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Патент USA US2136609

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Nov. 15, 1938.
L. B. BUTTERFIELD ET AL
2,136,609
ELECTRICAL DEVICE AND A METHOD OF MAKING THE SAME
Filed April 10, 1936
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F I 6. 2
IN VEN T0 RS
1. . a. BUT TERFIEL 0
R. r. 0.4 RRE r 1'
RI. PA mr JR.
A TTORIVE)’
Patented Nov. 15, 1938
2,136,609
UNITED STATES
PATENT OFFICE
2,138,809
‘
ELECTRICAL DEVICE AND A METHOD OF
MAKING THE SAME
Louis B. Butter?eid, Short Hills, Robert F. Gar
rett, Cranford. and Robert E. Park, In, Ailwood, N. 1., assignors to Western Electric Company,
Incorporated, New York, N. Y., a corporation
of New York
Application April 10, 1936, Serial No. 73,716
5 Claims. (CL 175-41)
This invention relates to electrical devices and
a method of makingv the same and more particu- ‘
larly to high precision electric condensers, coils
and the like and a method of making them.
5
Electrical devices such as condensers, coils,
transformers and the like used in apparatus of
high precision, e. g. such as are components of
the resonant circuits employed in the communi
cations arts, must be of a high degree of accuracy
10 of predetermined value of electrical character
istics and of invariance of such values under
service conditions. Such devices are frequently
placed for protection against the effects of at
mospheric changes in temperature and moisture,
in containers of metal or other material and
sealed therein with a fusible asphaltic mixture
commonly called a ."potting" compound. Pene
tration of such compound into the device being
"potted" may affect its electrical characteristics.
An object of the present invention is to pro-‘
duce such devices of a simple and‘ reliable con
struction in a simple and rapid manner, to have
the desired accuracy and invariance of capaci- .
tance, inductance or whatever electrical char
acteristic may be of importance. in the given
device.
One embodiment of the invention contemplates
covering or wrapping the device with some suit
able protective covering and potting the protected
device, the covering being preferably a wrapping
of fibrous non-conductive non-hygroscopic ma
terial such as mineral wool, glass wool, baked
textile tape, baked paper or the like, or being an
inner can or casing of metal, mica, baked card
board or the like.
Other objects and features of the invention will
appear from the following detailed description of
several devices constructed in accordance with
the invention, taken in connection with the ac
companying drawing in which the same refer
ence numerals are applied to identical parts in
the several figures and in which.
I Fig. 1 is a broken perspective view of a wrapped
condenser ready to be potted;
45
Fig. 2 is a similar view of a container therefor,
and
'
Fig. 3 is a similar view of a‘coil potted in a
double container.
In the embodiment disclosed in Figs. 1 and 2,
The condenser proper, or other device, is as
sumed to have been baked or otherwise treated
to drive out substantially all moisture; and, while
still hot or otherwise ensured against entry of
moisture thereinto, it is provided with a wrap a
ping or covering 24 of some suitable substantially
moistureless and preferably non-hygroscopic ma
terial. Mineral wool in a roughly felted, roughly
sheet form has been found eminently satisfactory
and may be wrapped on by hand. Preferably this
wool should have been previously baked also or
otherwise dehydrated, e. g. in a vacuum desiccator
with calcium chloride present. Preferably also,
after being wrapped, the wrapping may be se
cured in place with predried textile thread or 15
tape 25 or with metallic wire, care being taken
in the latter case to avoid short circuiting the
terminals. However in some cases it will be found
that the mineral wool will interfelt with itself
while being wrapped, sufficiently to make a self M0
retaining cover.
Other substances beside mineral wool may be
used, e. g. glass wool, asbestos, or even vegetable
?bre or animal fiber materials provided that these
latter are carefully predried and that access of 2
moisture is barred during the process. The point
is that the wrapping 24 must be substantially free
of moisture when in place, must be electrically
non-conductive, and must be su?lclently thick
and dense to prevent the asphaltic potting com 0
pound from coming into contact with and enter
ing between the laminae of the stack of ‘the con
denser or other electrically active elements of an
other kind of devicebeing potted. In the case of
the condenser shown it is the edges of the laminae
which must be protected; contact of the com
pound with the outer faces of the clamping plates
2i or with the screws 22 is harmless, unless the
compound is corrosive. In the case of a coil, and
particularly of a coil having a core compacted of 40
granular magnetic material, it may be of im
portance to prevent access of the potting com
pound to the wound conductor and to the core
if any. Thus the condenser, coil or other device
being potted need not always be completely en
closed within the protective material so long as
this is so disposed as to'protect the active parts.
If the wrapping material used needs more con
an electrical condenser has an intercalated stack
straint than is conveniently aiforded by a thread,
III of metal and dielectric laminae held between
two clamping plates 2i (only one shown) which
are held together by four screws 22. Terminal
members 28, 23 are attached to groups of alter
tape, wire or other strand, it may be provided
with an outer wrapping of some suitable moisture
less sheet material 28. Mica has been found sat
isfactory for this purpose; but also other mate
rials might well be used such as predried paper
nate metal laminae.
.
