Classification and Characteristics of Grease Classification by Thickener Types

Soap Grease

Calcium Soap Grease

In a typical manufacturing process 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 a 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 the 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.
The use of caster oil fatty acid results in grease that 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 temperatures, 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 the 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 a reaction of lithium hydroxide with a 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 properties, as well as longer life at high temperatures than lithium soap grease.

Non-Soap Greases

Urea Grease

Typical urea grease formulation uses an organic compound containing more than two urea groups (-NH-CO-NH-) as a thickening agent. Because of its excellent heat and water resistance, urea grease is an optimum choice for continuous casting lines and iron mills and is the most widely used nonsoap grease.
Urea grease is also widely used for automotive electrical components. For high-temperature conditions, 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 temperatures.
The grease can offer other advantages like good shear stability, but its application is limited because of rather poor rust prevention, the hardening tendency when exposed to high-temperature conditions (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 terephthalate Grease, Copper Phthalocyanine Grease, Teflon (PTFE) Grease, Mica Grease, and Silica Gel Grease.

Comparison of properties of grease due to thickener

Soap Thickener

	Thickener type	Maximum temperature limit	Water resistance	Shear Stability	Remarks
Metalic soap	Calcium soap (stearate)	70°C	F	F	Contains water (1%) as a structural stabilizer.
	Calcium soap (hydroxystearate)	100°C	G	G	Contains no water.
	Aluminum soap	80°C	G	P	Excellent adhesive characteristics.
	Sodium soap	120°C	P	F	Emulsifies with water.
	Lithium soap (stearate)	130°C	G	G	All-purpose with least weak points.
	Lithium soap (hydroxy stearate)	130°C	G	E	All-purpose with least weak points.
Complex soap	Calcium complex	150°C	G	G	Tends to harden with time and heat.
	Aluminum complex	150°C	E	E	Water-repellent type: good pumpability
	Lithium complex	150°C	G	E	Lithium soap grease with better heat resistance.

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

Non-Soap Thickener

	Thickener type		Maximum temperature limiter	r resistance	Shear Stability	Remarks
Urea	Diurea	Aromatic diurea	180°C	O	O	Most stable urea; optimum for sealed application.
		Aliphatic diurea	180°C	E	E	All-purpose shear-softening type; optimum for a centralized system.
		Alicyclic diurea	180°C	E	E	All-purpose but some tend to harden by shear.
	Triurea		180°C	G	F	Hardens by heat.
	Tetraurea (Polyurea)		180°C	G	F	Softens by shear; wide batch to batch variation.
Organic	Sodium terephthalamate		180°C	G	G	High oil separation tendency, susceptible to oxidation due to its constituent metal group.
Organic	PTFE		250°C	O	O	Most stable but costly and requires high usage.
Inorganic	Organic bentonite		200°C	F	G	Carbonized if used at high temperature for prolonged periods.
Inorganic	Silica gel		200°C	P	P	Susceptible to rusting in the presence of moisture.