|Standards||ASTM D 445|
To determine the ISO viscosity grade of a lubricant, put simply, to determine its resistance to flow, essentially “thickness”.
Oil samples are passed through a capillary tube which is immersed in an oil bath at a sustained temperature.
Each capillary has a reservoir with a sensor at either end; this effectively acts as a “speed trap” to the oil passing through.
From the time taken to pass between the sensors, combined with the dimensions of the capillary tube, the viscosity of the sample can be generated.
Viscosity testing is a useful tool for determining if the correct grade of oil is currently in use for a given application. It can help determine potential oil mixes, or monitor variations in the oil due to additive shear, oxidation, thermal degradation, fuel dilution etc.
Samples are typically run at 40, 60 and 100 degrees, however any temperature between ambient and 100 degrees can be selected.
The viscosity index can also be determined from this data when both 40 and 60 degree tests are performed. This tells us about how the lubricant might behave at a range of temperatures.
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