KR20010053571A - Fiber coating assembly having a cooled guide die and method of using the same - Google Patents

Abstract

The optical waveguide fiber coating assembly is functionally connected to the guide die with the guide die land area 48, a sleeve for receiving the pressurized coating material 34, the sizing die 38 and the guide die to cool the guide die. Thereby including a cooling device 40 for lowering the temperature of the pressurized coating material in the region near the guide die land region. Keeping the coating material at a relatively low temperature reduces the likelihood of coating overflow.

Description

FIBER COATING ASSEMBLY HAVING A COOLED GUIDE DIE AND METHOD OF USING THE SAME

Optical waveguide fibers must have a high strength to withstand the stresses that are encountered when bonded to the protective sheath or cable, when the cable is mounted and when used as a fiber. The fiber is typically strong because it is drawn from the base material, but its strength drops sharply due to surface defects that occur in the course of handling the fiber.

In order to preserve the strength of the originally drawn fibers, it was common to form one or two protective coating layers on the fibers as soon as they were drawn so that the surfaces would not wear out. Generally, the coating layer comprises an organic or inorganic coating material. In a two layer embodiment, a first or main coating is formed directly on the fiber and a second or auxiliary coating is formed on the main coating. Typically, this coating step is done as part of the fiber manufacturing process to ensure that the coating material is applied before the clean fiber surface is damaged.

An assembly for coating glass optical waveguide fibers is disclosed in US Pat. No. 4,531,959, the relevant portion of which is shown in FIG. The coating assembly 10 includes a guide die 12, a flow distribution sleeve 14 disposed below the guide die 12, and a sizing die 16 below the sleeve 14. The coating assembly 10 is shown mounted in the support structure 17.

To produce the optical waveguide fibers, the drawn fiber material is introduced into the coating assembly 10 in the direction of the arrow A through the guide die 12. The coating material is delivered to the coating assembly 10 through the aperture 22 of the sleeve 14. The coating material is pressurized and delivered in the direction of arrow B at a constant temperature through the conduit. As described below, generally, an upper meniscus of the coating material is formed at the interface between the fiber and the coating material in the guide die land region 18. As the fiber passes through the coating assembly 10, the coating material is accelerated. As the coating material and fibers enter the sizing die 16, a portion of the coating material is withdrawn from the sizing die 16 along with the fibers to coat the fibers. The coating material not drawn out with the fibers is recycled in the coating assembly 10.

Each coating assembly component plays a role in making the coated fibers. The sizing die sets the amount of coating to be applied to the fibers. By tapering the outlet of the sizing die, the sizing die functions to center the fiber and concentrate the coating. See, for example, US Pat. No. 4,246,299. A method of controlling the coating diameter is disclosed in US Pat. No. 5,366,527. The method for a temperature controlled sizing die (TCSD) relates to a method of changing the local temperature of the sizing die to change the coating viscosity inside the sizing die. Lowering the coating temperature increases the coating viscosity. Therefore, the lower the temperature of the die, the less the coating on the optical fiber, the higher the temperature of the die is coated a lot.

By placing the aforementioned sizing die, the flow distribution sleeve keeps the coating material pressurized between the sizing die and the guide die. As mentioned above, the coating is delivered pressurized to a constant temperature. The fluid pressure of the coating must be high enough so that the meniscus can be formed at the bottom along the guide die land area, but not near the bottom of the sleeve.

The guide die functions like a cap for the pressurized coating assembly and prevents the coating from leaking out of the top of the coating assembly. If the guide die loses function due to low or overpressure inside the coating assembly, a so-called "coating overflow" occurs and the drawing process must be stopped. Interruption of the drawing process is costly because it reduces the availability of the machine and reduces the available fiber length.

At high speeds, coating flooding accidents occur. Conventional methods for minimizing the risk of coating overflow have been to make the guide die compact in order to increase the drawing speed. For example, a fiber drawing process of about 20 m / sec or more typically uses a coating guide die having an internal orifice diameter of 20 mils (508 μm) or less, with the orifice diameter being greater when the drawing speed is increased. It must be made small. Obviously, the narrower the orifice, the greater the chance of abrasion by the fiber coming into contact with the orifice wall. Therefore, it is difficult to increase the drawing speed to more than 20 m / sec without increasing the susceptibility of the fiber to wear caused by the narrow orifice of the coating guide die. This conventional method is quite good in practice and is consistent with the theoretical understanding of hydrodynamics in the guide die. That is, smaller guide dies have higher overpressure limits.

