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Патент USA US3061718

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Oct. 30, 1962
'r. H. STIEBEL
3,061,707
PRESSURE TEMPERATURE OPERATED ELECTRICAL SWITCHING APPARATUS
Filed Oct. 20, 1959
2 Sheeis-Sheet 1
uv l/EN TOR
THEOOO
H. S 776'BEL.
Oct. 30, 1962
T. H. STIEBEL
3,061,707
PRESSURE-TEMPERATURE OPERATED ELECTRICAL SWITCHING APPARATUS
Filed Oct. 20, 1959
2 Sheets-Sheet 2
INVENTOR
B
y THEOO I? H. ST/EBL'L
l
Free
3,061,707
Patented Oct. 30, 1962
2
mations of the casing may occur, causing sticking of the
3,061,707
movable components of the switch.
PRESSURE-TEMPERATURE QPERATED ELECTRI
However, in accordance with this invention, these dis
CAL SWITCHING APPARATUS
advantages can be avoided by no longer housing the
Theodor Hermann Stiebel, Luchtringer Weg 11,
pressure responsive element and the electrical switch
Holzminden (Weser), Germany
mechanism each in separate regions of the handle casing.
Filed Oct. 20, 1959, Ser. No. 847,509
An object of the invention is to eliminate the need
10 Claims. (Cl. 219-41)‘
for justi?cation of the relative positions of the pressure
This invention relates to an electrical switching ar
responsive element and the switch per se by permanently
rangement within a casing or head actuatable by a hy 10 ?xing their relative positions before assembling them with
draulic drive by way of a force transmitting member.
the housing or handle.
The drive per se consists of a probe tube terminating in
a pressure sensitive element, the probe tube preferably
Still a further object is to facilitate the installation of
the heating element and the pressure-temperature respon
containing a thermally expansive liquid. The pressure
sive switching mechanisms in cooking utensils and vessels,
variations are transmitted to the pressure responsive ele 15 and to permit ready replacement thereof with a minimum
ment either directly by way of the temperature acting
or“ simple assembly and disassembly operations.
on the free, closed end of the probe tube or indirectly,
I accomplish the foregoing, and other, objects by pro
in the manner known from the manometer art, by way
viding an insulating plate upon which both the pressure
of an open probe tube end.
responsive element and the electrical switch are mounted,
Temperature disconnect switches or control devices
which mounting plate is readily insertable in a housing
employing these principles are used, for example, in im<
or handle. So to mount the pressure-temperature respon
mersion heaters. In such heaters it is prior knowledge to
sive member, the latter is provided with tongue-like pro
house the electrical switch and the pressure sensitive ele
jections which preferably are inserted through corre
ment (a membrane or a bellows) separately, each in
sponding apertures or grooves in the mounting plate and
one of the half-shells of the handle casing or in one 25 are bent over, and/or twisted, to the rear thereof while
of the handle casing portions, and to separate them by
the electrical switch and the line connections are sup
means of an insulating plate clamped between the parts
ported on the face of the mounting plate remote from a
of the handle casing, the plate having an aperture or
?exible wall or membrane of the pressure-temperature
recess for a pressure transmitting element. Such im
responsive member. The so assembled parts provide a
mersion heater is, for example, shown in Patent 2,902,581
structure which is as simple as possible, is fully self
for “Miniature Immersion Heater With Electric Con
troller Sealed in Handle,” issued to me on September
1, 1959.
The predetermined relative position of the pressure re
sponsive element and the electrical switch for obtaining
positive switching sequences is assumed thereby only
after assembly of the handle casing in immersion heater
handles so constructed. Consequently, only after assem
bly of the complete device can it be ascertained whether
the switching temperature is the required temperature.
Subsequent justi?cation is then practically impossible, par
ticularly where the half-shells of the handle, or the cas
ing components, are joined, as by welding them together,
contained and independent of the position of the casing
portions relative to each other, is positively operable at
the predetermined desired temperature of the heated con
tents of the cooking utensil, and completely and readily
interchangeable.
If desired, this structure can be atq
tached to a handle or housing portion by means of a
screw simultaneously serving as a portion of a line con
nector.
-
Where the handle casing consists of a bell-shaped hous
ing into the open end of which a ?anged plate is in
sertable which supports both of the end regions of the
tubular heater and the probe tube and simultaneously
serves as the sealing cover, such as shown in my copend
as occurs extensively in making handles for immersion 45 ing application for patent, Serial Number 812,935, ?led
heaters of synthetic materials.
