Thermally actuated cut-off link or switch and method of making the same

An ambient thermal actuated cut-off link comprising:

• a casing of electrically conductive material;
• a first power lead in said casing exposed to the outside of said casing through an opening in said casing where it is insulated therefrom, said first power lead having at the inner end thereof laterally outwardly extending, inwardly deformable contact-forming arm means making a low resistance contact with the inner conductive surface of said casing;
• a second exposed power lead making a permanent low resistance contact with the inner conductive surface of said casing;
• a second exposed power lead making a permanent low resistance connection with said casing;
• a sandwich of serially located elements urged under spring pressure between fixed spaced points in said casing and comprising first fully compressed spring means, arm-deforming means on one side of said arm means and urged by said fully compressed spring means toward said arm means to deform the same inwardly when the fully compressed spring means is allowed to expand, backing mean on the other side of said arm means and against which said arm means bear and are expanded against said casing to establish a given low resistance contact therewith, second compressed spring means for keeping said first spring means fully compressed and for taking up any play in said sandwich of elements, and a fusible body which melts at a given control temperature, said backing means being located between said fully compressed spring means and second spring means so that the position of said backing means is fixed within said sandwich of elements as long as said fully compressed means remains full compressed, whereby the contact resistance between said arm means and casing does not vary with the degree of compression of said second spring means, the melting of said body of meltable material at said control temperature first causing said second spring means to expand, after which said fully compressed spring means expand to force said arm deforming means against said contact-forming arm means to disengage the same from said casing.

An ambient thermal cut-off link comprising:

• a casing of electrically conductive material having inner conductive surfaces;
• a first power lead extending longitudinally into one end of said casing at a point where it is insulated therefrom, said first power lead terminating within said casing in laterally outwardly extending, inwardly deformable contact-forming arm means making a low resistance contact with said curved inner conductive surface of said casing and which are integral with said first power lead so that no separable contact interface is formed therewith;
• a second power lead extending longitudinally into the other end of said casing and making a permanent low resistance connection with said casing, the interface between said arm means and casing thus being the only separable contact interface between said power leads;
• a longitudinally extending sandwich of elements held under spring pressure located between the ends of said casing and comprising, in the order named, first fully compressed spring means, arm-deforming means positioned immediately between said fully compressed spring means and said arm means and urged by said fully compressed spring means toward said arm means to deform the same inwardly when the fully compressed spring means is allowed to expand, backing means for said arm means against which said arm means bear and are expanded against said casing to establish a given low resistance contact therewith, partially compressed spring means for taking up any play in said sandwich of elements, and a fusible body which melts at a given control temperature and is engaged by said other end of said casing at the sides thereof to efficiently receive heat externally of the casing thereto, said backing means being located between said fully compressed spring means and partially compressed spring means so that the position of said backing means is fixed within said sandwich of elements as long as said fully compressed means remains fully compressed, whereby the contact resistance between said arm means and casing do not vary with the degree of compression of said partially compressed spring means;
• the melting of said fusible body at first causing the partially compressed spring means to expand at said control temperature after which said fully compressed spring means forces said arm-deforming means against said arm means to disengage the same from said casing.

A method of making an ambient thermally actuated switch comprising a casing of electrically conductive material having at least one initially open portion to receive switch-forming elements during the assembly of the switch;

• a first exposed power conductor within and insulated from said open portion of said casing and associated laterally outwardly inclining contact-forming arm means initially in electrical contact with a conductive surface associated with said casing;
• a sandwich of elements within said casing, said sandwich of elements including arm-deforming means contiguous to one side of said contact-forming arm means and adapted when forced thereagainst with a given force to contract and bend said contact-forming arm means away from said conductive surface, a backing member on the opposite side of contact-forming arm means against which member said contact-forming arm means are forced to expand the same into good electrical contact with said conductive surface, spring means, and a fusible body of material which melts at a given control temperature, said spring means being in a stressed condition while the fusible body remains unmelted and moving to an unstressed state to push said arm-deforming means against said arm means to move the same out of contact with said conductive surface;
• and closure means closing said initially open portion of said casing so that it maintains said spring means in said stressed condition to force said contact-forming arm means against said backing member;
• said method comprising;
• inserting said sandwich of elements and said first power conductor and associated contact-forming means into said casing, then externally forcing said closure means against said sandwich of elements and said first power conductor and contact-forming arm means toward said backing member, to stress said spring means and force said contact-forming arm means against said backing member so as to expand said contact-forming arm means into forced engagement with said casing, adjusting said force against said first power conductor and contact-forming arm means to a value such that the contact resistance measured between said casing and said contact-forming arm means is at a desirably low predetermined value, and, while maintaining said adjusted force on said first power conductor, permanently anchoring said closure means over said initially open portion of said casing to fix the stress on said spring means and the pressure of said contact-forming arm means against said conductive surface.

An ambient thermal actuated cut-off link comprising:

• a casing of electrically conductive material;
• a first power lead exposed to the outside of said casing through an opening in said casing at a point where it is insulated therefrom, said first power lead having at the inner end thereof laterally outwardly extending, inwardly deformable contact-forming arm means making a low resistance contact with an inner conductive surface associated with said casing;
• a second exposed power lead making a permanent low resistance connection with said casing;
• a sandwich of serially located elements urged under spring pressure between fixed spaced points in said casing and comprising stressed spring means, arm-deforming means on one side of said arm means which arm-deforming means is urged by said spring means toward said arm means to deform the same inwardly when the spring means is allowed to move to the unstressed state thereof, backing means for said arm means on the other side of the same and against which backing means said arm means is urged to expand the same against said casing to establish a given low resistance contact therewith, and a fusible body which melts at a given control temperature, the melting of said body of meltable material at said control temperature causing said spring means to move to an unstressed state to force said arm-deforming means against said contact-forming means to bend the same away from said casing;
• and closure means anchored in and sealing said casing opening, said closure means being a resilient contracted member into which said first power lead extends and around which the defining walls of said casing opening extend to contract the same around the said first power lead to hold the same in a position where the contact-forming arms at the inner end thereof are forced against said backing means.