| |
| Lubricants & Greases |
| |
Lubrication & Tribology
The art of reducing friction between rubbing/rolling surfaces is called Lubrication. The external Solid or Fluid used as a medium to reduce friction in rubbing/rolling surfaces is called lubricant. The whole mechanism including lubricant used for ensuring lubrication through lubricant is called lubrication system. In the recent past two terminologies have gained importance – Tribology which means science of Rubbing and Rheology which means science of stream/flow. Thus Tribology includes Lubrication, Rheology, material properties, material surface properties etc. Lubrication was known to mankind centuries ago as evident from grease lubricated chariot wheels. However the rapid development of this science can be said to have started from 18th century and significant technological progress, commercial usage was made in 20th century.
Lubricating Oils
Most lubricants used in variety / quantity are liquids. Water is natural lubricant but has extremely limited application due to very low viscosity, very low boiling point and water causes rusting/ corrosion. Vegetable oils have excellent lubrication property but also have many limitations like very poor oxidation stability, high pour point rapid thickening and may even give foul smell after some operation. Vegetable oils like Castor Oils were used on very large scale till 1925 or so. Vegetable oils are still used directly or as an additive in some applications. Most of the liquid lubricants used at present all over the world are mineral oils, which are petroleum-based oils. These are very complex mixture of variety of hydrocarbons having desired lubrication properties segregated from other hydrocarbons through various processes to remove undesired hydrocarbons like aromatics, olefins, waxes, mercaptans asphaltenes etc. Thus the process is by removing undesired hydrocarbons.
Base Oils
The latest process technology in vogue for decades for making lubricating oil base stocks is by transforming undesired hydrocarbons into desired hydrocarbons through hydrocracking, hydrofinishing hydrodesulfuring etc. This process technology improvement gives benefit of improving colour to almost waterwhite, improving viscosity index, reducing sulphur & benzene content, isomerisation causing lower pour point and increasing the yield. Such highly refined lube base stocks are called Group II and Group III base oils where as previous conventional method processed base oils are called Group I base oils. Haldia Refinery of Indian Oil produces Group I / II/III base oils at Haldia. CPCL refinery of Indian Oil produces Group I base oils at Chennai.
Lubricating oil is not a specific chemical to have fixed chemical formula. Nor it is a definite mixture of hydrocarbons in exactly specific component distribution pattern. Lubricants are therefore decided by their group property or group behaviour. Thus lubricating oil base stocks can have different colours, viscosities, stabilities, properties etc depending on several factors – source – refining technique etc.
Viscosity of Lubricating Oil is most important characteristic. As viscosity changes with change in temperature, this behaviour becomes another important characteristic of lubricant. Thermal/ chemical/Oxidation stabilities, demulsibility property, air release property, de-foaming property etc are other important characteristics for lubricant.
Additives are added at different proportions to impart or to promote certain lubrication properties as per the application requirements. Thus lubrication formulation becomes complex subject, formulations vary from application to application, manufacturer to manufacturer and this is how the lubricants become proprietary grades of manufacturers/marketers. At the same time OEs and institutions may bring out some specifications and standards to evaluate lubricants or to specify lubricants.
Synthetic Lubricants
Synthetic Lubricants are generally hydrocarbons as in case of mineral oils or may be hydrocarbons with some oxygen as in case of vegetable oils or can be even void of hydrocarbons. What actually differentiates is that synthetic lubricant means specially synthesized lubricant – to make it specific chemical or mixture of extremely small range of chemicals which will give sharp focused lubrication properties as per exacting requirements. Therefore synthetic lubricants can be much superior to mineral lubricants, but will be extremely costly and therefore user has to make trade off. This is why mineral lubricants constitute major portion in lube market.
Lubricating Greases
These are primarily lubricating oils thickened with some thickener like metallic soaps/ non metallic other materials like clay. Thickening is to ensure that the lubricant remains where it is applied without leaking/ dripping. The Lubricating Oil used does the basic lubrication. The thickener used also imparts some specific lubrication properties. Additives are also used as in case of lubricating oils to impart / promote specific properties. Use of grease is limited as compared to use of lubricating oil but there are several situations warranting use of grease only.
|
|
|
|
|