Methods of and apparatus for heating a glass tube

摘要

In order to react gases and/or vapors to deposit optically suitable layers of doped silicon dioxide on an inner wall of a glass substrate tube to produce a preform from which optical fibers are drawn, the glass tube is heated by a mixture of combustible gases. The combustible gases are directed along passageways in a housing of a torch assembly which confines a portion of the length of the tube and then out of the passageways to produce a flame that engages the confined portion of the length of the tube. The housing and walls that define ends of the passageways adjacent the tube are cooled to an extent which substantially eliminates oxidation of the material from which the housing and the walls of the passageways are constructed. The torch assembly provides a variable confinement of the tube, radially and longitudinally, which is effective to control the temperature profile produced at the surface of the tube as it is rotated about its longitudinal axis, and as the torch assembly is moved to heat successive portions of the length of the tube.