Flat formed submerged entry nozzle for continuous casting of steel

In a flat casting nozzle 10 having a taper 13, the position of the terminal end 14 of the taper 13 formed on the long edge side and the position of the terminal end 17 of a taper 16 formed on the short edge side are mutually shifted.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a submerged entry nozzle (SEN) for steel and, in 
particular, to a casting nozzle having a flat taper. 
More specifically, this invention relates to a flat continuous casting 
nozzle particularly preferred as a thin slab continuous casting submerged 
entry nozzle (SEN). 
2. Description of Related Art 
In casting steel, a submerged entry nozzle (SEN) is used in order to 
prevent oxidation of molten steel. A flat SEN having a lateral width 
extended toward the bottom so as to be suitable for continuous casting of 
a thin slab or plate has been used for a long time. 
FIG. 5 shows a conventionally used flat continuous casting SEN, wherein a 
side view showing the long edge side is on the left, and a side view 
showing the short edge side on the right. In FIG. 5, a flat SEN 1 has a 
flange 3 on the upper part, and the flange 3 is engagingly locked to a 
locking fitting 4, whereby the SEN 1 is engaged with the tundish nozzle 2. 
The respective corresponding positions of the left side view and the right 
side view of FIG. 5 are mutually connected by broken lines, and tapered 
parts 5, 6 of the SEN are formed so that the respective terminal positions 
are mutually conformed on the long edge side and short edge side of the 
SEN as shown in the drawing. 
As a result of various examinations for the generating form of thermal 
stress with respect to such a conventional SEN in which the terminal 
positions of the tapered surfaces of a flat SEN are mutually conformed, it 
was recognized that stress concentration exists in the taper terminal 
positions of the nozzle. This was confirmed also by finite-element 
analysis based on the physical properties shown in Table 1. 
TABLE 1 
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Physical Properties of Member Used for Analysis 
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Bulk Density 2.37 
Thermal Expansion (%) (1000.degree. C.) 
0.29 
Young's Modulus (kgf/cm.sup.2) 
0.09 .times. 10.sup.6 
Poisson's Ratio 0.2 
Thermal Conductivity (cal/cm.deg.sec) 
12.1 
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Under the boundary condition for analysis that molten steel of 1540.degree. 
C. is poured into a nozzle inner hole at an outside air temperature of 
30.degree. C., the stress generated in the nozzle was calculated. The 
analysis was performed with a 1/4 divided nozzle as a model. A 
constraining force of 4.4 kg/cm.sup.2 was imparted to the flange on the 
nozzle upper end. Thus, in the stress analytic result, the stress 
generated in the neck part, which is based on constraining force, is 
excluded from the examination of the generated stress by the coincidence 
of the taper terminal parts. 
SUMMARY OF THE INVENTION 
In consideration that the concentrating position of thermal stress in the 
conventional flat SEN corresponds to the position where the terminal 
positions of the nozzle long-edge side taper and short-edge side taper are 
mutually conformed, an object of the invention is to provide a flat 
continuous casting nozzle in which the thermal stress generated in the 
whole nozzle is relaxed by shifting the terminal position of the long-edge 
side taper from the terminal position of the short-edge side taper. 
The invention thus comprises a flat formed SEN for continuous casting of 
steel having a taper part and flattened at least in the lower end part 
wherein the position of the taper terminal formed on the long edge side 
and the taper terminal formed on the short edge side are shifted from the 
same horizontal plane when the casting nozzle is vertically supported 
(claim 1), a flat formed SEN for continuous casting of steel, according to 
claim 1 wherein the taper terminal position formed on the long edge side 
is shifted from the position of the taper terminal formed on the short 
edge side by at least 10 mm or more (claim 2), a flat formed SEN for 
continuous casting of steel, according to claim 1 or 2 wherein the taper 
terminal parts are shifted from the same plane in both the inner and outer 
surfaces of the nozzle hole (claim 3), a flat formed SEN for continuous 
casting of steel, according to claim 1, 2 or 3 wherein the start ends of 
the tapers are also shifted from the same plane (claim 4), and a flat 
formed SEN for continuous casting of steel according to either one of 
claims 1 to 4 which is for thin slab casting (claim 5).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows the long edge side and short edge side of a flat continuous 
casting SEN according to one preferred embodiment of this invention. In 
FIG. 1a, the long edge side of the nozzle is shown on the left, and the 
short edge side on the right, wherein the respective corresponding 
positions are mutually connected by broken lines. 
In FIG. 1a, a flat continuous casting nozzle 10 having a cylindrical upper 
part 11 and a flange 12 on the top end is shown. In the long edge side 
shown on the left of FIG. 1a, the lower side of the cylindrical part of 
the nozzle upper part 11 is laterally extended at a gentle angle to form a 
taper 13. The terminal part 14 of the taper 13 is extended further more 
laterally. A nozzle bottom part 15 has a rectangular section. The short 
edge side which is the side surface of the nozzle is shown on the right of 
FIG. 1a. The upper part 11 and the flange 12 of the nozzle are the same as 
described above on the long edge side as shown in the drawing, but the 
terminal part 17 of a taper 16 is situated in a position shifted upward 
from the long-edge side terminal part 14. In the taper 16, the width is 
gradually narrowed so that the nozzle is flattened. The taper 16 is 
extended from the terminal part 17 to the nozzle bottom part 15 with a 
fixed width. 
