Method and apparatus for the production of flat, transparent vitreous silica slabs of low bubble content
AssigneeHeraeus Quarzschmelze GmbH
InventorsLutz Brandt, Karl Kreutzer, Karlheinz Rau, Horst Schmidt, Fritz Simmat
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Abstract
Flat, transparent slabs of vitreous silica of optical quality are produced by melting granular starting material in a vacuum by means of an electrical heating system. The starting material is melted while sustaining a heat flow from the top to the bottom of the crucible. The bottom of the crucible is made permeable to gases. The heat isolation power of the crucible wall increases from the bottom to the top of the crucible.
Claims15
In an apparatus for the formation of optical slabs comprising an evacuable housing, an electrical heating means and a crucible for receiving the material to be melted and formed into a slab, the improvement wherein the crucible bottom is gas-permeable, and the heat isolation power of the crucible wall (10, 12) increases from the crucible bottom (8) to the crucible upper edge, and electrical heating means (18) is disposed at a predetermined distance above the crucible.
Dependencies are inferred from the claim text.