Method of making a transformer with an improved insulation system

A potted transformer winding and a method of manufacturing the same are disclosed. The method of manufacture includes the steps of inserting a temporary core pin in a hollow bobbin, winding a first coil of wire on the bobbin, placing a bobbin sleeve over the bobbin, and winding a second coil of wire on the sleeve to form a transformer winding assembly. Other sleeves and coils can be provided if desired. The transformer winding assembly is located in the interior of a casing, the casing and winding are heated, the casing interior and winding are subjected to a vacuum, and a potting compound is introduced into the casing interior in continuation of the vacuum and heat. The potting compound then flows between the core pin and the bobbin to form an electrically insulative coating inside the bobbin hollow. After the casing, winding and potting compound have cooled, at least one hole is formed in the casing adjacent an end of the pin and the pin is removed from the bobbin casing. A leg of a transformer core member may then be inserted into the cylindrical space defined by the thus exposed potting compound layer.

BACKGROUND OF THE INVENTION 
This invention relates generally to flyback transformers and like 
electrical devices and more particularly concerns a novel embodiment of at 
least one segment of such a transformer, and a method of manufacturing the 
device. 
Flyback transformers are used extensively in domestic television receivers 
and other electronic devices to provide suitable voltage and current to 
other circuit components. These transformers usually include a large 
number of turns of fine wire comprising a secondary winding which is 
commonly encased within a housing. A primary winding and a transformer 
core are associated with the secondary winding in any of a variety of 
ways. In addition, a potting compound is often introduced to the wire 
coils and housing interior in order to provide mechanical stability and 
improve various electrical characteristics of the unit. 
Since vast numbers of transformers are required by the television industry, 
the method by which these devices are manufactured must be economical and 
efficient; and small increments in manufacturing costs can make the 
difference between a highly profitable operation and considerable 
financial difficulty. Furthermore, the finished transformer must meet 
rigid electrical performance specifications and operate satisfactorily 
over a long service life. Failure to meet these criteria can severely 
impair the component manufacturer's reputation within the trade. 
It is accordingly an important object of the present invention to provide a 
method of manufacturing a flyback transformer unit which facilitates 
manufacture at low cost, yet provides a high-quality end product. 
Another object of the invention is to provide a transformer winding which 
is especially adapted to receive a portion of a particular transformer 
core, which is provided throughout with invested potting compound, and 
which can be offered at an attractive unit cost. 
A related object is to provide, at an attractive cost, a winding assembly 
which is fully invested with potting compound, even to the extent of 
including a layer of compound inside the winding core adjacent the space 
to be occupied by the transformer core member leg. 
Other objects and advantages of the invention will become apparent upon 
reading the following detailed description and upon reference to the 
drawings. Throughout the drawings, like reference numerals have been used 
to refer to like parts.

