| 摘要 |
PROBLEM TO BE SOLVED: To provide a furnace equipped with a core tube through which an object to be heated is passed into the furnace, capable of efficiently heating the object, by changing thickness of the core tube in the longitudinal direction so as to change width of a rise-up section of temperature distribution in a heat zone in the furnace in such a way to facilitate control of temperature in the heat zone. SOLUTION: This furnace is equipped with a core tube 11, whose thickness is changed in the longitudinal direction, preferably by decreasing its thickness for a certain distance A in the longitudinal direction. As a result, a rise-up section of temperature distribution in a heat zone in the furnace becomes narrower and sharper, making the temperature distribution pattern shorter, when the core tube 11 is heated by an electrical heater 12 provided around the external surface of the thinner thickness section 11a. At the same time, the heat zone becomes roughly as long as the distance A, a length of the thinner thickness section 11a. For example, when a base material for optical fiber is to be heated and drawn in the core tube 11, the outer diameter variable sections at the upper and lower ends of the fiber can be shortened, thus reducing the wasteful fiber portions. |
