US3563712A - Laminated thermostatic metal - Google Patents

Abstract

A THREE LAYER LAMINATED METAL STRIP FOR USE IN CIRCUIT BREAKERS HAVING ADVANTAGES FLEXIVITY AND RESISTIVITY CHARACTERISTICS AND FORMED FROM A HIGH EXPANDING METAL LAMINATION, A LOW EXPANDING METAL LAMINATION AND AN ADDITIONAL LAMINATION DISPOSED BETWEEN THE LOW EXPANDING AND HIGH EXPANDING LAMINATIONS.

Description

Feb. 16, 1971 c, zElGLER 3,563,712

LAMINATED THERMO-STATIC METAL Original Filed April 15, 1965 FJG. 4

INVENI OR CHARLES F. ZEIGLER BY M2 2 M ATTORNEYS United States Patent O 3,563,712 LAMINATED THERMOSTATIC METAL Charles F. Zeigler, 4960 Broomfield Lane, Birmingham, Mich. 48010 Continuation of application Ser. No. 448,370, Apr. 15, 1965. This application May 2, 1968, Ser. No. 726,113 Int. Cl. B23p 3/00 U.S. Cl. 29-195.5 1 Claim ABSTRACT OF THE DISCLOSURE CROSS REFERENCE TO RELATED APPLICATION This is a continuation of application S.N. 448,370, filed Apr. 15,, 1965, now abandoned.

SUMMARY OF THE INVENTION In accordance with the principles of my invention, I provide a laminated metal strip having a first outer layer of high expanding metal such as 22% nickel, 3% chromium, balance iron; a second outer layer of low expanding metal such as 42% nickel, balance iron; and a third inner layer interposed between and bonded to both outer layers, the third layer being formed from a metal of low electrical resistivity such as nickel. Typically, the outer layers are of substantially equal thickness and the inner layer is about twice as thick as either outer layer. The strip is formed with a dished center section.

This strip finds its main present application in circuit breakers which are maintained closed until the ambient temperature increases toward same preselected maximum value at which the breaker is to snap open. This snap action is to be reversed when the temperature drops below the preselected values.

My strip with the dished center section exhibits the desired properties for this type of application, since it has low flexivity at temperatures ranging from perhaps 50 F. to about 300 F. and snaps over (high flexivity) at temperatures above 300 F. Moreover, my strip exhibits low electrical resistivity and will not respond to high current transients; without low resistivity, these transients would cause heating of the strip itself and initiate snap action when the ambient temperature remained below the selected value.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is an elevational view of a circuit breaker utilizing the improved thermostatic metal of this invention, and showing the circuit breaker contacts in engaged positions;

FIG. 2 is an elevational View of the circuit breaker of FIG. 1, showing the thermostatic element of this invention in a deflected position so as to open the circuit breaker contacts;

FIG. 3 is a top View of the circuit breaker shown in FIG. 1; and

FIG. 4 is a diagrammatic sectional view of a thermostatic element constructed in accordance with the concepts of this invention.

3,563,712 Patented Feb. 16, 1971 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 3 an element formed of the thermostatic metal of this invention, and indicated generally at 10, is disposed in an illustrative circuit breaker 12 which itself forms no part of the present invention and is illustrated only for the purpose of illustrating the element 10 in an operative environment. The circuit breaker 12 consists of a first conductor 16 having a fixed contact 18 mounted on the terminal end thereof and a second conductor 20 which is secured to one end 22 of the thermostatic element 10, which end will be hereinafter referred to as the fixed end 22. The opposite or movable end 24 of the element 10 has a contact 26 secured thereto at a position such that the contacts 18 and 26 are engaged as shown at temperatures between room temperature and a temperature of about 300 F. An insulating and spacer block 30 is secured to and positioned between conductors 16 and 20 so as to maintain the conductors in a relatively insulated and spaced relation. Element 10 is provided with a downwardly dished center section 28.

The element 10 in the illustrated embodiment of the invention is of generally rectangular shape, although it is to be understood that it can be of other shapes, and in the illustrated circuit breaker 12 the element 10 is cantilever mounted at its fixed end 22 on the conductor 20.

One important feature of the element 10 is its inherent or intrinsic snap action capability at the predetermined temperature of about 300 F. At this temperature, the element 10 will snap over to the position shown in FIG. 2 in which the contact is spaced from the contact 18. This snap action is accomplished by forming the element 10 with a dished center section 28, which is dished downwardly as referred to above.

The function of the element 10 is to maintain the movable contact 26 in engagement with the fixed contact 18 at temperatures below temperatures of about 300 F. as shown in FIG. 1, and to move the contact 26 to a position spaced from the contact 18 at a temperature above temperatures about 300 F., as shown in FIG. 2. It is intended that the element 10 also maintain the contact 26 in engagement with the contact 18 during flow of high overload currents of short duration (transients) through the conductors 16 and 20, when the temperature of element 10 is below 300 F.

Referring now to FIG. 4, element 10' consists of two outer laminations 34 and 36 and a center lamination 38. The outer lamination 34 is a low expanding metal lamination consisting of about 42% nickel with balance iron. The lamination 36 is a high expanding metal lamination consisting of about 22% nickel, about 3% chromium with balance iron. The center lamination is nickel. The lamination 34 is labeled lo in FIG. 4 and the lamination 36 is labeled hi to signify that the lamination 36 has a higher coeflicient of thermal expansion than the lamination 34.

In order to obtain the desired flexivity and electrical resistivity characteristics in the element 10, the laminations must have relative proportions at which laminations 34 and 36 are of approximately equal thicknesses and the combined thicknesses of the laminations 34 and 36 must constitute about one half of the total thickness of the element 10. In a preferred embodiment of the invention, each of the laminations 34 and 36 constitutes 26.7% of the total thickness and the lamination 38 constitutes 46.6% of the thickness of the trimetal billet which is subsequently rolled out to provide an element 10 which is only a few thousandths of an inch thick. Since, during roll out, one or more of the laminations 34, 36 and 38 may be elongated more than the others, the final relative thicknesses of the laminations 34, 36 and 38 may vary slightly from the initial relative thicknesses.

The resulting trimetal has a flexivity in the range of temperatures between 100 F. and 300 F. of 0.0000093 and an electrical resistivity at 75 F. of 100 ohms per circular mil. ft. A resistivity on the order of this magnitude is required to preclude undesirable response of element 10 to high electrical current transients, for if the element were to respond to these transients, the breaker would open when it should remain closed.

The element 10 has the desirable characteristics of sufficiently low electrical resistivity to prevent a response of the element 10 to high electrical currents and a low flexivity at temperatures below 300 F. At a temperature of about 300 F. or above, the element 10 has a higher flexivity so that, with the use of the dished center sectiou, it will quickly deflect and snap over. As shown in FIG. 4, the movable contact 26 is secured to the high expanding lamination 36 at the movable end 24 of the element 10. Lamination 36 is formed on the concave side of the section 28. Consequently, when the element 10 responds to a high temperature, it flexes in a direction to move the contact 26 away from the contact 18, as shown in FIG. 2.

From the above description it is seen that this invention provides an improved thermostatic metal which is operable, in an environment such as in a circuit breaker 12, to maintain the contacts 18 and 26 engaged when the temperature of the element 10 is below the critical temperature of about 300 F. Such construction also provides for lack of deflection of element 10 in response to high overload current conditions of short duration.

It will be understood that the laminated thermostatic metal which is hereindisclosed and described is presented for purposes of explanation and illustration and is not intended to indicate limits of the invention, the scope of which is defined by the following claim.

What is claimed is:

1. A thermostatic lamination adapted for use in a snap acting circuit breaker comprising:

a central nickel layer;

a first high expanding outer layer parallel to the central layer and bonded metallurgically to one exposed surface of the central layer, said first layer consisting essentially of 22% by weight of nickel, 3% chromium, balance iron;

a second low expanding outer layer parallel to the central layer and bonded metallurgically to the opposite exposed surface of the central layer, the second layer consisting essentially of 42% by weight of nickel, balance iron; said first and second layers having equal thicknesses, the sum of the thicknesses of the first and second layers being equal to the thickness of the central layer; and a deformed region extending transversely through all of the strips to define a circular dished center section which is concave as viewed from the exposed surface of the first layer and is convex as viewed from the exposed surface of the second layer.

References Cited UNITED STATES PATENTS 2,240,824 5/1941 Alban 29195.5 2,241,902 5/1941 Drapeau 29195.5 2,714,668 8/1955 Zinn 29195.5 2,481,087 9/1949 Crise 29195.5 3,102,793 9/1963 Aban 29-195.5

HYLAND BIZOT, Primary Examiner

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