Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates generally to electrodes
utilized in electric-arc furnaces, and has to do particu-
larly with the construction of a composite electrode intended
to provide advantages over the electrodes currently in use.
Electrode consumption contributessubstantially to
the total cost of electric furnace steelmaking. Electrode
consumptions can be broken down into tip losses, side oxida-
tion losses and column breakage losses.
Conventional practice typically utilizes an elec-
trode configuration consisting of multiple sections of
graphite cylinders threaded together with graphite nipples.
An electrode clamp holds this column in position and transfers
the electrical power to the graphite cylinders. The diameter
of conventional cylinders must be uniform and the surface
must be machined smooth in order to promote the best electrical
transfer without "hot spots" or arcing. During use, the
electrode column is "slipped" as tip erosion takes place, and
new sections are added at the top. The high temperature and
oxidizing atmosphere in the furnace consumes the
exposed area of the electrode and promotes a taper towards
the tip. The graphite oxidation losses of this kind typically
amount to ~rom 50% to 70% of the total consumed.
The taper also reduces the wall thickness at the
ioints, thus rendering the column more prone to breakage.
The most serious breakage occurs when scrap movement within
the furnace cause the upper joint to fail, with the resultant
loss of an entire column. The taper also makes it difficult
to seal the region between the electrode and the roof of the
furnace to prevent fumes from escaping.
Various attempts to com~at these problems have been made
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in the past. In an atte~pt to reduce the rate of el~ctrode
oxidation, coating or cladding has been applied to the
surface utilizing temperature^resistant materials. Because
of problems with electrical transfer in the clamp area,
most such materials have been applied only below the clamp.
Marginal success has been obtained with such materials
because of the difficulty of wetting and sticking to the
graphite. The application of a conductive coating applied
over the entire electrode under vacuum or by plasma arc spray-
ing have proven uneconomical.
In view of the foregoing difficulties with conven-
tional practice, it is an aspect of this invention to
provide a composite electrode construction capable of reducing
side oxidation of the graphite portion and of reducing column
breakage losses. Additional advantages of light weight and
greater utilization of the graphite of the electrode are
also aspects of this invention. A further aspect is to
make less critical the dimensions and surface characteristics
of the graphite portion of the electrode.
2~ Accordingly, this invention provides a composite
electrode for electric arc furnaces, comprising:
an elongated, substantially cylindrical metall~c
portion having a top end and a bottom end, the portion
- including an outer wall of substantially uniform section
along its len~th, the outer wall having an outside surface
and an inside surface, an inner wall spaced inwardly from
the outer wall to define therewith a passage of annular
section, a pipe constituting conduit means longitudinally
within said metallic portion, the pipe being spaced inwardly
from said inner wall and communicating with the bottom of
said passage to allow cooling liquid to move within said
portion along a path which brings cooling liquid into
intimate contact with substantially all of the inside
surface of said ou~er wall, said path having a downward leg
and an upward leg, one leg being along said pipe and the
o~ler leg being along said passage,
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an elongated consumable portion having a top end
and a bottom end,
and connector means for joining the top end of the
consumable portion to the bottom end of the metallic portion.
One embodiment of this invention is illustrated in
the accompanying drawings, in which like numerals denote
like parts throughout the several views, and in which:
Figure 1 is a perspective view of the composite
electrode of this invention; and
Figure 2 is a longitudinal sectional view thereof.
In Figure 1, the composite electrode 10 is seen
to include an upper metallic portion 12 and a lower consum-
able portion 14. Means are provided at the joint 15 for
securely connecting the two portions together, these means
to be described subsequently. A typical electrode clamp
16 is provided, having a support arm 18 extending from
control apparatus (not shown) of the conventional type which
is adapted to pass electrical current along the arm 18 through
the clamp 16 and to the composite electrode, and which also is
capable of adjusting the vertical height of the composite
electrode to bring about the most desirable arc characteris-
tics in accordance with conventional practice.
At the top of the portion 12, two cooling wat~r
lines 19 and 20 are provided to carry cooling water to and
from the upper portion 12.
It is to be understood that the composite electrode
10 shown in Figure 1 would be inserted downwardly through the
conventional opening in the roof of a standard electric arc
furnace, with conventional means for substantially sealing
the remainder of the roof opening against the escape of gases.
107~3~1
These parts are conventional, and have not been illustrated.
Turning now to Figure 2, the construction of the
upper or metallic portion 12 of the composite electrode 10,
which may be of ferrous material,
is seen to include an outer wall 22 of cylindrical configura-
tion and an inner wall 24 which is also cylindrical but which
is spaced inwardly and concentrically with respect to the
outer wall 22 to define a passage 26 of annular section
~etween the two walls. The passage 26 is intended to be the
upward leg of a cooling-water circulation path within the
metallic section 12 of the composite electrode
Spanning across the top of both walls 22 and 24
is a circular top wall 28 which is dimensioned to extend
beyond the outside surface of the outer wall 22, as can be
seen in both figures.
