RESEARCH ARTICLE High resolution monitoring of an unsteady glass ﬁbre drawing process Fabrice Onofri Anne Lenoble Stefan Radev Paul-Henri Guering Received: 18 July 2005 / Revised: 16 January 2007 / Accepted: 24 January 2007 / Published online: 17 February 2007 Ó Springer-Verlag 2007 Abstract We report unsteady experimental results on the stability of ﬁbre diameter in a continuous glass forming process, using two unique laser systems: a high resolution diffractometer and a backward phase Doppler interferometer. For draw ratios close to those used in the industry, the glass ﬁbre diameter exhibits small ﬂuctuations, which cannot be consid- ered to be a result of draw resonance. It is shown that the amplitude of ﬁbre diameter ﬂuctuations decreases with increasing draw ratio, while the corresponding frequency increases with the temperature of the molten glass. Although the origin of these ﬂuctuations is still not well understood, it appears that their fre- quency depends on the characteristics of the molten glass jet. 1 Introduction Glass ﬁbres used in reinforced plastics are produced by drawing glass melt as it comes out of a bushing nozzle, see Fig. 1. The ﬁbre solidiﬁes in the draw zone and the solidiﬁed jet is wound on a rotating wheel (drum or take-up roller) which provides the required mechanical tension for the ﬁbre in the draw zone. Depending on the composition of the glass, which is determined by various requirements and constraints (end use, melting characteristics, ﬁbre sizing, environmental and cost requirements, etc.) the mean diameters of commonly produced glass ﬁla- ments are in the range of D f = 4–25 lm (Gupta 1988). The drawing process is usually subjected to various perturbations and instabilities which may be harmful from the viewpoints of both manufacturing efﬁciency (ﬁbre breaking) and quality (diameter ﬂuctuations). Among the possible sources of perturbations are vari- ations in the input parameters (such as glass composi- tion and temperature), variations in winding velocity (drift, vibrations) or certain external factors (radiative transfer coupling with other nozzles, turbulence generated by the winding). According to some authors (Gliksman 1968; Donnelly and Weinberger 1975; Fisher and Denn 1976; Geyling and Homsy 1980; Schultz and Davis 1984; Gupta et al. 1996; Yarin et al. 1999), for high viscosity materials such as glasses the most important instability mode is what is referred to as the ‘draw resonance’. This instability is characterized by self- sustained oscillations of the tension of the drawn ﬁlament (in relation to the diameter) that may induce ﬁbre breaking. It is now well established that for an isothermal drawing process, draw resonance takes place when the draw ratio (i.e. the ratio of the average ﬁbre velocity at the winder to that at the nozzle, E = V f /V 0 ) exceeds a value close to E = 20.21. F. Onofri (&)  A. Lenoble CNRS UMR 6595-IUSTI, University de Provence, Technopo ˆ le de Cha ˆ teau-Gombert, 13453 Marseille Cedex 13, France e-mail: fabrice.onofri@polytech.univ-mrs.fr S. Radev Institute of Mechanics, Bulgarian Academy of Sciences, 4, Acad. G. Bonchev Str., 1113 Soﬁa, Bulgaria P.-H. Guering Saint-Gobain Recherche, 39 Quai Lucien Lefranc, B.P. 135, 93303 Aubervilliers Cedex, France 123 Exp Fluids (2007) 42:601–610 DOI 10.1007/s00348-007-0268-4