Covering of Electrical Conductors.
Year: 1885

page_text: This Specification was, upon the 30th day of March 1887, amended under
Sections 18 to 21 of the Patents, Designs, and Trade Marks Act, 1883.
Covering of Electrical Conductors.
I BENJAMIN JOSEPH BARNARD MILLS of the firm of Harris and Mills of
23 Southampton Buildings in the County of Middlesex, Patent Agent do hereby
declare the nature of the said Invention for IMPROVEMENTS IN THE MODE OF
VULCANIZING THE INSULATING COVERING OF ELECTRICAL CONDUCTORS ધી com-
munication to me from abroad by John Joseph Charles Smith of Passaic in
the County of Passaic and State of New Jersey, in the United States of America
to be as follows:-
The object of this invention is to vulcanize such coverings in such a manner as
to avoid the detrimental effect of moisture on the insulating coverings of electric
conductors while such coverings are in process of vulcanization.
It has been found that any moisture which may come in contact with the
insulating covering of electric conductors while such covering is being vulcanized
will seriously affect and impair if it does not destroy the insulating qualities of the
covering.
In order that those skilled in the art of producing highly insulated electric
conductors, may fully understand the novelty and importance of the present
invention I will first relate some facts which were observed during a long series
of experiments on an extensive scale for the purpose of producing a high insulation
of electric conductors by the use of a vulcanized rubber compound.
Under the principal methods now used to vulcanize the covering of electric
conductors either the insulating compound is made so that it may be vulcanized in
a dry heat chamber where no pressure can be applied to the compound during the
process of vulcanization; or the covered conductors are packed in dry soap-stone
powder and are placed in a vulcanizing vessel, where steam is admitted which
produces the required heat and pressure at the same time. The last named is
very troublesome on account of the difficulty of properly packing a long piece of

page_text: insulated wire in the soap-stone. In both cases the compounds used for insulating
coverings are made up with a view to being of such nature that they can be
vulcanized in either one or the other way and therefore are not of such high
insulating qualities as they otherwise might be. Many slight modifications of
these systems are in use but the principles remain the same.
While carrying out these experiments both of these systems and many of the
sundry modifications in vogue were used but it was found invariably that the
insulation resistance of the compounds was very much lower after vulcanization
than before and too often was lost altogether. By close observation it was found
that the compound absorbed more or less moisture during vulcanization by one or
the other mode. When vulcanized in dry heat without pressure, the compound
was full of fine pores unless it was mixed in considerable quantity with heavy
ingredients not suitable for producing high insulation. Such observation led to
the adoption of the present new method the principle of which is to enclose the
insulating covering in a hermetical envelope through which moisture cannot
penetrate under pressure and to vulcanize the covering under such a protection.
This effectually prevents moisture from coming in contact with the compound
while it is being vulcanized.
The present invention has been carried into effect with complete success in the
following manner: A sheet of the insulating compound is laid firmly on a long
sheet of heavy tin foil, and then both are cut in long narrow strips.
Such strips of tin foil in combination with the vulcanizable insulating material
are laid on the wire by means of the covering machine.
Under the present invention the tin foil answers the same purpose as the fibrous
sheet in affording facility for laying and pressing the covering closely on the wire
but in addition to this it serves the very important purpose of providing an
impervious envelope for the insulating covering and protecting it fully against the
influence of moisture during vulcanization thus permitting the direct pressure and
heat of steam without injurious effect.
It also differs from the fibrous covering in that it does not become inseparably
incorporated with the insulating covering. It has long been known that all
vulcanizable compounds become much better and of closer texture if vulcanized
under pressure. Many cannot be vulcanized in a solid condition without pressure.
Others which can be vulcanized in dry heat without pressure possess this capability
because they are heavily loaded with ingredients injurious to good insulation.
When the insulating cover is to be vulcanized the covered wire is coiled on a
large but light metallic reel in two or three layers. This reel is so arranged that it
may be put readily in and out of the vulcanizer, and that it can be revolved
horizontally in the vulcanizer while the same is closed and in operation. The
revolving of the reel is accomplished by means of a shaft extending through the
stuffing box in the head of the horizontal vulcanizer, and provided with a driving
gear on the outside.
The reel may be advantageously made to contain about two miles of wire at one
charge and is rotated for the purpose of continually changing the position and weight
of the wire and its covering which keeps the wire central in the covering while it
is softened by heat before the vulcanization takes place.
When the vulcanization is completed the wire is taken out and the tin foil
envelope having performed its function is removed from the insulating covering
leaving a smooth and dense surface.
To illustrate the importance of a tin foil, or other metallic foil covering on the
outside of the insulation covering as a protective envelope during vulcanization,
I will state the results of a number of experiments in vulcanization by other
methods and the results when the metallic envelope was used.
An insulation compound such as is used in one of the best known manufactures
of insulated wire and which I designate as compound N° 1 was laid 1-24th of an
snch thick on 1000 feet of No 14 copper wire. Before vulcanization the insulation
resistance of the cover was 108 megohms. It was then vulcanized in a dry heat