A first intermediate transverse partition 30 is
provided in spaced relationship below the upper wall 28
extending only within the inner wall 24 and welded thereto.
Above the partition 30, the inner wall 24 is provided with
a plurality of openings 31 for the purpose of allowing the
cooling water passing upwardly along the annular passage
26 to move readily and with low resistance to an opening
33 communicating with an outlet pipe 34 extending radially
outwardly from the upper end of the outside wall 22.
A further intermediate partition 36 is provided
toward the lower end of the portion 12, again spanning
only within the confines of the inner wall 24 and welded
there~o.
A central, axial pipe 37 passes downwardly through
the upper wall 28 and the partition 30, and terminates at a
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central opening 38 in the partition 36, whereby water may
pass down the pipe 37 to the area below the partition 36.
At the lower end of the outside wall 22 there
is provided a member 40 which is radially symmetrical and
which defines an annular, upwardly open channel 42 between
an outer cylindrical wall 43, a lower annular wall 45, and
an inner, frusto-conical wall 46. Across the upper open
end of the inner, frusto-conical wall 46 is a circular
plate 48. The chamber defined by the annular channel 42j
the plate 48 and the partition 36 constitutes, in effect,
a generally circular passage (with a downward peripheral
portion) for carrying cooling liquid from the bottom of
the pipe 37 radially outwardly to the bottom of the passage
26 of annular section. As can be seen especially in Figure 2,
the inner wall 24 extends downwardly within the annular
channel 42, and thus requires the cooling water to move
continuously along the inner surface of the member 40,
ensuring that it will be cooled uniformly. If the inner
wall 24 did not extend down into the channel 42, there is
a risk that the water at the lower end of the channel 42
would remain static, become overheated, and flash to
steam, thus resulting in an explosion.
Located in the lower end of the annular passage
26 are a plurality of longitudinally oriented vanes 47
for the purpose of minimizin~ turbulence in the passage 26
and for promoting laminar flow of cooling liquid therealong.
The upper end of the outer wall 22 is welded to
an annular flange 50 which has the same outer diameter as
the top wall 28. The flange 50 and the top wall 2~ are
adapted to be bolted together as by bolts 52 with a gasket
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between them, in order to seal the upper end of the annular
passage 26. It will be appreciated that there is no
permanent, bracing contact between the inner wall 26 (includ-
ing the partitions 30, 36 and the central pipe 37) and the
outer wall 22 (including the lower member 43). It is desirable
to be able to remove the entire inner portion from the outer
portion for maintenance, inspection, etc. It is for this
reason that the flange 50 has been provided, so that the
only location of attachment between the two parts is at the
top, by way of the bolts 52.
A T-coupling 54 is threaded to the upper end of the
pipe 37, and a water inlet pipe 56 is connected thereto.
Threaded into the other opening of the T-coupling 54 is a
safety head 57 of conventional construction.
At the lower end of the portion 12, the inner
surface of the frusto-conical wall 46 is formed to define
threads which are adapted to receive the mating threads
of a graphite nipple 59 which is of the usual type utilized
in conventional practice to connect two graphite cylinders
together. The consumable, graphite electrode 14 also has
a threaded, female recess 60 in its upper end, to receive
the other end of the double-male threaded nipple 59.
It can be seen especially in Figure 2 that the
diameter of the consumable graphite portion 14 of the
composite electrode has a smaller diameter than the upper
portion. In conventional practice, the electrodes tend
to be somewhat oversized for the sake of mechanical strength,
i.e. the diameter of the electrodes has been somewhat greater
than the electrical requirement would call for. With the
present construction, however, the diameter of the graphite
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portion of the composite electrode may be reduced tc the
minimum necessary for considerations other than mechanical
strength, because the inherent cooling of the upper end
of the graphite portion 14 due to contact the water cooled
metallic portion 12 will reduce the extent to which the
graphite material oxidizes away at the surface, and will
allow the initial strength of the connection between the
two portions to be maintained. Also, as pointed out
previously, the surface characteristics of the graphite
portion 14 of the composite electrode do not need to meet
the high standards previously called for due to the
necessity of making good electrical connection therewith.
In the case of the present composite electrode,
the clamp 16 is mounted directly to the upper metallic
portion 12, and this will be a metal-to-metal contact
with excellent electrical conduction characteristics.
It will be appreciated that, by keeping the
greater part of the interior volume of the upper portion 12
free of water, the weight of the entire section can be
reduced to a minimum. In fact, the construction illustrated
in Figure 2 is one which can reduce the total weight of the
upper section to less than that of a conventional graphite
electrode with the same diameter. This will lower the
weight that the electrode mast (associated with the arm
18) must lift, and thus will decrease maintenance costs while
increasing the lifting speed.
