Coating apparatus – Immersion or work-confined pool type – Running length work – longitudinally traveling
Reexamination Certificate
1999-09-03
2003-03-25
Lamb, Brenda A. (Department: 1734)
Coating apparatus
Immersion or work-confined pool type
Running length work, longitudinally traveling
C118S125000
Reexamination Certificate
active
06537377
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for coating optical fibers such that the coating is concentrically applied and the thickness of the coating is uniform.
2. Discussion of Related Art
After an optical fiber has been drawn from a preform, it is conventional to cover the optical fiber with a protective coating, such as an acrylate-based composition which is curable by exposure to ultraviolet (UV) light, to prevent the surface of the fiber from being damaged either during the subsequent manufacturing steps or subsequent use. This coating step is generally performed as an integral part of the drawing process using coating dies. The coating material may be applied in one or more layers.
In the process of applying the coating layers, it is important that the coating layers be applied concentrically to the fiber and that the diameter of the coating or coatings be consistent as well. These features are important in contributing to the ease with which the optical fibers can be spliced and connected.
As discussed in U.S. Pat. No. 5,366,527 to Amos et al., which is incorporated herein by reference, significant efforts have been made to ensure that the coating is applied concentrically and ever more consistently at increasing draw rates. Higher draw rates are needed to reduce the cost of manufacturing and to increase the fiber output but they may affect adversely the consistency of fiber coating if draw techniques fail to be adequately adapted.
A direct consequence of draw rate increase is to reduce the delay between fiber forming at temperatures close to 2000° C. and fiber coating. As a consequence, the temperature of the fiber entering the coating device may still be too high to allow good coating application unless forced cooling is applied. Various systems have been disclosed in U.S. Pat. No. 4,594,088 to Paek et al., U.S. Pat. No. 4,514,205 to Darcangelo et al. and U.S. Pat. No. 5,043,001 to Cain et al. for cooling the drawn optical fiber prior to receiving the first layer of coating.
High temperature of the entering fiber is not the only source of heat likely to disturb coating application: draw rate increase also results in an important increase in the heat produced by viscous losses in the coating flow. Thermal power associated with viscous losses may be computed easily knowing the draw speed and the viscous drag affecting the fiber in the coating applicator. Thermal power produced at current draw speeds of 900 to 1000 m/min for an observed drag force per applicator of 1 N is around 15 W. None of the above systems was designed to cope with or to get rid of this overly different source of heat.
Viscous losses occur most intensively where shear stress is highest in the coating flow, i.e. around the fiber in the applicator chamber and, especially, in the narrowest part of the sizing die, the cylindrical land region. In the latter land region, high shear rate and viscous losses are shown to be concentrated in a narrow radial range limited by the inner wall of the die. This is a consequence of optimal coating conditions in which shear rate is minimized around the fiber and is highest on the inner wall of the die as a consequence. Heat production is highest over this peripheral region.
This heat source may be especially detrimental to coating consistency as coating diameter and coating concentricity are mostly governed by temperature and pressure profiles in the land region as shown by numerical simulations. This fact is indirectly confirmed by U.S. Pat. No. 5,366,527 which discloses a technique by which the coating diameter is controlled by adjusting the die temperature in the land region and by PCT Publication No. WO 97/20237-A2 which discloses a fiber coating system in which concentricity of the coating is controlled by non-axisymmetrically heating the land region in the sizing die. The latter system may be capable of compensating for spurious non-axisymmetrical heating or temperature profiles occurring in the coating flow. However, these systems are very complex requiring the ability to monitor the diameter and/or the concentricity of the coating as well as the ability to control the temperature of the coating die in a localized manner (e.g., portions of the bottom surface of the die).
An object of the present invention is to provide a relatively simple apparatus for coating an optical fiber with coatings that are applied concentrically to the fiber to provide a consistent coated diameter.
An other object of the invention is to restore as much as possible coating conditions prevailing at low draw rates and to suppress most of the effect of viscous loss rather than compensate it by means of feedback.
SUMMARY OF THE INVENTION
These and other objects of the invention have been achieved by providing a coating die that includes an insert having a high thermal conductivity, which is greater than 1 W/cm*K. According to the preferred embodiment, the insert is made of diamond having a thermal conductivity in the range of 5 to 20 W/cm*K.
Use of this highly conductive insert helps dissipate most efficiently the heat produced by viscous losses in the coating as most of these losses occur very close to the inner wall of the die in the land region.
It also reduces to negligible level the wall temperature unbalance between opposite sides of the fiber when this fiber is off-centered thus restoring conditions prevailing at low draw rates and subsequent satisfactory centering force.
It has been discovered that the high conductivity of the insert minimizes the differences or imbalances between the inner wall temperatures of the die so that the temperature of the inner wall is generally uniform. Therefore, the affects discussed above with regard to the generation of de-centering forces due to the variation in wall temperature is substantially reduced or even eliminated. In particular, whereas localized heat generated due to a non-uniform viscosity profile is relatively high in a die having a low thermal conductivity due to poor heat dissipation, the heat generated in a die having a high conductivity is quickly dissipated such that temperature uniformity is substantially improved. Therefore, even if one side of the fiber begins to be offset toward the adjacent wall of the die, there is a minimal temperature increase on that side of the fiber. As a result, the viscosity and pressure profile around the fiber remains generally uniform around the fiber in the land region so that the fiber is not drawn to one side and centering can be restored as best as possible by the centering force generated in the tapered region of the die.
REFERENCES:
patent: 3944459 (1976-03-01), Skobel
patent: 4046103 (1977-09-01), Yakuboff
patent: 4253731 (1981-03-01), Anderson et al.
patent: 4514205 (1985-04-01), Darcangelo et al.
patent: 4531959 (1985-07-01), Kar et al.
patent: 4594088 (1986-06-01), Paek et al.
patent: 4649856 (1987-03-01), Shannon et al.
patent: 4678274 (1987-07-01), Fuller
patent: 4955689 (1990-09-01), Fuller et al.
patent: 5043001 (1991-08-01), Cain et al.
patent: 5151306 (1992-09-01), Andrews et al.
patent: 5186870 (1993-02-01), Fuller et al.
patent: 5366527 (1994-11-01), Amos et al.
patent: 5648139 (1997-07-01), Sussmann et al.
patent: 198 01 700 (1998-01-01), None
patent: 1371318 (1974-10-01), None
patent: 2 170 738 (1986-08-01), None
patent: WO/9720237 (1997-06-01), None
CRC Handbook of Chemistry and Physics CRC Preso, Inc Boca Raton, FLA (1985) p. F19.
Alcatel
Lamb Brenda A.
Sughrue & Mion, PLLC
LandOfFree
Apparatus for coating optical fibers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for coating optical fibers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for coating optical fibers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3002546