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Is Oil Contamination Affecting the Performance of Your Equipment?

Often, the particles we don’t see are the ones that affect us most. For instance, we can’t see bacteria or germs but those can easily get into our body and make us sick. Something similar occurs with our equipment and the lubricants which are used to help them work more efficiently. SKF notes that contamination and ineffective lubrication are responsible for 51% of bearing, coupling, chain and other machine component failures in equipment.

Logically, if we control the amount of contamination, we can control the number of failures and all the resulting consequences, such as unscheduled downtime and rush expenses (for called out or specialized labor and parts). In this column, we explore how contamination can impact the performance of your equipment, ways to combat contamination and some examples.

What Is Contamination?

Contamination is anything that is foreign to the environment. For machinery lubricants, these are usually classified in three main groups: Gases, liquids and solids. When speaking about gases, this can be air or other gases (such as ammonia or methane) that encounter the lubricant. For liquids, this includes water, fuel or any other liquid that can enter the lubricant, particularly other lubricants or liquids that can be added knowingly or unknowingly. Lastly, solids can mean dirt (from outside the process), metals (from inside the machine) or any other solid particle in the lubricant.

Gases

Gases are the most unsuspected forms of contamination since many people believe that a gas will not affect the lubricant or by extension the machine. However, if air gets trapped in a closed loop system, this can lead to foaming (if the oil makes its way to the surface) or to microdieseling if it remains entrained in the oil.

With foaming, this typically occurs in gearboxes or equipment that are subjected to high churn rates of oil. Foam can settle at the top of the oil and cause the lubricant to not form a full film to separate the contacting surfaces. As such, this can lead to wear of the equipment.

On the other hand, microdieseling or the entrainment of air in the system can also prove to be dangerous because the trapped air bubbles can give rise to temperatures in excess of 1,000°C if they move between different pressure zones. This will lead to oil degradation, often producing some coke or tar insoluble as final deposits. Additionally, this trapped air/gas can also advance to cavitation inside the equipment.

Additionally, if the gas trapped is not air but a catalyst to a chemical reaction, this can incite further or more rapid degradation of the oil making it no longer able to protect the equipment. Therefore, identifying the presence of unwanted gases in your lube oil systems or preventing their entry in the first place is important.

 

Liquids

Liquids are trickier than gases because they somehow seem to enter the lubricant more easily or get mixed in unknowingly. When a liquid enters a lubricant, it can directly impact the viscosity of the lubricant, either increasing it or decreasing it. In either of these cases, this can be detrimental to the equipment.

If the lubricant’s viscosity increases above the essential value, then the machine will demand more energy to execute its required functions. This will directly impact its efficiency and energy consumption. On the other hand, if the lubricant’s viscosity decreases outside of the essential value, then the lubricant may not be able to adequately protect the contacting surfaces. Therefore, this increases the amount of wear that may occur on the inside of the machine.

Typically, water and fuel are the most common culprits of liquid contamination. These can easily get into your lubricants through poor storage and handling practices. Water can increase the viscosity of your lubricant and cause some additives to drop out of it, reducing its level of protection. Fuel will decrease the viscosity and possibly add to the fire risk of the system. Both can severely damage your equipment.

Another common culprit is the mixing of different types of oil. On an average day, things are busy, and people can get confused and pick up the wrong oil to perform a top up on a system. If we add gear oil or hydraulic oil to an engine oil system, we can have a catastrophe! These oils would have different viscosities, and their additive packages (or even base oils) may not be compatible. This can cause the equipment to stop working, leading to unplanned downtime and then exorbitant resources to get the machine operating again.

Solids

Solids can easily get into our equipment either from the outside or the inside. If there are openings to allow solids to enter then they will. However, sometimes solids enter our lubrication systems without us knowing. This can happen through poor storage and handling practices.

