Improvements in the Manufacture of Electrical Hot-plates and other Electrical Apparatus for Cooking and Heating Purposes.
Year: 1896

page_text: Date claimed for Patent under Sect, 103 of Act,
being date of first Foreign Application (in 8th Nov., 1895
New Zealand),
Date of Application (in United Kingdom), 4th Jan., 1896
Complete Specification Left, 31st Oct., 1896-Accepted, 5th Dec., 1896
New Zealand),
Date of Application (in United Kingdom), 4th Jan., 1896
Complete Specification Left, 31st Oct., 1896-Accepted, 5th Dec., 1896
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Electrical Hot-plates and other
Electrical Apparatus for Cooking and Heating Purposes.
I JOHN CHAMBERS of Mokopeka in the Provincial District of Hawke's Bay in the
Colony of New Zealand Sheep-Farmer do hereby declare the nature of this invention
to be as follows:-
My invention relates to the insulation and embedding of the electrical resistance-
wires used in electrical hot-plates and in other electrical apparatus for cooking and
heating purposes.
The insulating media ordinarily used for insulating and embedding electrica!
resistance-wires in hot-plates and other electrical apparatus used for cooking and
heating purposes are subject to the following disadvantages. A skilled artisan and
special appliances are required for the embedding and insulation of the resistance-
wires in the first instance and when they become worn out they must be replaced at
a manufactory and in the chipping away of the insulating and embedding material
(which is very hard) there is a risk of cracking the plates. Also the first cost of the
embedding is considerable.
Now the object of my invention is to simplify and facilitate the insulation and
embedding or the re-embedding of the said wires so that the work may be readily and
cheaply done by any person of ordinary intelligence.
For this purpose I use either plaster of Paris and water or a mixture of plaster of
Paris and pulverised fire-clay or a mixture of plaster of Paris and any other electrical
insulating medium or media (such as powdered asbestos or powdered pumice-stone)
which in admixture with plaster of Paris and water will form a sufficiently hard
cement which will stand the necessary heat without becoming so damaged thereby as
to allow the resistance-wires to become displaced by ordinary usage. Or (which I
much prefer and which I have found to answer all practical requirements) a mixture
of plaster of Paris oxide of iron and water.
In the plaster of Paris paste or in any one of the foregoing mixtures I embed the
resistance-wire or wires (where two are used) between the upper and under plates
constituting the hot-plate. The proportions which I have by experiment up to the
present date found to be suitable may be stated as two parts by volume of plaster of
Paris to one part of the other constituent or mixture of constituents these to be mixed
with sufficient water to form a moderately stiff paste. I first coat to a sufficient depth
with a dilution of the paste that part of the hot-plate which is formed with a rim and
therefore constitutes a kind of dish and on that part so coated I fix the wire or wires
in position by means of the said paste applied here and there which paste sets almost
immediately. By this means I render it possible to fix non-magnetic wires without
difficulty. Having thus fixed the wire or wires in position and soldered the terminals

page_text: to the ends thereof I pour the said paste into that part of the hot-plate until it is
filled up in a convex form to slightly above the rim thereof and while this is being done
I continually tap the plate to insure that the mixture shall thoroughly enclose the wire
or wires and also to cause any air bubbles that may be imprisoned by the falling paste
to rise to the surface. I then screw or bolt down the flat plate or cover and thus con-
solidate the said paste and press out the surplus thereof. I then dry the hot-plate
thus made by keeping it for several days in a hot oven and when the cement is
perfectly dry I connect the terminals of the resistance-wires to a source of electricity
at the required voltage and when the plate is at its maximum temperature and there-
fore all or nearly all the air is expelled from the cement I scal up the exposed parts or
junctions in one or other of the following ways. If the hot-plate is to be used dry
(i.e. in an oven or in any other way in which it is not immersed or partially immersed
in water) I coat the said junctions or exposed parts with a mixture of pitch and paraffin
wax of (say) one third wax to two thirds pitch to seal those parts which being done
the hot-plate is ready for uso. If however the said hot-plate is to be used immersed
in water I simply solder up the joints which being done the said hot-plate is ready
for use.
When it has become necessary to affix fresh wires in the hot-plate all that is required
is to unscrew the flat bottom plate remove the cement fix the fresh wires in position
and then proceed as herein-before described.
My invention may be also applied to the manufacture of electrical frying-pans
kettles and other cooking utentils sad-irons radiators and other apparatus for cooking
and heating by electricity. The mode of application to such articles will be understood
from the description herein-before given.
Dated this Dial
Improvements in the Manufacture of Electrical Hot-plates and other
Electrical Apparatus for Cooking and Heating Purposes.
I JOHN CHAMBERS of Mokopeka in the Provincial District of Hawke's Bay in the
Colony of New Zealand Sheep Farmer 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 :-
My invention relates to the insulation and embedding of the electrical resistance
wires used in electrical hot-plates and in other electrical apparatus for cooking and
heating purposes.
The insulating media ordinarily used for insulating and embedding electrical
resistance wires in hot plates and other electrical apparatus used for cooking and
beating purposes are subject to the following disadvantages. A skilled artisan and
special appliances are required for the embedding and insulation of the resistance wires
in the first instance and when they become worn out they must be replaced at a manu-
factory and in the chipping away of the insulating and embedding material (which is
very hard) there is a risk of cracking the plates. "Also the first cost of the embedding
is considerable.
Now the object of my invention is to simplify and facilitate the insulation and
embedding and the re-embedding of the said wires so that the work may be readily
and cheaply done by any person of ordinary intelligence.
For this purpose I use a cement consisting of plaster of Paris and oxide of iron
mixed together and brought to a condition suitable for use by addition of water in
which cement I embed the resistance wire or wires of the apparatus. The proportions
in which I prefer to use the said matters are two parts by volume of plaster of Paris

