Classification and Characteristics of Grease

Classification by Thickener Types
Classification By Base Oil Types

Soap Grease
Non-Soap Greases
Comparison of properties of grease due to thickener
Electron Micrograph (x10⁴) of Thickener Fiber Structure

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 type	Maximum temperature limit	Water resistance	Shear Stability	Remarks
Metalic soap	Calcium soap (stearate)	70°C	F	F	Contains water (1%) as 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 (hydroxystearate)	130°C	G	E	All-purpose with least weak points.
Complex soap	Calcium complex	150°C	G	G	Tends to harden by 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 limit	Water 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 centralized system.
		Alicyclic diurea	180°C	E	E	All-purpose but some tends 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.

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

Electron Micrograph (x10⁴) of Thickener Fiber Structure

Soap Thickener

Soap Thickener

Soap Thickener

Soap Thickener

Non-Soap Thickener

Non-Soap Thickener

Mineral oil based grease
Synthetic oil based grease
Comparison of properties of grease due to base oil

Mineral oil based grease

Most of the greases used today are based on mineral oil.

Synthetic oil based grease

Synthetic oil grease is used for certain conditions where conventional mineral oil grease fails (in low-temperature property, heat resistance, low-torque property or longer life). Synthetic greases come in many different characteristics depending on the type of the oil used.

Ester oil based grease (diester, polyol ester, etc.)

Provides excellent lubricity; Usable over a wide temperature range from very low to very high; Tends to swell rubber.

Synthetic hydrocarbon oil based grease

Usable over a wide temperature range from very low to very high; Good rubber/plastic compatibility (because of the absence of polar group in the hydrocarbon molecular structure) except natural rubber and EPDM.

Polyethylene glycol oil based grease

Optimum for applications in contact with rubber because of little adverse effect on rubber including natural rubber and EPDM.

Phenyl ether oil based grease

Optimum for automotive electrical components for its excellent thermo-oxidative stability; Good radiation resistance.

Silicone oil based grease

Excellent thermo-oxidative stability and usable over a wide temperature range; Poor steel-on-steel lubricity.

Fluorinated oil based grease

Offers the best thermo-oxidative stability and high chemical resistance of all existing greases, but has the drawback of being very expensive. Optimal for chemical plants, high-temperature drying ovens and copying machine heat rollers.

Comparison of properties of grease due to base oil

		mineral oil	diester	polyol ester oil	hydrocarbon oil	polyethylene glycol oil	phenyl ether oil	silicone oil	fluorinated oil
Chemical structural formuls (typical)		mixed hydrocarbon
Performance	Oil type	mid viscosity paraffinio	DOS	mid viscosity PET	mid viscosity PAQ	mid viscosity PPG	ADE	dimethyl silicone	mid viscosity PFAE
	Lubricity (oiliness)	G	E	E	G	F	G	P	G
	Heat resistance	P	F	G	G	G	E	O	O
	Oxidative stability	P	F	G	G	F	E	O	O
	Low-temp. property	F	O	E	E	G	G	O	G
	Rubber compatibility	F	P	P	E	O	G	O	O
	Plastic compatibility	F	P	P	E	P	E	O	O
Remarks		low cost	poor rubber compatibility		good rubber compatibility except natural rubber and EPDM	good rubber compatibility including natural rubber and EPDM	excellent radiation resistance	poor steel - on - steel boundary lubricity	best chemically stable of all existing greases; very costly