US3913054A

US3913054A - Thermally responsive switch

Info

Publication number: US3913054A
Application number: US414025A
Authority: US
Inventors: Denis G Wolfe
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1973-11-08
Filing date: 1973-11-08
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14

Abstract

A thermally responsive switch includes a pair of contact elements, at least one of which is a bimetallic element, extending through slots in a ceramic container, and a mass of non-volatile, inorganic base cement disposed in the container and surrounding anchor portions of the contact elements disposed interiorly of the container, the cement being hardened to interact with the container to form an integral support for the contact elements holding the anchor portions rigid.

Description

United States Patent [1 1 Wolfe I p451 Oct. 14, 1975 THERMALLY RESPONSIYE SWITCH [75] Inventor: Denis G. Wolfe, Santa Ana, Calif. [73] Assignee: Robertshaw Controls Company,

Richmond, Va.

[22] Filed: Nov. 8, 1973 [21] Appl. No.: 414,025

[52] US. Cl. 337/362; 29/464; 29/622;

. 337/112 [51] Int. Cl. B23Q 3/00; HOlH 37/52 [58] Field of Search 337/101, 109, 111, 112, 337/113, 362, 363, 373, 379, 380, 399; 29/464, 468, 622; 335/154; 200/275, 283, 61.19

[56] References Cited UNlTED STATES PATENTS 3,127,484 3/1964 Hansen ZOO/61.19 x

I, f r I, 222 4, 75*; 39 2 9/1964 Dales 337/381 X 6/1972 Rattan 337/112 Primary Examiner-L. T. Hix Assistant ExaminerFred E. Bell Attorney, Agent, or Firm-Anthony A. OBrien FIG.2

US. Patent 00:. 14, 1975 THERMALLY RESPONSIVE SWITCH BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention pertains to thermally responsive switches and, more particularly, to an improved thermally responsive bimetal switch.

2. Description of the Prior Art Thermally responsive switches have long been utilized in connection with various electrical control net works to make or break an electrical circuit in response to sensed heat energy. It is often desiredto have such control networks operate at aprecise. temperature as in the case where the thermally responsive switch is positioned within heating proximity of a device to be monitored and the control network is responsive to any overheating of such device to initiate corrective'a'ction. Thus, an important specification in the manufacture of thermally responsive switchesis to provide consistent operation at precise temperatures. This requirement places stringent standards upon switch design and construction techniques especially where mass-production techniques are employed in order that all of the manufactured switches are actuatable at the same 'preselected temperature. It is, therefore, desirous toproduce thermally responsive switches in a manner'suchthat the switches are accurately calibrated during production thereby eliminating the need for calibration'of the assembled switches and assuring reliable and accurat operation of the finished product.

The prior art, as characterized by US. Pat. Nos. 2,745,924, 3,148,258 and 3,230,607, is generally cogniz ant of electrical switches which are calibrated during manufacture; US. Pat. No. 2,745,924, for example, disclos es a switch in which a pair of contact elements are placed in a multiple section housing with the contact ends held in a fixed position by a spacer. A base material is' molded about the contact elements and is cured at the operating temperature of the switch. Thereafter, the spacer is removed to complete the assembIy. U.S. Pat. No. 3,148,258 is generally similar to the previously described patent" wherein'c'ontact elements are placed in a multis'ectioned housing and are held during the curing of a plastic mass. US. Pat. No. 3,230,607 pertains to a switch in which a cylindrical post isaxially movable by a bimetallic contact element during the curing of a thermo-se tting material.

While the prior art electrical switches, as exemplified by the above-mentioned patents, have generally served the purpose,they have proven to be disadvantageous in ever, there is still room for improvement'in thermally responsive switches, particularly with respect to contact contamination, flexibility of the anchored portions of the contact elements, and the use of precious metals in the construction of the contact elements.

SUMMARY OF THE INVENTION The present invention is generally summarized in a thermally responsive switch including a ceramic container having a base with a pair of slots therein; a pair of elongate contact elements including at least one bimetallic element, each of the contact elements having an anchor portion and a contact portion and extending through one of the slots in the base of the container, the anchor portions being disposed interiorly of the container; and, a mass of inorganic base, chemical setting cement disposed in the containers surrounding the an- 'chor portions of the contact elements and cured to interact with the container to form a hardened integral support for the contact elements holding the anchor portions rigid whereby the contact portions of the contact elements are relatively movable to assume a predetermined relationship at a particular temperature.

Accordingly, it is a basic object of the present invention to construct a thermally responsive switch representing an improvement over the above described prior art.