page_text: chamber without pressure.
After vulcanization the insulation resistance of the
covering stood only 27 megohms and it fell to 15 megohms after immersion in
water for three days. This proved that fine pores must have formed during
vulcanization which absorbed moisture, thereby injuring the insulation.
Another 1000 feet of wire covered with the same compound (N° 1) 1-24th of an
inch thick showed 112 megohms before vulcanization.
It was vulcanized in a dry soap-stone powder bed carefully packed and heated
under steam pressure. After vulcanization the insulation resistance of this covering
was 37 megohms.
Three days immersion in water brought it down to 23 megohms. A third piece
of 1000 feet was covered with the same compound N° 1 to the same thickness and
was protected by what is commonly called a water-proof tape. This piece was
vulcanized in steam under pressure in the manner in which soft rubber goods are
cured. After vulcanization it showed only 7 megohms insulation, and in less than
three hours immersion in water it came down to megohm.
A fourth piece of 1000 feet was covered with the same compound the same
thickness but protected by, according to the present invention with a metallic
envelope. Before insulation this piece indicated 113 megohms insulation resistance.
It was vulcanized in steam under 60 pounds pressure. After vulcanization this
piece indicated an insulation resistance of 163 megohms which showed a great
increase of the insulation resistance.
Three days immersion in water proved it to be unalterable.
The rubber compound called akonite showed still more remarkable results. This
compound is absolutely water proof and one of the best insulators. It was laid
on 1000 feet of N° 14 copper wire 1-24th of an inch thick the same thickness as in
the previous experiments with compound N" 1. When raw this compound showed
an insulation resistance of 240 megohms. After vulcanization in dry soap-stone
powder under pressure of steam, it showed an insulation resistance of 92 megohms,
falling to 47 after three days immersion. A second piece covered with the said
compound and with water-proof tape as a protection and vulcanized in steam
under pressure, showed only 72 megohms insulation after vulcanization, falling to
40 megohms after three days immersion in water. A third piece of 1000 feet of
wire covered with this compound .but protected by the metallic envelope was
vulcanized in steam under pressure. After vulcanization it showed an insulation
resistance of 570 megolms. Immersion in water for weeks had no influence
upon it.
Repeated trials with the same compounds and many others showed corresponding
results proving the fact that if an electric conductor insulated with a vulcanizable
compound is covered with a metallic envelope in the manner described and is
vulcanized under such protection the insulation resistance of the covering is very
much improved. All the named trials were made with equal accuracy and all tests
and measurements taken with the most sensitive instruments and galvanometers.
In order to avoid any possibility of mistake about one or the other compound,
hard rubber or ebonite compound which is known as one of the best insulators was
used it was laid on the wire to the same thickness as the other.
The first sample vulcanized in dry soap stone showed an insulation resistance of
97 megohms but fell to 40 after immersion.
The second example vulcanized in steam showed only megohm after vulcani-
zation. The third sample was vulcanized under the protection of the metallic
envelope. After vulcanization it stood 280 megohms and did not change by
immersion in water.
This trial proved conclusively that all vulcanizable compounds suffer in their
insulating qualities when vulcanized in such a manner that moisture may come in
contact with the material in process of vulcanization.
If vulcanized in dry heat or soap stone it suffers from want of pressure on the
compound and a fine porous formation takes place or the compound must be so
much loaded with other ingredients as to affect its insulating qualities.

page_text: I am well aware that tin foil or other metallic sheets are used in the manufacture
and vulcanization of rubber goods, to obtain smooth surfaces or to keep the rubber
in shape or to facilitate moulding and pressing in special forms; but it will be
apparent that the impervious metallic envelope performs an essentially different
and novel function in the present process of vulcanizing insulation coverings of
electric conductors.
The tin foil or other pliable metal sheets are used as an envelope that cannot be
penetrated by moisture so that the insulating compound may be fully protected
against the detrimental influence of moisture while it is vulcanized permitting the
use of the direct action of steam as the best and most convenient medium to
produce the required heat and pressure at the same time.

