Lube Oil Appearance (chromaticity)

The color of oil products can often reflect their degree of refining and stability. For base oil, the higher the degree of refining, the cleaner the removal of hydrocarbon oxides and sulfides, and the lighter the color. However, even if the refining conditions are the same, the base oil produced by crude oils of different oil sources and bases may have different colors and transparency.

For new finished lubricants, due to the use of additives, color has lost its original meaning as an indicator of the degree of refining of base oils.

Density

Density is the simplest and most commonly used physical performance indicator of lubricating oils. The density of lubricating oil increases with the increase of the amount of carbon, oxygen, and sulfur in its composition. Therefore, under the same viscosity or the same relative molecular mass, lubricating oils containing more aromatics, more colloids and more asphaltene have the highest density, those containing more cycloalkanes are in the middle, and those containing more alkanes have the lowest density.

Viscosity

Viscosity reflects the internal friction of oil products and is an indicator of oiliness and fluidity of oil products. Without adding any functional additives, the greater the viscosity, the higher the oil film strength and the worse the fluidity.

Viscosity index

The viscosity index indicates the degree to which the viscosity of the oil changes with temperature. The higher the viscosity index, the less the viscosity of the oil is affected by temperature, and the better its viscosity-temperature performance, and vice versa.

Flash point

The flash point is an indicator of the volatility of the oil. The lighter the fraction of the oil, the greater the volatility and the lower its flash point. Conversely, the heavier the fraction of the oil, the lower the volatility and the higher its flash point. At the same time, the flash point is also an indicator of the fire hazard of petroleum products. The hazard level of oil is divided according to the flash point. The flash point below 45°C is flammable, and the flash point above 45°C is flammable. It is strictly forbidden to heat the oil to its flash point temperature during the storage and transportation of oil. Under the same viscosity, the higher the flash point, the better. Therefore, when selecting lubricants, users should choose according to the use temperature and working conditions of the lubricants. It is generally believed that the flash point is 20 to 30°C higher than the use temperature, and it can be used safely.

Pouring point and pour point

The pour point refers to the highest temperature at which the oil stops flowing under the specified cooling conditions. The solidification of oil products is very different from the solidification of pure compounds. Oil products do not have a clear solidification temperature. The so-called "solidification" only means that the oil loses its fluidity as a whole, not that all components become solid.

The solidification point of lubricating oil is an important quality indicator of the low-temperature fluidity of lubricating oil. It is of great significance for production, transportation and use. Lubricating oils with high solidification points cannot be used at low temperatures. On the contrary, it is not necessary to use lubricating oils with low solidification points in areas with higher temperatures. Because the lower the solidification point of the lubricating oil, the higher its production cost, resulting in unnecessary waste. Generally speaking, the solidification point of lubricating oil should be 5~7℃ lower than the lowest temperature of the use environment. However, it should be mentioned in particular that when selecting low-temperature lubricating oils, the solidification point, low-temperature viscosity and viscosity-temperature characteristics of the oil should be considered comprehensively. Because the low-temperature viscosity and viscosity-temperature characteristics of oil products with low solidification points may not meet the requirements.

Both solidification point and pour point are indicators of low-temperature fluidity of oil products. There is no principled difference between the two, but the determination methods are slightly different. The pour point and pour point of the same oil are not completely equal. Generally, the pour point is 2 to 3°C higher than the pour point, but there are exceptions.

Acid value

The acid value is an indicator of the acidic substances contained in the lubricating oil, and the unit is mgKOH/g. The acid value is divided into strong acid value and weak acid value, and the combination of the two is the total acid value (TAN for short). What we usually call "acid value" actually refers to "total acid value (TAN)".

Alkalinity is an indicator of the content of alkaline substances in lubricating oil, and the unit is mgKOH/g.

Alkalinity is also divided into strong alkalinity and weak alkalinity, and the combination of the two is the total alkalinity (TBN for short). What we usually call "alkalinity" actually refers to "total alkalinity (TBN)".

Neutralization value

The neutralization value actually includes the total acid value and the total alkalinity. However, unless otherwise specified, the "neutralization value" generally referred to actually only refers to the "total acid value", and its unit is also mgKOH/g.

Moisture content

Moisture content refers to the percentage of water in lubricating oil, usually in weight percentage. The presence of water in lubricating oil will destroy the oil film formed by lubricating oil, make the lubrication effect worse, accelerate the corrosion of metal by organic acid, rust equipment, and make the oil product easy to produce sediment. In short, the less water in lubricating oil, the better.

Mechanical impurities

Mechanical impurities refer to precipitates or colloidal suspensions in lubricating oil that are insoluble in solvents such as gasoline, ethanol and benzene. Most of these impurities are sand and iron filings, as well as some organic metal salts that are difficult to dissolve in solvents brought by additives. Usually, the mechanical impurities of lubricating oil base oil are controlled below 0.005% (mechanical impurities below 0.005% are considered to be zero).

Sulfate ash

Ash refers to the non-combustible material left after burning under specified conditions. The composition of ash is generally considered to be some metal elements and their salts. Ash has different concepts for different oil products. For base oil or oil products without additives, ash can be used to judge the refining depth of oil products. For oil products (new oil) with metal salt additives, ash content becomes a means of quantitatively controlling the amount of additives added. Abroad, sulfated ash content is used instead of ash content. The method is: add a small amount of concentrated sulfuric acid before burning the oil sample to convert the metal elements of the additive into sulfates.

Carbon residue

The charred black residue formed after the oil product is heated and evaporated and burned under the specified experimental conditions is called carbon residue. Carbon residue is an important quality indicator of lubricating oil base oil, and is a project specified to judge the properties and refining depth of lubricating oil. The amount of carbon residue in lubricating oil base oil is not only related to its chemical composition, but also to the refining depth of the oil product. The main substances that form carbon residue in lubricating oil are: colloids, asphaltene and polycyclic aromatic hydrocarbons in the oil. These substances are decomposed and condensed by strong heat under the condition of insufficient air to form carbon residue. The deeper the refining depth of the oil product, the smaller its carbon residue value. Generally speaking, the smaller the carbon residue value of the blank base oil, the better.