An Improved Method of Heating Ores and other Substances by an Electric Current for Effecting Metallurgical, Chemical, and other Operations, and Furnaces or Apparatus therefor.
Year: 1887

page_text: Date of Application, 24th June, 1887
Complete Left, 26th Mar., 1888
Complete Accepted, 25th May, 1888
An Improved Method of Heating Ores and other Substances by an
Electric Current for Effecting Metallurgical, Chemical, and other
Operations, and Furnaces or Apparatus therefor.
1, WILLIAM CROSS, of 15 Sharsted Street, Kennington Park, in the County of
Surrey, Engineer, do hereby declare the nature of this invention to be as follows:-
My invention relates to an improved method of heating ores and other substances
by an electric current whereby the heating effect of electrical, energy may be con-
centrated and utilized for effecting various metallurgical, chemical, melting, and other
operations requiring an intense degree of heat; and to furnaces or apparatus in
which such operations may be carried on in a continuous manner.
According to this invention the heating of ores and other substances is effected
by generating within the mass of such ores or other substances one or more centres
or places of intense heat by the use of a refractory conductor or conductors situate
within or traversing the said mass, and heated or rendered incandescent by the
passage of an electric current therethrough. Such internal heating may in some cases
be aided by exterior heat produced by causing the furnace chamber or vessel, or parts
thereof, to be rendered incandescent at will, either by the passage of an electric
current therethrough, or by the combustion of gaseous or other fuel.
The refractory conductor or conductors is or are formed of suitable resistance
material and it or they may each be of various forms as for example a rigid rod, bar
or mass. Such a conductor or conductors is or are hereinafter called a resistance rod
or rods.
An electric heating or smelting furnace or apparatus for carrying my improved
method of heating ores and other substances into practice comprises a chamber or
vessel, hereinafter called a heating chamber, of refractory material within which is or
are arranged the resistance rod or rods. The heating chamber may be of cylindrical,
conoidal rectangular or other suitable form and be arranged to rotate or not as
desired; it is provided with suitable charging and outlet openings, and in some cases
may be suitably insulated. The resistance rod or rods may be fixed in a vertical,
horizontal or in an inclined position in the heating chamber; or it or they may in

page_text: some cases be so mounted and arranged as to be capable of receiving rotary move-
ment at will, relatively to the heating chamber, in order that the ores or other
substances treated may be well mixed and uniformly heated. The inner wall or the
floor, or both, of the beating chamber may, when it is desired to aid the internal
heating by exterior heat, be wholly or partially formed of refractory conducting
material that may be rendered incandescent at will by the passage of an electric
current therethrough; or the refractory conducting material may be imbedded in the
walls or floor, or both, of the chamber; or the chamber may be heated externally by
gaseous or other fuel as herein before mentioned.
In one arrangement of heating furnace the resistance rod or rods is or are arranged
vertically within a heating chamber that is partly of cylindrical and partly of conoidal
form. In a modification the resistance rod or rods is or are arranged horizontally in
a similarly arranged cylindrical or rectangular heating chamber. When several rods
are used they may be placed in one or more rows.
To enable certain substances, as for example some of the single or double salts of
aluminium, to be electrolysed whilst they are heated in the manner hereinbefore
described, the furnace or apparatus may be provided with means for causing an
electric current to traverse the substance under treatment. This electrolysing
current may be a shunt current from the heating current circuit, in which case
one or more of the resistance rods hereinbefore mentioned may also serve as an
electrode, say the positive, the heating chamber, or a part thereof or a rod or plate
therein serving as the negative electrode; or a separate current may be used in which
case a separate positive electrode must be employed.
In an arrangement of furnace or apparatus for this purpose, the resistance rod or
rods for carrying the heating current, and the positive electrode are arranged
approximately horizontal, the negative electrode, of curved form in transverse section
and slightly inclined longitudinally, being arranged below them.
The heating
chamber is provided as before with suitable charging and outlet openings to admit
of operations being carried on continuously.
For the purpose of admitting gas or vapour to the interior of the heating
chamber for effecting certain chemical operations, the said chamber may be provided
with an inlet opening or openings or with other suitable means in communication
with a generator of the gas or vapour employed.
