5 Must-Have Features in a pour point depressant for diesel oil

Lubricants have several physical properties that serve their function and performance.

• Viscosity
• Specific gravity and density

• Pour point
• Film strength
• Flashpoint
• Oxidation resistance
• Water separation

• Rust and corrosion protection

Viscosity

The most important property is viscosity. Viscosity, which measures oil’s resistance to flow, is the most important property of a lubricant. Water has a relatively low viscosity; molasses has a much higher viscosity. However, if you heated molasses, it would get thinner. Likewise, oils also get “thinner” as they get hot. Viscosity has an inverse relationship with temperature. As pressure increases, the viscosity of oil increases, too. Therefore, the viscosity of oil in service varies with its temperature and pressure.

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The viscosity of industrial oils is generally reported at 40˚C. The International Standards Organization uses this as the standard for its ISO VG grading system that ranges from ISO VG 2 to ISO VG . The ISO VG is defined as the midpoint of a range that is + 10%. For example, a hydraulic fluid with a viscosity of 31.5 cSt at 40C has an ISO VG of 32. The viscosity of crankcase oils is typically measured at 100C. Lubricating oils can range from very low viscosity like solvents and kerosene used for rolling metals, to high viscosity fluids that barely flow at room temperature, such as steam cylinder oils or gear oils used in sugar mills.

A characteristic of viscosity is the Viscosity Index. This is an empirical number that indicates the effect of change on the viscosity of a lubricant. A lubricant with high viscosity index does not thin down very fast as it heats up. It would be used for oils that are used outdoors in summer and winter. Multi-viscosity engine oils have a high viscosity index.

Specific Gravity and Density

Specific Gravity – the mass per unit volume of a substance is called density and is expressed in pounds per gallon, kg/m, or g/cc. The specific gravity is defined as the density of a substance divided by the density of water. A substance with a specific gravity greater than one is heavier than water and vice versa. It is a measure of how well a substance floats on top of water (or sinks below the surface.) Water has a density of approximately 1 g/cc at room temperature. Petroleum fluids generally have a specific gravity of less than 1, so they float. Oil slicks float on the surface of a puddle.

Water drains in reservoirs are positioned at the bottom of the reservoir. The lower the specific gravity, the better the oil floats. Oil with a specific gravity of 0.788 floats very well. The density of oils decreases with temperature; they float better as they heat up. Density of petroleum products is often expressed as API gravity which is defined as Degrees API = (141.5/ Sp Gravity @60˚F – 131.5). The API gravity of water is 10. Since API gravity is the reciprocal of specific gravity, the higher the API gravity, the lighter the oil; therefore the better it floats.

Pour Point

The Pour Point of oil is the lowest temperature at which it will pour, or flow, when chilled without disturbance. The very first additive that was used in engine oil was a Pour Point depressant additive.

Film Strength

Film strength is a measure of a fluid’s lubricity. It is the load-carrying capacity of a lubricant film. Film strength can be enhanced by the use of additives. Many synthetic oils have greater film strength than petroleum oils.

Flash Point

Flashpoint is the temperature at which the vapors of a petroleum fluid ignite when a small flame is passed over the surface. In order for combustion to occur, there has to be a certain air/fuel mixture. If there is too much air, the mixture is too lean – there’s not enough fuel. If there’s too much liquid, it essentially suffocates the flame.

The flashpoint is the temperature where there are enough molecules bouncing around in the air above the surface to produce an air/fuel mixture that will burn (if there is a spark to ignite them as evidenced by a popping sound.

The flashpoint is directly related to evaporation rate. A low viscosity fluid will generally evaporate faster than high viscosity oil, so its flash point is typically lower. For safety, it is a good idea to choose oil that has a flashpoint of at least 20°F higher than the highest operating temperature in the equipment. Fire point is the temperature that supports combustion for 5 seconds.

Oxidation Resistance

Oxidation resistance affects the life of the oil. Turbines and large circulating systems, in which oil is used for long periods without being changed, must have oils with high resistance to oxidation. Where oil remains in service only a short time or new oil is frequently added as make-up, those grades with lower oxidation resistance may serve satisfactorily.

The rate of oxidation of petroleum oils tends to double for every 18˚F (10°C) rise in temperature, therefore for every 18˚F(10°C) that you raise the temperature of a system, expect to change the oil twice as often. Another way of stating this is for every 18˚F decrease in oil temperature, oil life is doubled.

Water Separation

The separation of oil from water is called demulsibility. Water can cause rust, corrosion and wear, among many other detrimental factors such as foaming and cavitation. Some base oils have a natural repulsion to water whereas others are readily miscible. Certain additives can be used to offset the potential mixing which would lead to emulsification.

Circulating oil systems require oils that demulsify well. Once-through systems do not require demulsifiers because the oil doesn’t recirculate and collect enough water to cause rust. Demulsifiers are not necessary if the system is hot enough to boil off any water such as an engine. In certain instances, oil is mixed with water to improve fire retardancy or metalworking fluid cooling. Emulsions are important for fire resistance and metalworking cooling.

