Electric arc furnace having a space provided on one side of the furnace vessel for accommodating charging material

An arc furnace having a space for accommodating charging material, said space being disposed on one side of the furnace vessel and communicating with the interior of the furnace vessel and being disposed at least partly in the region of radiation of the arc of at least one arc electrode. The arc electrode is movable towards and away from the charging material accommodating space, and thereby permits better utilization of the radiant heat generated by the arc.

DESCRIPTION 
The invention relates to an electric arc furnace having at least one space 
for accommodating charging material, which is provided on one side of the 
furnace vessel. 
In the arc furnace of that kind which is disclosed in EP-Al No. 56,773, the 
arc furnace has a lateral bulge portion, the sole of which is at a higher 
level than the sole of the furnace hearth. The charging material is 
introduced into the outwardly bulged portion of the furnace and is stored 
in a heap on the elevated sole. The hot furnace gases are passed through 
the upper part of the heap of charging material, while in addition that 
heap of charging material is exposed to and heated by the radiant heat 
from the arc furnace. The charging material, which has been preheated, is 
conveyed from the lowermost section of the heap of material into the 
furnace hearth by a pusher member. The sole of the lateral outwardly 
bulged portion of the furnace is arranged to have a fall towards the 
furnace hearth. 
US Pat. Spec. No. 3,441,651 discloses an electric arc furnace having a 
shaft-like charging material preheater which is disposed at one side of 
the furnace vessel and the interior of which communicates with the 
interior of the furnace vessel through a connecting zone which is provided 
approximately at the mid-height position of the furnace vessel. The 
connecting zone serves on the one hand to conduct the hot furnace gases 
which are produced in the smelting process into a column of charging 
material which is formed in the charging material preheater, and to pass 
those gases through the downwardly moving charging material in 
counter-flow relationship therewith, thereby to preheat such material, 
while on the other hand the connecting zone also serves as a discharge 
opening for the heated charging material in the floor region of the 
charging material preheater. The respective lowermost portion of the 
column of charging material, which has been preheated, can be conveyed by 
means of a hydraulically operable pusher member through the connecting 
zone into the furnace hearth, that is to say, the charge material is fed 
to the smelting vessel by a thrust motion. A charging means which is 
disposed at the top of the preheater permits a continuous feed of charging 
material into the preheater, while a gas outlet which is disposed in the 
vicinity thereof provides for removal of the furnace gases which are 
cooled down by being in heat-exchange relationship with the charging 
material within the column thereof. 
In an electric arc furnace according to the present invention the object is 
to increase the possible conveyance of heat into the charging material, 
thereby to reduce the time taken for heating up the charging material. The 
invention seeks to provide for better utilisation of the radiant heat as 
well as the hot furnace gases which are produced, when heating up the 
charging material, thereby to improve the level of thermal efficiency. The 
invention also seeks to reduce the thermal loading of the furnace walls, 
as well as permitting a continuous flow of material from the charging 
material accommodating space or chamber into the furnace hearth, and thus 
also permitting more uniform operating conditions. The invention further 
seeks to provide for a reduction in fluctuations in temperature and 
fluctuations in the chemical composition of the smelting bath. 
In the construction according to the invention, the electrodes can be 
brought into the direct vicinity of the charging material accommodating 
space or chamber which is provided on one side of the furnace vessel, by a 
change in respect of position either of the arc electrodes or the furnace 
vessel together with the accommodating space or chamber, so that the 
radiant heat which is generated by the arcs can act to an increased degree 
on the charging material and at the same time the radiation loading on the 
free wall regions of the arc furnace is reduced. The hot gases which are 
produced in particular when adding coal and other batch materials in the 
region of the arcs are conducted directly into the charging material so 
that the sensible heat thereof can be utilised to the optimum degree. 
Those two effects make it possible substantially to enhance the level of 
thermal efficiency. 
By virtue of the direct action of the arcs on the lower region of the heap 
or column of charging material, the charging material may be put into a 
pasty or plastic and fluid condition so as to permit a continuous flow 
from the charging material accommodating space or chamber into the furnace 
hearth. 
