'May 26, 1942.
F. s. BLOCH
BIMETALLIC ELEMENT
Filed.Ju1y a, 1939
- 2,284,082
2,284,082
Patented May 26, 1942
UNITED STATES2,28i,082"PATENT
OFFICE“ '
BIMETALLIC ELEMENT
Franz Georg Bloch, Le Sentier, ‘Switzerland’
Application July 8,, 1939, Serial No. 283,511
In Czechoslovakia May 30, 1938 '
2 Claims. " (01. 297-16)
mechanical connection betweenadiacent ends oiv V
This invention relates to bimetallic elements
f and particularly to coiled orhelical bimetallic
the pair of. coils, a support for the other end of
one coil, a pointer at the free end of the second
coil, a casing enclosingthe coils, andv a body of
low heat capacity and high heat conductivity
elements for use in thermometers, thermo-elec
tric telemetric systems, thermal switches and the
like.
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within the coils.’
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Coils formed from bimetallic strip material
These and other objects and advantages of the
exhibit a slight‘ increase in ‘diameter in, the
invention will be apparent from the following
course of time due to the gradual relief of sec
speci?cation when taken with the accompany
ondary stresses and strains resulting from-the
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process of manufacture. A sensitive thermome 10 ing drawingin which:
Fig. _1 is a side elevation of'a strain-compen
ter having a bimetallic helixof5 mm. diameter _
sated bimetallic assembly embodying the inven
for displacing a pointer over an arcuate scale
tion;
may show an error of several angular degrees
Fig. 2 is a fragmentary side elevation, with
upon an increase of the coil diameter, of about
0.1 mm. The errors of the several coils are 15 parts in section;ofa bimetallic strip thermome- '
ter embodying the invention;
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cumulative in thermometers, such as described
, Figs. 3 and 4 are plan views of alternative con
, in my prior Patent No. 1,970,219, in which a
single length of bimetallic. strip material is , structions of the bimetallic coils shown in Fig. l;
wound to form inner and outer‘ helices.’ This
drift in the calibration of the apparatus may be 20
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reduced by employing relatively heavy strip ma
terial but this expedient is often-objectionable
.in view of the slow response of thermal elements
of high heat capacity.
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An object of this invention is to provide ther
mally responsive devices, including a plurality
of bimetallic elements, that maintain- substan
tially the same operating characteristics over
and
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Figs. 5 and 6 areschematic dia'grains‘illus
trating the strain-produced dimensional changes
in the outer and inner bimetalliccoils, respec
tively, of assemblies such as shown in Figs. 1
and
2.
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In the drawing, the reference numerals I and
2 identify two’ coaxial and concentric coils of
bimetallic strip material, the upper end of the
outer coil i being anchored to a supporting mem
ber 3 and‘ the upper end of the inner coil 2
long periods. An object is to provide thermally
responsive elements that include a plurality of 30 carrying a staff 4 on which a pointer l or other
control or indicating member" is mounted. The
coils of bimetallic strip material of such design
lower ends of the bimetallic. coils are mechani
and so connected that dimensional changes in
the coils due to temperature variations produce ' cally coupled in such manner that temperature?
produced changes in the dimensions of the two
additive effects while‘ dimensional changes due
to secondary stresses in the individual bimetallic 35 coils produce additive angular displacements of
the staff 4 and the member I that is mounted
coils neutralize each other. An object is to pro
thereon. Asrshown in Fig. 3, the coils land 2
' vide a temperature responsive system including
are formed from a single strip of bimetallic ma
at least two coils of bimetallic strip material that
terial and the intermediate section 8 of the strip
are mechanically connected to produce additive
displacements of a pointer or the like as each 40 thus constitutes the mechanical connection be
tween the coils. Alternatively, as shown in Fig.
coil changes in dimension with temperature
4, the coils i and 2 may be formed from indi
changes, the metal of the higher, rate of expan
vidual strips which are each secured. by solder
sion being at the exterior of one coil and at the
ing or welding, to the coupling member ‘I.
interior of another. More speci?cally, an object
' is to provide a temperature responsive ‘system 45 In accordance with this invention, the helical
coils I and 2. are wound in the same sense, but
including a single strip of bimetallic material
the component metal layers a, b of the metallic
having portions thereof wound as two coils, the
strips are reversely arranged in the coils 1 and
relative locations of the two metals being re
2. This reversal of therelative locations of the
versed in the two coils, a ?xed support for the
end of one coil, and a pointer or the like secured 50 components ofthe bimetallic strips is obtained
by folding the bimetallic strip back upon it
to the end of the other coil. A further object is
self at the junction section 6 in the embodiment
to provide a bimetallic element comprising at
of'Figs. 1 and 3. The geometry of the multiple
least two concentric coils of bimetallic strips
helix thus differs from that of the thermostats
wound in the same sense but with the relative
. location of the component metals reversed, a 55 of my prior patent in which there is no reversal
2,284,082
in ‘the relative location of the bimetallic strip
placed counterclockwise by the increment Am.
components in adjacent helices, and in which
The coilv 2, which is wound counterclockwise as
viewed from its point of support 1, has an ini
tial angular spread p that is decreased‘to the
value p'I as the diameter oi’ the coil is increased,
the adjacent helices are wound in opposite sense
and joined by a spiral connecting section cor
responding generally to the reverse bend I of
the present construction. Temperature changes \
result in a cumulative angular displacement of
by‘the relief of secondary strains, thus displac- ‘
ing the free end of the coil I clockwise by .the
the stat 4 when coils I. and 2 are mechanically
~ increment‘A/S.