Once solids enter the system, they can:

  • Increase the viscosity of the oil
  • Increase the amount of wear occurring inside the equipment
  • Act as a catalyst (depending on their nature)
  • Block smaller clearances causing unwanted downtime in the equipment

Typically, solids are usually dirt, which can enter from outside the equipment. However, these hard particles can cause some metal to be damaged on the inside the equipment which can then lead to the metal being a catalyst for another degradation mode.

Some solids are formed inside the equipment as deposits. These deposits can occur if another contaminant (liquid, gas or another solid) enters the system and reacts with the oil to produce them. As such, these deposits may clog injectors, other valves or tight clearances causing the equipment to malfunction.

The Future of Gear Oils

According to (Industry ARC (Analytics. Research. Consulting), 2024), the global industrial gear oil market size is forecasted to reach USD 5.2 B by 2027. While the Asia-Pacific market holds a significant market share for industrial gear oils in 2021 at around 56.2%, it is interesting that its nearest rival is Europe, at 17.7% or less than ⅓ of its size.

The rise in the Asia Pacific market can be accounted for due to the increase in the rising population and, by extension, the needs of that population and the service sectors they support, including the energy, oil & gas, construction, and steel industries. The figure below depicts the global industrial gear oil market revenue share by Geography for 2021.

Figure 6: Industrial Gear Oils (Mineral & Synthetic) Market Revenue Share by Geography 2021 adapted from (Industry ARC (Analytics. Research. Consulting), 2024)
Figure 6: Industrial Gear Oils (Mineral & Synthetic) Market Revenue Share by Geography 2021 adapted from (Industry ARC (Analytics. Research. Consulting), 2024)

From the research conducted by (Industry ARC (Analytics. Research. Consulting), 2024), helical gears appear to be the most popular choice for industrial gears. Interestingly enough, synthetic gear oil held the largest market share and is forecasted to grow by a CAGR of 5.6% for the forecasted period of 2022-2027.

Smaller gearboxes are being manufactured, tasked with outperforming their previous counterparts and producing more torque in a smaller space. With the advent of better, more precise machining tools for gears, there is an increase in the amount of pressure these gears now must handle in smaller spaces.

As such, we will continue to see the rise in the use of synthetic gear lubricants formulated to handle these extreme conditions, as well as more advanced additive packages that can help minimize foaming, reduce oxidation, and aid in the demulsibility of these oils.

References

Industry ARC (Analytics. Research. Consulting). (2024, September 04). Industrial Gear Oils (Mineral & Synthetic) Market - Forecast(2024 - 2030). Retrieved from Industry ARC: https://www.industryarc.com/Report/20008/industrial-gear-oils-mineral-and-synthetic-market.html

Mang, T., & Dresel, W. (2007). Lubricants and Lubrication - Second Edition. Weinheim: WILEY-VCH GmbH & Co. KGaA.

Mang, T., Bobzin, K., & Bartels, T. (2011). Industrial Tribology - Tribosystems, Friction, Wear and Surface Engineering, Lubrication. Weinheim: WILEY-VCH Verlag GmbH & Co. KGaA.

Pirro, D. M., Webster, M., & Daschner, E. (2016). Lubrication Fundamentals - Third Edition, Revised and Expanded. Boca Raton: CRC Press, Taylor & Francis Group.

Rensselar, J. v. (February 2013). Gear oils. Tribology and Lubrication Technology - STLE, 33.

Sander, J. (2020). Putting the simple back into viscosity. Retrieved from Lubrication Engineers: https://lelubricants.com/wp-content/uploads/pdf/news/White%20Papers/simple_viscosity.pdf

Santora, M. (2018, March 20). Tips on properly specifying gear oil. Retrieved from Design World: https://www.designworldonline.com/tips-on-properly-specifying-gear-oil/#:~:text=CLP%20Gear%20Oils&text=Often%2C%20a%20gear%20manufacturer%20will,a%20CLP%20polyglycol%20PAG%20oil

Gear Oil Storage and Handling

Similar to most oils, gear oils should be stored in a clean and dry space. Often (especially in the past), these gear oils see a settling of the additives to the bottom of the container, indicating a slightly shorter oil life span than other lubricants. However, this is no longer a highly occurring incident with the advancements in additive technology and improved blending practices.

