Viscosity Index Improver (VI Improver). Additives for motor oils.
These additives are designed to increase the viscosity of oils and improve their temperature properties
Viscosity, or internal friction – the most important property of lubricating oil. In the case of liquid friction, the friction surfaces are completely separated by a layer of lubricant. The thinner the separating layer of the grease, the greater the danger of its destruction and the appearance of dry friction.
As the viscosity of the oil increases, the adhesion of its molecules increases. This leads to an increase in the strength and thickness of the separating layer of the lubricant.
The reliability of the liquid lubricant increases with the increase in the viscosity of the oil, the sliding speed of the rubbing surfaces and the reduction of the load on the rubbing parts.
The higher the sliding speed of the rubbing surfaces and the less the load on them, then you need an oil with a lower viscosity. And if there is a slow friction between the parts and an increased load. So you need a more viscous oil.
The viscosity of the oil for lubricating the engine is selected depending on the specific conditions of its operation.
Engine oil should less change the viscosity when the temperature changes.
Viscosity qualities of oils improve the additives to them. Additives for hanging viscosities. Additives to reduce viscosity.