A substance used to reduce friction between two surfaces moving in contact with each other. It is most often a liquid, such as a mineral or vegetable oil, but it can be a solid, such as a wax and, importantly, graphite. Some conditions call for special lubricants; for example, molybdenum sulphite is useful at high temperatures. Gases (eg air, helium) can be used, the gas being pumped into the bearing to maintain sufficient pressure between the faces.
Typically lubricants contain 90% base oil (most often petroleum fractions, called mineral oils) and less than 10% additives. Vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicone, fluorocarbons and many others are sometimes used as base oils.
Non-liquid lubricants include grease, powders (dry graphite, PTFE, Molybdenum disulfide, etc.), teflon tape used in plumbing, air cushion and others.
Lubricants such as 2-cycle oil are also added to some fuels.
In addition to automotive and industrial applications, lubricants are used for many other purposes, including K-Y Jelly, often used as a personal lubricant, bio-medical applications (e.g.
General composition
Lubricants are generally composed of a majority of base oil and a minority of additives to impart desirable characteristics.
Types of lubricants
Liquid including emulsions and suspensions Solid Greases Pastes===1'Liquid lubricants'
Liquid lubricants may be characterized in many different ways.
Water Mineral oils Vegetable (natural oil) Synthetic oils OthersNote that although generally lubricants are based on one type of base oil or another it is quite possible to use mixtures of the base oils to meet performance requirements.
Water
Water can be used on its own or as a major component in combination with one of the other base oils.
Mineral oil
This term is used to encompass lubricating base oil derived from crude oil. API designates several types of lubricant base oil identified as:
Group I - Saturates < 90% and/or Sulfur >0.03% and Viscosity Index >= 80 to <120 Group II – Saturates >= 90% and Sulfur <=0.03% and Viscosity Index >= 80 to <120 Group III – Saturates >= 90% Sulfur <=0.03% and Viscosity Index >= 120 Group IV – Poly alpha olefins (PAO) Group V – All others not included aboveThe lubricant industry commonly extends this group terminology to include:
Group I+ with a Viscosity Index of 103 - 108 Group II+ with a Viscosity Index of 113 - 119 Group III+ with a Viscosity Index of >= 140Vegetable (natural) oils
These are primarily triglyceride esters derived from plants and animals. For lubricant base oil use the vegetable derived materials are preferred. Common ones include high oleic canola oil, palm oil, sunflower seed oil and rapeseed oil from vegetable and Tall oil from animal sources.
Synthetic oils
Polyalpha-olefin (PAO) Synthetic esters Polyalkylene glycols (PAG) Phosphate esters Alkylated naphthalenes (AN) Silicate esters Ionic fluidsNote: In the USA certain Group III base stocks may be designated as synthetic;
Solid lubricants
Graphite Molybdenum disulphide Teflon Boron nitride ()Additives
A large number of additives are used to impart performance characteristics to the lubricants. The main families of additives are:
Anti-oxidants Viscosity index improvers Anti-wear Metal deactivators Corrosion inhibitors Rust inhibitors Friction modifiers Extreme Pressure Anti-foaming Demulsifying / EmulsifyingApplication by fluid types
Automotive Engine oils Petrol (Gasoline) engine oils Diesel engine oils Automotive transmission fluids Gearbox fluids Brake fluids Hydraulic fluids Other motors 2-stroke engine oils Industrial Hydraulic fluids Compressor oils Gear oils Aviation Gas turbine engine oils Piston engine oils Marine Top engine oil Crankcase fluids Stern tube lubricantsDisposal and environmental issues
It is estimated that 40% of all lubricants are released into the environment.
Disposal:
Recycling, burning, landfill and discharge into water may achieve disposal of used lubricant.
There are typically strict regulations in most countries regarding disposal in landfill and discharge into water as even small amount of lubricant can contaminate a large amount of water.
Burning the lubricant as fuel, typically to generate electricity, is also governed by regulations mainly on account of the relatively high level of additives present.
Unfortunately, most lubricant that ends up directly in the environment is due to general public discharging it onto the ground, into drains and directly into landfills as trash. This base oil is then treated much the same as virgin base oil however there is considerable reluctance to use recycled oils as they are generally considered inferior. Used lubricant may also be used as refinery feedstock to become part of crude oil.
Environment:
Lubricants both fresh and used can cause considerable damage to the environment mainly due to their high potential of serious water pollution.
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