Improvements in Insulating and Supporting Electric Wires intended to Act as Resistances, applicable as Radiators of Heat for Cooking, Warming, and other Purposes.
Year: 1892

page_text: Date of Application, 24th Sept., 1892
Complete Specification Left, 24th July, 1893-Accepted, 9th Sept., 1893
PROVISIONAL SPECIFICATION.
Improvements in Insulating and Supporting Electric Wires intended
to Act as Resistances, applicable as Radiators of Heat for
Cooking, Warming, and other Purposes.
We ROOKES EVELYN BELL CROMPTON Engineer, and HERBERT JOHN
DOWSING, Engineer, both of Mansion House Buildings, in the City of London,
do hereby declare the nature of this invention to be as follows:-
Our improvements consist of various methods of coating metallic surfaces with
enamel and afterwards attaching to this enamel electric conductors which are
intended to be raised by the passage of electric current to high temperatures, in
order that the metallic plates may serve as radiators of heat for electric cooking,
electric warming and similar purposes.
We are aware that the use of enamelled wires has been proposed, and that it was
proposed to use enamelled wire or foil for heating water or other liquids. The use
of wire attached by enamel to a supporting plate has also been described in which
the use of enamel as a means of attaching the conductor to be heated to a supporting
plate was mentioned but no hint is given as to the means to be adopted to ensure a
sufficiently perfect continuity of the insulating enamel to prevent short circuits
Occurring between the various parts of the conductor itself or between the conductor
and the inetallic support.
In our improvements we prefer to first coat the metallic support with a layer of
enamel or glass the heat coefficient of expansion of which approaches as nearly as
possible to that of the metal backing. This first coating we call the supporting
enamel, the materials of which it is composed should be such that it will soften and
fuse sufficiently to run into a continuous surface between the temperatures of 1300
and 1600 Fahr. We carry this out by heating the metallic support covered with a
thin layer of the enamel powder in a properly arranged muffle furnace and at the
point when the flowing of the enamel is complete we remove the metallic plate from
the furnace and sprinkle over the surface of the still liquid supporting enamel, a
We return the support to
thin layer of enamel powder of a more fusible nature.
the furnace and as soon as this second layer begins to fuse and run we place upon it
and press into it the wire or strip conductor required to be attached and enamelled
to the support. We sift over this conductor a third layer of the second or more
fusible quality of enamel and heat the whole until the last layer fuses down to a
sufficiently even surface.
By this method of using two qualities of enamel of different fusibility we ensure
that our conducting wire does not sink through and come in contact with the
metallic support. We also find that it is a convenience to apply the metallic
conductor at the point when the second layer has just fused as at this point it is
viscous and serves to hold the wire, which as it often requires to be made into
wavy, zigzag or other complicated forms, is somewhat difficult to keep in its place.
We shall hereafter find it convenient to call the three successive applications of the
We can use as
enamel the supporting, the attaching and the covering enamels.
supporting enamel a powder, each 100 parts by weight of which contains approxi-
In cases where
mately 52 parts of felspar, 34 parts borax, 14 parts China clay.
the metal plate to which the enamel is to be applied is nearly flat an enamel made
of the above ingredients previously fused together and ground fine can be sifted on
in the form of a powder sufficiently even in thickness for the purpose but in other
cases where curved surfaces have to be coated it is necessary to form an enamel of
approximately the same ingredient into a paste. To do this we proceed in the
following manner.

page_text: We take approximately of the felspar and fuse it with the borax, afterwards
grind it to a fine powder and then mix it into a paste with water adding the
remainder of the felspar and the China clay and two parts of magnesia carbonate.
This paste may be plastered or painted on to the surface to be coated and if
properly dried will adhere to it sufficiently firmly to allow the plate to be moved,
tilted or even revolved in the furnace and so will allow the whole of the surface to
be coated with the liquid supporting enamel previous to the application of the other
two coats.
