US 2543177 A
Description (OCR text may contain errors)
Patented Feb. 27, 1951 UNITED STATES PATENT OFFICE ELECTRIC TEMPERATURE DEVICE Theodore Y. Korsgren, Reynoldsburg, Ohio, as-
signor to The Arco Manufacturing Company, Columbus, Ohio, a corporation of `Ohio Application September 23, 1948, Serial No. 50,781
8 Claims. l
The present invention relates to electrical thermally-actuated switches, and more specifically to thermally-actuated switches of the type einbodying a pair of electrodes separated by a body of fusible and ionizable material which, when fused, is electrically conductive and when solid is non-conductive. One type of switch of this general character is disclosed in detail in United States Patent to Kernen, Number 2,316,872, April 20, 1943.
In operation, kswitches of this general character are usually employed as safety switches for a fluid fuel heating system, and as such, are positioned in close proximity to the flame of a constant-burning pilot burner used to assure ignition cf an associated main fuel burner, whereby an electrical circuit associated with the fuel flowcontrol valve of the main burner is controlled in response to the heat of the pilot burner flame thereby insuring against the introduction of fuel to the main burner in the absence of a pilot name to ignite such fuel. It will be manifest that switches of this general character must necessarily be capable of withstanding relatively constant and elevated temperatures due to their presence within an associated pilot burner flame, and generally such switches comprise an outer casing formed from a suitable heat corrosion-resistant metal or metallic alloy which is capable of withstanding the relatively extreme elevated temperatures and the heat-corrosive properties of the pilot flame without mechanical failure or deterioration. Generally, the outer casings of such switches when formed from stainless steel or similar metal alloys capable of withstanding the relatively high temperatures of the pilot flame, are relatively poor conductors of heat. Due to the relatively poor heat-conducting properties of such metals or alloys, the operation of such switches is greatly hindered, due to their inability to quickly dissipate heat upon extinguishment of an associated pilot flame, whereby its fusible material may quickly change from its liquid conducting state to its solid non-conducting state.
It is, therefore, highly desirable that switches of this type be able to dissipate heat rapidly upon extinguishment of an associated pilot flame or the removal of the heat source, in order that an associated electrical circuit may be quickly and efliciently controlled.
Accordingly, it is the primary object of the present invention to provide a thermally-actuated safety switch which is highly resistant to heat corrosion, yet at the same time, functions to quickly dissipate heat in the absence of a heat source to assure prompt control over an associated electrical circuit.
It is another object of this invention to provide a thermally-actuated switch of the character described which comprises an outer electrode casing formed from a suitable heat corrosion-resistant metal or metallic alloy which is electrically conductive, an inner core of fusible and ionizable material, and an inner electrode formed from a metal having a relatively higher coefcient of heat conductivity than the metal of the outer casing whereby heat may be quickly dissipated from the switch to permit the fusible material to solidify and become non-conductive in the absence of a heat source capable of fusing the fusible material.
It is still a further object of the present invention to provide a thermally-actuated switch which embodies an outer tubular casing of heatresistant metal which functions as one electrode of the switch, an inner core or body of fusible and ionizable material, and a centrally or axially disposed inner electrode formed from a different metal having a higher coefficient of heat con--y ductivity than the metal of the outer casing, yet provided with an outer sheathing or clad of the same metal or alloy as the outer casing of the switch, whereby galvanic action upon ionization of the intermediate layer of fusible material is prevented.