As usual, it is always best to adhere to the OEM’s expiry dates for these products, as different OEMs recommend varying storage times for their products. Generally, synthetic lubricants have an estimated shelf life of 5-10 years, while mineral oils usually last for around 2-3 years, but this is heavily dependent on the OEM and storage conditions.

In some cases, customers tend to store these drums outside in the elements as it makes it easier for them to be readily accessible for decanting into the equipment. However, in these environments, the drums can collect water, which will enter the oil and then, by extension, enter the gearbox. This can cause issues for the equipment and lead to accelerated oil degradation.

Ideally, these oils should be stored in a cool, dry place with ready access to decanting equipment where the decanted oil will not be easily contaminated. Many industrial gearboxes typically require larger quantities of oil, and decanting can take place directly from the drum into the equipment or via a pump.

In these cases, the level of contamination must be minimized by ensuring that the fittings, hoses, etc., are clean and have not been used to decant other types of oils.

Degradation of Gear Oils

The first set of additives to decrease in gear oils is often the antiwear or extreme pressure additives. This is no surprise, as these oils are subjected to high levels of wear and must withstand extreme pressures. One can also notice a decline in the rust and oxidation additives or even a change in the air release values.

 

All these properties significantly impact how a gear oil functions. As such, they should be monitored when establishing the health of the oil.

When monitoring the health of these lubricants, some guidelines can be utilized. If there is a change in viscosity of either ±10%, one should look for any other correlating changes.

Typically, if the viscosity increases by 10%, we’re looking at increases in wear metals or the risk of oxidation and development of some deposits in the oil or even contamination of the oil with some water. However, for a decline of 10%, one can expect some form of contamination, typically fuel or another substance which will thin out the lubricant.

The lubricant’s warning levels for wear metals will vary depending on the manufacturer/OEM. However, any consistent rise in wear metals indicates that some component on the inside of the equipment is slowly wearing away.

Gear Oil Characteristics and Naming Systems

From the information covered thus far, we can appreciate that gear oils need to accommodate many changes to their environment. A few characteristics stand out when looking at industrial gear oils (Mang, Bobzin, & Bartels, Industrial Tribology—Tribosystems, Friction, Wear and Surface Engineering, Lubrication, 2011).

These include viscosity-temperature, Fluid Shear Stability, Corrosion and Rust Protection, Oxidation Stability, Demulsibility and Water Separation, Air release, Paint Compatibility, Seal Compatibility, Foaming, Environmental, and Skin Compatibility.

Depending on where you are in the world, you may use a different system to classify gear oils. The ISO Viscosity grade system is used internationally, but the AGMA (American Gear Manufacturer’s Association) system is used in the Americas and some parts of Asia. A chart can be used to move that across these grading systems, as shown below in Figure 5.

Figure 5: Various gear oil grading systems as adopted from (Sander, 2020)
Figure 5: Various gear oil grading systems as adopted from (Sander, 2020)

As per (Sander, 2020), the AGMA numbers have some particular meanings as stated:

  • No additional letters (only a number) – Contains only R&O additives
  • EP – Mineral oil with Extreme Pressure additives
  • S – Synthetic gear oil
  • Comp – Compounded gear oil (3-10% fatty or synthetic fatty oils)
  • R – Residual compounds called diluent solvents which reduce the viscosity to make it easier to apply

Another rating that is seen a lot is the CLP rating. This is a German oil standard defined by ASTM DIN 51517-3, in which the test requirements to meet the CLP specification are documented.

