Note: Descriptions are shown in the official language in which they were submitted.
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D:l:RECT CURRENT_S~IELTI~G FIJ~'~NACE
The presen-t invention relates to electrlc smelting
furnaces, ~ore particularly, it relates to clirect current
electric smelting fllrnaces.
Direct current sm~elting furnaces have been known for
; a large nurnber o r ~ears. These comprise a single top
` ~ electrode serving as the anode and the bot~o~ of the
- .furnace pot -is connected to act as the cathode. While
this t~Re of furnace was employed for a great number of
years 3 it has largel~ fallen into disuse with the advent
of alternating current 3-phase generators. These generators
resulted in subs~antially improved power transmlssi.on ancl
have resulted in the 3-phase alternatL~g currerlt sme'l~i.n~
~urnace hsing virtual:L~ ~he on:Ly one I.n use ~oda~.
There have recently been developed dry-type rectiflers
for converti.ng transmitted alternating current to direct
current~ With these improved rectiiers, it is possible
to take advantage o the improved transmission properties
of alternating current while still being able to use
direct current at the furrlace site, ~.lith these new dry-
type rectifiers, it is possible to convert a standard three
electrc)de 3-phase al-ternating current smelting urnace to a
direct current- furnace by simply connecting the tbree
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electrodes to be direct current anodes while maintainin~
the furnace bottom as the cathode. UnEortunately, dry-
type recti:Eiers are comparatively large and expensive
equipment and it is auite doubtful that large direct
current furnaces of the type just clescribed could
compete with 3-phase alternatin~ current furnaces.
While the concept is certainly possible, the practicali-
ties do not appear to he present.
The inventor has now discovered an electrical
arrangement of the electrodes which mak.es it possible
to increase the volta~e and the furnace load of a direct
~ current furnace without re~uirin~ a corresponding increase
.~ in the expense of electrical equipment. The econo~ics
of this system are such that a direct current smelting
furnace can ~e made which can compete with 3-phase
alternatiny current furnaces and, in addition, will have
substantial additional advanta~es including especially
load capacity. Thi~ is primarily because of the lack
of the "s~i.n e:~fect" property in usinc~ direct current,
an undesirable property which is present in alternating
current smelting furnaces.
According to the present invention there is
provided an electrical smeltinq furnace comprising a
furnace pot adapted to contain a charge to be smelted,
there being provide~. at least two pairs of electrodes
with each pair of electrodes being connected in serles
with a source of dc power wherein one electrode within
each pair acts as a cathode.and the other acts as an
anode. Switching means is provided which is capahle
of reversing the polarity of each of the ~air of
electrodes inde~endently of the switchin~ of each other
pair of electrodes.
. .
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In the invention the bottom o the eurnace
is no longer used as an electrode. ~1ith the arran~emen-t
described, there is obtained an increase in load
capacity of the urnace as compared to existing direct
current furnaces and as compared to existing alternatin~
current furnaces.
According to another aspect of the present
invention there is provided a method of operating an
electric smelting furnace having at least two pairs
of electrodes connected in series. In the method
; direct current is fed to each pair of electrodes at a
first polarity whereby one electrode of each pair is
the cathode and the other is the anode. The polarity
is reversed to one of the pair of electrodes without
.
reversing the polarity of another of the pair of
electrodes. Subsequently, the po]arity is reversed to
the other pair of electrodes.
These and other aspects of the ~resent invention
may be more Eully under~tood with respect to the clrawing
wherein:
the Pigure is a top view of a typical furnace
according to the present invention.
The art of electric smelting furnaces is quite
well developed and the structure of electric smelting
furnaces is quite ~7ell known in the art. In this
connection reference is made to U.S. Patent Nos. 3,895,175
and 4,00l,488 for representative showings of electric
smeltin~ furnaces. Since the general configuration of
electric smelting furnaces is so well known, the figure
of the present invention is limited to a somewhat
schematic top view which shows the novel construction
of a smeltiny furnace accoxdin~ to the present invention.