       Water/Oil Mixture     Partial Separation           Full Separation  

Rust and Corrosion Inhibiting

When machinery is idle, the lubricant may be called upon to act as a preservative. When machinery is in actual use, the lubricant controls corrosion by coating lubricated parts. Once at rest, the lubricant rust and corrosion inhibiting film has now coated the surface protecting it from water.

Lubricant Chemistry

Lubricants are built with a base oil(s) and additives. Petroleum oils account for most of the two general categories of industrial and transportation lubrication. They are refined from crude oil, which, as everyone knows, was formed from billions and billions of tiny microorganisms that converted over time and pressure to oil. The term hydrocarbon simply means that it is predominantly comprised of hydrogen and carbon, although there are small amounts of other elements such as sulfur and nitrogen.

The two principal types of petroleum oils used for lubricants are paraffinic and naphthenic. When you think of paraffin, you think of wax. That gives you a good idea of the strengths of paraffinic oil. Wax is an excellent lubricant; it is slippery and quite stable at high temperatures. It is ineffective at low temperatures because it turns solid. For this reason, paraffinic oils are recommended for most industrial and transportation lubricants, except where they run at cold temperatures. Another characteristic of wax is that it leaves very little residue when it oxidizes, but the small amount of residue is hard and sticky.

Naphthenic oils are not waxy, so they can be used to very low temperatures. While they tend to leave more deposits than paraffinic oil, what is left behind is soft and fluffy. Compressor manufacturers often prefer naphthenic oils because the deposits get blown out with the compressed air rather than building up on discharge valves. Naphthenic oils are also used in many refrigeration applications because of their good cold temperature properties.

Physically, paraffinic oils can be distinguished from naphthenic oils because of their higher pour points and lower density. Paraffinic oils typically weigh between 7.2 and 7.3 pounds per gallon, while naphthenic oils are slightly heavier. Be careful about characterizing the base stock of a formulated product based on physical properties because additives can strongly affect physical properties.

(a) and (b) - Paraffin, (c) - Naphthene, (d) - Aromatic

With the advent of more sophisticated refining techniques, base stocks have been categorized into Group I, Group II and Group III. Group I base stocks is conventionally refined oils. Group II is base stocks that contain greater than 90% saturates and less than .03% sulfur with a VI between 80-119. They are often produced by hydrocracking.

 Base Oils

Satures Content

Sulfur Content

Viscosity Index

 Group I

<90 %

>0.03 %

80 – 120

 Group II

>90 %

<0.03 %

80-120

 Group III

>90 %

<0.03 %

>120

White oils are highly refined petroleum oils that meet food and drug requirements for direct food contact. Customers may ask that the product be certified as USDA H-1 for incidental food contact. While the USDA has disbanded the organization that tested and approved H-1 lubricants for incidental food contact, producers can now self-certify that their products were formally approved under H-1 or currently meet the requirements set forth by that standard.

Synthetic Base Oils

Synthetic base oils are produced, mainly, from low molecular weight hydrocarbons, the process produces high quality and extended service life capability base oils under extremes operating conditions. In general terms, synthetic base oils are able to handle a wider range of application temperatures, so they provide the best protection both to high and low temperatures.

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Base Oils

Type of Base

Group IV

Polyalphaolefin

Group V

Other Synthetic Bases

[Text Wrapping Break] API Classification (2nd part)

Synthetic Hydrocarbon Fluids

The SHFs comprise the fastest-growing type of synthetic lubricant base stock, they all are compatible with mineral base stocks.

Polyalphaolefins (PAO) are unsaturated hydrocarbons with the general formula (-CH2-)n, free of sulfur, phosphorus, metals and waxes. Provide excellent high-temperature stability and low-temperature fluidity, high viscosity indexes, low volatility and compatible with mineral base oils. Although the oxidation stability is lower than mineral oils and their solvency of polar additives is poor, usually PAOs are combined with other synthetic oils. This base oil is recommended for engine oils and gear oils.

Alkylated Aromatics formed by alkylation of an aromatic compound, usually benzene or naphthalene. Provide excellent low-temperature fluidity and low pour points, good solubility for additives, thermal stability and lubricity. Although their viscosity index are about the same as mineral oils, they are less volatile, more stable to oxidation, high temperatures and hydrolysis. They are used as the base of engine oils, gear oils and hydraulic fluids.

Polybutenes are produced by controlled polymerization of butenes and isobutylenes. Compared with other synthetic base oils they are more volatile, less stable to oxidation and their viscosity index is lower; their tendency to produce smoke and shoot deposits is very low so they are used to formulate 2-Stroke engine oils, also as gear oils combined with mineral or synthetic base oils.

