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Патент USA US2500632

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' March 14, 1950
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Telephone Laboratories, Incorporated, New
York, N. Y., a corporation of New York
1
Application Decemberv 28, 1946, Serial No. 718,945
4 Claims. (Cl. 175-315)
'
2
of the type having means for relieving high gas -
Fig. 4 is an enlarged sectional view of a frag
ment of the modification shown in Fig. 3, a por
tion of the plugging material being shown in
pressures created within the capacitors because
section.
This invention relates to electrolytic devices
and more particularly to electrolytic capacitors
conditions.
There are a number of conditions giving rise
to high internal gas pressures arising among
_
Referring now to the drawing, the electrolytic
capacitor there shown comprises a container l
. qt a heating thereof due to abnormal operating .
which may be- of metal. such as aluminum, an
electrolytic capacitor or capacitor element 2,
having wires 1 connected to terminals 4 which
which may be mentioned: over-voltages such as
might occur under open-circuiting'conditions oi 10 may be embedded in a cover 5 of insulating
material, for example, a phenolic condensation
the load in rectifying circuits, application of po
product, having a boss or stud B integrally formed
tentials with reverse polarity or polarized capac~
therewith. The purpose of the boss is to provide
itors, and improper electrolyte and poor oxide film
better sensitivity to the heat emitted by the
formation permitting large direct current leakage
capacitor element. The cover plate 5 is held in
currents at elevated temperatures.
place by crimping the edge 25, a suitable gasket
Usually the capacitor element of an electro
lyte capacitor is sealed in a container of metal,
26 being interposed between the cover plate 5
such as aluminum.
and a shoulder 21 on the container i. Anv aper
It the condenser is over
ture Ill extends through the cover plate 5 and the
heated due to abnormal operating conditions,
the vaporized moisture of the electrolyte oi the 20 center of the boss 6. This aperture I0 is tapered
where it passes through the main portion of the
capacitor can result in a very violent explosion
cover plate.
unless the container is properly vented.
A shoulder H and a threaded portion l2 are
Although a satisfactory form of vent from a
provided in the boss portion of the aperture for
safety standpoint might be one which functions
as a result of pressure alone, it is dimcult to pro 251 the plugging materials.
Plugging materials for vents, such as waxes
vide such a vent.
and asphalts, usually used, have a very high co
One object of this-invention therefore is to
e?icient of expansion which frequently causes
increase the reliability of electrolytic capacitors.
them to loosen in the vent and destroy the seal,
Another object of the invention is to decrease
the dangers due to explosion of electrolytic .30 especially at low temperatures.
To overcome this difficulty a plugging material
capacitors.
for the inner end of the aperture Hi, i. e., in the
Another object of the invention is to improve
boss, is provided consisting of an eutectic metal
the sealing and venting of electrolytic capacitors.
alloy element in the form of a disc 15 (Fig. 2)
In accordance with one feature of this inven
which is ?rst disposed in the aperture of the boss
tion, a combination thermal and pressure vent is
and a hot melt plastic material It having ethyl
provided for an electrolytic capacitor to enable
alcohol as a base combined with iron oxide to im
the escape of gases when it becomes overheated.
In accordance with another feature of the
invention the sealing means for the pressure
relief means for an electrolytic'device has a co
prove its heat conductivity is then deposited in
said aperture.
40
'
The plastic material preferably has a thermal
coe?lcient of expansion vsimilar to that of the
eflicient of expansion substantially the same as
insulating material of the cover l0 so that a gas
that portion of the device wherein it is situated.
tight seal in the cover over the required range 01'
These and other features oft-he invention will
temperature may be maintained. At tempera
be understood more clearly and fully from the
following detailed description when read in con 45 turcs sufficiently high to generate explosive gas
pressures the plastic material softens or lique
nestion with the accompanying drawing in which:
?es and is ejected to relieve the pressure. The
Fig.1 is an elevational view. partly in section of
liquefying temperature of one of the plastic
anelectrolytic capacitor including a vent con
materials employed in carrying out vthis invention
structed in accordance with this inventionwa
was about 165° C. This material will extrude at
portion of the container being broken away;
100° C. due to cold ?ow through the aperture
Fig. 2 is an enlarged sectional view of the vent
under a gas pressure of live to ten pounds per
embodied in the device shown. in Fig. 1, a por
square inch.
