Kinimatic Viscosity @ 40 & 100 C Calculations / Charts

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Everyone involved in lubrications has a viscosity equivalents chart but does anyone know how they went about lining up the Kinematic Viscosity (in cSt) @ 40 & 100 C? I found the below formula for calculating the VI when you know cST@40 & 100 but nothing that inverts this equation so that I can calculate cSt@100 or cSt@40 using a set VI. Has anyone inverted this formula for use in a spread sheet?

VI = 100+(10^(LN((EXP(1.0727+0.6175*LN(cSt@100)+0.9744*(LN(cSt@100)^2)+(-0.3764)*(LN(cSt@100)^3)+0.04824*(LN(cSt@100)^4)))/cSt@40)/LN(cSt@100))-1)/0.00715

8/12/099:04 AM

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docviscMember

Jay,
I use an online calculator at
http://www.dynavis.net/viscosityindex.html

It lets you enter a visc and and a VI to calculate the other visc.

-Doc

8/13/096:58 AM

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robertcMember

A decent visual tool is at:

http://www.widman.biz/Seleccio...nes/Graph/graph.html

8/13/099:45 AM

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lamontbdumontMember

Bear in mind you vis result will be an estmate. VI is calculated from 40C & 100C viscosities. If you only have one of those results, by definition you have an assumed VI. It may be product typical, which means it's probably pretty close. If it's a general number for the product type (i.e., 95 for a mineral, 140 for a syn) it's going to be a little more wobbly.
Even if you are going from the actual new oil value, the VI can change in service as the degradation products affect the viscometrics of the oil.

8/30/097:38 AM

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johnmMember

Agree with Lamont. On a side note, regarding the link provided by Robert C: there is an error on the Metric and Viscosity Conversion. It shows 2.54 milimeters as the equivalent to 1 inch. In fact, 1 inch is equivalent to 2.54 centimeters or 25.4 milimeters.

9/4/0912:10 AM

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robertcMember

Never used that page, but you are correct.

9/8/098:24 AM

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akakeithMember

Here is the same equation solved for cST@40 =EXP(((1.0727)+((0.6175*(LN(H8)))+(0.9744*(LN(H8)^2))+((-0.3764)*(LN(H8))^3)+(0.04824*(LN(H8)^4)))))/EXP(LN(H8)*LOG(0.00715*(L8-100)+1))

H8 = cST@100
L8 = VI

8/17/101:33 PM

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