IMPROVEMENTS IN SMELTING ORES BY AN ELECTRIC CURRENT AND IN FURNACES OR APPARATUS THEREFOR
Year: 1885

page_text: I, WILLIAM PHILLIPS THOMPSON, Fel. Inst. P.A. of the Agency for Foreign
Patent Solicitors, 6 Lord Street, Liverpool, in the County of Lancaster, and
323 High Holborn, in the County of Middlesex, Civil Engineer, do hereby declare
the nature of the said invention for " IMPROVEMENTS IN SMELTING ORES BY AN
ELECTRIC CURRENT AND IN FURNACES OR APPARATUS THEREFOR" (a communication
from abroad by Eugene H. Cowles, and Alfred H. Cowles, both of Cleveland,
Cuyhoga County, State of Ohio, United States of America, Inventors) and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement :-
The present invention relates to the class of smelting furnaces which employ an
electric current solely as a source of heat. Heretofore it has been attempted to
reduce ores and perform metallurgical operations by means of an electric arc, the
material to be treated being brought within the field of the arc, or passed, or fed
through it, but numerous experiments have demonstrated that the arc system is not
adapted for long and continuous operations on a scale of any considerable magni-
tude, for the reason, that the heat, though intense, is localized and cannot be evenly
distributed over any considerable area; moreover, it is very difficult to maintain
with an arc, a constant resistance when used for such purpose. But by means of
an incandescent furnace, we have been able to secure most favourable results and
to maintain a high temperature for a long period of time.
The object of this invention is to provide a process by which clectricity can bo
practically employed for metallurgical operations, and for this purpose to secure a
distribution of the intense heat which, it is well known, electricity is capable of
generating over a large area, or through a large mass in such a manner that a high
temperature can be sustained for a long time and controlled and to provide an
apparatus by means of which these metallurgical operations and chemical operations
which require an intense heat, cau be carried on with electricity as the heat pro-
ducing agent operating on the incandescent principle.

page_text: The invention consists of a furnace or apparatus in which this improved process
can be carried out, and in the use, for metallurgical purposes of a body of granular
material of high resistance or low conductivity interposed within the circuit in such
a manner as to form a continuous and unbroken part of the same, which granular
body, by reason of its resistance is made incandescent and generates all the heat
required. The ore or like material to be reduced, as for example, the hydrated
oxide of aluminium, alum, chloride of sodiumn, oxide of calcium, or sulphate of
strontium, is usually mixed with the body of granular resistance material and is
thus brought directly in contact with the heat at the points of generation, at the
same time the heat is distributed through the mass of granular material, being
generated by the resistance of all the granules and is not localized at one point or
along a single line. The material best adapted for this purpose is electric light
carbon, as it possesses the necessary amount of electrical resistance and is capable
of enduring any known degree of heat when protected from oxygen, without dis.
integration or fusing, but crystalline silicon or other equivalents of carbon can be
employed for the same purpose.
This is pulverized or granulated, the degree of granulation depending upon the
size of the furnace. Coarse granulated carbon works better than finely pulverized
carbon and gives more even results, the electrical energy is more evenly distributed
and the current cannot so readily form a path of highest temperature and conse-
quently of least resistance through the mass along which the entire current or the
bulk of the current can pass.
But the scope of this invention is not limited by the degree of granulation as
that may vary with the conditions of the case, and with a large furnace and a
powerful current, the size of the carbon particles inay pass beyond what is ordinarily
understood by the term granular, and be in fact pieces of carbon of considerable
size, still the resistance body is ordinarily composed of grains or pieces proximately
equal in size in order to secure an even distribution of the electrical energy.
The operation must necessarily be conducted within an air tight chamber or in
a non-oxidizing atmosphere, as otherwise the carbon will be consumed and act as
fuel. The carbon acts as a deoxidizing agent for the ore or metalliferous material
treated and to this extent it is consumed, but otherwise than from this cause it
remains unimpaired.
