Shin-Sung Yoo

Frictional Characteristics of Sub-100-

The frictional characteristics of ~62-μm diameter borosilicate glass balls used as rolling elements for a miniature electromagnetic linear actuator were assessed. The glass balls were placed between two silicon plates of the actuator with linear bearing tracks fabricated in the shape of V-grooves on the silicon surface. Rolling friction experiments were conducted using the electromagnetic linear actuator as well as a tribotester. It was shown that the glass balls were effective in generating a low friction coefficient of ~0.01 over 11 million cycles under a load of 6.6 mN. For the durability test using the tribotester, a relatively high load of 245 mN was applied. In this case, evidence of silicon surface damage could be found. The feasibility of using Au as a solid lubricating film on the silicon surface was investigated. It was found that the friction coefficient and surface damage depended on the thickness of the film, which was varied from 7~20 nm. It was postulated that the low shear strength of Au aided in reducing the friction coefficient from ~0.017 to ~0.013. With improved adhesion of the Au coating on silicon, the use of sub-100-μm borosilicate glass balls as rolling elements for miniature actuators seems promising.

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Friction of mechanical components affects the life and reliability of various machines. In order to improve the wear resistance of mechanical components, grease has been used as a lubricant. However, depending on the operating condition of the machine, the grease may be contaminated with water, which lowers the its lubricating ability. In this work, the effect of the water content on the lubricating ability of grease was investigated. Friction tests using grease were performed between a stainless steel ball and an acrylic plate. Water content in the grease was varied (0, 5, 10 wt.%). It was found that the contact angle varied due to the addition of water in the grease. The friction and wear of the specimens were assessed with respect to amount of water content. Wear of the specimens was relatively severe when water was added. A water content of 10 wt.% resulted in significant lubricant degradation.