Ultrasonic Measurement of Film Thickness in Partial Water Repellent Full-Flat Thrust Bearing

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  • 部分撥水処理を施した平坦なスラスト軸受の超音波膜厚測定

Abstract

A flat thrust bearing, that has a structure which generates a pressure flow by using the discontinuity of shear flow rate between a water-repellent surface and a hydrophilic surface, was developed. In this study, ultrasonic pulse echo technique was employed for the investigation of the film thickness influenced by the static contact angle θ (≅10°, 60°, 110°) and the water-repellent area ratio β(=0.25, 0.5, 0.75). Since the occurrence of the slip of water at a water-repellent surface having 110° of static contact angle is easy, observed lubrication film thickness is thicker than that of θ≅60°, and the film thickness at θ≅10° becomes thinnest. The film thickness is different by the area ratio β of water-repellent region against a bearing surface area, and it thickens in order of β=0.25, 0.75, 0.5. Thickest film is formed around of the β where the area of water-repellent region is equal to hydrophilic area. Calculation results of the infinite long bearing approximation, which considered the slip on a wall, agree with the characteristics of measured film thickness mentioned above. Therefore this thrust bearing operates under similar mechanism with conventional bearing having lubrication surfaces which shapes a wedge film. The order of measured film thickness agrees with order of satisfactory bearing of friction characteristics in each bearing tested. Consequently it can be conclude that the main factor of which coefficient of friction under a same load and speed is different by static contact angle θ and water-repellent area ratio β is a variance of film thickness in each bearing.

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