Fora further and more detailed understanding of this invention and the various additional objects and advantages realized therefrom, reference is made to the following description and the accompanying drawing wherein:
Fig. 1 is a diagrammatic view of a heating systern and electrical control circuit embodying a thermally-actuated switch formed in accordance with the present invention;
Fig. 2 is an enlarged medial vertical sectional view taken throughl a switch formed in accordance with the present invention;
Fig. 3 is a horizontal sectional view taken along the lineI 3-3 of Fig. 2;
Fig. 4 is a detailed horizontal sectional view taken along the line 4-4 of Fig. 2.
lReferring now to the drawing, the numeral lil designates a cylindrical tubular outer shell or casing which is formed from a heat corrosionresistant metal or metal alloy, such as, stainless steel, or other suitable nickel-chromium ferrous alloy which is conductive to heat and electricity. The outer casing l0 is closed at its upper end by means of a top wall Il and is open at its lower end and terminates in an outwardly extending annular flange I2. Carried within the outer casing IG are a pair of longitudinally spaced insulating guides I3 which are preferably formed from porcelain or other suitable refractory material which is capable of withstanding relatively elevated temperatures without deterioration, and which at the same time possesses good dielectric properties. The guides I3 are formed with axially disposed bores I4 for the reception of an inner electrode member, generally designated by the numeral I5. The inner electrode member I5 comprises an inner core or rod I6 which is preferably formed from copper or other suitable metal having a high coefficient of electrical and heat conductivity. The core or rod I6 of the inner electrode is provided with an outer tubular casing, clad, or sheathing formed from the same heat corrosion-resistant metal as the outer casing I0. The rod I5 and its outer sheathing are rigidly and electrically connected by thermal bonding or other suitable means. l
Carried within the outer casing I between the guides I3 is an annular core of fusible and ionizable material I8, such as glass or sodium tetraborate which, when heated to fusion temperatures, is a good conductor of electricity, and which when solid is non-conductive or dielectric. It has been found through experience that either glass or sodium tetraborate possesses the desired qualities of a material having a negative coeflicient of resistance capable of being fused or liquified at temperatures created by the usual pilot flame, and capable of -relatively rapid solidiflcation upon a material drop in temperature, such as would occur upon extinguishment or removal of a pilot flame from contact with the outer casing of the switch. AThe inner electrode I is provided immediately beyond the open end of the casing I0 with an outwardly directed circular retaining ilange I9 which serves as a support for a pair of annular insulating washers 2li and 2I preferably formed from mica or porcelain, and which provide a seal for the lower open end of the cuter casing I0. Disposed immediately adjacent to the insulating washer 2I is an annular metallic washer 22 formed from copper or brass which is electrically connected with the end portion of a flexible metallic tube or sleeve 23. The sleeve 23 forms an intermediate ply of a iiexible armored cable and constitutes one of a pair of electrical conductors carried therein. The cable comprises an inner core of wire 24 formed from copper or other suitable electrical conducting metal, an intermediate sleeve 25 of insulating material, the metallic tube 23,v and an outer covering o-r casing of insulating material 26. Preferably the insulating material of the cable is formed from a suitable heat-resistant material, such as leached glass fibre, asbestos or the like. The core 24 of the cable is joined, as by soldering, as at 21, to the outer end of the copper core or rod I6 of the inne-r electrode member I5. The upper end portion of the metallic wire sleeve 23 is electrically connected with the outer casing I0 of the switch by means of a metallic ferrule 23 which is crimped at its respective ends around the outward flange I2 of the outer casing, the insulating washers 20 and 2I, the metallic washer 22 and the outer end of the metallic wire sleeve 23. The outer insulating covering 26 of the cable extends around the outer surface of the ferrule 28 and is clamped Within a second outer ferrule 29 to complete the base assembly of the switch. In this manner, the inner electrode member and the lead wire 24 are electrically insulated from l the outer electrode casing.
the second metallic wire sleeve conductor 23 of the cable and the outer casing I0 of the switch.