Polyalkylene Glycols (PAG) are polymers made from ethylene oxide (EO), propylene oxide (PO), or their derivatives. Solubility in water or other hydrocarbon is depending on the type of oxide. Both provide good viscosity/temperature characteristics, low pour point, high-temperature stability, high flash point, good lubricity, and good shear stability. PAGs are not corrosive for most metals and compatible with rubber. The main disadvantages are low additive solvency and pour compatibility with lubricants, seals, paints and finishes.

They are used as a base for hydraulic brake fluids (DOT3 and DOT 4) due to their water solubility, 2-Stroke engine oils due to the low deposits at high temperatures, compressor lubricants and fire-resistance fluids.

Synthetic Esters are oxygen-containing compounds that result from the reaction of an alcohol with an organic acid. They have good lubricity, temperature and hydrolytic stability, solvency of additives and compatibility with additives and other bases. 

But some esters can damage seals so they require special compositions. They are used as base oils for engine oils, mixed with other synthetic bases, because they improve low-temperature properties, reduce fuel consumption, increase wear protection and viscosity-temperature properties.

Also, as 2-Stroke engine base oils, they reduce deposit formation, protecting rings, pistons and sparks. They allow you to reduce the quantity of lubricant from 50:1 of mineral oils to 100:1 and up 150:1 due to their outstanding lubricity.

Phosphate Esters are used as anti-wear additives due their high lubricity and as base oils for hydraulic fluids and compressor oils due to their low flammability. But their hydrolytic and temperature stability and viscosity index is low and their low-temperature properties are poor. Also, they are aggressive with paints, coats and seals.

Polyol Esters have good high-temperature stability, hydrolytic stability and low-temperature properties, low volatility and low Viscosity Index; the polyol esters also may have more effect on paints and cause more swelling of elastomers. To take advantage of their miscibility with hydrofluorocarbon (HFC) refrigerants, polyol esters are used in refrigeration systems.

Perfluorinated Polyethers (PFPE) with a density nearly twice that of hydrocarbons, they are immiscible with most of the other base oils and non-flammable under all practical condition. Very good viscosity-temperature and viscosity-pressure dependence, high oxidation and water stability, inert chemically and radiation stable; these properties joined their shearing stability. They are suitable as hydraulic fluids in spacecraft and as dielectric in transformers and generators.

Polyphenyl Ethers have excellent high-temperature properties and resistance to oxidation but they have fair viscosity-temperature properties, they are used as hydraulic fluid for high temperature and radiation resistance.

Polysiloxanes or Silicones have high viscosity index, over 300, low pour point, high-temperature stability and oxidation stability so they run well in a wide range of temperatures; they are chemically inert, non-toxic, fire-resistant, and water repellent, they have low volatility and are compatible with seals and plastics.

Their disadvantage is the formation of abrasive silicon oxides if oxidation does occur, effective adherent lubricating films are not formed due to their low surface tension, and they also show poor response to additives. They are used as brake fluids and as antifoam agents in lubricants. The table compares different synthetic base oils properties against mineral oil. Comparison among base oils.

 Bio-bases Oils

They are mainly produced from soybeans, rapeseed, palm tree, sunflowers and safflowers. Their advantages are high biodegradability, superior lubricity, higher flash point and viscosity index; but their pour point is high and the oxidative stability is poor, also the recycling is difficult.

Main applications are hydraulic fluids, transmission fluids, gear oils, compressor oils and greases. Better when application is total loss, indoors or where low pour point is not an issue, food industry or environmentally-sensitive areas.

Additives

Lubricants require additional ingredients beyond a base oil to provide functionality. The following is a list of the common materials used. Additives 5% to 30% of an oils formula with engine oil using the highest concentration.

Typical passenger car engine oil contains detergents, dispersants, rust inhibitors, anti-wear additives, pour depressants, antioxidants, anti-foam additives and friction modifiers. Anti-wear additives help reduce wear between heavily loaded engine parts; detergents and dispersants help prevent buildup of contaminants, sludge, soot and varnish; and oxidation inhibitors help prevent lubricant breakdown at high operating temperatures.

Extreme Pressure (EP) Agents – a phosphorus, sulfur, or chlorine-based additive typically used in gear oils that prevents sliding metal surfaces from seizing under conditions of extreme pressure. At high local temperatures it combines chemically with the metal to form a surface film. The EP additives made of sulfur, phosphorus, or chlorine. They become reactive at a high temperature (160+F) and will attack yellow surfaces and can be slightly corrosive to some metals, especially at elevated temperatures.

Antifoam or Foam Inhibitor – silicone-based additives used in turbulent systems, it helps combine small air bubbles into large bubbles which rise to the surface and burst. It decreases the surface tension of the bubble to thin and weakens it so that it pops. Most oils contain foam inhibitors that work by altering the surface tension of the oil. It allows bubbles to combine and break. Foam inhibitors are either based on silicone or are organic antifoam agents.

