What is moly grease and why should you use moly grease in your equipment? This blog post will go in depth about what molybdenum disulfide is and how it works, along with a discussion of the various types of greases that can have moly blended into them.
What is Molybdenum Disulfide?
Molybdenum disulfide, or moly for short, is one of the best known solid lubricants in the field of lubrication. In its pure form, molybdenum disulfide appears to look like lead. It shares the same gray color and is almost the same weight.
Moly, though, is far stronger than lead. It has a melting point of 4,370 degrees Fahrenheit, which is double the melting point of steel. Interestingly, molybdenum is one of the main components found in the toughest and hardest steel alloys.
Molybdenum disulfide can be found naturally throughout the world. There are only a few places where this unique mineral is abundantly found. Luckily, the Rocky Mountains of Colorado is one of these few places where moly is mined. About 60% of the world’s production of molybdenum is done in these Rocky Mountain mines.
It takes more than 1 ton of ore to be mined to be able to get only 4 pounds of molybdenum. Molybdenite, which is the geological term, is the main ore we’re interested in. Molybdenum disulfide is the primary substance that is derived from the molybdenite ore. When it is extracted, it is a black powder that has found a home in the lubricant industry.
What Makes Moly an Excellent Lubricant?
The main function that molybdenum disulfide, or MoS2, delivers is its ability to reduce friction and wear.
Molybdenum disulfide is physically classified as a lamellar solid. What this means is that the molecular structure of MoS2 is designed as layered crystals or lamellae. These layered crystals are virtually impossible to compress and have the capacity to support and withstand incredible loads of up to 500,000 psi (pounds per square inch,) which is far beyond the yield point of a majority of metals.
Also, these MoS2 layered crystals provide very little resistance to shear forces, which allows the crystal layers to slide over one another. In other words, moly’s ability to withstand incredible loads, along with its unique sliding action, are the two main factors that give it superior friction and wear reducing performance.
A very simple way to visually see and understand how moly functions is to use a deck of playing cards. Place a stack of playing cards on the table. Then, press down on them with as much force as possible. The fact is, there is no amount of pressure or force that will compress the playing cards beyond a specific point. Next, start to apply force (pressure) at an angle to those playing cards and notice immediately how those cards start to easily slide over one another. Molybdenum disulfide functions in exactly the same manner.
There is yet an additional property that makes molybdenum disulfide a unique and useful protective lubricant. It has a very powerful affinity (attraction) to metal. As heat and pressure is found within the parts that moly is exposed to, the moly layered crystals start to literally plate themselves onto the metal surfaces by chemically bonding themselves to the metal they are exposed to.
If you take a seemingly smooth metal surface and look at it through a very powerful microscope, you will notice many hills and valleys that are in fact present on all bearing and metal surfaces. By exposing these metal surfaces to moly, the moly layered crystals will eventually completely fill in all those peaks and valleys, thus creating an extremely durable protective film. The two MoS2 plated metals surfaces will literally slide over each other very easily like the playing card demonstration.
Also, this tough moly barrier will keep these two metals surfaces from coming into physical contact because the smooth durable molybdenum disulfide film will withstand up to 500,000 psi. If temperatures within the metal or bearing surfaces reach between 600 to 700 degrees Fahrenheit, the molybdenum found in the lubricant film literally diffuses itself into the bearing material, thus creating a tougher and enhanced alloy.
In other words, when the environment becomes this difficult, most lubricants break down when exposed to these high temperatures, but not moly. Moly actually will not only protect the metal, but enhance it.
How is Moly Used?
Due to the fact that molybdenum disulfide offers such useful and unique lubricating properties, many manufacturers utilize the pure moly powder for initial break-in protection. Typically, the moly powder is carried to the part by either an aerosol or a paste.
A typical example of using moly powder for a break-in lubricant would be applying it to cam shaft lobes in a motor at the factory.
Dry moly has found uses in a variety of applications, such as sleeve bearings, chain drives, liquid oxygen valves, and electrical contacts for switches and relays. The point is, wherever there is a lot of dust or extreme temperatures that make oil or grease a poor choice, moly powder is usually the lubricant of choice.
