BETON REFRACTAIRE

REFRACTORY CONCRETE

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
This invention is concerned with a refractory concrete
based on zircon and aluminous cement. In known refractory con-
crete based on zircon and aluminous cement, which is used in
particular for manufacturing linings or molded bodies resistant to
molten metal, particularly aluminum melts, the high thermal con-
ductivity due to the high bulk density is often detrimental. The
new refractory concrete should have a lower thermal conductivity
with good resistance to molten metal and in particular to aluminum
melts. The new refractory concrete contains as a further consti-
tuent 10 to 50% by weight, based on the solid constituents, of
light refractory materials, particularly expanded vermiculite,
expanded perlite, light fireclay and/or mineral fibers.

Revendications

23843-190

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:


1. Refractory concrete for manufacturing linings or molded
bodies resistant to molten metal, in particular aluminum melts,
comprising zircon as the refractory aggregate and aluminous cement
as the hydraulic binder, characterized in that it continues to
comprise 10 - 50% by weight, based on the solid constituents, of
light refractory materials.



2. Refractory concrete according to claim 1, characterized
in that the light refractory material includes vermiculite,
perlite, light fireclay and/or mineral fibers.



3. Refractory concrete according to claim 1 or 2,
characterized in that it comprises 30 to 50% by weight, based on
the solid constituents, of light refractory materials.



4. Refractory concrete according to claim 1, characterized
in that it comprises 15 - 25% by weight, based on the solid
constituents, of aluminous cement.



5. Refractory concrete according to claim 1, characterized
in that it comprises 40 - 60% by weight, based on the solid
constituents, of zircon.

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23843-190


6. Refractory concrete according to claim 5, characterized
in that the proportion of zircon with a grain size less than or
equal to 0.09mm totals 60 - 40% by weight, based on the total
amount of zircon present.

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Description

~27~3 23~43-190

The inven-tion relates to refractory concrete for
manufacturing linings or molded bodies resistant to molten metal,
in particular aluminum melts, comprising zircon, i.e. zirconium
silicate, as the refractory aggregate and aluminous cement as the
hydraulic binder.
Refractory concrete based on zircon and aluminous cement
is known. If such refractory concrete is used for manufacturing
linings or molded bodies resistant to aluminum mel-ts, this
refractory concrete should not contain any other silicates or free
sio2 if possible, apart from the SiO2 bound in the zircon, since
the resistance particularly as against aluminum melts is sharply
reduced by such other constituents containing SiO2. Linings or
molded bodies manufactured from the known refractory concrete
based on zircon and aluminous cement have a high thermal
conductivity as a result of their high bulk density caused by the
zirconium silicate.
It is the object of ths present invention to provide a
refractory concrete for manufacturing linings or molded bodies
which are resistant to molten metal, and in particular aluminum
melts, and which have a lower thermal conductivity, i.e. better
insulating properties.
It was surprisingly found that it is possible to reduce
the bulk density of such refractory concrete despite the use of
materials of a silicate nature.
The invention therefore relates to refractory concrete
of the aforenamed kind, characterized in that it ad~itionally
contains 10 - 50% by weight, based on the solid constituents, of


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-- 1 --

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23843-190


light refractory materials.
According to a preferred embodiment, the refractory
concrete according to the invention contains as light material
vermiculite, perlite, light fireclay and/or mineral fibers. The
vermiculite and perlite are used for this invention in their
expanded form. The li~ht fireclay is a fireclay which has a low
bulk density. Such a light fireclay can be obtained, for example,
by mixing fireclay powder and a burn-out material, for example
sawdust or cork powder, manufacturing molded bodies, calcining the
molded bodies, burning out the burn-out materials and comminuting
the obtained light fireclay molded bodies to the desired
granulation.
Mineral fibers can also be used as the light materials
in refractory concrete according to the invention, i.e. fibers
which do not melt the linings or molded bodies manufactured from
the refractory concrete according to the invention. Examples of
such mineral fibers include rock wool fibers, and also the
so-called ceramic fibers, i.e. fibers having an A12O3 content
less than or equal to 45% by weight. Ceramic fibers with an A1203
content have, for example, application temperature limits of
less than or equal to 1260C.
In accordance with a preferred embodiment the refractory
concrete according to the invention contains 30 to 50% by weight,
based on the solid constituents, of light refractory materials.
Through this it is possible to keep the bulk density of the
linings or molded bodies manufactured from the refractory concrete
especially low.
In accordance with a further preferred embodiment the




