. When the brick analyze less than
about 50% A12O3, they are typically characterized in the
art as fire clay brick. If they analyze more than 50%
A12O3, they are t~pically characterized as high alumina
brick. Very generally, the properties of alumino-silicate
brick vary with the percentage alumina they contain. This
may be explained to a large extent by the quantity and type
of mineral and glass phases formed by the alumino-silicate ;~
materials when the brick are burned.
As the alumina content of fire clay and high
alumina brick is increased, resistance to load at elevated
temperatures tends to increase. Also, resistance to
spalling on rapid temperature change tends to increase.
These property changes are usually attributed to a reduction
in quantity of low refractory and brittle silicate glasses
present in the groundmass of the brick. On the other hand,
increasing the alumina usually results in an increase in
porosity making the brick physically more vulnerable to the
chemical attack of metallurgical slags. In addition, bric~
higher in alumina tend to have less resistance to alkali
vapors and shrink in service after cooling from high `~
temperatures.
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A few words here are appropriate as to what is
meant by silicious groundmass. Alumina and silica present
in alumino-silicate refractories react on firing to form,
for the most part, the mineral mullite. Three moles of
alumina react with two moles of silica. If the ratio of
alumina to silica exceeds 3 to 2, the burned brick will also
contain coroundum. If the ratio is less than 3 to 2, the
burned brick will be substantially mullite and one of the
crystalline or glassy forms of silica. Depending on the
impurities present and the heat treatment, the silica will,
to some extent, be in the form of a glass. The lower the
alumina to silica ratio, the more SiO2 that will be present
in a crystalline or glassy form. ~he amount of glass then
relates to the amount of shrinkage encountered.
It is among the objects of the present invention
to provide alumino-silicate refractory shapes characterized
by the absence of shrinkage after coking at 2000F.
In accordance with the present invention, there is
provided carbon bonded refractory shapes comprising from
about 1 to 35%, by weight, carbon and the balance a non-
basic refractory aggregate. The refractory aggregate
consists essentially of at least about 75~, by weight,
andalùsite.
Preferably, the balance of the refractory
aggregate, if not all andalusite, is pure alumina or another
aluminum silicate. The shapes preferably contain from about
0 to 30~, by weight, flake graphite. They may also contain
less than about 7.5~, by weight, amorphous graphite and/or
carbon black. Generally the shapes have between about 0.1
and 1~ volume expansion with andalusite compri~ing at least
about 65% of the total weight of the batch. This expansion
is important because it will prevent brick linings from
becoming loose when cooling from high temperatures takes
place.
Andalusite is a mineral having the same chemical
formula (A12SiO5) as sillimanite and kyanite but with
different physical properties.
A better understanding and further ~eatures and
advantages of the practice of this invention will ~ecome
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readily apparent to those skilled in the art by a study of
the following detailed description and examples. It should
of course, be understood that these examples are given by
way of explanation, and not by way of limitation. All size
gradings are according to the Tyler Series, unless otherwise
specified. All chemical analyses, unless otherwise
specified, are on the basis of an oxide analysis in
conformity with the conventional practices of reporting the
chemical content of refractory materials. All analyses
should be considered typical. All parts and percentages are
by weight.
The mixes of the examples were all fabricated into
brick in the same manner. The refractory aggregate was size
graded and mixed with a phenolic novolak r~esin.
The size graded batches were tempered in a muller-type mixer
to render the batch pressible. The batches were pressed
into brick at about 18,000 psi and the brick were dried at
about 250F for about 12 hours. After cooling, the brick
were submitted to tests to determine their dried density and
volume change properties after coking. Various
alumina-silicate shapes were prepared as shown in Table I
below.
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Mixes comprising predominantly a different
alumino-silicate grain had shrinkage properties running from
-0.4 to about -1.5~. The brick in which another refrac-tory
material was added had shrinkages somewhere in between. The
example mix No. 3 containing equal amounts of alumino-
silicate grain and pyrophyllite expanded, but the expansion
was accompanied by bloating.
Mixes 9 through 14 in Table II were made with the
following andalusite to alumino-silicate grain ratios:
50-50, 55-45, 60-40, 65-35, 70-30; and 75-25.
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All of the mixes excep-t mix 14, with 75/25
andalusite-alumino silicate grain, exhibited volume
shrinkage after coking.
Mixes in Table III below were made with andalusite
as the only refractory agg,regate. However, the mixes
contained from O to 30% flake graphite and up -to 5% of
amorphous graphite and one with 5% carbon black.
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Mixes 15 through 18 contained 0 -to 30% flake
graphite. As the amount of flake graphite increased from 0
to 30%, the amount of volume expansion after coking at
2000F, decreased from 1.2% to 0.4%. Mix 15 with only the
resin present in addition to andalusite, would contain about
1.3% carbon derived entirely from the resin. Mixes 19 and
20 which contain 2.5% and 5%, respectively, amorphous
graphite expanded after coking. Additional testing
indicated that expansion was achieved when less than 7.5%
arnorphous graphite was used. Mix 21 which contains 5%
carbon black and no graphite, expanded after coking~ -
The sizing of the refractory aggregates used in
the above examples were as follows: -3+10 mesh --30 to 40%;
-10+28 mesh --lS to 25%; -28+65 mesh --10 to 15%; and the
balance -65 mesh. The typical chemical analyses of the
refractory materials used in the examples are set forth in
Table IV below.
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The other materials used in the exernplary
refractory compositions and not included in Table IV, are
calcined alumina and tabular alumina. Both of these
materials contain about 99~ A1203, the balance trace
impurities and are well known in the art. Similarly, the
crystoballite and volatilized silica are high purity
silicious materials, i.e. 99% SiO2, and are also well known
in the art.
Having thus described the invention in detail and
with sufficient particularity as to enable those skilled in
the art to practice it, what is desired to have protected by
Letters Patent is set forth in the following claims.