DETAILED DESCRIPTION 
While the invention will be described in connection with a preferred 
embodiment and procedure, it will be understood that it is not intended to 
limit the invention to this embodiment or procedure. On the contrary, it 
is intended to cover all alternatives, modifications and equivalents as 
may be included within the spirit and scope of the invention as defined by 
the appended claims. 
More particularly, the drawings illustrate an electro-mechanical device 10 
which comprises the secondary winding of a flyback transformer especially 
adapted for use in domestic television receivers and the like. As is best 
shown in FIG. 4, the device 10 includes an outer, insulating casing or 
housing 11 within which is carried a tubular bobbin 12. A first coil of 
copper or other conductive wire 13 is wound upon this bobbin 12 and a 
first bobbin sleeve 14 is telescoped over both the hollow bobbin 12 and 
the first wire coil 13. Upon this first sleeve 14 is wound a second wire 
coil 15. A second bobbin sleeve 16 surrounds the first sleeve 14 and the 
second coil 15; and a third coil 17 of wire is wound upon this second 
sleeve 16. In like manner, a third sleeve 18 is fitted over the second 
sleeve 17; and a fourth coil of wire 19 is carried upon this outer or 
third sleeve 18. As will be appreciated, the housing, bobbin and sleeves 
are fabricated from a suitable resinous plastic material; and suitable 
electrical connections are made between the various coils. 
The casing 11 is provided with embossments 21 for receiving electrical 
connector or mounting pins 22 as is shown in FIG. 2; and bobbin mounting 
structure comprising pairs of ledges 24 and 25 and associated mounting 
flats 26 and 27 is also formed upon the casing interior surface 28. Within 
this housing or casing 11, the bobbin 12 will ultimately be secured. 
In accordance with the invention, provision is made for the association of 
the finished device 10 with a transformer core member (not shown) in the 
course of component manufacture. To this end, a temporary cylindrical core 
pin 32, which is headed at one end, is inserted within bobbin 12 to be 
temporarily retained against axial dislocation in one direction by a 
suitable number of radially inwardly extending embossments 33 formed on 
the interior surface 34 of the bobbin adjacent one end thereof, as is 
shown in FIG. 3. The embossments 33 cooperate with the flanged head of pin 
32 in maintaining a uniform spacing between these parts; and as will be 
appreciated, embossments or other discontinuous spacers may be substituted 
for the flanged head of pin 32. Upon the outer surface 35 of bobbin 12 
there is wound the first coil of wire. Furthermore, the core pin 32 may be 
fabricated from metal or from a thermally resistant, antifriction material 
such as polytetrafluoroethylene resin. 
After the first wire coil 13 has been wound upon the bobbin 12, the second 
sleeve 14 is slipped axially over bobbin 12 and over the first wire coil 
13. The second wire coil 15 is then wound upon the sleeve 14. In the same 
manner, additional sleeves 16 and 18 of progressively greater diametric 
size can be axially installed over preceding sleeves and over the 
corresponding wire coils 15, 17 (and, when necessary, 19). This winding 
assembly consisting of bobbin 12, the invaginated core pin 32, sleeves 14, 
16 and 18 and wire coils 15, 17 and 19 is then mounted within the cavity 
29 defined by the casing interior surface 28. To this end, the bobbin 12 
is provided with a suitable number of axially extending mounting fingers 
36 (FIG. 3) which are positioned and adapted to mate with or rest upon the 
ledges 24 and 25 and on the cooperating flats 26 and 27 formed within the 
housing interior 29. Thus, the winding coils are preliminarily positioned 
within the housing 11. Flanges 36 may be adhesively secured to the flats 
26 and 27 if desired. 
To provide the desired electrical insulative qualities, and to secure the 
various parts within the housing 11, the housing interior 29 is filled 
with a potting compound 40 (FIGS. 4 and 5). This potting compound is 
caused to invest or fill those spaces 41 between the individual turns of 
the wire coils 13, 15, 17 and 19 and the adjacent sleeves 14, 16 and 18 
and the bobbin 12 itself. In accordance with the present invention, the 
housing 11 and mounted parts are first heated to a suitable temperature 
and thereafter subjected to a suitable vacuum on the order of 100 microns. 
The potting compound, in its molten or liquid state, is then introduced 
into the housing interior 29. Under these conditions, the potting compound 
40 substantially fills the housing interior 29 and flows between the 
winding coils and adjacent winding structure to provide the desired 
electrical insulation to the coils in an intimate manner. 
Moreover and in accordance with an important feature of the present 
invention, a layer 48 of potting compound is formed between the internal 
surface of the bobbin 12 and the external surface of core pin 32 so as to 
accommodate a subsequent insertion of a ferromagnetic or other type of 
transformer core leg (not shown) and to achieve total encapsulation of the 
coil assembly within the housing 11. To this end, providing first heat and 
then vacuum to the preliminarily assembled unit prior to introduction of 
the potting compound 40 has the effect of axially extending the 
polytetrafluoroethylene core pin 32 so as to expand the core pin into snug 
engagement with confronting flats 44 and 45 formed on the casing walls 28. 
Sealing the ends of pin 32 against flats 44 and 45 exposes the annular 
space between the pin 32 and bobbin 12 to the subsequently applied vacuum 
and ensures invasion of the potting composition. Presence of a continuous 
layer of potting compound on the interior of bobbin 12 compensates for 
imperfections in the union of the material of casing 11, and this is 
particularly important at the high voltage end of the transformer. 
Thereafter, the potted assembly is cooled and circular blanks 46 and 47 are 
cut out or reamed from the casing wall, in alignment with the opposite 
ends of the core pin 32 and oversize with respect to the respective ends 
of the core pin, as is suggested in FIG. 4. Next, the core pin itself is 
forced from its position within the assembly generally in the direction of 
arrow 50 to leave a cylindrical cavity surrounded by the layer 48 of 
potting compound. After appropriate quality control procedures are 
accomplished, one leg of a C-shaped transformer core is inserted into the 
cavity left by the pin 32, generally through the apertures 50 and 51 
defined by the removal of the blanks 46 and 47. 
The drawings and the foregoing descriptions are not intended to represent 
the only forms of the invention in regard to the details of its 
construction and method of manufacture. Changes in form and in the 
proportion of parts, as well as the substitution of equivalents, are 
contemplated as circumstances may suggest or render expedient; and 
although specific terms have been employed, they are intended in a generic 
and descriptive sense only and not for the purposes of limitation, the 
scope of the invention being delineated in the following claims.