Treffer: Thermal and mechanical behaviors of optical silica glass fiber during the drawing process

The process of fiber drawing in a vertical furnace is described using the lubrication approximation coupled to heat transfer. The radiative heat transfer is detailed by studying the emitted and absorbed fluxes experimented by the fiber. The emissivity is carefully determined with high spectral resolution. Using a two-band gray absorption coefficients, the Planck average emissivity is overestimated by 24 % in comparison with a high spectral resolution of absorption coefficient. The profile of the heating area is obtained from the experimental data. The steady state lubrication model is solved numerically using a finite difference method. A numerical prediction obtained under certain operating conditions allows a comparison of the fiber radius profiles obtained experimentally and numerically. The convective heat transfer after the neck-down region is needed to control the cooling and the fiber shape. Drawing forces obtained experimentally are compared to numerical results. When the operating temperature is equal to 1950 • C, the agreement is satisfying. The effects of variations in drawing velocity and furnace wall temperature on the relevant operating conditions for adjusting the cooling rate, drawing force, and other variables are numerically studied.