Improvements in Electric Arc Furnaces.
Year: 1896

page_text: Date of Application, 1st Dec., 1896
Complete Specification Left, 1st Oct., 1897-Accepted, 27th Nov., 1897
PROVISIONAL SPECIFICATION.
Improvements in Electric Arc Furnaces.
We, THE ACETYLENE ILLUMINATING COMPANY LIMITED of 63 Queen Victoria
Street in the City of London, and PERCY CRUNDALL DAY of Foyers, County of
Inverness, N.B. Engineer, do hereby declare the nature of this invention to be
as follows:-
This invention relates to improvements in or connected with furnaces for
smelting materials in an electric arc maintained between the 2 electrodes, but is
more particularly adaptable to those furnaces which comprise a carbon electrode
suspended over a fixed crucible or hearth, such as are used for the production
of carbide of calcium and other substances.
In furnaces of this class, the arc is usually "struck" in the first instance by
lowering the suspended carbon electrode on to the hearth or crucible bottom,
the latter being in metallic or electric connection with the dynamo circuit. As
soon as the carbon electrode touches the hearth or crucible bottom the electrode
is raised, so that an arc is struck. The material to be smelted or treated is then
shovelled into the furnace or allowed to gravitate from suitable shoots, and the
calcium carbide or other smelted material gradually forms between the hearth
and the carbon electrode. The length of the arc is diminished by the formation
of smelted material and the carbon electrode must be continually withdrawn in
order to maintain, as nearly as possible, a constant current of electricity, and
consequent constant load on the dynamo and on the steam engine or turbine er
other motor employed to drive the dynamo.
In the manufacture of calcium carbide it is necessary in order that material
of pulverized coke and lime or limestone. In this instance in addition to the
comparatively gradual variation in resistance due to the gradual formation of
calcium carbide, the arc is subject to sudden fluctuations of its electric resistance
caused by portions of raw material falling suddenly into the arc.
In the manufaucture of calcium carbide it is necessary in order that material
of high quality may be produced that the proportion of carbon to calcium in the
pulverized raw material shall not differ materially from the theoretical pre-
portions acessary for the carrying out of the chemical reactions involved.
For this reason it is necessary that the raw material shall, after being fed into
the furnace be acted upon by the intense heat of the arc as quickly as possible.
If the pulverized material is allowed to remain near to, but not in the arc, minor
reactions occur which destroy the quantitative proportions and intimate mixture
of the ingredients so that the final smelting produces carbide of inferior quality.
In order that the material may be fed quickly under the arc, the carbon
electrode shoulod not, as a rule, be buried to a depth of more than about six inches
in the pulverized mixture. In practice the mixture is forced into and under the
arc by an attendant with a pole or suitable implement.
This forcing of material is another cause of sudden fluctuations in the resistance

page_text: Hitherto the raising or lowering of the carbon electrode for the purpose of
regulating the depth of the electrode has been usually effected by an attendant
in accordance with the indications of an ammeter placed in the circuit of the
furnace.
The attendant who raises or lowers the electrode cannot do so with sufficient
rapidity to prevent very large fluctuations in the load on the engine and dynamo,
resulting in undue wear and tear to both, and, if direct current is employed, in
considerable wear and tear to the brushes and commutator from sparking.
Again, such control and regulation by means of an attendant is costly, and not
always reliable owing to inattention of the attendant to the ammeter and other
causes.
Now this invention has for object to provide apparatus which will successfully
perform the following operations:-
(1) The automatic withdrawal of the carbon electrode as the smelted material
accumulates beneath it.
(2) The automatic raising or lowering of the .carben electrode with sufficient
rapidity to prevent any serious fluctuations in the speed of the engine and
dynamo.
(3) The production of a slight reciprocating movement of the carbon, sufficient
to cause the pulverized material to be fed continuously into the are with sufficient
rapidity to ensure the manufacture of calcium carbide of high quality thereby
dispensing with the services of the attendant hitherto required for that purpose.
