[0001] The present invention relates to a discharge nozzle for moulds in continuous casting
machines and, more specifically, to a discharge nozzle of molten metal having directed
outlets for moulds in continuous casting machines.
[0002] The application of discharge nozzles to transfer the liquid metal from a separator,
commonly known as a tundish, to the respective mould is known. During transfer of
the molten metal, the speed at which the old is fed has a considerable influence on
the quality of the finished product. In fact, one problem that is found is that of
a non-homogeneous distribution of the metal in terms of speed and/or temperature.
This problem can result in the surface of the bath being too cold or moving too much.
In this case, solidification is irregular and the dust covering normally found on
the surface of the bath itself can be incorporated into the bath.
[0003] Another problem is found if the streams of molten metal from the discharge nozzle
hit the side walls of the old with excessive energy, resulting in re-founding of the
top skin which, if excessive, can compromise process regularity.
[0004] Given the high productivity levels normally required from continuous casting machines,
the above problems are very strongly felt when dealing with large flow rates, because
any irregularity in the heat exchange and in the possibility to capture surface powders
can detract from the quality of both the surface and the inside of the product.
[0005] To solve the above mentioned problems a number of methods have been used. One known
method is that of using a device external to the old, known as an electromagnetic
brake which, by means of an electromagnetic field induced in the bath, influences
the movement of the metal, thus reducing stirring in the bath. The disadvantage of
a device of this kind is that it involves extremely high costs and, like all external
devices in a system, the additional need for maintenance and control.
[0006] Another method to solve the above mentioned problems is that of particular care when
designing the geometry of the discharge nozzle. From this point of view, the most
common practice is that of creating discharge nozzles with outlets that point downwards.
[0007] Furthermore, is known another embodiment in which the discharge nozzle has four horizontal
holes instead of two, so as to decrease the energy of the jet of metal.
[0008] However, the above solutions only partially solve the problems indicated above, because
their object is the effect of the phenomenon, that is to say, for example, excessive
surface movement, rather than the cause thereof, which is the excessive energy of
the metal to be dealt with. Furthermore, improvements are obtained with reduced flow
rates, but not with higher flow rates and so at increased machine productivity.
[0009] Therefore, the object of the present invention is to solve the above mentioned problems
by providing a discharge nozzle having its outlets arranged in such a way as to induce
a damping effect on the energy of the jet of metal passing through said outlets, and
such that said damping effect increases proportionally to the increase of flow rate,
thus decreasing stirring in the bath of the old.
[0010] A further object of the present invention is to provide a discharge nozzle for moulds
that is of simple construction, provides a high level of reliability and in which
only normal maintenance operations are required.
[0011] According to the present invention, a discharge nozzle for moulds in continuous casting
machines comprises:
a main body of substantially cylindrical shape;
an outflow duct formed inside said main body;
at least two first outlets arranged in a substantially symmetrical manner along the
external perimeter of said main body one respect to the other, and at the lower end
of said main body, in order to communicate said outflow duct towards the outside;
at least two second outlets arranged in a substantially symmetrical manner along the
external perimeter of said main body one respect to the other, and above said at least
two first openings, in order to communicate said outflow duct towards the outside;
characterised in that each outlet of said at least two first outlets has a prevalently
upward direction, and in that each outlet of said at least two second outlets has
a prevalently downward direction, and in that said outflow duct is optionally downwardly
frustoconical.
[0012] The present invention will be illustrated in greater detail in the following by a
description of an embodiment thereof, given as a non-limiting example and with reference
to the enclosed drawings, in which:
figure 1 is a schematically perspective view of a discharge nozzle of the prior art;
and
figure 2 is a longitudinal cross section view of a discharge nozzle according to the
present invention.
[0013] With reference to figure 1, a discharge nozzle according to the prior art is shown.
[0014] The discharge nozzle has a body 1 with a substantially cylindrical shape, within
which an outflow duct 2 for the molten metal is formed. Initially, said duct 2 has
a steady cross-section until a predetermined length, at which point two outlets 3
are formed (only one of them is shown in the figure). From that length onwards, the
section of the duct 2 decreases and extends for a further determined distance, at
which point, in a similar manner to that above, two outlets 4 are formed (only one
of them is shown in the figure), which are larger than the two openings 3.
[0015] The openings 3 and 4 are arranged in an horizontal direction, that is to say at right
angles to the longitudinal direction of the discharge nozzle.
[0016] With reference now to figure 2, a longitudinal cross section view of the discharge
nozzle according to the present invention is shown.
[0017] The discharge nozzle has a body 5 with a substantially cylindrical section, inside
which an outflow duct 6 is formed.
[0018] In this embodiment, at the top end of said body 5, the duct 6 has a thread 7 for
the engaging with the feeder duct of the discharge nozzle (not shown in the figure)
in a known manner.
[0019] It should be noted that the duct 6 is frustoconical along its length, that is to
say it has a cross-section that decreases as said duct advances.
[0020] At approximately one third of the total length of the duct 6 and starting from the
lower end of the body 5, two outlets 8 are formed, both of same size and arranged
in a diametrically opposite position. Said outlets 8 are directed upwards so that
their longitudinal axis X forms an angle α with the longitudinal axis Y of the discharge
nozzle.
[0021] Above said outlets 8 and at approximately two thirds of the total length of the duct
starting from the lower end of the body 5, two outlets 9 are formed, both of same
size but larger than the openings 8 and arranged in a diametrically opposite position.
