An alumina-spinel monolithic refractory consists essentially of 50-90 percent by weight of alumina clinker, 5-40 percent by weight of MgO--Al.sub.2 O.sub.3 spinel clinker not larger than 1 mm in size and 1-25 percent by weight of alumina cement. Another alumina-spinel monolithic refractory consists essentially of 50-90 percent by weight of alumina clinker, 5-40 percent by weight of MgO--Al.sub.2 O.sub.3 spinel clinker, 1-25 percent by weight of alumina cement and not more than 5 percent by weight of magnesia clinker. The alumina-spinel monolithic refractories are used for lining the inner walls of ladles, vacuum degassing vessels, hot-metal mixers, blast-furnace troughs and their covers, not-metal mixer cars, tundishes and the like.

BACKGROUND OF THE INVENTION 
This invention relates to highly durable alumina-spinel monolithic 
refractories. 
Alumina monolithic refractories have been commonly used for lining ladles, 
vacuum-degassing vessels, hot-metal mixers, blast-furnace troughs and 
their covers, hot-metal mixer cars, tundishes and the like. However, they 
are damaged as a result of erosion caused by FeO,MnO or CaO contained in 
the molten metal or slag or as a result of structual spalling induced by 
the penetration of slag. To prevent the penetration of the slag, all 
attempts have been made to add carbon, silicon carbide and other elements 
that are less likely to be wet by slag. However, it has been found that 
such added elements do not function properly when they become oxidized. 
When added in large quantities, furthermore, they have proved to cause 
structural deterioration and heavier erosion upon oxidation. 
Alumina-spinel monolithic refractories combined with MgO-Al.sub.2 O.sub.3 
spinel clinker (hereinafter called spinel clinker) have also been 
proposed. Japanese Provisional Patent Publication No. 55-23004, for 
example, discloses a material consisting of 10-85 percent by weight of 
spinel clinker, 5-30 percent by weight of alumina, and 10-25 percent by 
weight of high-alumina cement. Japanese Provisional Patent Publication No. 
59-128271 discloses a material consisting of 50-95 percent by weight of 
spinel and a remainder of aluminum oxide. Japanese Provisional Patent 
Publication No. 60 -60985 discloses a material consisting of at least 60 
parts by weight of spinel clinker, 10-35 parts by weight of alumina 
clinker and 10-10 parts by weight of alumina cement. Spinel clinkers are 
free of the problems associated with oxidation. When combined with alumina 
clinker, they become less likely to produce low melting point substances. 
Conventional alumina spinel monolithic refractories have been useful as 
refractories for various applications, notably for ladles and vacuum 
degassing vessels. Recently, however, furnaces have come to be operated 
under increasingly severe conditions. Also, there is a pressing need to 
decrease the consumption of refractories. Therefor, more durable 
monolithic refractories are in great demand. 
SUMMARY OF THE INVENTION 
The present inventors discovered that the resistance of alumina-spinel 
monolithic refractories to erosion and slag penetration is remarkably 
improved when more alumina clinker than in conventional refractories is 
mixed together with specific amounts of fine spinel clinkers not larger 
than 1 mm. 
A first alumina-spinel monolithic refractory according to this invention 
consists of 50-90 percent by weight of alumina clinker, 5-40 percent by 
weight of MgO-Al.sub.2 O.sub.3 spinel clinker not larger than 1 mm in 
size, and 1-25 percent by weight of alumina cement. 
The present inventors also discovered that magnesia clinker added to the 
above-described first refractory reacts with the alumina clinker contained 
in the refractory to produce spinel at high temperatures. Reacting at high 
temperatures, magnesia clinker and alumina clinker form a spinel with an 
expansion in volume. The permanent linear change after firing becomes that 
of expansion. This expansion proved to remarkably reduce cracking that 
might result from contraction. A second alumna-spinel monolithic 
refractory of this invention consists of 50-90 percent by weight of 
alumina clinker, 5-40 percent by weight of MgO-Al.sub.2 O.sub.3 spinel 
clinker not larger than 1 mm in size, 1-25 percent by weight of alumina 
cement and not more than 5 percent by weight of magnesia clinker.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Either electro-fused or sintered spinel clinker/ or a combination of the 
two types/ may be used in the preparation of monolithic refractories 
according to this invention. The ratio of MgO to Al.sub.2 O.sub.3 that 
make up the spinel may but need not coincide with the theoretical ratio. 