page_text: Improvements in the Mode of Vulcanizing the Insulating
Covering of Electrical Conductors.
I BENJAMIN JOSEPH BARNARD MILLS of the firm of Harris and Mills of
23 Southampton Buildings in the County of Middlesex, Patent Agent do hereby
declare the nature of the invention, a communication to me from abroad by John
Joseph Charles Smith of Passaic in the County of Passaic and State of New
Jersey in the United States of America, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
The object of this invention is to vulcanize such coverings in such a manner as
to avoid the detrimental effect of moisture on the insulating coverings of electric
conductors while such coverings are in process of vulcanization.
It has been found that any moisture which may come in contact with the
insulating covering of electric conductors while such covering is being vulcanized
will seriously affect and impair if it does not destroy the insulating qualities of the
covering.
In order that those skilled in the art of producing highly insulated electric
conductors, may fully understand the novelty and importance of the present
invention; I will first relate some facts which were observed during a long series
of experiments on an extensive scale for the purpose of producing a high insulation
of electric conductors by the use of a vulcanized rubber compound.
Under the principal methods now used to vulcanize the covering of electric
conductors either the insulating compound is made so that it may be vulcanized in
a dry heat chamber where no pressure can be applied to the compound during the
process of vulcanization; or the covered conductors are packed in dry soap-stone
powder and are placed in a vulcanizing vessel, where steam is admitted which
produces the required heat and pressure at the same time. The last named is
very troublesome on account of the difficulty of properly packing a long piece
of insulated wire in the soap stone. In both cases the compounds used for
insulating coverings are made up with a view to being of such nature that they
can be vulcanized in either one or the other way and therefore are not of such high
insulating qualities as they otherwise might be. Many slight modifications of
these systems are in use but the principles remain the same.
While carrying out these experiments both of these systems and many of the
sundry modifications in vogue were used but it was found invariably that the
insulation resistance of the compounds was very much lower after vulcanization
than before and too often was lost altogether. By close observation it was found
that the compound absorbed more or less moisture during vulcanization by one or
the other mode. When vulcanized in dry heat without pressure, the compound
was full of fine pores unless it was mixed in considerable quantity with heavy

page_text: ingredients not suitable for producing high insulation. Such observation led to
the adoption of the present new method the principle of which is to enclose the
insulating covering in a hermetical envelope through which moisture cannot
penetrate under pressure and to vulcanize the covering under such a protection.
This effectually prevents moisture from coming in contact with the compound while
it is being vulcanized.
The present invention has been carried into effect with complete success in the
following manner: A sheet of the insulating compound is laid firmly on a long
sheet of heavy tin foil and then both are cut in long narrow strips: Such strips of
tin foil in combination with the vulcanizable insulating material are laid on the
wire by means of the covering machine.
Under the present invention the tin foil answers the same purpose as the fibrous
sheet in affording facility for laying and pressing the covering closely on the wire
but in addition to this it serves the very important purpose of providing an
impervious envelope for the insulating covering and protecting it fully against the
influence of moisture during vulcanization thus permitting the direct pressure and
heat of steam without injurious effect. It also differs from the fibrous covering in
that it does not become inseparably incorporated with the insulating covering. It
has long been known that all vulcanizable compounds become much better and of
closer texture if vulcanized under pressure. Many cannot be vulcanized in a solid
condition without pressure. Others which can be vulcanized in dry heat without
pressure possess this capability because they are heavily loaded with ingredients
injurious to good insulation.
When the insulating cover is to be vulcanized the covered wire is coiled on a
large but light metallic reel in two or three layers. This reel is so arranged that
it may be put readily in and out of the vulcanizer, and that it can be revolved
horizontally in the vulcanizer while the same is closed and in operation. The
revolving of the reel is accomplished by means of a shaft extending through the
stuffing box in the head of the horizontal vulcanizer, and provided with a driving
gear on the outside.
The reel may be advantageously made to contain about two miles of wire at one
charge and is rotated for the purpose of continually changing the position and
weight of the wire and its covering which keeps the wire central in the covering
while it is softened by heat before the vulcanization takes place.
When the vulcanization is completed the wire is taken out and the tin foil
envelope having performed its functions is removed from the insulating covering
leaving a smooth and dense surface. To illustrate the importance of a tin foil or
other metallic foil covering on the outside of the insulation covering as a protective
envelope during vulcanization, I will state the results of a number of experiments
in vulcanization by other methods and the results when the metallic envelope
was used.
An insulation compound such as is used in one of the best known manufactures
of insulated wire and which I designate as compound No. 1, was laid 1-24th of
an inch thick on 1000 feet of No. 14 copper wire. Before vulcanization the
insulation resistance of the cover was 108 megohms. It was then vulcanized in a
dry heat chamber without pressure. After vulcanization the insulation resistance
of the covering stood only 27 megohms and it fell to 15 megohms after immersion
in water for three days. This proved that fine pores must have formed during
vulcanization which absorbed moisture, thereby injuring the insulation. Another
1000 feet of wire covered with the same compound (No 1) 1-24th of an inch thick
showed 112 megohms before vulcanization. It was vulcanized in a dry soap stone
powder bed carefully packed and heated under steam pressure. After vulcanization
the insulation resistance of this covering was 37 megohms. Three days immersion
in water brought it down to 23 megohms. A third piece of 1000 feet was covered
with the same compound No. 1 to the same thickness and was protected by what
is commonly called a water proof tape. This piece was vulcanized in steam under