Another object of the present invention is itofutilize a ceramic container and a non-volatile, inorganic base ceramic cementfor anchoring alpair ofcontact elements within the container to provide a non-volatile inorganic base, thermallyresponsive switch structure.

A further object of the present invention is to form ribs on anchor portions of a pair of contact elements in a thermally responsive switch to increase rigidity andto minimize the flexing of the anchor portions. I

The present invention has an additional object in that contact elements in a thermally responsive switch have only the contact portions thereof clad, the contact portions being formed by welding small, pre-clad contact members on the contact elements, such pre-clad contact members preferably taking the form of a tape having a gold cladding over a copper-nickel backing, or the contact portions being formed by bending the ends of the contact elements and plating only the bent ends.

Yet another object of the present invention is to form a small opening on a cover member for a thermally rethat the various contact elements are not provided with any means to positively locate such elements in the switch assembly and are not held on a durable integral support, and the various contact elements are held dur- .ing the curing step by a spacing member which caneasily damage the contacts or bend the contactelements sponsive switch to allow moisture to escape from the interior of the switch structure during curing of cement, the opening being sealed thereafter.

Some of the advantages of the present invention over the prior art are that calibration can be performed during manufacture without sacrificing accurate and reliable operation, the use of precious metals in constructing the contact elements is reduced to a minimum, and

out of tolerance as it is removed In addition, the inethstruction of thermally responsiveswitche's have bleen substantially overcomejby the thermally responsive" switch disclosed in U.S Pat. Application Ser. No. 323,616, filed Jan. V15, 1973 and the method for m'akf ing thermally responsive switches disclosed in U.S.'Pat. Application Ser. No. 323,617, filed Jan. 15, 1973; how- 'contamination'from organic materials is obviated.

"Other objects and advantages of the present invention will become apparent from the following description o'f'the preferred embodiment taken in conjunction with the accompanying drawings.

Y-BIRIEFTDESICRIPTION OF THE DRAWINGS FIG. 1 is a cross section of a thermally responsive switch according to the present invention.

FIG. 2 is a top plan view of the'co'ntainer of the thermally responsive switch of FIG. 1.

FIG. 3 is a front elevational view of a contact element of the thermally responsive switch of FIG. 1.

FIG. 4 is a section taken along line 4-4 of FIG. 1.

FIG. 5 is a section taken along line 55 of FIG. 3.

FIG. 6 is a cross section illustrating calibration of the 5 DESCRIPTION OF THE PREFERRED EMBODIMENT A thermally responsive switch 10 according to the present invention is illustrated in FIG. 1 and includes, as basic components, a cup-shaped container 12 supported in a cover tube 14 and mounting a pair of elongate,

bimetallic contact elements

16 and 18, the container 12, the cover tube 14 and the

contact elements

16 and 18 being secured together by masses of

cement

20 and 22.

The container 12 is constructed of a ceramic material, preferably steatite, and has a cylindrical wall 24 with a base 26 having a pair of

slots

28 and 30 formed therein. As best shown in FIG. 2, the slots 28 and 30' have generally straight configurations in parallel relation with offset V-like portions in the center thereof. The container 12 is positioned within the cover tube 14 with base 26 abutting a rolled peripheral groove 32 or suitable indents forming a step in the side wall of the tube. The cover tube 14 is preferably formed of aluminum has a rounded closed end 34 with a recess 35 ther'ein'and a small opening 36 communicating with the recess to vent the interior of the switch during cement curing, the opening being sealed after curing by a cement 37, such as Ar'e'mco No. 540-5l.

The

contact elements

16 and 18 are identical in 'structure; and, accordingly, only contact element 16 will be described in detail with identical parts of "contact elements 16 being given the same reference numbers with primes. The contact element 16 is formed of a strip of bimetal arranged with the high expansion side facing inwardly such that the contact element 16 will bend clockwise or toward the left, looking at FIG. 1, with increasing temperature. An anchor portion 38 of the contact element 16 is disposed interiorly of container 12, and a longitudinal rib having a V- shaped configuration in cross section is formed on the anchor portion 38. The outer surface of rib 40 has lateral serrations 39 formed therealong, as best shown in FIG. 5, and the rib 40 terminates at a flat inner end wall 41 which forms a protruding stop to locate the contact element in the container 12. The contact element 16 is substantially flat from the inner end wall 41 of rib 40 to a contact portion 42 at the distal end thereof, and a contact member 44 is welded to the distal end of the switch blade at approximately a 45 angle to the longitudinal axis of the contact element. The bimetal strip of the contact element is preferably stamped to form the rib- 40, and the contact member 44 is preferably "tape adapted to be cutand welded to the bimetal strip,

