Tubes for casting molten metal

A tube for continuous casting of molten metal is composed of a thin sheet-metal cladding and of an internal lining of heat-insulating material which is sinterable at the casting temperatures involved. The upper end of the casting tube is attached in air-tight manner to the discharge outlet of a first vessel for containing molten metal. The lower end of the casting tube dips into the molten metal of a second vessel located downstream with respect to the first vessel. In conjunction with the sheet-metal cladding, the casting tube comprises a tubular reinforcement member embedded within the lining material. The reinforcement member extends to the full depth of that portion of the casting tube which is in contact with the molten metal.

The present invention relates to casting tubes for conducting molten metal 
in transfer operations. 
Practical experience in this field has shown that all casting tubes of 
insulating material, and especially those described in French Pat. Nos. 
2,333,599 and 2,433,995 are subject to certain disadvantages and 
limitations which the present invention proposes to overcome. 
In particular, in the forms of construction described with reference to 
FIGS. 5, 6 and 7 of French Pat. No. 2,333,599, it has been found in 
practice that the casting tube exhibits deficient air-tightness at the 
beginning of casting operations. As the molten steel flows down the 
casting tube, the interior of the tube is in fact subjected to a 
succession of positive and negative pressures. When the interior of the 
tube is at a negative pressure or partial vacuum, the above-mentioned 
designs of the prior art allow air to pass to the steel through the pores 
of the insulating material and through the holes of the perforated 
reinforcement member, which is liable to affect the purity of the steel at 
the beginning of the casting operation. 
However, the embodiments described with reference to FIGS. 1, 3 and 4 of 
the patent cited above are not subject to this particular disadvantage by 
virtue of the fact that the casting tube is provided with a continuous 
sheet-metal cladding. On the other hand, when the end of said casting tube 
is immersed in the molten steel, the sheet-metal cladding which comes into 
contact with the steel is heated to a temperature such that it either 
melts or else completely looses its mechanical strength. As the steel 
flows down within the casting tube, the overpressure which exists within 
said tube often results in fracture of the entire immersed portion of this 
latter since the insulating material of said tube does not have sufficient 
strength. The debris thus produced are liable to form scoria within the 
steel. Furthermore, the jet of molten steel is thus liable to be put into 
contact with the surrounding air. 
In order to provide a remedy for this situation, it has also been proposed 
to mount an external reinforcement sleeve around the immersible end of the 
casting tube (show in FIG. 1 of French Pat. No. 2,433,995, said 
reinforcement sleeve being directly attached to the sheet-metal cladding 
of the casting tube. The aim of this expedient is to prevent the molten 
steel from destroying the metal cladding of the immersible portion of the 
casting tube. While this protection often proves to be effective, a 
disadvantage nevertheless arises from the need to increase the external 
diameter of the tube end, thus in turn increasing the weight and capital 
cost involved. A tedious requirement is also imposed on the user when it 
proves necessary under certain circumstances to fit the sleeve on the 
casting tube at a service location. 
In order to overcome this drawback, a logical expedient open to anyone 
versed in the art would be to increase the strength of the insulating 
material by increasing its thickness. This clearly has the disadvantage, 
however, of increasing the weight and cost while at the same time reducing 
the ease of handling of the casting tube. Another logical answer to the 
problem would be to increase the thickness of the sheet-metal cladding or 
its resistance to melting but the same disadvantages would again be 
encountered. 
The French Pat. No. 2,333,599 also describes a casting tube made from 
sinterable material which is reinforced internally by a metallic sleeve 
associated with anchoring means such as a perforated sheet-metal element 
or a wire-mesh element. However this metallic sleeve has a thermal 
expansion considerably different from that of the sinterable lining and 
thus craks are formed in said lining. These cracks create passages in the 
lining which enables the molten metal to come into contact with the 
metallic sleeve and melt the latter. 
The object of the present invention is to remove the disadvantages 
mentioned in the foregoing. 
