An Improved Method of and Apparatus for the Production of Calcium Carbide, applicable also to other purposes.
Year: 1897

page_text: Date of Application, 17th Aug., 1897
Complete Specification Left, 15th June, 1898-Accepted; 16th July, 1898
An Improved Method of and Apparatus for the Production of Calcium
Carbide, applicable also to other purposes.
We, HUDSON MAXIM, of Thurlow Lodge, 377, Norwood Road, London, S.E.,
Chemist and Mechanical Engineer, and WILLIAM HENRY GRAHAM, of Sunny-
hurst, Trowbridge, Wiltshire, Chemist and Mechanical Engineer, do hereby
declare the nature of this invention to be as follows:-
Our invention relates generally to electro-thermally treating materials including
especially the manufacture of calcium carbide and other metallic carbides; more
particularly it relates to a method and apparatus for producing calcium carbide in
an electric furnace.
The object of our invention is to provide for the continuous operation of the
furnace, a marked simplicity in its construction, a great reduction in the necessary
electrical apparatus, economy in the energy required for maintaining the operation
of the furnace, and it has other useful and novel advantages.
In carrying out the invention a furnace is provided having an electrode com-
mon to a number of separated electrodes opposed to the said common electrode,
that is to say, an electric furnace in which a number of electric currents enter the
furnace through a number of separated electrodes and thence to one common
electrode.
Heat is produced by means of either an electric arc or a core of any suitable
material placed between each of the separate electrodes and the common electrode
and raised to a great heat or incandescence by its resistance to the electric current
which is passed through it. We prefer to produce the heat by the latter method
of incandescence and may employ a core consisting of a small carbon rod for the
purpose.
The invention also consists in electrically connecting the electrodes so that the
current enters the furnace through one or more of the separate electrodes to the
common electrode and back through the remaining separate electrodes. This
arrangement possesses a number of advantages, namely, it requires half the
quantity of leads used in any other system; it dispenses with all outside connec-
tion with the common electrode and allows the same to be made much smaller,
and admits of the current passing through each electrode being ineasured separately
and independently of the others. It also allows the current through any electrode
to be broken without causing any appreciable alteration in the current passing
through the others. It further permits the use of a higher and more economical
voltage than could be employed if the current were passed only once through the
furnace, for, it is understood, in the above arrangement, that the current not only
passes once through an incandescent conductor, which serves as a resistance, but
also returns by additional resistances or conductors which obviously require
additional electro-motive-force.
Specifically, there are two principal arrangements which produce this result,
first, one lead from a direct but preferably an alternating current is divided so

page_text: as to connect respectively with half the number of separate electrodes, while
the other lead is divided in a like manner and is connected with the other half
of the said electrodes; and secondly, each of the separate electrodes are connected
with one lead of a polyphase current of a number of phases equal to the number
of separate electrodes of the furnace. We prefer the latter arrangement, as it
requires much simpler electric connections and secures the current through each
separate electrode from any fluctuation which may be due to alteration or stoppage
of the current through any of the other electrodes.
Our invention also consists in means for maintaining contact of the electrodes
with the incandescent conductor which may be placed or formed between them,
and in means for facilitating the removal of the product from the furnace and for
supplying incandescent conductors and the material to be treated therein.
The furnace may be made of firebrick in the form of a long open box having the
common electrode formed of a large upright carbon slab or plate fixed along one
side, and the separated electrodes consisting of six equi-distant circular carbon rods
extending into the furnace horizontally in the same plane through the opposite
side. The outer end of each electrode is electrically connected respectively by a
clamp, a cable, a switch and an ammeter on a switchboard, to a lead or cable of
an electric generator. Between each separate electrode which are unattached
in the wall of the furnace, and the common electrode, is placed a small carbon rod,
kept in firm contact with these electrodes by means of a spring, under pressure
applied to the outer end of each separate electrode. The spring bears against the
switchboard and is supported on an iron rod which is rigidly attached to the outer
end of the electrode. The electrode is additionally supported by the iron rod
which projects through the switchboard and bears on a key therein. The rod is
threaded for a portion of its length to receive, on the front side of the switch-
board a handle, which, when rotated, is used to slightly withdraw the electrode
from the furnace, and is normally at a suitable distance from the switchboard to
allow the electrode to move slightly forward into the furnace to maintain the con-
tact with the incandescent conductor therein. The furnace is preferably covered
with a hood, which is in communication with a stack to receive the gases given off
while the furnace is operating. A hopper holding the material to be treated and
normally closed by a door is preferably placed at one side of the hood above each
electrode so that the furnace may be charged or supplied with fresh material
with facility.
