振動캐비테이션 實驗에서 被覆複合材와 金屬材간의 比較實驗 方法의 最適化

Abstract

Cavitation is a hydrodynamic phenomenon which results in the formation and collapse of vapor bubbles in a liquid.

In recent year, an equipment, an automobile, an aeroplane, ship and many industrial fields show a tendency of high output and lightweight along with industrial growth. In fluid machinery, if the speed of running fluid and rotative speed of machine become increase, the cavitation erosion happens because of partial cavitation bubbling with decreasing of static pressure and fluid shock.

Cavitation damage is encountered in a wide variety of fluid handling machinery and over a broad range of liquid pressures and temperatures.

Laboratory tests to establish the relative resistance of materials are usually made in experimental facilities standardized to their most appropriate operating conditions. The vibratory facility is the most commonly used of these and has generated most of the available data.

At the first test, cavitation test(ASTM G-32) was compared with coated composite material and metals, but coated composite material specimens appeared to generating a low bubbles due to damping vibration and having a hard time testing for many hours due to interface delamination between metal and composite material.

In this study, to use cavitation apparatus, such as the piezoelectric vibrator with 20kHz, 50㎛ to cavity generation, we compared with the traditional cavitation testing method (ASTM G-32) and modified cavitation testing method.

Throughout this test, we investigated the optimization of testing method in comparison with the coated composites and metals by vibratory cavitation test.

The main results obtained from this cavitation erosion test are as follows:

(1) Test liquid temperature of nearby specimen was measured by using digital thermometer, and observation time was done at 1min. later of testing and 1min. before of finishing. In the result, the case of standard test show up changing temperature of ±2℃, but modified test appear to change temperature of ±9℃.

(2) Weight loss between metals and coated composite materials was compared with standard test(ASTM G-32) and modified test. Weight loss of metals obtained from modified test was 40-60% lower than that of standard test. On the other hand, the weight loss of coated composite materials obtained from modified test has a tendency to decrease and below 30% than that of standard test.

(3) It was calculated to estimate weight loss of standard test with weight loss of coated composite materials obtained from modified test. And cavitation erosion between metals and coated composite materials was compared with standard test.

(4) MDPR(Mean depth penetration rate) between metals and estimated amount of coated composite materials by standard test compared with distilled-water and sea-water. Erosion rate was in the order of DL < SUS316L < SS400 ≒ Bronze < Cast iron < CL in distilled-water and in the order of DL ≒ SUS316L < SS400 ≒ Bronze < Cast iorn < CL in the sea- water.

(5) The optimized test condition looked out for comparing with temperature change and weight loss according to various space in modified test.