Grease

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      NLGI ( National Lubricating Grease Institute) American standard Grease is a solid and semi-solid gelatinous substance composed of petroleum derivatives and a metal soap, which is used for indoor.nuy77

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)
  • Synthetic oils (polyalphaolefin, ester, polyalkylene glycol, polyisobutylene, silicone oil, perfluoropolyether)
  • Vegetable oils (rapeseed oil)
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.
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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
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 this table is very importan 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
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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.
 
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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 Example 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.