Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With measuring – controlling – sensing – programming – timing,...
Reexamination Certificate
1998-06-01
2001-04-24
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With measuring, controlling, sensing, programming, timing,...
C065S384000, C065S491000
Reexamination Certificate
active
06220057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for drawing a glass ingot wherein the glass ingot is drawn to a predetermined outer diameter to obtain a glass rod or preform for an optical fiber having the predetermined outer diameter.
2. Description of the Prior Art
For the drawing of a large-sized glass ingot having a diameter exceeding 100 mm, there is known a method wherein the ingot is heated and softened in an electric furnace, under which it is applied with a given tension thereto.
Such a large-sized ingot has, as shown in
FIG. 3
, a tapered portion or stepped portion
4
which is formed at opposite sides thereof during the course of its fabrication.
FIG. 5
is a conventional apparatus of drawing a glass rod. For the drawing of such a large-sized ingot
25
, dummy shafts provided at opposite sides of the ingot are held so that the ingot is set in the drawing apparatus and is drawn into a glass rod
36
.
As an ingot increases in size and diameter, it becomes necessary to further increase the diameter of the heater and a heating zone in the heating furnace.
Where such a large-sized heater is used and an large-sized glass ingot having a tapered portion whose diameter changes in vertical directions is drawn, not only a region of the ingot to be softened and deformed, but also the tapered portion with a smaller diameter is heated and starts to be softened and drawn. Accordingly, the resultant rod cannot have a given diameter throughout its length. As is particularly shown in
FIG. 6
, there arises the problem that the diameter greatly changes particularly at completion of the drawing.
In this case, there is a further problem that the drawn glass rod should be subjected to finishing drawing by use of a glass-working lathe in order to meet standards for a diameter of the drawn rod, coupled with another problem that the greater change in the diameter results in a longer finishing time.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method for drawing a glass ingot which overcomes the problems of the prior art methods, and wherein when a large-sized ingot is drawn, the controllability in the diameter of a drawn rod is so improved that the resultant rod has a given diameter even from the tapered portions whose shape abruptly changes.
The method for drawing a glass ingot according to the invention comprises holding a vertically suspended glass ingot at its upper end, and passing the glass ingot through a heating furnace having upper and lower openings under which the glass ingot is drawn while moving one or both ends of the glass ingot, characterized in that a plurality of heating means are provided in the heating furnace along vertical directions, and are individually controlled in temperature to control a temperature distribution within the heating furnace.
According to the invention, a rod with a given diameter can be obtained upon drawing of a tapered portion, in which the diameter of an ingot abruptly changes. This is advantageous in that any correction of the rod diameter in a subsequent step using a glass-working lathe is unnecessary, thereby ensuring low fabrication costs.
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Hirasawa Hideo
Kemmochi Soichiro
Shimada Tadakatsu
Yamamura Waichi
McDermott & Will & Emery
Shin-Etsu Chemical Co. , Ltd.
Vincent Sean
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