Ellipticity of the cross section of a glass capillary formed by narrowing a cylindrical tubular billet

Abstract

The effect of two process parameters—the azimuthal inhomogeneity of the wall thickness (thickness nonuniformity) of the tubular billet and the azimuthal inhomogeneity of the temperature field of the high-temperature furnace—on the ellipticity of the cross section of a drawn capillary have been experimentally investigated. Thin-wall tubes made from SL-97-1 vacuum glass were used in the experiments. It was established that the thickness nonuniformity of the capillary coincides with that of the tubular billet when a furnace with an azimuthally homogeneous temperature field is used, regardless of the “subcollapse” (incomplete collapse) of the tubular billet as it narrows into a capillary. However, the ellipticity of the drawn capillary, on the contrary, depends on the subcollapse, increasing as it increases. Azimuthal inhomogeneity of the temperature field causes appreciable ellipticity of the cross sections even in capillaries drawn from tubular billets with small thickness nonuniformity.