If in addition the construction includes nozzles and/or burners which are 
directed on to the lower region of the charging material accommodating 
space, that area may be additionally heated, or oxygen, coal or other 
additives may be introduced for the purposes of temperature control and 
for controlling the composition of the smelting bath. 
Preferably, the floor of the charging material accommodating space is 
arranged at such a depth that, when a liquid sump pool is formed in the 
furnace hearth, the pool extends into the accommodating space and permits 
direct material exchange and conductive heat exchange in the lowermost 
region of the heaped charging material. That provides for an additional 
flow of heat for the lowermost region of the column of charging material 
which is standing in the liquid sump pool. An intensive material and heat 
exchange effect takes place in that region, caused by the movement of the 
bath which always occurs in the furnce hearth. In that way, the molten 
material which is overheated in the region of the arcs supplies heat to 
that region whereby the material which has already been preheated is 
caused to melt in that region. The liquefied material flows continuously 
out of the charging material accommodating space into the liquid molten 
bath of the furnace hearth so that there the operating conditions can be 
kept substantially constant. In addition, the region of the solid-liquid 
transition is the site of chemical-metallurgical conversion phenomena such 
as the formation of slag, carburisation, etc, which can be promoted by the 
controlled feed of oxygen, coal or additive materials. In that way, not 
only is it possible for the thermal conditions in the furnace hearth to be 
kept constant and adjusted to an optimum operating point, but in addition 
it is possible to prevent major fluctuations in the composition of the 
molten material and to control the composition thereof. 
When a sufficient pool has been formed in the furnace hearth, but at the 
latest when the level of the molten material has reached the tapping-off 
level, the electrodes are returned to the middle of the furnace by a 
change in position either of the arc electrodes or the furnace vessel 
together with the charging material accommodating space, and in that 
position the bath is heated up to the necessary tapping-off temperature. 
Due to the mobility of the electrodes or the furnace, it is thus possible 
in the course of the smelting process to alter the position of the heat 
source within the furnace in such a fashion that both the smelting process 
and also metallurgical procedures can take place in the optimum fashion 
within the furnace.

Referring to FIGS. 1 and 2, the furnace assembly shown therein in vertical 
section and in plan respectively includes an arc furnace 1 comprising a 
furnace vessel 2 and a removable cover 3 through which are passed three 
electrodes 4/1, 4/2, and 4/3. The furnace vessel 2 is formed by a furnace 
hearth 5, comprising a refractory lining, and preferably fluid-cooled wall 
elements 6. Disposed on one side of the furnace vessel which, in the 
present case, as shown in FIG. 2, is round in cross-section, is a 
shaft-like charging material preheater 7 having a space (chamber) 8 
therewithin, for accommodating charging material, which, in a region 
adjoining its floor 9, communicates with the chamber 11 inside the furnace 
vessel 2, by way of a connecting zone 10. The charging material preheater 
is provided in its upper region with a gas-tight charging arrangement 12, 
for example a double bell closure arrangement of known design, as well as 
a gas outlet to which a suction removal means (not shown) is connected. 
As shown in FIG. 2, the preheater 7 extends approximately over a quarter of 
the periphery of the furnace vessel 2, while the shaft wall 14 of the 
preheater, which is towards the furnace vessel, matches the outside 
contour of the furnace vessel. It will be seen from FIG. 1 that the 
cross-section of the space 8 within the preheater 7 is of an enlarging 
configuratio in a downward direction. That is intended to permit the 
charging material to move unimpededly downwardly in the charging material 
preheater 7. Burners 15 or nozzles for injecting gases, such as oxygen, or 
solids, such as coal or additive materials, discharge into the connecting 
zone 10. 
The charge material 16 which is charged into the charging material 
preheater 7 may comprise metal scrap, in particular steel scrap and other 
iron-bearing materials such as crude or pig iron in lump form, sponge iron 
and additive and flux materials. The material introduced into the 
preheater 7 forms therein a gas-pervious column of material, referred to 
as the charging material column 17. The molten metal bath (sump pool) 
which is formed in the arc furnace 1 is denoted by reference numeral 18 
while the level of molten material is denoted by reference numeral 19. 