An apparatus for the purposes of this invention consists in its most simple form
of a "relay" electro-magnet controlling the positions of a reversing switch
placed in the armature circuit of an electric motor which moves the carbons up
or down by means of worm or other suitable gearing.
Assuming, to give a concrete example that the working circuit is 1000 amperes
and it is desired to keep the load substantially constant: (1) between very narrow
limits say between 980 and 1020 amperes or (2) between broader limits say
between 800 and 1200 amperes.
In case (1) the relay spring would be adjusted so that for 980 amperes the
switch would be moved to cause the motor to lower the carbon electrode, whilst
for 1020 amperes it would be moved in the opposite direction to cause the motor
to raise the electrode, thus keeping the carbon practically at rest except during
fluctuations.
In case (2) the relay spring might be adjusted so that the switch will be
moved in one direction at or below 800 amperes, and in the other direction at
or above 1200 amperes thereby imparting a continually reciprocating motion to
the carbon electrode.
In either case the motor will be contibually moving, first in one direction and
then in the other, but in case (2) the movements will be of longer duration, thereby
imparting a longer reciprocating motion to the carbon electrode, and causing it
to force the pulverized material down into the arc.
A suitable practical arrangement of apparatus for carrying out this invention
is as follows:-
A soft iron armature is fixed to a light wooden beam pivoted between centres.
Beneath the armature is a soft iron magnet which is separated from the armature
by a considerable air gap and is adapted to be energized by the main current
passing through the cables or conductors forming part of the main circuit. The
armature is free to play between adjustable stops working on a brass tongue
fixed to the armature. By adjusting the stops both the angular movement of the
beam and the initial and final width of the gap can be varied to suit the working
conditions. The pull of the electro magnet on the farmature is opposed by an
adjustable spring. The armature will rest on the upper or lower stop, according
as the circuit is greater or less. The variations of current necessary to effect the
movement of the armature from one stop to the other or vice versa can be adjusted
by altering the air gap and varying the pull of the spring.

page_text: The mean working current can be adjusted by altering the initial tension on
the spring by any suitable means. At the other extremity of the beam is pivoted
a bush through which passes a rod having a slotted portion and attached at its
lower end to a very light spring which serves to keep the rod vertical whilst
allowing of the necessary play. The nod can be raised or lowered in the bush
by means of nuts or other devices in order that the slot in the rod may be adjusted
after each adjustment of the stops.
A suitable arrangement of reversing switch may comprise an ebonite barrel
pivoted between centres and carrying at each end a copper bow or fork and con-
tact pieces dipping into mercury cups. The four ends of the bows dip into four
large and deep mercury cups which are cross connected and also connected to
the motor armature. The first mentioned mercury cups are connected to the
mains.
The switch is preferably immersed in glycerine contained in a glass tank to drown
the sparking in the larger mercury cups. The switch is actuated by the afore-
said slot engaging a ball attached to a short screw fixed in the ebonite barrel.
The whole apparatus is enclosed in a wooden box. The arrangement of the slot,
ball and barrel allows of considerable range of movement of the contact pieces
for a very small movement of the armature without introducing any appreciable
friction.
In an electric arc furnace of the kind herein before mentioned, fitted with
this apparatus, the furnace hearth or bottom is connected to one lead or terminal
of the dynamo or main circuit and the movable suspended electrode is connected
by means of a flexible conductor or of a sliding or other suitable electric contact
connection with the other lead or terminal. The movable electrode is suspended
by means of a chain led over suitable guide pulleys to a drum upon which it is
wound and from which it is unwound according to the direction of rotation of
the drum. The drum is supported in suitable bearings and is adapted to be
rotated in either direction by means of suitable worm gear operated from the
armature shaft of an electric motor the direction of rotation of which is con-
trolled by the reversing switch of our improved controlling apparatus.
terminals of the motor armature winding are connected to two inner terminals
of the reversing switch. The motor field magnet winding in which a suitable
resistance is inserted forms a shunt between the main leads. The outer terminals
of the reversing switch are also suitably connected to the main leads.
