Improvements in Electric Heaters or Rheostats.
Year: 1895

page_text: This Print is in accordance with the Original Specification as it stands after
Amendment (under Section 11 of the Patents, &c. Act, 1883) as required by
the decision of the Comptroller General of the 10th day of March 1896.
Date of Application (in United Kingdom), 16th May, 1895
Complete Specification Left, 16th May, 1895-Accepted, 27th July, 1895
COMPLETE SPECIFICATION (AMENDED).
Improvements in Electric Heaters or Rheostats.
I, JAMES HENRY DELANY of 446 West 23rd Street in the City, County and
State of New York, in the United States of America Inventor, 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:
66
Heretofore in this class of devices it has been proposed to mold around the
heating or resistance conductors an insulating mass of plastic material that
subsequently sets" or is hardened by baking. Special means are required to
hold the conductors in proper relative position during the placement of the mass
around them, and difficulty is experienced in securing proper relative positions of
the conductors or separate sections of the same conductor, in the finished article.
A more serious objection to this class of such devices is due to the different
degrees of expansion and contraction of the conductors and the inclosing mass, and
the liability of the mass, when baked, to crack or check, there being a tendency to
cleavage in the planes in which the conductors lie. Where the mass is not baked
but is of a character to "set' under ordinary atmospheric conditions, it lacks the
requisite hardness and stability and is liable to granulation or disintegration
because of variations of atmospheric conditions or changes of temperature due to
the heating and cooling of the conductors. In these ways the integrity of position
and insulation of the conductors or sections of conductors, are impaired and the
usefulness of the apparatus deteriorated. It has also been proposed as in the
Carpenter enamel rheostat and heater to attach the heating or resistance conductors
to a metal base or support by enamel or vitreous material applied as a wash or
powder that is hardened by firing. The usual process is to first coat the metal base
The
with a layer of such enamel or vitreous material and harden it by firing.
:

page_text: conductors are then placed upon such coating, a layer of powdered or liquid enamel
dusted or washed over them and then fired, several such layers being applied and
each separately fired. Such devices so made have gone into use to some extent,
but they are expensive and possess certain objectionable features not incident to my
improved devices.
.
resistance conductors are united
or
In carrying my invention into effect I employ a base or support of china,
porcelain, terra-cotta, tiling, or such like earthy or vitreous material molded in
manufacturing to which the heating or
attached by vitreous enamel, making a homogeneous mass under heat. The material-
of which the base is composed is in its process of manufacture fired at relatively
high temperatures, and may of course be molded into such form as is required.
The vitreous enamel which is an article well known in the art and familiar to
those skilled in the art of what is known as enamel rheostats is also fired at a
relatively high temperature, say from 1,500° to 2,000°, when applied to the base
to attach and cover the wires. The enamel and the base of the character
described have practically the same co-efficient of expansion. That is to say, the
grade of enamel employed may be selected with reference to the known expansive
qualities of the base, so that the co-efficient of expansion of the enamel and base
shall be the same or substantially the same; and shall be so nearly the same that
there is no disruption of the enamel or base when the article is raised to high
temperatures either in use or during the course of its manufacture. The base and
enamel have more or less elasticity that compensates for any difference, if such
there be, between the co-efficients of expansion of the conductor and enamel and
base. When the enamal is applied to the base either in the form of a dust or
wash and fired a most perfect junction between the two is secured. One or more
coats of enamel may be applied to attach the conductors or semi-conductors to the
base and as each coat is relatively thin any difference in expansion between the
base, conductor and enamel will not cause impairment of the enamel coating in
firing, and by successive coats and firings a layer of solid enamel of the desired
thickness may be obtained.
Among the advantages incident to the use of an insulating base and enamel as
above described in carrying my invention into effect, the following may be, men-
tioned:
First. The insulating base or support may be molded in any desired shape and
may be formed with projections around which the heating or resistance conductors
may be arranged; or with recesses or apertures within which the conductors may
be placed, the enamel being then applied as indicated. Whether the base or
support be so shaped or has a plane surface to which the conductors are secured, no
preliminary surfacing with enamel or insulating material is required, as is necessary
where a conducting base is used, that is to say the bare conductors may be placed
directly in position and the enamel coating applied, and as before mentioned the
enamel and base unite more intimately and securely than where the base
is of metal.
Second. There is no chance for the grounding or short circuiting of the
conductors through the base, and inductive action that would occur if the base
were a mass of metal is eliminated.
Third. Since the base is of non-conducting material there is no chance for the
breaking down of the insulation between the base and conductor as might occur
from disruptive discharge or from the use of currents of high intensity or frequency
when the base is of metal.
Fourth. The base is a poor conductor of heat and hence will act as a reflector of
heat and tend to concentrate it at points desired according to the arrangement of
the conductors upon the surface of the base. This feature is more especially
advantageous in the case of heating and cooking devices.
Fifth. Since the base is of insulating material no special provision against the
grounding of terminal contacts of the conductors need be employed, and after,
firing, such terminals may be readily finished in an acid bath a mode of finishing"

