Abstract
Viscous elongation of glass rods has been investigated to improve procedures for producing parabolic capillaries from straight capillaries for use as intensity concentrating x-ray optical elements. Experiments and simulations have been carried out pulling Corning 7740 borosilicate glass rods in a cylindrical furnace. Simulations were based on one-dimensional and two-dimensional finite difference/element calculations, assuming that deformation occurred by linear viscous flow and that the temperatures in the glass remained in equilibrium with the temperatures measured along the axis of the furnace. Rates of elongation in experiments were smaller than those in simulations for later stages of the elongation process. Further experimental and analytical investigations ruled out explanations based on increased viscosities caused by structural relaxation or by partial crystallization and showed that the simulations gave incorrect results because they did not incorporate the dependence of local heat transfer processes on the glass rod radius.
Published Version
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