ASTM D6080 for defining the viscosity characteristics of hydraulic fluids
1. Scope
1.1 This practice is applicable to all hydraulic fluids based either on petroleum, synthetic, or naturally-occurring base stocks. It is not intended for water-containing hydraulic fluids.
1.2 For determination of viscosities at low temperature, this practice uses millipascal•second (mPa•s) as the unit of viscosity. For reference, 1 mPa•s is equivalent to 1 centipoise (cP). For determination of viscosities at high temperature, this practice uses millimetre squared per second (mm2/s) as the unit of kinematic viscosity. For reference, 1 mm2/s is equivalent to 1 centistoke (cSt).
1.3 This practice is applicable to fluids ranging in kinematic viscosity from about 4 to 150 mm2/s as measured at a reference temperature of 40°C and to temperatures from -50 to +16°C for a fluid viscosity of 750 mPa•s.
NOTE 1 - Fluids of lesser or greater viscosity than the range described in 1.3 are seldom used as hydraulic fluids. Any mathematical extrapolation of the system to either higher or lower viscosity grades may not be appropriate. Any need to expand the system should be evaluated on its own merit.
2. Referenced Documents
2.1 ASTM Standards:
D445 Test Method for Kinematic Viscosity of Transparent and Opaque Liquids (and the Calculation of Dynamic Viscosity)
D2270 Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 and 100°C
D2422 Classification of Industrial Fluid Lubricants by Viscosity System
D2983 Test Method for Low-Temperature Viscosity of Lubricants Measured by Brookfield Viscometer
D5621 Test Method for Sonic Shear Stability of Hydraulic Fluids
E 29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
2.2 Society of Automotive Engineers (SAE) Standards:
J300 Engine Oil Viscosity Classification
J306 Axle and Manual Transmission Lubricant Viscosity Classification
3. Terminology
3.1 Definitions:
3.1.1 viscosity - the ratio between the applied shear stress and shear rate.
3.1.1.1 Discussion - Viscosity is sometimes called the coefficient of dynamic viscosity. This coefficient is a measure of the resistance to flow of the liquid.
3.1.2 kinematic viscosity - the ratio of the viscosity to the density of a liquid.
3.1.2.1 Discussion - Kinematic viscosity is a measure of the resistance to flow of a liquid under gravity.
3.1.3 shear stress - the motivating force per unit area for fluid flow.
3.1.4 shear rate - the velocity gradient in fluid flow.
3.1.5 Newtonian fluid - a fluid that at a given temperature exhibits a constant viscosity at all shear rates or shear stresses.
3.1.6 non-Newtonian fluid - a fluid that exhibits a viscosity that varies with changing shear stress or shear rate.
3.1.7 density - the mass per unit volume.
3.1.8 hydraulic fluid - a fluid used in hydraulic systems for transmitting power.
3.1.9 viscosity index (VI) - an arbitrary number used to characterize the variation of the kinematic viscosity of a fluid with temperature.
3.1.10 shear degradation - the decrease in molecular weight of a polymeric thickener (VI improver) as a result of exposure to high shear stress.
3.1.11 in-service viscosity - the viscosity of fluid during operation of a hydraulic pump or circuit components.
3.1.12 shear stability - the resistance of a polymer-thickened fluid to shear degradation.