It is, of course, conceivable that the actuating mecha
nism of a justifying arrangement, in the form of a regulat
May 13, 1959, for “Watertight Handle for Immersion
Heaters,” it is recommended that the mounting plate be
anchored to the tubular heater connecting terminals which,
ing screw, be brought out through the handle housing;
for this purpose, are made rigid and preferably in the
but by so doing the immersion heater handle is no longer 50 form of lugs of known type, and are mechanically con—
watertight. Furthermore, in such a construction, the
nected rigidly to the line connector supported on the
point at which the switch operates to open the heater
mounting plate.
circuit might be irresponsibly altered by an unauthorized
To increase the stability of the switching arrangement
according to the invention within elastic handle housings,
adjusted to above the boiling point, might, in the least 55 indirectly mechanically supporting the same by way of
objectionable case, be actuated during ordinary heating,
the temperature probe tube on the ?anged plate, has been
that is, below the boiling point; or vice versa, a tempera
found to be appropriate. Hence, the instant invention
ture regulating arrangement normally operating at below
further proposes to make the temperature probe tube
the boiling point may fail completely, that is, not be ac
rigid at least from the ?exible membrane of the pressure
tuated at all when the disconnect point is adjusted to a 60 temperature responsive member to its exit portion beyond
temperature above the boiling point.
the ?anged plate, or to reinforce the per se readily de
Likewise, in the case where a temperature disconnect
fortmable temperature probe tube with an enveloping rigid
arrangement is housed in the immersion heater handle, the
sleeve or tube at such region. In addition, the mounting
. predetermined relative position of the parts housed in
plate can advantageously be secured in its position by
i‘ the individual half-shells of the handle or in the indi 65 providing tongue-like extensions at the edge thereof to-‘
vidual portions of the handle housing will not be ob
ward the ?anged plate and providing corresponding re:
.tained positively, where these handle portions are, wholly
cesses in the ?anged plate. The mounting plate, prior
or partially, of a material of perceptible elasticity, pref
to making the electrical connections, is then forcibly and
erably synthetics. In the course of reclosing the switch
positively inserted into the recesses. Furthermore, it has
by thumb-pressure on the portions of the handle provided 70 been found advantageous, in addition to supporting the
therefor, below which the temperature and pressure re
structure (switch, pressure-temperature responsive mem
sponsive switching element is located, undesirable defor
ber, and mounting plate) at one side of the ?anged plate,
person. Thus, an excess temperature disconnect switch,
3,061,707
3
I
,
1
4
to push the mounting plate drawerlike, with its lateral
(FIGURE 3) in mounting plate 18 and are twisted or
sides in grooves provided therefor Within a portion of the
bent over on the other side against the mounting plate
to support the casing thereon. A hollow rivet 23 fastens
housing, into the housing, or, vice versa, to push the hous
ing provided with grooves over the assembled complete
mounting plate. By so doing damage to the electrical
switching arrangement either on pushing the mounting
one end of a contact spring 24 to the other face of the
mounting plate, that is, to its surface opposite membrane
2%, a button 25 of electrical insulating material being
carried by the contact spring. ‘Button 25 extends through
an aperture 26 de?ned by the mounting plate with one
end of the button engaging resilient membrane 2t) and its
exerted upon it, is avoided.
Two illustrative embodiments of the invention are now 10 other end engaging a soft, manually depressible region 27
plate in, or on manual reconnection of the switch be
cause the mounting plate has too great a bending moment
descraibed in detail with the aid of the annexed draw
ing, in which:
FIGURE 1 shows a top view, partially in section, of a
?rst embodiment of the invention comprising a heating
element combined with a temperature-responsive dis
connect switch installed in a container for heating liquids;
FIGURE 2 an exploded perspective view or" the switch
ing head of the embodiment of FIGURE 1 in the order
in which the head is assembled;
FIGURE 3 a section along line III-III of FIGURE 2
showing the temperature responsive member and the dis
connect switch assembled with the mounting plate as a
unitary component;
FIGURE 4 a section along line IV~—IV of FIGURE 1;
FIGURE 5 a section along line V-V of FIGURE 1;
FIGURE 6 a longitudinal view, partially in section, of
of cover 17 ‘(FIGURE 4).
spring 24 carries a contact
a ?xed strip contact 31}
which in turn is connected to
The free end of contact
29 which is juxtaposed to
on the mounting plate,
an elongated contact lug 31
(‘FIGURES l and 4) which at its opposite end electrical
ly connects with a bow or loop 32 in recess 41 of body
141 into which one rigid terminal 33 (FIGURE 4) of heat
ing element 3 is slid on assembly of the heating element
with base 1% to electrically connect that side of the heat
ing element to strip contact 30.
