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USEFUL
INFORMATION
The following might be helpful
and many suppliers also have very good information on
their websites. It is for info only and has not been
reviewed for accuracy or does this constitute any
particular recommendation or action.
US Army Corp of Engineers Lubrication Manual
New SKF program for
grease relube intervals
'Grease Basic'
by Jeremy Wright, Machinery Lubrication
Magazine, May 2008, 4 pages, 2 references
Society of Tribologists and
Lubrication Engineers Park Ridge, IL
STLE Toronto Section
2005 STLE Awards - re local member Ken J. Brown
VISCOSITY
ONE OF
THE MOST IMPORTANT CHARACTERISTICS OF A LUBRICANT IS ITS
VISCOSITY. VISCOSITY IS THE MAIN FACTOR AFFECTING
THE ABILITY OF A LUBRICATING FLUID TO REDUCE FRICTION
AND PREVENT WEAR. SELECTING THE CORRECT VISCOSITY
LUBRICANT FOR A PARTICULAR APPLICATION IS
FUNDAMENTAL.
TOO LOW
A VISCOSITY AND EXCESSIVE FRICTION AND WEAR MAY RESULT
FROM METAL-TO-METAL CONTACT.
TOO
HIGH A VISCOSITY AND FLOW TO CRITICAL AREAS MAY BE
IMPEDED AND EXCESSIVE ENERGY LOSSES MAY OCCUR AS A
RESULT OF VISCOUS DRAG.
REF: ESSO
KINEMATICS
THAT BRANCH OF MECHANICS THAT
DEALS WITH MOTION IN THE ABSTRACT, WITHOUT REFERENCE TO
THE FORCE OR MASS.
REF: WEBSTER'S NEW
WORLD DICTIONARY
KINEMATIC VISCOSITY
COMMONLY USED TO DEFINE LUBRICANT
VISCOSITY AND IS MEASURED BY TIMING THE FLOW OF A FIXED
VOLUME OF OIL THROUGH A CAPILLARY TUBE UNDER THE FORCE
OF GRAVITY.
THE
OFFICIAL SI UNIT IS SQUARE METERS PER SEC (m2/s).
FOR
LUBRICANTS THE CENTISTOKE (cSt) WHICH IS EQUIVALENT TO
SQUARE MILLIMETRES PER SECOND (mm2/s), IS MORE GENERALLY
USED.
OTHER
UNITS ARE SAYBOLT UNIVERSAL SECONDS (SUS), REDWOOD
SECOND AND ENGLER DEGREE.
| VISCOSITY |
= SHEAR STRESS / SHEAR
RATE |
| |
= (FORCE / AREA) /
(SPEED / THICKNESS) |
| |
= (N / m2) / ((m/s)
/ m) |
| |
= N۰s / m2 |
| |
= Pa۰s |
DYNAMIC
VISCOSITY
MEASURED USING A ROTATIONAL VISCOMETER
AND FOR THE RANGE OF VISCOSITIES NORMALLY ENCOUNTERED
WITH LUBRICANTS THE MILLIPASCAL SECOND (mPa@s) IS
USED. HOWEVER, FOR OILS IT HAS BEEN TRADITIONAL TO
USE CENTIPOISE (cP) WHICH IS EQUIVALENT.
SWITCHING
SYSTEMS
TO GO FROM
DYNAMIC TO KINEMATIC VISCOSITY, IT IS NECESSARY TO KNOW
THE DENSITY OF THE OIL.
DYNAMIC
VISCOSITY = KINEMATIC VISCOSITY X DENSITY
EXAMPLE
AN OIL
HAS AN KINEMATIC VISCOSITY OF 136 cSt AT 100°C.
WHAT IS THE ABSOLUTE VISCOSITY?
FIRST
THE DENSITY IS 0.88 g/ml, WHICH IS TYPICAL OF MANY
MINERAL OILS:
136 cSt X 0.88 g/ml = 120 cP
|
ISO VISCOSITY
GRADES* |
|
VG** |
MID-POINT |
RANGE |
| |
cSt @
40°C |
cSt @
40°C |
|
32 |
32 |
28.8 -
35.2 |
|
46 |
46 |
41.4 -
50.6 |
|
68 |
68 |
61.2 -
74.8 |
|
100 |
100 |
90-110 |
|
150 |
150 |
135-165 |
|
220 |
220 |
198-242 |
|
320 |
320 |
288-352 |
|
460 |
460 |
414-506 |
|
680 |
680 |
612-748 |
|
* Full range
goes from 2 to 1500 cSt
** Values are all
±10% | | 