Electric heating – Metal heating – By arc
Reexamination Certificate
1999-06-08
2001-04-10
Walberg, Teresa (Department: 3742)
Electric heating
Metal heating
By arc
C427S573000, C065S391000, C164S046000
Reexamination Certificate
active
06215092
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and associated apparatus for increasing the over cladding rate in perform production while maintaining the integrity of the glass quality of the cladding.
2. Discussion of Related Art
Due to the market pressure to decrease the price of optical fibers, there is a continuous demand to increase the overall productivity of the fabrication process. One of the first steps in the process of manufacturing an optical fiber is the plasma process. This process involves making more than 90% of the preform glass by fusing quartz sand onto the primary preform as a cladding with the aid of a hot plasma fireball.
There are two important parameters associated with this process. The first is the deposition speed (grams/min.) Of the glass and the second is the quality of the deposited glass. For a particular process, these two parameters are antagonistic to each other. Specifically, as the deposition speed increases, the glass quality is degraded.
Both of these parameters are affected by the usable power available to generate the plasma fireball. The higher the power, the greater the deposition speed and the better the glass quality. However, the conventional plasma setup has limited power capability. This limitation is not due to the output of the generator, but to the thermal resistance of the plasma torch. When the power in the plasma torch reaches a given value, the plasma torch cannot sustain the required temperature and its lifetime is shortened. It is estimated that the plasma torch only uses approximately ⅔ of the output capacity of the generator.
Conventional processes only use a single plasma torch such as is disclosed in U.S. Pat. No. 4,221,825. Thus, the full capacity of the generator is not realized and the deposition speed and quality of glass are limited.
SUMMARY OF THE INVENTION
An object of the invention is to utilize the full capacity of the generator to thereby improve the overall deposition speed without sacrificing the quality of the glass. In particular, it is estimated that the process of the present invention will increase the deposition speed by approximately 50% for a given glass quality. This object is achieved by utilizing two or more plasma torches, instead of just one, that are driven by the same power generator.
Thus the present invention is directed to a process and apparatus for applying quartz sand to a perform. The process of over cladding a perform includes the steps of supporting the perform on a lathe; providing first and second plasma torches having nozzles angled toward the perform; powering the first and second plasma torches with a common generator such that the plasma torches create plasma flames directed toward a surface of the perform; introducing a quartz sand at a junction between the first plasma torch and the surface of the perform to fuse the quartz sand on the surface of the perform; and moving the perform with respect to the plasma torches.
According on one aspect of the invention, the second plasma torch is provided upstream of the first plasma torch so as to preheat the surface before the fusing of the quartz sand by the first plasma torch. According to a second aspect of the invention, the second plasma torch is located downstream of the first plasma torch to heat up the quartz sand after the initial fusing by the first plasma torch. According to a third aspect of the invention, the quartz sand is introduced at junctions between the surface of the perform and both of the plasma torches to fuse the quartz sand with both the first and second plasma torches simultaneously.
The apparatus for performing this process includes a lathe for supporting the preform; first and second plasma torches having nozzles angled toward the perform; a generator for powering the first and second plasma torches such that the plasma torches create plasma flames directed toward a surface of the preform; one or more feeder(s) for feeding the quartz sand at a junction between the one of the torches and the surface of the preform to fuse the quartz sand on the surface of the perform; and means for moving the preform with respect to the plasma torches.
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Goudeau Jacques
Humbert Patrick
Ripoche Pierre
Alcatel
Sughrue Mion Zinn Macpeak & Seas, PLLC
Van Quang
Walberg Teresa
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