Note: Descriptions are shown in the official language in which they were submitted.
CA 02563472 2006-10-17
WO 2006/042597
DESCRIPTION
The invention relates to a tapping tube for a metallurgical
melting vessel. A metallurgical melting vessel is defined
as an apparatus in which a metallurgical melt is produced,
treated, and/or transported, for example a converter or an
arc furnace.
Metal melt in the melting vessel is fed to a downstream
apparatus via the tapping tube. For example, steel is fed
from the converter to a downstream continuous casting
installation via a ladle.
The metal melt should be as free from impurities as
possible when it is transported. For example, contact with
the ambient atmosphere (oxygen, nitrogen) should be avoided
as well as the inclusion of slag.
A converter tapping spout is known from EP 0 057 946 Bl
which includes a plurality of fireproof blocks or discs,
connected to each other axially. The converter tapping
spout may also be monolithic with the same geometry. Figure
1 shows this prior art, which has proven its commercial
value for a long time. The central through-flow channel for
the metal melt material may be conical, cylindrical, or
reduced in steps from the inflow end to the outflow end. In
any case, when metal melt is passed through, it quickly
causes erosion of the outer wall in the through-flow
channel, so that its cross section is constantly being
enlarged during operation, as is shown schematically in
Figure 2.
It is evident that as the cross section of the through-flow
channel changes, the quantity of metal melt flowing through
the tapping tube per time unit also changes. This change is
all but completely uncontrolled, since the removal of the
refractory material is also largely uncontrolled.
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Attempts have therefore been made to repair the tapping
tubes of the kind described after a certain tapping time,
for example by introducing a cylindrical template into the
through-flow channel that was enlarged by erosion and
spraying a refractory mass behind the template. This method
is time-consuming and is associated with considerable
difficulties at the hot furnace unit.
The object of the invention is to provide a tapping tube
(spout) that enables tapping times to remain as constant as
possibly for the entire period of use, while minimising
nonproductive times.
The main idea of the invention is to construct the tapping
tube in two functional parts, a first part that may be
configured in accordance with prior art, and a second part
that may be connected to the first part thereby creating a
complete tapping tube and which is easily replaceable
(exchangeable).
The invention is based on the realisation that the section
of the tapping tube that determines the nature of the flow
is the outflow end. The cross section at the outflow end
determines the outflow quantity and thus also the outflow
time (tapping time) of the metal melt. This is the "outer"
part, that is to say the part farthest from the melting
bath in the metallurgical vessel, so that the relatively
lowest temperatures occur here, which makes it easier to
replace a corresponding tapping part.
The basic inventive concept is presented in Figure 3 based
on Figures 1 and 2. It should be noted that the upper part
of the tapping arrangement, starting from inflow end E, has
been taken without changes from prior art, and an
approximated condition of wear of Figure 2 is reflected in
Figure 3.
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The essential difference compared with prior art consists
in that an end A at the outflow side of the tapping tube is
designed as a separate, replaceable assembly B, which is
sealingly connected to the adjacent part of the tapping
tube, as will be described in detail.
The replaceable component B, which is essentially
cylindrical in shape, has a through-flow channel Dl, the
cross sectional area of which corresponds to a target cross
sectional area of the through-flow channel without any
wear.
Of course there will be as well a wear of the refractory
material in the area of through-flow channel Dl, and the
cross section of this area will increase over time as well.
But as soon as this cross section increase reaches a given
value, assembly B is quickly replaced without making or
having to make any changes to the upstream section in the
direction of flow (referred to in the following as the
upper section). When a new assembly B has been fitted, an
annular shoulder S will be formed in the transition region
to the upper part of the tapping tube, but this is
deliberately accepted, because repairing of the upper part
of the tapping tube is not acceptable for the reasons
given, and is also not necessary from a technological point
of view, because the tapping time and the mass flow of the
tapped metal melt is determined only by the cross section
of the through-flow channel at outflow end A.
Of course, the connection zone between replaceable
component B and the fixed part of the tapping tube must be
leak-proof, but it must also be designed such that
component B is easily detachable. To this end, the
following suggested solutions are described.
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It is also evident that the "loose" component B must be
firmly secured in the position shown in Figure 3 to ensure
that it does not become detached from the upper section of
the tapping tube. To this end, the invention offers several
different solutions, which are also presented in the
following.
In its most general embodiment, the invention thus relates
to a tapping tube for a metallurgical melting vessel having
the following features:
- the tapping tube has a through-flow channel for a
metal melt, which channel connects an inflow end and
an outflow end,
- starting from the outflow end, the tapping tube
encloses a cylindrical end section that is constructed
as a separate, cylindrical part adjacent the through-
flow channel,
- the first end of the part, the end that comprises the
outflow end of the tapping tube, is constructed to
ensure a fixed but detachable fitting of the part in a
retaining device, the second end of the part has a
front surface facing the inflow end, which surface
being tightly arranged against an axially adjacent
section of the tapping tube when the part is in a
retained position.
The term cylindrical includes sections having a circular
cross section, but also all other sectional geometries.
