| 摘要 |
Apparatus for heating a vertically suspended preform from which lightguide fiber is drawn includes a torch having a plurality of ducts that open to a surface adjacent to a lower end of the preform. Fuel and oxidizing gases flow from the ducts, mix at the surface and flame about a necked-down, lower portion of the preform to form a melt cone from which the fiber is drawn. The ducts and the preform are positioned to cause a combustion zone of each flame to impinge upon the preform. In a preferred embodiment, the openings of the ducts are arrayed in a circle which is referred to as a pitch circle and which has a diameter that is less than that of the preform. Also, the ducts are arranged so that the gases are directed at a predetermined angle to the axis of the preform.
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