In my experience, flash point is one of the most misunderstood numbers on a product data sheet. Most people ignore it, as it is rare for oil system temperatures to approach the flash point range (typically >200°C). When it does become a concern, there is often confusion regarding safe working limits, operating limits, and flammability versus flash.

Quick summary:

1. Flash point is not a physical property of a lubricating oil
2. The flash point of an oil can be used as a diagnostic tool
3. The manufacturer should define safe working limits

So, First of All, What Is Flash Point?

The flash point of lubricating oil is not a physical property similar to viscosity at 40oC or water content; instead, the result is defined only in terms of the test method used.

If that’s a little difficult to understand, think about it this way: you have a defined height – it is a physical property of your body. There are numerous methods to measure that as accurately as possible.

But what about your strength? Strength measurements can be standardized by making people lift weights, making the units for strength kilograms. But the number would vary depending on whether the weights were lifted on a cable machine, a barbell, a dumbbell, or whether the lifting type is a squat, deadlift, bench press, etc.

Flash point testing is designed to measure the temperature at which the vapors of a lubricant ignite. However, this temperature will vary greatly depending on conditions. For example, a thin puddle of lubricants in the sun will experience a different flash point than the same puddle in which a light breeze displaces the vapors.

From the ASTM D6450 document, we have the following:

Flash point values are not a constant physical-chemical property of materials tested. They are a function of the apparatus design, the condition of the apparatus used, and the operational procedure carried out.

What Are the Common Flash Point Test Methods?

Two predominant types of Flash Point tests have been developed – closed and open cup. All the methods generally have the following features:

1. The lubricant sample is held in a vessel
2. The sample is heated in temperature increments
3. At each increment, an ignition source is introduced
4. If no ignition is detected, the sample is heated to a higher temperature

Open cup methods allow the vessel to be open to atmosphere while the vessels in closed cup methods are sealed chambers.

The venting of light ends to the atmosphere causes open-cup methods to register higher flash point values than closed-cup methods; as most industrial thermal systems are closed to atmosphere, closed-cup methods have been adopted by industry in the belief that they more closely simulate the operating conditions.

Within closed cup flash point test methods, the most popular is the Pensky Marten Closed Cup test (PMCC – ASTM D93a). In this test method, the sealed chamber contains 75mL of oil mixed by a magnetic stirrer. After heating to the test temperature, a flame is passed over the oil – the sample is deemed to have flashed if:

A large flame appears and instantaneously propagates itself over the entire surface of the test specimen.

There are several limitations to this test, which have prompted the development of more modern test methods:

• Safety concerns over open flames in laboratory conditions
• Large volume of oil required for the test
• In some circumstances, application of the test flame can cause a blue “halo” or enlarged flame that is mistaken for a flash, resulting in “false positives”

To address the issues outlined above, ASTM D6450 was developed. In this method, a 4mL vessel containing 1mL of oil is heated in increments, and an electric arc passes through the sample container.

If no flash is detected, 1.5mL of fresh air is pumped into the vessel to ensure that the vessel contains enough oxygen to promote flashing of the sample. This test method has tighter controls and therefore improved repeatability and reproducibility over the D93a test method for oils with flash points above 65°C:

In previous experience with a major oil supplier, I have found variations between flash point testing methods of over 100°C across different laboratories.

If Flash Points Vary Depending on The Test Method, How Can We Use Them?

Firstly, any limits prescribed by the OEM should be test-specific. Once again, from ASTM D6450:

If the user’s specification requires a defined flash point method other than this test method, neither this test method nor any other method should be substituted for the prescribed method without obtaining comparative data and an agreement from the specifier.

For these reasons, among others, we cannot draw a straight line between an oil’s flash point and the safe working temperature of an oil system. Not only will different test methods yield different results, but operating conditions will dictate an oil’s proclivity to ignition, such as whether the system is open or closed.

Therefore, if an oil user is seeking guidance on a safe flash point for a system, they should consult the OEM. The OEM should give both a flash point deemed safe for the equipment AND the test criteria used to determine this flash point.

Often, safe working temperatures will be guided by the oil’s auto-ignition temperature, with some safety margin and an emphasis on ensuring there are no ignition sources close by.

While flash point testing cannot yield a safe operating temperature under normal circumstances, changes in flash point over time can give information about system degradation. For example, decreases in flash points indicate the production of “light ends” that are likely a direct consequence of thermal cracking.

A localized hot spot in the system is potentially contributing to this cracking. Alternatively, a gradually increasing flash point could indicate that the light ends are being vented. A slight increase in the bulk oil viscosity would typically accompany this.

Finally, abrupt changes in flash point could indicate contamination of the system with an incorrect oil top-up, as is the case when large viscosity changes are observed in oil systems.

I recommend that any operator of a thermal system review OEM documentation for the thermal oil systems to obtain any recommendations regarding test limits for Flash Point. These test limits must be defined in terms of a specific test method.

Fuel economy is a crucial aspect of modern vehicle maintenance and fleet management. With rising fleet fuel costs and ever-tighter environmental regulations, achieving better fuel efficiency has never been so important.

The lubricant in use is often an overlooked factor that plays a significant role; there is an intricate relationship between engine oils and fuel economy. Synthetics, low HTHS viscosity lubricants, and oil detergency can significantly improve fuel efficiency.

The Role of Bulk Viscosity

Viscosity is the thickness of the oil. For almost a generation, the diesel engine world has been dominated by standard semi-synthetic, multigrade 15W-40 engine oils. These oils are largely backward compatible, making lubricant selection a relatively straightforward exercise for fleet operators.

The recent emphasis on fuel economy has led to many OEMs exploring the use of lower viscosity engine oils, with 10W-40 and 5W-30 diesel engine oils hitting the market, being included in 2016’s API FA-4 engine oil spec, and even becoming the factory-fill lubricant for several (mostly European) OEMs.

This has all been done to reduce fluid friction. If viscosity is the resistance to flow, then less viscosity means lower resistance, and therefore, less energy is consumed merely to circulate the oil throughout the engine.

High-Temperature, High-Shear (HTHS) Viscosity

Even though we think of lubricants as incompressible Newtonian fluids (which are relied upon for hydraulic systems), lubricants can exhibit different flow behaviors under pressure, flow, and shear conditions.

High-temperature high-shear (HTHS) viscosity measures an oil’s resistance to flow under high temperature and shear conditions typical of engine operation and better simulates the behavior of oil in loaded cam surfaces or gears.

