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Патент USA US2288788

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July 1,1942.
E. K. CLARK Em
2,288,188
METHOD OF TREATING THE HEAT-RESPONSIVE ELEMENTS OF‘ THERMOSTATS
Filed Nov. 22, 1940
FIG- /.
FIG- 2
WITNESSES:
'
'
INVENTOR
EA/PL K. CLARK ¢
67
'
'
GEORGE f. prefca
-
BY
W??}
ATTORNEY
Patented July 7, 1942
2,288,788
: UNITEDSTATES PATENT OFFICE‘
METHOD OF' TREATING THE HEAT-RE
SPONSI‘VE ELEMENTS OF THERMOSTATS
Earl K. Clark and George vn. Price, Mans?eld,
'-0hlo, assignors to Westinghouse Electric &
:-Manufacturing Company, East Pittsburgh, Pa.,
a corporation of Pennsylvania
~
Application November 22, 1940, Serial No. 366,786
'
4 Claims. ‘(Cl.148-'-,6)
Our invention, relates to thermostat structures
of the expansible or volatile-?uid type and has
for an object to provide an improved method of l
have, in general, been unable to maintain oven
treating the heat-responsive elements of appa~
temperatures within a 40° F.- amplitude, the fig
ure which now represents the maximum ampli
tude permitted by such utilities or testing; labo
ratus of this kind.
rat-ories; The thermostats provided heretofore
.
V,
'
A further object of the inventionris to provide
more sensitive thermostatic apparatus of‘ the
type set forth whichmay be readily produced in
large. substantially uniform, quantities.
prove the heat-absorbing and heat-radiating
properties of the heat-responsive elements ‘of
'
low ‘heat-absorbing and heat-radiating capaci
ties that a relatively large differential obtains be
. A still'further object of the invention is to im
?uid-type thermostats."
have their ?uid-containing bulbs formed of cop
per or other metal, and, when new, have such
’
10 tween the oven air temperature and ?uid tem
perature. In other words, changes in the tem
perature of the ?uid lag behind temperature
changes in the oven air so thatthe temperature
These and other objects are effected by our‘ in
differential of the ovenair is higher than the
vention as will be apparent from the following 15 ?gure now required. A further disadvantage of
description and claims taken in accordance with
these prior thermostats is that the heat-absorp
the accompanying drawing, forming a part of
tion capacity of the thermostat changes with use
this application, in which:
'
‘or as the surface ofthe bulb becomes oxidized.
Fig. 1 is a diagrammatic view of an oven, the
This change in heat-absorbingcapacity usually
temperature of which is controlled by va thermo
20 necessitates a visit of the service man, after a
stat constructed and treated in ‘accordance with _
period of use, for adjustment of the thermostat.
our invention; and,
In accordance with our invention, we treat the
Fig. 2 is an enlarged view of the bulb or heat
bulb of the thermostat prior to'its application to
responsive element of the thermostat.
In the drawing, a heat insulated oven space
is diagrammatically shown at Ill- and heated by
an element H which we have shown of the 'elec
trically-energized type. A thermostat of the ex
pansible ?uid type is shown generally at I! and
includes a switch i3 arranged‘within a casing I4
exteriorly of the oven and controlling a circuit
I5, the latter including the heating element II.
The circuit 15 is connected to a suitable source
of electrical energy (not shown) as is well un
derstood.
Operation _of the switch 13 is effected by an
expansible and contractible element l6, such as,
for example, a bellows. The bellows is con
nected by a relatively small tube [1, commonly
referred to as a capillary tube, to a bulb or reser
voir l8 arranged in heat transfer relation with
the heated air in the oven space H).
A suitable
expansible liquid is contained in the bellows l6.
tube l1 and bulb l8, which liquid retains its
liquidity at temperatures up to 650° F. and which
expands and contracts as its temperature is in
creased and decreased, respectively.
As the operation of the apparatus referred to
heretofore is well understood in the art, no de
scription thereof is deemed necessary. Fluid
type thermostats which have been employed
heretofore for controlling ovens of electric ranges
have not been sufficiently sensitive to meet re
quirements now imposed by certain utilities and
testing laboratories. These prior art thermostats
the apparatus to be controlled, so that the heat
absorbing and radiating qualities of the bulb are
materially increased and so that substantially no
change in these qualities obtains during extended
use of the thermostat. We ?rst etch the surface
of the bulb for materially increasing its‘ area and
then blacken by an oxidation reaction the etched
or matted surface of the bulb. Preferably, the
smooth metal bulb is cleaned in a vapor de
greaser for removing oil or grease spots and the
bulb is then acid etched by dipping for two to
10 Li ?ve minutes in a} solution of four parts muriatic
acid, one part nitric acid and one part water.
We have found that the ,suface of the bulb may
be increased to 300% of its original surface when
so treated.
The bulb is then rinsed in clear
water and may be blackened or oxidized by dip
ping from ten to thirty seconds in a poly-sul
phide and water solution. During the latter step
the bulb should be dipped just long enough for
obtaining a blackened surface, as an excessive
‘ time in this dip may cause ?aking. After the
oxidizing process, the bulb is rinsed in clean
water and then suitably dried.
