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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.