PURPOSE OF LUB OIL :

 To reduce friction and wear in the engine.

 To act as a sealant between the piston ring and liner.

 To cool the internal parts of the engine.

To clean the engine interior of dirt and carbon.

       To dampen noise.

      To protect metal against corrosion

LUB OIL PROPERTIES AND ADDITIVES

1.   Dispersivity    Capacity to keep sludge forming insolubles in suspension i.e. to keep cold parts clean.

Additives               Metallo-organic compounds such as napthenates and sulphonates, organic salts containing metals like calcium, co­balt and strontium. These additives break down insoluble products into finely divided colloidal parts which remain in suspension

2.      Detergency    Capacity to keep hot surfaces clean by preventing oil soluble oxidation products becoming insoluble and depositing.

Additives    Metallo-organic compounds such as phosphates, phenolates, sulphonates, alcoholate, high molecular weight soaps containing magnesium, tin, calcium and barium.

3.      Resistance to oxidation   Capacity to resist action of oxygen.

Additives   Phenols, aromatic amines and zinc-di-alkyl di-thiophosphate!

Chain reaction of oxidation of oil (peroxide formation) is prevented by chemicals which combines with peroxides to form harmless compounds.

4.Anti -wear/ Anti Scuffing (oiliness)   Capacity to contain wear by preserving an oil film even at high load and pressure.

Additives   Combination of fatty acids (oleic or stearic acid) and metallic soaps (lead oleate), called polar agents. Extreme pressure agents are chlorinated fatty compounds (upto 300°C) and sulphur compound (upto 650°C). These additives increase the oiliness or metal wetting property and adhere to the metal surface, there by reducing friction and wear in boundary lubrication.

5 Anti - Corrosive/
Anti – rust                  Capacity to resist corrosion.

Additives    Sulphonates, amines, fatty oils, phosphates prevent rust and neutralises corrosive acids.

6          Alkalinity Reserve - Capacity to neutralise acids.

Additives                        Organic compounds containing active sulphur, phosphorus or nitrogen.

7  Demulsibility ----   Capacity to separate water contaninents, and to reduce affinity for water.

Additives ------------------ Organo silicon and other polymers, provides water resistant properties.

8  Low Pour Point ------    Capacity to resist separation of wax crystal from solution.

Additives ------------------  Pour Point Depressant Napthalene or Phenol and their polymers, methacrylate polymers. Wax crystals in oils are coated to prevent growth and oil absorption at reduced temperature.

9 High Viscosity Index ---- Viscosity Index is the relationship of change in viscosity with change in temperature and depends on the molecular structure of the oil. Less is the variation of viscosity with temperature change means higher is the viscosity index.

Additives -------------------- V.I.Improvers - High molecular weight long chain organic polymers. Improvers are less affected by temperature change than oil.

10 Anti-foam Additives ---- Capacity to resist froth formation.

Additives -------------------- Silicone polymers. Reduces interfacial tension so that small air babbles are combined by the additive to form larger air bubbles that can separate or vent faster.

Anti bacterial activity ---- Common micro - organisms in oil are bacteria and fungi. Their growth is enhanced with the presence of water, oxygen and favourable temperature. These micro - organisms devours the oil and degrades it by forming bio - polymer (slime).

Additives -------------------- Biocides.

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