This DIN standard covers petroleum-based gear lubricants with additives designed to improve rust protection, oxidation resistance, and EP protection. Some typical classifications seen are CLP-M (which represents mineral gear oil), CLP HC (which represents synthetic oils [SHC, PAO, POE]), and CLP PG (which represents polyglycol PAGs), according to (Santora, 2018).

There are three main DIN 51517 classifications as per (Rensselar February 2013), namely;

  • DIN 51517 CGLP – contains additives that protect from corrosion, oxidation, and wear at the mixed friction spots and additives that improve the characteristics of sliding surfaces
  • DIN51517-3 CLP – contains additives that protect against corrosion, oxidation, and wear in the mixed friction zone
  • DIN 51517-2 CL – contains additives that protect against corrosion and oxidation suitable for average load conditions

The above are some of the more prevalent naming systems for industrial gear oils, and they are found on most gear oils globally.

Is there more than one type of gear?

Gears are used in all aspects of life, from bicycles to tiny watch gears, car transmissions, and even highly specialized surgical equipment. Gears keep the world moving. However, when they move, they often rub against each other, and if this friction is not managed, it can cause wear and eventually lead to significant damage or failure. This is where gear oil makes a difference.

In this article, we will explore the various types of gear lubricants, their composition, how they degrade, some storage and handling tips, and what the future holds for these types of oils.

Figure 1: Different types of gears according to (Mang & Dresel, Lubricants and Lubrication – Second Edition, 2007) Chapter 10
Figure 1: Different types of gears according to (Mang & Dresel, Lubricants and Lubrication – Second Edition, 2007) Chapter 10

If you’re familiar with gears, you know that despite the standard emoji keyboard, more than one type of gear exists. There are several types of gears, each suited for various applications. As such, each application will have varying environmental conditions, which will require specialized lubricants to reduce friction and wear.

One of the main operational conditions for gears is the transfer of torque. Even when torque is transferred, gears will have sliding and rolling contact, leading to frictional losses and heat generation. Therefore, the lubricants selected for these applications must be able to significantly reduce these frictional losses and cool the gears.

As per (Pirro, Webster, & Daschner, 2016), several types of gears can be classed into three groups based on the interaction of the teeth of these gears and the types of fluid films formed between the areas of contact:

  • Spur, Bevel, Helical, Herringbone, and spiral bevel
  • Worm gears and
  • Hypoid gears

Figure 1 shows some of the types of gears which exist.

It must be noted that hypoid gears transmit motion between nonintersecting shafts at a right angle. Additionally, there is a difference between rolling and sliding.

Rolling indicates continuous movement, whereas sliding varies from a maximum velocity in one direction at the start of the mesh through zero velocity at the pitch line and then back to maximum velocity in the opposite direction at the end of the mesh, as seen in Figure 2.

According to Mang, Bobzin, and Bartels (Industrial Tribology—Tribosystems, Friction, Wear and Surface Engineering, Lubrication, 2011), hypoid gears require heavily loaded lubricants. These should have high oxidation stability, good scuffing, scoring, and wear capacity, as the tooth contacts have a high load.

The lubricant must also have a high viscosity at operating temperature such that the formed film can sufficiently support the load while cooling the gears.

Conversely, hydrodynamic gears such as torque converters, hydrodynamic wet clutches, or retarders require high oxidation stability characteristics but do not need good scuffing or scoring load capacity characteristics. Unlike hypoid gears, hydrodynamic gears experience viscosity-dependent losses, so they must have a lower viscosity at operating temperature.

Figure 2: Meshing of involute gear teeth. These photographs show the progression of rolling and sliding as a pair of involute gear teeth (a commonly used design) pass through mesh. The amount of sliding can be seen from the relative positions of the numbered marks on the teeth adapted from (Pirro, Webster, & Daschner, 2016), Chapter 8.
Figure 2: Meshing of involute gear teeth. These photographs show the progression of rolling and sliding as a pair of involute gear teeth (a commonly used design) pass through mesh. The amount of sliding can be seen from the relative positions of the numbered marks on the teeth adapted from (Pirro, Webster, & Daschner, 2016), Chapter 8.