2
2,130,009
or cardboard, predried thin wood veneer, or even
if care be used to prevent short circuiting, a metal
foil or thin sheet. The strands II if then used
may be applied either over or under the sheet II
of the invention as pointed out in and limited
as most convenient.
of an unimpregnated stack of metal and dielectric
laminae with means to protect the same compris
The wrapped condenser, or other device, is then
preferably inserted into the container II which
is here shown as a sheet metal box or can, open
at its upper end. A measured quantity of molten
10 potting compound 21 is placed in the can Just
prior to the introduction of the device, being such
in quantity that the device and compound will
just substantially ?ll the can, the compound ?ow
ing ordinarily over the top of the device generally
15 within the can and thus sealing the device com
pletely therein except for the terminals 23, 2!.
While the can I! is shown as metal, it may also
be of non-magnetic and electrically non-conduc
tive material, e. g. of wood, plain cardboard, im
20 pregnated cardboard, molded resinous material,
or any other mechanically and electrically suit
able substance.
When the potting compound has set, the oper
ation and the device are completed. The device
proper is then completely enclosed and sealed, ex
cept for its terminals, within a seamless and
completely enveloping sheath of the solidi?ed
potting compound, while at the same time the
only by the appended claims.
What is claimed is:
1. The combination in an electrical condenser
ing a protective sheath of substantially moisture
less mineral ?bres substantially completely sur
rounding the stack, a cast sheath of moisture
proof asphaltic material thereover substantially 10
completely and seamlessly enclosing the sheath
of mineral ?bres on all sides and prevented from
entering the stack by the sheath of mineral ?bres,
and a preformed casing thereover. having the cast
sheath molded therein.
2. The combination in an electrical condenser
of an unimpregnated stack of metal and dielec
tric laminae with means to protect the same
comprising a protective sheath of ?brous sub
stantially moistureless electrically non-conduc
tive material substantially completely surround
ing the stack, a wrapping of molstureless sheet
material around the sheath, a cast sheath of
moisture-proof asphaltic material thereover sub
stantially completely and seamlessly enclosing the
wrapping on all sides and prevented from enter
ing the stack by the ?brous sheath and the wrap
ping, and a preformed casing thereover having
compound has not been permitted to come in
30 contact with or enter between electrically active
the cast sheath molded therein.
parts of the device and thus aiIect and alter pre
determined and accurately adjusted electrical
characteristics and properties of the device.
Another embodiment of the same concept of
~35 providing an electrical device with a seamless
of an unimpregnated stack of metal and dielec
tric laminae with means to protect the same com
prising a protective sheath of substantially
moistureless mineral ?bres substantially com
protective sheath enclosing it completely except
for protruding terminals yet not in contact with
the device, is disclosed in Fig. 3. Here a coil II
or a condenser or other device, with or without
a core, is placed in an inner can II which prefer
ably completely encloses the coil on all six sides
except for the terminals 32, II of the coil which
are brought out through the can. The inner
can, with the coil sealed therein by closing all
seams as by soldering, gluing, crimping or other
wise su?iciently tightly to prevent entrance of
3. The combination in an electrical condenser
pletely surrounding the stack, a wrappins of
moistureless sheet material around the sheath, a
cast sheath of moisture-proof asphaltic material
thereover substantially completely and seamlessly
enclosing the wrapping on all sides and prevented
from entering the stack by the sheath of mineral
?bres and the wrapping, and a preformed casing
thereover having the cast sheath molded therein.
4. The combination in an electrical condenser
of an unimpregnated stack of metal and dielec
tric laminae with means to protect the same com
the inner can in a sheath of the compound com
prising a protective sheath of mineral wool sub
stantially completely surrounding the stack, a
wrapping of sheet mica around the mineral wool
sheath, a cast sheath of moisture-proof asphaltic
potting compound, is then potted in an outer can
26 with su?icient potting compound to enclose
plete except for the terminals 32. As before, the
material substantially completely and seamlessly
can It, and also the can it may be of any mate
rial appropriate to the case in hand.
enclosing the wrapping on all sides and prevented
from entering the stack by the mineral wool
In either embodiment, the potting may be done
as described, by placing a sufdcient quantity of
sheath and the mica wrapping, and a preformed
casing thereover having the cast sheath molded
compound in the outer can and then inserting the
wrapped device or the inner can containing the
device into the compound; or the inner can or
wrapped device may be placed or suspended in
the outer can and the molten potting compound
poured around it and allowed to set.
‘A suitable compound for use in potting is a
mixture of 85 parts by weight of asphalt melted
down with 10 parts by weight of rosin and 5 parts
by weight of rosin oil, although any other. satis
factory mixture may be used, there being many
such well known in the art.
The embodiments disclosed are clearly illus
trative only and may be departed from in many
ways without departing from the scope and spirit
therein.
-
5. A method of making protected unimpreg
nated electrical condensers which comprises the
steps of dehydrating a supply of ?brous electri
cally non-conductive material, wrapping the
dried ?brous material about an unimpregnated
stack of metal and dielectric laminae, and casting
a substantially seamless sheath of moisture proof
asphaltic material as a cover completely enclos
ing the wrapped device on all sides, the wrapping
of ?brous material preventing the molten asphal
tic material from entering the stack.
‘
LOUIS B. BU'I'I‘ERHEID.
ROBERT F. GARRE'I'I‘.
ROBERT E. PARK, Jr.
46
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