Note: Descriptions are shown in the official language in which they were submitted.
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TRANSLATION (HM-684):
Translation of WO 2004/110,104A1 (PCT/EP2004/005,122)
with Amended Pages Incorporated Therein
DIRECT-CURRENT ARC FURNACE
The invention concerns a direct-current arc furnace with at
least one electrode, which is held inside the furnace and can be
advanced to compensate electrode consumption, and with a counter
electrode in the furnace, for example, a bottom electrode,
wherein the entire electrode train with an electrode holder and
an advancing device is mounted as a suspension system on a
furnace platform or a frame above the furnace.
Direct-current arc furnaces for melting steel scrap
generally have at least one centrally arranged electrode and at
least one bottom electrode to produce a flow of current through
the steel bath. As is well known, the electrode, which projects
into the furnace vessel from above, is held and guided by a
support arm construction, which is arranged to the side of the
furnace and extends with an L shape above the roof of the
furnace. The electrode is guided vertically into the furnace by
the support arm and is advanced inside the furnace to compensate
consumption of the tip of the electrode. Since the furnace roof
is swung away to charge the furnace, for example, with scrap,
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the electrode can also be moved out of the furnace by this
support arm construction. A support arm construction of this
type is described, for example, in DE 36 40 298 Al and DE 195 26
161 C2.
In reduction furnaces, it is well known that the electrode
train can be arranged above the furnace roof with an electrode
mount, as is described, for example, in DE 43 42 511 Al,
according to which the electrode projecting into the furnace is
held by a clamping ring of an advancing device, which is
supported on a frame by a lifting cylinder. An electrode mount
is mounted on the frame, and an electrode holding ring, which
likewise embraces the electrode, is arranged on the electrode
mount. The frame is supported on a control and maintenance
platform by a regulating cylinder. The electrode can also be
moved back by the advancing device.
In the previously known support arm construction of direct-
current arc furnaces, a large support arm travel distance is
necessary to embrace the newly attached electrode length. Due
to the vibrations produced by the direct-current operation, the
support arm that holds and guides the electrode is also caused
to vibrate. This vibrational motion of the support arm leads to
uncontrolled movement of the electrode at the seal in the
furnace roof. This results in wear and thus leakage.
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Furthermore, the power supply to the furnace must be
interrupted during advancing and attachment of the electrode.
In addition, the furnace crane needs large lifting power to hold
the electrode during advancing and attachment.
Proceeding on the basis of this prior art, the objective of
the invention is to avoid power loss during the advancing and
attachment operation in a furnace operated with direct current
and to improve the sealing of the electrode in the furnace roof,
especially when the furnace is operated with a highly
concentrated CO atmosphere.
Advantageous features and refinements of the invention are
further described hereafter.
The basic idea of the invention is to use an alternating-
current electrode train that is typical for a reduction furnace
or a typical electrode body design in a direct-current arc
furnace. The electrode train consists essentially of an
electrode holder and an advancing device, which is mounted on a
furnace platform or frame located above the furnace.
This electrode train makes it possible to advance the
electrode and to move it back without having to interrupt the
furnace power supply and without the use of heavy equipment,
such as the furnace house crane. The same is true for the
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connection of a new electrode length. In addition, advancing and
attachment are possible while power is still being supplied to
the furnace. This means a large yield of molten metal, because
fewer scheduled furnace shutdowns and thus fewer process
interruptions are necessary.
Vibrations of the electrode and undesired horizontal
movements that occur in combination with a support arm mount are
avoided by the electrode train that is used. This results in
better sealing of the electrode in the furnace roof, which is an
advantage with respect to safe furnace operation, especially with
a highly concentrated CO atmosphere.
Preferably, the electrode of the electrode train can also
be designed as a hollow electrode, through which charge
material, for example, fine charge material, can be conveyed
into the furnace.
