Heat limiters and method of manufacture

A circuit interrupting device, for opening an electric circuit at a predetermined temperature, including in combination:

• a cylindrical housing having first and second ends,
• first and second spaced apart coaxially aligned terminals, each having a free end portion, said first terminal extending into said first end of said housing and said second terminal extending into said second end of said housing,
• a coil spring having a base portion and a tip portion, said base portion being secured adjacent said second, open end of said housing,
• a conductive member having first and second ends, said conductive member extending between said free end portions of said first and second terminals,
• first and second masses of fusing conductive material,
• said first end of said conductive member being normally connected to said first terminal by said first mass of fusing conductive material and said second end of said conductive member being normally connected to said second terminal by said second mass of fusing conductive material,
• said tip portion of said coil spring being attached to said second end of said conductive member thereby to outstretch and tension said coil spring,
• said first and second masses of fusing conductive material being softenable at a predetermined temperature, sufficiently to break said connections between said first end of said conductive member and said first terminal and between said second end of said conductive member and said second terminal, respectively, thereby permitting said coil spring to relax, moving said conductive member away from said first terminal to open the circuit between said first and second terminals.

The method of manufacturing a temperature sensitive circuit interrupting device, comprising the steps of:

• providing a housing having first and second open ends;
• said housing including a bushing defining a central aperture, said bushing being mounted in said first open end, and an indentation formed in said housing near said second open end thereby to reduce the width of said housing thereat;
• providing a coil spring having a conical volute shape when in tension and a planar volute shape when relaxed with an elongated conductive member extending perpendicular to the plane of the spring in its relaxed shape;
• providing first and second elongated terminals, each having a tip and a free end;
• positioning said terminals in coaxially spaced relation with respective tips opposite one another;
• providing first and second masses of fusing conductive material, softenable at a predetermined temperature;
• connecting said elongated conductive member by means of said first fusible mass of conductive material at one end to the tip of said first elongated terminal and by means of said second fusible mass of conductive material at the other end to the tip of said second elongated terminal;
• providing a washer having a predetermined aperture defined therein;
• inserting the free end of said second elongated terminal into said aperture in said washer;
• inserting the free end of said first elongated terminal into said cylindrical housing and through said aperture in said bushing;
• urging said first terminal partially through said housing to cause the base of said spring to contact with indentation in said housing;
• further urging said first terminal substantially through said aperture in said bushing sufficiently to place said spring under tension;
• securing said first terminal with respect to said bushing;
• sliding said washer into contacting engagement with said spring;
• and
• bending over said second end of said housing to secure said washer in engagement with said spring and to close off said second end of said housing.

The method of manufacturing a circuit interrupting device for opening an electrical circuit at a predetermined temperature, said method comprising the steps of:

• providing a first subassembly including a housing having first and second ends, the first end including therein an insulative bushing defining an aperture therethrough, the opposite end of said housing being open;
• providing a second subassembly including first and second co-axially aligned, spaced terminals, electrically connected to each other at first opposing ends by a conductive member, the first end of said conductive member being joined to a first end of said first terminal by means of a first mass of fusing conducting material, and the second end of said conductive member being joined to said first end of said second terminal by means of a second mass of fusing conductive material, and a coil spring having tip and base portions, said coil spring being conical volute shaped when outstretched and in tension and planar volute shaped when relaxed. The second end of said conductive member being joined to said tip of said coil spring, said conductive member extending perpendicular to the plane of said spring when said spring is relaxed;
• inserting said second subassembly into the open end of said housing of said first subassembly to pass the free end of said first terminal into said aperture in said bushing at the opposite housing end;
• securing said base of said coil spring at the second end of said housing while further inserting said second subassembly into said housing, thereby to outstretch said coil spring to its conical volute shape;
• and
• securing said first terminal with respect to said bushing to maintain said coil spring under tension.