The mole ratio of MgO to Al.sub.2 O.sub.3 may be within the range of, for 
example, 0.7:1.3 to 1.3:0.7. The spinel clinker having a composition 
within this range can be chosen from among commercially available ones. 
FIG. 1 graphically shows the relationship between the maximum particle size 
of spinel clinker and the resistance of alumina-spinel monolithic 
refractories to slag penetration. The penetration of slag was measured by 
the same method as was used with the preferred embodiments described 
later. The refractories consisted of 70 percent by weight of sintered 
alumina clinker, 20 peccant by weight of sintered spinel clinker and 10 
percent by weight of alumina cement. 
As is obvious from FIG. 1, the refractories containing spinel clinker not 
larger than 1 mm in particle size exhibit good resistance to slag 
penetration. The resistance becomes more pronounced with refractories 
having spine clinker of 0.5 mm or smaller. It is thought that fine-grained 
spinel clinker uniformly and closely fills the gaps in matrix, and that 
the spinel clinker then prevents the penetration of slag by completely 
turning FeO and MnO in the slag into a solid solution. When the particle 
size of spinel clinker is coarser, by contrast, slag will penetrate inward 
through the openings left between the individual particles thereof. 
FIGS. 2a and 2b show the penetration of FeO and MnO, respectively, into 
steel ladles lined with three different types of monolithic refractories 
A, B, and C prepared under the same conditions as those used in the 
preparation of the refractories shown in FIG. 1, using spinel clinkers not 
larger than 0.5 mm, not larger than 1 mm, and from 1 mm to 5 mm in 
particle size, respectively. The particle size of the spinel clinker 
contained in monolithic refractories A and B was within the range 
according to this invention. Slag penetration with refractories A and B 
was limited substantially to the working surface and was not very deep. 
Five to 40 percent by weight of spinel clinker not larger than 1 mm or 0.5 
mm produces satisfactory results, with the best result obtained at 
approximately 20 percent by weight. FIG. 3 shows the slag penetration with 
monolithic refractories A and B containing spinel clinker not larger than 
1 mm and 0.5 mm, respectively. The amount of spinel clinker not larger 
than 1 mm is preferably 10-30 percent weight of the refractory. 
The tendencies shown in FIGS. 1 to 3 are exhibited by both sintered and 
electro-fused spinels. 
Addition of alumina clinker improves erosion resistance and volume 
stability. One, two, or more alumina clinkers can be chosen from among 
artificial ones such as sintered and electro-fused alumina and natural 
ones such as aluminous shale, bauxite and sillimanite. Since SiO.sub.2 
triggers the production of low melting point products, alumina clinkers 
containing less SiO.sub.2 are preferable. To facilitate the close packing 
of monolithic refractories, coarse, intermediate and fine particles may be 
mixed appropriately, with the maximum particle size chosen from within the 
range of, for example 1 mm to 40 mm. 
The amount of alumina clinker in the refractory is 50-90 percent by weight, 
and or preferably 60-80 percent by weight. Good resistance to erosion and 
slag penetration is unattainable if the amount is under 50 percent by 
weight. If the amount exceeds 90 percent by weight, the resulting decrease 
in the ratio of spinel clinker lowers the resistance to slag penetration. 
The content of alumina clinker in conventional monolithic refractories is 
lower than in the products according to this invention. The resistance of 
conventional monolithic refractories to erosion etc. depends principally 
on spinel clinker. In contrast, monolithic refractories of this invention 
contain more alumina clinker, which when combined with fine-grained spinel 
clinker greatly increases the resistance to slag penetration. 
The alumina cement which is employed in the present invention loan be of 
the type that is commomly used as a binder for refractories. The particle 
size is not larger than 180 mesh. The amount employed is 1-25 percent by 
weight and preferably 3-20 percent by weight. When the amount is less than 
1 percent by weight, the alumina cement dose not function as a binder that 
imparts adequate strength to refractories. When used in an amount greater 
than 25 percent by weight, MgO-Al.sub.2 O.sub.3 in the spinel clinker and 
CaO-Al.sub.2 O.sub.3 in the alumina cement react with each other to 
produce a larger amount of products that melt at as low a temperature as 
about 1350.degree. C., thereby lowering the erosion resistance of the 
refractories. 
