 Definition
The usual definition of a lubricating grease is : a plastic solid to semi-fluid
product in dispersion of a thickening agent in fluid lubricant. The thickeners, called
normally soap or base, may be:
metallic soap, mixture of soaps, metallic soap-salt combination (complex), non-soap
substances.
To improve the performance of the grease some other chemical products are joint. They are
called : additives. The nature of this additives, may be different.
The Society of Automotive Engineers (SAE) at the Information Report J310a describes:
"Grease are most often used instead of fluids where a lubricant is required to
maintain its original position in a mechanism, especially where opportunities for frequent
re-lubrication may be limited or economically unjustifiable. This requirement may be due
to the physical configuration of the mechanism, the type of motion, the type of sealing,
or the need for the lubricant to perform all or part of any sealing function in the
prevention of lubricant loss or the entrance of contaminants. Because of their essentially
solid nature, greases do not perform the cooling and cleaning functions associated with
the use of a fluid lubricant. With these exceptions, greases are expected to accomplish
all other functions of fluid lubricants."
Grease types and properties
Structure, performance properties of any types of grease are always determined by the
base, fluid selected, additives, complementary components and packaging processes. |
| 1 |
Simple base: |
formed by combination of fatty acid (animal or vegetable origin) and active metal |
| 2 |
Complex base: |
formed by reaction of an active metal with a fatty acid and a non fatty acid |
| 3 |
Non- base
(soap): |
. |
| . |
3/a |
inorganic, soap of mineral origin : various metallic oxides, carbon black,
graphite, silicate, Molybdenum disulfide, titanate, bentonite |
| . |
3/b |
principally
polymeric like : polyurea, polyethylene, polypropylene, polycarbohydrates,
polytetrafluoroethylene (PTFE) |
| . |
3/c |
perfluoropolyethere
(PFPE) and tetrafluoroethylene |
| 4 |
Intermediate: |
formed by
sodium tereftalamate with ester fluid, mineral, fluorine |
| NLGI - NATIONAL LUBRICATING GREASE INSTITUTE |
| Number |
60 Strokes Worked Penetration at
25 °C/77 °F (ASTM D 217)* |
| NLGI No. 000 |
445-475 |
| NLGI No. 00 |
400-430 |
| NLGI No. 0 |
355-385 |
| NLGI No. 1 |
310-340 |
| NLGI No. 2 |
265-295 |
| NLGI No. 3 |
220-250 |
| NLGI No. 4 |
175-205 |
| NLGI No. 5 |
130-160 |
| NLGI No. 6 |
85-115 |
* penetration depth measured in tenths of a millimeter |
