Patent ID: 8613207
Filing Date: 2013-12-24
Classification: C03B

Abstract:
1. An apparatus for drawing a quartz glass cylinder, the apparatus comprising: a melting crucible receiving a SiO a heating device softening the start material; a draw die provided in the bottom region of the melting crucible, said draw die having an upper region that faces the crucible interior, and having a flow channel therein defined partially by a flow constriction that widens downwards such that the flow channel has an outlet that has an opening width larger than a width of the flow constriction, such that a first enveloping circle around the flow constriction has a diameter that is not more than 30% of a diameter of a second enveloping circle around the quartz glass strand; wherein the draw die has an outlet which is in the form of an annular gap and which is defined by a bottom opening and an interior part of the draw die, with the flow constriction terminating downwards in a cavity and the interior part of the draw die has a mandrel which projects into the cavity while maintaining the flow channel and has a maximum outer circumference greater than the width of the flow constriction; and wherein the mandrel is held on at least one web or is centered by means of said web and the web extends from the crucible sidewall to the mandrel.