This latter process will be found particularly useful in attaching by enamel
resistance coils in the form of spirals or helices of wire to the inner or outer
surfaces of tubes or cones through or over which water or other liquids which are
to be heated must circulate. For the purposes of the two coats of enamel to be
last applied we may use a powder enamel of more fusible character consisting in
each 100 parts of weight 30 parts of quartz, 20 parts borax, 34 parts stannic oxide,
9 parts soda carbonate, 7 parts potash nitrate. We mention this as one of the
fusible glasses or enamels which may be used for attaching the wire and which will
soften and run into the supporting enamel at a temperature when the latter remains
sufficiently viscous to prevent the wire conductor from sinking sufficiently so as to
touch and come into electric contact with the supporting plate.
In cases where the enamelled surface is intended to be in direct contact with the
liquids to be heated it is advisable not to use borax enamel for the attaching or for
the outer layers as it is found in practice that such enamels are slowly acted on by
the heated liquids and for these cases it is better to employ metallic oxides the
addition of which reduces the temperature at which the enamel begins to flow.
The above mentioned enamels will be found very suitable for use with iron plates
as supports but if in cases where we find it convenient to use copper or bronze
alloys as the supporting plate, we sometimes use both in the supporting, attaching
and covering enamels a considerable portion of Thuringian glass to which can be
added stannic or other metallic oxides sufficient to reduce the temperature at which
the two outer layers fuse. In some cases we add lead oxides to the two last
enamels.
We find that by following this mode of procedure of adding enamel powder of
different fusibilities in three successive layers the wire to be enamelled and attached
being pressed into the second layer we ensure that the wire will be surrounded with
evamel in a more perfect manner and better insulated from the supporting plate 3
than has been the case in the past when the plate has been first enamelled and the
wire applied and afterwards allowed to coat itself, as by the latter mode of pro-
cedure there is a liability to pin holes existing in the outer coat so that when the
apparatus is used as a means of heating liquids the insulation being imperfect at
these pinholes allows electrolytic action to take place and the wire may be speedily
eaten through.
Dated the 64th
a
WM. BROOKES & SON,
55 & 56, Chancery Lane, London, Agents for the Applicants.
SPECIFICATION.
COMPLETE
Improvements in Insulating and Supporting Electric Wires intended
to Act as Resistances, applicable as Radiators of Heat for
Cooking, Warming, and other Purposes.
We ROOKES EVELYN BELL CROMPTON Engineer and HERBERT JOHN
DowSING Engineer both of Mansion House Buildings in the City of London,
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 :—
Our improvements consist of various metho:ls of coating metallic surfaces with

page_text: heating water or other liquias. The use of wire attached by enamel to a supporting
plate has also been described in which the use of enamel as a means of attaching
the conductor to be heated to a supporting plate was mentioned but no hint or
information is given as to the means to be adopted to ensure a sufficiently perfect
continuity of the insulating enamel to prevent short circuits occurring between the
various parts of the conductor itself or between the conductor and the metallic
support.
Fig. 1 shews a vertical sectional view of a portion of a flat radiator plate
complete.
Fig. 2 is a diagramatic plan shewing the course the wires may be made to take ;
in this case 4 separate parallel resistances are shewn although any convenient
number may be used.
Fig. 3 shews in section the rigid support a with the supporting coat of enamel a¹
applied.
Fig. 4 shews the same as the last figure but with the second or fixing coat a²
applied.
16 are
Fig. 5 shews the same as the previous figure but with the wire affixed.
Fig. 6 shews how a resistance made as set forth may be applied around
a column or cylinder a being the cylindrical radiator and supporting fixing
and insulating layers whilst b is the spirally arranged resistance. The
middle portion of the column is broken away to economise space.
terminals. In our improvements we prefer to first coat the metallic or other rigid
support a with a layer a¹ of enamel or glass the heat coefficient of expansion of
which approaches as nearly as possible to that of the metal or other backing.
This first coating a' we call the supporting enamel the materials of which it is
composed should be such that it will soften and fuse sufficiently to run into a
continuous surface between the temperatures of 1300 and 1600 Fahr.
We carry
this out by heating the metallic support a covered with a thin layer of the enamel
powder in a properly arranged muffle furnace and at the point when the flowing of
the enamel is complete we remove the metallic plate from the furnace and sprinkle
over the surface of the still liquid supporting enamel, a thin layer of enamel powder
of a more fusible nature. We return the support a to the furnace and as soon as
this second layer a² begins to fuse and run we place upon it and press into it the
wire or strip conductor b required to be attached and enamelled to the support.
We sift over this conductor a third layer a³ of the second or more fusible quality
of enamel and heat the whole until the last layer fuses down to a sufficiently even
surface. By this method of using two qualities of enamel of different fusibility we
ensure that our conducting wire does not sink through and come in contact with
this metallic support.
We also find that it is a convenience to apply the metallic
conductor at the point when the second layer has just fused as at this point it is
viscous and serves to hold the wire, which as it often requires to be made into wavy
zigzag or other complicated forms, is somewhat difficult to keep in its place. We
shall hereafter find it convenient to call the three successive applications of the
enamel, the supporting, the attaching and the covering enamels. We can use as
supporting enamel a powder, each 100 parts by weight of which contains
approximately 52 parts of felspar, 34 parts borax, 14 parts China clay.
In cases where the metal plate to which the enamel is to be applied is nearly
flat an enamel made of the above ingredients previously fused together and ground
fine can be sifted on in the form of a powder sufficiently even in thickness for the
purpose but in other cases where curved surfaces have to be coated it is
necessary to form an enamel of approximately the same ingredients into a
paste. To do this we proceed in the following manner.
We take approximately

page_text: of the felspar and fuse it with the borax, afterwards grind it to a fine
powder and then mix it into a fine paste with water adding the remainder
of the felspar and the China clay and two parts of magnesia carbonate.
This paste may be plastered or painted on to the surface to be coated and if
properly dried will adhere to it sufficiently firmly to allow the plate to be moved,
tilted or even revolved in the furnace and so will allow the whole of the surface to
be coated with the liquid supporting enamel previous to the application of the
other two coats. This latter process will be found particularly useful in attaching
by enamel resistance coils in the form of spirals or helices of wire to the inner or
outer surfaces of tubes or cones through or over which water or other liquids
which are to be heated must circulate. For the purposes of the two coats of
enamel to be last applied we may use a powder enamel of more fusible character
consisting in each 100 parts of weight 30 parts of quartz, 20 parts borax, 34 parts
stannic oxide, 9 parts soda carbonate, 7 parts potash nitrate. We mention this as
one of the fusible glasses or enamels which may be used for attaching the wire and
which will soften and run into the supporting enamel at a temperature when the
latter remains sufficiently viscous to prevent the wire conductor from sinking
sufficiently so as to touch and come into electric contact with the supporting plate.
In cases where the enamelled surface is intended to be in direct contact with the
liquids to be heated it is advisable not to use borax enamel for the attaching or
for the outer layers as it is found in practice that such enamels are slowly acted on
by the heated liquids and for these cases it is better to employ metallic oxides the
addition of which reduces the temperature at which the enamel begins to flow.
The above mentioned enamels will be found very suitable for use with iron plates
as supports but if in cases where we find it convenient to use copper or bronze
alloys as the supporting plate we sometimes use both in the supporting attaching
and covering enamels a considerable proportion of Thuringian glass to which can
be added stannic or other metallic oxides sufficient to reduce the temperature at
which the two outer layers fuse. In some cases we add lead oxides to the two last
enamels. We find that by following this mode of procedure of adding enamel
powder of different fusibilities in three successive layers the wire to be enamelled
and attached being pressed into the second layer we ensure that the wire will be
surrounded with enamel in a more perfect manner and better insulated from the
supporting plate than has been the case in the past when the plate has been first
enamelled and the wire applied and afterwards allowed to coat itself, as by the
latter mode of procedure there is a liability to pin holes existing in the outer coat
so that when the apparatus is used as a means of heating liquids the insulation
being imperfect at these pin holes, allows electrolytic action to take place and the
wire may be speedily eaten through.
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. The herein before described method of and means for supporting fixing or
attaching and covering wires intended to act as electrical resistances applicable as
conductors or radiators of heat for cooking warming and other purposes substantially
as set forth.
2. An electrical resistance supported fixed and insulated substantially as and for
the purposes herein before set forth.
Dated the 22nd do I.1 1000
WM. BROOKES & SON,
55 & 56, Chancery Lane, London, Agents for the Applicants.