Composite refractory member

A composite refractory member includes at least one insert formed of an oxide ceramic material having a high resistance to molten material. The insert defines a discharge opening or other molten material contacting surface. A base structure encloses and supports the insert and is formed by molding a chemically setting refractory concrete including a refractory granulate of low-iron sintered magnesia with a MgO content of over 80 weight percent. Mold cores extend into the refractory concrete during molding such that the molded structure has expansion joints which later are filled with mortar.

BACKGROUND OF THE INVENTION 
The present invention relates to a composite refractory member having 
therethrough a discharge opening and for use in discharging molten 
material, particularly molten metal, from a vessel, particularly a 
metallurgical vessel. The present invention particularly is directed to 
such a refractory member which may be employed as a movable or stationary 
plate assembly in a sliding closure unit, or as an inlet or outlet nozzle 
in such sliding closure unit. More particularly, the present invention is 
directed to such a refractory member of the type having at least one 
insert which at least partially defines the discharge opening of the 
refractory member and which is formed of an oxide ceramic material having 
a high resistance to the molten material, and a refractory base structure 
enclosing and supporting the insert. 
Furthermore, the present invention is directed to a method for the 
formation of such a refractory member. 
West German DE-AS No. 27 19 105 discloses a refractory plate assembly 
including an oxide ceramic insert enclosed by a refractory base structure 
of refractory concrete. The insert is of an oxide ceramic material 
particularly adapted to withstand the molten metal, and particularly the 
insert is formed of MgO, Cr.sub.2 O.sub.3, Al.sub.2 O.sub.3 or ZrO.sub.2 
or a mixture of such oxides. On the other hand, the refractory concrete of 
the base structure is composed of 70 to 95 weight percent tabular alumina 
and 5 to 30 weight percent of alumina cement with a content of 80 to 96 
weight percent of Al.sub.2 O.sub.3. 
This and similar alumina compositions are employed for the refractory 
concrete due to the relatively high thermal shock resistance of such 
materials. However, the use of such refractory concrete compositions has 
certain inherent disadvantages. Thus, such materials have low corrosion 
resistance to molten metals, and this is a problem when a molten metal 
contacts a base structure formed of such composition. This can occur, for 
example, when the two plates of a sliding closure unit are formed of 
composite refractory members. Specifically, it can occur that the molten 
metal will penetrate between the two plates and come into contact with the 
base structures. Further, such alumina compositions have relatively low 
friction resistance. 
In view of the above disadvantages of conventional alumina compositions, it 
would be desirable to form the base structure of a refractory concrete 
having greater abrasion resistance and resistance to erosion by molten 
metal. However, refractory concretes of such type, for example magnesia, 
have a relatively low thermal shock resistance and therefore have been 
considered to be too brittle for use as a refractory concrete for forming 
a base structure of a composite refractory member of this type. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide such a 
composite refractory member including at least one insert formed of an 
oxide ceramic material having high resistance to the molten metal and a 
base structure enclosing and supporting the insert and being formed of a 
refractory concrete having greater durability, abrasion resistance and 
erosion resistance than materials employed in the past. It is a more 
specific object of the present invention to employ materials of a type 
which have been considered in the past to be unsuitable for such purpose 
due to relatively low thermal shock resistance and brittleness, by 
employing a particular composition of such materials combined with an 
alteration of the base structure to compensate for such undesirable 
property. 
It is a further object of the present invention to provide a method for the 
formation of such specific composite refractory member. 
These objects of the present invention are achieved in the following 
manners. 
Thus, the composite refractory member of the present invention includes at 
least one insert at least partially defining the discharge opening of the 
refractory member and formed of an oxide ceramic material having a high 
resistance to the molten metal. The base structure enclosing and 
supporting the insert is formed of a chemically setting refractory 
concrete including a refractory granulate of low-iron sintered magnesia 
with a MgO content of over 80 weight percent. The base structure has 
therein at least one expansion joint which is filled with mortar, the 
expansion joint being positioned and extending in directions to minimize 
the relatively low thermal shock resistance of the magnesia material. 
