著者

橋村 真治 小松 恭一 大津 健史 関戸 裕二郎

出版者

一般社団法人 日本トライボロジー学会

雑誌

トライボロジスト (ISSN:09151168)

巻号頁・発行日

vol.62, no.3, pp.205-216, 2017-03-15 (Released:2017-03-16)

参考文献数

12

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In recent years, self-loosening detail mechanisms of bolted joints had been revealed using three dimensional FE analysis in which the bolts and the nuts have almost perfect configurations geometrically. However the configurations of actual bolts and nuts have certainly errors. Wear on contact surfaces also occurs in the actual bolted joint. Hence it is not easy to accurately simulate the actual bolted joint by only FEM. In this study, an influence of lubricants on self-loosening characteristics have been investigated in order to understand actual phenomena in self-loosening process. The self-loosening tests for a hexagon head cap screw M10 due to transverse vibration were performed under lubricated conditions by Machine oil ISO VG46, Molybdenum disulfide grease and Polyisobuthylene which is used as a special lubricant for bolt tightening. A bearing surface configuration of the bolt was controlled in this study. The results showed that the bolted joints lubricated by Polyisobuthylene had a higher resistance for self-loosening than the bolted joints lubricated by Molybdenum disulfide grease and Machine oil ISO VG46. The number of cycle until loosening depended on bearing surface configurations.

著者

橋村 真治 伊藤 隼人 小松 恭一 大津 健史

出版者

一般社団法人 日本トライボロジー学会

雑誌

トライボロジスト (ISSN:09151168)

巻号頁・発行日

vol.61, no.12, pp.882-892, 2016-12-15 (Released:2016-12-15)

参考文献数

14

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It is well known that a main cause of tightening error on the torque control method is changes of the frictional coefficients in thread surfaces and bearing surfaces in bolt tightening. It has been shown in the previous study that the frictional coefficients depend on surface roughness of contact surface, lubrication conditions and bolt configuration errors. The frictional coefficients can be changed by the bolt configuration errors such as a bend of bolt shank and inclination of bolt bearing surface, if large wear and seizure do not occur on the lubricated surfaces.In this study, an influence of the squareness error of bolt bearing surface on the tightening accuracy has been investigated. Results clearly showed that the squareness error of bearing surface causes variations of torque coefficients and the clamping force error. It was shown by FEM analysis that the variation of torque coefficient between bearing surfaces is caused by change of an apparent frictional coefficient. Tightening accuracy also depended on the squareness error of bearing surface.

著者

大津 健史 小松 恭一 橋村 真治 今戸 啓二

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.855, pp.17-00319-17-00319, 2017 (Released:2017-11-25)

参考文献数

27

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This paper describes that the film formation and shear properties of screw tightening lubricant PIB (Polyisobutylene) under the oil starvation condition. The point contacted pure sliding tests were conducted, and the film thickness was measured using the interferometry method with the spacer layer. The result showed that the starvation region occurred at the inlet of the conjunction becomes large with time. It was also shown in the initial time of the test that the film thickness decreases due to the oil starvation, however, the thickness is thicker than the value equivalent to surface roughness. The friction coefficient depended on the starved area, and that showed the constant value of 0.16-0.17 in the fully starved condition. The relationship between the friction coefficient and the shear rate suggested that the coefficient in the high shear rate condition is the constant value, that revealed the film may be changed to the solid like film with the high shear strength in the fully starved condition. The long term test showed that the breakdown of film is appeared at about 120 s and then the wear area expands in the remainder of the test. The test results suggested that the PIB lubrication film has the high shear strength and enable to protect the contact surface in the tightening screw from the direct contact and the wear.

著者

大津 健史 西田 一樹

出版者

一般社団法人 日本トライボロジー学会

雑誌

トライボロジスト (ISSN:09151168)

巻号頁・発行日

vol.61, no.2, pp.127-136, 2016-02-15 (Released:2016-05-23)

参考文献数

27

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This paper describes that the behavior of growth of cavitation formed in the journal bearing and the effect of cavity growth on the bearing performance. The journal bearing test apparatus in which the bearing was made of transparent acrylic plastic was used, and cavitation in lubrication film was observed by the fluorescent method in this study. Results show that the cavity is formed by the bubble occurred at the edge of bearing, and the angle of start and end position of cavity depends on applied weight. The cavity grows with time at a constant load of 45 N because the cavity coalesces with small cavities occurred at the edge of bearing, and the eccentricity ratio and the attitude angle are also changed during the time of growth. It is also shown by a numerical analysis that the cavity growth is related with the oil flow generated by the negative pressure at the outlet of the cavity.