Synthetic lubricating greases
Composition and industrial uses

Synthetic lubricating greases are widely utilised due to their inherent ability to cling to the friction point and ensure an effective hydrodynamic film under centrifugal conditions and potential detachment from the friction zones.  The correct balance of the components of a lubricating grease ensures the right balance between adhesiveness and the coefficient of low static and dynamic friction. Lubricating greases are essentially composed of four elements:

• Base oil – determines the basic film-forming properties of contact surfaces
  
  
• Thickeners – metallic, organic or inorganic, which determines the adhesive, cohesive and filamentous power by helping to regulate oil release and recovery under dynamic loads
  
  
• Additives – contribute to improved anti-wear, anti-oxidant, anti-corrosive and visco-dynamic properties
  
  
• Solid lubricants – help in contexts of emergency application, where other elements are unable to withstand critical thermal or dynamic conditions, creating a protective barrier whilst improving the coefficient of friction and reduce mechanical wear (for example, PTFE, MoS₂, Graphite)

The choice and correct combination of its basic components enables the lubricating grease to suit the application context in which it operates, namely the tribosystem – as the set of conditions affecting the immediate surroundings of a friction process.

The element that affects the performance of a grease more than any other is the base oil, which can be up to 90% by weight in the softest grades of grease (NLGI 000).

It can be distinguished by:

• Mineral – obtained through a process of refining and distilling oil
  
  
• Synthetic – directly obtained through a chemical polymerisation process from basic blocks

In terms of performance, in a comparison between mineral and synthetic oils, the latter are able to withstand much harsher conditions:

• Thermal resistance at low and high operating temperatures
• Resistance to chemical leaching 
• Lubricating power
• Compatibility with plastics and rubbers

A modern design of mechanical components in the automotive, appliance, military and aerospace sectors need synthetic oils, which are divided into five main macro-families within which specific differences can be isolated:

• Polyalphaolefin Oils (PAO)
• Polyalkylene Glycol Oils (PAG)
• Ester, Diesters and Polyester Oils (EST)
• Silicon Oils (SIL)
• Fluorinated Oils (PFPE)

Synthetic lubricating greases thus inherit the strengths of the oils from which they are formulated and are the obvious choice in conditions of:

• An absence of hermetic containment of the lubrication chamber
• Continuous thermal operating conditions below -30° C and above 120° C
• Contact with "oil-sensitive" plastics or rubbers (EPDM, ABS, PC)
• The presence of high concentrations of oxygen in the lubrication zone
• Contamination of the lubrication zone with aggressive chemicals
• Application requirements of minimum viscous friction variation at temperature

Synthetic lubricating greases are the preferred choice in all application contexts involving long-life lubrication – the assembly of the mechanical component coincides with the only possible lubrication foreseen due to the objective impossibility of performing intermediate maintenance operations to restore the lubrication film.

The mechanical devices that comprise and equip a vehicle are a classic example of the need to find a lubricant solution that is effective and long-lasting enough to complete the drive and reset cycles that occur throughout the life of the vehicle. Other examples include:

• Gearmotors for windscreen wiper movement
• Brake calliper drive cylinders
• Hydraulic clutch controls
• Stop lamp drive switches
• Mirror movement switch controls
• Dampers and soft-closing rotational dampers
• Interior cabin armrests
• Wheel hub bearings
• Pneumatic cylinders

Amongst the most effective and tested product families for the lubrication of original equipment components are:

• Silicone greases > characterised by a minimal change in viscosity at temperature, being excellent in mixed metal-plastic or rubber-metal bearings and offering superior performance
  
  
• Fluorinated greases > for the best thermo-oxidative stability in the broadest temperature range (-90 to +300° C) compared to all synthetic greases, non-flammable and suitable for the lubrication of amorphous plastics such as polycarbonate and ABS – oxygen compatibility is even guaranteed
  
  
• Polyalphaolefin greases > the first choice for value for money amongst synthetic greases, excellent lubricating power and load-bearing capacity, along with good thermoviscous stability
  
  
• Ester-based greases > excellent heat resistance up to 180° C, ideal for metal-to-metal couplings due to high polarity, offering superior performance under conditions of sliding friction and high loads
  
  
• Polyglycol-based greases > effective for lubricating metal-to-metal couplings in gearboxes with high sliding friction and metal-to-metal combinations, leaving no carbon residue and offering by far the lowest dynamic friction coefficient