Particularly, the expansion joint extends in a direction generally 
parallel to the axis of the discharge opening. After the chemically 
setting refractory concrete of this composition has set, and after heat 
treatment of the refractory member, mortar is filled into the expansion 
joint, and such mortar may be of the same composition as the refractory 
concrete material employed for the base structure. 
As a result of the use of the above magnesia refractory concrete, it is 
possible to impart to the base structure a greater durability than has 
been possible in the past, particularly when the refractory members are 
employed as plates in a sliding closure unit, since any molten metal 
penetrating between the plates and reaching the surface of the base 
structure over the insert during operation of the sliding closure unit 
will cause less corrosive and erosive damage to the base structure than 
has occurred in accordance with prior art arrangements. Further, the base 
structure of sintered magnesia according to the present invention is 
extremely resistant to any damaging frictional forces that might occur 
between the two plates due to freezing therebetween of the metal. The use 
of a refractory concrete with sintered magnesia as a refractory granulate 
is possible without the risk of stress cracks due to the relatively low 
thermal shock resistance of the magnesia due to the provision of the 
system of expansion joints. Particularly, the expansion joints counteract 
the relatively low thermal shock resistance of the magnesia material and 
prevent stress cracks which otherwise would occur during heat treatment of 
the plate after the base structure has set or dried. It is only the 
combined effect of the use of the particular sintered magnesia material 
with the provision of the expansion joints which makes possible the 
improved composite refractory member of the present invention. As a 
result, there is uniform wear of the base structure and the oxide ceramic 
insert, thereby increasing the useful life of the refractory member. 
Particularly, it is possible to use a refractory member according to the 
present invention for a longer time for a greater number of molten metal 
discharge operations, thereby making the refractory member more cost 
competitive. 
The refractory material employed for the base structure of the present 
invention is a refractory concrete which is chemically setting (in a 
manner known in the art) and which includes a refractory granulate of 
low-iron sintered magnesia with a MgO content of over 80 weight percent. 
As employed herein the term "low-iron" is intended to indicate, as would 
be understood by those skilled in the art, that the sintered magnesia is 
very pure, for example sea water magnesia, i.e. recovered from sea water 
by treatment with slaked lime or slightly calcined dolomite having an iron 
content of no more than approximately 0.5 weight percent. One example of 
the overall composition of the sintered magnesite according to the present 
invention, in approximate values, is 97 weight percent MgO, 2 weight 
percent CaO, 0.2 weight percent Fe.sub.2 O.sub.3 and 0.8 weight percent 
residual oxide. It is not intended however that this specific composition 
be limiting of the scope of the present invention, and those skilled in 
the art would understand from the present disclosure other compositions 
that may be employed, the important limitations being that the sintered 
magnesia of the refractory granulate have a low iron content and a MgO 
content of over 80 weight percent. 
The present invention particularly is useful as a composite refractory 
member in the from of a plate for a sliding closure unit, since such 
members are subjected to particularly harsh operating conditions. Although 
the operating conditions for inlet and outlet sleeves or nozzles of 
sliding closure units are not as severe, the concept of the present 
invention equally applies to composite refractory members of such type, 
since the durability of such sleeves or nozzles is increased according to 
the present invention. 
In accordance with the method aspect of the present invention, the oxide 
ceramic insert is positioned within a mold such that there is a space 
defined between the insert and the mold. At least one mold cure is 
extended from the mold into the space to form the expansion joint. The 
chemically setting refractory concrete of the above composition is filled 
into the space, and the refractory concrete is set chemically (as is known 
in the art), thereby forming the base structure enclosing and supporting 
the insert. The thus, formed refractory member is removed from the mold, 
and the mold core is removed from the refractory concrete, thereby forming 
the expansion joint in the base structure. After heat treatment of the 
refractory member, the expansion joint is filled with refractory mortar, 
which can be of the same composition as that of the refractory concrete. 
Advantageously, the mold core is wedge-shaped with a wider end directed 
toward the mold. As a result, the expansion joint will be formed 
wedge-shaped with a wider end at a surface of the base structure or 
refractory member. This facilitates the removal of the mold core from the 
base structure after setting thereof. 