Each resistance rod, which when in use is placed in the electric circuit, is formed
of suitable resistance material such for example as carbon, or a mixture thereof with
other material. The part of such rod to be rendered incandescent by the passage
of an electric current therethrough may have its resistance increased to the necessary
extent by reducing its cross sectional area; it may be by means of a core, or by
forming the rod hollow at this part. The heating surface of the rod may be increased
in any convenient manner as for instance by curving or corrugating it, and in some
cases may be coated with refractory non-conducting material.
Suitable resistances and electrical measuring and indicating apparatus such as am-,
volt-, and ohm-meters may be provided in the electrical circuit or circuits for controlling
the action of the heating furnace or apparatus. Also a transformer for producing
electric currents of large quantity may be employed when necessary.
Dated this 24th day of June A.D. 1887.

page_text: An Improved Method of Heating Ores and other Substances by an
Electric Current for Effecting Metallurgical, Chemical, and other
Operations, and Furnaces or Apparatus therefor.
I, WILLIAM CROSS, of 15 Sharsted Street, Kennington Park, in the County of
Surrey, Engineer do hereby declare the nature of this invention, and in what manner
the same is to be performed, to be particularly described and ascertained in and by
the following statement :-
My invention relates to an improved method of heating ores and other substances
by an electric current, whereby the heating effect of electrical energy may be concen-
trated and utilised for effecting various metallurgical, chemical, melting, and other
operations requiring an intense degree of heat; and also to furnaces or apparatus in
which such operations may be carried on a continuous manner.
According to this invention, the heating of ores and other substances, is effected by
generating within the mass of such ores or other substances, ono or more centres or
zones of intense heat by the use of a refractory conductor or conductors situate within
or traversing the said mass, and heated or rendered incandescent by the passage there-
through of an electric current, such internal heating being aided by exterior heat
produced by causing the furnace chamber or vessel or parts thereof, to be rendered
incandescent either by the passage of an electric current therethrough or by the
combustion of gaseous or other fuel.
The refractory conductor or conductors is or are formed of suitable resistance
material and it or they may each be of various forms such as a rigid bar plate or mass.
Such a conductor or conductors is or are hereinafter called a resistance rod or rods.
An electric heating or smelting furnace or apparatus for carrying my improved
method of heating ores and other substances into practise, comprises a chamber or
vessel, hereinafter called a heating chamber, of refractory material, within which, is or
are arranged, the resistance rod or rods. The heating chamber may be of cylindrical,
conoidal, rectangular or other suitable form, and be arranged to rotate or not, as
desired; it is provided with suitable charging and outlet openings for the substances
treated and may be insulated both electrically and thermally in any suitable manner.
The resistance rod or rods may be fixed in a vertical, horizontal or in an inclined
position in the heating chamber, and it or they may, in some cases, be so mounted and
arranged as to be capable of receiving rotary movement at will, relatively to the
heating chamber, in order that the ores or other substances treated, may be well mixed
and uniformly heated. The inner wall or the floor, or both, of the heating chamber,
may, when it is desired to aid the internal heating by exterior heat, be wholly or
partially formed of refractory conducting material that may be rendered incandescent
at will, by the passage of an electric current therethrough, or the refractory conducting
material may be imbedded in the walls or floor, or both, of the chamber; or the
chamber may be heated by gaseous or other fuel, as herein before mentioned.
To enable certain substances, as for example, some of the single or double salts of
aluminium, to be electrolysed whilst they are heated in the manner hereinbefore
described, the furnace or apparatus may be provided with means for causing an electric
current to traverse the substance under treatment. This electrolysing current may be
a shunt current from the heating current circuit, in which case one or more of the
resistance rods hereinbefore mentioned, may also serve as an electrode, say the positive,

page_text: the neating chamber, or a part thereof, or a rod or plate therein serving as the negative
electrode or a separate current may be used in which case a separate positive electrode
must be employed.
For the purpose of admitting gas or vapour to the interior of the heating chamber
for effecting certain chemical operations, the said chamber may be provided with an inlet
opening or openings, or with other suitable means, in communication with a generator
of the gas or vapour employed. Electric furnaces or heating apparatus according to
this invention may be constructed in various forms.
Each resistance rod, which when in use is placed in an electric circuit, is formed of
suitable resistance material such for example as carbon or a mixture thereof with other
suitable resistance material. The part of such rod to be rendered incandescent by the
passage of an electric current therethrough, may have its resistance increased to the
necessary extent, in any convenient manner, as for instance, by reducing its cross
sectional area, it may be by forming it with a core of non conducting material, or by
forming the rod hollow at the required part. The heating surface of the rod may be
increased in any convenient manner, as for instance by curving or corrugating it. In
some cases the rod may be coated with refractory non conducting material to protect it
from any action of the substance treated.
