UV Coloring of Optical Fiber Final Report

Transcription

1 UV Coloring of Optical Fiber Final Report Why Change the Process? Alcatel Telecommunications Cable located in Claremont, North Carolina, manufactures optical fiber and cable. After fiber is produced, it is shipped to a co-located facility and incorporated into a variety of cables and ribbon used in the telecommunications and cable television industry. Similar to electrical wire, optical fiber strands are color coded for field recognition during cable installation. Traditionally, fibers were colored using a solvent based (Methyl Ethyl Ketone) ink prior to being placed into cables. As with the paint on any surface, ink on a fiber could easily be removed from abrasion or faded fiom environmental conditions. Although the majority of fiber coloring problems were caught prior to shipment to customers, several in field complaints occurred annually as a result of the missing and/or inadequate color. In 1996, solvent inking generated MEK emissions in excess of 16 tons. An additional 5 tons of hazardous waste was generated from scrap and waste ink. On November 6, 1996 a synthetic minor permit was issued to Alcatel by the North Carolina Division of Air Quality limiting MEK emissions to less than 10 tons per year. Since production projections for 1997 would result in emissions exceeding the synthetic minor permit threshold of 10 tons, a thermal oxidation air pollution control device was placed into operation in February 1997 to insure compliance. The installed cost for the unit was $500,000 with an anticipated annual operating cost of approximately $22,000. Similarly, $30,000 of waste disposal costs were anticipated from the use of the inks annually. The potential costs fiom customer complaints and the environmental issues associated with the use of MEX ink drove Alcatel to pursue a fiber coloring alternative. Process Descriation The first production step in making optical fiber at Alcatel involves a process referred to as Chemical Vapor Deposition (0). Silica Tetrachloride (SiC14), Phosphorus Oxychloride (POCl3), Germanium Tetrachloride (Gec14), and Freon 116 vapors are passed through the inside of a pure silica glass tube mounted on a lathe. The heat provided by an oxy-hydrogen torch traversing the outside of the rotating glass, causes a reaction to take place inside the tube. Deposition of soot (oxides of silica, germanium, and phosphorous) and subsequent sintering into clear glass occurs. After desired thickness and optical characteristics are achieved on the CVD lathe, the glass tube is placed onto a collapse lathe. While being traversed by an electric furnace, Freon 116 is passed through the glass tube etching the interior. A vacuum is

2 I 1 subsequently pulled on the interior of the tube forming a solid glass rod. The collapsed glass rod is referred to as a primary. After the primary is completed, it is forwarded to the Preform Refractive Index Profile (PRP) area where the refractive index profile is checked and prepared for additional processing. The second step in optical fiber production at Alcatel involves a process referred to as overcladding. Using argon and air plasma at a temperature above 8000 K, silica grains are injected into the plasma plume and subsequently deposited on the primary preform substrate generated by the CVD process. Mer desired diameter is achieved, the preform (primary + overcladding) is forwarded to PFUP where it undergoes several quality checks, The preform is comprised of a high refractive core surrounded by a lower refractive overclad. This glass combination promotes total internal reflection of light once the fiber is drawn. The draw process converts the preform, from the CVD and overcladding process, to a coated optical fiber encased in two layers of protective coating. The glass rod (preform) is suspended in a fbrnace in which a computer precisely controls the temperature and feed rate. As the temperature increases, the glass becomes fluid and a small ccg~b of molten glass falls from the fbrnace. Carefbl control of draw speed and tension will provide a glass diameter of 125 microns. Primary and secondary acrylate coatings are applied to the fiber during the draw process to promote attenuation and preserve intrinsic strength. The acrylates are cured via ultraviolet lamps placed on the draw towers. The formed fiber is wound at the bottom of the draw tower before being qualified and tested to verify that the fiber produced meets the optical qualities specified by Alcatel standards. Fiber used internally, is shipped to the co-located cabling facility. The clear fibers are threaded through various coloring dies and placed into protective polyproplyene buffer tubes. The buffer tubes, with the fiber, are placed into a variety of cables that are shipped to external customers. Process Changes The original fiber production process called for a clear primary and secondary UV curable acrylate coating to be applied to the fiber during the draw process. Instead of using a clear UV curable secondary coating, Alcatel has modified the process and equipment to use a pigmented secondary coating for fiber coloring. The Alcatel W coloring process has been trademarked as ColorLock. One particular advantage to incorporating coloring into the draw process is that very few changes needed to be made to the general fiber production, As such, the amount of so ware and hardware changes required was minimal. The following is a detailed description of process modifications.

