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Grease Ready Reference

ABBREVIATIONS


ASTM
American Society for Testing and Materials

ISO
International Standards Associations

FDA
Food and Drug Administration

JIS
Japan Industry Standard

NLGI
National Lubricating Grease Institute

OEM
Original Equipment Manufacturer

SAE
Society of Automotive Engineers

AGMA
American Gear Manufacturers Association

Source : NTN BEARING CORPORATION

Relubrication Guidelines
It cannot be stated strongly enough that when relubricating a bearing unit it is essential to choose a clean lubricant compatible with the grease already in the bearing.

Whether or not different kinds of grease may be mixed depends on the thickening agents used in making the grease. Mixing different types of grease can affect key properties and alter the grease’s performance. If these key properties are diminished, the grease can become ineffective, leading to premature bearing failure. (Refer to Table 1 for further information.)
Pump the grease gun once prior to connecting it to the fitting to purge the nozzle of any contaminants that may have accumulated and wipe it with a clean towel. The grease fitting also merits inspection for contaminants and should also be wiped clean.

Taking these precautionary measures to prevent the introduction of contaminants into the bearing will help ensure the proper operation of the bearing and performance to and beyond the rated life of the bearing.

Table 1: Grease thickener compatibility


Table key

Circle: Mixing greases will not produce any appreciable change in properties
Square: Mixing greases may produce considerable variation in properties
Triangle: Mixing greases will cause drastic changes in properties

As for the quantity of lubricant used, most applications require only two pumps of grease. This is an instance where more is not better. Over packing the bearings during relubrication should be avoided. Too much grease may create a "churning" action within the bearing, which in turn results in the bearing running hotter. This leads to premature deterioration of the grease and ultimately bearing failure.

ROLLING ELEMENT BEARINGS FAILURE INVESTIGATION
Rolling element bearings may fail for many reasons. Research by expert engineers have determine the cause of failures through experiential tests and have been carefully documented.
The data base documents failures of rolling element includes :
  • FATIGUE FLAKE
  • CORROSION
  • FALSE BRINELLING
  • OUTER RACE FRETTING
  • INNER RACE SPINNING
  • UNEVEN FATIGUE
  • ROLLER END COLLAPSE
  • ROLLER PEELING
  • UNEVEN WEAR MARKS
  • ROLLER END CHIPPING
  • ROLLER BREAKAGE
  • MAGNETIC DAMAGE
  • GREASE FAILURE
  • OVERHEATING
  • ABRASION
  • ROLLER STAINING
  • BRINELLING
  • FRACTURED FLANGE
  • INNER RACE FRETTING
  • SKEW RUNNING MARKS
  • LADDER MARKING
  • MOLTEN CAGE
  • SMEARING
When machines experience a failure, your first approach is to collect technical information and failure history.
Take an OVERVIEW rather than the NARROWER approach of investigating the apparent immediate problem and carry out a macro-analysis.

Definition Of Terms Relating To Lubricating Grease

DROPPING POINT
The drop point of a particular type of grease is that temperature at which the first drop of liquid separates when the grease is heated under prescribed conditions.

PENETRATION
The measure which indicates the softness or hardness of a grease. The NLGI has developed a numerical scale to classify the consistency of grease based upon their worked 60-stroke penetration values.

NLGI GRADE NUMBERS / PENETRATION
NLGI Grade
ASTM worked Penetration, 60 stroke
Penetration and Typical Methods of Application
000
445 - 475
Very Fluid; used in centralized systems
00
400 - 430
Fluid; used in centralized systems and enclosed gear boxes
0
355 - 385
Semi-Fluid; used in centralized systems
1
310 - 340
Very soft; used in grease gun, centralized systems or normal application
2
265 - 295
Soft; used in grease gun, centralized systems or normal application
3
220 - 250
Medium Hard; used in grease gun or normal application
4
175 - 205
Hard; used in grease gun or normal application
5
130 - 160
Very Hard; used for special application
6
85 - 115
Extremely Hard; block grease; used in open grease cellars or special application

EXTREME PRESSURE (EP) ADDITIVE

Chemical compound imparting extreme pressure characteristics to a lubricant with the objective of reducing wear under conditions where rubbing or sliding accompanies high contact pressures, as in heavily loaded applications.

Molybdenum Disulphide (MOS2) And Graphite

A very effective solid lubricant that is used for back-up lubrication in extra high temperature and high load applications.

 

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