Rust and Corrosion Inhibitors – carbon-based molecules designed to absorb onto metal surfaces to prevent attack by air and water. Rusting and corrosion work by slowing the deterioration of a component surface due to a chemical attack by acidic products of oil oxidation. Rusting refers to the process of a ferrous surface oxidizing due to the presence of water in oil. Oils that contain rust and oxidation inhibitors are known as R&O oils in the US, and HL oils overseas.

Oxidation Inhibitors – amine and phenolic antioxidants act by interrupting the free radical chain reaction that results in oxidation. Essentially, as the oil starts to decompose in the presence of oxygen, these inhibitors interrupt the reaction. They also keep metal from speeding up the oxidation reaction by deactivating the metal. Oxidation inhibitors are added to extend the life of the oil. Oxygen reacts with the oil to produce weak acids that can pit surfaces. Oxidation inhibitors slow the rate of oxidation.

Oxidation stability is important in most compressor applications because of the heat that is generated. Oxidized oil can create deposits that build up on discharge valves allowing them to stick open. This causes hot air to get sucked back into the compression chamber where it is recompressed. The air can generate enough heat to ignite the deposits and cause a fire or explosion. Use of synthetics can minimize this possibility.

Anti-wear Additive – Zinc dialkyl dithiophosphate (ZDDP) is the most common anti-wear additive, although there are many zinc-free additives based on sulfur and phosphorus that also impart anti-wear properties. The zinc-sulfur-phosphorus end of the molecule is attracted to the metal surface allowing the long chains of carbons and hydrogens on the other end of the molecule to form a slippery carpet that prevents wear.

Not a chemical reaction, rather a super-strong attraction. There are other anti-wear additives that do not contain zinc. Some are based on sulfur, and some on fatty materials. Anti-wear additives, as a rule, are not as aggressive as extreme pressure additives. Oils that contain anti-wear additives are often called AW oils in the US or carry the HLP designation in Europe. Zinc containing anti-wear oils are generally not recommended for air compressors because the anti-wear package may compromise the oxidation stability of the oil.

Demulsifier – carbon-based polymers affect the interfacial tension of contaminants, so they separate out from oil rapidly. Hydrolytic stability is the ability of the oil to resist degradation in the presence of water. This is important because any system open to the atmosphere will be exposed to some moisture from humidity and condensation. Some ester-based fluids have relatively poor hydrolytic stability and will rapidly turn acidic in the presence of water.

Pour Point Depressants – chemicals designed to reduce the solidification of the oil to the lowest temperature at which it will pour under an ASTM laboratory test. Typically, these are methacrylate molecules and will inhibit the crystallization of the wax molecules.

Viscosity Index Improvers – chemicals designed to reduce the thinning of an oil when the temperature increases. These chemicals are typically methacrylate molecules and will inhibit the thinning of the oil by expanding their molecular footprint this reducing flowability as the temperature increases.

Detergents – typically used in engine oil formulas, they are designed to keep the system clean of deposits. Often, they are alkaline by nature thus contribute to increase then TBN of the oil. Diesel engine lube oils are compounded with alkaline additives to help neutralize acids from combustion. They also provide antioxidant properties. Typical compounds contain calcium or magnesium.

Detergents have their disadvantages. Detergents move deposits downstream where they may build up on heat transfer surfaces in coolers. Detergent oils absorb water. If water can build up in the oil, it will cause rust and will accelerate oxidation. Compressors generate water because the humidity from the air condenses as the air is compressed. It is generally removed in a coalescer or knockout drum, but some water gets into the oil. For this reason, detergent oils are only used in limited applications.

Dispersants – designed to capture particulates such as soot to form a micelle and keep in suspension. These compounds can be part of the detergent chemistry or be metal-free so they can be used in an ashless formulations. Some additives can actually contribute to wear. Too much metallic detergent/dispersant can leave ash type deposits that can be abrasive. There is a test to measure the amount of ash left behind when an oil is burned. It is commonly known as a sulfated ash test. Some engine manufacturers limit the amount of ash that is in an oil. An “ashless” oil required for some aviation engines has less than 0.1% ash, while a high ash oil used in some marine engines with high sulfur fuel can have ash in excess of 1.5%.

Additives can be depleted in service. There is a quick field test used to measure the level of detergency and dispersant of used oils. It is commonly known as the Oil spot (or patch) test. A simple test is when oil is filtered through a patch and treated with a solvent. If particles are concentrated in the center of the patch, it indicates that water or anti-freeze may be impairing dispersancy. The oil spot test can also pick up fuel soot, which are particles formed from fuel that is not completely burned. The filter patch can show evidence of dirt contamination, too.

Compatibility

Lubricant additives were developed to enhance the existing characteristics of the base oil(s) a lubricant is formulated with, to reduce the deficiencies of the base oils(s) or impart new performance characteristics. Engine oils were the first lubricants to be formulated with additives. They have been and still are the largest market segment for lubrication. So, it is no surprise that most of the research and development efforts have been placed on engine oil enhancement.