The electrical connection of terminal pin 15 to con
tact spring 24 is by way of a conductor 34 in base 10,
conductor 34- terminating in a metal nut 35 sunk in
supporting surface 36 of base It) for mounting plate
15}. A metal bolt 37 is threaded into nut 35 and in con
ductive contact extends into the hollow rivet 23 which
a second embodiment of the invention in an electric im
holds mounting plate 18 and contact spring 24 together.
mersion heater handle with the handle casing open;
FIGURE 7 a section along line VII-VII of FIG
URE 6;
!FIGURE 8 a section along VIII—VIII of FIGURE 6;
Thus metal bolt 37 serves in a ?rst aspect as a current
supply member, and in second aspect to af?x tempera
ture switching arrangement 4 to body 11). The elec
trical connection of terminal 16 to the other end of heater
FIGURE 9 a view of the second embodiment similar
coil 3 is by way of a direct connection in the form
of a metal tube 39 embedded in body It} and end 28 of
body 11) adjacent to vessel 2, into which the correspond
to the view of F-IGURE 6 but with the handle casing
35 ing connecting pin 33’ of the heater coil slides on as
closed.
sembly exactly as does connecting terminal pin 33 into
Referring to the drawing, the ?rst illustrative embodi
ment of my invention is shown in FIGURES 1 through
loop 32.
Assembly of pressure-temperature switching arrange
5. Through an aperture 1 de?ned in the cylindrical wall
ment 4 with heater element 3, and the installation there
of a vessel '2 for heating liquids, for example a water
kettle, a tubular heating element 3, of known construc 40 of, proceed as follows: The above described pressure
temperature switching arrangement 4 constructed as a
tion per se, projects into the interior of the vessel and is
completely independent structural element, with mount
provided, exterior to the vessel wall, with a temperature
responsive disconnect switching arrangement 4. The
heater end of heating element 3, broken away and not
shown in FIGURES 1 and 3, maybe in the form of a hol
low cylinder or an open helical coil, the latter being
shown in FIGURES 6 and 9. The switching arrange
ing plate 18 positioned on supporting surface 36 and
laterally in guide grooves 40 of body 10, is slid into the
base body whereby contact lug 31 and loop 32 are posi
tioned in a suitably formed recess 41 provided, as has
been stated, in the base body.
Thereupon metal bolt
37 is tightly screwed through metal nut 35, and cover
tending into the vessel and containing a thermally ex
117, with its dove-tailed shaped lateral edges 42 in corre
pansible liquid 6. The probe tube 5 is enveloped by pro 50 sponding grooves 43 of the base body, is slid into the
base body as previously was the mounting plate, where
tective pipe 7 which is connected by heat conductive
by the rim of recess 44 in end 38, adjacent to vessel 2,
bridge 8, at its region extending into vessel 2, to tubular
of cover 17, slides on the temperature probe tube until
heating element 3. The shanks of the heating element 3,
a longitudinal extension 45 of the mounting plate, to
together with pipe .7, pass through plate ?ange 9, on the
interior surface of the wall of vessel 2, to rigid base 55 wards the end of the insertion, enters into, and termin
ates in, a corresponding opening 46 in such cover end
body 10 of a material non-conductive both thermally and
38, so that mounting plate 18, which is subjected to a
electrically, positioned on the exterior surface of the wall
of the vessel of a switch housing or head. Obviously, the
bending stress on re-connection of the switch, as below
end of protective pipe 7 within vessel 2 is closed to pre
described, also has a support at its ‘forward end which
vent leakage of the liquid being heated into the switching 60 otherwise is not supported on supporting surface 36.
arrangement. Base body 10 and rim region 12 of the
The assembled switch head is ‘so placed in front of aper
vessel wall de?ning aperture 2 are rigidly and tightly
ture 1 and plate ?ange 9 positioned in back thereof,
ment 4 is provided with a temperature probe tube 5 ex
sealed, by bolts 13 and packing 14, to plate ?ange 9, with
the baseiody serving as the housing for temperature re—
sponsive‘switching arrangement 4 (FIGURES 2 and 3),
while simultaneously inserting the probe tube 5 pro
jecting therefrom into protective tube 7, that metal tube
65 39 and loop 32 of contact lug 31 on pushing it further
forward in the direction of plate ?ange 9, will push over
the terminal pins 33, 33’ of heater 3. Thereupon the g
switch housing-as initially stated-is bolted to plate
able cover 17.
