When is it best to use a high viscosity index oil?

1.What is Viscosity Index (Viscosity Index):

Viscosity index (VI: Viscosity index) is the degree to which the viscosity of a liquid changes with temperature. Temperature affects the viscosity of a liquid, just like cooking oil, if the temperature is lowered, the oil will thicken or even stop flowing; if the temperature is raised, the viscosity of the oil will decrease and become thinner and the fluidity will increase. When selecting lubricating oil, equipment requires a suitable viscosity, so we hope that the viscosity of lubricating oil can remain relatively stable in temperature changes. The viscosity of lubricating oil will change with temperature, but the higher the viscosity index of lubricating oil, the viscosity can remain relatively stable in the temperature change, the lower the viscosity index, the more easily the viscosity of the oil is affected by temperature. Lubricating oils with a high viscosity index show better viscosity-temperature characteristics.

2.The role of viscosity index improvers:

At low temperature, the lubricating oil should have good fluidity, so the viscosity should not be too large to prevent the lubricating oil from not fully flowing to the lubricated part, resulting in dry friction. The dry friction of mechanical cold start is an important cause of machine wear. When the machine heats up gradually after starting, the fluidity of the lubricating oil is good, but if it becomes too thin, the thickness of the oil film formed on the lubricating part is not enough, which will lead to poor lubrication, intensified friction and wear, so the viscosity-temperature property of the lubricating oil is Good (high viscosity index) helps provide better lubrication protection and reduces the potential for wear.

Lubricating oil is prepared by adding various additives to the base oil. The additives can improve the performance of the base oil. The VI improver is an additive that improves the viscosity index of the lubricating oil, and is also called a tackifier in some places. The viscosity index of lubricating oil is related to the type of base oil. Some base oils have higher viscosity indices (such as PAO, III oils, etc.) before using viscosity index improvers, and some base oils have lower viscosity indices. Then need to add more viscosity index improver.

3.What is a viscosity index improver:

The viscosity index improver is an oil-soluble chain polymer, which is sensitive to temperature. At low temperature, the molecular chain of the polymer shrinks, and at high temperature, the molecular chain expands. Viscosity index improvers mainly include polyisobutylene, polyacrylate, ethylene propylene copolymer, etc.

Viscosity index improvers are generally solid at room temperature. This polymer is dissolved in lubricating oil and will form a coil structure. At low temperature, the polymer is in a curled state, which has little effect on the fluidity of the oil. . As the temperature rises, the molecular chain stretches out, and the friction between the base oil molecules increases, which hinders the fluidity of the oil, that is, the viscosity increases, which relieves the viscosity decrease of the lubricating oil to a certain extent.

Viscosity index improvers are mainly used in automobile engine oil (multi-grade oil), gear oil, automobile transmission oil, hydraulic oil, grease, etc., mostly related to automobile lubrication. Taking oil as an example, the viscosity of the oil should not be too high when starting at a low temperature, otherwise the oil pump will not be able to suck the oil to the top of the engine, but the temperature of the engine gradually rises after starting, and finally reaches the normal working temperature. Up to 100 degrees or more, the use of oil with a high viscosity index is beneficial to protect the engine.


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