CAVITATION EROSION IN METALLIC MATERIALS USING THE ROTATING DISK DEVICE Gil Bazanini e José Divo Bressan
Resumo: In the rotating disk device, a steel disk with cavitation inducers and specimens fixed on it rotates inside a water chamber to provide the cavitating flow and erosion. In this work, a new concept of the horizontal axis rotating disk device is presented and discussed as well as some preliminary results obtained from its operation. The purpose of the device is to generate the bubbles that will erode the specimens fastened in the disk surface and close to the bubbles inducers. To prevent vibration problems, each pair of holes and specimens are diametrically opposite.
When bubbles collapse near solid surfaces, damage may occur. Two are the already known damage mechanisms: liquid micro-jets impingement and shock waves. The micro-jets are caused by the bubble splitting in two parts near the solid surface (influenced by the surface proximity) in the final stages of the collapse and the shock waves are caused by instant variable pressure fields (the time necessary for the collapse is about few milliseconds). These micro-jets and shock waves are responsible for loss of material from the surface, basically by wear failure.
After several hours of device operation in cavitating conditions, the specimens are weighted to obtain the mass loss by erosion, comparing it to the initial weight. Pitting formation resulting from the erosion process can also be seen with the aid of a scanning electronic microscope. Working with different metallic materials, the relative resistance to erosion by cavitation can be evaluated and comparison with existing results is made. In the present work, erosion and pitting formation in aluminum and brass specimens as well as mass loss due to erosion by the cavitation phenomena was observed and measured.
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