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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 / m
  = 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 100C. 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 @ 40C

cSt @ 40C

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%

 
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