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Viscosity
Table of Contents Physical & Chemical Properties Viscosity is the property of a fluid that causes it to resist flow, which mechanically is the ratio of shear stress to shear rate. Viscosity may be visualized as a result of physical interaction of molecules when subjected to flow. Lubricating oils have long chain hydrocarbon structures, and viscosity increases with chain length. Viscosity of an oil film, or a flowing column of oil, is dependent upon the strong absorption of the first layer adjacent to the solid surfaces, and the shear of adjacent layers. Viscosity is by far the most significant property for establishing the thickness, pressure, and temperature of an oil film in hydrodynamic lubrication (HDL) and in elastohydrodynamic lubrication (EHL). Viscosity is also a significant factor in predicting the performance and fatigue life of rolling element bearings and gears. Plastohydrodynamic lubrication accounts for the existence of hydrodynamic effects in metalworking. Calculations for oil film thickness require knowledge of the viscosity of the oil film at the temperature, pressure, and shear rate in the component. Viscosity is in the numerator of all equations predicting oil film thickness, fluid friction or hydraulic pressure. Oil film thickness increases with viscosity. Viscosity is also in equations for calculating the Sommerfeld Number, velocity in an oil film, shear stress, fluid friction force, and power loss for hydrodynamic bearings. For more information call 1-888-HERGUTH (437-4884) |
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