Refractory, heat insulating articles

The invention relates to preformed, shaped, refractory, heat-insulating articles for use in an expendable sidewall lining of a molten metal handling vessel. The lining has a face at part of which is exposed a zone of matter of high resistance to erosion by molten metal and accompanying slag. The vessel may be e.g. a tundish for use in the continuous casting of molten metal e.g. steel.

The invention relates to refractory, heat-insulating articles, to molten 
metal handling vessels lined with such articles and to the use of such 
vessels. 
In the continuous casting of metals, e.g. steel, molten metal is poured 
from a ladle into a continuous casting mould via an intermediate vessel 
which acts as a constant head reservoir and is called a tundish. The 
tundish has a metal floor and sidewalls and one or more outlet nozzles set 
in the floor or a sidewall. To protect the metal floor and walls of the 
tundish from the effects of molten metal it is usual to line the interior 
of the tundish with a relatively permanent lining, often made of bricks. 
The tundish may additionally be provided with an inner, expendable lining 
of refractory, heat-insulating slabs. This is described in U.K. patent 
specification No. 1364665 and is highly advantageous. 
Although the expendable lining described above is intended to be 
expendable, it needs to survive satisfactorily for the duration of a cast 
and this may involve the passage of more than one ladleful of metal 
through the tundish, a practice known as sequence casting. The lining 
needs to withstand not only the temperature of the molten metal but also 
erosion by the metal and any slag associated with it. 
To extend the usefulness of expendable tundish linings much work has been 
done over the years to enhance the erosion resistance of the linings. 
Enhanced erosion resistance has been achieved in various ways e.g. by 
increasing the density of the linings and/or by use of materials e.g. 
graphite that lead to enhanced erosion resistance. Improvements in erosion 
resistance have been accompanied by increased thermal capacity and 
conductivity and these consequences have been accepted as inevitable and 
tolerated for the sake of the improved erosion resistance. 
According to the invention a preformed, shaped, refractory, heat-insulating 
article for use in an expendable sidewall lining of a molten metal 
handling vessel has a face at part of which is exposed a zone of matter of 
high resistance to erosion by molten metal and accompanying slag. 
In molten metal handling vessels some areas are more subject to erosion 
than others and, in particular, areas that come into contact with molten 
slag are more inclined to be eroded than areas which only come into 
contact with molten metal. Use of articles of the invention enables molten 
metal handling vessels to be provided with expendable linings having a 
valuable combination of erosion resistance properties and other properties 
e.g. thermal capacity and conductivity properties. 
During continuous casting the level of molten metal in the tundish usually 
changes relatively little and thus the same area of the sidewall lining is 
in prolonged contact with slag on the surface of the molten metal and is 
therefore particularly subject to erosion. Articles of the invention in 
the form of slabs are particularly advantageous for lining tundish 
sidewalls and for this purpose the high erosion resistance zone of the 
slab is at or near the upper end of the slab in use. The uppermost part of 
the slab in use is usually subject to little or no contact with molten 
metal and slag and thus it is generally preferred that the high erosion 
resistance zone of the slab should be somewhat spaced from the upper edge 
of the slab in use. 
Part of the article maybe of lower specific heat and thermal conductivity 
than the high erosion resistance zone which can be of great value in that 
it enables advantageous thermal properties to be achieved in those areas 
of the lining where these properties are particularly important. When 
molten metal is initially introduced into a molten metal handling vessel, 
the hot metal is chilled by contact with the colder lining and, even if 
the thermal properties of the lining are subsequently adequate, the 
initial chilling of the metal can lead to problems. For example, in the 
case of tundishes the initial chilling can lead to difficulties at the 
start of casting and require special measures to be taken in preparing the 
tundish for use and/or require supplying the metal at a higher 
temperature. As the molten metal initially introduced contacts first the 
lining of the base of the vessel and the lower part of the sidewall 
lining, the thermal properties of these parts of the lining are 
particularly important in relation to the initial chilling effect. 
Accordingly, sidewall lining slabs according to the invention in which the 
lower part in use is of relatively low specific heat and thermal 
conductivity enable the initial chilling effect to be kept low and such 
slabs are particularly useful in tundishes. 
Alternatively, in circumstances where the initial chilling effect is not a 
particular problem or the lining is preheated before introduction of the 
molten metal into the tundish, the part of the face other than the high 
erosion resistance zone may be of higher specific heat and thermal 
conductivity than the zone. 
Other factors which influence the form which tundish lining slabs of the 
invention may have are related to the steelmaking practice in use at the 
steelworks where the slabs are used. 
In some instances a low viscosity slag may be used as a cover for the 
molten steel in a tundish for the purpose of removing deleterious alumina 
inclusions from the steel. Such low viscosity slags generally have a high 
residual level of sodium oxide present which reacts with sidewall lining 
slabs, containing as principal fillers, magnesite, silica and olivine or 
mixtures of these, causing severe erosion in a short time period at the 
slag/slab reaction interface. Failure of the slabs in this way is most 
disadvantageous since the slabs will need replacement thus interrupting 
the continuous casting sequence which is clearly undesirable. 