Should it be desired to connect a lead directly to the common electrode, it may be
extended out of the furnace and electric connection made therewith by any suitable
device. It is obvious, however, that a lower voltage is needed if the current is
sent only once through the furnace, and therefore a greater number of amperes
are necessary to produce an equal amount of heat, consequently a greater quantity
of metal in the leads or cables is required to carry the increased amount of current.
The voltage, however, in both cases is dependent on the distance between the
separated and the common electrodes. It is also obvious that, without departing
from the spirit of our invention, currents from a number of separate generators
may be passed though the same furnace.
The furnace may be operated as follows: the small carbon rod being in position,
the material which may consist of a fine pulverulent mixture of sixty-five parts
of coke and one hundred parts of lime, is placed in the furnace around the rod,
preferably completely covering the electrodes, the electric circuits are then com-
pleted by the switches, whereupon each rod becomes heated to intense incan-
descence, which fuses the surrounding material between the electrodes, and converts
it into calcium carbide. The carbide thus formed conducts the electric current
and gradually increases in quantity, causing a corresponding increase of the
resistance between the electrodes, and therefore a similar increase in the electric
current until a maximum amount of carbide has been formed, which is denoted
by the current ceasing to increase, and is indicated by the ammeter. The current
is then stopped by the switch, the electrodes withdrawn slightly by the handle,

page_text: disengaging the formed calcium carbide, which is then removed by a pair of
tongs or other suitable means, from the surrounding material and from the furnace
in the form of an ingot, the small carbon rod having been converted into carbide.
The operation is continued by again placing a small rod between the electrodes
supplying more material and proceeding as before. The gases disengaged during
the process usually burn on emitting from the material and the products, then
pass up the stack.
The current is passed through a series of electrodes, successively
forming a series of operations and allowing a lapse of time between the commence-
ment of each, so that after the last of one series is finished, the first of the next
series may be attended to, and so on in rotation.
The common electrode is connected in the above described manner by rods to the
separate electrodes respectively, each of which are in turn connected through the
switches, ammeter and cable to a generator, capable of giving in this case a
six-phase current.
common
By a modification the springs upon the electrodes are dispensed with, the
position of the electrodes being positively determined by a fixed handle, and the
contact between the electrodes and the rod efficiently secured by a mass of
pulverulent carbon or carbon dust in a trough, back of the
electrode, and a quantity of the same material within, the electrode. The
rod may be placed in position through an opening in the side of the furnace,
through the carbon dust and trough and an opening in the electrode to the interior
of the separate electrode also containing carbon dust. When an ingot of carbide
has been formed and removed, the rod is replaced as before, the ends left in the
electrode being forced out through the iron cylinder, which is made hollow for this
purpose. The ends left in the trough may be continuous with the fresh rod and
forced through the material in the furnace to the opposite electrode. If not con-
tinuous they may be forced merely into the material in the furnace and converted
into calcium carbide.
By a modification, the common electrode may lie horizontally at the bottom of
the furnace and the separate electrodes be vertically suspended above it. Electric
arcs may be struck between the electrodes, the material being placed in the ares
and calcium carbide be formed thereby, by independent electric currents.
In carrying out a modification of our said invention for the manufacture of
calcium carbide, we may proceed as follows:-A suitable mixture of calcium oxide
and carbon, and, preferably, compressed into a hard block or cylinder, is prepared.
