Classification and Characteristics of Grease-NEWS-www.fv-bearing.com
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Classification and Characteristics of Grease

Apr 21, 2022

Soap Grease

Calcium Soap Grease

In a typical manufacturing process of calcium soap grease, mineral oil, fatty acid, calcium hydroxide (hydrated lime) and water are mixed and cooked to bring to saponification. The process is complete after adjustment of water content. Grease made with tallow contains a small amount of water as structural stabilizer, and, when heated above 80°C, it loses its associated water, resulting in structure breakdown and separation of oil from thickener. Due to this poor heat resistance, it is used for general plain bearings operating under rather low speed and low load where temperature would not rise above 70°C in service. The water resistance is good on the other hand, and thus the grease performs well in applications exposed to water.

Use of caster oil fatty acid results in a grease which contains no water. Because the structure is stabilized without water, it can be used up to about 100°C.


Lithium Soap Grease

Lithium soap grease is the most widely used multi-purpose grease, from general industrial uses to automobiles, bearings and home electric products. It consists of mineral or synthetic oil and lithium stearate or lithium salt, a hardened fatty acid derived from castor oil. Usable in a wide range of temperature, and has excellent water resistance and mechanical stability.


Aluminum Complex Soap Grease

Aluminum complex grease is made from a complex soap which is formed by reaction of aromatic carboxylic acid and stearic acid on aluminum hydroxide. Aluminum complex grease is characterized by a very fine fiber structure, high dropping point (200°C or above) , excellent heat and water resistance and mechanical stability.


Lithium Complex Soap Grease

The soap is formed by reaction of lithium hydroxide with the mixture of fatty acid and dibasic acid. The dropping point of the finished grease is 250°C or higher. Lithium complex grease has excellent heat and water resistance and rust preventing property, as well as longer life at high temperature than lithium soap grease.




Non-Soap Greases

Urea Grease

Typical urea grease formulation uses organic compound containing more than two urea groups (-NH-CO-NH-) as thickening agent. Because of its excellent heat and water resistance, urea grease is an optimum choice for continuous casting lines and iron mills, and actually is the most widely used nonsoap grease.

Urea grease is also widely used for automotive electrical components. For high temperature condition, synthetic oil based urea grease is preferred.


Bentonite Grease

This grease thickened by organic bentonite is often called "grease without dropping point" or "grease without melting point," because it does not lose the grease structure even at extremely high temperature.

The grease can offer other advantages like good shear stability, but its application is limited because of rather poor rust prevention, hardening tendency when exposed to high temperature condition (200°C or above) for a long time, and poor ability to keep oil film on the bearing race surface during high speed rotation.


Other Non-Soap Greases

Other nonsoap greases include Na terephthalamate Grease, Copper Phthalocyanine Grease, Teflon (PTFE) Grease, Mica Grease and Silica Gel Grease.



Comparison of properties of grease due to thickener

Soap Thickener


Thickener typeMaximum temperature limitWater resistanceShear StabilityRemarks
Metalic soapCalcium soap (stearate)70°CFFContains water (1%) as structural stabilizer.
Calcium soap
(hydroxystearate)
100°CGGContains no water.
Aluminum soap80°CGPExcellent adhesive characteristics.
Sodium soap120°CPFEmulsifies with water.
Lithium soap
(stearate)
130°CGGAll-purpose with least weak points.
Lithium soap
(hydroxystearate)
130°CGEAll-purpose with least weak points.
Complex soapCalcium complex150°CGGTends to harden by time and heat.
Aluminum complex150°CEEWater-repellent type: good pumpability
Lithium complex150°CGELithium soap grease with better heat resistance.

O: Outstanding   E: Excellent   G: Good   F: Fair   P: Poor


Non-Soap Thickener


Thickener typeMaximum temperature limitWater resistanceShear StabilityRemarks
UreaDiureaAromatic diurea180°COOMost stable urea; optimum for sealed application.
Aliphatic diurea180°CEEAll-purpose shear - softening type; optimum for centralized system.
Alicyclic diurea180°CEEAll-purpose but some tends to harden by shear.
Triurea180°CGFHardens by heat.
Tetraurea (Polyurea)180°CGFSoftens by shear; wide batch to batch variation.
OrganicSodium terephthalamate180°CGGHigh oil separation tendency, susceptible to oxidation due to its constituent metal group.
PTFE250°COOMost stable but costly and requires high usage.
InorganicOrganic bentonite200°CFGCarbonized if used at high temperature for prolonged periods.
Silica gel200°CPPSusceptible to rusting in the presence of moisture.

O: Outstanding   E: Excellent   G: Good   F: Fair   P: Poor


Electron Micrograph (x104) of Thickener Fiber Structure

Soap ThickenerSoap ThickenerSoap Thickener

Calcium soap

(stearate)


Sodium soap

(stearate)


Lithium soap

(stearate)


Soap ThickenerNon-Soap ThickenerNon-Soap Thickener


Lithium soap

(hydroxystearate)


Aliphatic diurea


PTFE

Lubrication of Roll Neck Bearings.pdf

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