Suitable resistances, switches, and electrical measuring and indicating apparatus,
such as am-, volt-, and ohm-meters may be provided in the electrical circuit, or
circuits, for controlling the action of the heating furnace or apparatus. Also a
transformer designed to produce electric currents of large quantity may be employed
when necessary.
In the accompanying three sheets of illustrative drawings,
Fig. 1 is a vertical section of an electric furnace or heating apparatus according to
this invention ;
Fig. 2 is a horizontal section, and
Figs. 3, 4, 5, 6, 7, 8 and 9 are vertical sections, illustrating various modifications,
hereinafter described, in the construction of such furnaces or apparatus.
Figs. 10 and 11 illustrate respectively in vertical section, and in horizontal section,
a further modification in which the resistance rods are arranged to be rotated relatively
to the heating chamber.
Figs. 12 and 13 illustrate respectively in longitudinal vertical section and in
transverse section on the line A. B. fig. 12 a rotary electric furnace or heating
apparatus.
Fig. 14 illustrates partly in longitudinal section and partly diagrammatically, an
arrangement of apparatus adapted to simultaneously melt and electrolyse certain
substances, for example cryolite. Fig. 15 is a transverse section thereof. Fig. 16
illustrates a modified arrangement. Fig. 17 illustrates in cross section, resistance rods
of various forms, having a corrugated, curved or extended exterior surface.
Referring to fig. 1., 1 is a heating chamber, partly of cylindrical and partly of
inverted truncated conical form; it is constructed with a lining 2 of refractory material
surrounded by an outer wall or case 3 of brickwork or refractory material. 4 is a
layer of powdered carbon, or other bad conductor of heat, interposed between the
lining 2 and the wall or case 3. The lining 2 may be formed wholly of refractory
conducting material, such as carbon, as indicated at 2 fig. 2, or partly of refractory
conducting material and partly of refractory non-conducting material, as indicated
at 2 of the same figure. The conducting portion or portions of the lining are
connected up in circuit with an electric generator so as to form a continuous rigid
portion of such circuit. 5 is a tap hole; it serves for the discharge of metal, or other
substance, in a fused state from the heating chamber when desired, and enables
metallurgical and other operations to be carried on in a continuous manner.
7 is an
exit passage for gaseous or vaporized products from the substances treated; this
passage may be dispensed with when gas or vapour will not be produced from the
substances to be heated. 8 is an opening, preferably provided with a hopper, by
which the chamber 1 may be charged when desired, with the ores or substances to be
treated. Sa is a brick or cover to close the opening 8. The heating chamber may in

page_text: some cases be provided with a second tap hole 9 for the discharge when necessary of
slag or other secondary product of an heating operation; 9a is a plug for closing the
said tap hole 9. 10 is a resistance rod of refractory conducting substance, such as
carbon, located within the heating chamber, and extending upwardly through a top or
cover 11 of refractory material; it is electrically connected at its upper end to one
pole of an electric generator 12, and at its lower end is cemented or otherwise
electrically secured to a block 13 of suitable conducting material, such as carbon, in
electrical connection with the other pole of the electric generator. The resistance rod
thus forms a rigid integral part of an electric circuit. The block 13 is preferably
compressed within a box or in a ring 14 of metal, as shewn, part of which extends to
the exterior of the furnace, where it is connected with the electric generator. The
heating chamber may be of circular form in transverse section as indicated at the left
hand side of fig. 2, or of rectangular form, as indicated at the right hand side of the
same figure. The conducting portion or portions of the lining 2 and the resistance
rod 10 may be arranged in separate electric circuits, or in the same circuit, and either
in parallel or in series with each other.
In carrying out my improved method of heating, I charge the heating chamber with
the ore or other substance to be heated, for example, with a mixture of the oxide of a
metal such as copper and carbon. By then passing an electric current through the
lining and the resistance rod (or rods), these parts may be raised to a very high
temperature, the degree of which will be proportional to the strength of the electric
current employed, and which may be regulated according to requirements. The
mixture will thus be heated throughout its mass to a high temperature, and the
metallic compound reduced The ore mixture may be added at intervals, or continuously.
