US3242290A - Thermally responsive switch construction and method of making the same - Google Patents

Description

March 22, 1966 H. J. TYLER 3,242,290 THERMALLY RESPONSIVE SWITCH CONSTRUCTION AND METHOD OF MAKING THE SAME Filed Feb. 20, 1962 l IO U IO 34| 2 2 20 (I2 32 l 5 6 i 22 3O fi -7 Q l 3 3| 36 28-1 27f 29 25 2| I3 I? A; 1 I A 24 i FIG-2 INVENTOR. HUGH JEAN TYLER ATTORNEY United States Patent 3,242,290 THERMALLY RESPONSIV E SWITCH CONSTRUC- TION AND METHOD OF MAKING THE SAME Hugh Jean Tyler, Jeannette, Pa., assignor to Robertshaw Controls Company, Richmond, Va., a corporation of Delaware Filed Feb. 20, 1962, Ser. No. 174,423 17 Claims. (Cl. 200-417) This invention relates to an improved electrical switch construction and to an improved method for making such a switch construction or the like.

It is well known in the art to provide a fusible electric switch wherein there is normally an electrical interconnection between the terminals of the switch until the switch structure is heated above a predetermined. temperature whereby the electrical current between the terminals is terminated.

For example, such a switch construction can include a movable contact member normally held in electrical contact with one of the terminals thereof by a fusible material placed either under tension or compression. When the fusible material is heated to its melting point thereof or to a point where it loses its tensile strength the fusible material fails whereby the movable contact arm moves out of contact with its respective terminal to terminate flow of electrical current between the terminals of the switch construction.

However, it has been found that when the fusible material is utilized in tension, there is a possibility of premature opening of the switch construction due to creepage of the fusible material.

Further, when the fusible material is placed in compression, it has been found that similar switch constructions have varying electrical resistance due to variations in the contact pressure of the switch constructions.

According to the teachings of this invention however, an improved fusible switch construction is provided wherein the fusible material is actually a conductor in the circuit and thereby eliminates the varying electrical resistance of the contacts. Further, there is no premature opening due to creepage, and expensive gold plating needed to protect contacts from resistance build-up is eliminated.

Accordingly, it is an object of this invention to provide an improved switch construction having one or more of the novel features of this invention set forth above or hereinafter shown or described.

Another object of this invention is to provide an improved method for making such a switch construction or the like.

Other objects, uses and advantages of this invention are apparent from a reading of this description which proceeds with reference to the accompanying drawings forming a part thereof and wherein:

FIGURE 1 is a cross-sectional view of the improved switch construction of this invention disposed in the normal operating position thereof to permit electrical current to flow between the terminals thereof.

FIGURE 2 is a view similar to FIGURE 1 and illustrates the switch construction in the position thereof when electrical current between the terminals is terminated.

FIGURE 3 is a view similar to FIGURE 1 and illustrates one of the assembly steps in forming the switch construction of this invention.

FIGURE 4 is a view similar to FIGURE 3 and illustrates other steps in the assembly of the switch construction of this invention.

FIGURE 5 is a view similar to FIGURE 4 and illus trates another step in the method of this invention.

FIGURE 6 is a top plan view of the switch construction illustrated in FIGURE 1.

3,242,290 Patented Mar. 22, 1966 While the various features of this invention are hereinafter described as being particularly adaptable to form an electrical switch construction, it is to be understood that the various features of this invention can be utilized singly or in any combination thereof to form other constructions, as desired.

Therefore, this invention is not to be limited to only the embodiment illustrated in the drawings, because the drawings are merely utilized to illustrated one of the wide variety of uses of this invention.

Referring now to FIGURE 1, the improved switch construction of this invention is generally indicated by the reference numeral 10 and comprises an insulating casing or base member 11 carrying a pair of L- shaped terminals 12 and 13.

