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All About Oil

INTRODUCTION:


Lubricant aka Lube, is typically a viscous substance introduced between two moving surfaces to reduce the friction and wear between them. The property of reducing friction is known as lubricity (or slipperiness).  It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. More than 75 million tons of lubricants are consumed worldwide annually of which, automotive engine lubricants comprise approximately 50% and Hydraulic fluids with Transmission oils comprise 30% of it.

Typically lubricants contain between 85 & 90% base oil (most often petroleum fractions, called mineral oils) and approximately, 10 to 15% additives. Vegetable or synthetic fluids are sometimes used as base oils.  Additives deliver reduced friction and wear, increased viscosity, resistance to corrosion and aging, etc.  Sodium and lithium based additives are used in automotive greases to stabilize the grease against high temperatures.  This is particularly important in the grease used to pack wheel bearings, and especially those used with disc braking systems.




A good lubricant generally possesses the following characteristics:


·        high boiling point and low freezing point (in order to stay liquid within a wide range of temperature)

·        High viscosity index

·        Thermal stability

·        Hydraulic stability

·        Demulsibility

·        Corrosion prevention

·        High resistance to oxidation.

 


LUBE vs FRICTION:


Lubricants are typically used to separate moving parts in a system. This has the benefit of reducing friction 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 hydro planning, 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.


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 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 valve train in a car engine at start-up.

 

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