In accordance with the invention, the casting tube is composed of a thin 
sheet-metal cladding and of an internal lining of heat-insulating material 
which is sinterable at the casting temperatures involved. The upper end of 
said casting tube is attached in a substantially airtight manner to the 
discharge outlet of a vessel for containing molten metal. The lower end of 
the casting tube dips into the molten metal of a second vessel located 
downstream with respect to the first vessel. In conjunction with the 
sheet-metal cladding, the casting tube essentially comprises a tubular 
reinforcement member embedded within the lining material. Said 
reinforcement member extends to the full depth of that portion of the tube 
which is in contact with the molten metal. 
The reinforcement member is constituted by a layer of material which has 
high mechanical strength and is different from the lining material, said 
material of said layer being chosen among the group consisting of: 
A--carbon fibers, graphite fibers, ceramic fibers, mineral fibers and 
mixtures of said fibers, said fibers being woven or not woven. 
B--refractory particles joined together by the means of a binder, said 
particles being chosen among the group comprising SiO.sub.2 or MgO as main 
components, CaO, Al.sub.2 O.sub.3, Fe.sub.2 O.sub.3, wherein, when the 
lining of the casting tube contains as main component SiO.sub.2 and is of 
acid nature, the tubular reinforcement layer contains MgO as main 
component and is of basic nature and wherein, when the lining of the 
casting tube contains as main component MgO and is of basic nature, the 
tubular reinforcement layer contains SiO.sub.2 as main component and is of 
acid nature, 
C--metal particles chosen among the group comprising Mg, Fe, Zn, Ca, Mn, 
Co, Ni and mixtures thereof mixed with Al.sub.2 O.sub.3, said mixture 
being converted into an oxide double of aluminum and of the metal(s) 
chosen among the above group under the heat involved by the molten metal 
casted into the casting tube. 
The unexpected result found by practical experience is that said 
reinforcement member is capable of preventing the immersed portion of the 
casting tube from breaking-away as it comes into contact with the 
surrounding molten metal when the sheet-metal cladding has either 
disappeared or lost its resistance. 
The casting tube as thus arranged has a wide range of potential 
applications. The tube can thus be mounted beneath the discharge outlet of 
a vessel for molten metal such as a casting ladle or a transfer vessel and 
can form part in particular of a slide-valve system which is capable to 
transverse displacement with respect to the axis of the casting tube. 
The casting tube can also constitute a removable nozzle which is engaged in 
the top end of a casting tube proper and connects this latter in air-tight 
manner to the discharge outlet of the casting vessel located upstream.

In FIG. 1, which illustrates a complete continuous-casting system, there is 
shown at 10 the base of the casting ladle with its refractory lining 12, 
the element of sinterable heat-insulating refractory lining 12, the 
element of sinterable heat-insulating refractory material being designated 
by the reference 22 and the seating brick for the fixed nozzle 21 being 
designated by the reference 23. 
The orifice of the nozzle 21 can be closed-off by means of a slide-valve, 
the movable plate of which is shown at 30 and the stationary plate of 
which is shown at 35, both plates being pierced by an orifice through 
which the molten metal passes. The slide-valve is shown in the closed 
position in FIG. 1. 
Beneath said slide-valve is placed the casting tube 3 which is capable of 
sliding transversely with respect to its axis at the same time as the 
plate 30, and a small removable connecting nozzle 19 which is mounted in 
air-tight manner by means of a refractory cement seal between the plate 30 
for mounting said nozzle and the top portion of the casting tube 3 in 
which it is engaged. In the example shown, the small nozzle 19 is applied 
against a metallic and/or refractory internal reinforcement ferrule 17 
arranged at the top of the casting tube 3. 
The assembly formed by the moving parts mentioned above is guided in 
transverse sliding motion relative to the axis of the casting tube 3 by a 
support 8 which is capable of displacement in translational motion (as 
shown by the arrows), said support being in turn guided by stationary lugs 
8a. The aforesaid assembly of parts constitutes a slide-valve system. 