page_text: pressure in the manner in which soft rubber goods are cured.
After vulcanization
it showed only 7 megohms insulation, and in less than three hours immerson in
water it came down to megohm. A fourth piece of 1000 feet was covered with
the same compound the same thickness but protected by according to the present
invention with a metallic envelope. Before insulation this piece indicated
113 megohms insulation resistance. It was vulcanized in steam under 60 pounds
pressure. After vulcanization this piece indicated an insulation resistance of
163 megohms which showed a great increase of the insulation resistance.
Three days immersion in water proved it to be unalterable.
The rubber compound called abonite showed still more remarkable results.
This compound is absolutely water proof and one of the best insulators. It was
laid on 1000 feet of N° 14 copper wire 4th of an inch thick the same thickness as
in the previous experiments with compound No 1. When raw this compound
showed an insulation resistance of 240 megohms. After vulcanization in dry
soap stone powder under pressure of steam it showed an insulation resistance of
92 megohms, falling to 47 after three days immerson, A second piece covered
with the said compound and with waterproof tape as a protection and vulcanized
in steam under pressure, showed only 72 megohms insulation after vulcanization,
falling to 40 megohms after three days immersion in water. A third piece of
1000 feet of wire covered with this compound but protected by the metallic
envelope was vulcanized in steam under pressure. After vulcanization it showed
an insulation resistance of 570 megohms. Immersion in water for weeks had no
influence upon it.
Repeated trials with the same compounds and many others showed corresponding
results proving the fact that if an electric conductor insulated with a vulcanizable
compound is covered with a metallic envelope in the manner described and is
vulcanized under such a protection the insulation resistance of the covering is very
much improved. All the named trials were made with equal accuracy and all tests
and measurements taken with the most sensitive instruments and galvanometers.
In order to avoid any possibility of mistake about one or the other compound
hard rubber or ebonite compound which is known as one of the best insulators
was used; it was laid on the wire to the same thickness as the other.
The first sample vulcanized in dry soap stone showed an insulation resistance of
of 97 megohms but fell to 40 after immersion.
The second example vulcanized in steam showed only
vulcanization.
megohm after
The third sample was vulcanized under the protection of the metallic envelope.
After vulcanization it stood 280 megohms and did not change by immersion in
water.
This trial proved conclusively that all vulcanizable compounds suffer in their
insulating qualities when vulcanized in such a manner that moisture may come in
contact with the material in process of vulcanization. If vulcanized in dry heat
or soap stone it suffers from want of pressure on the compound and a fine porous
formation takes place or the compound must be so much loaded with other
ingredients as to affect its insulating qualities.
I am well aware that tin foil or other metallic sheets are used in the manu-
facture and vulcanization of rubber goods, to obtain smooth surfaces or to keep the
rubber in shape or to facilitate moulding and pressing in special forms; but it will
be apparent that the impervious metallic envelope performs an essentially different
and novel function in the present process of vulcanizing insulation coverings of
electric conductors.
The tin foil or other pliable metal sheets are used as an envelope that cannot be
penetrated by moisture so that the insulating compound may be fully protected
against the detrimental influence of moisture while it is vulcanized permitting the
use of the direct action of steam as the best and most convenient medium to
produce the required heat and pressure at the same time.

page_text: Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, I declare that what
I claim is
The mode or process herein described of vulcanizing the insulating covering of
electrical conductors, the same-com-isting in enveloping the covered wire in a tight
and impervious cover of tin foil or other pliable metal and subjecting it to the
combined and simultaneous-nction of heat and pressure.

