Lubrication grease

Lubrication grease is used to minimise mechanical friction and wear. Lubrication grease forms a film that is established between the lubrication points (lubrication surfaces and bearings) and thus prevents direct contact of the moving bearings and surfaces.

In contrast to oil lubrication, lubrication grease provides the advantage that the lubricant does not run or drop off any lubrication points that are stationary or only moved at low speed. However, lubrication grease is not suited for fast operating bearings since the base oil in the grease mixture is decomposing due to high temperatures, which reduces the lubrication capacity of the substance.

The benefits of grease lubrication are the high degree of consistency (resistance of the grease against deformation) and good penetration properties of lubrication grease. It ensures lubrication of almost all bearing and support points, and prevents the ingress of dirt, and its water-repellent properties also prevent the occurrence of corrosion. Ingress of dirt particles causes malfunctions in the central lubrication system and leads to destruction at the friction points.

In the field of lubrication grease, the expression "consistency" refers to the plastic deformation capacity of a substance, which is identified by the penetration number. The penetration number is determined on the basis of the depth of penetration of a test cone (according to DIN 51804). For this determination according to DIN ISO 2137, grease is filled into a standardised container at a room temperature of 25 °C, and the penetration depth of the test cone is measured. From those values the consistency classification of lubrication grease is developed. Classification is performed in NLGI classes 000, 00, 0, 1, 2, 3, 4, 5, 6, which have been defined by the National Lubrication Grease Institute and applied in the DIN standard 51 818. The higher the number, the lower the deformation properties.

Very soft grease of class 000 to 0 is also referred to as viscous oil and is used in the central lubrication systems of utility vehicles, among others. Central lubrication systems that are operated with grease of NLGI class 000 or 00 may be used in a temperature range between -25 °C and +80 °C. For use of grease of NLGI class 0, application is only permitted in a restricted temperature range between -10 and +80 °C.

Greases of NLGI class 6 are no longer used in modern systems.

Lubrication grease products are not chemically pure substances. They consist of up to 90% of additivated base oils, which are consolidated by means of a thickening agent that prevents them from running, similar to a sponge. All types of mineral oils and synthetic oils can be used as base oil. The additives used are similar to those of oils. The thickening agents mostly used are what is referred to as metallic soaps on the base of e.g. lithium, calcium, sodium or aluminium or combinations thereof. These soaps are made of powdered raw materials. In a boiling process, the thickening agents develop sponge-like basic structures which bind the oil added during boiling and release the oil again at the friction point when needed.

Lubrication grease comprises:

• Base oil: Conventional oil (refined oil), unconventional oil (synthetic hydrocarbons), vegetable oil (rapeseed oil)
• Thickening agent: Metallic soaps (sodium soap), other thickening substances (bentonite)
• Additives: Surfactants (corrosion and rust protection agents), grease protecting substances (ageing protection)