Improvements in the Manufacture of Flexible Sheets for Electrical Insulation.
Year: 1895

page_text: Date of Application, 23rd Mar., 1895
Complete Specification Left, 21st Dec., 1895-Accepted, 25th Jan, 1896.
Improvements in the Manufacture of Flexible Sheets for Electrical
Insulation.
Communicated from abroad by CHARLES W. JEFFERSON of Schenectady, in the County
of Schenectady & State of New York, United States of America, Electrician
& General Manager of the Mica Insulation Company.
I CARL BOLLE of 57 Barton Arcade Manchester in the County of Lancaster,
Consulting Engineer, do hereby declare the nature of this invention to be as
follows:
This invention relates to flexible sheets for electrical insulation and consists in
improvements in the composition of or combination of materials for said sheets and
in the manner or methods of manufacturing the same.
Mica sheets have been employed heretofore for the purpose of electrically insu-
lating electrical conductors, as for example the laminae of field magnets the grooves
in armature cores, commutator segments and other elements of different shapes used
in electrical machines and instruments. The great expense of such mica sheets
however has prevented their extensive adoption. The objects of this invention are
to reduce the cost of insulating sheets containing mica, while retaining the insu-
lating qualities of mica sheets to substantially the same extent, and to produce
insulating sheets which are fireproof as well as waterproof with or without the
admixture of mica.
The improved mica sheets are formed preferably of alternate layers of mica and a
fibrous material, such as paper, cloth or asbestos fabric, cemented together by
means of fine sheets of gutta percha, commercially known as gutta percha tissue,
interposed between each two layers. The number and sequence of the layers may
vary, for instance there may be two or more of mica with one of fibrous material
interposed between each two, or one of mica with one of asbestos or one or on each
zide thereof, or any other sequence or number of layers of these materials, a layer of
gutta percha tissue being in each case interposed between each two layers of other
material.
In some cases the fibrous material may be omitted and the sheets formed of layers
of mica and gutta percha tissue only, while in other cases the sheets may be formed
of one or more layers of asbestos cloth and outer layers of paper or textile fabric,
with layers of gutta percha tissue between each two layers.
The manner or method of manufacturing composite sheets of mica and other
07

page_text: materials is as follows. A sheet of fibrous material and one of gutta percha are fed
forward together, for instance by a machine similar to the doubling machines used
in india rubber and gutta percha manufacture, the sheets being beated till the gutta
percha is soft and adhesive. Mica scales are then placed upon the gutta percha side
by side either abutting against or overlapping each other till the surface is covered
and the three ply sheet thus formed is pressed by means of rollers or otherwise while
the gutta percha is still soft and adhesive or rendered so by heat. The three ply
sheet so formed may then be fed again through rollers and the other side of the
fibrous material covered by gutta percha tissue and mica placed upon this and
attached thereto by pressure while the gutta percha is softened by heat. In other
cases the three ply sheet may be fed through heated rollers along with a sheet of
gutta percha tissue facing the mica and one of fibrous material, and thus a sheet
formed with mica in the centre and fibrous material on both sides. It is evident
that various combinations or successions of layers of mica and other materials can
be formed in this way, the adhesion being in all cases produced by softening the
gutta percha tissue and applying pressure.
Sheets composed of mica and gutta percha tissue only may be produced by build-
ing a mica sheet of given superficial area by placing side by side mica scales on a
table, placing a gutta percha tissue upon the scales, laying upon this tissue a second
layer of mica scales, heating the mass thus formed till the gutta percha becomes soft
and adhesive and subjecting the sheet to a heavy pressure. In some cases the mica
layers may be attached upon a tissue by an adhesive glue or its equivalent soluble in
water, and two sheets thus formed with a sheet of gutta percha tissue interposed
between the mica facings passed through heated rollers or otherwise heated and
pressed, and when cooled the outer layers of tissue removed by dissolving the glue
or its equivalent. The sheets formed of one or more layers of asbestos cloth and
outer layers of paper or textile fabric with intermediate layers of gutta percha tissue
may be formed by passing them together through heated rollers. Asbestos sheets by
themselves have been used for insulating, but are not waterproof, while the
composite sheets of asbestos, gutta percha and fibrous fabrics are waterproof and
adapted for use in situations where electrical conductors are exposed to moisture
or other conductors assisting in leakage. The asbestos will remain as suitable
insulator also for electrical apparatus exposed to accidental or other heating, although
the gutta percha and fibrous material may be injured thereby, while the outer
coating of such fibrous material serves to make the asbestos more suitable for trans-
portation and handling.
The sheets formed in the manner herein before described may be cut and bent while
warm into any desired shape or form, and may be cut into strips or bands and lapped
round conducting cables, producing a perfect electrical insulation as well as protection
against moisture.
Dated the 20th day of March 1895.
Improvements in the Manufacture of Flexible Sheets for Electrical
Insulation.
I, CARL BOLLÉ of 57 Barton Arcade, Manchester in the County of Lancaster,
Consulting Engineer, do hereby declare the nature of this invention, which has been
communicated to me by Charles W. Jefferson of Schenectady in the State of New
York, 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.
This invention relates to flexible sheets for electrical insulation and consists in

