Viscosity Classifications

Dynamic viscosity
Kinematic viscosity
Viscosity Index (VI)
ISO 3448 Viscosity classification
AGMA 9005-D94 Viscosity classification for gear oils
SAE J300 Automotive Viscosity classification, engine oils
SAE J306 Automotive Viscosity classification, gear oils
Comparative Viscosity Classifications
Dynamic viscosity [mPaˇs = cP]
The dynamic viscosity is the viscosity that relates shear stress τ and shear rate du/dz in a fluid, i.e. τ=η du/dz. The viscous shear stress τ is proportional to the shear rate, the dynamic viscosity η being the proportionality factor. So, thicker oils have a higher viscosity value causing relatively higher shear stresses at the same shear rate.

Dynamic viscosities are usually measured under high shear conditions, for example, the cone on plate or cylinder viscometer in which the viscous shear torque is measured between two cylinders.

With the viscosity known at two reference temperatures the viscosity can be calculated for intermediate temperatures with specific interpolation functions those from Reynolds or Vogel & Cameron.

Kinematic viscosity [mm2/s = cSt]
The kinematic viscosity is the quotient of the dynamic viscosity η and the fluid density ρ, ν=η/ρ. The physical principle of measurement is based on the rate at which a fluid flows under gravity through a capillary tube.

With the viscosity known at two reference temperatures the viscosity can be calculated for intermediate temperatures using the interpolation function of Ubbelohde-Walther, which is adopted by ASTM D341.

Viscosity Index ISO 2909 / ASTM D2270-226
In many cases the temperature dependency is expressed in the Viscosity Index standardized by ISO 2909 / ASTM D2270-226.

ISO 3448 Viscosity classification
The ISO viscosity classification is recommended for industrial applications. The reference temperature of 40 °C represents the operating temperature in machinery. Each subsequent Viscosity grade (VG) within the classification has approximately a 50% higher viscosity, whereas the minimum en maximum values of each grade ranges ą10% from the mid point. For example, ISO VG 22 refers to a viscosity grade of 22 cSt ą 10% at 40°C. The viscosity at different temperatures can be calculated using the viscosity at 40°C and the viscosity index (VI), which represents the temperature dependency of the lubricant.

 ISO 3448 Viscosity class Kinematic viscosity at 40°C [mm2/s = cSt] Mid-point Minimum Maximum ISO VG 2 2.2 1.98 2.42 ISO VG 3 3.2 2.88 3.52 ISO VG 5 4.6 4.14 5.06 ISO VG 7 6.8 6.12 7.48 ISO VG 10 10 9.0 11.0 ISO VG 15 15 13.5 16.5 ISO VG 22 22 19.8 24.2 ISO VG 32 32 28.8 35.2 ISO VG 46 46 41.4 50.6 ISO VG 68 68 61.2 74.8 ISO VG 100 100* 90 110 ISO VG 150 150 135 165 ISO VG 220 220 198 242 ISO VG 320 320 288 352 ISO VG 460 460 414 506 ISO VG 680 680 612 748 ISO VG 1000 1000 900 1100 ISO VG 1500 1500 1350 1650
Any viscosity can be obtained with a mixture of two ISO VG base oils

AGMA 9005-D94 Viscosity classification for gear oils
 AGMA lubricant no. viscosity mPa.s at 40°C Equivalent ISO viscosity class (ISO 2448) EP gear oils AGMA min max lub. no. 0 28.8 35.2 32 1 41.4 50.6 46 2 61.2 74.8 68 2 EP 3 90 110 100 3 EP 4 135 165 150 4 EP 5 198 242 220 5 EP 6 288 352 320 6 EP 7C 1) 414 506 460 7 EP 8C 1) 612 748 680 8 EP 8AC 1) 900 1100 1000 8 A EP

SAE Viscosity Grades for Engine Oils1  SAE J300 Dec 99
The actual viscosity grade of a lubricant is determined by the Society of Automotive Engineers, for example SAE-15W40 for a multigrade oil and SAE-40 for a monograde oil. The first number (15W) refers to the viscosity grade at low temperatures (W from winter), whereas the second number (40) refers to the viscosity grade at high temperature.

 Automotive Lubricant Viscosity Grades1 Engine Oils  SAE J 300, Dec. 1999 SAE Low Temperature Viscosities High-Temperature Viscosities Viscosity Grade Cranking2 (mPa.s) max at temp °C Pumping3 (mPa.s) max at temp °C Kinematic4 (mm2/s) at 100°C High Shear5 Rate (mPa.s) at 150°C, 10/s min max min 0W 6200 at -35 60 000 at -40 3.8   5W 6600 at -30 60 000 at -35 3.8   10W 7000 at -25 60 000 at -30 4.1   15W 7000 at -20 60 000 at -25 5.6   20W 9500 at -15 60 000 at -20 5.6   25W 13 000 at -10 60 000 at -15 9.3   20   5.6 <9.3 2.6 30   9.3 <12.5 2.9 40   12.5 <16.3 2.96 40   12.5 <16.3 3.77 50   16.3 <21.9 3.7 60   21.9 <26.1 3.7
 1 All values are critical specifications as defined by ASTM D3244 2 ASTM D5293 3 ASTM D4684. Note that the presence of any yield stress detectable by this method constitutes a failure regardless of viscosity. 4 ASTM D445 5 ASTM D4683, CEC L-36-A-90 (ASTM D 4741) or ASTM DS481 6 0W-40, 5W-40 & 10W-40 grades 7 15W-40, 20W-40, 25W-40 & 40 grades

SAE Viscosity of Automotive Gear Oilsa  SAE J306 Jan 2005
 Automotive Lubricant Viscosity Grades Gear Oils  Except SAE J 306, 1998 SAE Viscosity Grade Maximum Temperaturefor a viscosity of150,000 cP (°C) Minimum Viscosityat (cSt) a 100°C Maximum Viscosityat (cSt) a 100°C ASTM D 2983 ASTM D 445 ASTM D 445 70W -55 4.1 -- 75W -40 4.1 -- 80W -26 7.0 -- 85W -12 11.0 -- 80 -- 7.0 <11.0 85 -- 11.0 <13.5 90 -- 13.5 <18.5 110 -- 18.5 <24.0 140 -- 24.0 <32.5 190 -- 32.5 <41.0 250 -- 41.0 --
 1 Using ASTM D 2983, additional low temperature viscosity requirements may be appropriate for fluids intended for use in light-duty synchronized manual transmission. 2 Limit must also be met after testing in CEC l-45-T-93, Method C (20 hours) 3 The precision of ASTM D 2983 has not been established for determinations made at temperatures below 40 °C. This fact should be taken into consideration in any producer-consumer relationship.

Comparative Viscosity Classifications
 ISO 3348 Industrial oils AGMA 9005-D94 Gear oils SAE J300 Engine oils SAE J306  Gear oils
 1500 250 1000 8A 680 8 140 460 7 320 6 60 90 220 5 50 150 4 40 85 W 100 3 30 80W 68 2 20 75W 46 1 32 0 15W 22 10W 15 5W, 10W 10 7 3 2
ISO and AGMA are specified at 40°C. SAE 75w, 80w, 85, 5w, & 10w are
specified at low temperature. SAE 90 to 250 and 20 to 50 are specified at 100 deg C. Viscosities can be related horizontally assuming 96 VI single grade oils.

Rule of Thumb:  SUS @ 100ēF / 5 = cSt @ 40ēC.

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