In the tire industry, the preparation of silica-filled compounds requires relatively complicated compounding operations, which involve several dumping, cooling, and remixing steps, to eventually obtain quality final batches. The various and complex sets of events that take place along the mixing tine remain, however, poorly understood. The objectives of this study, reported in two companion articles, were to deepen the understanding of silica-silane compounding operations. Two approaches were used in parallel: first, we performed a deep analysis of the engineering performance of an existing-and successful-mixing line by paying attention to the various curves that are nowadays recorded during internal mixing, and second, we studied the variations of the nonlinear viscoelastic properties along the mixing line using so-called Fourier transform rheometry, implemented on a commercial torsional dynamic rheometer. The first article of the series is devoted to the performance analysis of the mixing line through mixing trials along an industrial line. Silica dispersion and the treatment with silane were initiated during a master-batching process; then, two remixing steps were performed to achieve the right silanization degree. Curatives were added during a final mixing step. Mixing signatures, containing information such as mixing power, ram position, compound temperature, and rotor speed, gave some insight to the dispersion-silanization processes and, among other results, showed that the dumping, cooling, and remixing of the compound comprised a more efficient process than the maintenance of a very high batch temperature for an extended time, essentially because one could make use of stress-induced dispersing effects. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 942-952, 2009