The said block, or cylinder, is then included in an electric circuit, and an electric
current is passed through it. As the material, before being converted into carbide,
offers high resistance to electric currents, we preferably employ a high voltage
current for first obtaining contact through the material or the passage of the
electric current, and for converting the material into carbide in the direct path of
the current, thus establishing a conductor of carbide through the material. We
then, preferably, lower the voltage and pass a larger current through the material
by the carbide conductor thus established. The carbide conductor becoming very
highly heated, quickly converts the adjacent portions of the material surrounding
it, into carbide, which, in turn, becomes an electric conductor. When the carbide
conductor becomes so large as to offer too little resistance to the electric current, the
voltage may again be lowered, and the amperage increased as desired. When a
sufficiently large body has been converted into carbide, the same is removed, and
replaced by a fresh mixture, and the process is then repeated.
We have found that a great advantage is secured by compressing the material
previous to subjecting it to the electric current, because contact is thereby more
easily established through the same, and, furthermore, as the material, in being
formed into carbide in a fused mass, is increased in density, it is advantageous to
employ the material in as dense a state as possible at the start. However, when
not employing material that has been previously compressed, pressure may be
applied simultaneously with the passage of the electric current through the

page_text: material, thereby maintaining close contact between the converted and the un-
converted material.
We have also found electric contact through the material to be more readily
established when the material is preliminarily heated before being subjected to
the electric current.
The attainment of electric contact through the material may be facilitated,
especially with a current of low voltage, by forming a mass or block or cylinder
of the material, mixed in suitable proportions for making calcium carbide, but
with a core containing a sufficient excess of carbon to allow passage of an electric
current through it, which core may be made of small broken pieces of carbon.
These may be previously rolled into a cylinder, and be held in position by a paper
tube or roll of paper, or other suitable material surrounding them; or, a continuous
conductor, such as a carbon or metallic rod or tube may be employed for establishing
an electric current through the body of the material. The preferable form of core,
however, is one consisting of broken pieces of carbon, or a mixture of carbon and
calcium oxide, but having an excess of carbon, as above described, on account of
a large number of small arcs being formed between the particles or pieces of the
core, when an electric current is passed through the core, thereby producing a very
high heating effect.
The carbon and the calcium oxide may be prepared in sufficiently large pieces,
in mass form, to permit the pieces of carbon, or a portion of them, to come in con-
tact with one another, and thus facilitate the establishment of an electric current
through the mass. The preferable mode, however, is to employ calcium oxide, or
lime, in lumps, or in small broken pieces, and the carbon in a fine state of division.
The carbon being in a fine state of division, is made to fill the interstices or spaces
intermediate of, or between the pieces of calcium oxide. The mass is then pre-
ferably pressed together. An electric current may then be easily established
through the mass by reason of the continuity or continuous distribution of the
carbon throughout the mass.
In carrying out the invention for the reduction of other metals from their
oxides or other compounds, we may proceed in a similar manner to that above
described for the manufacture of calcium carbide.
1000
HUDSON MAXIM.
WILLIAM HENRY GRAHAM.
An Improved Method of and Apparatus for the Production of Calcium
Carbide, applicable also to other purposes.
We, HUDSON MAXIM, Chemist and Mechanical Engineer, formerly of 377,
Norwood Road, London, S.E., at present residing at 47, Effra Road, Brixton, Lon-
don, S.W., and WILLIAM HENRY GRAHAM, Chemist, formerly of Trowbridge,
Wiltshire, at present residing at 30, Romola Road, Herne Hill, S.E., do hereby
declare the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
Our invention relates generally to electro-thermally treating materials including
especially the manufacture of calcium carbide and other metallic carbides; more
particularly it relates to a method and apparatus for producing calcium carbide in
an electric furnace.
The object of our invention is to provide for the continuous operation of the

page_text: furnace, a marked simplicity in its construction, a great reduction in the necessary
electrical apparatus, economy in the energy required for maintaining the operation
of the furnace, and it has other useful and novel advantages.
In carrying out the invention a furnace is provided having an electrode com-
mon to a number of separated electrodes opposed to the said common electrode,
that is to say, an electric furnace in which a number of electric currents enter the
furnace through a number of separated electrodes and thence to one common
electrode.
Heat is produced by means of a core consisting of a small carbon rod
placed between each of the separate electrodes and the common electrode
and raised to a great heat or incandescence by its resistance to the electric current
which is passed through it.
