Pouring spout

A pouring spout to for delivering molten steel into a continuous casting mold with longitudinal and transverse sides, especially for casting thin slabs. The outer wall (12) of the pouring spout (10) is shaped in its longitudinal-side region (17) facing the longitudinal mold side (21) so that is has a substantially constant distance (d) relative to the longitudinal sides (21) of the mold, regardless of the immersion depth of the pouring spout into the melt in the continuous casting mold. In addition, the outer wall of the pouring spout, in its transverse-side regions (16) facing the transverse mold sides (22), has form elements that oppose a minimum resistance to the horizontal flow of the molten steel and the casting powder floating thereon.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an pouring spout or a submerged nozzle for 
delivering molten steel into a continuous casting mold with longitudinal 
and transverse sides, especially for casting thin slabs, which is 
connected at one end to a casting vessel and at the other end extends so 
far into the mold that its opening is immersed during casting into the 
molten steel in the mold. 
2. Description of Related Art 
Typically, pouring spouts have a round, substantially circular or 
elliptical shape at their connection to the casting vessel. This shape may 
continue to the opening region of the pouring spout or may change into a 
different shape, for example, a rectangular shape. For example, a pouring 
spout is known and described in German patent publication OS 24 42 187 in 
which at least the section that is immersed into the melt has 
substantially rectangular outer and inner cross-sections. The longitudinal 
edges of this pouring spout are parallel to the longitudinal sides of the 
continuous casting mold, so that, particularly in the case of rectangular 
strand cross-sections, an optimal space is used for the flow 
cross-section. 
The flow cross-section that is available between the transverse side of the 
mold and the outer wall of the pouring spout in the case of normal slabs 
does not exist in molds for manufacturing thin slabs. Furthermore, given 
the casting outputs required today, the molten steel fed through the 
pouring spout is supplied at significantly higher casting speeds than were 
usual for the mold described in the patent. The flow of molten steel is so 
great that distinct bath surface movements occur, especially in the region 
between the pouring spout and the longitudinal sides of the mold. 
It is known from WIPO patent publication 89/12519 to use pouring spouts 
whose section for immersion into the melt is shaped like a flattened tube 
with side walls that run parallel to each other. This wide-mouthed spout 
section has openings that, alone or together with flow guiding elements, 
guide the outflow of molten steel from the pouring spout so that 
individual streams of molten metal intersect each other and thus reduce 
the flow. 
In addition, a pouring spout for introducing molten steel into a mold is 
described in patent publication 41 42 447 C2 in which the inner wall of 
the section where the spout cross-section expands and the wall sections 
opposite thereto of the bottom piece together form flow channels. This 
pouring spout exercises an influence on the melt that flows through it, 
and in particular, on the emergence impulse of the casting stream. 
When pouring spouts in known shapes are used, the flow of steel creates 
turbulence and whirlpools, especially in the corner areas in the 
transverse-side region of the mold. As a result, wave crests and valleys 
occur in the longitudinal-side region of the pouring spout. The 
disadvantageous consequence is an uneven supply of slag in the region of 
the free mold cross-section in the shadow of the pouring spout. This leads 
to uneven lubrication and irregular heat transfer between the strand shell 
being formed from the molten steel and the mold wall, which in turn 
results in slag and casting powder being drawn below the bath surface. 
The object of the present invention, therefore, is to provide a pouring 
spout with a simple design which; breaksdown the Kinetic energy of the 
molten steel in the region between tile section of the spout immersed into 
the melt and the longitudinal sides of the mold and to influences in a 
predeterminable manner the flow formation of the molten steel in the mold 
in the region of the bath surface. 
SUMMARY OF THE INVENTION 
The present invention relates to a pouring spout or submerged nozzle for 
delivering molten steel into a continuous casting mold with longitudinal 
and transverse sides, particularly for casting thin slabs, which is 
connected at one end to a casting vessel and at the other end extends so 
far into the mold that, during casting, the mouth is immersed into the 
molten steel in the mold. The outer spout wall of the pouring spout has, 
in its longitudinal-side region facing the longitudinal mold side, a shape 
that, regardless of the immersion depth of the pouring spout into the melt 
in the continuous casting mold, has a virtually constant distance to the 
longitudinal sides of the mold. In addition, the outer spout wall of the 
pouring spout has, in its transverse-side regions facing the transverse 
mold sides, form elements that oppose a minimum resistance to the 
horizontal flow of the molten steel and the casting powder floating 
thereon. 
