An Electric Furnace for the Application of Polyphase Currents.in Processes of Fusion or Decomposition by means of the Voltaic Arc.
Year: 1897

page_text: Date of Application, 17th July, 1897-Accepted, 21st Aug., 1897
An Electric Furnace for the Application of Polyphase Currents.in
Processes of Fusion or Decomposition by means of the Voltaic Arc.
I CHARLES BERTOLUS of 8 Place Paul Bert, St. Etienne in the Republic of France,
Electrical Engineer, do hereby declare the nature of this invention and in what
manner the saine is to be performed, to be particularly described and ascertained
in and by the following statement:—
At the present time, electric furnaces are worked with continuous or, alternating
monophase currents, and, where, polyphase currents have to be dealt with, they are
resolved into as many monophase currents as there are: furnace elements. This
arrangement complicates the use of polyphase currents, annuls their properties
and renders it preferable to employ monophase alternating-current furnaces.
All polyphase currents. are applicable without exception, from the biphase up to
whatever number of phases are possible to the builders of electrical machinery.
In existing furnaces worked with continuous or alternating currents, the field of
fusion or decomposition is formed by an are passing from the extremities of the
electrodes through the mass to be. treated, which is interposed within the electric
circuit.
The power of the field is limited to the intensity of the circuit current. Since the
intensity of the current is itself limited to the dimensions of the electrodes, which
may not exceed practical dimensions, the power of the furnace, as regards strength of
are or field of fusion or decomposition and elevation of temperature, is therefore
limited to the maximum current of the circuit.
Further, the necessity of changing the electrodes which wear out;.necessitates the
interruption of the current, and consequently the working of the arc, and of the
furnace; the fusion or the decomposition cannot then continue.
My invention for utilizing polyphase currents direct in electric. furnaces, enables
ine to obtain furnaces of greater power and economy than heretofore.
The field of fusion or decomposition is established upon the new principle, with. a
number of arcs corresponding to the number of phases of the polyphase system.
These phase currents are divided. currents utilizing and necessitating. distinct
circuits and products in the same electrical apparatus,, the winding of which
corresponds to the number of phases desired.
The main advantages that polyphase currents offer as.applied to furnaces over all
other systems, are the following:-
1. In existing furnaces, a certain density per square millimeter of section of
electrode cannot be exceeded (said density varying with the quality of the electrodes),
because the terminals or leaders of the current connecting.the conductors with the
carbons become heated; the contact becomes bad; and small ares are formed between
the carbon and the metallic terininals.
i
•
These phenomena augment the resistance of the electric. circuit,"
current, and give rise to material inconveniences.
'cause loss of
The power of the furnaces is therefore limited to the intensity of current which
the electrode carries, whereas it has-been-sought. to augment. it by having more
powerful fields. For this reason, jackets have been designed for the circulation of
water to cool the electrodes.

page_text: With the system of polyphase currents; while keeping, for each electrode, the
maximum density of current practicable, the power of the furnace is multiplied as
many times as the system has phases.
Besides, having a more powerful furnace, the use of polyphase currents allows of
diminishing the density of current in the electrodes and of having weaker parts, more
easily handled, and working under better conditions.
2. It is possible to obtain with each circuit of phases, with the same parts,
conductors, electrodes, and the same losses of current as with other systems, a more
powerful current and consequently a more powerful are, and thereby a more intense
calorific action and fusion.
3. It is possible to obtain in the same furnace several circuits of phases not hitherto.
obtained.
4. It is possible to obtain as many arcs as there are phases employed, either striking
the arcs across the mass to be treated-direct between the electrodes, or between each
electrode and the mass to be treated, this latter being connected to a neutral point
of the polyphase system, or vice versa.
5. It is possible to obtain several ares in the same field.
6. By means of these polyphase arcs, the power of the furnace is proportional to the
number of phases.
7. It is possible to produce this maximum power by causing the maximum density
of current (ampères)-to pass at every phase which the organ of the electrodes will
carry.
A furnace may be set up for industrial working by supplying any number of phase
currents to a corresponding number of electrodes, and striking an are between each
of these electrodes and the inass to be treated.
It is true that, in an electric furnace, a certain number of electrodes may be
arranged, each acting as an element of the furnace, or so grouped as to behave as a
single multiple carbon electrode, with either continuous currents or alternating
monophase currents, but in this case it is evident that the variable resistance of the
electrodes sets up variations in the current prejudicial to the proper working of the
furnace, and necessitates a continual supervision, and minute a ljustment.
8. This system permits, moreover, of obtaining the formation of arc (the evidence
of the phase currents) in the field according to the system of winding employed in the
construction.
For the sake of illustration, I give an example of three-phase currents, which may
be produced either by:
:-
(a) triangular-winding, or (b) star winding.
(a) The arcs are struck between the electrodes passing through the material to be
treated.
.
(6) The arcs are struck from the electrodes to the mass to be treated, this latter
constituting the neutral point at the centre of the arcs, connected electrically or not
to the corresponding part of the electrical apparatus (transformer or alternator).
9. It is also possible to remove one or more of the carbons or phase electrodes
without stopping the operation of the furnace.
This is of considerable importance, for during the renewal of the carbons of the
electrodes, when worn out, the are corresponding to the phase that is removed only
disappears; the others continue working.
: A continuous action of the furnace is thus obtained, and the renewal of the carbons
takes place successively during the running, while now, for the renewal of the carbons,
the furnace has to be stopped..
10. An important advantage of polyphase currents is, that they render absolutely
independent the materials to be treated, of all density of currents and direct electrical
contacts.
The thicknesss of the mass to be treated inay be augmented without having to
take special measures against leakages of currents produced by the increase in
thickness of the mass. This is very important for furnaces not provided with a
runner hole, and in which the material accumulates at the bottom.