?ange 9. Dismantling and disassembly of the switch
The switching arrangement 4 per se is a?‘ixed to mount
ing plate 18 of electrically insulating material and con 70 housing is obviously in the reverse order.
The switching sequence is as follows: Spring mem
sists of a relatively ?at, pressure casing 19, connected to
brane 21), as the result of the increasing pressure applied
the temperature probe tube 5, and the pressure casing
to it with increasing temperature of the liquid in vessel
wall facing the mounting plate is provided with a resilient
2 by thermally expansible liquid 6 in temperature probe
membrane 20. The pressure casing is provided also with
tongues 21 which pass through corresponding slots 22 75 tube 5, which liquid 6 can be of such type that when the
as also for terminal pins 15 and 16 (FIGURES 4 and 5)
connectable to the electric line, and is provided with slid
5
3,061,707‘
liquid to be heated or the heating coil reaches the pre
determined switching temperature it evaporates, is dis
tended to such a degree that it snaps into its convex
position (FIGURES 3, 4) thereby lifting insulating but
ton 25 in impact-like manner, by which action contact 29
is moved away from ?xed contact strip 30 with the re
6
head or the housing wall, and the membrane 20 is so
constructed that it has but a single normal position, at
which the switch is closed, to which at all times it tends
to restore even when distended sufficiently to open the
switch.
What I claim is:
sult that the heating circuit is opened. Such snap-action
I. A switching arrangement for electrical heaters in
direct heat transferring contact with liquids to be heated
in detail in my copending application above mentioned.
comprising an electrical heating element having a pair
Reconnection of the current is obtained manually by 10 of terminals, a ?xed ?rst contact, a spring of electrically
depressing soft portion 27 of cover 17. When so do
conductive material of which one end is spatially ?xed,
ing, the insulating button 25 is depressed to such extent
a second contact supported at the free end region of the
membranes for pressure casings are shown and describedv
as to exert su?‘icient pressure on the resilient membrane
spring end movable to engage with the ?rst contact, a
20 that the latter will spring back into its opposite, or
pair of line supply conductors of which one is connected
concave (and connect) position, shown in FIGURES 3 15 to one of the ?rst and second contacts and the other to
and 4 by the dashed or broken lines. Simultaneously,
one terminal of the heating element, the other of the ?rst
prebiased contact spring 24 will spring back into its
and second contacts being connected to the other terminal
connecting position when contact 29 presses tightly
of the heating element, a hollow housing of electrical
against ?xed contact strip 30.
and thermal insulating material, a longitudinal internal
The immersion heater of FIGURES 6 through 9 is, 20 shoulder in each of a pair of opposite longitudinal walls
with minor variations, provided with the same switching
of the housing, a support plate of insulating material slid
arrangement as shown in FIGURE 3.
Like reference
ably supported on the housing shoulders, the ?rst contact
characters in this embodiment denote the same elements
and the spatially ?xed end of the spring being attached
as in the ?rst, and above described, illustrative embodi
to one longitudinal face of the support plate, a heat probe
ment. Speci?cally, the following changes in construc 25 tube in heat transfer relation with the heating element,
tion are involved in this second illustrative embodiment
a thermally expansive liquid within the heat probe tube,
of the invention. The protective tube 7 for probe tube
a closed reservoir into which the heat probe opens hav
5 is dispensed within the switch housing, constructed in
ing one wall which is ?exible, a pin of insulating ma—
the form of the handle for the immersion heater, is
terial supported in and extending through the spring, one
not, as in the ?rst embodiment, adapted for incorporation 30 end of the pin engaging the ?exible wall of the reservoir,
or building into a heating vessel and thus need not, even
the support plate de?ning a central aperture through
temporarily, be separated from the heating element. The
which the pin extends, and means mounting the heat
form of the handle housing of this second embodiment
probe tube and the reservoir on the longitudinal face of
renders inadvisable the use of the threaded connection
the support plate opposite to that to which the ?rst con
of a conductive bolt 37 and a conductive nut 35 as in .35 tact and the ?xed end of the spring are attached.
the ?rst embodiment.