The
The increasing or diminishing accumulation of the material under treatment
between the movable electrode and the furnace hearth will cause corresponding
fluctuations in the resistance in the main leads and consequently in the amount
of current passing through that portion of the circuit which serves to energize
the "relay" electromagnet of the controlling apparatus. The said electromagnet
will therefore be energized in a varying degree, with consequent oscillation of
the armature according as the attractive force of the magnet overcomes or is
overcome by the pull of the opposing spring. The oscillation of the armature
will cause the beam of the reversing switch, to rock in one or the other direction
whereby owing to the cross connection of the mercury cups of the switch, current
will be sent in one or the other direction to the armature of the electric motor,
with the result of causing rotation of the same in a corresponding direction. This
rotation is transmitted to the drum around which the chain passes by which the
movable electrode is suspended in such a manner as to wind up or pay out the
said chain, and thus raise or lower the said electrode accordingly. This action
is entirely automatic and acts as required and therefore renders special control
of the depth of the movable electrode unnecessary.
Sparking at the contacts of the reversing switch may also be avoided by inserting
an additional resistance in the circuit of the motor armature before breaking con-
tact. In such an arrangement one contact breaks first, inserting the resistance
and reducing the motor current and the other two contacts break simultaneously
inimediately afterwards.

page_text: For very large furnaces an arrangement may be employed in which the motor
reversing switch is pulled up or down by two powerful electromagnets which are
connected in series with each other across the mains. In such an arrangement
the rocking switch is provided with a simple bow, and three terminals and
mercury cups. The common terminal of the two electro magnets is connected
to the middle terminal of the rocking switch and the two outer terminals of the
electro-magnets to the two outer mercury cups of the rocking switch.
The function of the rocking switch is then to short circuit one or other of the
electro magnets, the sparking being reduced by suitable resistance.
The electro magnets operate suitable mechanism for effecting the reversal of a
switch with knife contacts, which would have too much friction to allow of its
being operated directly by the relay electromagnet herein before mentioned. The
switch is provided, in addition to the knife contacts with a set of carbon contacts
which meet before the knife contacts are closed, and remain together until after
the knife contacts aer separated. In this manner all sparking on breaking the
motor circuit is confined to take place between carbon rods instead of between the
prepared metal surfaces of the knife contacts, thus saving great wear and tear of
the switch.
Dated this 1st day of December 1896
J. C. MEWBURN & ELLIS,
55 and 56 Chancery Lane, London, Chartered Patent Agents.
We, THE ACETYLENE ILLUMINATING COMPANY LIMITED of 63 Queen Victoria
Street in the City of London, and PERCY CRUNDALL DAY of Foyers, County of
Inverness, N.B. Engineer do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
This invention relates to improvements in or connected with furnaces for
smelting materials in an electric are maintained between two electrodes, and is
more particularly adaptable to those furnaces which comprise a carbon electrode
suspended over a fixed crucible or hearth, such as are used for the production
of carbide of calcium and other substances.
In furnaces of this class, the arc is usually "struck" in the first instance by
lowering the suspended carbon electrode on to the hearth or crucible bottoni,
the latter being in metallic or electric connection with the dynamo circuit.
soon as the carhon electrode touches the hearth or crucible bottom the electrode
is raised, so that an arc is struck. The material to be smelted or treated is then
shovelled into the furnace or allowed to gravitate from suitable shoots, and the
calcium carbide or other smelted material gradually forms between the hearth
and the carbon electrode. The length of the arc is diminished by the formation
of smelted material and the carbon electrode must be continually withdrawn in
order to maintain, as nearly as possible, a constant current of electricity, and
consequent constant load on the dynamo and on the steam engine or turbine or
other motor employed to drive the dynamo.
In the manufacture of calcium carbide, the raw material consists of a mixture
of pulverized coke and lime or limestone. In this instance in addition to the
comparatively gradual variation in resistance due to the gradual formation of
calcium carbide the arc is subject to sudden fluctuations of its electric resistance
caused by portions of raw material falling suddenly into the arc.