This applies for both internal and external sections of the
tube. In the axial direction (direction of flow of the
metal melt) , the tube may be cylindrical or conical in
shape. Other shapes are also possible, for example a
stepped surface. Besides a circular cross section, the
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internal and the external cross section may be polygonal or
oval. Any polygonal shape is possible.
The most critical point for the tapping tube of the
invention is that the replaceable part delimits through-
flow channel D (D1) peripherally.
This includes embodiments, as shown in Figure 3, in which
part B extends over the entire cross sectional area of the
tapping tube. However, it also includes embodiments in
which the part is implemented in the lower (outflow side)
end section of the tapping tube, as will be illustrated in
the following.
The cylindrical part may have any internal cross section.
For example, the through-flow channel has a round or oval
internal cross section in the area of the part. The cross
sectional area should match the target cross section area
for the purpose of assuring the desired mass flow and
tapping time.
The through-flow channel in the area of the part may have a
constant internal cross section when viewed from the top of
the part but it may also be conformed to be slightly
conical or stepped towards the outflow end.
As was indicated previously, the cylindrical component
(part) may be fitted in an outer, cylindrical end section
of the tapping tube. In this way, the target length of the
tapping tube remains unchanged. Only a changing sleeve is
disposed detachably on the outflow end.
However, as shown in Figure 3, this may also be shortened
for a predetermined length of the tapping tube, in which
case when the replaceable part is installed it restores the
tapping tube to its original length.
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The replaceable component (part) may be fixed on or in the
other part of the tapping tube in various ways. One
possibility is to construct the part with an external
thread, which cooperates with a corresponding internal
thread. This internal thread may be arranged as a separate
part in the outflow area of the tapping tube at the
associated metallurgical melting vessel. It may also be an
integral component of the outflow end of the tapping tube,
particularly in the case of the inserted part as described.
A bayonet connection is also possible instead of a threaded
connection.
According to one embodiment, the cylindrical replaceable
part has buffers along its outer surface or at its outlet
end for compression means acting in the direction of the
inlet end onto said part.
The compression means may be springs, for example, that are
disposed on a retaining mechanism, which in turn is fixed
to the outside of the metallurgical melting vessel.
The determining feature is that the replacement component
is biased towards the inflow end of the tapping tube in
such a manner that a leak-proof joint is created with the
remaining part of the tapping tube. The corresponding
retaining means are therefore disposed particularly at the
free lower front surface or on the outer periphery of the
part.
The quality of the seal may be improved if the front face
on the mounted end of the part has a contoured surface,
i.e., it is not smooth. Such contouring may consist of
individual, discrete knobs or ridges. The contouring may
also comprise rib-like projections in a concentric or
spiral arrangement.
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Alternatively or additionally, the surface of the tapping
tube against which the front surface of the changing
component is pressed may also be conformed in the same way.
A further alternative provides for placing a seal between
the corresponding surfaces of the tapping tube and the
component. Particularly if the corresponding surface
sections of the fireproof material are more or less flat,
it is sensible to conform the normally annular seal with
surface contouring such as was described previously.
Regardless of whether these profiles are formed within the
refractory material and/or being part of the sealing
component, these profiling enable a certain elasticity and
thus also deformability when the part is mounted onto the
remaining section of the tapping tube.
A suitable sealing material is graphite, for example, since
this also has the corresponding thermal resistance. The
seal may also be produced from a sealing compound, for
example as an emulsion of flake graphite and oil.
The contact surface (frontal surface) of the described part
with the ceramic section of the other part of the tapping
tube may be flat (in particular perpendicular to the
central longitudinal axis of the tapping tube) or convex,
particularly cambered, which is to say arched towards the
inflow end.
At the same time, the part may include a temporary barrier
for a "first slag". This first slag flows into the tapping
tube (and subsequently into the downstream metallurgical
melting vessel) when the converter is tipped, and this is
undesirable. The invention therefore provides that the
component be constructed with a blocking element that
temporarily fills the entire internal cross section
(through-flow channel), In this context, "temporary" means
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that the blocking effect only needs to be very short, a few
seconds for example, before metal melt flows into the
tapping channel in the tapping process.
Such a blocking element mav be a thin metal panel, for
example, or a type of cup, which are placed in the through-
flow channel of the component (part), for example via
spring arms (claws) on the peripheral surface thereof.
The component may generally be of any length. The most
important is, as described above,the outflow cross section
at the outflow end. However, the operating life of the part
may be prolonged if it is at least 1.5 times as long as the
smallest internal diameter, a ratio of 1.5 to 3 usually
being sufficient. This length is also important for
obtaining the desired characteristic of the outflowing
melt. In particular, a uniform outflow of the melt is
achieved.
Because the endpiece is easily exchanged, the tapping tube
described enables highly constant tapping times to be
achieved, and thus also improved availability of the
melting unit. Replacement of the end component may be
automated. Since it is replaced from the outside, this may
be performed easily and quickly. It is fitted in such
manner that the outflow end of the tapping tube lies more
or less flush with the outer wall of the metallurgical
melting vessel.
