Viscosity index

Viscosity index

Viscosity index is a petroleum industry term. It is a lubricating oil quality indicator, an arbitrary measure for the change of kinematic viscosity with temperature. The viscosity of liquids decreases as temperature increases. The viscosity of a lubricant is closely related to its ability to reduce friction. Generally, you want the thinnest liquid/oil which still forces the two moving surfaces apart. If the lubricant is too thick, it will require a lot of energy to move the surfaces (such as in honey); if it is too thin, the surfaces will rub and friction will increase.

As stated above, the Viscosity Index highlights how a lubricant's viscosity changes with variations in temperature. Many lubricant applications require the lubricant to perform across a wide range of conditions: for example, in an engine. Automotive lubricants must reduce friction between engine components when it is started from cold (relative to engine operating temperatures) as well as when it is running (up to 200 °C). The best oils (with the highest VI) will not vary much in viscosity over such a temperature range and therefore will perform well throughout.

The VI scale was set up by the Society of Automotive Engineers (SAE). The temperatures chosen arbitrarily for reference are 100 °Fahrenheit (40 °C) and 210 °F (100 °C). The original scale only stretched between VI=0 (worst oil, naphthenic) and VI=100 (best oil, paraffinic) but since the conception of the scale better oils have also been produced, leading to VIs greater than 100 (see below).

VI improver additives and higher quality base oils are widely used nowadays which increase the VIs attainable beyond the value of 100. The Viscosity Index of synthetic oils ranges from 80 to over 400.


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • viscosity index — klampos indeksas statusas T sritis Standartizacija ir metrologija apibrėžtis Sutartinės skalės skaičius, apibrėžiantis alyvos klampos kitimą kintant temperatūrai. atitikmenys: angl. viscosity index vok. Viskositätsindex, m rus. индекс вязкости, m …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

  • viscosity index — klampos indeksas statusas T sritis chemija apibrėžtis Sutartinės skalės vienetas; rodo skysčio (ppr. naftos ar jos perdirbimo produktų) priklausomybę nuo temperatūros. atitikmenys: angl. viscosity index rus. индекс вязкости …   Chemijos terminų aiškinamasis žodynas

  • viscosity index — noun : an arbitrary number assigned as a measure of the constancy of the viscosity of a lubricating oil with change of temperature such that a high index indicates that the viscosity changes little with temperature * * * Auto., Mach. an arbitrary …   Useful english dictionary

  • viscosity index — [1] (VI) A measure of how the viscosity of a liquid (especially oil) changes with temperature: the higher the VI, the smaller the change of viscosity with temperature [2] A measure of an oil s ability to resist changes in viscosity when heated …   Dictionary of automotive terms

  • viscosity index — noun Date: 1929 an arbitrary number assigned as a measure of the constancy of the viscosity of a lubricating oil with change of temperature with higher numbers indicating viscosities that change little with temperature …   New Collegiate Dictionary

  • viscosity index — Auto., Mach. an arbitrary scale for lubricating oils that indicates the extent of variation in viscosity with variation of temperature. [1935 40] * * * …   Universalium

  • viscosity index — viscos′ity in dex n. mac aum an arbitrary scale for lubricating oils that indicates the extent of variation in viscosity with variation of temperature …   From formal English to slang

  • Viscosity index — Коэффициент вязкости …   Краткий толковый словарь по полиграфии

  • viscosity index improver — An oil additive which reduces thinning at high temperature, thus improving the VI …   Dictionary of automotive terms

  • viscosity — index adhesion (affixing) Burton s Legal Thesaurus. William C. Burton. 2006 …   Law dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”