Note: Descriptions are shown in the official language in which they were submitted.
1;~3~856
Docket C-1~52
REFRACTORY CEMENT
RONALD A. STARK
Williamsville Road
Hubbardston, Massachusetts 01542
TECHNICAL FIELD
This invention relates to a cement for use in
vessels containing molten alloys of aluminum with metals
selected from the group consisting of lithium, magnesium,
copper and zinc.
BACKGROUND ART AND INFORMATION DISCLOSURE STATEMENT
The following publications are representative of
the most pertinent prior art known to the Applicant at the
time of the filing of this application.
10 UNITED STATES PATENTS
3,342,616 Alter et at Sept. 19, 1967
3,492,383 Heimgartner June 27, 1970
3,587,198 Hansel June 28, 1971
3,625,721 Snyder Dec. 7, 1971
15 3,751,571 Burrows Aug. 7, 1973
3,767,375 Richard et at Oct. 23, 1973
3,974,249 Roy et at Aug. 10, 1976
4,138,455 Schick et at Ye. 6, 1979
A containment problem has arisen in the manufacture
of certain alloys of aluminum and particularly alloys of
aluminum and lithium. The metals are melted together in
either channel or cureless induction furnaces and the molten
metals are transported or carried or passed through various
processing steps in ladles, filter boxes, tundishes or come
in contact with mold tops etc. These elements of the metal
processing equipment are lined in various ways with
refractory elements designed to hold the molten metal and
protect the structural support elements of the equipment from
chemical attack and the thermal stresses produced by the high
fusion temperature of the flute bath contained in such
equipment Dylan the melting and alloying of the metals.
Various kinds of refractory lines have been
proposed for use in induction furnaces and the like as
illustrated in the following United states Patents:
Patents 3,492,3~3 and 3,587,198 are early examples
of plural layers of refractory coatings in furnaces. The
earlier patent shows a sistered liner that is backed-up by a
cushion layer designed to contain molten metal in an
induction furnace.
The Burrows patent 3,751,571 shows a somewhat more
advanced version of the cushion layer design. In furrows, a
monolithic cast and cured liner is formed in a furnace, the
inner surface of which is sistered when a melt is produced in
the furnace to produce a crust backed-up by a soft friable
zone that has a hard hydraulically cured outer zone beyond
the friable layer. This treason type of liner tends to
protect the supporting structure from heat damage and
corrosive metal attack by providing the friable layer to
catch molten metal that issues through cracks that inevitably
form in the sistered inner face.
3,767,375 discloses the use of prefabricated
refractory bricks having the joints between the bricks filled
with a powdered material such as carbon, alumina, Crimea or
other material that is not wetted by molten metal so that the
metal does not penetrate through the restricted spaces
between the particles of the filler material.
As taught herein, a preferred refractory liner for
induction furnaces and the like can take the form of a dry
cement that may be placed in the vessel to be protected and
vibrated into a compacted layer. The dry vibrated layer is
then subjected to a sistering action to form a crust or hard
layer on the surface of a semi-sintered and/or unsintered
compacted cement forming a back up support which retains the
form of a compacted plastic or granular layer behind the
sistered surface layer to insulate the structural support
means of the vessel from direct contact with the molten bath
3~8~
and simultaneously produce a stress accommodating layer
between the Sinatra crust and back wall or support Ion the
molten liquid container. such refractory liner is well
adapted to provide a vessel for holding the molten metal
while protecting the supporting structure from thermal
expansion without subjecting any part of the furnacing
equipment to an undue stress.
This above described invention builds on the above
noted patented teachings and provides a container structure
for particular kinds of molten alloys wherein a sistered
crust is backed-up by a semi-sintered and/or granular layer
to control the transmission of heat and expansion stresses
from the container to the support means. The granular
backing layer serves a further function as here taught by
having included therein materials for reacting with any spurs
of molten alloy metal flowing through the inevitable cracks
that form in the sistered container to form reaction products
that seal off the crack and prevent the further flow of
molten metal much beyond the containment vessel. This
desired result is accomplished by providing a dry vibratable
cement composition having a specific chemical composition
adapted to react with the aluminum lithium, or aluminum
magnesium or aluminum zinc alloy being produced, as will
appear more fully below.
The novel cement proposed for such use herein
includes a base grain component of stoichiometric, or
magnesia rich hyperstoichiometric spinet or magnesia grain
either calcined or fused mixed with the added flux mix also
containing a lithium fluoride flux added to this base grain,
fine fractions of alumina, silica magnesia and/or spinet
fractions.
In connection with the chemical aspects of this
invention, it is known that loath stabilizes periclase based
solid refractory solutions including spinet as taught in
3,342,616. This stabilized refractory composition has been
suggested for use in metallurgical furnaces, refractory tubes,
spark plug insulators and the like.
856
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A permeable refractory brick has been formed with
alumina, a lithium compound, a small amount of magnesia and
other metal oxides as shown in 3,625,721.
In a non elated art, a patent has been note
showing a combination of materials like those shown herein,
for example Patent 3,974,249 shows a method of forming a
solid light transmitting refractory body that is produce by
combining equal molar amounts of magnesia and alumina that
can be calcined in the presence of a small addition of
lithium fluoride to react the mass to form spinet, which can
then be cooled and pressed to form a self sustaining compact
that can then be fired in a wet hydrogen atmosphere to
produce a transparent ceramic body.
