Improvements in and Relating to Electric Furnaces.
Year: 1898

page_text: Date of Application, 9th May, 1898-Accepted, 18th June, 1898
COMPLETE SPECIFICATION.
Improvements in and Relating to Electric Furnaces.
I, THOMAS JACKSON, of 23, Hargreaves Street, Burnley, in the County of Lancaster,
Dental Surgeon, 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 has reference more particularly to that class of electric furnaces,
which are used by dentists for the manufacture of artificial teeth, and for the process
of continuous gum work, but my invention is also applicable to electric furnaces used
for other purposes.
According to my present invention, I construct the furnace with an inner fixed
shell, composed of a compound of fireclay or other analogous substance or substances
capable of withstanding extreme heat, and being electrically non-conducting. The
top, bottom, sides and back of this inner fixed shell are wound with separate and
independent coils of fine platinum wire, which are preferably embedded therein.
These walls of the inner shell of the furnace are so jointed together, that in case one
of them should crack or break by the excessive heat another may be substituted in
its place, without having to replace a complete shell.
An essential feature of my invention consists in bringing into action, any one, two,
three, or more of the coils as may be desired, or according to the heat required. By
this means, I am enabled to vary the heat or intensity of the furnace to any required
degree without introducing to the circuit a rheostat or like device for varying or
determining the resistance and consequently the strength of the current.
This novel feature of my invention consists in connecting the ends of the coils to a
series of brass blocks at desired distances apart, and shaped for the reception of small
metal plugs. A small plate connects the blocks at each end with the terminals com-
municating the supply of electricity. When all the plugs are inserted in the
intervening spaces between the blocks, the current passes over them, and refuses to
traverse the highly resisting medium of the coils, which is a well known and funda-
mental principle of this natural agency, but in case any of the plugs are withdrawn,
the current is compelled to choose as its path the coil connected to the blocks freed
from such plug and consequently that portion of the inner shell of the furnace, which
is encircled by such coil or coils becomes heated by the current. In this way, the
top, bottom, sides and back portions of the inner shell may be heated either altogether
or separately and independently of each other.
My invention also consists of a new and improved construction of the outer case of
the furnace, arranged so that the top and sides can be removed to expose the coils, so
that in case of damage by fusion or mechanical injury, the parts are so exposed as
to facilitate repairs. The connections and inner parts can thus be inspected, or can be
taken out and repaired, and any part renewed or duplicated as need he.
My invention will be fully understood by reference to the accompanying sheet of
drawings, in which

page_text: Fig. 2 a side elevation, and Fig. 3 a sectional elevation of an electric furnace con-
structed in. accordance with my invention.
Referring to Fig. 3, the furnace is provided with an inner shell A composed of a
compound of fireclay, round the five sides of which, and embedded therein are wound
five separate and distinct coils of fine platinum wire. The ends of these coils are
connected to the brass blocks B, as shewn, having intervening spaces such as C formed
between them, to allow of the insertion of plugs F, G, H and J. Small brass
strip D at each end communicates the terminals E with the blocks B. The top of the
outer case of the furnace is constructed of slate or other non-conducting material.
Assuming that the current is on, it is obvious that as the furnace is arranged in
Fig. 3, the current will traverse the good conducting medium of the brass blocks B
and the plugs F, G, H and J, until it reaches the intervening space C, when it
traverses the coil K, encircling the back of the inner shell of the furnace, raising it to
incandescence. This coil K is shewn disconnected from the back of the inner shell to
prevent confusion, but it is coiled round the same exactly and in a similar manner
to the other coils.
By the removal or insertion of any one, or more, or all of the metal plugs, F, G, H
and J; any one, or more, or all of the respective fine platinum coils forming the circuit,
and completing the path of the current are brought into effective use, thereby heating
any one, or more, or all of the top, bottom, sides or back of the inner, shell of, the
furnace.
My improved means or method of governing the furnace may be applied to other
electric furnaces than that above described, where it is required to bring respective
parts of the heating medium into use or otherwise, and either singly or together..
The top. and side plates constituting the outer case of the furnace are so constructed
that they may be readily removed to facilitate repairs. This feature of my invention
will be at once recognized by reference to Fig. 2 of the accompanying drawings,
wherein the side plates L forming part of the outer case of the furnace are detachably
secured together by screws M. The top plates N and O of the furnace are similarly
fastened by screws.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is :--
1. The improved arrangement and construction of an electric furnace, substantially
as described and illustrated in the accompanying drawings.
2. In an electric furnace, the combination with blocks B and plugs F, G, H
and J, of fine platinum coils encircling the respective parts of an inner shell A,
composed of a compound of fireclay or like material, so that any particular part or the
whole inner shell may be brought into requisition, substantially as described, and
illustrated in Fig. 3.
3. In an electric furnace, the improved means or method of governing the furnace
as described in combination with respective parts of the heating medium, so that any
particular part or the whole may be heated either separately or simultaneously,
substantially as described and illustrated.
Dated this 4th day of May 1808
RICHMOND & Co.,
Agents for the Applicant, 12, Standish Street, Burnley.