Improvements in Electric Heaters or Rheostats.
Year: 1897

page_text: Date of Application, 14th Dec., 1897-Accepted, 28th May, 1898
COMPLETE SPECIFICATION.
Improvements in Electric Heaters or Rheostats.
I, FRANK KRAEMER, of 80, Diversey Place, in the City of Chicago, State of
Illinois, United States of America, Electrician, do hereby declare the nature of
my invention and in what manner the same is to be performed, to be particu-
larly described and ascertained in and by the following statement:
My invention relates to a novel construction in a rheostat or electric heater,
the object being to provide a device of this character comprising carbon sticks
embedded in a plastic material of a composition which has practically the same
coefficients of expansion and contraction as the carbons, thus preventing fracture
of the carbons by unequal strains, and consists in the features of construction
and combinations of parts hereinafter fully described and claimed.
In the accompanying drawings illustrating my invention:
Figure 1 is a horizontal section of a rheostat or heater constructed in accord-
ance with my invention, taken on the line 1-1 of Fig. 3 and showing said
rheostat connected with a face plate or switch board of suitable construction.
Fig. 2 is a transverse section on the line 2-2 of Fig. 1. Fig. 3 is a longitudinal
section on the line 3-3 of Fig. 1.
Referring now to said drawings, A indicates a metal casing or frame which is
covered at its ends with wire cloth or gauze B, between which said frame A is
filled with a plastic material D in which the carbons C are completely embedded.
Said, carbons C are composed of sticks of very high resistance and which con-
sequently are very fragile and need to be strongly reinforced. To this end the
frame A is first partially filled with plastic material and the carbon sticks C then
embedded in the same. The said carbons C are then connected with the bind-
ing posts E, which are in and insulated from the frame A in the ordinary manner,
by means of wires passing through perforations in the ends of said carbons and
clasped thereon by means of metal clasps. After these connections have been
made the casing A is filled to the level of its upper end with the plastic material
which is pressed down so as to completely surround said carbons and is then
covered by the wire gauze B, thus forming a compact mass which is not liable
to fracture.
In constructing the said rheostats or heaters it is indispensable that the plastic
material employed should have practically the same coefficient of expansion and
contraction, under varying degrees of temperature, as said carbons, and that the
coefficients of expansion and contraction of the carbons, plastic material and iron
casing, shall be so related to each other that neither of them shall exert sufficient
compression, pressure or tensile strain upon the others to fracture any part. It
will be obvious that if the coefficient of expansion and contraction of the plastic
material, under varying degrees of temperature, is greater than that of either the
carbons or the metal casing, the latter would be in constant danger of fracture,
particularly the carbons, while, on the contrary, if it were less the
carbon would either burst the plastic material or be fractured by the
pressure thereon, while the metal casing would fracture the outer portions
P
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page_text: of the plastic material. To find a plastic material, therefore, having the pro-
perties conforming to the above requirements involved long and tedious experi-
ments, but I have now found that a plastic material made from the following
ingredients, answers the purpose, that is, a plastic material composed of baryte
10 parts and silicic acid 1 part by weight. The baryte used is the kind employed in
the manufacture of porcelain.
Another plastic material, which also fulfills the requirements, is composed of
the following ingredients; pulverized granite 6 parts and pebbles 2 parts, mixed
with lime 1 part, silicic acid 1 part and dextrine 1 part, all by weight.
The ingredients are mixed while hot to form stiff plastic mass, in which the
carbons are immediately embedded. It is then allowed to dry and becomes as
hard as stone. The proportions are approximate and may be slightly varied. When
utilized as a rheostat my device is connected with a face plate or switch board F
in such a manner that when the arm is turned in the direction of the arrow to
the first button all the carbons will be thrown into circuit and at every succeeding
button one of said carbons will be thrown out of the circuit until the last of said
buttons is reached when the entire number of carbons is out of the circuit. It
will be obvious that any number of carbons can be used.
When utilized as a heater my device is preferably constructed in such a manner
that a large radiating surface is secured and to this end I prefer to embed the
carbons individually in tubes, though I have not show this construction.
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. In an electric rheostat or heater, solid carbon sticks of a high resistance
completely embedded in a plastic material having a coefficient of expansion and
contraction, under varying degrees of temperature, coinciding with the coefficient
of expansion and contraction of said carbon sticks to a degree which will prevent
a sufficient amount of compression, pressure and tensile strain to fracture any
portion of the mass, substantially as described.
2. In an electric rheostat or heater, solid carbon sticks of a high resistance
completely embedded in a plastic material having a coefficient of expansion and
contraction, under varying degrees of temperature, coinciding with the coefficient
of expansion and contraction of said carbon sticks to a degree which will prevent
a sufficient amount of compression, pressure and tensile strain to fracture any
portion of the mass, and a metal casing around said plastic material, substan-
tially as described.
3. In an electric rheostat or heater, solid carbon sticks embedded in a plastic
material contained in a metal casing, said carbons, plastic material and metal
casing having coefficients of expansion and contraction, under varying degrees
of temperature, so related to each other that no compression, pressure or tensile
strain sufficient to fracture any portion of the device will result; substantially as
described.
4. A rheostat or electric heater comprising a metal casing filled with plastic
material having one or more solid carbon resistance sticks embedded therein, sub-
stantially as described.
FRANK KRAEMER.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.