Improvements in Methods of and Apparatus for Heating Crucibles by Means of Electricity.
Year: 1894

page_text: Date claimed for Patent under Sect. 103 of Act,
being date of first Foreign Application (in 19th Feb., 1894
France),
Date of Application (in United Kingdom), 16th Aug., 1894
Complete Specification Left, 13th May, 1895-Accepted, 15th June, 1855
PROVISIONAL SPECIFICATION.
Improvements in Methods of and Apparatus for Heating Crucibles
by Means of Electricity.
We, ADAM CHARLES GIRARD, Chemist, of 7 Rue Du Bellay, and ERNEST
AUGUSTE GEORGES STREET, Engineer, of 39 Rue Joubert, both of Paris, in the
Republic of France, do hereby declare the nature of this invention to be as
follows:-
-
This invention relates to methods of and apparatus for heating, by means of
electricity, materials contained in crucibles which are conductors of electricity
and which preferably consist of carbon. One of the characteristic features of this
invention is that a rotary movement is imparted to the are, as will hereinafter be
described. The are is subjected to the action of a suitable magnetic field which
causes it to turn round the axis of the crucible with greater or less rapidity, and
travel upon the surface of the crucible on the one hand, and that of the other
electrode on the ther hand, or upon the surface of two electrodes in the interior
of which is placed the crucible.
Our invention enables us to obtain a maximum utilization of the heat produced
and an equal distribution of such heat, which is of great importance as regards the
preservation of the crucible.
The are can turn either upon the exterior surface of the crucible or upon the
interior surface thereof, or yet upon the edge of the crucible; or as before
stated upon independent electrodes, in the interior of which is placed the
crucible.
:
The crucible is preferably made of carbon and in the type, which we will
describe first, it is suspended in the centre of the furnace by its upper flange which
rests upon a shoulder provided in a carbon block. Said block is placed in a
cavity provided in a block of suitable refractory material for example a block of
imagnesia or silica and rests upon a bottom block also of refractory material; a top
refractory block of similar nature rests upon the upper part of the two first
mentioned blocks. Lastly two other inner carbon blocks complete the whole
interior of the furnace.
All these parts are located in the interior of an iron tube or envelope closed at
its upper and lower ends by two plates or covers which are made of bronze
for example and are insulated from the said iron tube while making a joint
therewith.
The blocks at the lower part of the furnace are pierced to permit of the
passage therethrough of a carbon electrode the form of which is such as to
surround the lower part of the crucible without however touching the same.

page_text: The said carbon electrode is pierced with a small hole along its axis and may be
furnished at its upper end with a carbon ball. It is mounted in a carbon-holler
fixed in a cap secured by the aid of a bayonet or other joint to the lower plate
of the furnace; the said cap carries a cock and nozzle for purposes hereafter
described.
The crucible is held upon its seat by means of a carbon plug which is mounted
in a carbon holder the latter being placed in a cap in which it is maintained by
means of a spring and a stop ring. The cap is secured by the aid of a bayonet
or other joint to the upper plate of the furnace and may receive at its upper part
a screw plug for securing in place a plate of mica for example.
The carbon plug which holds the crucible in place has a central axial
thoroughfare passing completely through it. By pressing the cap or cover upon
the upper plate of the furnace the carbon plug is caused to bear upon the
crucible with a pressure proportional to the pressure of the spring above
referred to.
By placing the upper and lower plates of the furnace respectively in communi-
cation with the two poles of a suitable source of electricity, an arc may be struck
between the crucible and the carbon electrode. Or the arc may be struck by
introducing a lighting carbon through the central hole of the carbon electrode;
this lighter is brought into contact with the bottom of the crucible and then
withdrawn. The arc thus struck will continue between the crucible and the carbon
electrode. We provide outside the iron envelope surrounding the furnace two
solenoids which are traversed by an electric current enabling poles of opposite
kinds to be produced at the extremities of the said surrounding tube or envelope.
We thus obtain in the interior of the furnace a magnetic field which compels
the arc to turn about the axis of the crucible in a plane perpendicular to such
axis.
We sometimes strike the are by the aid of the carbon ball before referred to
placed in the cavity provided in the carbon electrode. For this purpose we fix an
india-rubber pipe upon the beforementioned nozzle at the base of the furnace and
connect the other extremity of this pipe with a hollow indiarubber ball of suit-
able dimensions. By pressing upon this ball we force the carbon ball upwards
so that it simultaneously touches the bottom of the crucible and the edge of the
The cock at the
cavity provided in the carbon electrode, and strikes the are.
lower extremity of the furnace enables the communication between the interior
atmosphere of the furnace to be cut off from the exterior after the lighting has
been accomplished.
