GB481227A - Improvements in and relating to the manufacture of filaments for electric incandescent lamps - Google Patents

Abstract

481,227. Making electric incandescent lamp filaments. VEREINIGTE GLUHLAMPEN UND ELEKTRIZITATS AKT.- GES. Feb. (i, 1937, No. 3639. Convention date, March 3, 1936. [Class 39 (ii)] In the manufacture of helical filaments, more particularly coiled-coil filaments for electric incandescent lamps, rigidity is given to the ends or other parts of the filaments by the retention therein of that part of the core wire on which they were coiled. The wire constituting the filaments is coiled upon a molybdenum core wire in known manner and, after heat treatment, is cut into lengths. Both ends of the resulting filaments are then dipped into a solution of shellac in alcohol, which forms a protective coating, so that when the bodies are introduced into a mixture of concentrated sulphuric and nitric acids, the molybdenum core is dissolved out at all points where no protecting coating has been applied. The bodies are then washed in distilled water and laid in caustic soda which dissolves off the protective layer. When the filaments are of the coiled-coil type the secondary windings are spaced along their core and divided at the intervals, so that at the completion of the process the filaments have ends which are only singly coiled and have part of the primary core retained therein.