page_text: Covering of Electrical Conductors.
I BENJAMIN JOSEPH BARNARD MILLS of the firm of Harris and Mills of
23 Southampton Buildings in the County of Middlesex, Patent Agent do hereby
declare the nature of the said Invention for IMPROVEMENTS IN THE MODE OF
CONDUCTORS
VULCANIZING THE INSULATING COVERING OF ELECTRICAL
a com-
munication to me from abroad by John Joseph Charles Smith of Passaic in
the County of Passaic and State of New Jersey, in the United States of America
to be as follows:-
The object of this invention is to vulcanize such coverings in such a manner as
to avoid the detrimental effect of moisture on the insulating coverings of electric
conductors while such coverings are in process of vulcanization.
It has been found that any moisture which may come in contact with the
insulating covering of electric conductors while such covering is being vulcanized
will seriously affect and impair if it does not destroy the insulating qualities of the.
covering.
In order that those skilled in the art of producing highly insulated electric
conductors, may fully understand the novelty and importance of the present
invention I will first relate some facts which were observed during a long series,
of experiments on an extensive scale for the purpose of producing a high insulation
of electric conductors by the use of a vulcanized rubber compound.
Under the principal methods now used to vulcanize the covering of electric
conductors either the insulating compound is made so that it may be vulcanized in
a dry heat chamber where no pressure can be applied to the compound during the
process of vulcanization; or the covered conductors are packed in dry soap-stone
powder and are placed in a vulcanizing vessel, where steam is admitted which,
produces the required heat and pressure at the same time. The last named is
very troublesome on account of the difficulty of properly packing a long piece of

page_text: insulated wire in the soap-stone. In both cases the compounds used for insulating
coverings are made up with a view to being of such nature that they can be
vulcanized in either one or the other way and therefore are not of such high
insulating qualities as they otherwise might be. Many slight modifications of
these systems are in use but the principles remain the same.
While carrying out these experiments both of these systems and many of the
Bundry modifications in vogue were used but it was found invariably that the
insulation resistance of the compounds was very much lower after vulcanization
than before and too often was lost altogether. By close observation it was found
that the compound absorbed more or less moisture during vulcanization by one or
the other mode. When vulcanized in dry heat without pressure, the compound
was full of fine pores unless it was mixed in considerable quantity with heavy
ingredients not suitable for producing high insulation. Such observation led to
the adoption of the present new method the principle of which is to enclose the
insulating covering in a hermetical envelope through which moisture cannot
penetrate under pressure and to vulcanize the covering under such a protection.
This effectually prevents moisture from coming in contact with the compound
while it is being vulcanized.
The present invention has been carried into effect with complete success in the
following manner: A sheet of the insulating compound is laid firmly on a long
sheet of heavy tin foil, and then both are cut in long narrow strips.
Such strips of tin foil in combination with the vulcanizable insulating material
are laid on the wire by means of the covering machine.
Under the present invention the tin foil answers the same purpose as the fibrous
sheet in affording facility for laying and pressing the covering closely on the wire
but in addition to this it serves the very important purpose of providing an
impervious envelope for the insulating covering and protecting it fully against the
influence of moisture during vulcanization thus permitting the direct pressure and
heat of steam without injurious effect.
It also differs from the fibrous covering in that it does not become inseparably
incorporated with the insulating covering. It has long been known that all
vulcanizable compounds become much better and of closer texture if vulcanized
under pressure. Many cannot be vulcanized in a solid condition without pressure.
Others which can be vulcanized in dry heat without pressure possess this capability
because they are heavily loaded with ingredients injurious to good insulation.
When the insulating cover is to be vulcanized the covered wire is coiled on a
large but light metallic reel in two or three layers. This reel is so arranged that it
may be put readily in and out of the vulcanizer, and that it can be revolved
horizontally in the vulcanizer while the same is closed and in operation. The
revolving of the reel is accomplished by means of a shaft extending through the
stuffing box in the head of the horizontal vulcanizer, and provided with a driving
gear on the outside.
The reel may be advantageously made to contain about two miles of wire at one
charge and is rotated for the purpose of continually changing the position and weight
of the wire and its covering which keeps the wire central in the covering while it
is softened by heat before the vulcanization takes place.
When the vulcanization is completed the wire is taken out and the tin foil
envelope having performed its function is removed from the insulating covering
leaving a smooth and dense surface.
To illustrate the importance of a tin foil, or other metallic foil covering on the
outside of the insulation covering as a protective envelope during vulcanization,
I will state the results of a number of experiments in vulcanization by other
methods and the results when the metallic envelope was used.
An insulation compound such as is used in one of the best known manufactures
of insulated wire and which I designate as compound No 1 was laid 1-24th of an
inch thick on 1000 feet of No 14 copper wire. Before vulcanization the insulation
resistance of the cover was 108 megohms. It was then vulcanized in a dry heat

