The prime functions of engine oil are to lubricate, cool, clean, protect and seal. In the early days of the automobile neat mineral oil was used to perform these functions. Improvements in engine design and engineering techniques soon lead to parts being manufactured to finer tolerances, higher engine operating temperatures, more power and increased speeds.

Consequently, lubrication problems started to occur. Oils deteriorated rapidly, wear rates increased, engines failed and performance was generally unacceptable. In the early 1900s it was discovered that the addition of chemicals, referred to as additives, could improve the performance of the mineral base oils.

Oils deteriorated rapidly, wear rates increased, engines failed and performance was generally unacceptable. In the early 1900s it was discovered that the addition of chemicals, referred to as additives, could improve the performance of the mineral base oils.

Today engine oils may contain anything between 3% additives in a basic monograde oil and up to 30% in a superior high performance multigrade lubricant. Following is a typical composition of a modern good quality multigrade engine oil:

The base oil component of engine oils may be mineral, synthetic or semisynthetic (a mixture of mineral and synthetic stocks). Most lubricants sold today are still blended using mineral base oils. Synthetic base stocks are used whenever petroleum (mineral) based oils have reached their performance limit. Synthetic lubricants have improved high temperature characteristics and are more stable over a wide range of operating temperatures.

Additives are extensively used to improve and maintain modern oil performance. Following is a brief discussion of the additives found in reputable brands of engine oil:

Viscosity Modifiers (also called viscosity index improvers) are used to produce multigrade engine oils. They reduce the tendency of the oil to thicken with decreasing temperature and also resist thinning out at elevated temperatures. Viscosity modifiers (VM’s) are not used in monograde engine oils and if the oil in the above example was a monograde, the 8% VM would simply be replaced by base oil.

Detergents operate on high-temperature surfaces, such as the piston-ring area and the piston under-crown, to prevent the formation of harmful deposits on these surfaces.

Dispersants help to keep internal engine surfaces clean by finely suspending contaminants in the oil until they can be safely removed at the next oil change.

Antiwear Agents protect metal surfaces against wear when the lubricating film breaks down. Zinc dialkyl- dithiophosphate (ZDDP) is a long-used favourite to reduce friction between metal surfaces. Some oils also contain friction modifiers to reduce friction even further but their effectiveness tends to diminish during the life of the oil.

Antioxidants inhibit oxidation of the oil.  Oxidation results from exposure of the lubricant to oxygen at high temperatures. The results of such exposure accelerate aging of the oil contributing to oil thickening, sludge and deposits. Antioxidants therefore also help to keep engines running clean.

Rust and Corrosion Inhibitors coat metal surfaces inside the engine to provide a protective film, preventing moisture, oxygen and acids from reaching the metal and causing rust and corrosion.

Pour Point Depressants (PPD’s) provide good oil flow at low temperatures. Oil contains wax particles that can congeal and reduce flow when cooled down. PPD’s modify wax crystal growth at low temperatures and oil continues to flow smoothly.

Foam Inhibitors do not prevent air from mixing with the oil.  Foam inhibitors weaken the surface tension of the air bubbles that are formed allowing them to ‘burst’ more readily and thereby reducing foam.

Another critical characteristic of engine oil is its ability to neutralize acids that are formed during combustion of the fuel. The Total Base Number (TBN) measures the ability of engine oil to neutralize these acids. Detergent and dispersant additives (detergents in particular) are highly alkaline by nature and contribute to the neutralization of acids by proving the engine oil with an alkalinity reserve (TBN).

Although additive technology has improved significantly over the years, the ever increasing stress placed on the oil by modern engines demands that the oil still has to be changed at regular intervals as prescribed by engine manufacturers. Reasons for changing the oil are as follows:

• To drain contaminants out of the engine when the used oil is replaced. Contaminants include dirt and dust, unburned fuel, combustion byproducts, water/coolant, wear metals and cross-contamination with other lubricants.
• Additives are consumed during the service life of the oil in the engine and may get depleted.

Then why not simply put more additives into the oil? You can’t necessarily improve the oil’s performance by increasing the additive concentration. In fact, you can make things worse. Engine oils are carefully designed and finely balanced lubrication packages that are scientifically formulated and rigorously tested before they are released in the market. By upsetting this delicate balance you will produce different results than those originally intended.  This raises another issue…supplemental oil additives.

