Improvements in Electrical Furnaces.
Year: 1897

page_text: Date of Application, 24th July, 1897-Accepted, 28th Aug.,
1897
COMPLETE SPECIFICATION.
Improvements in Electrical Furnaces.
I, CHARLES DENTON ABEL, of No. 28, Southampton Buildings, Chancery Lane,
in the County of London, Consulting Engineer and Chartered Patent Agent, do
hereby declare the nature of this invention (which has been communicated to me
from abroad by Siemens & Halske, an incorporated company, of No. 94 Markgrafen
Strasse, Berlin, Germany) and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement:-
With the electrical furnaces heretofore employed, the operative end surface of
the vertically arranged upper carbon is formed flat, and the lower electrode also
forms a flat horizontal table on which the material to be acted upon is placed. As
it is a necessity to pass all material through the electric arc if a satisfactory yield
is to be obtained, it has been proposed to push the material by means of a con-
veying worm from the side through the arc or to impart a lateral to and fro motion
to the crucible. With this arrangement however all the material is not passed
through the arc, and in addition it is disadvantageous to provide special means for
so moving the material.
The essential feature of the present invention consists in imparting to the
electrodes such a form that the feed of the material towards the arc shall be effected
automatically by means of gravity.
I will describe the invention with reference to the accompanying drawing in
which Figure 1 shews a vertical section through one construction of electrical
furnace according to this invention, Figure 2 shews a sectional plan. Figures 3
and 4 shew similar views of a modified construction. The upper electrode Kis
not formed flat on the under face as is usual, but is of a wedge shape, conical or
pointed form, and the lower electrode K2 is formed with a correspondingly conical
or funnel shaped recess so that the material situated in the space between the two
electrodes can descend automatically as in the case of a filling hopper.
It has been found that such automatic descent will also take place in a regular
manner, when the material in consequence of its nature, shews a tendency to cake,
as the small movements which must necesssarily be imparted to the upper carbon,
for regulating the strength of the current are quite sufficient to loosen the caking
particles; to assist in this action there may be provided on the moveable carbon
projecting bars or flanges W as shewn at Figures 1, 2, 3 and 4.
It has also been found that the form of the electrodes is not materially altered
by the burning. Both the upper and the lower carbon burn away slowly during
the working, so that the conical or wedge shape of both remains the same, and the
surfaces remain parallel.
As furthermore the electric arc is always formed at the part where the two
electrodes are nearest together, these parts will burn away more than the other
parts and consequently the arc will shift to another point which will have become
the nearest; every point of the conical space must thus at some time be the point
of nearest approach, and will consequently receive the arc. By this means the are
will necessarily be made to travel by degrees over the entire electrode surface, and
it is thereby made to fulfil two important conditions of working.