According to (Mang & Dresel, Lubricants and Lubrication – Second Edition, 2007), there are some frequent failure criteria for gears and transmissions, including:

  • Extreme abrasive wear
  • Early endurance failure, fatigue of components in the form of micropitting and pitting
  • Scuffing and scoring of the friction contact areas

Continuous abrasive wear is usually observed at low circumferential speeds and during mixed and boundary lubrication. Typically, continued wear can cause damage that extends to the middle sector of the tooth flank. Understandably, lubricants with a high viscosity and a balanced quantity of antiwear additives promote a higher tolerance to wear.

Micropitting can be observed on tooth flanks at all speed ranges. Those with rough surfaces are prime candidates for micropitting. Typically, this develops in negative sliding velocities or the slip area below the pitch circle.

Usually, microscopic, minor fatigue fractures occur first, which can lead to further follow-up damage such as pitting, wear, or even tooth fractures. A lubricant with a sufficiently high viscosity and a suitable additive system can help reduce this type of fatigue.

At predominantly high or medium circumferential speeds, scuffing and scoring of the tooth flanks occur, and the contacting surfaces can weld together for a short time. Due to the high sliding velocity, this weld usually breaks, causing scuffing and scoring.

Typically, this damage is seen on the corresponding flank areas at the tooth tip and root, which experience high sliding velocity. In this case, lubricants with higher EP (Extreme Pressure) additives can help reduce this damage.

According to (Ludwig Jr & McGuire, March 2019), the type of gear can aid in determining the most appropriate industrial gear oil. The following table is an adaptation from the article:

Table 1: Gear type and appropriate lubricant adapted from (Ludwig Jr & McGuire, March 2019)
Table 1: Gear type and appropriate lubricant adapted from (Ludwig Jr & McGuire, March 2019)

As per (Mang & Dresel, Lubricants and Lubrication – Second Edition, 2007), transmission gears can be broken down into two main types: those with a constant gear ratio and those with a variable gear ratio. These can be seen in Figures 3 and 4 below.

Figure 3: Gears with a constant gear ratio adapted from (Mang & Dresel, Lubricants and Lubrication – Second Edition, 2007), Chapter 10
Figure 3: Gears with a constant gear ratio adapted from (Mang & Dresel, Lubricants and Lubrication – Second Edition, 2007), Chapter 10
Figure 4: Gears with a variable gear ratio adapted from (Mang & Dresel, Lubricants and Lubrication – Second Edition, 2007), Chapter 10
Figure 4: Gears with a variable gear ratio adapted from (Mang & Dresel, Lubricants and Lubrication – Second Edition, 2007), Chapter 10

What are some innovations and future trends of Viscosity Index Improvers?

Innovations in Viscosity Index Improvers

As per Mortier, Fox, & Orszulik (2010), the three most important commercial VII families represent critical commercial techniques for manufacturing high molecular weight polymers. These are polymethacrylates produced by free radical chemistry, olefin copolymers produced by Ziegler chemistry, and hydrogenated styrene-diene or copolymers produced by anionic polymerization. While they are critical, these formulations will not be discussed in detail in this article, but we will take a look at some of the innovations within this space.

PARATONE®a, a family of viscosity index improvers currently belonging to Chevron Oronite, boasts of having developed the first Olefin Copolymer VII (Mid Continental Chemical Company Inc, 2024). However, upon further investigation, it must be noted that Exxon Chemicals was the original developer behind this product. Back in 1998, Oronite Additives, a division of Chevron Chemical Co. LLC, acquired the assets of Exxon Chemical’s Paratone crankcase olefin copolymer (OCP) Viscosity Index Improver Business (Chevron Chemical Co. LLC, 1988).

