Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a pouring tube for
feeding molten steel into the pouring zone of a mold
consisting of broad side walls and narrow side walls,
particularly for casting thin steel slabs. The pouring tube
includes a tube portion connected to a pouring container and
an end portion which is provided with outlet openings
directed toward the narrow side walls and a bottom piece at
the end face of the pouring tube.
2. Descrit~tion of the Related Art
In a pouring tube known from DE-A 37 09 188, to the
cylindrical tube portion is connected a flattened end portion
having slot-like outlet openings and a bottom piece with a
raised inner contour. The extension of the bottom piece in
the direction of the outlet openings is greater than the
distance between the walls which form the upper limit of the
outlet openings.
Although the known pouring tube is of complicated and
expensive construction, it is not capable of providing the
necessary operating safety and service life because of the
high demands made during continuous steel casting. The
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molten steel emerges from the narrow outlet openings in
concentrated form with a kinetic energy which is too high.
As a result, particularly in a thin steel slab casting mold,
washings may occur at the strand shell which is still thin
and a surge wave may occur in front of the narrow side walls.
Moreover, 'the uneven flow distribution within the mold
occurring when pouring with the known pouring tube results in
the formation of an irregular surface structure.
The present invention starts from the finding 'that the
reason for the non-uniform, unstable molten steel
distribution within the mold is the uneven speed with which
the molten steel is discharged over the cross-sectional areas
of the outlet openings,
Since the discharge speed is the greatest at the lower
portion of the outlet slot, a strong vortex each is formed
underneath the outlet openings and corresponding upwardly
directed compensating flows occur in front of the short side
walls which lead to a surge wave on the bath surface.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a.
pouring tube for pouring molten steel into a meld,
particularly~for casting thin steel slabs, which is simple to
manufacture, robust and safe to operate. Also, by providing
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CA 02018079 1999-06-28
a better flow distribution, a surge wave on the bath
surface and washings in the formed strand shell by the
liquid steel are to be substantially reduced or avoided and
a cast strand, particularly steel strip, with excellent
structure and uniformly free from defects is to be
obtained. Moreover, during the initial pouring procedure,
splashing and adhering of molten steel to the mold walls
are to be avoided.
In accordance with the present invention, the above
object is met in a pouring tube of the above-described type
by providing the bottom piece having a width between the
lower ends of the outlet openings which is at most 80~ of
the distance between the inner wall surface of the side
wall of the tube at the upper ends of the outlet openings,
wherein the bottom piece is substantially flat and lipless
adjacent the lower ends of the outlet openings.
As a result, the discharge speed in the region of the
lower edge of the outlet openings and, thus, the widening
of the molten metal stream resulting in washing of the
strand shell are reduced. In addition, the vortices which
are formed and the corresponding compensating flows are
weaker, so that a better f7_ow release is obtained and the
surge waves are substantia7_ly reduced. The novel pouring
tube is simple to manufacture and has a long service life.
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CA 02018079 1999-06-28
In accordance with another feature of the invention,
the bottom piece has :in the direction of the outlet
openings a width which is between 30~ and 80g of the
distance between the walls which define the upper limits of
the outlet openings.
The inner surface of the bottom piece may be plane,
raised or trough-shap~sd.
In accordance with another development of the
invention, the side surfaces of the pouring tube may
converge at an angle 'toward the bottom piece.
Alternatively, the side surfaces may extend beyond the
width of the bottom piece for guiding the pouring streams.
Finally, the floe distribution can be further improved
by reducing the width of the outlet openings in the
direction of the bott~~m piece.
For a better und~erstand.ing of the invention, its
operating advantages .attained by its use, reference should
be had to the drawing and descriptive matter in which there
are illustrated and described preferred embodiments of the
invention.
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BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
Fig. 1 is longitudinal sectional view of a continuous
casting mold with a pouring tube extending into the pouring
zone.
Fig. 2 is a top view of the continuous casting mold of
Fig. 1~
Fig. 3 is a sectional view of the pouring tube parallel
to the outlet openings
Fig. 4 is a sectional view of the pouring tube
transversely of the outlet openings and
Fig. 5 is a sectional view of another pouring tube
parallel to the outlet opening.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As illustrated in Fig. 1 of the drawing, a pouring tube
3 is mounted at the bottom outlet 1 of a pouring container 2.
The pouring tube 3 extends with its lower end into a steel
strip casting mold 4 and under the pouring level 5. The
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steel strip casting mold 4 has two cooled broad side walls 6
and two narrow side walls 7 which are adjustably arranged
between the broad side walls 6. As seen in Figs. 1 and 2,
the broad side walls 6 form a widened ;pouring zone 8
extending over a portion of the mold height for receiving the
pouring tube 3.
The pouring tube 3 has an upper portion 9 with an
approximately circular cross-section and a lower or end
portion 10 having an oval shape. Outlet openinc;s 1:1 are
arranged in each of the narrow sides of the oval-shaped end
of 'the tube 3. The outlet openings 17. are limited 'toward the
bottom by a bottom piece 12 whose width a is smaller than the
distance b between the walls located thereabove. The width a
of the bottom piece advantageously is 30 to 800 of the
distance b.
In the embodiment illustrated in Fig. 3, the wide
pouring tube walls 13 which arc of flat construction extend
at an angle relative to the bottom piece 12.
Alternatively, as shown in Fig. 5, the wide walls 14 of
the pouring tube can extend at the full width to the end of
the pouring tube, so that additional guiding surfaces 15 are
formed in front of the outlet opening.
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The outlet openings 11 are upwardly extending ovals 16.
As can be seen in Fig. ~, the width of the outlet openings 11
may narrow toward the bottom.
The pouring tube according to the present invention may
also be used for molds which have shapes different from those
described above. Particularly, the mold may have a mold
space which becomes continuously narrower toward the mold
end.
While specific embodiments of the invention have been
shown and described in detail to illustrate the application
of the inventive principles, it will be understood that the
invention may be embodied otherwise without departing from
such principles.
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