The outer spout wall of the transverse side of the pouring spout has, in 
the opening region, a shape that ends in a pointed tip like the hull of a 
boat. Alternatively, the opening region of the outer spout wall of the 
pouring spout may have a rectangular shape. In another embodiment of the 
invention, the outer spout wall of the longitudinal spout side is an area 
equidistant to the longitudinal side of the mold, and the inner spout wall 
is a flat area, while the inner spout wall of the pouring spout transverse 
side has a conical expansion and the angle of inclination of the conical 
expansion is between 4.degree. and 2 .degree.. 
In a preferred embodiment, the distance between the outer spout wall of the 
pouring spout and the longitudinal mold side to the maximum mold breadth 
is between 0.15 and 0.3. 
Another embodiment of the invention form elements are arranged on the 
transverse sides of the outer wall of the pouring spout facing the 
transverse mold sides in the shape of a wedge with the tip pointing 
against the flow. In a preferred embodiment, the wedge angle of the form 
element embodied as a wedge is between 30.degree. and 6.degree.. 
In still another embodiment the form elements may have a semi-circular 
outer contour. The form element may alternatively be embodied in the 
opening region of the pouring spout as a Taylor bulb. In any of these 
different form element embodiments, the form elements may be independent 
components which are attached to the outer spout wall of the pouring spout 
by holding elements. In a preferred embodiment the independent form 
elements are spaced a distance between 3 mm and 10 mm from the outer spout 
wall of the pouring spout. 
The molten steel emerging from the pouring spout initially moves in the 
conveying direction of the strand. Depending on the direction of the exit 
openings in the pouring spout and on the flow speed of the molten steel, 
the melt moves away from the mouth of the pouring spout to a point at 
which the flow direction of the molten steel reverses and then, is divided 
into two individual streams, i.e., flows, in the vicinity of the 
transverse sides of the mold, opposite to the strand discharge direction 
and toward the bath surface. In the region of the bath surface, the two 
separate streams of molten steel move in the direction of the pouring 
spout. The two streams are diverted at the outer spout walls, which 
incline toward the transverse sides, and then move into the empty space 
between the longitudinal side of the mold and the longitudinal side of the 
pouring spout. The individual molten steel streams, which are moving in 
the horizontal direction, collide at the level of the central mold axis in 
the empty spaces located on both sides of the pouring spout and flow off 
together in the strand discharge direction. 
Regardless of the shape of its inner wall, the outer wall of the pouring 
spout according to the invention is shaped so that, at any desired 
immersion depth of the spout into the continuous casting mold, the outer 
spout wall is at a substantially constant distance relative to the 
longitudinal sides of the mold. 
On the transverse sides of the pouring spout, in the region that is 
immersed into the melt, form elements are provided that offer a minimum 
resistance to the horizontal flow of the melt in the mold and the casting 
powder floating thereon. The outer wall of the spout region immersed in 
the melt may directly produce a minimum flow resistance against the 
horizontally flowing melt or independent components may be provided which 
are arranged in front of the transverse side of the pouring spout. The 
inner wall as well as the outer wall of the pouring spout are shape to 
that allow optimum flow conditions both in and around the spout. In the 
case of one-piece pouring spouts, changes in wall thickness will occur. 
When independent are provided as form elements, immersed pouring spouts 
with an even wall thickness, based substantially on the shape of the inner 
wall, are used. 
The following are several embodiment of the shapes for the transverse sides 
of the pouring spout: an embodiment shaped like the hull of a boat, a 
wedge-shape embodiment, a semicircular embodiment and the so-called 
"Taylor bulb." 
Separate from the aforementioned shapes of the outer wall of the pouring 
spout, the transverse sides of the inner wall of the spout have a conical 
expansion or widening preferably with an inclination angle of 4.degree. 
and 7.degree.. This angle of inclination influences the flow in the region 
of the casting surface so that the surface flows in a particularly calm 
manner. The special embodiment of the outer contour of the transverse side 
of the pouring spout subsequently has an optimum influence on the flow in 
the empty space between the longitudinal sides of the immersed spout and 
the longitudinal sides of the mold.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS. 