Including a continuous casting SEN having discharge ports 18 for molten 
steel on both sides of the short edge side as shown in FIG. 1b, the nozzle 
is tapered in the same manner as in FIG. 1a. 
The nozzles of this invention were analyzed by finite element method, and 
the stress concentrating positions of the nozzles were examined on the 
basis of this. The results are shown in FIG. 2 and FIG. 3 showing 
partially vertical sections of the nozzles. The result for a conventional 
nozzle is also shown in FIG. 4 in the same manner. 
In the nozzle shown in FIG. 2, the terminal part 21 of a taper 20 formed on 
the long edge side of the nozzle is shifted down by 50 mm from a terminal 
part 23 of a taper part 22 formed on the short edge side. Therefore, the 
encircled stress concentrating positions are vertically shifted and 
dispersed to the two positions in the nozzle shown in FIG. 2. 
Consequently, the stress generated in the respective positions are 
minimized, so that the damage of the nozzle can be remarkably reduced. 
FIG. 3 shows a part of a nozzle of this invention, which is basically the 
same as that shown in FIG. 2, wherein the terminal part 31 of a taper 30 
formed on the long edge side of the nozzle is shifted down by 100 mm from 
the terminal part 33 of a taper 32 formed on the short edge side thereof. 
FIG. 4 shows a conventional nozzle in the same manner as the above. Namely, 
the position of the terminal part 41 of a taper part 40 formed on the long 
edge side of the nozzle coincides with the position of the terminal part 
43 of a taper 42 formed on the short edge side in the horizontal 
direction. Since the encircled stress concentrating positions horizontally 
coincide between the terminal part of the long-edge side taper and the 
terminal part of the short-edge side taper, in this case, the stress 
concentration in this part is increased. 
Table 2 shows the stresses generated in the short-edge side terminal parts 
43, 23, 33 and delta parts D, D', D" of a conventional nozzle (Type C) and 
nozzles (Types A, B) shown in FIGS. 2 and 3 employed in the analysis 
described above. 
TABLE 2 
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Maximum Tensile Stress Generated in Nozzle 
(MPa) 
Type A B C 
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Short edge side taper terminal part 
11.07 10.30 12.06 
Delta part 10.66 9.89 9.18 
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Nozzles having the long edges and short edges shown in FIG. 2 or FIG. 3, 
which have characteristics as shown in Table 3, were manufactured with 
alumina-graphite material. Low carbon aluminum killed steel was casted at 
1545.degree. C. for 60 minutes with these nozzles. The nozzles were then 
examined to determine whether the short-edge side taper terminal part of 
each nozzle was cracked. As a result, although the nozzles of type A and 
type B shown in FIG. 2 and FIG. 3 were not cracked, the nozzle of type C 
(conventional type) shown in FIG. 4 was cracked in the short-edge side 
taper terminal position. 
TABLE 3 
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Material Characteristics of Specimen Nozzle 
Al.sub.2 O.sub.3 -Graphite 
Material 
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Chemical Component (%) 
Al.sub.2 O.sub.3 
48 
C + SiC 30 
SiO.sub.2 20 
Physical Characteristics 
Bulk Density 2.37 
Modulous of Rupture 
8.5 
Young's Modulus (GPa) 
9.0 
Thermal Expansion 
0.29 
(% at 1000.degree. C.) 
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According to this invention, the positions of the long edge-side taper 
terminal part and short edge-side taper terminal part of a flat continuous 
casting nozzle are not mutually conformed but shifted, whereby the thermal 
stress apt to be collectively generated in the taper terminal parts of the 
flat nozzle can be relaxed to improve the spalling resistance of the 
nozzle. Although the spalling resistance of the nozzle can be, of course, 
improved by the selection of material, the spalling resistance can be also 
structurally improved according to this invention, in addition to the 
selection of material. 
In thin slab casting devices, particularly, it is difficult to impart a 
sufficient strength to the SEN because the internal space of a mold to 
which the nozzle is installed for casting is narrow, and the mold 
short-edge side allowable thickness of the nozzle to be inserted is 
significantly controlled. 
This invention thus aims at finding and providing a form and structure 
sufficiently resistant to a thermal shock or thermal stress by molten 
steel flow under such a condition. 
This invention is attained by improving the form of a nozzle developed 
mainly for thin slab casting device, since the nozzle is frequently 
cracked when flatted for thin slab. In this invention, raw materials of 
various compositions practically applicable to casting refractory 
materials can be used without being limited to the material described in 
the above embodiments, and the flange may be extended so as to act as a 
slide gate plate. The nozzles of this invention may be integrally molded 
or formed by adhering or bonding a plurality of members. Further, the 
angle part formed as the taper terminal part or start end part may be 
rounded. 
While this invention has been described with reference to embodiments 
having two-stage taper parts, it can be, needless to say, applied to taper 
parts having three stages or more without being limited to this number of 
stages. In case of three stages, for example, "taper terminal part" is 
replaced by "one or more terminal parts of each taper part" in execution 
of this invention, whereby the application is facilitated.