Browsing by Author "Falipou, Marc"

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    New method for measuring the friction between hot viscous glass and metals
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Falipou, Marc; Sicloroff, François; Donnet, Christophe
    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.
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    Sticking temperature investigations of glass/metal contacts Determination of influencing parameters
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Falipou, Marc; Donnet, Christophe; Maréchal, François; Charenton, Jean-Claude
    Sticking experiments between hot viscous glass and metallic Substrates have been performed with a glass press apparatus on a laboratory scale, allowing a precise determination of the sticking temperatures, Ts, versus selected experimental parameters (nature of the Substrate, composition of the glass). Complementary surface analyses have also been carried out to identify the surface and interface reaction products following the glass/metal contact. Experimental results have been compared to ternary phase diagrams, in order to test the reliability of thermodynamic calculations to predict the nature of the phases produced by the contact at high temperature. The sticking phenomenon is governed by a coupling between the rheological behaviour of the glass melt and the physicochemical reactivity of the contacting surfaces. Sticking occurs when the temperature at the interface remains sufficiently high, so that the glass viscosity remains low enough to enhance the real contact area and thus, to induce physicochemical interactions between Substrate and glass. Sticking is attributed to the presence of an interfacial oxide layer which strongly adheres onto the glass. Chemical analysis of the sticking surfaces identifies a physicochemical driving force contributing to the sticking phenomenon. The predominant reaction consists in the reduction of the sodium oxide of the glass at the expense of the oxidation of the metallic elements of the Substrate during pressing, in agreement with thermochemical calculations presented by the ternary phase diagrams. The strong chemical reactivity of the soda-lime-silica glass is thus attributed in particular to the highly reactive sodium oxide constituent.