Glass manufacturing – Processes – With shaping of particulate material and subsequent fusing...
Patent
1989-04-14
1990-10-30
Lacey, David L.
Glass manufacturing
Processes
With shaping of particulate material and subsequent fusing...
65 13, C03B 3701
Patent
active
049666150
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of cooling an optical fibre when the fibre is being drawn from a heated glass blank, in which method
the drawn fibre is passed through a cooling space, and
a gaseous cooling medium is supplied in the axial direction of the fibre around the fibre through the cooling space.
In the manufacture of optical fibres, a fibre drawn from a glass blank (preform) has to be coated with a primary coating after the heating apparatus so as to protect the surface of the fibre and to increase the strength of the fibre. In order to cool a hot fibre to a suitable temperature prior to coating, the fibre is passed through a cooling apparatus, in which the fibre is brought into heat transfer contact with a cooling medium.
U.S. Patent Specification 4,388,093 suggests cooling a fibre by passing it through a cooling vessel filled with a liquid cooling medium. The cooling liquid, however, causes considerable sealing problems at the high drawing rates aimed at in modern fibre drawing processes.
According to the teachings of Swedish Patent Specification 433,605, a fibre is cooled by passing it through a cooling apparatus in which a gaseous cooling medium, preferably dry nitrogen gas, is blown towards the fibre through a tubular wall of a porous material. In this way the cooling gas is distributed evenly and the fibre is not exposed to the effects of disadvantageous transverse forces. The use of this kind of cooling arrangement, however, makes it difficult to circulate the cooling medium axially through the cooling space against the direction of movement of the fibre, which would be preferable in view of the transfer of heat.
In an article "Method for cooling and bubblefree coating of optical fibres at high drawing rates", C. Jochem and I. Van der Ligt, Electronics Letters, Aug. 29, 1985, Vol. 21, No. 18, p. 786, it is suggested to cool a fibre by passing it through a water-cooled cooling pipe which is filled with helium gas circulated axially through a cooling space formed by the cooling pipe. Helium gas has a good coefficient of heat transfer, which ensures that the fibre is cooled sufficiently even at high fibre drawing rates. A disadvantage, however, is that large quantities of expensive helium gas are required for cooling the fibre.
The object of the present invention is to provide a method of cooling an optical fibre, which method avoids the above-mentioned disadvantages and enables the achievement of a high cooling efficiency with a relatively small cooling medium flow. This object is achieved by means of a method according to the invention, which is characterized in that the cooling gas is caused to flow turbulently around the fibre at least at one point in the cooling space.
The invention is based on the idea that the turbulence of the cooling medium breaks up the laminar flow of the cooling medium occurring around the fibre to be cooled; consequently, the heat transfer contact between the cooling medium and the surface of the fibre is improved. In addition, the flow of the cooling medium through throttle points provided therefor causes pressure losses, so that the cooling space is divided into compartments in which the medium is pressurized, which improves the heat transfer. The invention thus provides a high cooling efficiency with a smaller consumption of cooling medium, without any risk that the axial flow of the cooling medium causes a disadvantageous laminar flow around the fibre.
The invention is also concerned with a cooling apparatus for effecting the method according to the invention. The apparatus comprises a cooling pipe defining a tubular cooling space, and an inlet and an outlet for passing the fibre axially through the cooling space, and means for supplying a gaseous cooling medium axially through the cooling space. The cooling apparatus is characterized in that the cooling space comprises at least one partition wall positioned between the fibre inlet and the fibre outlet, the partition wall comprising a common opening for the fibre and the cooling gas to pass through, which op
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Jochem et al., Cooling and Bubble-Free Coating of Optical Fibers . . . 7/1986, Journal of Lightwave Technology, vol. LT-4, No. 7, 739-742.
Pack et al., Forced Convective Cooling of Optical Fibers . . . 10/1979, Journal of Applied Physics, vol. 50, No. 10, 6144-6148.
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International Search Report, Nov. 14, 1988, Swedish Patent Office.
Linden Antti
Pennanen Risto
Stormbom Lena
Bruckner John J.
Lacey David L.
Oy Nokia AB
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