2. The switching arrangement according to claim 1 in
Furthermore, the form of the direct connection made
by metal tube 39 from the connecting line 47 to the
terminal prong of the heater 3 is, in this embodiment, in
which the support plate is mechanically positioned in the
housing by a metallic threaded member threaded into
and through the spatially ?xed end of the spring, through
the form of a conductor 89' directly supported on mount 40 the support plate and into the housing wall, the threaded
ing plate 18 to maintain bell-shaped, thin handle 48, free
member electrically connecting to one of the line supply
of all conductors. Handle housing 48 is made of a per—
conductors.
ceptibly elastic thin walled synthetic material in order
3. 'In combination with a vessel for heating liquids, an
to obtain the soft portion 27 by thinning the wall thick
immersion heater of which the heating coil of the im
ness of the handle housing, and, as below described, 45 mersion heater extends through an aperture de?ned in
to connect the handle housing with the ?anged cover
the heating vessel wall, means sealing the heating coil
plate 9'. Loop 32 (32') and contact lug 31 (31’), in
liquid tight within the vessel with its terminals external
this embodiment, are provided at each connecting ter
to the vessel, a housing of electrical and thermal insulat
minal 33 (33') of heating element 3 with such terminal
ing material external to the vessel, the housing de?ning a
pins being of rigid material to function as supports for
cavity into which the terminals of the immersion heater
mounting plate 18 and being soldered to the loops upon
extend, a heat probe extending through the sealing means
previously having inserted extension 45 of the mounting
and containing a thermally expansive liquid, a closed con
plate into aperture 49 of ?anged cover plate 9’. The
tainer into which the end of the probe external ‘to the ves
two last-mentioned expedients, together with sleeve 50
sel connects, one wall of the container having a ?exible
extending through cover plate 9' and reinforcing tem 55 region, a support plate of insulating material within the
perature probe tube 5, function to stabilize the inter
housing cavity, an electrical switch having a spring throw
connection of mounting plate assembly 18, having switch
biased to closure and connectable to a line supply of elec~
ing arrangement 4 mounted thereon, with ?anged cover
trical potential, means supporting the switch and the con—
plate 9’. Such immovable and rigid disposition of the
tainer on the plate, an insulating member supported in and
switching arrangement relative to the ?anged cover plate 60 extending through the spring throw of the switch and ex
is absolutely required also for the reason that on as
tending through an aperture de?ned in the plate to engage
sembling bell-shaped handle housing 48, which guides
the container ?exible wall, and a ?exible portion in a
the lateral edge regions of mounting plate 18 in grooves
51 during such assembly, the housing on further ‘advance
ment must be positioned in a predetermined relation to
?anged cover plate 9' when the bell-shaped housing,
automatically distending its open rim end 52., tightly en
gages rim 53 of ?anged cover plate W with internal an
nular projection 54 of the bell-shaped housing.
As will be obvious to the skilled worker in the art, the
temperature disconnect switch in both switch head 11
and in handle housing 48 may house a temperature reg
ulating arrangement, that is, a controller, in place of the
disconnect switch shown in both embodiments. In such
case, there is no need for a soft portion 27 in either the
wall of the housing aligned with insulating member for
depressing the insulating member manually to restore the
container ?exible region and the switch each to its pre
operated condition after operation thereof by the ex
pansion of the thermally expansive liquid at a predeter
mined temperature.
4. The combination of claim 3 in which the heat probe
is removably within a protective pipe integral with the
sealing means and extending into the vessel, and a heat
conductive bridge connects the protective pipe to the
heating coil.
5. The combination of claim 3 in which the housing
consists of a body de?ning a longitudinal recess extending
3,061,707
8
8. The switching arrangement according to claim 7 in
which a plurality of elongated projections integral with
the enclosure extend through apertures de?ned in the
from one end of the body to close its other end, and a
cover having an integral ?ange at one end to close the
open end and the top of the recess when slid into the
supporting plate and are deformed at their ends project
.ing beyond the plate securely to attach the enclosure to
the plate, and a rivet attaches one end of the movable
body, the body has a pair of grooves in opposite longi
tudinal walls for guiding the support plate with the switch
and the container mounted thereon into the cavity of
contact to the support plate.
