Credibility Evaluation of Sand-Casting Technique for Manufacturing Francis Runner

Francis turbine with its intricate design and the critical nature of its components, involves several complexities and challenges for manufacturing. Francis runners are usually fabricated using high-quality alloy steel. In this study, a 2 kW model Francis runner was manufactured from brass material with sand casting. 3D printing technology was used to create separate molds for the hub, shroud, and runner blade of the Francis turbine. Each component was then sand cast and later joined by brazing. Compared to traditional casting techniques this approach proved to be faster and more cost-effective. Moreover, the defects encountered in the turbine components achieved through the method employed were observed to be less compared to that of investment casting used in previous models. The accuracy of the fabricated model was checked by conducting 3D scanning using the highly precise EinScan HX 3D scanner with a precision of 0.1 mm. The comparisons were made between the 3D scan and the original design. It was found that the deviations on the fabricated runner dimensions as compared to the original designs were below 2 mm. The efficiency measurement of the runner was made at a low head of 4.3 meters and the maximum efficiency obtained was 51.5% at 35% opening of guide vanes. Overall, this method of fabrication proved to be effective in terms of cost and time required for fabrication. This method could be a valuable alternative for smaller-scale turbine production. Further evaluation will be necessary for full-scale commercial applications of this method using high-quality alloy steel.