I will first illustrate and describe a furnace embodying the invention as applic-
able for the reduction of zinc from which the application of the same to the
reduction or smelting of other kinds of ores will be readily understood, especially
of aluminium, silicon, magnesium, boron, and other rare metals which are not
reducible by the smelting processes heretofore known.
Figure 1 is a vertical longitudinal section through the centre of a zinc retort, of
a forin similar to those used in the Belgian furnaces, and
Figure 2 is a front view of the same, and
;
Figures 3 to 6 illustrate other forms of furnace in which the invention can be
carried into practice.
Referring to Figures 1 and 2: This retort consists of a cylinder A, made of silica
or other non conducting material, suitably embedded in a body B, of powdered
charcoal, mineral wool, or of some other material which is not a good conductor of
heat. The rear end of the retort cylinder is closed by means of a carbon plate C,
which plate forms the positive electrode, and with this plate the positive wire of
the electric circuit is connected. The outer end of the retort is closed by means of
an inverted graphite crucible D, to which the negative wire of the electric circuit
is attached. This graphite crucible serves as a plug for closing the end of the
retort; it also forms a condensing chamber for the zinc fumes; and it also consti-
tutes the negative electrode. The term electrode is used in this case as designating
the terminals of the circuit proper, or that portion of it which acts simply as an
electrical conductor, and not with the intention of indicating the ends of a line
between which there is no circuit connection. The circuit between the electrodes
so called, is continuous, being, established by means of and through the body of

page_text: broken carbon. There is no deposit made on either plate of the decomposed con-
stituents of the material reduced. The mouth of the crucible is closed with a luting
of clay, or otherwise, and the opening d made in the upper side of the crucible,
near its extremity, comes entirely within the retort and forms a passage for the
zinc fumes from the retort chamber into the condensing chamber. The pipe E,
serves as a vent for the condensing chamber. The zinc ore is mixed with pulverized
or granular carbon, and the retort charged nearly full through the front end with
the mixture, the plug D being removed for this purpose.
A small space is left at the top as shown. After the plug has been inserted and
the joint properly luted, the electric circuit is closed, and the current allowed to
pass through the retort, traversing its entire length, through the body of mixed oro
and carbon. The carbon constituents of the mass become incandescent, generating
a very high degree of heat, and being in direct contact with the ore, the latter is
rapidly and effectually reduced and distilled.
The heat evolved reduces the ore and distils the zinc and the zinc fumes are con-
densed in the condensing chamber, precisely as in the present method of zinc
making, with this important exception, that, aside from the reaction produced by
heating carbon in the presence of zinc oxide, the electric current in passing through
the zinc oxide, has a decomposing and disintegrating action upon it not unlike the
effect produced by an electric current in a solution. This action accelerates the
reduction and distillation and promotes economy in the process.
It will be observed, that the intimate mixture of incandescent carbon and ore,
affords the most effective utilization of all the heat evolved none of it is lost by
transmission through any intervening bodies or spaces. Moreover, the maximum
degree of heat generated by the furnace, is within the ore body, and the retort and
furnace receive only the heat which is transmitted outward from the ore and carbon
contained within, consequently the retort or the furnace is not subjected to the
highest degree of heat, as is the case in the Belgian and English methods of zinc
smelting, and the life time of a retort is thus materially increased. It is proposed
to use a number of these retorts in the same circuit in series or multiple arc as
desired.
It has been found in practice, that a mixture of about one part of carbon with
one and a half parts of zinc ore, by weight, gives most satisfactory results, with the
particular ore which has been treated, but the proportions to be used will depend
upon the character of the ore and the degree of heat required to reduce it, and the
degree of heat evolved will be determined by the resistance or conductivity of the
mass and the strength of the current employed.
Referring to Figures 3, 4, and 5 which are a perspective view, longitudinal and
transverse sections respectively, of a furnace embodying the invention adapted
for the reduction of ores and salts of non volatile metals and similar chemical
compounds.
