The Secret Keeper (Lubrication)

The world of mechanics and machinery, where metal meets metal, where gears turn, and where engines roar, there is an essential factor the secret keeper that keeps things running smoothly and silently – lubrication.

Lubrication is the unsung hero of mechanical engineering; It ensures the longevity and efficiency of our most complex and critical systems.

In this article, we will delve deeper into lubrication technologies, exploring the different methods used to reduce friction, dissipate heat, and prevent wear in the world of mechanics.

The history of the secret keeper( grease and lubrication )dates back to 1400 BC, when building stones slid on oil-soaked wood at the time of the pyramids. In Roman times, lubricants were based on olive oil and rapeseed oil, as well as animal fats.

The growth of lubricants accelerated in the Industrial Revolution with the accompanying use of mineral-based machines. At first, natural oils were relied upon. In the Middle Ages, more complex machines using iron and copper spread, and many different products appeared, leading to the emergence of multiple types of oils.

Lubricating oils spread in their current form with oil exploration in Pennsylvania in the 19th century, where sperm whale oil was used to lubricate textile machines. Since then, lubricating oils began to be rapidly replaced by products made from petroleum. With the entry of the twentieth century, the composition of Equipment such as: cars, planes, trains, missiles, and large ships... Therefore, lubricant products must be able to work with this recent progress, and lubricant manufacturers also have a great responsibility in terms of friendliness with the environment.

Lubricants generally consist of the majority of base oils in addition to a variety of additives, the function of which is to penetrate the openings between metal surfaces, such as the gaps between gears or joints, and form a layer of grease that works to slide those moving surfaces and reduces the intensity of their friction, thus reducing their wear and prolonging their life.

Lubrication techniques vary greatly based on the application. Here are some examples:

Automotive industry: Engines, gearboxes and chassis components are lubricated with compound oil and grease. Some parts, such as wheel bearings, use grease.

Aviation: Specialized synthetic lubricants are used in the aviation industry to handle extreme conditions at high altitudes and speeds.

Heavy Machinery: Solid lubricants are used on bulldozers, excavators and construction equipment for durability in tough conditions.

Food Industry: Lubricants used in food manufacturing must meet stringent health and safety standards, as they may come into contact with the product.

Wind Turbine Devices: Specialized lubricants are used in the gearboxes of wind turbine devices to ensure long-term reliability and performance

The importance of lubrication

Lubrication is the process of introducing a lubricant, usually a liquid, between two moving surfaces in contact with each other. This seemingly simple action plays a crucial role in mechanical systems:

Reducing friction: The main goal of lubrication is to reduce friction between moving parts. Friction generates heat, which can cause wear and tear, reduce efficiency, and ultimately can lead to component failure.

Heat dissipation: Lubricants help in dissipating the heat produced during the operation of machinery. By absorbing and transferring heat away, it prevents overheating and associated damage.

Corrosion prevention: Lubrication forms a protective layer between surfaces, preventing direct metal-to-metal contact. This reduces wear and increases the life of machine components.

Prevent rust and corrosion: Lubricants often contain additives that protect against rust and corrosion, especially in outdoor environments.

There are many lubrication technologies and methods used in mechanical engineering and industry. Each technology is selected based on specific system requirements and characteristics. Here are some common lubrication techniques:

Lubricating oil/grease

This is the most traditional and commonly used form of lubrication. It involves applying oil or grease to moving parts directly or via a central system.

Oil: It is commonly used in engines, turbines, and other machines with complex systems. Oil circulates within the machine, transferring heat and providing lubrication (Refer to article:Oil Characterstics).

Grease: This is a thicker lubricant and is used on bearings, gears, and other components. It adheres to surfaces and provides long-lasting protection.there are several types of suspension grease available in the market. Here are the most common ones.

-Silicone Grease: is suitable for lubricating rubber components like bushings. This type has excellent lubricating properties, reducing friction and wear between components and providing protection against water and corrosive substances.

