Profile development in drawn hollow tubes

Finite element and asymptotic analyses were used to study the profile development in isothermal drawing of hollow tubes. The transition from die flow to extensional flow is considered to occur over a distance comparable to the annular thickness; considerable extrudate swell can occur with the flow rearrangement; the final ratio of inner to outer radius can fall below that at the die despite an increase in this ratio over the entire draw zone. Asymptotic 'thin-filament' equations, which are utilized in a study of polyethylene terephthalate fibres, are used to describe flow beyond the region of flow rearrangement.