However, a problem with the use of small guide dies is that the fibers are more sensitive to wear before coating. As the guide die orifice decreases, the gap between the fiber and the guide die decreases. Fiber vibration and pull misalignment are unavoidable under manufacturing conditions. If the fiber is perturbed from the guideline centerline by fiber vibration or drawing misalignment, the fiber is more easily rubbed against the walls of the small diameter guide die. This friction is called wear before coating, because it occurs before the coating is formed.

Wear before coating is not beneficial because it can severely weaken the fibers and / or cause coating defects. Weakened fibers are more easily broken during drawing, off-line warranty, or use. Thus, the use of smaller guide dies can somewhat resolve coating overflow at high speeds, while increasing the likelihood of undesirable precoating wear.

The foregoing difficulties are not exhaustive and are some of the many difficulties that reduce the effectiveness of conventional fiber coating assemblies and fiber coating methods. In addition, other problems may exist. However, the foregoing problem is sufficient to claim that the conventional apparatus and method should be improved.

The present invention relates to a novel coating assembly for coating optical waveguide fibers and a method of use for inhibiting coating flooding. In particular, the present invention relates to an optical fiber coating assembly comprising a chiller to suppress optical waveguide coating flooding in a guide die.

The accompanying drawings, which form a part of this specification, illustrate the preferred embodiments of the present invention together with the foregoing general description and the following detailed description, and serve to explain the principles of the present invention.

1 is a cross-sectional view of a conventional coating assembly for coating an optical waveguide fiber,

2 is a cross sectional view of a coating assembly for coating an optical waveguide fiber in accordance with the present invention;

3A-3C are cross-sectional views of the guide die and sleeve of a conventional coating assembly, showing possible meniscus shapes in the guide die land region of the guide die,

4 is a cross-sectional view of a second embodiment of a coating assembly for coating optical waveguide fibers in accordance with the present invention;

5 is a cross sectional view of a third embodiment of a coating assembly for coating optical waveguide fibers in accordance with the present invention;

6 is a cross-sectional view of a fourth embodiment of a coating assembly for coating optical waveguide fibers in accordance with the present invention.

Many advantages can be obtained by the present invention. For example, the present invention provides a fiber coating assembly that minimizes coating overflow at high speed draw. Another advantage of the present invention is that the fiber coating assembly operates at high speed and is stable. Another advantage of the present invention is that the fiber coating assembly employs a relatively large diameter guide die to minimize pre-coating wear.

Preferred embodiments of the present invention for implementing at least some of the aforementioned advantages include a coating die having a die land area, a sleeve for receiving a pressurized coating material, and a coating assembly having a sizing die. The coating assembly further includes a chiller operatively connected with the guide die to cool the guide die such that the temperature of the pressurized coating material is lowered in a predetermined region near the guide die land region. The chiller acts as a heat sink. The device locally cools the pressurized coating material and reduces viscous heating generated at high speed drawing. Otherwise, uncontrolled viscous heat will lower the coating viscosity and increase the likelihood of coating overflow. Thus, the coating assembly according to the present invention maintains the pressurized coating material at a relatively low temperature near the guide die land area, thus reducing the possibility of coating overflow in the guide die.

The cooling device may be mounted on an outer wall of the guide die. The chiller may completely wrap at least a portion of the outer wall, or optionally the chiller may intermittently wrap the outer wall to partially cool the guide die. Most importantly, the lower third of the outer wall of the guide die is cooled, but the cooling device can extend along the entire length of the outer wall.

The cooling device includes a cooling jacket mounted around the guide die and a fluid conduit for transferring cooling fluid (gas or liquid) to the cooling jacket. In another embodiment, the cooling device may comprise a thermoelectric chip in thermal communication with the guide die. The thermoelectric chip acts as a heat pump to absorb heat from the guide die, thereby cooling the fluid in the region near the guide die.

