The surfaces of rolling or moving parts in all kinds of machines rub against each other. The mutual rubbing of various parts of a machine imparts resistance their movement. This resistive force is called friction.
Friction causes a significant wear and tear to the surfaces of moving parts of machines. To reduce this force of resistance, some substances are introduced between the moving surfaces. These are called lubricants. The main purpose of lubricants is to keep the moving surfaces away from each other, so the friction and the resulting damage to the moving parts can be reduced.
The process of reducing the force of resistance or friction between moving surfaces of machines by the introduction of a lubricant is called lubrication.
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What causes friction?
There are many theories that explain why friction occurs between moving parts of machines.
The welding theory suggests that all metal surfaces, irrespective of how finely they are finished, have a series of troughs and crests. So, when such surfaces are rubbed against one another, only the crests from both surfaces come in actual contact. When the surfaces are rubbed under load, the local pressure at the crests is sufficient to deform the peaks and create welding junctions between them.
The electrostatic attraction theory suggests that the stick-slip phenomenon between the moving parts results in the flow of electrons, which produce charges of opposite polarities at the interface. These charges keep holding the surfaces with each other by virtue of electrostatic attraction.
Another theory, the mechanical interlocking theory, states that when the moving surfaces come in contact with each other, the crests and troughs of both surfaces interlock with each other, thus restricting the movement of one surface over the other.
How Lubricants work?
Some lubricants are applied as thick fluid films between the moving surfaces. These films separate the moving surfaces from each other, avoiding the direct contact between surfaces which consequently results in reduced friction.
In cases where a continuous film of lubricants cannot persist between moving machine parts, a material is applied that can get adsorbed on both surfaces by virtue of either physical or chemical forces. This thin film of adsorbed substances help the moving surfaces remain away from each other, at least upto the height where crests are present on the surfaces.
In some cases characterized by very high pressure and speed between moving machine parts, either a thick or a thin film fails to stick to the surfaces. This happens as the high local temperature attained at the surfaces decomposes or even vaporizes the lubricant films. To meet these conditions, special additives are added to commonly used lubricants, making them more durable.
Global Scenario:
Lubricants are as necessary as the machines themselves in any industrial segment. If it was not for the use and introduction of lubricants, of a variety of forms in a variety of products, industrial machines would have to be either repaired or replaced within few years of their use.
The wide range of applications of lubricants in a variety of industrial segments has made this industry a billion dollar global market. This industry has huge scope of growth in the coming years as well, owing to the growth of industries such as automotives.
The automotives industry has huge growth prospects in the Asia pacific region, a region where every industry seems to flourish in the current market scenario due to rapid economic development, abundant raw materials and cheap labor. This indirectly would lead to the growth of the lubricants industry in the coming times.
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