This particular Viscosity Index Improver has seen developments since the 1970s and offers solid and liquid VIIs for companies to include in their formulations (Chevron Oronite, 2024). It also allows improved formulating flexibility for developers, which can significantly reduce the costs involved or specialized base stocks depending on the product to be made. This is just one company that specializes in producing VIIs for the wider global market.

There are many other companies that have innovated in the Viscosity Index Improver space, but most of this work is patented as it involves heavy-balanced formulations. Other companies have also innovated on the production side of the VIIs by engineering equipment that can help produce a higher-quality VII.

Future Trends

(Future Market Insights, 2024) estimates the Viscosity Index Improver market will be USD 4.06B in 2024 and will increase to USD 5.39B by 2034. Additionally, in 2024, vehicle lubricants account for around 51.6% of the VII market. This is not just limited to the multigrade oils but includes transmission fluids, greases, and other oils. On the other hand, with the move towards more sustainable oils, Ethylene propylene Copolymer (OCP) is projected at a 30.4% industry share in 2024. Given the move towards more sustainable products, this is expected to increase.

If we take a global view of the compound annual growth rate (CAGR) per country to 2034, we can find some interesting facts. The United States shows a CAGR of 1.6%, with a heavy allocation towards more vehicle engine oil use and the manufacturing sector for pharmaceuticals and chemicals. On the other hand, Spain is projected to see a CAGR of 2.2% with auto manufacturers and power generation equipment (hydraulic oils, turbine oils, and greases).

Venturing to China, they have a CAGR of 3.2% due to the increased number of vehicles and significant industrialization. Their involvement in complex machinery will also drive this growth. The United Kingdom is positioned to see a CAGR of 1.1% resulting from its rise in high-performance engines and heavy industrialization. On the other hand, India should experience a CAGR of 4.3% with its high demand for industrial production, commerce, and automobiles.

Figure 2: CAGR% per country to 2034
Figure 2: CAGR% per country to 2034
  • With these positive CAGRs, it is conclusive that there will be a lot of growth within the VII industry. (Future Market Insights, 2024) also list some of the recent developments in the VII Market, which include:
  • In July 2023, Chevron Phillips Chemical announced a capacity expansion of its VII productions to meet the increasing demand for VIIs in the automotive and industrial sectors.
  • In April 2023, Lubrizol introduced a new line of viscosity index improvers (VIIs) for automotive lubricants, claiming to offer enhanced performance, including improved oxidation and thermal stability.
  • In March 2023, ABB completed the Marunda 2.0 oil blending plant extension project, doubling production capacity within three years despite challenges during the pandemic.
  • In October 2022, LCY Chemical Corp., a Taiwanese material science company, showcased its thermoplastic elastomer portfolio at K 2022. It highlighted its innovative approach to material science for a sustainable future, backed by a global distribution network.
  • In August 2022, Evonik’s Oil Additives division in CIS countries partnered with ADCO to enhance the energy productivity and effectiveness of industrial lubricants for construction, agriculture, mining, and manufacturing equipment.

From this, the future of Viscosity Index Improvers can only be enhanced by several of the major key players expanding their operations and innovating their creations to adapt to ever-evolving standards/guidelines set by OEMs and governments. As new regulations emerge regarding improved efficiency, increased oxidation stability, and thermal stability for lubricants, VII developers will be challenged to innovate new solutions for the lubricants to conform.

References

Chevron Chemical Co. LLC. (1988, October 08). Oronite Additives Acquires Exxon’s Paratone Viscosity Improver. Retrieved from Pharmaceutical Online: https://www.pharmaceuticalonline.com/doc/oronite-additives-acquires-exxons-paratone-vi-0001

Chevron Oronite. (2024, June 29). PARATONE® viscosity modifiers. Retrieved from Oronite: https://www.oronite.com/products-technology/paratone-products.html

Future Market Insights. (2024, April 15). Viscosity Index Improver Market Forecast by Vehicle and Industrial Lubricant for 2024 to 2034. Retrieved from Future Market Insights: https://www.futuremarketinsights.com/reports/viscosity-index-improvers-market

Gresham, R. M., & Totten, G. E. (2006). Lubrication and Maintenance of Industrial Machinery – Best Practices and Reliability. Boca Raton: CRC Press.