A method for suppressing coating overflow in an optical waveguide coating assembly according to the present invention comprises the steps of passing optical waveguide fiber through a coating die containing a guide die and a pressurized coating material, and the guide die at a temperature of 90 ° C. Maintaining. In addition, the guide die may be maintained at a predetermined temperature lower than the inlet temperature of the coating material. That is, it can be maintained at a predetermined temperature lower than the temperature of the coating material when entering the coating sleeve of the coating assembly. That is, the guide die is kept at a lower temperature than when no cooling is achieved. The guide die can be maintained at a relatively low temperature by mounting a cooling device on the guide die. For example, a cooling jacket can be mounted to the outer wall of the guide die.

Other objects and advantages of the invention are set forth below, and in part will be apparent from the description or by practice of the invention. The objects and advantages of the invention may be realized by the devices and combinations thereof indicated in the appended claims.

Referring now to the accompanying drawings, in which like parts are represented by like reference numerals, FIG. 2 shows a coating assembly 30 for coating optical waveguide fibers in accordance with the present invention. The coating assembly 30 is 5 m / sec or more, when coating overflow occurs, for example, 20 m / sec or more, more preferably 25 m / sec or more, most preferably 30 m / sec or more It is particularly suitable for coating optical waveguide fibers at drawing rates above. The coating assembly includes a guide die 32, a flow distribution sleeve 34 with a through hole 36, which is a passage through which the coating material 37 passes, and a sizing die 38. The coating assembly according to the present invention is suitable for use with various coating materials such as UV curable materials, thermosets and thermoplastic polymers. The coating material is pressurized to a constant temperature, that is, the inlet temperature is delivered through the through hole (36). By keeping the coating material pressurized, the level of coating material inside the die assembly can be maintained at substantially the same level throughout the entire fiber manufacturing process.

In addition, the coating assembly 30 is adapted to cool the guide die 32, in particular the guide die land region 48, to lower the temperature of the pressurized coating material 37 in the region near the guide die 32. And a chiller 40 functionally connected to 32. In FIG. 2, the cooling device 40 is mounted on and encloses the outer wall 42 of the guide die 32. The cooling device 40 serves as a local heat sink to cool the guide die 32. As described below, by locally cooling the guide die 32, coating overflow at high speed drawing can be suppressed.

When the uncoated fiber 44 (or primary coated only fiber) is introduced through the guide die 32, the upper meniscus 46 of the coating material is formed between the fiber 44 and the coating material 37. It is formed at the interface. The upper meniscus 46 may be assumed to have three shapes in the guide die land region 48 as shown in FIGS. 3A to 3C. As shown in FIG. 3A, the meniscus 46a may be concave at the corner of the guide die land region. As shown in FIG. 3B, the meniscus 46b may be floating within the guide die land region. Finally, as shown in FIG. 3C, the meniscus 46c may rise near or even above the top of the guide die land region. The last form represents the coating overflow phenomenon, and the viewer looking down the guide die can see the upper meniscus.

By increasing the fiber drawing speed, optical waveguide fibers can be made more economically. However, for example at high speed drawing of 20 m / sec or more, more preferably 25 m / sec or more, most preferably 30 m / sec or more, the drawing process becomes more challenging and the possibility of coating overflow Increases.

The coating assembly has a window for stable operation. The upper limit of the window represents the maximum pressure the coating assembly can support at a given rate without coating overflow. That limit is sometimes called the "overpressure limit". If this limit is exceeded, the upper meniscus is augmented, ie the coating material rises in the guide die land area, and the coating material may leak from the top of the coating assembly through the guide die. This phenomenon is illustrated in Figure 3c.

Experimental data show that the overpressure limit is reduced at high speed coatings in excess of 5 m / sec, for example 20 m / sec or more, more preferably 25 m / sec or more, most preferably 30 m / sec or more. Appears to be. For this high speed draw, there is a lack of correlation between the experimental data and the model used to predict the overpressure limit. The model did not explicitly take into account the phenomenon occurring at high speed draw. The hypothesis to explain this difference is that as the draw rate increases, the viscosity of the coating in the guide die land region decreases below the normal value corresponding to the inlet temperature of the coating, ie about 50 ° C. Two phenomena, shear thinning and viscous heating, readily cause a local decrease in coating viscosity.