In terms of very extreme examples of where molybdenum disulfide shows its amazing capabilities, look no further than NASA. NASA and its space program has always been a huge fan and believer in molybdenum disulfide. It has the ability to lubricate over an extreme range of operating conditions and temperatures, from very cold cryogenic temps all the way up to 750 degrees Fahrenheit in normal air, right up to super extreme high temperatures of 2,000 degrees F when exposed to the vacuum of space.
Conventional lubricants simply are not up to the task to withstand such brutal and extreme environments without burning up or solidifying.
Now that we understand a bit better what exactly molybdenum disulfide is, let’s take a step closer in finding out what is moly grease and more specifically, why you would add moly to a grease.
What is Moly Grease?
Statistically, the vast majority of molybdenum disulfide found in the lubricant industry finds its way into greases. Many of the equipment manufacturers such as Caterpillar, General Motors, Ford, etc. specify or utilize moly grease in one form or another.
To use molybdenum disulfide powder by itself or in a paste would be rather expensive. It is more cost effective to simply blend in anywhere from 1% to 5% MoS2 to a grease rather than just use a very high percentage of moly alone. Side by side testing shows the performance level is very similar for moly grease vs. a lot of MoS2 by itself.
Once plated to the metal surfaces, moly tends to offer a long service life. Still, over time, if not replaced, it will wear away. On the other hand, a grease blended with molybdenum disulfide that lubricates a ball joint, a bearing, or any other part will always provide a reservoir of moly via the grease.
The grease acting as a reservoir for moly allows the moly to continually plate and re-plate itself on all the surfaces it comes in contact with as long as there is grease available. In the event of a serious failure caused by the complete loss of grease, the tough, thin barrier of MoS2 will still be present, effectively providing an armor-like barrier against wear until the grease is finally replaced.
History of Molybdenum Disulfide
As far back as 1764, history records identified a gray mineral substance that was being rubbed onto tools and presses of that period.This gray mineral was rubbed into the metal surfaces and polished to the point where it became known as burnished black. The historical records mention that this mineral would reduce friction and greatly protected the metal against rust and corrosion. Molybdenum could not have been identified during that time due to the fact that it was first chemically identified many years later. Still, the only naturally occuring substance that could have been used was molybdenum disulfide.
Amazing Test Results When Using Moly
A major telephone company, during the early 1970s, was conducting tests with a moly based grease in the hopes of finding a lubricant that could protect the miniature ball bearings found in their very small electric motors that were being utilized in their switching systems. The tests were conducted for over 4,000 hours in extremely humid conditions ranging from 60% to 100% humidity.
At the end of the tests, all the external components of these tiny electric motors were completely destroyed by rust and corrosion. The miniature ball bearings that the moly grease was lubricating were studied under a microscope and the surfaces of these bearings showed the common blue-black color of molybdenum disulfide. Amazingly, there was virtually no sign of wear, rust, or pitting even though the bearings had been run during these torturous 4,000 hours without protective shields.
From these positive experiences, this major telephone company went on to utilize moly grease for the bearings found in their large power generators that were found throughout the United States. Interestingly, many technicians over time conducted tests to determine if the moly was in fact lowering friction and the results were quite eye opening.
When air temperatures were taken near the bearings of these large power generators, findings showed a drop of 35 degrees Fahrenheit, thus substantiating that friction was being reduced, meaning that heat reductions were taking place.
Molybdenum disulfide does more than reduce friction and protect metal from rust and corrosion. By reducing friction, thus reducing heat, moly will also decrease the potential of the lubricant oxidizing.
Back in the late 1960s, General Motors’ Research Department conducted tests to determine whether simply adding a small amount of moly could improve the performance of a non-moly grease. The tests were conducted on a special apparatus designed by General Motors engineers that utilized Cadillac ball joints. The tests would put the grease through torque, wear, and bearing conditions.
The first series of tests were conducted with a grease that contained no moly. It failed the test miserably. A series of tests were then conducted, progressively adding small amounts of moly to the grease. The simple act of adding a small amount of moly to the grease changed the results from a failing mark to a pass in the torque, wear, and bearing condition categories of the tests. In fact, this addition of moly to the non-moly grease had corrected the tendency of the grease to breakdown and deteriorate.
In summary, by simply adding only 1% of MoS2 had converted a very poor grease into a well performing grease.
