Changes in Permeability of Grease with Its Composition and Their Effect on Thick EHL Film Formation at Low Speeds

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  • グリースの組成によるパーミアビリティの変化および低速EHL厚膜への影響
  • グリース ノ ソセイ ニ ヨル パーミアビリティ ノ ヘンカ オヨビ テイソク EHL アツマク エ ノ エイキョウ

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Abstract

<p>The EHL film thickness decreases in reducing the entrainment speed, but with grease, it increases again after passing a minimum. This behavior was revealed in preceding works, which showed that it was caused by the increase in the viscosity of grease due to that in thickener concentration. The present work starts with the measurement of oil separation from grease by centrifuging, and its result is interpreted to the permeability as a function of the thickener concentration by employing a modified Kozeny-Carman equation. The permeability is then used as a key factor governing the Darcy flow of base oil through thickener network in a numerical analysis of the grease flow by taking it as a two-phase flow of base oil and thickener, and its result shows reasonable agreement with that of experiments by the optical interferometry. On this basis, the changes in the thickener concentration and the permeability in the inlet region to the EHL contact is discussed, and a chart showing the relation between the minimum film thickness and the initial permeability of the greases is developed, which will serve as a guide map for selecting a grease to have the desired thick EHL film formation characteristics.</p>

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