Heating filament with resistance wire helix - is loosely wound on glass-fibre or asbestos sleeve on support wire

摘要

The heating filament consists of a helix of resistance wire (1) through which a glass-fibre or asbestos sleeve (4) passes. The sleeve outer dia. is less than the inner dia. of the helix and the sleeve serves to prevent the ends of an overload burnt-out helix from contacting the adjacent filament (or earth etc). A support wire passes through the sleeve and may serve as return line. The filament is made by winding a wire tightly over a mandrel. The wanted length of filament is then cut and removed from the mandrel. The sleeve is the slid inside.