The floor 9 of the preheater 7 which is preferably arranged to have a fall 
towards the furnace hearth 5 is arranged at such a depth that, over a 
substantial part of the smelting process, a liquid sump pool 18 which is 
formed in the furnace hearth extends into the lowermost region 20 of the 
column 17 and there permits direct material exchange and conductive heat 
exchange to take place. Provided in the floor of the furnace hearth 5 is 
an eccentric bottom tapping hole 21 which is shown in dotted line in FIG. 
2. In the present case, the furnace vessel 2 is designed to be tilted. The 
tilting plane, that is to say, the plane in which the tilting movement 
occurs, is denoted by reference numeral 22. The preheater 7 is disposed in 
a direction which is transverse with respect to the tilting plane of the 
furnace vessel. 
Each of the electrodes 4/1, through 4/3 inclues a liquid-cooled metallic 
upper portion 23 and a lower portion 24 which forms the electrode tip and 
which comprises a consumable material such as graphite. The lower portion 
24 is releasably secured to the upper portion 23. Each electrode 4/1, 4/2 
and 4/3 is gripped with its upper portion 23 in a respective electrode 
carrier arm 25/1, 25/2 and 25/3; each electrode carrier arm can be raised 
and lowered by means of an electrode lift mechanism 26/1, 26/2 and 26/3 
respectively. The electrode lift mechanism 26/1 through 26/3 are arranged 
beside the furnace vessel 2, on the side which is in opposite relationship 
to the charging material accommodating space or chamber, that is to say, 
the shaft-like charging material preheater 7. 
In the case of the embodiment illustrated in FIGS. 1 and 2, each of the 
electrode carrier arms 25/1 through 25/3 is connected to the respectively 
associated lifting mechanism 26/1, 26/2 and 26/3 by way of a horizontal 
guide means 27/1, 27/2 and 27/3 respectively, and can be reciprocated 
along the guide means by a drive means which is not shown in the drawing 
but which is operative in two directions. The guide means 27/1 and 27/3 of 
the two outer electrode carrier arms 25/1 and 25/3 are each curved 
outwardly so that, upon the reciprocating movement of the electrode 
carrier arms 25/1 and 25/3, those arms are pivotable through a restricted 
angle in a horizontal plane. The paths of movement of the centre lines of 
the electrodes 4/1 through 4/3, during the forward and backward movement 
of the electrode carrier arms along the guide means 27/1 through 27/3 are 
shown in dash-dotted lines in FIG. 2 and are denoted by references 28/1 
through 28/3. It will be seen that the paths of movement 28/1 and 28/3 are 
also curved outwardly, due to the curved guide means 27/1 and 27/3. The 
ends of the paths of movement are marked by transverse bars which thus 
show the limit positions in respect of the centre lines of the electrodes. 
In the left-hand limit position shown in FIG. 2, the electrodes 4/1, 4/2 
and 4/3 are each disposed at approximately the same spacing from the 
charging material accommodating space or chamber 8. 
The horizontal guide means 27/1 through 27/3 for the electrode carrier arms 
25/1 through 25/3 may be of the configuration shown in FIG. 3. FIG. 3 
shows a view in section taken along line III--III in FIG. 1, on an 
enlarged scale. As shown in FIG. 3, the guide means 27/2 includes two 
slide bars or rails 29/2 which are disposed in mutually opposite 
relationship and which are of trapezoidal cross-section, each having an 
upper and a lower slide track 30/2, the slide tracks being formed by a 
coating or applied portion of sliding material. Bearing against the slide 
tracks 30/2 are the sliding surfaces of a carriage 31/2 which is thereby 
fixed in its position while being displaceable along the rails 29/2. The 
carriage 31/2 carries the carrier arm 25/2 which is fixed on the carriage 
31/2 with the interposition of a cover plate 32/2 and an insulating plate 
33/2, by means of a screw bolt 34/2. The insulating plate 33/2 which is of 
the same length as the carriage 31/2 is also shown in part in FIG. 2. It 
will be ssen from that view that, for reasons of stability, the carriage 
31/2 extends over approximately one third to one half of the length of the 
guide means 27/2. 