The crucible is provided at the side with an outlet which is opposite a channel
pierced in the surrounding blocks and iron envelope or tube. When the material
in the crucible is at the melting point we discharge the same by causing the whole
apparatus to turn about a horizontal axis perpendicularly to the tap hole where-
upon the material flows out and is collected. The hole in the side of the crucible
may be replaced by a tap nozzle provided at the upper part of the crucible. This
tap nozzle corresponds with a tap hole through a suitable channel provided in the
pieces which constitute the interior lining of the furnace.
The axis of oscillation of the apparatus in the above described types of furnace
is made in two parts electrically insulated from the material of the furnace, and
each of these parts is in electrical communication one with the crucible by means
of the upper carbon plug and cap and the other with the lower carbon electrode
by means of the lower cap which supports the carbon electrode. The before
mentioned solenoids are included in the circuit thus established by a suitable
grouping either in series with the are or in parallel circuit. The current is con-
ducted to the two insulated parts of the axis of oscillation of the apparatus through
the supports or hearings of said axis, which enables the furnace to be turned
without extinguishing the arc and consequently without permitting the material
contained in the crucible to become cool.
The tap hole may be closed during the heating process by a hermetic closing

page_text: device in a similar manner to the axial hole provided in the upper carbon plug.
For this latter purpose the plug may carry a carbon rod which enters freely into
the hole in the said plug but serves to limit the gas spaces in the apparatus and
helps to concentrate the heat upon the material contained in the crucible.
We in some instances provide suitable gas inlets and outlets so as to be able to
operate in appropriate atmospheres and pressures.
The mode of tilting the furnace varies with the size and weight of the same,
for example we may provide for this purpose a handle fixed to one of the pivots.
We will now indicate by way of example one method of constructing the furnace
when we wish to effect the heating of the crucible by means of an are turning upon
the interior surface of the crucible.
In this construction the crucible is enclosed in a carbon block which is surrounded
by a material which is a bad conductor of heat, such as for example magnesia,
silica or the like. Two carbon-blocks serve to concentrate the heat upon the
crucible and above these there are placed two other blocks of a material which is
a bad conductor of heat. The two blocks for concentrating the heat as aforesaid
are arranged in the furnace in such a manner that they are insulated both from
the crucible and from the electrode. The latter is tubular and mounted upon a
carbon holder fixed by a bayonet joint upon the upper cover of the furnace which
cover is mounted upon and insulated from the iron containing envelope of the same.
The carbon electrode may be mounted upon an oscillatory carbon-holder similar to
those already employed in various are lamps enabling it to be put in contact with
the crucible in order to cause the arc to strike which are being subjected to the
action of a suitable magnetic field, for example of the kind hereinbefore described
rotates upon or turns round the interior surface of the crucible and the exterior
surface of the electrode.
The current is passed to the crucible by means of a carbon electrode mounted
in a carbon holder which is pressed forward by a spring. Said spring is fixed in
a box mounted by a bayonet or other joint upon the outer metallic envelope. The
current passes through the carbon electrode, through the block surrounding the
crucible and finally through the crucible. By removing the electrode and its
containing box we may cause the contents of the crucible to flow to the outside
of the apparatus as hereinbefore explained. In case however it is desired to empty
the crucible while maintaining the current in the furnace the carbon electrode for
the admission of the current to the crucible is placed upon the diameter opposite
to that of the tap hole and the latter is plugged during the heating by a device
similar to that used for admitting the current in order to enclose the furnace and
concentrate the heat upon the crucible.
We will now describe the arrangement which we may adopt when the arc is
required to turn upon the upper surface of the crucible or more generally upon an
axis parallel to the element of current which constitutes the arc.
In this case the
envelope is by preference made of non-magnetic metal.
The magnetic field is excited by an iron ring concentric with the furnace which
is for example covered with two circuits traversed by two alternating currents
which differ in phase by a quarter period; the maximum point of one of the
phases therefore corresponds to the zero point of the other.
Four coils are wound on the ring two coils which are at opposite ends of a
diameter forming one circuit and the other two coils forming the second circuit.
