US3816910A

US3816910A - Method for making thermally responsive switches

Info

Publication number: US3816910A
Application number: US00323617A
Authority: US
Inventors: T Jess; W Jackson
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-02-17
Filing date: 1973-01-15
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18

Abstract

A thermally responsive switch and method for making the same in which a pair of contact elements including at least one bimetallic element are mounted within an integral support base molded from a mass of thermosetting material which is cured at the desired operating temperature for the switch. The contact elements each have a protruding stop and are biased during manufacture such that the stops abut the support base while the contact ends are maintained in a predetermined relationship with each other whereby the switch is calibrated at the same time the thermosetting material is cured.

Description

United States Patent 11 1 [111 3,816,910 Jess et al. [4 June 18, 1974 [54] METHOD FOR MAKING THERMALLY 2,745,924 5/1956 Coates 337/380 RESPONSIVE S S 3,148,258 9/1964 Dales 337/381 3,230,607 1/1966 Gelzer 337/94 Inventors: Thurman J 288 ai ie 3,747,208 7/1973 Rattan 29/622 Dr., Mundelien, 111. 60060; Wilbur F. Jackson, 27352 Ridge RCL, Prima E Ch 1 W L h ry xamznerar es an am Rollmg H1115 Cahf' 90274 Assistant Examiner-James R. Duzan [22] Fil d; Ja 15, 1973 Attorney, Agent, or Firm-Anthony A. OBrien [2]] Appl. No.: 323,617 57 ABS CT Related US. Application Data 1 [62] Division of Ser No 116 185 Feb 11 197] A thermally responsive swltch and method for making abandoned. the same in which a pair of contact elements including at least one bimetallic element are mounted within an 52 us. ca. 29/622 29/630 R 29/630 B integral support base molded from a mass of thermo- 51 Im. Cl. H0111 11/00 setting material which is cured at desired 5 Field f Search" R A, B ll'lg temperature fOI' the SWitCh. The COl'lttiCt elements 29/ 30 C 30 D. 95 11 12 374 each have a pI'OtIUdlIlg stop and are biased during 378 6 2 6 6 manufacture such that the stops abut the support base while the contact ends are maintained in a predeter- 56] References Cited mined relationship with each other whereby the switch is calibrated at the same time the thermosetting mate- UNITED STATES PATENTS rial 1s cured. 1,799,651 4/1931 Siegmund 200/166 BH 2,248,531 7/1941 Harris 337/112 7 Claims, 12 Drawing Figures PATENTEBJM 1 8 m4 SHEEI 1 BF 2 I INVENTOPS 77/URMAN s. JESS W/LBU/B E JACKSON vflww ATTORNEYS PATENTEDJUN 18 mm SHEET 2 0f 2 INVENTORS THURMAN .S JESS W/LBUR F. JACKSON METHOD FOR MAKING THERMALLY RESPONSIVE SWITCHES CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to thermally responsive switches and more particularly to an improved thermally responsive switch and method for making the same.

2. Description of the Prior Art Thermally responsive switches have long been utilized in connection with various electrical control networks to make or break an electrical circuit in response to sensed heat energy. It is often desired to have such control networks operate at a precise 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 deviceto initiate corrective action. Thus, an important specification in the manufacture of thermally responsive switches is 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 actuable at the same preselected temperature. It is therefore desirous to provide a method of making thermally responsive switches whereby the switches are accurately calibrated during manufacture thereby eliminating the need for calibration of the assembled switches and assuring reliable and accurate operation of the finished product.

The prior art, as characterized by U.S. Pat. Nos. 2,745,924, No. 3,148,258 and No. 3,230,607, is generally cognizant of electrical switches which are calibrated during manufacture. U.S. Pat. No. 2,745,924, for example, discloses 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 23 as illustrated in FIG. 8. A base material 24 is molded about the contact elements and is cured at the operating temperature of the switch. Thereafter, spacer 23 is removed to complete the assembly. U.S. Pat. No. 3,148,258 is generally similar to the previously described patent wherein contact elements 1 and 2 are placed in a multisectioned housing and are held, by structure not shown, during the curing of a plastic mass 24. U.S. Pat. No. 3,230,607 pertains to a switch in which a cylindrical post is axially movable by a bimetallic contact element during the curing of a thermosetting material.

