*2.1.1 Application based on properties of base oil*

Group I base oils are processed by solvent processing in which wax and multiring aromatics are removed while some sulfur and aromatics remain. These base oils are typically used in marine and diesel engine oils, heat transfer oils, hydraulic oils, conventional greases, industrial gear oils, and machine tool oils. These oils have high solvency, very high viscosity but poor viscosity index. The maximum operating temperature is 93°C.

Group II base stocks have undergone catalytic conversion to remove wax, aromatics and sulfur compounds. These base oils are used as automotive engine oil, automatic transmission fluid, gear oils and turbine oils. The maximum operating temperature of these base stocks is 121°C.

Group III base oils are similar to Group II oils but have a higher viscosity index. The severity of hydroprocessing removes any ring structures, as a result, its solvency is poor. These base oils are used in premium passenger vehicles, automatic transmission fluids, and food grade lubricants. The maximum operating temperature is 121°C.

Group IV oils are synthetically produced Polyalphaolefins from low molecular weight organic material. They have uniform molecular structures. They provide excellent high temperature performance and oxidation stability and therefore used in high performance engine and gear applications, heavy duty industrial


**173**

*Lubricant and Lubricant Additives*

temperature of 232°C.

stock in the same API category.

and regulations set by industry bodies.

**2.2 Lubricant additives**

and 140.

*DOI: http://dx.doi.org/10.5772/intechopen.93830*

PAOs have a maximum operating temperature of 132°C.

compressor, power transmission fluid, hydraulic fluid, heat transfer fluid and in bearings as greases or liquid or lubricants. A wide range of viscosity grades of PAOs can be produced by varying the number of olefin molecules linked together.

Group V base stocks can be either naphthenic or synthetic in origin. The naphthenics provide very good low temperature performance and hence are used in applications which operate in a narrow temperature range such as transformer oil, process oils, grease. These oils have high solubility and available in a wide range of viscosities. The synthetics on the other side vary widely in their types and properties. These include polyglycols, silicones, polybutenes, organic esters, phosphate esters and they are used as compressor oils, brake fluids, heat transfer oils, aviation engine oil. Their maximum operating temperature is dependent on the nature of their molecular structure. Silicon oils are known to have a maximum operating

Finally, Group II+ and Group III+ are two types of base stocks that are not included in the original API classification. The plus refers to increase in viscosity index (VI) in the higher limit of the API specification. Group II+ has VI minimum between 110 and 115 and Group III+ has minimum VI somewhere between 130

As mentioned previously, mineral oils are mixtures of hydrocarbons containing paraffins, naphthenics and aromatics of various structures and carbon numbers ranging between 20 to 40+, at varying amounts depending on their degree of refining and processing. Typical composition of various API groups have been identified, but their exact structures are still not known. There is a considerable variability in the performance among the mineral origin base oils owing to the source of the crude. Therefore, lubricant manufactures conduct performance tests on their formulations to ascertain satisfactory performance with any new base

The primary function of Lubricant additives is to improve the properties of the base stock under different operating conditions and the high performance requirements of any machinery. Lubricant additives are chemical components that need to blend well with the base oil to function as a single fluid. Additive manufactures often sell several additives combined into an additive package and diluted with a base oil at a higher concentration. The additive package is then dosed into the lubricant blend by the lubricant manufacturer at an appropriate treat rate to give the desired performance. The concentration of various additives is constrained by various factors such as their primary function (for example dispersancy, wear protection and so on), their synergetic or antagonistic behaviour with other additives,

In a nutshell, lubricant additives can be categorized into various kinds based on their general roles of performance improvement and service life extension. First category are additives that impart new properties to the lubricant also known as surface protective additives. Examples include antiwear additives, extreme pressure additives, corrosion inhibitors, detergents and dispersants. The second kind of additives enhance the existing properties already present in the lubricant hence known as performance additives. Viscosity index improvers, viscosity modifiers, friction modifiers, pour point depressants belong to this type. The third type of additives known as lubricant protective additives, are the ones that counteract the negative effects or changes that take place during the service life of the lubricant. These include antifoamants and, antioxidants. In this chapter only the major types

**Table 1.** *API base stock classification.*

#### *Lubricant and Lubricant Additives DOI: http://dx.doi.org/10.5772/intechopen.93830*

*Tribology in Materials and Manufacturing - Wear, Friction and Lubrication*

Society of Automotive Engineers (SAE) to name a few.

performance requirements.

*2.1.1 Application based on properties of base oil*

maximum operating temperature is 93°C.

temperature of these base stocks is 121°C.

