Method and apparatus for the manufacture of large optical grade SiO.sub.2 glass preforms
First Claim
1. A process for producing an optical quality SiO2 glass ingot comprising:
- rotating a cylindrical horizontal furnace about its central axis, said furnace having spaced electrodes extending along said central axis into the furnace interior;
establishing a gas plasma arc between said electrodes to heat the furnace;
feeding SiO2 into said furnace and melting said SiO2, within said furnace at a temperature of at least 2400°
C. to form a hollow cylindrical melt by centrifugal force generated by said rotating, while controlling the rate of said feeding to provide a rate of decrease of the inner radius of said cylindrical melt no greater than the escape rate toward the inner cylindrical surface of said melt at said temperature for the smallest bubble compatible with the desired optical quality of the glass ingot product, said rate of said feeding being decreased in proportion to the rate of change of surface area of the inner surface of the hollow cylindrical melt.
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Abstract
The disclosed process involves the feeding of particulate SiO2 into a rotating cylindrical furnace in which a gas plasma arc has been established, for melting the feed at a temperature of at least 2400° C. The feed rate is regulated so that the rate of growth of the radius of the ingot melt will not exceed the rate at which bubbles move through the melt to the inner cylindrical surface. The preferred apparatus is a rotating horizontal furnace having a pair of opposing hollow electrodes mounted in its opposing end surfaces for establishment of an arc therebetween. A feeding device introduces the SiO2 feed through the open bore of one of the electrodes for melting by the plasma arc.
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Citations
11 Claims
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1. A process for producing an optical quality SiO2 glass ingot comprising:
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rotating a cylindrical horizontal furnace about its central axis, said furnace having spaced electrodes extending along said central axis into the furnace interior; establishing a gas plasma arc between said electrodes to heat the furnace; feeding SiO2 into said furnace and melting said SiO2, within said furnace at a temperature of at least 2400°
C. to form a hollow cylindrical melt by centrifugal force generated by said rotating, while controlling the rate of said feeding to provide a rate of decrease of the inner radius of said cylindrical melt no greater than the escape rate toward the inner cylindrical surface of said melt at said temperature for the smallest bubble compatible with the desired optical quality of the glass ingot product, said rate of said feeding being decreased in proportion to the rate of change of surface area of the inner surface of the hollow cylindrical melt. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. Apparatus for producing an optical grade SiO2 glass ingot, said apparatus comprising:
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a cylindrical furnace housing closed by a flange at each end to define a sealed furnace interior; a loose granular refractory lining the interior surface of said furnace housing and held in place by centrifugal force generated by rotation of said cylindrical furnace housing; means for rotating said furnace housing about its central longitudinal axis with said axis approximately horizontal; a pair of electrodes, said electrodes having axial bores and extending through said flanges into said furnace interior; power supply means for supplying power to said electrodes to establish a plasma arc therebetween; and means for introducing a SiO2 feed through a bore of one of said electrodes for melting by said plasma arc and for controlling the rate of said feed to decrease in proportion to rate of change of surface area of the inner surface of a hollow cylindrical melt formed by melting the feed and to provide a rate of decrease of the inner radius of said cylindrical melt no greater than the escape rate toward the inner cylindrical surface of said melt of the smallest bubble compatible with the desired optical quality of the glass ingot product. - View Dependent Claims (10, 11)
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Specification