Viscometers based on wave mechanics measure absolute viscosity times density, λ = ηρ, and lubricant temperature. By using the ISO-VG (ASTM D2422) classification as a continuous (non-banded) system and fitting data for classes of lubricants at Patm, equations relating (a) absolute viscosity times density to (b) temperature and (c) ISO-VG number have been developed with good practical accuracy.
Five classes of lubricants have been correlated with ISO-VG numbers. They are paraffinics, naphthenics, PFPE (perfluoroalkylpolyether), diesters and polyol esters.
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