Improvements in connection with Electrical Insulating Materials.
Year: 1895

page_text: Date of Application, 7th Mar., 1895-Accepted, 10th Aug., 1895
COMPLETE SPECIFICATION.
Improvements in connection with Electrical Insulating Materials.
We TRESSILLIAN PERCY WIGGINS and GEORGE HERBERT WIGGINS trading
in co-partnership as F. Wiggins and Sons of 102 Minories and 10 Tower Hill, both
in the Administrative County of London, Mica Merchants and Importers, 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 :-
At the present time it is the practice to insulate the parts of dynamos, commu-
tators and other electrical apparatus by means of mica plates. Natural plates of
mica which are sometimes used are very expensive especially when large and on
account of this and of other defects and disadvantages attendant upon their use,
natural mica plates have been largely supplanted by plates of mica which are built
up from lamine or sheets of mica secured together by an adhesive or by other
suitable means. A serious disadvantage accompanying the use of such artificial
plates of mica, as well of the natural plates, is that after a little time the laminae of
which they are respectively composed slide off in a transverse direction in the form
of scales leaving the plates of uneven thickness in parts thus rendering the
insulation imperfect and interfering with the continuous working of the dynamo or
other apparatus.
The object of our invention is to build up a plate of mica in such a manner that
the breaking away, sliding or scaling off of its lamium transversely is practically
impossible.
In carrying our invention into practical effect we proceed as follows:-Wo take
pieces of mica of the required thickness and of convenient size and by means of dies
or other suitable tools we serrate or otherwise form the edges or sides of said mica
pieces in such a way that the edges or sides of one piece will interlock with
or dovetail or fit into the edges or sides of the other pieces. These pieces we fit
together to form a continuous sheet of the size required, the pieces being all of the
saine width and so disposed that the serrated or otherwise formed edges or sides
thereof are arranged transversely of the finished sheet.
In the accompanying drawings which serve to illustrate the invention
Figure 1 represents a piece of mica having serrated or vandƑked edges, and
Figure 2 represents a sheet of mica made up from such pieces all of which are of
the same width although not necessarily of the same length; the ends of the sheet
are cut off square. The pieces of mica need not be all of the same width unless the
finished sheet is required to be of equal width throughout, which however is
usually the case. Several of these sheets are produced and are laid one upon the
other and secured to each other or together by gum, shellac, or other adhesive
material or by any other suitable means until the plate is of the required
thickness.
Figures 3, 4 and 5 shew other shapes in which the edges or sides of the mica
pieces may be formed so as to effect the same result, i.e. :-to interlock or dovetail
or fit oue into the other. The invention is not limited to any special shape.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. An electrical insulating plate composed of mica sheets each formed of a number
of mica pieces whose sides interlock transversely of the finished sheet, said mica

page_text: sheets being laid one upon the other and secured to each other or together by
adhesive or other means.
2. The method herein described of producing a built up electrical insulating
plate consisting in forming continuous mica sheets from pieces of mica whose sides
interlock transversely of the finished sheets, laying said sheets one upon the other
to the desired thickness of the plate and securing said sheets to each other or
together by adhesive or other suitable means.
3. A built up electrical insulating plate composed of mica sheets each formed of
a number of mica pieces whose sides interlock transversely of the finished sheet, and
sheets of other insulating material, said sheets being laid one upon the other and
secured to each other or together by adhesive or other means.
Dated this 7th day of March 1895.
F. W. GOLBY,
36 Chancery Lane, London, W.C., Patent Agent for the Applicants.