Effect of glass lubrication on metal flow in hot extrusion of stainless tube in an example of Ugine-Sejournet process has been investigated experimentally and theoretically, which has been closely related to the surface defect of products. First, a relationship between viscosity of glass lubricants and friction coefficient is measured with a hot friction test. Friction coefficient is proportional to logarithmic viscosity of glass lubricant. Glass lubrication for hot tube extrusion is found in hydrodynamic condition. Then finite element analyses of metal flow during hot tube extrusion is carried out to simulate metal flows, strains and stresses. Computed extrusion forces and metal flows are in good agreement with experimental measurements. Quantitative flow characteristics such as redundant work and abrupt change of metal flow in bearing portion are evaluated with finite element analyses. It may be possible to optimize an extrusion condition of hot tube extrusion to reduce surface defects such as transversal crack of products.