The L- shaped terminals 12 and 13 are respectively secured in suitable apertures 14 and 15 formed in the casing 11 and respectively have threaded bores 16 and 17 formed through the legs 18 and 19 thereof, the other legs 20 and 21 of the terminals 12 and 13 projecting beyond the casing 11 and having suitable slots 22 and 23 formed therein to form electrical lead connection means in a manner well known in the art.

A first contact means 24 is carried by the switch construction 10 and comprises a bolt having a threaded shank portion 25 and an enlarged head 26, the shank portion 24 being threadedly received in the bore 17 of the terminal 13 and sandwiching a pair of contact legs or arms 27 and 28 and a spacer 29 between the enlarged head 26 thereof and the leg 19 of the terminal 13.

The contact arm 27 is rigid and forms a support while the contact arm 28 is flexible and normally tends to be disposed fiat against the contact arm or support 27 for a purpose hereinafter described.

A second contact means 30 is carried by the switch construction 10 and comprises a threaded member threadedly received in the threaded bore 16 in the leg 18 of the terminal 12, the contact means 30 having a bifurcated end 31 to provide means for initially adjusting the position of the other end 32 of the contact means 30 relative to the contact arm or support 27 for a purpose hereinafter described.

The flexible contact arm 28 is normally held in the position illustrated in FIGURE 1 by solder means 33 and 34, the solder means 33 being secured to one side of the contact arm 28 and to the end 32 of the contact means 30 whereby the solder means 33 is placed under tension by the natural resiliency of the contact arm 28 tending to move away from the contact means 30 toward the support 27. The solder means 34 is secured to the other side of the contact arm 28 and to the support 27 whereby the solder means 34 is placed under compression by the natural resiliency of the contact arm 28 tending to move toward the support 27.

The solder means 34 has a melting point lower than the melting point of the solder means 33 while the solder means 33 has its tensile properties reduced when heated to a temperature corresponding to the melting temperature of the solder means 34.

While the switch construction 10 can be utilized in any desired application to provide means for terminating flow of electrical current through a circuit when the temperature of the switch construction 10 reaches the meltng point of the solder means 34, one such use for the switch construction 10 would be in conventional, domestic, gas-fired clothes dryers or the like.

For example, in such a gas-fired clothes dryer or the like, a normally burning pilot thereof energizes a thermocouple lead leading to an electrical coil of a safety valve whereby the safety valve remains open as long as the thermocouple is being heated so that .gas can flow to the main burner of the clothes dryer. By placing the switch construction of this invention in the thermocouple lead, the same will terminate the current flowing to the safety valve should the temperature of the dryer exceed safe limits thereof due to exhaust blockage, broken fan belt or other reasons whereby the safety valve would close and prevent gas from being fed to the main burner of the clothes dryer.

Since the switch construction 10 of this invention is non-recycling, corrective servicing of the clothes dryer is necessary before it is again put into operation whereby it is impossible to operate the dryer until the cause for the high temperatures has been remedied.

The operation of the switch construction 10 will now be described.

When the switch construction 10 is disposed in the position illustrated in FIGURE 1, electrical current is adapted to flow between the terminals 12 and 13 because the contact arm 28, being electrically interconnected to the contact means 24, is placed in electrical connection with the contact means 30 by the solder means 33, the solder means 33 comprising an electrical conductor whereby varying electrical resistance between the contact arm 28 and the contact means 30 is eliminated because the solder means 33 is secured respectively to the contact arm 28 and to the contact means 30.

Further, the solder means 34 is an electrical conductor wherebycurrent can flow from the contact means 30 to the support 27 which is electrically interconnected to the contact means 24.

In this manner, expensive gold plating needed to protect electrical contacts from resistance build-up is elimihated by this invention because the solder means 33 and 34 provide good electrical connection between the termirials 12 and 13 of the switchconstruction 10.

Further, even though the solder means 33 is placed under tension, no premature opening of the switch construction 10 from creepage is possible because the solder means 34 is placed under compression to hold the contact arm 28 in place.

As long as the contact arm 28 of the switch construction 10 remains in the position illustrated in FIGURE 1, electrical current is adapted to flow between the terminals 12 and 13 thereof.

