Complete Description of Lubricants

Types of lubricants

The Complete Description of Lubricants

In 1999, an estimated 37,300,000 tons of lubricants were consumed worldwide.Automotive applications dominate, but other industrial, marine, and metal working applications are also big consumers of lubricants. Although air and other gas-based lubricants are known, e.g., in fluid bearings), liquid and solid lubricants dominate the market, especially the former.

Lubricants are generally composed of a majority of base oil plus a variety of additives to impart desirable characteristics. Although generally lubricants are based on one type of base oil, mixtures of the base oils also are used to meet performance requirements.

Base oil groups

Mineral oil term is used to encompass lubricating base oil derived from crude oil. The American Petroleum Institute (API) designates several types of lubricant base oil

• Group I – Saturates <90% and/or sulfur >0.03%, and Society of Automotive Engineers (SAE) viscosity index (VI) of 80 to 120

Manufactured by solvent extraction, solvent or catalytic dewaxing, and hydro-finishing processes. Common Group I base oil are 150SN (solvent neutral), 500SN, and 150BS (brightstock)

• Group II – Saturates over 90% and sulfur under 0.03%, and SAE viscosity index of 80 to 120

Manufactured by hydrocracking and solvent or catalytic dewaxing processes. Group II base oil has superior anti-oxidation properties since virtually all hydrocarbon molecules are saturated. It has water-white color.

• Group III – Saturates > 90%, sulfur <0.03%, and SAE viscosity index over 120

Manufactured by special processes such as isohydromerization. Can be manufactured from base oil or slax wax from dewaxing process.

• Group IV – Polyalphaolefins (PAO)
• Group V – All others not included above such as naphthenics, PAG, esters.

In North America, Groups III, IV and V are now described as synthetic lubricants, with group III frequently described as synthesised hydrocarbons, or SHCs. In Europe, only Groups IV and V may be classed as synthetics.

The 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 at least 140

Can also be classified into three categories depending on the prevailing compositions:

• Paraffinic 
• Naphthenic 
• Aromatic

Lubricants for internal combustion engines contain additives to reduce oxidation and improve lubrication. The main constituent of such lubricant product is called the base oil, base stock. While it is advantageous to have a high-grade base oil in a lubricant, proper selection of the lubricant additives is equally as important. Thus some poorly selected formulation of PAO lubricant may not last as long as more expensive formulation of Group III+ lubricant.

Biolubricants made from vegetable oils and other renewable sources

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, castor oil, palm oil, sunflower seed oil and rapeseed oil from vegetable, and Tall oil from tree sources. Many vegetable oils are often hydrolyzed to yield the acids which are subsequently combined selectively to form specialist synthetic esters. Other naturally derived lubricants include lanolin (wool grease, a natural water repellent).

Whale oil was a historically important lubricant, with some uses up to the latter part of the 20th century as a friction modifier additive for automatic transmission fluid.

In 2008, the bio lubricant market was around 1% of UK lubricant sales in a total lubricant market of 840,000 tonnes/year.

Lanolin is a natural water repellent, derived from sheep wool grease, and is an alternative to the more common petro-chemical based lubricants. This lubricant is also a corrosion inhibitor, protecting against rust, salts, and acids.

Water can also be used on its own, or as a major component in combination with one of the other base oils. Commonly used in engineering processes, such as milling and lathe turning.