Accordingly, in one aspect, the present invention resides in
a direct-current arc furnace with at least one electrode, which
is held inside the furnace and can be advanced to compensate
electrode consumption, and with a counter electrode in the
furnace, wherein an entire electrode train with an electrode
holder and an advancing device is mounted as a suspension system
on a furnace platform or a frame above the furnace, wherein the
suspension system comprises an electrode guide frame, which is
mounted on the furnace platform, electrode regulating cylinders
having pistons, which extend along an axis of the electrode, are
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mounted on a cylinder side by suspension on the guide frame, and
are connected on a furnace side with an electrode holding ring by
said pistons, such that the holding ring operates with two
pressure stages, and lifting cylinders, which are supported on
the holding ring and by which a first electrode advancing ring
can be moved along the electrode axis within the electrode
regulating cylinders, such that to advance the electrode, the
first electrode advancing ring is released and moved upward by
means of the lifting cylinders, the first electrode advancing
ring is then reclamped around the electrode to hold said
electrode, and then the electrode is advanced into the furnace by
a stroke movement in the opposite direction.
BRIEF DESCRIPTION OF THE DRAWINGS.
The invention is explained below with reference to the
specific embodiment illustrated in the drawings.
-- Figure 1 shows a side view of a direct-current arc
furnace of the invention in combination with an electrode train
typically used for a reduction furnace.
-- Figure 2 shows detail of the suspension system of the
electrode train of Figure 1.
-- Figure 3 shows the sectional view A-A of Figure 2.
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-- Figure 4 shows the sectional view B-B of Figure 3.
Figure 1 shows an arc furnace 1 that is operated with
direct current. It comprises essentially a furnace vessel 2 and
a furnace roof 3 with a central roof section 4. The furnace
vessel 2 is rigidly mounted by means of a frame construction 5
on columns 6. The furnace wall 7 is lined on the inside with
refractory material 8. Two bottom electrodes 10, 11 are mounted
in the furnace bottom. An electrode 12 extends into the inside
of the furnace from above. It is not mounted on a support arm
located next to the furnace, as is customary in conventional
furnaces of this type, but rather on an electrode train 14,
which is mounted on the furnace platform 13 and is designed as a
suspension system in the embodiment illustrated here. The
electrode train 14 is mounted on a guide frame 16, which is
arranged above the furnace 1 along the furnace platform 13.
The direct-current arc furnace 1 with the electrode train
14 is preferably used for the production of slags that contain
Ti02, for ferrochromium, ferromanganese, and other ferroalloys,
and for nonferrous slag processes customarily carried out in a
reduction furnace. For this purpose, charge material, for
example, ilmenite in sand form, is charged into the furnace as
the base product, specifically, through the electrode, which is
designed as a hollow electrode. Ilmenite is mixed with reducing
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agents and melted. The pig iron formed during the reduction,
which, together with the bottom electrodes, forms an extended
anode, is then tapped through a side tap hole 17. The charge
material is stored in vessels 18 above the furnace platform 13
and charged into the inside of the furnace through vertical or
lateral charging lines 19a, b and through the hollow electrode
12.
The individual components of the electrode train are shown
in detail in Figure 2. The guide frame 16 surrounds a guide
roller 20 on the electrode side to avoid tilting during the
advancing of the electrode 12. The suspension system 15
consists, first, of hydraulically operated electrode regulating
cylinders 21, 22, which take on the suspension of the entire
electrode train 14. These cylinders are mounted on the cylinder
side by suspension on the guide frame 16 by connecting elements
23, 24 and extend along the longitudinal axis of the electrode.