However, should the temperature of the atmosphere surrounding the switch construction 10 heat up to such a temperature to cause the solder means 34 to fuse or melt, the solder means 34 collapses and the solder means 33, although remaining solid, loses at least some of its tensile properties whereby the natural resiliency of the contact arm 28 moves the contact arm 28 toward the support 27 in the manner illustrated in FIGURE 2 and makes a smooth break across the solder means 33 to move out of electrical connection with the contact means 30 to terminate the flow of electrical current between the terminals 12 and 13.

Because the solder means 33 is not fused or melted at the temperature causing fusing or melting of the solder means 34, a clean break is effected across the solder means 33 by the moving contact arm 28 whereby no stringers of the solder means 33 are provided which would still permit electrical connection between the contact means 28 and the contact means 30 when the contact arm 28 is moved to the position illustrated in FIGURE 2.

Therefore, it can be seen that an improved electrical switch construction of this invention is provided which will accurately terminate flow of electrical current between the terminals thereof when the temperature of the switch construction reaches the melting point of the fusible material 34 because the melting point of the solder means 34 can be predetermined.

Further, because the switch construction 10 opens when the fusible material 34 fuses or melts, a more accurate operation thereof is effected than when a switch construction opens solely on a fusible material losing its tensile properties at a particular temperature because the resilient properties for movable contact arms can vary.

The method of this invention for making the switch construction 10 of FIGURE 1 will now be described and reference is made to FIGURES 3-5.

Preferably, but not necessarily, the solder means 33 is first placed on the end 32 of the contact means 30 before the contact means 30 is assembled to the switch construction 10 in the manner illustrated in FIGURE 3.

When the contact means 30 is disposed in the position illustrated in FIGURE 3, a suitable shim 35 is forced between the support 27 and the contact arm 28 to hold the contact arm 28 in its biased condition against the solder means 33 carried by the contact means 30 in the manner illustrated in FIGURE 4, the shim 35' being formed of any suitable material, such as Teflon or the like.

After the shim 35 has been placed in the position illustrated in FIGURE 4 to hold the contact arm 28 in contact with the solder means 33, the contact means 30 is adjusted toward the contact arm 28 by rotating the same through a quarter turn or the like to press the solder means 33 against the contact arm 28 with a certain pressure.

Thereafter, solder paste 36 is disposed around the contact means 30 and the terminal 12 as Well as around the shank and head 26 of the contact meaiis 34 in the manner illustrated in FIGURE 4.

Subsequently, a wire or the like of the solder means 34 is inserted between the support 27 and the contact arm 28 in the manner illustrated in FIGURE 5.

Thereafter, the entire switch construction illustrated in FIGURE 5 is heated to melt all of the solder means 33, 34, and 36. For example, the switch construction as illustrated in FIGURE 5 can be placed upright in the position shown in an oven or the like and heated to 507 to 525 F. for approximately three to five minutes.

In this manner, the solder means 33, 34, and 36 fully wet the desired surfaces of the switch construction 10 so that upon subsequent removal of the switch construction 10 from the oven to cool and solidify the solder means 33, 34, and 36, the solder means 33 is fully secured to the contact arm 28 and to the contact means 30 while the solder means 34 is fully secured to the contact arm 28 and to the support 27 to hold the contact arm 28 in the position illustrated in FIGURE 1 when the shim 35 is subsequently removed. In addition, the solder means 36 firmly holds the contact means 30 and 24 in place in the proper adjusted positions thereof.

Prior to the cooling of the heated switch construction 10, the switch construction 10 can be immersed in hot water to remove all solder flux therefrom, as desired.

Therefore, it can be seen that the switch construction 10 of this invention can be made in a relatively simple and a relatively rapid manner to produce the switch construction 10 which is not only economical but which is also accurate in the operation thereof.

Accordingly, it can be seen that an improved electrical switch construction is provided by this invention as well as an improved method of making such a switch construction or the like.

