EoW January 2009

technical article Advances in High Speed Optical Fibre Colouring By Dr Harri Turunen, Timo Hietaranta, Jukka Mönkkönen, Dr Tim Dougherty, Nextrom (USA) Inc, Conover, North Carolina, USA; and Nextrom OY, Vantaa, Finland

Abstract A high speed optical fibre colouring/ upcoat line has been developed to improve productivity and to provide the flexibility to manufacture a variety of quality products. This paper focuses upon the design of key line components to achieve speeds up to 3,000m/min for colouring. A robust mechanical and electrical design, in combination with optimised tooling, improved UV lamp system, UV monitoring instrumentation and increased spool sizes provide the capability to produce longer fibre lengths with faster set-ups. The result is a significant productivity improvement. 1 Introduction The fibre optic industry is steadily recovering and is very competitive. This has generated a renewed interest in process productivity and the need for equipment flexibility to manufacture a variety of new products. During the past few years, the development of faster curing UV acrylate resins provided the opportunity for higher line speeds. In addition, the development of new fire retardant coatings has led to a new generation of fibre upcoat products for premise cable applications [1] [2] . This work focuses upon productivity improvements for optical fibre colouring/ upcoat equipment. A new machine has been developed to achieve higher speeds in combination with longer lengths and faster set-ups to provide the flexibility to efficiently manufacture a variety of products. The new line is shown in Figure 1 . It consists of a large capacity spool pay-off in the lower left, a dancer for pay-off speed control, a coating station in the upper centre, followed by a series of high powered UV lamps below the coater. The capstan is located in the lower right. The fibre then passes through a dancer and a ‘tension balancer’, which reduces loops causing OTDR steps, before being precisely wound onto a large capacity traversing take-up spool.

Figure 1 ▲ ▲ : OFC 52i

Figure 2 ▲ ▲ : Prototype line

appropriate pressure inside the coater to seal the die entrance while maintaining acceptable fibre tension levels. The line performance was demonstrated using DSM Desotech Cablelite® 751 and DX-1000 series inks over a range of operating parameters. The results were then compared to theoretical models. The die tensions, fibre pay-off or back tensions, and total or maxi- mum tensions are presented in Figure 3 for the average of 751 and DX-1000 colours. Note that die tensions did not significantly increase with speeds. This is due to both shear thinning and shear heating of the polymer at high speeds. Also note that the DX-1000 series processed with slightly higher tensions. This was due to its higher viscosity as shown in Figure 4 . The higher viscosity provides stability by reducing settling during storage and between runs. An Arrhenius model was used to fit viscosity data. Note that 10-15°C higher processing temperatures for DX-1000 inks would produce viscosities similar to 751 inks. Optical grade fibres were coloured during some of the high speed trials to allow attenuation measurements at 1,310nm and 1,550nm. The attenuation increases were less than 0.01 dB/km at 3,000m/min for the 751 and DX-1000 inks.

Optional are available, as well as ring marking. Other options include UV intensity and oxygen measurements to assure proper UV cure during long production runs [3] . Colouring trials were conducted on a prototype line, which is shown in Figure 2 for reference. The primary difference between the prototype and commercial lines was the relocation of the capstan to the bottom to make room for optional ring marking at the top. The high speed manufacture of coloured fibres requires improved designs for key line components. Development focused upon the pay-off and take-up design to allow larger and heavier spools, improved coater tooling to facilitate set-up and fibre string up, as well as a robust precision motor drive and control system. New efficient UV power supplies provide continuously variable power to the UV lamps to assure proper cure from start-up to 3,000m/min. 2.1 Die design A new colouring applicator was developed and tested for operation up to 3000m/ min. The challenge was to create the pay-off/take-up sizes 2 Critical line components

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EuroWire – January 2009