The joint location where the consumable and the
non-consumable portions of the composite electrode are attached
together can be placed lower on the electrode as a whole than
the lowermost joint normally occurs on conventional electrodes.
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Thus, accidental scrap caves or furnace movements which
exert a force on the side of the electrode will generate
less torque in the joint area (due to the shorter moment
arm), thus reducing the possibility of breakage. Also, any
joint breakage which does occur will lose less electrode
weight because the joint is lower.
It is considered important to construct a female
joint on the water cooled section, so that any expansion
which occurs due to heating of the bottom portion and the
graphite connecting pin will tighten the joint rather than
loosen it.
By providing a single metallic upper portion 12
for the electrode, various diameter electrodes can be
accomm~dated for the bottom section. In the past, the
electrode diameter has been fixed to a single size because
of the high cost of changing electrode clamps.
If desired, the lower electrode section can be
coated with an oxidation resistant coating. The coating can
be applied over the entire surface since the electrodes will
not be gripped by clamps for electrical transfer. The
material could even be applied during manufacture of the
graphite portion of the electrodes. Alternatively, a
cladding material could be used to slow oxidation losses.
On an ordinary electrode, the dissimilar properties of the
graphite and the cladding material tend to cause non-uniform
expansion and slippage of the cladding. Also, rivet or
screw fastening of the cladding to the electrode tends to
be difficult because of the brittle nature of graphite. In
the present invention, howe~er, cladding material could be
suspended from the non-consumable top section with some form
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of support system. This could be designed to easily
accommodate the replacement of electrode sections.
In actual trials on several 25 ton electric
furnaces, it was found that electrode consumption was
reduced by roughly 15% for the composite electrode, com-
pared to the conventional construction utilizing all
graphite portions. It was also observed that cooling in
the joint area between the consumable and non-consumable
portions prevented tapering of the graphite lower portion
for almost 2 feet more than on the conventional consumable
string of graphite cylinders.
It was further observed that the joint between
the consumable and non-consumable sections remained cool,
and was easy to unscrew for the purpose of replacing one
graphite section with another.
To summarize the advantages provided by this
invention, there is firstly a reduction of electrode
consumption because no oxidation of the non-consumable top
section takes place.
There isa f~her reduction of electrode consumption
from breakage because of the cooling feature of the joint,
which causes reduced taper and permits lower level of joints
in the furnace.
Because the diameter of the upper portion of the
electrode dces not change, an improved furnace sealing possi-
bility is provided, allowing greater fume control.
There is further a flexibility in the diameter,
tolerance and surface characteristics of the electrodes
utilized.
Finally, the complete electrode, including both
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portions, weighs less than the conventio;lal electrode made
of all graphite having the same diameter.
~07~3~1
SUPPLEMENTARY DISCLOSURE
Additional drawings are added by this
supplementary disclosure, in which:
Figure 3 is a longitudinal sectional view of
a further embodiment of a composite electrode; and
Figure 4 is a perspective view of several
components of the further embodiment, in exploded
relation.
In Figures 3 and 4, the upper metallic portion
12' is substantially identical to the upper metallic portion
12 shown in Figure 2, with the exception that the circular
plate 48 is not present. Instead, the upwardly converging
threaded female recess defined by the frusto-conical
wall 46' opens directly through to the interior of the
portion 12. Of course, the intermediate partition 36'
blocks the access in terms of the air-filled part of the
portion 12.
The main difference between the second embodiment
shown in Figure 3 and the first embodiment shown in Figure 2
relates to the internal construction of the double-male
nipple59'. In the case of the second embodiment shown in
Figure 3, the double-male nipple 59' is not of graphite but
is machined from a metal such as copper or steel.
The double-male threaded nipple 59' is hollow with a
central cavity 65 having the upper end 66 open and the lower
end 67 closed.
The central, axial pipe 37' in the second embodiment
extends further downwardly than does the pipe 37 in the first
embodiment. As can be seen in Figure 3, the pipe 37' extends
axially down into the interior cavity 65 of the nipple 59'.
Thus, when cooling liquid is forced downwardly along the
central pipe 37', its path includes a portion which extends
from the bottom of the central pipe 37' upwardly out of the
interior of the threaded nipple 59', thence radially outwardly
and downwardly to the lower end of the passage of annular
section defined between the outer wall 22' and the inner wall
24'.
With regard to original Figure 2, it may be pointed
out that the remainder of the volume within the upper
metallic portion 12 of the composite electride, i.e. that
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not forming part of the liquid flow system, is entirely
sealed from communication with the liquid-flow path described
in the principal disclosure, and communicates with the atmos-
phere through a communication pipe 67. Thus, the
pipe 67 is in the nature of a breather or vent, the
purpose of which will be self-evident to the man skilled
in the art.
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