The guide means 27/1 and 27/3 for the two outer carrier arms 25/1 and 25/3 
are of a similar construction. As can be seen from FIG. 2 however, they 
are curved, that is to say, when considered in plan view, the respective 
rails 29/1 and 29/3 are of a correspondingly curved configuration. 
In order to permit the paths of movement 28/1 through 28/3 of the 
electrodes 4/1 through 4/3 when the cover is in the closed condition, the 
cover is provided, for each electrode, with a slot-like means for passing 
the electrode therethrough, said slot-like means being adapted to the path 
of movement of the respective electrode. The slot-like electrode-passing 
means are covered over by cover plates 35/1, 36/1, 37/1 through 35/3, 
36/3, 37/3 which are displaceable along the horizontal path of movement 
and one of which has a through opening which is adapted to the electrode 
cross-section. The cover plates 35/1 through 37/3 close off the slot-like 
electrode-passing means in the cover in any position of the electrode 
along the path of movement 28/1, 28/2 and 28/3 respectively thereof. 
FIGS. 4 and 5 show the position of the cover plates 35/1 through 37/1 of 
the electrode 4/1 in the two limit positions thereof, in diagrammatic 
form. A similar situation applies in regard to the cover plates of the 
other two electrodes 4/2 and 4/3. 
The slot-like electrode-passing means in the cover 3, which can be seen in 
the views shown in FIGS. 4 and 5, is denoted by reference numeral 38/1, 
while the through opening in the cover plate 36/1, being adapted to the 
electrode cross-section, is denoted by reference numeral 39/1. 
As can be seen from FIGS. 4 and 5, the ends of the middle cover plate 36/1 
each engage over one end of the respective outer cover plates 35/1 and 
37/1 respectively. Provided at the overlapping ends of the above-indicated 
cover plates are entrainment members 40/1 which, in the event of 
displacement of the electrode 4/1 along the path of movement 28/1, and the 
resulting movement of the middle cover plate 36/1, each entrain the outer 
plates by a respective distance and thus ensure that the electrode 
through-passing means 38/1 is completely closed off, with the electrode 
4/1 in any position. 
The smelting process using the furnace assembly described with reference to 
FIGS. 1 through 5 will now be described. 
The solid charge material 16 in lump form is charged into the space or 
chamber 8 of the charging material preheater 7 by the charging arrangement 
12 until the material has formed an adequate column 17 of material 
therein. In the region of the connecting zone 10, the solid charge 
material passes partly into the furnace hearth, because of the natural 
angle of slope adopted by the bulk charging material, as indicated at 41. 
The electrodes 4/1 through 4/3 are now moved towards the preheater 7 and 
the smelting process is commenced by lowering the electrodes in the region 
of the heap of charging material. The liquid metal pool which is then 
formed collects in the furnace hearth and causes an intensive material and 
heat exchange effect to occur due to the movement of the bath in the 
lowermost region of the column of charging material 17. That region may 
also be the site of desired metallurgical conversion phenomena which are 
controlled by the control feed of oxygen, coal or additive or fluxing 
materials in the region indicated by the burners 15, or by virtue of 
additive materials which are mixed with the charging material. Heat may 
additionally be applied by means of the burners 15. At the same time as 
the smelting process takes place, the material 16 in the column 17 moves 
downwardly so that it is also caused to undergo melting in the lowermost 
region of the column 17. In order to promote the above-indicated downward 
movement, the cross-section of the chamber 8 of the preheater 7 is of an 
enlarging configuration, in a downward direction. 
As long as the electrodes 4/1 through 4/3 are in the position adjacent the 
shaft-type furnace or preheater 7, that is to say, in the view shown in 
FIG. 2, in the vicinity of or at the left-hand limit position of the paths 
of movement 28/1 through 28/3, the radiant energy of the arcs is applied 
to an increased degree to the lower region of the column 17 of material, 
and thus optimum use is made thereof for causing the material to melt. The 
same also applies in regard to the furnace waste gases which, by virtue of 
their being sucked away by way of the gas outlet 13, pass directly out of 
the regions of the arcs into the column 17 of material. 