When the composite refractory member is in the form of a refractory plate 
assembly for a sliding closure unit, and particularly wherein such 
assembly has two spaced long sides, then preferably at least one expansion 
joint is provided at approximately the middle of each long side, with each 
expansion joint extending longitudinally at a right angle to such long 
side across the entire width or dimension of the base structure at such 
position. Further, the expansion joint extends into the base structure for 
a depth at least equal to the thickness of the insert. It is to be 
understood that additional expansion joints may be provided in the base 
structure around the periphery of the insert at suitable locations as 
necessary to counteract the development of thermal stress cracks, as would 
be understood by one skilled in the art for a particular structural 
configuration. Further, it is possible for the expansion joints to extend 
to a depth throughout the thickness of the base structure. 
When the composite refractory member is in the form of an inlet or outlet 
sleeve or nozzle for a sliding closure unit, then the insert is in the 
form of a tube or a sleeve and the base structure also is in the form of a 
tube or a sleeve surrounding the insert. In such situation, the expansion 
joint has a longitudinal direction parallel to the axis of the sleeves and 
has a depth in a radial direction of the sleeves. The expansion joint may 
extend entirely through the thickness of the base structure or through 
only a portion thereof. Further, a plurality of expansion joints may be 
spaced around the periphery of the tube or sleeve-shaped base structure 
and may have depths extending less than the thickness thereof.

DETAILED DESCRIPTION OF THE INVENTION 
FIGS. 1 and 2 illustrate a composite refractory member in the form of a 
movable refractory plate assembly 1 for use in a sliding closure unit of 
the rectilinearly movable type. The assembly 1 has spaced, parallel long 
sides and includes a plate-shaped insert 3 forming a sliding surface 4 of 
the plate assembly 1. A ring-shaped insert 5 abuts insert 3, and the two 
inserts have therethrough openings defining a discharge opening 6 through 
the plate assembly. Inserts 3, 5 are formed in a known manner of an oxide 
ceramic material having a high resistance to the molten material, for 
example metal, to be discharged. Inserts 3, 5 are fabricated of such oxide 
ceramic material, for example a highly refractory oxide such as zirconium 
oxide, as would be understood by one skilled in the art. 
After any necessary adjustments of inserts 3, 5 the inserts are positioned 
within a mold, and around such inserts is molded a cold chemically setting 
refractory concrete, for example pourable or vibratable, to form a base 
structure 2 enclosing and supporting the inserts. The refractory concrete 
includes a refractory granulate of low-iron sintered magnesia with a MgO 
content of over 80 weight percent. Extending into the space filled by the 
refractory concrete are mold cores, for example as shown at 8 in FIGS. 3A 
and 3B. The refractory concrete is chemically set, as would be understood 
by one skilled in the art, for example with the addition of phosphate. 
After setting, the resultant formed composite refractory member 1 is 
removed from the mold. Mold cores 8 are removed, such that expansion 
joints 7 are formed in the base structure 2. The combination of the use of 
the particular refractory concrete and the provision of the expansion 
joints makes possible the use for the base structure of a material having 
high durability, abrasion resistance and erosion resistance, without 
concern for the formation of thermal stress cracks in such material. 
As shown in FIGS. 1 and 2, expansion joints 7 are formed at approximately 
the middle of each long side of the refractory member 1, and each 
expansion joint 7 has a longitudinal direction extending at a right angle 
to such long side. As shown in FIG. 2, each expansion joint 7 has a depth 
extending into base structure 2 at least equal to the thickness of 
plate-shaped insert 3. The wedge-shape of the mold cores 8, as shown in 
FIG. 3B, facilitates removal of the mold cores from the set refractory 
concrete of base structure 2. The expansion joints 7 avoid thermal 
stresses in the base structure that lead to cracks during the heat 
treatment of the assembly 1. Following the heat treatment of base 
structure 2, which essentially is a tempering operation, the expansion 
joints 7 are filled and sealed with a refractory mortar which is smooth. 
Filling of the expansion joints is facilitated by the wedge shape thereof. 
The refractory mortar may be material of the same composition as the 
refractory concrete of the base structure. FIG. 2 shows the expansion 
joints 7 extending from the level of sliding surface 4 into the base 
structure 2 for a depth at least equal to the thickness of plate insert 3. 