The end part may be made from the same material as the rest
of the tapping tube. Or the two sections may also be
produced from different materials. For example, the part
may be constructed from a highly wear-resistant material
grade.
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Different thermal expansions of different materials may be
compensated by the sealing area described previously,
and/or by an elastic retaining mechanism for the component.
Additional features of the invention are described in the
dependent claims and in the other application documents.
In the following, the invention will be explained in
greater detail with reference to various embodiments. The
drawing shows, in schematic form:
Figure 4: a partial cross section of an end section of a
tapping tube,
Figure 5: a top view of and a section through surface 24
of the replaceable component of the tapping
tube of Figure 4,
Figure 6: a partial sectional view of another embodiment
of a tapping tube, in which only the lower
part is shown.
Identical or equivalent parts in the figures are identified
with the same reference numbers.
Figure 4 shows the lower part of a tapping tube 10, which
is fitted in a refractory lining of a converter 12 which
shows on outer metal envelope 14. These features all
represent prior art and will therefore not be described
further.
Starting from outflow end 16 of flow-through channel D, an
end section 18 of tapping tube 10 has an extended inner
recess 20, in this case with a cylindrical wall surface. A
metal ring 22 is adhered to the wall area of end section 18
directly adjacent outflow end 16, and has an internal
thread.
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This internal thread cooperates with an external thread
provided peripherally on a mounting component B. Component
B is cylindrical. The external diameter of component B
corresponds to the internal diameter of recess 20. This
enables component B to be inserted into recess 20 along the
described thread until it lies flush in closing manner with
end section 18 and metal envelope 14 at outflow end 16.
Component B has a central through-flow channel Dl which has
a circular cross section, and which matches a target cross
section of through-flow channel D at the outflow end of
tapping tube 10.
A graphite seal 28 is situated between an upper frontal
surface 24 of component B and the corresponding contact
surface 26 of section 18, and is compressed into recess 20
when component B is screwed in, so that the size of seal 28
is exaggerated in the drawing.
When tapping tube 10 becomes worn, as shown in Figures 2,
3, component B is also susceptible to wear, but only
component B is replaced, thereby creating an arrangement
that essentially corresponds to that of Figure 3. In these
circumstances, component B is unscrewed from recess 20 and
a new component with a defined through-flow channel Dl is
inserted instead.
Figure 5 shows a cross section (bottom) and a top view
(top) of the conformation of frontal surface 24 of
component B with concentric, raised ribs 24r, wherein seal
28 is advantageously able to be pressed into the
depressions formed between ribs 24r, thus enhancing the
sealing effect.
In the embodiment of Figure 6, Component B is not disposed
in a recess 20 of end section 18 of tapping tube 10. The
upper part of tapping tube 10 is shortened by the length
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(height) of component B, with the result that contact
surface 26 for component B extends over the entire wall
thickness of tube 10.
The exterior shape of component B with central through-flow
channel Dl - which has a circular cross section - is a
truncated cone and is disposed in a corresponding metal
sleeve 30, which is furnished with a ridge 32 running
radially.
Retaining arms 34 abut this ridge 32, and are biased
towards the upper part of taping tube 10 via compression
springs 36. Springs 36 are supported on arms 38, which are
fixed at the metal envelope 14 of the metallurgical melting
vessel (not shown in detail) . Projecting parts form a
retaining mechanism for component B.
In this way, the upper frontal surface 24 of component B is
forced under the effects of springs 36 against matching
contact surface 26 of the upper part of tapping tube 10. A
seal, for example a graphite foil, may also be disposed
between surfaces 24, 26, which may also be contoured.
As wear occurs (shown by dashed line L) component B may be
replaced quickly by detaching the retaining mechanism. The
new component B (with through-flow channel Dl) is then
fixed with the retaining mechanism and then provides an
outflow cross section with defined target diameter for
subsequent tapping operations.
Even as the wear on tapping tube 10 becomes more advanced
(shown by dotted line P), the upper part of tapping tube 10
remains unchanged. However, component B is replaced again
as soon as it reaches the wear condition corresponding to
the dashed line L again.
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Figure 6 also shows a schematic representation of a pot-
shaped blocking element 40, produced from thin sheet metal,
and the peripheral lip of which rests on the upper frontal
surface 24 of component B when the component is pressed
against corresponding contact surface 26. Blocking element
40 prevents the first slag from getting into a downstream
melting vessel when the metal melt is tapped along through-
flow channel D. Only a small amount of slag is able to
advance through-flow channel D up to blocking element 40.
As soon as the first slag has been transported past the
inflow end of tapping tube 10 by tilting of the melting
vessel, only molten metal remains at the top of the inflow
end. Now the slag in the inflow part of tapping tube 10 can
either float upwards or drain out as part of the slag when
blocking element 40 has melted. Thereafter, only molten
metal passes through tapping tube 10.
The illustrated blocking element represents just one
possible design solution. The essential feature is that
when component B is changed, a fresh blocking element with
the same function is able to be installed at the same time,
which then blocks through-flow channel D temporarily.