Lamination thinning is a common phenomenon in non-Newtonian fluids such as polymers. When the fluid is subjected to a large shear rate, the molecules of the fluid are aligned such that the viscosity of the fluid falls below the value at zero shear.

Viscous heating is a phenomenon in both Newtonian and non-Newtonian fluids. When a fluid is subjected to a large shear rate, friction between the fluid molecules generates heat. This exotherm locally increases the temperature of the fluid. In the case of optical waveguide fibers, shear stresses occur due to the speed of the fibers passing through the coating material. This shear stress generates heat and raises the temperature of the coating material. Increasing the temperature of the coating material decreases its viscosity. A significant amount of viscous heating takes place in the guide die lands; This viscous heating can result in a local coating temperature higher than the inlet temperature of the coating. Increasing the temperature significantly reduces the coating viscosity in the guide die land region. Therefore, the inventors of the present application determined that viscous heating is the main phenomenon of reducing the overpressure limit at high speed drawing.

Thus, the cooling device 40 manages and lowers the temperature of the guide die land region 48 by conducting heat away through the guide die wall 42. Referring again to FIG. 2, heat extraction from the guide die wall 42 is via a cooling device 40 in the form of a cooling jacket. By locally cooling the guide die land region, the increase in coating temperature caused by viscous heating is reduced. Lowering the coating temperature increases the coating viscosity. High coating viscosity increases the overpressure limit of the coating assembly, making the coating assembly less susceptible to flooding.

The cooling jacket 40 shown in FIG. 2 is disposed around and completely surrounds the outer wall 42 of the guide die 32. Since the guide die dissipates heat, the temperature control of the outer wall 42 changes the temperature of the inner wall, including the guide die land region 48. Therefore, the cooling jacket 40 can lower the temperature of the inner wall by lowering the temperature of the outer wall 42.

The cooling jacket 40 includes a fluid conduit 50 attached to the cooling jacket, through which a cooling fluid (gas or liquid) such as cold helium or cold water passes to optimally cool the temperature of the cooling jacket 40. Keep at temperature. Fluid enters the cooling jacket 40 through the inlet conduit and then exits the outlet conduit in the direction of arrow (C). The optimum temperature of the cooling fluid may be changed to change the temperature of the cooling jacket 40. Once determined, the optimum temperature of the cooling jacket 40 is preferably kept constant. The optimum temperature is determined by experimental or mathematical modeling.

The coating assembly 30 may further comprise a temperature control member 49 mounted near the sizing die 38, preferably at the bottom of the sizing die 38. As disclosed in US Pat. No. 5,366,527, the temperature control member 49 controls the coating diameter of the fiber as it is drawn through the sizing die.

It will be appreciated by those skilled in the art that the cooling jacket 40 can be designed in an alternative way to achieve the same cooling effect. For example, the cooling jacket may be designed to extend along only a portion of the guide die outer wall 42 length. In one embodiment, the cooling jacket 40 extends only along the bottom of the guide die outer wall 42. The cooling jacket preferably extends at least as long as the length of FIG. 2, which corresponds to at least the bottom third of the outer wall. This length is similar to the length of the land area 48, where the inner diameter of the guide die is limited to a generally constant area. In this embodiment, cooling is localized to the most important area of the guide die, and under normal conditions, the coating material is present in this low guide die land area. However, because heat dissipation occurs throughout the guide die, heat will be absorbed from all regions, including the top of the guide die.

In another embodiment, the cooling device may intermittently wrap the outer wall of the guide die. That is, the cooling device does not "wrap" the outer wall of the guide die, but instead heats the guide die at a given point to partially cool the guide die. Since heat is emitted from the entire guide die, cooling only a predetermined point of the guide die outer wall may be satisfactory in many respects.

As shown in FIG. 4, in a second embodiment of the present invention, the cooling jacket 40 determines an optimum temperature based on a signal collected from a sensor 54 mounted on a guide die. Can be controlled by The sensor 54 checks the information indicative of viscous heating in the guide die land region 48. For example, the sensor 54 may check the guide die temperature of the inner wall in the guide die land area, or check the height of the upper meniscus in the guide die land area. The control system 52 communicates with a temperature control system 56 that controls the temperature of the cooling fluid (gas or liquid) in response to the data generated from the control system 52. The cooling fluid temperature is changed depending on the detected conditions in the guide die land area to maintain an optimal operating state. This embodiment can be used when the experiment shows that a set of variable data, such as guide die inner wall temperature and upper meniscus height, correspond to the optimum temperature.