Said outlets 9 are directed downwards and in such a way that their longitudinal axis
W forms an angle β with the longitudinal axis Y of the discharge nozzle.
[0022] The arrangement of both upper outlets 9 and bottom openings 8 is such to give to
both the flows of metal passing through them a direction that tends to gather the
two flows, i.e. in such a way that the upper flow meets the bottom flow, providing
a damping effect on the kinetic energy of both flows, said damping effect increasing
as the flow rate increases, and therefore during high production function.
[0023] For optimum sizing of the cross-sections, that is to say of the outlets and the duct,
calculations have been made using numeric simulation with a commercial calculation
code (more specifically the PHOENICS code). Then, once optimum sizing was obtained,
a 1:1 scale model was prepared, made of Plexiglas and tested in a old using water
as working fluid.
[0024] When selecting the dimensions, the dissipation of energy in the top surface and at
the side walls of the moulds has been taken into account, as well as the temperature
of both.
[0025] Subsequently, the performance of the discharge nozzle was compared with a standard
two-outlets discharge nozzle. The performance concerned to:
1) the impact speed and depth of the jet on the side walls of the old;
2) the tendency to generate a wavy and/or turbulent surface;
3) the level of thermal homogeneity on the surface; and
4) the index of a good metal flow through the upper portion of the old.
[0026] Herebelow two tables representing the optimum dimensions for a model of a discharge
nozzle according to calculations and the experimental results thereof, are given.
[0027] Table 1 illustrates the parameters for optimum sizing of the discharge nozzle, in
a non-dimensional form and with reference to figure 2, according to the present invention.
[0028] Table 2 illustrates performance parameters, expressed as normalised values, resulting
from comparison of the discharge nozzle according to the present invention and a standard
two-outlets discharge nozzle.
TABLE 1
DISCHARGE NOZZLE DIMENSIONS |
NON-DIMENSIONAL PARAMETERS |
Top diameter of duct |
D |
Bottom diameter of duct (D') |
0.7 ∼ 0.8 D |
Top external diameter of discharge nozzle |
1.71 D |
Bottom external diameter of discharge nozzle |
1.57 D |
Position of bottom outlets starting from lower end of discharge nozzle |
1.03 D |
Position of upper outlets starting from lower end of discharge nozzle |
2.32 D |
Angle α between X axis of bottom outlets and longitudinal axis Y of discharge nozzle |
75° ± 15° |
Angle β between W axis of upper outlets and longitudinal axis Y of discharge nozzle |
75° ± 15° |
Diameter of upper outlets |
0.92 D |
Diameter of bottom outlets |
0.85 D |
TABLE 2
PARAMETERS |
Standard discharge nozzle |
Discharge nozzle according to the invention |
Impact speed (m/s) |
0.22 |
0.13 |
Impact point (mm) |
320 |
250 |
Wave index |
100 |
90 |
Vortex index |
100 |
50 |
Lack of thermal uniformity |
2% |
3% |
[0029] As can be seen, with the discharge nozzle sized according to table 1 and according
to the results obtained and illustrated in table 2, the response was extremely positive.
[0030] In particular, the impact speed on the side walls of the old decreased by approximately
40%, the wave level by 10% and the formation of vortexes by 50%. Only the index of
lack of thermal uniformity is slightly worse, but on the basis of the experience of
any technician skilled in the art the overall values give a strong indication of improvement.
[0031] The present invention is not limited to the embodiment described above, but comprises
any alternative version thereof.
1. A discharge nozzle for moulds in continuous casting machines, comprising:
a main body (5) of substantially cylindrical shape;
an outflow duct (6) formed inside said main body (5);
at least two first outlets (8) arranged in a substantially symmetrical manner along
the external perimeter of said main body (5) one respect to the other, and at the
lower end of said main body (5) in order to communicate said outflow duct (6) towards
the outside;
at least two second outlets (9) arranged in a substantially symmetrical manner along
the external perimeter of said main body (5) one respect to the other, and above said
at least two first openings (8), in order to communicate said outflow duct (6) towards
the outside;
characterised in that each outlet of said at least two first outlets (8) has a
prevalently upward direction, and in that each outlet of said at least two second
outlets (9) has a prevalently downward direction, and in that said outflow duct (6)
is optionally downwardly frustoconical.
2. A discharge nozzle according to claim 1, wherein said at least two second outlets
(9) are greater than said at least two first outlets (8).
3. A discharge nozzle according to claim 1 or 2, wherein each outlet of said at least
two first outlets (8) has its geometrical axis (X) directed upwards and forming an
angle (α) less than 90° with the longitudinal axis (Y) of said outflow duct (6).
4. A discharge nozzle according to any of the preceding claims, wherein each outlet of
said at least two second outlets (9) has its geometrical axis (W) directed downwards
and forming an angle (β) less than 90° with the longitudinal axis (Y) of said outflow
duct (6).
5. A discharge nozzle according to claim 3, wherein said angle (α) is comprised between
60° and 90°.
6. A discharge nozzle according to claim 5, wherein said angle (α) is 75°.
7. A discharge nozzle according to claim 4, wherein said angle (β) is comprised between
60° and 90°.
8. A discharge nozzle according to claim 7, wherein said angle (β) is 75°.
9. A discharge nozzle substantially as described above with reference to the enclosed
drawings.