The casting tube 3 is located between the ladle 10 and the tundish 13 which 
in turn carries a small casting tube or nozzle 4. Said nozzle can also 
form part of a slide-valve system and is located between the tundish 13 
and the continuous-casting ingot-mold 15. 
In the example considered, the invention is applied both to the casting 
tubes 3 and 4 and to the connecting nozzle 19. 
The tubes 3 and 4 are thus constituted respectively by a sheet-metal 
cladding element 1 and 2 having a small thickness of the order of one 
millimeter. In the case of the casting tube 3, the thin sheet-metal 
cladding 1 has an annular boss 7 which is intended to bear on the sliding 
support 8. 
The metal cladding 1 and 2 are each lined with an acid or basic sinterable 
heat-insulating material 3a and 4a having a density which can vary between 
0.7 and 2. 
EXAMPLE I 
An acid formula can contain: 
SiO.sub.2 : . . . 80 to 95% 
CaO: . . . 0 to 2% 
Al.sub.2 O.sub.3 : . . . 0 to 2% 
binder such as: 
phenol-formol, 
urea-formol or 
synthetic resin: . . . 0.5 to 3% 
organic fibers: . . . 0 to 3% 
residual water: . . . traces, 
wastage of the material by burning being advantageously less than 6%. 
EXAMPLE II 
A suitable basic formula for the lining 3 is as follows: 
MgO: . . . 60 to 90% 
CaO: . . . 0 to 3% 
SiO.sub.2 : . . . 0 to 20% 
Fe.sub.2 O.sub.3 : . . . 0.5 to 3% 
Binder: (as above) . . . 0.5 to 3% 
Organic fibers: . . . 0 to 3% 
Residual water, 
wastage by burning being advantageously less than 6%, 
In accordance with the invention, an internal reinforcement member 5 and 6 
is incorporated respectively within the lining 3a and 4b of the tubes 3 
and 4. The action of the said reinforcement member is combined with that 
of the metal cladding 1 or 2 of the tube considered. 
The internal reinforcement member 5 or 6 can preferably be made from carbon 
fibers, graphite fibers, ceramic fibers, such as kaolin or alumina fibers, 
mineral fibers such as glass, rock fibers and mixtures thereof. These 
fibers can be woven or non woven. These fibers are incorporated in the 
lining of sinterable material by using the method described in U.S. Pat. 
No. 4,432,396. When a certain thickness of the sinterable material of the 
lining is obtained, the end of the casting tube is dipped in a water 
suspension of fibers, containing eventually an inorganic or organic 
binder, then a second layer of sinterable material is formed on the 
fibrous layer. 
The reinforcement member thus obtained has a high mechanical strength with 
respect to the tube-lining material in which it is incorporated. 
Furthermore, no cracks are observed in the tube-lining material due to the 
heat of the metal passing in the tube. The thickness of the internal 
reinforcement member is advantageously within the range of 0.3 to 15 mm as 
a function of the thickness of the lining 3a or 4a of the casting tube. 
In the case of both of the tubes 3 and 4, the height of the internal 
reinforcement members 5 and 6 is such that it reaches--or preferably 
extends above--the top level of the molten metal which is being cast and 
comes into contact with the exterior of the tube. 
In the advantageous embodiment hereinabove described, the small removable 
connecting nozzle 19 of the casting tube 3 is also constructed in 
accordance with the present invention and is provided (as shown in FIG. 3) 
with an internal reinforcement member 31 which is similar to the 
reinforcement members 5 and 6 and extends throughout the height of said 
nozzle. The connecting nozzle 19 is thus composed of a solid and/or 
perforated metal jacket 20 lined internally with suitable refractory 
insulating material 19a which is similar to the internal linings 3a and 4a 
and in which the internal reinforcement member 31 is embedded. 
As shown in FIG. 1, the tundish 13 is filled with molten metal 14 up to the 
level N-N1. The continuous-casting ingot mold 15 is shown with its metal 
ingot 16 in process of solidification. 
The mode of action of the means proposed by the invention has been 
demonstrated by practical experience and will now be explained with 
reference to FIG. 2. 