One, two, or more magnesia clinkers can be chosen from among natural 
magnesia and artificial products such as sintered and electro-fused 
magnesia. Because SiO.sub.2 triggers the production of low melting point 
products, magnesia clinkers containing low amounts of SiO.sub.2 are 
preferable. When the amount of magnesia clinker exceeds 5 percent by 
weight, the expansion occurring upon the production of spinel becomes too 
large to maintain volume stability, and metal penetration and refractories 
spalling may then result. Thus, the preferable amount is 0.5-4 percent by 
weight. 
Though not limited, the particle size should preferably be not be larger 
than 3 mm. When the particle size is less than 0.1 mm, for example. The 
hydrating reaction of magnesia clinker gives rise to the problem of 
digestion undesirable to refractories under some service conditions. 
FIG. 4 shows the relationship between the content of sintered magnesia and 
the permanent linear change of monolithic refractories consisting of 60 
percent by weight of sintered alumina, 25 percent by weight of sintered 
spinel not larger than 0.5 mm in particle size and 15 percent by weight of 
alumina cement. Clearly, the permanent linear change after firing at 
1500.degree. C. is small when the amount of sintered magnesia is kept 
below 5 percent by weight. Though not shown in the graph, electro-fused 
magnesia also shows a similar tendency. 
The basic compositions of the monolithic refractories according to this 
invention are as described previously. However, various types of organic, 
inorganic, metallic and other fibers, metal powders, silica flour, 
dispersing agents containing phosphate, acrylate and lignin sulfonate and 
other refractory materials may be added to the extent that they do not 
detract from the effects of this invention. Especially, up to 4 percent by 
weight of silica flour effectively improves the strength of alumina spinel 
monolithic refractories at ordinary temperatures and above. If the 
addition of silica four exceeds 4 percent by weight, a larger amount of 
readily meltable products will be produced, thereby lowering the strength 
and erosion resistance at high temperatures. 
The monolithic refractories according to this invention can be cast into 
frames, with 4-15 percent by weight of water added thereto, according to 
the conventional method. The packing of the monolithic refractories can 
generally be facilitated by means of vibrator attached to the frame or a 
rod vibrator inserted into the refractories. For localized repairs, the 
monolithic refractories may be applied by troweling, patting or other 
conventional methods. 
A number of examples of this invention will next be described. Table 1 
shows the chemical compositions of the refractory materials used in the 
preparation of the examples. 
Table 2 shows the results of tests conducted on the examples of this 
invention and some conventional monolithic refractories prepared for the 
purpose of comparison. The tests were performed on monolithic refractories 
which had been cast and vibrated in frames, together with appropriate 
quantities of water, and dreid at 110.degree. C. for 24 hours. The test 
procedures were as follows. 
Bending test: According to JIS R 2553 
Linear change test: According to JIS R 2554 
Rotary erosion test: 
Slab: Steel ladle slag=1:1 (by weight) 
This test was conducted at 1650.degree. C. for 5 hours, and the amount of 
erosion and slag penetration were measured. 
TABLE 1 
__________________________________________________________________________ 
Chemical Composition of Refractory Materials (percent by weight) 
Sintered alumina 
Aluminous shale 
Sintered spinel 
Alumina cement 
Sintered magnesia 
__________________________________________________________________________ 
Al.sub.2 O.sub.3 
99.3 84.5 70.0 81.5 -- 
MgO -- -- 29.6 -- 98.9 
CaO -- 0.14 -- 18.5 -- 
SiO.sub.2 
0.4 9.9 0.3 0.2 0.7 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Examples of Present Invention and Conventional Products for 
__________________________________________________________________________ 
Comparison 
Present Invention 
1 2 3 4 5 6 7 8 9 
__________________________________________________________________________ 
Components of Monolithic Refractories (percent by weight) 
Sintered alumina, 1-40 mm 
35 40 30 40 45 50 40 35 40 
Sintered alumina, 1 mm max. 10 15 10 
Sintered alumina, 0.074 mm max. 