Oils with lower HTHS viscosity correlate with better fuel economy, providing sufficient lubrication with less drag on the engine. Many “fuel economy” oils exhibit lower HTHS viscosities than their standard cousins.

This property emerges from both the bulk oil viscosity and the behavior of polymers (such as viscosity index improvers) in the high shear zones.

HTHS viscosity is also one of the landmark differences between the standard, backward-compatible CK-4 engine oils (min 3.5 cP) versus the newer FA-4 specification (2.9 – 3.2 cP).

Balancing Economy and Wear

This raises an obvious concern – lower viscosity oils have historically had lower load-carrying capabilities, making the engines and associated components prone to higher wear rates.

For this reason, most 5W-30 diesel engine oils are full-synthetic formulations, with the higher film-carrying capability of Group III and Group IV PAO base oils trading for the reduced bulk viscosity compared with a 15W-40. This maintains wear protection over the long term.

Advances in antiwear additives have also improved wear protection performance in heavily loaded parts of the engine, and modern oil formulations often contain a combination of zinc, boron, and molybdenum additives working together.

HTHS viscosities have also become more consistent over the oil’s life, with modern viscosity index improvers exhibiting substantially improved shear stability relative to their earlier variants.

Converging Technologies

Using all these technologies together ensures that engines stay robust while delivering fuel economy improvements:

1. Lower bulk viscosity means more protection at engine startup
2. Lower bulk viscosity means less fuel is used to pump the oil around the engine
3. Shear stable VI improvers enable lower HTHS, resulting in less resistance
4. Improved additive technologies ensure wear protection

“Real-World” Examples

Several notable “real-world” case studies have been used to demonstrate the benefits of modern lower-viscosity oils. In the real world, weather variability, payload, traffic, and the driver’s right foot tend to overcome the marginal improvements observed from changing engine oils.

To truly compare lubricants, it is necessary to artificially control for these variables by completing tests on engine/chassis dynos and test tracks with repeatable driving or else to accumulate so much data as to reduce the variability to a statistically insignificant component.

The Shell Starship Initiative demonstrated how advanced lubricants can be used among a range of other technologies to enhance fuel efficiency. During a coast-to-coast run across the USA, Shell Starship 2.0 achieved a fuel economy of 10.8 mpg, significantly higher than the North American average of 6.6 mpg.

This was made possible by using low-viscosity oils, among other energy-efficient technologies.

When measuring the fuel economy benefits of a low-viscosity engine oil, it was found that switching from a Shell Rotella 15W-40 (synthetic blend) to a similar Rotella 10W-30 improved fuel economy by ~2%. A prototype 0W-20 fully synthetic oil showed an additional 1.7% improvement compared with the 15W-40.

Similarly, the development of Mobil Delvac 1 LE 5W-30 showed 3.4% mpg improvements in city driving and 2.8% for highway driving compared with a standard semi-synthetic 15W-40.

This test was slightly different because it was conducted on a test track, and the entire driveline was converted to run on synthetics, including a synthetic gear oil 75W-90 and synthetic transmission fluid.

The Economics

With fuel comprising up to 30% of some logistics company budgets, plus increased regulatory scrutiny around emissions, a switch to low-viscosity synthetic engine oils might likely make sense.

Even a modest 2% improvement in fuel economy would translate to 0.6% overall savings – which might seem modest until you realize that some trucking companies are spending tens of millions of dollars a year in fuel costs!

Along with the added benefits of more extended oil drains and improved engine cleanliness afforded by synthetics, full synthetic low-viscosity engine oils may well be the industry’s future.

As always, it is necessary to check with the engine OEM if this is appropriate, lest unintended harm occur. Pre-2016 engine models predate the FA-4 engine oil specifications, and some OEMs have slowly adopted these changes.

Look at the product data sheet for any full synthetic industrial lubricating oil, and you will likely discover that the base oil is a polyalphaolefin (PAO).

These lubricants have become the backbone of high-performance lubricants for the better part of 50 years, with new metallocene variants continuing to spur ever higher performance standards. However, half a century of technical innovation has brought some exciting alternatives that could soon make their way to market.

The Significance of PAOs in the Industry

PAOs have an exciting history as synthetic lubricants. Their development can be traced back to the research on the polymerization of olefins in the late 1930s. Initially, these studies focused on creating polymers and plastics, but like many molecules from the petrochemical world, their potential for applications in lubricants was soon recognized.

In the 1940s and 1950s, the process of oligomerization was developed. This process, critical in producing PAOs, involves the polymerization of alpha-olefins to create oligomers, short-chain polymers that serve as the building blocks for PAOs.

The real breakthrough in PAO development came in the 1960s. Researchers found that carefully controlling the oligomerization process could produce lubricants with excellent thermal and oxidative stability, high viscosity index, and low pour points. These characteristics made PAOs ideal for extreme temperatures and applications requiring stable, long-lasting lubrication.

Ever since, this molecule has been onward and upward—the significance of its use is even enshrined in the API base stock groups, where PAOs are the only synthetic base oil to receive their own category (Group IV).

This vaunted place owes much to the automotive industry, where high viscosity index is a prized property that allows for both high film strength at operating temperatures and good cold start-up performance.

The Performance of PAO Industrial Lubricants

Beyond automotive, many performance features make PAOs ideal for industrial lubricating oils. Its oxidative stability and response to antioxidant additives enable extended oil drains, even with high operating temperatures.

Its demulsibility helps water separate readily in reservoirs, allowing the volume to be drained readily. High viscosity index results in good flow properties and high hydraulic efficiency.

Its narrow molecular weights give them low volatility and flash point. And it’s combination of high film strength and low traction properties enables the use of synthetics when energy efficiencies are required.

Newer developments have seen the rise of metallocene catalysts creating higher-performance PAOs (sometimes called mPAOs to distinguish them from their conventional cousins).

These molecules offer even higher Vis, better demulsibility, and improved oxidative stability and are enabling technologies like the next generation of wind turbine gear oils, which are often warrantied for 10-year oil drains.

But all technologies have an Achilles Heel, and the same low polarity that gives PAOs their water separability and foam performance introduces challenges such as additive solubility and seal swell. In an era where bio-based and bio-degradable lubricants are becoming more popular, PAOs offer neither feature.

Emerging Alternatives

As the lubricants industry evolves, alternative base oils emerge as viable alternatives to traditional polyalphaolefins (PAOs). Driven by technological advancements and an increasing focus on sustainability, new molecules like Synnova and ethylene-propylene oligomers have emerged.

