Abstract: During the fire-polishing of a lengthwise extended glass body (3), for example a preform for drawing optical fibers, the glass body (3) is held by a holding device (5, 7), and is heated by a burner (23) moving at a variable advancing speed parallel to the lengthwise axis (19). The surface temperature of the glass body (3) is determined with a temperature measuring device (25). The mechanical stress condition of the glass body (3) is detected with an optical device (29) and can be controlled by varying the burner temperature and/or the advancing speed of the burner. The invention makes it possible to counteract the occurrence of high mechanical stresses in the glass body (3).

Abstract: An apparatus for heating an elongated glass body, which, for example, may be used as a pre-form for the drawing of glass fibers, includes a rotatable first chuck wherein the first end of the elongated glass body may be rotatably secured. In addition the apparatus includes a second rotatable chuck whereat the second end of the elongated glass body is introduced into a quartz tube and this quartz tube is clamped into the rotatable second chuck. A burner, which is adapted to slide parallel to the longitudinal axis of the elongated glass tube, heats the elongated glass body in such a manner, that a so called fire polish of the elongated glass body for the improvement of its surface quality occurs. A method for heating the elongated glass body is also disclosed.

Abstract: A method for manufacturing an optical fiber (11), wherein the fiber (11) is drawn from one end of a preform (9) which is heated to above the glass softening temperature. The preform (9) is surronded by a protective gas (14) whose flow direction corresponds to the fiber drawing direction. The flow of the gas surrounding the preform (9) in the drawing area (10) is stabilized by an additional flushing gas (16).