Improvements in Electric Arc Furnaces.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
Improvements in Electric Arc Furnaces.
We, PERCY CRUNDALL DAY, of 63, Queen Victoria Street, in the City of London,
Engineer, and THE ACETYLENE ILLUMINATING COMPANY LIMITED, of 63, Queen
Victoria Street, aforesaid, do hereby declare the nature of this invention to be as
follows:
The invention relates to electric are furnaces used for smelting refractory
materials in which there is an evolution of inflammable gases.
In the manufacture of calcium carbide, powdered coke and lime are mixed
together and fed into a crucible in which a carbon electrode is suspended. A
contact is first made between the carbon electrode and the bottom of the crucible,
and after an electric arc has been struck the material is fed into the space between
the electrode and the crucible walls.
Some of the raw material at once falls under the influence of the arc and an
ingot of calcium carbide begins to form beneath the carbon electrode, at the
bottom of the crucible.
Simultaneously with the production of carbide a large volume of carbon monoxide
gas is liberated, and this evolution continues so long as the process goes on.
Ordinarily the hot gas is allowed to rise through the powdered raw material and
escapes from the top of the crucible near the carbon. electrode; and on meeting
the air outside, it ignites and burns with an intensely hot flame.
The injurious effects on the efficient and economical working of the furnace
are:
1. That the powdered coke and lime mixture is partly blown out and a hollow
is formed round the carbon electrode, exposing it to the air.
2. That the carbon electrode is rapidly consumed where exposed, owing to the
action of the burning gas, and air, and
3. That the carbon holder, usually of iron, is rapidly destroyed by the intense
heat, both from the consuming gases and carbon and from exposure of the arc
due to the gases blowing through.
Now the chief object of our invention is to avoid these injurious effects.
According to our invention we provide vent holes in the ends of the crucible,
through which the gases are drawn off at the level of the arc, or nearly so. It
is found that by the provision of these vent holes the consumption of electrode
carbon and the wear and tear of the carbon holders are greatly reduced.
We also provide means whereby the level of the top of the crucible ends can
be kept near that of the carbon holder, so that the pulverized mixture may be
kept just below the carbon holder, but covering the carbons, and can be packed
down from time to time by the attendant with a wooden pole. This object can
be effected by fitting each crucible end with a door or preferably with two or
more doors arranged one above another so that as the ingot increases in height
and the carbon electrode is raised the height of the crucible ends can be raised

page_text: from time to time by closing one of the doors at each end. The doors as well as
the lower part of the crucible will be formed with the blow holes above described.
Dated this 20th day of June 1898.
J. C. MEWBURN & ELLIS,
55 and 56, Chancery Lane, London,
Chartered Patent Agents.
COLE BICCAICT urnaces.
We, PERCY CRUNDALL DAY, of 63, Queen Victoria Street, in the City of London,
Engineer, and THE ACETYLENE ILLUMINATING COMPANY LIMITED, of 63, Queen
Victoria Street, aforesaid, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and aseer-
tained in and by the following statement;-
The invention relates to electric arc furnaces used for smelting refractory
materials in which there is an evolution of inflammable gases.
In the manufacture of calcium carbide, powdered coke and lime are mixed
together and fed into a crucible in which a carbon electrode is suspended. A
contact is first made between the carbon electrode and the bottom of the crucible,
and after an electric arc has been struck the material is fed into the space between
the electrode and the crucible walls.
Some of the raw material at once falls under the influence of the arc and an
ingot of calcium carbide begins to form beneath the carbon electrode, at the
bottom of the crucible.
Simultaneously with the production of carbide a large volume of carbon monoxide
gas is liberated, and this evolution continues so long as the process goes on.
Ordinarily the hot gas is allowed to rise through the powdered raw material and
escapes from the top of the crucible near the carbon electrode; and on meeting
the air outside, it ignites and burns with an intensely hot flame.
The injurious effects on the eflicient and economical working of the furnace
are:-
1. That the powdered coke and lime mixture is partly blown out and a hollow
is formed round the carbon electrode, exposing it to the air.
2. That the carbon electrode is rapidly consumed where exposed, owing to the
action of the burning gas, and air, and
3. That the carbon holder, usually of iron, is rapidly destroyed by the intense
heat, both from the consuming gases and carbon and from exposure of the arc
due to the gases blowing through.
Now the chief object of our invention is to avoid these injurious effects.
According to our invention we provide vent holes in the ends of the crucible,
through which the gases are drawn off at level of the arc, or nearly so.
is found that by the provision of these vent holes the consumption of electrode
It
carbon and the wear and tear of the carbon holders are greatly reduced.
We also provide means whereby the level of the top of the crucible ends can
be kept near that of the carbon holder, so that the pulverized mixture may be
kept just below the carbon holder, but covering the carbons, and can be packed
down from time to time by the attendant with a wooden pole. This object can
be effected by fitting each crucible end with a door, or preferably with two or
more doors arranged one above another so that as the ingot increases in height
and the carbon electrode is raised the height of the crucible ends can be raised
from time to time by closing one of the doors at each end. The doors as well as
the lower part of the crucible will be formed with the blow holes above described.