The walls and floor L and L' of the furnace are made of fire bricks and do not
necessarily have to be very thick or strong, the heat to which they are subjected
not being excessive. Near each end of this fire brick box, there are plates M,
attached to rods M, which extend through the end walls of the furnace and have
the circuit wires m attached to their projecting extremities. These plates are pre-
ferably made of carbon, as being the material best adapted for this purpose and for
convenience, will be designated as carbon plates. These carbon plates are smaller
than the cross section of the box as shown, and the spaces between them and the
end walls are packed with fine charcoal.
The furnace is covered with a removable slab of fire clay N which is provided
with one or more vents n for the escaping gases.
The space between the carbon plates constitutes the working part of the furnace.
This is lined on the bottom and sides with a packing of fine charcoal O, or other
such material as is both a poor conductor of heat and electricity, as for example, in
some cases silica, or pulverized corundum or well burned lime and the charge P, of
ore and broken granular or pulverized carbon occupies the centre of the box,

page_text: extending between the carbon plates. A layer of granular charcoal O¹ also covers
the charge on the top. The charge thus forms a core extending lengthwise of the
box, in contact with the carbon plates M, at the ends and encased on all sides by
the jacket of fine charcoal. Fine charcoal, as is well known, is a very poor con-
ductor of heat, and the charcoal packing confines the heat within the core, protects
the walls of the furnace, prevents them from fluxing down and mingling with the
charge, thereby introducing deleterious matter, and it forms a deoxidizing shell for
the charge. The protection of the charge from the introduction of deleterious
matter by the fluxing down of the walls is a very important matter, and the pro-
tection afforded therefrom by the charcoal packing immediately surrounding the
charge is complete. It is also a much inferior conductor of electricity than the
carbon used in the core, and hence it confines the electricity as well as the heat:
The protection afforded by the charcoal jacket as regards the heat, is so complete
that with the covering slab removed, the hand can be held within a few inches of
the exposed charcoal jacket; but with the top covering of charcoal also removed
and the core exposed, the hand cannot be held within several feet.
The charcoal packing behind the carbon plates is required to confine the heat
and to protect them from combustion, as they would be consumed very rapidly if
exposed to the air. As it is the extremities of the rods M¹ become very hot and
have to be kept cool with wet cloths or otherwise.
In charging the furnace, the box is first filled with the packing material and
then a trench is dug between the end plates leaving a wall of charcoal or other
material on each side, and a floor of the same. Or the trench may be formed by
packing the charcoal in around a pattern core temporarily suspended within the
box. The trench is then filled to the top of the plates, with a charge of ore and
carbon, and covered over with granular charcoal to allow the escape of gases and
the covering slab put on and luted round the edges. A small space is left between
the top of the charcoal and the slab. It will be observed that the body of ore and
carbon is comparatively shallow in depth and has its longest dimensions in a hori-
zontal direction. The object of this is to allow the gases evolved during the
process of reduction, to escape with facility. It has been demonstrated that when
a deep and narrow body of ore and resistance material are treated in a furnace that
the gases generated near the bottom of the charge being confined by the material
above them, which does not sometimes allow them to escape as fast as generated,
exert great expansive force, sufficient at times to throw off the top of the furnace,
and even to eject part of the charge. When, however, the charge is spread out so as
to have comparatively little depth, the gases or vapors readily force a passage to the
surface to the interstices of the charge and pass off without acting detrimentally on
the charge or furnace. When coarse carbon is employed fine carbon is mixed with
the coarse carbon at the ends of the core, where they abut against the plates M. and
indicated at p, p' in order to secure a general contact and prevent an undue heating
of the plates.
This may be done by sifting fine carbon in between the interstices of the coarse
carbon close to the inner faces of the plates as the charge is being packed into the
furnace. The same result may be accomplished by flaring the core out at the ends
making it of larger cross section at the extreme ends than at the centre, so as to
make more points of contact between the carbon particles of the core and the
plates than would otherwise be made. In either case, there are a larger number of
points of contact between the particles of carbon in a cross section of the core taken
at the ends close to the plates, than in a cross section taken at the middle part of
the core, and hence the resistance is less at the ends and less heat is there
generated.