page_text: chamber without pressure. After vulcanization the insulation resistance of the
covering stood only 27 megohms and it fell to 15 megohms after immersion in
water for three days. This proved that fine pores must have formed during
vulcanization which absorbed moisture, thereby injuring the insulation.
Another 1000 feet of wire covered with the same compound (N° 1) 1-24th of an
inch thick showed 112 megohms before vulcanization.
It was vulcanized in a dry soap-stone powder bed carefully packed and heated
under steam pressure. After vulcanization the insulation resistance of this covering
was 37 megohms.
Three days immersion in water brought it down to 23 megohms. A third piece
of 1000 feet was covered with the same compound N° 1 to the same thickness and
was protected by what is commonly called a water-proof tape. This piece was
vulcanized in steam under pressure in the manner in which soft rubber goods are
cured. After vulcanization it showed only 7 mnegohms insulation, and in less than
three hours immersion in water it came down to megohm.
A fourth piece of 1000 feet was covered with the same compound the same
thickness but protected by, according to the present invention with a metallic
envelope. Before insulation this piece indicated 113 megohms insulation resistance.
It was vulcanized in steam under 60 pounds pressure. After vulcanization this
piece indicated an insulation resistance of 163 megohms which showed a great
increase of the insulation resistance.
Three days immersion in water proved it to be unalterable.
The rubber compound called akonite showed still more remarkable results. This
compound is absolutely water proof and one of the best insulators. It was laid
on 1000 feet of N° 14 copper wire 1-24th of an inch thick the same thickness as in
the previous experiments with compound No 1. When raw this compound showed
an insulation resistance of 240 megohms. After vulcanization in dry soap-stone
powder under pressure of steam, it showed an insulation resistance of 92 megohms,
falling to 47 after three days immersion. A second piece covered with the said
compound and with water-proof tape as a protection and vulcanized in steam
under pressure, showed only 72 megohms insulation after vulcanization, falling to
40 megohms after three days immersion in water. A third piece of 1000 feet of
wire covered with this compound but protected by the metallic envelope was
vulcanized in steam under pressure. After vulcanization it showed an insulation
resistance of 570 megohms. Immersion in water for weeks had no influence
upon it.
Repeated trials with the same compounds and many others showed corresponding
results proving the fact that if an electric conductor insulated with a vulcanizable
compound is covered with a metallic envelope in the manner described and is
vulcanized under such protection the insulation resistance of the covering is very
much improved. All the named trials were made with equal accuracy and all tests
and measurements taken with the most sensitive instruments and galvanometers.
In order to avoid any possibility of mistake about one or the other compound,
hard rubber or ebonite compound which is known as one of the best insulators was
used; it was laid on the wire to the same thickness as the other.
The first sample vulcanized in dry soap stone showed an insulation resistance of
97 megohms but fell to 40 after immersion.
The second example vulcanized in steam showed only megoùm after vulcani-
zation. The third sample was vulcanized under the protection of the inetallic
envelope. After vulcanization it stood 280 megohms and did not change by
immersion in water.
This trial proved conclusively that all vulcanizable compounds suffer in their
insulating qualities when vulcanized in such a manner that inoisture may come in
contact with the material in process of vulcanization.
If vulcanized in dry beat or soap stone it suffers from want of pressure on the
compound and a fine porous formation takes place or the compound must be so
much loaded with other ingredients as to affect its insulating qualities.

page_text: I am well aware that tin foil or other metallic sheets are used in the manufacture
and vulcanization of rubber goods, to obtain smooth surfaces or to keep the rubber
in shape or to facilitate moulding and pressing in special forms; but it will be
apparent that the impervious metallic envelope performs an essentially different
and novel function in the present process of vulcanizing insulation coverings of
electric conductors.
The tin foil or other pliable metal sheets are used as an envelope that cannot be
penetrated by moisture so that the insulating compound may be fully protected
against the detrimental influence of moisture while it is vulcanized permitting the
use of the direct action of steam as the best and most convenient medium to
produce the required heat and pressure at the same time.

