EFFECT OF DRAW FURNACE GEOMETRY ON HIGH-SPEED OPTICAL FIBER MANUFACTURING

Abstract

Optimal design of the draw furnace is particularly desirable to meet the need of high-volume production in the optical fiber industry. This article investigates the thermal transport and flow in optical fiber drawing at high draw speeds in a cylindrincal graphite furnace. A conjugate problem involving the glass and the purge gases is solved. The transport in the two regions is coupled through the boundary conditions at the free glass surface. The neck-down profile of the preform at steady state is determined by a force balance, using an iterative numerical scheme. To emphasize the effects of draw furnace geometry, the diameters of the preform and the fiber are kept fixed. Only the length and the diameter of the furnace are changed. For the purposes of comparison, a wide domain of draw speeds, ranging from 5 m/s to 20 m/s, is considered, and the form of the temperature distribution at the furnace surface remains unchanged. The dependence of the preform/fiber characteristics on the furnace geometry are demonstrated quantitively. Based on these numerical results, an optimal design of the draw furnace can be developed.