Improvements in Electric Furnaces.
Year: 1888

page_text: Improvements in Electric Furnaces.
I, JOHN COVERT HOBBS, of No. 183 Church Street, Lockport, New York, United
States of America, Electrician, do hereby declare the nature of this invention, and
in what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement:-
My invention relates to improvements in Electric Furnaces, and consists in the
use of sawdust as a lining for the furnace in lieu of carbon or charcoal as heretofore
employed for this purpose.
In what is known as the Cowlee-process of making aluminum it is necessary to
confine the charge within a lining or envelope that offers a higher resistance to the
electric current than the charge itself, and at the same time also a high resistance
to the passage of heat to the walls of the furnace, thereby protecting the walls and
confining the heat as much as possible to the charge. The more perfect this insulating
jacket, the better this result, and any improvement in this direction is valuable to
the art.
In the process aforesaid as now practiced the lining employed is carbon or finely
comminuted charcoal soaked in lime water. Originally the carbon or charcoal alone
was used, but experience taught that the addition to the charcoal of water impreg-
nated with lime considerably increased the resistance of the coal to the flow of the
electrical current as well as to the heat. The composition thus prepared was placed
around the charge in the furnace say about two and a half inches thick at the side
and ten inches at the ends.
I dispense with the charcoal and lime and use nothing but common sawdust. The
advantages of this discovery are material and valuable. In the first place there is a
great difference in initial cost of material. A ton of charcoal ground and mixed costs
seventeen dollars. Assuming that we make twenty runs in twenty four hours with
one hundred pounds weight to each run, we should consume 2,000 pounds of charcoal
in a day.
On the other hand one ton of saw dust will last two days, make forty runs, and
costs only $1.50 per ton. The saving is enormous when taken into account with a
number of furnaces running continuously.

page_text: Other advantages gained by the use of sawdust are;
First, Cleanliness. The charcoal after being subjected to the intense heat of the
furnace becomes an impalpable powder, filling the works and making it disagreeable
for every one around the works. This objection is wholly avoided by the use of
sawdust.
Second, The scarcity of charcoal. The difficulty of getting charcoal in sufficient
quantity and of suitable quality is a serious objection and drawback to its use, and its
cost adds materially to the cost of the products of the furnace.
Third, The sawdust bakes itself into a solid body at the bottom of the furnace
within an hour after the furnace is started. This is a great advantage because it
enables the tapping of the furnace from the bottom without danger of clogging, as
is the case with charcoal. Attempts have been made to tap in this way when char-
coal was used, but they had to be abandoned on account of clogging as. stated.
Hence to get the metal out of the furnace after the run was made, it was necessary
to allow the whole interior of the furnace time to cool off so that the metal became
solidified and could be handled with tongs. The consequence was that all this raw
material taken out of the furnace after each charge had to be re-melted in crucibles
in order to get it into marketable shape. This involved a great expense in labor,
cost of coke, and crucibles and the like, all of which is saved by the use of sawdust.
Referring to the drawings, Fig. 1 is a transverse section, and Fig. 2 a horizontal
section of an electric furnace in which my invention is embodied.
A represents the charge in the furnace. B are the electrodes at the ends of the
charge, and C the lining or envelope of sawdust which surrounds the charge. Of
course wood cut into fine particles in any other way than as sawdust would answer
the same purpose.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed, 1 declare that what I claim is :-
1. In an electric furnace, a lining for the walls thereof consisting of sawdust,
substantially as set forth.
2. In an electric furnace in which the current passes through the charge, an
envelope or covering for the charge consisting of wood cut into small particles, as
sawdust, or the like, substantially as set forth.
In testimony whereof I hereunto set my hand this 11th day of July A.D. 1888.