page_text: Covering of Electrical Conductors.
I BENJAMIN JOSEPH BARNARD MILLS of the firm of Harris and Mills of
23 Southampton Buildings in the County of Middlesex, Patent Agent do hereby
declare the nature of the invention, a communication to me from abroad by John
Joseph Charles Smith of Passaic in the County of Passaic and State of New
Jersey in the United States of America, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
The object of this invention is to vulcanize such coverings in such a manner as
to avoid the detrimental effect of moisture on the insulating coverings of electric
conductors while such coverings are in process of vulcanization.
It has been found that any moisture which may come in contact with the
insulating covering of electric conductors while such covering is being vulcanized
will seriously affect and impair if it does not destroy the insulating qualities of the
covering.
In order that those skilled in the art of producing highly insulated electric
conductors, may fully understand the novelty and importance of the present
invention; I will first relate some facts which were observed during a long series
of experiments on an extensive scale for the purpose of producing a high insulation
of electric conductors by the use of a vulcanized rubber compound.
.Under the principal methods now used to vulcanize the covering of electric
conductors either the insulating compound is made so that it may be vulcanized in
a dry heat chamber where no pressure can be applied to the compound during the
process of vulcanization; or the covered conductors are packed in dry soap-stone
powder and are placed in a vulcanizing vessel, where steam is admitted which
produces the required heat and pressure at the same time. The last named is
very troublesome on account of the difficulty of properly packing a long piece
of insulated wire in the soap stone. In both cases the compounds used for
insulating coverings are made up with a view to being of such nature that they
can be vulcanized in either one or the other way and therefore are not of such high
insulating qualities as they otherwise might be. Many slight modifications of
these systems are in use but the principles remain the same.
While carrying out these experiments both of these systems and many of the
sundry modifications in vogue were used but it was found invariably that the
insulation resistance of the compounds was very much lower after vulcanization
than before and too often was lost altogether. By close observation it was found
that the compound absorbed more or less moisture during vulcanization by one or
the other mode. When vulcanized in dry heat without pressure, the compound
was full of fine pores unless it was mixed in considerable quantity with heavy

page_text: ingredients not suitable for producing high insulation. Such observation led to
the adoption of the present new method the principle of which is to enclose the
insulating covering in a hermetical envelope through which moisture cannot
penetrate under pressure and to vulcanize the covering under such a protection.
This effectually prevents moisture from coming in contact with the compound while
it is being vulcanized.
The present invention has been carried into effect with complete success in the
following manner: A sheet of the insulating compound is laid firmly on a long
sheet of heavy tin foil and then both are cut in long narrow strips: Such strips of
tin foil in combination with the vulcanizable insulating material are laid on the
wire by means of the covering machine.
Under the present invention the tin foil answers the same purpose as the fibrous
sheet in affording facility for laying and pressing the covering closely on the wire
but in addition to this it serves the very important purpose of providing an
impervious envelope for the insulating covering and protecting it fully against the
influence of moisture during vulcanization thus permitting the direct pressure and
heat of steam without injurious effect. It also differs from the fibrous covering in
that it does not become inseparably incorporated with the insulating covering. It
has long been known that all vulcanizable compounds become much better and of
closer texture if vulcanized under pressure. Many cannot be vulcanized in a solid
condition without pressure. Others which can be vulcanized in dry heat without
pressure possess this capability because they are heavily loaded with ingredients
fnjurious to good insulation.
When the insulating cover is to be vulcanized the covered wire is coiled on a
large but light metallic reel in two or three layers. This reel is so arranged that
it may be put readily in and out of the vulcanizer, and that it can be revolved
horizontally in the vulcanizer while the same is closed and in operation. The
revolving of the reel is accomplished by means of a shaft extending through the
stuffing box in the head of the horizontal vulcanizer, and provided with a driving
gear on the outside.
The reel may be advantageously made to contain about two miles of wire at one
charge and is rotated for the purpose of continually changing the position and
weight of the wire and its covering which keeps the wire central in the covering
while it is softened by heat before the vulcanization takes place.
When the vulcanization is completed the wire is taken out and the tin foil
envelope having performed its functions is removed from the insulating covering
leaving a smooth and dense surface. To illustrate the importance of a tin foil or
other metallic foil covering on the outside of the insulation covering as a protective
envelope during vulcanization, I will state the results of a number of experiments
in vulcanization by other methods and the results when the metallic envelope
was used.
An insulation compound such as is used in one of the best known manufactures
of insulated wire and which I designate as compound No. 1, was laid 1-24th of
an inch thick on 1000 feet of No. 14 copper wire. Before vulcanization the
insulation resistance of the cover was 108 megohms. It was then vulcanized in a
dry heat chamber without pressure. After vulcanization the insulation resistance
of the covering stood only 27 megohms and it fell to 15 megohms after immersion
in water for three days. This proved that fine pores must have formed during
vulcanization which absorbed moisture, thereby injuring the insulation. Another
1000 feet of wire covered with the same compound (N° 1) 1-24th of an inch thick
showed 112 megohms before vulcanization. It was vulcanized in a dry soap stone
powder bed carefully packed and heated under steam pressure. After vulcanization
the insulation resistance of this covering was 37 megohms. Three days immersion
in water brought it down to 23 megohms. A third piece of 1000 feet was covered
with the same compound No 1 to the same thickness and was protected by what
is commonly called a water proof tape. This piece was vulcanized in steam under