In , the American Society of Automotive Engineers (SAE) established the oil classification system. This was related only to oil viscosity and not performance. Until the s, engine oils did not contain any additives. They were only base oils. Prior to the introduction of additive chemistry, the oil drain intervals were 750 miles. Due to increasing consumer demands and economic pressures, internal combustion engines became more sophisticated. Engine oils were becoming increasingly stressed and challenges on their performance reserves gave rise to a need for additives.

The first oil additive developed was the pourpoint depressant. These acrylate polymers were developed in the mid-s. Anti-wear additives such as zinc dithiophosphate were introduced in the early s followed by corrosion inhibitors and then sulfonate detergents. The sulfonate detergents were found to provide acid neutralization as well as oxidation inhabitation as well as rust and corrosion inhabitation.

In , the American Petroleum Institute (API) established a specification system for engine oil performance classification. This is an important consideration because it is the only system by which a lubricant can be deemed compatible with another from a different manufacturer without the need to test compatibility. As long as the oils are of the same viscosity grade and have the same API classification and SAE viscosity, the oils are compatible; the user can mix oils if need be. This is not the case for other lubricants.

When mixing different lubricants, an adverse reaction may occur between two oils at certain working conditions in a system. This is considered ‘lubricant incompatibility’. Most often the cause of incompatibility is the neutralization of an acidic additive in one oil by an alkaline additive in the other oil. The result is that the additives react with each other instead of the metal surface, particle or free radicals in the oil.

The newly formed compound becomes ineffective and precipitate (drop out). Most all additives are polar which is what drives this reaction. This is by design. The polarity affords surface reaction as well as contamination reactions all that benefit the asset. During the reaction of incompatibility, often a soap forms that can precipitate a grease-like gel that interferes with lubrication and oil flow.

However, mixed oils may not always lead to incompatibility issues. They can exist without precipitation or reaction in an operating system for an indefinite period until water is introduced. Water can quickly lead to a reaction between the polar additives. Iron and copper found on the molecular level can act as catalysts in these reactions. Incompatibility reactions are not reversible. Removing water by drying the system and the oil does not remove the formed gel or eliminate the soap.

Typically, acidic additives can be found in gear, hydraulic and some circulating oils. Alkaline-based additives are used in engine oils. There are some additives that are neither acidic nor basic but neutral, these types of additives are used in compressors and refrigeration oils. Additives that are acidic are identified as being strong acids and will react faster than acids that are formed during the initiation stage of oxidation, which are typically carboxylic acids or nitric acids, and are weak acids due to the limited number to protons donated.

Weak acids react slower than strong acids. This is the reason why oils that have incompatible additive chemistry react so fast. Additives are not the only culprit. Propylene glycols, polyglycols, phosphate esters, polyol esters base oils have fair to poor compatibility with mineral oil-based lubricants. While these oils may not for solid substances, they may form a sludge. Many will not mix with the mineral-based lubricants.

Lubrication professionals often become very familiar with the base oil viscosity of their lubricants. After all, viscosity is the most important property of a base oil.

Baselines for incoming oils are set and the health of the lubricant is monitored based on viscosity alone. However, there is more to lubricants than just viscosity. It’s crucial to understand the role of additives and their function(s) within the lubricant.

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Lubricant additives are organic or inorganic compounds dissolved or suspended as solids in oil. They typically range between 0.1 to 30 percent of the oil volume, depending on the machine.

Additives have three basic roles:

• Enhance existing base oil properties with antioxidants, corrosion inhibitors, anti-foam agents and demulsifying agents.

• Suppress undesirable base oil properties with pour-point depressants and viscosity index (VI) improvers.

• Impart new properties to base oils with extreme pressure (EP) additives, detergents, metal deactivators and tackiness agents.

Polar Additives

Additive polarity is defined as the natural directional attraction of additive molecules to other polar materials in contact with oil. In simple terms, it is anything that water dissolves or dissolves into water.

A sponge, a metal surface, dirt, water and wood pulp are all polar. Things that are not polar include wax, Teflon, mineral base stock, a duck’s back and water repellents.

It’s important to note that additives are also sacrificial. Once they are gone, they’re gone. Think about the environment you work in, the products you produce and the types of contaminants

that are around you daily. If you are allowing into your system contaminants that additives are attracted to, such as dirt, silica and water, the additives will cling to the contaminants and settle to the bottom or will be filtered out and deplete your additive package.

Polar Mechanisms

There are a few polar mechanisms such as particle enveloping, water emulsifying and metal wetting that are worthy of discussion.

Particle enveloping means that the additive will cling to the particle surface and envelop it. These additives are metal deactivators, detergents and dispersants. They are used to peptize (disperse) soot particles for the purpose of preventing agglomeration, settling and deposits, especially at low to moderate temperatures.

You generally will see this in an engine. It offers a good reason to repair and eliminate any issues as soon as they are detected through an appropriate oil analysis test slate.

Water emulsifying occurs when the additive polar head clings to a micro-droplet of moisture. These types of additives are emulsifying agents. Consider this the next time you observe water in a reservoir.