On their own the original additives in modern engine oil are extremely effective but they can become harmful if used in combination with aftermarket or over-the-counter oil additives.  It is therefore no surprise that engine manufacturers do not approve the use of supplemental oil additives. When using a properly formulated motor oil you do not need any additional additives whatsoever. In fact, the additives you may put in can react negatively with the additives the oil company has carefully blended into the engine oil and may result in engine damage and even engine failure.

The SAE J306 standard specifies viscosity limits for the classification of automotive gear lubricants. SAE J306 viscosity grades should not be confused with the SAE J300 viscosity grading system for engine oils (please refer to OilChat #3).

SAE J306 is intended for use by equipment manufacturers when defining and recommending automotive gear, axle and manual transmission lubricants and for oil marketers when labelling such lubricants with respect to their viscosity. It is also used in Owners’ Manuals to advise operators which viscosity grade to use.

The SAE J306 classification is based on the lubricant viscosity at both high and low temperatures. The high temperature kinematic viscosity values are reported in centistokes (cSt). The low temperature viscosities are determined at sub-zero temperatures and are reported in centipoise (cP). High temperature viscosity is related to the hydrodynamic lubrication characteristics of the oil and test results must meet the 100°C viscosity limits listed in the table below.

Low temperature viscosity requirements are associated with the ability of the fluid to flow and to provide adequate lubrication to critical parts under low ambient temperature conditions. The 150 000 cP viscosity value used to define low-temperature properties is based on a series of tests in a specific rear axle design. These tests have shown that pinion bearing failure has occurred at viscosities higher than 150 000 cP in the test axle. The Brookfield test method is used since it provides adequate precision at this viscosity level.

For many years the SAE J306 standard comprised four low temperature grades (SAE 70W, 75W, 80W & 85W) and three high temperature grades (SAE 90, 140 & 250). During 1998 the standard was revised to incorporate two additional viscosity grade designations, SAE 80 and SAE 85. These new grades were included to specify the viscometrics for manual transmission lubricants. Another two viscosity grades were added to the viscosity classification as part of the January 2005 update.

These new grades are SAE 110 (100 °C viscosity between 18.5 and 24.0 cSt) and SAE 190 (100 °C viscosity between 32.5 and 41.0 cSt). The need for these two grades were necessitated  by the wide variation in kinematic viscosity possible within prior versions of J306 for the SAE 90 grade (100 °C viscosity between 13.5 and 24.0 cSt) and the SAE 140 grade (100 °C viscosity between 24.0 and 41.0 cSt). The effect of such wide ranges of kinematic viscosities could result in an axle being serviced with a lubricant that had a viscosity significantly lower or higher than the lubricant that the axle had been designed for, even if the same viscosity grade had been used. Prior to 2005 OEMs may also have been forced to specify a higher viscosity grade than what they actually required, because the wide range of kinematic viscosities of the next lower grade could result in customers using a lubricant with a too low kinematic viscosity.

The current J306 Viscosity Classification for Automotive Gear Oils is:

 

 

 

 

 

 

 

 

 

 

To classify the viscosity grade of automotive gear oils, a lubricant may use one W grade numerical designation, one non-W grade numerical designation, or one W grade in combination with one non-W grade. In all cases the numerical designation must be preceded by the letters “SAE”. In addition, when both a W grade and a non-W grade are listed, the W grade is always recorded first (i.e. SAE 80W-90).

A lubricant which meets the requirements of both a low-temperature and a high-temperature grade is commonly known as a multiviscosity-grade oil. For example, an SAE 80W-90 lubricant must meet the low-temperature requirements for SAE 80W and the high-temperature requirements for SAE 90. Since the W grade is defined on the basis of maximum temperature for a Brookfield viscosity of 150 000 cP and minimum kinematic viscosity at 100 °C, it is possible for a lubricant to satisfy the requirements of more than one W grade. In labelling a W grade or a multiviscosity grade lubricant, only the lowest W grade conformed to may be mentioned on the label. Thus a lubricant meeting the requirements of both SAE 75W and SAE 85W as well as SAE 90 would be labelled as SAE 75W-90, and not SAE 75W-85W-90.