The electric current is now turned on and the reduction of the orc takes place.
The liberated gases escape through the vent holes n and burn with great vigor.
The changes that take place in the appearance of the flames as the reduction
progresses afford a means of determining when the reduction is complete. The
reduced metal is found, at the close of the operation, filling the interstices between

page_text: the particles of carbon; mixed with it, and plated as it were into the same; and
when the carbon is very coarse it works down through it and collects in the
bottom of the charge on the charcoal floor.
With this furnace aluminium can be reduced direct from its ores, and chemical
compounds, from corundum, cryolite, clay, etcetera, and silicon, boron, calcium,
manganese, magnesium and other metals are in like manner obtained from their
ores and compounds. The reduction of ores, according to this process, can be
practiced, if circumstances require it without any built furnace. For example, a
floor of charcoal can be prepared, the carbon plates set up on it at the proper
distance apart, with the circuit wires attached thereto, the charge packed in
between the carbon plates and the whole covered over with charcoal and on top of
all earth: The mound thus formed will be not unlike a heap for burning charcoal
in external appearance:
Referring to Figure 6:-
==
Similar letters of reference refer to similar parts.
The furnace or rotort chamber F, has an inclined floor sloping from both ends
down to a discharge hole f through which the metal and slag, or residue can be
withdrawn. His outlet to a condenser, and I, I, I, aro hoppers for charging the
furnace; several being provided to distribute the chargo evenly along the chamber.
The hoppers I, and the discharge opening fare closed with fire clay plugs. This
furnace admits of the use of heavy walls and solid permanent construction, and
also a prolonged heat. A nice regulation of the resistance of the charge is secured
by means of the several feed hoppers, an additional amount being fed in when the
resistance is too high, and a portion of the charge being withdrawn through the
bottom when the resistance is too low,
In the reduction of an ore composed of a non volatile metal, or a metal which is
not volatilized at the heat generated in the furnace, the metal remains in the
furnace, mixed with the carbon filling the interstices between the grains while the
gases produced pass off. In the reduction of rare metals, where a pure product is
desired it is necessary to use a pure carbon, or a carbon free from iron or other
foreign ingredient, otherwise the iron or other substance will go into the product.
I am aware that the existence is known of a carbonizing apparatus, consisting of
a muffle or case adapted to contain a filling of pulverized carbon, in which the
articles to be carbonized are embedded and provided with an electrode at each end,
to which the wires of an electric circuit are connected, one of the electrodes having
a movement lengthwise of the muffle to preserve the contact between the electrodes
and the contents of the muffle as the carbonization progresses. In such apparatus
the muffle stands in a vertical position, and the movable electrode fits the same in
such a manner that it can descend by its own weight and space is left between it
and the walls of the muffle. An apparatus thus constructed is not adapted for the
reduction or smelting of metals since it lacks some of the essential requisites fully
set forth in the foregoing description of the apparatus.
It is also known that an electric heating furnace has been devised in which the
walls of a vertical chamber are lined with a solid electrical resistance material and
provided with oppositely located electrodes of graphite, to which the wires of an
electric circuit are connected. Such chamber is accessible through a top lid and is
designed to receive a crucible containing the material to be fused.
In such apparatus it is the lining of the chamber that is heated by the electric
current and there is no provision for the escape of gases that would be evolved if
metallurgical operations were performed therein and hence it is not adapted for the
reduction of metals which is the chief aim and object of this invention.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, as communicated to
me by my foreign correspondent, I declare that what I claim is
1. The method of generating heat for metallurgical operations herein described;
which consists in passing an electric current through a body of broken or pulverized

page_text: resistance material that forms a continuous part of the electric circuit, the ore to be
treated by the process being brought in contact with the broken or pulverized
resistance material whereby the heat, is generated by the resistance of the broken
or pulverized body throughout its mass and the operation can be performed solely
by means of electrical energy.