In both cases, the molecular structure of these novel base oils bears striking similarities to PAOs, and that is reflected in their performance.

Synnova (currently made by Novvi) is derived from renewable feedstocks. Formerly made from sugarcane derivatives, Synnova base oil production is carbon-negative, and the low molecular-weight variants are 100% bio-based and 70% biodegradable by OECD 301b. Its performance characteristics closely mirror PAOs, although the pour point is slightly higher.

Synnova offers the possibility of creating bio-lubricants without the use of esters. For many years, esters and PAGs have been the only pathway to the creation of bio-based lubricants, with esters generally preferred due to the incompatibility concerns using PAGs.

However, ester instability in the presence of water has always been a challenge when using them in applications. When formulated with the right co-bases and additives, Synnova could be a fluid that overcomes these challenges.

EPOs (ethylene-propylene oligomers) are another base oil class that warrants attention. The molecules produced by companies such as Mitsui and Daelim look like a hybrid of PAOs and VI improvers. These polymers exhibit exceptional shear stability, film strength, and viscosity control, making them suitable for demanding operating conditions.

As a substitute for heavy PAOs, VI improvers, and thickeners like polybutenes, EPOs offer interesting formulation flexibility as they can replace multiple functions. With slightly better solubility performance than PAOs, they can also help reduce the seal swell agents often needed in PAO lubricants.

The likelihood that any of these contenders entirely displace PAOs is virtually zero. PAOs command a level of scale and formulation history that makes them one of the industry’s backbones. However, alternative base oils such as Synnova and EPO polymers offer promising pathways with the potential to redefine industry norms and reshape the competitive landscape.

In the intricate world of lubrication and tribology, the 4-ball test has become a core experimental procedure and is commonly listed as a performance parameter on lubricant and grease data sheets.

These tests are designed to measure friction and a lubricant’s wear resistance and are indispensable tools in rapidly screening lubricant and grease formulations.

However, end users often cite the results of 4-ball testing as primary criteria in selecting gear and circulating oils. Should this be the case? Let’s examine what the 4-ball test is and its limitations.

Understanding 4-Ball Wear and Weld Tests

At its heart, the 4-ball test is elegantly simple. The test involves three stationary steel balls arranged in a triangular formation in a cup, with a fourth ball, held by a chuck, rotating against them.

This assembly is often bathed in the lubricant under examination, ensuring a thorough assessment of its properties under simulated conditions of use. By adjusting the speed of the rotating ball and the load applied to it, tribologists and lubricant formulators can simulate several conditions.

A distinctive feature of the 4-ball test is its ability to evaluate two critical aspects: the weld load and the wear scar. The weld load test (ASTM D2783 for lubricants and ASTM D2596 for greases) is primarily concerned with determining the extreme pressure properties of the lubricant.

This procedure progressively increases the load until welding between the balls is detected. In applications involving high pressures and loads, the base oil viscosity is often insufficient to prevent metal-to-metal contact. In these boundary lubrication regimes, extreme pressure additives in the form of sulphurised olefins, fatty acids, and solid lubricants are often required to protect machine surfaces.

In contrast, the wear scar test (ASTM D2266 for greases and ASTM D4712 for lubricants) focuses on the lubricant’s wear-preventive characteristics.

Here, a constant load is applied, and the test measures the diameter of the wear scars on the stationary balls after a predetermined period. The wear scar’s size indicates the lubricant’s ability to protect against wear, a vital attribute in prolonging machinery life and ensuring smooth operation.

From the Laboratory Bench to Reality in the Field

As with all bench tests, the 4-ball test attempts to create a reliably repeatable condition that can be performed relatively inexpensively and in much less time than would be required for field trials. In this respect, it has succeeded immensely, and 4-ball test rigs are a common feature of tribology labs worldwide.

However, the conditions inside the test rig bear little resemblance to those seen in machinery. There are two components to this – the size of the interaction between the balls and the interaction type.

Concerning the size of the interaction, the intersection between two spheres is a point. Theoretically, the test load is being placed through a vanishingly small area, drastically increasing the surface pressure.

Additionally, the contact is a sliding interaction. This combination is rarely observed in machinery, where the most severe combinations are line contact with sliding (as in journal bearings) or point contact with rolling (ball bearings).

So, it is established that the test rig does not accurately simulate real-world contacts, but is there any downside to using the test results to indicate lubricant performance?

A Disconnect Between Test Results and Performance

In a 2008 research paper, members of the FZG Institute in Germany evaluated test methods for gear lubricants. Among other curiosities, the paper assessed many of the bench test methods available and their relevance to real-world performance.

A surprising result from the paper was the relative performance of common household liquids such as milk and beer, which scored higher on 4-ball weld load than a non-EP mineral ISO 220 gear oil and an antiwear ISO 46 hydraulic oil.

Yet on the FZG scuffing test, the relative performance of these three liquids was as we would expect, with the performance of the AW hydraulic oil achieving the highest rating, followed by the mineral gear oil, milk, and beer, respectively.

As the FZG test more closely simulates actual conditions inside industrial gearing (the interaction between two specified gear profiles), this would be more reflective of real-world performance.

As a development test, the 4-ball weld and wear scar test carries considerable weight. It is inexpensive and repeatable and can give tribologists and formulators an idea if their formulation is directionally correct. But as a tool for lubricant selection, we should be skeptical and look to other test procedures to indicate the likely performance.

Many questions surround hydraulic oil selection, from viscosity grades to base oil types to additives. This article answers pressing questions like: How do temperatures influence oil choice? Should you use zinc-based or non-zinc fluids? Should engine oils be used in hydraulics? And why does oil cleanliness matter so much?

How Do Weather Conditions Affect the Choice of Hydraulic Oils?

It might affect your choice in two ways: viscosity and viscosity index. Hydraulic oil viscosity tends to vary between ISO 32-100, and part of the decision process may include the ambient temperature, which can affect the bulk oil operating temperature.

As the viscosity (thickness) of the oil is highly temperature dependent, colder climates may require thinner oils, while hotter parts of the world may require thicker oils.

The viscosity index is also a fundamental consideration. This index measures the oil’s change in viscosity with temperature variation. You can classify hydraulic oils into two primary categories based on their viscosity index:

• Standard Viscosity Index: Typically ranges from 80 to 110.
• High Viscosity Index: Ranges from 120 up.

