Cavitation Wear of Polymers

The cavitation wear tests of six polymers were carried out. There were polymers of different classes chosen: Teflon, high-density polyethylene, plexiglass, polyamide, polyurethane, epoxy compound K-153. The cavitation attack was executed in mild fresh water, the latter was kept at temperature of 20 ± 3 ℃. The test apparatus was an ultrasonic magnetostrictive device, the frequency and the amplitude of horn butt-end oscillations being equal to about 22 kHz and 28 μm respectively. The polymers samples were in the shape of cylinders. The test surfaces were the sample flat ends, which were ground and polished. The Shore hardness, sound speed and density of the polymers were measured before putting them to test. During the experiments the mass loss and the roughness of the test surfaces were measured and dependences of the mass loss and arithmetical mean deviation of the assessed profile on cavitation attack duration were built. The wear of all the polymers tested occurs with incubation period. In order to avoid the rough error in the determination of the incubation period the latter was evaluated by profilometry. There was the tough-brittle transition indicated on the dependences of the incubation period and wear rate on the cavitation attack duration, and in the tough failure zone the influence of the hardness on the wear resistance is the opposite to that in the brittle failure zone. In both the tough failure zone and the brittle failure zone the cavitation wear resistance goes down as the acoustic impedance increases, however the polymers suffering brittle damage in cavitation attack and ones suffering tough damage form the separate dependences of wear resistance on the acoustic impedance. The acoustic impedance has strong influence on the wear resistance of polymers in the brittle failure zone and weak influence in the tough failure zone. To secure the highest cavitation resistance it is necessary to choose the polymers having the Shore hardness as nearly as possible to the tough-brittle transition, that is the Shore hardness has to be in value from 65 to 70.

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