Expansion joint 7 however could extend to a deeper depth or entirely 
through the thickness of the base structure. Further, additional joints 
other than the two joints shown in FIG. 1 could be provided around the 
circumference of the assembly. 
FIGS. 4 and 5 illustrate the features of the present invention applied to a 
composite refractory member in the form of an outlet nozzle 11 for example 
intended for use with the plate assembly 1 of FIGS. 1 and 2. Thus, the 
highly erosion resistant insert is in the form of a sleeve 13, and the 
base structure 12 also is in the form of a sleeve surrounding insert 13. 
Sleeve insert 13 defines discharge opening 16, for example aligned with 
discharge opening 6 of plate assembly 1 during assembly and use of a 
sliding closure unit. The base structure 12 of FIGS. 4 and 5 is formed of 
the same material as base structure 2 discussed above. An expansion joint 
14 has a longitudinal dimension extending parallel to the axis of 
discharge or outlet opening 16, and as shown in FIG. 5, expansion joint 14 
extends radially thereof. Also illustrated is the fact that expansion 
joint 14 is wedge-shaped, as formed by mold core 18 and is removed 
radially from set base structure 12. FIG. 5 illustrates a single expansion 
joint 14 extending entirely through the thickness of base structure 12. 
Alternatively, depending upon the particular installation, and as would be 
understood by one skilled in the art, a plurality of expansion joints may 
be spaced around the circumference of the base structure, and such 
expansion joints can be provided to have smaller radial depths of 
penetration into the base structure. 
FIG. 6 illustrates a composite refractory member 21 in the form of a bottom 
or stationary plate assembly for use in a sliding closure unit. Assembly 
21 includes a plate-shaped insert 23, a generally tubular shaped insert 
25, the two inserts together defining a discharge opening 26, and a base 
structure 22 enclosing and supporting the inserts. Assembly 21 has two 
long sides, in approximately the middle of each of which is formed an 
expansion joint 27. Expansion joint 27 is formed similar to the manner 
discussed above regarding the embodiment of FIGS. 1 and 2, except FIG. 6 
illustrates the expansion joint as extending through the entire thickness 
of the base structure. 
In all of the above embodiments of the present invention, the expansion 
joints 7, 14, 27 are filled with a refractory mortar after heat treatment, 
i.e. tempering, of the assemblies in a manner which would be understood by 
one skilled in the art, for example for approximately twelve hours at a 
temperature of 250.degree. to 300.degree. C. 
The thickness of the expansion joints 7, 14, 27, their formation and 
arrangement in the particular refractory shapes, such as 1, 11, 21, depend 
substantially on the shape and size of the refractory assembly. For 
example, in relatively large format plate assemblies, for example for 
sliding closure units for furnaces, a thickness of the expansion joints of 
from 3 to 4 mm has proven to be appropriate. This is exemplary however, 
and one skilled in the art would understand how to select a suitable joint 
shape, thickness and location for a particular installation. 
FIG. 6 further illustrates, somewhat schematically, the method of the 
present invention for the formation of the composite refractory member 21. 
Thus, initially plate-shaped insert 23, for example prefabricated from 
zirconium oxide, is placed with sliding surface 24 on a smooth backing 
plate 20 of a mold. An aligning member 29 of the mold is employed to align 
the discharge openings 26 in plate-shaped insert 23, and ring-shaped 
insert 25 is positioned thereon or built up, in a manner as would be 
understood by one skilled in the art. Mold 30 then is positioned over the 
assembly to define a space between inserts 23, 25 and mold 30. It will be 
understood that mold 30 may be provided to allow for adjustment in a known 
manner. Extending into the space from the inside of mold 30 along the long 
sides are opposing wedge-shaped mold cores 28. The refractory concrete 
discussed above then is filled into the space through suitable fill 
openings, such as shown schematically at 31 and 32. Specifically, the 
above discussed refractory concrete may include a phosphate binder, and 
after the filled refractory concrete has set, the resultant assembly 21 is 
removed from the mold. The mold cores 28 are removed, and after heat 
treatment the expansion joints 27 are filled by refractory mortar. 
Although the present invention has been described and illustrated with 
respect to preferred features thereof, it is to be understood that various 
changes and modifications may be made to the specifically described and 
illustrated features without departing from the scope of the present 
invention.