Lubrication & Greasing: Working Principles & Tips
The goal of lubrication is to reduce friction between two moving parts. When two surfaces come into touch, a fluid must be injected between them to separate them. When grease is used to lubricate something, it is referred to as greasing.
Lubrication and greasing: definition and examples
What are the most important functions of lubrication?
Lubrication makes it possible to:
- Reduce friction (rubbing or deformation)
- Prevent pieces from wear
- Absorb/reduce shocks
- Protect from corrosion
- Isolate components from contamination
- Clean/get rid of contaminants.
Lubricants are designed to reduce friction between moving parts as well as the passive resistance of stationary parts. They are made by refining heavy crude oil fractions (remaining crude oil parts after refining hydrocarbons such as gas, fuel oil or kerosene). Lubricants are classified as liquid or fluid (oils), semi-solid (grease, silicon gels), or solid (Teflon, graphite).
Although the performance and properties of each lubricant differ, they all share the same primary component, known as “base oil.” Lubricants typically comprise between 75 percent and 85 percent mineral or synthetic base oil.
Base oil groups
There are two main base oil groups:
Mineral base oil
Crude oil is used to make mineral base oils. They are by far the most widely used lubricants in both the automotive and industrial industries. Mineral base oils are made from of re-refined hydrocarbons.
Synthetic base oil
Synthetic base oils are created by combining multiple ingredients in a chemical reaction. Esters and synthetic hydrocarbons are the two primary types of products used to make lubricants. These goods’ viscosity is extremely consistent regardless of temperature. When opposed to mineral oil bases, which require additives to improve viscosity in larger volumes, this feature is a significant benefit. They’re also more resistant to oxidation, which means they’ll last longer and require fewer oil changes. There are also semi-synthetic base oils, which are made up of a blend of mineral (70-80%) and synthetic oils (from 20 -30 % ).
Oils are a blend of lubricating base oil and additives that provide lubrication.
The amount of additives in finished oils varies between 15% and 25% for two reasons which are Either to enhance some of the base oil’s properties or to offer the base oil new ones
Viscosity improvers are used to make oil more fluid at both high and low temperatures, preventing moving parts from colliding. Polymers are added to lubricating oil bases as improvers. This type of oil is referred to as multi-grade. Long polymer chains constrict at lower temperatures, providing insufficient resistance to the flow of oil molecules, but uncoil at higher degrees, preventing the mixture from fluidizing.
Antifatigue ingredients boost the lubricant’s antifatigue properties. An instantaneous reaction, or when the reaction product comes into touch with metal surfaces, forms a protective coating.
Antioxidant additives help to spread out oil change intervals by delaying the oxidation of the lubricant and increasing its resistance to higher temperatures.
Detergent additives prevent deposits or coating from forming in the fuel system’s hottest sections, such as the piston rings. They improve detergent action, especially inside engines, where they prevent deposits or gums on metal surfaces caused by combustion char or oxidised chemicals. Basic nitrogen compound polymers, which do not produce ashes, are the most recent additions. On older fuel systems, detergent oils must be used with caution because their ability to remove sedimented deposits (calamine, for example) may clog the lubricating system.
Solid contaminants generated while the engine is running are suspended by dispersant additives: unburned residues, gums, sludge, ashes, and deposits removed by detergents. They keep solid deposits from clumping together and sludge from accumulating in the engine’s cool sections (carter).
Additives for basicity They neutralise acid deposits that occur as a result of fuel combustion, primarily in diesel engines.
Anti-corrosion additives are substances that prevent metal from corroding. They shield ferrous metals against assaults by water, oxygen, air, and certain oxides produced during burning. On the surface to be protected, a protective film or passivating layer is created.
Antifreeze additives keep the lubricant fluid at low temperatures (between -15°C and -45°C).
Other additions can cause oil foaming (detergent additives react to oil the same way as soap reacts to water: they clean the engine but they tend to foam). It could also be due to the design of the lubrication system, which can cause turbulence when the lubricant is pumped into the engine, making air/oil mixing easier. The purpose of these additives is to prevent a considerable amount of air from spreading into the oil.
Extreme pressure additives:
Extreme pressure additives are designed to reduce friction torques, saving energy and protecting surfaces subjected to extremely high pressure. These additives give the lubricant certain sliding capabilities, which are especially useful in organs with gears or friction linings that are immersed in oil (limited-slip differentials, automatic or manual transmissions, oil immersed brakes, etc.)
Grease is made up of the following ingredients:
- 70 – 95 % base oil (mineral, synthetic or vegetable)
- 0 – 10 % additive as previously mentioned
- 3 – 20 % thickening or gelling agent which boost the viscosity of lubricant (semi-fluid, fluid, soft or hard) and to trap base oil and additives and to avoid leaking.
Greases are notable for their excellent adherence to the surfaces to be lubricated; they are also insoluble in water, resistant to shearing, and have a longer shelf life. Grease should not be heated above 300°C in general (temperature at which the base oil separates from the thickener). Copper or aluminum-based thermal pastes or coatings are better acceptable above this temperature.
Grease serves as a waterproof barrier against external elements in addition to its lubricating function (reduction of mechanical fatigue and energy losses due to friction) (dust, water, solvents, heat, etc.).
Silicon greases are thermally stable, chemically inert, and electrically insulating polymers based on silicon organic compounds. High temperatures, oxidation, and UV radiation do not affect silicon. Oil, elastomer, and resin are the three types of silicon.
Food-grade lubricants: these greases are safe to come into touch with food in the event of an accident. These additives and gelling lubricants must comply with CNERNA regulations in France (National Center for Study and Research on Nutrition and Feeding). The CNERNA is still the only European institution that refers to raw materials that may come into contact with food.
Solid lubricants are used for lubrication.
The two main lubricants used in severe environments are graphite and molybdenum disulfide (high vacuum, too high or too low temperatures). In the presence of air, graphite can be utilised up to 400°C, and in an inert atmosphere, it can be used up to 1900°C. Molybdenum disulfide is suitable for usage up to 450°C, after which it becomes abrasive. Teflon, nylon, or a variety of polyamides are recommended for usage at lower temperatures
Cutting oils are used for lubrication
During cutting operations, several substances are utilised to cool and lubricate the machinery. The chilling process extends the tool’s life and makes routine cuttings on final parts easier. Lubrication minimises friction, which prevents excessive heat emission and lowers the amount of energy required for a specific cutting. Aqueous solutions, chemically inert oils, or synthetic liquids make up these cutting oils.
Choosing lubricants is an important part of the lubrication process.
The lubricant selection process must take into account the lubricating mechanism’s operational characteristics, including working temperature, pressure force, relative velocity, and environmental variables. The most knowledgeable people to choose which lubricant to use based on the mechanism to be lubricated are oil and grease producers.
Manufacturers and machine designers, on the other hand, now sell lubricants for their own equipment, as well as a lubricant replacement schedule.