While the prior art switch assemblies, as exemplified by the above, have generally served the purpose, they have proven to be disadvantageous in that the various contact elements are not provided with any means to positively locate such'elements within the housing or base and are not constructed with a durable integral support base, and the various contact elements are held during the curing step by a spacing member which can easily damage the contacts or bend the contact elements out of tolerance as it is removed. In addition, the methods of making such prior art structures are generally not adaptable to high speed mass-production tech niques, resulting in increased costs. While the problems associated with the design and construction of thermally responsive switches have been recognized for a considerable period of time, an accurate, calibrated thermally responsive switch and a. simple and inexpensive technique for manufacturing the same have heretofore been unavailable.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to inexpensively construct a thermally responsive switch which is calibrated during manufacture for accurate and reliable operation.

Another object of this invention is to manufacture a calibrated thermally responsive switch which is accurately responsive to a preselected temperature.

The present invention is summarized in a thermally responsive switch and method for making the same, the thermally responsive switch being generally characterized as including a unitary container having an open end and a closed end defining a pair of parallel slots, a pair of elongated flat contact elements including at least one bimetallic element, each of the contact elements having a supportable portion opposite a contact ing end and a protruding stop me-diately formed adjacent the supportable portion, each of the stops abutting an edge of one of the slots with the supportable portions of the contact elements disposed interiorly of the container, a mass of thermosetting material disposed in the container surrounding the supportable portions of the contact elements and cured at a particular temperature while the distal ends of the contact elements are held in a fixed predetermined relationship, the unitary container and the mass of material interacting to form an integral support base for the contact elements whereby the contact elements assume such predetermined relationship upon being heated to the particular temperature.

The present invention has a further object in that a unitary container interacts with a mass of thermosetting material to form an integral support base for a pair of contact elements of a thermally responsive switch.

An additional object of this invention is to construct an accurate thermally responsive switch by a simple and inexpensive method.

This invention has a further object in that a pair of switch contact elements are precisely positioned within an integral support base during assembly thereby increasing reliability and decreasing cost.

Some of the advantages of the present invention reside in its simplicity of construction, accuracy in operation, effectiveness in providing precise calibration, and ability to accurately position a pair of contact elements during manufacture without damaging the electrical contacts carried thereon or varying the switch calibration.

Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a detail of a plurality of base containers in strip form for use in making a thermally responsive switch according to the present invention;

FIG. 2 is a sectional view taken on line 22 of FIG.

FIG. 3 is a side elevational view of a detail of a contact element for use in a thermally responsive switch according to the present invention;

FIG. 4 is a front elevational view of the contact element of FIG. 3;

FIG. 5 is a sectional view of a preferred embodiment of a thermally responsive switch according to the present invention with a cover member partially installed;

FIG. 6 is a sectional view similar to FIG. 5 illustrating a completed thermally responsive switch according to the present invention;

FIG. 7 is a side elevational view of a support sleeve for supporting the switch assembly of FIGS. 5 and 6 during manufacture;

FIG. 8 is a plan view of the support sleeve of FIG. 7; and

FIGS. 9-12 are sectional views illustrative of a method for making a thermally responsive switch according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1-6, a preferred embodiment of a thermally responsive switch according to the present invention is generally designated at and includes a cylindrical base mold or container 22 having a bottom end closed by a wall 24 having an annular shoulder 26 formed upon the bottom surface thereof. Bottom wall 24 also defines a pair of centrally located, spaced parallel slots 28 having inclined, outwardly divergent, side walls best illustrated in FIG. 2.

The upper end of container 22 is open and has a pair of frangible fingers 30 radially extending from either side to a pair of outside runners 32. Fingers 30 have a tapered cross-section with the narrow end or apex attached to an upper peripheral edge of the container such that the fingers will be sheared off when pushed into a cover for the switch assembly, as will be more fully described below.