When a sufficient amount of charge material has been caused to melt, the 
electrodes are returned to the right-hand limit position of the paths of 
movement 28/1 through 28/3, as shown in FIG. 2, and the bath is brought up 
to the necessary tapping temperature. The tapping operation is carried out 
by way of the tapping arrangement 21 which is disposed in the floor of the 
arc furnace. In that operation, a part of the pool of metal in the furnace 
vessel is preferably retained therein for the next smelting operation. 
Due to the horizontal displaceability of the electrodes, the arcs can 
always be put into the respective position which is advantageous for a 
given situation, in regard to the smelting process, heating of the liquid 
molten bath and the loading applied to the furnace walls. The electrodes 
4/1 through 4/3 may adopt any intermediate positions along their paths of 
movement 28/1 through 28/3. In that way it is also possible, during the 
smelting process, for the arcs to be caused to burn only on a liquid pool 
which is already in existence, directly adjacent to the material which is 
still in a solid state, thereby making it possible to achieve more uniform 
operating conditions. As the important consideration in each case is only 
the relative position of the electrodes within the furnace vessel, it is 
also possible for the furnace vessel 2 to be moved, together with the 
charging material accommodating space 8, instead of moving the electrodes. 
Instead of the provision of the slot-like electrode-passing means 38/1 in 
the cover 3, it is also possible for the cover 3 to have a round 
electode-passing means for each electrode, at the two limit positions in 
respect of the relative movement of the cover 3 and the electrodes. In 
that case, before horizontal movement of the electrodes or the furnace 
vessel is effected, the electrodes must be lifted to a position above the 
upper edge of the cover by operation of the electrode lift mechanism 26/1 
through 26/3. 
In the second embodiment illustrated in FIGS. 6 and 7, each of the 
electrodes 4/1, 4/2 and 4/3 is gripped in a telescopically extensible 
electrode carrier arm 51/1, 51/2 and 51/3 respectively. The guide means 
52/1, 52/2 and 52/3 for the electrode carrier arms can be raised and 
lowered by electrode lift mechanisms 26/1, 26/2 and 26/3 respectively, and 
are also rotatable through a restricted angle about vertical axes as 
indicated at 53/1, 53/2 and 53/3 respectively. The guide means 52/1 
through 52/3 are thus respecitvely connected to the associated electrode 
lift mechanism 26/1 through 26/3 by way of a connection which is provided 
with a drive means and which is rotatable within a limited angle. 
As in the case of the first embodiment, in the second embodiment as shown 
in FIGS. 6 and 7 the arc electrodes 4/1 through 4/3 can be moved from a 
configuration which is triangular in plan view, in the middle of the 
furnace vessel, as can be seen from FIG. 7, into an arcuate configuration 
adjacent to the charging material accommodating space or chamber, and back 
again. In addition, each of the two outer carrier arms 51/1 and 51/3 is 
capable of limited rotational movement about its longitudinal axis 54/1 
and 54/3 respectively, although that possiblity is not shown in the 
drawing. In that way, the outer electrodes 4/1 and 4/3 may be inclined at 
a slight angle so that, in addition to the change in spacing between the 
tips of the electrodes by virtue of the predetermined paths of movement of 
the electrodes, the spacing between the electrode tips can also be altered 
by setting the electrodes in an inclined position. As the electrodes in 
the above-described furnace assemblies are no longer endangered by scrap 
material collapsing or caving in when the electrodes burn into a scrap 
charge in the furnace, the electrodes which are referred to as permanent 
electrodes are particularly suitable for this purpose, such electrodes 
comprising a fluid-cooled metal upper portion and a lower portion which 
forms the electrode tip, comprising a consumable material, which is 
releasably secured to the upper portion. 
In the second embodiment, as shown in FIG. 6, the connecting zone 10 is of 
an enlarging configuration inclinedly upwardly from the interior 11 of the 
furnace vessel 2 to the chamber 8 of the charging material preheater 7, 
and a partitioning wall 56 which is provided with gas through-flow 
openings 55 is disposed in the enlarged region of the connecting zone 10. 
In that way, the hot furnace gases can be conducted into the column 17 of 
charging material, over a larger cross-sectional area thereof.