While the form of the invention now preferred has been disclosed as required by the statutes, other forms may be used, all coming within the scope of the claims which follow.

What is claimed is:

1. A switch construction comprising a casing, a pair of electrical contact means carried by said casing, a support carried by said casing, a resilient contact arm carried by one of said contact means and normally disposed out of contact with the other contact means, a first means disposed between said contact arm and said other contact means and holding said contact arm in a biased condition toward said other contact means whereby said contact arm is placed in electrical connection with said other contact means and said first means is placed under ten sion, and a second means disposed between said support and said contact arm and holding said contact arm in said biased condition toward said other contact means whereby said second means is placed under compression, said second means having a lower melting point than said first means and said first means having its tensile properties reduced when heated to the melting point of said second means whereby electrical connection between said contact means is terminated when said switch construction is heated to said melting point of said second means to cause said contact arm to break said first means and move away from said other contact means.

2. A switch construction comprising a casing, a pair of electrical contact means carried by said casing, a support arm carried by one of said contact means, a resilient contact arm carried by said one contact means and normally disposed out of contact with the other contact means, a first means disposed between said contact arm and said other contact means and holding said contact arm in a biased condition toward said other contact means whereby said contact arm is placed in electrical connection with said other contact means and said first means is placed under tension, and a second means disposed between said support arm and said contact arm and holding said contact arm in said biased condition toward said other contact means whereby said second means is placed under compression, said second means having a lower melting point than said first means and said first means having its tensile properties reduced when heated to the melting point of said second means whereby electrical connection between said contact means is terminated when said switch construction is heated to said melting point of said second means to cause said contact arm to break said first means and move away from said other contact means.

3. A switch construction as set forth in claim 2 wherein said first means electrically interconnects said contact arm with said other contact means.

4. A switch construction as set forth in claim 2 wherein electrical terminals are respectively electrically interconnected to said contact means.

5. A switch construction as set forth in claim 2 wherein said other contact means is adjustably carried by said casing.

6. In combination, a casing, a pair of contact means carried by said casing, a movable spring contact arm electrically interconnected to one of said contact means and normally tending to be disposed in a position away from the other of said contact means, a first means disposed on one side of said contact arm and tending to hold said contact arm in another position thereof toward said other contact means whereby said contact arm is electrically interconnected to said other contact means and said first means is placed under tension, and a second means disposed on the other side of said contact arm and tending to hold said contact arm in said other position thereof whereby said second means is placed under compression, said second means having a lower melting point than said first means whereby electrical connection between said contact means is terminated when said first and second means are heated to said melting point of said second means to cause said contact arm to overcome the holding force of said first means and move away from said other contact means.

7. A combination as set forth in claim 6 wherein said first means is an electrical conductor.

8. A combination as set forth in claim 6 wherein said second means is a solder.

9. A combination as set forth in claim 6 wherein said first and second means are solder.

10. In a switch construction, a movable spring contact arm disposed in one position thereof and tending to move to another position thereof, a first means secured to one side of said contact arm and to said switch construction whereby said first means is placed under tension, and a second means secured to the other side of said contact. arm and to said switch construction whereby said second means is placed under compression, said second means having a lower melting point than said first means whereby said contact arm moves to said other position thereof by breaking said first means when said first and second means are heated to said melting point of said second means.

11. In a switch construction as set forth in claim 10, said first means having its tensile properties reduced when heated to the melting temperature of said second means.

12. A method for making a switch construction comprising the steps of placing a first means on one contact means of a switch structure, holding a movable contact arm in contact with said first means, said contact arm being electrically interconnected to another contact means of said switch structure and normally tending to move away from said one contact means, placing a second means between said contact arm and a support of said switch structure, said second means having a lower melting point than said first means, and securing said means to said contact arm whereby said contact arm is held in one position thereof by said first and second means to electrically interconnect said contact means together until said second means is heated to said melting point thereof to terminate said electrical interconnection between said contact means.