page_text: pressure in the manner in which soft rubber goods are cured. After vulcanization
it showed only 7 megohms insulation, and in less than three hours immersion in
water it came down to megohm. A fourth piece of 1000 feet was covered with
the same compound the same thickness but protected by according to the present
invention with a metallic envelope. Before insulation this piece indicated
113 megohms insulation resistance. It was vulcanized in steam under 60 pounds
pressure. After vulcanization this piece indicated an insulation resistance of
163 megohms which showed a great increase of the insulation resistance.
Three days immersion in water proved it to be unalterable.
The rubber compound called abonite showed still more remarkable results.
This compound is absolutely water proof and one of the best insulators. It was
laid on 1000 feet of N° 14 copper wire 11th of an inch thick the same thickness as
in the previous experiments with compound N° 1. When raw this compound
showed an insulation resistance of 240 megohms. After vulcanization in dry
soap stone powder under pressure of steam it showed an insulation resistance of
92 megohms, falling to 47 after three days immersion. A second piece covered
with the said compound and with waterproof tape as a protection and vulcanized
in steam under pressure, showed only 72 megohms insulation after vulcanization,
falling to 40 megohms after three days immersion in water. A third piece of
1000 feet of wire covered with this compound but protected by the netallic
envelope was vulcanized in steam under pressure. After vulcanization it showed
an insulation resistance of 570 megohms. Immersion in water for weeks had no
influence upon it.
Repeated trials with the same compounds and many others showed corresponding
results proving the fact that if an electric conductor insulated with a vulcanizable
compound is covered with a metallic envelope in the manner described and is
vulcanized under such a protection the insulation resistance of the covering is very
much improved. All the named trials were made with equal accuracy and all tests
and measurements taken with the most sensitive instruments and galvanometers.
In order to avoid any possibility of mistake about one or the other compound
hard rubber or ebonite compound which is known as one of the best insulators
was used; it was laid on the wire to the same thickness as the other.
The first sample vulcanized in dry soap stone showed an insulation resistance of
of 97 megohms but fell to 40 after immersion.
The second example vulcanized in steam showed only
vulcanization.
megohm after
The third sample was vulcanized under the protection of the metallic envelope.
After vulcanization it stood 280 megohms and did not change by immersion in
water.
This trial proved conclusively that all vulcanizable compounds suffer in their
insulating qualities when vulcanized in such a manner that moisture may come in
contact with the material in process of vulcanization. If vulcanized in dry heat
or soap stone it suffers from want of pressure on the compound and a fine porous
formation takes place or the compound must be so much loaded with other
ingredients as to affect its insulating qualities.
I am well aware that tin foil or other metallic sheets are used in the manu-
facture and vulcanization of rubber goods, to obtain smooth surfaces or to keep the
rubber in shape or to facilitate moulding and pressing in special forms; but it will
be apparent that the impervious metallic envelope performs an essentially different
and novel function in the present process of vulcanizing insulation coverings of
electric conductors.
The tin foil or other pliable metal sheets are used as an envelope that cannot be
penetrated by moisture so that the insulating compound may be fully protected
against the detrimental influence of moisture while it is vulcanized permitting the
use of the direct action of steam as the best and most convenient medium to
produce the required heat and pressure at the same time.

page_text: Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, I declare that what
I claim is
The mode or process herein described of vulcanizing the insulating covering of
electrical conductors, the same consisting in enveloping the covered wire in a tight 5
and impervious cover of tin foil or other pliable metal and subjecting it to the
combined and simultaneous action of heat and pressure.