as illustrated in FIG. '3 I The V-shaped configuration of the ribs 40 and 411' of the

contact'element

16 and 18 mates with the configuration of

lead wires

46 and 48, which extend within the concave or grooved sides of the ribs, to permit precise location of the lead wires and facilitate welding of the lead wires to the contactelements. The

contact elements

16 and 18 are inserted through the

slots

28 and 30 with the

inner end walls

41 and 41 of the

ribs

40 and 40 acting as stops to limit penetration of the contact elements through the container. While

contact elements

16 and 18 are preferably both bimetals, only 10 one of: the contact elements need be bimetallic to provide thermally responsive operation. When both contact elements are bimetals, the contact elements are disposed in opposing relation to reduce premature opening of the switch contacts below the normal oper- 5 ating temperature when subjected to shock and/Orvibration in that due to the opposing relation of the bimetals, the contacting force is doubled to assure that the switch contacts are maintained closed at all temperatures below the operating temperature. If it is desired that the thermally responsive switch open when temperature is reduced or cooled to an operating temperature, the low expansion sides of the bimetals should be disposed facing each other.

The anchor portions 38 and 38' of the contact ele- 25 ments are anchored in the container '12 by the massof 0 form a hardened integral support for

contact elements

16 and 18. The serrations 39 receive the cement 20 to stabilize and secure the contact elements in thecontainer. After curing or setting of the cement 20, the upper edges of the cover tube 14 can be crimped prior 35 to filling with the mass of inorganic base, chemical setting cement 22 of the same type as cement 20.

Assembly and calibration of the thermally responsive switch 10 will be described with reference to FIG. 6 wherein a calibration assembly 50 is illustrated including a support sleeve 52, used as a calibration jig, cut at its lower end to provide four tabs "54, at least two ofwhich are folded inwardly to close the bottom of the sleeve. A plurality of apertures 56 are formed in the lower half of the sleeve to permit air circulation in the interior of the sleeve during the curing and calibration procedure to be described hereinafter. The upper half of the sleeve 52 is divided into four ar'cuate sections which are swaged at the open ends thereof to provide a gripping surface engaging the container 12. A cylindrical aligning plug 58' is slidably disposed in the lower portion of sleeve 52 and has a conical bore in the upper surface thereof. Plug 58 is biased upwardly by a low rate spring 62 mounted within the sleeve between the bottom of plug 58 and tabs 54.

In order to assemble and calibrate the thermally responsive switch 10, the

contact elements

16 and 18 are inserted into

slots

28 and 30, respectively, in the base of the container with the inner end walls of the ribs 40 and 40' limiting the extension of the blades through the base 26 to permit precise location of the contact elecontainer is seated within the sleevef52. The conical bore 60 in plug 58 cooperates with the contact elements l6 and 18 under the'influericeiof lo'w'rate spring 62 to maintain both contact'elements in proper longitudinal'alignmentwith e'ach'otherand with container 12 to assure proper positioning of the contact elements within the container and to exert a small inwardly directed force adjacent and behind the contact members 44 and 44' to hold the contact members in engagement without stressing thesame during assembly.

With the container and contact elements in this position, the mass of inorganic base, chemical setting cement is positioned in the container surrounding the anchor portions 38 and 38' of the contactelements. The entire assembly illustrated in FIG. 6 is then subjected to heat and is maintained at a particularoperating temperature for the switch. The ceramic cement 20 is selected to have a setting or curing temperature range inclusive of the particular operating temperature of the thermally responsive switch such that as the ceramic cement is hardened the contact elements will assume and maintain a flexed or bowed shape corresponding to their desired calibrated positionsfDuring the curing step, the ceramic container 12 interacts with the cement 20 to provide an integral inorganic support structure which is stable and non-contaminating.

1 Following the curing step, the heat source is removed and the calibration jig separated from thecalibrated subassembly composed of the contact element'sl16 and 18 and the integral supportformed of container 12 and the hardened ceramic cement 20. Thereafter, the

lead wires

46 and 48 are positioned in the grooves formed by

ribs

40 and 40, respectively, and soldered to the anchor portions 38 and 38' of the contact elements, and the sub-assembly is inserted into the cover tube 14. Cement 22 is placed in the open end of the tube 14 and cured to anchor the sub-assembly in the cover tube with the opening 36 venting the interior of the cover tube during curing and thereafter sealed by cement 37.