While it is important to remove the water, determine where the water entered the system and repair it using a root-cause maintenance approach, you must also keep in mind that the additive package has been affected. In lubrication terms, this is known as additive depletion. A proper oil analysis report can determine the health of the additives remaining in the lubricant.

Metal wetting is when additives anchor to metal surfaces, which is what they are supposed to do. They attach to the interior of the gear casing, gear teeth, bearings, shafts, etc.

Additives that perform this function are rust inhibitors, anti-wear (AW) and EP additives, oiliness agents and corrosion inhibitors.

AW additives work specifically to protect metal surfaces during boundary conditions. They form a ductile, ash-like film at moderate to high contact temperatures (150 to 230 degrees F).

Under boundary conditions, AW film shears instead of surface material.

One common anti-wear additive is zinc dialkyldithiophosphate (ZDDP). It reduces the risk of metal-to-metal contact, which can lead to increased heat, result in oxidation and negatively affect the film strength.

Whether they are enhancing, suppressing or imparting new properties to the base oil, additives play an important role in the lubrication of machinery. Remember, when the additives are gone, they’re gone, so don’t forget to check your additive package.

Types of Lubricant Additives

There are many types of chemical additives mixed into base oils to enhance the properties of the base oil, to suppress some undesirable properties of the base oil and possibly to impart some new properties.

Additives typically make up about 0.1 to 30 percent of the finished lubricating oil, depending upon the target application of the lubricant.

Lubricant additives are expensive chemicals, and creating the proper mix or formulation of additives is a very complicated science.  It is the choice of additives that differentiates a turbine (R&O) oil from a hydraulic oil, a gear oil and an engine oil.

Many lubricant additives are available, and they are selected for use based upon their ability to perform their intended function. They are also chosen for their ability to mix easily with the selected base oils, to be compatible with other additives in the formulation and to be cost effective. 

Some additives perform their function within the body of the oil (e.g., anti-oxidants), while others do their work on the surface of the metal (e.g., anti-wear additives and rust inhibitors).

Conventional Lubricant Additives

These include the following general types of additives:

Anti-oxidants

Oxidation is the general attack of the weakest components of the base oil by oxygen in the air.  It occurs at all temperatures all of the time but is accelerated at higher temperatures and by the presence of water, wear metals and other contaminants. 

It ultimately causes acids (which produce corrosion) and sludge (which results in surface deposits and viscosity to increase) to form.  Oxidation inhibitors, as they are also called, are used to extend the operating life of the oil. 

They are sacrificial additives that are consumed while performing their duty of delaying the onset of oxidation, thus protecting the base oil.  They are present in almost every lubricating oil and grease.

Rust and Corrosion Inhibitors

These additives reduce or eliminate internal rust and corrosion by neutralizing acids and forming a chemical protective barrier to repel moisture from metal surfaces. 

Some of these inhibitors are specific to protecting certain metals. Therefore, an oil may contain several corrosion inhibitors.  Again, they are common in almost every oil and grease.  Metal deactivators are another form of corrosion inhibitor.

Viscosity Index Improvers

Viscosity index improvers are very large polymer additives that partially prevent the oil from thinning out (losing viscosity) as the temperature increases.  These additives are used extensively when blending multi-grade engine oils such as SAE 5W-30 or SAE 15W-40.

They are also responsible for better oil flow at low temperatures, resulting in reduction in wear and improved fuel economy.  In addition, VI improvers are used to achieve high-VI hydraulic and gear oils for improved start-up and lubrication at low temperatures.

To visualize how a VI-improver additive functions, think of the VI improver as an octopus or coil spring that stays coiled up in a ball at low temperatures and has very little effect on the oil viscosity. 

Then, as the temperature rises, the additive (or octopus) expands or extends its arms (making it larger) and prevents the oil from thinning out too much at high temperatures. 

VI improvers do have a couple of negative features.  The additives are large (high molecular weight) polymers, which makes them susceptible to being chopped or cut up into small pieces by machine components (shearing forces).  Gears are notoriously hard on VI-improver additives. 

Permanent shearing of the VI-improver additive can cause significant viscosity losses, which can be detected with oil analysis.  A second form of viscosity loss occurs due to high shearing forces in the load zone of frictional surfaces (e.g., in journal bearings). 

It is thought that the VI-improver additive loses its shape or uniform orientation and therefore loses some of its thickening ability. 

The viscosity of the oil temporarily drops within the load zone and then rebounds to its normal viscosity after it leaves the load zone.  This characteristic actually aids in the reduction of fuel consumption.

There are several different types of VI improvers (olefin copolymers are common).  High-quality VI improvers are less susceptible to permanent shear loss than low-cost, low-quality VI improvers. 

Anti-wear (AW) Agents

These additives are typically used to protect machine parts from wear and loss of metal during boundary lubrication conditions.  They are polar additives that attach to frictional metal surfaces. 