The containers 22 may be used singly or in strip form, as illustrated in FIG. 1, depending upon the contemplated production techniques to be employed. In either case, the runners 32 facilitate rapid handling of the containers thereby reducing time and costs during assembly of the switch. It is important to note that the containers are constructed as a unitary structure and are preferrably molded as such from a suitable plastic material. The unitary construction assures proper positioning of the contact elements of the switch assembly and precludes the possibility of container leakage during manufacture. In this manner, additional manufacturing steps formerly required in carefully assembling and aligning sectioned containers are effectively eliminated.

Thermally responsive switch 23 further includes a pair of identically constructed elongated, flat contact elements 34. Each of the contact elements has a diagonal contact 36 formed near one end thereof by any suitable means such as by swaging with the contact face parallel to the fiat surface of the element as shown in FIGS. 3 and 4. The diagonal positioning of the contacts is preferred since it permits the use of identical contact elements for lower cost while assuring positive contact in the event of slight misalignment. The contact end of elements 34 is also preferably rounded to enable cooperation with a calibration jig as will be described more fully below.

At some point, generally about three-fifths of the total length of element 34 from the contact end, a protruding stop 38, in the form of a dimple, tab, step or the like, is provided in the flat surface of the contact elements to assure proper positioning of the elements in base container 22 during calibration. The portion of the contact elements above stop 38 is angularly offset, as illustrated in FIG. 3, and serves as a supporting means for the element. The supporting portion defines a pair of centrally located apertures 40 which serve to rigidly lock each element in position after assemblyv It should be understood that the contact elements could also be provided with serrated or cutout edges in addition to or in place of apertures 40, if desired.

Each of the contact elements 34 further defines a centrally located hole 42 in a rounded terminal end with the lateral sides 44 of the hole arcuately offset from the plane of the Contact elements so as to receive the bare end of one of a pair of lead wires 45 for the switch. As seen in FIGS. 5 and 6, the offset sides 44 of hole 42 act to laterally support the lead wires 45 and provide an increased area to which the wires may be soldered.

At least one of the contact elements 34, and preferably both, are bimetals and are inserted from the terminal end up into the slots 28 of container 22 with their high expansion sides facing each other. It is noted that the contact elements may be disposed with their low expansion sides facing each other if it is desired to have the switch contacts open upon being cooled. The contact elements are preferably gold-plated for environmental protection and to improve their electrical conductivity. In the preferred embodiment, two bimetal contact elements are disposed in opposing relation to reduce premature opening of the switch below the normal operating temperature when subjected to shock and/or vibration. Because of the opposing relation of the bimetals, twice the contacting force is provided to maintain the switch closed at all temperatures below the operating temperature.

After the contact elements 34 have been assembled with the container 22, a mass of a suitable thermosetting material 46, such as epoxy resin, in its uncured, liquid or semi-liquid form is poured into the container surrounding the supportable portions of the contact elements to secure the same within the base. After curing, the completed switch assembly is inserted into a cylindrical cover, indicated generally at 48 in FIG. 5, having a rounded closed end. The cover 48 has a lower portion 50 interconnected with a slightly larger diameter upper portion 52 at an inclined annulus 54. Annulus 54 cooperates with shoulder 26 and the lower peripheral edge of container 22 to position the container, and thus the contact elements, in the cover as seen in FIG. 6. Cover 48 is preferably made of a metal or metal alloy since such materials exhibit good thermal conductivity characteristics, but may be made of any other suitable material, such as plastic or glass, as desired. The active portion of the bimetal contact elements 34 is enclosed within the lower portion 50 of the cover with the space between the elements filled with air or gas. Sufficient clearance is provided in this area to permit the elements to operate over a wide temperature range without contacting the cover wall.

Referring to FIG. 5, as the container 22 is installed in the cover member 48, the upper peripheral edge of the cover contacts the projecting fingers or protrusions 30 of the container adjacent the edge thereof. Because of the small cross-section of the fingers at their point of attachment to the container, they are sheared off as the container is pushed into the cover during final assembly. Some residual material will be left after the fingers are sheared so as to provide a lateral retaining force against the inside surface of the cover to secure the switch assembly within the cover. Thereafter, the container may be sealed in place by filling the open end with a mass of suitable sealing material 56, as shown in FIG. 6, or the entire assembly may be dip-coated.