Oils with a high viscosity index are beneficial when stable viscosity is required at elevated temperatures. This stability is especially crucial when the ambient temperature is high or the operating machinery, like plastic injection molding machines, imposes high thermal stress on the oil.

Mobile equipment with high power density is another example where a high viscosity index hydraulic fluid would be advantageous.

When Should I Choose Zinc or Non-Zinc Hydraulic Oil?

The zinc in hydraulic oils is usually related to the antiwear package and essential oil components primarily responsible for the pump’s wear protection. There are primarily two categories:

• Zinc-Based: Contains zinc or ZDDP, a widely-used antiwear additive found in many engine and hydraulic oils.
• Zinc-Free: Oils without zinc. In some cases, oils may be advertised as “zinc-free” when elemental analysis shows traces of zinc – this is likely due to zinc-containing detergents rather than the antiwear additive.

It’s essential to understand that while zinc is a popular additive, it comes with challenges. Zinc toxicity can pose environmental concerns, especially if machinery, such as cranes, operates over water. In such cases, a zinc-free formulation might be preferable.

Additionally, zinc tends to break down at very high temperatures, leading to sludge formation. Thus, many of the newer “ashless” antiwear additives produce less sludge, making them a better choice in high-temperature situations.

What Kind of Hydraulic Fluids Are on the Market, and What Is the Best?

This question doesn’t have a straightforward answer. The “best” choice often hinges on specific applications and scenarios. So, let’s discuss the various hydraulic fluids available in the market.

Hydraulic fluids can be primarily classified based on their base oil into the following categories:

1. Mineral-Based Hydraulic Oils: These are the most prevalent type, chosen in approximately 90 to 95% of applications. The inherent properties of mineral oil can be enhanced using additives. For instance, if a high viscosity index is desirable, formulators usually add viscosity index improvers to the mineral oil to achieve the desired performance.
2. PAO (Polyalphaolefin) Synthetics: These are synthetic hydraulic oils. The primary advantage of transitioning from a high VI mineral to a PAO synthetic is primarily evident in frigid temperatures, where they carry a pour point advantage. For example, the pour point performance of neat PAO is in the order of -60°C at the lower viscosity grades. Thus, a fully synthetic hydraulic oil might be the ideal choice when machinery operates in exceptionally frigid environments, like wind turbines in northern Canada or mine sites in Russia.
3. Synthetic & Natural Esters: These are frequently found in eco-friendly lubricants. If there is a requirement for a biodegradable hydraulic fluid, it will likely be an ester-based fluid, whether derived from vegetable sources or synthesized. Natural esters usually have reduced oxidation stability relative to mineral oils, while synthetic esters offer excellent temperature performance and low varnish formation.
4. Phosphate Esters: Lubricants often consist of polyol esters or phosphate esters in high-temperature scenarios demanding fire-resistant properties.

On top of the base oil type, different oils will contain varying additive combinations (see zinc versus zinc-free above), which will cause the performance to vary.

So deciding which is “best” is not so straightforward – but rather, the conditions and application should be matched to the product.

Why Do Some Hydraulic Fluids Have an SAE Grade While Some Have an ISO Grade?

Navigating through the world of hydraulic oils, you’ll encounter various classifications that can be somewhat perplexing. In the industrial sector, the typical viscosity grades for hydraulic oils are identified as ISO grades like 32, 46, 68, or 100. However, if your domain is mobile equipment, you might stumble upon hydraulic oils labeled with SAE grades such as 10W or 30, 40.

The distinction between these two types is rooted in their formulation traditions. In the realm of mobile equipment, there was a history of creating “cheap and dirty” formulations. This process involves taking an engine oil and reducing the concentration of its additive package.

Despite this reduction, the oil retains many characteristics of an engine oil, including antiwear properties and the presence of detergents, which are uncommon in industrial hydraulic oils. This type of oil is often called a “cutback engine oil,” and it’s why you’ll find mobile equipment hydraulic oils using the SAE (Society of Automotive Engineers) viscosity grading system.

Nowadays, having an SAE viscosity grade does not necessarily mean that the hydraulic fluid is a cutback engine oil, but rather can signify it is designed for mobile equipment applications.

One of the significant differences between hydraulic oils tailored for mobile equipment versus those for industrial applications lies in their detergency level. Detergents in hydraulic oil play a pivotal role in how the oil interacts with water.

Oils with detergency will typically hold onto water—a characteristic that might benefit systems with small sumps where the maintenance team is likely to remove contaminants by performing an oil change. Conversely, in industrial systems where the reservoirs are significantly larger, the desired property is for the oil to allow water to separate, forming a distinct layer that can be easily drained off.

Can I Use Engine Oil as Hydraulic Oil?

While technically, this is possible, it’s generally not advisable. To understand why, let’s examine engine oils’ distinct functions and formulations compared to hydraulic oils.

Engine oils are crafted to withstand the harsh conditions of combustion engines. They need to handle contaminants like soot, water, and acids, which are byproducts of combustion. This is why engine oils typically have a high Total Base Number (TBN) and include dispersants to cope with these elements—features not commonly found in hydraulic oils.

In contrast, hydraulic oils are designed with different priorities in mind. Where an engine oil is over-engineered to retain contaminants until the next oil change, hydraulic systems often require the opposite.

For instance, in many industrial applications, you’d want water to separate from the oil easily so it can be removed, ensuring the smooth functioning of the hydraulic system.

Employing engine oil in a hydraulic system could lead to suboptimal performance. The engine oil’s propensity to hold onto water and other contaminants might disrupt the hydraulic system’s operation, which could be designed to purge these contaminants efficiently.

Is Oil Cleanliness Important to Hydraulic Oils?

In the world of hydraulics, the cleanliness of oil is not just a preference—it’s a mandate for the longevity and efficient operation of the system. An excellent demonstration of the effects of cleanliness on the life of hydraulic assets can be found in publicly accessible life extension tables, demonstrating a direct correlation between oil cleanliness and component lifetime.

Consider this: by improving the ISO cleanliness code of hydraulic oil from, let’s say, 24/22/19 to 19/17/14, the theoretical life extension is 4x – a remarkable return on investment considering the typical costs for oil filtration versus the capital cost of a new hydraulic system.

This significant life extension is primarily due to reducing contaminants that can cause wear and tear on the system’s components.

Contaminants are a primary contributor to wear in hydraulic systems, but their impact doesn’t stop there. Hydraulic controls, particularly servo valves, operate under tight tolerances, making them highly sensitive to contamination.