2. The method of smelting or reducing ores or metaliferous compounds herein
described, which consists in subjecting the ore in the presence of carbon to the
action of heat generated by passing an electric current through a body of broken
or pulverized resistance material that forms a continuous part of the electric circuit,
the ore being in contact with the broken or pulverized resistance material whereby
the ore is reduced by the combined action of the carbon and of the heat generated
solely by the resistance of the broken or pulverized body throughout its mass.
3. The method of smelting or reducing ores or metaliferous compounds herein
described, which consists in pulverizing the ore, mixing with it pulverized or
broken carbon or like material, then introducing the mixed ore and carbon within
an electric circuit of which it forms a continuous part, the said circuit being
established through the carbon constituents of the mass, whereby the heat is
generated by the electrical resistance of the carbon throughout, the mass, and the
operation can be performed entirely by means of the carbon re-agent and the
electrical energy.
4. The method of smelting or reducing ores or metaliferous compounds herein
described, which consists in subjecting the ore in the presence of a reducing agent
to the action of heat generated by passing an electric current through a body of
broken or pulverized resistance material that forms a continuous part of the electric
circuit, the ore being in contact with the broken or pulverized resistance material
whereby the ore is reduced by the combined action of the reducing agent, and of
the heat generated solely by the resistance of the broken or pulverized body
throughout its mass.
5. In an electric smelting or reducing apparatus, a chamber or casing having its
longest dimensions in a horizontal direction and adapted to contain a charge of ore
and electrical resistance material previously pulverized and mixed together the
oppositely located electrodes in conductive relation to the charge but otherwise
insulated, from one another, and an exit for the escape of the gases and vapors
evolved from the charge during the process of reduction, substantially as herein set
forth.
6. In an electric smelting or reducing apparatus, the sinelting chamber formed
of side and bottom walls of closely packed pulverized or granular material, and the
permeable top wall formed of a layer of granular non-heat conducting material,
and the electrodes oppositely located at the ends of the core or sinelting chamber,
substantially as herein set forth.
7. In an electric smelting or reducing furnace the combination of a chamber or
casing, the side and bottom layers of closely packed pulverized or granular material,
and the top covering of similar material made permeable for the escape of gases and
vapors, with the electrodes oppositely located at the ends of the chamber or casing
and surrounded by the packing or filling which encloses a charge of carbon and ore,
substantially as herein set forth.
8. In an electric smelting or reducing apparatus a smelting chamber formed of
closely packed granular or pulverized material, of a non-heat conducting nature,
and of lesser electrical conductivity than the charge to be smelted in the furnace,
with two electrodes arranged at the opposite ends of said chamber for conducting
the electricity to the said charge substantially as herein set forth.
9. In an electric furnace, a body or core of pulverized granular or broken
resistance material interposed between two electrode plates, substantially as
described, having a greater number of points of contact in a cross section of the
body taken close to the plates than in a cross section of the saine taken in inter-
mediate parts thereof, whereby there is less resistance and consequently less heat
at the ends of the core than at other parts thereof,

page_text: 10. In an electric furnace a body or core of pulverized granular or broken
resistance material interposed between two electrode plates, substantially as
described, with fine carbon filling the spaces between the particles of coarse
carbon at the ends only of the core abutting against the plates, whereby there is
less resistance and consequently less heat at the ends of the core than at other
parts thereof.
11. In an electric smelting or reducing apparatus, a smelting chamber formed of
closely packed pulverized material of non-heat conducting nature and of lesser
electrical conductivity than the charge to be smelted within it, a layer of similar
material permeable for the escape of gas for closing the said chamber, and two
electrodes arranged at the opposite ends of the said chamber for conducting
electricity to the charge, substantially as set forth.
T
012
ст
1007
WM P. THOMPSON & Co.,
Agents for the Applicants.