The invention relates to electrical fuses employing tubular fuse casings.
Electrical fuses are used to conduct current under normal conditions and to break a circuit under overload conditions by the melting of fusible elements of the fuses. In some fuses, tubular fuse casings are used to contain the fusible elements The ends of the fuse casings are sealed shut by crimped ferrules to which the fusible elements are electrically connected. The fuse casings must be resistant to the axial and radial mechanical stresses and to thermal stresses experienced during blowing of the fuse. The fuse casings must also exhibit dimensional stability so as to maintain good contact with the crimped ferrules during use. The casing should ideally be a good thermal insulator in order to contain the heat and provide for quick melting of the fusible elements under overload conditions.
Healey, Jr., U.S. Pat. Nos. 3,979,709; 3,983,525; and 3,984,800 disclose fuses employing fuse casings made by wrapping a plurality of fabric and fiber mat plies on stationary tubular mandrels that have holes for injecting and impregnating resin into the plies. Kozacka U.S. Pat. No. 3,240,905 and Wilks U.S. Pat. No. 4,124,836 disclose fuses having fuse casings with outer tubes and asbestos liners inside.