Lubricants: design features that save energy & protect against wear
High-performance products of tribology
Lubricants to reduce friction in sliding and rolling elements
Which lubricants exist?
- Engine oils
- Gear oils
- Brake fluids
- Hydraulic fluids
- Gear oils
- Compressor oils
- Turbine oils
- Corrosion protection products
- Cooling lubricants
- Insulating oils and white oils
- Lubricating greases
Base fluids for lubricants
Synthetic base fluids (Polyalphaolefins, Esters)
Benefits of synthetic lubricants
The most important property of lubricating oils is their so-called viscosity, which is the measure of the internal friction during the flow of oil. It is dependent on temperature: at low oil temperature, the internal friction is large and the viscosity is high. The hotter the oil temperature, the lower the internal friction and viscosity. A distinction is made between kinematic and dynamic viscosity, with the kinematic viscosity being derived from the dynamic viscosity by dividing this by the density.
All lubricants are classified according to the ISO viscosity classification. The only exception is the engine and gear oils of the automotive sector, which are divided into SAE grades. In the ISO VG (International Organisation for Standardisation- Viscosity Grade) 18 viscosity grades of 2 mm2 / s to 1500 mm2 / s are standardised and a mean viscosity of 40 ° C set, from which inside of a viscosity grade, there may be a deviation of 10% upward or downward.
- Viscosity-Temperature-Behaviour (Viscosity index)
Depending on the oil, viscosity changes may differ completely due to rising or falling temperature. The viscosity-temperature behaviour is denoted by a dimensionless parameter, the so-called viscosity index (VI). The higher the viscosity index, the lower the viscosity drop when the temperature increases.
The viscosity of oil is dependent not only on the temperature but also on the pressure exerted on the lubricant film. This feature is particularly important for tribological calculations when oils of different base fluids are available
- Shear rate/shear stability
In multi-grade oils containing viscosity index improver, the viscosity is also influenced by the shear rate. In mono-grade oils without viscosity index improvers, known as Newtonian fluids, the velocity gradient has no effect on the viscosity
- Pour Point
The Pour Point indicates the so-called flow limits of the lubricating oil, which was previously described by the solidification point. To determine the Pour Point, the solidification point is ascertained and then 3°C added to this.
- Evaporation loss
The evaporation loss is dependent on the viscosity and the degree of refining of mineral oils. Hydrocrack oils have a significantly lower evaporation loss than conventional mineral oils.
Lubricant additives (H3)
Additives are added to lubricants to confer special properties. Type and quantity should be precisely matched to the particular application and the additive percentage can be between 1% and 30%. Depending on their mode of action, these additives can be divided into three types:
- Surface-protecting additives
These include detergents, dispersants, high-pressure and wear protection additives, corrosion and rust protection additives, friction modifiers and surface-sealing additives such DuraGear® and PowerShot®, which use the friction occurring in aggregates to form a protective surface layer of silicon. (Link to landing page)
- Oil-improving additives
Viscosity improvers reduce a potential drop in viscosity when the temperature rises. Pour point improvers work more in the low temperature range and delay the formation of wax crystals so that the oil can flow longer even at low temperatures.
- Oil-protecting additives
Anti-ageing additives, or antioxidants, slowing the ageing of the oil caused by the entry of oxygen, high temperatures and catalytic metals. Oil-ageing products are decomposed and adverse reactions ended. Antifoaming agents modify the surface tension of the oil and thus prevent the formation of stable surface foam.
Lubricating greases are solid lubricants usually containing mineral oil, which in a wide consistency or penetration range are manufactured solidly from liquid to tallow-like. They are used when liquid lubricants are not suitable due to their liquid nature and for example, run away from the lubricating point on roller and friction bearings, open gearboxes, wire ropes or chain drives. Lubricating greases consist up to 70-95% of a base oil, 3-30% of thickeners and 0 - 5% of additives.