Why Do Lubricants Need Additives?
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The Importance of Additives in Lubricants: An Overview of Lube Additives.
Lubricating oil generally consists of two parts: base oil and additive. Base oil is the main component of lubricating oil, and determines the basic properties of lubricating oil, additives can make up for and improve the performance of base oil deficiencies, give some new properties, and are an important part of lubricating oil.
Lubricating base oil is mainly divided into mineral base oil, synthetic base oil, and biological base oil. Mineral base oils are widely used in large quantities (over 95%).
Mineral oil base oil is refined from crude oil. The main processes of lubricating base oil are atmospheric and vacuum distillation, solvent deasphalting, solvent refining, solvent dewaxing, and clay or hydro-refining. In 1995, China revised the current lubricating base oil standard, mainly modified the classification method, and added two special base oil standards for low point and deep refining. For mineral lubricating oil, the most important is to choose the best crude oil.
API Classification of Lubricant Base Oils
The American Petroleum Institute (API) divides the base oils used in internal combustion engine lubricating oils into 5 categories according to the saturated hydrocarbon content, sulfur content, and viscosity index, and is recognized worldwide.
| API Classification of Lubricant Base Oils | |||
| ITEM | Sulphur % | Saturated hydrocarbon % | VI(viscosity index) |
| API Ⅰ | >0.03 | ＜90 | 80≤ VI ＜120 |
| API Ⅱ | ≤0.03 | ≥90 | 80≤ VI ＜120 |
| API Ⅲ | ≤0.03 | ≥90 | ≥120 |
| API Ⅳ | Polyalphaolefin(PAO) | ||
| API Ⅴ | Other base oils(non-class Ⅰ, Ⅱ, Ⅲ, Ⅳ) | ||
Lubricant additive is the essence of modern lubricants. Proper selection and reasonable addition can improve its physical and chemical properties, give new special properties to lubricating oil, or strengthen its original performance to meet higher requirements. According to the required quality and performance of lubricating oil, careful selection, careful balance and reasonable allocation of additives are the key to ensuring the quality of lubricating oil. Common additives are Viscosity Index Improvers, Pour Point Depressants, Antioxidants, Dispersants, Friction Modifiers, Oiliness Additives, Extreme Pressure Additives, Anti-foam Additives, Metal Deactivator, Emulsifiers, Demulsifiers, Antioxidant Additives, anti-corrosion agents, etc.
Classification and functions of common lubricant additives
| Lubricant Additives | Additives to protect metal surfaces | Antiwear and Extreme Pressure | --Reduces friction and wear, prevents chafing & sintering |
| Corrosion and Rust Inhibitors | --Prevents corrosion and rusting of metal parts in contact with lubricants | ||
| Detergent Additives | --Keep surfaces free of deposits | ||
| Ashless Dispersing agent | --Keeps insoluble contaminants dispersed in the lubricant | ||
| Friction Modifier | --Reduce coefficient of friction | ||
| Additives that extend the scope of applications | Pour Point Depressant | --make lubricant able to flow at low temperature | |
| Seal Swell Additive | --Expand the Elastomeric Seals | ||
| Viscosity Index Improver | --Reduce viscosity changes rate with temperature | ||
| Additives to increase the life of lubricants | Antifoam Additive | --Prevents lubricants from forming persistent foam | |
| Antioxidant | --Reduce oxidative decomposition | ||
| Metal Deactivator | --Reduce catalytic oxidation of metals | ||
| other Lubricant Additives | Tackifier | ||
| Emulsifier | |||
| Demulsifier | |||
| Bactericide |