While we prefer to employ the described meth
od of roughening the bulb for increasing its sur
face area, it will be understood that this step
may be effected other than by an acid etching
operation. For example, the bulb may be rough
ened for increasing its surface area by sand
blasting or other mechanical means. The ?nally
treated and blackened bulb I8 is shown in Fig. 2.
?uid > type for aheated- appliance, which: thermo
We have foundhthat the maximum temperature
stat embodies a‘ thermostatic bulb-formed of: a;
amplitudes in ovens" controlled by thermostats
treated in accordance'withpur‘ invention have‘:
_ metal_ which I progressively-9 oxidizes-z inwsaida appli.»
been materially reduced to a valuev offthe. order
> its, heat-absorbing property‘ increases during
of 27° F._when measuredv with a" bare thermo
such-.q-perbiodé saidirbulbnrr containing; a.v tempera
Furthermore," we" have‘ found» th-atithelwheatiéabé i-J
'sorbing and heat-radiatingpapacity of. the bulbs
assembly of; the thermostat/‘for. use inithe heated
ance over; an extendedi periodi of‘ time soithatv
couple disposj'edi ext-‘the: center ofi;thetfrangeipveng‘
ture-grespons-__,eg ?uid; Iyv'i ch; "method‘. includes,
the step of providing thei- bulb-g1, prior" to the
,‘ance, .Vwithj a;i_dja>rkt coating having a high.
so treated does not vary‘materially when‘in‘ ser
absorbing property which i'snot substan
vice, so that’ adjustment or-calibration.Qf?the',
thermostat after a period of' useisgnothecessar
From the foregoing it will be‘ ‘apparent that I
Atia
we have provided improved‘i t
ratus of the fluid type where;
_ alteredv during ‘use; inthe heatedi appliance.
“2:. JIZhe ;n>1eth0d;ofimaking a thermostat. ofv the
" ‘
e
heatedlappliance,whichther-mor
'
_V
static bulb formedv ofa av
Xidizes 1n-v said' ap—
materially increased and wh'éreinf‘variation
operation after an extended peribd‘of- useare ob
property increases during.v
viated. Furthermore; the operatiomof'the'liea-tei-'1
suchlperiod, said-bulbcontaining
'
a temperature
responsive element", when" produced- i‘n,_ large v“ its‘_,h_eat'—absorbing
uniform, so that, the original’a'di- ""‘5 respon-sive,,- fluid; a which. metho djnclud’es. the‘ step
quantities , is
of}:-applying anioxidijzing SOHlti'OIl-WO the bulb,
iszmorerl'
justmeht a: h ‘the'armostati‘c“structure.z
We consider." ‘this man." import: '3
prior.v to: v the-assembly. of t'he-‘therm'ostat' for use
readily’ ‘effect
invention- as; in ‘the past, the;
tant" teatur’e" ‘of j our
and “radiating capacities‘ :of: um;
ave‘ ; vari'édi so‘ ‘widely? thatqgthe
iii-b3.
._
.
'librationfof-‘the thermostat.’ could? only n
b1’ litalnedgafter "ma " y and widely different; a
statsvo‘f,
‘servi.
t 'ermos a‘
mg* necessary i 3to- *Jma‘intaim ;thei
.
_ ""pro'p‘er adjustment; ?
a.
_
11W‘ tile ‘we haveif‘sho'wn our inventionairrv “uti
one‘ sfbrm, it'will-‘beobvious- t'o-'thosei-skilledirin
the art'that it_ is nlot'so limited-,'=but=is susceptible
of various other’changesand modi?cations.‘with-rv
'out' departing jfroml‘ the“- _'spirit‘ thereofiandr
we
sorbirigproperty
thatlisnot: substantially 'a-lt’eredf
'
during use in‘ theiheateclliappli'ance.
3. The‘ method as plai'med" in-v claim‘ 2'; wherein
' The:“noneunlformity'i'50f the: .‘z-bulbsi
etofor'e' hasftherefor‘a:increased the;
cost of " produci'iig ‘uniform v‘thermo-l
I; type and has~been~the cause" of»:
’
ingther heated appliance";
to:
provide
a! predeter
' H
"
: aidjgmetal: on
high; heateable
the-bulb which: QOl‘IlpQuIlgk has
.;- mined coating of a; compound; ‘
; theoxjdizing,solutiona_<iomprises a- sulphide, '
30
-, ‘ii-mas; method pr making a; thermostat:- of; the ,
?uict-v typeigr axhea d5 appliance; which-thermo
stat embodies a.v thermostatic. bulbi ' formed" otl
I
copper, said bulb‘
containing‘: a.‘ temperatureere;
sponsive :fluid, Which-method includes" the step
" of applyinga sulphide solutionéto-the-bulbz prior
to’ the-assembly of the. thermostat ‘in the heated.
appliance to provi‘deiv a1 coatlin'g?o‘n the‘bulb:
whose‘ heatfabsorbingv property is: relatively high
desire; therefore; that v'ienly" "such: limitations
and is not substantially‘ altered,‘ duringt, usein, the»_
shall‘be placed thereupon-‘as 'I'a‘r'ei speci?callyset 40
heatedqappllancet'
iortthjf in, the appendedi claims;
a 1; ,IIfhe;weyclaim'
‘method. "or melting; athermostat: of? the
’
j
v,
_
v
v
I
‘ EARL-,K. CLARK.
_V
., ; GEORGE E; PRICE.
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