9. The switching arrangement according to claim 7
in which a hollow, electrically conductive, rivet a?'ixes
the recess, a conductive threaded member passes through
one contact of the switch and the insulating plate into the
body when the plate is in its predetermined position with
in the cavity, a line conductor is embedded in the body 10 one end of the movable contact to the support plate and
has an externally threaded portion extending through the
and electrically connected to the threaded member, a
longitudinal projection is integral with the trailing end
of the support plate, the projection extending into an
support plate, the other side of the line supply being
connected to an internally threaded, electrically conduc
tive, member embedded in the housing into which the
extending portion of the rivet is screwed, to mechanically
position the support plate at the predetermined position
within the housing and to attach the support plate to the
aperture de?ned in the integral ?ange of the cover on
closing the cover on the body with the plate in its prede
termined position, and means secure the body with its
cover closed to the sealing means.
housing.
6. The combination according to claim 5 in which the
body de?nes a second recess, a pair of line terminals is
disposed within the second recess of which one terminal
is connected to the line conductor embedded in the body,
10. The switching arrangement according to claim- 1
in which the housing consists of a bell-shaped body and
a cover ?tted over the open end thereof, the spring is
biased to closure of its free end on the ?rst contact and
a conductive tube is embedded longitudinally in the body
and connected at one end to the other line terminal, and
a conductive rod embedded transversely in the body con
nected at one end to the other switch contact with the
plate in its predetermined position, the other end. of each
conductive tube and the conductive rod electrically
engaging the terminals, respectively, of the immersion
is movable by the pin moved by the ?exible Wall of the
reservoir at a predetermined elevated temperature of the
“ liquid within the reservoir to disengage the free spring
end from the ?rst contact, and one wall of the body has
a ?exible portion registering with the insulating pin when
the cover is secured to the body with the plate at a prede
termined position within the housing for manually de
pressing the ?exible body portion to depress the insulating
pin after the liquid within the reservoir has cooled from
heater.
7. A switching arrangement actuatable at a predeter~
mined temperature to disconnect an electrical supply line
in which it is connected comprising an enclosure having
at least one pressure-sensitive wall, a thermally expansive
the predetermined elevated temperature to restore both
the ?exible wall of the reservoir and the ?exible portion
liquid ?lling the enclosure, an electrical heating element
of the body to their preoperated positions, both the ?ex
for connection to the electrical supply line, a portion of
ible portion of the body and the ?exible wall of the reser
the enclosure remote from its ?exible wall being ex
voir being su?iciently stiif that with pressures thereon in
posed to heat from the heating element, a ?xed elec
either the outward or the inward direction of magnitudes
trically conductive contact electrically connected to one
less than that corresponding to the predetermined ele
side of the heating element, the other side of the heating
vated temperature they each retain the position deter
element being connected to one side of the line supply, 4.0 mined by the last applied pressure and the direction
a movable electrical contact electrically connected to the
thereof.
other side of the line supply, the movable contact nor
References Cited in the ?le of this patent
mally engaging the ?xed contact, a support plate of elec
trical insulating material on one face of which the ?xed
UNITED STATES PATENTS
and movable contacts are mounted while the enclosure 45
is mounted on the opposite face thereof, an interconnec
tion of electrical insulating material passing through an
aperture de?ned in the support plate between the ?exible
wall of the enclosure and the movable contact, an open
top housing of electrical insulation material, a pair of 50
spaced longitudinal shoulders on opposite walls of the
housing adjacent the open top of the housing, and a cover
1,620,183
1,833,996
2,024,060
2,369,986
2,432,169‘
Bersted _____________ __ Mar. 8,
Johnstone et al _________ __ Dec. 1,
Peralta _____________ __ Dec. 10,
Schaefer _____________ __ Feb. 20,
Morgan et al. ________ __ Dec. 9,
1927
1931
1935
1945
1947
\ 2,576,688
Landgraf ____________ __ Nov. 27, 1951
2,732,478
Stiebel ______________ __ Jan. 24, 1956
of electrical insulating material for the housing supported
2,902,581
Stiebel ______________ __ Sept. 1, 1959
on the shoulder the nearer to the open top of the housing,
» 2,977,456
Stiebel _____________ -_ Mar. 28, 1961
the support plate being slidably supported on the other 55
shoulder.
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