Other types of slags encountered in a tundish which are particularly 
troublesome from the point of view of rapid erosion of the sidewall lining 
slabs at the slab/slag interface are lime-fluorspar slags carried over 
into the tundish i.e. generally not deliberately added as a covering slag 
by a steelmaker, but present in the tundish as a result of the secondary 
ladle steelmaking process and high manganese oxide containing slags which 
are often encountered in a tundish when the steel therein is produced 
using a basic oxygen process. 
In each case the articles according to the invention are formed with the 
high erosion resistant zone exposed at the face destined to face the 
molten metal. The zone may have the following characteristics: 
(i) a higher density than the density of the matter at the remainder of the 
face of the article where both are formed from substantially the same 
composition especially having regard to the refractory filler content and 
types: or 
(ii) a higher density than the remainder of the matter at the face of the 
article where the zone is formed of a different composition from the 
remainder of the face especially having regard to the refractory filler 
content and type: or 
(iii) a lower density than the remainder of the face where the zone is 
formed of a different composition from the remainder of the face having 
regard to the refractory filler content and type. 
In articles of the invention the high erosion resistance zone is exposed at 
a face of the article but it is generally preferred that this zone should 
not extend throughout the thickness of the article. 
An advantage of the articles of the invention is that compared with 
articles composed wholly of dense material of high erosion resistance the 
articles can be made with lower overall densities, thereby rendering 
handling of the articles easier. Moreover, material of relatively low 
specific heat and thermal conductivity is generally more permeable than 
material of high erosion resistance and this aids escape through the 
lining rather than into the molten metal of any deleterious gases formed 
as a result of the metal contacting the lining. Furthermore the inclusion 
of the high erosion resistance zone may enable suitable properties to be 
achieved with thinner, and therefore lighter and more easily handled, 
articles. 
The high erosion resistance zone of an article of the invention may 
comprise refractory filler and binder. Examples of suitable refractory 
fillers are silica, olivine, alumina, aluminosilicates and chromite. 
Preferably the refractory filler comprises one or more of calcined 
magnesite, calcined bauxite, corundum and zircon. The binder may be 
organic and/or inorganic. Examples of suitable organic binders are 
phenol-formaldehyde, urea-formaldehyde resins and starches. If organic 
binder alone is used the amount is preferably 3 to 6% by weight. Examples 
of suitable inorganic binders are silicates, especially sodium silicate, 
and phosphates. Inorganic binder if used is preferably present in an 
amount of 3 to 12% by weight. 
The high erosion resistance zone may be made by a slurry-forming technique 
i.e. an aqueous slurry of the ingredients is de-watered in a suitably 
shaped permeable mould and the product then heated to dry it and render 
the binder effective. If the zone is made by a slurry-forming technique, 
it preferably contains inorganic fibre, e.g. calcium silicate fibre, 
fibreglass and aluminosilicate fibre, preferably in an amount of 0.2 to 5% 
by weight. Alternatively, the high erosion resistance zone may be made by 
ramming a damp mixture of its ingredients into a suitable mould or former 
or into a recess formed in the face of the article. 
The erosion resistant zone may also be made by casting a pourable slurry or 
paste of the ingredients comprising a cementitious binder into a suitable 
mould or former and allowing the slurry or paste to set. As above, the 
casting of the zone can be into a recess formed in the face of the 
article. The ingredients for casting in the manner prescribed above may 
comprise a high purity source of alumina e.g. corundum or aluminosilicate 
e.g. bauxite and a high-alumina cement. 
The other part or parts of the article may also comprise refractory filler 
and binder and the same or different refractory fillers may be used and 
the same binders may be used. Lightweight refractory fillers e.g. expanded 
perlite may be included e.g. in amounts of 2 to 8% by weight. The part is 
preferably made by a slurry-forming technique and may contain 0.5 to 3% of 
organic fibre e.g. scrap paper. Inorganic fibre is preferably present if 
there is no organic fibre and may be present in any event e.g. in amounts 
of 2 to 8% by weight. Suitable inorganic fibres include calcium silicate 
fibre and fibre-glass. 
The formation of the high erosion resistance zone and the remainder of the 
face have been separately described above but it is in fact preferred to 
form the zone first and then form the rest of the face around it. In 
particular in the case where all the components are formed from aqueous 
slurries it is preferred to form the high erosion resistance zone first, 
(but not to heat it to dry it and render the binder effective) and then to 
form the material of the rest of the face around the already formed zone 
and heat the article to dry it and render the binder effective throughout 
the article. As an alternative after formation of the high erosion 
resistance zone, this zone may be heated to dry it and render the binder 
effective and the rest of the face then formed around the high erosion 
resistance zone in a "keying" relationship and heated to dry it and render 
the binder effective. Similarly, the cement bonded material may be 
preformed and the face formed around it in a "keying" relationship. 
Furthermore, the preformed high erosion resistance zone may be adhered to 
the face of an article according to the invention by any suitable means 
e.g. a refractory cement or adhesive. 