-Lithium-Based Grease: is designed to withstand extreme temperatures and loads, making it ideal for heavy-duty vehicles.

-Synthetic Oil: is the most expensive type of suspension grease available. It’s usually made from polyalphaolefin (PAO) or ester-based oils. Similar to lithium-based grease, this type is also designed for high-performance vehicles.

Lubrication of boundaries

This occurs when the lubricant forms a thin film that prevents direct contact between metals. It is used in situations where the load and speed are relatively low.

Dynamic lubrication with oil

In this technique, a thick layer of lubricant is maintained between the moving parts. This layer separates the surfaces and allows them to easily slide over each other. This type is commonly used in high-speed, heavy-load applications.

Solid lubrication

Some applications, especially in extreme conditions, use solid lubricants such as molybdenum disulfide and graphite. These substances are embedded in surfaces and provide long-lasting lubrication.

Spray and air lubrication

In some cases, lubricants are sprayed as a fine mist or air into machines. This technique is effective and works well in hard to reach places.

Automatic lubrication systems

These systems are used in situations where constant lubrication is required. It can be time-based, condition-based, or on-demand, and ensures that the right amount of lubrication is delivered at the right time.

Types of lubrication

There are many types of lubricants that differ according to the additives to the oil that work to protect against corrosion. Lubrication is divided into the following:

-Complete lubrication

Complete lubrication is divided into two forms, which are as follows:

? Hydrodynamic: Hydrodynamic lubrication occurs when two surfaces are completely separated by sliding using a layer of fluid.

? Hydrodynamic elastin lubrication: This type occurs in the same way as hydrodynamic lubrication, but when the separation process is carried out in a rolling motion, but in this case the liquid layer used for separation in the case of hydrodynamic elastin is less dense than the lubricating fluid used in hydrodynamic lubrication, which is known as Elastohydrodynamic.

-Boundary lubrication

This type of lubrication is most commonly used in areas where there are frequent starts and stops because it is most effective in such places.

-Mixed lubrication

It is a mixture of boundary lubrication and hydrodynamic lubrication, as it is used to separate large parts of surfaces by placing a layer of mixed lubricant in the places that are still in contact with each other, where these materials are introduced to them for ease of separation and to protect these surfaces from corrosion as a result of the separation. Lubrication also helps It reduces the surface temperature and reduces energy consumption during the separation process. The separation process can also be carried out using oils, lubricants, liquids or gases.

Selection Strategies

A reasonable starting point for selecting a low/high-temperature grease is to consider the nature of the temperatures and the causes of product degradation. Greases could be divided by temperatures along the lines in Table1 below.

There is general correlation between a grease’s useful temperature range and the expected price per pound. For instance, a fluorinated hydrocarbon-based (type of synthetic oil) grease may work effectively as high as 570oF (300oC) in space applications but may also cost hundreds of dollars per pound.

The grease’s long-term behavior is influenced by the causes of degradation, three of which are particularly important: mechanical (shear and stress) stability, oxidative stability and thermal stability. Oxidative and thermal stresses are interrelated. High-temperature applications will generally degrade the grease through thermal stress, in conjunction with oxidative failure occurring if the product is in contact with air. This is similar to what is to be expected with most industrial oil-lubricated applications

Properties of High-Temperature Grease

Base Oils

When selecting lubricants?for oil-lubricated applications, one often begins with the consideration of base oil performance properties. This is also a good starting point for grease products. Grease is composed of three components: the base oil, the thickener and the additive package. There is a variety of options from which the manufacturer creates the final product. Table 2 includes some of these options.?

Base oils can be subdivided into mineral and synthetic types. Mineral oils are the most widely used base oil component, representing approximately 95 percent of the greases manufactured. Synthetic esters?and PAO (synthetic hydrocarbons) are next, followed by silicones and a few other exotic synthetic oils.?2

The American Petroleum Institute divides base oils into five categories that are useful in initially selecting base oil by performance limits.