page_text: Tauny
the acid will attack the base, and the use of copper or similar metal as a base
would be too expensive.
T
Sixth. Owing to the material of which my devices are constructed, they may
be used in acids or in the presence of gases that would have a destructive effect
on a metal base.
Seventh. Since in my apparatus, there is no liability of the insulation breaking
down or the conductors being grounded through the base, the fire risk is greatly
reduced.
Having thus described the general characteristics of apparatus employed in carrying
my invention into effect I will now refer to a number of specific forms in which the
invention may be embodied, some of which have specific features of novelty in
construction and arrangement.
In the accompanying drawings,
Figures 1 and 2 are respectively detail views in section illustrating a small portion
of apparatus constructed in accordance with my invention.
Figure 3 is a plan view of a starting rheostat showing ordinary circuit connections
and indicating the motor.
Figure 4 is a cross-section of Figure 3.
In all the figures the non-conducting base of the character described is indicated
by the letter X. The enamel or vitreous coating is indicated by Y, and Z indicates
the conductor.
In Figure 1 the plate or base is beveled, being thinnest at one edge, the purpose
being to obtain a more equal distribution of heat. The conductors Z are shown as
of different cross-sectional area, and are designed to carry currents of different
strength or quantity, and the mass or thickness of the plate at any particular point,
is intended to be in proportion to the relative amount of current which the
conductor Z there situated is to carry.
Figure 2 shows a precisely similar construction, except that the exterior face of
the plate is ribbed or corrugated, the ribs being located opposite the respective
conductors.
Figure 3 indicates a familiar arrangement of conductors used as a variable
resistance or starting box, P being the terminals that may be swept by the switch
arm of the device. M indicates.the electric motor.
Such constructions as are indicated in Figs. 1 and 2 are intended more especially
as heaters, although they may of course be used as rheostats.
In all of the illustrations the mass or thickness of the enamel is perhaps greater
than is desirable, but this is a point that may be varied at pleasure.
In such constructions as are shown in Figures 1 and 2, the heating or resistance
conductors may be located at or slightly below the surface of the enamel coating and
the base being relatively a non-conductor of heat, the heat will be concentrated upon
or at the enamel surface, a feature that is especially desirable in devices for heating
and cooking.
In my improved device as before stated the base used is of a vitreous earthy
character, and is capable of withstanding very high temperatures. The enamel is of a
similar character and the two being united at a high temperature an intimate union is
effected; and since the co-efficient of expansion of the two is substantially the same
and may be approximately that of the heating or resistance conductor, the heater
or rheostat may be raised to relatively high temperatures without injuring it, or in
any way affecting its integrity.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
An electric beater or rheostat consisting of a base or support of varying thickness,
heating or resistance conductors of different cross-sectional area, and a layer or
namal unitiam the have and condratore and intimately united therewith

page_text: the conductors of greatest cross-section being placed on or opposite that portion of
the base of greatest thickness or mass..
Dated this 16th day of Mor 1805
HARRIS & MILLS,
23 Southampton Buildings, London, W.C., Agents.