In the manufacture of calcium carbide it is necessary in order that material

page_text: of high quality may be produced that the proportion of carbon to calcium in the
pulverized raw material shall not differ materially from the theoretical pro-
portions necessary for the carrying out of the chemical reactions involved.
For this reason it is necessary that the raw material shall, after being fed into
the furnace be acted upon by the intense heat of the arc as quickly as possible.
If the pulverized material is allowed to remain near to, but not in the arc, minor
reactions occur which destroy the quantitative proportions and intimate mixture
of the ingredients so that the final smelting produces carbide of inferior quality.
In order that the material may be fed quickly under the arc, the carbon
electrode should not, as a rule, be buried to a depth of more than about six inches
in the pulverized mixture. In practice the mixture is forced into and under the
arc by an attendant with a pole or suitable implement.
This forcing in of material is another cause of sudden fluctuations in the resistance
of the arc.
Hitherto the raising or lowering of the carbon electrode for the purpose of
regulating the depth of the electrode has been usually effected by an attendant
in accordance with the indications of an ammeter placed in the circuit of the
furnace.
The attendant who raises or lowers the electrode cannot do so with sufficient
rapidity to prevent very large fluctuations in the load on the engine and dynamo,
resulting in undue wear and tear to both, and, if direct current is employed, in
considerable wear and tear to the brushes and commutator from sparking.
Again, such control and regulation by means of an attendant is costly, and not
always reliable owing to inattention of the attendant to the ammeter and to other
causes.
Now this invention has for object to provide apparatus which will successfully
perform the following operations:-
(1) The automatic withdrawal of the carbon electrode as the smelted material
accumulates beneath it.
(2) The automatic raising or lowering of the carbon electrode with sufficient
rapidity to prevent any serious fluctuations in the speed of the engine and
dynamo.
(3) The production of a slight reciprocating movement of the carbon, sufficient
to cause the pulverized material to be fed continuously into the arc with sufficient
rapidity to ensure the manufacture of calcium carbide of high quality thereby
dispensing with the services of the attendant hitherto required for that purpose.
An apparatus for the purposes of this invention consists in its most simple form
of a "relay" electro-magnet controlling the positions of a motor-reversing switch
placed in the armature circuit of an electric motor which moves the carbons up
or down by means of worm or other suitable gearing.
Assuming, to give a concrete example, that the working current is 1000 amperes
and it is desired to keep the load substantially constant (1) between very narrow
limits say between 980 and 1020 amperes, or (2) between broader limits say.
between 800 and 1200 amperes :-
In case (1), the relay spring would be adjusted so that for 980 amperes the
switch would be moved to cause the motor to lower the carbon electrode, whilst
for 1020 amperes it would be moved in the opposite direction to cause the motor
to raise the electrode, thus keeping the carbon practically at rest except during
fluctuations.
:
In case (2), the relay spring might be adjusted so that the switch will be
moved in one direction at or below 800 amperes and in the other direction at
or alvove 1200 amperes thereby imparting a continually reciprocating motion to
the carbon electrode.
In either case the motor will be continually moving, first in one direction and
then in the other, but in case (2) the movements will be of longer duration, thereby
imparting a longer reciprocating motion to the carbon electrode, and causing it
to force the pulverized material down into the arc.

page_text: Suitable practical arrangements of apparatus for carrying out this invention
are shown in the accompanying illustrative drawings in which :-
Figures 1 and 2 are respectively a front and a side elevation of a combined
relay magnet and reversing switch for the purposes of this invention for use with
electric furnaces of small and medium size, and also in combination with the
arrangement shown in Figures 3 and 4 for use with furnaces of large sixe.
Figures 3 and 4 are respectively a front and a side elevation of lan arrangement
of intermediate magnets and reversing switch designed for use with electric fur
naces of very large size. In this case the relay magnet switch (Figures 1 and 2)
is used to effect the operation of the magnet reversing switch (Figures 3 and 4)
which in turn operates the motor.
Figure 5 is a diagram illustrating a modified arrangement of apparatus applied
to an electric arc furnace for the purposes of this invention.