The figures show a pouring spout 10 with an inner wall 11, an outer wall 
12, a region 13 on the casting vessel side and an opening region 14. The 
region 13 on the casting vessel side is tubular in shape and is connected 
to a casting vessel (not shown). The opening or mouth region 14 has a 
substantially crushed or depressed or flattened shape, whose region 16 on 
the mold transverse side is clearly shorter than the region 17 on the mold 
longitudinal side. 
FIG. 1a shows a mold 20 with longitudinal sides 21 and transverse sides 22. 
Arranged in the center of the mold 20 is tile pouring spout 10. In the 
first embodiment shown in the right side of FIG. 1a, the pouring spout 10 
has a rectangular cross-sectional shape. In front of the region 16 on the 
mold transverse side, there is a form element 31 embodied as a wedge 32 
with the tip of the wedge pointing against the direction of flow of the 
molten steel. The wedge angle 13 of the wedge 32 is between 30.degree. and 
60.degree.. The longitudinal sides of the spout are substantially parallel 
to one another. The outer spout wall 12 is separated from die longitudinal 
mold side 21 by a distance d and the longitudinal mold sides are separated 
from one another by a maximum mold breadth B. The distance d between the 
outer spout wall 12 and the longitudinal mold side 21 to the maximum mold 
breadth B is preferably between 0.15 and 0.3. 
A second embodiment is shown in the left side of FIG. 1a in which the 
pouring spout 10 is shaped; 
The left side of the immersed pouring spout 10 (in horizontal section in 
FIG. 1) is shaped like the hull 35 of a boat. The pouring spout 10 has a 
wedge-shaped bottom piece 18 in its center. In this embodiment the mold is 
convex. 
The flow of molten material is roughly indicated by the directional arrows 
shown in the left side of FIG. 1a. In the region of the transverse side of 
the mold, the molten material rises to the bath surface as indicated by 
arrow tips, i.e., circles with a dot therein. From there, the flow moves 
toward the immersed pouring spout, evenly divided by the tip of the 
transverse side of the immersed pouring spout, which is shaped like the 
hull of a boat. In the center of the longitudinal side of the pouring 
spout as indicated by arrow ends, i.e., circles with an "x" therein, the 
molten steel flows in the strand discharge direction. FIG. 1b shows 
longitudinal cross-sectional views through the mold and the spout; and 
specifically, of a first embodiment along line C--C through the convex 
mold and of a second embodiment along line E--E through the mold with 
parallel side walls. 
In both embodiments regardless of the shape of the inner wall 11, the outer 
wall 12 is shape to have a constant distance to the inner wall of the 
longitudinal mold side 21 at various immersion depths into the mold or the 
melt. 
FIGS. 2a, 2b, 3a and 3b show a section through a pouring spout 10 that has, 
on the side of its opening 14, a conical expansion or wideing 15, in the 
center of which is a wedge-shaped bottom piece 18. The angle of 
inclination .alpha. of the conical expansion 15 is between 4.degree. and 
20.degree.. 
In FIGS. 2a and 2b the outer wall 12 of the pouring spout 10 shape along 
its transverse side in the region immersed into the melt in such a manner 
that the horizontal flow of the molten steel and the casting powder 
floating thereon provides a minimum resistance. On the left side of 
Figures 2a and 2b, the outer wall 12 is shaped like the hull 35 of a boat 
that ends in a pointed tip. On the right side of FIGS. 2a and 2b, is a 
Taylor bulb 34, also known from navigation. Both of these form elements 
may also be embodied with a constant wall thickness of the spout as 
denoted by the dashed line. 
FIG. 3a shows a pouring spout 10, in which the form elements 31 are 
embodied as independent components, which are attached to the pouring 
spout by holding devices 37 is shown on the left side or by a holding 
piece 38 as shown on the right side. The form elements 31 are separated 
from the outer spout wall 12 of the pouring spout 10 by a distance c 
between 3 mm and 10 mm. Pouring spout 10 has a constant wall thickness. 
The form elements 31 embodied as independent components may have any 
desired cross-sectional shape. FIG. 3b shows a semicircular outer contour 
33 on the left side and, on the right side, the shape of a wedge 32.