The circuits are so joined that consequent poles are formed in the iron rings.
In a modification the coils are wound on radial arms projecting externally from
the four quarters and connected in circuit in such a manner as to form poles of
opposite names at the points of contact of the magnetic core of the windings and
the ring. The second pair of coils are connected so as to produce respectively the
same effect.
If under these conditions one pair of coils is traversed by an alternating current
and the other pair of coils by another alternating current, these two currents being
listinct and the maximum point of one corresponding to the zero point of the other

page_text: as aforementioned we produce in the interior of the ring a magnetic field which
will turn about the centre of this ring at a velocity which will be a function of the
number of alternations of the currents employed.
It will be understood that such a field acting upon an element of arc, will cause
this element to turn about an axis which is parallel to it and which passes through
the centre of the ring which serves to excite the magnetic field as hereinabove
described.
Suitable devices may be employed for effecting the lighting of the furnace either
automatically or by hand.
We provide the furnace with tap holes, tilting apparatus and contact brushes
or other devices enabling the crucible to be emptied without interrupting the
heating.
In another arrangement of furnace we employ two carbon tubes and by the aid
of a definite magnetic field as above described cause an arc to be formed and to
rotate at the extremity of said tubes which serve as electrodes for the arc and
between which the crucible is placed. Owing to this magnetic field we obtain an
are which turns at a great velocity about the crucible and heats it in a symmetric
manner.
The whole of the electrodes and of the crucible may be placed in a heat
accumulating enclosure; the crucible may be supported by pieces of carbon suitably
insulated from the said electrodes.
Dated this 16th day of August 1894.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, Loudon, W.C., Agents for the Applicants.
Improvements in Methods of and Apparatus for Heating Crucibles
by Means of Electricity.
We, ADAM CHARLES GIRARD, Chemist, of 7 Rue Du Bellay, and ERNEST
AUGUSTE GEORGES STREET, Engineer, of 39 Rue Joubert, both of Paris, in the
Republic of France, 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 :-
This invention relates to methods of and apparatus for enabling materials
contained in crucibles to be heated by a voltaic arc, said crucibles being composed
of some substance that is a conductor of electricity such as carbon. One of the
characteristic features of this invention is that a rotary movement is imparted to
the voltaic arc. For this purpose the are is subjected to the influence of a suitable
magnetic field whereby it is caused to rotate with more or less speed around the
axis of the crucible. The are can be caused to rotate upon the external or the
internal surface of the crucible or upon the edge thereof. Or independent electrodes
may be employed which may be so arranged that the arc will travel around the
crucible without coming into actual contact therewith.
Our invention enables us to obtain a maximum utilization of the heat produced
by the are and an equal distribution of such heat which is of great importance as
regards the preservation of the crucible.
In order that our invention may he clearly understood and readily carried into
effect we will proceed to describe the same more fully with reference to the
accompanying drawings.
Figure 1 is an elevation and
Figure 2 a vertical section of a heating apparatus or furnace constructed in
accordance with our invention, the arc in this case being formed on and rotating
around the exterior surface of the crucible

page_text: Figure 3 is a vertical section of a modified construction of the furnace in
which the arc is formed on and rotates around the interior surface of the
crucible.
Figure 4 is also a vertical section of another modified construction of the
furnace in which the arc is formed on and rotates around the upper part or edge of
the crucible.
Figures 5 and 6 are diagrammatic views shewing the manner in which we may
arrange the windings on the ring for producing the magnetic field.
Figure 7 is a fragmentary view of an arrangement in which the arc rotates
around the crucible without coming into actual contact therewith.
Like letters of reference indicate similar parts in all the figures.
A is the shell or casing of the furnace; B the surrounding solenoids for producing
the magnetic field within the furnace; and C the crucible.
Referring more particularly to Figures 1 and 2 the shell A is encircled by a
ring A having trunnions A2 A2 which are carried by standards A3 and one of said
trunnions is provided with a handle A' for enabling the furnace to be tilted when
it is desired to discharge the contents of the crucible. The interior of the furnace
is composed of carbon blocks D E F which are surrounded with blocks G H I of
magnesia, silica, or other suitable refractory material the whole being enclosed by
the aforesaid shell A. By forming the body of the furnace in the manner explained
the blocks can be readily taken to pieces when desired. The crucible C is located
within a cavity provided for its reception within the internal carbon blocks and is
furnished with a rim c by which it is suspended from the carbon block D which
latter is formed with a shoulder for said rim to rest on. This carbon block D is
also formed with a shoulder d which rests upon a corresponding shoulder on the
refractory block H and thereby keeps the block D out of contact with the
block E. JJ are end covers with which the shell or casing A is provided said
covers being advantageously made of bronze and insulated from the shell or
casing.