page_text: and one part by volume of oxide of iron and water in sufficient quantity to produce a
thin paste but I do not confine myself to the said proportions. The plaster of Paris
and oxide of iron I thoroughly mix together in a dry state and I take portions of this
mixture and add the water thereto when required for use. As the cement or com-
position thus made sets very rapidly the paste should be mixed immediately before it
is to be used and only a small quantity should be mixed at one time.
In order to explain the practical application of my invention I will describe a
convenient method of using the said composition in the insulation of the resistance
wires of an electrical hot plate.
I take the dish shaped portion of the casing which when the hot plate is in use
constitutes the upper part thereof and I invert the said portion of the casing and apply
to the inner side thereof a coating of the paste hereinbefore described by means of a
soft brush and allow the said coating to set and then apply in like manner another
coating or several coatings allowing each to set before the next is applied. When
the last coating bas set I take the resistanco wire (which may be crimped if desired)
and arrange the said wire within the said casing in contact with the surface of the
said coating and apply portions of the paste hereinbefore described over the said wire
so as to hold it down to the said surface at intervals sufficiently close to prevent it
from shifting. 1 then secure the terminals to the ends of the wire in the ordinary
mauner and completely cover the said wire by brushing more of the said paste over it
and allow the paste to set and then fill the unoccupied part of the casing by pouring
the said paste into it and while filling the casing I continually tap it to cause escape
of any air which may enter with the paste in the form of bubbles. I then dry the
paste or cement within the casing by exposing it to heat which at starting should not
be higher than about 200 degrees Fahrenheit and when the said cement is thoroughly
dried I connect the terminals of the resistance wire to a source of electricity at the
required voltage and when the plate is at its maximum temperature and therefore all
or nearly all the air is expelled from the cement I prevent absorption of air and
moisture by the cement in one or other of the following ways according to the manner
in which the hot plate is to be used. If the hot plate is to be used dry (i.e. in an
oven or in any other way in which it is not immersed or partially immersed in water)
I either simply coat the whole of the exposed surface of the cement with a mixture
of pitch and paraffin wax of (say) one third wax to two thirds pitch in order to seal
the said exposed surface or I secure a flat plate to the casing over the said surface of
the cement either after coating it with the mixture of pitch and paraffin or without
so coating it and I seal the junctions of the said plate and the casing by applying the
mixture of pitch and paraffin to the said junctions. Or in either case instead of
using the pitch and paraffin in admixture I first apply paraffin to the parts to be sealed
and afterwards apply pitch thereto. If however the said hot plate is to be used
immersed in water I simply solder up the joints and in this case I screw a tube into
the casing to surround and protect the terminal wires which being done the said hot
plate is ready for use.
If by the passage of electricity through the wires of the heater the cement is not
sufficiently heated to cause it to absorb the sealing matters the said cement must be
further heated by other means.
Where the casing is to be closed by securing a plate thereto over the surface of the
cement the said cement may be compressed in the casing by putting the said plate
in place and pressing it on the said cement while it is in the fluid state. The said
plate must however be removed before drying the cement prior to closing and sealing
the casing as herein before described.
When it has become necessary to secure fresh wires in the hot plate all that is
required is to unscrew the flat bottom plate remove the cement fix the fresh wires in
position and then proceed as herein before described.
In applying my invention to the manufacture of electrical frying pans kettles and
other cooking utensils sad irons radiators and other apparatus for cooking and heating
by electricity I proceed substantially as herein before described with reference to the
manufacture of an electrical hot plate.

page_text: 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
I claim -
First. The improvements hereinbefore described in the insulation and embedding
of the electrical resistance-wires used in electrical hot-plates and in other electrical
apparatus for cooking and heating purposes that is to say the insulation and embedding
of the said wires in a cement or composition consisting essentially of plaster of Paris
and oxide of iron substantially as hereinbefore described.
Secondly. The sealing of exposed portions of an absorbent cement, or composition
in which the resistance wires of electrical hot plates and other electrical apparatus for
cooking and heating are embedded by means of pitch and paraffin for the purpose of
preventing absorption of moisture by the said cement or composition substantially as
hereinbefore described.
Dated this Twenty-ninth day of October 1896
W. T. WHITEMAN,
Agent for the Applicant.