|
VISCOSITY |
Dynamic viscosity
Kinematic viscosity
SI Viscosity classification
SAE Viscosity classification
Coaxial Cylinder viscometer
Cone on plate viscometer
|
|
Dynamic viscosity |
|
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 proportianality factor. So, thicker oils have a
higher viscosity value causing relatively higher shear stesses at the same
shear rate. Dynamic viscosities are usually
measured under high shear conditions, for example, the cylinder viscometer
in which the viscous shear torque is measured between two cylinders.
|
|
Kinematic viscosity |
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 vertically
downwards under gravity through a small-diameter tube.
|
|
SI Viscosity classificaton |
ISO 3448, where ISO VG 22 refers to a viscosity grade
of 22 cSt ± 10% at 40°C.
|
|
SAE Viscosity Grades for Engine Oilsa
— 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.
|
SAE |
Low Temperature Viscosities |
High-Temperature Viscosities |
|
Viscosity
Grade |
Crankingb (mPa.s)
max at temp °C
|
Pumpingc (mPa.s)
max at temp °C
|
Kinematicd
(mm2/s)
at 100°C
|
High Sheare Rate (mPa.s)
at 150°C
|
| |
|
|
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 |
2.9 |
|
40 |
— |
— |
12.5 |
<16.3 |
3.7 |
|
50 |
— |
— |
16.3 |
<21.9 |
3.7 |
|
60 |
— |
— |
21.9 |
<26.1 |
3.7 |
|
|
www.tribology-abc.com |