page_text: 0
5
or in the COLT
used before for the purpose of
mprovements in the manufacture or composition of the same
ination of materials forming said sheets.
Sheets built up of mica scales have been
lectrically insulating electrical conductors, as for example the laminae of field
nagnets, the grooves in armature cores, cominutator segments and other elements
f different shapes used in electrical machines and instruments. The mica scales in
uch sheets have been cemented together by means of shellac or similar substance
endering such sheets very stiff and incapable of being bent to a small radius
without heating them and softening the cement and this as well as their expense
has prevented their extensive adoption. The objects of this invention are to reduce
the costs and the stiffness and inflexibility of insulating sheets containing mica
scales and at the same time to produce insulating sheets which are to a great extent
fire proof as well as waterproof. These objects are attained by combining a layer
or several layers of mica scales with a sheet or several sheets of gutta percha tissue
with or without the addition of a fibrous material, such as paper, cloth or asbestos
fabric.
The improved flexible sheet is illustrated on the drawing appended hereunto,
Fig. 1 showing a section of a portion of an insulating sheet on an enlarged scale in
thickness.
Fig. 2. a plan of the same.
Fig. 3. a perspective view of a mica trough for armature grooves to illustrate one of
the forms into which the sheet may be cut or bent.
Fig-4-shows-a-modified-form-of-insulating-sheet,-and;
Fig. 45 a perspective view of an application of the product.
The improved flexible sheets are formed preferably of alternate layers of inica scales
and a fibrous material such as paper, cloth, or asbestos fabric, with a fine sheet of
gutta percha, commercially known as gutta percha tissue, interposed between each
two layers of other material. The number and sequence of the layers may vary.
In the sheet represented by Figs. 1 and 2, the lowest layer A of the whole sheet
is formed of mica scales of which the edges may-simply-abut-as-at-A¹-or overlapasat A².
Above this layer of mica scale is a sheet of fibrous
and do not simply abut at A².
Between the fibrous sheet B and
material B, which may be paper, cloth or asbestos.
the layer of mica scales A is a sheet of gutta percha tissue C. Next comes a second
sheet of gutta percha tissue D and then another mica layer E, and the layers may
I be repeated in the same or different relative orders until the desired thickness is
obtained.
It has been found that if the gutta percha tissue forms the outer covering of the
sheet, the finished sheets are not so satisfactory. as when the outer coatings are of
mica scales or fibrous material, because when packed they stick together, and also
stick too much to the articles to which they are applied as insulators.
The whole product is heated until the gutta percha tissue becomes adhesive and is
then pressed, and consequently when the sheet becomes cool, the layers adhere to
one another and form such a flexible sheet that it can be cut and bent into any form.
The fibrous material may be omitted in some cases, so that the sheet consists first
of a layer of mica; then of the gutta percha tissue and then again of a layer of
mica. Any number or sequence of layers may be used, a layer of gutta percha tissue
being interposed in each case between each two layers of other material. Where
.asbestos fabric is used in combination with mica scales, the asbestos will protect the
gutta percha tissue, against the effects of heat and render the sheets to a great
extent fire proof, while the gutta percha tissue renders them water proof, and both
gutta percha and asbestos are electrical insulators and their use renders the sheets
less costly than when these are entirely composed of mica.
In-some-eases-the-sheets-may-be-formed-of-one-or-more-layers-of--asbestos--eloth
and--outer--layers of paper-or-textile-fabric-with--a-layer--of-gutta--pereha-tissue
between-each-two-other-layers. In-Figure-4-the--sheet-consists--of--the--following
elements--a--sheet-a-of-any-suitable-cloth-or-tabrie-of-fibrous-material, for instance,
Japanese--tissue--paper,--6--gutta-percha-tissue,-c-a-sheet-of-asbestos-cloth;-6'-gutta