17 20 25 20 20 29 20 17 20 
Aluminous shale, 1-40 mm 10 5 
Aluminous shale, 1 mm max. 5 10 
Sintered spinel, 1-3 mm 
Sintered spinel, 1 mm max. 
40 40 
Sintered spinel, 0.5 mm max. 
30 25 13 5 5 30 
Sintered spinel, 0.15 mm max. 20 
Sintered magnesia, 1 mm max. 0.5 1 
Alumina cement 8 10 15 5 20 1 15 7.5 9 
Silica flour 2 
Sodium hexametaphosphate (percent by (0.1) 
weight of refractories) 
Water Added (percent by weight 
(7.1) 
(6.5) 
(7.4) 
(7.4) 
(7.2) 
(6.8) 
(7.0) 
(6.9) 
(7.0) 
of refractories) 
Tests 
Modulus of 
Ordinary temperature 
33 43 41 47 52 30 53 33 40 
rupture 
1400.degree. C. 
58 62 56 65 53 61 58 59 59 
(kg/cm.sup.2) 
Permanent Linear Change (%) 
-0.13 
-0.21 
-0.27 
-0.25 
-0.25 
-0.07 
-0.19 
-0.07 
-0.09 
1500.degree. C. .times. 3 hours 
Rotary Erosion (mm) 
4.3 4.5 4.7 4.5 4.8 4.6 4.5 4.4 4.6 
Erosion 
Slag Penetration (mm) 
2.8 2.2 2.3 2.0 2.1 2.4 1.9 2.7 2.3 
__________________________________________________________________________ 
Conventional Products 
Present Invention 
for Comparison 
10 11 12 13 1 2 3 4 
__________________________________________________________________________ 
Sintered alumina, 1-40 mm 
30 40 10 50 30 50 30 50 
Sintered alumina, 1 mm max. 
10 10 10 19 5 
Sintered alumina, 0.074 mm max. 
25 20 10 25 15 20 12 
Aluminous shale, 1-40 mm 
10 5 40 
Aluminous shale, 1 mm max. 5 
Sintered spinel, 1-3 mm 40 
Sintered spinel, 1 mm max. 
Sintered spinel, 0.5 mm max. 
20 12 15 5 1 1 50 
Sintered spinel, 0.15 mm max. 
8 
Sintered magnesia, 1 mm max. 
2 3 5 5 
Alumina cement 5 5 10 5 10 10 8 30 
Silica flour 
Sodium hexametaphosphate (percent by 
(0.1) 
(0.1) (0.1) 
weight of refractories) 
Water Added (percent by weight 
(7.2) 
(7.5) 
(7.8) 
(6.9) 
(6.8) 
(6.7) 
(7.7) 
(7.6) 
of refractories) 
Tests 
Modulus of Ordinary temperature 
32 29 40 32 43 42 35 64 
rupture 1400.degree. C. 
54 52 51 57 50 52 49 17 
(kg/cm.sup.2) 
Permanent Linear Change (%) 
+0.07 
+0.11 
+0.17 
+0.20 
-0.11 
+0.17 
- 0.10 
-0.45 
1500.degree. C. .times. 3 hours 
Rotary Erosion (mm) 
4.7 4.7 4.9 4.4 4.9 5.3 5.0 7.8 
Erosion Slag Penetration (mm) 
2.1 2.2 2.4 2.4 4.2 5.2 5.3 3.1 
__________________________________________________________________________ 
Due to higher resistance to erosion and slag penetration, the 
alumina-spinel monolithic refractories according to this invention proved 
to be at least 1.8 times more durable than the conventional products. 
Therefor, the alumina-spinel monolithic refractories of this invention are 
very useful in today's industrial environments in which furnaces are used 
under increasingly severe conditions and the need to reduce refractories 
consumption grows increasingly acute. 
The monolithic refractories according to this invention can be used not 
only for ladles, vacuum degassing vessels and hot-metal mixers but also 
for other equipment conventionally lined with monolithic refractories such 
as blast-furnace troughs and their covers, hot-metal mixer cars and 
tundishes.