Lubricant Oil: Understanding Types of Lubrication, Benefits and Examples
27 Sep 2024
Lubricant oil is vital for machinery's smooth functioning and longevity across various industries. By reducing friction and wear between moving parts, lubricants enable equipment to operate efficiently for extended periods without breakdown. Choosing the appropriate type of lubricant oil is crucial based on factors like operating conditions, load, pressure, and temperature.
Table of Contents
- What is Lubricant Oil?
- Types of Lubrication
- Types of Lubricating Oils
- Additives in Lubricant Oils
- Functions of Lubricant Oils
- Criteria for Lubricant Selection
- Major Applications of Lubricants
- Lubricant Testing
- Lubricant Suppliers and Cost Considerations
- FAQs
Read on to get an understanding of lubricant oils - their purpose, types, applications, and proper use.
What is Lubricant Oil?
Lubricant oils are viscous fluids that provide a protective film between two surfaces in relative motion, reducing friction and enabling smooth operation. They are specially formulated to reduce wear and tear caused by metal-to-metal contact. The function of lubricants is by virtue of the mechanism of fluid film.
Types of Lubrication
Understanding the different lubrication regimes is critical to selecting the right lubricant oil. The three main lubrication regimes are:
1. Boundary Lubrication
It occurs when two surfaces directly interact with a thin lubricant film in between. It is common in highly loaded, slow-moving parts and requires robust oil additives that protect by bonding to metal surfaces. Examples of this regime are gear tooth contact or cam-tappet contact in engines.
2. Mixed Lubrication
Involves partial separation between surfaces. The asperities of surfaces occasionally make contact and get separated. Oils with additives like Extreme Pressure (EP) additives and Anti-Wear (AW) additives will help protect the surface in this regime. This is observed when the sliding speed of the surfaces increases, such as in piston-ring and liner contacts in the engine.
3. Hydrodynamic Lubrication
It occurs when the lubricant film completely separates the surfaces. It is prevalent in journals and bearings. High-viscosity fluids are needed to form thick films.
Types of Lubricating Oils
Numerous speciality lubricant oils cater to particular applications. But based on the nature of the base oil used to make them, they fall under four broad categories:
1. Mineral Oils
They are derived from petroleum crude oil. They offer good viscosity characteristics and cost benefits. They are extensively used in engine oils, gear oils and hydraulic oils.
2. Synthetic Oils
These are generally produced by chemically modifying crude oil molecules or artificially synthesising organic compounds. These oils display excellent viscosity-temperature properties, resistance to heat and oxidation and sludge buildup.
3. Semi-Synthetic Oil
These oils contain a combination of both mineral and synthetic oils and have superior viscosity behaviour when compared to a full mineral oil, particularly at lower temperatures.
4. Bio-based Oils
They are manufactured from natural fats and are 100% renewable and biodegradable. They have improved lubricity when compared to mineral oils. Have viscosity and lubricity comparable to mineral oils.
Additives in Lubricant Oils
Additives (speciality chemicals) impart additional properties like EP and AW performance, detergency (cleanliness) and corrosion protection to lubricants, or boost existing properties like viscosity, pour point and oxidation inhibition.
Some critical additives are:
A. Anti-wear Agents & Extreme Pressure Additives
Compounds containing sulphur, phosphorus, or nitrogen that prevent metal-to-metal contact on surfaces through protective film formation. EP additives can protect the metal at higher loads. Zinc dialkyl dithiophosphate (ZDDP) is an example of an AW agent
B. Oxidation Inhibitors
Neutralise acids formed by oil degradation, and further prevent sludge formation and corrosion. It helps increase the life of the oil. Commonly used chemistry includes phenols, amines, and phospho-sulfurised hydrocarbons to improve oxidation resistance.
C. Detergents and Dispersants
Additives that can solubilize sludge or soot formed in the lubricant, and neutralize acids formed during the oil’s life. Help extend the fluid life and maintain the viscosity of the oil in the system
D. Corrosion Inhibitors
Forms a layer of protective film on the metal, protecting it from chemically active compounds that can corrode the metal.
E. Viscosity Modifiers
Oil-soluble polymers which help control how the viscosity of an oil changes as the temperatures change. Helps maintain the viscosity of an oil across a range of temperatures. This ensures high enough viscosity at high temperatures for better protection, and lower viscosity at low temperatures for reduced drag.
F. Pour Point Depressants
Oil-soluble polymers that lower the pour point to improve flow at lower temperatures. Help avoid wax precipitation issues.