Any slag produced may be drawn off through the tap hole 9, whilst molten metal
may be drawn off at intervals through the tap hole 5. The heating and reducing
operations may thus, when desired, be carried on in a continuous manner
In fig. 3, the heating chamber is of cylindrical form throughout its length, and is
traversed by a series of resistance rods 10, connected to the block 13 of conductory
mateiral with which the lining 2 is also connected.
In fig. 4 the lining 2 is formed of refractory non-conducting material the heating
being effected solely by the resistance rod (or rods) 10. The layer 4 of bad con-
ducting material and the tap hole 9 for slag shown in fig. 1, are omitted in this
arrangement though they be provided if desired.
In figs. 5 and 6, which are respectively a longitudinal and a transverse section, the
resistance rods are arranged horizontally in rows within a rectangular chamber so
that they may be located or embedded within the substance treated. The refractory
lining 2 may be formed either of conducting material, arranged in an electric circuit
so as to be heated by the passage therethrough of an electric current, or of non-
conducting material as desired.
In fig. 7 the heating chamber is of double conoidal form with central charging
opening. The lining 2 is formed of refractory conducting material connected to the
blocks 13 13 a of similar material, which are compressed within or connected to
metal rings 14 14ª, parts of which extend to the exterior of the furnace for connection
to the electric generator.
In fig. 8 the beating chamber 1 which is of crucible form, is provided with two
resistance rods 10 that are connected at their lower ends to a plate or block 13 and
at their upper ends are connected to positive and negative main conductors; the
electric current passes down one rod and up the other. The heating chamber is
placed in a chamber or flue 15, and is heated externally by the combustion of gaseous
or other fuel.
In fig. 9 the chamber 1 and outer case 3 are constructed of two crucibles of
refractory material placed one within the other, with a layer of powdered charcoal or
other bad heat-conducting material, placed between the two; the chamber 1 is pro-
vided with a pair of resistance rods connected with each other and with the main
conductors in a similar manner to that shown in fig. 8. For many purposes this
forms a simple, cheap, and effective form of electric furnace.

page_text: In figs. 10 and 11 the heating chamber, the lining 2 of which may be heated by
the passage therethrough of an electric current or not as desired, is shown provided
with a series of resistance rods 9 so mounted and arranged that they may be rotated
relatively to such chamber. In the arrangement illustrated each resistance rod 10 is
of tubular form, and is carried by the cover 11, which is so arranged that it may be
rotated when desired by any convenient means, as for instance, by a worin 16 that
engages with a worm wheel 17 carried by the said cover. Each rod is connected at
its upper
end to a metal plate 18 with which a brush 19 makes contact to maintain
the circuit closed during rotation. The lower end of each tube is closed, and in it is
embedded (as shewn) one end of a rod 20 of conducting material such as metal. The
upper end of each rod 20 is connected to a metal plate 21, with which a brush 22,
makes electrical connection to complete the circuit. 16, 16 are anti-friction balls,
located between the top of the wall 3, and the cover 11, to reduce friction. With
this arrangement, when the nature or the state of the ore or substance treated will
permit, the resistance rods may be rotated relatively to the furnace, and such
substances be consequently well mixed and uniformly heated.
In figs. 12 and 13 the heating chamber 1 is so arranged that it can be rotated, when
desired, about its axis by any suitable means. In the example illustrated it is mounted
upon rollers 23 and is rotated by a worm 16 operated in any suitable manner, and
engaging with a worm wheel 17 secured to the chamber. The resistance rods 10
pass through the end walls of the chamber, which walls as well as the lining 2 may be
of refractory conducting material as before. The resistance rods are connected to
metal plates 24 provided with cylindrical extensions 25, against which bear brushes 19
and 22 that are connected with the poles of an electric generator. When gas or
vapour is produced as a result of the heating operation, such gas or vapour may be
permitted to escape periodically through holes 26, formed in the covers or plugs 8",
secured within the charging openings 8. The holes 26 are closed by covers 27
during the greater part of each rotation, to prevent escape of the substance treated,
but they may be opened when approaching their highest positions and be afterwards
closed, by any suitable arrangement of tappets that act upon the covers 27 at the
required times. The chamber may be arranged with its axis inclined instead of
horizontal, if desired.
