Erosion test due to impingement of a cavitating jet was performed using plastic and metal specimens. The experimental conditions were specified by the following : supply pressure of 9.9 MPa, cavitation coefficient of 0.02, stand-off distance of 25.0 mm and test fluid being tap water. The specimens tested were seven kinds of metals and six kinds of plastics. The metal specimens were made from austenitic (SUS316 in JIS) and martensitic (SUS403, SUS440B) types of stainless steel, precipitation hardening stainless steel (SUS630-H900, SUS630-H1075), stellite (No. 6) and aluminum alloy (A5056BD). The plastic specimens were made from polytetrafluoroethylene matrix composite (pure PTFE, PTFE reinforced with 60% bronze, PTFE reinforced with both 5% graphite and 20% glass fiber), polyetheretherketone (PEEK-450FC30, PEEK-EXL6) and polyimide resin (AURUM-JCL4030). These specimens made from aluminum alloy, PTFE, PEEK, stainless steels and stellite were eroded in that order. Erosion resistance was evaluated by the indices composed of their hardness, elastic modulus and mechanical strength. A modified ultimate resilience was proposed as a normalized erosion index and it showed good correlation.

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In this paper, the hysteresis characteristics of a commercial direct drive hydraulic servovalve are investigated experimentally in cases by adding dither into a low speed driving signal, a PWM drive and with fluid flowing through the valve. It is considered that hysteresis is caused by Coulomb friction between the spool and the sleeve. In the case of adding a dither signal, computer simulation was also conducted. Simulation results show that the average friction force approaching zero is an important factor in hysteresis reduction. Experimental results show that the fiction characteristic obtained under a semi-static condition changes because of spool vibration in a radial direction, which is caused by dither, PWM or oil flow through the valve. For a direct drive hydraulic servovalve, it is considered that a dither's hysteresis reducing effect can not be discussed by focusing only on velocity amplitude.

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The method referring to the ISO standard concerned with the purpose of measuring effective area is frequently used to determine the flow rate characteristics of a test valve. This method is to measure the flow rate through a valve and differential pressure across the test valve. However, the experiment and calculation is complex and the accuracy of the method depends to a great extent on the precision of the flow meter. On the other hand, a simple method to measure the effective area is defined by JIS B 8373. In this method, compressed air is discharged from chamber through the test valve without using flow meter. The effective area is measured indirectly from the pressure response of air in the chamber. Due to discharging, the chamber air temperature drops about 40 [K], and the cool air enters the pipe but recovers because of the heat transfer between air and the pipe. This study shows the effect of connecting pipe air temperature recovery on the measurement of effective area. In this research, experiments and simulation were carried out to estimate the air temperature recovery effect. Generally, the connecting pipe effect caused by air temperature recovery is about 2% to 3%.

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In manufacturing technology, it is a dominant tendency in recent years that machine tools for machining, grinding and so on, employ electric operated actuators such as a servo-motor equipped with a ball screw. Some problems of these electric driving systems are, they are excessively large-sized with complex machinery and expensive, as seen in their application to, for example, NC-machine. In order to solve these problems, this study aims to develop a precision driving system actuated by a hydraulic cylinder. The hydraulic driving system consists of a cylinder and four ON/OFF solenoid valves. The valves are the same as those used in a fuel injector of an automobile and thus are capable of high speed switching such as 1.5 ms. It was confirmed in experiments that the developed system had a moving resolution of 1.2 μm and, as a result, was applicable to a precision driving table for micro processing.

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