Mid Continental Chemical Company Inc. (2024, June 29). Viscosity Modifiers / Viscosity Improvers. Retrieved from Mid-Continental Chemical Company: https://www.mcchemical.com/lubricant-additives/viscosity-index-improvers

Mortier, R. M., Fox, M. F., & Orszulik, S. T. (2010). Chemistry and Technology of Lubricants – Third Edition. Dordrecht: Springer.

What impact do Viscosity Index Improvers have on Efficiency, Wear, and Degradation?

If we filled a swimming pool with honey during the winter when no heating was available, the honey would crystallize and become more viscous. Hence, if anyone tried to walk through the pool, moving would be difficult and require more energy. However, if heating was available to the pool, then the honey would be more fluid, and someone could walk a bit more freely (although still sticky at the end of the day!). As such, they would not have to exert as much energy.

The same applies to lubricants and their viscosities. If the lubricant is too viscous (thick honey in the winter), then more energy is required for the components while they are moving. For systems with varying temperatures, finding a lubricant that can maintain the desired viscosity for those changes is challenging.

However, with the invention of Viscosity index improvers, oils can now maintain a desired viscosity at variable temperatures. This significantly affects the energy the system requires and can reduce the energy needed, making some systems more efficient.

As such, the system’s overall efficiency is impacted, and less energy is required to overcome the internal frictional forces of the lubricant (as its viscosity remains within the required range). Passenger car engine oils saw this change with the integration of VIIs when multigrade oils were invented. They no longer needed one oil for summer and another oil for winter. This significantly saved many owners from draining and replacing their oils seasonally or finding their oil frozen in the winter!

Viscosity index improvers, therefore, enhance the overall efficiency of these systems by maintaining the lubricant’s viscosity throughout the changing temperatures. Subsequently, there is no need for additional heaters in the lube oil system, which would also require additional energy. This is another area where cost and energy savings can also be achieved.

Maintaining a particular viscosity at variable temperatures allows the lubricant to form a full film (also known as hydrodynamic or elastohydrodynamic lubrication) between the two surfaces, thus offering them protection from wear.

If the viscosity became reduced (due to an increase in temperature without the VII), then the lubricant would not form a full film or experience boundary or mixed lubrication. In this case, there is the potential for increased wear, which will negatively impact the components in the system. As such, using VIIs can also reduce the potential occurrence of wear or aid in reducing wear.

As per (Gresham & Totten, 2006), this does not mean that the viscosity never changes. When the viscosity of a lubricant changes, its viscosity index will change accordingly. If the viscosity index decreases, this can likely be because of the breakage of the polymeric Viscosity Index Improver polymer molecules to produce smaller chains, which essentially reduce its originally intended effect. If there is a reduction in the molecular weight of the VII, then the lubricant will see a reduced viscosity at both 40 & 100°C. This also reduces the temperature related viscosity effect.

Viscosity Index Improvers significantly improve a system’s overall efficiency and can help reduce wear. However, these additives can degrade over time with high temperatures and shear stress.

What is the role of Viscosity Index Improvers in Lubricants?

Viscosity Index Improvers began their commercial debut around the 1950s to accommodate the new developments in automotive oils, which were then adapting multigrade viscosities. However, they were used even before (back in the 1930s) when workers in crude distillation realized that small amounts of rubber improved the VI of the oil but also increased sludge formation.