Referring to Figures 1 and 2, a soft iron armature 1 is fixed to a light brass
framing 2 suspended by means of a spring 3 from the upper cross piece 4" of brass
frame standards 4, 4 fixed to a suitable base 5. Above the armature 1 is a soft
iron magnet 6, 6 which is separated from the armature 1 by a considerable air-
gap and is adapted to be energized by the main current passing through the cables
or conductors 7 which form part of the main circuit and are arranged so as to be
embraced by the limbs of the magnet 6, 6. The magnet 6, 6i is supported by
screwthreaded spindles 8, 8" carried by the frame standards 4, 4.
The armature 1 carries at its lower part on a screw 1" a depending platinum-
tipped contact 9 which is free to play between adjustable stationary platinum-
tipped spring contacts 10 and 11 carried on brass terminal screws 12 and 13
connected respectively to the ends 12, 13 of two oppositely wound field coils of
the motor and then on through the armature of the same in the case of small
furnaces, or connected to the two electro magnets 16, 17 Figure 3 (hereinafter
described) when used with large furnaces. The field coils just referred to are in
series with the armature so that the electric current which passes through the
reversing switch and one or other of the field coils passes through the armature.
A flexible conductor 15 is soldered or otherwise suitably connected to the
arntature contact 9 and is connected at its other end to a third terminal 9" on the
base 5. The pull of the electro magnet 6, 6 on the armature 1 is opposed by
the spring 3 the pull of which is capable of regulation by means of a milled
nut. The armature contact 9 will rest on the upper or lower contact (10 or 11),
according as the current passing through the cables 7 is greater vr less. The
variations of current necessary to effect the movement of the armature contact 9
frim one contact 10 to the other contact 11 or vice versa, can be adjusted by altering
the air gap and varying the pull of the spring 3. The armature 1 is guided
in its up and down movements by means of guide rollers 14 mounted in the frame
standards 4; 4.
The mean working current can be adjusted by altering the initial tension on
the spring 3.
In an electric are furnace of the kind hereinbefore mentioned, fitted with this
apparatus, the furnace hearth or bottom is connected to one lead or terminal of
the dynamo or main circuit and the movable suspended electrode is connected
by means of a flexible conductor or of a sliding or other suitable electric contact
connection with the other lead or terminal. The movable electrode is suspended
by means of a chain led over suitable guide pulleys to a drum upon which it is
wound and from which it is unwound according to the direction of rotation of
the drum. The drum is supported in bearings and is adapted to be rotated in
either direction, by means of suitable worm gear operated from the armature shaft
of an electric motor the direction of rotation of which is controlled by the
reversing switch of our improved controlling apparatus. The motor field magnet
winding in, which a suitable resistance is inserted forms a shunt hetween the
main leads. "
The increasing or diminishing accumulation of the material under treatment

page_text: between the movable electrode and the furnace hearth will cause corresponding
fluctuations in the resistance in the main leads and consequently in the amount
of current passing through the portion 7 of the circuit which serves to energise
the "relay" electro-magnet 6, 6 of the controlling apparatus. The said electro-
magnet 6, 6 will therefore be energised in a varying degree, with consequent
oscillation of the armature 1 according as the attractive force of the magnet 6, 6
overcomes or is overcome by the pull of the opposing spring 3. The oscillation
of the armature 1 will cause its contact 9 to make contact with one or the other
of the stationary contacts 10, 11, whereby current will he sent through one or
the other of the two field coils of the electric motor with the result of causing
rotation of the motor in a corresponding direction. This rotation is transmitted
to the drum around which the chain passes by which the movable electrode is
suspended in such a manner as to wind up or pay out the said chain, and thus.
raise or lower the said electrode accordingly. This action is entirely automatic
and acts as required and therefore renders special control of the depth of the
movable electrode unnecessary.
Sparking at the contacts 10, 11 of the reversing switch may be avoided by
inserting an additional resistance in the circuit of the motor armature before
breaking contact.
For very large furnaces we prefer to employ an arrangement in which the
motor reversing switch is operated by two powerful electro-magnets which are
connected in series with each other and are energized in the manner required to
effect the desired operation of the motor reversing switch by means of the relay
magnet switch hereinbefore described with reference to Figures 1 and 2.