The connecting elements 23, 24 are anchored in the guide frame
16. The ends 25, 26 of their pistons are rigidly connected with
a holding ring 27 for the electrode 12. Two hydraulic lifting
cylinders 28, 29 that can be operated at both ends are mounted
on the side of this holding ring 27 that faces away from the
furnace. A first or upper advancing ring 30 can be
hydraulically moved along the longitudinal axis of the electrode
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by these lifting cylinders 28, 29. The oil lines are numbered
31 and 32. Current is conducted to the electrode 12 through the
holding ring 27. To this end, a power supply line 33 is guided
to the holding ring 27 first through a rigid line and then a
flexible line. Two power supply lines 33a, b can also be
provided, as shown in the detail drawing of Figure 2.
The manner of operation of the lower holding ring 27 is
apparent from the detail drawings of Figures 3 and 4. The lower
holding ring 27, which simultaneously serves as a second
advancing ring, surrounds a power supply jaw 34 and two clamping
jaws 35, 36, which can be pressed with varying intensity on the
circumferential surface of the electrode. To this end, the
holding ring 27 is provided with a hydraulic contact pressure
element 37. In a first pressure stage, the clamping jaws 35, 36
come to rest against the surface of the electrode, so that an
effective flow of current from the power supply lines is
possible. In this pressure stage, however, the electrode can be
pushed through the holding ring 27. In a second pressure stage,
the clamping jaws 35, 36 clamp tightly around the surface of the
electrode by means of the expanding contact pressure element 37,
so that the holding ring 27 can hold the electrode by itself.
The manner in which an advancing operation is carried out
in the direct-current arc furnace of the invention will now be
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explained. The electrode 12 is guided into the interior of the
furnace and held by means of the suspension system 15. The
electrode 12 extends into the furnace 1 through the guide frame
16 and through the central section 4 of the roof. Figure 2
shows that the opening in the furnace roof is sealed from the
circumferential surface of the electrode with a seal 38.
Initially, the electrode is held by the upper advancing ring 30.
When the electrode 12 is then to be advanced, this advancing
ring 30 is released and moved upward by the advancing stroke
distance x in the direction of the guide frame 16 by extension
of the double-acting lifting cylinders 28, 29. In this way, the
distance between the holding ring 27 and the advancing ring 30
is increased. The advancing ring 30 in its displaced position
is then clamped to the electrode 12 again. The holding ring 27
is placed in the first pressure stage by releasing the contact
pressure element 37. While current can continue to flow, the
electrode can be pushed farther into the furnace through the
released holding ring 27 by moving the lifting cylinders 28, 29
back and reducing the distance between the advancing ring 30 and
the holding ring 27. During this operation, the electrode 12
slides vertically along the guide rollers 20 of the guide frame
16 and the seal 38 of the opening in the furnace roof. When the
advancing operation has been completed, the holding ring 27 is
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again pressed against the electrode 12 with increased contact
pressure.
All together, the replacement of a support arm construction
by an electrode train supported above the furnace has been found
to be very advantageous for a direct-current arc furnace. By
making it possible to advance the electrode without shutting
down the furnace, the total yield is increased. Compared to the
previous system, this system operates more smoothly and thus
more effectively and economically. The elimination of
vibrations reduces wear in guide locations and sealing
locations, especially in the furnace roof. Due to the better
and longer-lasting seals, safety is improved in processes in
which CO is produced.
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List of Reference Numbers
1 direct-current arc furnace
2 furnace vessel
3 furnace roof
4 central section of roof
frame construction
6 columns
7 furnace wall
8 refractory material
9 furnace bottom
bottom electrode
11 bottom electrode
12 electrode
13 furnace platform
14 electrode train
suspension system
16 guide frame
17 tap hole
18 vessel
19 vertical charging line or lateral charging line
guide roller
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21 electrode regulating cylinder
22 electrode regulating cylinder
23 connecting element
24 connecting element
25 piston end
26 piston end
27 electrode holding ring or lower advancing ring
28 lifting cylinder
29 lifting cylinder
30 first or upper advancing ring
31 oil line
32 oil line
33 power supply line (33a and b)
34 power supply jaw
35 clamping jaw
36 clamping jaw
37 contact pressure element
38 seal
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