Today, VIIs are still primarily used as engine lubricants. They can also be found in automatic transmission fluids, multipurpose tractor transmission fluids, power steering fluids, shock absorber fluids, hydraulic fluids, manual transmission fluids, rear axle lubricants, industrial gear oils, turbine engine oils, and aircraft piston engine oils. (Mortier, Fox, & Orszulik, 2010)

Essentially, VIIs try to maintain the oil’s viscosity at varying temperatures. They try to ensure that the oil does not experience a loss of viscosity, which can occur due to high temperature or shear. VIIs can be considered polymers, which are tightly wound coils. When temperature or shear is applied to these coils, they unravel (lose their viscosity). Depending on the amount of shear, they may never recover their original shape (or viscosity).

As seen in Figure 1 below, Mortier, Fox, & Orszulik (2010) describe the change in the shape of the VIIs as a result of high temperature or shear. They can coil and uncoil depending on the shear stress, but if the bonds are broken, they will not reform their original coil and lose their intended viscosity.

Figure 1: Mechanical Polymer Degradation (excerpted from (Mortier, Fox, & Orszulik, 2010)
Figure 1: Mechanical Polymer Degradation (excerpted from (Mortier, Fox, & Orszulik, 2010)

Interestingly enough, it must be noted that some VIIs provide lubricants with additional functions of Pour point depression and dispersancy. This is highly dependent on their composition.

What are Viscosity Index Improvers?

Viscosity Index Improvers (VIIs) are additives that help maintain the viscosity of lubricating oils across a wide temperature range, ensuring consistent performance.

This article will explore the nature of viscosity index improvers and their role in industrial and automotive lubricants. We will also look at their impact on lubricant efficiency, innovations involving this type of additive, and future trends.

Before discussing the nature of viscosity index improvers, we need to understand the role of viscosity. Essentially, this is one of the most critical functions of a lubricant, as it directly affects its flow rate and ability to keep the two interacting surfaces apart.

By nature, all base oils have an assigned viscosity based on their blend. However, other properties are required when we’re creating finished industrial or automotive lubricants. For instance, we may need the oil to withstand higher temperatures while still maintaining a particular viscosity, which not only provides wear protection for the equipment but also flows at a rate that does not incur frictional losses. Those are a lot of functions!

Typically, as temperature increases, viscosity decreases, and as the temperature decreases, the viscosity increases. One example is the state of water: when heated, it can turn into a gas (lower viscosity), or when frozen, it can transform into ice (higher viscosity). However, depending on the type of material, there will be varying rates of viscosity change with temperature. The viscosity/temperature relationship is called the viscosity index (VI).

As per Mortier, Fox, & Orszulik (2010), the kinematic viscosity of oil is measured at 40°C and then at 100°C. The viscosity change is then compared with an empirical reference scale initially based on two sets of crude oils: a Pennsylvania crude arbitrarily assigned a VI of 100 and a Texas Gulf crude assigned a VI of 0.

The higher the VI, the less effect that temperature has on the oil, which means that the oil can maintain a particular viscosity for a longer time at a more extensive temperature range. This is ideal for lubricants in environments experiencing temperature changes. However, not all oils have a high viscosity index. Typically, paraffinic oils can have a very high viscosity index. On the other hand, naphthenic oils have a low or medium viscosity index. The table below gives an overview of the viscosity index for various oils.

Table 1: Viscosity index of API Groups I-III
Table 1: Viscosity index of API Groups I-III

When trying to manage or alter the viscosity index of the oils above, the use of Viscosity Index Improvers (VII) can help by adding that property to an oil to allow it to have other beneficial properties. As per (Mortier, Fox, & Orszulik, 2010), viscosity index improvers consist of five main classes of polymers:

  • Polymethylmethacrylates (PMAs).
  • Olefin copolymers (OCPs).
  • Hydrogenated poly (styrene-co-butadiene or isoprene) (HSD/SIP/HRIs).
  • Esterified polystyrene-co-maleic anhydride (SPEs)
  • A combination of PMA/OCP systems.