13. A method for making a switch construction comprising the steps of placing a first solder means on one contact means of a switch structure, holding a movable contact arm of said switch structure in contact with said first solder means, said contact arm being electrically interconnected to another contact means of said switch structure and normally tending to move away from said one contact means, placing a second solder means between said contact arm and a support of said switch struc- .ture, said second solder means having a lower melting point than said first means, securing said solder means to said contact arm and respectively to said one contact means and said support whereby said contact arm is held in one position thereof by said first and second means to electrically interconnect said contact means together until said second means is heated to said second melting point thereof to terminate said electrical interconnection between said contact means.

14. A method for making a switch construction comprising the steps of placing a first solder means on one contact means of a switch structure, holding a movable contact arm of said switch structure in one position thereof and in contact with said first solder means, said contact arm being electrically interconnected to another contact means of said switch structure and normally tending to move away from said one contact means, placing a second solder means betwen said contact arm and a support of said switch structure, said second solder means having a lower melting point than said first solder means, heating said switch structure to a temperature of at least the melting point of said first solder means while still holding said contact arm in said one position thereof whereby said solder means wets said contact arm and respectively wets said one contact means and said support, cooling said switch structure to solidify said solder means so that said solder means tends to hold said contact arm in said one position thereof, and ceasing to hold said contact arm in said one position thereof whereby said solder means holds said contact arm in said one position thereof until said switch structure is heated to the melting point of said second solder means.

15. A method as set forth in claim 14 wherein said step of holding said contact arm in said one position thereof includes the step of inserting a member between said support and said contact arm.

16. A method as set forth in claim 14 wherein said first solder means has its tensile properties reduced when heated to the melting temperature of said second solder means.

17. A method as set forth in claim 14 wherein said one contact means is adjusted relative to a casing of said switch structure to a desired position thereof and is subsequently secured in said desired position.

Metzgar 200-123 Bussmann 200123 McAlister 200142 Milton et a1. 200-123 Milton et a1. 200-442 BERNARD A. GILHEANY, Primary Examiner.

Claims (1)

1. A SWITCH CONTRACTION COMPRISING A CASING, A PAIR OF ELECTRICAL CONTACT MEANS CARRIED BY SAID CASING, A SUPPORT CARRIED BY SAID CASING, A RESILIENT CONTACT ARM CARRIED BY ONE OF SAID CONTACT MEANS AND NORMALLY DISPOSED OUT OF CONTACT WITH THE OTHER CONTACT MEANS, A FIRST MEANS DISPOSED BETWEEN SAID CONTACT ARM AND SAID OTHER CONTACT MEANS AND HOLDING SAID CONTACT ARM IN A BIASED CONDITION TOWARD SAID OTHER CONTACT MEANS WHEREBY SAID CONTACT ARM IS PLACED IN ELECTRICAL CONNECTION WITH SAID OTHER CONTACT MEANS AND SAID FIRST MEANS IS PLACED UNDER TENSION, AND A SECOND MEANS DISPOSED BETWEEN SAID SUPPORT AND SAID CONTACT ARM AND HOLDING SAID CONTACT ARM IN SAID BIASED CONDITION TOWARD SAID OTHER CONTACT MEANS WHEREBY SAID SECOND MEANS IS PLACED UNDER COMPRESSION, SAID SECOND MEANS HAVING A LOWER MELTING POINT THAN SAID FIRST MEANS AND SAID FIRST MEANS HAVING ITS TENSILE PROPERTIES REDUCED WHEN HEATED TO THE MELTING POINT OF SAID SECOND MEANS WHEREBY ELECTRICAL CONNECTION BETWEEN SAID CONTACT MEANS IS TERMINATED WHEN SAID SWITCH CONSTRUCTION IS HEATED TO SAID MELTING POINT OF SAID SECOND MEANS TO CAUSE SAID CONTACT ARM TO BREAK SAID FIRST MEANS AND MOVE AWAY FROM SAID OTHER CONTACT MEANS.

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