page_text: percha-tissue-and-a₁ a sheet of Horous materia: svestes-sheets-have-been-used-for
insulating purposes-before, but they-are-not-waterproof-and-cannot--be--conveniently
handled. By-the-addition-of-gutta-percha-tissue-they-are-rendered-water-proof, while
the-outer--layers--of-cloth-or-paper-prevent-the-gutta--pereha-from-sticking-to-the
articles-on-which-the-sheet-is-used-or-to-itself-when-rolled--up,--and--the--insulating
power-is increased. -At-the-same-time-when the insulating-sheet-is used-in-connee-
tion--with-el eetrical-apparatus--exposed-to-accidental-or-other-kinds of heating, the
asbestos-will-remain-as-a-suitable-insulator, although-the-gutta-percha and fibrous
material-may-become-injured, and-yet-these-make-the-sheet-more-suitable-for-trans-
portation-and-handling. The-sheets-of--fibrous--material--may--however-be-omitted
and-the-sheet-formed-of-asbestos-and-gutta-percha-and-tissue-only.
Figure 3 shows a trough for armature grooves to illustrate one of the forms into
which the sheets formed as hereinbefore described may be cut and bent, and Figure 54,
their application to insulating cables. In the manufacture and use of underground
cables it has been found difficult to protect the electric conductor or cable properly
from moisture and other conductors assisting leakage. The invention as above
described solves this problem as illustrated in Figures 45 when F is a conductor
and G a strip of the improved flexible insulating sheet, which is wound spirally around
the conductors as to form a complete covering.
The manner of manufacturing the composite sheets of mica scales and other
materials herein before described is as follows: A sheet of fibrous material and one of
gutta percha are fed forward together by means of a pair of rollers in a machine
similar to a doubling machine for manufacturing water proof cloths upon a table, which
can be heated by steam or otherwise, so that the gutta percha is on the top. Mica
scales are then placed upon the gutta percha side-by-side-or overlapping each other
until the surface is covered while the sheet is heated till the gutta percha is soft and
adhesive. The three ply sheets so formed may then be fed again through rollers or
other-wise pressed so as to make the different layers adhere firmly to each other. It
may then again be fed through rollers along with another sheet of gutta percha tissue so
as to cover the other side of the fibrous material with the same, and mica scales placed
upon this and attached thereto by pressure while the gutta percha is softened by
heat. A sheet is thus formed having mica scales on each side and a fibrous material
in the centre, and a layer of gntta percha tissue between the mica and fibrons material
on each side thereof. Or the three ply sheet may be fed through heated rollers along
with a sheet of gutta percha tissue facing the mica and one of fibrous material, thus
forming a sheet with inica in the centre and fibrous material on both sides. It is
evident that various combinations or successions of layers may be formed in this way,
the adhesion being in all cases produced by softening the gutta percha tissue and
applying pressure.
Sheets composed of mica scales and gutta percha tissue only may be produced by
forming a mica sheet of the desired superficial area by placing mica scales side-by-side
er overlapping each other upon a table, placing a gutta percha tissue upon the scales,
laying upon this a second layer of overlapping mica scales, heating the mass
thus formed till the gutta percha becomes soft and adhesive and subjecting the sheet
to heavy pressure. Further sheets of gutta percha tissue and layers of overlapping
mica scales may be added if desired and united together in the same manner.
The-sheets-composed of one-or-more-layers-of-asbestos-eloth-and--outer--layers--of
paper--or-textile-fabric--with--intermediate--layers-of-gutta-pereha-tissue-may--be
formed-by-pressing-the-whole-together through-heated-pressing-rollers.
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. The manufacture and use of flexible insulating sheets composed of two or more
layers of overlapping mica scales cemented together by means of a layer of gutta
percha tissue between each two layers of mica scales,
2. The manufacture and use of flexible sheets for electrical insulation composed of
one layer or of several layers of overlapping mica scales and one layer or several layers

page_text: of fibrous material cemented together by means of a layer of gutta percha tissue
between each two other layers.
3. In an insulated sheet the combination of alternate layers of overlapping
mica scales and gutta percha tissue substantially as hereinbefore described.
4. In an insulating sheet the combination of two or more layers of overlapping
mica scales and a layer of gutta percha tissue between each two layers of mica scales,
substantially as herein before described.
5, In an insulating sheet the combination of layers of asbestos sheet, overlapping
mica scales and gutta percha tissue substantially as hereinbefore described.
6. In an insulating sheet the combination of layers of fibrous sheet, overlapping
mica scales and gutta percha tissue substantially as hereinbefore described.
7. In-an-insulating-sheet-the-combination-of-layers-of-asbestos-sheet--and-gutta
percha
tissue,-with-or-without-the-addition-of-other-fibrous--sheets, substantially as
hereinbefore-described.