~ ~ h
m~ 3 -
~ s there shown, there is a circular urnace
pot 10 having a plurality of electrodes 12, 1~, 16,
18 positioned therein. It has been found -that an
arran~3ement of four electro~es in a circular furnace
pot ~ives quite excellent results in accordance
with -the present invention. The electrodes are
electrically connected to rectifier 20 by means of
a seriès of wires as shown. Rlectrodes 12 and 14 form
an electrode pair with electrode 14 belng positive and
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mb/!, - 3a -
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electrode 12 being negati~e in the igure. Similarly,
electrodes 16 and 18 form an electrode pair with 16 being
the positive and 18 being the negative. This arrangement 7
by itsel~ will work. However, it has been found that
' substantial advantage can be obtained if the polarity of
the electrode pairs' can be reversed. This advantage is
i,n terms o both heat buildup and evenness of electrode
wear,
For accomplishing the polarity swltching, there is
preferably employed a switching mechanism 22 7 24 between
the rectifier 20 and the electrode pairs. It is, of course~
, possible to activate switches 22 and 24 simultaneously
so that there will be a simultaneous rever~aL o polari~
in the two electrocle pairs. However~ i~ has been d~.~s-
covered tha~ ~V~Il greater advantage CaLl be obtaLned lf ~he
switches are controlled so that four dlferent electrical
arrangements are obtained in the furnace pot. Starting
from the embodiment shown, this can suitably be obtained
by~ after a first predetermined period of time, flopping
switch 22 to reverse the polarity of electrodes 16 and 18,
after a seeond predetermined period o time floppin,g
switch 24 to reverse the polarit~ of electrodes 14 and 12,
ater a third predetermined period oE time flopping switch
2.2 to ret~Lrn electrodes 16 and 18 to the polarity shown
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in the fig-lre a~d, Einally, after a fourth p-redetermined
period of time 3 flopping sw-.itch 24 to i-ts orlginal po9:ition
to reobta:in the polarity shown in the ~igure The electrocles
have thus been arranged in four diferent electrical con
:Eigurations and it has been ~ound that this is the most
desirable arrangement.
.
It will be app:reciated thak~ in~operation, ~he
el.ectrodes do not know the other electrodes with which
the~ are paired. Therefore, current will flow through
,
10 the charge from all electrodes operating as anodes to
all electrodes operating as cathodes. Naturally, the
chief flow of current will be through the smelting bath
(not shown) at the bottom o~ the.furnace pot
As mentLoned be:~ore, the arra~ ertl~n~ o:~ ~h~ preserlt
lnven~i.on has substclntLal Llcl~antage over Icnown d-Lrect
current and alternating current furnace arrangements.
With respect first to known direct current furnaces,
which are all of the single electrode ~ype, the use of two
electrodes in the top of the furnace in accordance wikh
the present invention enables one, using the same
rectif-;er as in the single electrode ~urrlace~ to obtain
double the vo].tage with the same arnount o~ current.
Furthermore~ since there are two pairs of top electrodes,
each pair of which is connected i.n series, the same
electrod~ d-Lmenslon wiLl result in a doubli~g o~ the
currenk as well as a doubling of the voltage so khat
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the furnace load will be four times as large as compared
to a furnace with a single top electrode and the bottom
of ~he furnace pot acting as the other electrode.
When comparing the present invention to a standard
3-phase a1ternating current furnace, the load oE the furnace
of the present~invention will be 4/3 the load of the
alternating current furnace if the electrode dimension is
the same. This alone is an advantage. However, the
advantage becomes even greater as larger elec~rodes are
employed since electrodes employing alternating current
are subject to the undesirable "skin effect" property and
this property becomes more and more of a problem as
electrode diameter incre~ses. Because o~ thi5, electrode.s
in a direct curren-~ Eurnace can be ~ed witll consi.derEIbly
more cu~ren~ than corresponding electrocles ln an alternat-
ing current furnace. In addition to the "skln effect"
problem~ alternating current furnaces of the dimensions
customarily used today also su~fer losses because o~ eddy
currents and hysteresls Losses of this nature are no~
encountered with direct current. Because of the savings
whLch direct current has over alternating current in terms
o:E the losses through "skin effect"~ edcly currents and
hysteres~s~ the additional expense of the electrical
equipment necessaYy for a direct currer-t :Eur~ace is soon
reco~ered~ after which the savirlgs represent profit.
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:[t has been found that even greater e:E~iciency can
be obtalned by coupling two or more :Eurnaces in series so
that a larger nunlber of electrodes is connected in series.
In this way, the best utilization of the recti-Eier is
obtained,
It will be understood that the claims are intended
to cover all changes and~modifications of the pre:Eerred
embocliments of the invention7 hexein chosen for the
purpose of illustration~ which do no~ constitute de-
partures from the sp-lrit and scope of the invention.
