NLGI : National Lubricating Grease Institute)) is a American standard .
Grease is a solid/semi-solid gelatinous substance composed of petroleum derivatives and a metal soap, which is used for indoor.The place of use of any type of grease must be the closed and internal space of any food and industrial machinery, and the purpose is to absorb contaminated particles in addition to lubrication.
Base oils for lubricating greases
The base oil as the main component of a lubricating grease has a
significant influence on its lubricating and service properties. The
thermal and oxidative resistance of the base oil influences the usable
temperature range and the ageing stability of the grease.
Lubricating
greases for low-temperature applications contain selected base oils with
a particularly low pour point. The viscosity
and viscosity-temperature behaviour of the base oil are important
influencing factors for the formation of load-bearing lubricating films
and the torque behaviour of the grease under the respective operating
conditions. In addition, compatibility with elastomer sealing materials
also depends on the base oil selected.
The following base oil types can be used in lubricating greases:
- Mineral oils (naphthenic oils, paraffinic oils, aromatic oils, white oils) :Known for their excellent lubricating properties, mineral-oil-based lubricants typically are used for multipurpose lubrication of mechanical components
– such as bearings, chains, gears, slides and threaded connections –
where operating temperatures typically range from -17°C to 150°C.
- Synthetic oils (polyalphaolefin, ester, polyalkylene glycol, polyisobutylene, silicone oil, perfluoropolyether):Conventional greases employ a petroleum-based product, such as mineral oil. Synthetic greases use a synthetic lubricant, such as silicone. Consequently, they can withstand temperature extremes and maintain lubricating effectiveness better than conventional greases.
- Vegetable oils (rapeseed oil):Vegetable oils have several properties that are required in a lubricant, such as a high
viscosity index, high lubricity, low volatility, and advanced
properties that can be compared to mineral oil, including low toxicity
and high biodegradability
Base oil mixtures of mineral oils with synthetic oils can also be
used for fat production, which ultimately results in semi-synthetic
products
Composition of lubricating greases
Lubricating greases are semi-liquid to solid lubricants which are produced by introducing a suitable thickening agent into a liquid base oil. Certain properties of a lubricating grease can also be specifically improved by adding additives and solid lubricants.
Compared to lubricating oils, lubricating greases are more complex lubricants in terms of their basic structure. The performance of a lubricating grease is influenced by the properties of all its individual components, such as base oil, thickener, additives and solid lubricants.
The multitude of possible combinations of different base oils in different viscosities with different thickener types and different additives allows the production of a large number of different lubricating greases.
Greases have high adhesion and suitable temperature and should be used for each special grease device and one of the most important quality factors of grease is the type of soap and the type of thickener.
Types of greases: Greases are divided into 9 types based on the degree of viscosity.
Table
this table is very important to all industrial
Lubricants are also named according to the NLGI standard, and of course the type of grease used, additives used, the type of base, the degree of NLGI grease, the maximum and minimum operating temperature.
Depending
on the thickener type selected and the desired consistency of the
grease (which in turn is characterized by NLGI classes), lubricating
greases contain a proportion of thickeners in the range of 3% to 30%.
The proportion of added additives can be up to 10%. If a lubricating
grease contains solid lubricants, their proportion is a maximum of about
10%.
Consistent lubricants with solid lubricant contents greater than 40%
are classified as pastes. For fat-like special products with a solid
lubricant content between 10% and 40%, the term grease paste is commonly
used.
Grease = Metal Soap + Lubricant
In general, grease does not cool the devices during operation and has less permeability. They are absorbent in terms of maintenance, moisture and dust.
Jointly developed by ASTM International, the National Lubricating Grease Institute (NLGI) and SAE International, standard ASTM D4950 “standard classification and specification for automotive service greases”
was first published in 1989 by ASTM International. It categorizes
greases suitable for the lubrication of chassis components and wheel
bearings of vehicles, based on performance requirements, using codes
adopted from the NLGI's “chassis and wheel bearing service classification system”:
- LA and LB: chassis lubricants (suitability up to mild and severe duty respectively)
- GA, GB and GC: wheel-bearings (suitability up to mild, moderate and severe duty respectively)
A given performance category may include greases of different consistencies.
The measure of the consistency of grease is commonly expressed by its NLGI consistency number.
The main elements of standard ATSM D4950 and NLGI's consistency classification are reproduced and described in standard SAE J310 “automotive lubricating greases” published by SAE International.