The invention also consists in electrically connecting the electrodes so that the
current enters the furnace through one or more of the separate electrodes to the
common electrode and back through the remaining separate electrodes. This
arrangement possesses a number of advantages, namely, it requires half the
quantity of leads used in any other system; it dispenses with return current wires
from the common electrode and allows the same to be made much smaller
and admits of the current passing through each electrode being measured separately
and independently of the others. It also allows the current through any electrode
to be broken without causing any appreciable alteration in the current passing
through the others. It further permits the use of a higher and more economical
voltage than could be employed if the current were passed only once through the
furnace, for it is understood, in the above arrangement, that the current not only
passes once through an incandescent conductor, which serves as a resistance, but
also returns by additional resistances or conductors which obviously require
additional electro-motive force.
Specifically there are two principal arrangements which produce this result,
first, one wire from a direct but preferably an alternating current is divided so
as to connect respectively with half the number of separate electrodes, while
the other lead is divided in a like manner and is connected with the other half
of the said electrodes; and secondly, each of the separate electrodes are connected
with one branch of a polyphase circuit of a number of phases equal to the number
of separate electrodes of the furnace. We prefer the latter arrangement, as it
requires much simpler electric connections and secures the current through each
separate electrode from any fluctuation which may be due to alteration or stoppage
of the current through any of the other electrodes.
Our invention also consists in means for maintaining contact of the electrodes
with the incandescent conductor which may be placed or formed between them,
and in means for facilitating the removal of the product from the furnace and for
supplying incandescent conductors and the material to be treated therein.
In the accompanying drawings, Fig. 1 is a plan view of the furnace. Fig. 2 is
a cross-sectional view at one of the electrodes. Fig. 3 is a front view of part of
the switchboard. Fig. 4 is a diagram of the electrical connections of the furnace,
and Fig. 5 is a cross-sectional view of a modified form of the furnace.
The furnace is made of firebrick in the form of a long open box 1, having the
common electrode 2 formed of a large upright carbon slab or plate fixed along one
side, and the separated electrodes consisting of six equi-distant circular carbon
rods, extending into the furnace horizontally in the same plane through the
opposite side. The outer end of each electrode is electrically connected respec-
tively by a clamp 4, a cable 5, a switch 6, and an ammeter 7 on a switchboard 8,
to a lead or cable 9, of an electric polyphase current generator 19, see Fig. 4.
Between each separate electrode which are unattached in the wall of the furnace,
and the common electrode, is placed a small carbon rod 10, kept in firm contact
with these electrodes by means of a spring 11, under pressure applied to the
outer end of each separate electrode. The spring bears against the switchboard
and is supported on an iron rod 12, which is rigidly attached to the outer end of the

page_text: electrode. The electrode is additionally supported by the iron rod which projects
through the switchboard and a bearing 13 therein. The rod is threaded for a
portion of its length to receive, on the front side of the switchboard a handle 14,
which, when rotated, is used to slightly withdraw the electrode from the furnace,
and is normally at a suitable distance from the switchboard to allow the electrode
to move slightly forward into the furnace to maintain the contact with the
incandescent conductor therein. The furnace is preferably covered with a hood 15,
which is in communication with a stack 16, to receive the gases given off while
the furnace is operating. A hopper 17 holding the material to be treated and
normally closed by a door 18 is preferably placed at one side of the hood above
each electrode, so that the furnace may be charged or supplied with fresh material
with facility.
A wire 20 to equalize irregularities in the polyphase currents may be connected
to the common electrode and the generator or dynamo 19.
It is obvious that a lower voltage is needed if the current is sent only once
through the furnace, and therefore a greater number of amperes are necessary to
produce an equal amount of heat, consequently a greater quantity of metal in the
wires or cables is required to carry the increased amount of current. The voltage,
however, in both cases is dependent on the distance between the separated and
the common electrodes. It is also obvious that, without departing from the spirit
of our invention, currents from a number of separate generators may be passed
through the same furnace.
The common electrode is connected in the above described manner by rods to the
separate electrodes respectively, each of which are in turn connected through the
switches 6, ammeters 7, cables 5, to the generator 19, capable of giving in this
case a six-phase current.