page_text: The electrodes being movable, they may be moved proportionally to the augmentation
of the thickness of the mass, so that the field of fusion suffers no variations.
11. More or less intense arcs may be equally obtained in the same furnace, according
to the strength of current passing over the circuit of phases corresponding to these
ares, and the temperature varied in any one part of the material to be treated, to
produce predetermined results.
12. A great advantage of the system is, that one or several fields of fusion may be
obtained, at pleasure, by increasing the phase circuits.
The existence of these numerous arcs plays a great part in the out-put of the
furnace. The calorific action has more field to operate on the mass to be treated.
This last undergoes also a mixing effect, which prepares it for the action of the arc.
13. It will be understood, also, that by a convenient graduation of the intensity
of the currents supplied to the successive electrodes, it is possible, by employing a
furnace of elongated rectangular form with an inclined hearth, to obtain, at the.
various points of the furnace, from the extremity of where the material to be treated
enters, to where it leaves, gradually rising or suitable temperatures. It is also
possible, by introducing at one or more of these points, new raw material, or material
already treated or under treatment, to obtain, by the combination of these with the
bodies resulting from the previous treatment of the primary material, new bodies or
new combinations capable of forming only at temperatures, to which the materials
are subsequently subjected in the furnace."
14. Finally, the use of polyphase currents allows of obtaining, in an electric
furnace, a succession of fields with no interruption between them, and constituting,
so to speak, an uninterrupted chain, of which the links are constituted by the
carbons, and by the arcs sprung between them.
In this way, each of the electrodes participates in the production of the two ares
which are formed between it and the adjacent electrodes immediately
adjoining on each side of it, a result unobtainable with alternating monophase
currents, or with continuous currents, but this constancy of temperature in a
furnace, on the passage of the material in motion, necessary in order that there
may be no alternations and fluctuations which would cause the progressive
fusion or decomposition to be stopped.
The electric furnace that I claim is adapted more especially for use with polyphase
currents.
With it, all the above signal advantages are obtained by employing these currents.
It enables any number of electrodes to be arranged in a group corresponding to the
number of independent circuits produced by separate windings of the machines, or
polyphase alternating monophase or continuous current electrical apparatus, forming
the combinations of arcs in the mass to be treated.
In a multiple arc furnace, the power is proportional to the number of circuits
employed It is really continuous in working by reason of the employment of several
circuits.
It is also economical by reason of having a much larger field of action, and by
submitting the mass to a previous mixing action, and thus favoring the action of
the arc.
Further, its construction permits of using, while preserving the advantages of the
furnace, monophase alternating currents, and even continuous currents, each electrode
having an independent generator circuit..
In the accompanying drawings:-
Fig. 1 is a vertical section of the furnace, shewing one of the charging shoots, and
indicating the mechanism for moving the electrodes.
Fig. 2 is a plan view of the furnace and its electrodes.
The essential parts of the furnace are the following:
1. A foundation of masonry.
2. A battery of electrodes.
3. An arrangement of cover composed of a chimney and movable dampers.
4. Mechanisin for moving the electrodes.
:

page_text: "
The foundation of masonry a is constructed of refractory bricks, and lined inside
with a layer of agglomerated carbon, or with the material to be treated, forming a
crucible.
The furnace may be of any shape.
In the walls are arranged shoots b.b, for-the introduction of the material to be
treated.
Working holes or tuyeres c, c, traverse the foundation of the furnace.
The hollow d for the reception of the materials treated is separated from the hearth
proper by a bridge e, the height of which varies with the materials under
treatment.
The bottom of the furnace carries a metal. plate f', capable of being put into
communication with the electrical apparatus by means of the terminal of the
conductor g.
The top part of the furnace is made to receive the electrodes of carbon f, which dip
into the cavity of the furnace at a certain incline, so that the flames coming from the 1
hearth shall pass between the electrodes without corroding or burning them, and
freely escape to the chimney i, which crowns the top of the furnace.
The electrodes are. mounted in the metal terminals j, to which are attached the
flexible cables k, leading the current also to the rack bars l, and their mechanical
operating apparatus.
This latter is composed of a pinion m keyed on the same shaft as the flywheel n.
The whole of the fly wheel , pinion m, and rack l, is movable in all directions round
the pillar p, which supports them, so as to give to the electrodes any inclination
necessary. Each of the racks is conveniently guided by rollers, on which it slides
and which rollers are mounted upon a piece 12 fixed to the support o, which carries.
the whole mechanism, adjustable on the column p. In place of a rack, a screw may
be used.
A supplementary regulating inechanism permits (by means of a screw q acting
upon the extremity of a lever q', pivotted at q2, and at its other extremity which is
forked, and to which is pivotted a ring q³, having cords, cables, or chains qt, attached
to it, supporting the counterweights, and passing over the pulleys or fly wheels n) of
withdrawing longitudinally, and simultaneously, all the electrodes f..
Movable dampers r, of refractory material, close the opening left between the upper
wall of the furnace and the base of the chimney i, for the passage of the electrodes f
and their manipulation.
These dampers close this space as hermetically as possible, and are supported by
the masonry of the furnace and the walls of the chimney i. As they are movable,
any number of electrodes may be introduced into the furnace during working.
Some of these dampers are perforated with sight holes for observing the operations
inside the furnace.. The furnace is closed by a movable chimney i, which shelters it
from the atmosphere, and allows of the recovery of the hot gases and dust, for the
purpose of putting them to various industrial uses. The mouth of the chimney is
movable, and cooled internally by a circulation of water. It rises on working a lever
with the aid of the counterweights 8, so as to allow of its being separated from the
foundation of the furnace, for repairs or cleaning.
The action of the furnace is as follows:-
Suppose a three-phase current is being used for, say, the production of carbide of
calcium. The three electrodes are arranged as symmetrically as possible in the
interior of the furnace, and the movable dampers closed. The materials to be treated
are introduced into the furnace, either by passages made between the electrodes, or
by the charging shoots b', b, and either in a pulverulent state, or natural, or in the
form of continuous cylindrical or prismatic bodies (obtained by preliminary
agglomeration), which are fed into the shoots b, b. The feeding may be effected by
pressure exerted artificially and externally upon the material to be treated, by the aid,
for example, of a hammer or rammer actuated by a to and fro movement, through a
lever worked by a cam conveniently controlled, so as to allow of the number of blows

page_text: being varied to suit the material, and the time it shall remain in contact with the arc
to be decomposed or melted.
The electrodes are first brought into contact. After the current is switched on
through the electrodes, the carbons are parted, and the arc struck.
The working of the furnace is observed through the dampers.
After a minute or so, the material is fed down out of the hearth.
The melting being established, the material suitably treated passes out over the
bridge to the hollow d, whence it may be removed as and when required. Each of
the carbons f may be advanced or withdrawn separately by the fly wheels n. Also, on
working the lever q¹, all the electrodes are set in motion simultaneously, and their
movements are simultaneous.
The renewal of the carbons, without stopping the fusion, is done in the following
manner. A supplementary electrode is added to the furnace. When this has been
conveniently placed, the current is transferred thereto from the worn out one, by the
action of a commutator. The worn-out carbon is then withdrawn, and so on
throughout the whole series of electrodes.
When a supplementary carbon cannot be introduced, the worn-out electrode is
withdrawn, with its rack, and replaced by another ready mounted.
In all ways the working is continuous. The manipulations are simple, do not
involve loss of time, and the furnace, being always subjected to the same temperature,
lasts longer.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed, I declare that
what I claim is :-
1. The herein before described method of utilizing polyphase currents of any number
of phases in electric furnaces, for treating, fusing, and decomposing materials by the
voltaic arc, said method consisting in supplying any number of phase currents to a
corresponding number of electrodes, and in striking the arcs, either directly between
each of the electrodes, through the material to be treated, or between each of the
electrodes and the mass to be treated, this latter being then connected to a point of
the polyphase systein.
2. The electric furnace above described, adapted for putting into practice the
method described in Claim 1 for the application of polyphase currents to processes of
fusion and decomposition of materials by the voltaic arc, and at the same time suitable
for using alternating monophase currents, and even continuous currents, the said -
furnace comprising masonry foundation a, shoots b, hollow (such as d) separated from
the hearth proper by a bridge (such as e), inclined electrodes dipping into the cavity
of the furnace at an angle, and capable of individual and simultaneous adjustment by
means of suitable controlling gear, dampers (such as r), and movable chimney (such
as ), all arranged and operating substantially as set forth.
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