The presence of contaminants can lead to ‘silting’ or ‘servo sticking,’ where the valves do not actuate smoothly. This issue can cause a delay or ‘lag’ in the system’s response, where the actual movement does not align with the commanded action, leading to operational errors.

Gears are everywhere. These versatile machine elements are present in all industries and used in pumps and drives of all sizes as a reliable way to transfer power. Industrial gear oils are a vital component of that reliability, helping to maintain separation between the teeth and preventing wear.

But gear oil formulations might be about to change thanks to macro shifts in the base stock market. These alterations always have downstream impacts – and in the coming years, we may see the prevalence of varnish increase in gearboxes worldwide.

To understand these changes, we need to understand the role of Group I Bright Stocks in the global lubricants value chain. To recap – the American Petroleum Institute classifies base oils into five distinct groups, with the first three being mineral oils based on products refined from paraffinic crudes.

Generally, oxidation stability increases when moving from Group I – III, but the opposite is true for the solvency characteristics. Moreover, a general principle of refining is that the more crude is refined, the lower the viscosity of the finished product.

So, Group I’s are available in wider viscosity ranges than their Group II and III counterparts. This viscosity range is critical to industrial gear oils, where Group II and III base oils cannot create ISO 220 – 680 without heavy additization. So, for the vast majority of mineral gear oils, Group I is the base oil of choice.

Unfortunately, this venerated position is under threat. Lubes’n’Greases estimates that between 2010 and 2020, demand for Group I globally decreased by some 20%, and the overwhelming reduction of base oil production capacity from 2015 – 2022 was in the Group I’s.

The decline in demand is primarily driven by tightening lubricant specifications in the automotive market, forcing lubricant blenders to use the more oxidatively stable Group II, III, and IV base oils. Additionally, there are environmental concerns regarding the higher sulfur levels in Group I base oils and the solvent extraction methods used to refine them.

The potential impact on industrial gear oil formulations is four-fold:

1. Price: Historically, Group I Bright Stocks have been a cost-effective option for producing high-quality lubricants. With its declining availability, formulators may be forced to source alternative base oils, many of which might be pricier.
2. Oxidation Stability: A move to Group II gear oils would help increase the oxidation resistance of mineral gear oil formulations, increasing their longevity, particularly in high-temperature applications.
3. Additive Solubility: One of the defining features of Group I Bright Stock is its solvency, ensuring that additives are effectively dissolved. These additives, ranging from anti-wear agents to viscosity modifiers, are crucial for gear oil’s performance. Manufacturers might have to invest more in co-base stocks to maintain effective additive solubility.
4. Varnish Formation: Group I Bright Stocks’ solvency ensures oxidation products stay dissolved in the bulk oil. Doing so prevents them from settling out and forming harmful deposits. Without the superior solvency of Bright Stock, gear oils may witness increased chances of varnish formation.

It may initially seem paradoxical to list the effects of Group II gear oil formulations when the earlier discussion explained that the low viscosity of Group II base oils precludes them from use.

However, base oil manufacturing innovations will soon enable higher-viscosity base oils to be produced. ExxonMobil recently announced that expanding capacity in Singapore will include the production of EHC 340 MAX, a “heavy neutral” bright stock replacement with a viscosity slightly higher than ISO 460.

While this is a welcome innovation that plugs the gap left by the closure of Group I refineries, the potential for the rise in varnish formation is of particular concern. Anyone with experience in turbomachinery would be well aware of the increase of varnish impacting the performance of turbines and compressors in the last 20 years.

This change was (in part) due to the formulations moving from Group I to II and III and the reduced solvency of these formulations promoting the dropout of oxidation products.

This same phenomenon could be coming for gear sets. The coating effect of varnish impairs heat transfer, elevating temperatures in both the gear teeth and gear oil. This elevated bulk oil temperature further increases the oxidation rate, a vicious cycle that creates more varnish and deposits.

Not only this, but by reducing clearances in already tight gear meshes, varnish can negatively impact the efficiency of gear drives and dramatically increase wear rates.

While the value of many gear sets may generally not be as high as in the turbomachinery world, the sheer prevalence of gears throughout industrial machinery means this issue could become a severe problem for asset management teams in the coming decade.

It is instructive to learn from the varnish mitigation techniques used to good effect in the turbomachinery world – this can help reliability teams prepare to deal with the issue. Some modifications to existing practices may be required.

Varnish removal skids and solvency enhancement for turbomachinery often come in the form of large filtration skids that might not be appropriate for small, distributed assets like gear sets.

As always, the future is not set in stone, and the increase in varnish is not a foregone conclusion. Based on the macro industry environment, asset managers should begin preparing.

Wind energy has become an increasingly important component of our energy grid as the world moves toward more sustainable power generation sources. Although harnessing wind power to do helpful work extends back to ancient times (think sail ships and windmills), stable electricity generation is a reasonably modern development.

With this development has come a growing appreciation for the role of lubricants in wind turbine reliability and an accompanying evolution in wind turbine gear oil formulations as the operating requirements are better understood.

Early Wind Turbines and Their Lubricants

The modern wind industry begins in the late seventies and early eighties. At this stage, the units were relatively small, with a capacity of no more than 100-200 kilowatts. As with many new technologies, there was a great deal of design experimentation, and many turbine variations co-existed.

Typical blade configurations sported anything from two to six blades, with some vertical-axis turbines thrown in the mix. Eventually, the “Danish” design (three-blades, horizontal axis) would cement its place as the industry standard configuration.

In these early years, wind turbine gear units were generally industrial gearboxes, repurposed. The approach was relatively crude and simple: rather than pushing electricity into an electric motor and extracting power through a gear reducer, engineers put the process in reverse, spinning the gearbox through power derived from the wind to drive a generator. But as Jim Carey (former ExxonMobil wind turbine gear oil formulator) explained in Episode 24 of Lubrication Experts:

“they would put [industrial gearboxes] up the tower and run for 6, 8, 10, 12 months. And they would all fail; broken teeth, bearings that would wipe out, you would have shafts that would snap. Seven to 10 years into the early nineties or so, or through the eighties into the early nineties, people realized, oh, wait a minute, if we want reliable power generation, you must increase the quality [of the gearing]. Not to the degree of, say, aircraft machining quality and whatnot, but we have to get a little bit better at devising machines that have tighter tolerances and are capable of more sustained power throughput from wind events to generate electricity.”