The furnace may be operated as follows: the small carbon rod being in position,
the material, which may consist of a fine pulverulent mixture of sixty-five parts
of coke and one hundred parts of lime is placed in the furnace around the rod,
preferably completely covering the electrodes, the electric circuits are then com-
pleted by the, switches, whereupon each rod becomes heated to intenve
incandescence, which fuses the surrounding material between the electrodes and
converts it into calcium carbide. The carbide thus formed conducts the electric
current and gradually increases in quantity, causing a corresponding decrease of
the resistance between the electrodes and therefore a similar increase in the electric
curent until a maximum amount of carbide has been formed, which is denoted by
the current ceasing to increase and is indicated by the ammeter. The current
is then stopped by the switch, the electrodes withdrawn slightly by the handle,
disengaging the formed calcium carbide Y, which after cooling is then removed
by a pair of tongs or other suitable means from the surrounding material, and
from the furnace in the form of an ingot, the small carbon rod having been
converted into carbide. The operation is continued by again placing a small rod
between the electrodes, supplying more material, and proceeding as before. The
gases disengaged during the process usually burn on emitting from the material
and the products then pass up the stack. The current is passed through the
series of electrodes, successively forming a series of operations and allowing a lapse
of time between the commencement of each, so that after the last of one series
is finished, the first of the next series may be attended to, and so on in rotation.
In carrying out the invention for the reduction of other metals from their oxides
or other compounds, we may proceed in a similar manner to that above described
for the manufacture of calcium carbide.
The common electrode 2 may consist of a mass of carbide, which may or may
not have been previously formed in the furnace. It is to be understood that
by a common electrode we mean any electrode which may be in one piece, or two
or more pieces, all of which are electrically connected, such as the arrangement
shown in Fig. 5. It is obvious that the common electrode may be called a common
terminal.

page_text: In Fig. 5, the furnace box is divided into a number of separated compartments 21,
each of which contains a pair of opposed electrodes 3 and 22, both being adjustable
as in Figs. 1 and 2. The electrodes along one side are connected together by a
cable 23, and serve as the common electrode. In this case clamps are not employed
as the cables 5 are connected to the rod 12, so that the electrodes may be rotated
or rocked by the handle 24 on the end of the rod. This prevents the ends of the
electrodes in the furnace from wearing away only at the bottom.
By a modification of the process of making carbide in operating a furnace
such as shown in Figs. 1 and 2, the separated electrodes may be placed at a
suitable distance apart and an electric current passed through them simultaneously,
with the result that the separate ingots of carbide melt and run together, thus
making one large ingot extending the whole length of the furnace.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is:-
1. The herein described process for making a carbide, which consists in forming
carbide in an electric furnace on a plurality of incandescence conductors, and
removing the formed carbide at each conductor separately, and at different times,
whereby the electric furnace continually absorbs a nearly uniform quantity of
electric energy.
2. In the manufacture of calcium carbide, the method of converting carbide-
forming materials into carbide by an incandescent carbide conductor in electrical
contact with terminals of a polyphase current and passing a polyphase current
through the said conductor.
3. An incandescent electric furnace having an incandescence heating conductor
of carbide connected with one branch of a polyphase circuit.
4. An incandescence electric furnace having a plurality of incandescence heating
conductors, each of which are connected with one branch of a polyphase circuit,
substantially as described.
5. An electric furnace, having a number of electrodes, each of which are con-
nected with one branch of a polyphase circuit at one end, and with an incandescent
heating conductor at the other end, the latter being in turn in contact with a
common terminal of the polyphase currents, substantially as described.
6. An electric furnace having two or more separated electrodes, an electrode
or electric terminal common to the separated electrode, and incandescent heating
conductors of carbide in electrical contact between the separated electrodes and
the common electrode or terminal, substantially as described.
7. The electric furnace, substantially as described, with reference to Figs. 1,
2 & 3.
8. The electric furnace, substantially as described, with reference to Fig. 5.
Dalad this 18th day of May 1808
HUDSON MAXIM.
WILLIAM HENRY GRAHAM.