page_text: In the accompanying drawings which illustrate a furnace crucible made of
metal and constructed according to this invention,―
Figure 1 is an end elevation of the crucible, and
Figure 2 is a central vertical cross-section of the same; the upper electrode
holder, the upper electrode, and the ingot being shown in side elevation.
In these figures, A is the body of the crucible; it is shown here as being formed
in one piece with the crucible bottom A. B is the lower carbon electrode resting
upon the crucible bottom A. C is the upper carbon electrode held in a holder
which is carried by a rod E that is suspended by suitable means from an overhead
support (not shown) in such a manner as to allow of the upper electrode C being
moved up and down as required. is the raw material consisting of unreduced
lime and coke, and G is the ingot of calcium carbide in process of formation
between the two electrodes B and C. H, Hare two opposite sides or ends of the
crucible which is assumed to be of rectangular shape in cross section. They may
form part of the crucible body A and they are carried up to the full height of the
crucible as shown.
The other two sides or ends are constituted according to this invention by a
number of doors arranged one above the other. In the arrangement shown, the
said two sides are each constituted by six doors I¹ 12 13 14 1³ 1º, and J¹ J2 J³ J J³ J6
respectively. The lowermost doors I and J are conveniently made higher than
the remaining doors which are preferably made of one uniform height. The
doors to I are hinged in the vertical axis to one end of the side H of the
crucible, and they are adapted to be closed by means of latches & snapping into
catches formed on the corresponding, end of the side H. The doors to Jö
are hinged to the opposite end of the side H of the crucible and they are adapted
to be closed by means of latches snapping into catches formed on the corres
ponding end of the side H. In the figures the three uppermost doors I* I³ I
are shown swung wide open.
In each of the doors, preferably in the middle, as shown, there is formed a
vent hole having an upward and outward inclination. Into these vent holes
there may be inserted short spouts, or the sides of the vent holes K may be extended
upwardly and outwardly in the form of short spouts L, as shown, with the object
of preventing as far as possible the raw material from passing out with the
escaping gases through the vent holes. M indicates the electric arc formed between
the upper electrode C and the ingot G.
The mode of operation of this furnace crucible in the manufacture of calcium
carbide is as follows:-All the crucible doors being swung open with the exception
of the two bottom doors I and J which are closed, a suitable quantity of the raw
material consisting of powdered coke and lime mixed together, is fed on to
the lower electrode B, and the electric arc is struck. Then the raw material F is fed
into the space enclosed by the lower parts of the crucible sides H and H¹, and
the two closed bottom crucible doors I and J. By the action of the are an ingot
of calcium carbide & begins to form beneath the upper electrode C and the lower
electrode B. Simultaneously, a large volume of carbon monoxide gas is liberated,
and finds an easy way of escape through the vent holes K in the two bottom
doors IJ. As the ingot of calcium carbide increases in size, and the top level of
the raw material rises first, the doors 12 and J2 and then the next higher doors 13
and J and so on are closed, and the gas then escapes through the vent holes K
in those doors. By these means the level of the top of the crucible ends can be
kept near to the level of the carbon holder D, so that the raw material F can
be kept just below the carbon holder, and covering the carbon C. Also as the
loors are closed one by one as the ingot is being built up in the middle of the
crucible a large excess of raw material can be fed into the crucible so that the
ingot is always separated from the crucible walls by a considerable quantity of
anreduced raw material F which protects the latter from the intense heat of the
arc M and ingot G.

page_text: N are the passages by which the gases escape through the raw material to the
blow-holes R. These passages are first opened by the furnaceman, who inserts a
long iron rod through the hole from which he wishes to withdraw the gases, and
then gently withdraws it again, the operation being repeated until successsful.
As soon as the gases begin to blow, their heat cakes the raw material round the
passages N, so that they blow for some time if the passage falls in it is again
cleared with the iron rod. Two or more holes on the same side may be kept
blowing together, the lower ones becoming choked up as the ingot rises beyond
them. In this manner the gases are being always drawn off at about the level of
the arc, and as the powdered materials are not blown out by the gas pressure from
around the upper electrode the said materials will always be in close contact with
the said electrode whereby the efficiency of the action of the arc will be increased
and the wear and tear of the electrode and electrode holder will be greatly
diminished.
The crucible may be fixed in position, or it may be mounted on a trolley or the
like, as desired. It is preferably made of metal as shown, but it may also be made
wholly or partly of fire-brick, carbon, or other suitable material.
In such cases the vent holes K may be left at intervals in the walls as the
latter are built up.
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 an electric arc furnace, a crucible formed with vent holes in its sides or
ends approximately at the level of the electric arc for the escape of the gases
evolved, substantially as described and for the purposes specified.
2. In an electric arc furnace, a crucible formed with vent holes in its sides or
ends at different levels corresponding approximately to the different levels of the
electric arc in the operation of the furnace, substantially as described and for the
purposes specified.
3. In an electric arc furnace, a crucible having one or more of its sides or ends
constituted wholly or partly by one or more doors or removable segments arranged one
above another and each preferably provided with a vent hole, arranged and operat-
ing substantially as described and for the purposes specified.
4. In an electric are furnace, a crucible having two opposite sides or ends each
constituted wholly or partly by two or more doors or hinged segments each pro-
vided with an upwardly directed vent hole, constructed, arranged and operating
substantially as and for the purpose specified, with reference to the accompanying
drawings.
Dated this 20th day of March 1899
J. C. MEWBURN & ELLIS,
55 and 56, Chancery Lane, London,
Chartered Patent Agents.