A suitable arrangement of this kind is illustrated in Figures 3 and 4 in
which 16, 16 and 17, 17 are two electro-magnets mounted vertically and symme-
trically on a base 18 on either side of the central partition 18 of an enclosing
box 18. The magnet cores 16", 16 and 17, 17" are movable and are respectively
connected through the medium of links. 19, 19 multiplying levers 20, 20³, and
links 21, 21", to the outer ends of oppositely directed levers 22, 22 fixed at their
inner ends on a rocking axle 23 which is mounted in bearings 24, 24 on a
bracket 24 fixed on the top or cover 18 of the box 18. On the outer ends of
the axle 23 are fixed rocking beams 25, 26 adapted to make contact at their
ends 25 and 26 with knife spring contacts 27 and 28 respectively when
the beams 25 and 26 are tilted in one direction, whilst the other ends 25 and
26b are adapted to make contact with knife spring contacts 29 and 30 respectively
when the beams 25 and 26 are tilted in the other direction.
The beam 25 has further mounted on it near its ends springs 31, 31* carrying
in clips carbon contact pieces 32, 33 adapted to make contact with stationary
carbon contact pieces 34, 35 corresponding to and connected with the knife spring
contacts 27 and 29. The beam 26 is provided with a similar set of springs 36, 36
and carbon contact pieces 37, 38 adapted to make contact with stationary carbon
ontact pieces 39, 40 corresponding to ond connected with the knife spring
contacts 28 and 30.
The arrangement is such that when one beam, say 25 is pulled over by the
attraction of the electro magnet 17, 17 upon its cores 17", 17" contact will be
first established between the carbon contacts 33 and 35, and then by the con-
tinued descent of that end of the beam-25, contact will be established between the
metal contacts 25 and 29, the spring 31 yielding sufficiently for that purpose.
When the beam 25 is pulled over in the other direction by the pull of the
electro-magnet 16, 16 the contact existing between the metallic contacts 25 and 29
will first be broken, and then that still existing between the carbon contacts 33
and 35.
By this means sparking at the metallic contacts is prevented. The same suc-
cessional making and breaking of the contacts takes place at the other end of
the beam 25, and also at both ends of the beam 26. The electro-magnets 16. 16
and 17, 17 are energized as above stated by the passage of current controlled by

page_text: the relay magnet switch described with reference to Figures 1 and 2, the terminals
of the electro magnets 16, 16 and 17, 17 being for this purpose properly connected
to the stationary spring contacts 10 and 11 of the said relay magnet switch.
A modified arrangement of apparatus particularly applicable to furnaces using
an alternating current of electricity, but suitable als for those using a direct
current, comprises two independent relay electro-magnets, one of which comes
into action only when the electric current exceeds the desired maximum limit,
and the other when the current falls below the desired minimum limit. Each
relay electro-magnet is provided with a re-setting device by means of which it
is automatically returned to the normal position immediately after being pulled
into oneration by any irregularity in the electric current passing through the
furnace.
The relay electro-magnets bring more powerful electro-magnets into operation,
the latter in turn controlling the carbon hoisting gear.
By the means of a re-setting device the controlling movements are made by a
series of short impulses or steps with a pause between each thereby effecting the
improvement that the current in the furnace is enabled to settle down between
each successive step, and any tendency to raise or lower the carbons beyond the
correct amount is obviated.
To give an example:-Assuming it is desired to run a furnace with a mean
amperage of 5000,-The two relays would be set in their normal positions and
adjusted to operate, in the one instance if the current exceed (say) 5200 amperes,
and in the other if the current fall below (say) 4800 amperes. Then if through a
fluctuation in the resistance of the are the current rises to 5500 amperes, the
maximum limit being exceeded, the corresponding relay will be pulled over bringing
the controlling gear into operation for a short interval sufficient to raise the
carbon electrode a distance of (say) one sixteenth of an inch. In coming into
operation the relay will reset itself ready to take another step. If the carbon has
not been sufficiently raised in the first stop so that the current only falls from 5500
to 5300 amperes; the relay will at once take a second step, thereby further
reducing the current and so on until the current falls within the normal limits.