page_text: On the one hand, all the material between the electrodes must come by degrees
under the action of the arc, and on the other hand, the form of the carbons remains
practically unaltered.
The described form of the electrodes would however be subject to a considerable
disadvantage as compared with the flat carbons heretofore employed, unless special 5
precautionary measures were adopted.
Namely, on treating materials in the electrical furnace there often occurs a
considerable development of gas. If this gas penetrates through the layer of
material it does so with considerable force, and there is formed a narrow channel
through which comparatively little gas escapes at a high pressure.
There are 1
consequently produced on the surface of layer of material strong shooting flames
which are continually changing in position, and which attack the moveable carbon
electrode to a considerable extent so that the electrical current is subject to strong
fluctuations.
This disadvantage is obviated by surrounding the cylindrical part of the upper 1
carbon by a casing which leaves a sufficiently large free space between its inner
surface and the outer surface of the carbon, through which the gases can escape
freely, with only slight pressure.
The lower part of the casing K4 Figure 1 is formed of carbon, in order the
better to resist the high heat, while the upper part is made of iron. The purpose 2
of the casing can also be accomplished by forming longitudinal grooves on the
outer surface of the upper carbon. Also, in place of using the casing L K 4 of the
construction shewn at Figure 1, the required object may be attained by employing
the material to be treated, not in the form of powder as heretofore, but in the form
of more or less coarse pieces or lumps which offer sufficiently large interstices 2
between them for allowing of the free escape of the gases.
For this purpose
the pulverulent material is mixed with a suitable binding
substance such as tar, pitch, asphalt or the like, and is pressed in moulds, under
heating if required.
Figure 3 shews a vertical section of the furnace with the material formed in this 3
manner.
From the conical form of the electrodes there also results a farther essential
advantage, which cannot be obtained, or only imperfectly, with the existing
arrangements.
It is not difficult with this construction to apply tapping devices which enable 3.
the finished product to be removed without interrupting the working.
For this purpose the arrangements shewn in Figures 1 and 3 can be employed.
In the arrangement at Figure 1 the hollow of the lower electrode is provided at
its lower end with a hole. This however is not alone sufficient, as experience
shows that if the hole is made so small that the unconverted material cannot fall
through, it will easily and often become clogged with the solidified cake of the
finished product.
4
There is consequently provided below a sufficiently large hole, a roof shaped
closing piece K3 which projects sufficiently on either side to insure that the falling
material accumulating on the incline will be retained and lie upon the closing 4
piece.
Experiment has shown that the liquid product can then force its way through
the pulverulent raw material and flow off over the closing piece K 3, so that it can
be collected in suitable appliances. In this way however the product is obtained
in comparatively thin streams, and consequently offers to the air as it issues, a 5
comparatively large surface. This arrangement could therefore not be used if the
product is of such a nature as to deteriorate under the action of the air.
If the melted material produced by the electric arc is easily oxidised or solidified,
the tapping arrangement shewn at Figures 3 and 4 can be employed with advantage,
where the tapping is effected periodically from the side.
The lateral opening formed in the lower electrode which is closed at bottom, is
in the first instance closed by the descending material and soon gets clogged up by
5

page_text: a cake R of the solidified melted product after the working has commenced. The
cake R Figure 3 will have automatically a funnel shaped recess formed in its
upper side in which the liquid product collects.
For withdrawing this there is provided opposite the opening a boring tool B.
Whenever a sufficient quantity of the liquid product. has accumulated, the cake R
is bored through so as to form a tapping hole through which the liquid material is
discharged into a collecting vessel.
The boring tool can also be employed in other ways for tapping off the molten
material, for example by boring upward vertically from below.
Lastly, Figures 3 and 4 shew another advantage which is attained by the conically
formed electrodes. Namely under the fixed funnel shaped electrode there are
formed free corner spaces M which are suitable for being formed into combustion
chambers by which the crucible can be subjected to a preliminary heating. By
means of such a preliminary heating the temperature of the material is already
raised to a high degree without the action of the electric arc, and the working
expenses are thus considerably reduced.
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. In an electrical furnace, constructing the acting surface of the upper electrode
of a conical or wedge shape, while the surface of the lower electrode is made of a
hollow conical or funnel shape, for the purpose of producing an automatic down-
ward feed of the material acted upon, substantially as described.
2. In an electrical furnace such as is referred to in the first claim, providing the
cylindrical part of the upper electrode with flange-like projections W; for the
purpose of loosening the material by the regulating motion of the upper electrode,
in order to counteract the caking action, substantially as described.
3. In an electrical furnace such as is referred to in the first claim, surrounding
the cylindrical part of the upper electrode with a casing between which and the
electrode is left a sufficient space for allowing the free escape of the gases generated
by the electric arc, substantially as described.
4. In an electrical furnace such as is referred to in the first claim, forming the
material to be acted upon into lumps or briquettes for the purpose of providing
sufficient interstices between the material for the free escape of the gases,
substantially as described.
5. In an electrical furnace such as is referred to in the first claim, the provision
of a tapping device by forming a hole in the bottom of the funnel shaped surface
of the bottom electrode and providing at a suitable distance a laterally extending
closing piece substantially as described.
6. In an electrical furnace such as is referred to in the first claim, a periodically
operated lateral tapping device consisting in forming a lateral opening in the
funnel shaped surface of the lower electrode and providing opposite such opening
a boring tool for periodically boring a hole through the solidified material R
through which hole the fluid material F can be drawn off, substantially as
described.
7. In an electrical furnace such as is referred to in the first claim, utilising the
corner spaces at the side of and underneath the funnel shaped electrode as com-
bustion chambers for the preliminary heating of the crucible containing the
material, substantially as described.
Dated this 24th day of July 1007
ABEL & IMRAY,
Agents for the Applicant.