Self-closing residential fire hinge apparatus

A door hinge with a fire-actuated release mechanism for a door, comprising:

• a hinge plate having a door plate, a jamb plate, and a central cylinder rotatably coupling the door plate with the jamb plate, the door plate being configured to couple to the door, the jamb plate being configured to couple to a door jamb, the central cylinder having a cylindrical channel therein extending throughout a length of the central cylinder, the hinge plate having an open position and a closed position, the jamb plate being separated from the door plate when the hinge plate is in the open position, the jamb plate directly contacting the door plate when the hinge plate is in the closed position;
• a hinge pin being inserted into the cylindrical channel, the hinge pin having a hinge pin length ranging between 3 inches and 4 inches and a hinge pin diameter ranging between ⅛ inch and ½ inch;
• a first hinge arm affixed to the hinge pin above the hinge plate, the first hinge arm contacting the jamb plate and being immovably affixed to the hinge pin and configured to maintain contact with the jamb plate whether the hinge plate is in the open position or the closed position, the first hinge arm having a first hinge arm length ranging between ½ inch and 1 inch and a first hinge arm width ranging between ⅛ inch and ½ inch;
• a second hinge arm rotatably attached to the hinge pin above the first hinge arm, the second hinge arm contacting the door plate and being configured to rotate around the hinge pin to exert a pushing force on the door plate which causes the door plate to transition between the open position and the closed position, the second hinge arm having a second hinge arm length ranging between ½ inch and 1 inch and a second hinge arm width ranging between ⅛ inch and ½ inch;
• a spring having a distal end opposite a proximal end, the spring being wrapped around the hinge pin above the second hinge arm, the distal end of the spring extending toward the first hinge arm and the second hinge arm;
• a first gear connected to the proximal end of the spring;
• a second gear stacked on the first gear, the second gear being opposite the first gear from the spring;
• the first gear and the second gear being configured to rotate the proximal end, thereby twisting the spring to a preloaded position, the spring being preloaded with a torsion sufficient to close the door when the spring is in the preloaded position, the torsion having a torsion range between 10 pounds and 15 pounds;
• the first gear and the second gear having a plurality of pin slots therein extending through the first gear and the second gear;
• a gear pin removably inserted into the plurality of pin slots, the gear pin being configured to retain the torsion;
• a bismuth coating encasing the spring, the bismuth coating being configured to retain the spring in the preloaded position while the bismuth coating is in a solid phase, the bismuth coating melting and transitioning into a liquid phase when the bismuth coating is exposed to surrounding environmental temperatures exceeding 520° F.,
• a copper spring assembly cap having a generally cylindrical shape formed by a wall and a top surface, the spring assembly cap covering the gear pin, the first gear, the second gear, and the spring, the distal end of the spring extending downward past the wall opposite the top surface to contact the second binge arm, the spring assembly cap having a cap length ranging between 1½ inch and 2 inches and a cap diameter ranging between ½ inch and 1 inch;
• and
• the door hinge having a total length ranging between 5 inches and 6 inches and a total weight ranging between ⅛ pound and 1 pound.