Group V Synthetics and naphthenics and

other stocks not included in Group I, II, III or IV

professional bodies, and international institutions like American Petroleum Institute (API), International Lubricant Standardization and Approval Committee (ILSAC),

Owing their origin to petroleum crudes, lubricant base stocks are also mixtures of long chain hydrocarbons containing three types of chemical groups. i.e. paraffins, naphthenes and aromatics. The paraffins can be further classified into branched or straight chains. The chain length and branching affects the melting point and crystallization temperature of the paraffins. During the production of lube base stock, most of the unsaturated bonds, paraffin wax and sulfur content are removed, however depending on the severity of hydroprocessing, some wax, unsaturates and sulfur may remain. Base Stocks have been classified into 5 categories by the API according to the presence of saturates, sulfur content and viscosity as shown in **Table 1**. Group I, II and III are derived from petroleum crude while Group IV is reserved for Polyalphaolefins (PAO) which are synthesized from gaseous hydrocarbons. Group V is for all other base stocks that are not included in other four groups such as mineral based napthenics, synthetic esters, polyglycols, silicones, polybutenes, phosphate esters etc. These oils are designed for severe

Group I base oils are processed by solvent processing in which wax and multiring aromatics are removed while some sulfur and aromatics remain. These base oils are typically used in marine and diesel engine oils, heat transfer oils, hydraulic oils, conventional greases, industrial gear oils, and machine tool oils. These oils have high solvency, very high viscosity but poor viscosity index. The

Group II base stocks have undergone catalytic conversion to remove wax, aromatics and sulfur compounds. These base oils are used as automotive engine oil, automatic transmission fluid, gear oils and turbine oils. The maximum operating

Group III base oils are similar to Group II oils but have a higher viscosity index. The severity of hydroprocessing removes any ring structures, as a result, its solvency is poor. These base oils are used in premium passenger vehicles, automatic transmission fluids, and food grade lubricants. The maximum operating temperature is 121°C. Group IV oils are synthetically produced Polyalphaolefins from low molecular weight organic material. They have uniform molecular structures. They provide excellent high temperature performance and oxidation stability and therefore used in high performance engine and gear applications, heavy duty industrial

Group I Solvent refined <90 >0.03 80 to <120 Group II Hydrofinished ≥90 ≤0.03 80 to <120 Group III Hydrocracked ≥90 ≤0.03 ≥120 Group IV Polyalphaolefins — — —

**Type Saturates (%) Sulfur (%) Viscosity** 

— — —

**index**

**172**

**Table 1.**

*API base stock classification.*

compressor, power transmission fluid, hydraulic fluid, heat transfer fluid and in bearings as greases or liquid or lubricants. A wide range of viscosity grades of PAOs can be produced by varying the number of olefin molecules linked together. PAOs have a maximum operating temperature of 132°C.

Group V base stocks can be either naphthenic or synthetic in origin. The naphthenics provide very good low temperature performance and hence are used in applications which operate in a narrow temperature range such as transformer oil, process oils, grease. These oils have high solubility and available in a wide range of viscosities. The synthetics on the other side vary widely in their types and properties. These include polyglycols, silicones, polybutenes, organic esters, phosphate esters and they are used as compressor oils, brake fluids, heat transfer oils, aviation engine oil. Their maximum operating temperature is dependent on the nature of their molecular structure. Silicon oils are known to have a maximum operating temperature of 232°C.

Finally, Group II+ and Group III+ are two types of base stocks that are not included in the original API classification. The plus refers to increase in viscosity index (VI) in the higher limit of the API specification. Group II+ has VI minimum between 110 and 115 and Group III+ has minimum VI somewhere between 130 and 140.

As mentioned previously, mineral oils are mixtures of hydrocarbons containing paraffins, naphthenics and aromatics of various structures and carbon numbers ranging between 20 to 40+, at varying amounts depending on their degree of refining and processing. Typical composition of various API groups have been identified, but their exact structures are still not known. There is a considerable variability in the performance among the mineral origin base oils owing to the source of the crude. Therefore, lubricant manufactures conduct performance tests on their formulations to ascertain satisfactory performance with any new base stock in the same API category.

#### **2.2 Lubricant additives**

The primary function of Lubricant additives is to improve the properties of the base stock under different operating conditions and the high performance requirements of any machinery. Lubricant additives are chemical components that need to blend well with the base oil to function as a single fluid. Additive manufactures often sell several additives combined into an additive package and diluted with a base oil at a higher concentration. The additive package is then dosed into the lubricant blend by the lubricant manufacturer at an appropriate treat rate to give the desired performance. The concentration of various additives is constrained by various factors such as their primary function (for example dispersancy, wear protection and so on), their synergetic or antagonistic behaviour with other additives, and regulations set by industry bodies.

In a nutshell, lubricant additives can be categorized into various kinds based on their general roles of performance improvement and service life extension. First category are additives that impart new properties to the lubricant also known as surface protective additives. Examples include antiwear additives, extreme pressure additives, corrosion inhibitors, detergents and dispersants. The second kind of additives enhance the existing properties already present in the lubricant hence known as performance additives. Viscosity index improvers, viscosity modifiers, friction modifiers, pour point depressants belong to this type. The third type of additives known as lubricant protective additives, are the ones that counteract the negative effects or changes that take place during the service life of the lubricant. These include antifoamants and, antioxidants. In this chapter only the major types

of lubricant additives are discussed. Other additives such as demulsifiers, emulsifier, biocides may be added depending on the intended applications.
