Editing Lubricant (section)

== Functions of lubricants ==
One of the largest applications for lubricants, in the form of [[motor oil]], is protecting the [[internal combustion engine]]s in motor vehicles and powered equipment.
<!--Lubricants such as [[2-cycle oil]] are added to [[fuel]]s like gasoline, which has low lubricity. [[Sulfur]] impurities in fuels also provide some lubrication properties, which is absent in low-sulfur [[Diesel fuel|diesel]]. [[Biodiesel]] is a popular diesel fuel additive providing lubricity.

Another approach to reducing friction and wear is to use [[bearing (mechanical)|bearings]] such as [[ball bearing]]s, [[roller bearing]]s or [[air bearing]]s, which in turn require internal lubrication themselves, or to use sound, in the case of [[acoustic lubrication]].-->

=== Lubricant vs. anti-tack coating ===
'''Anti-tack or anti-stick coatings''' are designed to reduce the adhesive condition (stickiness) of a given material. The rubber, hose, and wire and cable industries are the largest consumers of anti-tack products but virtually every industry uses some form of anti-sticking agent. Anti-sticking agents differ from ''lubricants'' in that they are designed to reduce the inherently adhesive qualities of a given compound while lubricants are designed to reduce friction between any two surfaces.

=== Keep moving parts apart ===
Lubricants are typically used to separate [[moving parts]] in a system. This separation has the benefit of reducing friction, wear and surface fatigue, together with reduced heat generation, operating noise and vibrations. Lubricants achieve this in several ways. The most common is by forming a physical barrier i.e., a thin layer of lubricant separates the moving parts. This is analogous to hydroplaning, the loss of friction observed when a car tire is separated from the road surface by moving through standing water. This is termed hydrodynamic lubrication. In cases of high surface pressures or temperatures, the fluid film is much thinner and some of the forces are transmitted between the surfaces through the lubricant.

=== Reduce friction ===
Typically the lubricant-to-surface [[friction]] is much less than surface-to-surface friction in a system without any lubrication. Thus use of a lubricant reduces the overall system friction. Reduced friction has the benefit of reducing heat generation and reduced formation of wear particles as well as improved efficiency. Lubricants may contain [[Chemical polarity|polar]] [[oil additive|additives]] known as friction modifiers that chemically bind to metal surfaces to reduce surface friction even when there is insufficient bulk lubricant present for hydrodynamic lubrication, e.g. protecting the [[Valvetrain|valve train]] in a car engine at startup. The base oil itself might also be polar in nature and as a result inherently able to bind to metal surfaces, as with [[polyolester]] oils.

=== Transfer heat ===
Both gas and liquid lubricants can transfer heat. However, liquid lubricants are much more effective on account of their high [[specific heat capacity]]. Typically the liquid lubricant is constantly circulated to and from a cooler part of the system, although lubricants may be used to warm as well as to cool when a regulated temperature is required. This circulating flow also determines the amount of heat that is carried away in any given unit of time. High flow systems can carry away a lot of heat and have the additional benefit of reducing the thermal stress on the lubricant. Thus lower cost liquid lubricants may be used. The primary drawback is that high flows typically require larger sumps and bigger cooling units. A secondary drawback is that a high flow system that relies on the flow rate to protect the lubricant from thermal stress is susceptible to catastrophic failure during sudden system shut downs. An automotive oil-cooled [[turbocharger]] is a typical example. Turbochargers get red hot during operation and the oil that is cooling them only survives as its residence time in the system is very short (i.e. high flow rate). If the system is shut down suddenly (pulling into a service area after a high-speed drive and stopping the engine) the oil that is in the turbo charger immediately oxidizes and will clog the oil ways with deposits. Over time these deposits can completely block the oil ways, reducing the cooling with the result that the turbo charger experiences total failure, typically with seized [[Bearing (mechanical)|bearings]]. Non-flowing lubricants such as greases and pastes are not effective at heat transfer although they do contribute by reducing the generation of heat in the first place.

=== Carry away contaminants and debris ===

Lubricant circulation systems have the benefit of carrying away internally generated debris and external contaminants that get introduced into the system to a filter where they can be removed. Lubricants for machines that regularly generate debris or contaminants such as automotive engines typically contain detergent and dispersant additives to assist in debris and contaminant transport to the filter and removal. Over time the filter will get clogged and require cleaning or replacement, hence the recommendation to change a car's oil filter at the same time as changing the oil. In closed systems such as gear boxes the filter may be supplemented by a magnet to attract any iron fines that get created.

It is apparent that in a circulatory system the oil will only be as clean as the filter can make it, thus it is unfortunate that there are no industry standards by which consumers can readily assess the filtering ability of various automotive filters. Poor automotive filters 
significantly reduce the life of the machine (engine) as well as make the system inefficient.

=== Transmit power ===

{{main|Hydraulics}}

Lubricants known as [[hydraulic fluid]] are used as the [[working fluid]] in hydrostatic power transmission. Hydraulic fluids comprise a large portion of all lubricants produced in the world. The [[automatic transmission]]'s [[torque converter]] is another important application for power transmission with lubricants.

=== Protect against wear ===

Lubricants prevent wear by reducing friction between two parts. Lubricants may also contain anti-wear or extreme pressure additives to boost their performance against wear and fatigue.

=== Prevent corrosion and rusting ===
Many lubricants are formulated with additives that form chemical bonds with surfaces or that exclude moisture, to prevent corrosion and rust. It reduces corrosion between two metallic surfaces and avoids contact between these surfaces to avoid immersed corrosion.

=== Seal for gases ===
Lubricants will occupy the clearance between moving parts through the capillary force, thus sealing the clearance. This effect can be used to seal pistons and shafts.