In operation, the contact members 44 and 44' of the assembled thermally responsive switch 10 will remain closed until the particular calibrated operating temperature is reached at which point the contact elements will assume the shape in which they were maintained during the curing process with the contact members 44 and 44' just touching. Upon being heated above the operating temperature, the contact members will be separated to provide an open electrical circuit. Once the temperature is reducedbelow the operating temperature, the contact members will be moved to contact each other again thereby providing a closed electrical circuit. In this manner, the thermally responsive switch 10 effectively operates at the preselected operating temperature at which the integral support was cured.

A modification of the contact elements in the thermally responsive switch 10 is illustrated in FIGS. 7 and 8 with parts similar to the contact'elements of FIGS. 1 and 3 being given the same reference numbers with 100 added. Since the pair of contact elements utilized in the thermally responsive switch of the present invention are identical, only a single contact element 116 is illustrated in FIGS. 7 and 8, it being understood that an identical contact element would be disposed facing the contact element 1 16 in the same manner as

contact elements

16 and 18 are shown in FIG. 1. The contact portion 142 of contact element 1 16 is bent at the distal end to extend angularly from the flat side of the bimetal strip to form a contact member 144 diagonally disposed relative to the longitudinal axis of the contact element 116. Only the bent end forming the contact member 144 is plated thereby substantially reducing the amount of precious metal required, and the inner edges of the bent ends form the contacts.

Both of the contact element configurations illustrated in FIGS. 1 and 3 and FIGS. 7 and 8 have the advantages that the contact members arediagonally oriented relative to the longitudinal axes of the contact elements to provide a cross wire effect and that the entire contact element need not be plated with precious metals, such as silver and gold, but rather, the contact elements of FIGS. 1 and 3 need only have the contact members 44 plated, as described above, and the contact elements of FIGS. 7 and 8 need only have the bent ends thereof plated. l I By stamping the bimetal strips forming the contact elements to form longitudinal ribs 40 and 40' along the anchor portions thereof, the anchor portions have increased rigidity and flexingthereof is minimal. The inner end walls of the ribs act as stops abutting the base 26 of the container' 12 to limit penetration of the contact elements through the base of the container.

The construction of the integral support formed of the ceramic container 12 and the mass of inorganic base cement 20 interacting therewith provides an essentially inorganicstructure thereby reducing contamination of the contacts of the thermally responsive switch from the vaporizing, outgassing or decomposition of organic materials.- Additionally, the inorganic base cement can be cured or hardened at the predetermined operating temperature as described above to facilitate assembly and calibration of the thermally responsive switch.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter described above or shown in the accompanying drawings beinterpreted as illustrative and not in a limiting sense.

What is claimed is: 1. A thermally responsive switch comprising a ceramic container having a base with a pair of slots therein; 7

a pair of elongated contact elements including at least one bimetallic element, each of said contact elements having an anchor portion and a contact portion and extending through one of said slots in said base of said container, said anchor portions being disposed interiorly of said container; and

a mass of inorganic base, chemical setting cement disposed in said container surrounding said anchor portions of said contact elements and cured to interact with said container to form a hardened integral support for said contact elements holding said anchor portions rigid whereby said contact portions of said contact elements are engageable and relatively movable to assume a predetermined relationship at a particular temperature,

2. A thermally responsive switch as recited in claim 1 and further comprising a cover member surrounding said integral support and said contact elements.

3. A thermally responsive switch as recited in claim 2 wherein said cover member has a rounded end with a small opening therein for venting the interior of said thermally responsive switch during curing of said mass of cement, and cement means sealing said opening.

4. A thermally'responsive switch as recited in claim 2 and further comprising a pair oflead wires each attached to an anchor-portion of a respective one of said pair oficontact e lements, said integral support being secured within said cover member by an additional mass ofinorganic base, chemical-settingcernent surrounding said lead wires and said anchor portions of said contact elements, f i r 2 t t 5. A thermally responsive switch as recited in claim 1 wherein said contactportions of-said contact ele ments are diagonallydisposecl relative to the longitudinal axespfi said contactelements, v

6. A thermally responsive switch as recited in claim 5 whereirteach of said contact. elements'is a bimetal strip and each of said contact portions includes a clad copper-nickel backing having a gold cladding thereon.

,8. thermally responsive switchas recited in claim S Wherein each otf saidcontac t elements is a bimetal strip having an end carrying said contact portion, each of said erids being plated andlbent substantially transverse to. said bimetal strip. I j

9. A thermally responsiveswitch as recited in claim 1 wherein the anchor" portion of each of said contact elements has alongitudinal rib extending therealong with an inner end wall abutting said base lof'said container to limit' the extension of said contact elements through said slotsl g i A thermally responsive switch as recited inclaim 9'w'lierein' said rib of each of 'saidcontact elements h as a generally V-shaped configuration. in cross section, andlsaidslots in said container each have a generally V-shaped configuration t o-r et :ei ve said ribs.

