UTILIZAÇÃO DE REVESTIMENTOS POLIMÉRICOS EM ROTOR FRANCIS DANIFICADO POR CAVITAÇÃO

Abstract

This work evaluates the performance of polymeric coatings in terms of cavitation resistance, with the objective of reducing costs in rotor maintenance services, increasing the availability of turbines and an alternative in the welding process. In the laboratory, ultrasound-induced cavitation tests were performed, quantified by mass loss, later transformed into thickness loss and traction loss, as an adhesion parameter. As a field test, the coatings were applied to bronze rotors, type Francis, at the Gafanhoto Plant, belonging to Companhia Energética de Minas Gerais CEMIG. The specimens as well as the coating materials were supplied by the manufacturers themselves, while the testing laboratories were provided by the Federal University of Minas Gerais-UFMG. Laboratory tests have found that polymeric coatings of monos that are resistant to cavitation than carbon steel ABNT 1020 drawn and stainless steel AISI 309 L15, deposited by welding with a coated electrode. In the field observations, it was verified that the Devcon brand resin, called COMBO WEAR FC Soia, which presents the best practical performance, contrary to the expectation of the laboratory test, where it obtained the greatest loss of mass. It was also observed that the procedure is not recommended for repairs in cracks, which required more time for modeling the coating in order to restore the geometrical characteristics of the blades. This need is met with WEAR GUARD FINE LOAD resin. During the following three years, the good behavior of this resin certified the use of polymeric coatings in recovery of Francis rotors damaged by cavitation.