Consideration will be given to the case of the casting tube 3 since the 
casting nozzle 4 is identical and the operating conditions are fairly 
similar to the case of the connecting nozzle 19. 
In that portion of the casting tube 3 which dips into the steel bath, the 
tubular region 26 forming part of the lining 3a and located behind the 
thin sheet-metal cladding 1 is capable of sintering only when the 
corresponding portion of said sheet-metal cladding 1 has melted 
approximately along the line 1b located in the vinicity of the level N-N1. 
The face 25 corresponding to the bottom edge of the tube sinters freely 
since it dips into the molten steel bath 14 without hindrance. 
The internal face 24 of the casting tube which is substantially in contact 
with the jet of metal sinters progressively during the sequential casting 
operation of operations until the sintering process reaches the sintered 
portion 26. This progressive sintering of the mass of the lining material 
3a is made possible only by the internal reinforcement member 5 which, 
while strengthening the immersed portion of the casting tube, enables said 
tubes to undergo this transformation without any attendant danger of 
fracture. 
FIG. 1 illustrates the casting tubes 3 and 4 immediately before the lower 
portion of their sheet-metal cladding 1 and 2 has melted. 
When the lower portion of the metal cladding has melted along the line 1b, 
the degree of development attained by the sintering process at this moment 
is not usually sufficient to permit the immersed end of the tube (which is 
assumed to be homogenous) to offer resistance to the effect of internal 
pressure and to the turbulent movements which take place in the molten 
steel at this point. 
It is precisely for the reason just given that, during this time interval, 
the internal reinforcement members such as those which are designated by 
the references 5, 6 or 31 and which are embedded within the sinterable 
material take over and ensure the necessary continuation to permit 
completion of the sintering process without any interruption. 
Breaking-away of the immersed end of the tube which usually took place 
along the line 1b is accordingly suppressed, thus preventing any contact 
between the molten metal and the surrounding air. 
As can readily be understood, the internal reinforcement member provided by 
the invention must be adapted to the shape of the casting tube while 
remaining coaxial with this latter. 
The internal reinforcement member 5, 6 or 31 can also be made from 
refractory particles joined together by the means of binder, said 
particles being chosen among the group comprising SiO.sub.2 or MgO as main 
components, CaO, Al.sub.2 O.sub.3, Fe.sub.2 O.sub.3, wherein, when the 
lining of the casting tube contains as main component SiO.sub.2 and is of 
acid nature, the tubular reinforcement layer contains MgO as main 
component and is of basic nature and wherein, when the lining of the 
casting tube contains as main component MgO and is of basic nature, the 
tubular reinforcement layer contains SiO.sub.2 as main component and is of 
acid nature. 
In other words, when the composition of the sinterable lining of the tube 
is acid (see above example I), the composition of the internal 
reinforcement layer 5, 6, 31 will be basic i.e that of above example II; 
when the composition of the sinterable lining of the tube is basic 
(example II), the composition of the internal reinforcement layer 5, 6, 31 
with be acid (example I). 
Alternatively the internal reinforcement member 5, 6, or 31 can also be 
made from metal particles chosen among the group comprising Mg, Fe, Zn, 
Ca, Mn, Co, Ni and mixtures thereof mixed with Al.sub.2 O.sub.3, said 
mixture being converted into a double oxide of aluminum and of the 
metal(s) chosen among the above group under the heat involved by the 
molten metal casted into the casting tube. 
When for example the metal particles are Mg, under the heat involved at the 
casting temperature, the layer composed of Mg and Al.sub.2 O.sub.3 is 
converted into a spinel which withstands a temperature up to 2135.degree. 
C. and which reinforces considerably the lining of the casting tube. 
In the case where the reinforcement layer is constituted by fibers or 
refractory particles, it is advantageous to mix with the same, metallic 
particles such as metallic power or wires. The effect of these metallic 
particles is to obtain a uniform temperature at the end of the tube, said 
uniform temperature being favourable to prevent any crack formation in the 
tube lining.