Referring to FIGS. 7 and 8, a support sleeve 60, used as a calibration jig, is cut at its lower end to provide four tabs 62, at least two of which are folded inwardly to close the bottom of the sleeve. A plurality of apertures 64 are formed in the lower half of the sleeve to permit air circulation into the interior of the sleeve during the curing and calibration process to be described below. The upper half of the sleeve 60 is divided into four arcuate tabs 66 which are swaged at their upper edge to provide a gripping surface for container 22.

As seen in FIG. 9, a cylindrical aligning plug 68 is slidably disposed in the lower half of sleeve 60 and de fines a conical bore 70 in an upper surface thereof. Plug 68 is biased upwardly by a low-rate spring 72 mounted interiorly of sleeve 60 between the bottom of plug 68 and tabs 62. A plurality of inwardly directed dimples 74 in the wall of sleeve 60 serve as stops to retain plug 68 within the sleeve and define its upper limit of movement.

The method of assembling and calibrating the thermally responsive switch 20 of the present invention is illustrated in FIGS. 9-12. Initially, contact elements 34 are inserted from their terminal ends up into slots 28 of container 22 as illustrated in the exploded view of FIG. 9. The container carrying the bimetals 34 is then inserted into the open upper end of sleeve 60 whereupon the rounded contact end of the contact elements 34 engage conical bore 70 of plug 68. As the container 22 is moved down into the sleeve, the contact elements 34 are forced into the container until stops 38 engage the inclined walls of slots 28; additional movement of the container 22 causes plug 68 to be moved down against the biasing force of spring 72 until the container 22 is seated within the sleeve 60 as shown in FIG. 10.

As can be seen in FIGS. and 11, the conical bore 70 in plug 68 cooperates with contact elements 34 under the influence of low-rate spring 72 to maintain both elements 34 in proper longitudinal alignment with each other and with container 22, to assure proper positioning of the contact elements within the container 22 by forcing the elements upwardly such that stops 38 abut the walls of slots 28, and to exert a small inwardly directed force near to and behind contacts 36 so as to hold the contacts together without stressing the same during assembly. Thus, the construction of stop 38 of contact elements 34, the slotted base container or mold 22, and the calibration jig including sleeve 60, plug 68 and spring 72 provides a simple, yet accurate means for assemblying the thermally responsive switch of the present invention for final processing.

Referring to FIG. 12, a mass of thermosetting material 46 is poured into the container 22 so as to surround the supportable portions of the contact elements 34, the material 46 flowing in its raw or uncured state into the apertures 40 in the contact elements to'preclude their removal after curing. The entire assembly illustrated in FIG. 12 is then subjected to heat and is maintained at a desired operating temperature for the switch. The thermosetting material 46 is selected to have a curing temperature range within which the desired operating temperature of the switch lies such that as the material is being cured, the contact elements 34 will assume and maintain a flexed shape corresponding to their desired calibrated positions. In this regard, it is pointed out that the divergent walls of slots 28 allow free movement or flexure of the contact elements such that the contact elements are not subjected to stresses which would otherwise adversely affect the switch calibration. The flexure of the contact elements 34 may be seen from a comparison of FIG. 10, illustrating the assembly prior to heating, and FIG. 12, showing the assembly during the curing step. It is noted that during the curing step, the plastic container 22 interacts with the mass of material 46 to provide a hardened integral support base for contact elements 34 which increases the durability of the completed assembly. It is noted that a removable mold may be utilized in place of container 22 in which case the molded base assembly would be so sized as to cooperate with the cover memher to provide a proper fit. Following the curing cycle, the heat source is removed and the calibration jig separated from the calibrated switch sub-assembly including the bimetal elements 34 and the integral support base formed of container 22 and the cured mass of material 46. Thereafter, the lead wires 45 are soldered to the terminal ends of contact elements 34 and the subassembly is inserted into cover member 48 as shown in FIG. 5. As the subassembly is pushed into the cover, the fingers 30 will be sheared off and the unit may be subsequently sealed as shown in FIG. 6.

