Heraeus Quarzglas Gmbh & Co Kg

Rainer Berg

Nigel Robert Whippey

Helmut Leber

Martin Trommer

Joerg Becker

In a known method for drawing a tubular quartz glass strand, SiO-containing starting material is fed to a melting crucible, softened therein into a viscous quartz glass mass (), and said mass is pulled vertically downward as a cylindrical quartz glass strand () through a die () provided in the bottom region of the melting crucible (), said die having a gap-shaped outlet (), which is defined by a bottom opening and a die inside part, and thereafter the quartz glass cylinder is cut to length. In order to provide a method starting from this which facilitates the production of homogeneous quartz glass cylinders, even if the lateral dimensions thereof are in the range of the inside diameters of conventional melting crucibles (), according to the invention the viscous quartz glass mass is drawn over a flow constriction () provided in an upper region of the die () and leading downward into the outlet () via a flow channel, said region facing the crucible interior, wherein the outlet has an opening width that is larger than the width of the flow constriction (), and wherein a first minimum circumscribed circle around the flow constriction () has a diameter that is a maximum of 30% of the diameter of a second minimum circumscribed circle around the quartz glass strand () to be drawn. The invention further relates to a corresponding apparatus.

Method and apparatus for producing a quartz glass cylinder

In a known method for coating a crucible for use at a high working temperature in a crucible drawing method for quartz glass, a base body wall of tungsten has applied thereto a protective layer containing a coating metal consisting of the group selected from iridium, rhenium, osmium and ruthenium. Starting therefrom, to provide a method for producing such a component exhibiting high corrosion resistance to the quartz glass melt at low material costs, it is suggested according to the invention that the protective layer should be produced from a layer material which contains tungsten and the coating metal, and in which the amount of the coating metal should be dimensioned such that it exceeds the limit amount of a coating metal-rich phase boundary of a solid mixture phase of tungsten and the coating metal, with the solid mixture phase being thermodynamically stable at the working temperature, by not more than 25 at. % (based on the total amount of tungsten and the coating metal in the layer material).

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Langenselbold, Germany

Rainer Berg