An article according to the invention may be formed which comprises a 
facing layer at the surface of which the zone is exposed and a backing 
layer of lower specific heat and thermal conductivity than that of the 
facing layer. 
According to a further aspect of the invention a molten metal handling 
vessel has an expendable sidewall lining comprising one or more articles 
of the invention so positioned that the high erosion resistance zone faces 
into the vessel. 
Whilst the invention has been described chiefly in relation to tundishes, 
the articles of the invention may be used in other molten metal handling 
vessels e.g. ladles. The invention is particularly valuable in relation to 
ferrous metals e.g. steel and iron. The vessel may be a tundish for 
continuously casting steel or a ladle for making iron or steel castings by 
pouring the molten metal into a mould from the ladle.

The slab of FIGS. 1 and 2 has a zone 1, of high resistance to erosion by 
molten metal and accompanying slag, towards the upper end of the inner 
face of the slab and the remainder of the slab is a part 2 of lower 
specific heat and thermal conductivity than the zone 1. 
The slab of FIG. 3 has a zone 1 of high resistance to erosion by molten 
metal and accompanying slag, towards the upper end of the inner face of 
the slab and the remainder of the inner face is a part 2 of the same 
composition as zone 1 but having a lower density and behind part 2 is a 
different composition of highly heat-insulating material 3. 
In FIG. 4 a slab is shown which has a zone 1 formed of a preformed castable 
cementitious composition partly in a recess formed in the remainder 2 of 
the slab. 
In FIG. 5 a slab is shown which has a zone 1 formed of a preformed castable 
cementitious composition adhered to the face 2 of a two layer slab having 
a backing layer 3 by means of a refractory cement. 
Examples of suitable compositions for the high erosion resistance zone are 
as follows: 
______________________________________ 
Ingredient % by weight 
______________________________________ 
1 calcined magnesite 91.5 
boric acid 0.5 
calcium silicate fibre 
3.0 
scrap paper 1.0 
phenol-formaldehyde resin 
4.0 
2 zircon sand 55.2 
calcined bauxite 30.8 
calcium silicate fibre 
2.5 
scrap paper 1.5 
phenol-formaldehyde resin 
3.0 
urea-formaldehyde resin 
1.5 
fibreglass 0.5 
sodium silicate (SiO.sub.2 :Na.sub.2 O 
5.0 
ratio 3.37:1) 
3 calcined magnesite 85.0 
carbon (electrode scrap) 
10.0 
sodium hexametaphosphate 
4.0 
aluminosilicate fibre 
1.0 
______________________________________ 
Compositions 1 and 2 may be formed by slurry-forming techniques to give 
shapes having densities of 1.7 and 1.6 g.cm.sup.-3 respectively whilst 
composition 3 can be formed into a shape of density 2.1 g.cm.sup.-3 by a 
ramming technique. 
Examples of suitable castable cementitious compositions for the high 
erosion resistance zone are as follows: 
______________________________________ 
Ingredient % by weight 
______________________________________ 
4 alumina (corundum) 83.0 
calcium-aluminate cement 
17.0 
5 aluminosilicate (andalusite) 
72.0 
alumina (corundum) 11.0 
calcium-aluminate cement 
17.0 
6 alumina 86.0 
silica 4.0 
calcium-aluminate cement 
10.0 
______________________________________ 
Compositions 4, 5 and 6 were formed by the addition of sufficient water to 
form a pourable slurry or paste and allowed to set for 24 hours in a 
former or mould, to give shapes. The shapes when subsequently dried at 
110.degree. C. for 2 hours and heated to 600.degree. C. and cooled to 
ambient over an extended period had a density of 3.0 g.cm.sup.-3, 2.4 
g.cm.sup.-3 and 3.4 g.cm.sup.-3 respectively. 
Examples of suitable compostiions for the remainder of the face are as 
follows: 
______________________________________ 
Ingredient % by weight 
______________________________________ 
A calcined magnesite 82.5 
ball clay 5.75 
phenol-formaldehyde resin 
4.0 
scrap paper 2.5 
expanded perlite 4.75 
boric acid 0.5 
B calcined magnesite 75.3 
silica sand 15.0 
starch 3.0 
calcium silicate fibre 
3.0 
fibreglass 0.2 
urea-formaldehyde resin 
1.5 
scrap paper 2.0 
______________________________________ 
Compositions A and B may be formed by slurry-forming techniques to give 
shapes having densities of 1.15 and 1.4 g.cm.sup.-3 respectively. 
In the case where the part of the article other than the zone comprises a 
plurality of layers, the backing layer may be formed of the following 
highly heat-insulating composition: 
______________________________________ 
Ingredient % by weight 
______________________________________ 
olivine 84.2 
paper 6.3 
phenol-formaldehyde resin 
3.2 
slag wool 6.3 
______________________________________ 
The density of the above slurry-formed composition after drying for 4 hours 
at 180.degree. C. was 0.87 g.cm.sup.-3.