3 Curing of the primary coating needed to be accelerated prior to the application of the pigmented secondary coating since UV light has difficulty penetrating the pigments. As such, additional UV lamps were installed on each draw. (Fig 1) The pigmented coating is stored in 55 gallon drums in a temperature controlled coating room prior to use. (Fig 2) Fig. 1 To avoid the pigment from settling in the bottom of the 55 gallon drums, the pumps periodically circulate the coating. (Fig 3). In the coating room, the coating is distributed to one of several 10 gallon process tanks through a series of one inch stainless-steel lines. (Fig. 4) A manual control panel is used to initiate individual coating fills. Based on an analog reading from a floor scale, the filling terminates once a predetermined level of coating is reached. Fig. 3 Fie. 4 The process tank is then pressured and allowed to settle to remove suspended air bubbles. (Fig 5) After the settling period is complete, the production-ready tank is attached to the draw tower coating distribution system. A color distribution panel, comprised of twelve color specific disconnects, (and one spare) have been attached to the frame of the draw structure. A black nylon line is connected from the process tank to the color distribution panel. The tank is connected to an air line that pressurizes the tank. (Fig 6)

4 Fin. 5 Fin. 6 The coating is fed though stainless steel piping, a solenoid valve, and a flexible nylon line that connects to the secondary coating application head. In order to insure uniform color application, a purge of the entire secondary coating system occurs for approximately 20 minutes prior to draw operations. (Fig. 7) Only small adjustments to die size, tower tension set-points, and coating temperature were made to accommodate the ColorLock conversion. The final colored fiber is placed onto spools after being drawn. (Fig. 8) It is estimated that an annual internal savings of 1.8 million dollars has been realized in reduced labor costs, a reduction of raw material, and the elimination of customer complaints. Difficulties and Thinm We Would Do Differentlv The following are some problems that were encountered during the start-up and operation of the UV coloring equipment. 1. The purge cycle was too short resulting in a mixing of colors. In order to correct the problem, the purge cycle was simply lengthened to insure color purity.

5 The automatic coating fill station failed to shut off resulted in a 55 gallon drum of coating to spill into the coating storage room. The procedure for filling a container was modified. An operator is now required to be present at all times during a container fill evolution. Use of 10 gallon intermediate containers added an unnecessary labor expense and material handling complications. As such, the coating delivery system has recently been modified to accommodate 55 gallon drums thereby eliminating the need for intermediate containers. The white colored fiber could not be used with the existing OTDR for quality checks. As a result, an interim unit was obtained from PK Technology while a new unit could be designed and fabricated specific for Alcatel s needs. The pigment increased the viscosity of the secondary coating. Since viscosity is a function of pressure and temperature, these two parameters were adjusted at the coatinglfber interface to insure uniform coating application and proper diameter of the fiber. The dip tubes (drum extraction piping) were lengthened to insure that pigments (that collected on the bottom) were re-suspended into the coating. Costs and Savings The total price of the project was over one million dollars. Costs included the following: Spares $150,000 Coating Storage Room In-tower plumbing $12,700 W exhaust duct $425 W lamps $1 1,600 Training Pk Spectrophotometer Improved Output W lamps $25,000 Total $1.032,800 Estimated annual savings are based on the following: Ink reduction $540,000 W Ink (Cabling) $1 86,000 Labor Savings (Cabling) $460,000 Remake reduction $535,000 Waste Savings $30,000 Acetone Reduction $28,000 Customer Service Issues $60,000 Air pollution control $22,000 Total $

6 Based upon the aforementioned costs and savings, the project return on investment is estimated to be around 0.6 years. Training was minimal since the operating procedures for manufacturing the fiber did not change drastically. Significant costs were incurred, however, during the qualification of each ColorLock color. Specifically, the draw tower being used for the qualification could not be used for production purposes - resulting in a decrease of production capacity by 10%. Because these costs are difficult to quanti@, the project pay back may be actually around 1.O years. Summarv The ColorLock process modifications eliminated 5 tons of hazardous waste annually, reduced air emissions by approximately 16 tons annually, and allowed for an air pollution control device to be removed from service. The ColorLock conversion has exceeded Alcatel's original expectations. Not only has MEK virtually been eliminated from the production floor at the cabling facility, but the durability of the ColorLock color has virtually eliminated all customer complaints since the projects completion.