New method for measuring the friction between hot viscous glass and metals

Abstract

The present study proposes a new experimental approach to quantify the shding of hot viscous glass on a Substrate material, in conditions being representative of the loading of glass gobs into forming moulds. Using a gob-loading sensor, the method consists in calculating the energy dissipated by the glass gob when crossing a feeding funnel, with a direct measurement of the velocity loss of the gob following its dynamic contact with the funnel. Experimental data combined with a mechanical modelling has been performed with two funnel geometries: a cylindrical funnel and a conical funnel. The strain dissipation energy induced by the deformation of the viscous gob inside the funnel has been first calculated. It is shown that the cylindrical funnel allows strain modes consuming four times less energy than the conical funnel, in agreement with experimental observations. A global analysis of the motion allowing the calculation of the total energy lost by the gob during the contact with the funnel is then proposed, taking into account the previous dissipation energy calculation. A motion equation is thus deduced, giving the velocity of the gob as a function of time, glass/gob friction coefficient and other experimental parameters. The dissipated kinetic energy is strongly influenced by the dissipated strain energy, thus influencing the value of the calculated friction coefficients. The gob-loading sensor is a powerful tool increasing knowledge in the forming of viscous materials, together with a comparison and discrimination of various materials and surface states, which may be used in the glass forming process with the aim to avoid the use of lubricant and to make the process more competitive.