Apparatus for controlling lightguide fiber tension during drawing

Apparatus for regulating the flow of a cooling gas into a lightguide furnace to control the drawing tension of a lightguide comprising:

• means for directing a cooling gas into the furnace so that the cooling gas flows at least partially around the lightguide fiber and generally upwardly along the walls of the lightguide furnace away from the lightguide fiber to cool the fiber, said means having at least one cooling gas opening therein;
• and
• a sleeve coaxially aligned with, and rotatable about, said cooling gas directing means, said sleeve having at least one cooling gas opening therethrough in communication with, but substantially misaligned relative to, said cooling gas directing means opening so that cooling gas entering said cooling gas directing means is directed substantially tangentially to the inner surface of said cooling gas directing means to cool the lightguide fiber, the amount of cooling being controlled by rotating said sleeve relative to said cooling gas directing means to vary the degree of misalignment of each said sleeve opening relative to each said cooling gas directing means opening.