Many OEMs Recommend Moly
Molybdenum disulfide greases have become the grease of choice for many vehicle manufacturers. It is a factory fill lubricant. The list of OEM manufacturers that consider moly grease to be an imperative requirement are the who’s who of OEMs, names such as Rolls Royce, Chrysler, Ford, Cadillac, Mercedez-Benz, Caterpillar, Terex, and many others.
For example, Caterpillar Tractor Company specifies only molybdenum disulfide based greases for all grease points. They call out a moly grease that must contain 3% to 5% MoS2.
Terex were experiencing abnormal wear issues with the huge kingpins they utilized in their articulated scraper earth movers. Terex engineers tested a grease that contained 25% moly. This grease solved the problem. They decided to err on the side of caution, so Terex decided to specify a specialty grease for that specific application that contained 75% moly.
More and more, fleet operators are learning that moly based greases can provide many useful benefits to their operation, such as a reduction in friction and wear, plus extending the service life of the equipment. Also, they’ve noticed more and more the ability to prolong grease intervals.
Superior Investment, Superior Results
Even though a moly grease requires a slightly higher investment versus a non-moly grease, consumption levels are reduced and less man hours are required due to extended lube intervals.
During a 2 year study conducted by Southwest Research Institute on 38 semi trucks, city buses, and police cars, some interesting statistics were realized. This test utilized a lithium based grease that contained 3% MoS2, which resulted in a 26% to 38% reduction in chassis point wear on the police cars. For the buses and trucks, kingpins, universal joints, and shackles showed anywhere from 18% to 88% less wear. These results are in comparison to testing the same grease without moly.
Another eye opening test was conducted years ago by a large commercial bakery that had a fleet of 190 delivery trucks, 5 semi trucks, and 22 sales rep vehicles that were dealing with a horrendous amount of wheel bearing failures. The commercial bakery decided to try moly grease to get this severe problem under control. During a 36 month trial, the wheel bearing failures were almost completely eliminated. Another example of the value of moly in a grease.
Components of Moly Grease
The next part of answering the question of what is moly grease has to include a discussion about the components that make up such a grease. There are three components that make up the anatomy of a grease. The first component is the base oil, whose volume can range from 70% to 95%. The second component of a grease is the thickener, whose volume can range from 3% to 30%. The third and last component is the additives, which can account for volumes ranging from 0% to 10%. Let’s look at the base oil first.
The majority of lubricant manufacturers primarily utilize mineral or petroleum base oils. For most normal operating conditions, a mineral or petroleum based grease will deliver a satisfactory performance. For operating environments that are more severe in both temperature range and demands on machinery, then the better choice would be a grease manufactured with synthetic base oils.
Synthetic base oils can operate from extremely low temperatures through high temperatures, they are more thermally stable, and overall they can deliver an excellent return on investment.
The grease thickener is a component that when blended with the base oil will create a solid to semi-fluid structure. The main type of thickener that is commonly utilized today by grease .manufacturers is metallic soap. These soaps include lithium, calcium, aluminum, sodium, clay, and polyurea.
The latest trends in grease manufacturing involve the use of complex thickener type greases. They offer superior load carrying capabilities, along with an ability to withstand higher temperatures. Complex greases are engineered by blending a standard metallic soap such as lithium with a complexing agent such as boric acid or aromatic acid.
In more specialized applications such as extreme temperature operating conditions, bentonite clay is one example of a thickener that can be used when designing a high temperature or no-melt grease. It should be noted that when using a no-melt grease that utilizes bentonite as a thickener, be aware that even though the thickener does not melt, the base oil can only withstand so much high temperature. Eventually, the base oil will oxidize when temperatures become elevated. In this type of situation, remember to re-grease more frequently.
The last component to consider when manufacturing a grease would be the additives. Additives are typically used to control rust, corrosion, oxidation, extreme pressure, friction, and wear. We’ve already discussed in depth the function of a boundary lubricant known as molybdenum disulfide. As stated before when answering the question of what is moly grease, its main function is to withstand heavy loading and to reduce friction and wear without creating adverse chemical reactions to the metal surfaces.
For those fleet operators looking for a way to improve their maintenance program, the question of what is moly grease has been answered in this blog post. The long term benefits of moly have been proven over the last 70 years and continue to be an important component in every professional’s maintenance arsenal.