In figs. 14 and 15 the resistance rods 10 are arranged longitudinally the lower
one 10" being arranged to serve as a positive electrode. 28 is a negative electrode of
curved form in transverse section and is slightly inclined towards the tap hole 5.
29 is a switch by which the negative electrode may be put in the circuit of the electric
generator 12 and a shunt electrolysing current passed through the substance melted
by heat from the resistance rods. The rods may be protected from action of the
substance treated by a coat or sheath refractory non conducting material 10° as shown.
30 is a resistance, (which may be a resistance rod or rods in another furnace),
arranged in the circuit of the said generator. 31 is an am-meter. In Fig. 16
positive electrodes 10ª arranged in the circuit of a separate electric generator 12ª are
employed, the negative electrode being in the form of a cylinder.
The main conductors and the connections to the resistance rods should be large or
of low resistance in order that the greater part of the electrical energy employed
should be expended in heating the rods by incandescence, no are being produced.
Furnaces or apparatus according to this invention may be strengthened externally
in any suitable manner care being taken not to short circuit the resistance rods
within them.
I am aware that it has previously been proposed to heat a chamber by the passage
of an electric current through refractory conducting material located within or
forming the wall or floor of such chamber. I am also aware that it has been proposed
to employ a refractory conductor heated by the passage through it of an electric
current and arranged within a chamber or containing vessel the wall or lining of which
was not separately heated. I therefore do not separately claim these features. In
such arrangements however the heating would either not be so effective as in my
arrangement of furnace, unless the chamber was of small dimensions, or heating operations

page_text: for effecting metallurgical chemical, and other processes could not be carried on in a
continuous manner on a commercial scale.
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed I declare that what I
claim is :-
1. Heating ores or other substances in the manner hereinabove described by the
combined action or effect of heat applied to or through the wall or walls of a chamber
or vessel containing the substance to be heated and of heat resulting from electricity
caused to pass through a continuous resistance rod or conductor (or continuous rods or
conductors) traversing the said chamber or vessel and its contents and forming part or
parts of an electric circuit (or circuits).
2. For the purpose of heating ores and other substances in the manner referred to
in claim 1 a furnace or apparatus having a heating chamber constructed with an
inner wall or lining made wholly or partly of refractory conducting material
arranged as a rigid continuous part of an electric circuit and in combination therewith
a refractory resistance rod or conductor (or rods or conductors) also made to form a
rigid continuous part (or parts) of an electric circuit the arrangement being such that
a mass of substance placed within the said heating chamber will be traversed by the
resistance rod or conductor (or rods or conductors) and will derive heat from the
same as well as from the refractory inner wall or lining of the chamber substantially
as hereinabove described.
3. A furnace or apparatus for heating ores and other substances by electricity
constructed with a heating chamber of refractory material having separate openings
respectively for charging with substances to be heated and for discharging substances
treated, and a refractory resistance rod or conductor (or rods or conductors)
traversing the said chamber and forming a rigid continuous part (or parts) of an
electric circuit (or circuits) the whole arranged to be worked in a continuous manner
substantially as hereinabove described.
4. In a furnace or apparatus for heating ores and other substances by electricity and
comprising a heating chamber of refractory material and a refractory resistance rod
or conductor located therein, so mounting and arranging the said resistance rod or
conductor that it can be rotated relatively to the heating chamber substantially in the
manner hereinabove described for the purposes specified.
5. In a furnace or apparatus for heating ores and other substances by electricity
mounting and arranging the heating chamber or vessel in such a manner that the
said chamber or vessel can be continuously rotated for the purpose of agitating the
substance therein whilst the same is being heated by electricity substantially in the
manner herein before described.
6. In a furnace or apparatus for heating ores and other substances wherein heat is
produced by the passing of electricity through refractory conducting material,
providing the chamber wherein the heat is produced with positive and negative
electrodes so connected up and arranged in an electric circuit that ores or substances
in the heating chamber besides being heated can be also electrolysed therein without
the use of an arc.
7. My improved electric furnaces or apparatus for heating ores and other substances
constructed substantially as herein before described with reference respectively to and
shown in figs. 1 and 2 in fig. 3, in fig. 4, in figs. 5 and 6, in fig. 7; in fig. 8; in fig. 9;
in figs. 10 and 11; in figs. 12 and 13; in figs. 14 and 15; and in fig. 16, of the
drawings annexed.