Find the best lubricating oils to maximize your machinery’s lifespan. This article will help you find the best lubricating oils by considering all important factors.

Definition of Lubricating Oil:

Lubricating oil is a liquid lubricant that creates a thin membrane or barrier between two moving parts of a machine or engine to partially or completely prevent the two surfaces from coming into direct contact. As a result, it introduces slipperiness between the parts, significantly reducing heat generation and frictional loss.”

6 functions of engine oil

1. Lubrication: The primary function of lubricating oil is to keep the moving parts of the engine slippery, thereby reducing wear due to friction and minimizing power loss.
2. Cooling: Through rapid and frequent circulation, lubricating oil cools various moving parts and bearings during engine operation.
3. Sealing: The space between the cylinder wall and piston ring is sealed with lubricating oil. This acts as a barrier against compression leaks or burnout, improving engine performance.
4. Cleaning: During its flow through the engine, lubricating oil carries away metal particles, carbon, dust, and other debris produced by friction, transporting them to the crankcase. This is why lubricants are considered cleaning agents.
5. Noise Reduction: Lubricating oil absorbs and reduces noise from bearings and other engine components.
6. Rust Prevention and Removal: Bearings and other parts are always coated with lube oil, protecting them from rust. Engine oil also helps to remove existing rust on various engine parts due to acid gas exposure.

Description of Some Properties of Lubricating Oil

Viscosity: Viscosity is the internal friction of a fluid or the degree of resistance to flow. It controls the flow rate of oil and is directly proportional to temperature. Viscosity actually refers to the “body” of the oil, which prevents the oil film from breaking down under heavy load. As temperature increases, viscosity decreases and flow rate increases. The ability of lubricating oil to flow and spread is known as its viscosity. Higher viscosity generally means greater resistance to flow. Engine oil must have the appropriate viscosity to achieve hydrodynamic lubrication, as higher viscosity can reduce engine power due to increased resistance.

Flash Point and Fire Point: The flash point is the lowest temperature at which an oil generates enough vapor to ignite when a flame is brought near, but extinguishes when the flame is removed.

The lowest temperature at which the vapor continues to burn even after the flame is removed is called the fire point. The fire point is usually found within 18°C above the flash point. The flash point of lubricating oil should be higher than the temperature generated in the bearing to avoid fire hazards. The flash point of lube oil typically ranges between 190°C and 290°C.

Volatility: When lube oil is kept at a high temperature for several hours, it loses some weight due to evaporation, known as evaporation loss. Lube oil should have low volatility at operating temperature to prevent excessive oil consumption.

Cloud Point: The temperature at which paraffin wax or other materials dissolved in the oil at normal temperature start to separate and form small particles, creating a cloudy appearance, is called the cloud point. Lube oil should have a low cloud point to ensure easy flow at low temperatures. The cloud point generally occurs at temperatures 50 to 60°C above the pour point.

Pour Point: The lowest temperature at which lube oil can still flow is called the pour point. It is considered to be about 5°F (28°C) above the temperature where oil flow ceases. A low pour point is necessary to ensure flowability of lubricating oil at low temperatures.

Oiliness: The property by which lube oil adheres to the bearing or cylinder wall is called oiliness. Between two fluids of the same viscosity, the one with greater adhesion to the bearing surface is said to have higher lubricity. Generally, lubricating oil should have high oiliness, particularly when two surfaces in contact are exposed to high pressure; the oil layer protects the metal and reduces frictional wear.

Film Strength: Lube oil can form a coating, or film, between parts, known as the oil film. Lube oil should have high film strength. Although related, oiliness and film strength are distinct properties. If an oil has high oiliness, the film should also be strong enough to maintain its integrity under heavy loads or stresses.

Corrosiveness: The presence of mineral acids, petroleum acids, fatty acids etc. in lube oil is very harmful for metal surfaces.  Lube oil should not be chemically attacked by any metal it comes in contact with.  It should not cause decay but prevent decay.  The oil should not contain sulphur, as sulfur oxidizes and mixes with water to form sulfuric acid which corrodes cylinders.

