| 摘要 |
The amount of emitter paste which can be applied to the filament used in fluorescent tubes can be increased by winding the filament, as previously proposed, about an iron or molybdenum mandrel which can be dissolved; in contrast to the prior art, however, the wound filament is not annealed at a temperature which removes winding stresses but, rather, at a lower temperature of about for example 900 DEG C. for tungsten wire, thus retaining some of the winding stresses. Upon dissolving-out of the iron core or mandrel, the remaining stresses will cause adjacent windings of the filament to slightly relieve their stresses by springing back to some extent, resulting in relatively offset end portions of the wires with respect to each other, when the wires have been wound on a mandrel which has an essentially rectangular cross section in which the ratio of length to width-in cross section-is greater than 2. The resulting surface roughness of an envelope of the filament permits retention of a larger amount of emitter material with better retention capabilities, and thus increases the lifetime of lamps by about 30% with respect to lamps having filaments in which adjacent windings are congruent. |