DISCLOSURE OF THE INVENTION
It has been found that molten alloys of aluminum
with lithium can be melted together more efficiently in
channel and cureless induction furnaces by providing a cement
liner for such furnaces, that can be sistered in situ, to
produce an inner crust that forms a container for the molten
mass that is supported by an unsintered granular or
semi-sintered plastic layer of the same refractory cement
mix. After the cement has been compacted in place in the
furnace the production of the molten aluminum-lithium alloy
may be commenced and as the heat develops in the melting
mass, the surface layer of the dry vibrated refractory cement
is sistered to form a crust that is supported by the
unsintered granular mix behind it. As suggested above, such
a granular or plastic cement liner surrounding the sistered
crust insulates the support structure of the furnace from
heat damage and serves to cradle the sistered crust that
forms the container for the melting mass to insulate the
crust from expansion stresses to which it would otherwise be
subjected if it were supported in a solid refractory bray.
The herein disclosed cement mix that is recommended
for use in the production of an aluminum lithium alloy,
includes a magnesia spinet or a magnesia and alumina mix to
form a spinet which upon being heated together with a flux of
36
lithium fluoride, alumina, silica, titanic, magnesia and/or
spinet first is reacted to form a low temperature bond if, the
crust forming zone that provides a form of container for the
molten metal while the temperature increases and the
sinterlng process proceeds. After a suitable liner mix has
been compacted in place, heat is applied to the furnace to
melt the metals to be alloyed. As the temperature increases,
a fluxing reaction takes place between the fluxing compounds
to form first a liquid phase which may be an aqueous solution
and/or glass depending on temperature and composition, then
to Lucia; Lyle; Lowe; Lucia and/or
Lawlessly to produce a hard crust on the surface of
the liner which provides a low temperature bond Lo the crust
and serves to support the molten metal bath until the
ultimate sistering of the crust can be completed.
The resulting fully sistered crust and unsintered
layer forms a composite liner structure that has a hard dense
sistered crust or container like surface for holding the
molten alloy, the container being supported by partially or
totally unrequited semi-sintered or granular cement mix layer
between it and the back wall of the furnace. The crusted
layer or container element can shift with thermal expansion
in the granular or plastic supporting bed to reduce the
incidence of cracking while the granular layer further serves
as an insulating back wall to shield the outer furnace walls
from direct exposure to the heat of the melt.
If a crack should occur in the sistered crust or
container supported in the plastic or granular mix, the
molten metal flowing through the crack and coming in contact
with the granular backing, produces the fluxing reaction
above described to form a sistered shell to surround the spur
that subsequently becomes fully sistered whereby the leak is
contained.
DESCRIPTION OF THE PREFERRED EM~ODI~ENT~
The cement of this invention includes predominantly
a base grain in the range of 85% or more by weight of the
final mix, the base grain being stoichiometric, or magnesia
68~
I,
non ~y~erstoich1ometric, spinet o magnesia grain. Tins
base grain may be either used an crusted or calcined. It
is purred in a size range distribution to produce a maximum
density with minimum porosity when the cement mix is
compacted in place with a conventional dry vibrating
procedure.
To the base grain, a lithium fluoride flux is added
in a percent by weight within a range of up to I by weight
of the mix but preferably 0.5% will be found to be
sufficient. The remainder of the cement mix to make up to
100% is alumina, silica, magnesia and/or spinet. These
components of the mix are added as fine fractions that are
adapted to react with the lithium. Very fine particles such
as calcined periclase, electrical magnesia dust collector
fines, alumina dust collector fines, reactive alumina,
and Potters Clint are the preferred additions used for this
purpose.
A small addition of boric acid in the form of
HBO2 H3BO3 or an hydrous boric acid about equal to the
lithium fluoride content may also be added to the mix but
this is not deemed essential.
Examples of preferred mixes are as follows;
train _ _ C
Spinet .5-4 mm 55 55 56
25 Spinet .12-5 mm 15 15 15
Spinet 0-.12 mm 16 16 16
Calcined Periclase 100F 4 4
Boron content 300 ppm min.
Eluded Mg0 electrical 200F 5
30 38 Aluminum Oxide EYE 4 4 4
Boric Acid .5 .5 .5
May be boric acid or
an hydrous boric acid; the
latter in lesser quantity
to compensate for loss of
water of hydration.
Lithium Fluoride (Luff .5 .5
Reactive Alumina - 5 5
Potters Flint - - 3
- / -
The cement mix described herein is particularly
suggester or use in channel and cureless induction furnaces
used in the production of aluminum-lithium alloys. It may
find use also in other pieces of equipment for holding molten
alloy material such as in transport vessels, laddies, filter
boxes, tundishes, mold taps and the like.
The cement may also be used to contain other
aluminum alloys with magnesium and zinc. The lithium
fluoride flux together with the additions of periclase
alumina dust collector fines, magnesia fines, reactive
alumina and/or Potters Flint will react to contain any metal
spurs escaping from the hardened face supported by the
granular mix. The herein described flux will react with the
magnesium and zinc additions to the aluminum metal to first
produce the sistered crust container for the molten metal an
will further react with any molten metal leaking from the
crust into the granular backing to contain the leak and
prevent it from flowing outwardly into contact with the
support structure for the furnace or other molten metal
processing equipment.
The above description is based on the best mode
known to the inventor at the present time and is not to be
considered limiting. The product of this invention is a raw
batch adapted to be fired in situ to produce a more
satisfactory refractory liner for use in the production of
aluminum alloys with lithium, magnesium or zinc in furnaces,
and other containers or conduits for the molten metals. The
ultimate refractory liner has improved stress accomodatiny
characteristics as well as insulating and metal containing
properties.