Early wind turbine gear oil formulations were also reasonably crude; formulations resembled “cut back” engine oils, containing the same metal-containing antiwear, antioxidant, and detergent additives seen in the automotive formulating tradition.

The Emergence of Micropitting as a Failure Mode

The subsequent generations of turbines heralded an era of tighter tolerances and more sustained, higher power throughput. This evolution led to the rise of micropitting failures in wind turbine gear sets.

Micropitting is a surface fatigue failure arising with rolling or sliding contacts. It’s frequently seen in gears subjected to intense loads, especially if the loading is variable.

Under these conditions, the roughness of the tooth surfaces and the oil film thickness are on the same scale, so the surface asperities come into contact with one another. The high loads placed through wind turbine gear sets and the variation of load induced by changing wind patterns make the wind turbine gearbox an ideal environment for micropitting.

When the asperities make direct contact, there is a sudden increase in the contact pressure; this intense pressure leads to a plastic deformation on the material’s surface, and this plastically distorted surface is prone to crack under the strain of repeated cyclic loading and unloading. This culminates in the formation of micro-sized pits, hence the term “micropitting.”

Two Ways to Skin the Formulation Cat

To solve the issue of micropitting in wind turbines, two entirely different schools of thought emerged. The first approach leaned heavily into the automotive tradition, continuing to use heavily metal-laden formulations with a high reliance on antiwear tribofilms to reduce energy concentration in the gear tooth asperities.

The second approach was to almost entirely remove metal-containing additives from the formulation and rely instead on synthetic base oils (now mostly metallocene polyalphaolefins) to support the contact pressure and provide sufficient film strength to reduce the cyclic loading on asperities.

These differences may seem trivial at a surface level, but they led to dramatic outcomes – specifically radical lubricant incompatibility issues between lubricants from the two formulation philosophies.

The past decades have seen numerous gear oil foaming issues and additive precipitation when switching from one oil style to another. This could only be eliminated through the most intensive gearbox flushing procedures when a product change was required.

Fork in the Road

Today, most wind turbine gear oil formulations have adopted the metal-free style. This reflects a broader trend in industrial lubricant formulation, driven by the longer lubricant lifecycles.

Whereas a typical engine oil may last 15,000 miles (equivalent to approximately 2,000 hours), an industrial oil could see a drain interval closer to 8,000 hours. Additionally, the operation means a heightened risk of water contamination, an issue compounded by metal-containing formulations due to their hygroscopic nature.

The philosophy behind metal-free industrial lubricants is for the lubricant to withstand environmental contamination but still efficiently eject any infiltrating impurities.

The lubricant absorbs water from its environment with metallic additives, introducing unnecessary moisture to critical machine components such as bearings, gears, and shafts. Metal-free formulations allow contaminants to be dropped out on the first circulation, leaving nothing but clean lube oil in the machine.

This philosophy is concluded in wind turbines, where the latest gear lubricants are often sold with a ten-year warranty. For a lubricant to survive almost 100,000 hours of operation in water-rich offshore and coastal environments, the oil must readily separate from contaminants encountered in service, and the additive package must be robust enough not to deplete.

Future Wind Turbine Gear Oils

Today the limiting factor on gear oil life appears to be the depletion of the additive package. To date, most lubricant manufacturers have avoided commercializing additive packages that extend the life of the turbine oil.

But with the rising costs and logistical challenges of changing wind turbine gear oils in remote locations becoming a drag on wind farm profitability, it may be only a matter of time before these solutions come to market.

Unless OEMs are willing to adopt a radically different formulating strategy (such as the use of PAG base oils), it is unlikely that wind turbine gear oils will change much in the coming decades. Instead, the focus will likely shift to remote condition monitoring of the lubricants to ensure maximum service life.

It’s exceedingly rare to find a fleet of vehicles with the same make, model, and year of manufacture. I have never personally observed a single instance in my career. Fleet managers will be all-too-familiar with the challenge of stocking spare parts for their fleet, but an additional issue is that of engine oils.

Choosing the right oil type and keeping a supply is essential, as this can increase inventory costs and complicate inventory management. Moreover, API (American Petroleum Institute), ACEA (European Automobile Manufacturers’ Association), and OEM specifications are constantly changing in response to advances in engine technology and regulations.

So fleet managers must keep up to date to ensure optimal performance, engine longevity, and minimal risk of cross-contaminating with incorrect lubricants.

API C Category – Built for Backward-Compatibility

Backward compatibility is one of the most notable features of API C (Commercial) diesel engine oils. It means that engine oils of the latest generation can be used with older engines built for oil specifications from earlier years without any damage.

Each subsequent API C category specification is designed to be backward compatible. For example, the CK-4 oils can be used with engines designed for the CJ-4, CI-4, and CH-4 categories.

This compatibility is possible because each new API specification maintains the performance characteristics of older oils while adding enhancements that meet the needs of modern engine technology.

This feature is a significant advantage for fleet managers, as they will often have a mixture of different models and asset ages in their fleet. On top of that, engine rebuilds and replacements over the vehicle’s life can mean that engines may require newer generations of oil compared with the manufacturing specification.

API’s backward compatibility means that a single type of oil will meet the needs of older and newer engines, which reduces inventory complexity and the risk of errors.

PC-11, the API’s most recent specification, has introduced a new wrinkle. This product category was split in two, with CK-4 being introduced alongside FA-4.

While CK-4 retained the backward compatibility that has become synonymous with API’s commercial engine oil categories, the FA-4 specification is designed with a fuel economy objective.

This category’s lower HTHS and bulk viscosities make it incompatible with the oil specification that preceded it – meaning that fleets likely need to retain a mix of different oil specs unless the entire fleet comprises exclusively 2016 or later engine models.

ACEA – Complicating Things

Regarding ACEA (European Automobile Manufacturers’ Association) E-category diesel engine oils, the situation with backward compatibility differs somewhat from the API approach.

The ACEA specifications are designed to address the specific needs of European engines, often different from those manufactured in the US.

In the ACEA E sequence for heavy-duty engine oils, backward compatibility is not guaranteed. For example, E6 oil may not be suitable for an engine that requires E4 or E7. Each E category is tailored for specific engine technologies and exhaust treatment systems.

For example, using E6 oil in a machine designed for E4 could lead to complications due to differences in crucial properties such as Sulphated Ash, Phosphorus, and Sulphur (SAPS) levels.

Unlike the API Commercial category oils, ACEA has no tradition of maintaining a single category regularly updated along with engine technology requirements. Instead, ACEA maintains multiple active types to cater to various engine technologies and after-treatment devices.