They react chemically with the metal surfaces when metal-to-metal contact occurs in conditions of mixed and boundary lubrication. 

They are activated by the heat of contact to form a film that minimizes wear.  They also help protect the base oil from oxidation and the metal from damage by corrosive acids. 

These additives become “used up” by performing their function, after which adhesive wear damage will increase.  They are typically phosphorus compounds, with the most common being zinc dialkyldithiophosphate (ZDDP). 

There are different versions of ZDDP — some intended for hydraulic applications and others for the higher temperatures encountered in engine oils.  ZDDP also has some anti-oxidant and corrosion-inhibition properties.  In addition, other types of phosphorous-based chemicals are used for anti-wear protection (e.g., TCP). 

Extreme Pressure (EP) Additives

These additives are more chemically aggressive than AW additives.  They react chemically with metal (iron) surfaces to form a sacrificial surface film that prevents the welding and seizure of opposing asperities caused by metal-to-metal contact (adhesive wear).  

They are activated at high loads and by the high contact temperatures that are created.  They are typically used in gear oils and give those oils that unique, strong sulphur smell.  These additives usually contain sulphur and phosphorus compounds (and occasionally boron compounds).

They can be corrosive toward yellow metals, especially at higher temperatures, and therefore should not be used in worm gear and similar applications where copper-based metals are used.  Some chlorine-based EP additives exist but are rarely used due to corrosion concerns.

Anti-wear additives and extreme pressure agents form a large group of chemical additives that carry out their function of protecting metal surfaces during boundary lubrication by forming a protective film or barrier on the wear surfaces. 

As long as the hydrodynamic or elastohydrodynamic oil film is maintained between the metal surfaces, boundary lubrication will not occur and these boundary lubrication additives will not be required to perform their function. 

When the oil film does break down and asperity contact is made under high loads or high temperatures, these boundary lubrication additives protect the wearing surfaces.

Detergents

Detergents perform two functions.  They help to keep hot metal components free of deposits (clean) and neutralize acids that form in the oil.  Detergents are primarily used in engine oils and are alkaline or basic in nature.  

They form the basis of the reserve alkalinity of engine oils, which is referred to as the base number (BN).  They are typically materials of calcium and magnesium chemistry.  Barium-based detergents were used in the past but are rarely used now.

Since these metal compounds leave an ash deposit when the oil is burned, they may cause unwanted residue to form in high-temperature applications.  Due to this ash concern, many OEMs are specifying low-ash oils for equipment operating at high temperatures.  A detergent additive is normally used in conjunction with a dispersant additive.

Dispersants

Dispersants are mainly found in engine oil with detergents to help keep engines clean and free of deposits.  The main function of dispersants is to keep particles of diesel engine soot finely dispersed or suspended in the oil (less than 1 micron in size). 

The objective is to keep the contaminant suspended and not allow it to agglomerate in the oil so that it will minimize damage and can be carried out of the engine during an oil change.  Dispersants are generally organic and ashless.  As such, they are not easily detectable with conventional oil analysis. 

The combination of detergent/dispersant additives allows more acid compounds to be neutralized and more contaminant particles to stay suspended.  As these additives perform their functions of neutralizing acids and suspending contaminants, they will eventually exceed their capacity, which will necessitate an oil change.

Anti-foaming Agents

The chemicals in this additive group possess low interfacial tension, which weakens the oil bubble wall and allows the foam bubbles to burst more readily.  They have an indirect effect on oxidation by reducing the amount of air-oil contact. 

Some of these additives are oil-insoluble silicone materials that are not dissolved but rather dispersed finely in the lubricating oil.  Very low concentrations are usually required.  If too much anti-foaming additive is added, it can have a reverse effect and promote further foaming and air entrainment.

Friction Modifiers

Friction modifiers are typically used in engine oils and automatic transmission fluids to alter the friction between engine and transmission components.  In engines, the emphasis is on lowering friction to improve fuel economy. 

In transmissions, the focus is on improving the engagement of the clutch materials.  Friction modifiers can be thought of as anti-wear additives for lower loads that are not activated by contact temperatures.

Pour Point Depressants

The pour point of an oil is approximately the lowest temperature at which an oil will remain fluid.  Wax crystals that form in paraffinic mineral oils crystallize (become solid) at low temperatures.  The solid crystals form a lattice network that inhibits the remaining liquid oil from flowing. 

The additives in this group reduce the size of the wax crystals in the oil and their interaction with each other, allowing the oil to continue to flow at low temperatures.

Demulsifiers

Demulsifier additives prevent the formation of a stable oil-water mixture or an emulsion by changing the interfacial tension of the oil so that water will coalesce and separate more readily from the oil.  This is an important characteristic for lubricants exposed to steam or water so that free water can settle out and be easily drained off at a reservoir.

Emulsifiers

Emulsifiers are used in oil-water-based metal-working fluids and fire-resistant fluids to help create a stable oil-water emulsion.  The emulsifier additive can be thought of as a glue binding the oil and water together, because normally they would like to separate from each other due to interfacial tension and differences in specific gravity.