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aluminous cement content in the refractory concrete according to
the invention amounts to 15 to 25% by weight. ~hese quantities of
aluminous cement have proven particularly advantageous in order to
satisfactorily introduce the light tnaterials into the refractory
concrete, i.e. to avoid separation during processing.
In accordance with a further preferred embodiment the
refractory concrete according to the invention contains 40 - 60%
by weight, based on the solid constituents, of zircon, i.e.
zirconium silicate.
In accordance with a further preferred embodiment the
zircon contained in the refractory concrete has a grain size such
that 40 - 60% by weight is present as so-called "zirconium sand",
i.e. with a grain size of 0.09 to 0.5mm, whereas the remaining 60
- 40% by weight of the zircon is present as so-called "zirconium
powder", i.e. with a grain size less than or equal to O.O9mm.
This embodiment has the advantage that during processing
of the refractory concrete, i.e. with the addition of water, the
light materials of a silicate nature contained in the refractory
concrete according to the invention are preferably coated not only
with the fine constituents of the aluminous cement but also with
this very fine zirconium powder so that a particularly good
resistance as against molten metal, in particular aluminum melts,
is achieved~
The invention is explained in greater detail herebelow
on the basis of the following examples and the comparison test.
Example 1
A mixture of 22.5 parts by weight aluminous cement, 17.5




. .

~3~63 23843-190
parts by weight zirconium powder with a grain size less than or
equal to O.O9mm, 25 parts by weight zirconium sand with a
granulation of 0.09 to 0.5mm and 35 parts by weight light fireclay
with a grain size of 0 to Smm is prepared. 100 parts by weig'nt of
this dry mixture is mixed with 12 1 of water to refractory
concrete and test blocks are manufactured from this prepared
refractory concrete. The form work time totalled approximately
five hours. It is also to be noted that the processing time of
the refractory concrete according to the invention is
approximately one hour.
Comparison Test
As a comparison, refractory concrete using only
aluminous cement and zircon is prepared. The proportion of
aluminous cement in the dry mixture totals approximately 18~ by
weight, the remainder consists of zirconium sand and zirconium
powder in the ratio of the weight 2 : 1. Refractory concrete is
likewise prepared from this dry mixture, using 8 1 of water per
100 kg of dry mixture, and shaped into test blocks.
The physical properties of the test blocks obtained are
~0 compiled in the following table:


~2~ 3
23843-190


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U

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~e a


U U U U U U U U U
O O O O O O O O O
-100 .-100 000
O ~ ~O ~~ ~D CO

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a) o z ~1 u
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23843-lgO

Example 2
The procedure of Example 1 is repeated, however,
expanded vermiculite is used instead of light fireclay.
Test blocks are likewise manufactured frorn this
refractory concrete, said blocks having properties comparable to
the tes-t blocks of the composition given in Example 1.
Example 3
The procedure of Example 1 is repeated, however,
expanded perlite is used instead of the light fireclay of
Example 1.
Test blocks are likewise manufactured from this
refractory concrete, said blocks having properties comparable to
the test blocks of the composition given in Example 1.
Example 4
The procedure of Example 1 is repeated, whereby a
mixture containing 15 parts by weight aluminous cement, 35 parts
by weight zirconium powder, 30 parts by weight ~irconium sand and
20 parts by weight ceramic fibers with an application temperature
limit of 1260C is used.
Test blocks manufactured from this refractory concrete
mixture likewise have a low thermal conductivity and yet exhibit
good resistance to an aluminum melt.