Analogous action takes place if the current falls below the normal limit, tho
controlling gear in this instance being operated by the relay set for 4800 amperes.
Instead of using a direct current motor and electro magnetic reversing switch
as a means of raising or lowering the carbon electrode, an arrangement may be
employed, in which the carbon electrode is suspended by means of chains or wire
ropes from a winding drum fixed to a shaft carrying at one extremity a toothed
worm wheel in engagement with a worm on another shaft.
In the diagram, Figure 5 which illustrates this, A is the drum and worm
wheel, B is the engaging worm. The worm B is mounted on a shaft. b having
at each end a coil clutch C and C2 which clutches are operated by the electro
magnets d', d through the connecting levers e, e
The electro magnet d is controlled by the relay D' and d by D. The function.
of these relays has already been described.
Normally the clutches C Care both disengaged and the gear stands at rest.
F, F, are two small electric motors with heavy fly wheels f f running con-
tinuously in opposite directions, or they may form part of two systems of shafting
revolving oppositely.
The action of the apparatus is as follows:-Normally the clutches C, C² are
held out of gear by the springs g¹, g, and the winding drum A is at rest. If the
current should exceed the maximum limit the relay D causes the electro magnet di
to become energised for a short interval, during which the clutch C holds the
worm B in engagement with the revolving motor F, thereby mising the movable
carbon electrode H and in part restoring the current to its normal amount.
The operation is repeated until the current is again within the normal limits.
If the current falls below the normal limit the relay D energises the electro-
magnet, thereby engaging the shaft b with the oppositely revolving motor F

page_text: and consequently lowering the carbon electrode H. I is the stationary furnace
electrode. K is the dynamo.
When using alternating currents, a separate transformer is used for each
furnace, of such a type that the voltage on the furnace varies inversely as the
current. Advantage may be taken of this to cause the relay electro magnets
to be operated by variations in the voltage on the furnace, thereby enabling the
magnets. to be wound with fine wire coils and placed in a convenient position at
a distance from the heavy main conductors of the furnace. Such an arrangement
is illustrated in Figure 5.
Having now. particularly described and ascertained the nature of our said in-
vention and in what manner the same is to be performed, we declare that what
we claim is:
1. For automatically regulating the arc in arc electric smelting furnaces, a
relay electro magnet and a motor-reversing switch the positions of which are
controlled by the said relay electro magnet, the switch being in the armature
circuit of an electric motor adapted to move the movable furnace electrode towards
and away from the fixed furnace electrode, substantially as hereinbefore described.
2. In an electric arc furnace, means whereby a reciprocating movement is im-
parted to the movable furnace electrode sufficient to cause the pulverized material to
be fed continuously and with sufficient rapidity into the arc, substantially as and
for the purpose herein before described.
3. For carrying out the automatic regulation as specified in Claim 1 or for im-
parting the reciprocating movement as specified in Claim 2, the combined relay
electro magnet and motor-reversing switch, constructed, arranged and operating
substantially as hereinbefore described and shown in Figures 1 and 2 of the
accompanying drawings.
4. For carrying out the automatic regulation as specified in Claim 1 or for
imparting the reciprocating movement as specified in Claim 2, the combined
magnets and motor-reversing switch constructed, arranged and operating substan-
tially as hereinbefore described with reference to Figures 3 and 4 of the accom-
panying drawings.
5. In apparatus of the kind specified in the last preceding Claim, the arrange-
ment of carbon contacts for obviating sparking between the metallic switch
contacts, substantially as hereinbefore described with reference to Figure 3 of the
accompanying drawings.
6. For carrying out the automatic regulation as specified in Claim 1, the
arrangement of apparatus constructed and operating substantially as hereinbefore
described with reference to Figure 5 of the accompanying drawings.
1907
J. C. MEWBURN & ELLIS,
55 and 56 Chancery Lane, London, Chartered Patent Agents.