Biocides

Biocides are often added to water-based lubricants to control the growth of bacteria.

Tackifiers

Tackifiers are stringy materials used in some oils and greases to prevent the lubricant from flinging off the metal surface during rotational movement.

To be acceptable to blenders and end users alike, the additives must be capable of being handled in conventional blending equipment, stable in storage, free of offensive odor and be non‑toxic by normal industrial standards. 

Since many are highly viscous materials, they are generally sold to the oil formulator as concentrated solutions in a base oil carrier.

A couple of key points about additives:
More additive is not always better.  The old saying, “If a little bit of something is good, then more of the same is better,” is not necessarily true when using oil additives. 

As more additive is blended into  the oil, sometimes there isn’t any more benefit gained, and at times the performance actually deteriorates.  In other cases, the performance of the additive doesn’t improve, but the duration of service does improve.

Increasing the percentage of a certain additive may improve one property of an oil while at the same time degrade another.  When the specified concentrations of additives become unbalanced, overall oil quality can be affected. 

Some additives compete with each other for the same space on a metal surface.  If a high concentration of an anti-wear agent is added to the oil, the corrosion inhibitor may become less effective.  The result may be an increase in corrosion-related problems.

How Oil Additives Get Depleted

It is very important to understand that most of these additives get consumed and depleted by:

1. “decomposition” or breakdown,
2. “adsorption” onto metal, particle and water surfaces, and
3. “separation” due to settling or filtration.

The adsorption and separation mechanisms involve mass transfer or physical movement of the additive.

For many additives, the longer the oil remains in service, the less effective the remaining additive package is in protecting the equipment. 

When the additive package weakens, viscosity increases, sludge begins to form, corrosive acids start to attack bearings and metal surfaces, and/or wear begins to increase.  If oils of low quality are used, the point at which these problems begin will occur much sooner.

It is for these reasons that top-quality lubricants meeting the correct industry specifications (e.g., API engine service classifications) should always be selected.  The following table can be used as a guide for a more thorough understanding of additive types and their functions in engine oil formulations.

It is evident from the information above that there is a lot of chemistry occurring in most of the oils that are used to lubricate equipment.  They are complicated mixtures of chemicals that are in balance with one another and need to be respected. 

It is for those reasons that the mixing of different oils and adding additional lubricant additives should be avoided. 

After-market Additives and Supplemental Oil Conditioners

There are hundreds of chemical additives and supplemental lubricant conditioners available.  In certain specialized applications or industries, these additives may have a place in the improvement of lubrication. 

However, some manufacturers of supplemental lubricants will make claims about their products that are exaggerated and/or unproven, or they fail to mention a negative side effect that the additive may cause. 

Take great care in the selection and application of these products, or better still, avoid using them.  If you want a better oil, buy a better oil in the first place and leave the chemistry to the people who know what they are doing.  

Often oil and equipment warranties are voided with the use of after-market additives because the final formulation has never been tested and approved.  Buyer beware.

When considering the use of an after-market additive to solve a problem, it is wise to remember the following rules:

Rule #1         
An inferior lubricant cannot be converted into a premium product simply by the inclusion of an additive.  Purchasing a poor-quality finished oil and attempting to overcome its poor lubricating qualities with some special additive is illogical.

Rule #2         
Some laboratory tests can be tricked into providing a positive result.  Some additives can trick a given test into providing a passing result.  Often multiple oxidation and wear tests are run to obtain a better indication of the performance of an additive.  Then actual field trials are performed.

RULE #3       
Base oils can only dissolve (carry) a certain amount of additive.  As a result, the addition of a supplemental additive into an oil having a low level of solubility or being already saturated with additive may simply mean that the additive will settle out of the solution and remain in the bottom of the crankcase or sump.  The additive may never carry out its claimed or intended function.

If you choose to use an after-market additive, before adding any supplemental additive or oil conditioner to a lubricated system, take the following precautions:

1. Determine whether an actual lubrication problem exists.  For instance, an oil contamination problem is most often related to poor maintenance or inadequate filtration and not necessarily poor lubrication or poor-quality oil.

2. Choose the right supplemental additive or oil conditioner.  This means taking the time to research the makeup and compatibility of the various products on the market.

3. Insist that factual field-test data is made available that substantiates the claims made regarding the product’s effectiveness.

4. Consult a reputable, independent oil analysis laboratory.  Have the existing oil analyzed at least twice before adding a supplemental additive.  This will establish a reference point.

5. After the addition of the special additive or conditioner, continue to have the oil analyzed on a regular basis.  Only through this method of comparison can objective data regarding the effectiveness of the additive be obtained.

There is a great deal of controversy surrounding the application of supplemental additives.  However, it is true that certain supplemental lubricant additives will reduce or eliminate friction in some applications such as machine tool ways, extreme pressure gear drives and certain high-pressure hydraulic system applications.

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