Basic properties of lubricating grease

Lubricating oil is a technology-intensive product, a mixture of complex carbon compounds, and its real performance is the comprehensive effect of complex physical or chemical change processes. The basic properties of lubricants include general physical and chemical properties, special physical and chemical properties and simulation bench tests.

General physical and chemical properties

Each type of lubricating grease has its common general physical and chemical properties to indicate the inherent quality of the product. For lubricating oils these general physical and chemical properties are as follows:

(2) Density: Density is the simplest and most commonly used physical performance indicator of lubricating oil. The density of lubricating oil increases with the increase in the amount of carbon, oxygen and sulfur in its composition. Therefore, under the same viscosity or the same relative molecular mass, the density of lubricating oil containing more aromatic hydrocarbons, colloids and asphaltenes will The largest, the one containing more naphthenes is in the middle, and the one containing more naphthenes is the smallest.

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

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

(5) Flash point: Flash point is an indicator of the evaporability of oil. The lighter the oil fraction, the more evaporative it is and the lower its flash point. On the contrary, the heavier the oil fraction, the less evaporative it is and the higher its flash point. At the same time, flash point is an indicator of the fire hazard of petroleum products. The hazard level of oil products is divided based on the flash point. A product with a flash point below 45°C is a flammable product, and a product with a flashpoint above 45°C is a combustible product. It is strictly prohibited to heat the oil product to its flash point temperature during the storage and transportation of oil products. With the same viscosity, the higher the flash point, the better. Therefore, when selecting lubricating oil, users should make a selection based on the operating temperature and working conditions of the lubricating oil. It is generally believed that if the flash point is 20~30℃ higher than the use temperature, it can be used safely.

(6) Condensation point and pour point: Condensation point refers to the highest temperature at which oil stops flowing under specified cooling conditions. The solidification of oils is very different from the solidification of pure compounds. Oil does not have a clear solidification temperature. The so-called "solidification" means that the oil as a whole loses its fluidity. Not all components have become solid. The freezing point of lubricating oil indicates the low-temperature fluidity of lubricating oil.

An important quality indicator, which is of great significance for production, transportation and use. Lubricating oils with high freezing points cannot be used at low temperatures. On the contrary, in areas with higher temperatures, there is no need to use lubricants with low freezing points. Because the lower the freezing point of lubricating oil, the higher its production cost will cause unnecessary waste. Generally speaking, the freezing point of lubricating oil should be 5~7℃ lower than the lowest temperature of the use environment. But it is particularly important to mention that in When selecting low-temperature lubricating oil, comprehensive consideration should be given to the freezing point, low-temperature viscosity and viscosity-temperature characteristics of the oil. Because the low-temperature viscosity and viscosity-temperature characteristics of oils with low pouring points may not meet the requirements. Both pour point and pour point are indicators of the low-temperature fluidity of oil. There is no principled difference between the two, but the measurement methods are slightly different. The freezing point and pour point of the same oil are not exactly equal. Generally, the pour point is 2~3°C higher than the pouring point, but there are exceptions.

(7) Acid value, base value and neutralization value: Acid value is an indicator of acidic substances contained in lubricating oil, and the unit is mgKOH/g. The acid value is divided into two types: strong acid value and weak acid value. The combination of the two is the total acid value (TAN). What we usually call "acid value" actually refers to "total acid value (TAN)". The base number is an index indicating the content of alkaline substances in lubricating oil, and the unit is mgKOH/g. The base number is also divided into two types: strong base number and weak base number. The combination of the two is the total base number (TBN). What we usually call "base number" actually refers to "total base number (TBN)". Neutralization value actually includes total acid value and total base value. However, unless otherwise noted, the so-called "neutralization value" actually only refers to the "total acid value", and its unit is also mgKOH/g.

(8) Moisture: Moisture refers to the percentage of water content in lubricating oil, usually by weight. The presence of moisture in the lubricating oil will destroy the oil film formed by the lubricating oil, worsen the lubrication effect, accelerate the corrosion of metals by organic acids, corrode equipment, and make the oil prone to sink flow. In short, the less water in the lubricating oil, the better.