Functions of Lubricant Oils
Some essential functions that lubricants provide are:
- Friction and Wear Reduction
- Protection against Corrosion and Rust
- Cooling through Heat Dissipation
- Cleansing by Removal of Contaminants
- Neutralize acids from combustion products in engines
Criteria for Lubricant Selection
Consider the following aspects before choosing a lubricant oil:
A. Operating Temperature Range - Determine the max/min temperatures during equipment operation. Oils have a permissible viscosity range for effective film formation.
B. Load Carrying Requirement - Heavily loaded parts may need extreme pressure (EP) additives for seizing/pitting resistance
C. Speed of Moving Parts - High speeds demand low-viscosity oils that minimise fluid friction. Slower parts permit the use of high-viscosity or grease-type lubricants.
D. OEM recommendation - The Original Equipment Manufacturer (OEM) recommends the best option for the lubricant for the equipment, to maximize the equipment's life and performance. Referring to the equipment manual or guidelines is often the best method for lubricant selection.
Major Applications of Lubricants
Some prominent application areas of speciality lubricant oil are:
A. Automotive Oils - Engine oils, gear oils, automatic transmission fluids, and axle oils are critical in vehicle maintenance. They protect highly loaded contacts, dissipate heat, and keep components clean.
B. Hydraulic Oils - They require high anti-wear performance, with enhanced water handling and air release capabilities to ensure proper hydraulics performance. Mineral oils with Rust & Oxidation inhibitor additives, and/or AW additives are used. A viscosity modifier may also be used to improve the operating range.
C. Industrial Gear Oils - They require extreme pressure resistance and protection from micro-pitting wear. Mineral oils with sulfur, phosphorus, and EP additives are widely used.
D. Turbines Oils - The oils lubricate the turbine and generator bearings, and act as a hydraulic oil for pumps, torque convertors etc if the system requires. They have high oxidation resistance as the turbine operates at high temperatures continuously.
E. Compressor Oils - They are usually oils with good rust and oxidation inhibition, but may often have higher anti-wear protection. Different compressors work at different conditions and with different gases and may require different oils accordingly.
Lubricant Testing
It is prudent to test lubricant condition and properties periodically through analyses like:
A. Viscosity & Physical Properties Measurement - Kinematic viscosity changes warn about oxidative changes, additive depletion, and fuel dilution, necessitating oil replenishments. Other parameters like flash point will also provide additional information on the oil quality.
B. Base Number or Acid Number Analysis - The base number (BN) or the acid number (AN) is an indirect indication of the state of the oil and the additives in it. If the Base number of an engine has decreased significantly over time, it may be that the additive levels in the oil have dropped. On the other hand, if the acid number has increased, it signifies higher acid content in the oil.
C. Elemental Analysis - Analysing the elements in an oil can provide an indication of wear metals being generated which can help identify component wear and damage, and additive depletion
D. Spectrometric Oil Analysis - Identifies the “fingerprint” of an oil and can indicate the presence of contaminants like fuels or coolant in the lubricant.
Lubricant Suppliers and Cost Considerations
Leading lubricant manufacturers in India, like Gulf Oil, produce various oils and greases for automotive and industrial applications. With state-of-the-art R&D and manufacturing plants, Gulf Oil makes high-performance mineral, semi-synthetic and full synthetic lubricants tailored for operations ranging from passenger vehicle engine oils to industrial hydraulics.
Lubrication amounts to 2-4% of operational budgets in typical plants. Performance benefits like extended oil drain intervals and reliable operation offset total costs.
FAQs
Lubricating oils are broadly categorised based on their base oils into mineral, semi-synthetic, synthetic, and bio-based oils. Based on their applications, they are further classified into engine oils, gear oils, hydraulic fluids, etc.
Reduced friction from compelling lubricant films decreases power losses and operational costs. Efficiency gains by diminished component wear also cut replacement costs. Low-viscosity oils with the right additives can improve energy efficiency across the entire lubrication regime.
Contamination from wear debris, dust and water ingress degrades oil health, additive depletion, and formation of sludge and soot in the case of engine oils, occurs over time. Exposure to high temperatures also negatively impacts properties through oxidation, which reduces the remaining life of the oil
It is possible to use chemically modified vegetable oils. They offer biodegradability, improved friction reduction and reasonable viscosity characteristics, which will be suitable for certain applications. Rapeseed, sunflower and palm oils are among the popular renewable alternatives to conventional oils. However, they have limited application due to lower life, higher cost and poorer low-temperature properties.
EP additives contain reactive elements like sulphur, chlorine, and phosphorus compounds, which undergo chemical reactions under extreme loads to form protective films on surfaces that prevent scuffing, scoring, and wear. These additives are most commonly used in gear oils, both automotive and industrial.