In operation, referring to Fig. 1, the switch is normally placed in the path of, or in close proximity to the flame of a pilot burner 30, so as to be directly affected by the heat of such flame. Advantageously, the switch may be connected in series with an electro-responsive control, such as a solenoid 3|, which controls the operation of a fuel-flow control valve 32, the latter being interposed within a fuel supply line 33 connected to supply a main fluid fuel burner` 34. In the presence of a flame such as the pilot burner, the fusible material within the switch is maintained in a molten electrically conductive state, thereby establishing electrical connection between the outer electrode casing and the inner electrode member to maintain the switch in circuit closing condition, thereby conditioning the electrical circuit of the solenoid-actuated valve 32 for normal operation in response to a room thermostat, not shown. However, should the pilot flame become extinguished, the fusible material within the switch will cool and become solid and non-conductive; at which time, electrical connection between the outer electrode casing and the inner electrode will be broken and the switch opened. It will here be understood, that if no specic provision is made to dissipate heat from the switch, the time required for the fusible material to change from a liquid to a solid would be relatively great, and due to the use of metals or alloys which are relatively poor conductors of heat, such time interval is further extended. Hence, in utilizing a metal, such as copper, as the core of the center of inner electrode, heat stored within the fusible material may be more quickly dissipated upon removal of the heat source from contact with the outer casing, thereby, sharpening or decreasing the time interval required for the fusible material to change from its liquid to its solid state, over that required if such inner electrode were formed entirely from the same relatively low heat conductivity metal or alloy as It is, however, desirable that the outer casing of the switch which is in contact with the flame of the pilot burner, be formed from a material which is capable of withstanding the corrosive affects of the flame, hence, metals, such as coppel` or other relatively high heat conductivity metals, may not be eiliciently employed as an outer casing, due to their inability to withstand prolonged contact with a name without deterioration.
It is likewise impractical to use dissimilar metals in direct contact with the fusible material, due to the natural galvanic action which takes place upon ionization of the fusible material and the presence of two dissimilar metals in contact with the ionized material during the passage of electrical current therethrough. Hence, by utilizing a relatively thin covering of the same metal as the metal of the outer casing for the inner copper electrode, the possibility of galvanic action is eliminated while the property of high heat conductivity is utilized to aid in the dissipation of heat from the switch and the overall sharpening of the switch action.
In View of the foregoing, it will be seen that the present invention provides an improved thermally-actuated switch which is characterized by its ability to withstand the relatively constant elevated temperatures of a pilot burner flame and the corrosive effects thereof without deterioration or mechanical failure and its abil- 5 ity to respond expeditiously to temperature variations. Switches formed in accordance with the present invention are further characterized by their structural simplicity and ruggedness and their mechanical ei'ciency through the elimination of movable parts.
While a single preferred form of the present invention has been disclosed in detail, it will be manifest that changes in constructional details are possible without departing from the spirit of the invention or the scope of the following claims.
1. An electrical thermo-responsive switch comprising an outer hollow electrode of corrosion-resistant electrical and heat-conducting metal, an inner electrode carried within said outer electrode in spaced normally non-conducting relation thereto and extending outwardly therefrom, said inner electrode being formed from a metal possessing relatively higher heat conductivity than the metal from which said outer electrode is formed whereby to provide for the rapid dissipation of heat from said switch, a thin sheathing of said corrosion-resistant electrical and heat-conducting metal carried in intimate heat-exchange relation to said inner electrode and electrically connected therewith, and a filler between said sheathing and said outer electrode of fusible material which is conductive when fused and non-conductive when solid, said sheathing serving to prevent galvanic action between said inner and outer electrodes upon fusion of said fusible material.
2. An electrical thermo-responsive switch comprising a tubular electrode of corrosion-resistant heat and electrical-conducting metal, a tubular inner casing of the same metal as said tubular electrode carried in spaced non-conducting relation within the latter, a body of fusible material disposed between said tubular electrode and said inner casing, said fusible material being electrically conductive when fused and nonconductive when solid, and a second electrode of a metal having a higher coeflicient of heat conductivity than the metal from which said tubular electrode and said inner casing are formed carried within and in direct contact with said inner casing. l
3. In an electrical thermo-responsive switch; an outer tubular electrode of corrosion-resistant, electrical and heat-conducting metal; yan inner electrode of a different relatively higher heatconducting metal positioned within said tubular electrode in spaced non-conducting relation thereto and extending exteriorly of said tubular electrode, said inner electrode having a relatively thin outer covering of the same metal as said outer electrode; and a body of ionizable fusible material which is electrically non-conductive when splid and conductive when fused, positioned between said inner and outer electrodes, said inner electrode providing for increased thermal conductivity from within said switch, and said outer covering therefor serving to prevent galvanic action between said inner and outer electrodes upon ionization of said fusible material.