K is a carbon rod or electrode which projects into the furnace through suitable
openings formed in the lower end cover, and the blocks F G. The inner end of
this electrode is recessed so that when in place it surrounds the lower part of the
crucible without coming into contact therewith.
The lower end of this electrode is fitted into a carbon holder which is affixed
within a surrounding detachable cap k². This cap is secured to the lower cover of
the furnace by a bayonet or other joint and is electrically insulated therefrom.
kis a longitudinal channel extending completely through said electrode and
coinciding with a similar channel formed through the holder and cap k³ ³ is a
tap for closing the channel k, and is a carbon sphere which normally lies
immediately above the upper end of the said channel.
Passing through the upper cover J and the block 1 is a carbon rod or plug L
whose lower end is so shaped as to fit into and cover the mouth of the crucible.
This rod or plug is hollow and terminates at its upper end in a carbon holder
having a central opening therein. 12 is a detachable cap, which is secured to the
upper cover by a bayonet or other joint and is electrically insulated from said cover.
This cap encloses the upper end of the plug L and is provided with a central
opening which is furnished with a screw cap. is a plate of mica or other
suitable transparent material which is situated between the screw cap and the top
of the cap for enabling the contents of the crucible to be observed. is a spiral
spring which by acting upon the upper end of the carbon plug L keeps the lower
end of this latter constantly pressed against the crucible and in good electrical
contact therewith. is a stop ring situated within the cap 2 and which serves to
upport the plug 1 when the cap (2 is detached.
The furnace is formed with a lateral pouring channel M and the crucible is
provided with a lateral opening c¹ that lies in contiguity to said pouring channel so
that when the furnace is tipped about its bearings by means of the handle A* the
contents of the crucible can be conveniently discharged.

page_text: By connecting the upper and lower caps with the two poles of a suitable
electric generator a voltaic arc can be formed between the crucible C and the carbon
rod K the said crucible and the carbon rod thus constituting electrodes. In order
to strike the are we employ the before mentioned carbon sphere k. For this
purpose a tube is connected to the nozzle this tube being provided with an inlia
rubber ball at its free end. By compressing the india rubber ball, air can be
injected up the passage thereby forcing the sphere against the bottom of the
crucible, but without causing it to come out of contact with the electrode K. The
arc is thus struck and the sphere drops back into its original position. Or we may
strike the are by inserting a carbon rod through the longitudinal passage k and
bringing said rod into contact with the bottom of the crucible, the rod being after-
wards withdrawn again. When the arc has been struck, the tap k³ may be shut
so as to cut off the interior of the furnace from communication with the external
atmosphere.
The are may be caused to rotate by means of two solenoids B B which respectively
surround the upper and lower part of the furnace.
When these solenoids are
traversed by an electric current the casing A becomes polarized and we thereby
produce within the furnace a magnetic field which has the effect of causing the
.arc to rotate horizontally about the axis of the crucible in a
understood.
manner well
The before mentioned trunnions A², by means of which the furnace is pivotally
suspended, are insulated from the furnace but are in electrical connection one
with the crucible C through the plug L and cap, and the other with the
electrode K through the cap. The solenoids B are also included in the circuit
and are arranged either in series therewith or in parallel circuit thereto. By
connecting the standards A³ with the source of electricity, the current passes to
the furnace by the trunnions A². The furnace can then be tilted without breaking
the electric circuit and thus the are remains uninterrupted during the pouring
operation and the contents of the crucible are maintained in their heated
condition.
It is obvious that we may employ any convenient means for tilting the furnace
said means depending upon the size and weight of the furnace.
The pouring hole may be closed during the heating operation by means of a cap
similar to the one represented by P. This cap may also carry a carbon rod which
is adapted to fit into the hole M said rod thereby serving to limit the gas space in
the furnace and to concentrate the heat upon the material within the crucible.
Appropriate inlets and outlets may be provided for enabling any suitable gas to
flow through the furnace.
Instead of forming an aperture e in the side of the crucible as shewn in the
drawings we may provide the crucible with a spout in its rim said spout coinciding
with a suitably arranged pouring hole.