Similar to the SAE J300 grading system for engine oils, the SAE J306 standard only specifies viscosity limits for automotive gear lubricants. Other lubricant characteristics such as performance level and service classification are not considered. These will be discussed in future issues of OilChat.

The earliest attempts to classify motor oils were made when automobiles first appeared. Even at this early stage, viscosity was recognized as one of the most important characteristics of oil. For this reason the Society of Automotive Engineers (SAE), in co-operation with engine manufacturers, developed the original SAE BOO viscosity grading system for engine oils way back in 1911.

Oils were assigned numbers based on viscosities at certain temperatures. Over the years these standards were updated several times to keep in pace with engine developments and technology advancements.

It has been recognized that oil viscosity at colder temperatures, as well as at high operating temperatures, is very important in the performance of an engine. The SAE has therefore devised two separate viscosity measurement systems, one at a high temperature (100°C) and one at very low temperatures. A rotating viscometer, called a cold cranking simulator, is used to measure viscosities at temperatures as low as -35°C. Because the viscosities are measured in two different temperature ranges, the results are reported in two different units.

The first unit is the centipoise (cP). It is used to  report  the  absolute  viscosity  of  motor  oil  at  low temperatures. This number indicates the ease with which the oil can flow when cold. The other unit is the Centistoke (cSt) which is used to report the kinematic viscosity of motor oil at higher temperatures.

Oils that are suitable for use in colder temperatures are identified by the letter “W” when indicating the SAE viscosity grade. These oil grades must meet maximum viscosity limits at specified sub-zero temperatures and must also meet maximum requirements for the borderline pumping temperatures at very low temperatures. Oils that are suitable for use at higher temperatures have viscosities within specified ranges at 100°C. The standards below have been used to classify engine oil viscosities for a number of years:

SAE BOO Engine Oil Viscosity Grades

If we draw graphs of typical SAE SW and SAE LiO monograde oils with viscosity plotted as a logarithmic function on the vertical axis against temperature as a linear function on the horizontal axis, we will end up with the two solid red lines in the diagram below:

The SAE SW oil will flow sufficiently at low temperatures to protect engines during startup on cold mornings but will be too thin to provide adequate protection at operating temperatures. The SAE LiO oil on the other hand will perform satisfactorily at operating temperatures but will be too viscous to flow sufficiently during startup on cold mornings. The solution? An oil that is ‘thin’ on cold mornings but with a viscosity similar to that of a SAE LiO at operating temperature. But how do we achieve that? With a viscosity modifier (viscosity index improver).

A viscosity modifier (VM) is an oil additive that is sensitive to temperature. At low temperatures, the VM contracts and does not impact the oil viscosity. At elevated temperatures, it expands and an increase in viscosity occurs. If we use a thin oil (let’s say the SAE SW above) as base and add sufficient VM to meet SAE LiO viscosity limits at 1oo·c, we end up with a SAE SW-LiO multigrade oil – the red dotted line. Similarly there are SAE 1 SW-LiO, SAE

20W-SO, etc. multigrade engine oils available in the market. Multigrade oils provide better engine protection at low and high temperatures than monograde 0·11s because they maintain optimum viscosity over the full engine operating temperature range.

Of particular interest is the inclusion of three new high temperature viscosity grades in the latest revision of the SAE BOO Engine Oil Viscosity Classification Standard. They are SAE 16, SAE 12 and SAE 8 (not shown in the table above). These new grades reflect the continued industry push for lower viscosity engine oils to achieve improved fuel economy. They establish specifications to standardize new lower viscosity lubricants such as SAE SW-12, or even SAE OW-8, in the marketplace.

Viscosity is probably the single most important property of oil in terms of lubrication but what is viscosity really? Informally viscosity is the “thickness” of a liquid. For example, if you pour water into a container with a hole at the bottom, the container drains quickly.

However, if you fill the same container with honey, you will find the container drains very
slowly. That is because the viscosity of honey is high compared to that of water. We can
therefore say that viscosity is an indication of a fluid’s resistance to flow.

More formally, viscosity is a measure of the internal friction of a moving fluid. Most liquids are both cohesive and adhesive. Cohesiveness is the intermolecular attraction by which the molecules of the fluid are held together and result in internal friction. A fluid with high viscosity resists motion because its molecular makeup renders it a lot of internal friction. A fluid with low viscosity flows easily because its chemical structure results in very little friction when the oil molecules are in motion.

Imagine you have two horizontal plates or metal surfaces with oil in-between. The oil will cling to the two surfaces because it is adhesive. If the top plate moves horizontally relative to the stationary bottom plate the speed of the oil molecules in between will vary from zero at the bottom to the same speed as the top plate. As the oil layers slip over each other they create friction as a result of the cohesiveness of the oil molecules.

The most commonly used unit for measuring viscosity is the Centistoke(cSt). Viscosity is frequently measured using a device called a capillary viscometer – a U-shaped, graduated glass tube with a capillary of known diameter in the one arm. This method measures the time taken for a defined quantity of fluid to flow through the capillary. When two fluids of
equal volume are placed in the same viscometer and allowed to flow under the influence of gravity, a viscous fluid takes longer than a less viscous fluid to flow through the capillary and a higher viscosity is recorded. Since this method uses gravity as the driving force; the result is kinematic viscosity. The metric unit of kinematic viscosity is mm2
/s (1cSt = mm2/s).

One disadvantage of the capillary viscometer is that the capillary is too small for highly viscous liquids. From everyday experience, it is common knowledge that viscosity varies with temperature. Honey flows more readily when heated. Likewise oils thicken noticeably on cold days with a resultant increase in viscosity. Since viscosity is so dependent on temperature, it should NEVER be quoted without reference to the temperature at which it was measured. Kinematic viscosity is generally measured at li0°C and 1oo·c.

The low-temperature characteristics of certain lubricants are important to their properoperation. Measurement of the sub-zero viscosity of automatic transmission fluids, engine oils, etc. is often used to specify their suitability for service. To measure the viscosity of oils at low temperature, dynamic (or absolute) viscosity is often employedusing a Brookfield viscometer.

Brookfield viscometers rotate a spindle (at a defined speed) in the viscous cold oil and measure the torque required to rotate the spindle in the oil and report viscosity values using the centipoise (cP) or milliPascal-second (Another key property of lubricating oil is Viscosity Index (VI). It is an arbitrary measuring scale (without units) that indicates the change in oil viscosity with change in temperature.

The lower the VI, the greater the change in viscosity of the oil with change in temperature. For example honey is thick at room temperature but when you heat it to say 60°C, it flows readily because the viscosity is reduced significantly and thus has a low VI. However there is hardly any visible change in the viscosity of water from room temperature to 60°C and we can therefore say water has a high VI compared to honey. Failure to use an oil with the proper VI when temperature extremes are expected may result in poor lubrication and equipment failure.

And finally oil viscosity selection. When choosing an oil for a specific application the first
consideration should always be an oil with a viscosity that is sufficient to keep the metal surfaces apart. Unfortunately viscosity cannot be considered in isolation. Selection of the correct viscosity will depend on the temperature, load and speed encountered in a specific application.

Temperature: For machines operating under constant load, constant speed and constant ambient temperature, such as an industrial gearbox in a factory, the ideal viscosity very often results in the lowest stabilized oil temperature. Oils of lower or higher viscosities (than the optimum viscosity) will typically increase the oil’s stabilized temperature due to either drag/churning losses (too much viscosity) or mechanical friction (too little viscosity). If conditions are not constant (variable loads, changing speeds, extreme temperatures, etc.), then there is a need for not only the optimum viscosity but also a high viscosity index to stabilize the optimum viscosity. The wider the temperature range,the greater the need for higher VI oils.

Load: Operating conditions determine the load on machinery. The load on an engine in a vehicle under acceleration or going uphill is higher than that of a vehicle cruising down the highway. Load refers to the pressure on the moving surfaces. Effective lubrication means being able to separate the load carrying surfaces and, if the load changes, then the optimum viscosity of the oil required to separate the surfaces can change. If the load is too high, the oil film may be squeezed too thin to protect the metal surfaces from making contact. This will result in solid friction, meaning an increase in heat, wear and ultimately machine failure.

Speed: The faster a machine operates the stronger the oil film will become as more oil is dragged into the area between the metal surfaces. Therefore, for high speed applications, a low viscosity oil is required. Conversely, forlow speed applications, a high viscosity oil needed to maintain a solid oil film and separate moving surfaces.

In summary, oil viscosity must be sufficient to keep metal surfaces apart yet it must not be so viscous that it will increase drag and waste energy.

In this two-part series of our newsletter we are looking at friction and wear reducing agents that are added to lubricants. In the previous issue of OilChat we discussed anti-wear (AW) additives and how they work. In this edition we are delving into the basics and operation of extreme-pressure (EP) additives.

Extreme-Pressure Additives are designed for higher load applications such as gears and sliding surfaces where AW compounds are not adequate. EP agents are tougher and chemically more aggressive than anti-wear additives. Extreme-pressure additives typically contain organic sulphur, phosphorus or chlorine compounds with sulphur-phosphorus (SP) additives being the most commonly used for automotive and industrial gear oils and grease.

Sulphur-phosphorus additives function in a different manner than anti-wear compounds. They form an actual chemical reaction with the metal surface to create a resilient protective layer that reduces wear between two mating metal surfaces. SP additives require temperatures in excess of 90˚C to activate the chemical reaction and the reaction is restricted to localized areas where metal-to-metal contact occurs.

The friction between sliding surfaces generates sufficient heat (hot spots) to activate the additive. The chemical reaction between the additive and the metal surface is confined to this area. If hydrodynamic lubrication (explained in OilChat 22) is maintained, the SP additive will not be activated. EP additives are often supplemented with anti-wear additives to make the lubricant effective across a wide range of pressure and temperature conditions. Depending upon the amount used  sulphur-phosphorus extreme-pressure additives may not be compatible with oils containing zinc based anti-wear additives. It is therefore not recommended to mix AW and EP lubricants yourself.

When the loading and sliding conditions become too severe, extreme-pressure additives will also be scuffed away until the protective layer is depleted. Removal of the EP layer may also remove the metal to which it is chemically bonded, resulting in micropitting of the metal surface. One normally would not find high concentrations of sulphur-phosphorus based EP additives in manual transmission oils due to their aggressive nature toward the yellow metals that are commonly used in the manufacture of transmission synchronizers. Automotive transmission fluids are therefore formulated to balance wear protection with corrosiveness.

There are various other extreme-pressure additives, such as sulphurized fatty acids, chlorinated hydro-carbons, sulfates, nitrites and phenols. Not all of these compounds are temperature-activated and can provide wear protection at all temperatures. Unfortunately some of them persist in the environment and have a strong tendency for bio-accumulation. Bar fatty acids, their role is largely restricted to cutting fluid formulations. There are currently several international initiatives to replace them with more environmentally friendly alternatives.

Regardless of their chemical composition, both anti-wear and extreme-pressure additives operate primarily in boundary- and and mixed-lubrication phases where most of the lubricant is forced out of the contact zone. The metal-to-metal interface triggers the tribochemical reaction of the AW and EP additives on the metal surfaces to control friction and wear. Should you have any further questions about wear reducing agents simply mail us at info@bcl.co.za and we will respond by return message.

Various chemical compounds are added to lubricant base oils to improve the performance of the final product. Two such compounds are anti-wear (AW) and extreme-pressure (EP) additives. Although the terms anti-wear and extreme-pressure are often used interchangeably in the language of lubrication, there are noteworthy contrasts between the two additive packages. In this and the next edition of the newsletter we will endeavor to explain the differences between AW and EP additives.

Anti-wear and extreme-pressure additives are used to reduce friction and wear between moving metal surfaces in boundary- and mixed-lubrication conditions (for details please refer to OilChat #22). AW and EP agents both function by depositing a protective barrier on the metal surfaces but their chemistries and the way they function are poles apart.

Anti-Wear Additives are often phosphorus based polar compounds with oil soluble tails and polar heads that have an affinity for metal surfaces. These additives work by the polar heads physically bonding, or adsorbing, to the metal frictional surfaces (like iron to a magnet) to form a protective film as shown in Figure 1.  Under boundary- and mixed-lubricating conditions the heat generated by metal-to-metal contact, triggers the adsorbed additive layer to bond chemically with the metal surface to form a chemisorbed film as illustrated in Figure 2. This provides a more robust protective barrier or coating on the metal surface.

Zinc dithiophosphate (ZDP) compounds are the most commonly used anti-wear additives.  Zinc dialkyl-dithiophosphate (ZDDP) is typically used to formulate engine oils, hydraulic fluids, automatic transmission fluids and some greases. They also help to protect the base oil from oxidation and the metal from corrosion. ZDP compounds start decomposing at 130˚C to 170°C and are thus not suitable for very high temperature applications. Tricresyl phosphate (TCP) is a functional alternative for such uses since it can be used at temperatures well in excess of 200˚C. TCP is often used as AW additives in turbine oils and it is also suitable for applications with silver components because it does not contain zinc.

Some lubricant formulations and certain aftermarket engine oil additives use polytetrafluoro-ethylene (PTFE) for wear protection but its efficiency is controversial. A well-known trade name of PTFE is Teflon, a brand name of the DuPont Chemical Company.  DuPont, however, does not give an enthusiastic endorsement of PTFE as a lubricating oil additive. While DuPont says that Teflon is great for preventing food from sticking to frying pans, the company is equivocal about Teflon as an engine oil additive and they have never “promoted” such usage.

Under extreme-pressure conditions, the performance of AW additives becomes insufficient and designated EP agents are required. In the next issue of OilChat we will discuss the basics and operation of extreme-pressure additives.  If, in the interim, you have any questions concerning friction-reducing compounds, our experts are at your disposal and ready to provide you with advice and guidance. Simply mail us at info@bcl.co.za.

OilChat has been out of circulation for some time due to Covid-19 ramifications, but it is now back on track with this edition of the newsletter. In the last two issues of our bulletin (OilChat numbers 53 and 54) we have delved into the History of Lubrication. In this issue we will discuss how the pandemic is affecting the lubricants industry right now and the way forward.

Most lubricant users have recently experienced oil shortages and sharp price increases. But why is this and how has Covid-19 affected international lubricant supplies? We operate in a truly global economy and nothing has illustrated this more than the current, ongoing raw material shortages caused by the worldwide pandemic.

Base oils are the foundation of all lubricants. Lubricating base oils, both mineral and synthetics, are currently in short supply. One of the main reasons for this is that most base oils are a by-product of crude oil refining. Oil refineries distil crude oil into various streams to produce fuels such as  petrol, diesel and jet fuel, other hydrocarbon products for making synthetic rubbers, paints, plastics, and lubricant base oils.

During the global lockdown travel has been greatly reduced, both commercially and personally with many of us working from home and not commuting. There are still very few planes flying hence little demand for jet fuel, which as an industry is a major consumer of fuel. The overall demand for fuel has therefore dropped dramatically and subsequently oil companies are simply producing much less fuel. Consequently base oil production has also been slashed. This shortage has led to the sharp spike in lubricant costs and supply constraints.

Lockdowns across the globe have also reduced the number of staff working at lubricant base oil facilities, leading to bottlenecks in production and increased costs. As a result orders cannot be produced and delivered in a timely fashion.  The failure of a single production plant can significantly limit the global availability of certain commodities and components, especially since storage quantities are limited for budgetary reasons.

In addition to base oils all lubricant manufacturers are heavily reliant on the timely and full supply of additives and packaging. Since many feedstocks for for these commodities are by-products of the fuel manufacturing process, their production has been scaled down too. Lubricant manufacturers are therefore also experiencing a shortage of crude oil based additives and plastic containers.

These are just a few factors which have negatively impacted the oil industry and have primarily led to the shortage in raw materials and finished lubricants. Sadly, there is no way to predict or foresee what the future may hold and to determine when these shortages will be rectified.

At Blue Chip lubricants we have been proactive and have put strong contingency procedures in place to allow continued supply of our key products. We are pleased to advise that to date we have managed to supply all our customers OTIF (on time and in full) through all this chaos. Also, due to steel shortages the 208 litre drums are also in short supply but we have secured large volumes of these to ensure we have sufficient stock.

In addition we are importing container loads of heavy-duty engine oil directly from Q8Oils in Europe. We have ordered large volumes of the Q8 T750 SAE 15W40 engine oil at March pricing for delivery over the period June to August. This ensures adequate stock levels and extremely competitive pricing for all our distributors and customers.  These imports have also permitted us to free up the limited local base stocks to produce other key lubricant products for our customers.

At Blue Chip Lubricants we are continuously pulling out all stops to be ahead of the crisis, but the global scenario changes every day. We deliver orders on a FIFO (first in first out) basis and it is therefore in your own interest to place your orders early to ensure you are not last in the queue.

We would also like to make use of this opportunity to thank all our loyal customers for your continued support during the pandemic and for the confidence that you have placed in us and our products. We are certainly looking forward to a long and rewarding relationship with all our staunch supporters. Together we can keep the wheels of our country turning smoothly.

The American Gear Manufacturers Association (AGMA) has gone a step further than the ISO 3448 viscosity classification system for industrial oils in describing lubricant classifications for industrial gear lubricants. The AGMA standard provides the user with viscosity classifications as well as guidelines for minimum performance levels aimed at industrial gear oils. It aligns with the ISO viscosity standards and is verified by the American National Standards Institute (ANSI).

It is published as the AGMA/ANSI 9005 standard and describes the following four types of industrial gear lubricants:

Rust and Oxidation-Inhibited Gear Lubricants (also referred to as R&O gear oils) are petroleum or semisynthetic based oils formulated with additive systems that protect against rust and oxidation. Some R&O gear oils also contain minute amounts of anti-wear additives. The viscosity grades for R&O gear oils are identified by AGMA numbers 0 to 13.

Compounded Gear Lubricants are petroleum based oils with rust and oxidation inhibitors, demulsibility additives and 3 percent to 10 percent fatty oils. These gear lubricants are frequently used in worm gear drives to provide adequate lubrication and prevent sliding wear. Compounded gear oils are identified by single-digit AGMA numbers with the suffix “Comp” from 7 Comp to 8A Comp.

Extreme Pressure Gear Lubricants (commonly referred to as EP gear oils) are petroleum or semisynthetic based and are fortified with multifunctional additive systems. These additive packages generally contain rust and oxidation inhibitors, EP additives, demulsifiers, antifoam agents, and in some cases solid lubricants such as graphite. AGMA numbers combined with the suffix “EP” describe these lubricants and range from 2 EP to 13 EP.

Synthetic Gear Lubricants are formulated with fully synthetic base stocks and are used whenever petroleum based gear oils have reached their performance limit. Synthetic gear lubricants have the advantage of improved thermal and oxidation resistance and being stable over a wide range of operating temperatures. They normally contain additives similar to those found in EP gear oils. Synthetic gear lubricants are identified by AGMA numbers with the suffix “S” from 0 S to 13 S.

The table below illustrates how AGMA gear oil viscosities correspond to ISO industrial oil viscosities:

Residual compounds 14R and 15R (asphaltic cutbacks) are not included above since these lubricants are being phased out.

In this and previous articles we have discussed the following viscosity classification systems: SAE engine oils, SAE gear lubricants, ISO industrial fluids and AGMA industrial gear lubricants. The following chart brings all these together and provides a comparative illustration of all the various viscosity grades:

Not all viscosity grades appear on the chart as only the most commonly used grades are listed.

Viscosities relate horizontally only.

For example, the following oils have similar viscosities: ISO 150, AGMA 4, SAE 40 and SAE 90.

This may surprise you since many people think that gear oil is thicker.

After the industrial revolution many classification systems were devised to designate viscosity grades for lubricants used in manufacturing and other industrial applications. While all of these have served useful purposes to some degree or another, it was confusing since different units were used to report viscosities such as Saybolt Universal Seconds, Redwood Seconds, Engler Degrees, Centistokes, and more. To add to the confusion, two measures of temperature (Fahrenheit and Celsius) were used, not to mention that viscosities were specified at either 100°F or 40°C and 212°F or 100°C. This necessitated the need for a universally accepted viscosity classification system for industrial oils.

In response, the International Standards Organization (ISO) in collaboration with the American Society for Testing and Materials (ASTM), Deutsches Institut für Normung (DIN) and others formulated a common viscosity classification during 1975. The result is known as the International Standards Organization Viscosity Classification System, commonly known as ISO VG.

This classification is applicable to fluids for industrial applications, such as bearings, gears, compressor cylinders, hydraulics, turbines, etc. Viscosity values are reported in centistokes (cSt) and the reference temperature is 40°C which represents the operating temperature in machinery. The system comprises of 20 viscosity grades, ranging from 2 cSt to 3200 cSt.  This covers fluids from as thin as paraffin to oils with a consistency similar to that of syrup. The viscosity of each grade within the classification is approximately 50% higher than the viscosity of the previous grade. The minimum and maximum limits of each grade are the mid-point viscosity plus or minus 10%. For example, ISO VG 100 has a mid-point viscosity of 100 cSt at 40°C with viscosity limits 90 cSt and 110 cSt:

ISO 3448 Viscosity Classification

This system does not evaluate the quality of a lubricant and applies to no property of a fluid other than its viscosity at the reference temperature. It does not relate to those lubricants that are used primarily with automotive equipment and are identified with a SAE number.

In most instances lubricating oil is a blend of base oil and additives with the base oil content being anything between 70 percent and more than 99 percent depending on the final application of the lubricant. Base oils may be mineral, synthetic or semi-synthetic -a mixture of mineral and synthetic stocks. Most lubricating oils used globally (more than 90 percent) are blended using mineral base oils. Feed stocks from a number of streams at crude oil refineries are processed at base oil refineries to produce various viscosity grades of mineral base oils.

A typical mineral base oil refinery will have the following units to produce suitable quality base oils:

• Solvent Extraction to remove undesirable aromatic (unsaturated) compounds which are unstable and cause the formation of tar, varnish and carbon in engines,
• Propane De-asphalting removes asphaltic material from the base stocks to minimise the formation of deposits in machinery, and
• Dewaxing to improve low-temperature fluidity of the base oil.

These three (extraction) conversion processes generally produce Group 1 base oils with aromatic content between 15 and 20 percent. The colour of Group 1 base oils would normally vary from a light yellow to straw. The quality of such base oils can be further improved by a number of Hydrofinishing Processes. Hydrofinishing changes the remaining unsaturated/aromatic compounds in the oil by a chemical reaction involving hydrogen and produces base oils with improved chemical stability, lower sulphur content and much lighter colour. The final quality of the base oil is determined by the severity of the application, temperature and pressure in the hydrofinishing process and will normally be classified Group 2 or Group 3 base oils. The quality and characteristics of modern Group 3 base oils approach that of synthetics.

Synthetic base oils are manufactured from chemical building blocks and excel mineral oils in viscosity index, shear stability, low and high temperature performance, oxidation stability and volatility. A major disadvantage of synthetics is that they cost approximately 3 to 5 times more than mineral oils. They therefore tend to be used in specialty applications only where the performance of mineral oil is considered unsatisfactory. Typical examples are very high temperature applications and extended oil drain intervals.

The most commonly used synthetic oil is polyalphaolefin (PAO). PAO’s are classified Group Lj base oils and are used in a wide variety of automotive and industrial applications such as engines, transmissions and hydraulic systems. The use of Group 5 base oils (typically synthetic esters) are limited to very special applications such as refrigeration compressor oils and aviation turbine lubricants. The table on the reverse page shows the general  differences between the various Groups.

Mineral and synthetic base oils are produced in a number of viscosity grades. For instance low viscosity (thin) base oils would be used to produce automatic transmission fluids whilst thick, heavy ones are required to blend ISO 680 viscosity grade gear oils.

A final word of advice: avoid mixing different oil Groups. In an emergency situation mineral oils may be mixed with PAO’s, but Group 5 synthetics should preferably not be used with any other oil Group.

With complete control of our raw materials we can guarantee a consistency of product quality matched by few other companies and our customers con have complete confidence in the performance of our products.  To learn more please contact us today by visiting https://www.bcl.co.za