Furnaces having dual gas screens and methods for operating the same

Abstract

Furnace assemblies are provided including a furnace defining an internal process chamber extending therethrough. A first gas screen is coupled to the furnace. The first gas screen is configured to introduce a first gas into the internal process chamber at a first end of the furnace. A second gas screen is positioned adjacent to the first gas screen at an opposite end of the first gas screen from the furnace. The second gas screen is configured to introduce a second gas to provide a seal for the first end of the furnace. The furnace may be a draw furnace and the process chamber may be an internal draw chamber.

Description

FIELD OF THE INVENTION [0001] This invention relates to furnaces, and, more particularly, furnaces for manufacturing optical fibers and methods for using the same. BACKGROUND OF THE INVENTION [0002] With the expansion of telecommunications services, there has been a great demand for optical fibers. Optical fibers are typically formed by drawing while heating and melting a transparent optical fiber preform in an optical fiber drawing furnace. Such furnaces typically draw the optical fiber while maintaining a flow of process gas around the optical fiber during processing. Such fiber drawing furnaces further conventionally flow the process gases from an end of the furnace adjacent the preform through to an opposite end of the draw furnace, which direction will generally be referred to herein as a downward flow. Examples of such a draw furnace are described, for example, in U.S. Pat. Nos. 5,848,093 and 5,637,130. It is also known, however, to use an upward flow of process gas in a draw ...

AI Technical Summary

Benefits of technology

[0006] In other embodiments of the present invention, the first end of the draw furnace is a downstream end of the draw furnace and the draw furnace has an upstream end opposite from the downstream end. The process gas from the first gas screen flows into the internal draw chamber and from the downstream end to the upstream end of the draw furnace so as to pass between a preform in the internal draw chamber and an inner wall of the draw furnace defining the internal draw chamber while the preform is heated. The sealing gas from the second gas screen may, in such embodiments, flow downstream from the downstream end of the draw furnace so as to reduce introduction of contaminant gases into the internal draw chamber while the preform is heated.

[0007] In further embodiments of the present invention, a flow controller is provided that controls a flow rate of the process gas from the first gas screen and a flow rate of the sealing gas from the second gas screen. The flow rates may be controlled to provide a desired flow rate of the process gas from the downstream end to the upstream end of the draw furnace (or a desired internal furnace pressure) and to provide a desired flow rate of the sealing gas from the second gas screen downstream from the downstream end of the draw furnace so as to reduce introduction of contaminant gases into the internal draw chamber while the preform is heated.

[0009] In further embodiments of the present invention, draw furnace assemblies for manufacturing optical fiber are provided including a draw furnace defining an internal draw chamber extending therethrough. A first gas screen is positioned adjacent a downstream end of the draw furnace. The first gas screen is configured to introduce a process gas into the internal draw chamber at the downstream end of the draw furnace. A second gas screen is positioned adjacent to the first gas screen at an opposite end of the first gas screen from the draw furnace. The second gas screen is configured to introduce a sealing gas to provide a seal for the downstream end of the draw furnace. The sealing gas may be a heavier gas than the process gas. A flow controller is provided that controls a flow rate of the process gas from the first gas screen and a flow rate of the sealing gas from the second gas screen to provide a desired flow rate of the process gas from the downstream end to an upstream end of the draw furnace and to provide a desired flow rate of the sealing gas from the second gas screen downstream from the downstream end of the draw furnace so as to reduce introduction of contaminant gases into the internal draw chamber while a preform positioned in the internal draw chamber is heated.

[0010] In other embodiments of the present invention, methods are provided for providing a desired gas flow in a draw furnace for manufacturing optical fiber. A first gas screen is provided positioned adjacent a first end of the draw furnace. A second gas screen is provided positioned adjacent an end of the first gas screen opposite from the draw furnace. A process gas is injected into the draw furnace through the first gas screen at a process gas flow rate. A sealing gas is injected through the second gas screen at a sealing gas flow rate. The process gas flow rate and the sealing gas flow rate are selected to provide a desired flow rate of the process gas from the downstream end to an upstream end of the draw furnace and to provide a desired flow rate of the sealing gas from the second gas screen downstream from the downstream end of the draw furnace so as to reduce introduction of contaminant gases into the draw furnace while a preform positioned in the draw furnace is heated. For example, for a graphite furnace, the process gas flow rate and the sealing gas flow rate may be selected to provide a carbon monoxide concentration in the draw furnace while the preform is heated of less than about 50 parts per million (ppm) or an oxygen concentration of less than about 25 ppm.

Problems solved by technology

Such an approach may create difficulties when used in a process using upward gas flow of process gases during drawing of an optical fiber.

More particularly, while a gas screen in such a system may be provided with sufficient flow of process gas to cause such gas to flow both upward through the treatment area as well as downwards to contribute toward sealing the lower end of the draw furnace, an adequate seal will generally not be provided due to the limited desired range of process gas flow rates through the fiber draw process chamber.

In other words, it may not be possible to provide a sufficiently high flow rate for acceptable sealing without undesirably high flow rates in the process chamber.

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