4. In an electrical thermo-responsive switch; an outer electrode casing formed from a corrosion-resistant, electrical and heat-conducting metal; an inner casing of the same metal as said outer casing positioned within said outer casing in spaced non-conducting relation thereto; a
body of fusible and ionizable material separating said inner casing from said outer casing; and a core electrode formed from a different relatively higher heat-conducting metal than said inner and outer casings carried in direct contact with the inner surface of said inner casing and extending exteriorly of said outer casing to provide for the rapid transfer of heat from within said outer casing; said fusible material being electrically conductive when fused and nonconduc tive when solid.
5. The combination with an electrical thermoresponsive switch having spaced inner and outer electrodes formed from the same metal, and a body of fusible and ionizable material separating said electrodes; of an inner heat-dissipating core carried axially in direct contact with said inner electrode and extending exteriorly of said outer electrode and formed from a metal having a higher coefficient of heat conductivity than the metal from which said electrodes are formed.
6. In an electrical thermo-responsive switch, the combination with an outer tubular metallic electrode, an inner tubular metallic casing spaced from the inner walls of said outer electrode, and a body of fusible and ionizable material disposed between said outer electrode and said inner casing to separate and determine electrical conductivity therebetween; of a solid core electrode carried within and filling said inner casing and formed from an electrical conducting material having a higher coeicient of heat conductivity than said outer electrode and said inner casing.
7. In an electrical thermo-responsive switch having an outer heat and electrical conducting metallic electrode casing, and a core of fusible material which when fused is electrically conductive and when solid non-conductive; an inner electrode positioned within said core of fusible material in spaced relation to said outer electrode casing and comprising an inner core of metal extending exteriorly of said outer casing and having a higher coefficient of heat conductivity than the metal of said outer casing, and a relatively thin sheathing carried upon the outer surface of said inner core and formed from the same metal as said outer electrode casing.
8. An electrical thermo-responsive switch comprising a stainless steel outer electrode casing, a copper inner electrode carried within said outer casing in spaced non-conducting relation thereto, a thin stainless steel jacket covering at least a part of the outer surface of said inner electrode and carried in direct Contact therewith, and a body of fusible and ioniaable material which is electrically conductive when fused and non-conductive when solid carried between the jacket of said inner electrode and said outer casing.
THEODORE Y. KOR-SGREN.
REFERENCES CITED The following references are of record in the file of thisr patent:
UNITED STATES PATENTS Number Name Date 2,316,872 Kernen I Apr. 20, 1943 FOREIGN PATENTS Number Country Date 537 "i5 Great Britain June 11, 1941 Certificate of Correction Patent No. 2,543,177 February 27, 1951 THEODORE Y. KORSGREN It is hereby certified that the name of the assignee in the above numbered patent was erroneously described and specified as The Arco Manufacturing Company Whereas `said name should have been described and specified as The Acro Manufacturing Company; and that the said Letters Patent should be rea-d as corrected above, so that the same may conform to the record of the case in the Patent Oice.
Signed and sealed this lst day of May, A. D. 1951.
THOMAS F. MURPHY,
Assistant ommfsszoner of Patents.
Certificate of Correction Patent No. 2,543,177 February 27, 1951 THEODORE Y. KORSGREN It is hereby certified that the name of the assignee in the above numbered patent was erroneously described and Specified as The Arco Manufacturing Company Whereas said name should have been described and specified as The Acro M anwfactung Oompany; and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oice.
Signed and sealed this 1st day of May, A. D. 1951.
THOMAS F. MURPHY,
Assistant om/mzssz'ovner of Patents.