Resumo: Rotores de turbinas hidráulicas estão sujeitos a falhas ou trincas ou desgaste por cavitação. Atualmente, os rotores são fabricados em aço carbono ou aço inoxidável martensítico. Os reparos de regiões desgastadas ou trincadas são normalmente feitos por processos de soldagem a arco elétrico. Cada material de fabricação do rotor e/ou tipo de reparo necessita de procedimento específico, critérios de inspeção e aceitação adequados e precauções para garantir o sucesso do reparo, bem como prevenir futuras incidências precoces de falhas. Materiais de adição resistentes ao desgaste têm sido aplicados por soldagem ou aspersão térmica, sendo que essa última técnica não altera características metalúrgicas e propriedades mecânicas do material dos rotores. Por diversos anos, as empresas Copel GeT, Lactec, UTFPR e UFPR cooperam e tem colaborado com estudos de diferentes técnicas, metodologias de aplicação e processos de reparo de rotores hidráulicos. Este artigo objetiva apresentar uma breve compilação e exemplos de resultados obtidos nesses diferentes estudos aplicados a rotores reais.

Abstract: Hydraulic runners are susceptible to failures by cracks or wear by erosion, corrosion, or cavitation. The modern runners are fabricated in carbon steel and martensitic stainless steel. Arc welding processes normally do the repair of eroded areas, or cracked parts. Each material or type of repair needs specific criteria, procedures, and precautions to guarantee their success and prevent future issues, like the recurrence of the cracks or reduction of the useful life of the runner by modifications of the original material. Wear-resistant coatings are applied by welding or by thermal spray processes, considering this last one has no metallurgical interaction with the material of the runner, keeping the original properties of the material. For several years the companies Copel GeT, Lactec, UTFPR, and UFPR collaborate on the study of different techniques, methods, and processes to repair hydraulic runners, this work aims to present a short compilation, and examples of some results obtained applied on real runners.

AbstractHVOF thermal spray process produces coatings with low porosity and low oxide content, as well as high substrate adhesion. Small variations on the parameters of the HVOF process can generate coatings with different characteristics and properties, which also is chemical composition depended of the alloy. FeMnCrSi alloy is a cavitation resistant class of material with a great potential for HVOF deposition use. The main goal of this article is to study the influence of some HVOF parameters deposition, as standoff distance, powder feed rate and carrier gas pressure on three different alloys. FeMnCrSi experimental alloys with some variations in nickel and boron content were studied. Taguchi experimental design with L9 orthogonal array was used in this work. Porosity, oxide content, tensile adhesion strength and microhardness of the coatings were evaluated. The results indicated that all factors have significant influence on these properties. Chemical composition of the alloys was the most important factor, followed by the carrier gas pressure, standoff distance and powder feed rate. The addition of Ni, produces coatings with lower levels of oxide content and porosity. An experiment with improved parameters was conducted, and a great improvement on the coating properties was observed.