As vehicle technologies and emissions regulations advance, ACEA makes categories obsolete, as in 2022 when E8 and E11 replaced E6 and E9, respectively.

With all this complexity, careful oil selection based on the manufacturer’s recommendation becomes increasingly important when a fleet comprises vehicles from predominantly European OEMs that tend to follow the ACEA specifications.

OEM Specifications – A Challenge to Decode

Navigating the different OEM specifications for diesel engine oil is complicated. Each OEM sets its own specifications for each vehicle based on engine design, materials, and operating conditions.

These requirements are often based on those set forth by the API or ACEA but exceed those requirements in areas dictated by the OEM’s use of particular engine or emissions control technologies.

When selecting oil for a single vehicle, this can be a relatively simple exercise, with many industry tools available for matching vehicles to oil specifications.

The challenge for fleet managers comes when trying to minimize oil inventory while still covering all the necessary approvals to meet requirements and warranties.

At this point, some research may be required to understand where specifications overlap. For example, the Cummins CES 20086 specification is often grouped with ACEA E9, API CK-4, MB 228.31, Volvo VDS-4.5, MACK EOS-4.5, Renault RLD-3, MTU Type 2.1, and/or Caterpillar ECF-3.

The Future – Spoiler Alert: It Doesn’t Get Easier

There is a great deal of ongoing work and discussions in the ever-evolving realm of engine oils. With the recent release of ACEA 2022, the likely next specification release is API’s PC-12.

As with PC-11, it appears the category will be split into PC-12A and PC-12B, with PC-12A being a successor to CK-4 that retains its backward compatibility characteristics and PC-12B being the fuel-economy FA-4 equivalent (nominally FB-4).

Discussions on PC-12 oil drain intervals aren’t pushing for significant extensions beyond what’s currently in practice.

Interestingly, PC-12B is expected to introduce lower high-temperature, high-shear (HTHS) viscosities than we’re accustomed to. This proposal throws a wrench into the mix, adding an extra layer of complexity to the situation.

The lack of compatibility with older specs in Australia and the United States means that using FA-4 oil remains a niche practice. CK-4 oil (and earlier) is still the mainstay for most fleets.

However, if the proposed lower HTHS viscosity for PC-12B is approved, FB-4 may not be backward compatible with the current FA-4 allowance.

This would split the previously distinct API Commercial category into three competing specifications. It’s a fascinating discussion that many Original Equipment Manufacturers (OEMs) are grappling with.

The aim for Commercial Vehicle Lubricants (CVL) is heading in the same direction as passenger vehicles to improve fuel economy and meet the ever-stringent standards.

These changes are all part of the broader goal to increase fuel efficiency and miles per gallon in fleet operations, aligning with ongoing discussions around regulatory standards.

However, it introduces increased complexity for fleet owners, who must navigate an ever-more intricate web of diesel engine oil specifications.

In the complex and evolving world of the lubricants industry, we’re constantly faced with new challenges. Most end-users have recently suffered from the increasing cost of lubricants and greases. In most instances, these changes have their root cause in supply chain disruptions and challenges brought about by extreme weather events and the second-order effects of Covid-19 lockdowns.

Enter Calcium Suphonates

Calcium sulphonate complexes are an alternative thickener technology that has historically been sold as a high-performance (but also high-cost) alternative to lithium complex thickeners.

Often used in high-temperature or high-load applications, the major obstacle to broader adoption has usually been the steep price premium relative to lithium complexes.

Anecdotally the cost gap was 200-300%, but with the recent increase in lithium prices, this has shrunk to as little as 30-50%, making calcium sulphonates an attractive proposition.

These thickeners owe their performance properties to the unique structure of the thickener. Derived from the same over-based TBN 400 calcium sulphonates in engine oils detergents, these thickeners exhibit excellent corrosion resistance.

The complex gel structure gives them excellent shear stability, water resistance, and high-temperature performance. On the structure of these greases, Andy Waynick explains in episode 36 of Lubrication Experts:

“You’ll see drawings of it, and it will typically have a spherical core, which we do know exists, and presumably inside that core resides all the excess calcium carbonate in the amorphous form, calcium cations, carbonate anions, and some hydroxide anions because usually, you need some of that as well to make a stable structure. And then around the sphere pointing outward is the neutral calcium alkyl benzene sulfonate in what’s called a reverse micelle structure.”

 The excess calcium carbonate gives rise to yet another valuable property of these greases – the EP performance. Calcium carbonate (in the form of calcite) is a lamellar material on the nanometre scale with low shear stability that can act as an effective solid lubricant similar to Molybdenum Disulphide or Graphite. This makes them extremely useful in slow-speed high-load applications commonly associated with the mining industry.

One note of caution when selecting these greases – the manufacturing process is significantly more sensitive than that of standard simple and complex soaps. The result is some significant divergence in the quality of these thickeners available on the market.

I have tested several calcium sulphonate thickeners where the calcite particles were on the millimeter-scale or the thickener liquefied at temperatures less than 70°C. This makes a manufacturer’s quality control program essential to the procurement process.

Cost-Effective Alternatives

Given their performance and relative cost, calcium sulphonate complexes are a compelling alternative to lithium complex greases. Still, if the raw price of lithium continues to increase, options will also be needed for the standard lithium soap greases that dominate market share.

This is not so simple – lithium soaps have historically been used as multipurpose greases for their “jack-of-all-trades” performance profile.

Lithium greases don’t perform any function spectacularly well, but they also do not have a significant weakness.

This is untrue of other metal soaps – sodium greases, for example, are water soluble, and aluminium soaps are susceptible to shear. Simple calcium greases have historically had an upper operating temperature limit of around 60°C because water is part of the thickener structure.

Another form of calcium thickener may play a role. Some grease manufacturers have begun to make anhydrous calcium soaps (anhydrous, meaning “without water”).

These offer improved high-temperature performance allowing for sustained operating temperatures above 100°C and other properties similar to or exceeding lithium soaps.

Best of all, the raw material required is lime rather than lithium hydroxide. Lime is abundant, widely available, and can be purchased at a fraction of the cost.

Better still, anhydrous calcium-lithium soaps can be manufactured. Blending the two can offer a compromise of cost and performance when a performance profile almost exactly matching lithium greases is required.

The Future

There are still several barriers to adoption before lithium soaps can be displaced as the world’s most popular grease type. The first is the overwhelming approvals given to lithium and lithium complex greases by equipment OEMs, who will need to be convinced of the benefits of alternative technologies.