In operation, the contacts 36 of the completed switch assembly 20 will remain closed until the calibrated op erating temperature is reached at which point the contact elements will assume the shape in which they were maintained during the cure cycle, with contacts 36 just touching. Upon being heated above this temperature, the contacts will move apart to provide an electrical open circuit. After the switch is again cooled to the calibrated temperature, the contacts will contact each other, as before, to provide an electrical closed circuit. In this manner, the switch effectively operates at the preselected operating temperature at which the switch sub-assembly was cured.

Many of the advantages of the present invention can be seen in the above described simple method for making a thennally responsive switch, which method may be summarized as including the steps of forming a protruding stop on each of a pair of contact elements including at least one bimetal adjacent a supportable portion thereof, inserting the contact elements into a slotted container such that the supportable portions of the contact elements extend interiorly of the container, biasing the contact elements such that the stops abut an edge of the container and holding the distal ends of the contact elements in electrical contact with each other,

placing a thermosetting material into the container surrounding the supportable portions of the contact elements, and heating the filled container and the contact elements to a preselected operating temperature whereby the material is cured and the operating temperature of the contact elements is simultaneously calibrated.

Thus, the present invention enables the simple, rapid and inexpensive manufacture of thermally responsive switches on a mass-production basis with each of the switches having a precise operating temperature and being durably and accurately constructed for reliable operation.

inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is: l. A method of making a thermally responsive switch comprising the steps of forming a protruding stop on each of a pair of contact elements adjacent a supportable portion thereof, said pair of contact elements including at least one bimetallic element;

inserting said pair of contact elements into a slotted container such that the supportable portions of said contact elements extend interiorly of said container;

biasing said pair of contact elements such that said protruding stops abut said container, said biasing step including holding the distal ends of said contact elements in electrical contact with each other,

placing a mass of thermosetting material into said container surrounding the supportable portions of said pair of Contact elements, and

heating said filled container and said pair of contact elements to a preselected operating temperature whereby said thermosetting material is cured and the operating temperature of said contact elements is simultaneously calibrated.

2. The method as recited in claim 1 wherein said biasing step includes longitudinally aligning said contact elements with each other and with said container.

3. The method as recited in claim 1 wherein said biasing step includes engaging the distal ends of said contact elements with a plug member at a surface thereof defining a conical bore, and biasing said plug member against said contact elements to urge said contact elements toward each other and toward said container.

4. The method as recited in claim 1 wherein said container comprises a unitary plastic container, and wherein said heating step includes bonding said thermosetting material to said container to form an integral support base for said contact elements.

5. The method as recited in claim 4 wherein said container has a plurality of frangible fingers extending outwardly from an upper peripheral edge thereof, and further including the step of inserting said container into the open end of a cover member such that said plurality of fingers are sheared off by the edge of said cover member.

6. The invention as recited in claim 1 wherein said forming step includes cutting an aperture through the supportable portion of each of said pair of contact elements, and wherein said placing step includes disposing a portion of said thermosetting material into said aperture.

7. The method as recited in claim 1 including supporting said container within an open upper end of a sleeve, and wherein said biasing step includes engaging the distal ends of said contact elements with a plug member disposed within said sleeve at a conical bore defined by a surface of said plug member, and biasing said plug member against said contact elements to urge said contact elements toward each other and toward said container.

Claims

1. A method of making a thermally responsive switch comprising the steps of forming a protruding stop on each of a pair of contact elements adjacent a supportable portion thereof, said pair of contact elements including at least one bimetallic element; inserting said pair of contact elements into a slotted container such that the supportable portions of said contact elements extend interiorly of said container; biasing said pair of contact elements such that said protruding stops abut said container, said biasing step including holding the distal ends of said contact elements in electrical contact with each other, placing a mass of thermosetting material into said container surrounding the supportable portions of said pair of contact elements, and heating said filled container and said pair of contact elements to a preselected operating temperature whereby said thermosetting material is cured and the operating temperature of said contact elements is simultaneously calibrated.