tion of the vent being broken away,
In‘ order to prevent cold ?ow and premature
Fig. 3 is va fragmentary sectional view showing a
modi?cation of the vent oi Fix. 1; and
venting at the elevated temperatures and internal
3
8,500,888
gas pressures to which capacitors are subjected
in normal service, the disc or pellet oi eutectic
alloy is anchored adjacent to the plastic material
as an outer blocking or strengthening member.
The disc I 5 shown in Fig. 2 is an alloy of his
muth, tin and lead having a very sharp melting
point at about 97° C. A suitable proportion of
4
cessive 1pressure created within said container
by overheating said electrolyte, said means in
cluding an eutectic alloy member in combina
tion with a backing member of thermoplastic
material adapted to remain solid and sealed in
the container at normal temperatures and to
iuse at abnormal operating temperatures.
these materials is 50 per cent bismuth, 18.8 per
2. In an electrolytic device including a metallic
cent tin and 31.2 per cent lead. A disc having
container enclosing an electrolytic member
a diameter of .080 inch and a thickness of .030 ll) sealed therein, means for relieving excessive pres
inch has been employed successfully. The thick
sure within said container including a disc of
ness of the disc is dependent primarily on the
an eutectic alloy in combination with a plastic
strength required to resist the heat of the plastic
material having ethyl cellulose as a base com
material during injection. .
bined with iron oxide.
The hot plastic material may be inJected into
3. An electrolytic device comprising a metallic
the aperture in the boss under suitable pressure.
container, a cover of insulating material for said
The pressure must be suillcient to insure that
container having an aperture therein, and a plug
the plastic material is forced into the spaces
around the metal disc and into the anchoring
threads. The diameter of the disc I5 is made
slightly smaller than the diameter of the aper
ture in which it rests to facilitate assembly and
to insure sufficient air leakage around the disc
to prevent the trapping of air and the forma~
tion of bubbles in the plastic material.
The ‘
portion of the aperture occupied by the plastic
material is threaded to increase the effective
length of the seal and to retain the plastic ma
terial in position.
Figs. 3 and 4 show a modi?cation of the ar
in said aperture comprising an alloy of bismuth,
tin and lead and a plastic material having a
coe?icient of expansion substantially equal to
that of the insulating material of the cover.
4. An electrolytic device comprising a con
tainer having an electrolytic element therein,
said container having an aperture in a wall
thereof, one portion of the boundary of said
aperture being threaded, another portion of said
aperture being provided with a shoulder, a disc
of an eutectic alloy in said aperture resting
against said shoulder, and a thermoplastic ma
terial adjacent said disc and positioned in the
rangements shown in Figs. 1 and 2, the modi?ca
threaded portion of said aperture.
tion consisting of utilizing a phenolic insert 20
RALPH E. DRAKE.
instead of molding a boss integrally with the
cover member 5. The insert 20 may be cemented
REFERENCES CITED
?rmly into the cover by the use of any suitable 35
The following references are of record in the
cementing material, for example, a cold setting
file of this patent:
formaldehyde resin.
Although speci?c embodiments of the inven
UNITED STATES PATENTS
tion are shown and described, it is to be under
Number
Name
Date
stood, of course, that various modi?cations may 4 U 2,012,359
Sprague _________ __ Aug. 27, 1935
be made therein without departing from the
2,058,773
Cole ____________ __ Oct. 27, 1936
scope and spirit of the invention as de?ned in
2,282,459
Deeley __________ __ May 12, 1942
the appended claims.
OTHER REFERENCES
What is claimed is:
1. In an electrolytic device including a metallic 45
Handbook of Chemistry and Physics, 26th edi
container adapted to enclose an electrolyte her
tion, by Hodgman and Holmes, published by
metlcally sealed therein, means for relieving ex
Chemical Rubber Publishing Co., page 1200.
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