The second is manufacturing capacity and capability. Very little anhydrous calcium is currently being produced, and as remarked upon earlier, the quality of calcium sulphonate complexes can vary greatly, even batch-batch at certain facilities.

But suppose EV demand continues to increase at an exponential rate. In that case, the ever-increasing price of lithium will likely be a solid motivation to find, test and approve alternative formulations.

Just as there are various states of matter, there are different lubricant types. The four main categories are gas, liquid, cohesive (grease), and solids. In the industrial lubrication world, we deal with fluids and greases, but some operating environments make these unsuitable – in these circumstances, we often turn to solid lubricants.

The Lubrication Mechanism of Solid Lubricants

With oils and greases, we typically rely on the formation of a fluid film to separate two surfaces in relative motion. When loads are too high or speed too low, we enter the mixed and boundary regimes and rely on additives such as antiwear and EP agents to protect machine surfaces.

Solid lubricants act exclusively in the boundary regime. Their lubrication mechanism is based on their ability to form a thin film on the surfaces of moving components. This film (sometimes known as a “tribofilm”) acts as a barrier between the surfaces, helping to reduce adhesive wear. These particles can also reduce the friction between the surfaces thanks to their very low shear strength.

Structure of Solid Lubricants

Understanding the friction-reducing properties of solid lubricants helps to understand their underlying structure. Most solid lubricants are lamellar solid materials consisting of atomically-thin planes. That’s a bit of a word salad, so above is an image that will give you a better idea of what that means.

The individual layers (in the case of MoS2, three atoms thick) are held together only by weak Van der Waals forces and are easily sheared by relative motion. This action is like a person running on top of a floor covered in playing cards.

The thickness of the tribofilm is a crucial factor in the lubrication process. A thin film provides a low coefficient of friction and reduces wear, while a film that is too thick can cause an increase in friction and wear.

The thickness of the tribofilm can be influenced by several factors, including the type of solid lubricant used, the load on the moving parts, and the environment in which the lubrication is taking place.

Solid Lubricant Selection

There are several common choices when selecting a solid lubricant or grease containing solid lubricant. It’s helpful to understand the properties of each and their strength and weaknesses:

Graphite

Graphite is a naturally occurring form of carbon. It is a good lubricant for high-temperature applications and has a low coefficient of friction. It operates like the low friction contact between your graphite pencil and paper, as single layers of graphite (technically now known as “graphene”) shear off.

Graphite is unusual in that it requires environmental gases to form a tribofilm. As Dr. Juan Preciado Flores discussed in Episode 9 of the Lubrication Experts podcast, “carbon needs a passive layer to have a lower coefficient of friction.

That’s why for a pin-on-disk test in a dry environment, you may have a CoF (coefficient of friction) of 0.4. And if you add a little bit of water or increase the room’s humidity, you may have a coefficient of friction of 0.2 because you are helping that tribofilm by adding a reactive gas.”

It is also highly conductive, which may benefit slip-ring contact applications but can be detrimental elsewhere.

Molybdenum Disulfide (MoS2)

MoS2 (commonly just referred to as “moly”) is a compound that is a good lubricant for high-temperature and high-pressure applications and has a low coefficient of friction. It is mined from some sulphide-rich deposits, then refined to achieve a purity suitable for lubricants.

The high-temperature performance of MoS2 is limited to 400 °C, a limit at which the molecule experiences excessive oxidation. Water has the reverse effect on MoS2 compared with graphite, as it often reacts with the molecules, increasing the shear strength between the layers and therefore increasing the coefficient of friction. 

Boron Nitride (BN)

BN is a compound made of boron and nitrogen and is an excellent lubricant for high-temperature and high-pressure applications. It has a low coefficient of friction and is highly resistant to thermal shock. BN is often used in applications such as furnace door lubrication and in high-temperature chemical environments where MoS2 isn’t an option.

There are numerous forms of Boron Nitride (known as “polytypes”). Hexagonal boron nitride (h-BN) has a layered structure like graphite, whereas cubic boron nitride (c-BN) is analogous to diamond and used in abrasion applications.

Within each layer of h-BN, boron and nitrogen atoms are bound by strong covalent bonds, but weak van der Waals forces mean the layers aren’t firmly bound to each other. This gives it a low shear strength, typical of other solid lubricants. 

Fluoropolymers (e.g., PTFE)

Fluoropolymers (usually PTFE in lubricants) are the exception to the rule. Rather than having low-shear layers, the molecules of PTFE slip past each other very easily because the outer fluorine atoms are so tightly-packed. PTFE can typically be used up to a temperature limit of 260°C and has good resistance to reactive chemicals. 

Applications of Solid Lubricants

Un-mixed solid lubricants have a wide range of uses in industries where liquid lubricants and greases cannot be used. The space industry has long relied on dry lubricant coatings for spacecraft, satellites, and lunar/Mars landers as liquid lubricants would boil in the extreme space environment. Application methods vary, but the solid lubricants are frequently ionized and sputtered onto the equipment’s surface. 

We commonly see solid lubricants included in greases as an additive in an industrial environment. This is especially true in high-load, low-speed applications typical to the mining and construction industries, where greased gears, bushings, and even rolling element bearings cannot establish a fluid film.

They provide excellent wear protection and can withstand harsh operating conditions in these industries. In some high-washdown scenarios, we may rely on the residual solid lubricant that survives water blasting to lubricate a bucket pin before the element can be re-greased.

You may have also encountered the use of Moly and Boron in liquid lubricants. These are typically present in soluble forms like Molybdenum Dithiocarbamate or Borated Esters and work as multifunctional additives to provide some antiwear protection and anti-oxidancy.

Soluble molybdenum compounds provide their antiwear function by decomposing into MoS2, which then adheres to the load surface and functions the same way a solid lubricant would.

The Future

R&D into solid lubricant technologies continues to advance, with engineers and scientists developing solid lubricants that can withstand more severe conditions and offer better wear protection.

There are some exciting developments in nanocomposite solid lubricants. The lubricants can be made of nanoparticles from different types of solid oils (such as MoS2 combined with graphite in alternating layers). Combining the best properties of each molecule can achieve both high-temperature and high-pressure lubrication. 

They may also benefit from the sustainable transition; as more businesses look to reduce their use of fossil fuels, machine surfaces impregnated with solid lubricants or solid lubricants replacing liquid lubricants may become more common.