A third embodiment of the invention is shown in FIG. A guide die 60 is disposed above the flow distribution sleeve 62 and functions as an inlet through which the coating material 64 enters the coating assembly, as in the embodiment described above. A sizing die 66 is disposed below the flow distribution sleeve 62. In this embodiment, the guide die 60 has a generally flat top surface. A thermoelectric chip 68 is disposed on the upper surface of the guide die 60, and is in thermal communication with the guide die 60.

The thermoelectric chip 68 has a Peltier effect that acts as a heat pump to cool the guide die 60. Details on the Peltier effect are described, for example, in the Physical and Chemical Solidification of 1992, Vol. 53, No. 8, Kairat et al., Pages 121-129 (Bi _x Sb _1-x ). Thermoelectric properties of ₂ Te ₂ single crystal solid solution ”. As a heat pump, the thermoelectric chip 68 needs a heat reservoir to remove heat from the top of the chip 68. The reservoir (not shown) may consist of a heat sink in thermal communication with the chip 68. The temperature of the heat sink is maintained at a constant level, for example, by a recirculating water bath or a liquid bath. To cool the guide die 60, the heat sink removes heat from the top surface of the thermoelectric chip 60. In addition, the heat sink removes heat from the upper surface of the guide die 60 to remove heat from the guide die land region, thereby reducing the temperature of the coating material in the guide die land region. As the coating material is cooled, the viscous heating is reduced, the coating viscosity is increased, and the overpressure limit is increased, thereby reducing the likelihood of coating overflow. In order to control the temperature of the guide die 60, the polarity and voltage levels for the thermoelectric chip 68 can be adjusted.

6 shows a fourth embodiment of the present invention. Similar to the embodiment of FIG. 5, a guide die 70 is disposed above the flow distribution sleeve 72 and functions as an inlet through which coating material 74 enters the coating assembly. A sizing die 76 is disposed below the flow distribution sleeve 72. In the fourth embodiment, the guide die 70 has an inclined top surface. A thermoelectric chip 78 is disposed on the inclined top surface of the guide die 70, and is in thermal communication with the guide die 70. The thermoelectric chip 78 operates in the same manner as the thermoelectric chip 68 of FIG. 5.

The coating assembly of FIG. 6 also includes a thermocouple device 80 disposed on the inner surface of the guide die 70 in the guide die land region 82. The thermocouple device 80 measures the temperature of the land region 82. The measured temperature is used to control the thermoelectric chip 78 to adequately cool the guide die 70.

The thermocouple device 80 is disposed inside the thermocouple entry hole 84 passing through the guide die 70. The two leads 86a and 86b of the thermocouple device 80 extend out of the guide die 70 through the entry hole 84 to measure the temperature. The measured temperature may be transmitted to a controller (not shown) electrically connected to the thermoelectric chip 78. The controller can then adjust the voltage or current provided to the chip to control the temperature of the thermoelectric chip 78. Preferably, the thermocouple entry hole 84 is filled with an epoxy material.

The coating assembly may be used to further provide a coating layer on bare fibers or on fibers that are already semi-coated such that a composite coating is formed.

A method for suppressing coating overflow in an optical waveguide coating assembly according to the present invention comprises the steps of passing optical waveguide fibers through a coating die containing a guide die and a pressurized coating material; And maintaining the temperature of the guide die preferably at 90 ° C. or lower, more preferably at 75 ° C. or lower, most preferably at 60 ° C. or lower. In addition, the guide die may be maintained below the inlet temperature of the coating material, that is, below 50 ℃.

Without enumerating all the desirable features of the present invention, the present invention provides a coating assembly that can function at high speed drawing and solves the problem of coating overflow without reducing the orifice of the guide die.