-11. A thermally-responsive switch as recited in claim lowher'eiria plurality of serrations a're'formed in said rib. i t l y 12'. A thermally responsive switch as recited in claim 10 and tfurthe'r comprising a-pair'oflead wires each having an end disposed' in the concave' side ofa respective one of said ribs and attached thereto.

l3. A thermally responsive switch as recited in claim 11 andfu rther comprising: a tubular cover member surrounding said integral support'and said contact elements and having astep formed therein abutting the base ofsaid container, and an additional mass'of inorganic base, chemical setting cement disposed in said cover member surrounding sai d ends of said lead wires and said anchor portions of said contactelements.

114. Afthernially responsive switch as recited in claim 12 wherein e'ach of saidcontact elements is a bimetal strip an d each of said contact portions includes a clad contact member welded toi said bimetal strip.

15. A thermally responsive switch as recited in claim l wherein each of said contafct elements is a bimetal strip and 'e ach of said contact portions includes a clad contact memberwelded to said bimetal strip.

16 A thermally responsive switch as recited iii claim- 1 wherein each of said contact elements is a bimetal strip having an end carrying said contact portion, each of'said ends being plated and bent angularly from said bimetal strip. f v I

Claims

1. A thermally responsive switch comprising a ceramic container having a base with a pair of slots therein; a pair of elongated contact elements including at least one bimetallic element, each of said contact elements having an anchor portion and a contact portion and extending through one of said slots in said base of said container, said anchor portions being disposed interiorly of said container; and a mass of inorganic base, chemical setting cement disposed in said container surrounding said anchor portions of said contact elements and cured to interact with said container to form a hardened integral support for said contact elements holding said anchor portions rigid whereby said contact portions of said contact elements are engageable and relatively movable to assume a predetermined relationship at a particular temperature.

4. A thermally responsive switch as recited in claim 2 and further comprising a pair of lead wires each attached to an anchor portion of a respective one of said pair of contact elements, said integral support being secured within said cover member by an additional mass of inorganic base, chemical setting cement surrounding said lead wires and said anchor portions of said contact elements.

5. A thermally responsive switch as recited in claim 1 wherein said contact portions of said contact elements are diagonally disposed relative to the longitudinal axes of said contact elements.

6. A thermally responsive switch as recited in claim 5 wherein each of said contact elements is a bimetal strip and each of said contact portions includes a clad contact member welded to said bimetal strip.

7. A thermally responsive switch as recited in claim 6 wherein said contact members are each formed of a copper-nickel backing having a gold cladding thereon.

8. A thermally responsive switch as recited in claim 5 wherein each of said contact elements is a bimetal strip having an end carrying said contact portion, each of said ends being plated and bent substantially transverse to said bimetal strip.

9. A thermally responsive switch as recited in claim 1 wherein the anchor portion of each of said contact elements has a longitudinal rib extending therealong with an inner end wall abutting said base of said container to limit the extension of said contact elements through said slots.

10. A thermally responsive switch as recited in claim 9 wherein said rib of each of said contact elements has a generally V-shaped configuration in cross section, and said slots in said container each have a generally V-shaped configuration to receive said ribs.

11. A thermally responsive switch as recited in claim 10 wherein a plurality of serrations are formed in said rib.

12. A thermally responsive switch as recited in claim 10 and further comprising a pair of lead wires each having an end disposed in the concave side of a respective one of said ribs and attached thereto.

13. A thermally responsive switch as recited in claim 11 and further comprising a tubular cover member surrounding said integraL support and said contact elements and having a step formed therein abutting the base of said container, and an additional mass of inorganic base, chemical setting cement disposed in said cover member surrounding said ends of said lead wires and said anchor portions of said contact elements.

14. A thermally responsive switch as recited in claim 12 wherein each of said contact elements is a bimetal strip and each of said contact portions includes a clad contact member welded to said bimetal strip.

15. A thermally responsive switch as recited in claim 1 wherein each of said contact elements is a bimetal strip and each of said contact portions includes a clad contact member welded to said bimetal strip.

16. A thermally responsive switch as recited in claim 1 wherein each of said contact elements is a bimetal strip having an end carrying said contact portion, each of said ends being plated and bent angularly from said bimetal strip.