In the construction shewn at Figure 3 where the arc is produced within the
crucible the latter is supported within a cavity formed in the lower carbon block F,
and at a short distance above said block are arranged the carbon blocks D E. The
inner one D fits into the outer one E and is held in position by means of the
shoulder resting upon the upper surface of the block E. The carbon
blocks D E F serve to concentrate the heat upon the crucible and are, as in the
previous construction, surrounded by blocks of refractory material G H I. The
carbon blocks DE are so arranged that they are electrically insulated from
the crucible C and the electrode L. This electrode is hollow and is passed through
the upper cover of the furnace, where it is held in position by means of the carbon
holder and the detachable 12. The latter is insulated from the cover and is
provided with a peep hole 13 as in the previously described arrangement.
cap
The carbon L may be mounted in a carbon holder, similar to that employed in
various arc-lamps, for striking the arc. This arc is caused to rotate by means of a
magnetic field produced by a pair of solenoids similar to those shewn in Figures 1
and 2.

page_text: The current reaches the crucible through the block F and a laterally arranged
carbon rod N which latter is mounted in a carbon holder ¹ and is kept pressed
forward by a spring n³ mounted in a cap n² similar to that already described with
reference to Figure 2 save that no peep hole is in this case necessary. By removing
the cap n and carbon rod N the contents of the crucible can be poured out through
the opening M when the furnace is tilted.
Should it be desired to prevent the interruption of the arc during the pouring
operation, the electrode N may be situated on the opposite side of the furnace in
which case the pouring hole would be plugged with a detachable carbon rod as
explained with reference to Figure 2.
In
Figure 4 shews a furnace in which the arc is intended to rotate around the upper
surface or edge of the crucible that is to say about an axis parallel to the arc.
this case the furnace is similar in construction to the one illustrated by Figure 3.
The casing A is preferably made of some non-magnetic material and instead of
employing solenoids such as B, we produce the magnetic field by means of an iron
ring p arranged concentrically around the furnace. This ring is wound with two
coils traversed by alternating currents which differ in phase by a quarter period
so that the maximum point of one of the phases corresponds with the zero point
of the other..
Figures 5 and 6 shew diagrammatically and by way of example two methods of
arranging the coils. In Figure 5 four coils q q₁r rare wound on the ring in such
a manner that opposite coils are joined together so as to produce two pairs of coils
one of such pairs viz. q q' being arranged in one circuit, and the other viz. rin
another circuit. These circuits are so joined that consequent poles are formed in
the iron ring p. In Figure 6 the coils ggr rare wound on four equidistant radial
cores s¹tt extending from the ring and are so connected in circuit as to form
poles of opposite names at the inner ends of the cores where they meet the ring.
Thus when one pair of coils is traversed by an alternating current and the other
pair by another alternating current, these two currents being distinct and the
maximum point of one corresponding with the zero of the other as aforementioned,
we produce in the interior of the ring pa magnetic field rotating at a velocity
which will be a function of the number of alternations of the currents employed..
This magnetic field by acting upon the arc will cause it to revolve.
In a modified arrangement of the furnace we employ two carbon tubes 0 0
(Figure 7), serving as the electrodes, between the ends of which the arc is formed.
By the aid of a magnetic field produced in the manner described with reference
to Figure 4 the said are can be caused to rotate around the crucible at a great speed
and thereby uniformly heat the said crucible.
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. In apparatus for heating crucibles by electricity, the employment of a voltaic
are caused to rotate around the axis of the crucible by the action of magnetic
fields substantially as described.
2. In apparatus for heating crucibles by electricity, the employment of the
crucible itself as one of the electrodes for the rotating are substantially as
described and for the purpose specified.
3. In apparatus for heating crucibles by electricity, the manner of enabling
the apparatus to be tilted without interrupting the voltaic arc substantially as
described and for the purpose specified.
4. In apparatus for heating crucibles by electricity, the manner of concentrating
the heat by constructing the body of the apparatus or furnace of carbon blocks
surrounded with blocks of refractory material substantially as described.
5. In apparatus for heating crucibles by electricity the manner of conducting
the electric current to the crucible substantially as described.

page_text: 6. Apparatus for heating crucibles by a rotary voltaic arc substantially as
described with reference to one or other of the arrangements illustrated in the
accompanying drawings.
Dated this 10th day of May 1895
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicants.