Abstract: A device is set forth for interrupting a material flow by means of a shutter 5 fastened on a spindle 11, which spindle 11 is rotatably supported in a housing 1 of the device. The device is provided with a torsion spring 33 which is elastically deformable through rotation of the spindle 11, with substantially equal amounts of mechanical energy being stored in the torsion spring 33 through elastic deformation in a first position of the shutter 5. The material flow is shut off during this operation, and in a second position of the shutter 5 the material flow begins. The spindle 11 is provided with a permanent magnet 57 having pole shoes 61, 63 which are held against stops 109, 115 of a magnetic yoke 99 in the first position under the influence of the magnetic field of the magnet 57, and which are held against stops 111, 113 of the yoke 99 in the second position. The yoke 99 is provided with an electric coil 121.

Abstract: Porous bodies of a material comprising SiO.sub.2 as the main constituent are heated by passing a zone of high temperature through the body. This high temperature zone is obtained by irradiation with light of a wavelength which is obsorbed by the porous part of the body, but which is not absorbed by the densified part of the body. The device preferaby comprises a rotatable radiation source surrounding the body to be densified.

Abstract: Porous bodies of a material which comprises SiO.sub.2 as the main constituent are heated by passing a zone of high temperature through the body. The zone of high temperature is obtained by irradiation with light of a wavelength which is absorbed by the porous part of the body but is not absorbed by the densified part of the body (.lambda.<3 .mu.m). The device preferably comprises a rotatable radiation source (2) surrounding the body (6) to be densified.

Abstract: A method for continuously melting a glass by means of a high-frequency electromagnetic field in a melting tube is provided. In this technique, the electromagnetic field is coupled in the melt by means of a coil present within a cooling jacket surrounding the melting tube. A grounded screen and a tube of insulating material are present between the wall of the melting tube and the coil. The melt traverses a heating zone and a refining zone, and a solid elongated body is withdrawn from the bottom of the melting tube.

Abstract: A device for continuously making elongated bodies, particularly rods of glass or optical fibers, includes a melting tube for containing molten material and surrounded by a cooling jacket. Within the cooling jacket exists a high frequency electromagnetic coil for heating and melting the starting material in the melting tube. A plurality of metal wires extending parallel to the axis of the melting tube and being grounded as well as a tube of insulating material are located between the wall of the melting tube and the coil. The melt traverses a heating zone and a refining zone so that a solid elongated body is withdrawn from the bottom of the melting tube.

Abstract: Method of and apparatus for manufacturing optical fibers in which a preform is heated in a furnace which is provided with a graphite heating element and a fiber is drawn from the heated preform. The fiber is subsequently cooled, provided with a coating, and, after drying of the coating, the fiber is wound onto a reel.For applying a coating to the fiber, the fiber is passed through a nozzle which has a polygonal nozzle opening.

Abstract: Method of and apparatus for manufacturing optical fibers in which a preform is heated in a furnace which is provided with a graphite heating element and a fiber is drawn from the heated preform. The fiber is subsequently cooled, provided with a coating, and, after drying of the coating, the fiber is wound onto a reel.During drawing of the fiber, the preform and fiber are flushed with a gas. According to the invention the gas with which the fiber is flushed is passed along a condensation element.