Standard ISO 6743-9 “lubricants, industrial oils and related products (class L) — classification — part 9: family X (greases)”, first released in 1987 by the International Organization for Standardization,
establishes a detailed classification of greases used for the
lubrication of equipment, components of machines, vehicles, etc. It
assigns a single multi-part code to each grease based on its operational
properties (including temperature range, effects of water, load, etc.)
and its NLGI consistency number.
Engineering assessment and analysis
Lithium-based greases are the most commonly used; sodium and lithium-based greases have higher melting point (dropping point) than calcium-based greases but are not resistant to the action of water. Lithium-based grease has a dropping point at 190 to 220 °C (350 to 400 °F). However the maximum usable temperature for lithium-based grease is 120 °C.
The amount of grease in a sample can be determined in a laboratory by extraction with a solvent followed by e.g. gravimetric determination.
Additives
Some greases are labeled "EP", which indicates "extreme pressure". Under high pressure or shock loading, normal grease can be compressed to the extent that the greased parts come into physical contact, causing friction and wear.
EP greases have increased resistance to film breakdown, form sacrificial coatings on the metal surface to protect if the film does break down, or include solid lubricants such as graphite or molybdenum disulfide to provide protection even without any grease remaining.
Solid additives such as copper or ceramic
powder are added to some greases for static high pressure and/or high
temperature applications, or where corrosion could prevent dis-assembly
of components later in their service life.
These compounds are working as a release agent. Solid additives cannot be used in bearings because of tight tolerances. Solid additives will cause increased wear in bearings.
The
following table shows a detailed overview of the code letters and code
numbers defined according to DIN 51502 for the identification of
greases:
Code letter /
Product specification |
Possible code letters and code numbers acc. to DIN 51502 |
marking KPFHC
2 N-30 |
| Code letter Grease type |
K ... Grease for rolling bearings, plain bearings and sliding surfaces according to DIN 51825
G ... Grease for closed gears according to DIN 51826
OG ... Grease for open gears
M ... Grease for plain bearings and seals
|
K |
| Additional letter Additive |
P ... addition of EP additives
F ... addition of solid lubricants
|
PF |
| Additional letter Basic oil type |
Without ... Mineral oils
HC ... Synthetic hydrocarbons
PG ... Polyglycols
E ... Organic esters
PH ... Phosphoric acid ester
FK ... Perfluorinated oils
SI ... Silicone oils
X ... Others
|
HC |
| NLGI Class |
The code number corresponds to the numerical value of the NLGI class |
2 |
| Upper operating temperature and water resistance |
C-U ... Upper operating temperature in °C
Water resistance according to DIN 51807
|
N |
Lower operating temperature in
°C |
The code number corresponds to the numerical value of the lower operating temperature |
-30 |
More precise breakdown of operating temperature and water resistance:
| Code letter |
Upper operating temperature |
Water resistance according to DIN 51807 |
| C |
+60°C |
0-40 or 1-40 |
| D |
+60°C |
2-40 or 3-40 |
| E |
+80°C |
0-40 or 1-40 |
| F |
+80°C |
2-40 or 3-40 |
| G |
+100°C |
0-90 or 1-90 |
| H |
+100°C |
2-90 or 3-90 |
| K |
+120°C |
0-90 or 1-90 |
| M |
+120°C |
2-90 or 3-90 |
| N |
+140°C |
In agreement |
| P |
+160°C |
| R |
+180°C |
| S |
+200°C |
| T |
+220°C |
| U |
> 220°C |
Compared to lubricating oils, lubricating greases are characterized by higher adhesion and lower flowability. They thus remain more easily at lubrication points which cannot be sealed in a suitable manner due to a high design effort in order to prevent the flow away of alternatively usable lubricating oils from the lubrication point.
Rolling bearing lubrication is one of the main areas of application for lubricating greases. In grease-lubricated rolling bearings, the grease used performs an additional sealing function and protects the bearing against environmental influences such as high dust loads, high humidity or splashing water.
In contrast to lubricating oils, which can be circulated in oil circulation systems and can therefore perform transport functions in addition to their primary function as a lubricant, lubricating greases are not suitable for removing heat, impurities or wear particles of comparable size from the lubrication point.
Lithium Complex greases first entered the market in 1962. According to NLGI International, Today Lithium Complex grease accounts for 42% of all North American Grease production.
Lithium Complex Greases are favored over traditional Lithium greases because of their higher dropping points and improved heat resistance. They also work well in low temperatures.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------