I connected as ' above ‘described.
‘In the thermometer assembly of Fig. 2, the
supporting member 3 forthe outer coil I is se
to A5.
cured to a tubular‘ shell I of good heat con
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Thermal elements that are compensated in
this manner may be of relatively light weight in
ductivity that is ?xed toadisl: or plate a that
carries an arcuate'scale, ‘not shown, of tempera- .
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The ‘lengths of the coils‘ i, ‘I, ‘
their relative diameters and the thickness of the
strip material may be so related that, A: is equal
\ comparison with the prior devices in which ap
- ture graduations over which the pointer! is dis
proximately. constant calibration was obtained by
placed in accordance with the temperature-pro
employing, strip material of a strength far‘in
duced changes in the coils I’ and 2. The staff
4 extends through an opening Ill inv the plate l
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= excess of that required for mechanicalstability
ofthe system.
The ‘new elements therefore
i ' which forms a guide ‘and- loose bearing for the
have a low heat inertia and respond quickly to
- staff. , A thin tubularashell 'll of low heat ca-1 20 temperature changes. Full advantage ‘of the low _
pacity and high thermal-conductivity is prefer-v
ably arranged within the inner helical coil].
The lower end ‘ofthe shell ll ?ts over and is
in good heat transfer relationship‘ to'a boss at
the inner surface of the end wall of the‘outerv v25
shell 8. ' The ;_shell “provides a heat transfer
heat inertia is obtained when, as described above,
a body of ‘low heat-capacity and high thermal
conductivity is located within the innerjcoil. '
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It .’-s to be understood that the invention'is
not restricted ‘to'the particular constructions
me'thod'Imay-be applied to spiral coils‘a'swwell
herein shown and described as the compensation.
path for quicklyestablishingewithin the‘inner
helix '2 the temperature that is established at '
helical ‘coils,'-to_ ‘assemblies including ‘more I
the cylindrical and end, wallstof theshell a by_ as‘
coils, and to assemblies in which the :
the mediumto which thesh'ell l'ls exposed“~ vThe 30 'than’twm
coils- are? axially spaced or ‘laterally'spacedifrom ,I
thermometer, thus responds lquicklyf' to ‘zany ' each
othen'q '
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change in the temperatureof the medium as the
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same component metalaof the bimetallic stripl '
;.is adjacent bothttheouterishell I and the inner '
shell ll.
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The manner ' in v which the
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views, Figs. ‘51nd ; 6,1; The- reliefv of ‘winding
strains is always'in the same sense and results
in an ,increase'in the coil diameter, whether ‘the
component metal of higher thermal expansion
_ rate is at the inner or at the outer side of the -
coil. For simplicity of explanation. the angular
extent of the coil >,|I,-~as»initially,formed, is 'as
sumed to be equal to an angle a of less than 360’.
In the relief‘ot thesecondary strains‘ that are.
set up in-the‘» winding of the coil I, the diam- ‘
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strain-produced ' ‘
her helical coils I, 2 ‘is neutralized will be ap
parent from ‘a consideration of‘ the schematic
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‘commie?
> in‘; :a lplurality'of concentric‘helical coils‘ of bi- »
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variations in‘ the diameters oi’ the outerand in
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. 1; A- temperature responsive , device
metallic strip"ma_terial wound in the same sense
and with the‘component nietaisjof the strip ma
terial vreverselylarranged in said-coils,~a shell
‘enclosing said’ coils, means securing an’ end of
one, coilto said'shell, means mechanically con
:necting the other end‘ of that coil to an‘ end of
another coil;v a member connected to thesecond
‘end of said other cell, and a body of low ‘heat
capacityand high thermalsconductivity enclosed
withinsaid sheiiand located within the inner
most of said *c'oiis'an
_tiontosaidshell.i*
‘in good heattransier rela
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2. A temperature responsive device acclaimed
inclaimv 1, wherein said coils comprise 1a ‘single
strip or bimetallic material ~rev‘ersely bent upon‘
eteroi' the coil increases and the angular spread 50 itself at an intermediate portion.v
of the coil is thereby decreased to some smaller
angle a’, i. e. the liree end of the coil I is dis!- ~
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manz'onoaa‘
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