Prior to the present invention, a guide die with a small orifice was used for high speed drawing. Textile manufacturers have relied on small orifice guide dies because of the hydrodynamic phenomena that occur at high speed draws. When the drawing speed is increased, viscous heating occurs. The viscous heating reduces the coating viscosity in the guide die land region. Low coating viscosities lower the overpressure limit and thus can cause coating overflow. Guide dies with smaller orifices increase the overpressure limit to heal the coating overflow.

In the past, guide dies with a minimum orifice diameter of about 20 mils (508 μm) or less have been used for drawing speeds of about 20 m / sec or more. In general, the orifice diameter should decrease as the drawing speed increases. For example, prior to the present invention, in processes with a draw rate of 25 m / sec or higher, a guide die with an internal diameter as small as 13 mils (330.2 μm) had to be used to successfully coat the fibers. A side effect of guide dies with small orifices is an increased risk of wear before coating.

However, by using the cooled guide die assembly of the present invention, 25 m / sec, even 30 m in a guide die having a minimum orifice diameter of at least 15 mils (381 μm), more preferably 20 mils (508 μm) or more A speed of / sec or more can be obtained. The chiller of the coating assembly of the present invention locally cools the coating material and reduces the viscous heating occurring at high speed drawing. By lowering the temperature of the coating material within the guide die land region, the overpressure limit is increased and the possibility of coating overflow is reduced. Thus, the present invention enables the use of relatively large diameter guide dies at high speed draws and eliminates the risk of precoating wear.

Additional changes and modifications will be apparent to those skilled in the art. Accordingly, the present invention is not limited to what is disclosed in this application. Accordingly, various modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (20)

Guide die; A sleeve for receiving the pressurized coating material; Sizing dies; And And a cooling device functionally connected with the guide die to cool the guide die. The optical waveguide fiber coating assembly of claim 1 wherein the guide die comprises an outer wall and the cooling device is mounted to the outer wall. 3. An optical waveguide fiber coating assembly according to claim 2, wherein the cooling device completely surrounds at least a portion of the outer wall of the guide die. 4. The optical waveguide fiber coating assembly of claim 3 wherein the chiller extends along the entire length of the outer wall of the guide die. 3. The optical waveguide fiber coating assembly of claim 2 wherein the chiller intermittently surrounds the outer wall to point cool the guide die. The optical waveguide fiber coating assembly of claim 1 wherein the cooling device includes a cooling jacket mounted around a guide die and a fluid conduit for transferring cooling fluid to the cooling jacket. The optical waveguide fiber coating assembly of claim 1 wherein the cooling device comprises a thermoelectric chip in thermal communication with a guide die. 8. The assembly of claim 7, wherein the assembly further comprises a sensor mounted to the guide die to measure at least one of coating material height and guide die temperature within the guide die, and a controller in electrical communication with the sensor and the thermoelectric chip. An optical waveguide fiber coating assembly, characterized in that. The optical waveguide fiber coating assembly of claim 8 wherein the sensor is a thermocouple device. Passing the optical waveguide fibers through a coating sleeve containing a guide die and a pressurized coating material; And Maintaining the temperature of the guide die below 90 ° C .; The method of claim 10, wherein the guide die is maintained at or below 75 ° C. 12. The method of claim 10, wherein the guide die is maintained at or below 60 ° C. 12. 11. The method of claim 10, wherein the guide die is maintained below the inlet temperature of the pressurized coating material. The method of claim 13, wherein the inlet temperature is about 50 ° C. 15. 11. The method of claim 10, wherein the maintaining step includes using a chiller to cool the guide die. 16. The method of claim 15, wherein the cooling device in said using step comprises a cooling jacket mounted to an outer wall of the guide die. Passing the optical waveguide fiber at a speed of 25 m / sec or more through a guide die containing a pressurized coating material; And And maintaining the guide die at a temperature that allows the fiber to be completely coated during the passage step, wherein the guide die has a minimum inner diameter of 15 mils or more. 18. The method of claim 17, wherein the step of passing comprises passing the fiber through the guide die at a rate of 30 m / sec or more. 18. The method of claim 17, wherein the guide die has a minimum inner diameter of 20 mils or greater. Passing the optical waveguide fibers through a coating sleeve containing a guide die and a pressurized coating material; And And maintaining the temperature of the guide die below the temperature of the guide die in the absence of any active cooling.