The Group I products are naphthenic and solvent-refined paraffinic petroleum stocks with a high percentage of unstable ‘unsaturated’ molecules that tend to promote oxidation. Additionally, there are polar products that remain in the Group I base oils called heterocycles (nitrogen, sulfur and oxygen- containing molecules). Although the polar products are reactive, they help to dissolve or disperse additives to produce the final product.

The Group II and Group III are mineral oils that experience extensive processing to remove the reactive molecules and saturate (with hydrogen) the molecules to improve stability. In a sense, these base oils are more like the Group IV synthetic hydrocarbons (PAOs) than the Group I mineral oils. The oxidative and thermal properties can be very good as a consequence of the removal of the reactive heterocyclic molecules.

The Group IV synthetic hydrocarbons (SHC fluids) are produced by combining two or more smaller hydrocarbons to synthesize larger molecules. These fluids may have slightly better stability, but command a higher price. The Group V base oils have a defined but different degradation path (not primarily thermal or oxidative).

Mineral and synthetic base oils degrade thermally in conjunction with oxidative degradation if the product is in contact with air. The break point at which the individual oil molecules in a highly refined (Group II+, Group III) mineral oil and synthetic hydrocarbons will begin to unravel, releasing carbon atoms from the molecular chain, is about 536oF to 608oF (280oC to 320oC).?3,4

The grease manufacturer will select materials given their familiarity, and perhaps availability, of the raw materials. If the manufacturer makes a particular type of synthetic base fluid and is intimately familiar with the various destruction mechanisms of that fluid, then it is likely that this type of synthetic base will often be selected for new product development.

Thickeners

The materials selected as the grease thickeners may be organic, such as polyurea; inorganic, such as clay or fumed silica; or a soap/complex soap, such as lithium, aluminum or calcium sulfonate complex. The usefulness of the grease over time depends on the package, not just the thickening system or the type of base oil. For instance, silica has a dropping point of 2,732oF (1,500oC) as one extreme example.?5

However, because grease performance depends on a combination of materials, this does not represent the useful temperature range. Some clay-thickened (bentonite) greases may similarly have very high melting points, with dropping points noted on the product data sheets as 500oC or greater. For these nonmelting products, the lubricating oil burns off at high temperatures, leaving behind hydrocarbon and thickener residues.

The organic polyurea thickener system offers temperature range limits similar to the metal soap-thickened grease, but additionally it has antioxidation and antiwear properties that come from the thickener itself. Polyurea thickeners might become more popular but they are difficult to manufacture, requiring the handling of several toxic materials.

While the thickener has a high dropping point, the composition begins to thermally degrade at temperatures which limit its usefulness over time at high temperatures. However, it does not have the pro-oxidant tendencies of the metal soap-thickened greases. The exception is the calcium sulfonate complex thickener?system. Similar to the polyurea, it possesses inherent antioxidant, rust-inhibiting properties, but in addition has inherent high dropping points and EP/antiwear properties.

The third category option is the metal soap or complex soap thickener system. Lithium complex-thickened grease has maximum temperature limits superior to that of simple lithium grease, because the thickener offers higher thermal degradation limits.

Collectively, metal soap thickeners have thermal degradation limits that range between 250oF to 430oF (120oC and 220oC).?6?However, unless the grease composition is properly fortified against oxidation and thermal degradation, the end product showing a dropping point of 500oF (260oC) or greater would not be any more useful for long-term service than a grease with a low dropping point.

Additives

The additives selected for grease manufacture must likewise be viewed as parts of the whole rather than simply discrete parts that must withstand set test limits. The additives tend to provide properties for greases in fashion similar to lubricating oils: oxidation stability, corrosion resistance, wear resistance, low temperature flow characteristics, water resistance, etc.

The additive must be capable of working synergistically with the thickener and the oil to lead to a balanced, stable mixture of the three distinct components.

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Although lubrication is important, it is not without its challenges. Lubricants can break down over time, become contaminated, or lose their effectiveness. An excess of lubricant can also be harmful.

Finding the right balance and ensuring proper maintenance are the key.

M.Hamdi

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