An experimental study to detect cavitation erosion for different coated surfaces

This paper presents an experimental study to investigate the cavitation damage caused by bubble collapses in different surfaces coated by different methods. A cavitation air jet rig was constructed adapting similar specifications given in ASTM G134 Standard Test Method for cavitating liquid jet and the cavitation erosion tests were performed using this air jet rig. The tests were carried out under specified conditions in bubbly flow for the sample surfaces of CU1 (nickel-aluminium-bronze) alloy and CU3 (manganese-bronze) alloy in the cavitation test rig, which was setup for this study at ITU. The samples were coated by acrylic paint using different techniques such as dipping, spraying, brushing and acrylic paint by pen. One set of samples was left uncoated as the reference. Flow rate of the air and water, and stand-off distance of the samples were investigated and optimized. The tests were performed by intervals of 4 hours. Cavitation erosion on the surface of the samples was examined using a Reflective Light Microscope (RLM). Complementary experimental investigations, considering different test durations and coating techniques were conducted in the cavitation test rig. Results indicated a strong influence of the exposure time on the damage rate of the samples. On the other hand, it has been observed that the effect of stand-off distance is crucial on the development of cavitation erosion. The ultimate goal of the experimental study performed is try to explore similarity of the cavitation erosion formation to the erosion tests at cavitation tunnels for propellers. This will enable the replication of the propeller material and paint combination as an erosive indicator in a simpler setup.