 Stability: The ability to resist oxidation is called stability in lube oil.  Lube oil forms acids, liquors and snot due to oxidation.  All these cause problems in bottom lubrication.  So lube oil should have high stability to prevent oxidation.

 Specific gravity: How heavy or light lube oil is compared to water can be understood by relative gravity.  This gives an idea of the viscosity of the lube oil.  Relative importance is measured with a hydrometer.  The relative importance of lube oil ranges from 0.88-0.95.  Another scale for measuring the relative importance of oil has been approved by the API.  This is called API Gravity.  From SAE-10 to SAE-50, naphthenic oils have an API gravity of 18-22 and paraffin oils have an API gravity of 27-31.

 Detergency: Lube oil should have the ability to carry small particles such as alloy, dirt, carbon etc. and keep the engine parts clean.  All these impurities adhere to the parts and make the parts dirty and dirty.  Lube oil for lubrication should have high cleaning power.

 Emulsification: Lubricating oil mixes with water to form a milky substance which destroys lubrication properties.  The emulsification number is an indicator of the tendency of oil and water to form an emulsion.  Good lubricating oils do not emulsify easily.  Emulsification is more important in lube oil used in steam turbines and steam engines.

Neutralization Number: Oil may contain impurities even after refining, which can be either alkaline or acidic. The simplest test to determine the acidity or alkalinity of oil is the neutralization number test. The weight of potassium hydroxide (KOH) in milligrams required to neutralize the acid in one gram of oil is called the neutralization number.

Non-Foaming Quality: In the engine, lube oil undergoes heavy rotation, which reduces its interfacial tension and can cause foaming in the oil. This foaming reduces oil flow to the bearings and accelerates oxidation, disrupting lubrication. Therefore, the oil should have non-foaming properties.

Acidic Bottom (Insoluble Residue): Free carbon that decomposes from hydrocarbons at high heat levels becomes carbon, forming an insoluble residue. This residue is a type of insoluble matter and is undesirable in the oil.

Color: The quality of lubricating oil does not depend on its color. However, the color of lubricating oil produced from the same group of hydrocarbons in a refinery can be compared. A single type of lubricating oil may not always have the same color.

Job Description of Lube Oil Additives

Detergents: Enhances the cleaning ability in the piston ring belt area and other hot areas. Controls temperature-related deposits.

Dispersants: Controls the deposition of sludge and varnish at low temperatures.

Oxidation Inhibitors: Lube oil oxidizes to form tar-like substances that corrode and block engine parts. These corrosive substances are very harmful to bearings and other parts. Oxidation inhibitors are used to reduce the rate of oxidation.

Corrosion and Rust Inhibitors: Acids produced at high temperatures corrode metals. Rust inhibitors mix with acid to form alkalis, preventing water production.

Anti-Wear Agent: Prevents wear of rubbing parts, especially in the valve train, where only boundary lubrication is available.

Oiliness Agent: Reduces friction in rotating and reciprocating components under high loads. It is also called a high-pressure agent.

Anti-Foaming Agent: Due to the continuous circulation and churning of lube oil in the engine, air is added, creating foam. This reduces lube oil flow. Inadequate lubrication leads to engine overheating and rapid part wear. Anti-foaming agents are added to reduce the foaming tendency of lube oil.

Pour Point Depressant: Reduces the coagulation barrier and the pour point temperature of the oil, allowing lubrication to work smoothly at low temperatures.

Viscosity Index Improvers: Viscosity index improvers are added to lube oil to minimize changes in viscosity with temperature fluctuations. This reduces lube oil consumption and facilitates easier cold starting, as relatively thin lube oil can be used.

Anti-Carbon Forming Agents: Carbon is formed in lube oil due to pre-ignition and other factors. This reduces the lubrication ability of the lube oil. Anti-carbon forming agents are added to ensure that carbon formation occurs at a controlled rate.

Conclusion: Selecting the appropriate lubricating oil for machinery is crucial for ensuring optimal performance and longevity of equipment. The key takeaway is that understanding the specific requirements of the machinery and the properties of different lubricants is essential for making an informed choice.